JP2011195377A - Method for producing group iii nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a group III nitride crystal, in which the group III nitride crystal that grows up on a holding substrate can be peeled off without deteriorating the crystal quality.SOLUTION: The method includes (a) a step of forming a first group III nitride crystal layer 22 on a front principal surface on the holding substrate 20, (b) a step of irradiating a laser beam from a back principal surface side of the holding substrate 20 to laser-process the rear side of the first III-nitride crystalline layer 22, (c) a step of growing a second group III nitride crystal layer 24 on the front principal surface of the first group III nitride crystal layer 22, and (d) a step of separating from the interface between the holding substrate 20 and the first group III nitride 22, wherein (e) where in the step (b) an outgassing structure is provided that discharges decomposed gas generated in the front principal surface of the first group III nitride crystal layer 22 upon laser processing. This increases an area of a laser processed part to the whole area, thereby reducing cracks in crystal due to the stress upon peeling.

Description

  According to the present invention, a first group III nitride crystal layer is grown on a holding substrate, and then the interface between the holding substrate and the first group III nitride crystal layer is laser processed to be easily peeled off. The present invention also relates to a method for producing a group III nitride crystal in which a second group III nitride crystal layer is grown thereon and the group III nitride crystal layer is separated from a holding substrate.

  Group III nitride semiconductors such as gallium nitride (GaN) (hereinafter sometimes referred to as group III nitride compound semiconductors or GaN-based semiconductors) are attracting attention as materials for semiconductor elements that emit blue or ultraviolet light. Blue laser diodes (LDs) are applied to high-density optical discs and displays, and blue light-emitting diodes (LEDs) are applied to displays and lighting. Further, ultraviolet LD is expected to be applied to biotechnology and the like, and ultraviolet LED is expected as an excitation light source and a sterilization light source for various phosphors. In addition, application to electronic devices such as various high frequency devices and power devices is also expected.

  A group III nitride crystal (for example, GaN) substrate used as a substrate for LDs, LEDs, and various electronic devices is formed on a holding substrate (for example, sapphire substrate) by using an epitaxial growth method to form a group III nitride single crystal layer. Manufactured by heteroepitaxial growth. Examples of the crystal growth method include a hydrogen compound vapor phase growth method (HVPE method), a Na flux growth method, a high-pressure synthesis method, and an ammonothermal method. In order to use the group III nitride crystal layer as a free-standing substrate, it is necessary to peel off a holding substrate such as a sapphire substrate and a group III nitride crystal grown thereon. Laser lift-off has been proposed as the peeling method (for example, Patent Document 1 and Non-Patent Document 1).

  However, due to the difference in thermal expansion coefficient and lattice constant between the holding substrate and the group III nitride crystal, a large strain is inherent in the holding substrate and the group III nitride crystal after crystal growth. If the holding substrate and the group III nitride crystal layer are peeled off by laser processing in that state, cracks or the like are likely to occur in the crystal due to thermal shock of laser processing (for example, Non-Patent Document 1).

  The following methods have been studied as a method for examining the above problems.

  That is, after a group III nitride crystal having a thickness of about several μm to 100 μm is grown on the holding substrate, laser processing is performed from the main surface on the back side of the crystal, and the holding substrate and the group III nitride layer are easily separated in advance. Create a board. Next, a method is proposed in which a thick film of the second group III nitride crystal layer is grown on the seed substrate that is easily peeled off, and then the group III nitride crystal layer is peeled from the holding substrate (for example, a patent). Reference 2).

JP 2006-173147 A JP 2003-7616 A

M.M. K. Kelly et al. , Japan Journal of Applied Physics Vol38. ppL217-L219, 1999)

  The problem in the above conventional example is that the quality of the crystal deteriorates.

  This is because the decomposition gas (mainly nitrogen gas) generated when the first group III nitride crystal layer is laser-processed from the back side of the holding substrate cannot be released to the outside. It ends up.

