Patent ID: 8734967

Claim:
A magnetic disk glass substrate having a main surface which is a mirror surface, wherein the mirror surface is specified by a surface roughness Ra of 0.15 nm or less when a 2 μm×2 μm square measurement area of the main surface is measured using an atomic force microscope with a resolution of 256×256 pixels, wherein when laser light with a wavelength of 405 nm and a power of 25 mW is irradiated with a spot size of 5 μM onto the main surface of the substrate and scattered light from the main surface of the substrate is detected, a position of individual defects and the number of defects, which are detected to have a size of 0.1 μm or more and 0.3 μm or less and number less than 50 per 24 cm 2 , are determined, wherein, individual defects at specified positions have a shape specified using the atomic force microscope, wherein a bearing plot curve of each defect is drawn in a coordinate system with an ordinate and an abscissa and is obtained by measuring each defect by the atomic force microscope, and a virtual curve is also drawn in the coordinate system and is obtained by a virtual straight line connecting a position of 0% of the abscissa to a position of 45% of the abscissa in the coordinate system having the bearing plot curve; wherein a comparison is made in a direction of the ordinate between the virtual straight line and the bearing plot curve of each defect within an area between 0% and 45% along the abscissa; wherein a result of said comparison is that no defect is present that is a defect with a broad convex area, such defect being defined by a bearing plot curve of the defect that has a portion higher than the virtual straight line, and wherein a result of that comparison is that all detected defects are limited to a convex defect where there is a bearing plot curve for such convex defect that has a portion lower than the virtual straight line.