JP6526811B2 - Method of processing a group III nitride crystal - Google Patents

Description

(Cross-reference to related applications)
This application claims the benefit of U.S. Application Serial No. 62 / 086,699, entitled "Group III Nitride Crystals, Their Fabrication Method, and Method of Fabricating Crystals in Supercritical Ammonia", inventor Tadao Hashimoto, Agent Management Number SIXPOI-022 USPRV1. And claim the benefit of priority to filing date December 2, 2014, the contents of which are incorporated by reference in their entirety.

  This application is also related to the following US patent applications:

  PCT Practical Patent Application No. US 2005/024239, filed July 8, 2005, inventor Kenji Fujito, Tadao Hashimoto and Shuji Nakamura, Title of the Invention "METHOD FOR GROWING GROUP III-NITRIDE CRYSTALS IN SUPERCRITICAL AMMONIA USING AN AUTOCLAVE" Agent management number 30794.0129-WO-O1 (2005-339-1);

  U.S. Patent Application Serial No. 11 / 784,339, filed April 6, 2007, by Tadao Hashimoto, Makoto Saito, and Shuji Nakamura, entitled, "METHOD FOR GROWING LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS IN SUPERCRITICAL AMMONIA" AND LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS ", Agent Administration No. 30794.179-US-U1 (2006-204) (This application is filed on US Provisional Patent Application No. 60 / 790,310, filed April 7, 2006. Inventor Tadao Hashimoto, Makoto Saito, and S huji Nakamura, 35 U.S. of the invention "A METHOD FOR GROWING LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS IN SUPERCRITICAL AMMONIA AND LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS", Agent Management No. 30794. 179-US-P1 (2006-204) Claim interests under 利益 119 (e));

  U.S. Patent Application No. 60 / 973,602, filed September 19, 2007, inventor Tadao Hashimoto and Shuji Nakamura, entitled "GALLIUM NITRIDE BULK CRYSTALS AND THEIR GROWTH METHOD", Agent Management No. 30794.244- US-P1 (2007-809-1);

  U.S. Patent Application Serial No. 11 / 977,661, filed October 25, 2007, inventor Tadao Hashimoto, entitled "METHOD FOR GROWING GROUP III-NITRIDE CRYSTALS IN A MIXTURE OF SUPER CRITICAL AMMONIA AND NITROGEN, AND GROUP III -NITRIDE CRYSTALS GROWN THEREBY ", Agent management number 30794.253-US-U1 (2007-774-2);

  U.S. Patent Application No. 61 / 067,117, filed Feb. 25, 2008, inventor Tadao Hashimoto, Edward Letts, Masanori Ikari, title of the invention "METHOD FOR PRODUCING GROUP III-NITRIDE WAFERS AND GROUP III-NITRIDE WAFERS", Agent management number 62158-30002.00 or SIXPOI-003;

  U.S. Patent Application Serial No. 61 / 058,900, filed June 4, 2008, inventor Edward Letts, Tadao Hashimoto, Masanori Ikari, title of the invention "METHODS FOR PRODUCING IMPROVED CRYSTALLINITY GROUP III-NITRIDE CRYSTALS FROM INITIAL GROUP III-NITRIDE SEED BY AMMONOTHERMAL GROWTH ", agent management number 62158-30004.00 or SIXPOI-002;

  U.S. Patent Application Serial No. 61 / 058,910, filed June 4, 2008, Tadao Hashimoto, Edward Letts, Masanori Ikari, entitled "HIGH-PRESSURE VESSEL FOR GROWING GROUP III NITRIDE CRYSTALS AND METHOD OF GROWING GROUP III NITRIDE CRYSTALS USING HIGH-PRESSURE VESSEL AND GROUP III NITRIDE CRYSTAL ", Agent Control Number 62158-30005.00 or SIXPOI-005 (issued as US Patent No. 8,236,237);

  U.S. Patent Application Serial No. 61 / 131,917, filed 12 June 2008, inventor Tadao Hashimoto, Masanori Ikari, Edward Letts, entitled "METHOD FOR TESTING III-NITRIDE WAFERS AND III-NITRIDE WAFERS WITH TEST DATA ", Agent control number 62158-30006.00 or SIXPOI-001;

  U.S. Patent Application Serial No. 61 / 106,110, filed October 16, 2008, inventor Tadao Hashimoto, Masanori Ikari, Edward Letts, entitled "REACTOR DESIGN FOR GROWING GROUP III NITRIDE CRYSTALS AND METHOD OF GROWING GROUP III NITRIDE CRYSTALS ", Agent Management No. SIXPOI-004;

  U.S. Patent Application Serial No. 61 / 694,119, filed August 28, 2012, inventor Tadao Hashimoto, Edward Letts, Sierra Hoff, entitled "GROUP III NITRIDE WAFER AND PRODUCTION METHOD", Attorney Management No. SIXPOI -015;

  U.S. Patent Application Serial No. 61 / 705,540, filed September 25, 2012, inventor Tadao Hashimoto, Edward Letts, Sierra Hoff, entitled "METHOD OF GROWING GROUP III NITRIDE CRYSTALS," Agent Management Number SLXPOI-014;

  These applications are incorporated herein by reference in their entirety, as if fully set forth below.

