JP2011042542A - Method for producing group iii nitride substrate, and group iii nitride substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a semipolar group III nitride substrate having a low defect density and high quality. <P>SOLUTION: This method comprises the step of preparing a sapphire substrate 10, the step of forming an intermediate layer 11 containing aluminum and nitrogen on the sapphire substrate 10 by a vapor phase growth method at a growth temperature of 1,100-1,300°C, and the step of growing a group III nitride layer 12 on the intermediate layer 11. The sapphire substrate 10 has the principal plane on which the intermediate layer 11 is grown and which is vertical to the m-axis of the sapphire substrate 10 or is slant to the m-axis of the sapphire substrate 10. Further, in the step of growing the group III nitride layer 12, after a mask is formed on a first thin film layer 12a, a second thick layer 12b may be fromed, thereby lowering the bonding strength between the first thin film layer 12a and the second thick layer 12b, and easily separating the base substrate 10 at a relatively small stress, whereby a self-supporting substrate of the group III nitride layer 12 can be obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a group III nitride substrate and a group III nitride 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 group III-V nitride semiconductor is a polarization substance having the c-axis as a polarization axis, it has spontaneous polarization along the c-axis. Furthermore, when a laminated structure composed of different types of group III-V nitride semiconductors is produced, piezoelectric polarization due to distortion of the crystal structure due to the difference in lattice constant occurs, and this piezoelectric polarization causes a strong internal electric field in the c-axis direction of GaN. Arise. This internal electric field spatially separates electrons and holes injected into the light emitting layer of the light emitting device, lowers the recombination probability, and consequently reduces 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.

  On the other hand, since the a-plane and m-plane of hexagonal crystal are nonpolar planes, problems due to the above-described spontaneous polarization and piezoelectric polarization can be avoided. 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) discloses a technique for forming nonpolar plane GaN. Is disclosed. However, it is difficult to epitaxially grow a GaN crystal having a low dislocation density or stacking fault density on a nonpolar surface.

On the other hand, the polarization electric field is reduced even in a semipolar plane inclined with respect to the c-plane as compared with the c-plane. From the theoretical point of view of device performance, it is better to use the nonpolar surface as the growth surface, but considering the processing steps during actual device formation, the semipolar surface with some polar components is superior. it is conceivable that. In particular, it is shown in Non-Patent Document 1 (Applied Physics Letters 85 (2004) 31122.) that {11-22} plane GaN is practically superior, and this {11-22} plane GaN thin film is formed. For example, Patent Literature 5 (Japanese Patent Laid-Open No. 10-34160), Patent Literature 6 (Japanese Patent Laid-Open No. 2008-266113), Patent Literature 7 (Japanese Patent Publication No. 2008-533723), Non-Patent Literature 2 (Japanese Journal of Applied). Physics 45 (2006) L154-157), Non-Patent Document 3 (Japanese Journal of Applied Physics 46 (2007) 4089-4095.), Non-Patent Document 4 (physica status solidi (c) 5 (2008) 1815-1817.) And the like. In Patent Document 5, an Al _x Ga _(1-x) N buffer layer formed on a base sapphire substrate at a temperature of 400 to 700 ° C. is used. In Patent Document 6, ZnO is used as a base substrate. Patent Document 7 discloses a method of nitriding a base sapphire substrate at a low temperature.

JP 2002-284600 A JP 2005-320237 A JP 2000-216497 A JP 2008-053640 A Japanese Patent Laid-Open No. 10-34160 JP 2008-266113 A Special table 2008-533723

Applied Physics Letters 85 (2004) 3122. Japanese Journal of Applied Physics 45 (2006) L154-157. Japanese Journal of Applied Physics 46 (2007) 4089-4095. physica status solidi (c) 5 (2008) 1815-1817.

However, it is not easy to grow a semipolar {11-22} plane GaN layer, and a method that combines crystal quality sufficient for practical use of devices has not been established yet.
For example, the thickness of the {11-22} plane GaN disclosed in Non-Patent Documents 2 to 4 is about several μm to several tens of μm, and the half width of the X-ray rocking curve is 700 to 1600 arcsec (0.19 to 0. 44o) only.

According to the present invention,
Preparing a sapphire substrate;
Forming an intermediate layer containing aluminum and nitrogen on the sapphire substrate at a growth temperature of 1100 ° C. or higher and 1300 ° C. or lower by a vapor phase growth method;
Growing a group III nitride layer on the intermediate layer,
The sapphire substrate is provided with a method for manufacturing a group III nitride substrate in which a main surface on which the intermediate layer is grown is perpendicular to the m-axis of the sapphire substrate or inclined with respect to the m-axis of the sapphire substrate. .

