Reduction of surface roughness and aperture size effect for etching of Si with XeF2

Low etching pressure and high silicon substrate temperature successfully decrease the etched surface roughness and the aperture size effect, which represent challenges to the application of silicon etching with XeF 2 to the fabrication of microelectromechanical systems (MEMS). The etched roughness and aperture size effect are extremely high and limit factors for the design rules of MEMS devices. In order to express the extent of the aperture size effect, a uniformity of etched depth is defined as follows: (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 increasing 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 fewer constraints and to expand the field of applications of XeF 2 etching to MEMS.