Dual stage following method and apparatus

Details Dual stage following method and apparatus Dual stage following method and apparatus

1997-03-18

1998-08-11

Le, Que

Radiant energy

Photocells; circuits and apparatus

With circuit for evaluating a web, strand, strip, or sheet

250548, 356401, G01N 2186

Patent

active

057930520

ABSTRACT:
A method and apparatus minimizes the relative difference between motions of two stages driven by a single input signal, where the motions of the two stages ideally are perfectly synchronized. In practice, synchronization is imperfect due to mechanical/environmental disturbances in each stage as well as electrical differences affecting the stage controller. The two stages are serially coupled for control purposes so that a signal indicating the position of the first stage is used as an input driving signal to the second stage. The relative location error between the two stages is thereby minimized, compared to the case where the two stages are driven simultaneously but in parallel by a common input signal. Furthermore, by using the lower bandwidth stage as the driver (first) stage and the higher bandwidth stage as the follower (second) stage, the relative position error is no larger than the smaller of the absolute position errors of either stage alone. One exemplary application is improved alignment of a reticle stage and a wafer stage in a scanning exposure system for semiconductor lithography.

REFERENCES:
patent: 4871896 (1989-10-01), Kempter et al.
patent: 5255051 (1993-10-01), Allen
patent: 5633720 (1997-05-01), Takahashi

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