Diffusion enhanced carbon loss from SiGeC layers due to oxidation

The effect of annealing 25-nm-thick pseudomorphic Si0.7865Ge0.21C0.0035 layers on silicon substrates in nitrogen or oxygen at 850 degreesC was examined for different silicon cap thicknesses and annealing times by x-ray diffraction and secondary-ion mass spectrometry. Carbon is found to diffuse rapidly out of the SiGeC layer and even out of the sample entirely, an effect that is enhanced by oxidation and thin cap layers. All substitutional carbon can be removed from the sample in some cases, implying negligible formation of silicon-carbon complexes. Furthermore, it is found that each injected silicon interstitial atom due to oxidation causes the removal of one additional carbon atom for the SiGeC layer.