JP2017536325A - Group III nitride crystals, methods for their production, and methods for producing bulk Group III nitride crystals in supercritical ammonia - Google Patents

Abstract

In one case, the present invention provides a first side that exposes the nitrogen polar c-plane of a single crystal or highly oriented polycrystalline group III nitride, and a group III polar surface, polycrystalline phase, or non-phase of the group III nitride. A III-nitride crystal is provided having a second side that exposes the crystalline phase. Such a structure is useful as a seed crystal for ammonothermal growth of bulk III-nitride crystals. The present invention also discloses a method for processing such crystals. The present invention also discloses a method for processing a group III nitride bulk crystal by an ammonothermal method using such a crystal.

Description

(Cross-reference of related applications)
This application is a US application serial number 62 / 086,699, the title of the invention “Group III Nitride Crystals, Their Fabrication Method, and Method of Fabricating Crystals in SuperCriticals in SuperCritical. , Claiming the benefit of priority to the filing date of December 2, 2014, the contents of which are hereby incorporated by reference in their entirety.

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

  PCT Practical Patent Application No. US2005 / 024239, Filing Date July 8, 2005, Inventors Kenji Fujito, Tadao Hashimoto and Shuji Nakamura, and the title of the invention “METHOD FOR GROWING GROUPS CUP Agent management number 307944.0129-WO-Ol (2005-339-1);

  US Patent Application Serial No. 11 / 784,339, Filing Date April 6, 2007, Inventors Tadao Hashimoto, Makito Saito, and Shuji Nakamura, Title of Invention “METHOD FOR GROWING LARIGAL LARGE SURCE AND LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS ", Attorney Administration No. 30794.179-US-U1 (2006-204) (This application is US Provisional Patent Application No. 60 / 790,310, filing date April 7, 2006) , Inventors Tadao Hashimoto, Makito Saito, and S Huji Nakamura, title of invention “A METHOD FOR GROWING LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS IN SUPERCRITICAL AMMONIA AND LARGE SURFACE C. claims the benefit under §119 (e));

  U.S. Patent Application No. 60 / 973,602, filing date September 19, 2007, inventors Tadao Hashimoto and Shuji Nakamura, title of the invention "GALLIUM NITRIDE BULK CRYSTALS AND THEIR GROWTH METHOD", attorney control number 30-79. US-P1 (2007-809-1);

  US Patent Application Serial No. 11 / 977,661, filing date October 25, 2007, inventor Tadao Hashimoto, title of invention "METHOD FOR GROWING GROUP III-NITRIDE CRYSTALS IN A MIXTURE OF SUPERCRITICAL AMMONIRO" -NITRIDE CRYSTALS GROWN THEREBY ", agent management number 30794.253-US-U1 (2007-774-2);

  US Patent Application No. 61 / 067,117, filing date February 25, 2008, inventor Tadao Hashimoto, Edward Letts, Masanori Ikari, title of invention "METHOD FOR PRODUCING GROUP III-NITIDE WAFERS III UPER SFR Agent management number 62158-30002.00 or SIXPOI-003;

  US Patent Application Serial No. 61 / 058,900, Filing Date June 4, 2008, Inventor Edward Letts, Tadao Hashimoto, Masanori Ikari, Title of Invention “METHODS FOR PRODUCING IMPROVED CRYSTALLINITY GRO III-NITRIDE SEED BY AMMONOTHERM GROWTH ", agent management number 62158-30004.00 or SIXPOI-002;

  US Patent Application Serial No. 61 / 058,910, Filing Date June 4, 2008, Inventor Tadao Hashimoto, Edward Letts, Masanori Ikari GROWING GROUP III NITRIDE CRYSTALS USING HIGH-PRESSURE VESSEL AND GROUP III NITRIDE CRYSTAL ”, agent management number 62158-30005.00 or SIXPOI-005 (issued as US Pat. No. 8,236,237);

  US patent application serial number 61 / 131,917, filing date June 12, 2008, inventor Tadao Hashimoto, Masanori Ikari, Edward Letts, title of invention “METHOD FOR TESTING III-NITRIDE WAFERS AND IIIWERSS AND IIIWERS TEST DATA ", agent management number 62158-30006.00 or SIXPOI-001;

