Ion-etching of discharge-produced tetrafluoroethylene film with hydrogen, oxygen and noble gases. A mass spectrometric analysis

Abstract

Freshly deposited discharge-produced tetrafluoroethylene films were ion-etched with either helium, neon, argon, oxygen or hydrogen. The ions C +, CF +, CF 2 + and CF 3 + comprised most of the positive ions in rare gas discharges, with CF + always dominant. Sputtered fragments containing two or more carbon atoms were rare. These findings are compatible with the ion-etching of a highly crosslinked polymer film. Residual background gases were contributed to 1–3% of the total ion flux even though their actual partial pressures were very low. The concentration of neutral species corresponding to the ions observed was less than one part in ten thousand of the etching gas. With pure hydrogen, very little etching occurred and the degree of ionization relative to the rare gases was low. The principal reaction was the abstraction of fluorine from the polymer to give hydrogen fluoride and a more highly crosslinked film. Oxygen containing discharges produced the largest total yield of all the systems studied and the most evidence of chemical attack on the polymer. The ions observed were CO +, CO 2 +, COF +, COF 2 + as well as C +, CF +, CF 2 + and CF 3 +. Thus oxygen etches the polymer by preferentially attacking the carbon-carbon framework.