Plasma cleaning prior to wire bonding removes organic, oxide, and fluoride contaminations on the surface. It promotes better interfacial adhesion for wire bond and chip packaging, reduces non-stick-on-pad (NSOP) and bond lifting problems.
Bonding pads can be cleaned with pure argon plasma or argon mixed with oxygen/hydrogen. Surface cleaning is achieved through ion sputtering or a chemical reaction with radical species. There are two modes of plasma cleaning: direct mode and downstream mode. In the direct mode plasma cleaning, ic chips, and bonding pads will be subject to ion sputtering, chemical reaction, and UV radiation. In the downstream mode, the cleaning is mostly achieved through the surface chemical reaction.