JP2011184265A - Method for growing group iii nitride crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a group III nitride crystal by which a group III nitride crystal having a uniform thickness within a crystal growth plane is grown. <P>SOLUTION: The method for growing a group III nitride crystal includes a process for preparing a group III nitride crystal substrate 10 and a process for growing the group III nitride crystal 20 on the main plane 10m of the group III nitride crystal substrate 10 by repeating crystal growth a plurality of times by a liquid phase method. By the method, the group III nitride crystal having a uniform thickness within a crystal growth plane 20u is grown. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for growing a group III nitride crystal, and more particularly to a method for growing a group III nitride crystal in which a group III nitride crystal having a uniform thickness in a crystal growth plane is grown.

  Group III nitride crystals such as GaN crystals are very useful as materials for forming substrates of various semiconductor devices such as light emitting elements, electronic elements, and semiconductor sensors. Here, in order to improve the characteristics of various semiconductor devices, a group III nitride crystal substrate having a low dislocation density and good crystallinity is required.

  Here, a liquid phase method, particularly a liquid phase method using a solution in which nitrogen is dissolved in a Ga-containing melt, is a gas phase such as HVPE (hydride vapor phase epitaxy) or MOCVD (metal organic chemical vapor deposition). Compared to the method, it is expected that a group III nitride crystal having a low dislocation density and high crystallinity can be grown.

  For example, the republished WO99 / 34037 (hereinafter referred to as Patent Document 1) describes a high temperature atmosphere of 1000K to 2800K (preferably 1600K to 2800K) and a high pressure atmosphere of 2000 to 45000 atm (preferably 10,000 to 45000 atm). Below, a method of growing GaN crystals by dissolving nitrogen gas in Ga melt is disclosed.

In addition, H. Yamane and three others, “Preparation of GaN Single Crystals Using a Na Flux”, Chemistry of Materials, (1997), Vol. 9, pp. 413-416 (hereinafter referred to as Non-Patent Document 1), A GaN crystal growth method using Na as a flux is disclosed. In this method, sodium azide (NaN ₃ ) as a flux and metal Ga are used as raw materials, and sealed in a stainless steel reaction vessel (inner vessel dimensions; inner diameter = 7.5 mm, length = 100 mm) in a nitrogen atmosphere, By holding the reaction vessel at a temperature of 600 to 800 ° C. for 24 to 100 hours, a GaN crystal is grown at an atmospheric pressure of at most about 100 kgf / cm ² .

  However, in the crystal growth methods of Patent Document 1 and Non-Patent Document 1, the thickness of the growing GaN crystal varies greatly on the crystal growth surface, and the GaN crystal obtained from the GaN crystal having a nonuniform thickness. There is a problem that the yield of the substrate is reduced.

Republished WO99 / 34037

H. Yamane and three others, “Preparation of GaN Single Crystals Using a Na Flux”, Chemistry of Materials, (1997), Vol. 9, pp.413-416

  In order to solve the above problems, an object of the present invention is to provide a group III nitride crystal growth method for growing a group III nitride crystal having a uniform thickness in the crystal growth plane.

  The present invention comprises a step of preparing a group III nitride crystal substrate and a step of repeatedly growing a group III nitride crystal on the main surface of the group III nitride crystal substrate by a liquid phase method a plurality of times. This is a group III nitride crystal growth method for growing a group III nitride crystal having a uniform thickness in the growth plane.

  In the method for growing a group III nitride crystal according to the present invention, as a liquid phase method, a solution in which nitrogen is dissolved in a Ga melt is brought into contact with the main surface of the group III nitride crystal substrate to obtain a group III nitride crystal. A GaN crystal can be grown. Here, the growth of the GaN crystal can be performed at a growth temperature of 800 ° C. or more and 1500 ° C. or less and a growth pressure of 50 atm (5.06 MPa) or more and 2000 atm (202.65 MPa) or less. In addition, the group III nitride crystal substrate can include a main crystal region and a polarity inversion crystal region in which the polarity in the [0001] direction is inverted with respect to the main crystal region. Here, the main surface of the polarity reversal crystal region can be recessed in the main surface of the group III nitride crystal substrate as compared with the main surface of the main crystal region.

  ADVANTAGE OF THE INVENTION According to this invention, the growth method of the group III nitride crystal which grows the group III nitride crystal which has uniform thickness in a crystal growth surface can be provided.

