초록
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A method and the benefits resulting from the product thereof are disclosed for the growth of large, low-defect single-crystals of tetrahedrally-bonded crystal materials. The process utilizes a uniquely designed crystal shape whereby the direction of rapid growth is parallel to a preferred crystal direction. By establishing several regions of growth, a large single crystal that is largely defect-free can be grown at high growth rates. This process is particularly suitable for producing products for wide-bandgap semiconductors, such as SiC, GaN, AlN, and d...
A method and the benefits resulting from the product thereof are disclosed for the growth of large, low-defect single-crystals of tetrahedrally-bonded crystal materials. The process utilizes a uniquely designed crystal shape whereby the direction of rapid growth is parallel to a preferred crystal direction. By establishing several regions of growth, a large single crystal that is largely defect-free can be grown at high growth rates. This process is particularly suitable for producing products for wide-bandgap semiconductors, such as SiC, GaN, AlN, and diamond. Large low-defect single crystals of these semiconductors enable greatly enhanced performance and reliability for applications involving high power, high voltage, and/or high temperature operating conditions.
대표
청구항
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What we claim is: 1. A method for crystal growth of a low-defect, tetrahedrally-bonded, single crystal comprising the steps of: a) providing a crystal seed having a defined vertical central axis with said central axis having a top and said central axis being parallel within 5 degrees to a selected crystal direction, with said crystal seed having several connected major portions substantially cylindrically symmetric about said central axis, and said major portions comprising of (1) a base located at the top of said central axis and having a diameter and ...
What we claim is: 1. A method for crystal growth of a low-defect, tetrahedrally-bonded, single crystal comprising the steps of: a) providing a crystal seed having a defined vertical central axis with said central axis having a top and said central axis being parallel within 5 degrees to a selected crystal direction, with said crystal seed having several connected major portions substantially cylindrically symmetric about said central axis, and said major portions comprising of (1) a base located at the top of said central axis and having a diameter and opposite lower and upper ends, (2) a tapered portion extending downward from said lower end of said base, said tapered portion having a lower end that is smaller in diameter than said diameter of said base, (3) a columnar portion extending downward from said lower end of said tapered portion, and (4) a tip portion at the lowermost end of said columnar portion; b) providing a growth apparatus with first, second and third chambers respectively defining interlaced region 1, region 2, and region 3, with the first, second and third chambers being arranged vertically with said first chamber at the bottom, said second chamber in the middle, and said third chamber at the top, and said chambers providing at least a first passageway between first and second chambers and a second passageway between second and third chambers with said passageways arranged along said central axis; c) providing a holder located inside said third chamber for holding said base of said crystal seed so that said tapered portion of said crystal seed lies between both said first and second passageways and extends completely through said region 2, and with said columnar portion extending into said region 1; d) providing means within said first chamber for axial crystal growth of said tip portion of said crystal seed in a manner that maintains the diameter of said tip portion as measured perpendicular to said central axis, to be less than 10 percent of the diameter of said base of said crystal seed; e) providing means within said second chamber for lateral crystal growth of said tapered portion of said crystal seed; and f) providing means for moving said base of said crystal seed along said central axis and in a manner that maintains the location of the growing said tip portion fixed within 1 cm relative to said first growth chamber. 2. The method according to claim 1, wherein said single crystal has a desired length dimension defined to be the distance along said central axis from the uppermost portion of said base to said tip portion and wherein: a) said axial crystal growth and said lateral crystal growth are continued until said length of said single crystal has reached said desired length; and b) said single crystal is cut into two pieces comprising (1) said base and a selected portion of said single crystal that is adjacent to said base, wherein said base and said selected portion are designated as the crystal boule, and (2) remainder of said single crystal, wherein said remainder is used as said crystal seed in a subsequent growth run according to claim 1. 3. The method according to claim 2, wherein said cutting of said single crystal is comprised of cutting at a desired angle relative to said central axis. 4. The method according to claim 1, wherein said tip portion has a diameter measured perpendicular to said central axis and wherein said diameter of said tip portion is less than 1 mm, and said axial crystal growth of said tip portion is carried out in a manner that maintains said diameter of said tip portion to be less than 1 mm. 5. The method according to claim 1, wherein said crystal seed contains at least one axial screw dislocation that (1) is located approximately in the center of said tip portion, and (2) is parallel within 5 degrees to said central axis, and wherein said axial crystal growth in said first chamber takes place by a step-flow growth mechanism from steps created by said at least one axial screw dislocation. 