Diffusion and clustering of supersaturated carbon in SiGeC layers under oxidation

In this work we investigated the diffusion and Clustering Of Supersaturated substitutional carbon in 200 nm thick SiGeC layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N-2) or oxidizing (O-2) ambients at 850degreesC for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under oxidation enhances the C diffusion with respect to the N-2 annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the layer/cap interface dominates, This phenomenon saturates after an initial period (2-4 h) which depends on the C concentration. This saturation is due to the formation and growth of C containing precipitates which are promoted by the I injection and act as a sink for mobile C atoms. The competition between clustering and diffusion is discussed for two different C concentrations.