A new criterion about substrate cleanliness level was established by an adhesion measurement for Al and Cu thin films
deposited onto both Si and quartz glass substrates cleaned by various methods, such as swab scouring, ultraviolet light
irradiation, and oxygen plasma ashing. The substrate surface contamination level was controlled by exposing the
substrate itself to low vacuum impregnated with rotary pump oil mists. The new criterion about the substrate cleanliness
level was somewhat different from the water wettability one. In the case of the UV irradiation, adhesion strength
increased with exposure time, and then a constant maximum value was kept. On the other hand, the excess oxygen
plasma ashing resulted in adhesion degradation due to the Si surface oxidation.
|