A silicon dioxide film is partly etched away to form an opening thereby exposing a silicon substrate. The surface of the opening, which is almost entirely covered with Si-OH, is coated with hexamethyldisilazane (HMDS) to bring about a silylation reaction. This causes the silicon substrate surface to be covered with a molecular film formed by replacing the hydrogen part in Si-OH with Si((CH.sub.3).sub.3. Atoms of aluminum are ejected by a sputtering process. The ejected aluminum atoms collide with the molecular film. Although some hydrocarbons (CH.sub.x) are sputtered or ejected due to such collision, a SiO.sub.x C.sub.y H.sub.z film 12' transformed from the molecular film is left between an aluminum film deposited and the silicon substrate. This SiO.sub.x C.sub.y H.sub.z film 12' acts as a barrier metal. The presence of the SiO.sub.x C.sub.y H.sub.z film prevents the occurrence of counter diffusion in the Al-Si system. No spikes are formed as a result.