  US Patent Application Serial No. 61 / 106,110, Filing Date Oct. 16, 2008, Inventor Tadao Hashimoto, Masanori Ikari, Edward Letters, Title of Invention “REACTOR DESIGN FOR GROING GROUP GROUP III NITride GROUP RID III NITRIDE CRYSTALS ", agent management number SIXPOI-004;

  US patent application serial number 61 / 694,119, filing date August 28, 2012, inventor Tadao Hashimoto, Edward Letts, Sierra Hoff, title of invention "GROUP III NITRIDE WAFER AND PRODUCTION METHOD", agent management number SIXPO -015;

  US Patent Application Serial No. 61 / 705,540, filing date September 25, 2012, inventor Tadao Hashimoto, Edward Letts, Sierra Hoff, title of invention “METHOD OF GROWING GROUP III NITRIDE CRYSTALS”, agent control number SLXPOI-014;

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

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

This document refers to several publications and patents, as indicated using numbers in parentheses, for example [x]. The following is a list of these publications and patents.
[1] R.M. Dwilinski, R.D. Doradzinski, J. et al. Garczynski, L.M. Sierzputowski, Y.M. Kanbara (US Pat. No. 6,656,615)
[2] R.A. Dwilinski, R.D. Doradzinski, J. et al. Garczynski, L.M. Sierzputowski, Y.M. Kanbara (US Pat. No. 7,132,730)
[3] R.M. Dwilinski, R.D. Doradzinski, J. et al. Garczynski, L.M. Sierzputowski, Y.M. Kanbara (US Pat. No. 7,160,388)
[4] K.K. Fujito, T .; Hashimoto, S.H. Nakamura (International Patent Application No. PCT / US2005 / 024239, WO07008198)
[5] T.M. Hashimoto, M .; Saito, S .; Nakamura (International Patent Application No. PCT / US2007 / 008743, WO07117869. See also US20070234946, U.S. Application No. 11 / 784,339 (filed Apr. 6, 2007).)
[6] D'Evelyn (US Pat. No. 7,078,731)

  Each of the references listed herein is incorporated by reference in its entirety as if fully set forth herein, particularly with respect to its description of how to make and use a III-nitride substrate.

  Gallium nitride (GaN) and its related group 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 lighting, and LDs are used in data storage disk drives. However, most of these devices are epitaxially grown on dissimilar substrates such as sapphire and silicon carbide because GaN substrates are very expensive compared to these heteroepitaxial substrates. Group III nitride heteroepitaxial growth results in films with significant defects or even cracks, hampering the realization of high performance optical and electronic devices such as high intensity LEDs for general purpose lamps or high power microwave transistors.

In order to solve any fundamental problems caused by heteroepitaxy, it is essential to utilize a crystalline group III nitride wafer sliced from a bulk group III nitride crystal ingot. For the majority of devices, crystalline GaN wafers are preferred because it is relatively easy to control the conductivity of the wafer, and GaN wafers will provide minimal lattice / thermal mismatch with the device layers. . However, it is difficult to grow GaN crystal ingots due to 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 the 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, and high temperature solution growth have been developed. The ammonothermal method grows group III nitride crystals in supercritical ammonia [1-6]. The flux method and high temperature solution growth use a Group III metal melt.

Recently, high quality GaN substrates with dislocation density of less than 10 ⁵ cm ⁻² can be obtained by ammonothermal growth. Because the ammonothermal method can produce true bulk crystals, one or more thick crystals can be grown and sliced to produce a GaN wafer. In ammonothermal growth, a bulk crystal of GaN is grown on a seed crystal. However, since GaN or other group III nitride crystals are virtually absent, GaN seed crystals must be processed using other methods.