  The reason for this is that after the crystal is grown on the holding substrate, this crystal is peeled off from the holding substrate, and at this time, in order to make it easy to peel off the crystal from the holding substrate, a laser multiple drawing or the like is used. If the processing area for making the crystal easily peel from the holding substrate increases, further gas is generated and the pressure of the gas increases, and partial peeling of the first group III nitride crystal layer This is because deformation (swelling) occurs, which causes deterioration of crystal quality.

  Furthermore, in order to prevent the generation of gas, in the state where sufficient laser processing is not performed, the stress at the time of peeling becomes high, and the quality of the crystal deteriorates due to cracks in the crystal. .

Hereinafter, this problem will be further described with reference to FIGS.
A first group III nitride crystal layer 12 is grown on the holding substrate 11 in the range of several μm to 100 μm. Next, laser processing is performed from the rear surface side of the holding substrate 11, thereby forming the processed portion 18 mainly by thermal decomposition of the rear surface side of the group III nitride crystal layer 12. FIG. 11 shows a laser processing pattern viewed from the main surface side of the substrate. As the laser processing pattern, for example, concentric circles as shown in FIG. 11A or spiral shapes starting from the outer periphery as shown in FIG. In such a pattern, there is no escape space for gas (mainly nitrogen gas) in the concentric circles, and in the spiral pattern, there is only one system for escape gas, so that the decomposition gas cannot be taken out efficiently. As a result, the width of the laser-processed portion 18 is widened, that is, the area of the laser-processed portion 18 is made sufficiently large so that the group III nitride crystal layer 12 can be easily separated from the holding substrate 11 with respect to the entire area of the substrate. Can not do it.

  As a result, the adhesion strength between the holding substrate 11 and the first group III nitride crystal layer 12 cannot be lowered, and the stress at the time of peeling the group III nitride crystal layer 12 from the holding substrate 11 becomes high. Since the entire crystal is cracked, the quality of the crystal is deteriorated.

  Accordingly, an object of the present invention is to improve the quality of crystals.

The present invention
(A) forming a first group III nitride crystal layer on the front main surface on the holding substrate;
(B) irradiating a laser beam from the back substrate main surface of the holding substrate to laser-process the back surface side of the first III nitride crystal layer;
(C) growing a second group III nitride crystal layer on a front main surface of the first group III nitride crystal layer;
(D) separating from the interface between the holding substrate and the first group III nitride layer,
(E) A method for producing a group III nitride crystal in which, in the step (b), a gas releasing structure for releasing a decomposition gas generated during laser processing is provided on a front main surface of the first group III nitride crystal layer It is.

  Furthermore, the gas emission structure is a macro crack penetrating from the laser-processed portion to the first front main surface, and the length of the macro crack in the longitudinal direction is preferably 20 μm or more and 500 μm or less. Further, what is desired is a method for producing a group III nitride crystal in which the gas releasing structure is formed almost simultaneously with the step (b).

  Another desirable form is a gas discharge hole or a gas discharge groove through which the gas discharge structure penetrates to the front main surface of the first group III nitride crystal layer. The diameter is 20 μm or more and 500 μm or less, or the width of the gas discharge groove is 20 μm or more and 500 μm or less. It is further desirable that the longitudinal direction of the gas discharge groove is a <1-100> direction. It is to be. Furthermore, the gas discharge hole or the gas discharge groove is to be performed before the laser processing in the step (b), and it should be desired that the gas discharge hole or the gas discharge groove is formed in the first group III nitride. It is formed by laser processing from the front side main surface of the crystal layer.

  As another desirable mode, the first group III nitride crystal layer is a mask having a third group III nitride crystal layer grown on the holding substrate and a desired pattern formed thereon. This is a method for producing a group III nitride crystal which is a multilayer structure comprising a layer and a fourth group III nitride crystal layer grown thereon.

