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Proceedings Paper

Optimal control strategy using linear programming for load disturbance compensation in thermal processing systems
Author(s): Weng Khuen Ho; Arthur E.B. Tay; Charles D. Schaper
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Paper Abstract

An optimal control scheme is designed to improve repeatability by minimizing the loading effects induced by the common processing condition of placement of a semiconductor wafer/photomask at ambient temperature on a large thermal-mass bake plate at processing temperature. The optimal control strategy is a model-based method using linear programming to minimize the worst-case deviation from a nominal temperature set-point during the load disturbance condition. This results in a predictive controller that performs a pre-determined heating sequence prior to the arrival of the wafer as part of the resulting feedforward/feedback strategy to eliminate the load disturbance. This procedure is based on an empirical model generated from data obtained during closed-loop operation. It is easy to design and implement for conventional thermal processing equipment. Experimental results are performed for a commercial conventional bake plate and depict an order-of-magnitude improvement in the settling time and the integral-square temperature error between the optimal predictive controller and a feedback controller for a typical load disturbance.

Paper Details

Date Published: 3 September 1999
PDF: 12 pages
Proc. SPIE 3882, Process, Equipment, and Materials Control in Integrated Circuit Manufacturing V, (3 September 1999); doi: 10.1117/12.361294
Show Author Affiliations
Weng Khuen Ho, National Univ. of Singapore (Singapore)
Arthur E.B. Tay, National Univ. of Singapore (Singapore)
Charles D. Schaper, Stanford Univ. (United States)


Published in SPIE Proceedings Vol. 3882:
Process, Equipment, and Materials Control in Integrated Circuit Manufacturing V
Anthony J. Toprac; Kim Dang, Editor(s)

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