Back side etching method for integrated thinfilm diaphragm

PURPOSE: To eliminate the need for making accurate alignment by providing a sacrifice layer that can be selectively etched at a region where a web is scheduled to be formed on a substrate and using the sacrifice layer as an anisotropic etching stop part. CONSTITUTION: A sacrifice layer 13 that can be selectively eliminated, a thin- film layer 14 made of a dielectric, and a resistive thin-film layer 15 are formed on a wafer substrate 11 and are covered with silicon nitride layers 16 and 18. A nitride opening 19 is formed on the reverse side of the substrate 11 and a partial region of the substrate 11 is exposed. Then, after a first etch pit 19' is subjected to anisotropic etching until the layer 13 is reached, the layer 13 is eliminated by a selective etching liquid and a silicon anisotropic etching liquid is applied to a space 27 after elimination, thus forming a second anisotropic etch pit due to the operation to silicon 28. Then, a plane 29 is exposed and at the same time a drum-shaped hollow part is formed at the lower part of a web, thus separating the web from the substrate 11.