Yield improvement at the contact process through run-to-run control

This paper reports on part of an effort to improve the yield of a contact process through run-to-run (R2R) control. The two crucial processes involved are chemical mechanical polishing (CMP) and reactive ion etching (RIE). In this paper, the CMP process control element is considered in detail. Empirical models for the process on a target tool are obtained through a design of experiments (DOE) and a control solution is suggested for the two primary outputs of the CMP process, namely post-polish film thickness and film uniformity. With this factory-wide run-to-run control solution design, post process measurements made after every CMP run are used along with pre-process measurements, empirical process models, and drift compensation and noise rejection techniques to suggest new equipment settings for the next run. It has been observed that good control of post-polish film thickness can be obtained. However, for improving uniformity, a need is indicated for investigation of the impact of a nonradial uniformity gradient deposited on the wafer upstream at chemical vapor deposition (CVD).