The effect of laser light propagation through a self-induced inhomogeneous process gas on temperature dependent laser-assisted chemical etching

High resolution and precise surface morphology is a primary goal of laser-assisted chemical etching (LACE) for microfabrication. However, the interaction of the laser light with the process gas can change the intensity incident to the target surface due to self-induced, thermally developed inhomogeneities within the gas. The exponential relationship between LACE rates and surface temperature means that very small changes in intensity, and thus surface temperature distribution, has a very large effect on the etch profile. This paper models both the inhomogeneous light–process gas interaction and the etching to predict the regimes in time and absorption path length where this effect needs to be considered. Numerical calculations of LACE microfabrication of borosilicate glass in a sulfur hexafluoride process gas with a 10.6 (mu)m wavelength laser beam are given that show how the surface morphology of the glass wafer is changed by the inhomogeneous interaction.