In addition, the laser beam diameter used for the laser processing is 20 μm or more and 500 μm or less, preferably the average output power of the laser used for the laser processing is 0.4 W or more and 10 W or less, and preferably the laser The repetition frequency of the laser used for processing is 20 kHz or more and 100 kHz or less. More desirably, the pulse width of the laser used for laser processing is 20 nsec or more and 100 nsec or less.
Furthermore, it is desirable to grind or polish both main surfaces of the laminate of the first group III nitride crystal layer and the second group III nitride crystal layer peeled from the holding substrate, and more preferably It is desirable to remove the group III nitride crystal layer by any method of polishing, grinding, or slicing. More desirably, the group III nitride crystal includes a step of slicing at least the second group III nitride crystal layer, and forming a plurality of freestanding group III nitride substrates from the second group III nitride crystal layer. The manufacturing method is used.

  According to the present invention, a structure for releasing a decomposition gas generated during processing of a group III nitride crystal is prepared in advance or simultaneously with laser processing. As a result, the decomposition gas (mainly nitrogen gas) generated when the back side main surface of the first group III nitride crystal layer is laser processed can be efficiently extracted from the laser processed part to the outside.

  The usual laser lift-off method employs a method of laser processing without leaving an unprocessed portion from the outer periphery after crystal growth, and thus the above-mentioned problem has not been recognized at all. In addition, macro cracks, gas discharge holes, and gas discharge grooves generally deteriorate the crystallinity of the second nitride crystal that grows on the crack or newly crack the second group III nitride crystal layer. In the past, it was not considered at all. As a result of continuing a series of studies, the present inventors have discovered that decomposition gas can be quickly released by forming a gas discharge structure during laser processing or in advance. The present invention has been achieved in that the crystal quality of the second group III nitride crystal layer is not deteriorated. As a result, the area of the laser processed portion with respect to the entire substrate can be increased, so that the cracks of the crystal due to the stress acting on the crystal at the time of peeling can be reduced, and the group III nitride crystal layer is peeled from the holding substrate with good reproducibility. It becomes possible. As a result, the crystal quality can be improved.

The figure for demonstrating Example 1 of this invention The figure for demonstrating Example 1 of this invention The figure for demonstrating Example 1 of this invention The figure for demonstrating the 2nd Example of this invention The figure for demonstrating the 2nd Example of this invention The figure for demonstrating the 3rd Example of this invention The figure for demonstrating the 3rd Example of this invention The figure for demonstrating the 4th Example of this invention The figure for demonstrating the 5th Example of this invention The figure for demonstrating the conventional invention The figure for demonstrating the conventional invention

In the following description, various group III nitride crystals can be used as the group III nitride crystal layer, but most of the group III nitride crystal will be described as a GaN crystal layer for easy understanding. As the holding substrate, sapphire, perovskite, and various oxide crystals can be used as long as they are transparent to the laser beam to be used. Here, for the sake of simplicity, a case where a sapphire substrate is used will be described. . In addition, when a group III nitride crystal layer is grown on a sapphire substrate, a very thin buffer layer may be grown, but the description thereof is omitted here for simplicity.
This will be described below with reference to examples.

Example 1
The first embodiment of the present invention will be described with reference to FIGS.

  The first group III nitride crystal layer 12 grown on the holding substrate 20 is prepared. As the first group III nitride crystal layer, a GaN crystal layer having a thickness of about several μm to 100 μm can be used. Here, as the crystal growth method of the GaN crystal layer 22, the one grown by a normal HVPE method or MOCVD method was used, and a film thickness of 30 μm was used (FIG. 1A).

  Next, it processed with the pulse laser from the back surface side of the holding substrate 20. FIG. The laser for processing is a laser having a wavelength of 355 nm, which is the third harmonic of YAG. The laser power is an average output of 0.4 W to 10 W, the repetition frequency is 20 kHz to 100 kHz, and the beam diameter during processing is a diameter of 20 μm. To 500 μm and a pulse width of 20 nsec to 100 nsec can be used. Here, laser light having an average laser power of 1 W, a repetition frequency of 50 KHz, a beam diameter of 20 μm to 100 μm, and a pulse width of about 30 to 50 nsec was used.

