| 摘要 |
PROBLEM TO BE SOLVED: To provide a laser interference length measuring device which is capable of very accurately measuring the high speed movement of a mask stage by a method wherein the enumerated data of a first interference signal and the enumerated data of a second interference signal are added up or the enumerated data of a second interference signal are subtracted from the enumerated data of a first interference signal, sum is outputted as a synchronous scanning error between the mask stage and a wafer stage, and a subtraction result is outputted as a movement. SOLUTION: A part of measuring light which is ramified after it reciprocates twice between a certain object and a moving mirror 2a interferes with a reference light, and an interference signal Sig1 is obtained. Furthermore, a measuring light which reciprocates once between a certain object and the moving mirror 1a of a mask stage 1 after it reciprocates twice between a certain object and a moving mirror 2a interferes with a reference light, and an interference signal Sig2 is obtained. The interference signals Sig1 and Sig2 are processed by an operational circuit 30, addition or subtraction is carried out, the sum is outputted as a synchronous scanning error between the mask stage 1 and the wafer stage 2, and a subtraction result is outputted as a movement of the mask stage 1.
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