Source: http://www.freepatentsonline.com/y2010/0075175.html
Timestamp: 2020-02-28 07:02:26
Document Index: 265799431

Matched Legal Cases: ['Application No. 61', 'Application No. 61', 'art 2', 'art 2', 'art 2', 'art 2']

LARGE-AREA SEED FOR AMMONOTHERMAL GROWTH OF BULK GALLIUM NITRIDE AND METHOD OF MANUFACTURE - SORAA, INC.
United States Patent Application 20100075175
Poblenz, Christiane (Goleta, CA, US)
12/556558
SORAA, INC. (Goleta, CA, US)
117/88, 117/95, 117/103, 156/60
C30B23/02; B31B1/60; B32B9/00
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20070087209 Plastic-metal composite material with wire gauze April, 2007 Farhumand et al.
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Kilpatrick Townsend & Stockton, LLp / SLD 96019 (Mailstop: IP Docketing - 22 1100 Peachtree Street Suite 2800, Atlanta, GA, 30309, US)
1. A method for fabricating crystalline material comprising: providing a crystalline substrate material having a first surface and a second surface; maintaining the crystalline substrate material by engaging the second surface while exposing the first surface; forming a first thickness of first crystalline material overlying the first surface of the crystalline substrate material, the first thickness of first crystalline material having a first orientation; providing the crystalline substrate material having the overlying first crystalline material; exposing the second surface of the crystalline substrate material; and forming a second thickness of second crystalline material overlying the second surface of the crystalline substrate material such that the second thickness of second crystalline material and the first thickness of first crystalline material are configured to be substantially free from bow.
2. The method of claim 1 wherein the first thickness of first crystalline material and the second thickness of second crystalline material have an epitaxial relationship with the crystalline substrate material.
3. The method of claim 1 wherein the crystalline substrate material is selected from sapphire, silicon carbide, silicon, Mg2AlO4 spinel, ZnO, and ZrB2.
4. The method of claim 1 wherein the crystalline substrate material has a maximum lateral dimension ranging from about 0.5 centimeters to about 21 centimeters.
5. The method of claim 1 wherein the engaging comprises holding the crystalline substrate material by a susceptor coupled to the second surface of the crystalline substrate material.
6. The method of claim 1 wherein the maintaining is provided in a chamber of an MOCVD tool.
7. The method of claim 1 wherein the exposing comprises facing the first surface to a processing region of a chamber of an MOCVD tool.
8. The method of claim 1 wherein the first crystalline material and the second crystalline material comprise at least one of a gallium species and a nitrogen species, an aluminum species and a nitrogen species, or an indium species and a nitrogen species.
9. The method of claim 1 wherein the first crystalline material and the second crystalline material comprise substantially similar composition, such that the lattice constants of the primary constituent material within the first crystalline material and primary constituent material within the second crystalline material are within about 0.01 Å.
10. The method of claim 1 wherein the first crystalline material and the second crystalline material comprise substantially similar lattice constants, such that the lattice constants of the primary constituent material within the first crystalline material and primary constituent material within the second crystalline material are within about 0.05 Å.
11. The method of claim 10 wherein the first crystalline orientation and the second crystalline orientation are the same to within 10 degrees.
12. The method of claim 10 wherein the first crystalline orientation and the second crystalline orientation are substantially opposite to each other, wherein the difference in orientation between the first crystalline orientation and the second crystalline orientation is within a range of 170-190 degrees.
13. The method of claim 11 wherein the crystalline structure of the first crystalline material and the second crystalline material are wurtzite.
14. The method of claim 13 wherein the first crystalline orientation and the second crystalline orientation are within 10 degrees of (0001) or (000-1) crystallographic orientations.
15. The method of claim 13 wherein the first crystalline orientation and the second crystalline orientation are semipolar or nonpolar.
