JP2009231302A - Nitride semiconductor crystal thin film and its deposition method, semiconductor device, and its fabrication process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fabricate an element of high breakdown voltage using a nitride semiconductor even when a silicon substrate is used. <P>SOLUTION: A semiconductor device comprises a silicon substrate 101, a buffer layer 102 consisting of an AlN crystal grown epitaxially on the silicon substrate 101, a channel layer 103 consisting of GaN formed epitaxially on the buffer layer 102, and a carrier supply layer 104 consisting of Al<SB>0.25</SB>Ga<SB>0.75</SB>N formed epitaxially on the channel layer 103. The buffer layer 102 consists of a crystal of aluminum nitride (AlN) to which oxygen is added. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to crystal growth of a nitride semiconductor thin film used for optical / electronic devices, and more particularly to a nitride semiconductor crystal thin film that contributes to high performance such as improved breakdown voltage in an electronic device application, a manufacturing method thereof, and a semiconductor device And a manufacturing method thereof.

  As a typical electronic device using a nitride semiconductor, a high electron mobility field effect transistor (HEMT) is known. As nitride semiconductor thin film crystals for HEMT devices, AlGaN used for HEMT barrier layers (carrier supply layers) and GaN used for channels are generally used. In forming these elements using a nitride semiconductor, a method of growing a nitride semiconductor crystal thin film on a silicon carbide (SiC) substrate, a sapphire substrate, and a silicon substrate is used.

  In general, as a field of application of such a nitride-based HEMT device, high output and high breakdown voltage are required, and a large amount of heat is easily generated during device operation. Since this leads to deterioration of device characteristics, SiC or silicon substrate having good thermal conductivity is used. However, currently available SiC substrates are very expensive (about 100 times that of silicon substrates), and therefore have the disadvantage of limited application fields. On the other hand, the silicon substrate is inexpensive and is expected to be applied to a nitride-based device by utilizing the manufacturing technology in the silicon LSI process (see Non-Patent Document 1).

Osamu Machida et al., “High AlGaN / GaN HFET on Si substrate”, IEICE, IEICE Technical Report, 2003.

  These devices have a feature that a higher breakdown voltage can be achieved by using a nitride semiconductor material having a wide energy gap (wide gap) as compared with arsenic and phosphorus compound semiconductor materials that are conventionally used. . However, as described above, since the nitride semiconductor growth substrate is made of a different material, the nitride semiconductor growth layer has many point defects and line defects (such as dislocations) due to a difference in lattice constant and a coefficient of thermal expansion. Will be formed.

  In particular, when a nitride-based material is epitaxially grown on a silicon substrate, the lattice constant difference between the substrate and the crystal growth layer is larger than that of other substrate types such as sapphire and SiC, and the thermal expansion coefficient difference is also large. Since it is large, epitaxial growth with good quality is not easy. When a silicon substrate is used, it is very difficult to increase the thickness of an epitaxial growth layer useful for increasing the breakdown voltage of the device in terms of crystal growth. Due to imperfections in the quality of the epitaxial growth layer due to the difficulty of this epitaxial growth, there is a problem in that it has an adverse effect on the high breakdown voltage resulting from the physical properties of the nitride semiconductor and lowers the original breakdown voltage. there were.

  The present invention has been made to solve the above-described problems, and is capable of forming a high breakdown voltage element using a nitride semiconductor even when a silicon substrate is used. Objective.

  The nitride semiconductor crystal thin film according to the present invention is a crystal thin film made of a nitride semiconductor containing aluminum formed on a substrate, and the thin film is made to contain oxygen. In this nitride semiconductor crystal thin film, oxygen may be added to a partial region in the normal direction of the plane of the thin film substrate. The substrate is made of silicon.

  A semiconductor device according to the present invention includes a buffer layer made of a nitride semiconductor crystal containing aluminum to which oxygen is added, and an element made of a nitride semiconductor formed on the buffer layer. And at least. In this semiconductor device, oxygen may be added to a partial region in the normal direction of the plane of the silicon substrate of the buffer layer. Here, the element is formed on, for example, a carrier supply layer formed on the buffer layer and a buffer layer below the carrier supply layer, and a channel is formed by electrons supplied from the carrier supply layer. It comprises at least a carrier traveling layer, a gate electrode formed on the carrier supply layer, and a source electrode and a drain electrode formed on the carrier supply layer so as to sandwich the gate electrode. The substrate is made of silicon.

  The method for producing a nitride semiconductor crystal thin film according to the present invention includes at least a step of epitaxially growing a nitride semiconductor layer containing aluminum to which oxygen is added on a substrate. The substrate is made of silicon.

