Method for growth of bulk crystals by vapor phase epitaxy

• US 20040144301A1
• Filed: 01/24/2003
• Published: 07/29/2004
• Est. Priority Date: 01/24/2003
• Status: Abandoned Application

• Current Assignee: Administrator of The National Aeronautics and Space Administration
• Original Assignee: Administrator of The National Aeronautics and Space Administration
• Inventors: Neudeck, Philip G., Powell, J. Anthony
• Application Number:
  US10/352,552
• Publication Number:
  US 20040144301A1
• Time in Patent Office: Days
• US Class Current: 117/86
• CPC Class Codes: C30B 25/02 Epitaxial-layer growth
• CPC Class Codes: C30B 25/18 characterised by the substrate
• CPC Class Codes: C30B 29/36 Carbides

Abstract

Methods for vapor phase growth of relatively large bulk single crystals free (or nearly free) of extended structural crystal defects are disclosed. In one embodiment, an initial seed crystal is produced on an atomically-flat crystal surface which does not have to be of the same crystal structure and material as the seed crystal. For the bulk crystal growth, the methods of the present invention primarily utilize a growth mechanism based on crystal nucleation at the edge and corners of crystal facets of the growing crystal. The invention has application in growth of single crystals of wide bandgap semiconducting materials for use in harsh-environment and/or high power electronics and micromechanical systems.

Claims

1. A method for the vapor phase crystal growth of one or more single crystals of a selected second crystal material starting with a selected first crystal, wherein said first crystal material is different than said second crystal material, and wherein said method comprises the steps of:

(a) selecting said first crystal material whose chemical bonding structure is tetrahedral, and said first crystal material being characterized by exhibiting a behavior that a step-free basal plane surface is produced on a selected planar surface of said first crystal material, wherein said selected planar surfaces have a crystallographic orientation that is within one (1) degree of a basal plane orientation of said first crystal material, and wherein said step-free surface can be produced under selected crystal growth conditions;

(b) selecting said second crystal material whose chemical bonding structure is tetrahedral and whose crystal structure is cubic, and is characterized by exhibiting the behavior that (1) under a first set of selected growth conditions said second crystal material exhibits single-island heteroepitaxial crystal growth which is obtained having a sequence of bilayers of said second crystal material on selected step-free surfaces of said selected first crystal and (2) under a second set of selected crystal growth conditions said second crystal material subsequently exhibits homoepitaxial crystal growth of additional said second crystal material on said second crystal material by having step flow growth occurring at steps on the surfaces of said second crystal material initiated by an edge/corner nucleation mechanism at a rate that is more than a rate of crystal growth due to step flow growth at steps on the surfaces of said second crystal material initiated at defects in the second crystal material,

(c) preparing at least one step-free top surface on said selected first crystal, wherein said at least one step-free top surface is of selected shape and selected crystallographic surface orientation that defines at least one step free interface plane,

(d) initiating single-island heteroepitaxial crystal growth of bilayers of said second crystal material on top of said at least one step-free interface plane of said first crystal,

(e) continuing crystal growth by said homoepitaxial crystal growth of additional said second crystal material above said interface plane under said second set of selected crystal growth conditions that yields homoepitaxial crystal growth of said second crystal material by step flow growth at steps initiated by an edge/corner nucleation mechanism at said rate that is more than said rate of crystal growth due to step flow growth at steps initiated at said defects, and

(f) continuing said homoepitaxial crystal growth of said second crystal material in a selected manner so that said crystal growth occurs without impedance or convergence from other solid materials until desired said second crystal material crystal shape and height are achieved forming at least one first selected crystal stack.

2. The method according to claim 1, wherein said selected first crystal has a wafer-like shape with a selected topside defined as the side of said selected crystal wafer on which said second crystal material is deposited, and wherein an opposite side of said selected crystal wafer is defined as being the bottomside.

3. The method according to claim 2, wherein said at least one step-free top surface is comprised of an array of separated step-free top surfaces produced on top of mesas each with a selected shape, orientation, and mesa height formed by patterning trenches with selected trench depth and selected lateral trench width into the said first crystal material, whereby said at least one first selected crystal stack is comprised of multiple first selected crystal stacks.

4. The method according to claim 3 further comprising the steps of:

(g) selecting one or more of the said first selected crystal stacks;

(h) physically isolating one or more of said first selected crystal stacks of step (g), thereby producing one or more second selected crystal stacks;

(i) supporting the said one or more second selected crystal stacks on a support structure suitable for additional crystal growth.

(j) carrying out additional growth of said one or more second selected crystal stacks such that said second crystal material above the said interface plane is allowed to grow and expand without impedance or coalescence with any other solid material; and

(k) continuing growth of said one or more second selected crystal stacks until a desired stack size and shape is achieved.