16. The method of claim 15 wherein nonpolar orientations comprise orientations within 10 degrees of {10-10} or {11-20}.
17. The method of claim 15 wherein semipolar orientations comprise orientations within 5 degrees of (10-11), (10-1-1), (10-12), (10-1-2), (10-13), (10-1-3), (11-21), (11-2-1), (20-21), (20-2-1), (10-14), (10-1-4), (11-22) or (11-2-2), along with their associated families of planes.
18. The method of claim 1 wherein the same thickness ranges from 0.5 microns to 500 microns.
19. The method of claim 18 wherein the same thickness ranges from 0.5 to 10 microns.
20. The method of claim 18 wherein the same thickness ranges from 0.5 to 2 microns.
21. The method of claim 1 wherein substantially a same thickness refers to the thickness of the first crystalline material and the second crystalline material being within 100 nm of each other.
22. The method of claim 21 wherein substantially a same thickness refers to the thickness of the first crystalline material and the second crystalline material being within 50 nm of each other.
23. The method of claim 21 wherein substantially a same thickness refers to the thickness of the first crystalline material and the second crystalline material being within 10 nm of each other.
24. The method of claim 21 wherein substantially a same thickness refers to the thickness of the first crystalline material and the second crystalline material being within 5 nm of each other.
25. The method of claim 1 wherein the forming of the first thickness comprises a process selected from MOCVD, HYPE, or MBE.
26. The method of claim 1 wherein the forming of the second thickness comprises a process selected from MOCVD, HYPE, or MBE.
27. The method of claim 1 further comprising reorienting the crystalline substrate material to expose the second surface of the crystalline substrate material to a processing region of a chamber.
28. The method of claim 1 further comprising a mask or capping layer overlying the first crystalline material.
29. The method of claim 28 wherein the mask or capping layer(s) comprise at least one of AlN, SiN, Si3N4, SiO2, TaO, or Ti, Ta, Mo, Pt, Ag, Au, W, or silicides or nitrides of these materials.
30. The method of claim 1 wherein a mask or capping layer is deposited on the first crystalline material prior to forming the second crystalline material.
31. The method of claim 30 wherein the mask or capping layers are deposited by e-beam evaporation, sputtering, or chemical vapor deposition.
32. The method of claim 1 further comprising a sidewall encapsulant material.
33. The method of claim 32 wherein the sidewall encapsulant material contains silver, gold, platinum, nickel, chromium, or alloys of these materials.
34. The method of claim 33 wherein an adhesion layer is formed prior to forming the sidewall encapsulant material.
35. The method of claim 34 wherein the adhesion layer comprises titanium.
36. The method of claim 34 wherein the sidewall encapsulant material and the adhesion layer are formed by e-beam evaporation or sputtering.
37. The method of claim 1 wherein the first crystalline material and/or second crystalline material employs at least one of: a lateral epitaxial overgrowth (LEO) technique, a nano-masking technique, or a cantilever epitaxy technique.
38. The method of claim 1 wherein the crystalline substrate material comprises two separate crystalline wafers which have been bonded or fused together.
39. A method for fabricating crystalline material comprising: providing a first crystalline substrate material having a first surface and a second surface; maintaining the first crystalline substrate material by engaging the second surface while exposing the first surface; forming a first thickness of first crystalline material overlying the first surface of the first crystalline substrate material, the first thickness of first crystalline material having a first orientation; providing a second crystalline substrate material having a first surface and a second surface; maintaining the second crystalline substrate material by engaging the second surface while exposing the first surface; forming a second thickness of second crystalline material overlying the first surface of the second crystalline substrate material, the second thickness of second crystalline material having a second orientation; attaching the first crystalline substrate and the second crystalline substrate at their second surfaces, such that the first crystalline material and second crystalline material are substantially free from bow.
40. The method of claim 1 wherein the first crystalline material is composed of multiple layers possessing two or more different compositions.
41. The method of claim 1 wherein the second crystalline material is composed of multiple layers possessing two or more different compositions.
42. The method of claim 1 wherein the first crystalline material contains a compositional gradient or fluctuation in composition.
43. The method of claim 1 wherein the second crystalline material contains a compositional gradient or fluctuation in composition.
44. A method for fabricating crystalline material comprising: providing a crystalline substrate material having a first surface and a second surface; maintaining the crystalline substrate material by engaging the second surface while exposing the first surface; forming a first crystalline material overlying the first surface of the crystalline substrate material, the first crystalline material having a first lattice constant; providing the crystalline substrate material having the overlying first crystalline material; exposing the second surface of the crystalline substrate material; forming a second crystalline material overlying the second surface of the crystalline substrate material, the second crystalline material having a second lattice constant, such that the lattice constant of the second crystalline material is substantially the same as the lattice constant of the first crystalline material.
45. The method of claim 44 wherein the crystalline substrate material, the first crystalline material, and the second crystalline material are substantially free from bow.
46. The method of claim 44 wherein the crystalline substrate material, the first crystalline material, and the second crystalline material form a composite structure that is substantially free from bow, the bow being less than about 300 microns for a crystalline substrate material having a diameter of eight inches and greater, or the bow being less than bout 50 microns for a crystalline substrate material having a diameter of two inches to about four inches, or the bow being less than about 100 microns for a crystalline substrate material having a diameter of four inches to eight inches.
47. The method of claim 44, wherein the lattice constant of the first material and the lattice constant of the second material are within about 0.05 Å.
48. A method for fabricating crystalline material comprising: providing a crystalline substrate material having a first surface and a second surface; maintaining the crystalline substrate material by engaging the second surface while exposing the first surface; forming a first crystalline material overlying the first surface of the crystalline substrate material; providing the crystalline substrate material having the overlying first crystalline material; exposing the second surface of the crystalline substrate material; forming a second crystalline material overlying the second surface of the crystalline substrate material such that the such that the resulting substrate is characterized by first crystalline material and second crystalline material possessing relatively bow-free surfaces.
49. A crystalline material comprising a first crystalline material overlying a first surface of a crystalline substrate and a second crystalline material overlying a second surface of a crystalline substrate such that the first crystalline material and second crystalline material possess surfaces that are substantially free from bow.
This application claims priority to U.S. Provisional Application No. 61/096304 (Attorney Docket No 027364-003600US) filed Sep. 11, 2008 and U.S. Provisional Application No. 61/178460 (Attorney Docket No. 027364-006400US) filed May 14, 2009, commonly assigned, both of which are incorporate by reference in their entirety herein. This application is related to U.S. Patent Application of Attorney Docket No. 027364-005310US, filed Sep. 9, 2009, commonly assign, and of which is incorporate by reference in its entirety herein.
Conventional approaches to growth of GaN, AN or InN containing compounds (collectively referred to as “(Al,In)GaN” compounds) and devices employ foreign substrate materials (containing one or more primary chemical species which is different from Ga, Al, In, or N), a process known as “heteroepitaxy”. Heteroepitaxial approaches to growth of (Al,In)GaN containing compounds result in epitaxial films with high defect densities due to the large lattice mismatch, chemical dissimilarity and thermal expansion coefficient difference between the nitride materials and substrate. The presence of defects is well-known to be detrimental to device performance. The thermal expansion coefficient difference between the substrate and the epitaxial layer in heteroepitaxy results in strain gradients in the material which can lead to wafer curvature, referred to as bow or warp, after growth. As used herein, the terms bow and warp are used in a manner which is well understood in this art. Definitions, for example, can be found from SEMI (www.semi.org), but can be others commonly known. There is therefore a need for bulk GaN substrates of high crystalline quality, ideally cut from large volume bulk GaN ingots.
According to the present invention, techniques for manufacture of crystalline materials are described. More particularly, the present invention provides a seed crystal and method using back and front side deposition of crystalline materials, e.g., GaN, AN, InN. In a specific embodiment, the seed crystals can be used in an ammonothermal growth process or the like. Merely by way of example, the present substrate materials can be used in applications such as such as light emitting diodes, integrated circuits, MEMS, medical devices, combination of these, among others.
