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This thesis investigates the reactive formation of Ni mono-gernanosilicide, NiSi1-uGeu, for contact metallization of future CMOS devices where Si1-xGex can be present in the gate, source and drain of a MOSFET. Although the investigation has been pursued with a strong focus on materials aspects, issues related to process integration in MOSFETs both on conventional bulk Si and ultra-thin body SOI have been taken into consideration. The thesis work has taken a balance between experimental studies and theoretical calculations. The interaction between Ni films and Si1-xGex substrates, polycrystalline (poly) as in the gate or single-crystal (sc) as in the source/drain, leads to the formation of a ternary solid solution NiSi1-uGeu with the MnP structure in a wide range of temperature from 450 to 850oC. A linear variation of the lattice parameters of the NiSi1-uGeu with u is determined. A number of key observations are made: (1) the agglomeration of NiSi1-uGeu on Si1-xGex at a lower temperature compared to that of NiSi on Si, (2) the absence of NiSi2 up to 850 oC when Ge is present, and (3) a substantial Ge out-diffusion from the NiSi1-xGex and a precipitation of Ge-richer SiGe around the NiSi1-uGeu grains. These observations are interpreted referring to the ternary phase diagram for the Ni-Si-Ge system presented in this work. Possible factors influencing the morphological stability of NiSi1-uGeu films on Si1-xGex are discussed: (1) mechanical strain in the epitaxial Si1-xGex, (2) the favorable formation of NiSi at the expense of NiGe, (3) grain growth in poly-Si1-xGex, and (4) grain grooving in NiSi1-uGeu on sc-Si1-xGex. Energetically, the former two factors have been found to play a comparable, yet major role in the morphological instability of NiSi1-uGeu. The inter-diffusion of Si and Ge in NiSi1-uGeu and Si1-xGex provides the kinetic pathway for the morphological evolution. On Si1-xGex epitaxially grown on Si(100), a strong preferential orientation of the resulting NiSi1-uGeu film is found; NiSi films formed on Si show no specific film texturing. Furthermore, layer sequence and layer thickness of Si/SiGe or SiGe/Si are found to strongly affect the film texture in the resulting NiSi1-uGeu. Epitaxy of NiSi on NiSi1-uGeu, and vice versa, occurs across the compositional boundary, which confirms Ni as the dominant diffusion species during germanosilicide formation. The presence of Ge reduces the contact resistivity for NiSi1-uGeu on p-tyep Si1-xGex, as expected. For poly-Si1-xGex doped by B to 1020cm-3, a contact resistivity of 9x10-8 Ωcm2, 5 times lower than for the corresponding NiSi/Si contact, is obtained. On n-type Si1-xGex doped by As to 1020 cm-3, the opposite is true regarding the effect of Ge and a contact resistivity of 2x10-5 Ωcm2, 20 times higher than for the corresponding NiSi/Si contact, is obtained. When formed in the source/drain regions of a MOSFET fabricated on ultra-thin body SOI, a severe lateral growth of NiSi and Ni2Si into the channel region is revealed if the initial Ni thickness is too thick and if the silicidation conditions are not carefully controlled. This leads to a Schottky contact S/D MOSFET due to the consumption of the entire source/drain. In order to realize a low source/drain resistance for MOSFETs on ultra-thin SOI, satisfying the Roadmap recommendation for the 45-nm technology node, simplified calculations have been performed and an elevated source/drain structure is clearly shown to be advantageous. / QC 20101005

