JP2011026168A - Substrate, laminate, method for producing laminate, and method for producing substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate capable of obtaining a group III nitride semiconductor layer having good crystallinity grown on a nonpolar plane. <P>SOLUTION: The substrate 1 includes a base substrate 11 and an aluminum carbide layer 12 formed on the base substrate 11. A ä1-100} plane 121 of the aluminum carbide layer 12 is exposed on the side of the aluminum carbide layer 12 opposite to the base substrate 11. The ä1-100} plane 121 of the aluminum carbide layer is inclined to the principal plane 110 of the base substrate 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a substrate, a laminate, a method for producing a laminate, and a method for producing a substrate.

  In recent years, with the practical application of high-intensity light-emitting diodes (LEDs) and laser diodes (LDs) using gallium nitride (GaN) substrates, development of gallium nitride substrates with good crystal quality is desired. The GaN substrate is produced, for example, by using a sapphire substrate as a base substrate and heteroepitaxially growing a GaN crystal on the sapphire substrate by metal organic vapor phase epitaxy (MOVPE). Finally, a GaN substrate is formed by peeling the sapphire substrate from the GaN crystal. However, since there is a lattice mismatch and a difference in thermal expansion coefficient between sapphire and GaN, it is difficult to grow a GaN crystal directly on the sapphire substrate. Therefore, a technique has been developed in which a buffer layer made of aluminum nitride (AlN) or GaN is deposited on the c-plane of the sapphire substrate at a relatively low temperature, and then a GaN crystal is grown on the buffer layer at a high temperature. A method for manufacturing this type of GaN substrate is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-284600.

  Since the hexagonal III-V nitride semiconductor is a polarization substance having the c-axis as a polarization axis, spontaneous polarization occurs along the c-axis, and electrons and holes are separated by this spontaneous polarization. There is a nature. In addition, when a laminated structure composed of different types of III-V nitride semiconductors is produced, piezoelectric polarization is generated due to distortion of the crystal structure due to a difference in lattice constant, and this piezoelectric polarization generates a piezoelectric field in the c-axis direction of GaN. . This piezo electric field lowers the probability of recombination of electrons and holes injected into the light emitting layer of the light emitting device, thereby reducing the internal quantum efficiency. In addition, when the light emitting device has a c-axis oriented strained quantum well structure, a strong internal electric field is induced by the spontaneous polarization and piezoelectric polarization, and electrons and holes are spatially separated in one quantum well layer. There is. This reduces the recombination probability of electrons and holes that contribute to light emission, and lowers the internal quantum efficiency. Further, there is a problem that the emission wavelength is shifted to the longer wavelength side due to piezoelectric polarization, and it becomes difficult to shorten the emission wavelength.

  Since the a-plane and m-plane of the hexagonal crystal are nonpolar planes, if GaN can be formed on the nonpolar plane, problems due to the above-described spontaneous polarization and piezoelectric polarization can be avoided. As a technique for forming GaN on a nonpolar surface, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2005-320237), Patent Document 3 (Japanese Patent Laid-Open No. 2000-216497) or Patent Document 4 (Japanese Patent Laid-Open No. 2008-053640). Gazette).

JP 2002-284600 A JP 2005-320237 A JP 2000-216497 A JP 2008-053640 A JP 2002-145700 A

  However, it is difficult to obtain a nonpolar plane-grown GaN crystal with good crystallinity.

The present invention provides a substrate capable of obtaining a nonpolar plane-grown Group III nitride semiconductor layer having good crystallinity.

  According to the present invention, the substrate includes a base substrate and an aluminum carbide layer formed on the base substrate, and the m-axis of the aluminum carbide layer is inclined with respect to the main surface of the base substrate. A substrate is provided.

  According to the present invention, the m-axis of the aluminum carbide layer is inclined with respect to the main surface of the base substrate. When a group III nitride semiconductor layer is grown on an m-plane on such an aluminum carbide layer, a group III nitride semiconductor layer with good crystallinity can be obtained.

Here, the main surface of the base substrate is a flat surface perpendicular to the normal vector to the surface of the base substrate. In other words, the normal vector with respect to the base substrate is a vector along the stacking direction of each layer of the substrate.
Moreover, according to this invention, the laminated body provided with the board | substrate mentioned above and the group III nitride semiconductor layer formed on the aluminum carbide layer of the said board | substrate can also be provided.
In addition, the method includes a step of forming an aluminum carbide layer on the base substrate by metal organic vapor phase epitaxy, and in the step of forming the aluminum carbide layer, the m-axis of the aluminum carbide layer is a main surface of the base substrate. A method of manufacturing a substrate on which an aluminum carbide layer is formed so as to be inclined with respect to the substrate can be provided.
Furthermore, the manufacturing method of a laminated body including the process of obtaining a board | substrate with the manufacturing method of the board | substrate mentioned above, and the process of forming a group III nitride semiconductor layer by the hydride vapor phase growth method on the said aluminum carbide layer of the said board | substrate. Can also be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the board | substrate which can obtain the nonpolar surface growth group III nitride semiconductor layer with favorable crystallinity is provided.

