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

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 (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 90 eV. Notably, 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.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (235 K)Download as PowerPoint slideHighlights► Nascent ions in fluorocarbon (FC) plasmas were identified and energy analyzed. ► Ion effects are mediated both by plasma parameters and the choice of precursor. ► Highly energetic ions induce CFx scatter at surfaces. ► Low energy plasma ions recombine in the gas phase to promote FC film growth. ► FC deposition rates are strongly influenced by gas-phase oligomer concentration.