According to the present invention, a high-quality semipolar plane group III nitride substrate having a low defect density can be provided.
That is, according to the present invention, a group III nitride substrate manufactured by the above-described manufacturing method,
The growth surface is a semipolar surface,
The thickness T (nm) of the group III nitride layer of the group III nitride substrate is
10μm ≦ T ≦ 3000μm
And
Using the {11-22} plane as the diffraction plane, the angle dependence of the X-ray diffraction intensity obtained for X-rays incident on the X-ray incident from the direction perpendicular to the {11-22} plane and parallel to the m-axis A group III nitride substrate having a full width at half maximum of 0.28 ° or less can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method which can manufacture a semipolar surface group III nitride board | substrate with a low defect density and high quality is provided.

(A)-(D) are sectional drawings which show schematically the manufacturing process of the group III nitride board | substrate of one Embodiment concerning this invention. It is a pole figure based on X-ray diffraction intensity distribution with respect to {11-22} plane of GaN crystal. It is a figure which shows typically the arrangement | positioning relationship of the crystal axis of a sapphire substrate and an aluminum nitride crystal or a GaN crystal. (A) is a figure which shows typically the X-ray incident direction for measuring the X-ray rocking curve of a GaN layer, (B) is the measurement result of the X-ray rocking curve of GaN layer {11-22} plane diffraction. It is. It is a figure which shows the relationship between the inclination with respect to m surface of a base sapphire substrate main surface, and a X-ray rocking curve half value width. (A) is a diagram showing a state of forming a striped SiO ₂ mask GaN first layer is a diagram showing a state of forming a GaN second layer on top of (B) is (A). It is a pole figure based on the X-ray diffraction intensity distribution of a GaN free-standing substrate. It is a schematic diagram which shows a sapphire substrate. It is a schematic diagram which shows a sapphire substrate.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
As shown in FIG. 1 (A) to FIG. 1 (D), a method for manufacturing a group III nitride substrate according to an embodiment of the present invention is as follows.
(A) preparing a sapphire substrate 10 (hereinafter also referred to as a base sapphire substrate 10);
(B) forming an intermediate layer 11 containing aluminum and nitrogen on the sapphire substrate 10 at a growth temperature of 1100 ° C. or higher and 1300 ° C. or lower by a vapor phase growth method (FIG. 1A);
(C) a step of growing a group III nitride layer 12 on the intermediate layer 11 (FIGS. 1B and 1C)
including.
In the sapphire substrate 10, the main surface on which the intermediate layer 11 is grown is perpendicular to the m-axis of the sapphire substrate 10 or inclined with respect to the m-axis of the sapphire substrate 10.

The manufacturing method of this embodiment will be described in detail below with reference to FIG.
First, the base sapphire substrate 10 is prepared. The main surface on which the intermediate layer 11 of the underlying sapphire substrate 10 is grown is parallel to the hexagonal m-plane ({10-10} plane) or inclined with respect to the m-plane.
When the main surface of the sapphire substrate 10 is the m-plane, the substrate is as shown in FIG. 8 where the m-plane is exposed (in FIG. 8, the symbol S indicates the main surface of the sapphire substrate 10).
On the other hand, when the main surface S of the sapphire substrate 10 is inclined with respect to the m-plane of the sapphire substrate 10, a substrate as shown in FIG. When viewed microscopically, for example, as shown in FIG. 9B, the sapphire substrate 10 may be formed in a step shape, and the terrace portion 100 may be an m-plane. Moreover, it is not restricted to this, m surface may not be exposed to the sapphire substrate 10 surface, and the main surface S of the sapphire substrate 10 should just incline with respect to m surface of a sapphire substrate.
Note that the microscopic case means a case where the substrate is viewed using an atomic force microscope (AFM) or the like.

In particular, the main surface S of the sapphire substrate 10 is inclined with respect to the m-axis of the sapphire substrate 10, and the smaller angle among the angles formed by the main surface S and the m-axis is 80 ° or more (that is, Of the angles formed by the main surface and the m-plane, the smaller angle is preferably 10 ° or less. Thus, the crystallinity of the group III nitride layer 12 can be made favorable by using the sapphire substrate whose principal surface S is inclined with respect to the m-axis.
Here, the main surface S is a surface that can be grasped when viewed macroscopically directly with the naked eye, and is a flat surface perpendicular to the normal vector with respect to the sapphire substrate 10. In other words, the normal vector with respect to the sapphire substrate 10 is a vector along the stacking direction of the intermediate layer 11 and the group III nitride layer 12.

When the main surface S of the sapphire substrate 10 is the m-plane, the lattice matching with the intermediate layer 11 described later is good, the intermediate layer 11 acts as a buffer layer, and the crystallinity of the group III nitride layer 12 is good. Can be. Similarly, when the main surface of the sapphire substrate 10 is inclined from the m-plane, particularly when the angle formed by the main surface and the m-plane is 10 ° or less, the crystallinity of the group III nitride layer 12 is good. Can be.
The main surface S of the sapphire substrate is preferably inclined in the c-axis direction with respect to the m-axis of the sapphire substrate 10.
By doing so, the effect that the crystallinity of the group III nitride semiconductor layer can be improved due to the fact that interference between adjacent crystal islands is relaxed when the semipolar plane expands in the lateral direction. is there.

