PREPARATION METHOD OF SUBSTRATE FOR PHOTOMASK BLANK COMPRISING POLISHING SUBSTRATE CIRCULAR PLATE TO ALLOW MAIN SURFACE REGION OF SUBSTRATE TO HAVE SPECIFIC FLATNESS FOR PROVIDING POLISHED INTERMEDIATE PRODUCT, AND MORE POLISHING THE POLISHED INTERMEDIATE PRODUCT

摘要

PURPOSE: Provided is a method for preparing a substrate for photomask blank to provide a photomask used to expose a pattern having a minimum characteristic size reduced with a high precision on a wafer substrate. CONSTITUTION: The method comprises the steps of polishing a substrate circular plate to allow the difference between a maximum value and a minimum value to the height from a least square plane to a main surface region to be 1.5 micrometers or less, for a main surface region comprising a rectangular ring shaped region spreading by 2-10 mm inside each side and a patterning region located inside the inner circumference of the rectangular ring shaped region along the outer circumference of an upper surface of a substrate for providing a polished intermediate product; and more polishing the polished intermediate product, to prepare a substrate for photomask blank which is a rectangle with each side of at least 6 inch, and has a pair of band shaped regions in the each inside of a pair of facing sides according to the outer circumference of an upper surface of a substrate wherein a mask pattern is to be formed except a 2 mm edge part to length direction from each terminal part, the each band shaped region is sloped downward along the outer circumference, and the difference between the maximum value and the minimum value to the height from the minimum square plane to the band shaped region is 0.5 micrometers or less.