Measurement of the residual macro and microstrain in strained Si/SiGe using Raman spectroscopy

ABSTRACTThe use of laser Raman spectroscopy to assess the residual strain in strained silicon/silicon germanium devices is well established. The peak shift associated with the 520cm−1 silicon peak can be used to directly measure the strain in the cap layer provided that the strained silicon peak can be deconvoluted from the more intense Si in SiGe peak which occurs at slightly lower wavenumbers. However, though peak position gives a measure of the macrostrains in the layer it is not useful for the assessment of microstrains associated with point defects which may also influence device performance; such microstrains influence the intensity of the Raman peaks and can, in principle, be monitored by this method. In this study we have undertaken a study of peak shape as a function of processing conditions for strained silicon on SiGe. Changes in peak position may be correlated with macrostrains and macrostrain relaxation around extended defects such as dislocations. Changes in peak width can be correlated with processes which lead to changes in composition (e.g. germanium build-up in the surface after etching) and microstrain. Such changes are not necessarily correlated with changes in macrostrain but indicate that microstrain could also be an important factor influencing device performance.