Nitride containing wurtzite materials are commonly known as “polar” materials due to lack of inversion symmetry in the crystal structure. Such materials exhibit both spontaneous and strain-induced, or piezoelectric polarization along the c-axis, or [0001] axis. The c-direction, or [0001] direction, is a common growth direction for these materials, and is commonly known as the polar axis or polar growth direction. The net polarization and consequent internal electric fields in such materials are well known to influence electrical and optical properties and device performance. The polarity of these materials is commonly characterized as “Gallium-face” or “Gallium-polar” if the [0001] direction is the primary growth direction. The polarity of these materials is commonly characterized as “Nitrogen-face” or “Nitrogen-polar” if the [000-1] direction is the primary growth direction. In a specific embodiment of the present invention, the nitride containing material has an orientation within 10 degrees of (0001) or (000-1).
Primary growth orientations which are oriented at angles between 0 and 90 degrees of [0001] or [000-1] are known as “semipolar” orientations of the material. There are a wide variety of such semipolar planes, which can be defined as having both two nonzero h, i, or k Miller indices and a nonzero l Miller index. Families of such semipolar planes include {10-1l} and {11-2l}, for example, where l is a nonzero integer. Specific examples of commonly observed semipolar planes in GaN include {11-22}, {10-11}, and {10-13}. Other examples in the wurtzite crystal structure include, but are not limited to, {10-12}, {20-21}, {11-21} and {10-14}. Semipolar materials exhibit polarity, although the net polarization vector lies at an angle inclined relative to the plane's surface normal rather than in-plane or normal to the plane. Semipolar materials are characterized as “Ga-polar” or having “Ga-face polarity” if the [0001] direction is oriented toward the film surface normal. Semipolar materials are characterized as “N-polar” or having “N-face polarity” if the [000-1] direction is oriented toward the film surface normal. In a specific embodiment of the present invention the nitride containing material has an orientation within 5 degrees of (10-11), (10-1-1), (10-12), (10-1-2), (10-13), (10-1-3), (11-21), (11-2-1), (20-21), (20-2-1), (10-14), (10-1-4), (11-22) or (11-2-2), along with their associated families of planes.
Gallium face or Nitrogen face polarity can be realized with either growth technique depending on both the substrate and growth conditions. It has been established that using MOCVD, the polarity of a GaN film on c-plane sapphire is determined by the growth initiation procedures (See for example, E. S. Hellman, MRS Internet J. Nitride Semicond. Res. 3, 11 (1998) and references therein, M. Stutzmann, O. Ambacher, M. Eickhoff, U. Karrer, A. Lima Pimenta, R. Neuberger, J. Schalwig, R. Dimitrov, P. J. Schuck, and R. D. Grober, Phys. Status Solidi B 228 (2001) 505, M. Sumiya and S. Fuke, MRS Internet J. Nitride Semicond. Res. 9 (2004) 1, S. Keller, B. P. Keller, Y. F. Wu, B. Heying, D. Kapolnek, J. S. Speck, U. K. Mishra, and S. P. DenBaars, Appl. Phys. Lett. 68, (1996) 1525). A standard two-step process with growth initiated with a thin GaN or AN layer at low temperatures, for example, has been shown to result in c-plane Ga-face films with high crystalline quality suitable for devices. (See for example, H. Amano, N. Sawaki, I. Akasaki, and Y. Toyoda, Appl. Phys. Lett. 48, 353 (1986), and S. Nakamura, Jpn. J. Appl. Phys., Part 2 30, L1705 (1991)). Nitridation of sapphire at high temperature prior to growth can result in formation of a thin AlN surface layer (See for example, N. Grandjean, J. Massies, and M. Lerous, Appl. Phys. Lett. 69, 2071 (1996)), and N-face films typically result. (See for example, P. Cantu, F. Wu, P. Waltereit, S. Keller, A. E. Romanov, U. K. Mishra, S. P. DenBaars, and J. S. Spec, Appl. Phys. Lett. 83, 674 (2003), and M. Stutzmann, O. Ambacher, M. Eickhoff, U. Karrer, A. Lima