Optimal iterative learning control of wafer temperature uniformity in rapid thermal processing

Abstract

An optimal iterative learning control (ILC) technique based on a quadratic optimal criterion has been implemented and evaluated in an experimental rapid thermal processing (RTP) system fabricating 8-inch silicon wafers. The control technique is based on a time-varying linear state space model which approximates a nonlinear system along a reference trajectory. Also the control technique is able to make improvements in the control performance from one run to next and eventually converge to a minimum achievable tracking error despite model error. Through a series of experiments with wafers on which thermocouples are glued, it was observed that the wafer temperatures are steered to the reference trajectory reducing the diyerences overcoming various disturbances.

Iterative Learning Control

“…Between 2001 and 2003, the following literature was published in semiconductor applications of ILC: [537,255,94,113,89,112,87,392,111,110]. For a more detailed discussion of the application of ILC to semiconductor manufacturing processes, refer to [114].…”