Reduced pressure chemical vapor deposition of Si1−x−yGexCy/Si and Si1−yCy/Si heterostructures

Abstract

We have grown by reduced pressure chemical vapor deposition Si1−x−yGexCy/Si and Si1−yCy/Si heterostructures for electrical purposes. The incorporation of substitutional carbon atoms into Si is expected to play a double role. On the one hand, by creating a carrier confinement in the channel region of metal–oxide–semiconductor transistors, the compressive strained Si1−x−yGexCy and the tensile strained Si1−yCy layers can be used to improve transport properties. On the other hand, the addition of carbon atoms can compensate the compressive strain induced by large amounts of Ge. As far as high Ge concentration Si1−x−yGexCy layers are concerned (Ge=18 at. %), x-ray diffraction (XRD) measurements show the progressive shift of the Si1−x−yGexCy peak towards the Si substrate peak, evidencing the strain compensation due to the incorporation of carbon atoms into the substitutional sites of the SiGe matrix. Carbon incorporation results in a decrease of the growth rate, from 10 nm/min (for substitutional C=0.46 at. %) down to 9 nm/min (when substitutional C=1.26 at. %). High quality Si1−x−yGexCy layers with up to 1.26 at. % of substitutional carbon atoms were grown. Transmission electron microscopy imaging and the comparison between secondary ion mass spectrometry (SIMS) and XRD results revealed that a further increase of the SiCH6 flow leads to an increase of the carbon incorporation into interstitial sites, which translates into a rapid deterioration of the Si1−x−yGexCy layer. Slightly compressive-strained Si1−x−yGexCy layers (Ge=4 at. %) have also been grown. Through the increase of the SiCH6 flow we have managed to tailor the Si1−x−yGexCy layer strain from compressive to tensile. The Si1−x−yGexCy growth rate drops from 3.4 nm/min down to 3.0 nm/min when the substitutional carbon concentration increases from 0.4 up to 1.21 at. %. Finally, Si1−yCy/Si tensile-strained heterostructures were grown. Smaller growth rates (1.8 nm/min) for Si1−yCy than for Si1−x−yGexCy are obtained. SIMS and XRD measurements indicate that the highest carbon concentration Si1−yCy layer (substitutional C=1.12 at. %) also contains many interstitial carbon atoms (interstitial C=0.45 at. %).