6. The method according to claim 5, wherein said crystal seed is comprised of 4H--SiC, and wherein said selected crystal direction is in the or the 1> crystal direction. 7. The method according to claim 6, wherein said diameter of said tip portion is less than 5 mm. 8. The method according to claim 7, wherein said diameter of said tip portion is less than 1 mm, and wherein said at least one axial screw dislocation is a single axial screw dislocation. 9. The method according to claim 7, wherein said tip portion has a temperature and wherein said means within said first chamber for said crystal growth of said tip portion of said crystal seed is selected to be chemical vapor deposition carried out by impinging one or more gaseous precursors upon the said tip portion wherein said temperature of said tip portion is greater than 1400�� C., and wherein said one or more impinging gaseous precursors provide silicon atoms and carbon atoms to the said tip portion of said crystal seed. 10. The method according to claim 6, wherein said means within said first chamber for said crystal growth of said tip portion provides a vertical axial crystal growth rate measured in millimeters per hour (mm/hour) parallel to said central axis that exceeds 1 mm/hour. 11. The method according to claim 6, wherein said tapered portion has a temperature and wherein said means within said second chamber for said lateral crystal growth of said tapered portion of said crystal seed is selected to be chemical vapor deposition carried out by impinging one or more gaseous precursors upon the said tapered portion wherein the temperature of said tapered portion is less than 2000�� C., and wherein said one or more impinging gaseous precursors provide silicon atoms and carbon atoms to the said tapered portion of said crystal seed. 12. The method according to claim 1, wherein said crystal seed has said selected crystal direction in the or the 1> crystal direction and is of a material selected from the group comprising the hexagonal and rhombohedral polytypes of SiC, and wurtzite crystal forms of the Group III-Nitrides and alloys thereof. 13. The method according to claim 1, wherein said crystal seed has said selected crystal direction in the , , or crystal directions and is a material selected from the group comprising 3C--SiC, zinc blende crystal forms of Group III-Nitrides and alloys thereof, and diamond. 14. The method according to claim 1, wherein said crystal seed is selected from a group of material that includes the polytypes of SiC, the Group III-Nitrides, and alloys thereof, and diamond. 15. The method according to claim 1, wherein said means within said first chamber for said axial crystal growth of said tip portion of said crystal seed is selected to provide a deposition method selected from the group of crystal growth methods consisting of chemical vapor deposition (CVD), vapor-liquid-solid (VLS) crystal growth method, and a combination of the traveling solvent method (TSM) and the laser heated pedestal growth (LHPG) method. 16. The method according to claim 15, wherein said combination of the traveling solvent method (TSM) and the laser heated pedestal growth (LHPG) method comprises a TSM method that provides growth on said tip portion of said crystal seed, and a LHPG method that comprises one or more lasers that are used as a source of energy to maintain and control temperature of the crystal growth on said tip portion of said crystal seed. 17. The method according to claim 15, wherein said vapor-liquid-solid (VLS) crystal growth method, and a combination of the traveling solvent method (TSM) and the laser heated pedestal growth (LHPG) method utilize liquid chromium, or a liquid solution of several materials, as a solvent for growing a crystal selected from the polytypes of SiC. 18. The method according to claim 15, wherein said vapor-liquid-solid (VLS) crystal growth method utilizes one or more lasers that are used as a source of energy to maintain and control temperature and temperature gradient of said axial crystal growth on said tip portion of said crystal seed. 19. The method according to claim 1, wherein said means within said second chamber for growth of said tapered portion of said crystal seed is selected to provide deposition on said tapered portion of said crystal seed by using chemical vapor deposition (CVD). 20. The method according to claim 19, wherein said chemical vapor deposition is high-temperature chemical vapor deposition (HTCVD). 21. The method according claim 20, wherein said high temperature chemical vapor deposition is provided by hot-wall chemical vapor deposition. 22. The method according to claim 1, wherein said first chamber has a box-like configuration with said first passageway being located in an upper-central portion of said box-like configuration and wherein said means within said first chamber provided for said axial crystal growth of said tip portion of said crystal seed comprises; first inlet located in said first chamber at a position which is lower than said first passageway and receives a gaseous precursor from an external source; second inlet located in said first chamber at a position which is lower than said first passageway and receives a carrier gas for said gaseous precursor from an external source; a flow nozzle located near said first passageway and near said tip portion of said crystal seed and controlling the flow of said gaseous precursor; and a heater located in a said first chamber at a position which is lower than said first passageway so as to provide heat to said flow nozzle. 