Next, the intermediate layer 11 is formed directly on the sapphire substrate 10. The intermediate layer 11 is a layer containing nitrogen and aluminum, and is an aluminum nitride (AlN) layer in this embodiment.
The intermediate layer 11 is not limited to aluminum nitride, and may be an AlGaN layer. That is, the intermediate layer 11 is preferably Al _x Ga _y N (x> 0, y ≧ 0, x + y = 1).
The intermediate layer 11 may be formed by a metal organic vapor phase epitaxy method (MOVPE method) using a source gas containing an organoaluminum gas such as trimethylaluminum (TMA). By using the MOVPE method, not only a high-quality aluminum nitride layer with a controlled film thickness can be formed, but also the intermediate layer 11 forming step (FIG. 1A) and the group III nitride semiconductor layer 12 forming step ( 1B and 1C can be executed continuously in one apparatus.
The intermediate layer 11 may be formed by the HVPE method.

The film forming temperature of the intermediate layer 11 may be adjusted within the range of 1100 ° C. or higher and 1300 ° C. or lower, particularly preferably 1150 ° C. or higher. By setting the deposition temperature of the intermediate layer 11 to 1100 ° C. or higher, particularly 1150 ° C., a semipolar plane suitable as the orientation plane of the group III nitride layer 12, particularly the {11-22} plane, can surely appear. it can.
When the deposition temperature of the intermediate layer 11 is lower than 1100 ° C., not only a semipolar plane suitable as the orientation plane of the group III nitride layer 12 but also a {10-13} plane may appear. This is because the growth rate of the {11-22} plane is relatively slower than other plane orientations such as the c-plane and the a-plane at temperatures below 1100 ° C. This is because the risk of aggregating to form an atomic group having other orientation increases.
On the other hand, by setting the film forming temperature of the intermediate layer 11 to 1300 ° C. or lower, decomposition and deterioration of the sapphire substrate 10 and the intermediate layer 11 can be suppressed.
In order to form the intermediate layer 11 more stably, the film formation temperature is preferably 1200 ° C. or lower.
By appropriately adjusting the film formation temperature and the like in this manner, the intermediate layer 11 is a layer in which the semipolar surface is grown and the semipolar surface is exposed.

The film thickness of the intermediate layer 11 is adjusted to be in the range of 10 nm to 100 nm, preferably 20 nm to 60 nm.
By setting the thickness of the intermediate layer 11 to 10 nm or more, the surface of the underlying sapphire substrate 10 can be completely covered.
Further, since the growth rate of the intermediate layer is slower than that of other group III nitrides such as gallium nitride (GaN), for example, the growth time of the intermediate layer 11 is restricted in order to ensure practical throughput. The film thickness is preferably 100 nm or less.

Next, a group III nitride layer 12 having a semipolar plane as a growth plane is epitaxially grown on the intermediate layer 11 (FIGS. 1B and 1C). The group III nitride layer 12 can be formed in the temperature range of about 1000 to 1100 ° C. by the vapor phase growth method such as the MOVPE method or the HVPE (Hydride Vapor Phase Epitaxy) method as in the intermediate layer 11.
The group III nitride layer 12 is preferably a GaN layer. This group III nitride layer 12 grows semipolarly. The thickness of the group III nitride layer 12 is desirably 10 μm or more from the viewpoint of crystallinity. The thickness of the group III nitride layer 12 is preferably 3000 μm or less from the viewpoint of saving process time.

The group III nitride layer 12 need not be formed in a single process, and can be formed through two or more growth processes.
For example, after forming the first thin film layer (first group III nitride layer) 12a by the MOVPE method, the second thick film layer (second group III nitride layer thicker than the first thin film layer by the HVPE method). 12b may be additionally grown (FIG. 1C) The first thin film layer and the second thick film layer are made of the same material.
Further, as shown in FIG. 6A, a mask 14 having an opening is formed on the first thin film layer 12a, and the second film is formed on the mask 14 as shown in FIG. 6B. Forming the thick film layer 12b to reduce the adhesion between the first thin film layer and the second thick film layer, peeling the sapphire substrate 10 and making the group III nitride layer 12 self-supporting. It can also be made easier. During the growth of the group III nitride layer 12, crystal defects are reduced due to the effects of dislocation bending and the like, so that an improvement in crystal quality is expected as the thickness increases. From this point of view, the thickness of the group III nitride layer 12 is preferably 10 μm or more.
Furthermore, the step of forming the group III nitride layer 12 is faster than the growth step of forming the first group III nitride layer 12a having a thickness of 50 μm or less and the step of growing the first group III nitride layer 12a. The second group III nitride layer 12b may be formed on the first group III nitride layer 12a at a growth rate.
By doing in this way, there exists an effect that the layer of desired thickness can be formed in a short time, without impairing crystallinity.

