CN101179178B - Nitride semiconductor device and fabrication method thereof - Google Patents

Abstract

The invention discloses a nitride semiconductor device and a manufacturing method thereof. The device prevents the generation of cracks, has a nitride semiconductor thin film having a uniform thickness and good flatness of the growth surface, and thus has stable characteristics, and can be manufactured with a satisfactory yield. In this nitride semiconductor device, a nitride semiconductor thin film is grown on a substrate having an off angle between a direction perpendicular to a ridge surface and a crystal direction <0001>. This helps to reduce or intentionally accelerate the diffusion or movement of atoms or molecules of the source material of the nitride semiconductor thin film throughout its migration. As a result, a nitride semiconductor growth layer with good surface flatness can be formed, and thus a nitride semiconductor device with satisfactory characteristics can be obtained.

Description

Nitride semiconductor device and manufacturing method thereof

This application is a divisional application of Chinese Patent Application No. 200510119342.6 with a filing date of November 2, 2005 and an invention title of "Nitride Semiconductor Device and Manufacturing Method Thereof".

technical field

The present invention relates to a nitride semiconductor device. More specifically, the present invention relates to a nitride device using a semiconductor substrate having at least a surface formed of a nitride semiconductor, and a method of manufacturing such a nitride semiconductor device.

Background technique

Nitride semiconductors such as GaN, AlGaN, GaInN, and AlGaInN are characterized by having a larger band gap Eg than AlGaInAs-based or AlGaInP-based semiconductors, and are also direct transition semiconductor materials. For these reasons, nitride semiconductors are used in the manufacture of semiconductor light emitting devices such as semiconductor lasers capable of emitting light at short wavelengths from the ultraviolet to the green region of the spectrum and luminescence covering a wide emission wavelength range from the ultraviolet to the red region of the spectrum. Diode materials have attracted a lot of attention. Thus, nitride semiconductors are expected to be widely used in high-density optical disk drives, full-color displays and other devices, as well as in environmental, medical and other fields.

In addition, nitride semiconductors have higher thermal conductivity than GaAs-based or other semiconductors, and thus can be expected to be used in devices operating at high temperatures and high outputs. Furthermore, nitride semiconductors do not require any materials such as arsenic (As) used in AlGaAs-based semiconductors or cadmium (Cd) used in ZnCdSSe-based semiconductors, so they do not require any materials such as arsine (AsH ₃ ) source materials, etc., so that they are expected to be environmentally friendly compound semiconductor materials.

However, conventionally, among various types of nitride semiconductor devices, the manufacture of nitride semiconductor laser devices suffers from extremely low yield, that is, relative to the total amount of nitride semiconductor laser devices manufactured on a single wafer. , the number of defect-free is extremely low. One reason for the low yield is considered to be the formation of cracks. The cause of the crack may be in the substrate itself or in the process of placing a nitride semiconductor multilayer film including a plurality of nitride semiconductor layers (nitride semiconductor film) placed in sequence on the substrate.

It is inherently preferable to form a nitride semiconductor multilayer film of, for example, GaN by growing on a GaN substrate, since this helps to produce a nitride semiconductor multilayer film with good crystal quality and fewer defects. However, high-quality GaN single crystal substrates with good lattice matching with GaN have not been produced until now. Therefore, SiC substrates are often used instead due to their relatively small difference in lattice constants. Disadvantageously, however, SiC substrates are expensive, difficult to manufacture in large diameters, and generate tensile strain. As a result, the SiC substrate is prone to cracks. In addition, the substrate of the nitride semiconductor is required to be formed of a material that withstands a high growth temperature of about 1000° C. and is resistant to discoloration and corrosion in an ammonia atmosphere used as a source material.

Based on the above discussion, a sapphire substrate is generally used as a substrate for placing a nitride semiconductor multilayer film. However, the sapphire substrate causes a large lattice mismatch (about 13%). Therefore, on a sapphire substrate, a buffer layer made of GaN or AlN is first formed by low-temperature growth, and then a nitride semiconductor multilayer film is grown on this buffer layer. Nevertheless, it is difficult to completely relieve the strain, thus resulting in the formation of cracks depending on conditions such as film composition and film thickness.

The cause of such cracks may lie somewhere other than the substrate, as will be described below. When manufacturing a nitride semiconductor laser device, a nitride semiconductor multilayer film is placed on a substrate, and the nitride semiconductor multilayer film is composed of various types of films such as GaN, AlGaN, and InGaN. Here, the individual films constituting the nitride semiconductor multilayer film have different lattice constants, and thus exhibit lattice mismatch, causing cracks to occur. As a countermeasure against it, a method for reducing cracks has been proposed, according to which method, a substrate processed so that after the nitride semiconductor multilayer film is grown on the substrate, the surface of the nitride semiconductor multilayer film is not flat, but has a depressed region formed thereon (see Japanese Patent Application Laid-Open No. 2002-246698). By employing, for example, the method disclosed in Japanese Patent Application Laid-Open No. 2002-246698, it is possible to reduce cracks caused by lattice mismatch between layers constituting a nitride semiconductor multilayer film formed on a substrate. Disadvantageously, however, in the method disclosed in Japanese Patent Application Laid-Open No. 2002-246698, the depressed regions formed on the surface of the nitride semiconductor multilayer film degrade its flatness.

As a countermeasure against such lowering of the flatness of the surface of the nitride semiconductor multilayer film, the inventors of the present invention have developed a method according to which trenches and ridges are formed on a nitride semiconductor substrate (ridge portion), wherein the groove is in the form of one to a plurality of stripe-shaped grooves in each nitride semiconductor laser device, and the ridges are each located between two adjacent grooves and have a thickness of about 100 μm to 1000 μm width, and then, on this nitride semiconductor substrate, a nitride semiconductor multilayer film is provided. In this way, it is possible to prevent cracks and at the same time obtain a considerably improved surface flatness on the ridge surface.

When manufacturing a nitride semiconductor laser device by the above method developed by the inventors of the present invention, a nitride semiconductor multilayer film is structured as shown in FIG. 20, for example.

Specifically, the nitride semiconductor multilayer film 4 formed on the surface of a processed substrate 6 (see FIGS. 19A and 19B ) formed of etched n-type GaN or the like has, for example, the following layers in order of naming Laminated on the surface of the processed substrate 6: an n-type GaN layer 200 with a layer thickness of 0.2 μm; an n-type Al _0.05 Ga _0.95 N first clad layer (clad layer) 201 with a layer thickness of 0.75 μm; a layer with a 0.1 μm thick n-type Al _0.08 Ga _0.92 N second cladding layer 202; n-type Al _0.05 Ga _0.95 N third cladding layer 203 with a layer thickness of 1.5 μm; n-type GaN guide layer (guidelaycr) 204 with a layer thickness of 0.02 μm; The active layer 205 includes three InGaN well layers each having a layer thickness of 4 nm and four GaN barrier layers each having a layer thickness of 8 nm; a p-type Al _0.3 Ga _0.7 N evaporation preventing layer 206 having a layer thickness of 20 nm; having a layer thickness of 0.02 A p-type GaN guide layer 207 with a layer thickness of μm; a p-type Al _0.05 Ga _0.9 5N cladding layer 208 with a layer thickness of 0.5 μm; a p-type GaN contact layer 209 with a layer thickness of 0.1 μm. The active layer 205 has the following layers formed sequentially in the order of their names: barrier layer, well layer, barrier layer, well layer, barrier layer, well layer, and barrier layer. In the following description, when it is necessary to indicate a nitride semiconductor layer composed of sequentially stacked layers doped with Mg, that is, the p-type Al _0.3 Ga _0.7 N evaporation prevention layer 206, the p-type GaN guide layer 207, the p-type Al _0.05 Ga _0.95 N cladding layer 208 and p-type GaN contact layer 209, the term "p-layer" is used.

In this way, nitride semiconductor multilayer film 4 is provided on the surface of processed substrate 6 which has been previously processed by MOCVD. In this way, a nitride semiconductor wafer having recessed regions in the surface of the nitride semiconductor multilayer film 4 as shown in FIGS. 19A and 19B is manufactured. In Figures 19A and 19B, plane directions are labeled together.

Used as the processed substrate 6 shown in FIGS. 19A and 19B has grooves each having a stripe shape formed thereon in the <1-100> direction by a dry etching technique such as RIE (Reactive Ion Etching). 2 and ridge 1 on the n-type GaN substrate. Trenches were formed to be 5 μm wide and 5 μm deep with a distance of 350 μm between two adjacent trenches. On thus etched processed substrate 6, nitride semiconductor multilayer film 4 having a laminated structure as shown in FIG. 20 is formed by a growth technique such as MOCVD.

When a nitride semiconductor laser device is actually manufactured by the method developed by the inventors of the present invention, by using an n-type GaN substrate as the processed substrate 6, and then epitaxy by MOCVD or the like on the n-type GaN substrate Growing a nitride semiconductor multilayer film 4, it was found that this method was effective in reducing cracks, but could not significantly increase the yield. Specifically, through the above method, a plurality of nitride semiconductor laser devices are manufactured, and then 100 nitride semiconductor laser devices are randomly sampled from them and the full width at half maximum (full width half maximum) of the FFP in the horizontal direction and the vertical direction is measured. , FWHM). Here, a nitride semiconductor laser device whose actual FFP FWHM is within ±1 of the design value is considered to be defect-free. The result is that only 30 nitride semiconductor laser devices meet the FWHM requirements of their FFPs, which shows a very low yield.

This is because the surface of the formed nitride semiconductor multilayer film 4 is not flat enough. With insufficient surface flatness, the layer thicknesses of the respective layers are different in the nitride semiconductor multilayer film 4, resulting in variations in characteristics in individual nitride semiconductor laser devices. This reduces the number of devices having characteristics within the required range. Therefore, in order to improve the yield, it is not only necessary to reduce the occurrence of cracks, but also to make the layer thickness more uniform and the film surface smoother.

It was also found that when the electrode pads are formed on a surface that is very uneven due to the depressed regions, current leaking through the depressed regions makes it impossible to obtain normal current-voltage (CV) characteristics of the laser. Basically, an insulating film such as SiO ₂ is formed in the recessed region, and electrode pads are further formed thereon. Here, if the surface has an uneven region such as a depressed region, the insulating film formed thereon will not be uniformly formed. When the insulating film was analyzed, it was confirmed that it had many regions where small cracks and pits were generated and where the insulating film was extremely thin. It was also found that this uneven insulating film was the cause of current leakage.

In addition, surface flatness was measured within the wafer surface of the nitride semiconductor wafer formed as shown in FIGS. 19A , 19B and 20 . The measurement results of surface flatness along the <1-100> direction are shown in FIG. 21 . The measurement was performed under the following conditions: measurement length, 600 μm; measurement time, 3 s; probe pressure, 30 mg; horizontal resolution, 1 μm/sample. The level difference between the highest and lowest parts of the surface is 30 nm over the measured width of 600 μm, as can be seen from FIG. 21 . In this measurement, the nitride semiconductor wafer was assumed to have an off angle of 0.02° or less.

As shown in FIG. 19B , the film thickness of each layer of nitride semiconductor multilayer film 4 provided on the surface of processed substrate 6 varies with position within the wafer surface, thus causing a difference in flatness. As a result, the characteristics of nitride semiconductor laser devices vary depending on where they are formed on the wafer surface, and the thickness of the Mg-doped p layer (corresponding to p-type Al as shown in FIG. 20 ) significantly affects the characteristics of nitride semiconductor laser devices. _0.3 Ga _0.7 N evaporation preventing layer 206 to p-type GaN contact layer 209 (the total thickness of the p layer stacked in sequence) varies greatly at different positions within the substrate surface.

When the ridge structure as the current confinement structure was formed, 2 μm wide stripes remained at the ridge portion, and the other portion was etched away by a dry etching technique using an ICP (inductively coupled plasma) machine. Like this, if the thickness of p-layer is different at different positions on the wafer surface before etching, then the remaining p-layer film thickness, that is, the p-layer thickness that remains after etching and therefore most affects the characteristics of the nitride semiconductor laser device is There are also large variations at different positions on the wafer surface. As a result, not only the layer thickness differs in different nitride semiconductor laser devices, but even in the same nitride semiconductor laser device, the film thickness of the remaining p layer can be almost zero in some parts and considerably large in other parts. When the thickness of the remaining p-layer is changed in this way, it affects the lifetime of the nitride semiconductor laser device and, as mentioned above, also affects its characteristics such as FFP (far-field pattern, far-field pattern).

