CARBON SELF-ORGANIZATION IN THE TERNARY SI1-X-YGEXCY ALLOY

This article demonstrates for the first time the possible self-orderin g of carbon in Si1-x-yGexCy thin films pseudomorphically grown on sili con. Germanium and carbon atomic distributions have been studied for a C-rich Si0.9-yGe0.1Cy heterostructure using high-resolution transmiss ion electron microscopy (HRTEM), high-resolution x-ray diffraction, Ra man spectrometry, and secondary ion mass spectrometry (SIMS). HRTEM im ages show the spontaneous formation of carbon-rich tilted sublattices and local germanium fluctuations, despite constant growth parameters. X-ray diffraction confirms this thin sublayers formation. A complement ary insight into local ordering effects around C is obtained by Raman spectroscopy. A new model for perpendicular lattice parameter reductio n is proposed. It involves C atoms mostly in third-nearest-neighbor po sitions and the local formation of a distorted CSi3 graphitic arrangem ent. In these C-rich sublayers, the perpendicular lattice mismatch to silicon is as low as -0.014. This aperiodic structure remains highly d istorted and a statistical description of these strain fluctuations is detailed. The atomistic configuration of these delta layers indicates the likely contribution of surface steps during the growth, while SIM S measurements hint at the probable involvement of carbon interstitial s to explain this ordering. For technological applications, this self- organization of carbon is promising for the ultrashallow junction chal lenge. These carbon-rich embedded layers can be considered as quantum wells, etch stops or very thin barriers against transient enhanced dif fusion. (C) 1998 American Institute of Physics.