Silicon carbide single crystal and a method for its production
A bulk silicon carbide single crystal of good crystalline quality which includes a minimized number of structural defects and is free from micropipe defects can be produced by crystal growth in a melt of an alloy comprising Si, C, and M (wherein M is either Mn or Ti) and having an atomic ratio between Si and M in which the value of x, when express as Si 1-x M x , is 0.1≦x≦0.7 in the case where M is Mn or 0.1≦x≦0.25 in the case where M is Ti at a temperature of the melt which is below 2000° C. The C component is preferably supplied into the melt by dissolution of a graphite crucible which contains the melt such that the melt is free from undissolved C. One method of crystal growth is performed by cooling the melt after a seed substrate is immersed in the melt.
1. A method of producing a silicon carbide single crystal comprising the steps of: immersing a seed substrate of silicon carbide in a melt of an alloy comprising Si, C, and M (wherein M is either Mn or Ti) and having an atomic ratio between Si and M in which the value of x, when expressed as Si 1-x M x , is 0.1≦x≦0.7 in the case where M is Mn or 0.1≦x0.25 in the case where M is Ti, the melt being free from undissolved C; and allowing a silicon carbide single crystal to grow on the seed substrate by supercooling of the alloy melt as a molten solution at least in the vicinity of the seed substrate so as to create a state which is supersaturated with SiC.
2. A method as claimed in claim 1 wherein the supercooling of the alloy melt is achieved by cooling the alloy melt.
3. A method as claimed in claim 2 wherein the alloy melt has a temperature which is in the range of at least 1650° C. and at most 2000° C. when the substrate is immersed therein and wherein the cooling is performed at rate of 1-6° C./min.
4. A method as claimed in claim 2 wherein the growth of the silicon carbide single crystal on the substrate is continued by terminating the cooling of the alloy melt at a temperature which is higher than the solidus temperature of the alloy and subsequently performing supercooling repeatedly by repeated heating and cooling of the melt.
5. A method as claimed in claim 1 wherein the supercooling of the alloy melt is achieved by forming a temperature gradient in the alloy melt.
6. A method as claimed in claim 5 wherein the temperature gradient of the alloy melt is in the range of 5-100° C./cm and wherein the temperature of the alloy melt in the vicinity of the substrate is at least 1450° C. and at most 2000° C.
7. A method as claimed in claim 3 wherein the temperature is in the range of 1650-1850° C.
8. A method as claimed in claim 1 wherein the C in the alloy melt is supplied by dissolution of a carbonaceous crucible which contains the alloy melt.
9. A method as claimed in claim 6 where in the temperature is in the range of 1650-1850° C.
10. A method as claimed in claim 2 wherein the C in the alloy melt is supplied by dissolution of a carbonaceous crucible which contains the alloy melt.
11. A method as claimed in claim 3 wherein the C in the alloy melt is supplied by dissolution of a carbonaceous crucible which contains the alloy melt.
12. A method as claimed in claim 4 wherein the C in the alloy melt is supplied by dissolution of a carbonaceous crucible which contains the alloy melt.
13. A method as claimed in claim 5 wherein the C in the alloy melt is supplied by dissolution of a carbonaceous crucible which contains the alloy melt.
14. A method as claimed in claim 6 wherein the C in the alloy melt is supplied by dissolution of a carbonaceous crucible which contains the alloy melt.
15. A method as claimed in claim 7 wherein the C in the alloy melt is supplied by dissolution of a carbonaceous crucible which contains the alloy melt.