Large diameter, high quality SiC single crystals, method and apparatus

Abstract

A method and system of forming large-diameter SiC single crystals suitable for fabricating high crystal quality SiC substrates of 100, 125, 150 and 200 mm in diameter are described. The SiC single crystals are grown by a seeded sublimation technique in the presence of a shallow radial temperature gradient. During SiC sublimation growth, a flux of SiC bearing vapors filtered from carbon particulates is substantially restricted to a central area of the surface of the seed crystal by a separation plate disposed between the seed crystal and a source of the SiC bearing vapors. The separation plate includes a first, substantially vapor-permeable part surrounded by a second, substantially non vapor-permeable part. The grown crystals have a flat or slightly convex growth interface. Large-diameter SiC wafers fabricated from the grown crystals exhibit low lattice curvature and low densities of crystal defects, such as stacking faults, inclusions, micropipes and dislocations.

The invention claimed is: 
     
       1. A method of fabricating a SiC single crystal comprising:
 (a) sublimation growing a SiC single crystal on a surface of a seed crystal in the presence of a temperature gradient; and 
 (b) during step (a), controlling said temperature gradient such that a radial temperature gradient in the SiC single crystal is positive and substantially shallow, and controlling a flux of SiC bearing vapors by substantially restricting said flux to a central area of the surface of the seed crystal via a separation plate disposed between the seed crystal and a source of the SiC bearing vapors, wherein the separation plate includes an outer flux permeable part surrounding an inner flux permeable part that is more permeable to the flux of SiC bearing vapors than the outer flux permeable part, wherein the central area of the surface of the seed crystal is between 30% and 60% of a total surface area of the seed crystal around a center of the seed crystal, wherein a ratio of mass transport of the SiC bearing vapors through 1 cm 2  of area of the inner part of the separation plate versus the mass transport of the SiC bearing vapors through 1 cm 2  of area of the outer part of the separation plate is no less than 50/1. 
 
     
     
       2. The method of  claim 1 , wherein the central area of the surface of the seed crystal is between 30% and 60% of a total surface area of the seed crystal substantially around a center of the seed crystal. 
     
     
       3. The method of  claim 1 , wherein step (b) includes restricting the flux of SiC bearing vapors to the central area of the surface of the seed crystal via a separation plate disposed between the seed crystal and a source of the SiC bearing vapors. 
     
     
       4. The method of claim  3  1, wherein:
 the separation plate is spaced from the seed crystal at a distance between about 25% and 75% of the seed a diameter from of the seed crystal; and 
 the separation plate has a thickness between about 4 mm and 10 mm. 
 
     
     
       5. The method of claim  3  1, wherein the separation plate is either not reactive to the SiC bearing vapors or includes a coating to avoid contact between the separation plate and the SiC bearing vapors. 
     
     
       6. The method of  claim 3 , wherein the separation plate includes a first, outer part surrounding a second, inner part that is substantially more permeable to the SiC bearing vapors than the first, outer part. 
     
     
       7. The method of claim  6  1, wherein:
 the second, inner part of the separation plate comprises between 20% and 50% of a total area of the separation plate; or 
 the separation plate is made of graphite, or a refractory compound, tantalum carbide, or niobium carbide; or 
 a ratio of mass transport of the SiC bearing vapors through 1 cm 2  of area of the inner part of the separation plate versus the mass transport of the SiC bearing vapors through 1 cm 2  of area of the outer part of the separation plate is no less that about 50/1; and 
 the inner part of the separation plate that is more permeable to the flux of SiC bearing vapors than the outer part comprises between 20% and 50% of a total area of the separation plate. 
 
     
     
       8. The method of claim  3  1, wherein the separation plate is configured to substantially remove particles from the flux of the SiC bearing vapors. 
     
     
       9. The method of  claim 1 , wherein step (a) further includes sublimation growing the SiC single crystal in the presence of at least one of the following: an isotherm that is convex in a direction facing a the source of the SiC bearing vapors; and?, and a radial temperature gradient of no more than about 10 K/cm. 
     
     
       10. The method of  claim 9 , wherein a difference in thickness between a center of the SiC single crystal and a diameter of the SiC single crystal in a growth direction of the SiC single crystal is no more than about 6 mm. 
     
