METHOD OF SELECTING PHOTOMASK BLANK SUBSTRATE FOR EXPOSING PATTERNS HAVING REDUCED MINIMUM FEATURE SIZE TO HIGH ACCURACY ON WAFER SUBSTRATE

摘要

PURPOSE: A method of selecting a photomask blank substrate is provided to expose patterns having a reduced minimum feature size to high accuracy on a wafer substrate by improving a structure thereof. CONSTITUTION: A photomask blank substrate is a quadrangle having a length on each side of at least 6 inches. In the photomask blank substrate, a pair of strip-like regions(2) extends from 2 mm to 10 mm each inside of a pair of opposite sides along an outer periphery of a top surface(1) of a substrate on which a mask pattern is formed, except an edge part of 2mm at each end in a longitudinal direction thereof. A method of selecting the photomask blank substrate includes a measuring process and a selecting process. The measuring process is performed to measure the height from a least squares plane for the strip-like regions on the substrate top surface to the strip-like regions at intervals of 0.05 to 0.35 mm in horizontal and vertical directions. The selecting process is performed to select as a substrate having an acceptable surface shape, a substrate in which the difference between the maximum and minimum values for the height among all the measurement points is not more than 0.5 micrometers.