To obtain a layer to be etched having machining dimensions finer than the limit dimensions of the opening of a mask being patterned by an aligner in the fabrication of a semiconductor device.

A layer 21 to be etched is formed on a semiconductor substrate 11 and coated with a resist 31 containing a magnetic material and then the resist 31 is subjected to patterning through optical exposure. The semiconductor substrate is then placed in a parallel field and the flux of magnetic material in the resist 31 is arranged. Subsequently, the layer 21 is subjected to plasma dry etching using the resist 31 as a mask member. The plasma is deflected to the center of the opening of mask by the flux of magnetic material in the resist 31. According to the method, a layer 2 to be etched having machining dimensions smaller than the minimum exposure dimensions of resist 31 can be obtained thus realizing finer machining.