ANALYSIS FOR PRACTICAL USE OF AUTOMATIC FOCUSING USING STRIPE PATTERNPROJECTION TECHNIQUE

This report discusses subjects and countermeasures in order to apply t he stripe pattern projection technique to the automatic focusing equip ment used in microscopes. The effects of wafer circuit patterns, wafer defocus and illumination system on the detected signal wave of the pr ojected stripe pattern are analyzed. A technique to minimize the detec tion error of the stripe pattern contrast by eliminating the influence of the circuit pattern on the stripe pattern image is described. Usin g these techniques, a repeatability of +/-0.6 mu m (3 sigma) and an ac curacy of +/-1.0 mu m (3 sigma) in automatic focusing have been achiev ed.