The reason why the above-mentioned large layer thickness distribution exists in the wafer surface is that the growth speed of the film epitaxially grown on the ridge portion of the processed substrate including the nitride semiconductor substrate varies under the influence of the groove, resulting in Reduced uniformity within the surface.

Specifically, as shown in FIGS. 22A and 22B, on the processed substrate 6 having the trench 2 formed thereon, when the epitaxial growth starts, in the initial stage of growth, as shown in FIG. 22A, by the growth The trench growth portion 222 formed of the nitride semiconductor thin film on the bottom 224 and the side portion 226 of the trench 2 fills only a part of the trench 2 . Meanwhile, the top growth portion 221 formed of the nitride semiconductor thin film grown on the surface of the top 223 of the ridge 1 grows while keeping the nitride semiconductor thin film surface flat.

The epitaxial growth of the nitride semiconductor thin film proceeds from the above-described state shown in FIG. 22A to the state shown in FIG. 22B. In this state, the trench growth portion 222 formed by the nitride semiconductor thin film grown on the bottom 224 and the side portion 226 of the trench 2 almost completely fills the trench 2 and is connected to the substrate grown on the ridge 1 through the growth portion 225. The top growth portion 221 is formed of a nitride semiconductor thin film on the top 223 surface. In this state, atoms or molecules (for example, Ga atoms) deposited on the surface of the nitride semiconductor thin film grown on the top 223 of the ridge 1 as a source material undergo migration or the like under the influence of thermal energy to move to the growth portion 225 or The trench growth portion 222 . Such movement caused by migration of atoms or molecules occurs non-uniformly within the wafer surface, and the distance of movement varies from place to place within the wafer surface. As a result, as shown in FIG. 22B, the surface flatness of the top growth portion 221 is lowered.

Inhomogeneity in the nitride semiconductor substrate itself, such as the distribution of the tilt angle in the wafer surface and the distribution of the curvature of the substrate in the wafer surface or the inhomogeneity of epitaxial growth rate in the substrate surface or the groove in the substrate surface The flatness of the nitride semiconductor thin film also decreases in the <1-100> direction under the influence of unevenness in the groove formation process. Specifically, the time required to fill the trench 2 varies with the <1-100> direction; like this, where it is filled earlier, atoms or molecules of the source material of the nitride semiconductor thin film grow from the top of the ridge 1 part 221 Migrate or move to the growth portion 225 or the trench growth portion 222 . Where they are removed, it takes longer to form the nitride semiconductor film, with the result that the nitride semiconductor film formed in the trench 2 has a greater thickness. In contrast, where the trench 2 is filled later, atoms or molecules of the source material of the nitride semiconductor thin film do not migrate or move from the top growth portion 221 of the ridge 1 to the trench 2; It takes less time to form a nitride semiconductor thin film. Thus, the nitride semiconductor thin film in these trenches 2 has a smaller film thickness than where the trenches 2 are filled earlier.

In the case where the growth rate depends on the supply rate, that is, in the case where the growth rate of the nitride semiconductor thin film is controlled by the flow rate of atoms or molecules supplied to the wafer surface, etc., when the atoms or molecules of the source material of the nitride semiconductor thin film When migrating or moving into the trench 2, since the flux of atoms or molecules of the source material supplied to the entire wafer surface is constant, in the place where the nitride semiconductor thin film grows on the top 223 of the ridge 1, that is, in the top growth portion 221 , the film thickness is small. In contrast, in the case where atoms or molecules of the source material of the nitride semiconductor thin film do not migrate or move into the trench 2, where the nitride thin film is grown on the top 223 of the ridge 1, that is, in the top growth portion 221, The film thickness is larger.

Next, the layer thickness in the top growth portion 221 on the top 223 of the ridge 1 varies within the wafer surface, with the result that the flatness of the surface of the nitride semiconductor thin film decreases. Thus, in order to obtain better surface flatness, it is necessary to prevent the atoms or molecules of the source material of the nitride semiconductor thin film from migrating or moving from the top growth portion 221 on the ridge 1 to the growth portion 225 or the trench growth portion 22, and thus They are prevented from forming a nitride semiconductor film there.

Another way to obtain better flatness is to make the atoms or molecules of the source material of the nitride semiconductor thin film uniformly move over the entire wafer surface as they migrate or move from the top growth portion 221 on the ridge 1 into the groove growth portion .

Contents of the invention

In view of the above, it is an object of the present invention to provide a nitride semiconductor device that does not generate cracks, has a highly uniform layer thickness, has a nitride semiconductor multilayer film with a flat surface, can be manufactured with a high yield, and has no current flow. leakage. Another object of the present invention is to provide a method of manufacturing such a nitride semiconductor device. Specifically, the object of the present invention is to prevent the occurrence of cracks in the manufacture of a nitride semiconductor laser device manufactured by disposing a nitride semiconductor multilayer film on a substrate at least whose surface is formed of a nitride semiconductor, while preventing The atoms or molecules of the source material of the nitride semiconductor thin film migrate or move from the top surface portion located on the ridge surface into the grooves and thus prevent them from forming the nitride semiconductor thin film there, or by making the atoms of the source material of the nitride semiconductor thin film Or molecules uniformly migrate or move from the top surface portion on the ridge surface into the grooves over the entire wafer to form a nitride semiconductor multilayer film with good surface flatness.

According to crystallographic convention, if an index indicating a crystal plane or orientation is negative, the index is represented by its overlined absolute value. In this specification, since this notation is not possible, negative exponents are represented by absolute values preceded by a minus sign "-".

"Trench" means a recessed region formed in a stripe shape on the nitride semiconductor substrate as shown in FIG. 2 . 2 is a schematic cross-sectional view of a processed substrate 26 having trenches 22 and ridges 21 formed thereon by a trench formation process. The groove 22 does not necessarily have a rectangular cross-sectional shape, but may have a triangular or trapezoidal cross-sectional shape as long as they are shaped to create a level difference. The grooves 2 need not necessarily be formed to each include a single depressed region, but may be formed to each include a plurality of depressed regions with a narrow flat portion or intermediate portion.

"Ridge" means a raised portion formed in a shape similar to a stripe. FIG. 2 shows a stripe arrangement in which grooves 22 and ridges 21 are formed in the same direction. Alternatively, the grooves 22 and the ridges 21 may also be formed in a lattice-like arrangement in which they are formed in two directions crossing each other. It is also possible to form trenches 22 of different shapes, different depths or different widths on a single substrate. The trenches 22 may also be formed with varying periods on a single substrate.

"Treated substrate" means a non-nitride semiconductor substrate ( Such as sapphire, SiC, Si or GaAs substrates) produced by forming grooves and ridges.

"Nitride semiconductor substrate" means a substrate _{formed of} at least _AlxGayInzN (0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1). In the nitride semiconductor substrate, about 20% or less of nitrogen atoms contained therein may be substituted with at least one of the following group of elements: As, P, and Sb. The nitride semiconductor substrate may be doped with impurities such as n-type or p-type dopants. Examples of such impurities include: Cl, O, S, Se, Te, C, Si, Ge, Zn, Cd, Mg and Be. The total amount of impurities added is preferably not less than 5×10 ¹⁶ /cm ³ but not more than 5×10 ²⁰ /cm ³ . Among the impurities, Si, Ge, O, Se, or Cl are particularly preferable as providing n-type conductivity to the nitride semiconductor substrate. As the principal plane direction of the nitride semiconductor substrate, C plane {0001} can be employed.

A nitride semiconductor multilayer film grown on a processed substrate is called a nitride semiconductor multilayer film. Here, _{the nitride} semiconductor multilayer film is formed of _AlxGayInzN (0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1). In the nitride semiconductor multilayer film, about 20% or less of nitrogen atoms contained therein may be substituted with at least one of the following group of elements: As, P, and Sb. The nitride semiconductor multilayer film may be doped with impurities such as n-type or p-type dopants. Examples of such impurities include: Cl, O, S, Se, Te, C, Si, Ge, Zn, Cd, Mg and Be. The total amount of impurities added is preferably not less than 5×10 ¹⁶ /cm ³ but not more than 5×10 ²⁰ /cm ³ . Among the impurities, Si, Ge, O, Se, or Te are particularly preferable as providing n-type conductivity to the nitride semiconductor multilayer film, and Mg, Cd, or Be are particularly preferable as providing p-type conductivity thereof. .

In a semiconductor multilayer film, a nitride semiconductor layer first provided on a processed substrate is called a nitride semiconductor primer layer. The nitride semiconductor initial layer may be formed of, for example, GaN, AlGaN, AlInGaN, AlGaNP, or AlGaNAs.

An active layer generally refers to any layer that includes a well layer or includes one or more well layers and barrier layers. For example, an active layer having a single quantum well structure consists of a single well layer or a barrier layer, a well layer, and a barrier layer. On the other hand, an active layer having a multiple quantum well structure is composed of a plurality of well layers and a plurality of barrier layers.

In order to achieve the above objects, according to an aspect of the present invention, a nitride semiconductor device is provided with: a processed substrate formed as at least one groove by forming a groove on the surface of a nitride semiconductor substrate at least whose surface is formed of a nitride semiconductor. a recessed region and forming a ridge formed as a non-trench; and a nitride semiconductor growth layer including a plurality of nitride semiconductor thin films provided on the processed substrate, the nitride semiconductor growth layer having the same shape as {0001} The principal plane direction to which the plane is aligned. Here, the distance between a first vector extending from the surface portion of the ridge along its normal direction and a second vector extending parallel to the crystal direction <0001> assuming that the first and second vectors start at the same point The angle, that is, the inclination angle, is 0.05° or more but 4° or less.

In the above-mentioned nitride semiconductor device, preferably, the inclination angle of the processed substrate includes: a first inclination angle, which is the difference between the first vector and the crystal direction <0001> perpendicular to each other by projecting the second vector, Between the third vector obtained on the first plane formed by the crystal directions <0001> and <1-100> in <11-20> and <1-100> when assuming that the first and third vectors start at the same the angle at one point; and the second tilt angle, which is the angle between the first vector and the crystal direction by projecting the second vector into the mutually perpendicular crystal directions <0001>, <11-20> and <1-100> The angle between the fourth vector obtained on the second plane formed by <0001> and <11-20> when it is assumed that the first and fourth vectors start at the same point.

In the above nitride semiconductor device, preferably, assuming that the first off angle is θa and the second off angle is 0b, then |θa|≥|θb|.

In the above nitride semiconductor device, preferably, 0.09°≦|θa|°.

In the above nitride semiconductor device, preferably, 3×|θb|°<|θa|°<0.09°, while 0.05°≤|θa|°.

In the above nitride semiconductor device, preferably, assuming that the first off angle is θa and the second off angle is 0b, then |θa|≤|θb|.

In the above nitride semiconductor device, preferably, 0.2°≦|θb|°.

In the above nitride semiconductor device, preferably, the recessed regions formed as trenches extend in a stripe shape, and the extending direction of the recessed regions is parallel or substantially parallel to the crystal direction <1-100>.

In the above nitride semiconductor device, the recessed regions formed as trenches extend in a stripe shape, and the extending direction of the recessed regions is parallel or substantially parallel to the crystal direction <11-20>.

In the above nitride semiconductor device, preferably, the recessed region formed as the trench is formed in a lattice shape, and one of the two mutually perpendicular directions in which the lattice extends is parallel or substantially parallel to the crystal direction <11-20>, The other is parallel or substantially parallel to the crystallographic direction <1-100>.

In the above nitride semiconductor device, preferably, let the first off angle be θa and the second off angle be θb, then the direction parallel to the long side of the ridge is parallel or substantially parallel to the crystal direction <1-100>, and |0a|≥|θb|.

