n-Channel MOSFETs Fabricated on SiGe Dots for Strain-Enhanced Mobility

The silicon germanium dots grown in the Stranski-Krastanow mode are used to induce biaxial tensile strain in a silicon capping layer. A high Ge content and correspondingly high Si strain levels are reached due to the 3-D growth of the dots. The n-channel MOS devices, referred to in this letter as DotFETs, are processed with the main gate segment above the strained Si layer on a single dot. To prevent the intermixing of the Si/SiGe/Si structure, a novel low-temperature FET structure processed below 400°C has been implemented: The ultrashallow source/drain junctions formed by excimer-laser annealing in the full-melt mode of ion-implanted dopants are self-aligned to a metal gate. The crystallinity of the structure is preserved throughout the processing, and compared to reference devices, an average increase in the drain current of up to 22.5% is obtained.