JP2009120425A - METHOD FOR MANUFACTURING GaN SEMICONDUCTOR SUBSTRATE AND GaN SEMICONDUCTOR SUBSTRATE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a GaN semiconductor substrate by which a good quality nonpolar face GaN crystal can be formed. <P>SOLUTION: The method for manufacturing the GaN semiconductor substrate includes the steps of: forming a layer composed of a carbide selected from the group comprising titanium carbide, zirconium carbide, hafnium carbide, niobium carbide, vanadium carbide and tantalum carbide on an underlying substrate 10; nitriding the carbide layer; forming a nonpolar face GaN crystal layer 16 on the nitrided carbide layer 12 by epitaxially growing a GaN crystal by using a nonpolar face as a growth face; and obtaining the GaN semiconductor substrate containing the nonpolar face GaN crystal layer 16 by removing the underlying substrate 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a GaN semiconductor substrate, and a GaN semiconductor substrate obtained by this method.

In recent years, substrates made from gallium nitride (GaN) bulk crystals have been indispensable for blue-violet lasers and have been developed and applied, but they are also used as substrates for high-intensity white light-emitting diodes and electronic devices. Attempts are active. In the conventional technique, since a GaN crystal is grown on the c-plane of the sapphire substrate, the obtained GaN crystal is a c-plane GaN crystal (for example, Patent Document 1). However, the c-plane GaN crystal has a crystal termination surface in which the atomic plane composed only of Ga atoms and the atomic plane composed only of N atoms are alternately stacked in the growth direction so that electrical neutrality is maintained. Since one of these is a Ga atom plane and the other is an N atom plane, spontaneous polarization occurs along the c-axis, and electrons and holes are separated into opposing surfaces. Furthermore, due to the difference between the lattice constant in the a-axis direction of sapphire and the lattice constant in the a-axis direction of GaN, a piezoelectric field is generated in the c-axis direction of GaN, which causes the electrons injected into the light emitting layer to Holes leave, the recombination probability contributing to light emission decreases, and the internal quantum efficiency decreases. In addition, when this c-plane GaN crystal is used for a light emitting device, the emission wavelength shifts to the long wavelength side, and problems such as the emission wavelength changing depending on the applied voltage occur.
In order to avoid this problem, it is useful to use a nonpolar plane GaN crystal. There are a-plane and m-plane in the non-polar plane of GaN, but these non-polar planes contain the same number of Ga and N, so that they are kept electrically neutral and can suppress the occurrence of polarization along the growth direction. .
Patent Documents 2 and 3 describe GaN crystals having non-polar a-planes and m-planes as growth planes and their manufacturing methods.
JP 2002-284600 A JP 2005-320237 A JP 2000-216497 A

  However, with the conventional method, it has been difficult to obtain nonpolar plane GaN crystals with good crystal quality.

As a reason why the nonpolar plane GaN crystal cannot be stably obtained by the conventional method, it is considered that the lattice mismatch between the base substrate crystal and the nonpolar plane GaN crystal is large.
Thus, as a result of intensive investigations in view of the above circumstances, the present inventors have found that a nonpolar plane GaN crystal grows satisfactorily by providing a carbide layer on a base substrate, and have reached the present invention.
That is, the present invention includes forming a carbide layer selected from the group consisting of titanium carbide, zirconium carbide, hafnium carbide, niobium carbide, vanadium carbide, and tantalum carbide on a base substrate, and nitriding the carbide layer And a step of epitaxially growing a GaN crystal on the nitrided carbide layer using a nonpolar surface as a growth surface to form a nonpolar surface GaN crystal layer; and removing the base substrate to form the nonpolar surface And a step of obtaining a GaN semiconductor substrate including a GaN crystal layer. A method for manufacturing a GaN semiconductor substrate is provided.

As the base substrate, a sapphire substrate, SiC substrate, ZnO substrate, silicon substrate, GaAs substrate, GaP substrate, γ-LiAlO ₂ substrate, or the like can be used. In order to grow an a-plane GaN crystal using the base substrate, an r-plane sapphire substrate, a 6H—SiC (11-20) substrate, a 4H—SiC (11-20) substrate, and a 2H—SiC (11-20) substrate are used. A substrate, a 3C—SiC (100) substrate, a ZnO (11-20) substrate, a silicon (100) substrate, a GaAs (100) substrate, a GaP (100) substrate, a γ-LiAlO ₂ (110) substrate, and the like are preferable. In order to grow an m-plane GaN crystal, an m-plane sapphire substrate, 6H-SiC (10-10) substrate, 4H-SiC (10-10) substrate, 2H-SiC (10-10) substrate, 3C-SiC (110) substrate, ZnO (10-10) substrate, silicon (110) substrate, GaAs (110) substrate, GaP (110) substrate, γ-LiAlO ₂ (101) substrate and the like are suitable.
In particular, since a large-diameter substrate is available for the sapphire substrate and is stable against the source gas and the atmospheric gas during GaN growth, for example, by forming the carbide layer on the r-plane sapphire substrate, The a-plane GaN can be stably grown. Further, by nitriding the carbide layer, the r-plane sapphire substrate can be easily separated from the GaN crystal. That is, in the present invention, by forming a carbide layer on the base substrate and nitriding the carbide layer, lattice mismatch and thermal stress distortion generated between the base substrate and GaN are alleviated, and the non-polarity having excellent crystallinity is achieved. As a result, the GaN crystal can be obtained and the base substrate can be easily peeled off.

At this time, the step of epitaxially growing the nonpolar plane GaN crystal layer may include a step of growing the nonpolar plane GaN crystal layer while forming a faceted GaN film on the nitrided carbide layer. preferable.
By growing a nonpolar plane GaN crystal layer while forming a facet structure GaN film, dislocations extending in the growth direction from the base substrate are folded laterally by the facet structure, and in the upper nonpolar plane GaN crystal layer Transmission of crystal defects is suppressed. Thereby, a nonpolar plane GaN crystal layer with good crystal quality can be stably obtained.

