Annealing shallow Si/SiO$_2$ interface traps in electron-beam irradiated high-mobility metal-oxide-silicon transistors

TL;DR

This study demonstrates that forming gas annealing effectively removes shallow interface traps created by electron-beam lithography in high-mobility MOSFETs, restoring their mobility close to unexposed levels and reducing trap densities.

Contribution

It provides experimental evidence that forming gas anneal can mitigate e-beam induced shallow traps at the Si/SiO$_2$ interface in MOSFETs, improving device performance.

Findings

Forming gas anneal recovers mobility in e-beam irradiated MOSFETs.

ESR measurements show trap densities are nearly eliminated after annealing.

Transport data fit to a percolation model aligns with ESR trap measurements.

Abstract

Electron-beam (e-beam) lithography is commonly used in fabricating metal-oxide-silicon (MOS) quantum devices but creates defects at the Si/SiO$_2$ interface. Here we show that a forming gas anneal is effective at removing shallow defects ($\leq$ 4 meV below the conduction band edge) created by an e-beam exposure by measuring the density of shallow electron traps in two sets of high-mobility MOS field-effect transistors (MOSFETs). One set was irradiated with an electron-beam (10 keV, 40 $\mu$C/cm$^2$) and was subsequently annealed in forming gas while the other set remained unexposed. Low temperature (335 mK) transport measurements indicate that the forming gas anneal recovers the e-beam exposed sample's peak mobility (14,000 cm$^2$/Vs) to within a factor of two of the unexposed sample's mobility (23,000 cm$^2$/Vs). Using electron spin resonance (ESR) to measure the density of shallow traps, we find that the two sets of devices are nearly identical, indicating the forming gas anneal is sufficient to anneal out shallow defects generated by the e-beam exposure. Fitting the two sets of devices' transport data to a percolation transition model, we extract a T=0 percolation threshold density in quantitative agreement with our lowest temperature ESR-measured trap densities.