Method for preparing silicon carbide single crystal
A SiC single crystal is produced by the solution growth method in which a seed crystal attached to a seed shaft is immersed in a solution of SiC dissolved in a melt of Si or a Si alloy and a SiC single crystal is allowed to grow on the seed crystal by gradually cooling the solution or by providing a temperature gradient therein. To this method, accelerated rotation of a crucible is applied by repeatedly accelerating to a prescribed rotational speed and holding at that speed and decelerating to a lower rotational speed or a 0 rotational speed. The rotational direction of the crucible may be reversed each acceleration. The seed shaft may also be rotated synchronously with the rotation of the crucible in the same or opposite rotational as the crucible. A large, good quality single crystal having no inclusions are produced with a high crystal growth rate.
1. A method for producing a silicon carbide single crystal comprising immersing a seed crystal on which SiC is to be grown by the solution growth method and which is attached to a seed shaft in a melt in a rotating crucible, the melt comprises Si and C and at least one metal element M and containing silicon carbide (SiC) dissolved therein, and allowing a SiC single crystal to grow on the seed crystal by creating a supersaturated SiC concentration in the melt at least in the periphery of the seed crystal, characterized in that the melt is stirred by periodically changing the rotational speed or the rotational speed and the rotational direction of the crystal,
wherein M is at least one element selected from Ti, Mn, Fe, and Co, and when expressing the molar concentration of M in the melt as [M] and the molar concentration of Si as [Si], the value of [M]/([M]+[Si]) is,
at least 0.1 and at most 0.25 when M is Ti;
at least 0.1 and at most 0.7 when M is Mn:
at least 0.2 and at most 0.7 when M is Fe; and
at least 0.05 and at most 0.25 when M is Co.
2. A method as set forth in claim 1 wherein the rotational speed of the crucible is periodically varied by making
(1) acceleration to a first set rotational speed A 1 ,
(2) maintaining rotation at the first rotational speed A 1 , and
(3) decelerating to a second set rotational speed A 2 (A 2 <A 1 )
one cycle and repeating the cycle (wherein the set value of each of the rotational speeds A 1 and A 2 may be varied in each cycle).
3. A method as set forth in claim 1 wherein the rotational speed and rotational direction of the crucible are periodically varied by making
(1) acceleration to a first set rotational speed B 1 in a first rotational direction,
(2) maintaining rotation at rotational speed B 1 in the first rotational direction,
(3) decelerating to a second rotational speed of 0 rpm,
(4) accelerating to a set rotational speed B 2 in a second opposite rotational direction (wherein B 2 and B 1 may be the same or different from each other),
(5) maintaining rotation at set value B 2 in the second rotational direction, and
(6) decelerating to a rotational speed of 0 rpm
one cycle and repeating this cycle (wherein the set value of each rotational speeds B 1 and B 2 may be varied in each cycle).
4. A method as set forth in claim 1 wherein the seed shaft is rotated together with the crucible in the same or the opposite rotational direction.
5. A method as set forth in claim 4 wherein rotation of the seed shaft is synchronous with rotation of the crucible.
6. A method as claimed in claim 1 wherein the gas atmosphere during growth of the single crystal is a nonoxidizing gas having a viscosity η which satisfied η≦750 μP (μP=micropoise) at the temperature of single crystal growth.
7. A method for producing a silicon carbide single crystal comprising immersing a seed crystal on which SiC is to be grown by the solution growth method and which is attached to a seed shaft in a melt in a rotating crucible, the melt comprising (1) Si and C or (2) Si and C and at least one metal element M and containing silicon carbide (SiC) dissolved therein, and allowing a SiC single crystal to grow on the seed crystal by creating a supersaturated SiC concentration in the melt at least in the periphery of the seed crystal, characterized in that the melt is stirred by periodically changing the rotational speed or the rotational speed and the rotational direction of the crystal,
wherein the gas atmosphere during growth of the single crystal is a nonoxidizing gas having a viscosity η which satisfied η≦750 μP (μP=micropoise) at the temperature of single crystal growth.
8. A method as set forth in claim 7 wherein the rotational speed of the crucible is periodically varied by making
(1) acceleration to a first set rotational speed A 1 ,
(2) maintaining rotation at the first rotational speed A 1 , and
(3) decelerating to a second set rotational speed A 2 (A 2 <A 1 )
one cycle and repeating the cycle (wherein the set value of each of the rotational speeds A 1 and A 2 may be varied in each cycle).
9. A method as set forth in claim 7 wherein the rotational speed and rotational direction of the crucible are periodically varied by making
(1) acceleration to a first set rotational speed B 1 in a first rotational direction,
(2) maintaining rotation at rotational speed B 1 in the first rotational direction,
(3) decelerating to a second rotational speed of 0 rpm,
(4) accelerating to a set rotational speed B 2 in a second opposite rotational direction (wherein B 2 and B 1 may be the same or different from each other),
(5) maintaining rotation at set value B 2 in the second rotational direction, and
(6) decelerating to a rotational speed of 0 rpm
one cycle and repeating this cycle (wherein the set value of each rotational speeds B 1 and B 2 may be varied in each cycle).
10. A method as set forth in claim 7 wherein the seed shaft is rotated together with the crucible in the same or the opposite rotational direction.
11. A method as set forth in claim 10 wherein rotation of the seed shaft is synchronous with rotation of the crucible.