Introduction

SiGe epitaxy on Si has been extensively studied, for semiconductor gap modeling and band structure engineering. Quantitative measurement of the Ge concentration is not a trivial exercise at the microscopic level, where classical tools such as X-Ray diffraction, ellipsometry and SIMS cannot be used. A new quantitative microanalytical technique is proposed based on extinction distance measurements using Convergent Beam Electron Diffraction (CBED) combined with dynamical diffraction simulations. A Ge concentration accuracy of less than 2% is demonstrated on strain relaxed SiGe epitaxial layers.

Experiment

Unstrained SiGe epitaxial layers are analyzed for different Ge concentrations, with two-beam CBED, using the transmitted and the 004 diffracted disc. Energy filtered CBED patterns are acquired at 197 keV with a Philips CM 200 FEG transmission electron microscope, using the Ik x Ik CCD camera of the Gatan GIF energy filter. A liquid nitrogen cryo-holder is used, to sharpen up the CBED patterns and to avoid contamination and degradation of the samples.