Work holders – With fluid means – Vacuum-type holding means
Patent
1994-08-08
1996-10-15
Watson, Robert C.
Work holders
With fluid means
Vacuum-type holding means
269329, B25B 1100
Patent
active
055646824
ABSTRACT:
A wafer stage is provided with a plurality of through holes in its central and peripheral portions. To each of the through holes is coupled an end of a vacuum line the other end of which is coupled to a vacuum pump. With each of the vacuum lines is associated a respective one of electromagnetic valves. A controller controls the timing of opening of the electromagnetic valves by sensing the direction of a warp in the wafer. When a wafer placed on the stage is warped so that its central portion is higher than its peripheral portion, the electromagnetic valves associated with the vacuum lines coupled to the peripheral portion of the stage are opened first and the electromagnetic valves associated with the vacuum lines for the central portion of the stage are opened next. When a wafer placed on the stage is warped so that its central portion is lower than its peripheral portion, on the other hand, the electromagnetic valves associated with the vacuum lines coupled to the central portion of the stage are opened first and the electromagnetic valves associated with the vacuum lines for the peripheral portion of the stage are opened next. This permits a greatly warped wafer to be attracted to the stage in a state where it is made flat.
REFERENCES:
patent: 4131267 (1978-12-01), Ono et al.
patent: 4684113 (1987-08-01), Douglas et al.
patent: 4693458 (1987-09-01), Lewecke et al.
Kabushiki Kaisha Toshiba
Watson Robert C.
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