Hydrogen elimination as a key step for the formation of polymerlike hydrocarbon films

Recent experiments using H and CH3 radical beams as a model system for plas ma deposition of C:H films revealed that CH3 adsorption at dangling bonds a t the film surface is an important step for film formation. CH3 adsorption onto dangling bonds, which are created by hydrogen abstraction from incomin g H, implies a net incorporation of two hydrogen atoms per carbon atom duri ng steady state growth, although the H/C ratio of the deposited layers is o nly similar to1. Therefore, a reaction step of hydrogen elimination is esse ntial to describe C:H film formation consistently. This hydrogen eliminatio n is investigated by exposing polymerlike C:H films to quantified radical b eams of CH3 and H. The resulting C:H film formation is monitored by in situ ellipsometry and infrared reflection spectroscopy. Based on experimental d ata, a model is developed to describe hydrogen elimination via a two step p rocess: (i) first abstraction of surface bonded hydrogen from incoming H, f ollowed by (ii) the recombination of dangling bonds via a local rearrangeme nt of the C:H network. The latter process is self-limiting leading to a cha racteristic H/C ratio of 1 as a stoichiometric limit. Therefore, hydrogen e limination by atomic hydrogen corresponds to a key step for C:H film growth . (C) 2001 American Institute of Physics.