The thickness of the faceted GaN film is preferably controlled to 3 μm or more and 25 μm or less. When the thickness of the GaN film having the facet structure is smaller than 3 μm, the facet structure is unlikely to have a clear crystal plane, and the effect of improving the crystal quality becomes unstable. On the other hand, when the thickness is larger than 25 μm, many dislocations extend from the base substrate to the GaN film, and it becomes difficult to bend a large number of dislocations in the lateral direction by the facet structure formed on the surface layer portion of the GaN film. Becomes unstable.

The step of obtaining a GaN semiconductor substrate includes cooling the base substrate, the nitrided carbide layer, and the nonpolar plane GaN crystal layer from a growth temperature, and in the cooling process, from the nonpolar plane GaN crystal layer, A step of separating and removing the base substrate.
According to this method, the base substrate and the nonpolar GaN crystal layer can be easily separated using the stress generated by the difference between the thermal expansion coefficient of the base substrate and the thermal expansion coefficient of the nonpolar GaN crystal layer. Can do.

  Further, the thickness of the carbide layer is preferably 5 nm or more and 200 nm or less. When the thickness of the carbide layer is thinner than 5 nm, the carbide layer is mostly changed to nitride, and the generated carbon disappears as methane. Therefore, the nonpolar plane GaN crystal layer is separated from the base substrate through the nitride. It may be difficult to bond firmly and separate and remove the underlying substrate from the nonpolar plane GaN crystal layer. On the other hand, when it is thicker than 200 nm, the nitridation of the carbide layer becomes insufficient, and the carbide layer remains between the non-polar plane GaN crystal layer and the underlying substrate even after the epitaxial growth of the nonpolar plane GaN crystal layer. In some cases, cracks enter from the interface, and it is difficult to separate and remove the base substrate from the nonpolar plane GaN crystal layer.

  Furthermore, the step of nitriding the carbide layer is preferably performed at a temperature of 300 ° C. or higher and 1050 ° C. or lower. Below 300 ° C., the nitriding rate of the carbide layer is slow. Therefore, nitriding of the carbide layer becomes insufficient, and the carbide layer remains between the non-polar plane GaN crystal layer and the underlying substrate even after epitaxial growth, so that cracks are generated from the interface between the nitrided carbide layer and the remaining carbide. In some cases, it may be difficult to separate and remove the underlying substrate from the nonpolar plane GaN crystal layer. Further, when the temperature is higher than 1050 ° C., the methanation of carbon generated along with the nitridation of the carbide layer is promoted, so that the residual amount of carbon decreases at the interface with the base substrate, and the nonpolar plane GaN crystal layer passes through the nitride. Therefore, it may be difficult to remove the base substrate from the nonpolar plane GaN crystal layer. By setting the temperature for nitriding the carbide layer to 300 ° C. or more and 1050 ° C. or less, the base substrate can be more easily separated from the nonpolar plane GaN crystal layer.

  As a base substrate, a sapphire substrate is chemically stable in a GaN growth atmosphere, and a large-diameter substrate is easily available. Since the r-plane sapphire substrate has good lattice matching with the carbide layer, and the nitride produced by nitriding the carbide layer and a-plane GaN also have good lattice matching, an apolar GaN crystal layer with good crystal quality can be obtained. Can be obtained.

  Moreover, according to this invention, the GaN semiconductor substrate manufactured by one of the manufacturing methods mentioned above is also provided.

  According to the present invention, a nonpolar plane GaN crystal having a good crystal quality can be obtained, and a method for manufacturing a GaN semiconductor substrate is provided. Moreover, in the method for manufacturing a GaN semiconductor substrate according to the present invention, the base substrate can be easily peeled off, so that a nonpolar plane GaN crystal with good crystal quality can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

An outline of a method for manufacturing a self-supporting substrate according to the present embodiment will be described. The manufacturing method of the self-supporting substrate of this embodiment includes the following steps.
(I) forming a carbide layer selected from the group consisting of titanium carbide, zirconium carbide, hafnium carbide, niobium carbide, vanadium carbide and tantalum carbide on the base substrate;
(Ii) nitriding the carbide layer;
(Iii) forming a nonpolar plane GaN crystal layer by epitaxially growing a GaN crystal on the nitrided carbide layer using the nonpolar plane as a growth plane;
(Iv) removing the base substrate to obtain a GaN semiconductor substrate including the nonpolar plane GaN crystal layer.

Hereinafter, the method according to the present embodiment will be described in detail by taking as an example the case of growing an a-plane GaN crystal layer on an r-plane sapphire substrate.
(I) Carbide Layer Formation Step First, for example, an r-plane sapphire (Al ₂ O ₃ ) substrate 10 having a thickness of 550 μm and a 3-inch diameter is prepared as the r-plane sapphire substrate. A commercially available r-plane sapphire substrate can be used. Next, a carbide layer 11 is formed on the r-plane sapphire substrate 10 (FIG. 1A).

  The film forming conditions of the carbide layer 11 are as follows, for example.

