Abstract
For nano-semiconductor devices, how to enhance the device performance is one of the main goals of the semiconductor industries. As many devices are composed of thin-film systems in nano-scale, the carrier mobility would be directly governed by the strain of the thin film systems. The phenomenon could be applied to the strain-engineering [1-4] processes, which use the strain to improve the device performance and yet broaden their application [6]. Consequently, the strain is one of the important factors to the performeance of the device. However, the conventional methods of the strain measurement, transmission electron microscopy, TEM [7, 8], coherent X-ray diffraction image, CDI [9-13] and grazing incident X-ray diffraction, GIXD, are limited by destructive probing nature, the price of the instrument and the penetration depth, respectively. To dimension such a minor strain in strain-engineering processes, the depth profile with the sub-pico resolution of the interfacial strains are proposed by using three-beam Bragg-surface diffraction (BSD) [14, 15]. BSD is consisted of a symmetric Bragg diffraction at a wide-angle incidence and a surface diffraction, propagating along the interface of the sample. The three BSD, (004)/(202), (004)/ (0-22), (004)/ (4-22) were measured in this study. Moreover, we applied the hetero structure, Si0.7Ge0.3/Si, which are frequently used as semiconductor devices, to develop the technology of mapping the strain vs. depth with a sub-picometer resolution. Due to the structural proximity of the Si0.7Ge0.3 film and Si substrate, the surface diffraction of Si0.7Ge0.3 thin-film and Si substrate are simultaneously excited during the diffractive processes. Kiessig-like fringes are shown up in the vertical spatial intensity distributions (tth-scan). For mapping the stain in depth perpendicular to the hetero-junction, the spatial intensity were simulated by multi-layer dynamical theory [16-19] of X-ray diffraction for crystalline materials. Furthermore, the diffraction method reported in this dissertation may push the resolution of the current strain measurements from a dozen of nanometers to sub-pico meters regime in the future.