  It is difficult to rapidly grow seed crystals suitable for use in ammonothermal bulk growth. Most methods today rely on seeds obtained from crystals formed by ammonothermal growth. For example, seeds that are sufficiently thick for use in ammonothermal growth, produced by vapor phase epitaxy, typically crack, especially on the nitrogen polar face (such as the c-plane face) of the crystal. As a result, people may try to obtain seeds for ammonothermal crystal growth by forming seeds in a faster growth method, but people grow crystals faster in ammonothermal processes When producing seed 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 for processing group III nitride crystals that can be used for seed crystals in ammonothermal bulk growth. The present invention also discloses a method for growing group III nitride bulk crystals in supercritical ammonia using group III nitride crystals as seeds.

  In an example, the present invention provides a III-nitride wafer or other substrate having a first nitrogen polarity 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 Group III polar c-plane face in either the polycrystalline or amorphous phase of the Group III nitride. The structural quality of the III-nitride is highest on the first side and gradually deteriorates towards the second side. The structural degradation from the first side to the second side can therefore be gradual and continuous. By using this structure, crystal cracks are eliminated on the first side.

  In some cases, a wafer or crystal as disclosed herein is a single nitrogen group III nitride, a first nitrogen polar plane, an oriented polycrystalline group III nitride, a non-oriented polycrystalline group III. A second surface that is a group nitride, an amorphous group III nitride, or a mixture thereof. In certain other instances, a wafer or crystal as disclosed herein comprises a first nitrogen polar face that is an oriented polycrystalline III-nitride, an unoriented polycrystalline III-nitride, an amorphous III And a second surface which is a group nitride or a mixture thereof. In either case, the second surface is such that the wafer or crystal has a sufficiently low stress therein to prevent the resulting wafer or crystal from cracking on its first nitrogen polar surface. The structural quality is inferior to that of the first surface.

  The invention also provides a method of processing the aforementioned group III nitride crystal. By using an epitaxial growth method such as HVPE, the group III nitride crystal is grown on the substrate with the group III polar face exposed. By changing growth conditions such as temperature and / or ambient oxygen concentration during growth, the structure quality is gradually and preferably continuously degraded throughout the growth. Group III nitride crystals grown on the substrate can split into two wafers after 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 amorphous phase of the group III nitride. .

  In addition, the present invention provides a method for growing a group III nitride bulk crystal such as gallium nitride in supercritical ammonia using the group III nitride crystal described above.

  Reference is now 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 of the crystal that exposes the nitrogen polar c-plane surface 1B. 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 the III-nitride crystal.

In the figure, each number represents the following.
2. Substrate 3. 3. Group III nitride grown on substrate. Group III nitride grown with varying growth parameters so that the structural quality gradually and continuously degrades along the growth direction. 5. Location of separation that can occur in response to or after cooling 6. one of the split wafers containing the substrate; The group III nitride layer remaining on the substrate 2 after the group III nitride wafer 6 is separated from the substrate

(Overview)
The inventive group 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-xy N (0 ≦ x ≦ l, 0 ≦ x + y ≦ l) It can be a solid solution. The III-nitride crystal has a first side exposing the c-plane nitrogen polar surface and a group III polarity of either the c-plane, polycrystalline or amorphous phase of the III-nitride (eg, (In the case of GaN, Ga polarity) having a second side exposing the surface. The III-nitride crystal has a first surface of nitrogen polarity with high structural quality and a second surface of inferior structural quality. By using this structure, cracks exposed on the first side of the crystal can be eliminated.

  The structural quality on the first side is higher than that on the second side. “Structural quality” means the completeness of atomic arrangement in the bulk crystal (the overall uniformity of the unit cell of the crystal lattice across the plane of the bulk crystal, which is the surface of the substrate on which the bulk crystal is grown) Which can be evaluated using X-ray rocking curves or other analytical methods. When evaluated using an X-ray rocking curve, the FWHM of the 002 reflection rocking curve is smaller than the second side relative to the first side. The group III nitride crystal properties described herein may be suitable for use as seed crystals in ammonothermal bulk growth.

