Patent ID: 8858865

Claim:
A silicon nitride substrate manufacturing method in which a slurry is produced by mixing a silicon nitride powder, a sintering additive powder, a binder, and a dispersant in an organic solvent which is a dispersion medium in a raw material setting/mixing process, and the slurry is formed into a sheet, followed by degreasing and sintering, characterized in that an Al concentration in the silicon nitride substrate is 0.3 mass % or less in terms of Al 2 O 3 , the oxygen content of the silicon nitride powder is 2.0 mass % or less and the specific surface area of the silicon nitride powder is 3 to 11 m 2 /g, the additive ratio of the sintering additive powder is 4 to 15 mol %, the additive amount of the binder is 8 to 25 parts by mass relative to a total 100 parts by mass of the silicon nitride powder and sintering additive powder, and the water content ratio of the organic solvent is 0.03 to 3 mass %, and the additive amount of the dispersant composed of cationic dispersant is 0.1 to 1 mass % relative to the raw material powder, and the slurry is produced by mixing the silicon nitride powder, the sintering additive powder, the binder, and the dispersant in the organic solvent at a temperature of 10 to 45° C. in the raw material setting/mixing process, so that an oxygen increase from the silicon nitride powder before the mixing as compared to the silicon nitride powder after the mixing is in a range of 0.05 to 0.5 mass %, and a specific surface area of the silicon nitride powder after the mixing is 5 to 12 m 2 /g.