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Proceedings Paper

Minimum-time optimal feedforward control of conductive heating systems for microelectronics processing of silicon wafers and quartz photomasks
Author(s): Weng Khuen Ho; Arthur E.B. Tay
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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 substrate at ambient temperature on a large thermal-mass bake plate at processing temperature. A model-based optimal controller is presented based on minimum time control strategy for minimizing 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 substrate as part of the resulting feedforward/feedback strategy to eliminate the load disturbance. The controller is easy to design and implement for conventional thermal processing equipment. The minimum time control formulation also makes it more suitable for on-line implementation such as automatic on-line tuning of feedforward controller. 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: 20 October 2000
PDF: 9 pages
Proc. SPIE 4226, Microlithographic Techniques in Integrated Circuit Fabrication II, (20 October 2000); doi: 10.1117/12.404846
Show Author Affiliations
Weng Khuen Ho, National Univ. of Singapore (Singapore)
Arthur E.B. Tay, National Univ. of Singapore (Singapore)

Published in SPIE Proceedings Vol. 4226:
Microlithographic Techniques in Integrated Circuit Fabrication II
Chris A. Mack; XiaoCong Yuan, Editor(s)

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