5. The method according to claim 4, wherein each of said one or more second crystal stacks selected for step (i) is supported by said suitable support structure that passes through a movable baffle plate that (1) can be positionable close to the growing said second crystal stack throughout said steps (j) and (k), (2) can allow material deposition on the baffle plate in the vicinity of the growing said second crystal stack during said steps (j) and (k), and (3) can be moveable away from the growing said second crystal stack during said crystal growth so as to prevent said material deposition on the said baffle plate from coalescing with the growing said second crystal stack.

6. The method according to claim 4, wherein said additional growth of steps (j) and (k) includes supplying gas flow, wherein said gas flow is for a vapor growth process, and wherein said gas flow is non-uniform in composition with respect to a concentration of precursors applied to each of said selected second crystal stacks so as to minimize precursor concentration in the vicinity of said support structure so as to minimize crystal growth in the vicinity of the said support structure.

7. The method according to claim 4, wherein said additional growth of steps (j) and (k) includes supplying gas flow, wherein said gas flow is for a vapor growth process and is directed toward the growing crystal at a location furthest from said support structure for said additional growth of each of said second crystals stacks.

8. The method according to claim 4, wherein each said second selected crystal stacks is comprised of a single crystal stack.

9. The method according to claim 4, wherein said step (g) is comprised of steps of:

(g1) performing an analysis that reveals crystal defects in said selected second crystal material within said first selected crystal stacks; and

(g2) based upon inspection of the results produced by step (g1), selecting the one or more of the said first crystal stacks that exhibit the lowest defect density within the said second crystal material.

10. The method according to claim 9, wherein said performed analysis is selected from the group of treatments comprising:

a thermal oxidation technique, a defect-preferential chemical etch, an X-ray analysis technique, and a surface profilometry technique.

11. The method according to claim 4, wherein said physically isolating of said first crystal stacks is accomplished using a process selected from the group comprising cutting with a dicing saw, patterned dry etching, non-patterned dry etching, patterned wet etching, non-patterned wet etching, laser-based cutting, cleaving, mechanical lapping, and patterned application of a growth-inhibiting material.

12. The method according to claim 11, wherein at least one said selected processes for physically isolating said first selected crystal stacks is carried out on said bottom side of said first crystal, and wherein the bottom side of the said second crystal stack is defined to be the same side as the said bottom side of the said first crystal.

13. The method according to claim 12, wherein said processes are selected to be carried out by patterned etching of said first crystal bottom side, wherein the pattern is selected to have means to facilitate supporting said selected second crystal stack.

14. The method according to claim 13, wherein said selected pattern and said patterned etching are selected to produce a hole cavity in the said second crystal stack bottom side with a depth less than 80% of the height of the crystal stack.

15. The method according to claim 13, wherein said selected pattern and said patterned etching are selected to produce a hole cavity in the said second crystal stack bottom side that does not penetrate the said interface plane.

16. The method according to claim 12, wherein said selected process removes entirely said first crystal material so that second said selected crystal stack is comprised entirely of said selected second material.

17. The method according to claim 4, wherein said additional growth of steps (j) and (k) includes providing a support for said second selected crystal stack that does not reside above the said interface plane.

18. The method according to claim 1, wherein said first crystal material is selected from the group consisting of 4H—

SiC, 6H—

SiC, and 15R-SiC.

19. The method according to claim 1, wherein said second crystal material is selected from the group consisting of 3C—

SiC, diamond, cubic-GaN, cubic-AlN, cubic-AlGaN, cubic-InN, cubic-InGaN.

20. The method according to claim 1, wherein said first set of selected growth conditions comprise a set of growth parameters comprising at least crystal temperature, reactor pressure, concentration of reactor precursors for material being deposited, concentration gradients of said reactor precursors, composition of carrier gas used in said reactor, and flow rate of carrier gas within said reactor.

21. The method according to claim 1, wherein said first set of selected growth conditions provide a growth process selected from the group consisting of chemical vapor deposition, physical vapor phase epitaxy, and sublimation processes.

22. The method according to claim 1, wherein said first set of selected growth conditions provides a growth process consisting of chemical vapor deposition.

23. The method according to claim 22, wherein said chemical vapor deposition is carried out using precursor gases that are silane and a hydrocarbon for the growth of silicon carbide.

24. The method according to claim 23, wherein the said second crystal material is 3C—

SiC.

25. The method according to claim 24, wherein said second set of growth conditions for the crystal growth include a temperature in the range of 1000°

C. to 2000°

C.

26. The method according to claim 3, wherein said shape of said step-free top surfaces is selected to be devoid of concave border features.

27. The method according to claim 3, wherein the shape and orientation of said at least one step-free top surface is selected to conform to the preferred growth shape and orientation of said second crystal material on top of said first crystal.

