Feedforward control for reduced run-to-run variation inmicroelectronics manufacturing
Ruegsegger, S.; Wagner, A.; Freudenberg, J.S.; Grimard, D.S.
Semiconductor Manufacturing, IEEE Transactions on
Volume 12, Issue 4, Nov 1999 Page(s):493 - 502
Digital Object Identifier 10.1109/66.806127
Summary:Increased manufacturing yields can be obtained by reducing process
variation. One potential method to achieve lower process variance is
through interprocess feedforward control. During feedforward control, a
process recipe is adjusted to compensate for measured input deviations.
The potential benefits of feedforward control include reduced run-to-run
variance, rework, and scrap. Feedforward control has been used often in
manufacturing. However, there are two problematic issues associated with
feedforward recipe adjustment: 1) there is noise in the measurement tool
and adjusting for inaccurate measurements could increase the variance
and 2) it is difficult to alter one parameter in a manufacturing process
without worsening other key parameters. In this paper, we will address
both issues using a systems approach. Measurement noise poses a
significant threat to the success of feedforward control. If the
measurement noise is sufficiently large, the variance under feedforward
control could exceed the variance with no control. To address this
concern, we have integrated statistics theory into the feedforward
controller design. This detunes the recipe adjustment based on the
confidence in the accuracy of the sensor. These algorithms have the
effect of filtering the noise from the measurement tool. In order to
address the problem of altering one parameter without adversely
affecting others, one can use a feedforward controller that selects a
recipe from within a predefined set of allowable qualified recipes. We
call this feedforward recipe selection control (FRSC). We have developed
a design methodology for this type of controller. Preliminary versions
of our design algorithms have been implemented into a graphical user
interface (GUI)-based computer-aided design (CAD) environment. This
interactive software package guides the engineer through the design of
feedforward controllers using process data as inputs
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