Temperature dependence of the sticking coefficient of methyl radicals at hydrocarbon film surfaces

摘要

The temperature dependence of the interaction of methyl radicals with the surface of a hard, amorphous hydrognated carbon film is investigated using in situ real-time ellipsometry and infrared spectroscopy. This interaction is considered as an important process during plasma deposition of polymer-like hydrocarbon films or formation of polycrystalline diamond in methane-containing discharges. At room temeprature CH_3 adsorbs at s p~2-coordianted CC bonds at the hydrical surfce of the hard C:H film and forms a completely s p~3-hybridized C:H adsorbate with a thicknes of approx0.17 nm. In the following, steady-state film growth is observed with a sticking coefficient of s(CH_3)=10~9-4). At a substrate temeprature of T=570 K, incident CH_3 causes net erosion with an etching yield of Y(CH_3)=10~(-4). At temperatures above 650 K the sticking coefficient of CH_3 becomes positive again, leading to a graphite-like C:H adsorbate. CH_3 adsorption is described by a reaction scheme based on the creation of dangling bonded hydrogen by incoming CH_3 radicals. these dangling bonds act as CH_3 adsorpiton sites at room temperature or as a precursor for chemical erosion at elevated temeprature.