     
       11. The method of  claim 1 , further including slicing from the grown SiC single crystal a wafer having one or more of the following:
 a combined area of stacking faults no more than about 5%, 2%, or 1% of a total area of the wafer; or and 
 a lattice curvature of no more than about 0.2°, 0.1°, or 0.06°, over the total area of the wafer; or and 
 a full width at half maximum (FWHM) x-ray reflection of no more than about 50, 30, or 20 arc-seconds over the total area of the wafer; or and 
 a wafer-average micropipe density (MPD) of no more than about 1/cm 2  1 cm −2 , 0.2/cm 2  cm −2 , or 0.1/cm 2  cm −2 ; or and 
 a wafer-average dislocation density of no more than about 10,000 cm −2 , 5,000 cm −2 , or 1,000 cm −2 . 
 
     
     
       12. The method of  claim 1 , wherein the grown SiC single crystal has a diameter between about 100 mm and 200 mm  sufficient for slicing wafers of 100, 125, 150 or 200 mm in diameter. 
     
     
       13. The method of  claim 1 , further including slicing from the grown SiC single crystal a wafer having one or more of the following:
 a wafer-average micropipe density no more than about an average of 1/cm 1 cm −2 ; or and 
 a percentage of micropipe-free 2 mm×2 mm square dies extracted from the wafer of not less than about 95%; or and 
 a percentage of micropipe-free 5 mm×5 mm square dies extracted from the wafer of not less than about 90%; or and 
 a wafer-average density of dislocations not more than about 10 4 /cm cm −2 ; or and 
 a density of threading screw dislocations of not more than about 1000/cm cm −2 ; or and 
 a density of basal plane dislocations of not more than about 300 cm/cm 3 ; or and 
 zero density of foreign polytype inclusions; or and 
 one or more clouds of wafer areas populated by carbon inclusions of no more than about 5% of the total wafer area; or and 
 edge-to-edge lattice curvature no more that about than 0.15°; or and 
 a full width at half maximum (FWHM) x-ray reflection of no more than about 25 arc-seconds over the total area of the wafer. 
 
     
     
       14. A SiC sublimation crystal growth system comprising;
 a growth crucible configured to be charged with SiC source material and a SiC seed crystal in spaced relation; and 
 a separation plate separating the growth crucible into a source compartment where the SiC source material resides when the growth crucible is charged with the SiC source material and a crystallization compartment where the SiC seed crystal resides when the growth crucible is charged with the SiC seed crystal, wherein:
 the separation plate is spaced from both the SiC source material and the SiC seed crystal; 
 the separation plate includes a first, central part surrounded by a second an outer part, wherein the central part and outer part of the separation plate are both permeable to SiC bearing vapors originating from the SiC source material during sublimation growth of a SiC crystal on the SiC seed crystal; 
 thatthe central part of the separation plate has a higher permeability to the SiC bearing vapors originating from the SiC source material during sublimation growth of the SiC crystal on the SiC seed crystal than the outer part; 
 the outer part of the separation plate has a lower permeability to the SiC bearing vapors originating from the SiC source material during sublimation growth of a the SiC crystal on the SiC seed crystal than the first, central part; and 
 the central part of the separation plate has an area between 20% and 50% of the total area of the separation plate; 
 the separation plate is configured to restrict a flux of the SiC bearing vapors to a central area of the surface of the SiC seed crystal that is between 30% and 60% of a total surface area of the SiC seed crystal around a center of the SiC seed crystal; and 
 a ratio of mass transport of the SiC bearing vapors through the inner central part of the separation plate versus mass transport of the SiC bearing vapors through the outer part of the separation plate is no less that about than 50/1. 
 
 
     
     
       15. The system of  claim 14 , wherein the separation plate is made from at least one of the following: graphite, or a refractory compound, tantalum carbide, or niobium carbide. 
     
     
       16. The system of  claim 14 , wherein the separation plate is spaced from the SiC seed crystal at a distance between about 20 mm and 70 mm. 
     
     
       17. The system of  claim 14 , wherein the separation plate includes a coating of tantalum carbide, or niobium carbide, and the coating has a thickness between about 20 microns to 40 microns. 
     
     
       18. The system of  claim 14 , wherein the first, central part of the separation plate includes passages, each of which has a maximum diameter between about 0.1 mm and 1 mm. 
     