  Under this condition, laser processing is performed to form the laser processing portion 60. Here, by processing at a power about 5% to 30% higher than the limit value capable of laser processing, as shown in FIG. 1B, the macro cracks 50 penetrating the front side main surface and the transverse direction of the main surface propagate. The macro crack 52 to be formed is formed. By forming the macro crack 50, the decomposition gas (mainly nitrogen gas) decomposed by the laser processing can be efficiently taken out of the laser processing unit 60. This macro crack mode has not been known so far. Furthermore, the present invention is used for the first time in a gas discharge structure during laser processing.

  Conventionally, the macro crack 50 has not been studied at all in the case of laser lift-off because there is a concern that it may lead to the generation of a crack after the subsequent growth of the second group III nitride crystal layer.

  On the other hand, if the processing area is increased by using laser multiple drawing in the absence of gas escape, partial peeling or deformation (swelling) of the first group III nitride crystal layer occurs and the crystal quality is improved. On the contrary, it deteriorated.

FIG. 2 shows a schematic diagram of a macro crack 50 generated during laser processing, and FIG. 3 shows an enlarged photograph of the entire substrate and the macro crack after actual laser processing.
Next, a GaN crystal is grown as a second group III nitride crystal layer on the state of FIG. As a growth method of the GaN crystal, any growth method may be used. Here, a case where the Na flux method is used will be described. Here, the Na flux method was used as a method for producing the second group III nitride crystal because even if there is a macroscopic crystal defect such as a macrocrack, it grows so as to fill in that portion than other methods. This is because it is advantageous to obtain a crystal with good crystal quality. As shown in FIG. 1D, the GaN crystal layer 24 was grown from 1.5 to 2 mm. After removing the crucible from the growth apparatus after crystal growth and cleaning the flux, the group III nitride crystal laminate 70 having no cracks could be taken out in a state of peeling from the holding substrate 20 as shown in FIG. .

Thereafter, by performing peripheral grinding, double-side polishing, cleaning, and the like of the crystal, a 2-inch free-standing substrate 25 as shown in FIG. The self-supporting substrate 25 manufactured here has no cracks, and the obtained half width of the X-ray diffraction rocking curve of the crystal is (0002) Half width: 30 to 80 sec.
(10-12) Half width: 30 to 70 sec
Further, when the dislocation density (EPD) was measured by etching the GaN free-standing substrate 25,
EDP: 5 × 10 ^{4 to} 6 × 10 ⁵ (pieces / cm 2)
And showed good results.

  Table 1 shows the results when there are macro cracks as a gas release structure during laser processing. Under the conditions of laser processing with macro cracks, it was possible to make the laser processing part an area of 1/5 to 2/3 of the entire area of the substrate. On the other hand, under the condition without macro cracks, the area of the laser processed portion 60 could be processed only about 10% of the total area of the substrate. In addition, if the processing area is increased using laser multiple drawing in the absence of gas escape, partial peeling or deformation (swelling) of the first group III nitride crystal layer occurs, resulting in crystal quality. However, it deteriorated.

  As shown in Table 1, the separation yield when the macrocrack as the gas releasing structure was present was 70%, and the separation yield when there was no macrocrack was 20%. From this result, when the macro crack was used as the decomposition gas release mechanism of the present invention, the yield was improved 3.5 times that when the macro crack was not used.

（実施例２）
本発明の第２の実施例について、図４を用いて説明する。本発明は、ガス放出構造体がガス放出穴の場合の例である。

(Example 2)
A second embodiment of the present invention will be described with reference to FIG. The present invention is an example when the gas discharge structure is a gas discharge hole.

