Comparison Measurement between Fizeau Interferometer and Scanning Deflectomtric Profiler

There is a strong demand to measure an absolute surface profile with a few nanometer uncertainty. The National Metrology Institute of Japan (NMIJ) measure the absolute surface profile using two instruments based on difference methods: the Fizeau type flatness interferometer and the scanning deflectometric profiler. In the Fizeau type flatness interferometer, the measurand is a gap distance between a reference flat and a specimen. To obtain an absolute profile of the specimen, the reference flat was evaluated by a three flat test and a FEM analysis. The three flat test is one of the methods to measure absolute profile of a reference flat; however, the reference flat deforms under the force of gravity, and its absolute value cannot be detected by the three flat test. The deformation value of the reference flat was calculated by the FEM analysis. In the scanning deflectometric profiler, a local slope angle of a specimen is measured using an autocollimator and the surface profile is obtained by integrating with the local slope angles. To obtain an absolute profile of the specimen, the autocollimator which is key elements for the scanning deflectometric profiler was evaluated by using the self-calibration type rotary table. In this paper, we performed the comparison measurement between the Fizeau type flatness interferometer and the scanning deflectometric profile and verified the accuracy of the two instruments based on the different methods.