Patent ID: 9684232
Date: 2017-06-20
CPC Classifications: B24B,C03C,G03F

Claim:
1. A glass substrate for a mask blank, having a rectangular planar shape, wherein when a least square plane of a surface of the glass substrate for a mask blank is defined as an X-Y plane and a quality assurance region of the surface of the glass substrate for a mask blank is defined as a first region, in four strip regions each positioned in an area between one side of the first region and 8 mm inside the side of the first region and excluding areas of 8 mm from both edges in a length direction of the side of the first region, an angle between a least square plane in each the strip region and a least square plane in the first region is 1.5 μrad or less, and a PV value inside each the strip region which is relative to the least square plane in the first region is 15 nm or less, and in four square regions each positioned in the first region and contacted with each corner of the first region and having one side of 8 mm, an angle between a least square plane in each the square region and the least square plane in the first region is 3.0 μrad or less, and a PV value inside each the square region which is relative to the least square plane in the first region is 30 nm or less.