Process control and optimization methods for run-to-run application

In a typical semiconductor manufacturing process, within-run (or batch) variation is usually controlled by automatic controllers built into the equipment. Batch sizes may be as small as one wafer in some processes. A run-to-run (R2R) controller is necessary since specifications can change from batch to batch, the equipment may experience aging or wearing-out phenomena, maintenance operations can change the operating conditions of the process, or process disturbances may enter the system suddenly. This implies that equipment controllers cannot be kept operating at a fixed recipe. Thus, an R2R controller is needed to act as a supervisor, indicating whether a recipe change is needed and suggesting a new recipe for use in the next batch.