28. The method according to claim 3, wherein growth of the said first crystal material toward said interface plane is prevented by selectively coating bottom of said trenches in said first crystal material with a growth inhibiting material.

29. The method according to claim 3, wherein said mesas are selected with said mesa height that exceeds said desired height of said second material.

30. The method according to claim 3, wherein said growth of the said first crystal material toward said interface plane is prevented by selectively applying a growth inhibiting material to the said trenches.

31. The method according to claim 1, wherein said selected second crystal material is 3C—

SiC, and wherein said first crystal is a hexagonal polytype of silicon carbide with a stacking sequence and c-axis sequence repeat height, and wherein said single crystals of second crystal material has selected crystal orientation with respect to the said first crystal, and wherein said selected shape of said at least one step-free top surface is a triangle whose three sides are perpendicular to within 10 degrees to one of the two selected sets of three <

1{overscore (1)}00>

crystallographic directions with 120 degrees of angular separation, and wherein the following operational steps are carried out after said operational step (c) of claim 1 and before the initiation of said operational step (d) of claim 1;

(ci) providing a step-flow etch of said at least one step-free top surface with triangular shape so as to provide a sequence of concentric triangular plateaus wherein adjacent said plateaus are vertically separated by steps of said c-axis repeat height so that topmost two bilayers of said plateaus all have a selected stacking sequence;

(cii) depositing a homoepitaxial film on said sequence of concentric triangular plateaus under selected conditions so as to provide step-flow growth while suppressing two-dimensional nucleation; and

(ciii) continuing said deposition of said homoepitaxial film on said concentric triangular plateaus until said step-flow growth obtains an at least one step-free top surface that has topmost two bilayers of selected stacking sequence that defines at least one step-free interface plane.

32. The method according to claim 31, wherein said at least one step-free surface is comprised of an array of said step-free surfaces with triangular shape.

33. The method according to claim 32, wherein each three sides of said triangular shape step-free surfaces are perpendicular to within 10 degrees to the same said selected set of three <

1100>

crystallographic directions with 120 degrees of angular separation.

34. The method of 32 wherein said 3C—

SiC material is used in the fabrication of semiconductor devices.

35. A method for the vapor phase crystal growth of a relatively large single crystal of a selected crystal material starting from a selected seed crystal of the same crystal material, wherein said method comprises the steps of:

(a) selecting a seed crystal whose chemical bonding structure is tetrahedral, whose crystal structure is cubic, and which is characterized by exhibiting the behavior that under selected crystal growth conditions said selected crystal subsequently exhibits homoepitaxial crystal growth by having step flow growth occurring at steps on the surfaces of said selected seed crystal initiated by an edge/corner nucleation mechanism at a rate that is more than the rate of crystal growth due to step flow growth at steps on the surfaces of said selected seed crystal initiated at defects in the said crystal,

(b) supporting the said selected seed crystal with a selected support structure in a manner that during subsequent crystal growth under said selected growth conditions, said crystal growth occurs without impedance or convergence of the growing crystal with any solid material that is external to said growing crystal,

(c) initiating crystal growth of said crystal material on said selected seed crystal under said first set of selected crystal growth conditions that yields homoepitaxial crystal growth of low-defect crystal by step-flow growth at steps on the surface of the selected seed crystal initiated by said edge/corner nucleation mechanism at a said rate that is more than said rate of crystal growth due to step-flow growth at steps on the surface of said selected seed crystal initiated at defects in the said selected seed crystal, and

(d) continuing said homoepitaxial crystal growth of said seed selected crystal in a selected manner so that said crystal growth occurs without impedance or convergence of the growing said seed crystal with solid materials external to said growing crystal until a desired shape and height of said single crystal is achieved forming at least one large low-defect crystal of said selected crystal material.

36. The method according to claim 35, wherein said seed crystal is supported by said suitable support structure that passes through a movable baffle plate that (1) can be positionable close to the growing said seed crystal throughout said homoepitaxial crystal growth, (2) can allow material deposition on the baffle plate in the vicinity of the growing said seed crystal during said homoepitaxial crystal growth, and (3) can be moveable away from the growing said seed crystal during said homoepitaxial crystal growth so as to prevent said material deposition on the said baffle plate from coalescing with the growing said seed crystal.

37. The method according to claim 35, wherein said homoepitaxial crystal growth includes supplying gas flow, wherein said gas flow is for a vapor growth process, and wherein said gas flow is non-uniform in composition with respect to a concentration of precursors applied to said seed crystal so as to minimize precursor concentration in the vicinity of said support structure so as to minimize crystal growth in the vicinity of the said support structure.

38. The method according to claim 37, wherein said selected growth conditions are such that said gas flow for said vapor growth process is directed toward the growing said seed crystal at a location furthest from said support structure so as to minimize growth in the vicinity of the support structure.