In the peeling process of FIG. 1D, peeling is caused by using stress generated by the difference in thermal expansion coefficient between the base substrate 10 and the group III nitride layer 12, and thus the group III nitride layer 12 is thickened. Therefore, it is necessary to ensure sufficient stress. From this viewpoint, the thickness of the group III nitride layer 12 is preferably 50 μm or more.
On the contrary, when the laminated structure is used as a substrate without peeling, the thickness of the group III nitride layer 12 may be less than 50 μm. Similarly, when the group III nitride layer 12 is formed through two or more growth steps, the thickness of the first layer 12a may be 10 to 50 μm in order to prevent peeling.

In the step of forming the group III nitride layer 12, the group III nitride layer 12 may be doped with silicon or oxygen as an n-type impurity. When doping silicon, for example, dichlorosilane (Si ₂ H ₂ Cl ₂ ) gas may be included in the source gas. Alternatively, when oxygen is doped, an oxygen gas or an oxygen-containing mixed gas may be included in the source gas. An n-type impurity is introduced into the group III nitride layer 12 at a doping concentration of 5 × 10 ¹⁷ cm ^{−3 to} 5 × 10 ¹⁹ / cm ⁻³ through the m-plane which is the growth surface of the group III nitride semiconductor layer 13. Is possible.

In the peeling step of FIG. 1C, it is preferable to cool at least the base substrate 10 and the intermediate layer 11 among the base sapphire substrate 10, the intermediate layer 11, and the group III nitride layer 12 to release the base substrate 10. As described above, by forming the group III nitride layer 12 through two or more growth steps to provide a surface with low adhesion, the base substrate 10 and the group III nitride layer 12 are cooled, Using the stress generated by the difference in thermal expansion coefficient between base substrate 10 and group III nitride layer 12, base substrate 10 can be easily peeled off.
By forming the group III nitride semiconductor layer 12 by such a manufacturing method,
The growth plane is a {11-22} plane, or a semipolar plane with an angle of 10 ° or less with the {11-22} plane,
Thickness T (nm) is
10 μm ≦ T ≦ 3000 μm,
Using the {11-22} plane as the diffraction plane, the angle dependence of the X-ray diffraction intensity obtained for X-rays incident on the X-ray incident from the direction perpendicular to the {11-22} plane and parallel to the m-axis The group III nitride semiconductor layer 12 having a half-value width of 0.28 ° or less can be obtained, and a highly crystalline layer can be obtained.
Among these, in consideration of crystallinity, T is preferably 25 μm or more.

Hereinafter, a preferred method for manufacturing the self-supporting substrate 13 will be described in detail below. First, for example, a 3 inch φ m-plane sapphire (Al ₂ O ₃ ) substrate is prepared as the base substrate 10. Next, the sapphire substrate 10 is placed in a furnace, the furnace temperature is set to about 1150 ° C., and the sapphire substrate 10 is thermally cleaned for about 10 minutes.

(Formation process of intermediate layer 11)
Next, an aluminum nitride layer 11 is deposited on the sapphire substrate 10 by MOVPE using TMA and ammonia (NH ₃ ) as source gases (FIG. 1A). The source gas supplied at this time is TMA, NH ₃ gas and hydrogen (H ₂ ) gas, the film forming temperature is 1100 ° C. to 1300 ° C., the film forming time is 10 minutes to 100 minutes, and the film thickness of the aluminum nitride layer 11 May be 10 nm to 100 nm.
The carrier gas may be at least one of hydrogen gas and nitrogen gas, but is not limited to this, and a gas that does not easily react with TMA, such as hydrogen, nitrogen, or argon, is selected as the carrier gas. do it.

(Step of epitaxially growing the first group III nitride layer 12a)
Next, as shown in FIG. 1B, the GaN layer 12a is epitaxially grown on the intermediate layer 11 at 1000 ° C. to 1100 ° C. by the MOVPE method. The source gas supplied at this time may be a mixed gas composed of TMG, H ₂ gas, N ₂ gas and NH ₃ gas, and the film thickness of the GaN layer 12a may be 50 μm or less. The GaN layer 12a can be formed continuously from the step of forming the intermediate layer 11 in the MOVPE apparatus.

