Abstract

Recently, the resolving power of optical surface profilometry has been improved to below 1 nm. However, the phase change of reflected light, which depends on optical constants (n,k) of a sample, can reach several tens of nanometers. When a sample has inhomogeneity of optical constants, the phase variations of reflected light cannot be ignored in interferometric surface measurement. In measurement at a single wavelength, the influence of phase change cannot be distinguished from the true profile. However, it is possible to correct this influence if the dependence of the phase change on wavelength is used to identify the sample substances. To this end, we measure the phase changes at several wavelengths. A sample consisting of two kinds of metals in the same plane is fabricated, and its surface profile is measured by interferometry. In spite of the flat surface, the virtual step height (maximum value of 33 nm) is measured at the boundary of the two adjacent metals. The measured step height corresponds to the difference in the phase changes between two metals. The measured differences in the phase changes at several wavelengths agree well with the theoretical values. On the basis of the results, multiple-wavelength surface profilometry for correcting phase change is discussed.

© 1992 Optical Society of America