(Technical field)
The present invention is a substrate or semiconductor material of semiconductor material used to produce semiconductor wafers for various devices, including optoelectronic devices such as light emitting diodes (LEDs) and laser diodes (LDs) and electronic devices such as transistors. For bulk crystals. More specifically, the present invention provides crystals of Group III nitrides, such as gallium nitride. The invention also provides various methods of making these crystals.

This document refers to several publications and patents as indicated with the numbers in parentheses, eg [x]. The following is a list of these publications and patents.
[1] R. Dwilinski, R. Doradzinski, J.A. Garczynski, L. Sierzputowski, Y. Kanbara (US Pat. No. 6,656,615)
[2] R. Dwilinski, R. Doradzinski, J.A. Garczynski, L. Sierzputowski, Y. Kanbara (US Patent No. 7,132,730)
[3] R. Dwilinski, R. Doradzinski, J.A. Garczynski, L. Sierzputowski, Y. Kanbara (US Patent No. 7,160, 388)
[4] K. Fujito, T. Hashimoto, S. Nakamura (International Patent Application No. PCT / US2005 / 024239, WO07008198)
[5] T. Hashimoto, M. Saito, S. Nakamura (International Patent Application No. PCT / US2007 / 008743, WO07117689. See also US20070234946, US Application No. 11/784, 339 (filed on April 6, 2007).)
[6] D 'Evelyn (US Patent No. 7,078, 731)

  Each of the references listed herein is incorporated by reference in its entirety as well, particularly as it relates to the preparation and use of Group III nitride substrates, as is fully described herein.

  Gallium nitride (GaN) and its related III-nitride alloys are important materials for various optoelectronic and electronic devices such as LEDs, LDs, microwave power transistors, and solar-blind photodetectors. Currently, LEDs are widely used in displays, indicators, and general purpose lighting, and LDs are used in data storage disk drives. However, most of these devices are epitaxially grown on heterogeneous substrates such as sapphire and silicon carbide because GaN substrates are very expensive compared to these heteroepitaxial substrates. Heteroepitaxial growth of group III nitrides results in films that are significantly defective or even cracked, and hinders the realization of high performance optical and electronic devices such as high brightness LEDs for general purpose lamps or high power microwave transistors.

In order to solve any basic problems caused by heteroepitaxy, it is essential to utilize crystalline III-nitride wafers sliced from bulk III-nitride crystal ingots. For the majority of devices, a crystalline GaN wafer is preferred because it is relatively easy to control the conductivity of the wafer, and the GaN wafer will provide a minimal lattice / thermal mismatch with the device layer. . However, it is difficult to grow a GaN crystal ingot because of the high melting point and high nitrogen vapor pressure at high temperatures. Currently, most of the commercially available GaN substrates are produced by a method called hydride vapor phase epitaxy (HVPE). HVPE is one of the gas phase methods and it is difficult to reduce dislocation density to less than 10 ⁵ cm ^-2 .

In order to obtain a high quality GaN substrate having a dislocation density of less than 10 ⁵ cm ² , various growth methods such as ammonothermal growth, flux growth, high temperature solution growth, and the like have been developed. The ammonothermal method grows III-nitride crystals in supercritical ammonia [1-6]. Flux methods and high temperature solution growth use melts of Group III metals.

Recently, high quality GaN substrates with dislocation densities less than 10 ⁵ cm ^-2 can be obtained by ammonothermal growth. Because the ammonothermal method can produce true bulk crystals, it can grow one or more thick crystals, slice them, and produce GaN wafers. In ammonothermal growth, a bulk crystal of GaN is grown on a seed crystal. However, since GaN or other III-nitride crystals are virtually absent, the GaN seed crystals must be processed using other methods.

  Rapid growth of seed crystals suitable for use in ammonothermal bulk growth is difficult. Most of today's methods rely on seeds obtained from crystals formed by ammonothermal growth. Seeds thick enough for use in ammonothermal growth, for example produced by vapor phase epitaxy, typically crack, especially on the nitrogen polar face of the crystal (such as the face of the c-face). As a result, people may try to obtain a seed for amonothermal crystal growth by forming a seed in a faster growth method, but people will grow crystals faster in the ammonothermal process When producing seeds through the method, you will face a limited success rate.

  The present invention discloses group III nitride crystals that can be used for seed crystals in ammonothermal bulk growth. In addition, the present invention discloses a method of processing III-nitride crystals that can be used for seed crystals in ammonothermal bulk growth. The present invention also discloses a method of growing bulk crystals of group III nitride in supercritical ammonia using group III nitride crystals as a seed.

  In the case, the invention provides a III-nitride wafer or other substrate having a first nitrogen polar c-plane side and a second side opposite the first side. The first side has an exposed nitrogen polar face of single crystal or highly oriented polycrystalline III-Nitride. The second side has a face of the group III polar c-plane, which is either a polycrystalline phase or a non-crystalline phase of group III nitride. The structural quality of the group III nitride is highest on the first side and gradually degrades towards the second side. Structural degradation from the first side to the second side may therefore be gradual and continuous. By using this structure, the first side is free of crystal cracks.

