Metrology of sub-0.5 μm silicon epitaxial films

Abstract

Non-destructive thickness measurement of sub-0.5 μm silicon epitaxial films has been performed using spectroscopic ellipsometry (SE) in the near infrared to visible range (0.75–3 eV). The undoped epitaxial films were grown on heavily doped substrates by chemical vapor deposition at 700–900 °C. The effect of heavy doping on the optical properties of crystalline silicon in the spectral range 0.75–3 eV is precisely described by the Drude free carrier model. It is shown that SE can simultaneously determine the substrate dopant concentration, the thicknesses of the epitaxial film and native oxide, and if present, the thickness of the transition layer between the epitaxial film and the substrate. The epitaxial film thicknesses measured by SE were in excellent agreement with results of secondary ion mass spectrometry (SIMS). The substrate dopant concentrations measured by SE also agree well with SIMS results for n-type substrates, but are consistently higher than SIMS values for p-type substrates. It was also demonstrated that SE can be used for process monitoring in low temperature silicon epitaxy. This study identifies a non-destructive thickness measurement technique for sub-0.5 μm silicon epitaxial films which are expected to be widely used in future semiconductor devices.