| 摘要 |
PURPOSE:To sense deterioration in the performance of an electrostatic chuck, which retains wafer by suction, at an early point of time by superposing an AC power supply for monitoring over a high voltage DC power supply for generation of electrostatic attraction force, and by monitoring variation in the AC current. CONSTITUTION:A 50-60Hz AC power supply 1 for monitoring is superposed over a high voltage DC power supply 2 for generation of electrostatic attraction force, followed by impression on an electrostatic chuck having an electrostatic capacitance C through a resistance R of approx. 2-3W. The impedance Xc of this electrostatic capacitance C depends upon the angle frequency omega of the AC power supply 1 as expressed by Xc=1/omegaC, and variation in the electrostatic capacitance C causes variation in this impedance Xc to lead to variation of the AC current IAC flowing through the chuck, that is monitored with an ammeter 3 for sensing the degree of deterioration of the chuck. This enables detection of deterioration in the performance of an electrostatic chuck prior to insulation breakage, and its replacement is warned at an early point of time. |
