SIMS analysis of epitaxial layers for power- and micro-electronics

This paper gives an overview of recent secondary ion mass spectrometry (SIMS) studies of impurities and dopants in epitaxial layers of silicon and 6H silicon carbide (SiC). Detection limits in the 10¹² cm^-3 range are demonstrated for transition metal impurities like Ti in SiC. Hydrogen is found to be mobile in SiC at temperatures in excess of 600 °C despite strong trapping by defects and dopant atoms, and the effective diffusion coefficient exhibits an activation energy of ∼3.5 eV. In epitaxially grown Si layers, containing Ge delta distributions, profile broadening and shift during sputtering by Ar⁺ ions are accurately described by recoil mixing. For O⁺₂ ions oxide formation and surface swelling must also be considered. Further, at elevated sample temperature Ge is found to segregate out of the SiO₂ surface layer formed during oxygen bombardment, consistent with a larger heat of oxide formation for Ge than Si and a high enough mobility in SiO₂.