  The method for manufacturing a semiconductor device according to the present invention includes a step of epitaxially growing a nitride semiconductor containing aluminum to which oxygen is added to form a buffer layer on a silicon substrate, And at least a step of forming a device made of a nitride semiconductor. The substrate is made of silicon.

  As described above, according to the present invention, the crystal thin film made of the nitride semiconductor containing aluminum to which oxygen is added is formed on the substrate. However, an excellent effect that a high breakdown voltage element using a nitride semiconductor can be formed can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a configuration example of a semiconductor device according to an embodiment of the present invention. This semiconductor device includes a silicon substrate 101, a buffer layer 102 made of AlN crystal epitaxially grown on the silicon substrate 101, a channel layer 103 made of GaN epitaxially grown on the buffer layer 102, and the channel layer 103. And a carrier supply layer 104 made of Al _0.25 Ga _0.75 N epitaxially grown. On the carrier supply layer 104, a gate electrode 105 made of, for example, Ti / Au is formed, and a source electrode 106 and a drain electrode 107 made of Au / Ni / Ti / Al are formed so as to sandwich the gate electrode 105. Has been.

  Here, the present embodiment is characterized in that the buffer layer 102 is made of a nitride semiconductor crystal containing aluminum to which oxygen is added. Thus, in this embodiment, since the buffer layer 102 made of, for example, AlN crystal to which oxygen is added is provided, the breakdown voltage of the element made of the nitride semiconductor formed thereon is improved. In other words, if a silicon substrate on which a thin film of nitride semiconductor crystal containing Al to which oxygen is added is used, a high breakdown voltage nitride semiconductor element can be formed.

Next, description will be made on the breakdown voltage improvement by using an AlN crystal layer (buffer layer) to which oxygen is added. First, an element as shown in FIG. 2 is formed. The formation of this element will be described. On the silicon substrate 201, AlN doped with 8 × 10 ¹⁸ cm ⁻³ of oxygen is epitaxially grown on the buffer layer 202 by using a known MOVPE (Metal-Organic Vapor Phase Epitaxy) method. Is formed. For example, trimethylaluminum (TMA) is used as an Al source gas, ammonia (NH ₃ ) is used as an N source gas, and oxygen gas diluted to 0.1% with nitrogen as a carrier gas is used. , Oxygen can be added. Note that the growth temperature may be about 1000 ° C.

Next, epitaxial growth of GaN and epitaxial growth of Al _0.25 Ga _0.75 N are sequentially performed, and the GaN layer 203 and the Al _0.25 Ga _0.75 N layer 204 are stacked on the buffer layer 202. Note that trimethylgallium (TMG) may be used as a Ga source gas. Next, these laminated structures are processed into a predetermined shape by a known lithography technique and etching technique, and an electrode 205 is formed on the Al _0.25 Ga _0.75 N layer 204 by an electrode formation process. The electrode 205 is composed of a laminated structure in which a Ti layer with a thickness of 20 nm, an Al layer with a thickness of 200 nm, a Ni layer with a thickness of 10 nm, and an Au layer with a thickness of 300 nm are laminated in this order, so-called ohmic connection.

  The device thus fabricated is placed on a substrate stage 207 provided with a ground electrode 206, and a voltage is applied between the electrode 205 and the ground electrode 206 to cause a vertical direction (film thickness direction) within the device. Measure the flowing current value. By this measurement, the vertical breakdown voltage of the element can be evaluated.

  The measurement result of the current value described above is shown in FIG. 3A shows the result of the element using the buffer layer 202 made of oxygen-added AlN in this embodiment described above, and FIG. 3B shows the buffer layer made of AlN not added with oxygen. The result of the used element is shown. As can be seen from FIG. 3, the leakage current is clearly reduced in the element using the buffer layer 202 made of oxygen-added AlN. From this result, it can be seen that by using the buffer layer 202 made of oxygen-added AlN, the breakdown voltage characteristics can be improved.

It has been confirmed that the same effect as described above can be obtained even with an oxygen doping amount of 1 × 10 ¹⁸ cm ⁻³ or more. Further, it has been confirmed that the same effect can be obtained not only in AlN but also in a buffer layer using a nitride semiconductor containing Al such as AIGaN.

  By the way, oxygen does not need to be formed in the entire thickness direction of the buffer layer. As described later, oxygen is added to a part of the buffer layer in the thickness direction, for example, about an atomic layer. However, as described above, the breakdown voltage of the element formed on the buffer layer can be improved.

