초록 ▼

The present invention is related to a method that enables and improves wide bandgap homoepitaxial layers to be grown on axis single crystal substrates, particularly SiC. The lateral positions of the screw dislocations in epitaxial layers are predetermined instead of random, which allows devices to b

The present invention is related to a method that enables and improves wide bandgap homoepitaxial layers to be grown on axis single crystal substrates, particularly SiC. The lateral positions of the screw dislocations in epitaxial layers are predetermined instead of random, which allows devices to be reproducibly patterned to avoid performance degrading crystal defects normally created by screw dislocations.

대표청구항 ▼

1. A method for growing at least one single crystal layer on a selected single crystal substrate having an average density of replicating nonremovable stepsource dislocations, wherein said at least one single crystal layer contains at least one replicating nonremovable stepsource dislocation, confin

1. A method for growing at least one single crystal layer on a selected single crystal substrate having an average density of replicating nonremovable stepsource dislocations, wherein said at least one single crystal layer contains at least one replicating nonremovable stepsource dislocation, confined to selected lateral point locations, said method comprising the steps of:a) choosing a single crystal substrate material which exhibits a property that the material therein contains at least one growth plane orientation whereby under selected growth conditions the growth rate due to step-flow growth along the basal plane is greater than at least one hundred (100) times a growth rate perpendicular to the basal plane due to growth involving two-dimensional nucleation;b) preparing a planar first growth surface on said single crystal substrate that is parallel to within a predetermined angle relative to a selected crystal plane of said single crystal substrate;c) removing material in said first growth surface so as to define at least one selected separated second growth surface with top surface area that is selected to be less than twice the inverse of said average density of replicating nonremovable stepsource dislocations in the said single crystal substrate and with border shape selected to have at least one enclosed hollow region, said selected separated second growth surface defining a cumulative hollow region area enclosed by at least one interior border shape selected to obtain lateral coalescence at said selected lateral point location, wherein said cumulative hollow region area is selected greater than half the inverse of the said average density of replicating nonremovable stepsource dislocations in said single crystal substrate;d) treating said at least one selected separated second growth surface so as to remove any removable sources of unwanted crystal nucleation and any removable sources of steps therein;e) depositing a homoepitaxial film on said separated second growth surface under selected conditions so as to provide a step-flow growth while suppressing two-dimensional nucleation;f) continuing said deposition of said homoepitaxial film so that said step-flow growth results and produces at least one lateral cantilevered web structure growing laterally toward the interior of said at least one enclosed hollow region;g) continuing said deposition of said homoepitaxial film until said at least one lateral cantilevered web structure completes its lateral coalescence at said selected lateral location thereby completely covering said at least one enclosed hollow region with at least one complete crystal roof forming at least one selected separated third growth surface of desired size and shape; andh) continuing said deposition of said homoepitaxial film until homoepitaxial film of desired vertical thickness on top of said selected separated third growth surface is achieved. 2. The method according to claim 1, wherein vertical epitaxial film growth occurs in the said enclosed hollow region to a vertical hollow region film thickness. 3. The method according to claim 2, wherein said removal of material in step c) is carried out to a vertical depth that exceeds said vertical hollow region film thickness of claim 2. 4. The method according to claim 1, wherein the following step dd) is performed after said step c) of claim 1, but before said step e) of claim 1:dd) selectively depositing a growth-inhibiting material of a selected growth-inhibiting film thickness onto regions where material is removed in said step c) of claim 1 without depositing said growth inhibiting material onto said selected separated second growth surface. 5. The method according to claim 4, wherein said removal of material in step c) of claim 1 is carried out to a vertical depth that exceeds said selected growth-inhibiting film thickness. 6. The method according to claim 1, wherein said single crystal substrate has a predetermined volume and wherein said hom oepitaxial film of steps e, f, g, and h of claim 1 is grown to sufficient size so as to produce at least one large crystal of a greater volume than that of said single crystal substrate. 7. The method according to claim 6, wherein said at least one large crystal is further processed into one or more crystal wafers. 8. The method according to claim 7, wherein said one or more crystal wafers are employed as seed crystals for production of additional large crystals of greater size than the said single crystal substrate. 9. The method according to claim 1, wherein said homoepitaxial film is further processed into at least one semiconductor device, wherein said homoepitaxial film has a predetermined electrical breakdown field, and wherein said at least one semiconductor device is designed to operate at predetermined current density, wherein the said at least one semiconductor device is selected with a lateral pattern and alignment to avoid adverse electrical effects arising from said at least one replicating nonremovable stepsource dislocation confined to said selected lateral locations. 