Silicon member and method of producing the same

A method of producing a holding plate for a liquid crystal panel in deposition and heat treatment that is used in a condition where the holding plate is heated at a temperature ranged from 300°C. to 1100°C., the method comprising steps of:

• excising a large-sized plate material made of a poly-crystalline silicon or a pseudosingle-crystalline silicon from a unidirectionally solidified columnar crystal ingot;
• forming a coating layer composed of a product of silicon formed by reaction of the silicon on a surface of the large-sized plate material which has micro-cracks on the surface before forming the coating layer, wherein
• the large-sized plate material has the dimension:
• width W being 500 mm to 1500 mm;
• length L being 500 mm to 1500 mm;
• and thickness H being 5 mm to 50 mm,
• the step of forming the coating layer comprises the steps of:
• forming a silicon oxide film on the surface of the large-sized plate material in a furnace by pyrogenic oxidation;
• removing the silicon oxide film from the large-sized plate material using a buffered hydrofluoric acid solution;
• and
• forming a silicon nitride film on the surface of the large-sized plate material as the coating layer while flowing ammonia into the furnace;
• wherein
• a thickness of the coating layer, t10, is 15 nm or more and 50 nm or less, and after forming the coating layer,
• the surface of the holding plate is free of scratches and micro-cracks,
• a maximum load in four-point bending of the holding plate is between 188-265 MPa, and
• a penetration depth, t11, of the silicon nitride film into silicon on the surface toward an internal side of the large-sized plate material satisfies a formula t11≥0.88×t10 based on densities and molecular weights of Si and Si3N4, t10 and t11 being measured with a spectroscopic ellipsometer.