Abstract
With the refined lithography techniques that exist today, it is critical for overlay measurement tools to perform with great measurement precision. Tool induced shift, TIS, is one of the key factors taken into consideration when evaluating the performance of an overlay measurement tool. TIS can be observed as a numerical value, and the measurement value is corrected by the TIS value. However, in an overlay measurement tool with TIS, the measured values could be shifted due to an interaction between TIS and a film stack structure of wafer. Therefore, it is essential to minimize the TIS values. We extend our study on the lens surface aspheric error, which is known to be one of the root causes of TIS. As this point of view, we constructed our overlay measurement tool, NRM-3100, and were able to decrease TIS values.
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