ETCHING OF A-CH FILMS BY AN ATOMIC OXYGEN BEAM

Hydrogenated amorphous carbon (a-C:H) films are considered for real time monitoring of atomic oxygen in Low Earth Orbit, and during plasma etching processes. a-C:H layers were deposited onto quartz crystal microbalances (QCM) in a dual microwave/radio frequency (mw/rf) plasma in methane and methane/argon mixtures. The QCMs were exposed to a neutral atomic oxygen beam in a system simulating the space environment, using a flux of approximately 10(16) atoms/cm2 s at 2.5 eV average incident energy. The etch rate E(r) was determined from the mass loss by in situ measurement of frequency shift of the QCM oscillator. The E(r) values, ranging from 1 to 20 ng/cm2 s, were found to increase with the hydrogen concentration in the films, and to decrease with increasing film density. Systematically higher E(r) values were found for a-C:H with a polymerlike character and for very hard ''diamondlike films'' with bonded hydrogen, in contrast to films,with predominantly unbonded hydrogen. For comparison, E(r) values for crystalline chemical vapor deposited diamond and for several commercial polymers have also been measured, and found to be approximately 0.5 and approximately 50 ng/cm2 s, respectively.