Decreased hydrogen content in diamond-like carbon grown by CH4/Ar photoemission-assisted plasma chemical vapor deposition with CO2 gas

In this study, we tried to decrease the hydrogen content in diamond-like carbon (DLC) grown by photoemission-assisted plasma enhanced chemical vapor deposition (PA-PECVD) using Ar/CH4 mixed with CO2. When the CO2 flux was changed from 0 to 10 sccm with the Ar and CH4 fluxes maintained at 50 and 10 sccm, respectively, the growth rate decreased from 11 to 3 mu m/h. Secondary mass spectroscopy measurements confirmed that the amount of O mixed into the DLC was increased through incorporation of CO2 into feed gas flow. The 0 concentration in the DLC was quantitatively evaluated by X-ray photoelectron spectroscopy (XPS) to be 0.6 atomic % at a CO2 flow ratio of 14%. Raman spectroscopy and XPS revealed that the amount of H trapped in the DLC decreased as the CO2 flow ratio was increased and the sp(3)/sp(2) ratio remained almost unchanged. These results were interpreted by a model involving 0 radicals acting on the DLC surface associated with CO/CO2 and H2O, resulting in a decrease of the growth rate and H content. A portion of the O radicals also became incorporated into the DLC as C-O-C bonds.