Film forming method: reactive sputtering method Film forming temperature: 600 to 1000 ° C.
Deposition time: 1 to 40 minutes Target: M (M is Ti, Zr, Hf, Nb, V, or Ta)
Reaction gas: Methane film thickness: 5 nm to 200 nm

As the carbide, any selected from titanium carbide, zirconium carbide, hafnium carbide, niobium carbide, vanadium carbide or tantalum carbide is used. All of these carbides have a face-centered cubic crystal structure. As shown in FIG. 3, these carbides have a relatively small lattice mismatch with respect to the r-plane sapphire and the a-plane GaN, so that the crystallinity of the a-plane GaN crystal grown thereon is good. Among the above carbides, titanium carbide, zirconium carbide, hafnium carbide, niobium carbide, or tantalum carbide having a lattice mismatch rate smaller than that of r-plane sapphire and a-plane GaN is preferable.
Titanium carbide, zirconium carbide, hafnium carbide, niobium carbide, vanadium carbide or tantalum carbide is generally known to have a non-stoichiometric composition, and a C / M molar ratio (M is Ti, Zr, Hf, Nb). , V, or Ta) is not limited to 3/4 or 1/1. Note that excess carbon or M (M is Ti, Zr, Hf, Nb, V, or Ta) may be mixed in the carbide layer. In the process of nitriding the carbide layer, most of the excess carbon is lost by methanation, and excess M is nitrided, and is integrated with TiN, ZrN, HfN, NbN, VN, and TaN formed by nitriding the carbide.

Here, the r-plane of sapphire is the (1-102) plane, and the a-plane of GaN is the (11-20) plane.
The lattice mismatch between r-plane sapphire and carbide is defined as follows.
Carbide lattice mismatch (%) to Al ₂ O ₃ [11-20] = {[(a-axis length of sapphire unit cell) − (a-axis length of carbide unit cell)] / (a-axis length of sapphire unit cell) )} × 100 Formula (1)
Lattice mismatch of carbide to Al ₂ O ₃ [1-101] (%) = {[([1-101] axis length of sapphire unit cell) − (a axis length of carbide unit cell) × 3] / (sapphire [1-101] axial length of unit cell)} × 100 (2)

The lattice mismatch between a-plane GaN and carbide is defined as follows.
Lattice mismatch of carbide to GaN [1-100] (%) = {[[[1-100] axis length of GaN unit cell) − (a axis length of carbide unit cell)] / ([1 of GaN unit cell] −100] axis length)} × 100 (3)
Mismatch of carbide to GaN [0001] (%) = {[(c-axis length of GaN unit cell) − (a-axis length of carbide unit cell) × 3] / (c-axis length of GaN unit cell)} × 100 ... Formula (4)
In formulas (2) and (4), the a-axis length of the carbide unit cell is tripled. When three carbide unit cells are stacked in the a-axis direction of the carbide unit cell, the [1-101] axis of the sapphire unit cell It means that the length and consistency are maintained. Each axial length is shown in FIG.

(Ii) Step of nitriding carbide layer Next, as shown in FIG. 1B, the carbide layer 11 is nitrided at a temperature of 300 ° C. to 1050 ° C. to form a nitrided carbide layer 12.
The nitriding conditions for the carbide layer 11 are, for example, as follows.

Nitriding gas: ammonia (NH ₃₎ gas, NH ₃ and a mixed gas of _{H 2,} NH ₃ and _{H 2} mixed gas of _{N 2} or _{H 2} and _{N 2} in the mixed gas nitriding temperature,: 300 ° C. to 1050 ° C.
Nitriding time: 3-60 minutes

The nitriding of the carbide layer 11 can also be performed continuously from the step of forming the carbide layer 11 in the sputtering apparatus. It is also possible to nitride the carbide layer 11 in an HVPE (hydride vapor phase epitaxy) apparatus used for GaN growth and to epitaxially grow the a-plane GaN crystal layer continuously.
Titanium carbide layer, zirconium carbide layer, hafnium carbide layer, niobium carbide layer, vanadium carbide or tantalum carbide layer is formed by nitriding by TiN, ZrN, HfN, NbN, VN as shown in the following formulas (5) and (6) Alternatively, TaN is generated. When the reaction of the formulas (5) and (6) is completely advanced, TiN, ZrN, HfN, NbN, VN or TaN is formed on the base substrate. However, the titanium carbide layer, the zirconium carbide layer, and the hafnium carbide are formed. When the layer, niobium carbide layer, vanadium carbide or tantalum carbide layer is appropriately nitrided, TiC, ZrC, HfC, NbC, VC or TaC remains on the portion in contact with the r-plane sapphire substrate, on which TiC, ZrC, HfC, A nitrided carbide layer 12 having TiN, ZrN, HfN, NbN, VN, or TaN that inherits the crystal information of NbC, VC, or TaC is formed.
2MC + 2NH ₃ + H ₂ → 2MN + 2CH ₄ (5) Formula 6MC + 8NH ₃ → 6MN + 6CH ₄ + N ₂ (6) In Formulas (5) and (6), M is Ti, Zr, Hf, Nb, V or Ta.
Since Ti, Zr, Hf, Nb, V, or Ta have the same crystal structure of carbide and nitride, TiC to TiN, ZrC to ZrN, HfC to HfN, NbC to NbN, VC to VN, or TaC The transfer of crystal information to TaN is good.
In addition, the code | symbol 122 shown in FIG. 1 (B) shows the carbide | carbonized_material layer which is not nitrided, and the code | symbol 121 shows a nitride layer. That is, it is shown that a carbide that has not been nitrided remains in a portion in contact with the r-plane sapphire substrate 10, and a nitride that inherits the crystal information of the carbide is formed thereon.

(Iii) Step of epitaxially growing a nonpolar plane GaN crystal layer (formation of GaN facet structure)
Next, as shown in FIG. 1C, a faceted GaN film 14 is formed on the nitrided carbide layer 12. In order to easily form the facet structure, there is a method in which a GaN crystal is formed by a short-time thin film growth at a relatively low temperature, and a GaN film made of island-like crystals having facets can be obtained.
The film formation conditions of the GaN film 14 can be as follows, for example.
Film formation method: HVPE (hydride vapor phase epitaxy) film formation temperature: 300 ° C. to 1000 ° C.
Deposition time: 0.5 to 5 minutes Film thickness: 3 to 25 μm
In the HVPE apparatus (not shown), a Ga source is disposed, and HCl gas is supplied to the Ga source. HCl gas and Ga source are reacted and transported to a region in the vicinity of the sapphire substrate 10 including the carbide layer 12 in which GaCl is nitrided. Since NH ₃ gas is also supplied to this region, the NH ₃ gas and GaCl react to form a faceted GaN film 14.

