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Molecular Monolayer Doping (MLD)

Molecular Monolayer Doping (MLD)

To maintain transistor device scaling, industry has been forced to move from planar to non-planar device architectures. This has created the need to develop a radically new, conformal method for doping, which alters the electrical properties of a semiconductor, related to the access resistance.

Doping 3D Structures
Doping 3D structures (a) Schematic depicting mono directional nature of ion implantation, damage to crystal structure and incomplete recrystallisation after annealing. (b) Schematic depicting molecules attached to the surface of a 3D nanowire/fin and conformal diffusion of dopant after annealing.

Low access resistance is required for technology to be high performing with reduced power. The major roadblock to enabling high carrier mobility, when integrating into a technology platform, is that access resistances exponentially increase once the semiconductor device body is thinned. As a result of this, current drops. These devices will not be technologically relevant if the high-mobility benefit is swamped by losses associated with access resistances.

In these device designs, surfaces dominate, as there are proportionately more and more atoms bound-to or located close to the surface. Since it is highly likely that future FET devices will consist of these architectures, it is imminent that surface science and chemistry based studies of these systems will rapidly emerge as the key enabling technology in terms of device optimisation.

We are comparing doping process technologies to understand geometry effects for molecular monolayer doping and for small geometry fins or gate-all-around devices.

SEM image of the nanowire test structure
A representative top view SEM image of the nanowire test structure under evaluation, fabricated on high-mobility materials at Tyndall-UCC.

Researchers from the Materials Chemistry and Analysis Group in the Chemistry Department in UCC in conjunction with the SP&S fabrication team in Tyndall are using surface chemistry to introduce dopant atoms into devices, fabricated in-house, down to sub 10 nm dimensions.


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