Progress in optical imaging theory for trenches and lines

We have been developing imaging theory for the confocal microscope and for interferometric microscopes. We are particularly interested in developing techniques for improving the accuracy of measurements of the width of trenches and lines in arrays of photoresist lines and trenches. We are also interested in using the theory to help us interpret phase measurements of phase shift masks with our interferometric microscope, the correlation microscope, as described in an accompanying paper. The aim is to get down to the smallest critical dimensions possible, in the 0.3 micrometers range, and to eliminate the discontinuities sometimes seen in measurements of trenches and lines; these discontinuities are due to resonances of the optical waves in the structure. Since a wide number of well characterized samples is not usually obtainable, this theory is extremely useful for understanding how the various features of a structure affect the form of cloud plots and linescans. A basic aim is to use the theoretical calculations to train pattern recognition algorithms and to determine how the shape and size of trenches and lines influence the form of the linescans and cloud plots we observe. It is particularly important to understand whether pattern recognition algorithms, which make use of the whole cloud plot rather than thresholding on a single linescan, are only using the information from the top of a trench or line. We need to determine whether linescans at all levels are, in fact, influenced by the size at the top and bottom of a trench or line. In this paper, we show that this is indeed the case, and that the theory is fairly adequate at the present time to give a fairly good representation of experimental results.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.