Laser-induced front side etching of fused silica with XeF excimer laser using thin metal layers

Laser-induced front side etching (LIFE) is a method for laser etching of transparent materials using thin absorber layers, e.g., for precision engineering or even optical applications. Aluminium, chromium, molybdenum, silver as well as titanium with various layer thicknesses (5–100 nm) were applied as absorber for etching trenches in fused silica with nanosecond XeF excimer laser radiation. The sample surfaces were processed at laser fluences up to 10 J/cm2 and laser pulse numbers from 1 to 10 pulses. A linear growth of the etching depth at rising laser fluence was found. The film thickness dependency is more complex and mostly influenced by the optical properties of the thin metal films. The influence of the laser fluence, the number of pulses, the absorber material as well as the absorber layer thickness on the etching process, the etching depth, and the surface modification were presented and discussed. A simple model is given that allows the discussion of the etching depth in dependency on the laser fluence and the metal film thickness. The measurements represented a good agreement with the calculated results by a thermal model. The LIFE method allows nm-precision etching of fused silica with etching depths up to 150 nm.