| 摘要 |
A pair of position control circuits is employed for controlling the position of an interferometrically controlled stage along orthogonal X and Y axes of motion of the stage. Each of these position control circuits is provided with a variable phase shifter responsive to a reference signal and a control signal for producing an output signal of the same frequency as the reference signal but shifted in phase as determined by the control signal, and with a phase detector responsive to the output signal from the variable phase shifter and to a measurement signal obtained from the interferometrically controlled stage for producing a position control signal proportional to the difference in phase between those signals. The sum and the difference of the position control signals of selected phase produced by these position control circuits are employed to extend the resolution of the position control circuits.
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