Patent ID: 7671969

Claim:
A wafer stage apparatus comprising: a chuck having first and second vacuum holes and configured to receive a wafer, wherein the first vacuum holes are disposed under a central portion of the wafer and the second vacuum holes are disposed under a peripheral edge portion of the wafer; a first vacuum pump configured to apply a vacuum suction force via the first vacuum holes to the central portion of the wafer; a second vacuum pump configured to apply a vacuum suction force via the second vacuum holes to the peripheral edge portion of the wafer; a controller electrically connected to the second vacuum pump and configured to store a preset reference distance value “K”; and a wafer flatness unit electrically connected to the controller and comprising a distance measuring unit configured to measure a distance “L” between the distance measuring unit and a top surface of the wafer and provide the distance “L” to the controller, wherein the controller is further configured to compare the distance “L” with the preset reference distance “K”, and control operation of the second vacuum pump to apply the vacuum suction force via the second vacuum holes to the edge portion of the wafer such that the distance “L” becomes equal to the preset reference distance “K”.