Description
Hydrogen is a common impurity within semiconductors and devices. It is often introduced into devices intentionally to passivate bulk and surface defects, due to its high diffusivity and presence in many treatments it is also often introduced unintentionally. This is particularly problematic for boron-doped silicon as hydrogen will almost always electrically deactivate boron when introduced. Engineering devices to properly utilize hydrogen and avoid its drawbacks requires understanding its bonding and diffusive behaviours and understanding how its charge-state evolves.
We profile dopant deactivation by Electrochemical Capacitance–Voltage (ECV) in Boron-doped silicon and Hydrogen concentrations by Time-of-Flight Secondary-Ion Mass Spectrometry (ToF-SIMS) in Boron-doped float-zone Silicon exposed to Hydrogen plasmas at low (~125 °C) and high (~175 °C) temperatures, on polished and mechanically scratched surfaces. Strikingly, wafers recovered after roughly thirty years of ambient cupboard storage already showed significant near-surface dopant deactivation, illustrating how readily ambient hydrogen contamination alters electrical properties.
On polished samples, the low-temperature plasma produces a simple complementary-error-function ($\erfc(x)$) deactivation profile 8 µm deep, consistent with Fickian diffusion, whereas the high-temperature plasma yields a flatter, 25 µm-deep profile requiring a superposition of two $\erfc(x)$ functions, supporting reports of two independent Boron-Hydrogen subsystems active only above ~130°C. In both temperature regimes, the total Hydrogen exceeds the background Boron concentration near the surface and shows steep, kinked concentration profiles.
The effects of surface damage on Hydrogen infiltration are shown to be opposite between low and high temperature plasma treatments: the former having more extreme dopant deactivation near the surface but reduced depth, and the latter having less extreme surface dopant deactivation but a deeper profile. This suggests that damage sites can act as hydrogen sinks, with higher temperatures then driving this accumulated Hydrogen in.
Ongoing work investigates the bonding and charge states responsible, through modified surface films, varied plasma conditions and Hydrogen modelling.
| I am the presenting author | Yes |
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