ON THE LIMITATIONS OF THE CONFOCAL SCANNING OPTICAL MICROSCOPE AS A PROFILOMETER

We present a numerical study of the performance of a one-dimensional C onfocal Scanning Optical Microscope (CSOM) when used as a profiler of highly reflecting surfaces. The study is conducted by means of a compu ter simulation that describes the interaction between the incident bea m and the sample in a fairly rigorous manner. The degradation of the d epth discrimination as a function of the local surface slope is illust rated with examples, and a criterion for the maximum allowable slope i s proposed. We also show that the instrument has difficulties in profi ling surfaces that have steps or sharp edges and it is argued that, in general, problems are encountered when the surface profile cannot be considered locally flat in the scale of the Point Spread Function (PSF ) of the optical system. This implies that the lateral resolution of t he instrument is far worse as a profilometer than when used as an imag ing system, and that the unresolved features introduce spurious detail s on the estimated profile.