New fabrication method of step plate for measuring instrument transfer function of interferometer

Phase step plate has the property of step function, and it can be used to measure the interferometer system transfer function (ITF), which is used to objectively evaluate interferometer spatial frequency response characteristics. The traditional fabrication method of step plate is lithographic exposure combined with reactive ion beam etching method, which is costive, and not suitable for fabricating large diameter step plate. In this paper, a new fabrication method of step plate based on blade-mask coating technology is proposed. A step plate of 100mm diameter and 103.5nm step height is successfully fabricated, and the surface roughness, homogeneity, steepness of the step plate are satisfied for measurement requirements. Furthermore, the coated step plate is used to measure the ITF compared with an etched step plate, and the measurement results of two plates differ by no more than 5%, which shows a good consistency. Thus, the reliability of coated step plate for ITF measurements is proved.