An Adaptive Nonlinear Control Strategy for Photolithography

A closed-loop adaptive control technique for photolithography is proposed and evaluated, In this strategy, development time is manipulated in order to keep the output critical dimension at a desired value despite the disruptive effects of unmeasured process disturbances. The adaptive control strategy incorporates a three parameter reduced-order model of the photo-lithography process, a parameter estimator, and a nonlinear model-based controller. Simulation studies show that the adaptive controller is able to reject the detrimental effects of process disturbances and bring the critical dimension back to its desired value. In the simulations, PROLITH was used to represent the real lithography process.