Metal-oxide-semiconductor devices based on epitaxial germanium-carbon layers grown directly on silicon substrates by ultra-high-vacuum chemical vapor deposition

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Kelly, David Quest

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After the integrated circuit was invented in 1959, complementary metal-oxidesemiconductor (CMOS) technology soon became the mainstay of the semiconductor industry. Silicon-based CMOS has dominated logic technologies for decades. During this time, chip performance has grown at an exponential rate at the cost of higher power consumption and increased process complexity. The performance gains have been made possible through scaling down circuit dimensions by improvements in lithography capabilities. Since scaling cannot continue forever, researchers have vigorously pursued new ways of improving the performance of metal-oxide-semiconductor field-effect transistors (MOSFETs) without having to shrink gate lengths and reduce the gate insulator thickness. Strained silicon, with its ability to boost transistor current by improving the channel mobility, is one of the methods that has already found its way into production. viii Although not yet in production, high-κ dielectrics have also drawn wide interest in industry since they allow for the reduction of the electrical oxide thickness of the gate stack without having to reduce the physical thickness of the dielectric. Further out on the horizon is the incorporation of high-mobility materials such as germanium (Ge), silicongermanium (Si1-xGex), and the III-V semiconductors. Among the high-mobility materials, Ge has drawn the most attention because it has been shown to be compatible with high-κ dielectrics and to produce high drive currents compared to Si. Among the most difficult challenges for integrating Ge on Si is finding a suitable method for reducing the number of crystal defects. The use of strainrelaxed Si1-xGex buffers has proven successful for reducing the threading dislocation density in Ge epitaxial layers, but questions remain as to the viability of this method in terms of cost and process complexity. This dissertation presents research on thin germanium-carbon (Ge1-yCy) layers on Si for the fabrication of MOS transistors with improved drive currents. By incorporating a small amount of C in Ge, the crystal quality of Ge epitaxial layers grown directly on Si can be dramatically improved. The Ge1-yCy layers have been used to fabricate high-drivecurrent p-MOSFETs with high-κ dielectrics and metal gates. In addition to the electrical results, materials-related experimental data was acquired and analyzed to provide insights on the surface morphology, crystal quality, strain, C incorporation, and growth kinetics of the Ge1-yCy layers. This work describes an exciting new possibility for the ultimate goal of incorporating high-mobility semiconductor materials in CMOS technology.