Mesoscale And Microscale Experimental Investigation On Strained Silicon

The introduction of strain into some semiconductor material increases the optical and electrical properties greatly by enhancing its carrier mobility and reducing its energy consumption at the same time. The strained silicon technique has become the hot point in the field of scientific research and engineering application about microelectronics. Optical and electrical properties of strained silicon transistors are highly sensitive to their strain states. Meanwhile, the introduction of strain causes unneglectable problems about structural strength and reliability. Hitherto, numerous investigations had been carried out for the mechanical properties and behaviors of strained silicon materials. However, these existing studies were mostly limited in certain spatial scales or some specific properties. There is a lack of experimental study on multiscale study on the multi physical-mechanical properties and their interactive mechanism.In this work, the biaxial strained silicon materials with SiGe buffers were investigated. The material properties and surficial-interfacial mechanical behaviors of the multilayer semiconductor structures were measured by using some experimental methods in different spatial scales, including atomic force microscopy(AFM), white light interferometry, scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), nano-indentation, transmission electron microscopy(TEM) and micro-Raman spectroscopy(MRS). Based on the experimental results, the physical-mechanical mechanism of strained silicon was analyzed.For the analyses of multi-scale experiments, cross-section samples of strained silicon with ultra-low roughness were prepared. The surface roughness of cross-section samples were calibrated quantitatively by using atomic force microscopy and white light interferometry. Based on these cross-section sample with ultra-low roughness, the multilayer structures were analyzed by detecting the thicknesses of all the layers and the regularities of element distributions along depth direction quantitatively. The experimental results achieved by both scanning electron microscopy and energy dispersive spectroscopy proved that the material structure of the strained silicon samples were basically agreed with the expected design. The elastic modulus at different position in each layer was obtained point by point along depth direction by using nano-intentation. The lattice characteristics along depth direction in strained silicon cross-section sample were analyzed through transmission electron microscopy. With the TEM images, the lattice structure, size and thickness, dislocation distribution in each layer and each interface were achieved. Then, the nanoscale mechanical behaviors, such as the eutectic growth in between the strained silicon layer and buffer layer, and stress release through dislocations in buffer layers, were discussed.Raman-mechanical relationship of strain and residual stress in the surface and cross-section of both monocrystalline silicon and SiGe materials was deduced. Then, by Raman measurement on the surface of the strained silicon samples with different wavelengths lasers, the average strain and residual stress in strained silicon and constant SiGe buffer were achieved. Streamline Raman mapping were applied on the cross-section samples, obtained the high-resolution distributions of Raman shift, Raman intensity, Raman width at the vicinity of the interface region. Based on the experimental measurements from hundred micrometer scale to nanometer scale above, the material composition, crystal phase, defect, modulus, residual stress and other physical and mechanical parameters in strained silicon were investigated, and the interactive mechanism of physical-mechanical properties to structural performance in strained silicon were studied systematically.