  In some cases, a wafer or crystal as disclosed herein is a single crystal III-nitride, a first nitrogen polar surface, and an oriented polycrystalline III-nitride, a non-oriented polycrystalline III And a second surface which is a group nitride, an amorphous group III nitride, or a mixture thereof. In certain other instances, a wafer or crystal as disclosed herein is a first nitrogen polar face that is an oriented polycrystalline III-nitride, a non-oriented polycrystalline III-nitride, non-crystalline III And a second surface which is a group nitride or a mixture thereof. In either case, the second surface is of the wafer or crystal such that the wafer or crystal has a stress therein low enough so that the resulting wafer or crystal does not crack on its first nitrogen polar surface. It has a structural quality inferior to the first aspect.

  The invention also provides a method of processing the aforementioned Group III nitride crystals. By using an epitaxial growth method such as HVPE, a group III nitride crystal is grown on the substrate with the group III polar face exposed. By varying the growth conditions, such as temperature and / or ambient oxygen concentration, during growth, the structural quality is gradually degraded, preferably continuously through growth. Group III nitride crystals grown on a substrate may split into two wafers upon cooling inside the epitaxial growth reactor or outside the epitaxial growth reactor, depending on cooling inside the epitaxial growth reactor . One of the split wafers has a first side that exposes the nitrogen polar c-plane and a second side that exposes the group III polar c-plane polycrystalline or non-crystalline phase of the group III nitride. .