Next, as shown in FIG. 2A, an a-plane GaN crystal layer 16 is formed on the faceted GaN film 14 by epitaxially growing a GaN crystal with the a-plane as the growth plane.
The growth conditions of the a-plane GaN crystal layer 16 can be as follows, for example.

Film formation method: HVPE (hydride vapor phase epitaxy) film formation temperature: 1000 ° C. to 1080 ° C.
Deposition time: 30 minutes to 270 minutes Film thickness: 100 to 900 μm
In the HVPE apparatus (not shown), a Ga source is disposed, and HCl gas is supplied to the Ga source. HCl gas and Ga source are reacted to transport GaCl to a region near the substrate including the faceted GaN film 14. Since NH ₃ gas is also supplied to this region, the NH ₃ gas and GaCl react to form the a-plane GaN crystal layer 16. The non-nitrided carbide layer 122 is gradually nitrided with nitrogen atoms supplied from the GaN crystal to produce a nitride containing carbon. Finally, as shown in FIG. 2B, the a-plane GaN crystal layer 17 integrated with the nitride containing carbon is generated. In FIG. 2B, reference numeral 123 denotes a nitride layer containing carbon.

(Iv) Separation Step of Sapphire Substrate Next, as shown in FIG. 2C, the r-plane sapphire substrate 10 is peeled and removed from the a-plane GaN crystal layer 17 integrated with the nitride containing carbon. .
Specifically, the temperature of the HVPE apparatus in which the a-plane GaN crystal layer 17 is formed is lowered from the growth temperature, and the a-plane GaN crystal layer 17 is cooled to room temperature.
During this cooling, due to the difference in thermal expansion coefficient between the a-plane GaN crystal layer 17 and the r-plane sapphire substrate 10, these laminates are distorted, and the a-plane GaN crystal layer 17 and the r-plane sapphire substrate 10 are separated. The Rukoto.
Thereafter, by polishing the front and back surfaces of the peeled a-plane GaN crystal layer 17, an a-plane GaN substrate that is a flattened free-standing substrate can be produced.

Next, the effect of this embodiment is demonstrated.
By forming a carbide layer 11 on the r-plane sapphire substrate 10, nitriding the carbide layer 11, and then growing a GaN crystal on the nitrided carbide layer 12, an a-plane with good crystal quality GaN can be obtained.
Further, by forming a carbide layer 11 on the r-plane sapphire substrate 10 and nitriding the carbide layer 11, the sapphire substrate 10 can be easily formed from the a-plane GaN crystal layer 17 integrated with the nitride containing carbon. Can be removed. Therefore, unlike the prior art, there is no need to thermally decompose the GaN film or etch the metal film using laser light.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

The film thickness and manufacturing conditions of the carbide layer 11, the a-plane GaN semiconductor layer 17 integrated with the nitride containing carbon, and the manufacturing conditions in the above embodiment are merely examples, and depend on the composition and structure of the semiconductor layer to be formed. It can be changed as appropriate.
Although specific HVPE conditions are used as means for forming the faceted GaN film 14 on the nitrided carbide layer 12, the forming means is not limited to this. For example, a SiO ₂ film serving as a mask is formed on the carbide layer 12 nitrided by the same method as in the above embodiment, a stripe-shaped opening is provided on the sapphire substrate 10, and the facet-structured GaN film 14 is formed in the opening. When the GaN semiconductor layer 16 is formed and then grown, the crystal defects are suppressed from being transmitted into the a-plane GaN semiconductor layer 17 integrated with the nitride containing carbon that is finally generated. For this reason, the quality of the obtained GaN semiconductor substrate can be improved. For the mask pitch, the mask width, and the opening width between the masks, a configuration excellent in the effect of suppressing the transmission of crystal defects is selected. For example, the facet structure can be increased by changing the pitch of the mask or the width of the opening so as to have a certain regularity. Further, the shape of the opening is not limited to the stripe, and a lattice shape, a dot shape, or the like is also applicable.

Further, in the step of peeling off the r-plane sapphire substrate 10 of the embodiment, the r-plane sapphire substrate 10 and the a-plane GaN crystal layer 17 integrated with the nitride containing carbon are cooled, whereby the r-plane sapphire substrate. 10 is separated, but the present invention is not limited to this. Even if the r-plane sapphire substrate 10 is peeled off by applying a force that does not damage the a-plane GaN crystal layer 17 integrated with the nitride containing carbon. Good.
However, if the r-plane sapphire substrate 10 is separated and removed with little external force by cooling as in the above embodiment, the a-plane GaN crystal layer 17 integrated with the nitride containing carbon is formed. It is possible to reliably suppress the damage applied. For this reason, a high-quality a-plane GaN semiconductor substrate with little damage can be stably obtained.

  If a GaN-based device structure is fabricated on such an a-plane GaN semiconductor substrate, a light emitting device such as a light emitting diode or a laser diode having an up / down electrode structure on the upper and lower surfaces of the crystal can be fabricated. Application to electronic devices such as these is also possible. Preferably, the a-plane GaN semiconductor substrate is polished on a mirror surface, subjected to dry etching or chemical mechanical polishing (CMP), and then a light emitting element such as a light emitting diode or a laser diode, or an electron such as a transistor. A device is fabricated. Further, it is possible to grow a high-quality GaN crystal by using the a-plane GaN semiconductor substrate as a seed crystal by the HVPE method, the flux method, the ammonothermal method, or the like.

  Further, in the above embodiment, the r-plane sapphire substrate 10 is separated immediately after the growth of the a-plane GaN crystal layer 17 integrated with the nitride containing carbon. The r-plane sapphire substrate 10 may be removed after a light-emitting element such as a light-emitting diode or an electronic device such as a transistor is formed on the layer 17.