In the above nitride semiconductor device, preferably, let the first off angle be θa and the second off angle be θb, the direction parallel to the long side of the ridge is parallel or substantially parallel to the crystal direction <11-20>, and |θa|≤|θb|.

In the above nitride semiconductor device, preferably, the square root of the sum of the square of the first off angle and the square of the second off angle is 0.2° or more.

In the above nitride semiconductor device, preferably, the width of the ridge provided between two adjacent portions of the trench is 100 μm or more but 2000 μm or less.

In the above nitride semiconductor device, preferably, the nitride semiconductor thin film in contact with the processed substrate surface is GaN or AlGaN having a thickness of 0.5 μm or less.

In the above nitride semiconductor device, preferably, the recessed region formed as the trench has a depth of 1.5 μm or more.

In the above nitride semiconductor device, preferably, letting the total thickness of the nitride semiconductor growth layer formed on the ridge be T, the depth of the recessed region formed as the trench is T/2 or more.

In the above nitride semiconductor device, preferably, the opening of the recessed region formed as the trench is 3 μm or more.

In the above nitride semiconductor device, preferably, when the nitride semiconductor growth layer including a plurality of nitride semiconductor thin films is formed, at least one nitride semiconductor thin film is grown under the condition that the treated substrate surface temperature is 1050° C. or lower, and the ratio of the molar flow rate per unit time for supplying the source material containing group V atoms to the molar flow rate per unit time for supplying the source material containing group III atoms is 2250 or more.

According to the present invention as described above, when a nitride semiconductor device such as a nitride semiconductor laser device is manufactured by providing a nitride semiconductor growth layer on a substrate at least the surface of which is formed of a nitride semiconductor, the occurrence of cracks is prevented, and furthermore, the nitride semiconductor laser device is hindered. Atoms or molecules of the source material of the semiconductor thin film migrate or diffuse or move from the top growth portion on the ridge surface into the trenches, and thus hinder the formation of the nitride semiconductor thin film there. In this way, it is possible to form a nitride semiconductor growth layer with good surface flatness, and thus obtain a nitride semiconductor device with satisfactory characteristics.

Alternatively, according to the present invention described above, the atoms or molecules of the source material of the nitride semiconductor thin film are intentionally promoted to migrate or diffuse or move from the top growth portion on the ridge surface to the trench so that the atoms or molecules of the source material of the nitride semiconductor thin film Molecules spread or move uniformly across the entire surface of the wafer. In this way, it is possible to form a nitride semiconductor growth layer with good surface flatness, and thus obtain a nitride semiconductor device with satisfactory characteristics.

In order to achieve the above object, according to another aspect of the present invention, a nitride semiconductor initial layer first formed on a processed substrate having a trench formed thereon is formed of a compound including GaN.

With this structure, the occurrence of cracks is prevented, and the nitride semiconductor multilayer film formed thereafter has a highly uniform layer thickness and obtains a flat surface.

Here, preferably, the thickness of the nitride semiconductor initial layer is 0.5 μm or less. Preferably, the ratio of the layer thickness of the nitride semiconductor initial layer to the total layer thickness of the nitride semiconductor multilayer film is 15% or less. Preferably, an angle between a line perpendicular to the top end portion of the side wall surface of the trench and a line perpendicular to the surface other than the trench is 60° or more. Preferably, the width of the groove is 1 μm or more, and the period of the groove is 0.1 mm or more but 4 mm or less.

In the case where the aforementioned nitride semiconductor initial layer is formed of a compound including GaN, when the total layer thickness of the nitride semiconductor multilayer film is 4 μm or less, preferably, the depth of the trench is 1 μm or more but not more than 20 μm , and the width of the groove is 1 μm or more.

以下)，且因此获得提供稳定特性和长寿命的器件。In this way, it is possible to obtain an acceptable surface roughness (300

below), and thus a device providing stable characteristics and long life is obtained.

According to the present invention as described above, by manufacturing a processed substrate having a groove formed thereon, and then first disposing a nitride semiconductor layer on the processed substrate, it is possible to prevent the generation of cracks and at the same time Highly uniform layer thicknesses and good surface smoothness are obtained. That is, it is possible to increase the number of devices having characteristics satisfying the defect-free requirement, thereby improving the yield.

Description of drawings

1 is a schematic diagram schematically showing a processed substrate having an inclination angle of θa° used in a first embodiment of the present invention;

2 is a cross-sectional view schematically illustrating a processed substrate having grooves of various shapes formed thereon;

3 is a schematic view schematically showing a processed substrate having an inclination angle of θb° used in the first embodiment of the present invention;

Figure 4 is a schematic diagram schematically showing a processed substrate without an off-angle;

Fig. 5 is a schematic diagram showing the relationship between the standard deviation σ of the p-layer thickness and the yield;

6 is a schematic diagram showing the relationship between the inclination angle θa and the standard deviation σ of the p-layer thickness;

7 is a schematic diagram showing the relationship between the tilt angle θb and the standard deviation σ of the p-layer thickness;

8 is a graph of a level deviation of a wafer surface having a nitride semiconductor growth layer disposed on a processed substrate having an inclination angle of θb° employed in the first embodiment of the present invention;

9A and 9B are schematic diagrams schematically showing processed substrates used in Examples 1 to 4 of the present invention;

10 is a plot of level deviation of a wafer surface having a nitride semiconductor growth layer disposed on a processed substrate employed in Examples 1 to 4 of the present invention;

11A and 11B are diagrams schematically showing nitride semiconductor laser devices in Examples 1 to 4 of the present invention;

12A is a perspective view schematically showing a portion of a processed substrate surrounding a trench with a nitride semiconductor multilayer film formed thereon, and FIG. 12B is a cross section taken along line A-A shown in FIG. 12A picture;

FIG. 13A is a front view of a nitride semiconductor device, and FIG. 13B is a top view of FIG. 13A;

Fig. 14 is a sectional view of part B shown in Fig. 2;

15 is a schematic diagram showing the measurement results of the surface flatness of a nitride semiconductor multilayer film along the [1-100] direction;

16 is a schematic diagram showing the surface roughness of a nitride semiconductor multilayer film measured when the initial GaN layer thickness is varied;

17A is a cross-sectional view of a processed substrate having a nitride semiconductor multilayer film having good surface flatness formed thereon;

17B is a cross-sectional view of a processed substrate having a nitride semiconductor multilayer film having poor surface flatness formed thereon;

18 is a cross-sectional view of a processed substrate having formed thereon a nitride semiconductor multilayer film including an initial GaN layer having a thickness of 0.5 μm or less;

19A and 19B are schematic diagrams schematically showing a wafer having a nitride semiconductor growth layer formed on a conventionally processed substrate;

20 is a cross-sectional view schematically showing a conventional nitride semiconductor growth layer;

FIG. 21 is a plot of a level change of a wafer surface having a nitride semiconductor growth layer disposed on a conventionally processed substrate; and

22A and 22B are schematic views of models showing how reduced flatness occurs in conventional cases.

Detailed ways

first embodiment

A first embodiment of the present invention will be described below with reference to the drawings. The following description of the embodiments takes a nitride semiconductor layer as an example of a nitride semiconductor device, but it should be understood that the present invention can be implemented as any other type of nitride semiconductor device. 1 and 3 are diagrams schematically showing processed substrates 16 and 36 used in this embodiment, as viewed when nitride semiconductor multilayer film 4 is grown thereon. As shown in Figures 1 and 3, processed substrates 16 and 36 each have a fixed tilt angle. FIG. 4 is a schematic diagram schematically showing a processed substrate produced from a generally used substrate having an off-angle of 0.02° or less. In Figures 1, 3 and 4, planar directions are indicated together. In this embodiment, a nitride semiconductor laser device is manufactured by growing a nitride semiconductor multilayer film 4 on a processed substrate having a similar off angle to that of the processed substrates 16 and 36 .

First, a description will be given of how to manufacture a processed substrate 46 from a substrate having an off angle of 0.02° or less, that is, almost zero degrees, as shown in FIG. 4 . In this embodiment, it is assumed that a GaN substrate is used as the processed substrates 16, 36 and 46.

First, SiO ₂ or the like is vapor-deposited to a film thickness of 1 µm on the entire surface of the n-type GaN substrate by the sputtering method. Next, by a usual photolithography process, a stripe-shaped resist pattern is formed along the <1-100> direction such that when measured from the center line of one stripe to the center line of the other stripe in parallel to the <11-20> direction, the resist The etchant openings had a width of 5 μm, and the stripes were located at intervals of 350 μm (hereinafter referred to as “periods”). Next, by a dry etching technique such as RIE (Reactive Ion Etching), the SiO ₂ film and n-type GaN substrate were etched to form trenches 42 having a trench depth of 5 μm and an opening width of 5 μm. Then, SiO ₂ is removed by using an etchant such as HF (hydrogen fluoride). In this way, a processed substrate 46 is formed having grooves 42 and ridges 41 formed thereon.

In this embodiment, SiO ₂ is vapor deposited to form a SiO ₂ film on the surface of the GaN substrate. Alternatively, another dielectric material film or the like may be formed on the GaN substrate surface. The aforementioned SiO ₂ film may be formed by a method other than sputtering vapor deposition; for example, it may be formed by, for example, electron beam vapor deposition or plasma CVD. The period of the resist pattern is not limited to 350 μm specifically mentioned above, but may vary according to the width of the nitride semiconductor laser device to be manufactured. In this embodiment, the trenches 42 are formed by a dry etching technique; however, they may also be formed by a wet etching technique or the like.

The processed substrate 46 can be manufactured by directly forming the trench 42 on the above-mentioned n-type GaN substrate surface, or can be fabricated by forming the trench 42 on the n-type GaN substrate or on a nitride semiconductor substrate other than the n-type nitride semiconductor substrate. On the bottom, first grow nitride semiconductor films such as GaN, InGaN, AlGaN, and InAlGaN, and then form trenches on it.

Processed substrates 16 and 36 are formed by substantially the same method as processed substrate 46 . The differences are as follows. The substrate used to produce the processed substrate 16 has crystal directions <1-100> and <0001> rotated or inclined by θa° with respect to the crystal direction <11-20> as the axis of rotation, and thus in the crystal direction <0001 > have an inclination angle of θa from the direction perpendicular to the growth surface on the substrate. On the other hand, the substrate used to produce the processed substrate 36 has the crystal directions <11-20> and <0001> rotated or inclined by θb° with respect to the crystal direction <1-100> as the axis of rotation, and thus in There is an inclination angle of θb between the crystal direction <0001> and the direction perpendicular to the growth surface on the substrate. On each of these substrates having inclination angles of θa and θb, respectively, grooves 12 and 32 and ridges 11 and 31 are formed in the same manner as described above. Here, photoresist patterning, etching, and other processes are performed assuming that each substrate has a zero tilt angle.

The inclination angle can not only be inclined in one direction, such as the above-mentioned θa or θb alone, but also can be inclined in different directions at different angles (θa and θb) at the same time. Specifically, it is assumed that both the crystal directions <1-100> and <0001> are rotated or tilted by θa° about the rotation axis <11-20> direction, so that between the crystal direction <0001> and the direction perpendicular to the growth surface of the substrate There is an inclination angle of θa. Then, let the displacement vector A be the displacement vector starting from the unit vector (of length 1) along the crystal direction <0001> before the rotation and ending with the unit vector along the crystal direction <0001> after the rotation. Furthermore, it is assumed that both the crystal directions <11-20> and <0001> are rotated or tilted by θb° with respect to the rotation axis <1-100> direction, so that there exists between the crystal direction <0001> and the direction perpendicular to the growth surface of the substrate The tilt angle of θb. Then, let the displacement vector B be the displacement vector starting with the unit vector along the crystal direction <0001> before the rotation and ending with the unit vector along the crystal direction <0001> after the rotation. Then, let the displacement vector C be the sum of the displacement vectors A and B, and let the resulting vector D be the sum of the unit vector along the crystal direction <0001> and the displacement vector C before rotation. Then, the direction of the end point of this resultant vector D can be the direction in which the inclination angle is inclined. In this specification, in the case where the substrate has an off angle due to the tilt displacement vector C of the crystal direction <0001>, it is expressed by expressing both the above-mentioned off angles θa and θb.

