KR20030081594A - Method for growing Crystal of Nitride chemical semiconductor - Google Patents

Abstract

PURPOSE: A method for growing crystal of nitride semiconductor is provided to be capable of improving the light emitting efficiency of a semiconductor device by considerably increasing the rate of a low potential density region using a predetermined mask pattern. CONSTITUTION: The first nitride semiconductor layer is formed at the upper portion of a substrate. After coating mask material layer on the upper surface of the first nitride semiconductor layer, a plurality of windows(A) are regularly formed at the mask material layer. At this time, each window is shaped into an equiangular triangle. Then, the second nitride semiconductor layer is formed by laterally growing the crystal of the first nitride semiconductor layer through the windows. Preferably, the windows are formed into a zigzag shape.

Description

Method for growing Crystal of Nitride chemical semiconductor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method of a nitride semiconductor, and more particularly, to a nitride semiconductor crystal growth method for reducing crystal defects in an entire nitride thin film by using a mask pattern of a specific type such as a nitride crystal form.

In general, nitride semiconductor devices can be applied to optical devices that can emit light in a short wavelength region using a wide band gap, and high temperature, high frequency, and high power electronics due to excellent characteristics such as high electron saturation speed, large breakdown voltage, and high thermal conductivity. Research for the application to the device is actively progressing.

Conventionally, when growing a semiconductor thin film for fabricating a nitride semiconductor device, it was common to grow directly on top of a sapphire substrate, which is a heterogeneous material, to be suitable for growth of a wurtzite structure.

This is because the sapphire substrate has advantages of being easier to obtain than other substrates, simple process of substrate pretreatment, and stable at high temperature during nitride semiconductor growth.

However, since there is a big difference in the coefficient of thermal expansion and lattice constant with the nitride semiconductor thin film, there is a fundamental limitation in obtaining a high quality thin film by reducing crystal defects.

In other words, when the thin film is grown on the dissimilar substrate, the thermal expansion coefficient and lattice constant between the substrate and the thin film are different, so that defects such as penetration dislocations are generated.

To this end, a buffer film is formed between the dissimilar substrate and the nitride semiconductor thin film to reduce the driving force through which the penetration potential is transferred and propagated from the dissimilar substrate to the nitride semiconductor thin film, and through the heat treatment process after applying a large stress to the buffer film. Although there are ways to remove the defects from the outside, these methods also have limitations in reducing the defects.

Therefore, without growing a nitride semiconductor device directly on top of the sapphire substrate, it is necessary to first grow a first nitride substrate as a base material for subsequent growth of the optical device, and research on this is being actively conducted.

Recently, lateral growth methods such as Pendeoepitaxy and Lateral Epitaxial Overgrowth (LEO) have been reported to reduce the density of crystal defects. The two methods are briefly described.

First, the pendio epitaxy method will be described with reference to FIGS. 1A to 1C.

In the Pendo epitaxy method, the nitride layer 11 is first grown on the sapphire substrate 10 (FIG. 1A), a mask pattern is formed, and then the nitride layer and a portion of the sapphire are etched to form a stripe-shaped nitride pattern. Many are formed (FIG. 1B).

Subsequently, the mask pattern is removed to grow nitrides laterally from the surface where a portion of the sapphire substrate 10 is etched, and the grown nitride crystals coalesce to form crystal growth (FIG. 1C).

As described above, the Pendo epitaxy method forms a nitride layer in a plurality of stripe forms, and then laterally grows the substrate (Island) as a base material.

However, this method has a problem that the defect density at the side where the lateral growth occurs is low, but the defect density of the island which is the base material of the side growth cannot be changed, so that the overall average defect density cannot be reduced any more. If there are many defects of the part (Island), the crystallinity of the side-grown part is also not excellent.

Next, the LEO growth method will be described with reference to FIGS. 2A to 2C.