In addition, the present invention provides a method of growing bulk crystals of III-nitrides, such as gallium nitride, in supercritical ammonia using the aforementioned III-nitride crystals.
The present invention provides, for example, the following.
(Item 1)
Group III nitride crystal, and
(A) a first side having an exposed nitrogen polar c-plane surface with a miscut angle less than +/- 5 degrees;
(B) an exposed group III polar c-plane surface of said group III nitride, a polycrystalline phase, or a second side opposite said first side having an amorphous phase;
Group III nitride crystal, wherein the crystalline structure quality of the first side is superior to the crystalline structure quality of the second side.
(Item 2)
3. The group III nitride crystal according to item 1, wherein the first side surface is free of cracks.
(Item 3)
3. A III-nitride crystal according to item 1 or 2, wherein the crystal quality gradually deteriorates from the first side to the second side of the III-nitride crystal.
(Item 4)
3. The group III nitride crystal according to any one of items 1 to 3, wherein the oxygen concentration on the first side is lower than the oxygen concentration on the second side.
(Item 5)
The group III nitride crystal according to item 4, wherein the oxygen concentration on the second side is 10 times or more higher than the oxygen concentration on the first side.
(Item 6)
The half width of the X-ray rocking curve of the 002 reflection from the first side is smaller than the half width of the X-ray rocking curve of the 002 reflection from the second side according to any one of items 1 to 5. Group III nitride crystals.
(Item 7)
Item III. The III-nitride crystal of item 6, wherein the FWHM of the 002 reflection X-ray rocking curve from the first side is less than 1000 arcsec.
(Item 8)
Item III. The III-nitride crystal of item 7, wherein the FWHM of the 002 reflection X-ray rocking curve from the first side is less than 500 arcsec.
(Item 9)
9. The III-nitride crystal of item 8, wherein the FWHM of the 002 reflection X-ray rocking curve from the second side is greater than 500 arcsec.
(Item 10)
9. The III-nitride crystal of any of paragraphs 6-8, wherein the FWHM of the 002 reflection X-ray rocking curve from the second side is greater than 1000 arcsec.
(Item 11)
7. The Group III nitride crystal according to any one of Items 1 to 6, wherein the thickness of the crystal is more than 0.1 mm.
(Item 12)
The III-nitride crystal according to item 11, wherein the crystal is more than 0.5 mm thick.
(Item 13)
The group-III nitride crystal according to item 11, wherein the crystal is more than 1 mm thick.
(Item 14)
A III-nitride crystal according to any one of the preceding claims, wherein said first side is sufficiently polished such that said first side is suitable for ammonothermal growth of bulk crystals. .
(Item 15)
15. A III-nitride crystal according to any one of items 1 to 14, wherein the crystal is processed by hydride vapor phase epitaxy.
(Item 16)
16. Group III nitride crystal according to any one of items 1 to 15, wherein the transition of crystal quality from the first side to the second side is continuous.
(Item 17)
The group-III nitride crystal according to any one of items 1 to 16, wherein the group-III nitride is GaN.
(Item 18)
Item 19. The Group III nitride crystal according to any one of Items 1 to 17, wherein the crystal is free of cracks throughout the crystal.
(Item 19)
19. A crystalline III-nitride wafer according to any one of items 1 to 18.
(Item 20)
20. The group III nitride wafer according to item 19, wherein the wafer is a single crystal group III nitride wafer.
(Item 21)
A method of processing a group III nitride crystal, comprising
(A) growing a single crystal or highly oriented polycrystalline III-nitride layer on a substrate, the exposed surface of said layer being a III-polar c-plane,
(B) A single crystal or highly oriented polycrystalline group III having a crystal structure which is gradually degraded such that the exposed surface of the crystal is a group III polar c-plane, polycrystalline phase or non-crystalline phase Further growing nitride;
(C) removing the substrate to obtain a crystal having a first nitrogen polar c-plane surface and a second group III polar c-plane surface of the group III nitride, a polycrystalline phase, or an amorphous phase And, including, how.
(Item 22)
A method of processing a III-nitride crystal according to claim 21, wherein steps (a) and (b) are performed using hydride vapor phase epitaxy.
(Item 23)
23. A method of processing a group III nitride crystal according to item 21 or 22, wherein the substrate is a heterogeneous substrate.
(Item 24)
24. A method of processing a III-nitride crystal according to any one of items 21 to 23, wherein step (c) comprises self-separation of the substrate upon or after cooling.
(Item 25)
24. A method of processing a Group III nitride crystal according to any one of items 21 to 23, wherein the step (c) comprises grinding the substrate.
(Item 26)
24. A method of processing a III-nitride crystal according to any one of items 21 to 23, wherein step (c) comprises laser lift-off of the substrate.
(Item 27)
27. A method of processing a III-nitride crystal according to any one of items 21 to 26, wherein said step (b) is performed at a lower temperature than that of step (a).
(Item 28)
30. A method of processing a III-nitride crystal according to claim 27, wherein the temperature in step (b) is gradually reduced during growth.
(Item 29)
29. A method of processing a III-nitride crystal according to claim 28, wherein the temperature in step (b) is reduced linearly during growth.
(Item 30)
30. A method of processing a III-nitride crystal according to any of paragraphs 21 to 29, wherein said step (b) is performed at an oxygen concentration higher than that of step (a).
(Item 31)
34. A method of processing a III-nitride crystal according to item 30, wherein the oxygen concentration in step (b) is gradually increased during growth.
(Item 32)
34. A method of processing a III-nitride crystal according to item 31, wherein the oxygen concentration is increased linearly.
(Item 33)
(A) grinding the second surface;
(B) grinding the first surface;
(C) lapping the first surface;
33. A method of processing a Group III nitride crystal according to any one of Items 21 to 32, further comprising
(Item 34)
34. A method of processing a group III nitride crystal according to any one of items 21 to 33, wherein the group III nitride is GaN.
(Item 35)
34. A III-nitride crystal formed by the method of any of items 21-34.
(Item 36)
38. A method of processing bulk crystals of group III nitride in supercritical ammonia, using the group III nitride crystal according to any one of items 1 to 19 and 35 as a seed crystal in said supercritical ammonia.
(Item 37)
The method according to any one of items 21 to 34 and 36, wherein the group III nitride is GaN.
(Item 38)
A method of processing a bulk crystal of gallium nitride in a high pressure reactor, comprising:
(A) placing at least one gallium nitride seed crystal in the high pressure reactor;
(B) installing at least one type of mineralizer in the high pressure reactor;
(C) installing at least one flow restriction plate in the high pressure reactor;
(D) placing a gallium-containing nutrient in the high pressure reactor;
(E) installing ammonia in the high pressure reactor;
(F) sealing the high pressure reactor;
(G) heating the high pressure reactor with an appropriate temperature difference between the area for the seed crystal and the area for the nutrient;
The crystal structure quality of the nitrogen polar surface of the gallium nitride seed crystal is superior to the crystal structure quality of the gallium polar surface of the seed crystal.
(Item 39)
39. A method of processing a bulk crystal of gallium nitride according to item 38, wherein the nitrogen polar surface of the gallium nitride seed crystal is free of cracks.
(Item 40)
38. A method of processing a bulk crystal of gallium nitride according to item 38 or 39, wherein the oxygen concentration of the nitrogen polar surface of the gallium nitride seed crystal is less than the oxygen concentration of the gallium polar surface.
(Item 41)
The method for processing a bulk crystal of gallium nitride according to Item 40, wherein the oxygen concentration on the gallium polar surface is 10 times or more higher than the oxygen concentration on the opposite side.
(Item 42)
The gallium nitride according to item 38 or 39, wherein the half width of the 002 reflection X-ray rocking curve from the nitrogen polar surface of the gallium nitride seed crystal is smaller than the half width of the 002 reflection X-ray rocking curve from the opposite side How to process bulk crystals.
(Item 43)
43. A method of processing a bulk crystal of gallium nitride according to any one of Items 38 to 42, wherein the thickness of the gallium nitride seed crystal is more than 0.1 mm.
(Item 44)
45. A method according to item 43, wherein the thickness of the gallium nitride seed crystal is at least 0.5 mm.
(Item 45)
45. A bulk crystal of gallium nitride according to any one of items 38 to 43, wherein the nitrogen polar surface of the gallium nitride seed crystal is polished to obtain a surface suitable for amonothermal growth of bulk crystal. How to process.
(Item 46)
46. A method of processing a bulk crystal of gallium nitride according to any one of Items 38 to 45, wherein the gallium nitride seed crystal is processed by hydride vapor phase epitaxy.
(Item 47)
46. A method of processing a bulk crystal of gallium nitride according to any one of items 38 to 46, wherein the transition of crystal quality from the nitrogen polar surface to the opposite side of the gallium nitride seed crystal is gradual.

