POSITION CONTROL CIRCUIT

摘要

A projection lens is mounted between a movable stage and a stationary holder to project an image of a reticle held by the holder onto a semiconductive wafer held by a chuck mounted on the stage. The stage is movable along orthogonal X and Y axes in a horizontal plane to align different regions of the semiconductive wafer with the projected image of the reticle. First and second movable plane mirrors fixedly mounted on the stage for movement therewith are symmetrically disposed relative to the Y axis in first and second vertical planes intersecting one another at the Y axis. Similarly, first and second stationary plane mirrors fixedly mounted on a housing of the projection lens are disposed parallel to the first and second movable mirrors, respectively. As the stage is moved along the X and Y axes, first and second interferometer systems provide first and second measurement signals indicative of the velocities of the first and second movable mirrors (relative to the first and second stationary mirrors) while they are being moved along first and second measurement paths normal to the first and second movable mirrors, respectively. In response to the sum and the difference of these measurement signals, first and second position control circuits move the stage along precisely orthogonal X and Y axes with the Y axis bisecting the angle between the first and second movable mirrors. Each of these position control circuits may be 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 the first or second measurement signal 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 the position control circuits are employed to extend the resolution of the position control circuits.