First, an element as shown in FIG. 4 is formed, and this breakdown voltage is measured in the same manner as described above. The formation of this element will be described. On the silicon substrate 401, AlN is epitaxially grown using a known MOVPE method, and a buffer layer 402 including an oxygen introduction layer 405 into which oxygen is introduced at the center in the thickness direction is formed. It is assumed that The formation of the oxygen introduction layer 405 will be briefly described. During the epitaxial growth, the supply of the Al source gas (TMA) is stopped and oxygen is supplied instead. For example, the oxygen flow rate is 10 sccm and supplied for about 1 minute. Note that sccm is a unit of flow rate, and indicates that a fluid at 0 ° C. and 1 atm flows 1 cm ³ per minute.

After the oxygen supply, the oxygen supply is stopped and the supply of the Al source gas is started again. As a result, an oxygen introduction layer 405 having an atomic layer level thickness in which oxygen (1 × 10 ¹⁸ cm ⁻³ ) is added in a spike shape at the center in the thickness direction of the buffer layer 402 is formed. Is obtained.

Next, epitaxial growth of GaN and epitaxial growth of Al _0.25 Ga _0.75 N are sequentially performed, and the GaN layer 403 and the Al _0.25 Ga _0.75 N layer 404 are stacked on the buffer layer 402. Here, when the distribution of oxygen and Al is measured from the surface of the Al _0.25 Ga _0.75 N layer 404 by SIMS (Secandary Ion Mass Spectrometry) analysis, it is as shown in FIG. As shown in FIG. 5, the buffer layer 402 is formed at a depth of 1.7 to 1.8 μm from the surface of the Al _0.25 Ga _0.75 N layer 404, and there is a peak of oxygen concentration in a narrower region. This indicates that crystal growth including a region having an oxygen concentration peak of about 1 × 10 ²⁰ cm ⁻³ in a part of the buffer layer 402 is realized.

After laminating each layer as described above, the laminated structure is processed into a predetermined shape by a known lithography technique and etching technique as described above, and the Al _0.25 Ga _0.75 N layer 404 is formed by an electrode formation process. In addition, an electrode (not shown) is formed, and the value of current flowing in the vertical direction (film thickness direction) in the element is measured using this electrode.

  The measurement result of the current value described above is shown in FIG. In FIG. (A) shows the result of the device using the oxygen-introduced AlN oxygen-introducing layer 405 in the above-described embodiment, and (b) shows the result of the device using the AlN buffer layer to which no oxygen is added. Is shown. As is apparent from FIG. 6, the leakage current is clearly reduced in the element using the oxygen introduction layer 405. From this result, it can be seen that even with the oxygen introduction layer 405 as thin as an atomic layer, the breakdown voltage characteristics can be improved by using the oxygen introduction layer 405.

In the above description, the oxygen introduction layer 405 is formed by stopping the supply of the Al source gas and supplying the oxygen gas during the epitaxial growth of the buffer layer 402. However, the present invention is not limited to this. For example, the epitaxial growth by MOVPE is stopped in the middle of the epitaxial growth of the buffer layer, which is a nitride semiconductor containing Al, and the substrate temperature is cooled to about room temperature. Keep in. Next, the sample is again carried into the growth apparatus, and the epitaxial growth of the buffer layer is resumed. After that, as described above, layers of GaN and Al _0.25 Ga _0.75 N are sequentially stacked, and the same element as described above is manufactured. Even in the device fabricated in this way, the presence of an oxygen introduction layer at the atomic layer level in which oxygen of about 1 × 10 ¹⁹ cm ⁻³ is introduced into the buffer layer is confirmed. In addition, the improvement in breakdown voltage is confirmed from the measurement result of the current value similar to the above.

  In addition, a HEMT device made of a nitride semiconductor is fabricated on a silicon substrate including a buffer layer to which oxygen is added in the present embodiment, and a current corresponding to an applied voltage between the drain electrode and the source electrode of the HEMT device is produced. When the relationship is measured, the saturation current is suppressed as shown by black circles in FIG.

In FIG. 7, as described above, a black circle forms an oxygen introduction layer in a part of the buffer layer at the atomic layer level, and a channel layer made of GaN and a carrier supply made of Al _0.25 Ga _0.75 N on the buffer layer. This is a result of an element in which a layer is formed and a gate electrode and source / drain electrodes are formed on a carrier supply layer. On the other hand, the black square is the result of an element formed in the same manner as described above using a buffer layer into which oxygen is not introduced (added).

  The source / drain electrodes have a laminated structure in which a 20 nm thick Ti layer, a 200 nm thick Al layer, a 10 nm thick Ni layer, and a 300 nm thick Au layer are laminated in this order, so-called ohmic connection. is doing. The gate electrode is a so-called Schottky gate composed of a laminated structure in which an Au layer and a Ti layer are laminated in this order, and has a gate length of 1.5 μm and a gate width of 100 μm.

