Quantification of substrate cleanliness level based on thin film adhesion measurement

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.