RIE lag in diffractive optical element etching

Abstract

In this study, the pattern of a 4 mm diameter diffractive optical element with linewidth ranging from 12 to 0.5 μm was adopted. With the SiO 2 layer as the etch hard mask, silicon was etched based on HBr chemistry with additions of O 2 and SF 6. The effects of O 2 content on the sidewall anisotropy, etch rate, and etch selectivity over the SiO 2 mask were also examined. The RIE lag, where etching of a small trench (hole) lags behind a large trench (hole), was investigated to produce an optimum aspect ratio for each zone of the diffractive optical element. The regression relation of the etch depth versus zone width was determined as a guideline for the feasibility of this method.