PURPOSE: To improve the dimensional accuracy of a tapered section so as to improve the degree of integration by forming the tapered section together with a through hole by dry etching.

CONSTITUTION: This through hole forming method which forms a through hole 19 through an interlayer insulating film 13 by dry etching by utilizing the synergetic effect between a neutral active species 21 and reactive ions 22 forms a tapered section 18 by activating the species 21 (21a) adhering to the film 13 by heating the film 13 and isotropically etching the film 13 around the part where the through hole 19 is formed by using the activated species 21a. Simultaneously, the through hole 19 is formed through the film 13 by performing anisotropic etching by activating the species 21 by giving a shock to the species 21 with the reactive ions 22.