It is the schematic which shows an example of the group III nitride crystal substrate prepared in the growth method of the group III nitride crystal concerning this invention. (A) is a schematic plan view, (B) is a schematic sectional drawing in IB-IB of (A). It is a schematic sectional drawing which shows an example of the growth method of the group III nitride crystal concerning this invention. It is a schematic sectional drawing which shows an example of the growth method of a typical group III nitride crystal. It is the schematic which shows the other example of the group III nitride crystal substrate prepared in the growth method of the group III nitride crystal concerning this invention. (A) is a schematic plan view, (B) is a schematic sectional drawing in IVB-IVB of (A). It is a schematic sectional drawing which shows the other example of the growth method of the group III nitride crystal concerning this invention. It is a schematic sectional drawing which shows the further another example of the growth method of a typical group III nitride crystal. It is the schematic which shows the miscellaneous crystal | crystallization generated in the growth of a group III nitride crystal. (A) is a schematic plan view, (B) is a schematic sectional drawing in VIIB-VIIB of (A). In the growth of a group III nitride crystal, it is a graph which shows an example of the thickness of the group III nitride crystal after one crystal growth in 32 hours, 64 hours, and 128 hours, respectively. In the growth of a group III nitride crystal, it is a graph which shows an example of the thickness of the group III nitride crystal after 1 to 3 times of crystal growth. 4 is a graph showing an example of the growth rate of a group III nitride crystal after one to three crystal growths in the growth of a group III nitride crystal. In the growth of a group III nitride crystal, it is a graph which shows the other example of the thickness of the group III nitride crystal after one crystal growth in 32 hours, 64 hours, and 128 hours, respectively. In the growth of a group III nitride crystal, it is a graph which shows the other example of the thickness of the group III nitride crystal after 1 to 3 times of crystal growth. 6 is a graph showing another example of the crystal growth rate of a group III nitride crystal after one to three crystal growths in the growth of a group III nitride crystal. 4 is a graph showing a relationship between a single crystal growth time of a group III nitride crystal and a filling rate of a polarity reversal crystal region of a group III nitride crystal substrate in the growth of a group III nitride crystal. 4 is a graph showing the relationship between the number of times a group III nitride crystal grows and the filling rate of a polarity reversal crystal region of a group III nitride crystal substrate in the growth of a group III nitride crystal.

  With reference to FIGS. 1 to 2 and FIGS. 4 to 5, in one embodiment of a group III nitride crystal growth method according to the present invention, a step of preparing a group III nitride crystal substrate 10 (FIG. 1, FIG. 4) and a step (FIGS. 2 and 5) of repeatedly growing group III nitride crystal 20 on main surface 10m of group III nitride crystal substrate 10 by a liquid phase method multiple times. A group III nitride crystal 20 having a uniform thickness is grown in 20u.

  In the method for growing a group III nitride crystal of this embodiment, the group III nitride crystal 20 having a uniform thickness is grown in the crystal growth surface 20u by repeatedly growing the group III nitride crystal 20 a plurality of times. Can be made. The group III nitride crystal growth method of this embodiment will be described in detail below.

(Step of preparing a group III nitride crystal substrate)
First, referring to FIG. 1 and FIG. 4, the group III nitride crystal growth method of this embodiment includes a step of preparing a group III nitride crystal substrate 10. By preparing the group III nitride crystal substrate 10, the group III nitride crystal 20 having a low dislocation density and high crystallinity can be grown on the main surface 10m.

  Here, the prepared group III nitride crystal substrate 10 is not particularly limited as long as the group III nitride crystal 20 having a low dislocation density and high crystallinity can be epitaxially grown on the main surface 10m, In addition, HVPE (hydride vapor phase epitaxy) method, MOCVD (metal organic chemical vapor deposition) method, MBE (molecular beam epitaxy) method, sublimation method and other gas phase methods, and nitrogen is dissolved in a melt containing a group III metal. It may be produced by any growth method such as a solution method using a solution or a liquid phase method such as a flux method using a solution in which nitrogen is dissolved in a melt containing a group III metal and a flux.

  Referring to FIG. 4, group III nitride crystal substrate 10 to be prepared has a main crystal region 10s and a [0001] direction with respect to main crystal region 10s from the viewpoint of low dislocation density and high crystallinity of the substrate. And a polarity-reversed crystal region 10t having a reversed polarity. Since the group III nitride crystal substrate 10 has an extremely low dislocation density in the main crystal region 10s, the group III nitride crystal 20 having an extremely low dislocation density can be epitaxially grown on the main surface 10sm of the main crystal region 10s. it can.

