A NEW ALGORITHM FOR REAL-TIME THIN-FILM THICKNESS ESTIMATION GIVEN IN-SITU MULTIWAVELENGTH ELLIPSOMETRY USING AN EXTENDED KALMAN FILTER

We present a novel solution to the problem of thickness estimation fro m in situ ellipsometry measurements. A non-linear dynamic estimator is designed and implemented using the Extended Kalman Filter (EKF) theor y. Major advantages of this scheme include fast data processing, and r obustness to measurement noise and errors in the initial film thicknes s estimates. Since the number of function evaluations is much smaller than in the traditional non-linear least squares approach, EKF is comp utationally very efficient and has great potential for real-time appli cations. This technique is demonstrated on both simulated and experime ntal data gathered during plasma etching of a polycrystalline silicon (poly-Si) on silicon dioxide (SiO2)on silicon (Si) stack. (C) 1998 Els evier Science S.A.