(Step of epitaxially growing the second group III nitride semiconductor layer 12b)
Next, as shown in FIG. 1C, a group III nitride semiconductor layer 12b is epitaxially grown on the first layer 12a at 1000 ° C. to 1100 ° C. by HVPE or MOVPE. At this time, the film formation time may be 6 minutes to 1800 minutes, and the film thickness of the group III nitride semiconductor layer 13 may be 10 μm to 3000 μm. If the HVPE method is used, epitaxial growth in a relatively large area can be easily performed.
When an HVPE apparatus (not shown) is used, the HVPE apparatus supplies HCl gas to a Ga source disposed in the HVPE apparatus, and reacts the Ga source with HCl gas, thereby generating GaCl gas. To do. The GaCl gas and NH ₃ gas are transported and reacted on the sapphire substrate 10 to grow a GaN crystal.

(Peeling process of sapphire substrate 10)
Next, the in-furnace temperature of the HVPE apparatus or MOVPE apparatus is lowered to room temperature to cool the sapphire substrate 10 to the GaN layer 12. As a result, as shown in FIG. 1D, the sapphire substrate 10 is peeled off from the group III nitride semiconductor layer 12, and a group III nitride semiconductor substrate 13 is generated. That is, due to the difference in coefficient of thermal expansion between the sapphire substrate 10 and the group III nitride layer 12, a stress is generated in the laminate composed of the intermediate layer 11 and the group III nitride layer 12, thereby causing the sapphire substrate 10 to Is peeled off from the group III nitride semiconductor layer 12.
Thereafter, the front surface and the back surface of the group III nitride substrate 13 are polished, whereby a GaN substrate that is a flattened free-standing substrate can be produced.

The effect which the said embodiment show | plays is as follows.
In the manufacturing method, an intermediate layer 11 containing nitrogen and aluminum is formed on the base substrate 10 (FIG. 1A), and a hexagonal semipolar plane is formed on the intermediate layer 11 ({11- A group III nitride layer 12 having a growth surface that is a semipolar plane whose angle to the 22} plane or {11-22} plane is 10 ° or less is epitaxially grown (FIGS. 1C and 1D). Thus, a group III nitride layer 12 having a semipolar plane as a main surface can be formed, whereby a high quality semipolar plane group III nitride semiconductor substrate 13 with a low defect density can be manufactured.

  Further, as described above, the mask 14 is formed on the first thin film layer 12a, and then the second thick film layer 12b is formed, thereby forming the gap between the first thin film layer 12a and the second thick film layer 12b. The base substrate 10 can be easily peeled off with a relatively small stress, and a self-supporting substrate of the group III nitride layer 12 can be obtained.

As mentioned above, although embodiment of this invention was described with reference to drawings, the said embodiment is an illustration of this invention and can also employ | adopt various forms other than the above.
For example, in the above embodiment, the intermediate layer 11 is preferably formed by the MOVPE method using a source gas containing TMA, but is not limited thereto. As a method of forming the intermediate layer 11, a method of forming an aluminum nitride film on the base substrate 10 using a thin film forming apparatus such as a vacuum deposition apparatus or a sputtering apparatus (physical vapor deposition method), or heating the base substrate 10 Alternatively, a method of nitriding the surface by flowing NH ₃ gas or a method of nitriding by heating the base substrate 10 in a mixed atmosphere of nitrogen gas and carbon monoxide gas may be used.

In the above embodiment, the process up to obtaining the group III nitride semiconductor substrate 13 has been described. However, a group III nitride element structure is formed on the group III nitride semiconductor substrate 13 to form an LED, LD, or the like. A light emitting element may be manufactured. It is also possible to use the group III nitride semiconductor substrate 13 for producing an electronic device such as a transistor.
Furthermore, in the above-described embodiment, GaN is used as the group III nitride layer 12. However, the present invention is not limited to this, and the group III nitride layer 12 may be AlGaN, InGaN, AlInGaN, AlN, InN. . That is, the group III nitride layer 12 is preferably Al _a In _b Ga _c N (a + b + c = 1, a ≧ 0, b ≧ 0, c ≧ 0).

Next, various examples of the above embodiment will be described.
Example 1
A GaN layer (GaN substrate) was manufactured in the same manner as in the previous embodiment. In addition, the peeling process of the sapphire substrate 10 is not implemented.
As the sapphire substrate 10, a substrate (the principal surface is orthogonal to the m-axis) whose principal surface forming the intermediate layer 11 is parallel to the m-plane of the sapphire substrate 10 was used.
The sapphire substrate 10 was placed in the reactor of the MOVPE apparatus, the furnace temperature was set to about 1150 ° C., and the sapphire substrate 10 was thermally cleaned for about 10 minutes. Next, with the furnace temperature kept at 1150 ° C., an aluminum nitride intermediate layer 11 having a film thickness of 40 nm was deposited on the m-plane of the sapphire substrate 10 with a film formation time of 40 minutes (FIG. 1A). Here, TMA (supply amount 9 μmol / min), H ₂ carrier gas (flow rate 20 sccm), and NH ₃ gas (flow rate 1.5 liter / min) were supplied as source gases.