In the LEO growth method, first, a first nitride thin film 21 as a base material is grown on a heterogeneous substrate 20, and a linear repetitive mask pattern is formed on the grown first gallium nitride thin film 21 with a dielectric film 22. Deposit (FIG. 2A).

When the second nitride thin film is laterally grown by vapor phase growth or the like after the deposition of the mask pattern (FIG. 2B), growth is performed upward on the surface of the exposed first nitride thin film in which the mask pattern does not exist. In side growth, defects such as through dislocations are also grown, and a dotted line in FIG. 2B indicates such a defect.

Subsequently, the laterally grown nitrides are formed in the transverse direction to form a second nitride thin film having an overall flat surface (FIG. 2C).

Although the LEO growth method is effective for partially obtaining a region having a small defect density, stress is generated by the reaction with the mask while growing laterally on the mask, and defects such as penetration dislocations as shown in FIG. Is also growing together.

Therefore, the portion of the side growth through the mask pattern decreases the defect density, but the portion of the first nitride thin film, which is the lower base material, is transferred as it is, so that the defect is not excellent in crystallinity.

In addition, the parts with high and low defect densities are present at regular intervals, so that there is a limit in the average reduction of the defect densities.

According to the research results of the University of Tokushima, Japan, it can be seen that the penetration potential that grows together when the nitride thin film grows acts as a non-luminescent bonding center, thereby lowering the luminous efficiency of the device. It is a figure which measured the relationship between the dislocation density and luminous efficiency in n-type gallium nitride when the hole diffusion length is 50 nm.

As shown in the figure, the luminous efficiency reaches 0.5 when the dislocation density is 10 ⁸ / cm ^-2 , but the luminous efficiency drops to 0.95 when the dislocation density is 10 ⁹ / cm ^-2 .

In addition, when the dislocation density is 10 ¹⁰ / cm ^-2, the average dislocation distance corresponds to 100 nm, which is twice the average diffusion length. When all the carriers can reach the dislocation, the emission efficiency drops to zero. Means that.

This result is also applied to the fabrication of the actual optical device, and compared with the case of manufacturing a light emitting diode with a thin film having a dislocation density of about 10 ⁹ to 10 ¹⁰ cm ^-2 , the crystalline having a dislocation density of 10 ⁸ cm ^-2 or less It can be seen that the light output is greatly improved when the light emitting diode is manufactured from the thin film.

For this reason, it is important to lower the dislocation density of the nitride thin film, and as the ratio of the regions having lower dislocation densities increases, the luminous efficiency of the entire device is improved.

Therefore, it is necessary to find a way to increase the ratio of regions with low dislocation densities so that a stable and high-performance device can be manufactured.

Accordingly, an object of the present invention is to provide a nitride semiconductor crystal growth method for improving the light emitting efficiency of a device by greatly increasing the ratio of a region having a low dislocation density during nitride crystal growth.

To this end, the present invention forms a first nitride semiconductor layer on the dissimilar substrate, and a mask material is applied on the formed first nitride semiconductor layer, so that the surface of the nitride is formed using a mask pattern in which a regular number of regular triangular windows are zigzag-shaped. Let it grow.

Another embodiment of the present invention is to form a nitride semiconductor layer on the dissimilar substrate, the nitride semiconductor layer and a portion of the substrate are etched to form a nitride pattern in which a regular number of regular triangular windows are formed, and then use the nitride semiconductor crystal Let it grow.

1A to 1C are process schematic diagrams of nitride semiconductor crystal growth according to a general peneoepitaxy growth method,

2A to 2C are process schematic diagrams of nitride semiconductor crystal growth according to a typical latent epitaxial overgrowth (LEO) growth method.

3 is an experimental measurement of the relationship between the penetration potential generated during the growth of nitride semiconductor crystals and the luminous efficiency.

