Method for heat-treating a glass substrate

摘要

In each of the second and subsequent heat treatments, in a case where a glass substrate shrinks by heat treatment at the same average cooling rate as the average cooling rate in the immediately preceding heat treatment, the average cooling rate is set to be larger than that in the immediately preceding heat treatment, and inversely, in a case where the glass substrate extends, the average cooling rate is set to be smaller than that in the immediately preceding heat treatment.