Thereafter, with the furnace temperature lowered to 1050 ° C., a 0.5 μm-thick GaN layer 12a was formed on the intermediate layer 11 in a film formation time of 25 minutes (FIG. 1B). Here, TMG (supply amount 78 μmol / min), H ₂ carrier gas (flow rate 30 sccm), N ₂ gas (flow rate 4 sccm) and NH ₃ gas (flow rate 6.0 liter / min) were supplied as source gases.
Thereafter, the laminate shown in FIG. 1B is taken out of the MOVPE reactor, and placed in the HVPE reactor and epitaxially grown to form a GaN layer 12b having a thickness of 20 μm on the GaN layer 12a. A substrate was obtained (FIG. 1C). Here, the film formation temperature was 1050 ° C., and the film formation time was 12 minutes. In the HVPE apparatus, the flow rate of GaCl gas was 80 sccm, and the flow rate of NH ₃ gas was 1.2 liters / minute. The growth rate of the GaN layer 12b is faster than that of the GaN layer 12a.

(Comparative Example 1)
The step of forming the aluminum nitride layer 11 was omitted. In other respects, a laminate was produced under the same conditions as in Example 1, and this was designated as Comparative Example 1. In the laminate (substrate) of Comparative Example 1, the GaN layer 12 is directly formed on the m-plane of the sapphire substrate 10.

(Comparative Example 2)
The formation temperature of the aluminum nitride layer 11 was 600 ° C. In other respects, a laminate was produced under the same conditions as in Example 1, and this was designated as Comparative Example 2.

(Evaluation of Example 1, Comparative Examples 1 and 2)
2A is a pole figure based on the X-ray diffraction intensity distribution with respect to the {11-22} plane of the GaN crystal of the laminate of Example 1, and FIG. 2B is the pole of the laminate of Comparative Example 1. FIG. 2C is a pole figure based on the X-ray diffraction intensity distribution with respect to the {11-22} plane of the GaN crystal, and FIG. 2C shows the X-ray diffraction intensity with respect to the {11-22} plane of the GaN crystal of the laminate of Comparative Example 2. It is a pole figure based on distribution.
In the stacked body of Example 1, one diffraction peak corresponding to the {11-22} plane of the GaN crystal constituting the GaN layer 12 is clearly confirmed as shown in FIG. On the other hand, in the laminates of Comparative Example 1 and Comparative Example 2, irregular diffraction peaks are observed as shown in FIGS. 2B and 2C, so that the GaN crystal has {11-22} plane orientation. You can see that they are not.

As schematically shown in FIG. 3, in the laminated body of Example 1, the a-axis direction (<11-20> direction) of sapphire parallel to the main surface of the sapphire substrate 10 is the AlN crystal 11 or GaN crystal 12. It is considered to be parallel to the m-axis direction (<10-10> direction). Sapphire (Al ₂ O ₃ ), aluminum nitride (AlN) and GaN all have the same hexagonal crystal structure. When GaN is grown directly on the main surface (m-plane) of the sapphire substrate, the lattice mismatch in the a-axis direction of sapphire is 16.1%. As in Example 1, on the main surface (m-plane) of the sapphire substrate In the case where AlN grows, the lattice mismatch in the a-axis direction of sapphire is reduced to 13.2%. Furthermore, the lattice mismatch in the m-axis direction between AlN and GaN is as small as 2.5%. Therefore, it can be said that good lattice matching is established between the sapphire substrate 10 and the GaN layer 12 by introducing an aluminum nitride layer as an intermediate layer.

FIG. 4 shows the GaN {11-22} X-ray diffraction rocking curve of the GaN layer 12 in the stack of Example 1. As shown in FIG. 4 (A), the measurement result of X-ray incidence (hereinafter referred to as m-axis perpendicular incidence) perpendicular to the GaN m-axis direction (<10-10> direction) and the GaN { 11 shows a result obtained by measuring an X-ray incident perpendicularly to the 11-22} plane and parallel to the m-axis direction of GaN (hereinafter referred to as m-axis parallel incidence).
The full width at half maximum of the rocking curve is 516 arcsec (0.14 °) for m-axis normal incidence and 1786 arcsec (0.50 °) for m-axis parallel incidence (Fig. 4 (B)), especially for m-axis normal incidence. Shows better crystallinity than the prior art.