10. The method according to claim 9, wherein an electrically active region of the said semiconductor device having said lateral pattern and alignment is selected to be devoid of said at least one replicating nonremovable stepsource dislocation confined to said selected lateral locations. 11. The method according to claim 9, wherein said selected lateral pattern and alignment are selected such that an electric field at any of the said replicating nonremovable stepsource dislocations during designed device operation is less than 80% of said electrical breakdown field of the said homoepitaxial film. 12. The method according to claim 9, wherein said selected lateral pattern and alignment are selected such that the density of current flowing through any of the said replicating nonremovable stepsource dislocations during designed device operation is less than 50% of said predetermined device current density. 13. The method according to claim 1, wherein said homoepitaxial film is further processed into at least one micromachined device. 14. The method according to claim 1, wherein said at least one completely coalesced cantilevered web structure completely covering said at least one enclosed hollow region comprises a diaphragm in a sensor device. 15. The method according to claim 1, wherein said single crystal substrate is 15R—SiC, and wherein said selected crystal plane is a (0001) plane of said single crystal substrate and wherein said predetermined angle is less than 10 degrees. 16. The method according to claim 1, wherein said single crystal substrate has a hexagonal crystal structure with <0001>, <1{overscore (1)}00>, and <11{overscore (2)}0> crystallographic directions and crystallographic c-axis, and wherein said selected crystal plane is the (0001) plane and wherein said predetermined angle is less than 10 degrees. 17. The method according to claim 16, wherein said single-crystal substrate is selected from a group of materials consisting of 6H—SiC; 4H—SiC; 2H—GaN; 2H—AlN; 2H—AlGaN; and 2H—InGaN, 2H—InN. 18. The method according to claim 17, wherein said replicating nonremovable stepsource dislocation is a c-axis screw dislocation that replicates during growth along a direction within 15 degrees of parallel to said crystallographic c-axis. 19. The method according to claim 18, wherein said at least one interior border shape is a hexagon, with each side of each said hexagon aligned to within 5 degrees of being perpendicular to a said <1{overscore (1)}00> crystallographic direction. 20. The method according to claim 19, wherein said hexagon is an equilateral hexagon having a geometric center, and wherein said selected lateral location is the geometric center of the said equilateral hexagon having a geometric center. 21. The method according to claim 18, wh erein said at least one interior border shape is a hexagon, with each side of each said hexagon aligned to within 5 degrees of being perpendicular to a said <11{overscore (2)}0> crystallographic direction. 22. The method according to claim 18, wherein said interior border shape is a hexagon. 23. The method according to claim 18, wherein said interior border shape is a triangle. 24. The method according to claim 23, wherein said interior border shape forms an equilateral triangle having a geometric center. 25. The method according to claim 24, wherein each side of said equilateral triangle is aligned to within 5 degrees of being perpendicular to a said <1{overscore (1)}00> crystallographic direction, and wherein said selected lateral location is the geometric center of the said equilateral triangle. 26. The method according to claim 24, wherein each side of said equilateral triangle is aligned to within 5 degrees of being perpendicular to a said <11{overscore (2)}0> crystallographic direction, and wherein said selected lateral location is the geometric center of the said equilateral triangle. 27. The method according to claim 1, wherein said selected separated second growth surface contains a plurality of said enclosed hollow regions. 28. The method according to claim 1, wherein said single crystal substrate has a basal plane, and wherein said selected crystal plane is said basal plane. 29. The method according to claim 1, wherein said predetermined angle is less than 1 degree. 30. The method according to claim 29, wherein said single-crystal substrate has a crystallographic c-axis and is comprised of a hexagonal polytype of silicon carbide, and wherein said replicating nonremovable stepsource dislocations are screw dislocations occurring along said crystallographic c-axis of said single-crystal substrate. 31. The method according to claim 30, wherein said step of treating said at least one selected separated second growth surface in said step d) of claim 1 is provided by a gaseous step-flow etch and wherein said step-flow etch is carried out in a suitable growth/etching system at a temperature greater than 1000° C., but less than 2000° C. in a vapor selected from the group of vapors consisting of (1) hydrogen, (2) hydrogen plus hydrogen chloride, (3) and a mix of hydrogen with other gases selected from the group consisting of hydrocarbons, inert gases, and oxygen. 32. The method according to claim 30, wherein said step of treating said at least one selected separated second growth surface in said step d) of claim 1 is provided by a sublimation step-flow etch process and wherein said step-flow etch process is carried out in a growth/etching system at a temperature greater than 1800° C., but less than 2500° C. 33. The method according to claim 30, wherein said homoepitaxial growth is carried out in a suitable crystal growth system that supplies silicon containing growth precursor and carbon containing growth precursor to the said separated second growth surface at a substrate temperature between 1000° C. and 2500° C. 34. The method according to claim 1, wherein said removal of material in step c) of claim 1 is accomplished using a process selected from the group consisting of cutting with a cutting tool, patterned dry etching, patterned wet etching, and laser-based cutting. 