ABSTRACT

This chapter introduces some of the techniques to realize surface and thickness profile measurement of a transparent film by means of optical interferometry or interference color analysis. Various algorithms have been proposed to detect the peak position of modulation, most of which assume that the peak is single. Therefore, if a film-covered surface is measured, superposition occurs between the reflected beams from the front surface and the reflected beams from the back surface, hampering correct measurement of the surface profile. However, techniques based on the use of the interference color have rarely been used in the industry. The most serious problem with these techniques is that they require frequent calibration because the color thickness relation depends on a variety of environmental conditions such as the illumination and the target film structure. The computational cost of the nonlinear least-squares problem is very high. Hence, the method becomes impractical when the number of points is large.