Calibration of etching uniformity for large aperture multilevel diffractive optical element by ion beam etching

Ion beam milling is a suitable technique for manufacturing optical elements . It has the advantages of accurately controlling and maintaining a constan t optical index. However, it is very difficult to ensure etching uniformity on large areas due to the instability of the machine during sputtering. In this article, the etching speed is analyzed, and selection criteria of cor responding technological parameters are proposed. An available calibration method is put forth to improve etching depth uniformity. Etching is divided into several steps and the sample is rotated to change its position on the target after each step. It is proved by experiment that this is very pract ical for actual fabrication with a 5%-15% improvement of depth uniformity f rom previous results. (C) 2000 American Institute of Physics. [S0034-6748(0 0)69602-8].