| 摘要 |
A wafer position and clamp sensor. A circuit 114 monitors capacitance between two electrodes 22,24 within a wafer support 14,16,18,20. With no wafer 12 on the support, the capacitance falls in one range, with the wafer in place but not clamped, the capacitance falls in a second range and with the wafer held in place by an electrostatic attraction the capacitance falls in a third range. The sensed capacitance is converted to a frequency and then a DC voltage level 164 that can easily be sensed and used to confirm wafer placement and then confirm wafer clamping.
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