  Reference will now be made to the drawings in which like reference numerals represent corresponding parts throughout.

FIG. 1 is a schematic view of a group III nitride crystal.

In the figure, each number represents the following.
1. Group III nitride crystal 1A. The first side 1 B.1 of the crystal exposing the nitrogen polar c-plane surface. The second side opposite to the first side

FIG. 2 is a schematic view of the III-Nitride and substrate depicted in steps AE during processing of III-Nitride crystals.

In the figure, each number represents the following.
2. Substrate 3. Group III nitrides grown on a substrate III-Nitride grown with changing growth parameters such that the structural quality gradually and continuously deteriorates along the growth direction. Depending on the cooling, or afterwards, the place of separation that may occur. One of the split wafers containing a substrate After the group III nitride wafer 6 is separated from the substrate, the group III nitride layer remaining on the substrate 2

(Overview)
Invention III-nitride crystals are typically used as seed crystals for ammonothermal bulk growth. The Group III nitride is typically GaN but any of the Group III nitrides represented as Ga _x Al _y In _1-x-y N (0 ≦ x ≦ 1, 0 ≦ x + y ≦ 1) It can be a solid solution of The III-nitride crystal has a first side that exposes the nitrogen-polar surface of the c-plane, and a III-polarity of either the c-plane of the III-nitride, polycrystalline phase or amorphous phase (eg, In the case of GaN, the second side to expose the Ga polarity) surface is provided. Group III nitride crystals have a first face of nitrogen polarity of high structural quality and a second face of inferior structural quality. Using the present structure, the cracks exposed on the first side of the crystal can be eliminated.

  The structural quality of the first side is higher than that of the second side. “Structural quality” is the perfection of atomic arrangement within the bulk crystal (the overall uniformity of the unit cell of the crystal lattice across the plane of the bulk crystal, the plane being the surface of the substrate on which the bulk crystal is grown) (Parallel with), which can be evaluated using an X-ray rocking curve or other analysis method. When evaluated using an x-ray rocking curve, the FWHM of the 002 reflection rocking curve is less for the first side than the second side. The properties of Group III nitride crystals described herein may be suitable for use as seed crystals in ammonothermal bulk growth.

  Epitaxial growth methods such as HVPE can be used to process the aforementioned Group III nitride crystals. Other methods such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxial growth (MBE), flux method, high pressure solution growth, sputtering are also methods with different substrates such as sapphire, silicon carbide, silicon and gallium arsenide It can be used as long as it is compatible.

  The structural quality is degraded along the growth direction by changing the growth conditions as more III-nitride is deposited on the substrate. The growth conditions are changed to gradually degrade the structural quality such that the III-nitride has high quality in the plane parallel to the surface of the substrate but with inferior quality in the plane further from the substrate (Ie, unit cells become less uniform or perfect in new growth as growth proceeds, as shown, for example, by XRD results). The structural quality may be continuously degraded from the high quality surface to the surface further away from the substrate. The change may be, for example, linear, exponential, or other continuous function. The structural quality may alternatively be changed stepwise, preferably in small amounts, gradually. A sufficient amount of Group III nitride is deposited on the substrate to form a Group III nitride wafer that can be used in subsequent ammonothermal growth using the wafer. The quality is high quality group III nitride at or near the separation point from the substrate (the first side of the separated wafer will come), but the bulk group III nitride of the wafer at the second side Is degraded at such a rate to provide a sufficiently low quality to have low stress. The low stress level prevents the first nitrogen polar surface from cracking when the wafer is separated from the substrate on which the wafer was grown, but still high quality III-Nitride with its first nitrogen polarity. SUMMARY A wafer suitable for use in an ammonothermal process for growing on a surface is provided. The obtained group III nitride crystal thus maintains the crystal growth conditions constant during crystal growth, or adjusts the conditions during the crystal growth, with the first face of high structural quality nitrogen polarity, and the structure quality of the new growth An improved second version of the inferior structural quality with lower stress than the comparative crystal formed. The resulting crystals are also thick enough to be used as a seed in the subsequent ammonothermal growth of III-Nitride on its first nitrogen polar surface. The growth temperature and / or the concentration of impurities such as oxygen in the ambient gas may be varied during growth to degrade crystal quality. For example, the growth temperature can be lowered during group III nitride growth to reduce the crystal quality of the group III polar face. Alternatively, or in addition, during growth, the oxygen concentration in the environment may be increased to reduce the crystal quality of the group III polar face. The growth conditions can be continuously changed and the crystal quality can be degraded further from the substrate. The change may be linear, exponential, or other continuous function, such as by decreasing the temperature linearly or increasing the concentration of oxygen in the environment linearly. The change in growth conditions may alternatively be gradually, preferably stepwise, in stages. The resulting III-nitride substrate may thus have good crystalline quality on the nitrogen polar surface of the substrate, lower stress in III-nitride and inferior crystalline quality on III-polar surface it can.

