PURPOSE: To enhance the bonding property and long-term reliability of an Al pad by photoetching an LVD-SiO2 film on the pad with a mixed soln. of hydrofluoric acid and phosphoric acid to prevent roughening or discoloration of the pad surface.

CONSTITUTION: Al film 3 for wiring and a bonding pad portion is formed on Si wafer 1 covered with Si oxide film 2. In order to form a bonding pad, part 6 corresponding to the bonding pad portion out of Si oxide film 4 formed for passivation must be removed by photoetching. So, above 2 μ thick photoresist film 5 for protecting part of film 4 not to be etched is covered, and photoetching is carried out with an etching soln. of hydrofluoric acid diluted with H3PO4. Since the etching soln. is highly viscous, it is applied with ultrasonic waves to attain smooth convection is etching, thus carrying out good etching with little unevenness.