Reducing the incubation effects for rear side laser etching of fused silica

Abstract

Laser-induced back side wet and dry etching (LIBWE and LIBDE) were developed for precise etching of transparent materials. However, LIBWE and LIBDE feature characteristics such as incubation effects and etching depth saturation, respectively, that can be unfavourable for applications in ultra-precision machining. Therefore, the techniques of LIBDE and LIBWE were combined in such a manner that the dielectric material was supplied with a thin-film-modified surface before etching by LIBWE.With this goal fused silica samples were covered with a thin chromium film for surface modification before LIBWE etching in acetone with 25ns KrF excimer laser pulses. Etching with the first pulse was observed. At laser fluences adequate for hydrocarbon LIBWE (1J/cm2) the etching rate for LIBDE is much higher than for LIBWE. In consequence, the etching rate decreases with increasing pulse number up to ten. The surface morphology depends very strong on the laser fluence and the pulse number. Smooth etchings were achieved at high fluences and low pulse numbers. However, uneven, wavy etched surfaces and micron pattern formation were observed for moderate and low laser fluences.