Ultra-shallow junctions for sub-32 nm CMOS devices

IMEC has combined vapour-phase doping and sub-melt laser annealing to fabricate high-quality, defect-free, ultra-shallow junctions (USJs) with abrupt dopant profile.

The results demonstrate the benefits of using vapour-phase doping instead of classical beamline techniques to create the source and drain extension junctions of sub-32 nm CMOS devices.

Because of the need for alternative doping strategies for planar as well as non-planar devices, IMEC researchers have investigated the properties of USJs that were fabricated by the combination of vapour-phase doping and sub-melt laser anneal.

The doping process involves the deposition of boron or arsenic on 300 mm Si wafers, using a reduced-pressure chemical vapour deposition system.

Activation and driving in of the dopants were performed using a diode bar laser system with a laser wavelength of 808 nm.

The results were compared with those obtained by classical beamline ion implantation, using similar laser anneal conditions.

The results demonstrate the potential of the combined vapour-phase doping and laser anneal technique as a replacement technology for classical beamline and annealing techniques for creating the source and drain extension junctions in sub-32 nm CMOS technology.

These devices require sub-10 nm depth, which interferes with the achievement of low-enough sheet resistance.

Using classical beamline techniques, implantation damage can degrade the junction's quality. And for non-planar devices such as FinFETs, beamline ion implantation cannot meet the requirement of doping conformality.

With vapour-phase doping and laser anneal, the aggressive scaling of the source and drain extension junctions for planar as well as non-planar devices has now come within reach.

Sub-melt millisecond anneal is preferred over rapid thermal annealing since the latter results in excessive dopant diffusion and lower electrical activation.

For boron vapour doping, the technique enables the achievement of high-quality USJs with abrupt dopant profile and high activation level.

The arsenic vapour-phase doping wafers show a good junction profile and effective drive in of the dopant atoms into Si. However, only a fraction of the arsenic dopants has become electrically active and work is ongoing to understand and solve this issue.