The Characterization of Silicon Damaged by Low Energy Argon Ion Etching

We have used a variety of characterization techniques including electron spin resonance (ESR), photothermal deflection spectroscopy (PDS), ellipsometry, and I–V and C-V analysis to study silicon samples damaged by 500–1500 eV Ar ions from a Kaufman ion source. In agreement with our ballistic penetration calculations, PDS and ellipsometry data show that the majority of the lattice damage lies within 40A of the surface. The ellipsometry results are well modelled as a thin, damage-induced layer of a- Si with a high (4.63) refractive index, while the PDS measurements show an Urbach-like subgap adsorptance tail. In addition to Schottky barrier height alterations produced by Ar bombardment, we also observe marked changes in electrically active dopant densities in boron doped silicon samples. C-V analyses show that these changes extend quite far (1–2 μm) into the sample and are readily removed by a mild (150°C) thermal anneal. Hydrogen, injected from surface adsorbed H2O or hydrocarbons, appears to be the source of these effects. We will also discuss our upper limit estimate of 1013 “dangling bond” spins/cm2 for our damaged samples in light of prior ESR observations on similarly treated surfaces.