Micro-Raman spectroscopy as a complementary technique to high resolution X-ray diffraction for the characterization of Si1-xGex thin layers

In advanced transistor technology, Silicon-Germanium alloy (SiGe) is being used as a replacement for Si channels to achieve higher mobility. Among the various characterization techniques mu-Raman spectroscopy is a promising candidate due to a good spatial resolution and low detection threshold. This study presents the evaluation of the technique for the measurement of Ge concentration and comparison to other metrology techniques. As a first step to evaluate the mu-Raman capability, we considered a simple case of thin SiGe films from 12nm down to 4 nm thickness. Assuming an epitaxial pseudomorphic structure, the Ge content has been extracted for all samples with an average 0.3% stability and at least 1% accuracy as confirmed by high resolution X-ray diffraction (HRXRD) and secondary ion mass spectrometry analysis (SIMS). We then studied a more complex structure of SiGe on fully depleted-silicon on insulator (FD-SOI) as being critical for the development of condensation process of advanced transistor technology. Since mu-Raman requires prior knowledge of the structural state of the layer, we discuss the interest to combine mu-Raman measurements with X-rays diffraction in order to extract the Ge composition on such stacks. mu-Raman shows a real potential for thin SiGe film characterization and it does not suffers of the lack of precision for very thin films as HRXRD does, however there are still some developments to be made before using it as a metrology technique. Moreover, it could be interesting to couple the technique with HRXRD measurement. The approach to control SiGe condensation process on FD-SOI might suggest interesting experiment. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim