Wafer and method of manufactruring wafer

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/° 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.