It is a figure which shows the board | substrate of this invention. It is a figure for demonstrating the inclination of m surface of a base substrate. It is a figure for demonstrating the inclination of m surface of a base substrate. It is a figure for demonstrating the inclination of the m surface of an aluminum carbide layer. It is a figure for demonstrating the inclination of the m surface of an aluminum carbide layer. It is a figure which shows the manufacturing process of a GaN substrate. It is a figure which shows the manufacturing process of a GaN substrate. It is a figure which shows the growth process of GaN in case the m surface of an aluminum carbide layer is parallel with respect to a main surface. It is a figure which shows the advantage in case the m surface of an aluminum carbide layer inclines in the a-axis direction of an aluminum carbide layer with respect to the main surface. It is a figure concerning the modification of this invention. It is a figure concerning the modification of this invention. It is a figure which shows the state in which the GaN layer was formed on the aluminum carbide layer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
An outline of the substrate 1 of the present embodiment will be described with reference to FIGS.
1A is a view of the substrate 1 viewed microscopically, and FIG. 1B is a view of the substrate 1 viewed macroscopically.
The substrate 1 includes a base substrate 11 and an aluminum carbide layer 12 formed on the base substrate 11. The {1-100} surface 121 of the aluminum carbide layer 12 is exposed on the surface of the aluminum carbide layer 12 opposite to the base substrate 11.
The m-axis of the aluminum carbide layer is inclined with respect to the main surface 110 of the base substrate 11. That is, the {1-100} surface 121 of the aluminum carbide layer is inclined with respect to the main surface 110 of the base substrate 11.
The main surface 110 corresponds to the front and back surfaces of the base substrate 11 when the substrate 1 is viewed macroscopically, and is a flat surface perpendicular to the normal vector A with respect to the base substrate 11. The normal vector A with respect to the base substrate 11 is a vector A along the stacking direction of each layer of the substrate 1.
The substrate 1 is a group III nitride semiconductor layer forming substrate for forming a group III nitride semiconductor layer on the aluminum carbide layer 12.

As the base substrate 11, a substrate having a hexagonal crystal structure, for example, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, or an aluminum nitride substrate is preferable.
When viewed macroscopically, the pair of surfaces (macroscopic surfaces) of the base substrate 11 are flat and parallel to each other. A macroscopic surface is a surface that can be grasped when viewed directly with the naked eye.
When viewed microscopically, the surface (microscopic surface) of the base substrate 11 on the aluminum carbide layer 12 side is formed in a stepped shape. Here, the microscopic surface means a surface detected using an atomic force microscope (AFM) or the like. The terrace portion 111 of the stairs is the m plane ({1-100} plane) of the base substrate 11. The terrace portion 111 is inclined with respect to the main surface 110, and the inclination angle θ1 is preferably 1 ° or more and 20 ° or less. Especially, it is more preferable that inclination | tilt angle (theta) 1 is 5 degrees or more and 15 degrees or less. By setting the inclination angle θ1 to 1 ° or more, particularly 5 ° or more, the inclination angle θ2 of the terrace portion 121 of the aluminum carbide layer 12 to be described later can be set to 1 ° or more. The crystallinity of the group III nitride semiconductor layer formed in this way can be made favorable.
Further, by setting the inclination angle θ1 to 20 ° or less, particularly 15 ° or less, the inclination angle θ2 of the terrace portion 121 of the aluminum carbide layer 12 to be described later can be set to 20 ° or less, thereby disturbing the crystal orientation. This has the effect of avoiding the danger of the occurrence of

As shown in FIGS. 2 and 3, the terrace portion 111 can be inclined as in any one of the following (i) to (iii). In order to facilitate understanding of the inclination of the terrace portion 111, the case where the terrace portion (m-plane) is parallel to the main surface 110 is described as a plane L.
(I) The m-plane that is the terrace portion 111 is inclined in the direction (<0001> direction) along the c-axis of the base substrate 11 with respect to the main surface 110 (see FIG. 2A).
(Ii) Further, the m-plane which is the terrace portion 111 is inclined in the direction along the a-axis (<11-20> direction) of the base substrate 11 with respect to the main surface 110 (see FIG. 2B).
(Iii) The m-plane that is the terrace portion 111 is between the c-axis of the base substrate 11 and the a-axis of the base substrate 11, and the c-axis with the a-axis of the base substrate 11 as the rotation axis of the base substrate 11 It tilts along the axis k rotated by a predetermined angle to the side (see FIG. 3).
In FIG. 3, the terrace portion 111 is inclined with respect to the main surface 110 in the direction of the axis k. The axis k is an axis on the a axis-c axis plane.
In the case of (iii), the m-plane that is the terrace portion 111 is between the c-axis of the base substrate 11 and the a-axis of the base substrate 11 with respect to the main surface 110, and the a-axis of the base substrate 11 is The base substrate is inclined in the direction along the axis k (30 in the FIG. 3 is 30 ° or more and 60 ° or less) rotated about 30 ° or more and 60 ° or less to the c-axis side with the m axis as the rotation axis. preferable.
By doing in this way, the defect which generate | occur | produces by the coupling | bonding of c surface of the group III nitride semiconductor layer mentioned later, and the defect which generate | occur | produces by the coupling | bonding of a surface can be reduced to some extent.

