Smooth surface glass etching by deep reactive ion etching with SF6 and Xe gases

This article reports on a smooth surface glass etching using deep reactive ion etching with a mixture of sulfur hexafluoride (SF6) and xenon (Xe) gases. A surface roughness of 23 Å was achieved with SF6/Xe(=1/1) and 18 Å with SF6/Ar(=1/4) under a condition of −390 V self-bias voltage and 0.2 Pa pressure. The surface roughness in the order of several angstroms (5.9 Å) was obtained at a pressure of 0.1 Pa (SF6/Xe=1/1). The average surface roughness (Ra) after the etching by SF6/Xe gas was smaller than those after the etching with SF6 only or SF6/Ar at a same mole fraction of the inert gas to SF6+inert gas. Since heavy inert gas increases the physical sputtering effect, the addition of the heavy inert gas helps to remove contaminant residues remaining on the etched surface. The optimum condition of smooth glass etching with high etch selectivity (21) is a pressure of 0.2 Pa and a mole fraction of Xe to SF6 gas is 8 to 7. We also make an analysis of the relationship between the surface average roughness on the bottom and the etched depth. The average roughness of the etched surface was smooth not only for the bottom but also for the sidewalls. The average surface roughness of the sidewalls was about 16 nm for 50-μm-deep etching under the same optimum condition. This technology was applied to a deep etching of quartz crystal used for a mass sensor.