Observations of Si field evaporation

Field evaporation studies of crystalline 〈1 0 0〉 Si were performed in a three-dimensional atom-probe, which utilized a local electrode geometry. Several distinct phenomena were observed. Si field evaporation rates showed: (1) no measurable dependence on temperature below 110 K, (2) an exponential dependence on evaporation rate as a function of temperature above 110 K, and (3) no dependence on substrate doping (i.e., electrical conductivity) as high as 10 Ω cm in the temperature range of 40–150 K. Two distinct evaporation modes were observed. The first was associated with ∼1 at% H+ in the mass spectrum. Negligible amounts of H were detected in the mass spectra of the second mode. When the pulse fraction (pf) was increased from 5% to 30%, the presence of H+ in the mass spectra, i.e. operation in the first mode, was associated with a degradation in mass resolution by as much as 80% for the 10 Ω cm Si samples. Conversely, no loss in mass resolution was detected for the ∼0.001 Ω cm samples over the pf range studied.