Optimization of an amorphous silicon mask PECVD process for deep wet etching of Pyrex glass

Silicon is well known as an inert material in hydrofluoric acid and can be used during wet etching of glass as a mask with good results. In this paper, we report on the optimization of a PECVD amorphous silicon layer as etch mask for deep Pyrex glass micromachining in hydrofluoric acid solution. Our study reveals that the residual stress, especially the tensile stress, in the amorphous silicon masking layer is responsible for the defects generated during the etching process. The PECVD process and the subsequent annealing process have been optimized to reduce the compressive residual stress in the amorphous silicon layer. The maximum etch depth of glass achieved is as high as 300 μm.