  In a group III nitride crystal substrate 10 including a main crystal region 10s and a polarity inversion crystal region 10t, one main surface 10m has a (0001) plane orientation, and a group III nitride crystal is formed on the main surface 10m. When epitaxially growing 20, the main surface 10 sm of the main crystal region 10 s is a group III atomic surface having a (0001) plane orientation, and the main surface 10 tm of the polarity reversal crystal region 10 t has a (000-1) plane orientation. Nitrogen atom plane. In such a case, the group III nitride crystal 20 grown on the main surface 10sm of the main crystal region 10s is compared with the crystal region of the group III nitride crystal 20 grown on the main surface 10tm of the polarity reversal crystal region 10t. The crystal growth rate in the crystal region is extremely high. Therefore, the crystal region of group III nitride crystal 20 grown on main surface 10sm of main crystal region 10s embeds the crystal region of group III nitride crystal 20 grown on main surface 10tm of polarity reversal crystal region 10t. Thus, the crystal grows. Here, the crystal region of the group III nitride crystal 20 grown on the main surface 10 sm of the main crystal region 10 s of the group III nitride crystal substrate 10 grows while maintaining the crystallinity and crystal orientation of the main crystal region 10 s. Therefore, a group III nitride crystal 20 having a low dislocation density, high crystallinity, and a crystal growth surface 20u having a plane orientation of (0001) is obtained.

  Referring to FIG. 4, in the prepared group III nitride crystal substrate 10, the main surface 10tm of the polarity reversal crystal region 10t is more preferably recessed than the main surface 10sm of the main crystal region 10s. . Since the main surface 10tm of the polarity reversal crystal region 10t is recessed as compared with the main surface 10sm of the main crystal region 10s, the main surface 10tm of the recessed polarity reversal crystal region 10t is grown during the growth of the group III nitride crystal 20. Almost no group III nitride crystal grows thereon, and the polarity inversion crystal region 10t (by the crystal region of the group III nitride crystal 20 grown on the main surface 10sm of the main crystal region 10s of the group III nitride crystal substrate 10) Alternatively, embedding of the group III nitride crystal 20 crystal region slightly growing on the main surface 10tm of the polarity reversal crystal region 10t is promoted. From this viewpoint, the depth of the recess 10v of the main surface 10tm of the polarity reversal crystal region 10t with respect to the main surface 10sm of the main crystal region 10s is preferably 10 μm or more, and more preferably 20 μm or more.

  The method for forming the recess 10v in the main surface 10tm of the polarity reversal crystal region 10t of the group III nitride crystal substrate 10 is not particularly limited. For example, the main surface 10m of the group III nitride crystal substrate 10 may have a KOH melt, By contacting an alkaline melt such as NaOH melt, or an alkaline aqueous solution such as KOH aqueous solution or NaOH aqueous solution, the main surface 10tm of the polarity reversal crystal region 10t is more etched than the main surface 10sm of the main crystal region 10s. A method is mentioned.

(Step of repeatedly growing group III nitride crystal multiple times)
Next, referring to FIG. 2 and FIG. 5, in the method for growing a group III nitride crystal of this embodiment, a group III nitride crystal is formed on the main surface of the group III nitride crystal substrate a plurality of times by a liquid phase method. It includes a process of repeatedly growing. By repeatedly growing group III nitride crystal 20 a plurality of times, group III nitride crystal 20 having a uniform thickness can be grown in crystal growth surface 20u.

  Here, the growth of the group III nitride crystal 20 by repeating a plurality of times means that the growth of the group III nitride crystal 20 is interrupted one or more times and the crystal growth is performed a plurality of times. In addition to the method of performing crystal growth by putting the crystal taken out from the post-crystal growth vessel into the crystal growth vessel again, after the crystal is grown, the crystal is not taken out from the crystal growth vessel and then placed under conditions where the crystal does not grow again. Also included is a method of placing the crystal under conditions for crystal growth. In any method, the group III nitride crystal 20 having a uniform thickness can be grown in the crystal growth surface 20u.

  The liquid phase method is suitable because the group III nitride crystal 20 having a low dislocation density and high crystallinity can be epitaxially grown, and a solution using a solution 7 in which nitrogen 5 is dissolved in a melt 3 containing a group III metal. For example, a flux method using a solution 7 in which nitrogen 5 is dissolved in a melt 3 containing a group III metal and a flux is preferably used. Here, from the viewpoint of reducing impurities mixed in the group III nitride crystal 20 to be grown, a solution method using a solution in which nitrogen is dissolved in a melt containing a group III metal is particularly suitable.