  Here, the size and shape of each terrace portion 111 and the size and shape of the step portion are substantially equal, and a structure in which staircase portions constituted by the terrace portion and the step portion are regularly connected is preferable.

The width W1 of the terrace portion 111 is preferably 3 nm or more from the viewpoint of securing a sufficient width for nitride crystal growth, and 63 nm or less from the viewpoint of suppressing the mixing of a large number of crystal nuclei on the same terrace. Is preferred. Further, the height H1 of the step portion is about several atomic layers, and is preferably 1 nm or more from the viewpoint of securing a sufficient level difference effective for improving crystallinity, and from the viewpoint of preventing the terrace width from exceeding the upper limit. It is preferably 20 nm or less.
Such a base substrate 11 can be obtained, for example, by a method of etching the inclined substrate surface.

  The aluminum carbide layer 12 is formed on the base substrate 11 as shown in FIG. The aluminum carbide layer 12 has a stepped surface on the side opposite to the base substrate 11. This step shape is formed according to the step shape of the surface of the base substrate 11 on the aluminum carbide layer 12 side.

The terrace portion 121 of the stairs is the m-plane ({1-100} plane) of the aluminum carbide layer 12. The terrace portion 121 is inclined with respect to the main surface 110, and the inclination angle θ2 is preferably 1 ° or more and 20 ° or less. Especially, it is more preferable that inclination | tilt angle (theta) 2 is 5 degrees or more and 15 degrees or less. By setting the inclination angle θ2 of the terrace portion 121 of the aluminum carbide layer 12 to 1 ° or more, particularly 5 ° or more, the crystallinity of the group III nitride semiconductor layer formed on the aluminum carbide layer 12 is improved. be able to.
Further, by setting the inclination angle θ2 to 20 ° or less, particularly 15 ° or less, there is an effect that it is possible to avoid a risk of disorder of crystal orientation.

As shown in FIGS. 4 and 5, the terrace portion 121 can be inclined as in any of the following (i) to (iii).
(I) The m-plane which is the terrace portion 121 is inclined with respect to the main surface 110 in the direction along the a-axis (<11-20> direction) of the aluminum carbide layer 12 (see FIG. 4B).
(Ii) Further, the m-plane that is the terrace portion 121 is inclined in the direction (<0001> direction) along the c-axis of the aluminum carbide layer 12 with respect to the main surface 110 (see FIG. 4A).
(Iii) The m-plane which is the terrace portion 121 is between the c-axis of the aluminum carbide layer 12 and the a-axis of the aluminum carbide layer 12, and the c-axis of the aluminum carbide layer 12 is the m-axis of the aluminum carbide layer 12. It inclines along the axis k rotated by the predetermined angle to the a-axis side as a rotating shaft (refer FIG. 5).
FIG. 5 shows that the m-plane that is the terrace portion 121 is inclined in the direction of the axis k with respect to the main surface 110. The axis k is an axis on the a axis-c axis plane.
In the case of (iii), the m-plane that is the terrace portion 111 is between the c-axis of the aluminum carbide layer 12 and the a-axis of the aluminum carbide layer 12 with respect to the main surface 110, and the aluminum carbide layer 12 The direction along the axis k rotated 30 degrees or more and 60 degrees or less to the a axis side with the c axis as the m axis of the aluminum carbide layer 12 (θ4 in FIG. 5 is 30 degrees or more and 60 degrees or less) It is preferable to be inclined.
By setting θ4 to 30 ° or more and 60 ° or less, a group III nitride semiconductor layer having good crystallinity can be obtained with certainty.

The crystallinity of the group III nitride semiconductor layer is good in the direction in which the terrace portion is inclined with respect to the main surface. Therefore, which of (i) to (iii) is selected may be appropriately selected according to the use of the GaN layer.
The inclination angle, size and shape of each terrace portion 121, and the size and shape of the step portion are substantially equal, and a structure in which staircase portions constituted by the terrace portion and the step portion are regularly connected is preferable.
The width W3 of the terrace portion 121 is preferably 3 nm or more from the viewpoint of securing a sufficient width for nitride crystal growth, and 63 nm or less from the viewpoint of suppressing the mixing of a large number of crystal nuclei on the same terrace. Is preferred. Further, the height H2 of the step portion is within a range of 1 nm or more from the viewpoint of ensuring a sufficient level difference effective for improving the crystallinity and within 20 nm or less from the viewpoint of preventing the terrace width from exceeding the upper limit. preferable.
Furthermore, by setting the thickness of the aluminum carbide layer 12 to 40 nm or more, it is possible to prevent most of the aluminum carbide layer 12 from being nitrided in the nitriding step of the aluminum carbide layer 12 to be described later and making it difficult to peel off the base substrate. On the other hand, by setting the thickness of the aluminum carbide layer 12 to 120 nm or less, the aluminum carbide layer can be prevented from maintaining a strong bond with the upper surface of the base substrate 11, and the base substrate 11 can be easily peeled off.

