In the recent years threaded run-to-run (RtR) control algorithms have experienced
drawbacks under certain circumstances, one such trait is when applied to high-mix of
products such as in Application Specific Integrated Circuits (ASIC) foundries. The
variations in the process are a function of the product being manufactured as well as the
tool being used. The presence of semiconductor layers increases the number of times the
lithography process must be repeated. Successive layers having different patterns must be
exposed using different reticles/masks in order to maximize tool utilizations.
The objectives of this research are to develop a set of methodologies for
evaluation and extension of threaded control applied to overlay. This project defines methods to quantify the efficacy of threaded controls, finds the drawbacks of threaded
control under production of high mix of semiconductors and suggests extensions and
alternatives to improve threaded control.
To evaluate the performance of threaded control, extensive simulations were
performed in MATLAB. The effects of noise, disturbances, sampling and delays on the
control and estimation performance of threaded controller were studied through these
simulations. Based on the results obtained, several ideas to extend threaded control by
reducing overall number of threads, by improving thread definitions and combination
have been introduced. A unique idea of sampling the measurements dynamically based
on the estimation accuracy is also presented. Future work includes implementing the
extensions to threaded control suggested in this work in real production data and
comparing the results without the use of those methods. Future work also includes
building new alternatives to threaded control. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2010-12-2097 |
| Date | 14 February 2011 |
| Creators | Patwardhan, Ninad Narendra |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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