Laser induced backside dry etching of transparent materials

Laser induced backside wet etching (LIBWE) is a well-known procedure in the micromachining of transparent materials. We developed a modified technique in which the absorbing liquid of LIBWE was substituted by an absorbing solid thin film (laser induced backside dry etching, LIBDE). Fused silica plate having I mm thickness was coated by a 100 nm thick silver layer. The metal film was irradiated through the quartz plate by single pulses of a nanosecond KrF excimer laser. The applied fluence was varied in the range of 90-4030 mJ/cm(2), the illuminated area was 1.05 mm(2). At the appropriate fluences it was found that the silver was removed from the irradiated spots and here the fused silica was etched, simultaneously. The dependence of the etch rate (which corresponds to the etched depth, since this is a single-pulse technology) on the fluence was investigated. The results showed a linear relation between etching depth (0-600 nm/pulse) and applied fluence in the range of 0.2 (the etching threshold fluence) to 4 J/cm(2). With its higher etching rate, the LIBDE procedure is much more effective than LIBWE. The morphology of the etched holes was studied by an atomic force microscope. A thermal model was developed for the description of the etching mechanism which was in a good agreement with the experimental results. (c) 2007 Elsevier B.V. All rights reserved.