Process Transfer and Chamber Matching

It is seen that in any plasma assisted process for thin film deposition like sputtering, HiPIMS and ALD, plasma properties like electron and ion density or electron temperature, as well as the ion to neutral ratio of the film forming species are used to characterize the process conditions for the film formation. However, the plasma parameters are strong function of chamber geometry, applied power and working pressure. This means that no recipe can be qualified as universal, and one need to optimize the process each time for any external change happened to the process or chamber. In the following example (see figure 1) utilizing a parallel-plate electrode reactor with variable geometry, it is shown that these parameters cannot be transferred to reactors with different geometries in order to reproduce plasma polymer films using four precursors.

Measurements of ion flux using Octiv suite VI probe and power coupling efficiency confirm that intrinsic plasma properties vary greatly with reactor geometry at constant applied RF power. It is further demonstrated that controlling the ion flux, offers a more widely applicable method of defining plasma polymerization processes, particularly for saturated and allylic precursors.

Figure 1 Left: Parallel Plate Capacitively Coupled Plasma reactor used for polymerization process, Right: Deposition rate variation with different inter electrode spacing  (DOI: https://pubs.acs.org/doi/10.1021/am401484b )