Determination of inclination angle

As part of the description of this embodiment, how the inclination angle of the substrate affects the growth of a nitride semiconductor thin film disposed on a processed substrate having grooves and ridges formed thereon will first be given with reference to the relevant drawings. .

As shown in FIG. 4, when using a processed substrate 46 having an inclination angle of 0.02° or less, that is, almost zero, the direction perpendicular to the top 43 of the ridge 41 and perpendicular to the bottom 44 of the groove 42 is parallel to the crystal Direction <0001>. Furthermore, the three axes respectively aligned with the crystal directions <0001>, <1-100> and <11-20> are perpendicular to each other. In this case, the atoms and molecules 15 of the nitride semiconductor thin film material deposited on the top 43 of the ridge 41 do not diffuse in a specific direction with high probability, but diffuse isotropically from the position where they are deposited. As a result, atoms or molecules 15 of the nitride semiconductor thin film material migrate or diffuse isotropically, and a part of them moves into the trench 42 and forms the nitride semiconductor thin film.

Usually, when the grooves 12, 32 and 42 are formed, they are not completely uniformly formed on the entire wafer surface, but are formed during the photolithography process for forming the photoresist pattern and during the dry process. In an etching process such as etching, fluctuations attributable to the process occur. As a result, non-straight undulating boundary portions 17, 37, and 47 may be formed at the boundaries between the grooves 12, 32, and 42 and the ridges 11, 31, and 41, and at the sides 19, 39 of the grooves 12, 31, and 42. Where and 49 are not perpendicular to the bottoms 14, 34 and 44, undulating square portions 18, 38 and 48 may be formed.

When the grooves 12, 32, and 42 and the ridges 11, 31, and 41 are formed unevenly over the entire surface of the wafer due to the above-mentioned fluctuations attributable to the process, the The degree to which the atoms and molecules 15 of the nitride semiconductor thin film source material migrate or diffuse or move into the trenches 12, 31 and 42 is not uniform across the wafer but varies from region to region. That is, in some regions on the wafer, the atoms and molecules 15 of the source material of the nitride semiconductor film deposited on the tops 13, 33 and 43 of the ridges 11, 31 and 41 are more likely to migrate or diffuse or move to the grooves 12, 32 and 42, and in other regions on the wafer, the atoms and molecules 15 of the nitride semiconductor thin film source material deposited on the tops 13, 33 and 43 of the ridges 11, 31 and 41 are less inclined to migrate or diffuse or move to the grooves 12, 32 and 42.

As described above, if the atoms and molecules 15 of the nitride semiconductor thin film source material deposited on the tops 13, 33, and 43 of the ridges 11, 31, and 41 migrate or diffuse or move to the grooves 12, 31, and 42, the entire wafer is not uniform, which affects the flatness of the nitride semiconductor thin film grown on the ridges 11, 31 and 41, and as a result the film thickness of the nitride semiconductor thin film grown on the ridges 11, 31 and 41 varies across the wafer, a zone displays a different value from another zone.

If the thickness of the nitride semiconductor thin film grown on the ridges 11, 31 and 41 is so varied, it has an adverse effect on the nitride semiconductor laser device formed on the ridges 11, 31 and 41. FIG. 5 shows the degree of deviation of the p-layer thickness on the ridge (corresponding to the total p-layer thickness of the p-type Al _0.3 Ga _0.7 N evaporation preventing layer 206 to the p-type GaN contact layer 209 arranged in sequence shown in FIG. 20 . Thickness) the relationship between the standard deviation σ and yield. The graph in Fig. 5 shows that when the standard deviation σ of the p-layer thickness is 0.03 μm or less, a high yield of more than 90% is achieved, but when the standard deviation σ of the p-layer thickness is more than 0.03 μm, the yield drops sharply. decline.

The above-mentioned reason why the yield drops sharply when the standard deviation σ of the p-layer thickness is 0.03 μm or more is that if the thickness of the p-type GaN guide layer 207, the p-type Al _0.05 Ga _0.95 N cladding layer 208, etc. varies too much, when the manufacturing When devices are constructed on nitride semiconductor substrates, their electrical and optical properties change. Furthermore, if the nitride semiconductor laser device is manufactured in a region where the p-layer thickness shows a large standard deviation σ, current leakage occurs during energization. This also results in a low yield.

As described above, when manufacturing a nitride semiconductor laser device, in order to achieve a high yield, it is necessary to improve the flatness of the nitride semiconductor thin film grown on the ridge, including the thickness of the p-layer of the region where the nitride semiconductor laser device is to be manufactured . For this reason, the inventors of the present invention have invented the following two methods: a method by which the atoms or molecules 15 of the source material of the nitride semiconductor thin film are hindered from migrating or diffusing or moving to the trench; and a method by which nitrogen is consciously promoted. The atoms or molecules 15 of the source material of the compound semiconductor thin film migrate or diffuse or move to the trench.

Among the above two methods, the method of hindering the migration or diffusion or movement of the atoms or molecules 15 of the source material of the nitride semiconductor thin film to the trench involves the use of crystal directions <0001> and <1-100 as shown in FIG. >Substrates each rotated or tilted by θa° around the crystallographic orientation <11-20> as the axis of rotation yields a processed substrate 16, i.e., the crystallographic orientation <0001> after rotation has A substrate with an inclination angle of θa, and then a nitride semiconductor thin film is grown on the processed substrate. It has been found that, when a nitride semiconductor thin film is grown on such a processed substrate 16, the atoms or molecules 15 of the source material of the nitride semiconductor thin film deposited on the top 13 of the ridge 11 are more prominently aligned substantially parallel to the <1-100> direction, that is, migration or diffusion or movement in a direction parallel to the extending direction of the trench 2 rather than in the <11-20> direction. As a result, atoms or molecules 15 of the source material of the nitride semiconductor thin film deposited on top 13 of ridge 11 are prevented from migrating or diffusing or moving to trench 12 . Thus, on the top 13 of the ridge 11, the nitride semiconductor thin film is formed with good surface flatness.

On the other hand, of the above-mentioned two methods, the method in which the migration or diffusion or movement of atoms or molecules 15 of the source material of the nitride semiconductor thin film to the trench is intentionally promoted involves and <11-20> are both rotated or tilted by θb° around the crystal direction <1-100> as the rotation axis, that is, the crystal direction <0001> after rotation has a θb tilt angle with respect to the crystal direction <0001> before rotation substrate to produce a processed substrate 16, and then a nitride semiconductor thin film is grown on the processed substrate. It has been found that, when a nitride semiconductor thin film is grown on such a processed substrate 36, the atoms or molecules 15 of the source material of the nitride semiconductor thin film deposited on the top 33 of the ridge 31 are more remarkably aligned substantially parallel to The direction of the <11-20> direction, that is, migrates or diffuses or moves in a direction perpendicular to the groove extending direction and parallel to the surface of the top 33 of the ridge 31 rather than in the <1-100> direction. As a result, atoms or molecules 15 of the source material of the nitride semiconductor thin film deposited on top 13 of ridge 11 are greatly promoted to migrate or diffuse or move to trench 12 . Thus, despite the presence of the undulating boundary portion 37 and the undulating square portion 38, the atoms or molecules 15 of the source material of the nitride semiconductor thin film deposited on the top 33 of the ridge 31 uniformly migrate or diffuse over the entire wafer surface or move to the grooves. 32. Thus, on the top 13 of the ridge 11, the nitride semiconductor thin film is formed with good surface flatness.

It is known that a nitride semiconductor thin film such as a GaN-based semiconductor thin film grows faster in the <11-20> direction than in the <1-100> direction. Therefore, when the processed substrate 16 is produced by using a substrate in which both the crystal directions <0001> and <1-100> are rotated at θa° with the crystal direction <11-20> as the axis of rotation, then the nitride semiconductor thin film When growing on this processed substrate 16, the above-mentioned value θa needs to be large enough to promote the atoms or molecules 15 of the source material of the nitride semiconductor thin film deposited on the top 13 of the ridge 11, so that it is substantially parallel to The 1-100> direction migrates or diffuses or moves along the extending direction of the trench 12, and prevents the atoms or molecules 15 of the source material of the nitride semiconductor thin film deposited on the top 13 of the ridge 11 from moving along the direction parallel to the <11-20> direction. Migrate or diffuse or move into the trench 12 in a direction perpendicular to the direction in which the trench 2 extends.

The relationship between the above-described inclination angles θa and θb and the standard deviation σ of the p-layer thickness is shown in FIGS. 6 and 7 . 6 shows the relationship between the measured inclination angle θa and the p-layer on the ridge when the nitride semiconductor laser device is manufactured by using a processed substrate whose absolute value of the inclination angle θa is greater than or equal to the absolute value of the inclination angle θb. The relationship between the standard deviation σ of the thickness. 7 shows the relationship between the measured inclination angle θb and the p-layer on the ridge when the nitride semiconductor laser device is manufactured by using a processed substrate whose absolute value of the inclination angle θa is less than or equal to the absolute value of the inclination angle θb. The relationship between the standard deviation σ of the thickness. The signs (+ or -) along the horizontal axes of Figures 6 and 7 are determined by arbitrarily treating one direction intersecting the actual wafer used as positive; thus, in crystallographic terms, the signs + and - are equivalent , only the absolute values of the tilt angles θa and θb are meaningful.

Fig. 6 shows the following. In the case of using a processed substrate in which the absolute value of the inclination angle θa is greater than or equal to the absolute value of the inclination angle θb, when the absolute value of the inclination angle θa is 0.09° or more, the standard deviation σ of the p-layer thickness is Below 0.03 μm, such nitride semiconductor laser devices can be manufactured with high yield (see Figure 5). Even when the absolute value of the inclination angle θa is less than 0.09°, the standard deviation σ is 0.03 μm or less. Otherwise, the standard deviation σ of the p-layer thickness is greater than 0.03 μm; thus, it is impossible to obtain a good surface flatness on the growth surface, and thus it is impossible to achieve a high yield.

Fig. 7 shows the following. In the case of using a processed substrate in which the absolute value of the inclination angle θa is smaller than or equal to the absolute value of the inclination angle θb, when the absolute value of the inclination angle θb is 0.2° or more, the standard deviation σ of the p-layer thickness is 0.03 μm or less, and when the absolute value of the inclination angle θb is less than 0.2°, the standard deviation σ of the p-layer thickness is greater than 0.03 μm. That is, when the absolute value of the inclination angle θb is 0.2° or more, good surface flatness can be obtained on the growth surface, and the nitride semiconductor laser device can be manufactured with a high yield.

In the method of obtaining a good surface quality by assigning a large absolute value to the inclination angle θb, both the crystal directions <0001> and <11-20> are used to rotate or tilt at θb° with the crystal direction <1-100> as the axis of rotation The processed substrate 36 such that the crystal direction <0001> is inclined at 0b° with respect to the direction perpendicular to the top 33 of the ridge 31 . In this way, the atoms or molecules 15 migrate or diffuse or move to the trench 32 in one direction. Thus, as shown in FIG. 8, the surface of the nitride semiconductor thin film grown on the processed substrate 36 is inclined. FIG. 8 shows that a surface level difference detector is used to cross the surface of a nitride semiconductor thin film grown on a processed substrate 36 along a direction perpendicular to the extending direction of the trench 32 (substantially parallel to the <11-20> direction). The result of the scan. FIG. 8 shows that the surface of the nitride semiconductor thin film 32 formed on the top 33 of the ridge 31 is inclined in the direction in which the crystal direction is inclined. However, the height of the central portion of the ridge 31, that is, the raised portion of the ridge on which the nitride semiconductor laser device is formed is substantially uniform, and the p-layer thickness is also uniform. Thus, these do not cause problems in the manufacture of nitride semiconductor laser devices. Incidentally, when using the processed substrate 16 in which both the crystal directions <0001> and <1-100> are rotated or tilted at θa° with the crystal direction <11-20> as the axis of rotation, the source of the nitride semiconductor thin film The atoms or molecules 15 of the material are hindered from moving or diffusing into the groove 12, and thus, when the nitride semiconductor thin film is grown on the processed substrate 16 as described above, the nitride semiconductor formed on the top 13 of the ridge 11 The surface of the film is not inclined, but the surface is flat. Thus, it is more preferable to use the substrate 16 in which both the crystal directions <0001> and <1-100> are rotated or tilted by θa° with the crystal direction <11-20> as the axis of rotation.

