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Decentralized control of wafer temperature for multizone rapid thermal processing systems

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3 Author(s)
Schaper, Charles D. ; Dept. of Electr. Eng., Stanford Univ., CA, USA ; Kailath, T. ; Yong Jin Lee

Decentralized control is shown through analysis and experimentation to be an appropriate strategy for wafer temperature control in certain multizone rapid thermal processing (RTP) systems. An input-output controllability analysis is conducted to illustrate that the direction associated with the reference command (set-point) corresponding to a spatially uniform temperature trajectory specification is nearly in alignment with the “most” controllable direction associated with the maximum singular value for a multiple concentric lamp configuration. Consequently, the control structure need not alter the directionality of the plant and, thus, can be achieved by a simple decentralized controller where the lamps are paired individually to sensors to achieve a multiloop structure where all interactions are not taken explicitly into account. This result is shown to produce acceptable performance even for an ill-conditioned plant since the directions corresponding to the smaller singular values are irrelevant to the uniform temperature control criteria. Moreover, straightforward nonmodel-based tuning of the controller is enabled due to the simplicity of the decentralized control structure

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Semiconductor Manufacturing, IEEE Transactions on  (Volume:12 ,  Issue: 2 )