Pimenta, R. Neuberger, J. Schalwig, R. Dimitrov, P. J. Schuck, and R. D. Grober, Phys. Status Solidi B 228 (2001) 505). While N-face films by MOCVD have typically been of much poorer quality (high surface roughness and surfaces characterized by large hexagonal hillocks potentially due to inversion domains) (See for example, M. Sumiya, K. Yoshimura, T. Ito, K. Ohtsuka, S. Fuke, M. Mizuno, M. Yoshimoto, H. Koinuma, A. Ohtomo, and M. Kawasaki, J. Appl. Phys. 88, 1158 (2000), and J. L. Weyher, P. D. Brown, A. R. A. Zauner, S. Muller, C. B. Boothroyd, D. T. Foord, P. R. Hageman, C. J. Humphreys, P. K. Larsen, I. Grzegory, and S. Porowski, J. Cryst. Growth 204, 419 (1999)), it has been recently shown that high quality N-face GaN can be achieved using sapphire with higher degrees of miscut (See for example, S. Keller, N. Fichtenbaum, F. Wu, D. Brown, A. Rasales, S. P. DenBaars, J. S. Speck and U. K. Mishra, J. Appl. Phys. 102, 083546 (2007)). By MBE, for example, c-plane GaN with both polarities can also be achieved with varying growth conditions (See for example, S. K. Davidsson, M. F. Falth, X. Y. Liu, H. Zirath, and T. G. Andersson, J. Appl. Phys. 98, 016109 (2005) and K. Xu, N. Yano, A. W. Jia, A. Yoshikawa, and Kk. Takahashi, J. Cryst. Growth 237-239, Part 2, 1003 (2002)). Use of the dopant Mg has also been shown to result in polarity inversion under specific growth conditions by MBE (See for example, D. S. Green, E. Haus, F. Wu, L. Chen, U. K. Mishra and J. S. Speck, J. Vac. Sci. Tech. B 21, 1804 (2003)). Various semipolar orientations have also been experimentally realized. For example, (10-1-1) GaN on (100) MgAl2O4 spinel and (10-13) GaN on (110) MgAl2O4 spinel have been realized utilizing HVPE (See for example, T. J. Baker, B. A. Haskell, F. Wu, J. S. Speck, and S. Nakamura, “Characterization of planar semipolar gallium nitride films on spinel substrates”, Japanese Journal of Applied Physics 44, L920 (2005)), and (10-1-3) GaN on (1010) sapphire and (11-22) GaN on (10-10) sapphire (See for example, T. J. Baker, B. A. Haskell, F. Wu, J. S. Speck, and S. Nakamura, “Characterization of planar semipolar gallium nitride films on sapphire substrates”, Japanese Journal of Applied Physics 45, L154 (2006)). Use of any of these techniques and substrates, or a combination of them, can be used to give the desired orientation and polarity of nitride material in the present invention.
The sample is then mounted on a substrate holder with the metalized surface facing the direction of the heater during growth, and loaded into a chamber of the MBE system. The type of sample mounting and the configuration of the substrate holder will vary depending on the type and geometry of the MBE system being used. The substrate holder could include, but is not limited to, ceramic diffuser plates, backing wafers such as silicon, quartz , or sapphire, molybdenum, ceramic, or tungsten retaining rings, and molybdenum or tantalum faceplates, for example. In some cases the substrate could be indium-bonded to a carrier wafer. The substrate and holder should then be baked at high temperature (e.g. 100-800° C., but not limited to this range) prior to growth, in the growth chamber or preferably in a separate chamber, for ˜1 hour or a sufficient amount of time to outgas water and other impurities from the surface. The outgassing can be monitored by the chamber pressure and potentially using a residual gas analyzer. In this embodiment, the growth chamber of the MBE system is equipped with a radio frequency plasma source, an ammonia gas injector, a combination of these, or another suitable source of active nitrogen for growth. It is possible but not necessary that the nitrogen source gas is further purified using a getter-filter prior to introduction to the growth chamber. Conventional Knudsen cells are available for group III sources. Pumping of any or all of the MBE system chambers can be achieved utilizing cryogenic pumps, turbo pumps, ion pumps, among others, or a combination of these.
