The formation of very flat silicon sidewalls by dry etching

A dry etching system producing very flat wall profiles in bulk silicon is suggested. Wall angles down to 1 degrees were obtained at accurate aligned structures with well defined dimensions. The surface roughness is nearly the same as that prior to the etch. Pattern transfer was carried out in a conventional RIE system. A resist mask was not used but instead a special prepared bonded mask wafer with holes and diffusion channels for the reactive species from the plasma. After the etch this mask wafer is reusable by separating it from the substrate wafer.