CARBON CONTAMINATION OF ION-IMPLANTED LAYERS

Ion implantation induced carbon enrichment of the surface layer of iron and silicon after nitrogen ion implantation has been observed by AES and XPS combined with ion milling. In the range of ion doses implanted (4. 8 multiplied by 10**1**6 to 3 multiplied by 10**1**7 N atoms cm** minus **2) the carbon contamination level in a thin sub-surface layer has been found to be essentially independent of the dose. A graphite-like form of carbon was found on the surface of both iron and silicon while, in the sub-surface layer, a carbide-like form of carbon in the iron samples was observed. The origin of the carbon atoms is to be sought in the residual atmosphere of the target chamber. CO and CO//2 and hydrocarbons are its common constituents. Direct evidence of carbon atom absorption from residual gas molecules (**1**3CO) in a target chamber during titanium ion implantation has been obtained. A graphite-like carbon and non-volatile carbon compound overlayer may form on the implanted surface, serving subsequently as a source of carbon atoms for recoil implantation and diffusion into deeper layers. Diffusion might also be the main process responsible for the carbon transport into the sample.