RTE lag in diffractive optical element etching

In this study, the pattern of a 4 mm diameter diffractive optical element w ith linewidth ranging from 12 to 0.5 mum was adopted. With the SiO2 layer a s the etch hard mask, silicon was etched based on HBr chemistry with additi ons of O-2 and SF6 . The effects of O-2 content on the sidewall anisotropy, etch rate, and etch selectivity over the SiO2 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 dep th versus zone width was determined as a guideline for the feasibility of t his method. (C) 2000 Elsevier Science B.V. All rights reserved.