Adjustable plane mirror interferometer adapted for microelectronic mask with different thickness

Plane mirror interferometers are usually utilized to nano-position large-range scanning stage in microelectronic mask measurement systems. To avoid Abbe-error the centerline of measurement light beams of X Y Z should be intersected at the upper surface of the mask. But the different thickness of masks can also lead to Abbé errors. In this paper a novel plane mirror interferometer is designed, in which the measurement centerline can be accurately adjusted in coincidence with the upper surface of the mask according to their different thickness. The Abbé arm of this interferometer can be decreased to zero and the Abbe-error is avoided completely. The range of different thickness that can be adapted in this interferometer is ±3 mm. In this paper a quadrant photoelectric cell adapter is used to measure the centerline of the measurement light beams and the uncertainty of this method is better than 0.02 mm, which can meet the needs of nano-positioning of microelectronic mask measurement.