Using Variation Decomposition Analysis to Determine the Effect of Process on Wafer- and Die-level Uniformity in Oxide Cmp

Process optimization and control in oxide CMP require an understanding of the trade-offs in wafer and die-level uniformity, and their interaction, as functions of the polishing process conditions. We have examined the effects of down force and table speed, the two key factors affecting the polishing rate, on uniformity. Using variation decomposition analysis to decompose the measured variation into wafer, die, wafer-die interaction and residual components, we have determined that wafer-level variation can be improved by appropriate choice of process factors while die-level variation and the wafer-die interaction are largely process independent for the operating space examined. These results suggest the possibility of separate optimization of die-level pattern dependencies and the use of process parameter control for wafer-level uniformity.