4 is a view showing a mask pattern used in the growth of a conventional nitride semiconductor crystal,

5 is a view showing a mask pattern used in the growth of the nitride semiconductor crystal of the present invention,

FIG. 6A is a partial plan view of a mask pattern showing an arrangement of a mask window on a substrate;

6B is a view showing that the nitride crystals are laterally grown to the top of the mask window in a regular hexagonal shape.

FIG. 6C shows that regular hexagonal nitride crystals fill the mask in contact with adjacent crystals.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

First, the first embodiment to which the present invention is applied to the LEO growth method will be described.

<First Embodiment>

In the first embodiment, first, a chloride vapor growth method (Halide Vapor Phase Epitaxy), an organic metal chloride vapor deposition method (Metal Organic Chloride Vapor Phase Epitaxy) or an organic metal vapor deposition method (Metal Organic Chemical Vapor Phase Deposition) And the like to grow a first gallium nitride thin film.

At this time, the substrate uses a heterogeneous substrate such as sapphire (Al ₂ O ₃ ), silicon carbide (SiC), silicon and gallium arsenide (GaAs).

Subsequently, a dielectric film such as a silicon oxide film (SiO ₂ ), a silicon nitride film (Si ₃ N ₄ ), or a metal thin film such as W, Ta, or Pt is deposited on the first gallium nitride thin film.

Next, the deposited dielectric film or the metal thin film is formed using photolithography to form a mask pattern in which regular windows having a rectangular shape are formed.

In particular, since the crystal form of the first gallium nitride, which is a base material, is hexagonal, it is most preferable that the angular shape is an equilateral triangle as shown in FIG. 5, and a mask pattern in which a large number of such equilateral triangular windows are zigzag is formed. .

That is, as illustrated in FIG. 6A, it is most preferable to form a mask pattern so that a regular triangular window is formed centering on the vertex position of the regular hexagon group.

The width W1 of one side of the formed equilateral triangle is about several μm, and the range thereof is about 1 μm <W1 <30 μm, and the width W2 that is the distance between the equilateral triangles is most preferably about 1 μm <W2 <30 μm. .

Next, the first gallium nitride as a base material is laterally grown through the window of the equilateral triangle thus formed.

Then, a nucleus of gallium nitride crystals isolated by the window is formed, and the nucleus of gallium nitride crystals is expanded from the nucleus on which the gallium nitride crystal is formed to the surface direction along the upper portion of the mask pattern.

At this time, since gallium nitride has a hexagonal crystal form, it has symmetry in the direction of rotation by 60 ^{0. According} to the symmetry of the crystal, the crystal is enlarged into a pyramidal shape, and the orientation of the crystal is determined by the window crystal. Will match the orientation.

Therefore, when the mask pattern is formed on the [0001] -orientation gallium nitride layer, not only side growth occurs in a direction perpendicular to the [11-20] orientation, but also [2-1-10 rotated by 60 degrees each from side to side. Side growth also occurs in a direction perpendicular to the direction and in a direction perpendicular to the [-12-10] direction.

The negative amount of the crystallographic orientation is indicated by adding-above the number, but in front of the number because the expression cannot be expressed in the patent specification.

As described above, when the side growth is performed and the gallium nitride is grown to the thickness of the window, the crystals are returned to the upper side of the window and the crystal growth proceeds in the transverse direction. (FIG. 6B).

Then, the hexagonal crystals are coalesced and the hexagonal crystals such as honeycomb are repeatedly formed (FIG. 6c). At this time, it is important to make almost simultaneous contact, and then increase the thickness in the upward direction after the contact is made. Crystal grows.

Comparing the above crystal growth method with the conventional LEO crystal growth method has the following advantages.

In the conventional LEO crystal growth method, as shown in FIG. 4, since the portion where the dielectric film is located is laterally grown, the penetration potential located at the lower portion of the dielectric film is not transferred upward, and thus the dislocation density is relatively low.

However, in the window part without the dielectric film, since the through potential is transferred directly from the first gallium nitride thin film, the dislocation density is high and the overall performance of the device is not good.