  Referring to FIGS. 3 and 6, when thick group III nitride crystal 20 is epitaxially grown at a time by the liquid phase method, crystal growth surface 20u of group III nitride crystal 20 under the crystal growth condition is used during crystal growth. Due to the variation in the crystal growth rate, the crystal growth rate varies within the crystal growth surface 20u, so that the obtained group III nitride crystal 20 has a non-uniform thickness within the crystal growth surface 20u.

  On the other hand, referring to FIG. 2 and FIG. 5, by repeating the growth of group III nitride crystal 20 in a plurality of times, the crystal growth surface 20u of group III nitride crystal 20 under the crystal growth condition is obtained. Since the distribution of the thickness of each group differs for each growth of the group III nitride crystal 20, the group III nitride crystal 20 having a uniform thickness on the crystal growth surface 20u is obtained. For example, the crystal growth surface in each of the first crystal growth region 20a, the second crystal growth region 20b, the third crystal growth region 20c, and the k-th crystal growth region 20k of the group III nitride crystal 20. Therefore, the group III nitride crystal 20 having a uniform thickness in the crystal growth surface 20u is obtained.

  Here, the thickness of the group III nitride crystal 20 being uniform in the crystal growth surface 20u means that the ratio of the minimum thickness to the maximum thickness in the crystal growth surface 20u, that is, the average of a plurality of times in the crystal growth surface 20u. The ratio of the average minimum growth rate of the plurality of times to the maximum growth rate is 0.33 or more, preferably 0.50 or more, more preferably 0.66 or more, still more preferably 0.80 or more, and most preferably 0.8. It means 90 or more.

  Further, from the viewpoint of making the thickness of the group III nitride crystal 20 to be grown more uniform in the crystal growth surface 20u, the number of times of growth of the group III nitride crystal 20 is preferably 3 times or more. In the crystal growth, the ratio of the minimum thickness to the maximum thickness at the crystal growth surface 20u, that is, the ratio of the minimum growth rate at each time to the maximum growth rate at each time at the crystal growth surface 20u is preferably 0.33 or more, preferably 0.50 or more. Is more preferable, and 0.60 or more is more preferable.

  In the method for growing a group III nitride crystal of the present embodiment, the group III nitride crystal grown by polishing or etching the crystal growth surface of the grown group III nitride crystal during each crystal growth. It is preferable to make the thickness in the crystal growth plane uniform. By making the thickness uniform in the crystal growth surface by the above polishing or etching during each crystal growth, a group III nitride crystal having a uniform thickness in the crystal growth surface can be more efficiently grown. .

  Further, in the method for growing a group III nitride crystal of the present embodiment, as a liquid phase method, a solution 7 in which nitrogen 5 is dissolved in a Ga melt that is a melt 3 containing a group III metal is used as a group III nitride crystal substrate. It is preferable to grow a GaN crystal as the group III nitride crystal 20 by bringing it into contact with the 10 major surfaces 10 m. With this growth method, a GaN crystal having a uniform thickness on the crystal growth surface 20u can be obtained.

  Furthermore, in the growth of the GaN crystal, it is preferable that the growth temperature is 800 ° C. or more and 1500 ° C. or less, and the growth pressure is 50 atm (5.06 MPa) or more and 2000 atm (202.65 MPa) or less. By crystal growth at such growth temperature and pressure, a GaN crystal having a low dislocation density and high crystallinity can be obtained.

  As described above, referring to FIG. 4, in the group III nitride crystal growth method of the present embodiment, the prepared group III nitride crystal substrate 10 is divided into a main crystal region 10 s and a main crystal region 10 s. And a polarity-inverted crystal region 10t whose polarity in the [0001] direction is inverted. Since the group III nitride crystal substrate 10 has a very low dislocation density in the main crystal region 10 s as described above, the group III nitride crystal 20 having a very low dislocation density on the main surface 10 sm of the main crystal region 10 s. Can be epitaxially grown.