Such an aluminum carbide layer 12 is obtained by thermally cleaning the base substrate 11 and then using a metal organic vapor phase epitaxy method (MOVPE method) using a source gas containing an organic aluminum gas such as trimethylaluminum (TMA). ). Among organic aluminum gases, TMA is particularly preferable because it is easily decomposed on the heated base substrate 11 to form an aluminum carbide layer.
Moreover, crystal quality can be made high by producing an aluminum carbide layer by a vapor phase growth method.
The film forming temperature of the aluminum carbide layer 12 is preferably 300 ° C. or higher from the viewpoint of promoting the TMA decomposition reaction, and may be 1000 ° C. or lower from the viewpoint of preventing the formation of a simple substance of aluminum. It is preferable that the temperature is 800 ° C. or lower.
By setting the temperature to 800 ° C. or lower, the m-plane can be reliably oriented. Below 800 ° C., it is difficult for source atoms to move freely on the substrate surface and aggregate each other, and it becomes easy to be bound by the m-plane crystal arrangement of the base substrate, so that the m-plane can be surely oriented. It is done.
In order to prevent oxidation of the aluminum carbide layer 12 of the substrate, the surface of the aluminum carbide layer 12 may be nitrided to form an aluminum nitride layer (protective film). In this case, the substrate has an aluminum nitride layer provided on the aluminum carbide layer.
Further, in order to prevent the aluminum carbide layer 12 from being oxidized, a very thin group III nitride semiconductor layer (protective film), for example, a GaN layer may be formed. These protective films are preferably 10 nm or more in order to surely prevent oxidation of the aluminum carbide layer 12, and are preferably 200 nm or less from the viewpoint of shortening the process time.
As a protective film for preventing oxidation of the aluminum carbide layer 12, aluminum nitride (AlN), a mixed crystal of AlN and GaN (Al _x Ga _1-x N (0 <x <1), zinc oxide ( Any film of ZnO), gallium oxide (Ga ₂ O ₃ ), lithium aluminate (LiAlO ₂ ), or silicon carbide (SiC) may be used.
Since these are chemically stable films having a crystal structure close to that of a group III nitride semiconductor, they are preferable as protective films.

(Group III nitride semiconductor layer manufacturing method)
Next, a method of forming a laminated body having a group III nitride semiconductor layer using the substrate 1 as described above, and then obtaining a self-standing substrate of the group III nitride semiconductor will be described.
(Step of nitriding aluminum carbide layer 12)
First, the substrate 1 shown in FIG. 6A is nitrided. Specifically, as shown in FIG. 6B, the aluminum carbide layer 12 of the substrate 1 is nitrided in an atmosphere of 300 ° C. to 900 ° C. to form a nitrided aluminum carbide layer 13.
The nitriding conditions of the aluminum carbide layer 12 are, for example, as follows.

Nitriding gas: ammonia (NH ₃ ) gas, H ₂ gas, N ₂ gas Nitriding temperature: 300 ° C. to 900 ° C.
Nitriding time: 5 minutes to 60 minutes The nitriding temperature is more preferably 500 ° C. or more and 700 ° C. or less, and particularly preferably 550 ° C. or less. When the temperature is higher than 550 ° C., CH ₄ is decomposed and C is precipitated as shown in the formula (1), and the crystallinity of the group III nitride semiconductor layer may be deteriorated by mixing C with AlN. In order to suppress the precipitation of C, it is effective to increase the introduction of hydrogen and the partial pressure of ammonia.
CH ₄ → C + 2H ₂ (1) Further, the nitriding time is more preferably 30 minutes or less. By setting the nitriding time to about 30 minutes, the aluminum carbide layer 12 can be appropriately nitrided.

As a reaction gas when nitriding the aluminum carbide layer 12, ammonia is preferable. AlN can be formed even if nitrogen is used as the reaction gas in addition to ammonia. However, as shown in formula (2), when AlN and C are formed and C is mixed in AlN, the crystal of the group III nitride semiconductor layer is formed. May affect quality.
Al ₄ C ₃ + 2N ₂ → 4AlN + 3C (2) Formula The nitriding of the aluminum carbide layer 12 can be performed continuously from the formation step of the aluminum carbide layer in the MOVPE apparatus. it can.
Note that reference numeral 12A illustrated in FIG. 6B indicates aluminum carbide, and reference numeral 12B indicates aluminum nitride. That is, Al ₄ C ₃ remains in the portion in contact with the sapphire substrate (underlying substrate) 11, and an AlN layer that inherits the crystal information of Al ₄ C ₃ is formed thereon.

(Group III nitride semiconductor layer formation process)
In this step, the group III nitride semiconductor layer 17 is formed. Specifically, the buffer layer 14 is formed as the first group III nitride semiconductor layer, and the second group III nitride semiconductor layer is epitaxially grown on the buffer layer 14.
First, as shown in FIGS. 7A and 7B, a buffer layer 14 (first group III nitride semiconductor layer) is formed on the nitrided aluminum carbide layer 13 (see FIG. 12).
The film forming conditions of the buffer layer 14 can be set as follows, for example.