In the case where the crystal orientation of the substrate is shifted by the displacement vector C described above, that is, in the case where the crystal orientation of the substrate is inclined at the inclination angles θa and θb, when the sum of the square of the inclination angle θa and the square of the inclination angle θb When the square root of is 0.2° or more, the nitride semiconductor thin film grown on the processed substrate has good surface flatness.

The above description refers to the case where the groove 12, 32 or 42 extends parallel or substantially parallel to the <1-100> direction, but in the case where the groove 12, 32 or 42 extends parallel or substantially parallel to the <11-20> direction Similar advantages can also be obtained below. Even if the recessed area is not only formed parallel or substantially parallel to the <1-100> direction, such as grooves 12, 32 or 42, but also formed parallel or substantially parallel to the <11-20> direction, so that the grooves are formed in a lattice shape In the case of ridges, it is also possible to form a nitride semiconductor thin film with good surface flatness on the ridges. In this case, it is preferable to set the inclination angles θa and θb so that atoms or molecules of the source material of the nitride semiconductor thin film deposited on the ridges diffuse or move along the long sides of the ridges separated from each other by the trenches.

By changing the inclination angle of the crystal direction of the substrate as described above, it is possible to obtain good surface flatness on the nitride semiconductor thin film grown on the ridge.

When the inclination of the crystal direction of the above-mentioned substrate includes only the inclination angle θa or θb or both inclination angles θa and θb, even when each inclination angle is set to be less than 0.05°, it is practically difficult to make each substrate Both are fabricated with an inclination angle of less than 0.05°. Typically, cleavage is used to fabricate the laser emitting end surface. However, cleavage occurs in, for example, the {11-20} or {1-100} plane along the vector direction perpendicular to the {0001} plane, and thus the end surface is inclined. In this way, setting the inclination angle to 4° or more makes it difficult for the chip to crack. Therefore, it is preferable that the inclination angle, that is, the inclination angle of the crystal orientation of the substrate, is not less than 0.05° but not more than 4°.

Example 1

Next, a practical example of the first embodiment will be described with reference to the relevant drawings. It should be understood that although the examples presented below relate to a nitride semiconductor laser device as an example of a nitride semiconductor device, the present invention is applicable to any other type of nitride semiconductor device. FIG. 11A is a cross-sectional view schematically showing the nitride semiconductor laser device of the present example, and FIG. 11B is a plan view of FIG. 11A . FIG. 9B is a diagram schematically showing the processed substrate 90 before the nitride semiconductor thin film is grown thereon in the example of the first embodiment, and FIG. 9A is a plan view of FIG. 9B . In Figures 9A, 9B and 11A, 11B, the planar directions are shown together and it is assumed that the tilt angle is equal to zero. On the processed substrate 90 shown in FIGS. 9A and 9B , for example, a nitride semiconductor multilayer film 4 structured as shown in FIG. 20 is provided to manufacture a nitride semiconductor laser device as shown in FIG. 11 .

First, a processed substrate 90 is fabricated in the same manner as the above-described processed substrates 16, 36, and 46. However, what is used here to manufacture the processed substrate 90 is a substrate having an off angle θa of -0.35° and an off angle θb of -0.02°. The grooves 91 are formed with an opening width W of 5 μm, a depth Y of 5 μm, and a period between adjacent grooves 91 of 350 μm.

On processed substrate 90 thus produced, nitride semiconductor multilayer film 4 composed of a plurality of nitride semiconductor thin films as shown in FIG. 20 is provided by appropriately using conventionally known techniques such as MOCVD. Here, first, the n-type GaN layer 200 is grown at a growth temperature of 1075° C. and a source material V/III ratio of 1200 (that is, the supply flow rate of the moles of the source material containing V group atoms per unit time versus that of the source material containing Group III atoms The ratio of the number of moles per unit time to the flow rate) grows under the condition. Next, at a growth temperature of 1075°C, the following layers are sequentially provided: the first cladding layer 201 of n-type Al _0.05 Ga _0.95 N, the second cladding layer 202 of n-type Al _0.08 Ga _0.92 N, the n-type Al _0.05 Ga _0.95 N The third cladding layer 203 and the n-type GaN guiding layer 204. Next on top, the following layers are arranged in order of their names: active layer 205, p-type Al _0.3 Ga _0.7 N evaporation preventing layer 206, p-type GaN guiding layer 207, p-type Al _0.05 Ga _0.95 N cladding layer 208 and p-type GaN contact layer 209 . Here, the active layer 205 is grown at a growth temperature of about 800° C., and the p-type Al _0.3 Ga _0.7 N evaporation preventing layer 206, the p-type GaN guiding layer 207, the p-type Al _0.05 Ga _0.95 N capping layer 208, and the p-type GaN The contact layer 209 is grown at a growth temperature of about 1030°C.

Thus, on processed substrate 90 having grooves 91 and ridges 92 formed thereon, nitride semiconductor multilayer film 4 including a plurality of nitride semiconductor thin films is provided. Here, the opening width and the like of the groove 91 are not limited to the specific values set forth above. However, if the opening width X of trench 91 is smaller than 3 μm, trench 91 is easily filled when nitride semiconductor multilayer film 4 is formed. This not only hinders the release of strain occurring inside nitride semiconductor multilayer film 4 but also causes atoms or molecules of the source material of the nitride semiconductor thin film deposited on ridge 92 to migrate or diffuse or move into trench 91 . Thus, nitride semiconductor multilayer film 4 disposed on ridge 92 undesirably has poor surface flatness. Similarly, if the depth Y of the trench 91 is less than 1.5 μm, the trench 91 is undesirably easily filled up when the nitride semiconductor multilayer film 4 is formed. In this way, it is preferable that the opening width X of the groove 91 is 3 μm or more, and the opening depth Y of the groove 91 is 1.5 μm or more. In addition, if the total layer thickness of the nitride semiconductor multilayer film 4 formed on the processed substrate 90 is greater than twice the depth Y of the trench 91, when the nitride semiconductor multilayer film 4 is disposed on the processed substrate 90 When on, the groove 91 is undesirably easy to be filled. Thus, it is preferable that the depth Y of the trench 91 is greater than half the total thickness of the nitride semiconductor multilayer film 4 formed on the processed substrate 90 .

In addition, if the ridge 92 between adjacent grooves 91 is measured along the direction substantially parallel to the <11-20> direction, that is, along the direction perpendicular to the extending direction of the groove 91 and parallel to the surface of the ridge 92 If the width is less than 100 μm, the strain occurring in the nitride semiconductor multilayer film 4 is not released, resulting in the generation of cracks, and it is also difficult to manufacture a nitride semiconductor laser device on the ridge 92 . On the other hand, if the width of ridges 92 is larger than 2000 μm, they no longer prevent the generation of cracks in nitride semiconductor multilayer film 4 . Thus, it is preferable that the width of the ridge 92 is 100 μm or more and 2000 μm or less.

In the nitride semiconductor multilayer film 4, the n-type GaN layer 200 (see FIG. 20) migrates or diffuses or moves more easily than AlGaN or other layers. Therefore, if the layer thickness of n-type GaN layer 200 is greater than 0.5 μm, n-type GaN layer 200 grown on ridge 92 flows into trench 91 more easily. Also, the total layer thickness of nitride semiconductor multilayer film 4 is larger subsequently, with the result that trench 91 is easily filled with nitride semiconductor multilayer film 4 . Thus, the thickness of the n-type GaN layer 200 is preferably 0.5 μm or less. In consideration of migration, the thickness of the n-type GaN layer 200 is preferably 0 μm, that is, the growth starts from the n-type Al _0.05 Ga _0.95 N first cladding layer 201 .

It has been found that when the nitride semiconductor multilayer film 4 composed of a plurality of nitride semiconductor thin films is provided, the ease of migration or diffusion or movement of atoms or molecules of source materials of the nitride semiconductor thin films increases with the growth of the individual nitride semiconductor thin films. vary with growing conditions. In order to obtain good flatness of the surface of nitride semiconductor multilayer film 4 grown on ridge 92, each nitride semiconductor thin film needs to be grown under conditions preventing migration of atoms or molecules of the source material of the nitride semiconductor thin film. Preferable as such growth conditions are that the surface temperature of the treated substrate is 1050° C. or lower, and the V/III ratio (the molar supply flow rate per unit time of the source material containing group V atoms to that of the source material containing group III atoms) Molar supply flow rate ratio per unit time) is 2250 or more.

The surface flatness of the surface of the above-mentioned processed substrate 90 having nitride semiconductor multilayer film 4 formed thereon was measured. Measurement results of surface flatness measured in a direction substantially parallel to the <1-100> direction, ie, in a direction parallel to the extending direction of the groove 91 are shown in FIG. 10 . Measurements are made at the central portion of the ridge 92 . Here, as will be understood from the graph of FIG. 10 , within the measured 600 μm width region, the difference in level between the highest and lowest parts of the surface is about 20 nm, and is therefore comparable to that seen in the processed substrate 6 by using The measurement results (300 nm) obtained in the case where a wafer having an almost zero (0.02° or less) tilt angle was fabricated and then grown thereon the nitride semiconductor multilayer film 4 were very small. In this way, good surface flatness is obtained.

Further, by forming the nitride semiconductor multilayer film 4 on the processed substrate 90 as described above, the nitride semiconductor laser device shown in FIGS. 11A and 11B was fabricated. This nitride semiconductor laser device has a laser bar 93 serving as a laser waveguide and a _SiO2 film 94 for current constriction disposed to sandwich the laser bar 93, which are located on a processed substrate 90. On the surface of the nitride semiconductor multilayer film 4 formed on the ridge 92, the processed substrate 90 has the groove 91 formed thereon. Then, on the surfaces of the laser bar 93 and the SiO ₂ film 94 , a p-side electrode 95 is formed, and an n-type electrode 96 is formed on the bottom surface of the processed substrate 90 . The raised portion directly on the laser bar 93 formed on the surface of the p-side electrode 95 is called a stripe 97 .

A nitride semiconductor laser device having a ridge structure similar to the above can be manufactured by first disposing a nitride semiconductor multilayer film 4 on a processed substrate 90 and then appropriately using a conventionally known technique, and thus its manufacturing method etc. will not be given a detailed description of . Then, a plurality of nitride semiconductor laser devices thus manufactured by disposing nitride semiconductor multilayer film 4 on processed substrate 90 (wafer) can be divided into individual devices. Here, first, a part of the processed substrate 90 was removed so that the wafer had a thickness of about 100 μm. Then, as n-type electrode 96, on the bottom surface of treated substrate 90, an Hf/Al layer was formed in this order from the treated substrate 90 side. Next, the wafer is cleaved along a direction substantially parallel to the <11-20> direction, ie, perpendicular to the extending direction of the grooves 91 and parallel to the surface of the ridge 92, to form resonant cavity end faces. In this way, bars (not shown) each provided with a plurality of nitride semiconductor laser devices were manufactured. In this example, the cleavage plane of the nitride semiconductor is a {11-20} plane and is inclined at an off angle of θa°. This raises concerns that the wafer will be difficult to cleave and to obtain a good cleaved surface. However, it has actually been proved that as long as the inclination angle is 4° or less, a cleaved surface good enough to be used as a cleaved surface of a nitride semiconductor laser device can be obtained. Here, it is preferable that the cavity length of the nitride semiconductor laser device is 300 μm or more and 1200 μm or less. In this example, the cavity length is 600 μm. Furthermore, on the resonator end faces formed by cleaving the wafer as described above, SiO ₂ and TiO ₂ dielectric films are alternately vapor-deposited by electron beam deposition or the like to form dielectric multilayer films. The material of these dielectric multilayer films is not limited to SiO ₂ /TiO ₂ , but may be SiO ₂ /Al ₂ O ₃ or the like. The material of the n-type electrode 96 is not limited to those specifically mentioned above, but may be Hf/Al/Mo/Au, Hf/Al/Pt/Au, Hf/Al/W/Au, Hf/Au, Hf/Mo /Au etc.

