A novel doping technology for ultra-shallow junction fabrication: boron diffusion from boron-adsorbed layer by rapid thermal annealing

A new doping method to fabricate an ultra-shallow junction for the sub-0.1 μm pMOSFET was investigated, in which boron in an adsorbed layer diffused into Si substrate during rapid thermal annealing (RTA) at high temperature. This method made it possible to control the junction depth and doping concentration by varying quantitatively the boron coverage and to achieve a high doping efficiency due to the high surface localization of boron. The boron diffusion from an adsorbed layer with low boron coverage of below ∼0.45 ML produced extremely shallow junction (below ∼25 nm) with low sheet resistance (below ∼2.5 kΩ/sq.). This doping technique was applied to form a shallow source and drain extension region for sub-0.1 μm pMOSFET. The pMOSFET fabricated showed a fairly good performance, indicating an effective suppression of the short channel effect. This suggests that the boron atomic-layer doping is a more promising doping technique to form ultra-shallow junctions with good electrical characteristics.