In addition, there is a limit in increasing the relative ratio of the dielectric film width (the ratio of the portion where the dislocation density grows relatively low) by adjusting the dielectric film width W1 and the window width W2.

In other words, if the dielectric film width W1 is excessively increased, it is difficult to grow to fill all of the upper part of the dielectric film through lateral growth, and if the window width W2 is excessively reduced, the parts that need to be laterally grown are relatively increased. It will be difficult to secure.

On the other hand, as shown in FIG. 5, in the case of crystal growth according to the present invention, the ratio of the region grown on the top of the dielectric layer is relatively very high compared to the conventional LEO method shown in FIG. This improves the luminous efficiency of the device.

Next, a second embodiment in which the present invention is applied to the Pendeoepitaxy growth method will be described.

Second Embodiment

First, a gallium nitride thin film is grown on dissimilar substrates such as sapphire, silicon carbide and silicon.

Then, a dielectric film such as silicon oxide film (SiO ₂ ), silicon nitride film (Si ₃ N ₄ ), or a metal thin film such as W, Ta, or Pt is deposited on the first gallium nitride thin film.

After the deposited dielectric film or metal thin film is patterned by photolithography to form a mask pattern, the nitride pattern is formed by etching the gallium nitride thin film and a part of the substrate using the formed mask pattern.

In this case, it is preferable that the mask pattern is formed so that a regular number of windows having a angular shape is formed. In particular, it is most preferable to use a mask pattern in which a large number of equilateral triangle windows are zigzag, and the crystal of the nitride semiconductor has a hexagonal system shape. This is because it has symmetry in the direction of rotation by 60 degrees. In addition, the length W1 of the one side of the equilateral triangle is about several μm, and has a range of about 1 μm <W1 <30 μm, and the distance W2 between the equilateral triangles is most preferably in the range of about 1 μm <W2 <30 μm. Do.

Subsequently, after removing the mask pattern, the gallium nitride is laterally grown using a window of an equilateral triangle, and the growth process is the same as that of the side growth using the above-described LEO.

As described in detail above, the nitride crystal growth method according to the present invention increases the ratio of regions having low dislocation densities during nitride crystal growth to reduce crystal defects in the entire nitride thin film, thereby being used in optical devices, high output, and high power electronic devices. There is an effect that can improve the luminous efficiency.

Although the invention has been described in detail only with respect to the specific examples described, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims.

Claims (8)

Forming a first nitride semiconductor layer on top of the substrate; A second step of applying a mask material over the first nitride semiconductor layer and regularly forming a number of window-shaped windows; And a third step of forming a second nitride semiconductor layer by laterally growing a crystal of the first nitride semiconductor through the ridge-shaped window. The method of claim 1, wherein the second step; The nitride semiconductor crystal growth method is characterized in that a plurality of the ridge window formed in a zigzag form According to claim 1 or claim 2, wherein the angular window is; A nitride semiconductor crystal growth method, characterized in that it is a window of an equilateral triangle. The method of claim 1, The substrate is made of any one material selected from sapphire, silicon carbide and silicon, And the mask material is any one selected from a dielectric and a metal. Forming a nitride semiconductor layer over the substrate; Etching a portion of the nitride semiconductor layer and the substrate to form a nitride pattern having a plurality of regular windows having a reentrant shape; A nitride semiconductor crystal growth method comprising a third step of growing a nitride semiconductor crystal using the nitride pattern. The method of claim 5, wherein the second step; The nitride semiconductor crystal growth method is characterized in that a plurality of the ridge window formed in a zigzag form 7. The method of claim 5 or 6, wherein the angular shaped window; A nitride semiconductor crystal growth method, characterized in that it is a window of an equilateral triangle. The method of claim 5, The substrate is a nitride semiconductor crystal growth method, characterized in that made of any one material selected from sapphire, silicon carbide and silicon.