Comparison of interferometrical and stylus step height measurements on rough surfaces

Abstract

For interferometric measurements of step height standards with different roughness on either the upper or base levels, a shift of the reflection plane and hence a different height compared with a mechanical stylus measurement is assumed. This paper investigates an evaporated aluminium step height standard consisting of six steps with different roughnesses of the upper levels. Comparison measurements between a high-resolution stylus instrument, an interference microscope with two different objectives and two high-precision interferometers have been made. The agreement between the measurements of the two interference microscopes and the phase shifting interferometer was very good. The maximum deviation was less than 9 nm for steps up to 8 mu m height. Comparing the optically and the mechanically measured step heights, no systematic height differences were observable.