A study of within-wafer non-uniformity metrics

Abstract

This work reconsiders within-wafer nonuniformity (WIWNU) metrics for semiconductor processes. Simulations of typical chemical-mechanical polishing (CMP) scenarios are used to demonstrate that these metrics may vary with the pre-process thickness profile, the removal rate characteristics, and processing time. These metrics are compared and contrasted. Some of these metrics are shown to be biased with processing time, while others are shown to be insensitive to improvements in WIWNU. Finally, experimental data is compared with these simulations. It is suggested that multiple metrics may be necessary to determine the actual characteristics of a process.