Ion contributions to gas–surface interactions in inductively-coupled fluorocarbon plasmas

Abstract

The role of plasma-generated ions for plasma processing of substrates was investigated to develop a deeper understanding of the phenomena which occur at plasma–surface interfaces. Energy analyses were performed for nascent ions for a range of fluorocarbon (FC) plasma source gases, including CF4, C2F6, C3F8, C3F6, and hexafluoropropylene oxide (HFPO). Mean ion energies (<Ei>total) for all observed nascent ions in a given plasma system are strongly correlated with applied rf plasma power, with total average energies ranging from 15 to 90eV. Notably, <Ei>total values also influence surface scatter of CFx radicals from deposited FC films, determined from imaging of radicals interacting with surfaces (IRIS) experiments. In ion-limited IRIS studies, scatter coefficients for CFx species decrease considerably relative to ion-rich systems under all conditions, suggesting that ion-mediated processes are crucial for determining CFx behavior at the gas–surface interface. Mass spectrometric techniques were used to determine the relative gas-phase proportions of oligomeric film precursors. The amount of oligomeric species relative to CF3 in all systems influences film deposition significantly, substantiating the concept that oligomers contribute to FC film growth. Speculations on the role of low-energy ions in the plasma systems are presented for their expected contributions to FC film propagation.