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

摘要

Plasma processing is a standard industrial method for the modifi- cation of material surfaces and the deposition of thin films. Polyatomic ions and neutrals larger than a triatomic play a critical role in plasma-induced surface chemistry, especially in the depo- sition of polymeric films from fluorocarbon plasmas. In this paper, low energy CF_3~+ and C_3F_5~+ ions are used to modify a polystyrene surface. Experimental and computational studies are combined to quantify the effect of the unique chemistry and structure of the incident ions on the result of ion-polymer collisions. C_3F_5~+ ions are more effective at growing films than CF_3~+, both at similar energy/ atom of ≈6 eV/atom and similar total kinetic energies of 25 and 50 eV. The composition of the films grown experimentally also varies with both the structure and kinetic energy of the incident ion. Both C_3F_5~+ and CF_3~+ should be thought of as covalently bound poly- atomic precursors or fragments that can react and become incor- porated within the polystyrene surface, rather than merely donat- ing F atoms. The size and structure of the ions affect polymer film formation via differing chemical structure, reactivity, sticking prob- abilities, and energy transfer to the surface. The different reactivity of these two ions with the polymer surface supports the argument that larger species 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 the identities, number densities, and kinetic energies of higher mass ions and energetic neutrals.