35. The method according to claim 1, wherein said single crystal planar first growth surface contains selected plurality of regions that have relatively high nonremovable stepsource dislocation density and at least one selected region that has relatively low nonremovable stepsource dislocation density, wherein said high nonremovable stepsource dislocation density is at least ten (10) times greater than the said low nonremovable stepsource dislocation density. 36. The method according to claim 35, wherein said regions of high nonremovable stepsource dislocation density comprises an array of high dislo cation density island regions, wherein each said high dislocation density island region is enclosed by said region of relatively low nonremovable stepsource dislocation density. 37. The method according to claim 36, wherein said selected separated second growth surface is selected to reside substantially entirely within said selected at least one region that has relatively low nonremovable stepsource dislocation density. 38. The method according to claim 37, wherein said single crystal substrate is produced by a patterned lateral epitaxial overgrowth (LEO) process. 39. The method according to claim 38, wherein said single crystal substrate is a heteroepitaxial layer grown on top of a different crystal material than said single crystal substrate material. 40. The method according to claim 38, wherein said patterned lateral epitaxial overgrowth (LEO) process is accomplished using a first LEO selective growth seed region pattern selected to produce an array of first LEO enclosed hollow regions with cumulative first LEO hollow region area selected to be greater than the area of said first LEO selective growth seed region pattern, and wherein said first LEO enclosed hollow region shapes are selected to obtain first LEO film coalescence within selected first LEO coalescence regions. 41. The method according to claim 40, wherein said patterned lateral epitaxial overgrowth (LEO) process is accomplished using a second LEO selective growth seed region pattern selected to be an array of second LEO enclosed hollow regions with cumulative second hollow region area selected to be greater than the area of the said second selective growth seed region pattern, and wherein said second enclosed hollow region shapes are selected to obtain lateral epitaxial overgrowth film coalescence within second selected lateral epitaxial coalescence regions, and wherein the pattern overlap between the said first selective growth seed region pattern and said second selective growth seed region pattern is less than 20% of said area of the said first selective growth seed region, and wherein none of the second selective growth seed region pattern overlaps said first selected lateral epitaxial coalescence regions. 42. The method according to claim 41, wherein said selected second growth surface is selected to enclose regions where said first selective growth seed region pattern and said second selective growth seed region overlap, and wherein said second growth surface also encloses said second lateral epitaxial coalescence regions. 43. The method according to claim 42, wherein said single crystal substrate is selected from the group of hexagonal crystal structure materials with (0001) crystallographic basal plane consisting of 2H—GaN; 2H—AlN; 2H—AlGaN; and 2H—InGaN, wherein said first growth surface is within ten (10) degrees of parallel to the (0001) crystallographic basal plane. 44. A method for combining screw dislocations on a selected single crystal substrate having a basal plane, thickness in the direction normal to the basal plane, and an initial first average density of replicating nonremovable stepsource dislocations, said method comprising the steps of:(a) choosing a single crystal substrate material which exhibits a property that the material therein contains a basal plane whereby under selected growth conditions the growth rate due to step-flow growth along the basal plane is greater than at least one hundred (100) times a growth rate perpendicular to the basal plane due to growth involving two-dimensional nucleation;(b) preparing a planar first growth surface on the single crystal substrate that is parallel to within 10 degrees to the basal plane;(c) removing material in the first growth surface to form holes completely through the single crystal substrate thickness so as to define at least one selected separated second growth surface with border shape selected to have at least one enclosed hollow region with interior bord er shape selected to obtain lateral coalescence at a lateral point and a cumulative hollow region area selected greater than half the inverse of the said average density of nonremovable stepsource dislocations in said single crystal substrate;(d) treating said at least one selected separated growth surface so as to remove any removable sources of unwanted crystal nucleation and any removable sources of growth steps therein;(e) depositing a homoepitaxial film on said separated second growth surface under selected conditions so as to provide a step-flow growth along the basal plane while suppressing two-dimensional nucleation;(f) continuing said deposition of said homoepitaxial film so that the step-flow growth produces lateral growth toward the interior of said at least one enclosed hollow region; and(g) continuing said deposition of said homoepitaxial film until the lateral growth completes lateral coalescence at point within said at least one enclosed hollow region forming a third growth surface with second average screw dislocation density characteristic that is less than said first average screw dislocation density characteristic. 45. The method according to claim 44, further comprising:(h) continuing said deposition of said homoepitaxial film until homoepitaxial film of desired vertical thickness on top of the selected third growth surface is achieved. 46. The method according to claim 45, wherein said single crystal substrate has a predetermined volume and wherein said homoepitaxial film is grown to sufficient size so as to produce at least one large crystal of a greater volume than that of said single crystal substrate. 