High-Resolution X-Ray Diffraction Analysis of Epitaxial Films

Epitaxy technique has been widely used for semiconductor, ferroelectric and optical materials in the development of electronic and optoelectronic devices. Epitaxial structures with strain and defects may tune the physical properties or affect the performance of devices. High-resolution X-ray diffraction (HRXRD) has significant advantages over traditional XRD with the features of small divergence, monochromatic incident beam and high resolution detection of the diffracted beam. It is a key technique for accurate characterization of epitaxial structures in non-destructive way. In this paper, the techniques of HRXRD for epitaxial film structure characterization are outlined in terms of the relationship between diffraction and reciprocal space, the difference between high-resolution diffraction and powder diffraction such as the optical system and the geometry mode of scanning etc. Based on the corresponding relationship between the epitaxial film and the matrix structure in the reciprocal space, various factors affecting the shape of the diffraction spots are analyzed, including the state of lattice match in coherence and non-coherence, super lattice and inclined growth. The other effective factors are also demonstrated, such as finite size of film, tilt and strain of epitaxial film etc. Real examples, such as Si1-xGex(x=0.1) etc., are used to explain how to obtain the structure parameters of the epitaxial films by HRXRD spectrum analysis, including lattice constant, lattice mismatch, thickness and superlattice information. To obtain more epitaxy information, reciprocal space map (RSM) analysis can be feasibly used by reconstruction of a series of HRXRD patterns. By combining HRXRD spectrum and RSM, microstructure characterizations of PbTiO3 epitaxy films, such as micro-strain, domain structure, phase transformation can be quantitatively analyzed.