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

摘要

Electron-beam (e-beam) lithography is commonly used in fabricatingmetal-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 removingshallow defects ($\leq$ 4 meV below the conduction band edge) created by ane-beam exposure by measuring the density of shallow electron traps in two setsof high-mobility MOS field-effect transistors (MOSFETs). One set was irradiatedwith an electron-beam (10 keV, 40 $\mu$C/cm$^2$) and was subsequently annealedin forming gas while the other set remained unexposed. Low temperature (335 mK)transport measurements indicate that the forming gas anneal recovers the e-beamexposed sample's peak mobility (14,000 cm$^2$/Vs) to within a factor of two ofthe unexposed sample's mobility (23,000 cm$^2$/Vs). Using electron spinresonance (ESR) to measure the density of shallow traps, we find that the twosets of devices are nearly identical, indicating the forming gas anneal issufficient to anneal out shallow defects generated by the e-beam exposure.Fitting the two sets of devices' transport data to a percolation transitionmodel, we extract a T=0 percolation threshold density in quantitative agreementwith our lowest temperature ESR-measured trap densities.