Film forming method: MOVPE film forming temperature: 300 ° C. to 1000 ° C.
Deposition gas: Trimethylgallium (TMG) gas, H ₂ gas, N ₂ gas, NH ₃ gas Film thickness: 20 nm to 140 nm
The buffer layer 14 can be formed continuously from the step of nitriding the aluminum carbide layer in the MOVPE apparatus.
When the buffer layer 14 is a GaN layer, it diffuses from the group III nitride semiconductor epitaxially grown to the nitrided aluminum carbide layer 13 through the aluminum carbide layer 13 in which nitrogen atoms are nitrided through this epitaxial growth process. Therefore, it is considered that the nitriding reaction according to the following formula (3) proceeds in the nitrided aluminum carbide layer 13.

Al ₄ C ₃ + 4N → 4AlN + 3C (3)

  As a result, during epitaxial growth of the buffer layer 14, AlN forms a mixed crystal with GaN, and finally carbon is distributed at a relatively high concentration in the vicinity of the boundary surface between the base substrate 11 and the nitrided aluminum carbide layer. 12C is formed (see FIG. 7B). Since carbon is inactive to the group III nitride semiconductor and the base substrate 11, the bond strength between the base substrate 11 and the nitrided aluminum carbide layer is reduced, and the base substrate 11 is peeled off with a relatively small stress. I think it can be done.

  Here, the buffer layer 14 is preferably epitaxially grown at a temperature in the range of 500 ° C. to 1000 ° C., particularly in the range of 600 ° C. to 1000 ° C. By growing the buffer layer 14 at a temperature within this range, the crystallinity of the group III nitride semiconductor layer epitaxially grown on the buffer layer 14 in the next step can be improved. In particular, by growing the buffer layer 14 at a temperature of 600 ° C. or higher, the m-plane orientation of the group III nitride semiconductor layer can be remarkably improved.

(Step of epitaxially growing the second group III nitride semiconductor layer)
Next, a second group III nitride semiconductor layer is epitaxially grown on the buffer layer 14. The second group III nitride semiconductor layer can be grown by hydride vapor phase epitaxy. In the present embodiment, the second group III nitride semiconductor layer is a GaN semiconductor layer. Thereby, a group III nitride semiconductor layer 17 including the buffer layer 14 and the second group III nitride semiconductor layer is formed (see FIG. 7B).
The growth conditions of the GaN semiconductor layer can be as follows, for example.

Film forming method: HVPE (hydride vapor phase epitaxy) film forming temperature: 1000 ° C. to 1050 ° C.
Deposition time: 30 minutes to 270 minutes

  Here, when the buffer layer 14 is formed, as shown in FIG. 7A, the crystal nuclei of the group III nitride semiconductor are scattered on the terrace portion of the nitrided aluminum carbide layer. Then, scattered crystal nuclei grow, and adjacent crystals merge. At this time, since the m-axis of the aluminum carbide layer is inclined with respect to the main surface, a group III nitride semiconductor crystal having an inclined m-axis is formed and further grown as shown in FIGS. It is possible to suppress the occurrence of distortion when crystals are bonded to each other.

More specifically, when the m-plane which is the surface of the aluminum carbide layer is not inclined (when the m-axis of the aluminum carbide layer is perpendicular to the main surface of the substrate 11), it is shown in FIG. As described above, crystal nuclei of the group III nitride semiconductor are scattered. In FIG. 8, reference numeral 910 indicates a base substrate, and reference numeral 930 indicates a nitrided aluminum carbide layer. Reference numeral 912A denotes an aluminum carbide layer, and reference numeral 912B denotes an aluminum nitride layer.
For example, the + c plane and the −c plane, which have different growth rates of the group III nitride semiconductor layer, face each other to be distorted, and defects are likely to occur (see FIG. 8B).

  On the other hand, when the m-plane of the aluminum carbide layer is inclined with respect to the main surface in the c-axis direction of the aluminum carbide layer, the m-plane of the grown group III nitride semiconductor layer is also inclined with respect to the main surface ( 12), when the crystals are bonded to each other, the bonding between the + c plane and the −c plane facing each other can be reduced, and the occurrence of distortion can be suppressed.

  Further, when the m-plane of the aluminum carbide layer is inclined in the a-axis direction of the aluminum carbide layer with respect to the main surface, the crystals of the group III nitride semiconductor layer grow and bond with each other. Can be reduced by being opposed to each other, and distortion can be suppressed. Furthermore, when the m-plane of the aluminum carbide layer is inclined in the a-axis direction of the aluminum carbide layer with respect to the main surface, when the group III nitride semiconductor layer 17 is formed on the aluminum carbide layer, as shown in FIG. In addition, an m-plane facet surface is formed. For this reason, the transition generated at the interface between the group III nitride semiconductor layer 17 and the nitrided aluminum carbide layer is bent at the facet surface, and the dislocation is reduced. In FIG. 9, the shape of the substrate 11 is simplified.