(Examples 2-3)
Example 2 and Example 3 are the same as Example 1 except that the main surface of the underlying sapphire substrate 10 is inclined with respect to the m-plane (the main surface is inclined with respect to the m-axis). Then, a GaN layer was produced.
The main surface of the base sapphire substrate of Example 2 is inclined by 2 ° in the c-axis direction with respect to the m-plane of the sapphire substrate.
The main surface of the base sapphire substrate of Example 3 is inclined by 1 ° in the a-axis direction with respect to the m-plane of the sapphire substrate. FIG. 5 summarizes the half width of the X-ray rocking curve of the {11-22} plane GaN layer 12 in the stacks of Example 1, Example 2, and Example 3. The full width at half maximum of the rocking curve of Example 2 is 451 arcsec (0.13 °) in the case of m-axis vertical incidence and 1234 arcsec (0.34 °) in the case of m-axis parallel incidence. It can be seen that it is preferable to incline the main surface in the c-axis direction.
As a result of various experiments, it has been found that there is a risk that an orientation plane other than the {11-22} plane appears when the tilt angle exceeds 10 °. Therefore, the tilt angle is preferably within 10 °. Corresponding to the inclination of the m-plane of the base substrate, the growth surface of {11-22} plane GaN grown thereon also has an inclination of 10 ° or less with respect to the main surface of the substrate. .
As a result of various experiments, it was found that the film thickness of the intermediate layer 11 is desirably 10 nm or more and 100 nm or less.

Example 4
A GaN layer was fabricated in the same manner as in Example 1 except that a striped SiO ₂ mask 14 was formed on the GaN layer 12a (see FIG. 6A).
The SiO ₂ mask was formed by photolithography and hydrofluoric acid (HF) etching. As shown in FIG. 6 (A), the SiO ₂ mask shape is a square rod extending in the GaN <10-10> m-axis direction, the height is about 0.1 μm, the width is about 5 μm, and the stripe shape is The interval period was 10 μm. The figure highlights the height direction.
After forming the mask, a GaN layer 12b having a thickness of 20 μm was formed by HVPE (FIG. 6B). When the X-ray rocking curve of the {11-22} plane of this GaN layer was measured, its half-value width was 889 asec (0.25 °) for m-axis vertical incidence and 527 arcsec (0.15 ° for m-axis parallel incidence). Compared with Example 1, the half width of m-axis flat incidence was greatly improved, the anisotropy due to the incident direction was also improved, and good crystallinity was exhibited.

(Examples 5-6)
In Example 5, a structure having the underlying sapphire substrate 10, the intermediate layer 11, and the first GaN layer 12a by the same manufacturing method as in Example 2 except that the thickness of the GaN layer 12b is increased to 1200 μm. It was created.
Furthermore, in Example 6, a laminate was formed by the same manufacturing method as Example 4 except that the thickness of the GaN layer 12b was increased to 1200 μm. In Examples 5 and 6, the HVPE film formation time was extended to 500 minutes.
After the HVPE growth of Example 5, the temperature was lowered to room temperature, and the sapphire substrate 10 and the intermediate layer 11 were cooled. Thereafter, the sapphire substrate 10 was removed by grinding and etching, and the GaN layer 13 was separated. FIG. 7 is an X-ray pole figure of {11-22} GaN of a self-supporting substrate obtained by mirror polishing the surface of the separated GaN layer 13. One sharp peak is clearly seen, indicating that the orientation is good. The full width at half maximum of the X-ray rocking curve is 778 arcsec (0.22 °) for m-axis normal incidence and 996 arcsec (0.28 °) for m-axis parallel incidence. It can be said that it has sex.
In Example 6, when the sapphire substrate 10 and the intermediate layer 11 were cooled after the HVPE growth and the temperature was lowered to room temperature, thermal stress was concentrated near the interface between the mask and the GaN layer 12b. It was possible to obtain a GaN layer that was easily exfoliated and became self-supporting.

(Examples 7 to 9)
In Example 7, the temperature at which the aluminum nitride intermediate layer 11 was formed was 1100 ° C. With the furnace temperature kept at 1100 ° C., an aluminum nitride intermediate layer 11 having a film thickness of 40 nm was deposited on the m-plane of the sapphire substrate 10 in a film formation time of 40 minutes. The other points are the same as those in the first embodiment.
In Example 8, the temperature at which the aluminum nitride intermediate layer 11 was formed was 1190 ° C. With the furnace temperature kept at 1190 ° C., an aluminum nitride intermediate layer 11 having a film thickness of 40 nm was deposited on the m-plane of the sapphire substrate 10 in a film formation time of 40 minutes. The other points are the same as those in the first embodiment.
In Example 9, the temperature at which the aluminum nitride intermediate layer 11 was formed was 1300 ° C. With the furnace temperature kept at 1300 ° C., an aluminum nitride intermediate layer 11 having a film thickness of 40 nm was deposited on the m-plane of the sapphire substrate 10 in a film formation time of 40 minutes. The other points are the same as those in the first embodiment.
In Examples 7 to 9, the measurement result of X-ray incidence perpendicular to the m-axis direction (<10-10> direction) of GaN (hereinafter referred to as m-axis normal incidence) and the {11− Table 1 shows the results of measurement with X-rays incident perpendicularly to the 22} plane and parallel to the m-axis direction of GaN (hereinafter referred to as m-axis parallel incidence).

