Interprocess run-to-run feedforward control for wafer patterning
Wagner, A.B.; Ruegsegger, S.M.; Freudenberg, J.S.; Grimard, D.S.
Control Applications, 1999. Proceedings of the 1999 IEEE International Conference on
Volume 1, Issue , 1999 Page(s):789 - 795 vol. 1
Digital Object Identifier 10.1109/CCA.1999.807762
Summary:We consider run-to-run feedforward control from lithography to
etch in wafer patterning. Under feedforward control, measured deviations
in photoresist linewidth are corrected automatically by adjustment of
etch bias. Two potential problems with feedforward control are listed:
(1) the possibility of feeding measurement noise forward exists and
could result in increased final CD variability, and (2) it may be
difficult to adjust etch bias without disturbing other important etch
characteristics. First, a controller design that addresses concern (1)
is considered. Models of the lithography and measurement errors along
with minimum mean square error estimation are employed to reduce the
chances of acting on erroneous measurements. Building on the first, a
second controller is then designed to address concern (2). The
controller selects a recipe from a pre-qualified set rather than making
arbitrary etch adjustments. It is assumed the recipes in the set provide
a means for adjusting etch bias while guaranteeing acceptable results
for other characteristics. Both controllers are simulated using
industrial data
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