PURPOSE: To enhance the manufacturing yield in breakdown strength of an oxide film by a method wherein, when a surface of a wafer held by a plate is ground with an abrasive by a grinding cloth stuck to a grind base, the mean surface roughness of the wafer is measured using a phase shift interferometer.

CONSTITUTION: When a surface of a wafer 2 held by a plate 1 is ground with an abrasive 6 by a grinding cloth 4 stuck to a grind base 3, the mean surface roughness of the wafer 2 is measured using a phase shift interferometer, and the mean surface roughness of the wafer 2 is contolled to be 0.4mm or less. Thus, as the surface roughness of the wafer can quantitatively be measured, it can be used as an index of surface quality, and also by using the mean surface roughness measured, it is possible to enhance the manufacturing yield in breakdown strength of an oxide film of the wafer.