Patent ID: 7191618

Claim:
A method of producing a large-sized synthetic quartz glass substrate, comprising the steps of: preliminarily measuring the flatness of the face and back sides of a large-sized synthetic quartz glass substrate having a diagonal length of not less than 500 mm and having a thickness of 1 to 20 mm and the parallelness of the substrate by holding the substrate vertically; partially removing projected portions and thick portions of the face side of the substrate by a processing tool and then projected portions and thick portions of the back side of the substrate by a processing tool based on the measurement data so as thereby to enhance the flatness of the face and back sides of the substrate and the parallelness of the substrate; and finally polishing for finishing the substrate surface, thereby obtaining the large-sized synthetic quarts glass substrate having a diagonal length of not less than 500 mm, a thickness of 1 to 20 mm, a ratio of flatness/diagonal length of not more than 6.0×10 −6 the face side and the back side, and a parallelness of not more than 50 μm.