Effects of wall contamination on consecutive plasma processes

Plasma processes often go beyond the primary objectives focused on the subs trate, or targeted materials. For instance, sputtered materials deposit on surfaces other than the substrate, and plasma deposition extends to the wal ls of the reactor. In the process of plasma polymerization, or plasma chemi cal vapor deposition (PCVD), every surface (not just the substrate surface) participates in the overall plasma deposition process. Consequently the ch emical and physical natures of all surfaces within a reactor are very impor tant factors that determine the fate of the PCVD process. The materials dep osited on the wall surface (wall contaminants) are created in the previous run in a batch operation of PCVD. In a sequential plasma process, where pla sma polymerization of trimethylsilane (TMS) was followed by plasma polymeri zation of hexafluoroethane (HFE), F-containing oligomers (low molecular wei ght compounds), created during the plasma polymerization of HFE in the prev ious ran, remain on surfaces in the reactor. The wall contaminants were fou nd to migrate to the new substrate (aluminum alloy) surface in the subseque nt run upon the evacuation of the reactor. If an O-2 plasma treatment is ap plied, F-containing organic compounds chemisorbed on the new substrate surf ace are converted to F-containing inorganic compounds, which decreases the plasma-ablatable F on the surface. If no O-2 plasma treatment is applied, t he F-containing organic compounds are exposed to the environment of the TMS plasma. From the viewpoint of the sequence of plasma processes, a new HFE/ TMS sequence is created without the O-2 plasma treatment. The HFE/TMS syste m (reversed order to the normal cycle) causes adhesion failure at the inter face between the plasma polymers and the aluminum alloys, whereas the TMS/H FE system yields good adhesion of plasma deposited layers to the substrate and provides superior adhesion of a primer applied on the plasma polymer co ating. This difference was created by the difference in handling of the wal l contaminants. (C) 2001 American Vacuum Society.