Este trabalho apresenta um estudo da solidificação de metais puros utilizando o modelo de campo de fases. O modelo é utilizado para simular a solidificação com o intuito de obter a morfologia da interface sólido-líquido sob diversas condições de transferência de calor. Foram realizados testes de validação comparando as morfologias da interface sólido-líquido obtida com as morfologias apresentadas em trabalhos anteriores para os casos bi e tridimensionais. O modelo do campo de fases adotado consiste principalmente de duas equações diferenciais: uma para calcular a variável de campo de fases e outra para calcular o campo de temperaturas. As equações foram solucionadas numericamente para um oitavo do domínio devido a simetria do problema. Os cálculos do modelo indicam que um sólido esférico com um raio inicial menor que o raio crítico de nucleação refunde. Entretanto uma esfera de raio maior cresce. Quando o sólido inicial cresce em uma malha numérica relativamente grosseira, a forma do sólido desvia da forma esférica devido perturbações na interface sólido-líquido. Quando a malha é refinada, as perturbações não são detectadas; contudo, quando introduzidas artificialmente as perturbações crescem e distorcem o formato esférico. / This work presents a study of the solidification of pure metals using the phase field model. The model is used to simulate solidification in order to obtain the morphology of the solid-liquid interface under different heat transfer conditions. Validation tests were performed comparing the morphology of the solid-liquid interface with the morphologies obtained from previous works for two and three dimensional cases. The adopted phase-field model consisted mainly of two differential equations: one to calculate the field of phase variable and another for the temperature field. The equations were solved numerically in only one eighth of the domain owing to the symmetry of the problem. Model calculations show that a solid sphere with an initial radius smaller than the critical radius for nucleation shrinks, whereas a sphere with a larger radius grows. When it grows in a relatively coarse numerical mesh, the initial solid shape deviates from a sphere owing to perturbations at the solid-liquid interface. When the numerical mesh is refined, the growth of perturbations is not detected, but artificially introduced perturbations grow and distort the spherical shape.

Este trabalho apresenta um estudo da solidificação de metais puros utilizando o modelo de campo de fases. O modelo é utilizado para simular a solidificação com o intuito de obter a morfologia da interface sólido-líquido sob diversas condições de transferência de calor. Foram realizados testes de validação comparando as morfologias da interface sólido-líquido obtida com as morfologias apresentadas em trabalhos anteriores para os casos bi e tridimensionais. O modelo do campo de fases adotado consiste principalmente de duas equações diferenciais: uma para calcular a variável de campo de fases e outra para calcular o campo de temperaturas. As equações foram solucionadas numericamente para um oitavo do domínio devido a simetria do problema. Os cálculos do modelo indicam que um sólido esférico com um raio inicial menor que o raio crítico de nucleação refunde. Entretanto uma esfera de raio maior cresce. Quando o sólido inicial cresce em uma malha numérica relativamente grosseira, a forma do sólido desvia da forma esférica devido perturbações na interface sólido-líquido. Quando a malha é refinada, as perturbações não são detectadas; contudo, quando introduzidas artificialmente as perturbações crescem e distorcem o formato esférico. / This work presents a study of the solidification of pure metals using the phase field model. The model is used to simulate solidification in order to obtain the morphology of the solid-liquid interface under different heat transfer conditions. Validation tests were performed comparing the morphology of the solid-liquid interface with the morphologies obtained from previous works for two and three dimensional cases. The adopted phase-field model consisted mainly of two differential equations: one to calculate the field of phase variable and another for the temperature field. The equations were solved numerically in only one eighth of the domain owing to the symmetry of the problem. Model calculations show that a solid sphere with an initial radius smaller than the critical radius for nucleation shrinks, whereas a sphere with a larger radius grows. When it grows in a relatively coarse numerical mesh, the initial solid shape deviates from a sphere owing to perturbations at the solid-liquid interface. When the numerical mesh is refined, the growth of perturbations is not detected, but artificially introduced perturbations grow and distort the spherical shape.

Methods for and computed results of including the physics and spatial attributes of microstructures are presented for a number of materials applications in devices. The research in our group includes applications of computation of macroscopic response of material microstructures, the development of methods for calculating microstructural evolution, and the morphological stability of structures. In this review, research highlights are presented for particular methods for computing the response in: 1) ferroelectric materials for actuator devices; 2) coarse-graining of atomistic data for simulations of microstructural evolution during processing; 3) periodic and non-periodic photonic composites; and 4) re-chargeable battery microstructures. / Singapore-MIT Alliance (SMA)