     
       19. A method of forming a high-quality SiC single crystal wafer comprising:
 sublimation growing on a SiC single crystal seed a SiC single crystal boule having a diameter sufficient for slicing wafers between 100 and 200 mm in diameter, wherein said sublimation growth occurs in the presence of controlled axial and radial temperature gradients and a controlled flux of sublimated source material that is restricted, via a separation plate that is spaced from the source material and the SiC single crystal seed, to a central area of a surface of the SiC single crystal seed that is between 30% and 60% of a total surface area of the SiC single crystal seed around a center of the SiC single crystal seed, wherein the separation plate includes an outer flux permeable part surrounding an inner flux permeable part that is more permeable to the flux of sublimated source material than the outer flux permeable part, wherein a ratio of mass transport of the SiC bearing vapors through 1 cm 2  of area of the inner part of the separation plate versus the mass transport of the SiC bearing vapors through 1 cm 2  of area of the outer part of the separation plate is no less than 50/1; and 
 slicing from said SiC single crystal boule a SiC single crystal wafer having:
 a diameter between 100 and 200 mm inclusive; and 
 a lattice curvature of no more than about 0.2°, 0.1°, or 0.06° over the total area of the wafer; and 
 a full width at half maximum (FWHM) of the x-ray reflection of no more than about 50, 30, or 20 arc-seconds over the total area of the wafer. 
 
 
     
     
       20. The method of  claim 19 , wherein the SiC single crystal wafer further includes a combined area of stacking faults no more than about 5%, 2%, or 1% of a total area of the SiC single crystal wafer. 
     
     
       21. The method of  claim 19 , wherein the SiC single crystal wafer further includes at least one of the following:
 a wafer-average micropipe density (MPD) of no more than about 1 cm −2 , 0.2 cm −2 , or 0.1 cm −2 ; or and  
 a wafer-average dislocation density of no more than about 10,000 cm −2 , 5,000 cm −2 , or 1,000 cm −2 . 
 
     
     
       22. A method of forming a high-quality SiC single crystal wafer comprising:
 sublimation growing on a SiC single crystal seed a SiC single crystal boule having a diameter sufficient for slicing wafers between 100 and 200 mm in diameter, wherein said sublimation growth occurs in the presence of controlled axial and radial temperature gradients and a controlled flux of sublimated source material that is restricted, via a separation plate that is spaced from the source material, to a central area of the surface of the SiC single crystal seed that is between 30% and 60% of a total surface area of the SiC single crystal seed around a center of the SiC single crystal seed, wherein the separation plate includes an outer flux permeable part surrounding an inner flux permeable part that is more permeable to the flux of sublimated source material than the outer flux permeable part, wherein a ratio of mass transport of the SiC bearing vapors through 1 cm 2  of area of the inner part of the separation plate versus the mass transport of the SiC bearing vapors through 1 cm 2  of area of the outer part of the separation plate is no less than 50/1; and 
 slicing from said SiC single crystal boule a SiC single crystal wafer having a combined area of stacking faults no more than about 5%, 2%, or 1% of a total area of the SiC single crystal wafer. 
 
     
     
       23. The method of  claim 22 , wherein the SiC single crystal wafer further includes: a lattice curvature of no more than about 0.2°, 0.1°, or 0.06° over the total area of the SiC single crystal wafer. 
     
     
       24. The method of  claim 22 , wherein the SiC single crystal wafer further includes a full width at half maximum (FWHM) of the x-ray reflection of no more than about 50, 30, or 20 arc-seconds over the total area of the SiC single crystal wafer. 
     
     
       25. The method of  claim 22 , wherein the SiC single crystal wafer further includes at least one of the following:
 a wafer-average micropipe density (MPD) of no more than about 1 cm −2 , 0.2 cm −2 , or 0.1 cm −2 ; or and 
 a wafer-average dislocation density of no more than about 10,000 cm −2 , 5,000 cm −2 , or 1,000 cm −2 . 
 
     
     
       26. A high-quality SiC single crystal wafer having a diameter between 100 and 200 mm and comprising at least one of the following:
 a lattice curvature of no more than about 0.2°, 0.1°, or 0.06° over the total area of the wafer; or   a full width at half maximum (FWHM) of the x-ray reflection of no more than about 50, 30, or 20 arc-seconds over the total area of the wafer; or   a combined area of stacking faults no more than about 5%, 2%, or 1% of a total area of the wafer.   
     
     
       27. The SiC single crystal of  claim 26 , wherein the crystal comprises either a 4H polytype or a 6H polytype.