Spectroellipsometric characterisation of thin epitaxial Si1–xGexlayers

Abstract

Spectroscopic ellipsometry is assessed as a toolfor rapid and non-destructive determination of thicknesses and/or Ge concentrations of Si1–xGex epitaxial layers. An algorithmfor the extraction of optical constants from ellipsometric measurements carried out on strained uncapped Si1–xGex layers is developed. The smoothness of the extracted spectra of the Si0·92Ge0·08 optical constants indicates very high accuracy even in the region of the weak absorption. Spectroscopic ellipsometry measurements of Si capped Si1–xGex layers are interpreted using the established reference data and correlated with results from other techniques. The accuracy of this interpretation for the spectroellipsometric determination of Ge concentration and Si1–xGex layer thickness is numerically predicted. It is suggested that spectroscopic ellipsometry can also be applied to capped Si1–xGex layers ifmore accurate reference data in the low absorption region become available.MST/3295