  In the case where the terrace portion 121 is inclined toward the direction between the c-axis of the aluminum carbide layer 12 and the a-axis of the aluminum carbide layer 12, particularly when θ4 is 30 ° or more and 60 ° or less. Can reduce to some extent each of the defects generated by the coupling of the c-planes and the defects generated by the coupling of the a-planes.

(Sapphire substrate peeling process)
Next, the sapphire substrate 11 is peeled and removed.
Specifically, the temperature of the HVPE apparatus in which the GaN semiconductor layer 17 is formed is lowered, and the GaN semiconductor layer 17 is cooled to room temperature.
During this cooling, the stacked body is distorted due to the difference in thermal expansion coefficient between the GaN semiconductor layer 17 and the sapphire substrate 11, and the GaN semiconductor layer 17 and the sapphire substrate 11 are separated.
Thereafter, by polishing the front surface and the back surface of the peeled GaN semiconductor layer 17, a GaN substrate that is a flattened free-standing substrate can be produced.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the embodiment, the group III nitride semiconductor layer 17 is a GaN layer. However, the present invention is not limited to this, and may be InN or AlN. Moreover, two or more mixed crystals selected from GaN, InN, and AlN may be used.
Moreover, in the said embodiment, although the terrace part of the aluminum carbide layer 12 was m surface, surfaces other than m surface, for example, (10-12) surface, may be exposed to a part of terrace part. However, from the viewpoint of growing the group III nitride semiconductor layer 17 on the m-plane, it is preferable that no surface other than the m-plane is exposed at the terrace portion of the aluminum carbide layer 12.
In the embodiment, the surface of the base substrate on the side of the aluminum carbide layer or the surface of the aluminum carbide layer opposite to the base substrate has a regular stepped shape in which the inclination angle of the terrace portion and the height of the step portion are equal. However, as shown in FIG. 10, the terrace portion may be configured with stairs having different inclination angles and step portions having different heights.

Furthermore, in the said embodiment, although the surface of the aluminum carbide layer side of a base substrate and the surface on the opposite side to the base substrate of an aluminum carbide layer was formed in step shape, it does not need to be formed in step shape. . The m-axis of the aluminum carbide layer only needs to be inclined with respect to the main surface of the base substrate.
If the m-axis of the aluminum carbide layer is inclined with respect to the main surface of the base substrate, when forming the group III nitride semiconductor layer, the m-axis of the group III nitride semiconductor layer is inclined with respect to the main surface. A group III nitride semiconductor layer with high crystallinity can be formed.
For example, when the m-axis of the aluminum carbide layer 13 is inclined with respect to the main surface of the base substrate 11, as shown in FIG. The region where the c-planes of the layer 14 collide with each other can be relatively reduced, and the occurrence of distortion can be suppressed.
Note that the m-plane of the aluminum carbide layer does not necessarily have to be exposed at the surface, and may not be exposed at the surface. The m-axis of the aluminum carbide layer only needs to be inclined with respect to the main surface of the base substrate 11.

  Furthermore, in the said embodiment, although the sapphire substrate 11 was peeled and removed, the sapphire substrate 11 does not need to be removed. Even in this case, the aluminum carbide layer 12 is preferably nitrided in order to improve the crystallinity of the group III nitride semiconductor layer.

Next, examples of the present invention will be described.
Example 1
A process similar to that described in the previous embodiment was performed to obtain a GaN crystal having a thickness of about 250 μm. The conditions adopted in each process are as follows. First, the sapphire substrate was placed in the reactor of the MOVPE apparatus, the furnace temperature was set to about 1050 ° C., and the sapphire substrate was thermally cleaned for about 10 minutes.
Note that the sapphire substrate is the same substrate as in the above embodiment, and macroscopically, the front and back surfaces are flat and parallel, but microscopically, the surface on the side where the aluminum carbide layer is formed later. Is formed in a staircase shape, and the terrace portion of the staircase is m-plane. The m plane is inclined with respect to the main surface in a direction along the c-axis of the sapphire substrate, and the inclination angle θ1 is 1 °.
Next, the following steps were performed.
(Formation process of aluminum carbide layer)
Film forming method: MOVPE film forming temperature: 600 ° C.
Deposition time: 5 minutes Deposition gas: TMA 10 μmol / min, H ₂ gas 10 L / min, N ₂ gas 5 L / min
Film thickness: 70nm
In the formed aluminum carbide layer, the surface opposite to the sapphire substrate was formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane is inclined with respect to the main surface in a direction along the a-axis of the aluminum carbide layer, and the inclination angle θ2 with respect to the main surface is 1 °.

