A comprehensive mathematical model to calculate polish time for oxide chemical mechanical process (CMP)

Abstract

In chemical mechanical polishing process, oxide CMP is used to polish dielectric films. Material removal rate varies due to incoming material variations and CMP induced variations. Due to various variables, it is extremely difficult to calculate exact polish time. In this work, a comprehensive polishing time calculation model is explained. This model takes care of various variations. It helps to predict required polish time, reduce rework, process delay, improves polisher throughput. It reduces wafer-to-wafer thickness variation. Measurement methodology adopted helps to reduce wafer to wafer variation. This variation is caused by incoming wafer-to-wafer thickness variation. Many times, post CMP, one wafer is in but another wafer is out of control limits. OOC wafer is required to rework to bring inside control limits. It incurs rework cost, productivity loss. This model continuously improves polish time prediction as polishing progressed from one lot to another due to a dynamic thickness offset factor.