S Main surface 10 Sapphire substrate 11 Intermediate layer 12 Group III nitride semiconductor layer 12a First group III nitride layer (first thin film layer)
12b Second group III nitride layer (second thick film layer)
13 Group III nitride semiconductor substrate 14 Mask 100 Terrace portion

Claims (14)

Preparing a sapphire substrate;
Forming an intermediate layer containing aluminum and nitrogen on the sapphire substrate at a growth temperature of 1100 ° C. or higher and 1300 ° C. or lower by a vapor phase growth method;
Growing a group III nitride layer on the intermediate layer,
The sapphire substrate is a method for producing a group III nitride substrate in which a main surface on which the intermediate layer is grown is perpendicular to the m-axis of the sapphire substrate or inclined with respect to the m-axis of the sapphire substrate. In the manufacturing method of the group III nitride substrate according to claim 1,
In the step of growing a group III nitride layer, a method for producing a group III nitride substrate, wherein the semipolar surface of the group III nitride layer is grown as a growth surface. A method for producing a group III nitride substrate according to claim 1 or 2,
In the step of forming the intermediate layer,
A method for producing a group III nitride substrate, wherein the thickness of the intermediate layer is 10 nm or more and 100 nm or less. A method for producing a group III nitride substrate according to any one of claims 1 to 3,
In the step of growing a group III nitride layer on the intermediate layer,
A method for producing a group III nitride substrate, wherein the thickness of the group III nitride layer is 10 μm or more and 3000 μm or less. In the manufacturing method of the group III nitride substrate according to any one of claims 1 to 4,
In the step of forming the intermediate layer, a Group III nitride substrate manufacturing method of forming an AlN layer. A method for producing a group III nitride substrate according to any one of claims 1 to 5,
In the sapphire substrate, the main surface on which the intermediate layer is grown is inclined with respect to the m-axis of the sapphire substrate, and the inclination angle formed by the m surface of the sapphire substrate and the main surface is 10 ° or less. Manufacturing method of physical substrate. A method for producing a group III nitride substrate according to any one of claims 1 to 6,
In the step of forming the intermediate layer, the intermediate layer is grown by a hydride vapor phase epitaxy (HVPE) method or a metal organic vapor phase epitaxy (MOVPE) method,
In the step of growing the group III nitride layer, a method of manufacturing a group III nitride substrate in which the group III nitride layer is grown by a hydride vapor phase epitaxy (HVPE) method or a metal organic vapor phase epitaxy (MOVPE) method . A method for producing a group III nitride substrate according to any one of claims 1 to 7,
A method for producing a group III nitride substrate, wherein a main surface of the sapphire substrate is inclined in a c-axis direction with respect to an m-plane of the sapphire substrate. A method for producing a group III nitride substrate according to any one of claims 1 to 8,
In the step of forming the intermediate layer,
A method for producing a group III nitride substrate, wherein the growth temperature of the intermediate layer is 1150 ° C. or higher. A method for producing a group III nitride substrate according to any one of claims 1 to 9,
In the step of growing the group III nitride layer,
Growing said group III nitride layer in at least two stages;
Said step of growing a group III nitride layer comprises:
Forming a first group III nitride layer having a thickness of 50 μm or less;
Forming a second group III nitride layer on the first group III nitride layer at a growth rate faster than the first group III nitride layer growth step. Production method. A method for producing a group III nitride substrate according to claim 10,
After completing the step of forming the first group III nitride layer,
Forming a mask having an opening formed on the surface of the first group III nitride layer;
In the step of forming a second group III nitride layer, a method of manufacturing a group III nitride substrate, wherein the second group III nitride layer is formed on the mask. A method for producing a group III nitride substrate according to any one of claims 1 to 11,
A method for producing a group III nitride substrate, comprising: removing the sapphire substrate from the group III nitride layer to obtain a group III nitride substrate including the group III nitride layer. A method for producing a group III nitride substrate according to any one of claims 1 to 12,
In the step of growing the group III nitride layer,
The group III nitride substrate is doped with an n-type impurity of oxygen, and the doping concentration of the n-type impurity is set to 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁹ / cm ⁻³ or less. Production method. A group III nitride substrate manufactured by the manufacturing method according to claim 1,
The growth surface is a semipolar surface,
The thickness T (nm) of the group III nitride layer of the group III nitride substrate is
10μm ≦ T ≦ 3000μm
And
Using the {11-22} plane as the diffraction plane, the angle dependence of the X-ray diffraction intensity obtained for X-rays incident on the X-ray incident from the direction perpendicular to the {11-22} plane and parallel to the m-axis A group III nitride substrate having a full width at half maximum of 0.28 ° or less.

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