Raman mapping of microcrystalline silicon thin films with high spatial resolution

Raman maps, i.e., grids of individual spectra of Raman scattering from excitation laser beam focused by optical microscope, were used to characterize mixed phase silicon thin films. Raman maps measured with 442 nm and 785 nm lasers were compared with topography or local current maps recorded by conductive atomic force microscope (C-AFM) in the same field of view. The Raman measurement may irreversibly influence the thin film surface by thermal oxidation, as proved by the change of local conductivity observed in C-AFM. Resolution limit of individual grains in Raman mapping with 442 nm excitation was 350 nm, however, we were able to detect much smaller individual grains (down to ∼160 nm diameter measured by AFM) if they were isolated in amorphous matrix. Polarized Raman spectroscopy is able to detect the crystallographic orientation of the single microcrystalline grain. Resolution of the Raman mapping may be significantly improved by tip enhanced Raman measurement. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)