A new technique for crystallographic characterization of heteroepitaxial crystal films

Abstract

A new x-ray diffraction technique is proposed which enables us to characterize heteroepitaxial semiconductor films, including a mosaic structure and a variation in lattice spacing, in detail. The equipment can be constructed with a double-crystal spectrometer, a microfocus x-ray tube, and a narrow detector slit. The respective full widths at half maximum (FWHM) of an orientation distribution (Δθ1 ) and broadening due to a spacing distribution (Δθ2 ) are precisely measurable, while the conventional double-crystal method yields their superposition (Δθ<Δθ1+Δθ2 ). The FWHM Δθ1 is determined from a rocking curve obtained by the ω mode with a narrow detector slit admitting x rays diffracted from a given spacing to pass through exclusively. The FWHM Δθ2 is measured from a diffraction profile by the 2θ/θ mode with the slit. Here correction should be made for the spatial and spectral dispersion of the incident characteristic x rays, and hence the relation of observed values to broadening due to the spacing distribution (true value) is calculated. Thus Δθ2 can be determined with errors less than 5 s of arc at FWHMs above 15 s, which has never been attained by the use of the conventional diffractometer. The availability of the present method is explained with examples of the measurements for a silicon perfect crystal, a GaN film, a ZnSe film, and ZnSx Se1−x alloy films.