Carbon Diffusion through SiO₂ from a Hydrogenated Amorphous Carbon Layer and Accumulation at the SiO₂/Si Interface

Carbon diffusion in a SiO₂/Si system was investigated. The source was provided by chemical vapor deposition of a hydrogenated amorphous carbon layer onto the oxide at low temperature. From layers with low oxygen content, no carbon outdiffusion was detected up to 1190°C. If the O content was high, the diffusion would start suddenly at 1140°C, and carbon accumulation would be found on the Si side of the SiO₂/Si interface in the form of SiC precipitates. These results are interpreted by assuming oxygen-assisted dissociation of carbon atoms from the carbon layer in form of CO molecules, fast CO diffusion through SiO₂ and an exothermic reaction of CO with Si. No carbon segregation was found in SiO₂. Consequences of carbon island formation during SiC oxidation are pointed out.