In a nitride semiconductor laser device similar to that shown in FIG. 11, the p-side electrode 95 is formed of, for example, Mo/Au or Mo/Pt/Au, or a single layer of Au from the nitride semiconductor multilayer film 4 side. In this example, the SiO ₂ film 94 is used as an insulating layer for current confinement; instead, any other insulating material such as ZrO, TiO ₂ or Si ₃ N ₄ may be used.

The bars thus manufactured are then singulated into chips to obtain individual nitride semiconductor laser devices. Since this division is performed by conventionally known techniques, no detailed description thereof will be given.

In the nitride semiconductor laser device thus manufactured, the occurrence of cracks was not observed. In addition, from among the plurality of nitride semiconductor laser devices manufactured in this example, 100 nitride semiconductor laser devices were randomly selected, and the FWHM of their FFP (far-field pattern) in the horizontal and vertical directions was measured. (Full width at half maximum, full width at half maximum). Here, a nitride semiconductor laser device whose actual FFP FWHM is within ±1 degree of the design value is counted as defect-free. The result was 94 nitride semiconductor laser devices meeting the FWHM requirements of their FFP, showing a high yield.

As described above, by forming the nitride semiconductor multilayer film 4 by growing a plurality of nitride semiconductor thin films on the processed substrate 90 having the off angles of θa and θb, it is possible to reduce the variation in the thickness of the p layer and thus reduce the variation in the thickness of the nitride semiconductor It is also possible to suppress the generation of cracks by obtaining good flatness on the thin film and thus manufacture a nitride semiconductor laser device with satisfactory characteristics at a high yield.

Example 2

In this example, processed substrates were fabricated in the same manner as in Example 1. The difference is that: the substrate used to manufacture the processed substrate has an inclination angle θa of -0.05 and an inclination angle θb of -0.39°; the opening width of the trench is 80 μm; and the spacing between adjacent trenches is 300 μm. In other respects, a nitride semiconductor laser device was fabricated in the same manner as in Example 1.

In this example, as in Example 1, after the nitride semiconductor multilayer film 4 was provided on the processed substrate, the surface flatness of the surface of the nitride semiconductor multilayer film 4 formed on the ridge was measured. In the measured 600 μm wide area, the level difference between the highest and lowest parts of the surface was 24 nm, and a good surface flatness was obtained in this way.

In addition, from a plurality of nitride semiconductor laser devices manufactured in this example, 100 nitride semiconductor laser devices were randomly selected, and their FWHM (full half maximum value) of FFP (far field pattern) along the horizontal and vertical directions were measured. Width). Here, a nitride semiconductor laser device whose actual FFP FWHM is within ±1 degree of the design value is counted as defect-free. The result was 91 nitride semiconductor laser devices meeting the FWHM requirements of their FFP, showing a high yield.

Example 3

In this example, processed substrates were fabricated in the same manner as in Example 1. The difference is that the substrate used to manufacture the processed substrate has an inclination angle θa of 0.21° and an inclination angle θb of -0.21°. In other respects, a nitride semiconductor laser device was fabricated in the same manner as in Example 1.

In this example, as in Example 1, after the nitride semiconductor multilayer film 4 was provided on the processed substrate, the surface flatness of the surface of the nitride semiconductor multilayer film 4 formed on the ridge was measured. In the measured 600 μm wide area, the level difference between the highest and lowest parts of the surface was 10 nm, thus achieving good surface flatness.

In addition, from a plurality of nitride semiconductor laser devices manufactured in this example, 100 nitride semiconductor laser devices were randomly selected, and their FWHM (full half maximum value) of FFP (far field pattern) along the horizontal and vertical directions were measured. Width). Here, a nitride semiconductor laser device whose actual FFP FWHM is within ±1 degree of the design value is counted as defect-free. The result was 97 nitride semiconductor laser devices meeting the FWHM requirements of their FFP, showing a high yield.

Example 4

In this example, processed substrates were fabricated in the same manner as in Example 1. The difference is that: the substrate used to manufacture the processed substrate has an inclination angle θa of 0.10° and an inclination angle θb of -0.02°; among the layers constituting the nitride semiconductor multilayer film 4, the n-type GaN layer 200. n-type Al _0.05 Ga _0.95 N first cladding layer 201, n-type Al _0.08 Ga _0.92 N second cladding layer 202, n-type Al _0.05 Ga _0.95 N third cladding layer 203 and n-type GaN guide layer 204 at 1030°C and the n-type GaN layer 200 and the n-type GaN guiding layer 204 are grown under the condition that the V/III ratio of the source material is 4500. In other respects, a nitride semiconductor laser device was fabricated in the same manner as in Example 1.

In this example, as in Example 1, after the nitride semiconductor multilayer film 4 was provided on the processed substrate, the surface flatness of the surface of the nitride semiconductor multilayer film 4 formed on the ridge was measured. In the measured 600 μm wide area, the level difference between the highest and lowest parts of the surface was 28 nm, and a good surface flatness was obtained in this way.

In addition, from a plurality of nitride semiconductor laser devices manufactured in this example, 100 nitride semiconductor laser devices were randomly selected, and their FWHM (half-maximum value) of FFP (far-field pattern) along horizontal and vertical inversions were measured. full width). Here, a nitride semiconductor laser device whose actual FFP FWHM is within ±1 degree of the design value is counted as defect-free. The result was 90 nitride semiconductor laser devices meeting the FWHM requirements of their FFP, showing a high yield.

As described above, in this example, the inclination angle of the substrate was smaller than that in examples 1 to 3. However, among the layers constituting the nitride semiconductor multilayer film 4, the n-type GaN layer 200, the n-type Al _0.05 Ga _0.95 N first cladding layer 201, the n-type Al _0.08 Ga _0.92 N second cladding layer 202, the n-type The third cladding layer 203 of Al _0.05 Ga _0.95 N and the n-type GaN guide layer 204 are grown under the condition of hindering migration. This contributes to the manufacture of nitride semiconductor laser devices with satisfactory characteristics at a high yield.

second embodiment

trench formation

12A is a perspective view schematically showing a portion of a trench surrounding a processed substrate having a nitride semiconductor multilayer film disposed thereon, and FIG. 12B is taken along the line A-A shown in FIG. 12A cross-sectional view. Reference numeral 120 denotes a processed substrate, reference numeral 121 denotes a nitride semiconductor multilayer film, and reference numeral 122 denotes a trench.

In this embodiment, a nitride semiconductor substrate whose surface is C-plane (0001) is used. First, on the entire surface of the nitride semiconductor substrate, SiO ₂ or the like (not shown) is vapor-deposited by sputtering to have a film thickness of 1 μm. A film of SiO ₂ or the like can be formed by other methods such as electron beam vapor deposition or plasma CVD.

Next, through a common photolithography process, the resist is set as a strip window with a width of 5 μm (indicated by W in FIG. 12 ) and a period of 250 μm (indicated by T in FIG. 12B ) along the [1-100] direction. pattern. This period T depends on the width of the semiconductor laser chip; specifically, when the chip has a width of 200 μm, the period T is set to 200 μm. Then, by ICP (inductively coupled plasma), RIE (reactive ion etching, reactive ion etching) or the like, SiO ₂ is etched to expose the surface of the nitride semiconductor substrate in a width of 5 μm, and thus formed for A SiO ₂ mask for trench formation on a nitride semiconductor substrate. Then, the nitride semiconductor substrate is etched to form trenches 122 . As such, a nitride semiconductor substrate having trenches formed thereon is referred to as a processed substrate 120 .

The depth of the groove 122 (indicated by D in FIG. 12B ) is, for example, 5 μm. Here, it is preferable that the depth D of the groove 122 is not less than 2 μm and not more than 20 μm. If the depth D is less than 2 μm, the trench 122 may be filled with the nitride semiconductor multilayer film 121 . If the trench 122 is filled, cracks may occur, the layer thickness may become non-uniform within the surface, and other problems arise. However, if the total layer thickness of nitride semiconductor multilayer film 121 is 4 μm or less, it is possible to prevent cracks and maintain flatness as long as depth D including both ends is in the range from 1 μm to 2 μm. On the other hand, if the depth D is greater than 20 μm, problems may arise in photolithography and polishing processes. For example, in a photolithography process, the thickness of the resist on the surface of the processed substrate 120 tends to be non-uniform, and thus the resist can remain where it is not sufficiently exposed, on the other hand, in the polishing process , when the wafer is polished to be thinned to about 100 μm in preparation for chip singulation, the wafer may crack.

Preferably, the width W of the trench 122 is 1 μm or more. If the width W is smaller than 1 μm, the trench 122 is completely filled when the nitride semiconductor multilayer film 121 is grown. This is because the nitride semiconductor multilayer film 121 grown from both edges of the trench 122 forms a bridge at the top of the trench and is connected to the trench 122 . When trenches 122 are filled, cracks may develop, layer thickness may become less uniform within the surface, and other problems arise.

Here, the trench 122 is completely different from the technique of forming a trench on a substrate using a lateral (horizontal) growth effect in order to reduce defect density extending from the surface to a crystal growth film. In lateral growth, in order to obtain the horizontal growth effect, trenches are usually formed at a pitch approximately equal to or less than the film thickness of the formed layer, and even at the largest trench-to-trench pitch, at approximately three times the pitch. The interval of film thickness is formed.

In contrast, in this embodiment, the groove 122 is not formed for the above purpose, but for the purpose of preventing cracks. The pitch here is on the same order as the width of the nitride semiconductor laser device, specifically, the minimum is about 0.1 mm. Furthermore, simply forming the grooves 22 results in significantly reduced planarity. Thus, it is preferable that the pitch (period) is 4 mm or less. If the pitch (period) is greater than 4 mm, it is impossible to effectively release the lattice strain occurring in the film and the strain due to the difference in thermal expansion coefficient, thus generating cracks. Thus, it is preferable that the pitch (period) of the grooves 122 is 0.1 mm or more but 4 mm or less.

Then, after etching, SiO ₂ is completely removed by an etchant such as HF to complete substrate processing before the growth of the nitride semiconductor multilayer film 121 .

In the above description, SiO ₂ and nitride semiconductor substrates are etched by vapor phase etching; alternatively, they may be etched with an etchant in a liquid phase. Trench formation using etching may be performed after first growing a nitride semiconductor layer GaN, InGaN, AlGaN, InAlGaN, or the like. That is, it is also possible to grow the nitride semiconductor layer first, then form the trench 122, and then grow the nitride semiconductor multilayer film 121.

In the case of using a substrate other than a nitride semiconductor substrate (such as a sapphire, SiC, Si, or GaAs substrate), first form a nitride semiconductor layer such as GaN, InGaN, AlGaN, InAlGaN, and then grow a nitride semiconductor multilayer film 121.

Epitaxial Growth of Nitride Semiconductor Multilayers

FIG. 13A is a front view of a nitride semiconductor device, and FIG. 13B is a top view of FIG. 13A. FIG. 14 is a sectional view of part B shown in FIG. 13 . Now, referring to FIG. 14, how a nitride semiconductor device is manufactured will be described.

First, on the MOCVD machine, use NH ₃ as the V-group source material and TMGa (trimethylgallium) or TEGa (triethylgallium) as the III-group source material, and silane (SiH ₄ ) as the dopant source material added therein, An n-type initial GaN layer 123 having a film thickness of 0.2 μm was formed on the processed substrate 120 at a substrate temperature of 1100° C. The initial GaN layer 123 is an example of a nitride semiconductor initial layer; instead, any other nitride semiconductor initial layer such as AlGaN, AlInGaN, AlGaNP, or AlGaNAs may be used.

