Use of a protecting adhesive tape in a method of manufacturing a thin-film circuit substrate having a micro electro-mechanical systems (MEMS) structure section, which method comprises the steps of: (a) gouging a surface of a circuit substrate in advance in a depth which is at least approximately equal to a thickness of a final product of the circuit substrate, to form a section to have formed therein a penetrating structure; (b) providing a protecting adhesive tape to adhere to the surface of the circuit substrate subjected to the gouging step, before a backing surface of the circuit substrate is ground; (c) grinding the backing surface of the circuit substrate in such a thickness that the section subjected to the gouging step in advance would not penetrate through the substrate; (d) dry etching entirely the backing surface of the circuit substrate with plasma irradiation, while the protecting adhesive tape adheres to the circuit substrate, after completion of the grinding step for the backing surface of the circuit substrate; and (e) making the section subjected to the gouging step on the surface of the circuit substrate to penetrate, by the dry etching with plasma irradiation, thereby forming the penetrating structure section; wherein the protecting adhesive tape is constituted of a radiolucent film-like support and has such heat resistance that the protecting adhesive tape can withstand at least increase in substrate temperature in the dry etching with plasma irradiation; wherein, in the step of adhering the protecting adhesive tape to the surface of the circuit substrate, the adhering is performed in an atmosphere of a reduced-pressure state which is equal to that of the atmosphere in the dry etching with plasma irradiation; wherein the film-like support constituting the protecting adhesive tape is composed of a thermoplastic resin having a melting point of at least 100°C; wherein an adsorptive power between the film-like support constituting the protecting adhesive tape and a circuit substrate adsorptive-fixing stage of a plasma irradiation dry etching device is at least 1,500 Pa; wherein the film-like support constituting the protecting adhesive tape is formed by using a thermoplastic polyester resin, a polyester-series elastomer resin, a polyolefin-series resin which may have a branched structure, or a cross-linkable film; and wherein the film-like support constituting the protecting adhesive tape is in sufficient contact with a circuit substrate adsorptive-fixing stage of a dry etching device, to prevent defect from occurring due to shortage of adsorptive power in the dry etching. (a) gouging a surface of a circuit substrate in advance in a depth which is at least approximately equal to a thickness of a final product of the circuit substrate, to form a section to have formed therein a penetrating structure; (b) providing a protecting adhesive tape to adhere to the surface of the circuit substrate subjected to the gouging step, before a backing surface of the circuit substrate is ground; (c) grinding the backing surface of the circuit substrate in such a thickness that the section subjected to the gouging step in advance would not penetrate through the substrate; (d) dry etching entirely the backing surface of the circuit substrate with plasma irradiation, while the protecting adhesive tape adheres to the circuit substrate, after completion of the grinding step for the backing surface of the circuit substrate; and (e) making the section subjected to the gouging step on the surface of the circuit substrate to penetrate, by the dry etching with plasma irradiation, thereby forming the penetrating structure section;