Proceedings PaperPrecision Wafer Stepper Utilizing A Two-Dimensional Optical Encoder
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This paper describes a two-dimensional optical encoder that is used to control the x-y stepping stage of a modern state-of-the-art wafer stepper. Stage location is determined by measuring the position of a quartz grid plate that is attached to the stage. Accuracy and resolution of measurement are maintained by varying the null position of the grid. Operational principles and actual performance are discussed.