Wafer and method of manufactruring wafer
The wafer having a retardation distribution measured with a light having a wavelength of 520 nm, wherein an average value of the retardation is 38 nm or less, wherein the wafer comprises a micropipe, and wherein a density of the micropipe is 1.5/cm 2 or less, is disclosed.
1. A method of manufacturing a wafer comprising:
disposing a raw material and a silicon carbide seed crystal to face each other in an inner space of a reactor;
adjusting a temperature, a pressure, and an atmosphere of the inner space to sublime the raw material, thereby preparing a silicon carbide ingot grown from the seed crystal;
cooling the reactor and retrieving the silicon carbide ingot;
cutting the retrieved silicon carbide ingot, thereby preparing a wafer; and
flattening a thickness of the prepared wafer and polishing a surface of the wafer,
wherein the reactor comprises an insulating material surrounding an external surface of the reactor and a heater for adjusting a temperature of the reactor or the temperature of the inner space,
wherein a density of the insulating material is 0.14 g/cc to 0.28 g/cc and a coefficient of thermal expansion of the insulating material is 2.65×10 −6 1° C. to 3.05×10 −6 /° C., and
wherein the prepared wafer has a retardation distribution measured with a light having a wavelength of 520 nm, where an average value of the retardation is 38 nm or less or a maximum value of the retardation is 60 nm or less.
2. The method of claim 1 , wherein a flow of an inert gas proceeds in a direction from the raw material to the silicon carbide seed crystal while the silicon carbide ingot grows from the seed crystal, and a flow rate of the inert gas is from 70 sccm to 300 sccm.
3. The method of claim 1 , wherein the polishing comprises a chemical mechanical polishing.
4. The method of claim 1 , wherein the wafer after the flattening and the polishing has a FWHM value of 30 arcsec or less in a rocking curve according to XRD analysis.
5. The method of claim 1 , wherein a porosity of the insulating material is 72% to 95%.
6. The method of claim 1 , wherein a compressive strength of the insulating materials is 0.2 MPa to 3 MPa.
7. The method of claim 1 , wherein the insulating material comprises a graphite felt, a rayon-based graphite felt, a pitch-based graphite felt, or a mixture thereof.
8. The method of claim 1 , wherein the temperature and the pressure of the inner space are adjusted to 2000° C. to 2600° C. and 1 torr to 200 torr, respectively.
9. The method of claim 1 , wherein the temperature of the inner space reaches to 2000° C. to 2600° C. at a heating rate of 1° C./min to 10° C./min by the heater during the preparing the silicon carbide ingot.
10. The method of claim 1 , wherein the temperature of the reactor is cooled at a cooling rate of 1° C./min to 10° C./min during the cooling.
11. A silicon carbide ingot prepared from the method of claim 1 comprising a first surface and a second surface opposite to the first surface, wherein the first surface is an upper portion of the silicon carbide ingot and is a flat surface or a convex surface.
12. A wafer prepared from the silicon carbide ingot of claim 11 , wherein the wafer is prepared in a portion below the first surface, and wherein the wafer has a retardation distribution measured with a light having a wavelength of 520 nm and an average value of the retardation is 35 nm or less.