Moreover, in the said embodiment, although the a-plane GaN crystal layer 17 integrated with the nitride containing a single layer carbon was obtained, it is not restricted to this. The GaN semiconductor substrate manufactured by the present invention may have a multilayer structure.
In the above embodiment, the growth of the a-plane GaN crystal layer on the r-plane sapphire substrate has been described. However, the m-plane GaN crystal layer can also be grown by selecting the above-mentioned suitable base substrate. It is possible to stably obtain a planar GaN semiconductor substrate. The nonpolar plane GaN semiconductor is not limited to GaN, and may be a nitride semiconductor containing Al or In.

  Hereinafter, the present invention will be described in more detail, but the present invention is not limited to the following examples.

Example 1
In this example, the same steps as those described in the above embodiment (FIGS. 1 and 2) were used. In the present embodiment, a titanium carbide layer is formed as the carbide layer. An 85 mmφr-plane sapphire substrate was used as the base substrate.
1. Formation process of titanium carbide layer Film formation method: Reactive sputtering method Film formation temperature: 730 to 760 ° C.
Deposition time: 8 minutes Ar pressure: 0.3 Pa
Reaction gas pressure: Methane 0.1 Pa
Target: Ti
Target output: 150W
Film thickness: 40 nm
From the X-ray diffraction pattern of the obtained titanium carbide layer, it was confirmed that the titanium carbide formed on the r-plane sapphire substrate had (111) orientation (FIG. 5).

2. Process for nitriding titanium carbide layer Nitriding apparatus: HVPE apparatus Nitriding temperature: 300 ° C to 900 ° C
Nitriding time: 35 minutes Nitriding gas: NH ₃ gas, 3.3 l / min
In this step, the titanium carbide layer was nitrided in the temperature rising process from 300 ° C. to 900 ° C.

3. Epitaxial growth process of nonpolar plane GaN crystal layer (formation of faceted GaN film)
Film forming method: HVPE facet forming temperature: 900 ° C.
Deposition time: 5 minutes Source: Ga source (850 ° C.)
GaN film forming gas: HCl gas 0.18 l / min, NH ₃ gas 3.3 l / min
GaN film thickness: 25 μm
Next, the GaN crystal layer was epitaxially grown to a thickness of 300 μm. The NH ₃ gas was also supplied while the film formation temperature was raised to 1040 ° C.
(Epitaxial growth of GaN crystal layer)
Growth method: HVPE growth temperature: 1040 ° C
Growth gas: HCl gas 0.15 l / min, NH ₃ gas 1.5 l / min
Source: Ga source (850 ° C.)
Growth time: 90 minutes GaN layer thickness: 300 μm
FIG. 6 shows temperature profiles of the step of nitriding the titanium carbide layer and the step of epitaxially growing the nonpolar plane GaN crystal layer. In FIG. 6, the arrow on the lower side of GaCl indicates that GaCl is generated between 50 minutes to 55 minutes and 70 to 160 minutes, and the arrow on the lower side of NH ₃ is indicated with an arrow. In the figure, NH ₃ gas is supplied.

4). Separation process of sapphire substrate The temperature of the reaction tube of the HVPE apparatus on which the GaN crystal layer was formed was lowered and cooled to room temperature.
The GaN crystal layer was peeled from the sapphire substrate. An X-ray diffraction pattern of the obtained GaN crystal layer is shown in FIG. 7, and an X-ray rocking curve is shown in FIG. From these, it was confirmed that GaN is a-plane GaN and has a good crystal quality with a (11-20) half width of 800 arcsec.

9A and 9B show a microscopic image (100 times) of the GaN surface, and FIG. 10 shows a microscopic image (200 times) of the GaN surface.
11A and 11B are microscopic images (100 times) of the cross section of the GaN crystal layer, and FIG. 12 is a microscopic image (1000 times) of the cross section of the GaN crystal layer.
It can be seen that the surface of the GaN crystal layer obtained in this example is flat and has few pits. From the cross-sectional image of the GaN crystal layer, it can be seen that the GaN crystal layer is substantially flat at the growth stage of 300 μm.
From the above, it has been found that when a carbide layer is formed on an r-plane sapphire substrate and this carbide layer is nitrided and then a GaN crystal is grown, the a-plane GaN crystal layer can be obtained with good crystal quality.

(Example 2)
In this example, the same process as described in Example 1 was used except that the facet structure GaN film was not formed in the process of epitaxially growing the GaN crystal layer.
3. Epitaxial growth process of nonpolar plane GaN crystal layer (epitaxial growth of GaN crystal layer)
Growth method: HVPE growth temperature: 1040 ° C
Growth gas: HCl gas 0.15 l / min, NH ₃ gas 1.5 l / min
Source: Ga source (850 ° C.)
Growth time: 90 minutes GaN layer thickness: 300 μm

The GaN crystal layer was peeled from the sapphire substrate. The obtained GaN crystal layer was a-plane GaN, and the X-ray rocking curve half-value width of (11-20) was confirmed to have a relatively good crystal quality of 900 arcsec.

(Example 3)
In this example, the titanium carbide layer forming step and the step of nitriding the titanium carbide layer were changed to the zirconium carbide layer forming step and the step of nitriding the zirconium carbide layer, as described in Example 1. A similar process was used.
1. Formation process of zirconium carbide layer Film formation method: Reactive sputtering method Film formation temperature: 730 to 760 ° C.
Deposition time: 7 minutes Ar pressure: 0.3 Pa
Reaction gas: Methane 0.1 Pa
Target: Zr
Target output: 150W
Film thickness: 40 nm

2. Process for nitriding zirconium carbide layer Nitriding apparatus: HVPE apparatus Nitriding temperature: 300 ° C to 900 ° C
Nitriding time: 35 minutes Nitriding gas: NH ₃ gas, 3.3 l / min
In this step, the zirconium carbide layer was nitrided in the temperature rising process from 300 ° C to 900 ° C.

