A method of manufacturing a wafer comprising: a preparation step of disposing a material and a silicon carbide seed crystal to face each other in a reactor having an inner space; a growing step of adjusting the temperature, the pressure, and the atmosphere of the inner space to sublime the material and thereby preparing a silicon carbide ingot grown from the seed crystal; a cooling step of cooling the reactor and retrieving the silicon carbide ingot; a cutting step of cutting the retrieved silicon carbide ingot to prepare a wafer, the cutting step cutting the silicon carbide ingot to make a fixed off angle with the 0001 surface of the silicon carbide ingot, the angle being 0° to 10°; and a processing step of flattening the thickness or the prepared wafer and polishing the surface, wherein the reactor comprises an insulating material surrounding the external surface, and a heating mean for adjusting the temperature of the reactor or the inner space, wherein the density of the insulating material is 0.14 g/cc to 0.28 g/cc, the coefficient of thermal expansion of the insulating material is 2.65×10 -6 /°C to 2.75×10 -6 /°C at 1000°C, and the wafer processed by the processing step has retardation distribution measured with light of a wavelength of 520 nm, the wafer having a thickness of 200 to 600 μm, the retardation distribution being measured in a thickness direction of the wafer, and one or more between below i) and ii) items: i) the average value of the retardation is 38 nm or less; and ii) the maximum value of the retardation is 60 nm or less, wherein the diameter of the wafer is 15.3 cm (6 inch) or less. a preparation step of disposing a material and a silicon carbide seed crystal to face each other in a reactor having an inner space; a growing step of adjusting the temperature, the pressure, and the atmosphere of the inner space to sublime the material and thereby preparing a silicon carbide ingot grown from the seed crystal; a cooling step of cooling the reactor and retrieving the silicon carbide ingot; a cutting step of cutting the retrieved silicon carbide ingot to prepare a wafer, the cutting step cutting the silicon carbide ingot to make a fixed off angle with the 0001 surface of the silicon carbide ingot, the angle being 0° to 10°; and a processing step of flattening the thickness or the prepared wafer and polishing the surface, wherein the reactor comprises an insulating material surrounding the external surface, and a heating mean for adjusting the temperature of the reactor or the inner space, wherein the density of the insulating material is 0.14 g/cc to 0.28 g/cc, the coefficient of thermal expansion of the insulating material is 2.65×10 -6 /°C to 2.75×10 -6 /°C at 1000°C, and the wafer processed by the processing step has retardation distribution measured with light of a wavelength of 520 nm, the wafer having a thickness of 200 to 600 μm, the retardation distribution being measured in a thickness direction of the wafer, and one or more between below i) and ii) items: i) the average value of the retardation is 38 nm or less; and ii) the maximum value of the retardation is 60 nm or less, i) the average value of the retardation is 38 nm or less; and ii) the maximum value of the retardation is 60 nm or less, wherein the diameter of the wafer is 15.3 cm (6 inch) or less.