  In order to process the aforementioned group III nitride crystal, an epitaxial growth method such as HVPE can be used. Other methods such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), flux method, high pressure solution growth, sputtering also can be used 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 so that the III-nitride has a high quality in a plane parallel to the surface of the substrate but a poorer quality in the plane farther from the substrate. (Ie, the unit cell becomes less uniform or perfect in the new growth as it progresses, as shown, for example, by XRD results). The structural quality may be continuously degraded from a high quality surface to a surface farther from the substrate. The change may be, for example, linear, exponential, or other continuous function. The structural quality may alternatively be changed gradually, step by step, preferably incrementally. A sufficient amount of III-nitride is deposited on the substrate to form a III-nitride wafer that can be used in subsequent ammonothermal growth using the wafer. The quality is high quality III-nitride at or near the separation point from the substrate (where the first side of the separated wafer will come), but the bulk III-nitride of the wafer at the second side Is degraded at a rate that provides sufficiently low quality to have low stress. The low amount of stress prevents the first nitrogen polar face from cracking when the wafer is separated from the substrate on which the wafer is grown, but still maintains high quality III-nitride in its first nitrogen polarity. A wafer suitable for use in an ammonothermal method of growing on a surface is provided. The resulting III-nitride crystal is therefore the first surface of high structural quality nitrogen polarity and the crystal growth conditions remain constant during crystal growth, or the conditions are adjusted, and the new growth structural quality By having a second surface of inferior structural quality with a lower stress than the comparative crystal formed. The resulting crystal is also thick enough to be used as a seed in subsequent ammonothermal growth of III-nitrides on its first nitrogen polar face. The growth temperature and / or the concentration of impurities such as oxygen in the surrounding gas can be changed during growth to degrade the crystal quality. For example, the growth temperature can be lowered during group III nitride growth, reducing the crystal quality of the group III polar face. Alternatively or additionally, during growth, the oxygen concentration in the ambient may be increased to reduce the crystal quality of the Group III polar face. The growth conditions are continuously changed, and the crystal quality can be degraded as the distance from the substrate increases. The change may be linear, exponential, or other continuous function, such as by decreasing the temperature linearly or increasing the ambient oxygen concentration linearly. Changes in growth conditions may alternatively be changed gradually, step by step, preferably incrementally. The resulting III-nitride substrate may therefore have good crystal quality on the nitrogen polar face of the substrate, lower stress in the III-nitride, and poorer crystal quality on the III-polar face. it can.

  After the growth on the heterogeneous substrate is finished, in response to cooling or thereafter, the III-nitride crystals grown on the substrate may sometimes have a stepped structure, the substrate and the III-nitride. Can split into two pieces (referred to as self-separation) due to the difference in thermal expansion between and / or the lattice constant difference between the substrate and the group III nitride. Self-separation is often the case when a heterogeneous substrate is used to fabricate a crystal or wafer such that the III-nitride layer 7 is thicker than the III-nitride layer 3 on the substrate 2 as shown in FIG. Occurs in the new group III nitride deposited on the group III nitride layer 7. The layer 7 in this case may comprise a group III nitride layer 3 originally deposited on the substrate 2 and a part of a 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 crystal is suitable as a seed for ammonothermal bulk GaN growth. By using ammonothermal methods such as those disclosed in US patent application Ser. No. 61 / 058,910 (currently US Pat. No. 8,236,237), III-nitride bulk crystals are obtained from group III 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 show good crystal quality.
(Technical description of the present invention)

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

  The first side is a single crystal or highly oriented polycrystalline group III nitride and the second side is a single crystal, polycrystalline, or amorphous group III nitride. The structural quality on the first side is higher than that on the second side. As used herein, structural quality refers to the completeness of the atomic arrangement in the crystal and is typically characterized using X-ray diffraction or other analytical methods. In the case of 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 in either a polycrystalline phase or an amorphous phase, the 002 peak in X-rays cannot be detected. This means that the structural quality is inferior. Even when other analytical methods are used, it indicates that the crystal quality on the first side is higher than that on the second side. The change in structural quality from the first side to the second side is preferably gradual and may be gradual or continuous.

  The non-uniform structure quality along the c-axis direction eliminates cracks on the first side, as the low quality crystal just below the first side acts as a buffer to reduce residual stress in the crystal. Useful.

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

  As will be described later, the group III nitride crystal can be processed using an epitaxial growth method such as HVPE. Other methods such as MOCVD, MBE, flux method, high pressure solution growth, or sputtering should also be used as long as these methods are compatible with dissimilar substrates such as sapphire, silicon carbide, silicon, and gallium arsenide. Can do.