After bake and transfer to the growth chamber if necessary, the substrate is heated to the growth temperature (typically 650-800 C), and appropriate constituent elements are introduced to the chamber to form a (Al,B,In,Ga)N layer or combination of (Al,B,In,Ga)N layers necessary to result in epitaxial growth on the substrate with a total thickness in the approximate range of 0.5-2 microns. Various growth conditions which result in high quality nitride containing films by molecular beam epitaxy are known in the art and demonstrated in literature (See for example, B. Heying, R. Averbeck, L. F. Chen, E. Haus, H. Riechert, and J. S. Speck, J. Appl. Phys. 88, 1855 (2000), G. Koblmuller, S. Fernandez-Garrido, E. Calleja, and J. S. Speck, Appl. Phys. Lett. 91, 161904 (2007), and G. Koblmuller, F. Wu, T. Mates, J. S. Speck, S. Fernandez-Garrido, and E. Calleja, Appl. Phys. Lett. 91, 221905 (2007)). An AN nucleation layer could or could not be used, and varying Group III/Group V flux ratios are utilized throughout growth. A two-step process comprising a low III/V ratio in the first GaN growth step and a high III/V ratio in the second GaN growth step has been shown to control dislocation density and result in high quality films on both sapphire and silicon carbide substrates, for example (See for example, M. J. Manfra, N. G. Weimann, J. W. P. Hsu, L. N. Pfeiffer, and K. W. West, Appl. Phys. Lett. 81, 1456 (2002), and P. Waltereit, C. Poblenz, S. Rajan, F. Wu, U. K. Mishra, J. S. Speck, Japanese Journal of Applied Physics 43, L1520 (2004)). A method for using ammonia as a nitrogen source to produce high quality MBE GaN layers has also been shown, for example, see A. L. Carrion, C. Poblenz, F. Wu, and J. S. Speck, J. Appl. Phys. 103, 093529 (2008). The miscut angle of the substrate is not known to influence the polarity of the film, although could influence crystal quality. It is possible that dopants could be intentionally incorporated in the epitaxial layers. A typical n-type dopant is Si, a typical p-type dopant is Mg, and typical compensating dopants are Be or C, for example. Under certain conditions Mg doping can result in polarity inversion (See for example, K. Xu, N. Yano, A. W. Jia, A. Yoshikawa, and K. Takahashi, J. Cryst. Growth 237-239, Part 2, 1003 (2002)). If Mg doping is utilized the appropriate conditions should be utilized to control polarity.
After MBE growth, the sample is removed from the chamber. The metal containing layer on backside of the substrate is then removed by wet etching in hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, among others, or a combination of these. The metal containing layer could also be removed by dry etching techniques such as RIE. The substrate is then rinsed in de-ionized water and dried with nitrogen. A second metal containing layer, identical to what was just removed, is then deposited on the front side of the substrate, overlying the grown nitride-containing material. This layer will be utilized for heat transfer during the next growth step. To prevent metal diffusion into the GaN at the growth temperature, a two-layer mask or cap could be deposited where the first layer could be AlN, SiN, SiO2, TaO, among others, and the second layer could be the metal, for example.