  Further, in the group III nitride crystal substrate 10 including the main crystal region 10s and the polarity inversion crystal region 10t, one main surface 10m has a (0001) plane orientation, and the group III nitride is formed on the main surface 10m. In the case of epitaxial growth of the physical crystal 20, the main surface 10sm of the main crystal region 10s is a group III atomic surface having a (0001) plane orientation, and the main surface 10tm of the polarity reversal crystal region 10t is (000-1). In the case of the nitrogen atom plane having the plane orientation of the following, the crystal region of the group III nitride crystal 20 growing on the main surface 10tm of the polarity reversal crystal region 10t is on the main surface 10sm of the main crystal region 10s. The crystal growth rate of the crystal region of the growing group III nitride crystal 20 is extremely high. Therefore, the crystal region of group III nitride crystal 20 grown on main surface 10sm of main crystal region 10s embeds the crystal region of group III nitride crystal 20 grown on main surface 10tm of polarity reversal crystal region 10t. Thus, the crystal grows. Here, the crystal region of the group III nitride crystal 20 grown on the main surface 10 sm of the main crystal region 10 s of the group III nitride crystal substrate 10 grows while maintaining the crystallinity and crystal orientation of the main crystal region 10 s. Therefore, a group III nitride crystal 20 having a low dislocation density, high crystallinity, and a crystal growth surface 20u having a plane orientation of (0001) is obtained.

  As described above, referring to FIG. 4, in the prepared group III nitride crystal substrate 10, the main surface 10tm of the polarity reversal crystal region 10t is recessed as compared with the main surface 10sm of the main crystal region 10s. More preferably. Since the main surface 10tm of the polarity reversal crystal region 10t is recessed as compared with the main surface 10sm of the main crystal region 10s, the main surface 10tm of the recessed polarity reversal crystal region 10t is grown during the growth of the group III nitride crystal 20. Almost no group III nitride crystal grows thereon, and the polarity inversion crystal region 10t (by the crystal region of the group III nitride crystal 20 grown on the main surface 10sm of the main crystal region 10s of the group III nitride crystal substrate 10) Alternatively, embedding of the group III nitride crystal 20 crystal region slightly growing on the main surface 10tm of the polarity reversal crystal region 10t is promoted. From this viewpoint, the depth of the recess 10v of the main surface 10tm of the polarity reversal crystal region 10t with respect to the main surface 10sm of the main crystal region 10s is preferably 10 μm or more, and more preferably 20 μm or more.

Example 1
1. Preparation of GaN Crystal Substrate Referring to FIG. 1, a GaN crystal substrate (Group III nitride crystal substrate 10) having a diameter of 2 inches (50.8 mm) and a thickness of 400 μm was prepared. The average dislocation density at 10 m of the principal surface of the GaN crystal substrate was 5 × 10 ⁵ cm ⁻² when measured by a CL (cathode luminescence) method.

2. 2. Growth of GaN crystal Referring to FIG. 2, a GaN crystal substrate (group III nitride crystal substrate 10) is placed in a pBN (pyrolytic boron nitride) crucible (crystal growth vessel 1) having an inner diameter of 60 mm and a height of 50 mm. And 100 g of metal Ga having a purity of 99.99999 mass% was arranged.

  Next, nitrogen gas (nitrogen 5) having a purity of 99.9999% by mass was supplied into the pBN crucible, and the pBN crucible was heated from room temperature (25 ° C.) to 1150 ° C. under 30 atm (3.04 MPa). At this time, the metal Ga arranged in the pBN crucible melts to form a Ga melt (melt 3), and the solution 7 in which nitrogen 5 is dissolved in the Ga melt contacts the main surface 10m of the GaN crystal substrate. ing. However, under such conditions, since the dissolution of nitrogen in the Ga melt is small, the main surface of the GaN crystal substrate is etched without growing the GaN crystal, and the work-affected layer and the surface oxide layer in the vicinity of the main surface are formed. It was removed and the main surface was cleaned.

Subsequently, nitrogen gas was further supplied to the pBN crucible to adjust the pressure to 1950 atm (197.5 MPa) to grow three GaN crystals. The first GaN crystal growth time of the three GaN crystals was 32 hours, 64 hours, and 128 hours, respectively. For each of the obtained three GaN crystals, the thickness of the GaN crystal was measured at intervals of 5 mm from one end of the diameter on the crystal growth surface to the other end by cross-sectional observation with a fluorescence microscope. The average dislocation density at the crystal growth surface of the three GaN crystals was measured by the CL method, and the GaN crystals grown for 32 hours had a maximum thickness of 23 μm, a minimum thickness of 12 μm, and an average thickness of 17 μm, The average dislocation density at the crystal growth surface was 5 × 10 ⁵ cm ⁻² , and the GaN crystal grown for 64 hours had a maximum thickness of 42 μm, a minimum thickness of 26 μm, and an average thickness of 32 μm. The average dislocation density in the plane was 5 × 10 ⁵ cm ⁻² , and the GaN crystal grown for 128 hours had a maximum thickness of 90 μm, a minimum thickness of 26 μm, and an average thickness of 56 μm. The average dislocation density on the long face was 5 × 10 ⁵ cm ⁻² , and the results are summarized in Table 1 and FIG.