  High structural quality and crack-free properties on the first side (ie, the nitrogen polar c-plane surface) indicate that bulk III-nitride crystals are typically on the nitrogen polar c-plane in the present method. Because it is grown, it is beneficial for ammonothermal bulk growth. When the III-nitride crystal in the present invention is used as a seed crystal in ammonothermal growth, the first surface is preferably lapped and bonded for high levels of flatness and proper atomic arrangement on the surface. Polished. The first side is optionally polished using chemical mechanical polishing to obtain an atomically flat surface to remove subsurface damage caused by previous processes. Another seed on the second side of the crystal (the second side is attached together so that the sides with poor crystal quality face each other) or other masking material (silver foil, nickel foil, vanadium foil, or By coating with other metal foils, etc., a high quality bulk crystal of group III nitride can be obtained on the first side of the group III nitride crystal.

  In order to process the aforementioned group III nitride crystals, the group III nitride epitaxial growth is preferably carried out 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 are also 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 before the group III nitride is grown. In an epitaxial growth reactor such as an HVPE reactor, a single crystal or highly oriented polycrystalline group 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 decreased, and / or the concentration of impurities in the surrounding gas is gradually increased, and the structure quality is gradually deteriorated. Form. The gradual change in structure quality is depicted by crystal color darkening in the growth direction. After the growth is completed, the group III nitride crystal on the substrate is cooled. During or after the cooling process, the III-nitride crystals can 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 removing the substrate, the group III nitride crystal in the present invention is obtained.

  The present group III nitride crystal can be used as a seed crystal in ammonothermal growth of bulk GaN. As disclosed in US Patent Application No. 61 / 058,910 (currently US Pat. No. 8,236,237), for example, seed crystals, mineralizers such as sodium metal, flow restriction devices such as baffles, A gallium-containing nutrient such as crystalline GaN and ammonia are charged into the high pressure reactor. The inside of the high pressure reactor is divided into at least two regions, a seed region and a nutrient region. In the case of ammonobasic conditions (ie, using an alkali metal or alkaline earth metal such as a mineralizer), the seed region is located below the nutrient region. A baffle separates these two areas. The high pressure reactor is heated so that the appropriate temperature difference is provided and the group III nitride is grown.

  For ammonobasic growth of GaN, bulk GaN crystals typically exhibit superior quality on the nitrogen surface than on the gallium surface. Therefore, the group III nitride crystal in the present invention is useful for ammonothermal growth. By coating the group III polar side of the crystal, high quality GaN crystals can be selectively grown on the nitrogen polar side. There are several ways to mask the group III polar face. One method is to make one hybrid seed where both seeds are deposited on the Group III polar side and the nitrogen polar surface is exposed 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 group 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 decreased over 13 hours. The temperature was reduced linearly by 100 ° C. over 13 hours, resulting in a temperature drop rate of 100 ° C. per 13 hours. After a total of 16 hours of growth (3 hours at constant temperature and 13 hours at stepped temperature), the gallium chloride feed was stopped and the furnace was turned off. At about 800 ° C., the ammonia feed was stopped. The GaN crystal was cooled in the reactor until the temperature reached about 300 ° C. As the crystal was removed from the reactor, the GaN crystal was self-separated from the substrate portion.

Since the substrate portion has a layer of GaN, self-separation occurred somewhere inside the GaN crystal. The thickness of the 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. It was. The first side of the GaN crystal showed a clear color, while the second side of the GaN crystal showed a grayish / 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 polarity 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 was free of 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 showed no 002 peak. Next, both sides of the GaN crystal wafer were further ground and lapped with 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) (Amonothermal 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 seed, sodium metal, baffle, polycrystalline GaN nutrient, and ammonia. The high pressure reactor was then tightly sealed 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 number 0895)

Similar to Example 1, 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. Growth conditions and duration were the same as in Example 1, but the substrate and new crystals were not completely separated. 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 (ie, highly oriented polycrystal) on the exposed second surface. 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.
Benefits and improvements