47. The method according to claim 46, wherein said at least one large crystal is further processed into one or more crystal wafers. 48. The method according to claim 47, wherein said one or more crystal wafers are employed as seed crystals for production of additional large crystals of greater size than the said single crystal substrate. 49. The method according to claim 44, wherein said single crystal substrate is 15R—SiC. 50. The method according to claim 44, wherein said single crystal substrate has a hexagonal crystal structure with <0001>, <1{overscore (1)}00>, and <11{overscore (2)}0> crystallographic directions and crystallographic c-axis. 51. The method according to claim 50, wherein said single crystal substrate is selected from a group of materials consisting of 6H—SiC; 4H—SiC; 2H—GaN; 2H—AlN; 2H—AlGaN; and 2H—InGaN, 2H—InN. 52. The method according to claim 51, wherein said replicating nonremovable stepsource dislocation is a c-axis screw dislocation that replicates during growth along a direction within 15 degrees of parallel to said crystallographic c-axis. 53. The method according to claim 52, wherein said at least one interior border shape is a hexagon, with each side of each said hexagon aligned to within 5 degrees of being perpendicular to a said <1{overscore (1)}00> crystallographic direction. 54. The method according to claim 53, wherein said hexagon is an equilateral hexagon having a geometric center. 55. The method according to claim 52, wherein said at least one interior border shape is a hexagon, with each side of each said hexagon aligned to within 5 degrees of being perpendicular to a said <11{overscore (2)}0> crystallographic direction. 56. The method according to claim 52, wherein said interior border shape is a hexagon. 57. The method according to claim 52, wherein said interior border shape is a triangle. 58. The method according to claim 57, wherein said interior border shape forms an equilateral triangle having a geometric center. 59. The method according to claim 58, wherein each side of said equilateral triangle is aligned to within 5 degrees of being perpendicular to a said <1{overscore (1)}00> crystallographic direction. 60. The method according to claim 58 , wherein said interior border forms an equilateral triangle and wherein each side of said equilateral triangle is aligned to within 5 degrees of being perpendicular to a said <1{overscore (1)}20> crystallographic direction. 61. The method according to claim 44, wherein said selected separated second growth surface contains a plurality of said enclosed hollow regions. 62. The method according to claim 44, wherein said planar first growth surface is parallel to within 1 degree of the said basal plane. 63. The method according to claim 62, wherein said single-crystal substrate has a crystallographic c-axis and is comprised of a hexagonal polytype of silicon carbide, and wherein said replicating nonremovable stepsource dislocations are screw dislocations occurring along said crystallographic c-axis of said single-crystal substrate. 64. The method according to claim 63, wherein said step of treating said at least one selected separated second growth surface in said step d) of claim 1 is provided by a gaseous step-flow etch and wherein said step-flow etch is carried out in a suitable growth/etching system at a temperature greater than 1000° C., but less than 2000° C. in a vapor selected from the group of vapors consisting of (1) hydrogen, (2) hydrogen plus hydrogen chloride, (3) and a mix of hydrogen with other gases selected from the group consisting of hydrocarbons, inert gases, and oxygen. 65. The method according to claim 63, wherein said step of treating said at least one selected separated second growth surface in said step d) of claim 44 is provided by a sublimation step-flow etch process and wherein said step-flow etch process is carried out in a growth/etching system at a temperature greater than 1800° C., but less than 2500° C. 66. The method according to claim 63, wherein said homoepitaxial growth is carried out in a suitable crystal growth system that supplies silicon containing growth precursor and carbon containing growth precursor to the said separated second growth surface at a substrate temperature between 1000° C. and 2500° C. 67. The method according to claim 44, wherein said removal of material in step c) of claim 44 is accomplished using a process selected from the group consisting of cutting with a cutting tool, patterned dry etching, patterned wet etching, and laser-based cutting. 68. The method according to claim 44, wherein said single crystal planar first growth surface contains selected plurality of regions that have relatively high nonremovable stepsource dislocation density and at least one selected region that has relatively low nonremovable stepsource dislocation density, wherein said high nonremovable stepsource dislocation density is at least ten (10) times greater than said low nonremovable stepsource dislocation density. 69. The method according to claim 68, wherein said regions of high nonremovable stepsource dislocation density comprises an array of high dislocation density island regions, wherein each of said high dislocation density island region is enclosed by said region of relatively low nonremovable stepsource dislocation density. 70. The method according to claim 69, wherein said selected separated second growth surface is selected to reside entirely within said selected at least one region that has relatively low nonremovable stepsource dislocation density. 71. The method according to claim 70, wherein said single crystal substrate is produced by a patterned lateral epitaxial overgrowth (LEO) process. 72. The method according to claim 71, wherein said single-crystal substrate is selected from the group of hexagonal crystal structure materials with (0001) crystallographic basal plane consisting of 2H—GaN; 2H—AlN; 2H—AlGaN; and 2H—InGaN, and wherein said first growth surface is within ten (10) degrees of parallel to the (0001) crystallographic basal plane.