  Subsequently, when the GaN crystal layer was epitaxially grown and the sapphire substrate was peeled off, the GaN crystal layer was peeled from the sapphire substrate. The obtained GaN crystal layer was a-plane GaN, and the X-ray rocking curve half-width of (11-20) was confirmed to have a favorable crystal quality of 500 arcsec.

Example 4
In the present embodiment, the titanium carbide layer forming step and the step of nitriding the titanium carbide layer were changed to the step of forming the hafnium carbide layer and the step of nitriding the hafnium carbide layer as described in Example 1. A similar process was used.
1. Formation process of hafnium carbide layer Film forming method: reactive sputtering film forming temperature: 730 to 760 ° C.
Deposition time: 7 minutes Ar pressure: 0.3 Pa
Reaction gas: Methane 0.1 Pa
Target: Hf
Target output: 150W
Film thickness: 40 nm

2. Process for nitriding hafnium carbide layer Nitriding equipment: HVPE equipment Nitriding temperature: 300 ° C. to 900 ° C.
Nitriding time: 35 minutes Nitriding gas: NH ₃ gas, 3.3 l / min
In this step, the hafnium carbide layer was nitrided in the temperature rising process from 300 ° C. to 900 ° C.

  Subsequently, when the GaN crystal layer was epitaxially grown and the sapphire substrate was peeled off, the GaN crystal layer was peeled from the sapphire substrate. The obtained GaN crystal layer was a-plane GaN, and the X-ray rocking curve half-value width of (11-20) was confirmed to have a good crystal quality of 600 arcsec.

(Example 5)
In this example, the titanium carbide layer forming step and the step of nitriding the titanium carbide layer were changed to the step of forming the niobium carbide layer and the step of nitriding the niobium carbide layer, as described in Example 1. A similar process was used.
1. Formation process of niobium carbide layer Film forming method: reactive sputtering film forming temperature: 730 to 760 ° C.
Deposition time: 7 minutes Ar pressure: 0.3 Pa
Reaction gas: Methane 0.1 Pa
Target: Nb
Target output: 150W
Film thickness: 40 nm

2. Nitriding process of niobium carbide layer Nitriding equipment: HVPE equipment Nitriding temperature: 300 ° C to 900 ° C
Nitriding time: 35 minutes Nitriding gas: NH ₃ gas, 3.3 l / min
In this step, the niobium carbide layer was nitrided in the temperature rising process from 300 ° C to 900 ° C.

  Subsequently, when the GaN crystal layer was epitaxially grown and the sapphire substrate was peeled off, the GaN crystal layer was peeled from the sapphire substrate. The obtained GaN crystal layer was a-plane GaN, and the X-ray rocking curve half-value width of (11-20) was confirmed to have a good crystal quality of 600 arcsec.

(Example 6)
In this example, the titanium carbide layer forming step and the step of nitriding the titanium carbide layer were changed to the step of forming the vanadium carbide layer and the step of nitriding the vanadium carbide layer, as described in Example 1. A similar process was used.
1. Formation process of vanadium carbide layer Film forming method: reactive sputtering film forming temperature: 730 to 760 ° C.
Deposition time: 7 minutes Ar pressure: 0.3 Pa
Reaction gas: Methane 0.1 Pa
Target: V
Target output: 150W
Film thickness: 40 nm

2. Process for nitriding a vanadium carbide layer Nitriding apparatus: HVPE apparatus Nitriding temperature: 300 ° C to 900 ° C
Nitriding time: 35 minutes Nitriding gas: NH ₃ gas, 3.3 l / min
In this step, the vanadium carbide layer was nitrided in the temperature rising process from 300 ° C to 900 ° C.

  Subsequently, when the GaN crystal layer was epitaxially grown and the sapphire substrate was peeled off, the GaN crystal layer was peeled from the sapphire substrate. The obtained GaN crystal layer was a-plane GaN, and the X-ray rocking curve half-value width of (11-20) was confirmed to have a relatively good crystal quality of 900 arcsec.

(Example 7)
In this example, the titanium carbide layer forming step and the step of nitriding the titanium carbide layer were changed to the step of forming the tantalum carbide layer and the step of nitriding the tantalum carbide layer, as described in Example 1. A similar process was used.
1. Formation process of tantalum carbide layer Film forming method: reactive sputtering film forming temperature: 730 to 760 ° C.
Deposition time: 9 minutes Ar pressure: 0.3 Pa
Reaction gas: Methane 0.1 Pa
Target: Ta
Target output: 150W
Film thickness: 40 nm

2. Process for nitriding a tantalum carbide layer Nitriding apparatus: HVPE apparatus Nitriding temperature: 300 ° C. to 900 ° C.
Nitriding time: 35 minutes Nitriding gas: NH ₃ gas, 3.3 l / min
In this step, the tantalum carbide layer was nitrided in the temperature rising process from 300 ° C. to 900 ° C.

  Subsequently, when the GaN crystal layer was epitaxially grown and the sapphire substrate was peeled off, the GaN crystal layer was peeled from the sapphire substrate. The obtained GaN crystal layer was a-plane GaN, and the X-ray rocking curve half-value width of (11-20) was confirmed to have a favorable crystal quality of 700 arcsec.