The III-nitride crystals of the present invention have a higher structural quality on the nitrogen polar surface and are free of cracks. Such crystals are suitable for seed crystals in ammonothermal bulk growth. The method of processing a group III nitride crystal in the present invention uses the 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 deteriorated, thus avoiding cracking on the first side of the crystal. By using such crystals for ammonothermal bulk growth, high quality III-nitride bulk crystals such as GaN can be obtained.
Possible corrections

  While the examples illustrate GaN crystals, similar advantages of the present invention can 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 method, high pressure solution growth, or sputtering can be used as long as they are compatible with dissimilar substrates.

  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.

  Although 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. can also be applied to the surface structure. Can be used to assess quality.

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

  It is not essential to start the method using a dissimilar substrate on which the III-nitride material is deposited. Starting from the substrate, producing high structure quality III-nitride, then adjusting the deposition conditions and conditions that gradually form inferior structure quality III-nitride as further group III nitride deposition occurs It is also possible to start forming the group III nitride directly on the substrate. Furthermore, it is not essential to start with a heterogeneous substrate. Utilizing a III-nitride substrate and growing on the III-polar face of the substrate to form a high quality III-nitride, then changing the growth conditions to produce a lower quality III-nitride in subsequent growth May be formed gradually.

Claims (47)

A group III nitride crystal,
(A) a first side having an exposed nitrogen polar c-plane surface with a miscut angle less than +/− 5 degrees;
(B) a second side opposite to the first side having an exposed Group III polar c-plane surface, polycrystalline phase, or amorphous phase of the Group III nitride;
A Group III nitride crystal, wherein the crystal structure quality on the first side is superior to the crystal structure quality on the second side.   The group III nitride crystal according to claim 1, wherein the surface on the first side is not cracked.   The group III nitride crystal according to claim 1 or 2, wherein the crystal quality gradually deteriorates from the first side to the second side of the group III nitride crystal.   The group III nitride crystal according to any one of claims 1 to 3, wherein the oxygen concentration on the first side is lower than the oxygen concentration on the second side.   The group III nitride crystal according to claim 4, wherein the oxygen concentration on the second side is 10 times or more higher than the oxygen concentration on the first side.   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. Group III nitride crystals as described.   The III-nitride crystal of claim 6, wherein the FWHM of the X-ray rocking curve of the 002 reflection from the first side is less than 1000 arcsec.   8. The III-nitride crystal of claim 7, wherein the FWHM of the 002 reflection X-ray rocking curve from the first side is less than 500 arcsec.   9. The III-nitride crystal of claim 8, wherein the FWHM of the 002 reflection X-ray rocking curve from the second side is greater than 500 arcsec.   The Group III nitride crystal according to any one of claims 6 to 8, wherein the FWHM of the X-ray rocking curve of the 002 reflection from the second side exceeds 1000 arcsec.   The group III nitride crystal according to any one of claims 1 to 6, wherein a thickness of the crystal exceeds 0.1 mm.   The group III nitride crystal of claim 11, wherein the crystal is greater than 0.5 mm thick.   The III-nitride crystal of claim 11, wherein the crystal is greater than 1 mm thick.   14. The group III nitride of any one of claims 1 to 13, wherein the first side is sufficiently polished so that the first side is suitable for ammonothermal growth of bulk crystals. crystal.   15. The group III nitride crystal according to claim 1, wherein the crystal is processed by hydride vapor phase epitaxy.   The group III nitride crystal according to any one of claims 1 to 15, wherein the transition of crystal quality from the first side to the second side is continuous.   The group III nitride crystal according to any one of claims 1 to 16, wherein the group III nitride is GaN.   The group III nitride crystal according to any one of claims 1 to 17, wherein the crystal is free of cracks throughout the crystal.   A crystal group III nitride wafer according to any one of claims 1 to 18.   20. The group III nitride wafer according to claim 19, wherein the wafer is a single crystal group III nitride wafer. A method of processing a group III nitride crystal comprising:
(A) growing a single crystal or highly oriented polycrystalline group III-nitride layer on a substrate, wherein the exposed surface of the layer is a group III polar c-plane;
