A monitor wafer based controller for semiconductor processes

A monitor wafer based controller is described. The controller can be applied to equipment with or without in-situ sensors. The controller incorporates a novel multivariable adaptation methodology for the feedback controller that employs a layered process/equipment model. The layered model consists of an intrinsic component that corresponds to the initial settings to outputs model and an extrinsic component that transforms the inputs and the outputs of the intrinsic model. The adaptation strategy tunes the extrinsic model only and thus the adaptation strategy is independent of the intrinsic model form. The controller determines whether the process and equipment have changed state by using model based SQC to compare product parameter measurements with the composite model predictions. If a change in state is deduced, a model tuner is activated which adapts the extrinsic model to reflect the new state. To adapt the model, a local experiment design technique is applied that perturbs the equipment settings. Finally, a stepwise optimization technique that permits the specification and utilization of user preference toward changing some process inputs over others is used for determining the new process recipe. We report the controller´s application to the plasma enhanced chemical vapor deposition of silicon nitride (PECVD Nitride) process run on Applied Materials Precision Reactor (AMT 5000). The controller has been tested in two ways. First, single and multiple faults were introduced in the process equipment. Second, the controller performance was observed during an extended period of routine use. These evaluations indicate that the controller is able to detect process state change and to adjust the process recipe to keep the process on target