(Step of nitriding the aluminum carbide layer)
Nitriding temperature: 500 ° C
Nitriding time: 30 minutes Nitriding gas: NH ₃ gas 5 L / min, H ₂ gas 5 L / min, N ₂ gas 5 L / min

(Buffer layer formation process)
Film forming method: MOVPE film forming temperature: 600 ° C.
Deposition gas: TMG 10 μmol / min, NH 3 gas 5 L / min, H 2 gas 7 L / min, N ₂ gas 3 L / min
Film thickness: 70nm

(Process for epitaxial growth of GaN semiconductor layer)
Deposition method: HVPE Deposition temperature: 1040 ° C
Deposition gas: HCl gas 80cc / min, NH ₃ gas 1.5 L / min
Source: Ga source (850 ° C.)
Film thickness: 100 μm

(Sapphire substrate peeling process)
The temperature in the HVPE apparatus on which the GaN semiconductor layer was formed was lowered and cooled to room temperature.

(Example 2)
A sapphire substrate similar to that in Example 1, but a sapphire substrate having an inclination angle θ1 of 10 ° was used. Otherwise, a GaN semiconductor layer was obtained in the same manner as in Example 1. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane is inclined with respect to the main surface in a direction along the a-axis of the aluminum carbide layer, and the inclination angle θ2 with respect to the main surface is 10 °.

(Example 3)
A sapphire substrate similar to that in Example 1, but a sapphire substrate having an inclination angle θ1 of 20 ° was used. Otherwise, a GaN semiconductor layer was obtained in the same manner as in Example 1. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane is inclined in the direction along the a-axis of the aluminum carbide layer with respect to the main surface, and the inclination angle θ2 with respect to the main surface is 20 °.

(Example 4)
A sapphire substrate similar to that in Example 1, but a sapphire substrate having an inclination angle θ1 of 30 ° was used. Otherwise, a GaN semiconductor layer was obtained in the same manner as in Example 1. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane is inclined with respect to the main surface in the direction along the a-axis of the aluminum carbide layer, and the inclination angle θ2 with respect to the main surface is 30 °.

(Comparative Example 1)
As the sapphire substrate, one having θ1 of 0 °, that is, a substrate in which the m-plane of the sapphire substrate is parallel to the main surface was used.
The other points are the same as those in the first embodiment. The m-plane of the aluminum carbide layer formed on such a sapphire substrate was parallel to the main surface.

  Table 1 shows the full width at half maximum of the X-ray rocking curve (XRD) by X-ray analysis of the obtained GaN semiconductor layer in Examples 1 to 4 and Comparative Example 1. “GaN-a-axis incidence” in Table 1 means that x-rays are incident from the a-axis direction of the GaN semiconductor layer, and “GaN-c-axis incidence” is x-rays from the c-axis direction of the GaN semiconductor layers. It means that it was incident.

  In Examples 1 to 3, it can be seen that the crystallinity of GaN in the a-axis direction is improved as compared with Comparative Example 1. Moreover, in Example 4, it can be seen that the crystallinity of GaN in the c-axis direction is better than that of Comparative Example 1. On the other hand, in Comparative Example 1, it can be seen that the crystallinity of GaN in the a-axis direction is worse than in Examples 1 to 3.

(Example 5)
As the sapphire substrate, a substrate similar to the above-described embodiment, that is, a substrate in which the surface on which the aluminum carbide layer is laminated is formed in a staircase shape and the terrace portion of the staircase is an m-plane is used. The m plane is inclined with respect to the main surface in a direction along the a-axis of the sapphire substrate, and the inclination angle θ1 is 1 °.
. Other manufacturing conditions are the same as those in Example 1. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m plane was inclined with respect to the main surface in a direction along the c-axis of the aluminum carbide layer, and the inclination angle θ2 with respect to the main surface was 1 °.

(Example 6)
A sapphire substrate similar to that in Example 5, but a sapphire substrate having an inclination angle θ1 of 10 ° was used. A GaN semiconductor layer was obtained in the same manner as in Example 5. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane is inclined in the direction along the c-axis of the aluminum carbide layer, and the inclination angle θ2 with respect to the main surface is 10 °.

(Example 7)
A sapphire substrate similar to that in Example 5, but a sapphire substrate having an inclination angle θ1 of 20 ° was used. Otherwise, a GaN semiconductor layer was obtained in the same manner as in Example 5. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane is inclined in the direction along the c-axis of the aluminum carbide layer, and the inclination angle θ2 with respect to the main surface is 20 °.

  Table 2 shows the X-ray diffraction results of the peeled GaN semiconductor layers in Examples 5 to 7.

(Example 8)
As the sapphire substrate, a surface on which the aluminum carbide layer is laminated is formed in a stepped shape, and the stepped terrace portion is an m-plane. As shown in FIG. 3, the m-plane is inclined in the direction between the a-axis and the c-axis of the sapphire substrate (inclined toward the axis k shown in FIG. 3), and the inclination angle θ1 is 1 °. The angle θ3 formed by the axis k and the a axis was 30 °.
Other manufacturing conditions are the same as those in Example 1. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane of this aluminum carbide layer is inclined with respect to the main surface in the direction between the a-axis and c-axis of the aluminum carbide layer (the direction of the axis k shown in FIG. 5), and the inclination angle θ2 is 1 °. The angle θ4 formed by the axis k and the c-axis of the aluminum carbide layer was 30 °.

