Wafer stage apparatus for attracting and holding semiconductor wafer

A wafer stage apparatus comprising:

• a stage provided with a plurality of first through holes for attracting a wafer placed on its surface;
• a plurality of wafer attracting means placed in central and peripheral portions of said stage, each of said wafer attracting means having a second hole for attracting said wafer and being movable up and down so that it can project from the surface of said wafer;
• driving means for driving said wafer attracting means individually, said driving means bringing said wafer attracting means into contact with said wafer placed on said stage;
• a plurality of first vacuum lines each of which has its one end coupled to a respective one of said first through holes and its other end coupled to a vacuum pump;
• a plurality of second vacuum lines each of which has its one end coupled to a respective one of said second through holes and its other end coupled to a vacuum pump;
• first valves, each of which is provided in the intermediate portion of a respective one of said first vacuum lines, for breaking and opening said first vacuum lines;
• second valves, each of which is provided in the intermediate portion of a respective one of said second vacuum lines, for breaking and opening said second vacuum lines;
• and
• control means for, when said wafer has its central portion higher than its peripheral portion, opening said second valves to permit said wafer attracting means to attract said wafer and said driving means to move said wafer to the position of contact with said stage and opening said first valves to attract said wafer to said stage.