(Comparative Example 1)
In this comparative example, the same steps as those described in Example 1 were used except for the step of forming the titanium carbide layer and the step of nitriding the titanium carbide layer. An 85 mmφr-plane sapphire substrate was used as the base substrate.
1. Epitaxial growth process of nonpolar plane GaN crystal layer (formation of faceted GaN film)
Film forming method: HVPE facet forming temperature: 900 ° C.
Deposition time: 5 minutes Source: Ga source (850 ° C.)
GaN film forming gas: HCl gas 0.09 l / min, NH ₃ gas 3.3 l / min
GaN film thickness: 25 μm
Next, the GaN crystal layer was epitaxially grown to a thickness of 300 μm. The NH ₃ gas was also supplied while the film formation temperature was raised to 1040 ° C.
(Epitaxial growth of GaN crystal layer)
Deposition method: HVPE Deposition temperature: 1040 ° C
Deposition gas: HCl gas 0.15 l / min, NH ₃ gas 1.5 l / min
Source: Ga source (850 ° C.)
Growth time: 90 minutes Film thickness: 60 μm (target: 300 μm)

2. Separation process of sapphire substrate The temperature of the reaction tube of the HVPE apparatus on which the GaN crystal layer was formed was lowered and cooled to room temperature, but the target was because the GaN crystal layer was broken into amorphous pieces while closely contacting the sapphire substrate during epitaxial growth. The epitaxial growth was stopped before the film thickness of 300 μm was reached. The film thickness of the GaN crystal layer was 60 μm.

(Comparative Example 2)
In this comparative example, the same process as that described in comparative example 1 was used except that the epitaxial growth time of the GaN crystal layer was 10 minutes. An 85 mmφr-plane sapphire substrate was used as the base substrate.
1. Epitaxial growth process of nonpolar plane GaN crystal layer (formation of faceted GaN film)
Film forming method: HVPE facet forming temperature: 900 ° C.
Deposition time: 5 minutes Source: Ga source (850 ° C.)
GaN film forming gas: HCl gas 0.09 l / min, NH ₃ gas 3.3 l / min
GaN film thickness: 25 μm
Next, the GaN crystal layer was epitaxially grown to a thickness of 300 μm. The NH ₃ gas was also supplied while the film formation temperature was raised to 1040 ° C.
(Epitaxial growth of GaN crystal layer)
Deposition method: HVPE Deposition temperature: 1040 ° C
Deposition gas: HCl gas 0.15 l / min, NH ₃ gas 1.5 l / min
Source: Ga source (850 ° C.)
Growth time: 10 minutes Film thickness: 20 μm

2. Separation process of sapphire substrate The temperature of the reaction tube of the HVPE apparatus on which the GaN crystal layer was formed was cooled to room temperature, but the GaN crystal layer remained in close contact with the sapphire substrate and did not peel off. The X-ray rocking curve of the GaN crystal on the obtained sapphire substrate is shown in FIG. From these, GaN was a-plane GaN, and the (11-20) half width was 950 arcsec.

(Example 8)
In this example, the same process as described in Example 1 was used except that the thickness of the GaN film having the facet structure was changed.
(Formation of faceted GaN film)
Film forming method: HVPE facet forming temperature: 900 ° C.
Deposition time: 0.5 to 5 minutes Source: Ga source (850 ° C.)
GaN film forming gas: HCl gas 0.18 l / min, NH ₃ gas 3.3 l / min
GaN film thickness: The film thickness was controlled to 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, and 25 μm.

(Comparative Example 3)
In Comparative Example 3, the thickness of the GaN film was changed to 1 μm and 35 μm. Other conditions are the same as in Example 8.

(Results of Example 8 and Comparative Example 3)
The (11-20) X-ray rocking curve half-value width was evaluated for the crystallinity of the a-plane GaN semiconductor layer, and the following results were obtained.
1 μm GaN was a-plane GaN, and the half width of the X ship rocking curve was 900 arcsec.
3 μm GaN was a-plane GaN, and the X-ray rocking curve half-width was 700 arcsec.
5 μm GaN was a-plane GaN, and the X-ray rocking curve half-width was 600 arcsec.
10 μm GaN was a-plane GaN, and the X-ray rocking curve half-width was 600 arcsec.
15 μm GaN was a-plane GaN, and the X-ray rocking curve half-width was 700 arcsec.
20 μm GaN was a-plane GaN, and the X-ray rocking curve half-width was 700 arcsec.
25 μm GaN was a-plane GaN, and the half width of the X ship rocking curve was 800 arcsec.
35 μm GaN was a-plane GaN, and the X-ray rocking curve half-width was 1000 arcsec.

From the results of Example 8 and Comparative Example 3 described above, the thickness of the GaN film is preferably 3 μm to 25 μm.

Example 9
In this example, the same process as that described in Example 1 was used except that the film thickness was changed to 5 nm, 100 nm, 140 nm, and 200 nm in the titanium carbide layer forming process.
1. Formation process of titanium carbide layer Film formation method: Reactive sputtering method Film formation temperature: 730 to 760 ° C.
The film thickness was controlled by setting the film formation time to 1 minute, 20 minutes, 28 minutes, and 40 minutes.
Ar pressure: 0.3 Pa
Reaction gas: Methane 0.1 Pa
Target: Ti
Target output: 150W
Film thickness: Each film thickness was controlled to 5 nm, 100 nm, 140 nm and 200 nm.

(Comparative Example 4)
In Comparative Example 4, the film thickness of the GaN crystal film was changed to 3 nm and 240 nm by setting the film formation time to 0.5 minutes and 48 minutes. The other conditions are the same as in Example 9.

(Results of Example 9 and Comparative Example 4)
The following results were obtained regarding the peeling state of the a-plane GaN semiconductor layer.
Cracks occurred in 6 out of 7 GaN crystals produced at 3 nm and could not be peeled off.
7 out of 7 GaN crystals produced at 5 nm were cracked without peeling.
Seven out of seven GaN crystals produced with a thickness of 100 nm were peeled off without generating cracks.
Of the 7 GaN crystals produced with 140 nm, 7 were peeled off without generating cracks.
7 out of 7 GaN crystals produced at 200 nm were cracked and peeled off.
Cracks occurred in 5 out of 7 GaN crystals produced at 240 nm and could not be peeled off.
From the results of Example 9 and Comparative Example 4 described above, the thickness of the carbide layer is preferably 10 nm to 200 nm.

