Patent ID: 6910952

Claim:
A polishing composition for a substrate for memory hard disk, comprising silica particles in an aqueous medium, wherein the silica particles satisfy a relationship between an average particle size (r) of the silica particles on the number basis and a standard deviation (σ) on the number basis of the following formula (1): σ≧0.3 ×r (1) wherein r is an average particle size (nm) of the silica particles on the number basis, and σ is a standard deviation (nm) on the number basis, wherein the average particle size is obtained by a determination by transmission electron microscope (TEM) observation, and wherein a relationship between a particle size (R) and a cumulative volume frequency (V) in a range of particle sizes of from 60 to 120 nm satisfies the following formulas (2) and (3): V ≧0.5 ×R (2) V ≦0.25 ×R +75 (3) wherein R is a particle size (nm) of the silica particles, and V is a cumulative volume frequency (%) counted from a small particle size side of the silica particles.