  Referring to Table 1 and FIG. 8, in the GaN crystals after 32 hours growth and 64 hours growth, the ratio of the minimum thickness to the maximum thickness is 0.52 and 0.62, respectively. It was 33 or more. On the other hand, in the GaN crystal grown for 128 hours, the ratio of the minimum thickness to the maximum thickness was 0.29, which was less than 0.33. From these results, from the viewpoint of obtaining a GaN crystal (Group III nitride crystal 20) having a uniform thickness in the crystal growth plane, the growth time in one crystal growth of the GaN crystal is preferably 100 hours or less, 65 It can be seen that the time is more preferable.

Next, in a new pBN (pyrolytic boron nitride) crucible (crystal growth vessel 1) having an inner diameter of 60 mm and a height of 50 mm, the GaN crystal after the above-mentioned crystal growth in 64 hours and the purity are 99. 100 g of 99,999% by mass of metal Ga was placed, and a GaN crystal was grown for 64 hours in the same manner as described above (second crystal growth). The thickness of the GaN crystal after the two crystal growths thus obtained was measured in the same manner as described above. As a result, the maximum thickness was 75 μm, the minimum thickness was 60 μm, and the average thickness was 67 μm. The ratio of the minimum thickness to the thickness was 0.80. The average dislocation density in the crystal growth surface of the GaN crystal after the second crystal growth was 5 × 10 ⁵ cm ⁻² .

Next, in a new pBN (pyrolytic boron nitride) crucible (crystal growth vessel 1) having an inner diameter of 60 mm and a height of 50 mm, the GaN crystal after the above-mentioned two crystal growths and the purity is 99.99999 mass. GaN crystal was grown for 64 hours in the same manner as described above by placing 100 g of% metal Ga (third crystal growth). The thickness of the GaN crystal after the three crystal growths thus obtained was measured in the same manner as described above. As a result, the maximum thickness was 105 μm, the minimum thickness was 95 μm, and the average thickness was 100 μm. The ratio of the minimum thickness to the thickness was 0.90. The average dislocation density in the crystal growth surface of the GaN crystal after the third crystal growth was 5 × 10 ⁵ cm ⁻² .

  The above results are summarized in Table 1 and FIG. Based on the results, the maximum growth rate, the minimum growth rate, and the average growth in each of the GaN crystal after one crystal growth, the GaN crystal after two crystal growths, and the GaN crystal after three crystal growths. The speed was calculated and summarized in Table 1 and FIG.

  That is, the maximum growth rate, the minimum growth rate, and the average growth rate of the GaN crystal are the maximum thickness, the minimum thickness, and the average thickness after the single crystal growth for the GaN crystal after the single crystal growth, respectively. Is divided by 64 hours which is the first crystal growth time, and for the GaN crystal after the second crystal growth, each of the maximum thickness, the minimum thickness and the average thickness after the second crystal growth. Is divided by 128 hours, which is the sum of the first and second crystal growth times, and for GaN crystals after three crystal growths, the maximum thickness, the minimum thickness after three crystal growths, and The average thickness is divided by 192 hours, which is the sum of the first, second and third crystal growth times.

  Referring to Table 1 and FIG. 10, the GaN crystal after one crystal growth has a maximum growth rate of 0.656 μm / h, a minimum growth rate of 0.406 μm / h, and an average growth rate of 0.500 μm / h. h, and the ratio of the minimum growth rate to the maximum growth rate was 0.62. The GaN crystal after the second crystal growth has a maximum growth rate of 0.586 μm / h, a minimum growth rate of 0.469 μm / h, and an average growth rate of 0.523 μm / h. The ratio was 0.80. The GaN crystal after three crystal growths has a maximum growth rate of 0.547 μm / h, a minimum growth rate of 0.495 μm / h, and an average growth rate of 0.521 μm / h. The speed ratio was 0.90. Thus, the ratio of the minimum thickness to the maximum thickness (that is, the ratio of the minimum growth rate to the maximum growth rate) is 0.33 or more, preferably 0.50 or more, more preferably 0.66 or more, and even more preferably 0. A GaN crystal having a thickness of 0.80 or more, most preferably 0.90 or more and a uniform thickness on the crystal growth surface was obtained.