In another embodiment the substrate is c-plane-oriented sapphire, of any miscut orientation angle (i.e. within 10 degrees of (0001)). Both sides of the wafer are polished, for example with chemical-mechanical polishing, to provide atomically smooth surfaces suitable for epitaxy. In this embodiment metal organic chemical vapor deposition (MOCVD) is the growth technique utilized to produce the nitride containing epitaxial layers. In this embodiment the substrate could be cleaned with organic solvents such as, but not limited to, acetone, methanol and isopropanol, with or without use of an ultrasonic bath. The sample should be spin-dried or blown dry with nitrogen and introduced into the MOCVD growth chamber. Preparation for growth could include pre-baking and annealing in H2, for example >1000° C. Metalorganic sources such as trimethylgallium (TMGa), triethylgallium (TEGa), trimethylaluminum (TMAl), or trimethlyindium (TMIn2) with H2 or N2 carrier gas may be used with NH3 as precursors to deliver constituent elements to the growth surface. A nitride containing layer with approximate thickness 0.5-10 microns is grown on the first side of the substrate using techniques which have been demonstrated for growth of high quality Ga-polar or N-polar films.4-9,11-13 (See for example, T. M. Katona, M. D. Craven, P. T. Fini, J. S. Speck, and S. P. DenBaars, “Observation of crystallographic wing tilt in cantilever epitaxy of GaN on silicon carbide and silicon (111) substrates”, Applied Physics Letters 79, 2907 (2001), A. E. Romanov and J. S. Speck, Appl. Phys. Lett. 83, 2569 (2003), P. Cantu, F. Wu, P. Waltereit, S. Keller, A. E. Romanov, U. K. Mishra, S. P. DenBaars, and J. S. Spec, Appl. Phys. Lett. 83, 674 (2003), E. S. Hellman, MRS Internet J. Nitride Semicond. Res. 3, 11 (1998) and references therein, M. Stutzmann, O. Ambacher, M. Eickhoff, U. Karrer, A. Lima Pimenta, R. Neuberger, J. Schalwig, R. Dimitrov, P. J. Schuck, and R. D. Grober, Phys. Status Solidi B 228 (2001) 505, M. Sumiya and S. Fuke, MRS Internet J. Nitride Semicond. Res. 9 (2004) 1, H. Amano, N. Sawaki, I. Akasaki, and Y. Toyoda, Appl. Phys. Lett. 48, 353 (1986), S. Nakamura, Jpn. J. Appl. Phys., Part 2 30, L1705 (1991), and N. Grandjean, J. Massies, and M. Lerous, Appl. Phys. Lett. 69, 2071 (1996)). An aluminum nitride (AlN) containing buffer layer or GaN buffer layer may or may not be used and growth could occur at either atmospheric pressure or lower pressures. A mask or capping layer such as SiN, SiO2, TaO, among others, should be deposited after growth either in-situ or ex-situ. Such as mask or capping layer should be stable under GaN growth conditions and be able to be subsequently removed without damaging or reacting with the underlying nitride material. The sample is re-introduced into the MOCVD chamber and identical growth procedure is performed on the backside of the wafer. At the growth temperature and after cooldown, the double-sided wafer is free of bowing. After the double-sided wafer is removed from the growth chamber, the capping layer is etched off using dry or wet etching techniques.
Preparation of a Seed Crystal
As used herein, the term GaN substrate is associated with Group III-nitride based materials including GaN, InGaN, AlGaN, or other Group III containing alloys or compositions that are used as starting materials. Such starting materials include polar GaN substrates (i.e., substrate where the largest area surface is nominally an (h k l) plane wherein h=k=0, and l is non-zero), non-polar GaN substrates (i.e., substrate material where the largest area surface is oriented at an angle ranging from about 80-100 degrees from the polar orientation described above towards an (h k l) plane wherein l=0, and at least one of h and k is non-zero) or semi-polar GaN substrates (i.e., substrate material where the largest area surface is oriented at an angle ranging from about +0.1 to 80 degrees or 110-179.9 degrees from the polar orientation described above towards an (h k l) plane wherein l=0, and at least one of h and k is non-zero). Of course, there can be other variations, modifications, and alternatives
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