Glass-substrate manufacturing method

A glass-substrate manufacturing method comprising a forming step of forming a molten glass into a sheet glass by a down-draw process, and

• a cooling step of cooling the sheet glass, wherein:
• the cooling step includes a first cooling step of cooling the sheet glass at a first average cooling rate until the temperature of a central region of the sheet glass drops to the annealing point,
• a second cooling step of cooling the sheet glass at a second average cooling rate until the temperature of the central region drops from said annealing point to a temperature 50° C. below the strain point, and
• a third cooling step of cooling the sheet glass at a third average cooling rate until the temperature of the central region drops from said temperature 50° C. below the strain point to a temperature 200° C. below the strain point;
• the first average cooling rate is 5.0° C./second or faster;
• the first average cooling rate is faster than the third average cooling rate;
• and
• the third average cooling rate is faster than the second average cooling rate,
• wherein:
• the second average cooling rate is from 0.5° C./second to 5.5° C./second;
• and the third average cooling rate is from 1.5° C./second to 7.0° C./second.