AsH₃ gas-phase ex situ doping 3D silicon structures

Dopant incorporation in Si can be done in situ during epitaxial growth, or ex situ for localised material modification from a variety of sources including ion, solid, liquid, or gas. Gas-phase doping has the advantage that it does not require a thin film deposition, it is more effective at entering tight spaces than a liquid, and it is less damaging and more conformal than a beam-line ion implant. In this work, we apply arsine (AsH₃) gas at approximately atmospheric pressures in order to n-type dope three-dimensional (3D) Si device structures. It was observed that the gas-phase doping can be either corrosive or gentle to thin-body Si depending on the process conditions. Initial doping processes caused damage to the Si due to etching, but after process optimisation, the structural integrity of the Si nanostructures could be maintained successfully. Moreover, it was noted that evaluating doping processes entirely on planar Si surfaces can be misleading: processes which appear promising initially may not be transferrable to non-planar thin-body structures like fins or nanowires, due to unwanted Si etching. Overall, we found that gas-phase doping with AsH₃ could provide >10²⁰ cm⁻³ electrically active As concentrations. This high As incorporation makes gas-phase doping very attractive for future gate-all-around devices, where the space between features will decline with continued transistor scaling.