(Example 2)
1. 4. Preparation of GaN Crystal Substrate Referring to FIG. 4, a main crystal region 10s having a diameter of 2 inches (50.8 mm) and a thickness of 400 μm grown by the facet growth method described in Japanese Patent Application Laid-Open No. 2003-183100 A GaN crystal substrate (Group III nitride crystal substrate 10) including a polarity reversal crystal region 10t in which the polarity in the [0001] direction was reversed with respect to the main crystal region 10s was prepared. In this GaN crystal substrate, the polarity reversal crystal region 10t had a stripe shape with a width of 30 μm and a pitch of 400 μm when viewed from the main surface 10 m. This GaN crystal substrate is immersed in an aqueous solution of 10% by mass of KOH at 90 ° C. for 90 minutes, so that (000) The main surface 10tm having a surface orientation of -1) was recessed to a depth of 20 μm to 50 μm (dent 10v). The average dislocation density in the main surface 10 m of this GaN crystal substrate was 5 × 10 ⁵ cm ⁻² in the main crystal region and 10 ⁸ cm ⁻ in the polarity reversal crystal region as measured by the CL (cathode luminescence) method. ^There were ^two .

2. Growth of GaN Crystal In the same manner as in Example 1, the first crystal growth was performed for three GaN crystals. The crystal growth time was 32 hours, 64 hours and 128 hours, respectively. The GaN crystal grown for 32 hours has a maximum thickness of 23 μm, a minimum thickness of 14 μm, an average thickness of 18 μm, and a ratio of the minimum thickness to the maximum thickness of 0.61, and the average dislocation density at the crystal growth surface Was 5 × 10 ⁵ cm ⁻² . A GaN crystal grown for 64 hours has a maximum thickness of 43 μm, a minimum thickness of 25 μm, an average thickness of 32 μm, and a ratio of the minimum thickness to the maximum thickness of 0.58. Was 5 × 10 ⁵ cm ⁻² . The GaN crystal grown for 128 hours has a maximum thickness of 93 μm, a minimum thickness of 26 μm, an average thickness of 56 μm, and a ratio of the minimum thickness to the maximum thickness of 0.28. Was 5 × 10 ⁵ cm ⁻² . The results are summarized in Table 2 and FIG.

  Referring to Table 2 and FIG. 11, the ratio of the minimum thickness to the maximum thickness was 0.33 or more in the GaN crystal after 32 hours growth and after 64 hours growth, whereas it was 128 hours growth. In the GaN crystal, it was less than 0.33. From these results, from the viewpoint of obtaining a GaN crystal (Group III nitride crystal 20) having a uniform thickness in the crystal growth plane, the growth time in one crystal growth of the GaN crystal is preferably 100 hours or less, 65 It can be seen that the time is more preferable.

  Here, the percentage of the area embedded by the GaN crystal (group III nitride crystal) grown with respect to the entire area of the main surface of the polarity reversal crystal region of the GaN crystal substrate (group III nitride crystal substrate) (%) Is defined as the filling rate of the polarity inversion crystal region. At this time, the filling rate of the polarity inversion crystal region in the GaN crystal after growth for 32 hours is determined by mapping photography using a Nomarski microscope over the entire surface parallel to the main surface of the GaN crystal substrate and the GaN crystal grown on the main surface. The calculated value is 30%, the burying rate of the polarity inversion crystal region in the GaN crystal after 64 hours of growth is 55%, and the burying rate of the polarity inversion crystal region in the GaN crystal after 128 hours of growth is 60%. there were. The results are summarized in Table 2 and FIG.

  Here, referring to FIG. 7, when the pBN crucibles after the GaN crystals were grown for 32 hours, 64 hours and 128 hours were observed, the Ga melt (melt 3) was observed in any pBN crucible. The miscellaneous crystals 30 were deposited on the surface of the solution 7 in which the nitrogen 5 was dissolved. Here, the miscellaneous crystals 30 mean polycrystals deposited on the surface of the solution due to supersaturation of the nitrogen 5 in the solution 7. The miscellaneous crystals 30 increased in precipitation amount as the crystal growth time increased. For this reason, even if the crystal growth time is lengthened, the miscellaneous crystals become larger, so the growth of the GaN crystal is not promoted, and the filling rate of the polarity inversion crystal region is considered not to be higher than about 60%.