23. The method according to claim 22, wherein said heater comprises a laser source that emits at least one laser beam that is directed onto said flow nozzle. 24. The method according to claim 22, further comprising directing at least one laser beam from an external source onto said tip portion and said columnar portion of said crystal seed. 25. The method according to claim 22, further comprising a second heater located near said tip portion of said crystal seed. 26. The method according to claim 1, wherein said tip portion of said crystal seed is provided with a solvent thereon. 27. The method according to claim 1, wherein said first chamber has a box-like vertical cross-sectional configuration with an approximate cylindrical horizontal cross-section configuration perpendicular to said central axis and with said first passageway being located in an upper-central portion of said box-like configuration and wherein said means within said first chamber provided for said growth of said crystal seed in said region 1 comprises; first inlet located in said first chamber at a position lower than, but near said first passageway and receives a gaseous precursor from an external source; second inlet located in said first chamber at a position which is lower than said first passageway and receives a carrier gas for said gaseous precursor from an external source; a first exhaust outlet provided to exhaust gases from said first chamber; a plate with an orifice located near said first passageway and with said tip portion of said crystal seed extending through said orifice, with said orifice controlling said diameter of said tip portion of said crystal seed receiving said gaseous precursors. 28. The method according to claim 1, wherein said growth apparatus and said crystal seed are vertically flipped (about a horizontal axis of rotation), so that said third chamber and said base reside closer to the surface of the Earth than said first chamber, and wherein said holder is aided by Earth gravity holding said base of said crystal seed to a movable support residing inside said third chamber. 29. The method according to claim 1, wherein said means within said second chamber provided for said growth of said crystal seed in said region 2 comprises; an inductively heated two-cylinder susceptor having an inner cylinder and a substantially concentric outer cylinder with the inner cylinder being located adjacent to said tapered portion of said crystal seed, and with the outer cylinder having at least one opening and having thermal insulation on said outer cylinder, and with induction coils for heating said susceptor being placed about said thermal insulation; at least one inlet located near said first passageway for receiving gaseous precursor from an external source; at least one inlet connected to said opening in said outer wall of said susceptor for receiving a purge gas from an external source; and at least one outlet located near said second passageway for exhausting gas from said second chamber. 30. The method according to claim 29, wherein said inner cylinder of said two-cylinder susceptor comprises an arrangement selected from the group consisting of small channels and a permeable plate. 31. The method according to claim 1, wherein said third chamber comprises; a single-cylinder heater having an inside wall and an outside wall with the inside wall being located adjacent to said base portion of said crystal seed and with the outside wall having thermal insulation thereon, and with induction coils being placed about said thermal insulation; and at least one inlet connected to said third chamber for receiving a purge gas from an external source. 32. The method according to claim 31, further comprising providing a fourth chamber located above and interlaced to said third chamber by a fourth passageway therebetween. 33. The method according to claim 1, wherein said holder is a thermally-insulated rotary holder for providing rotation to the crystal seed. 34. The method according to claim 1, wherein said third chamber has an upper portion and wherein said method further comprises providing a third passageway at said upper portion of said third chamber. 35. A method for the crystal growth of a low-defect tetrahedrally-bonded single crystal comprising the steps of: a) providing a starter crystal seed having crystal directions and having a defined tip portion and having a defined vertical central axis parallel within 5 degrees to a selected crystal direction and having dimensions perpendicular to said selected crystal direction that are less than 5 mm; b) providing a growth apparatus with first, second and third chambers respectively defining interlaced region 1, region 2, and region 3, with the first, second and third chambers being arranged (1) substantially vertically along said central axis with the first chamber being lowest thereof and the third chamber being the highest thereof and; (2) to provide at least a first passageway between first and second chambers and a second passageway between second and third chambers with said passageways arranged along said vertical central axis; c) providing an elongated support rod having a lowermost end, a long axis and a defined length; d) mounting said starter