Effects of unique ion chemistry on thin-film growth by plasma-surface interactions

Plasma processing is a standard industrial method for the modification of m aterial surfaces and the deposition of thin films. Polyatomic ions and neut rals larger than a triatomic play a critical role in plasma-induced surface chemistry, especially in the deposition of polymeric films from fluorocarb on plasmas. In this paper, low energy CF3+ and C3F5+ ions are used to modif y a polystyrene surface. Experimental and computational studies are combine d to quantify the effect of the unique chemistry and structure of the incid ent ions on the result of ion-polymer collisions. C3F5+ ions are more effec tive at growing films than CF3+, both at similar energy/atom of approximate to 6 eV/atom and similar total kinetic energies of 25 and 50 eV. The compo sition of the films grown experimentally also varies with both the structur e and kinetic energy of the incident ion. Both C3F5+ and CF3+ should be tho ught of as covalently bound polyatomic precursors or fragments that can rea ct and become incorporated within the polystyrene surface, rather than mere ly donating F atoms, The size and structure of the ions affect polymer film formation via differing chemical structure, reactivity, sticking probabili ties, and energy transfer to the surface. The different reactivity of these two ions with the polymer surface supports the argument that larger specie s contribute to the deposition of polymeric films from fluorocarbon plasmas , These results indicate that complete understanding and accurate computer modeling of plasma-surface modification requires accurate measurement of th e identities, number densities, and kinetic energies of higher mass ions an d energetic neutrals.