Next, in the same manner as in Example 1, the GaN crystal grown for 64 hours at the first time was subjected to the second crystal growth for 64 hours and the third crystal growth for 64 hours. The GaN crystal after the above two crystal growths has a maximum thickness of 70 μm, a minimum thickness of 62 μm, an average thickness of 65 μm, and a ratio of the minimum thickness to the maximum thickness of 0.89. The average dislocation density in the plane was 5 × 10 ⁵ cm ⁻² . The GaN crystal after the above three crystal growths has a maximum thickness of 102 μm, a minimum thickness of 96 μm, an average thickness of 99 μm, and a ratio of the minimum thickness to the maximum thickness of 0.94. The average dislocation density at the crystal growth surface was 5 × 10 ⁵ cm ⁻² . The results are summarized in Table 2 and FIG.

  Based on the results, the maximum growth rate, the minimum growth rate, and the average growth in each of the GaN crystal after one crystal growth, the GaN crystal after two crystal growths, and the GaN crystal after three crystal growths. The speed was calculated and summarized in Table 2 and FIG.

  Referring to Table 2 and FIG. 13, the GaN crystal after one crystal growth has a maximum growth rate of 0.672 μm / h, a minimum growth rate of 0.391 μm / h, and an average growth rate of 0.500 μm / h. The ratio of the minimum growth rate to the maximum growth rate was 0.58. The GaN crystal after the second crystal growth has a maximum growth rate of 0.547 μm / h, a minimum growth rate of 0.484 μm / h, and a minimum growth rate of 0.508 μm / h. The ratio was 0.89. The GaN crystal after three times of crystal growth has a maximum growth rate of 0.531 μm / h, a minimum growth rate of 0.500 μm / h, and an average growth rate of 0.516 μm / h. The ratio was 0.94. Thus, the ratio of the minimum thickness to the maximum thickness (that is, the ratio of the minimum growth rate to the maximum growth rate) is 0.33 or more, preferably 0.50 or more, more preferably 0.66 or more, and even more preferably 0. A GaN crystal having a thickness of 0.80 or more, most preferably 0.90 or more and a uniform thickness on the crystal growth surface was obtained.

  In addition, the grown GaN crystal is embedded in the polarity reversal crystal region 10t of the GaN crystal substrate (Group III nitride crystal substrate 10) after the first crystal growth, after the second crystal growth, and after the third crystal growth. The percentages were 55%, 95% and 100%, as measured above. The results are summarized in Table 2 and FIG.

  Referring to Table 2 and FIG. 15, when a GaN crystal (Group III nitride crystal) is grown on a GaN crystal substrate (Group III nitride crystal substrate) including a main crystal region and a polarity inversion crystal region, 2 The majority of the polarity inversion crystal region can be embedded by performing crystal growth twice, and all the polarity inversion crystal regions can be embedded by performing crystal growth three times.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 Crystal Growth Vessel, 3 Melt, 5 Nitrogen, 7 Solution, 10 Group III Nitride Crystal Substrate, 10m, 10sm, 10tm Main Surface, 10s Main Crystal Region, 10t Polarity Inversion Crystal Region, 10v Recessed, 20 Group III Nitride Crystal, 20a first crystal growth region, 20b second crystal growth region, 20c third crystal growth region, 20k k crystal growth region, 20u crystal growth surface, 30 miscellaneous crystals.

Claims (5)

Preparing a group III nitride crystal substrate;
And a step of repeatedly growing a group III nitride crystal a plurality of times on the main surface of the group III nitride crystal substrate by a liquid phase method,
A group III nitride crystal growth method for growing the group III nitride crystal having a uniform thickness in a crystal growth plane.   2. The GaN crystal is grown as the group III nitride crystal by bringing a solution obtained by dissolving nitrogen in a Ga melt into contact with a main surface of the group III nitride crystal substrate as the liquid phase method. A method for growing Group III nitride crystals.   The method for growing a group III nitride crystal according to claim 2, wherein the growth of the GaN crystal is performed at a growth temperature of 800 ° C to 1500 ° C and a growth pressure of 50 atm to 2000 atm.   2. The group III nitride crystal substrate according to claim 1, wherein the group III nitride crystal substrate includes a main crystal region and a polarity inversion crystal region in which a polarity in a [0001] direction is inverted with respect to the main crystal region. Growth method.   5. The method for growing a group III nitride crystal according to claim 4, wherein a main surface of the polarity inversion crystal region is recessed on a main surface of the group III nitride crystal substrate as compared with a main surface of the main crystal region.

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