  FIG. 4A is the same as FIG. 1A of the first embodiment.

  Next, as shown in FIG. 4B, a gas discharge hole 54 is formed from the front main surface of the first group III nitride crystal layer 22 by laser processing. At this time, the laser power condition for processing is preferably about 10% to 50% smaller than the condition for processing the interface. This is because the processing of the crystal surface enables laser processing with lower power than processing at the interface. Here, the measurement was performed under the conditions of a beam diameter of 50 μmφ, a laser average power of 0.8 W, and a repetition period of 50 kHz. Under this condition, as shown in FIG. 4C, a gas release hole 54 for degassing is then formed in the first group III nitride crystal layer 22 from the surface. Here, the adjustment of the hole diameter was performed by multiple drawing of lasers. The hole diameter is suitably 20 μm to 500 μφ, but here it is 100 μmφ. Here, considering the degassing function, the larger the hole diameter, the better. However, if the hole diameter exceeds 500 μmφ, the second group III nitride crystal may not be completely filled even in liquid phase growth. 500 μmφ or less is preferable. On the other hand, if it is 20 μm or less, the degassing effect becomes small, which is not desirable. A processing pattern viewed from the main surface side is shown in FIG.

  Next, as shown in FIG. 4D, laser light is irradiated from the back side main surface of the holding substrate to laser process the back side main surface of the holding substrate 20 and the first group III nitride crystal 22, thereby performing laser processing. The part 60 is produced. The laser processing conditions at this time are the same as in Example 1, but since the decomposition gas discharge holes are formed, the amount of macro cracks generated during laser processing can be almost eliminated.

  The state shown in FIG. 4E was used as a seed crystal, and a GaN crystal layer 24 as a second group III nitride crystal layer was grown thereon by LPE growth using the Na flux method. The crystal growth conditions are the same as in Example 1.

  After the crystal growth, flux treatment is performed and the crystal is taken out from the crucible. As shown in FIG. 4G, the first group III nitride crystal layer and the second group III nitride grown on the holding substrate 20 are obtained. The laminate 75 of the crystal layer was peeled off and could be taken out.

  Finally, the front-side main surface and the back-side main surface of the laminate 75 obtained can be ground / mechanically polished, precision polished, washed, etc., to finally obtain a self-supporting substrate 25 of 2 inch diameter GaN crystal. FIG. 4 (h).

  Table 2 shows the yield of peeling depending on the presence or absence of gas discharge holes according to Example 2 of the present invention. Compared with the case where the gas discharge hole according to the present invention is not formed, the yield can be increased 4.5 times.

（実施例３）
本発明による第３の実施例を、図６を用いて説明する。本発明の実施例３では、分解ガス放出構造体として、ガス放出溝１００を形成した場合を説明する。保持基板や第1のＩＩＩ族窒化物結晶の状態は実施例２と同じである。表側にガス放出溝１００を形成とする。溝幅は２０μｍから５００μｍの範囲が望ましい。溝幅が５００μｍを越えると第２のＩＩＩ族窒化物結晶層を成長する時に溝が埋まらなくなり、溝幅が２０μｍ以下ではガス放出機能が十分に機能しないためである。ここでは、実施例２と同様にレーザ加工を用いた。ここで、ガス放出溝１００の長手方向がＩＩＩ族窒化物結晶であるＧａＮ結晶の＜１−１００＞方向と平行であることが望ましい。これは、ガス放出溝を＜１−１００＞方向に形成することによって、それとは垂直な＜１１−２０＞方向に横方向成長しやすいので、第２のＩＩＩ族窒化物結晶を成長するときに、ガス放出溝１００が埋まって成長し易いためである。また、第１のＩＩＩ族窒化物結晶層との裏面主面のレーザ加工部６０は、実施例１や実施例２と同様に作製した。 次にガス放出溝１００を形成した種結晶の上に実施例２と同様のＧａＮ結晶層を成長した。その後フラックス処理をして結晶を取り出した時の剥離の歩留りは約９０％であり、ガス放出溝の無い場合の４．５倍の歩留りを示した。

