Aggressive roadmaps impose stringent requirements not only on the metrology tools but on photoresist properties as well. In this article we investigate the interaction between electron beam in a CD SEM and different photoresists in an attempt to determine appropriate candidates from metrology point of view. We have evaluated sample damage (carryover) in order to find an approach leading to reduction of the sample degradation in the course of the measurement process and improve measurement precision. We have observed various linewidth changes under conditions expected in the case of single-tool repeatability, stability or multiple-tool matching procedures for CD SEM. The experimental data show that while all examined photoresists experienced certain changes some of them demonstrate less sensitivity. For modern CD SEM in addition to electron energy and current as factors defining the carryover, the possible effect of the clean room environment exposure should be considered as well. Recommendations have been made with respect to acceptable compromise based on the current precision requirements.
In a multiple tools environment the matching and stability performance of CD SEM becomes crucial for successful introduction of new technology generations. However proper evaluation procedure for CD SEM precision components represents a nontrivial issue when total precision budget is 1-2nm (according to the National Technology Roadmap for Semiconductors). Factors such as sample damage; process variation and measurement sample size should be carefully examined. In this article we address carryover - a very well known but not widely studied phenomenon, related to the sample damage, which directly affects the precision evaluation of a CD SEM. We have investigated the carryover in an attempt to reduce the effect of sample degradation due to repeated measurement and improve measurement precision. We present results based on relatively large data set and moderate range of variables. The experimental data show that for modern CD SEM both electron energy and current are very important factors defining the carryover. Although no complete elimination of the carryover effect have been observed under the conditions studied recommendations have been made with respect to acceptable compromise based on the current precision requirements.
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