Method for manufacturing silicon nitride substrate

A method for manufacturing a silicon nitride substrate, comprising:

• forming a slurry by mixing silicon nitride powder, a ceramic additive, and a solvent;
• molding the slurry to form sheets;
• forming a stacked structure by sandwiching at least one of the sheets between a lower plate and an upper plate;
• performing degreasing process on the stacked structure;
• and performing sintering process on the stacked structure, wherein:
• the lower plate comprises a plurality of first protrusions provided on an upper surface thereof, the upper plate comprises a plurality of second protrusions provided on a lower surface thereof, the first and second protrusions extend in parallel to each other in one direction, a first recess is defined between adjacent first protrusions, a second recess is defined between adjacent second protrusions, the stacked structure comprises a first gap defined by the adjacent first protrusions, the first recess, and a bottom surface of the sheet, and a second gap defined by the adjacent second protrusions, the second recess, and a top surface of the sheet, a heated gas is introduced which contacts the top surface and the bottom surface of the sheet through the first and second gap during the degreasing process, the sintering process comprises embedding the stacked structure, after the degreasing process, in bedding powder, the bedding powder comprises boron nitride powder and silicon nitride powder, and the bedding powder is in contact with the sheet through the first gap and the second gap.