Formation of SiGe Source/Drain Using Ge Implantation for Floating-Body Effect Resistant SOI MOSFETs

SiGe was formed by Ge implantation into silicon on insulator (SOI) substrates with the dosage range from 0.5 to 3×1016 cm-2 and subsequent annealing in N2. The implantation dosage dependence of the crystalline quality, bandgap and sheet resistance of the SiGe layers are investigated. The implantation damage for Ge dosage up to 1×1016 cm-2 can be removed at a temperature as low as 700°C. A SiGe crystalline network is formed by the annealing at the same time. With a Ge dosage of 1×1016 cm-2 or more, bandgap narrowing of the SiGe layer was detected. Sheet resistances of SiGe N+ and P+ layers gradually increase for higher Ge dosage. SOI MOSFET characteristics in terms of the floating-body effect with the SiGe source/drain layers are presented. The bandgap narrowing suppresses the floating-body effect of fully depleted SOI MOSFETs, while maintaining the reverse leakage current of the p-n junction between the source/drain and channel at a low level.