  As is clear from these measurement results, the saturation current is clearly suppressed in the black circle result than in the black square result, and the effect of improving the breakdown voltage by the buffer layer including the oxygen-added portion is higher than that of the element (higher This is also confirmed in the state in which the electron mobility transistor is configured.

  As described above, by using a silicon substrate on which a buffer layer of nitride semiconductor crystal containing Al to which oxygen is added is used, the breakdown voltage is greatly improved compared to a conventional structure in which oxygen is not added. Therefore, a high breakdown voltage device using a nitride semiconductor on a silicon substrate can be realized.

  This is because when the nitride semiconductor crystal is epitaxially grown using a silicon substrate, the added oxygen acts to suppress the generation of defects in the vicinity of the “epitaxial growth layer / substrate interface” where the highest density defects are introduced. It is thought that there is. As a result, the density of “defects” resulting in breakdown voltage degradation is reduced, and it is considered that higher breakdown voltage is realized. In addition, the technique of the present invention using the buffer layer added with oxygen is used when epitaxially growing a nitride semiconductor not only on a silicon substrate but also on another nitride semiconductor growth substrate (such as silicon carbide or sapphire). The present invention can also be applied to the case where an element is formed by this growth layer.

  In the above description, the element is a so-called high electron mobility transistor. However, the present invention is not limited to this. For other types of devices using nitride semiconductors, the use of a buffer layer made of a nitride semiconductor crystal containing Al to which oxygen is added can provide the effect of improving the breakdown voltage by reducing the leakage current. Needless to say.

It is sectional drawing which shows typically the structural example of the semiconductor device in embodiment of this invention. It is a block diagram which shows typically the structure of the element for measuring a vertical direction pressure | voltage resistance. It is a characteristic view which shows the result of a vertical direction pressure | voltage resistant measurement. It is a block diagram which shows typically the structure of the other element for measuring the pressure | voltage resistant confirmation. It is a measurement figure which shows the distribution measurement result of the oxygen and Al of the thickness direction of the other element for measuring a vertical direction proof pressure. It is a characteristic view which shows the result of a vertical direction pressure | voltage resistant measurement. It is a characteristic view which shows the relationship of the electric current with respect to the applied voltage between the drain electrode of a HEMT device, and a source electrode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Silicon substrate, 102 ... Buffer layer, 103 ... Channel layer, 104 ... Carrier supply layer, 105 ... Gate electrode, 106 ... Source electrode, 107 ... Drain electrode.

Claims (11)

A thin crystal film made of a nitride semiconductor containing aluminum formed on a substrate,
A nitride semiconductor crystal thin film characterized in that oxygen is added to the thin film. The nitride semiconductor crystal thin film according to claim 1,
Oxygen is added to a partial region of the thin film in the normal direction of the plane of the substrate. The nitride semiconductor crystal thin film, wherein The nitride semiconductor crystal thin film according to claim 1 or 2,
The nitride semiconductor crystal thin film characterized in that the substrate is made of silicon. A buffer layer formed on a substrate and made of a nitride semiconductor crystal containing aluminum to which oxygen is added;
A semiconductor device comprising at least an element made of a nitride semiconductor formed on the buffer layer. The semiconductor device according to claim 4.
Oxygen is added to a partial region of the buffer layer in the normal direction of the plane of the substrate. The semiconductor device. The semiconductor device according to claim 4 or 5,
The element is
A carrier supply layer formed on the buffer layer;
A carrier travel layer formed on the buffer layer under the carrier supply layer, in which a channel formed by electrons supplied from the carrier supply layer is formed;
A gate electrode formed on the carrier supply layer;
A semiconductor device comprising at least a source electrode and a drain electrode formed on the carrier supply layer so as to sandwich the gate electrode. The semiconductor device according to any one of claims 4 to 6,
The semiconductor device, wherein the substrate is made of silicon.   A method for producing a nitride semiconductor crystal thin film, comprising at least a step of epitaxially growing a nitride semiconductor layer containing aluminum to which oxygen is added on a substrate. In the manufacturing method of the nitride semiconductor crystal thin film of Claim 8,
The method for producing a nitride semiconductor crystal thin film, wherein the substrate is made of silicon. A step of forming a buffer layer on the substrate by epitaxially growing a nitride semiconductor containing aluminum to which oxygen is added; and
And a step of forming a nitride semiconductor element on the buffer layer. A method for manufacturing a semiconductor device, comprising: The method of manufacturing a semiconductor device according to claim 10.
The method of manufacturing a semiconductor device, wherein the substrate is made of silicon.

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