Tapered windows in phosphorus-doped SiO<inf>2</inf>by ion implantation

It has been shown that tapered windows can be made in both Nitrox deposited ∼ 1% phosphorus-doped SiO2(P-glass) and Silox deposited ∼7% P-glass as well as undoped SiO2by an ion implantation which produces a thin damaged layer at the top of the oxide. The damaged layer etches at a faster rate than the undamaged oxide. This fast-etching layer undercuts the photoresist which serves as the etching mask and results in window walls having slopes in the range of 30-40° with respect to the wafer surface.