39. The method according to claim 35, wherein said selected growth conditions comprise a set of growth parameters comprising at least crystal temperature, reactor pressure, concentration of reactor precursors for material being deposited, concentration gradients of said reactor precursors, composition of carrier gas used in said reactor, and flow rate of carrier gas within said reactor.

40. The method according to claim 35, wherein said selected growth conditions provide a growth process selected from the group consisting of chemical vapor deposition, physical vapor phase epitaxy, and sublimation processes.

41. The method according to claim 35, wherein said seed crystal material is selected from the group consisting of 3C—

SiC, diamond, cubic-GaN, cubic-AlN, cubic-AlGaN, cubic-InN, cubic-InGaN.

42. The method of claim 35, wherein said selected growth conditions provide a growth process consisting of chemical vapor deposition.

43. The method of claim 42, wherein said chemical vapor deposition is carried out using precursor gases that are silane and a hydrocarbon for the growth of silicon carbide.

44. The method of claim 43, wherein said seed crystal material is 3C—

SiC.

45. The method of claim 44, wherein said growth conditions for crystal growth include a temperature in the range of 1000°

C. to 2000°

C.

46. A method for producing an array of 3C—

SiC single crystals on a single crystal substrate having a crystal basal plane, wherein each of said 3C—

SiC single crystals has a predetermined crystal orientation with respect to the said single crystal substrate, said method comprising the operational steps of;

(a) selecting said single-crystal substrate from hexagonal polytypes of silicon carbide that have two possible sets of three <

1100>

crystallographic directions with 120 degrees of angular separation;

b) preparing a planar first surface on said single-crystal substrate wherein said planar first surface is tilted by an angle of less than ten (10) degrees with respect to the crystal basal plane;

(c) removing material from said planar first surface so as to define a plurality of mesas with separated planar top second surfaces, wherein each of said separated planar top second surfaces is selected to be a triangle whose three sides are perpendicular to, within 10 degrees, one of the said two possible sets of three <

1100>

crystallographic directions with 120 degrees of angular separation;

(d) treating said separated planar top second surfaces of said mesas so as to remove any removable sources of unwanted crystal nucleation and any removable sources of steps from said separated planar top second surfaces;

(e) depositing a first homoepitaxial film over said separated planar top second surfaces of said mesas under selected first growth conditions so as to provide a step-flow growth while suppressing two-dimensional nucleation;

(f) continuing said deposition of said homoepitaxial film until said step-flow growth obtains first step-free epitaxial film surface on at least one of the said separated planar top second surfaces;

(g) providing a step-flow etch of said first step-free epitaxial film surfaces so as to provide concentric triangular plateaus having sequentially increasing heights and forming structural steps;

(h) depositing a second homoepitaxial film on said sequence of concentric triangular plateaus under selected second growth conditions so as to provide step-flow growth while suppressing two-dimensional nucleation;

(i) continuing said deposition of said second homoepitaxial film on said concentric triangular plateaus until said step-flow growth obtains a second step-free epitaxial film surface that defines a step-free interface plane for each mesa;

(j) initiating single-island heteroepitaxial crystal growth of bilayers of 3C—

SiC on top of said step-free interface planes.

(k) continuing said crystal growth of additional 3C—

SiC above the said interface planes under a third set of selected crystal growth conditions that yields homoepitaxial crystal growth of 3C—

SiC by an edge/corner nucleation mechanism at a rate that is more than the rate of crystal growth due to step-flow growth at steps initiated at defects in said 3C—

SiC single crystals;

(l) continuing said homoepitaxial 3C—

SiC crystal growth in a selected manner so that said crystal growth occurs without impedance or convergence from other solid materials until the desired 3C—

SiC crystal shape and height is achieved on each of said mesas.

47. The method according to claim 46, wherein said 3C—

SiC crystals are used in the fabrication of semiconductor devices.

48. The method according to claim 46, wherein said selected first, second, and third growth conditions comprise a set of growth parameters comprising at least crystal temperature, reactor pressure used for said deposition, concentration of reactor precursors for material being deposited, concentration gradients of said reactor precursors, composition of carrier gas used in said reactor, and flow rate of carrier gas within said reactor.

49. The method according to claim 46, wherein said selected growth conditions provide a growth process selected from the group consisting of chemical vapor deposition, physical vapor phase epitaxy, and sublimation processes.

50. The method according to claim 46, wherein said selected growth conditions provide a growth process consisting of chemical vapor deposition.

51. The method according to claim 49, wherein said chemical vapor deposition is carried out using precursor gases that are silane and a hydrocarbon for the growth of silicon carbide.

52. The method according to claim 50, wherein the growth temperature is in the range 1000°

C. to 2000°

C.

53. The method according to claim 46, wherein said second selected growth conditions are selected to be the same as said first selected growth conditions.