Next, at a substrate temperature of 1050° C., by using a group V source material such as TMAl (trimethylaluminum) or TEAl (triethylaluminum), three layers of n-type cladding layers are grown, for example from the initial GaN layer 123 which includes: n-type Al _0.05 Ga _0.95 N cladding layer 124 with a layer thickness of 2.3 μm, n-type Al _0.08 Ga _0.92 N cladding layer 125 with a layer thickness of 0.2 μm and n-type Al _{0.05 Ga 0.95 N} cladding layer 126 with a layer thickness of 1.0 μm . As an n-type impurity, 5×10 ¹⁷ to 1×10 ¹⁹ /cm ³ of silicon is added.

Next, an n-type GaN photoconductive layer (having a Si impurity concentration of 1×10 ¹⁶ to 1×10 ¹⁸ /cm ³ ) 127 is grown to have a thickness of 0.2 μm.

Then, the substrate temperature was lowered to 800° C., and an active layer comprising three periods of In _0.1 Ga _0.9 N well layers each having a thickness of 4 nm combined with In _0.01 Ga _0.99 N barrier layers each having a thickness of 8 nm was grown in the following order. Layer (with multiple quantum well structure) 128: barrier layer, well layer, barrier layer, well layer, barrier layer, well layer and barrier layer. It is preferable to interrupt the growth between the barrier layer and the well layer or between the well layer and the barrier layer for more than 1 second but less than 180 seconds, because doing so helps to improve the planarity of the layers and thus reduces the light emission FWHM. Here, the addition of _SiH4 to the barrier layer or the barrier layer and the well layer can be arbitrarily avoided.

In case As is added to the active layer 1.28, _AsH3 (arsine) or TBAs (tributylarsine) is used as source material. In the case where P is added to the active layer 128, _PH3 (phosphine) or TBP (tributylphosphine) is used as a source material. In the case where Sb is added to the active layer 128, TMSb (trimethylantimony) or TISb (triethylantimony) is used as a source material. When the active layer 128 is formed, as the source material of N, instead of NH ₃ , any other source material can be used, such as N ₂ H ₄ (hydrazine, hydrazine), C ₂ N ₂ H ₈ (dimethylhydrazine, dimethylhydrazine) or any other N-containing source material.

Next, the substrate temperature was raised to 1000° C., and the following layers were sequentially grown: a p-type Al _0.2 Ga _0.8 N carrier blocking layer 129 with a thickness of 0.02 μm, a p-type GaN optical guide layer 130 with a thickness of 0.02 μm, a A p-type Al _0.05 Ga _0.95 N cladding layer 131 with a thickness of 5 μm and a p-type GaN contact layer 132 with a thickness of 0.1 μm. As a source material for p-type impurities, EtCP ₂ Mg (bisethylcyclopentadienylmagnesium) is used, and Mg is added at a concentration of 1×10 ¹⁸ to 2×10 ²⁰ /cm ³ . It is preferable that p-type GaN contact layer 132 has a higher and higher p-type impurity concentration toward p-electrode 133 . This helps to reduce the contact resistance caused by the p-electrode 133 . In order to remove hydrogen remaining in the p-type layer that hinders the activation of Mg serving as a p-type impurity, a trace amount of oxygen may be mixed in the growth of the p-type layer.

The sum of the thicknesses of the individual nitride semiconductor multilayer films 121 manufactured as described above is about 3.58 μm. The nitride semiconductor multilayer film 121 consists of an initial GaN layer 123, an n-type Al _0.05 Ga _0.95 N cladding layer 124, an n-type Al _0.08 Ga _0.92 N cladding layer 125, an n-type Al _0.05 Ga _0.95 N cladding layer 126, and an n-type GaN light guide layer 127, active layer 128, p-type Al _0.2 Ga _0.8 N carrier blocking layer 129, p-type GaN optical guiding layer 130, p-type Al _0.05 Ga _0.95 N cladding layer 131 and p-type GaN contact layer 132.

After the growth of the p-type GaN contact layer 132, all the gases in the reactor of the MOCVD machine were replaced by nitrogen carrier gas and NH ₃ , and the temperature was decreased at a rate of 60° C./min. When the substrate temperature became equal to 80°C, the supply of NH ₃ was stopped, and then the substrate temperature was maintained for 5 minutes, and then the substrate temperature was lowered to room temperature. Here, it is preferable that the temperature at which the substrate is held is between 650° C. and 900° C., and the time at which the substrate is held at this temperature is 3 minutes or more but 10 minutes or less. In addition, it is preferable that the rate of temperature decrease is 30° C./min or more.

The nitride semiconductor multilayer film 121 manufactured as above was evaluated by Raman measurement. As a result, p-type features (Mg activated) were observed immediately after growth even without p-type annealing after the wafer was removed from the MOCVD machine. In addition, the contact resistance due to the formation of the p-electrode 133 is lower. The above method can be combined with conventional p-type annealing to achieve a higher Mg activation rate.

In the above-described embodiments, the active layer 128 is structured so as to start with a barrier layer and end with a barrier layer; instead, it may also be structured so as to start with a well layer and end with a well layer. The number of well layers is not limited to three specifically mentioned above, but may be ten or less, since in this case they provide a low threshold current density and can sustain oscillation at room temperature. A particularly preferred range for the number of well layers is from two to six, since then they provide particularly low threshold current densities. The above-mentioned active layer 128 may additionally contain Al. Here, Si as an impurity is not added to the well layer and barrier layer 128 constituting the active layer; however, an impurity may be added. Adding impurities such as Si to the active layer 128 tends to increase light emission density. Such impurities include O, C, Ge, Zn, and Mg in addition to Si, and these may be used alone or in combination of two or more thereof. The total amount of impurities added is preferably about 1×10 ¹⁷ to 8×10 ¹⁸ /cm ³ . Impurities may be added to the well layer and the barrier layer or only to the well layer or the barrier layer.

The p-type Al _0.2 Ga _0.8 N carrier blocking layer 129 may have any other composition than those specifically mentioned above. AlGaN having In added thereto undergoes p-typification even when grown at a low temperature. This helps to reduce damage to the active layer 128 during crystal growth and is therefore preferable. The carrier blocking layer 129 itself can be omitted, but its presence contributes to a low threshold current density. This is because the carrier blocking layer 129 serves to seal carriers in the active layer 128 . The higher the Al composition in the p-type Al _0.2 Ga _0.8 N carrier blocking layer 129 is, the higher the density of carriers is blocked, and therefore the better. On the other hand, it is preferable to reduce the Al composition, as long as the carrier can be kept sealed (enclosure), because doing so helps to improve the carrier mobility in the carrier blocking layer 129, thus contributing to Reduce the resistance there.

In the above-described embodiments, the n-type cladding layers 124 to 126 and the p-type cladding layer 131 are each formed of Al _0.05 Ga _0.95 N or Al _0.08 Ga _0.92 N crystal. Alternatively, an AlGaN crystal having an Al composition other than 0.05 or 0.08 may be used. The higher the Al composition in these layers, the greater their energy gap and refractive index difference from the active layer 128 . This helps to effectively enclose carriers and light in the active layer 128, and helps reduce the threshold current density of laser oscillation. On the other hand, reducing the Al composition helps to increase the carrier mobility in the capping layers 124 to 126 and helps to lower the operating voltage of the device as long as the carriers and light are kept trapped.

In the above-described embodiments, the n-type AlGaN cladding layers 124 to 126 have a three-layer structure. This allows the vertical transverse mode to have a single peak, improves the light blocking efficiency, and helps to improve the optical properties of the laser and reduce the laser threshold current density. The number of n-type AlGaN cladding layers may be other than three; that is, one or more may be employed without causing any problem. In the above description, the cladding layer is formed of a three-element mixed crystal, that is, AlGaN; instead, a four-element mixed crystal, such as AlInGaN, AlGaNP, or AlGaNAs, may be used. For low resistance, the p-type cladding layer 130 may have a superlattice structure including a p-type AlGaN layer and a p-type GaN layer, or a superlattice layer including a p-type AlGaN layer and a p-type AlGaN layer, or include a p-type AlGaN layer. and a superlattice structure of p-type InGaN layers.

Properties of Nitride Semiconductor Multilayer Films

以下，且显示获得了具有很小的表面不规则性的平整表面。还在衬底的整个表面详细测量了Ra，且结果显示获得了平整表面。In the nitride semiconductor multilayer film 121 produced in this example, no cracks were observed. In addition, the surface flatness within the surface was measured on a touch-probe-type level difference tester. FIG. 15 shows the measurement results of the surface flatness of the nitride semiconductor multilayer film 121 in the [1-100] direction. The results show that the surface roughness (Ra) is 100 in the measured range of 600 μm

Below, and it is shown that a flat surface with little surface irregularity is obtained. Ra was also measured in detail over the entire surface of the substrate, and the results showed that a flat surface was obtained.

Furthermore, under a SEM (Scanning Electron Microscope), the distribution of the thickness of each layer of the nitride semiconductor multilayer film 121 within the surface of the substrate was measured. The results show that values of the standard deviation indicating the degree of variation are as small as a maximum of 5%. That is, it was found that the thickness of each layer of the multilayer film was uniform.

Device Separation Process

Next, a description will be given of a process of taking out the wafer having the nitride semiconductor multilayer film 121 provided on the ridge 12 from the MOCVD machine and then processing the wafer into nitride semiconductor device chips.

First, the ridge stripe portion 134 serving as a laser waveguide region is formed. This is formed by etching the epitaxial wafer from the epitaxial wafer surface side to the middle or bottom end of the p-type cladding layer 131 so that stripe-shaped portions remain. Here, the stripe width is 1 to 3 μm and preferably 1.3 to 2 μm. Then, an insulating film 135 is formed other than the ridge-stripe portion 134 . Here, the insulating film 135 may be formed of AlGaN. Since a portion of the p-type GaN contact layer 132 which remains unetched is exposed, on this portion as well as on the insulating film 135, the p-electrode 133 is formed by sequentially vapor-depositing Pd/Mo/Au.

Here, the insulating film 135 may be formed of materials other than those specifically mentioned above, such as oxides or nitrides of titanium, zirconium, tantalum, aluminum, or the like. The p-electrode (216) may alternatively be formed of Pd/Pt/Au, Pd/Au or Ni/Au.

In addition, the bottom surface of the epitaxial wafer (the surface of the nitride semiconductor substrate) is polished so that the wafer is 80 to 200 μm thick, thereby facilitating division of the wafer to be performed later. The n-electrode 136 is formed by sequentially disposing Hf/Al on the bottom surface 120 . The n-electrode 136 may instead be made of Hf/Al/Mo/Au, Hf/Al/Pt/Au, Hf/Al/W/Au, Hf/Au, Hf/Mo/Au or Ti or Zr in one of these An improved combination to replace Hf.

Finally, the epitaxial wafer was cleaved in a direction perpendicular to the ridge-stripe direction to produce a Fabry-Pérot cavity with a cavity length of 600 μm. Preferably the resonant cavity length is 250 μm to 1000 μm. Through this process, the wafer is diced into strips, each strip having a laterally extending array of connected nitride semiconductor devices. The cavity end face of the nitride semiconductor device having the ridge-stripe portion 134 formed in the <1-100> direction is the {1-100} plane of the nitride semiconductor crystal. Instead of feedback at the end face, a DFB (Distributed Feedback) in which feedback is realized by diffraction gratings provided inside, or a DBR (Distributed Bragg Reflector) in which feedback is realized by diffraction gratings provided outside may be used.

After the Fabry-Pérot cavity facets were formed, _SiO2 and _TiO2 dielectric films with a reflectivity of about 80% were alternately vapor-deposited on these facets to form a dielectric multilayer reflective film (not shown). The dielectric multilayer reflective film can be formed of any other dielectric material. Thereafter, the bar is divided into individual devices to obtain the nitride semiconductor device shown in FIG. 13 . This device has a laser waveguide region (ridge-stripe portion 134) disposed in the middle thereof, and has a lateral width of 250 μm.

Characteristics of Nitride Semiconductor Devices

Throughout the experiment, it was confirmed that the nitride semiconductor device achieved a laser oscillation life of more than 5000 hours under the following conditions: oscillation wavelength 405±2nm; laser output 60mW; ambient temperature 70°C. In addition, a flat surface with small surface irregularities is obtained, and the thickness of each layer of the nitride semiconductor multilayer film 121 is highly uniform within the substrate surface. In this way, there is little variation in characteristics among individual devices, thereby providing high reliability. As a result, the number of devices having characteristics not satisfying the requirements for a defect-free device is reduced, and the yield is improved.

