Use of plasma oxidation for conversion of metal salt infiltrated thin polymer films to metal oxide

Abstract

Oxygen plasma treatments for conversion of metal salt infiltrated polymer films to metal oxide films using an asymmetrical capacitively coupled plasma system were investigated. Hydroxylated Poly-2-Vinylpyridine (P2VP-OH) thin films grafted to silicon were exposed to metal salt-solvent solutions which swell the polymer enabling metal ion infiltration. Exposing the resulting film to oxygen plasma resulted in formation of polymer-free metal oxide films. Atomic oxygen and positive ions present in plasma can both influence the process outcome. A design of experiment approach was used to investigate the impact of RF power, gas pressure and process time on plasma composition and the resulting metal oxide films. A combination of Langmuir probe, retarding field energy analyser and optical emission spectroscopy measurements were used to monitor the plasma. The samples surfaces were examined using X-ray photoelectron spectroscopy, ellipsometry, transmission electron microscopy and energy dispersive X-ray analysis. Gas pressure and RF power were found to strongly influence both ion energy, and atomic oxygen to molecular ion ratios [O]/[O2 +] in the plasma which impacted the resulting surface layer. For the plasma conditions investigated conversion to a metal oxide was achieved in minutes. Sputter contamination was found to be significant in some cases.

From Basics to Frontiers: A Comprehensive Review of Plasma-Modified and Plasma-Synthesized Polymer Films

“…The densities of gaseous species play a critical role in defining the dynamics and characteristics of the plasma and, consequently, its applications. In the context of poly(2vinylpyridine) (P2VP) exposed to a low-pressure RF plasma supplied with molecular oxygen, it appears that an increase in atomic oxygen density (O) accelerates the breakdown of polymer chains and, therefore, the polymer etching, while an increase in molecular oxygen ion density (O 2 + ) escalates ion bombardment and sputtering, potentially contaminating the substrate [125]. The importance of oxygen density in etching processes is also evidenced when PMMA samples are exposed to He-O 2 plasma.…”