SiC single crystal sublimation growth method and apparatus
View Patent ↗A physical vapor transport growth system includes a growth chamber charged with SiC source material and a SiC seed crystal in spaced relation and an envelope that is at least partially gas-permeable disposed in the growth chamber. The envelope separates the growth chamber into a source compartment that includes the SiC source material and a crystallization compartment that includes the SiC seed crystal. The envelope is formed of a material that is reactive to vapor generated during sublimation growth of a SiC single crystal on the SiC seed crystal in the crystallization compartment to produce C-bearing vapor that acts as an additional source of C during the growth of the SiC single crystal on the SiC seed crystal.
1. A SiC single crystal sublimation growth method comprising:
(a) providing a growth chamber that is separated by a porous graphite membrane into a source compartment that is charged with a SiC source material and a crystallization compartment that includes a SiC seed crystal; and
(b) heating the interior of the growth chamber such that a temperature gradient forms between the SiC source material and the SiC seed crystal, the SiC source material is heated to a sublimation temperature, and the temperature gradient is sufficient to cause sublimated SiC source material to diffuse through the porous graphite membrane from the source compartment into the crystallization compartment where the sublimated SiC source material condenses on the SiC seed crystal and forms the SiC single crystal, wherein all of the sublimated SiC source material that condenses on the SiC seed crystal and forms the SiC single crystal diffuses through the porous graphite membrane from the source compartment into the crystallization compartment, wherein the porous graphite membrane is comprised of carbon that is reactive to silicon-rich vapor generated by precipitation of the sublimated SiC source material on the SiC seed crystal in the crystallization compartment, wherein the porous graphite membrane is positioned in the growth chamber such that the generated silicon-rich vapor diffuses in a direction from a growth interface of the SiC single crystal on the SiC seed crystal toward the porous graphite membrane, in spite of Stefan gas flow in an opposite direction, where the silicon-rich vapor reaches the porous graphite membrane and reacts with the carbon comprising the porous graphite membrane to produce a carbon-bearing vapor that acts as an additional source of C during the growth of the SiC single crystal on the SiC seed crystal, wherein:
a distance between the growing SiC single crystal and the porous graphite membrane is between 15 mm and 35 mm;
the temperature of the SiC source material is greater than the temperature of the porous graphite membrane;
the temperature of the porous graphite membrane is greater than the temperature of the SiC seed crystal; and
the porous graphite membrane is comprised of porous graphite grains, each having a maximum dimension between 100 micron and 500 micron.
2. The method of claim 1 , wherein step (b) occurs in the presence of between 1 and 100 Torr of inert gas.
3. The method of claim 1 , further including a capsule disposed in the source compartment, said capsule having an interior that is charged with a dopant, wherein:
said capsule has one or more capillaries of pre-determined diameter and length that extend between the interior and an exterior of said capsule; and
the diameter and the length of each capillary is selected whereupon the dopant is disposed spatially uniformly in the grown SiC single crystal.
4. The method of claim 3 , wherein:
the capsule is made of graphite; and
the dopant is either elemental vanadium or a vanadium compound in quantity sufficient for full electronic compensation of the grown SiC single crystal.
5. The method of claim 1 , further including, prior to step (a):
charging the growth chamber with elemental Si and C; and
heating the elemental Si and C to a temperature below the sublimation temperature for synthesis of the elemental Si and C into a solid SiC that comprises the SiC source material of step (a).
6. The method of claim 1 , wherein:
the mean, room temperature electrical resistivity of the grown SiC single crystal is above 10 9 Ohm-cm with a standard deviation below 10% of the mean value; and
the grown SiC single crystal is of the 4H or 6H polytype.
7. A SiC single crystal sublimation growth method comprising:
(a) providing a sealed growth crucible charged with a SiC seed crystal and SiC source material in spaced relationship and a porous graphite membrane comprised of carbon disposed between the SiC source material and the SiC seed crystal; and
(b) heating the growth crucible to a SiC sublimation temperature and establishing a temperature gradient between the SiC source material and the SiC seed crystal such that the SiC source material sublimates and diffuses, in the form of Stefan flow, through the porous graphite membrane, the sublimated SiC source material further diffuses in the form of Stefan flow to the SiC seed crystal where the sublimated SiC source material condenses causing growth of the SiC single crystal on the SiC seed crystal, wherein all of the sublimated SiC source material that condenses on the SiC seed crystal causing growth of the SiC single crystal on the SiC seed crystal diffuses through the porous graphite membrane from the source compartment into the crystallization compartment, wherein:
condensation of the sublimated SiC source material on the SiC seed crystal causes generation of silicon-rich vapor;
said silicon-rich vapor diffuses from a growth interface of the SiC single crystal on the SiC seed crystal in a direction opposite to the Stefan flow, reaches the porous graphite membrane and reacts with the carbon comprising the porous graphite membrane;
reaction between said silicon-rich vapor and the carbon comprising the porous graphite membrane produces a carbon-bearing species that diffuse back to the growth interface and acts as an additional source of carbon during growth of the SiC single crystal on the SiC seed crystal;
a distance between the growing SiC single crystal and the porous graphite membrane is between 15 mm and 35 mm;
the temperature of the SiC source material is greater than the temperature of the porous graphite membrane;
the temperature of the porous graphite membrane is greater than the temperature of the SiC seed crystal; and
the porous graphite membrane is comprised of porous graphite grains, each having a maximum dimension between 100 micron and 500 micron.
8. The method of claim 7 , wherein the porous graphite membrane is manufactured of porous graphite having a density between 0.6 g/cm 3 and 1.4 g/cm 3 , and a porosity between 30% and 70%.
9. The method of claim 7 , wherein the thickness of the porous graphite membrane is between 3 mm and 12 mm.
10. The method of claim 7 , wherein step (b) occurs in the presence of between 1 and 100 Torr of inert gas.
11. The method of claim 7 , wherein step (a) further includes providing in the source compartment a capsule having an interior that is charged with a dopant, wherein:
said capsule has one or more capillaries of pre-determined diameter and length that extend between the interior and an exterior of said capsule; and
the diameter and the length of each capillary is selected whereupon the dopant is disposed spatially uniformly in the grown SiC single crystal.
12. The method of claim 11 , wherein: the capsule is made of graphite; and the dopant is either elemental vanadium or a vanadium compound in quantity sufficient for full electronic compensation of the grown SiC single crystal.
13. The method of claim 7 , wherein the room temperature electrical resistivity of SiC substrates manufactured from the grown SiC single crystal is above 10 9 Ohm-cm with a standard deviation below 10% of the average resistivity value calculated for the substrate.
14. The method of claim 7 , wherein the grown SiC single crystal is of the 4H or 6H polytype.