Techniques for reduction in surface roughness and aperture size effect for XeF2 etching of Si

Low etching pressure and high temperature on silicon substrate successfully decrease the etched surface roughness and the aperture effect which represent challenges toward the application of silicon etching with XeF₂ to MEMS fabrication. Etched roughness and aperture effect are extremely high and limit factors for the design rules of MEMS devices. In order to express an extent of the aperture effect, an uniformity of etched depth is defined as followed: (depth at 25 μm)/(depth at 175 μm)×100%. By lowering the charge pressure from 390 to 65 Pa, the etched roughness decreased from 870.8 and 174.4 Å and the uniformity improved from 71.3 to 88.7%. By heightening the substrate temperature from 300 to 440 K, the etched roughness decreased from 151.4 and 44.5 Å and the uniformity increased from 71.3 to 91.6%. These results will allow us to design with less constraints and expand the field of applications of XeF₂ etching to MEMS.