Vivek G. Badami - Charlotte NC
Steven R. Patterson - Concord NC
Carl A. Zanoni - Middlefield CT
Zygo Corporation - Middlefield CT
University of North Carolina at Charlotte - Charlotte NC
The invention features a phase measurement system for minimizing cyclic errors in a relative phase between exit reference and measurement beams emerging from an interferometer. The phase measurement system includes: a first optical processing channel including a first polarizer and a first detector, wherein during operation a first portion of the exit reference and measurement beams pass through the first polarizer to produce a first mixed beam and wherein the first detector measures an intensity of the first mixed beam; a second optical processing channel including a quarter wave retarder, a second polarizer, and a second detector, wherein during operation a second portion of the exit reference and measurement beams passes through the retarder and then the second polarizer to produce a second mixed beam and wherein the second detector measures an intensity of the second mixed beam; and a signal processor which during operation receives signals from the first and second detectors indicative of the intensities of the first and second mixed beams and processes the signals to determine, and minimize cyclic errors in, the relative phase between the exit reference and measurement beams. The invention also features interferometry, lithography, and beam writing systems that include the phase measurement system to improve the accuracy of interferometric distance measurements.