PURPOSE: To prevent the abnormal etching of a substrate due to the production of a local battery by selectively forming an insulator layer on the upper surface of a substrate of a through hole forming region, foring a through hole which reaches the insulator layer from the back surface of the substrate, then removing the insulator layer via the through hole, and forming a metal layer which is connected to an input electrode wiring or an output electrode wiring via the through hole to the back surface of the substrate.

CONSTITUTION: A substrate 1 is contacted with a glass plate 9, and etched with mexture solution of nitric acid and hydrogen peroxide water as an etchant from the back surface of the substrate 1 until the thickness becomes approx. 30(μm). Then, a photoresist film is formed on the overall region except the through hole forming region of the back surface of the substrate, and with the photoresist film as a mask it is dipped together with the glass plate in the mixture solution of phosphoric acid and hydrogen peroxide water. According to this etching steps, the through hole is formed at the lower surface of the dioxidized silicon film 3', and not advanced any further. Accordingly, the contact of the source electrode 4, 5 with the etchant can be avoided, the possibility of producing local battery can be eliminated, and an undercut can be effectively prevented.