The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jan. 13, 1998
Filed:
Apr. 17, 1996
Hitoshi Tsuji, Kawasaki, JP;
Kabushiki Kaisha Toshiba, Kawasaki, JP;
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. 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.