Optical compensation of macroscopical surface curvature in rough surface scatterometry

摘要

While scatterometry of macroscopically plane rough surfaces by using quasi-parallel illumination is widely investigated, measuring light scatter from rough surfaces with a certain macroscopical curvature leads to the problem of separating the effects of micro-roughness from those of curvature in the scatter distribution. This is especially true for micro-roughness far beyond the smooth surface criterion. So for example, the scatter distribution of a cylinder with heavy traces of machining along a plane through the axis of rotation will be wide-spread perpendicularly to that plane for both reasons, the scatter pattern of the machining marks and the curvature of the surface. The curvature can be compensated by means of additional aspherical optical systems. In principal, this can be achieved by adaption of the illumination system or the receiver optics. Also both ways can be applied. The current paper deals with various design approaches theoretically and practically and gives some comparative measurement examples from actual applications for compensated and uncompensated systems.