(Example 3)
A third embodiment of the present invention will be described with reference to FIG. In the third embodiment of the present invention, a case where the gas discharge groove 100 is formed as the decomposition gas discharge structure will be described. The state of the holding substrate and the first group III nitride crystal is the same as in Example 2. A gas discharge groove 100 is formed on the front side. The groove width is desirably in the range of 20 μm to 500 μm. This is because if the groove width exceeds 500 μm, the groove is not filled when the second group III nitride crystal layer is grown, and if the groove width is 20 μm or less, the gas release function does not function sufficiently. Here, laser processing was used as in Example 2. Here, it is desirable that the longitudinal direction of the gas discharge groove 100 is parallel to the <1-100> direction of the GaN crystal which is a group III nitride crystal. This is because by forming the gas discharge groove in the <1-100> direction, it is easy to grow in the lateral direction in the <11-20> direction perpendicular thereto, so that the second group III nitride crystal is grown. This is because the gas discharge groove 100 is filled and easily grown. Further, the laser processing portion 60 on the back main surface with the first group III nitride crystal layer was produced in the same manner as in the first and second embodiments. Next, a GaN crystal layer similar to that of Example 2 was grown on the seed crystal in which the gas release groove 100 was formed. When the crystal was taken out after flux treatment, the separation yield was about 90%, which was 4.5 times higher than the case without the gas release groove.

  In addition, as a gas discharge groove | channel, the gas discharge groove | channels 100 and 110 of three directions equivalent in a <1-100> direction may be sufficient as FIG. As a result, the decomposition gas can be released more efficiently, and the GaN crystal can be peeled from the holding substrate with good crystal quality.

Example 4
A fourth embodiment of the present invention will be described with reference to FIG. Here, a lateral growth (ELOG) crystal layer using a mask is used as a seed crystal, and the third group III nitride film crystal layer, the mask, and the entire fourth group III nitride crystal layer are formed as the first crystal. The case of using for Group III nitride crystal layer 1 will be described.

  First, a GaN crystal 32 which is a third group III nitride crystal layer is grown on the holding substrate 20 by 2 μm. Next, a mask made of SiO2, SiN or the like is formed to a thickness of about 0.1 to 0.5 [mu] m, and a mask 80 patterned using vapor deposition or photolithography is prepared. Next, island-like crystals 46 are grown from the window portion of the mask by vapor phase growth such as HVPE or MOCVD (FIG. 8C). By continuing the growth as it is, the fourth group III nitride crystal layer 46 is grown from this island as a starting point (FIG. 8D). A multilayer structure 48 including the third group III nitride crystal layer 32, the mask 80, and the fourth group III nitride crystal layer is used as the conventional first group III nitride crystal layer.

  Next, as described above, laser processing is performed from the back side main surface of the holding substrate 20. Since the laser beam is absorbed by a thin layer of about 0.1 μm or less of the group III nitride crystal 12, it can be performed regardless of the above ELOG portion. The decomposition gas thermally decomposed by the laser processing unit 60 is discharged to the front side of the crystal main surface through the macro crack 50 formed simultaneously with the laser processing unit 60. In this example, it was possible to form the laser-processed portion 60 in a ratio of about 1/5 to 4/5 with respect to the entire 2-inch crystal main surface (FIG. 8F). Next, as in the other examples, a GaN crystal 24 was grown by about 1.5 to 2 mm. After the crystal growth, the crystal was taken out from the crucible. As a result, the holding substrate 20 and the layered group 90 of group III nitride crystals grown on the holding substrate were peeled off and could be taken out almost without cracks (FIG. 8 ( h)). At this time, the peeling yield was about 80%, which was four times the yield without macro cracks.

