Annealed Si/SiGeC Superlattices Studied by Dark-Field Electron Holography, ToF-SIMS and Infrared Spectroscopy

Si/SiGeC superlattices are used in the construction of new generation devices such as multichannel transistors. The incorporation of C in the SiGe layers allows for a better control of the strain and the Ge content. However the formation of {beta}-SiC clusters during annealing at high temperature limits the thermal stability of the alloy. It leads to a strong modification of the strain due to the reduction of the substitutional carbon content. Here, we investigated the behavior of Si/SiGeC superlattices that have been annealed using different characterization techniques: dark-field electron holography for the evaluation of strain; infrared spectroscopy and ToF-SIMS for the determination of the composition. It was found that after annealing at 1050 deg. C, the reduction of the substitutional C proportion leads to a recovery of the perpendicular strain in the superlattice. It was also proposed that the local arrangement of C atoms in a third nearest neighbor configuration is an intermediary step during the formation of the SiC clusters.