Frequency domain position estimation for lithographic alignment

  • Authors:

  • Alan Gatherer;Teresa H.-Y. Meng

  • Affiliations:

  • Information Systems Lab, Stanford University, Stanford, CA;Information Systems Lab, Stanford University, Stanford, CA

  • Venue:
  • ICASSP'93 Proceedings of the 1993 IEEE international conference on Acoustics, speech, and signal processing: digital speech processing - Volume III
  • Year:
  • 1993

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Abstract

We describe a frequency domain based algorithm for estimating the podtion of a symmetric pulse. The algorithm exhibits low estimation error variance and low computational complexity, making it ideal for the lithographic alignment task in integrated circuit manufacturing. We show that for additive, white stationary noise the position estimation is unbiased and that if the noise is also Gaussian this algorithm asymptotically achieves the Cramer Rao Bound as the noise power decreases. We also describe an adaptive algorithm that optimizes the position estimation of a pulse of unknown shape, given a training set. This adaptive procedure does not require knowledge of the position of the training pulses and is therefore a blind, adaptive optimizer. It achieves a steady state mean squared estimation error that is smaller than that of the LMS algorithm.