Neural networks fusion to overlay control system for lithography process

This paper presents a neural network based overlay control system for lithography process. The control system is structured to be compatible with the existing control system. The two main components of the control system are neural network prediction module for metrology prediction and a control module for various control methods. The prediction module utilizes various overlay metrologies and other process related parameters to assess the process conditions and make accurate predictions of the output metrologies. Based on the prediction results, control module calculates the appropriate control parameter settings. The prediction module is constructed using the Levenberg-Marquardt method to compensate for the small to medium size neural network and the demand for speed. The control module incorporates both popular control methods and specific engineering process control (EPC). Evaluation results are presented to illustrate the control system performance.