Application of Predictor Corrector Control to Polysilicon Gate Etching

A modification of Internal Model Control (IMC) was developed which produces excellent response when a process drift is present. The new controller, termed Predictor Corrector Control (PCC), employs a double exponential forecasting filter. Simulations were used to demonstrate that the PCC controller is quicker to respond to step changes and better tracks drifts than traditional controllers (which utilize single exponential filters). Thus, PCC is ideal for supervisory control of microelectronics manufacturing processes, which are known to suffer from machine aging. PCC was demonstrated on a polysilicon gate etch process with encouraging results. For this process, a single wavelength ellipsometer monitored the etch rate at the center of the wafer, and models were employed to relate the etch rate at other sites on the wafer with process conditions and the measured etch rate at the center. The supervisory controller produced setpoints (settings) for the equipment regulatory controllers which achieved a high etch rate process with a maximum specified nonuniformity.