Relationship Between Surface Flatness and Crack Generation

Now, the observed relationship between surface flatness and crack generation when the initial GaN layer 123 varies with the depth D and width W of the trench 122 will be given. FIG. 16 shows measurement results of the surface roughness of the nitride semiconductor multilayer film 121 observed when the thickness of the initial GaN layer 123 was varied from 0 to 2.0 μm.

以下。该厚度300相当于当p型层具有0.62μm厚度时器件总厚度的约5％。此外，如果表面粗糙度为5％，表明可比较的(comparable)变化存在于各层厚度中(此处，p型层的厚度)。p型层厚度的变化最影响激光特性。当作为电流限制结构的脊条纹部分134形成时，p层的2μm宽的部分被剩余作为脊条纹部分134，且剩余部分被通过气相蚀刻例如ICP而蚀刻。由于公知最显著影响激光特性的是脊条纹部分134的高度，即从有源层128到被蚀刻区的距离，如果p型层厚度在衬底表面内不同位置处是变化的，激光特性随着变化。这样，大的表面粗糙度不仅导致低的成品率，而且不利地影响器件寿命。Throughout the previous experiments, it is known that the allowable range of surface roughness for the variation of device characteristics and device lifetime is 300

the following. The thickness is 300 This corresponds to about 5% of the total thickness of the device when the p-type layer has a thickness of 0.62 μm. Furthermore, if the surface roughness is 5%, it shows that comparable variation exists in each layer thickness (here, the thickness of the p-type layer). Variations in the thickness of the p-type layer most affect the lasing characteristics. When the ridge stripe portion 134 as the current confinement structure is formed, a 2 μm wide portion of the p layer is left as the ridge stripe portion 134 , and the remaining portion is etched by vapor phase etching such as ICP. Because it is known that the height of the ridge stripe part 134 is the height of the ridge stripe part 134, that is, the distance from the active layer 128 to the etched region, if the thickness of the p-type layer varies at different positions in the substrate surface, the laser characteristics will increase with the Variety. Thus, large surface roughness not only leads to low yield, but also adversely affects device lifetime.

以下。这样，优选用在此实施例中的初始GaN层123的厚度为0.5μm以下。在氮化物半导体多层膜121包括初始GaN层123以外的GaN的情况下，优选在氮化物半导体多层膜121中的GaN层的总厚度为氮化物半导体多层膜121的总层厚的15％以下。FIG. 16 shows that when the thickness of the initial GaN layer 123 is 0.5 μm or less, the surface roughness is 300

the following. Thus, it is preferable that the thickness of initial GaN layer 123 used in this embodiment is 0.5 μm or less. In the case where the nitride semiconductor multilayer film 121 includes GaN other than the initial GaN layer 123, it is preferable that the total thickness of the GaN layers in the nitride semiconductor multilayer film 121 is 15% of the total layer thickness of the nitride semiconductor multilayer film 121. %the following.

Thus, sufficient research was conducted to find out why, when the thickness of the initial GaN layer 123 is greater than 0.5 mm, a large surface roughness as shown in FIG. 16 results, in other words, a large layer thickness distribution occurs within the surface. Through this study, it was found that the thickness of each layer of the nitride semiconductor multilayer film 121 varies because the initial GaN layer 123 is affected by it when the nitride semiconductor multilayer film 121 is epitaxially grown.

17A is a sectional view of a processed substrate 120 with a nitride semiconductor multilayer film 121 having good flatness, and FIG. 17B is a processed substrate 120 with a nitride semiconductor multilayer film 121 having poor flatness. A cross-sectional view of the processed substrate 120. Now, a detailed description will be given of a growth mechanism model that produces a change in thickness of each layer of nitride semiconductor multilayer film 121 with reference to FIGS. 12 and 17A, 17B.

It is found that when the angle θ between the line [0001] perpendicular to the surface 137 of the nitride semiconductor multilayer film 121 outside the trench 122 shown in FIG. When the angle is less than 60°, a large variation in the thickness of each layer of the nitride semiconductor multilayer film 121 occurs. In this case, the nitride semiconductor multilayer film 121 flows into the trench 122 as shown in FIG. 17B . This inflow occurs because the source material (mainly Ga) that has reached surface 137 at the time of epitaxial growth of nitride semiconductor multilayer film 121 is promoted by surface migration to flow into trench 122 .

As shown in FIG. 21, when the thickness of the initial GaN layer 123 is 1.0 μm, the surface flatness of the nitride semiconductor multilayer film 121 is such that the level difference between the highest and lowest parts thereof is 300 nm, showing that the surface has a large surface irregularities.

In addition, the layer thickness variation of the nitride semiconductor multilayer film 121 within the substrate surface was evaluated on a reflective film thickness detector. Here, fast Fourier transform processing (FFT) was performed on the reflection peak profile obtained from the reflection film thickness detector, and based on the p-type carrier blocking layer 129 having the largest refractive index difference among the layers and the p-type The reflection peaks at the interface between the GaN optical guiding layers 130 evaluate the p-type layer thickness distribution within the substrate surface. Here, the thickness of the p layer represents the total thickness of the following three layers: p-type GaN optical guiding layer 130 , p-type AlGaN cladding layer 131 and p-type GaN contact layer 132 . As a result, it was found that when the thickness of the initial GaN layer 123 is 0.5 [mu]m or more, the degree of variation (standard deviation) of the layer thickness within the substrate surface is 5% or more.

Furthermore, the growth in trench 122 was observed in detail under SEM. What was observed will be described in detail below with reference to FIGS. 12 and 18 . 18 is a cross-sectional view of a processed substrate having a nitride semiconductor multilayer film 121 in which an initial GaN layer 123 has a thickness of 0.5 μm or less. FIG. 18 shows that when the initial GaN layer 123 has a thickness of 0.5 μm or less, the thickness at the upper end of the trench 122 is greater than the thickness of the flat region E on the surface 137 by H. The thickness difference H is 0.2 to 1.5 μm.

Further, in this case, the line [0001] perpendicular to the surface 137 of the nitride semiconductor multilayer film 121 shown in FIG. The angle θ between them is greater than 60°. A surface with an angle θ equal to 60° is considered to correspond to the (11-22) plane. In this embodiment, the angle θ is 80°. The angle θ should be greater than 60°, and preferably 80° or greater. This is because the larger the angle θ is than 60°, the less likely is the (11-22) plane on which inflow occurs.

growth model

Based on the results presented so far, a description will be given of a growth mode model using the processed substrate 120 having the trench 122 formed thereon. When the supply of source material gas starts and growth starts, the Ga source material reaches the surface. Ga then migrates on the surface (surface diffusion), and when it reaches an energetically stable position, it is absorbed by the film. As this process is repeated, the membrane grows gradually. Meanwhile, when the thickness of initial GaN layer 123 becomes 0.5 μm or more, Ga atoms migrate from surface 137 toward trench 122 as shown in FIG. 17B . During this inflow process, the inflow of Ga atoms along the [11-22] direction is extremely inhomogeneous due to various reasons such as inhomogeneity in the trench formation process. In this way, although inflow occurs in some areas, inflow does not easily occur in other areas.

Where inflow into trench 122 occurs, surface 137 is thinned for reasons related to source material efficiency. Where inflow is less likely to occur, the surface 137 becomes thicker. Thus, poor flatness results. Therefore, by suppressing this inflow, it is possible to obtain good flatness. One growth method to suppress influx is to grow initial GaN layer 123 at the top of trench 122 at a higher growth rate than elsewhere so that a barrier wall (thickness difference H in FIG. 18 ) is formed that prevents Ga source material from flowing into trench 122. This is effective for making the layer thickness uniform. As previously described, such barrier ribs are formed when the initial GaN layer 123 has a layer thickness of 0.5 μm or less.

In addition, as previously described, it is preferable that the pitch between the grooves 122 is not less than 0.1 mm but not more than 4 mm. The initial GaN layer 123 preferably has a thickness of 0.5 μm or less. The thickness of the initial GaN layer 123 is preferably 15% or less of the total thickness of the nitride semiconductor multilayer film 121 . The angle θ should be greater than 60°, preferably greater than 80°. Preferably, the depth D of the trench 122 is not less than 2 μm and not more than 20 μm, and the width W of the trench 122 is not less than 1 μm.

The nitride semiconductor device according to the present invention finds wide application in laser devices, light-emitting devices, light-receiving devices, etc., and thus can be suitably used in optical disk storage/reproduction equipment, laser printers, barcode readers, projectors, display device etc.

Claims (10)

1. nitride compound semiconductor device comprises:

The substrate of handling, form on the surface by the nitride-based semiconductor substrate that forms by nitride-based semiconductor at least one surface as the groove of at least one depressed area and as the spine of non-groove form and

The nitride semiconductor growing layer comprises a plurality of nitride semiconductor thin films on the substrate that is grown in described processing,

The primary flat direction of set described nitride semiconductor growing layer with the 0001} planar alignment,

Inclination angle wherein, promptly first vector that extends from the surface portion of spine along the direction vertical with the top of spine be parallel to crystallographic direction＜0001 angulation between second vector that extends, when supposing that described first vector and described second vector start from same point, be more than 0.05 ° but below 4 °, and

The width of wherein said non-groove is greater than 100 μ m but below 2000 μ m,

Wherein the depressed area is stayed on the part surface of the described nitride semiconductor growing layer on the groove of the substrate that is positioned at described processing,

Wherein the inclination angle comprises: first inclination angle, this angle be second vector and by first vector is projected to by mutually perpendicular crystallographic direction＜0001,＜11-20 and＜1-100 in crystallographic direction＜0001 and＜1-100 between the 3rd vector that obtains on formed first plane, the angle when hypothesis the second and the 3rd vector starts from same point; With second inclination angle, this angle be second vector and by first vector is projected to by mutually perpendicular crystallographic direction＜0001,＜11-20 and＜1-100 in crystallographic direction＜0001 and＜11-20 angle between the four-vector that obtains on formed second plane, when hypothesis second and the four-vector start from same point

Make that first inclination angle is that the θ a and second inclination angle are θ b, then | θ a| 〉=| θ b|, 0.09 °≤| θ a|.

2. nitride compound semiconductor device as claimed in claim 1, extend with stripe-shaped the described depressed area that wherein forms groove, and described depressed area is parallel or be basically parallel to crystallographic direction＜1-100〉extend.

3. nitride compound semiconductor device as claimed in claim 1, extend with stripe-shaped the described depressed area that wherein forms groove, and described depressed area is parallel or be basically parallel to crystallographic direction＜11-20〉extend.

4. nitride compound semiconductor device as claimed in claim 1 is the GaN with the following thickness of 0.5 μ m with the contacted described nitride semiconductor thin film of the substrate surface of described processing wherein, or AlGaN.

5. nitride compound semiconductor device as claimed in claim 1, the degree of depth that wherein forms the described depressed area of described groove are more than the 1.5 μ m.

6. nitride compound semiconductor device as claimed in claim 1, wherein making the gross thickness that is formed on the described nitride semiconductor growing layer in the described spine is T, the degree of depth that then forms the described depressed area of described groove is more than the T/2.

7. nitride compound semiconductor device as claimed in claim 1, the A/F that wherein forms the described depressed area of described groove are more than the 3 μ m.

8. nitride compound semiconductor device as claimed in claim 1,

Wherein the nitride semiconductor growing layer comprises the nitride-based semiconductor initiation layer on the substrate that at first is formed on described processing, and

Wherein said nitride-based semiconductor initiation layer is the compound that contains GaN, and total bed thickness of described nitride semiconductor growing layer is below the 4 μ m.

9. nitride compound semiconductor device as claimed in claim 8, the degree of depth of wherein said groove are that 1 μ m is above but below 20 μ m.

10. nitride compound semiconductor device as claimed in claim 8, the width of wherein said groove are more than the 1 μ m.

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