In this state, the front and back of the main surface of the laminate 90 were polished and washed to obtain a GaN free-standing substrate crystal 25. (Fig. 8 (I))
The crystal produced here has no cracks, and the obtained X-ray diffraction rocking curve has a half-value width of (0002) Half-value width: 25 to 70 sec.
(10-12) Half width: 25-60 sec
And showed good results.

Further, when the dislocation density (EPD) was measured by etching with respect to the GaN free-standing substrate 25,
EDP: 1 x 104 to 1 x 105 (pieces / cm2)
And showed good results. The maximum value of this dislocation density is about 1/2 to 1/5 when the ELOG structure is not used, and it was possible to obtain a crystal substrate with good quality with reduced EPD.

(Example 5)
A fifth embodiment of the present invention will be described with reference to FIG.

  A group III nitride substrate layer 22 is grown on the holding substrate 20 by 20 μm using the HVPE method (FIG. 9A). Next, laser light is irradiated from the main surface on the back surface side of the holding substrate, and the back surface main surface of the first group III nitride crystal layer 22 is laser processed to form a laser processing portion 60. The processing conditions are the same as in Example 1 (FIGS. 9B and 9C). Next, the second group III nitride crystal layer 24 is grown by about 4 mm using the Na flux method (FIG. 9D). After the crystal growth, the flux treatment was completed, and the crystal was taken out from the crucible. As a result, a laminate 76 of GaN crystals exfoliated near the interface between the holding substrate 20 and the first group III nitride crystal layer was obtained (FIG. 9 (e)). )).

  Next, the second group III nitride crystal layer 24 was cut out to a desired thickness (here, 0.6 mm) using a wire saw or the like. Thereafter, grinding, precision polishing, cleaning and the like were performed, and 3 to 5 desired 2-inch substrates 26 could be obtained.

Most of the free-standing substrate 26 manufactured here is crack-free, and the half-value width of the X-ray diffraction rocking curve is (0002) Half-value width: 25 to 80 sec.
(10-12) Half width: 25 to 70 sec
And showed good results.

Further, when dislocation density (EPD) was measured by etching for each substrate,
EDP: 1 x 104 to 6 x 105 (pieces / cm2)
And showed good quality.

  Here, the third harmonic of the YAG laser is used as the laser processing laser, but a pulse laser having a wavelength of 370 nm or less, such as the third harmonic, the fourth harmonic, or the excimer laser of the YVO4 laser, may be used. Other lasers can also be used. Further, from the viewpoint of laser stability, a Q-switched third harmonic and fourth storm wave laser excited by a semiconductor laser has been desired.

  The group III nitride crystal has been described for the case of a GaN crystal, but it is needless to say that the present invention can also be applied to a multi-component group III nitride crystal such as AlN, AlGaN, InGaN, AlGaInG.

  According to the present invention, when laser processing is performed on the interface between the holding substrate and the group III nitride crystal, decomposition gas generated by laser processing can be efficiently taken out. As a result, the area of the laser-processed portion relative to the entire substrate can be increased, and the group III nitride crystal layer can be peeled off from the holding substrate, thus reducing crystal cracks due to stress acting on the crystal during peeling. As a result, the quality of the crystal can be improved. Therefore, the self-supporting substrate of the group III nitride crystal can be taken out with a high yield, which is very useful.

DESCRIPTION OF SYMBOLS 11 Holding substrate in conventional invention 12 1st group III nitride crystal layer in conventional invention 18 Laser processing part in conventional invention 15 2nd group III nitride crystal layer in conventional invention 20 Holding substrate 22 1st Group III nitride crystal layer (GaN crystal layer)
24 Second Group III Nitride Crystal Layer (GaN Crystal Layer)
32 Third Group III Nitride Crystal Layer (GaN Crystal Layer)
46 Fourth Group III Nitride Crystal Layer (GaN Crystal Layer)
48 Multi-layer structure of group III nitride crystal layer and mask 60 Laser processing section 25, 26 Free-standing substrate (GaN)
50 Macrocrack (penetrated into the main surface of the first group III nitride crystal layer)
52 Macrocrack (substantially parallel to the GaN layer of the first group III nitride crystal layer)
54 Gas Emission Hole 60 Laser Processed Section 70, 75, 76, 90 Grown Group III Nitride Crystal Stack 80 Mask 100 Gas Emission Groove 110 Gas Emission Groove

