| Recessed Si1-xGe x source/drain technology enhances the performance of state of the art metal oxide semiconductor field effect transistors (MOSFETs), by providing enhanced channel mobility and reduced source/drain contact resistivity. This dissertation focuses on the effects of recessed Si1- xGex junction parameters on the biaxial compressive strain in Si1-xGe x and their impact on the bandgap and contact resistivity. Due to its smaller size, boron can partially compensate the compressive strain in Si1-xGex. This behavior was modeled using the covalent radii of Si, Ge and B, to calculate the lattice parameter of the ternary Si1-x-y GexBy alloy. It was also shown using micro-Raman spectroscopy that Houghton's kinetic model accurately predicted the Si1-x-y GexBy critical thickness. Formation of NiSi1-xGe x on Si1-xGe x was also studied, and it was found that NiSi1- xGex induced tensile strain in Si1-xGe x, thereby reducing the compressive strain in the junctions. The impact of the NiSi1-xGe x thickness on Si1-xGe x bandgap was investigated using p+(Si 1-xGex)-n(Si) diodes, and it was demonstrated that increasing the NiSi1- xGex thickness led to an increase in the bandgap, due to loss in compressive strain. It was also shown that the barrier height followed the Si1-xGe x bandgap and increased with NiSi1- xGex thickness. The impact of the Si1-xGex bandgap and the barrier height on contact resistivity was studied using four-terminal Kelvin structures. It was shown that contact resistivity increased with Si 1-xGex thickness and NiSi1-xGe x thickness, due to reduced biaxial compressive strain. It was shown that with fully strained Si1-xGe x junctions, and a germanium concentration of x=0.28, a minimum contact resistivity of 2.5x10-8 Ocm 2 could be obtained. While the experiments in this dissertation are limited to Si1-xGe x and NiSi1-xGe x contacts, the fundamental knowledge gained from this work is expected to have a much wider impact. Specifically, this thesis introduces strain as a new parameter in contact engineering because of its impact on the semiconductor band structure and the metal-semiconductor barrier height, regardless of the metal and semiconductor choices. |
