Monitoring multistage integrated circuit fabrication processes

This paper presents a process monitoring system, which is designed to be used for monitoring VLSIC and other multistage manufacturing processes. The proposed process monitor can 1) simultaneously detect a variety of out-of-control conditions, 2) quantify the magnitude of process change, and 3) be used to compute the probability of meeting specifications. Average run length simulations show that for a single-stage process, the monitor is at least as good as the Shewhart-CUSUM charts for detecting changes in the distribution of the monitored characteristics. For a multistage process, however, the Bayesian monitor can significantly reduce the detection time by using in-line correlation information from earlier stages. The monitor has been applied to data from a state-of-the-art fabrication facility, and the results are promising.