1 June 1990 Reducing CD variation via statistically matching steppers
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Abstract
The complexity of integrated circuits processing has made CD control a challenging work, especially in a high volume manufacturing environment such as the one where this study was done. Many factors contribute to linewidth variability, namely previous process variation, consistency of equipment performance, and human intervention. To effectively reduce CD variations in such a high volume manufacturing Fab, a two phase study was carried out. In phase I, several sources of variation were evaluated through Variance Components Analysis. This analysis gave a better understanding of where variation seen in some critical layers was coming from as well as providing information needed to prioritize efforts in variance reduction. Variables selected for inclusion in this study were etchers, steppers, day to day litho process fluctuations, and lot to lot poly substrates. Findings from phase I showed that of those variables included in the study, stepper to stepper variation was the major contributor to the CD variation. In order to reduce this effect of stepper variation a two step plan was formulated. The first step was to place a customized exposure correction into the software for each stepper, thus bringing the stepper means together. A second step was initially considered but not implemented as of this writing for logistical reasons. The objective of this second step was to reduce the variance by grouping the least sensitive steppers (lowest variance) to process the most sensitive masking layers.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Chen-Show Lee, David A. Acree, Avatara Nuernberg, "Reducing CD variation via statistically matching steppers", Proc. SPIE 1261, Integrated Circuit Metrology, Inspection, and Process Control IV, (1 June 1990); doi: 10.1117/12.20033; https://doi.org/10.1117/12.20033
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