Example 9
Although it is the same sapphire substrate as Example 8, (theta) 3 of the sapphire substrate was 45 degrees.
The other points are the same as in the eighth embodiment. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane of this aluminum carbide layer is inclined with respect to the main surface in the direction between the a-axis and c-axis of the aluminum carbide layer (the direction of the axis k shown in FIG. 5), and the inclination angle θ2 is 1 °. The angle θ4 formed by the axis k and the c-axis was 45 °.

(Example 10)
Although it is the same sapphire substrate as Example 8, (theta) 3 of the sapphire substrate was 60 degrees.
The other points are the same as in the eighth embodiment. In addition, the aluminum carbide layer formed on the sapphire substrate had a surface on the side opposite to the sapphire substrate formed in a staircase shape, and the terrace portion of the staircase was an m-plane. The m-plane of this aluminum carbide layer is inclined with respect to the main surface in the direction between the a-axis and c-axis of the aluminum carbide layer (the direction of the axis k shown in FIG. 5), and the inclination angle θ2 is 1 °. The angle θ4 formed by the axis k and the c axis was 60 °.

  Table 3 shows the X-ray diffraction results of the peeled GaN semiconductor layers in Examples 9 to 10.

  In any of the examples, it was confirmed that the GaN semiconductor layer was m-plane oriented and grown on the m-plane. In any of the examples, the GaN semiconductor layer could be easily peeled from the sapphire substrate, and no cracks occurred.

1 Substrate 11 Sapphire substrate (underlying substrate)
12 Aluminum carbide layer 12A Aluminum carbide 12B Aluminum nitride 13 Nitrided aluminum carbide layer 14 Buffer layer 17 Group III nitride semiconductor layer 110 Main surface 111 Terrace portion 121 Terrace portion 910 Base substrate 912A Aluminum carbide layer 912B Aluminum nitride layer 930 Nitrided Aluminum carbide layer A normal vector

Claims (15)

A substrate comprising a base substrate and an aluminum carbide layer formed on the base substrate,
A substrate in which an m-axis of the aluminum carbide layer is inclined with respect to a main surface of the base substrate. The substrate according to claim 1, wherein
The surface of the aluminum carbide layer opposite to the base substrate is formed in a step shape,
The {1-100} plane of the aluminum carbide layer is a substrate that is a terrace portion of the staircase. The substrate according to claim 1 or 2,
The substrate in which the {1-100} plane of the aluminum carbide layer is inclined by 1 degree or more and 20 degrees or less with respect to the main surface. The substrate according to claim 3, wherein
The substrate in which the {1-100} plane of the aluminum carbide layer is inclined at 5 degrees or more and 15 degrees or less with respect to the main surface. The substrate according to any one of claims 1 to 4,
The substrate in which the {1-100} plane of the aluminum carbide layer is inclined in the <0001> direction of the aluminum carbide layer with respect to the main surface. The substrate according to any one of claims 1 to 4,
The substrate in which the {1-100} plane of the aluminum carbide layer is inclined with respect to the main surface in the <11-20> direction of the aluminum carbide crystal layer. The substrate according to any one of claims 1 to 4,
The {1-100} plane of the aluminum carbide layer is between the a-axis of the aluminum carbide layer and the c-axis of the aluminum carbide layer with respect to the main surface, and the m-axis of the aluminum carbide layer is A substrate inclined as an axis of rotation along an axis obtained by rotating the c-axis of the aluminum carbide layer by a predetermined angle toward the a-axis. The substrate according to claim 7, wherein
The {1-100} plane of the aluminum carbide layer is between the a-axis of the aluminum carbide layer and the c-axis of the aluminum carbide layer with respect to the main surface, and the m-axis of the aluminum carbide layer is A substrate tilted along an axis obtained by rotating the c-axis of the aluminum carbide layer 30 degrees or more and 60 degrees or less to the a-axis side as a rotation axis. The substrate according to any one of claims 1 to 8,
The substrate is a substrate for forming a group III nitride semiconductor layer for forming a group III nitride semiconductor layer on the aluminum carbide layer. The substrate according to any one of claims 1 to 9,
The substrate, wherein the base substrate is any one of a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, and an aluminum nitride substrate. A substrate according to any one of claims 1 to 10,
A laminate comprising a group III nitride semiconductor layer formed on the aluminum carbide crystal layer of the substrate. The laminate according to claim 11, wherein
The group III nitride semiconductor layer is a stacked body made of InN, GaN, AlN, or a mixed crystal thereof.   A substrate comprising a group III nitride semiconductor layer obtained by forming a group III nitride semiconductor layer on the substrate according to claim 1 and then removing the base substrate. A step of forming an aluminum carbide layer on a base substrate by metal organic vapor phase epitaxy;
In the step of forming the aluminum carbide layer,
A method for manufacturing a substrate, wherein the aluminum carbide layer is formed so that an m-axis of the aluminum carbide layer is inclined with respect to a main surface of the base substrate. A step of obtaining a substrate by the method for producing a substrate according to claim 14;
Forming a group III nitride semiconductor layer by hydride vapor phase epitaxy on the aluminum carbide layer of the substrate.

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