ETCHING OF A-CH FILMS BY AN ATOMIC OXYGEN BEAM

Hydrogenated amorphous carbon (a-C:H) films are considered for real ti me monitoring of atomic oxygen in Low Earth Orbit, and during plasma e tching processes. a-C:H layers were deposited onto quartz crystal micr obalances (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, usin g a flux of approximately 10(16) atoms/cm2 s at 2.5 eV average inciden t energy. The etch rate E(r) was determined from the mass loss by in s itu measurement of frequency shift of the QCM oscillator. The E(r) val ues, ranging from 1 to 20 ng/cm2 s, were found to increase with the hy drogen concentration in the films, and to decrease with increasing fil m 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 hydr ogen. For comparison, E(r) values for crystalline chemical vapor depos ited diamond and for several commercial polymers have also been measur ed, and found to be approximately 0.5 and approximately 50 ng/cm2 s, r espectively.