(Example 10)
In this example, in the step of nitriding the titanium carbide layer, the same step as that described in Example 1 was used except that nitriding was changed to 300 ° C. holding, 600 ° C. holding or 1050 ° C. holding.
2. Step of nitriding titanium carbide layer Nitriding apparatus: HVPE apparatus Nitriding temperature: Controlled at 300 ° C, 600 ° C and 1050 ° C.
Nitriding time: 35 minutes Nitriding gas: NH ₃ gas, 3.3 l / min

(Comparative Example 5)
In Comparative Example 5, the nitriding temperature was changed to 250 ° C. and 1100 ° C. Other conditions are the same as in Example 10.

(Results of Example 10 and Comparative Example 5)
The following results were obtained regarding the peeling state of the a-plane GaN semiconductor layer.
Cracks occurred in four of the seven GaN crystals produced at 250 ° C. and could not be peeled off.
300 deg. C. Seven out of the seven GaN crystals produced did not crack and were peeled off.
Six out of seven GaN crystals produced at 600 ° C., no cracks were generated and peeling occurred.
At 1050 ° C., 7 out of 7 GaN crystals produced were peeled off without generating cracks.
Cracks occurred in 6 of 7 GaN crystals produced at 1100 ° C. and could not be peeled off.
From the results of Example 10 and Comparative Example 5 described above, the step of nitriding the carbide layer is preferably performed at 300 ° C. or higher and 1050 ° C. or lower.

  In Example 1, the surface of the GaN crystal obtained by peeling the a-plane GaN semiconductor layer from the r-plane sapphire substrate and the back surface of the GaN crystal are polished with a diamond slurry, which is a planar self-supported substrate having a thickness of 200 μm. A GaN free-standing substrate was produced. FIG. 14 shows the produced a-plane GaN free-standing substrate.

It is a schematic diagram which shows the manufacturing process of the GaN semiconductor substrate concerning embodiment of this invention. It is a schematic diagram which shows the manufacturing process of the GaN semiconductor substrate concerning embodiment of this invention. It is a table | surface which shows the crystal structure and lattice mismatch rate of the carbide | carbonized_material and nitride which are used by this invention. It is a table | surface which shows the lattice constant of the carbide | carbonized_material, nitride, and sapphire which are used by this invention. 2 is a diagram showing an X-ray diffraction pattern of titanium carbide in Example 1. FIG. 4 is a diagram showing a temperature profile of a step of epitaxially growing a nonpolar plane GaN crystal layer of Example 1. FIG. 3 is a diagram showing an X-ray diffraction pattern of a GaN crystal layer of Example 1. FIG. 4 is a diagram showing an X-ray rocking curve of a GaN crystal layer of Example 1. FIG. 2 is a microscopic image of the surface of a GaN crystal layer of Example 1. FIG. 2 is a microscopic image of the surface of a GaN crystal layer of Example 1. FIG. 2 is a microscopic image of a cross section of a GaN crystal layer of Example 1. FIG. 2 is a microscopic image of a cross section of a GaN crystal layer of Example 1. FIG. 6 is a diagram showing an X-ray rocking curve of a GaN crystal layer of Comparative Example 2. FIG. It is a figure which shows the a-plane GaN board | substrate produced from the GaN crystal layer peeled in Example 1 of this invention.

Explanation of symbols

10 r-plane sapphire substrate 11 carbide layer 12 partially nitrided carbide layer 121 nitride layer 122 non-nitrided carbide layer 123 nitride layer 14 containing carbon 14 faceted GaN film 16 a-plane GaN crystal layer 17 carbon A-plane GaN crystal layer integrated with nitride containing

Claims (9)

Forming a layer made of a carbide selected from the group consisting of titanium carbide, zirconium carbide, hafnium carbide, niobium carbide, vanadium carbide, and tantalum carbide on an underlying substrate;
Nitriding the carbide layer;
Forming a nonpolar plane GaN crystal layer by epitaxially growing the nonpolar plane of the GaN crystal as a growth plane on the nitrided carbide layer;
Removing the base substrate to obtain a GaN semiconductor substrate including the nonpolar plane GaN crystal layer;
A method for producing a GaN semiconductor substrate, comprising:   The step of epitaxially growing a nonpolar surface of a GaN crystal as a growth surface includes the step of growing the nonpolar surface GaN crystal layer while forming a GaN film having a facet structure on the nitrided carbide layer. The method for producing a GaN semiconductor substrate according to claim 1, wherein the method is characterized in that:   3. The method of manufacturing a GaN semiconductor substrate according to claim 2, wherein a thickness of the GaN film having the facet structure is 3 μm or more and 25 μm or less.   The step of obtaining a GaN semiconductor substrate includes cooling the base substrate, the nitrided carbide layer, and the nonpolar plane GaN crystal layer from a growth temperature, and in the cooling process, from the nonpolar plane GaN crystal layer, The method for manufacturing a GaN semiconductor substrate according to claim 1, wherein the substrate is separated and removed. The GaN semiconductor substrate manufacturing method according to claim 1, wherein the base substrate is an r-plane sapphire substrate.   6. The method of manufacturing a GaN semiconductor substrate according to claim 5, wherein the nonpolar surface of the GaN crystal is an a-plane.   The method for manufacturing a GaN semiconductor substrate according to claim 6, wherein the carbide layer has a thickness of 5 nm to 200 nm.   The method for manufacturing a GaN semiconductor substrate according to claim 7, wherein the step of nitriding the carbide layer is performed at 300 ° C. or higher and 1050 ° C. or lower.   A GaN semiconductor substrate obtained by the method for manufacturing a GaN semiconductor substrate according to claim 1.