(B) a single crystal or highly oriented polycrystalline group III having a crystal structure that is gradually degraded so that the exposed surface of the crystal becomes a group III polar c-plane, polycrystalline phase, or amorphous phase Further growing the 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, polycrystalline phase, or amorphous phase of the group III nitride When,
Including a method.   The method of processing a group III nitride crystal according to claim 21, wherein steps (a) and (b) are performed using hydride vapor phase epitaxy.   The method for processing a group III nitride crystal according to claim 21 or 22, wherein the substrate is a heterogeneous substrate.   24. The method of processing a group III nitride crystal according to any one of claims 21 to 23, wherein step (c) includes self-separation of the substrate in response to or after cooling.   24. The method for processing a group III nitride crystal according to any one of claims 21 to 23, wherein the step (c) includes grinding the substrate.   24. The method for processing a group III nitride crystal according to any one of claims 21 to 23, wherein the step (c) includes laser lift-off of the substrate.   27. A method of processing a group III nitride crystal according to any one of claims 21 to 26, wherein step (b) is performed at a lower temperature than that of step (a).   28. The method for processing a group III nitride crystal according to claim 27, wherein the temperature in step (b) is gradually reduced during growth.   29. A method of processing a group III nitride crystal according to claim 28, wherein the temperature in step (b) is linearly reduced during growth.   30. A method of processing a group III nitride crystal according to any one of claims 21 to 29, wherein step (b) is performed at a higher oxygen concentration than that of step (a).   31. A method of processing a group III nitride crystal according to claim 30, wherein the oxygen concentration in step (b) is gradually increased during growth.   32. The method of processing a group III nitride crystal according to claim 31, wherein the oxygen concentration is increased linearly. (A) grinding the second surface;
(B) grinding the first surface;
(C) lapping the first surface;
The method for processing a group III nitride crystal according to any one of claims 21 to 32, further comprising:   34. The method for processing a group III nitride crystal according to any one of claims 21 to 33, wherein the group III nitride is GaN.   A group III nitride crystal formed by the method of any one of claims 21 to 34.   A method for processing a group III nitride bulk crystal in supercritical ammonia using the group III nitride crystal according to any one of claims 1 to 19 and 35 as a seed crystal in the supercritical ammonia. .   37. A method according to any one of claims 21 to 34 and 36, wherein the group III nitride is GaN. A method of processing a bulk crystal of gallium nitride in a high-pressure reactor,
(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) installing 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 region for the seed crystal and the region 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.   39. The method of processing a bulk crystal of gallium nitride according to claim 38, wherein the nitrogen polar surface of the gallium nitride seed crystal is free of cracks.   40. The method of processing a bulk crystal of gallium nitride according to claim 38 or claim 39, wherein an oxygen concentration of the nitrogen polar surface of the gallium nitride seed crystal is less than an oxygen concentration of the gallium polar surface.   41. The method of processing a bulk crystal of gallium nitride according to claim 40, wherein the oxygen concentration on the gallium polar surface is at least 10 times higher than the oxygen concentration on the opposite side.   40. The nitriding according to claim 38 or 39, wherein a half width of an X-ray rocking curve of 002 reflection from the nitrogen polar surface of the gallium nitride seed crystal is smaller than a half width of an X-ray rocking curve of 002 reflection from the opposite side. A method of processing gallium bulk crystals.   43. A method of processing a bulk crystal of gallium nitride according to any one of claims 38 to 42, wherein the thickness of the gallium nitride seed crystal is greater than 0.1 mm.   44. The method of claim 43, wherein the thickness of the gallium nitride seed crystal is at least 0.5 mm.   44. The gallium nitride bulk crystal of any one of claims 38 to 43, wherein the nitrogen polar surface of the gallium nitride seed crystal is polished to obtain a surface suitable for ammonothermal growth of the bulk crystal. How to process.   46. A method of processing a bulk crystal of gallium nitride according to any one of claims 38 to 45, wherein the gallium nitride seed crystal is processed by hydride vapor phase epitaxy.   47. The method of processing a bulk crystal of gallium nitride according to any one of claims 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.

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