Claims (18)

(A) forming a first group III nitride crystal layer on the front main surface on the holding substrate;
(B) irradiating a laser beam from the back substrate main surface of the holding substrate to laser-process the back surface side of the first III nitride crystal layer;
(C) growing a second group III nitride crystal layer on a front main surface of the first group III nitride crystal layer;
(D) separating from the interface between the holding substrate and the first group III nitride layer, and a manufacturing method comprising:
(E) A method for producing a group III nitride crystal in which, in the step (b), a gas releasing structure for releasing a decomposition gas generated during laser processing is provided on a front main surface of the first group III nitride crystal layer . 2. The method for producing a group III nitride crystal according to claim 1, wherein the gas releasing structure is a macro crack penetrating from the laser-processed portion to the first front main surface. 3. The method for producing a group III nitride crystal according to claim 2, wherein the length of the macro crack in the longitudinal direction is 20 μm or more and 500 μm or less. 3. The method for producing a group III nitride crystal according to claim 2, wherein the gas releasing structure is formed almost simultaneously with the step (b). 2. The group III nitride crystal production according to claim 1, wherein the gas release structure is a gas release hole or a gas release groove that penetrates to a front main surface of the first group III nitride crystal layer. 3. Method. 6. The method for producing a group III nitride crystal according to claim 5, wherein the diameter of the gas discharge hole is 20 μm or more and 500 μm or less. 6. The method for producing a group III nitride crystal according to claim 5, wherein a width of the gas discharge groove is 20 μm or more and 500 μm or less. 6. The method for producing a group III nitride crystal according to claim 5, wherein the longitudinal direction of the gas discharge groove is a <1-100> direction. 6. The method for producing a group III nitride crystal according to claim 5, wherein the gas discharge hole or the gas discharge groove is formed before the laser processing in the step (b). 10. The method for producing a group III nitride crystal according to claim 9, wherein the gas discharge hole or the gas discharge groove is formed by laser processing from a front main surface of the first group III nitride crystal layer. . The first group III nitride crystal layer is grown on the third group III nitride crystal layer grown on the holding substrate and a mask layer having a desired pattern formed thereon. 2. The method for producing a group III nitride crystal according to claim 1, wherein the group III nitride crystal is a multilayer structure including a fourth group III nitride crystal layer. 2. The method for producing a group III nitride crystal according to claim 1, wherein a beam diameter of a laser used for the laser processing is 20 μm or more and 500 μm or less. 2. The method for producing a group III nitride crystal according to claim 1, wherein an average output of a laser used for the laser processing is 0.4 W or more and 10 W or less. The method for producing a group III nitride crystal according to claim 1, wherein a repetition frequency of the laser used for the laser processing is 20 kHz or more and 100 kHz or less. 2. The method for producing a group III nitride crystal layer according to claim 1, wherein a pulse width of a laser used for the laser processing is 20 nsec or more and 100 nsec or less. 2. The group III nitride according to claim 1, wherein the principal surfaces on both sides of the laminate of the first group III nitride crystal layer and the second group III nitride crystal layer separated from the holding substrate are ground or polished. Method for producing physical crystals. 2. The method for producing a group III nitride crystal according to claim 1, wherein the first group III nitride crystal layer is removed by any one of polishing, grinding, and slicing. 18. The method according to claim 17, further comprising slicing at least a second group III nitride crystal layer, and forming a plurality of free-standing group III nitride substrates from the second group III nitride crystal layer. A method for producing a group III nitride crystal of

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