crystal seed on said lowermost end of said elongated support rod such that said central axis of said starter crystal is parallel to said long axis of said support rod and such that said defined length of said support rod is sufficient to span a distance from said region 3 to said region 1 through said first and second passageways; e) providing a holder located inside said third chamber for holding the uppermost end of a support rod in a manner that said support rod extends completely through said region 2, and with the lowermost end of said support rod with said starter crystal seed attached extending into said region 1; f) providing means within said first chamber for axial crystal growth of the tip portion of said starter crystal seed and in a direction downward along said central axis and in a manner that produces a columnar crystal having an axis which is parallel within 5 degrees to said central axis; g) providing means within said second chamber for the epitaxial lateral crystal growth of the growing said columnar crystal; h) providing means for moving said holder and said support rod upward along said central axis and in a manner that maintains the location of the growing said tip portion fixed within 1 cm relative to said first chamber and said vertical central axis; and i) continuing (1) said crystal growth in said first and second chambers and (2) said movement of said holder and support rod until said lowermost end of said support rod moves into said third chamber. 36. The method according to claim 35, wherein said crystal seed contains at least one axial screw dislocation that (1) is located approximately in the center of said tip portion, and (2) is parallel within 5 degrees to said central axis, and wherein said axial crystal growth in said first chamber takes place by a step-flow growth mechanism from steps created by said at least one axial screw dislocation. 37. The method according to claim 36, wherein said crystal seed is comprised of 4H--SiC, and wherein said selected crystal direction is in the or the 1> crystal direction. 38. The method according to claim 35, wherein said crystal seed has said selected crystal direction in the or the 1> crystal direction and is of a material selected from the group comprising the hexagonal and rhombohedral polytypes of SiC, and wurtzite crystal forms of the Group III-Nitrides and alloys thereof. 39. The method according to claim 35, wherein said crystal seed has said selected crystal direction in the , , or crystal direction and is a material selected from the group comprising 3C--SiC, zinc blende crystal forms of Group III-Nitrides and alloys thereof, and diamond. 40. The method according to claim 35, wherein said diameter of said tip portion is less than 1 mm, and wherein said at least one axial screw dislocation is a single axial screw dislocation. 41. A method for the crystal growth of a low-defect WBG single crystal of predetermined diameter and predetermined length of a tetrahedrally-bonded WBG crystal material, comprising the steps of: a) providing a starter crystal seed of said tetrahedrally-bonded WBG crystal material having crystal directions and having a tip portion and having a defined central axis parallel within 5 degrees to a selected crystal direction and having dimensions perpendicular to said selected crystal direction that are less than 5 mm; b) providing two separate crystal growth reactors, designated as growth reactor 1 and growth reactor 2; c) installing said starter crystal seed in said growth reactor 1 and providing means in said growth reactor 1 whereby axial crystal growth of the tip portion of the said starter crystal seed is carried out in a manner that maintains the diameter of said starter crystal, measured perpendicular to the central axis, to less than a first predetermined diameter; d) continuing said axial crystal growth in said growth reactor 1 until a columnar crystal of said first predetermined diameter and a predetermined length is produced; e) removing said columnar crystal from growth reactor 1, installing said columnar crystal in growth reactor 2, and providing means in said growth reactor 2 whereby lateral crystal growth of the said columnar crystal is carried out until a low-defect crystal of a second predetermined diameter is produced. 42. The method according to claim 41, wherein said tip portion has a center and wherein said starter crystal seed contains at least one axial screw dislocation that (1) is located approximately in the center of said tip portion and (2) is parallel within 5 degrees to said central axis, and wherein said axial crystal growth in said growth reactor 1 takes place by a step-flow growth mechanism from steps created by said at least one axial screw dislocation. 43. The method according to claim 42, wherein said crystal seed is comprised of 4H--SiC, and wherein said selected crystal direction is in the or the 1> crystal direction. 44. The method according to claim 41, wherein said crystal seed has said selected crystal direction in the or the 1> crystal direction and is of a material selected from the group comprising the hexagonal and rhombohedral polytypes of SiC, and wurtzite crystal forms of the Group III-Nitrides and alloys thereof. 45. The method according to claim 41, wherein said crystal seed has a selected crystal direction in the , , or crystal direction and is a material selected from the group comprising 3C--SiC, zinc blende crystal forms of Group III-Nitrides and alloys thereof, and diamond. 46. The method according to claim 41, wherein said dimensions of said starter crystal are less than 1 mm.
