A gauge for the precision measurement of the thickness of germanium and silicon wafers

Some of the difficulties associated with the precision measurement of the thickness of thin germanium and silicon wafers, together with several possible methods of measurement, are briefly discussed. A gauge which employs the optical-lever principle is described in which frictional restraint of the moving parts is reduced to that of a knife edge alone, thus ensuring good repeatability of reading with probe pressures of less than 3g. The gauge covers the range 0¿270 microns with an overall accuracy of ±0.5 micron.