  Group III nitride crystals grown on the substrate, depending on cooling, or later, may possibly have a graded structure, substrate and group III nitride, after growth on the foreign substrate is complete, or after cooling. Can be split into two fragments (referred to as self-separating) due to the thermal expansion difference between and / or the lattice constant difference between the substrate and the III-nitride. Self-separation often occurs when a dissimilar substrate is used to make a crystal or wafer so that the Group III nitride layer 7 is thicker than the Group III nitride layer 3 on the substrate 2 as shown in FIG. It occurs in the new group III nitride deposited on the group III nitride layer 7. The layer 7 in this case may comprise the group III nitride layer 3 originally deposited on the substrate 2 and a portion of the new group III nitride grown on the layer 3. If self-separation does not occur, the substrate can be removed using conventional removal methods such as grinding or laser lift-off.

The aforementioned Group III crystals are suitable as seeds for ammonothermal bulk GaN growth. By using an ammonothermal method such as that disclosed in US Patent Application No. 61 / 058,910 (now US Patent No. 8,236,237), bulk crystals of Group III nitrides can be It may be grown on a crystal. Due to the crack free surface on the first side and higher structural quality, bulk crystals grown on such seeds exhibit good crystal quality.
(Technical Description of the Invention)

  An outline of the group III nitride crystal in the present invention is presented in FIG. The III-nitride crystal has a first side (1A) exposing the nitrogen-polar c-plane of the III-nitride, with a miscut angle of less than +/- 5 degrees. The crystal also has a second side (IB) opposite to the first side, which exposes either the group III polar c-plane of the group III nitride, the polycrystalline phase or the amorphous phase.

  The first side is a single crystal or highly oriented polycrystalline III-nitride and the second side is a single crystal, polycrystalline or non-crystalline III-nitride. The structural quality on the first side is higher than on the second side. Here, structural quality refers to the perfection of the atomic arrangement in the crystal and is typically characterized using X-ray diffraction or other analytical methods. For X-ray diffraction, the FWHM of the X-ray rocking curve from the 002 reflection is recorded from both sides. The FWHM from the first side is smaller than that from the second side. The FWHM from the first side is typically less than 1000 arcsec, preferably less than 500 arcsec, more preferably less than 200 arcsec. The FWHM from the second side is typically greater than 500 arcsec, preferably 1000 arcsec. If the second surface is either a polycrystalline phase or an amorphous phase, the 002 peak in the x-ray can not be detected. This means that the structural quality is inferior. The crystal quality on the first side is shown to be higher than on the second side, even if other analysis methods are used. The change in the structural quality from the first side to the second side is preferably gradual and may also be gradual or continuous.

  The non-uniform structural quality along the c-axis direction is to eliminate the cracks on the first side, as the low quality crystals beneath the first side act as a buffer to reduce the residual stress in the crystal. Help.

  The thickness of the group III nitride crystal is typically more than 0.1 mm, preferably more than 0.3 mm, more preferably 0.4 to 1 mm, in order to maintain its shape.

  As described below, group III nitride crystals can be processed using epitaxial growth methods such as HVPE. Other methods such as MOCVD, MBE, flux methods, high pressure solution growth, or sputtering may also be used as long as these methods are compatible with different substrates such as sapphire, silicon carbide, silicon and gallium arsenide Can.

  The high structural quality and crack free properties on the first side (i.e. the nitrogen polar c-plane surface) is that bulk III-nitride crystals are typically in this method on the nitrogen polar c-plane. Because it is grown, it is useful for ammonothermal bulk growth. When Group III nitride crystals in the present invention are used as seed crystals in ammonothermal growth, the first surface is preferably lapping and for high level planarity on the surface and proper atomic arrangement. It is polished. The first side is optionally polished using chemical mechanical polishing to obtain atomically flat surfaces to remove the subsurface damage caused by the previous process. Another seed on the second side of the crystal (the second side is attached together so that the sides with inferior crystal quality face each other) or other masking material (silver foil, nickel foil, vanadium foil, or By coating with other metal foils etc., high quality bulk crystals of group III nitride can be obtained on the first side of group III nitride crystals.

  In order to process the aforementioned group III nitride crystals, epitaxial growth of group III nitride is preferably performed on the substrate using HVPE. The substrate may be a heterogeneous substrate such as sapphire, silicon carbide, silicon or gallium arsenide, or a homogeneous substrate such as GaN, A1N, InN, or a solid solution thereof. Other epitaxial growth methods such as MOCVD, MBE, flux methods, high pressure solution growth, or sputtering may also be used as long as these methods are compatible with dissimilar substrates such as sapphire, silicon carbide, silicon, and gallium arsenide be able to.

  FIG. 2 shows a specific sequence of process steps in the method according to the invention. FIG. 2A shows the substrate 2 prior to the growth of III-nitrides. In an epitaxial growth reactor, such as a HVPE reactor, a single crystal or highly oriented polycrystalline III-nitride layer 3 is grown. The growth temperature is typically 950 to 1150 ° C. After this step, the growth conditions such as temperature are gradually reduced, and / or the concentration of impurities in the ambient gas is gradually increased to gradually deteriorate the structural quality, and group III nitride crystal layer 4 Form. A gradual change in structural quality is depicted by crystal color darkening in the growth direction. After the growth is finished, the group III nitride crystal on the substrate is cooled. During or after the cooling process, the III-nitride crystal may crack along the horizontal line 5 and result in splitting into two wafers. One wafer 6 contains a substrate, and the other wafer is a group III nitride crystal in the present invention. We call this division self-separation.

  If self-separation does not occur, the substrate can be removed using conventional methods such as mechanical grinding and laser lift-off. After removal of the substrate, the Group III nitride crystals in the present invention are obtained.

  The present group III nitride crystals can be used as seed crystals in ammonothermal growth of bulk GaN. As disclosed in US Patent Application No. 61 / 058,910 (now US Patent No. 8,236,237), for example, seed crystals, mineralizers such as sodium metal, flow restriction devices such as baffles, poly Gallium-containing nutrients such as crystalline GaN and ammonia are loaded into the high pressure reactor. The inside of the high pressure reactor is divided into at least two zones: a seed zone and a nutrient zone. In the case of ammonobasic conditions (ie using alkali metals or alkaline earth metals such as mineralizers), the seed area is located below the nutrient area. The baffle separates these two areas. The high pressure reactor is heated to provide the proper temperature differential and to grow the group III nitrides.

  In the case of ammonobasic growth of GaN, bulk GaN crystals typically exhibit better quality on the nitrogen plane than on the gallium plane. Therefore, the group III nitride crystal in the present invention is useful for ammonothermal growth. By covering the group III polarity side of the crystal, high quality GaN crystals can be selectively grown on the nitrogen polarity side. There are several ways to mask group III polar faces. One method is to make one hybrid seed, depositing two seeds together on the III-polarity side and exposing the nitrogen polar surface on both sides. Another method is to mount the seed crystal on a metal plate such as vanadium, nickel, silver, and nickel-chromium alloy with the nitrogen polar face up. After ammonothermal growth, bulk GaN crystals are obtained on the nitrogen side of III-nitride crystals.

Example 1 (Growth Number 0858)
GaN crystals were grown by HVPE. A 2 inch c-plane sapphire substrate with a GaN layer grown by MOCVD was loaded into the HVPE reactor. After gradually increasing the substrate temperature to about 1000 ° C. under a constant flow of ammonia and nitrogen, gallium chloride gas was introduced to grow single crystal GaN. After 3 hours of growth, the growth temperature was gradually lowered over 13 hours. The temperature was linearly decreased by 100 ° C. over 13 hours, resulting in a 100 ° C. temperature drop per 13 hours. After a total of 16 hours of growth (3 hours of constant temperature and 13 hours of graded temperature), the gallium chloride supply was stopped and the furnace was turned off. At about 800 ° C., the ammonia feed was turned off. The GaN crystal was cooled in the reactor until the temperature reached about 300 ° C. When the crystals were removed from the reactor, the GaN crystals self-separated from the substrate portion.

Since the substrate portion has a layer of GaN, self-separation occurred at some point inside the GaN crystal. The thickness of c-plane sapphire is 0.45 mm, the thickness of the portion containing sapphire is 0.89 mm, and the thickness of the GaN crystal separated from the substrate is 1.78 mm The The first side of the GaN crystal showed a clear color, while the second side of the GaN crystal showed a greyish / blackish color. Clear GaN crystals contain less than about 10 ¹⁷ cm ⁻³ oxygen, while greyish / blackish GaN contains more than about 10 ¹⁹ cm ⁻³ oxygen. X-ray measurements showed a 002 peak from the first side (nitrogen polar side) but no peak from the second side. This means that the second side surface is coated with either polycrystalline or amorphous GaN. The first side had no cracks. The miscut angle measured using the X-ray rocking curve was within +/- 5 degrees.
(Example 2) (Crystal grinding / lapping)

Both sides of the GaN crystal were ground using a diamond grinder to obtain a GaN wafer having a thickness of 1.1 mm. The FWHM of the X-ray rocking curve from the first side was 1382 arcsec while the second side did not show the 002 peak. Then, both sides of the GaN crystal wafer were further ground and lapped using a diamond slurry. The total thickness was 0.85 mm, the Ra roughness on the nitrogen side was 0.5 to 0.8 nm, and the Ra roughness on the gallium side was 0.8 to 1.2 nm. The FWHM of the X-ray rocking curve from the first side improved to 1253 arcsec. The first side did not have any cracks.
(Example 3) (Amnothermal growth using the obtained GaN crystal)

The GaN crystal wafer obtained in Example 2 was used as a seed crystal for ammonothermal bulk growth. A high pressure reactor was charged with seeds, sodium metal, baffles, polycrystalline GaN nutrient, and ammonia. The high pressure reactor was then sealed tightly and heated to about 550 ° C. After 11 days of growth, bulk GaN crystals having a thickness of about 2.07 mm were obtained. The FWHM of the X-ray rocking curve from the first side improved to 1048 arcsec. The crystals also had no cracks.
(Example 4) (Growth No. 0895)

