GISAXS and GIWAXS analysis of amorphous–nanocrystalline silicon thin films

Amorphous–nanocrystalline silicon thin films were deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) on glass substrate with various silicon nano-crystal size distributions and volume fractions. The samples were examined by Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) at the Austrian SAXS beamline (Synchrotron Elettra, Trieste) using an X-ray beam energy of 8 keV. The grazing incidence angle varied from the critical angle to 0.2° above the critical angle. This allowed the examination of the samples at different depths, and the distinction of the surface scattering contribution from the particles scattering in the bulk. The sizes of the “particles” obtained from the horizontal and vertical sections of 2D GISAXS patterns were between 2 nm and 6 nm. Since GISAXS is sensitive to electron density differences (contrast) between the scattering bodies and the surrounding matrix, it is not evident whether the particles are nano-crystals or just voids embedded in amorphous matrix. However, the size of the crystals calculated from the line-shape analysis of peaks in GIWAXS spectra and the crystal size distribution obtained from High-Resolution Transmission Electron Microscopy (HRTEM) images agree well with the size of “particles” estimated from GISAXS, strongly indicating that the observed particles are silicon nano-crystals.