This invention aims to facilitate observation and structural analysis of crystal grains of aluminum wiring. In the process, a protective film of a semiconductor device is removed by dry etching. Next, said semiconductor device is inclined and rotated and an aluminum alloy film or laminated aluminum alloy film of the semiconductor device is scanned with a focused ion beam. Then, said aluminum alloy film or laminated aluminum alloy film is scanned with a cantilever, atomic force between said aluminum alloy film or laminated aluminum alloy film and the cantilever is measured, and the surface of said aluminum alloy film or laminated aluminum alloy film is observed in vacuum.