Similar to Example 1, a GaN crystal was grown by HVPE. A 2 inch c-plane sapphire substrate with a GaN layer grown by MOCVD was loaded into the HVPE reactor. Growth conditions and duration were identical to Example 1, but the substrate and new crystals did not completely separate. The thickness excluding the sapphire substrate portion was 2.63 mm. The FWHM of the X-ray rocking curve from the 002 reflection on the first side was about 925 arcsec, while the FWHM on the second side was 1580 arcsec. In this case, the Ga polar side had low quality crystalline GaN (i.e. highly oriented polycrystalline) on the exposed second side. The residual sapphire substrate was removed using a diamond grinder and then both sides of the GaN crystal were also ground to obtain a 0.44 mm thick wafer.
Advantages and improvements

Group III nitride crystals of the present invention have higher structural quality on nitrogen polar surfaces and are free of cracks. Such crystals are suitable for seed crystals in ammonothermal bulk growth. The method of processing group III nitride crystals in the present invention uses epitaxial growth of group III nitride on a substrate followed by self-separation or removal of the substrate. By gradually changing the growth conditions during crystal growth, the structural quality is gradually degraded, thus avoiding cracking on the first side of the crystal. By using such crystals for ammonothermal bulk growth, bulk crystals of high quality Group III nitrides such as GaN can be obtained.
Possible corrections

  Although the examples illustrate crystals of GaN, similar advantages of the present invention can also be expected for other III-nitride alloys of various compositions such as AlN, AlGaN, InN, InGaN, or GaAlInN. .

  Although the preferred embodiment describes HVPE as an epitaxial growth method, other methods such as MOCVD, MBE, flux methods, high pressure solution growth, or sputtering can also be used as long as they are compatible with the foreign substrate.

  Although the preferred embodiment describes a seed crystal having a diameter of 2 inches, similar advantages of the present invention are also anticipated for larger diameters such as 4 inches, 6 inches, and more.

  While the preferred embodiment describes X-ray characterization of structural quality, other methods such as Rutherford backscattering (RBS), reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM), etc. also surface structure It can be used to assess quality.

  Although the example describes diamond grinding to remove a sapphire substrate, laser lift off or other methods can also be used to remove the substrate.

  It is not essential to start the process using a heterogeneous substrate on which the III-nitride material is deposited. Starting from the substrate, producing high structural quality Group III nitrides, then adjusting the deposition conditions, conditions to gradually form inferior structure quality Group III nitrides as additional Group III nitride deposition occurs. , III-Nitride can also begin to form directly on the substrate. Furthermore, it is not essential to start with a heterogeneous substrate. Group III nitride substrates are used to grow on the Group III polar face of the substrate to form high quality Group III nitrides, then change the growth conditions and have inferior quality Group III nitrides in subsequent growth May be formed gradually.

Claims (13)

A method of processing a group III nitride crystal, comprising
(A) growing a single crystal or highly oriented polycrystalline III-nitride layer on a substrate, the exposed surface of said layer being a III-polar c-plane,
(B) A single crystal or highly oriented polycrystalline group III having a crystal structure which is gradually degraded such that the exposed surface of the crystal is a group III polar c-plane, polycrystalline phase or non-crystalline phase Further growing nitride;
(C) removing the substrate to obtain a crystal having a first nitrogen polar c-plane surface and a second group III polar c-plane surface of the group III nitride, a polycrystalline phase, or an amorphous phase When, only contains the step (b) is carried out at a temperature lower than that of step (a), method. Step (a) and (b) is carried out using a hydride vapor phase epitaxy, a method of processing a group III nitride crystal according to claim 1. The substrate is a heterogeneous substrate, a method of processing a group III nitride crystal according to claim 1 or 2. Wherein said step (c), depending on the cooling or after cooling, including self separation of the substrate, processing the III-nitride crystal according to any one of claims 1 3. The method for processing a Group III nitride crystal according to any one of claims 1 to 3 , wherein the step (c) comprises grinding the substrate. The method for processing a III-nitride crystal according to any one of claims 1 to 3 , wherein said step (c) comprises laser lift-off of said substrate. The method for processing III-nitride crystals according to claim 1 , wherein the temperature in step (b) is gradually lowered during the growth. The method for processing III-nitride crystals according to claim 7 , wherein the temperature in step (b) is linearly reduced during the growth. Wherein step (b) is carried out at a higher oxygen concentration than that of step (a), a method of processing a Group III nitride crystal according to any one of claims 1 to 8. 10. The method of processing a III-nitride crystal according to claim 9 , wherein the oxygen concentration in step (b) is gradually increased during growth. 11. The method of processing a III-nitride crystal according to claim 10 , wherein the oxygen concentration is increased linearly. (A) grinding the second surface;
(B) grinding the first surface;
(C) lapping the first surface;
The method of processing the group III nitride crystal according to any one of claims 1 to 11 , further comprising The method of processing a group III nitride crystal according to any one of claims 1 to 12 , wherein the group III nitride is GaN.

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