Error Reduction Method for Optical Surface Roughness Measurement System.

Abstract

Circular S-polarized light is proposed to reduce error in an optical surface roughness measurement system. Theoretical analysis of the focused circular S-polarized light shows that as the circular aperture ratio increases, 1) the spot size decreases, 2) the focal depth increases, and 3) the first-order defracted light increases. The measurement accuracy using the circular S-polarized light is experimentally evaluated. Circular S-polarized light is separated from randomly polarized light using a calcite crystal with birefringence. A nanometer-order step surface is then fabricated by sputtering carbon graphite on a glass plate. The step heights are measured mechanically with a stylus, and are used as standard measurements. The same step heights are also measured optically using randomly polarized light and circular S-polarized light. Comparison of the latter two measurements with the standard measurements shows that measurement error is reduced more with circular S-polarized light than with randomly polarized light.