RIE lag in diffractive optical element etching
In this study, the pattern of a 4 mm diameter diffractive optical element with linewidth ranging from 12 to 0.5 ?m was adopted. With the SiO2 layer as the etch hard mask, silicon was etched based on HBr chemistry with additions of O2 and SF6. The effects of O2 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 depth versus zone width was determined as a guideline for the feasibility of this method.
rie lag diffractive optical elements anisotropic etching