Patent ID: 9316902
Filing Date: 2016-04-19
CPC Classification: G03F,Y10T

Claim Text:
1. A square-shaped glass substrate for a photomask, the glass substrate having a pair of major surfaces and a patterned light-shielding film on one surface of the substrate which is chucked at chucking portions in an exposure tool, wherein the major surface where the chucking portions are disposed is delineated by four peripheral sides, two strip regions are defined on the major surface near a pair of opposed sides such that each region spans between 2 mm and 10 mm inward of the side and extends parallel to the side, but excludes end portions extending 2 mm inward from the longitudinally opposed ends of the side, a least squares plane is computed for each of the two strip regions, based on a distance from any common reference plane to a coordinate point within the strip region, the angle included between normal lines to the two least squares planes of the two strip regions is less than or equal to 10 seconds, on the assumption that F the height difference between the two strip regions is less than or equal to 0.5 μm.