Investigation of nanoscale Ge segregation in p-channel SiGe/Si field effect transistor structures by electron energy loss imaging

SiGe/Si p-channel heteroepitaxial field effect transistor test structures in Si were fabricated by molecular beam epitaxy. Combined high-resolution transmission electron microscopy and energy-loss filtered imaging have been used to quantitatively determine the nanoscale Ge distribution across the SiGe alloy channel. The alloy grading at the edges of the channel has been found to be asymmetrical due to Ge segregation, with an exponential-like extended distribution directed towards the surface. The results agree well with the predictions of segregation theory and indicate that the concentration of Ge in the extended distribution lay in the range 10%–1% over a distance of several nanometers from the body of the channel. Secondary ion mass spectrometry measurements upon the same samples were insensitive to this short range extended Ge distribution.