Loss of depth resolution with depth in secondary ion mass spectrometry (SIMS) due to variations in ion dose density across the rastered area

Abstract

Experiments were conducted to determine those factors fundamental, instrumental and sample specific that limit the depth resolution capability of our SIMS instrument. This involved the preparation, by silicon MBE, of a boron in silicon test structure 1.5 μm deep containing 31 buried dopant spikes, spaced 500 Å apart. The ‘true’ width of these spikes (fwhm) was estimated to be ∼10 Å. The SIMS analysis of this test structure revealed a linear degradation in the depth resolution with depth of the form Δz= a+ βz. Close inspection of the ‘apparent’ peak shapes (broadened by the SIMS process), boron channel chemical imaging and Talystep measurements of the final crater suggested that the α term was determined mainly by fundamental effects (ion beam induced broadening effects and near surface pre-equilibrium effects) whilst the β term was determined mainly by instrumental effects.