On the interplay between plasma ions, radicals and surfaces: who dominates the interaction?

Ions and radicals are known to be key players in many plasma processes, including anisotropic etching, film deposition and surface modification. How different plasma species influence the reactions and reactivity of each other is not, however, fully understood, especially with respect to surface interactions. Using our imaging of radicals interacting with surfaces (IRIS) technique, we have measured the effects of ion bombardment on the surface reactions of a number of plasma species. Results from IRIS experiments for SiF and SiF₂ in SiF₄ plasmas, CF₂ radicals in hexafluoropropylene oxide plasmas, and NH and NH₂ radicals in NH₃ plasmas are presented for a variety of substrates. Depending on the molecule, the applied rf power, and the substrate material, these species display a wide variety of surface interactions. Moreover, ion bombardment increases surface scattering in primarily etching regimes (SiF₂, CF₂, and NH₂), decreases surface scattering in one system (NH radicals on polymer substrates), and has no effect on SiF radicals in SiF₄ plasmas. Correlating radical and ion bombardment relationships leads to possible plasma processing mechanisms, which are also discussed.