Structure of amorphous hydrogenated carbon films prepared by radio frequency plasma enhanced chemical vapor deposition. An analogy with the structure zone model developed for metals

In a structure zone model (SZM), the temperature and the sputtering gas pressure have been proposed as major factors explaining the structural properties of both evaporated and sputtered metals. Nevertheless, there is no evidence that such models can be applied to amorphous hydrogenated carbon films synthesized by radio frequency plasma enhanced chemical vapor deposition (rf PECVD). This paper reports on an original experiment designed to test by atomic force microscopy the hypothesis of an analogy between the rf PECVD amorphous materials and the existing SZM model for metals (amorphous and crystalline). Our results show that four zone morphologies called 1, M, T, and 2 can be obtained for amorphous materials according to the adatom mobility conditions. The parameters that control these morphologies are the plasma pressure, the surface temperature, and the plasma composition. The SZM model enables control of the a-C:H and a-C:D growth process. Zone T was found particularly interesting for the preparation of an ultra-smooth surface regardless of the film thickness. This result is of fundamental importance for the next "megajoule" laser facility, in which a-C:H or a-C:D capsules of 175 mum in thickness and 20 nm in surface roughness are expected. (C) 2002 American Institute of Physics.