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In this dissertation, silicon films deposited at Ultra-High Vacuum using Electron-beam Evaporation (UHVEE) are investigated to form polysilicon films at low thermal budget (≤ 500oC) for enabling Micro-Electro-Mechanical System (MEMS) integration on top of Complementary Metal Oxide Semiconductor (CMOS). The investigations are focused on in-situ phosphorus doped UHVEE and Aluminium Induced Crystallization UHVEE (AIC UHVEE) films. The crystallographic, mechanical, and electrical properties of the in-situ phosphorus doped UHVEE films have been studied. Raman Spectroscopy, X-ray Diffraction (XRD), Transmission Electron Microscope (TEM) and Atomic Force Microscopy (AFM) are used for crystallographic and surface morphology investigations. Wafer curvature, deflection profile and resonance frequency measurements are used for mechanical property studies. Resistivity measurements are conducted to investigate the electrical properties of the films. The results show that thick, low stress, low stress gradient, smooth, electrically active and fully crystalline UHVEE polysilicon films can be formed at low thermal budget for the first time. Highly vertical high aspect ratio micromachining of UHVEE polysilicon have been developed. Comb-drive structure, made of 20 µm thick in-situ phosphorus doped UHVEE, has been designed, simulated, fabricated and measured. Measurement results demonstrate that UHVEE polysilicon allows realization of mechanically and electrically functional MEMS devices at low thermal budget. AIC UHVEE polysilicon films are formed and investigated for their crystallographic, electrical, piezoresistive and mechanical characteristics. Electron Backscattered Diffraction (EBSD), XRD, and TEM are employed for crystallographic studies. Electrical properties are investigated using hall effect measurements. AIC UHVEE Piezo resistors are integrated on cantilever beams and strained to measure gauge factors. The stress, stress gradient, and Young’s modulus are extracted from pull-in voltage measurements conducted on AIC UHVEE polysilicon cantilever and clamped-clamped beams. The results show that AIC UHVEE piezo resistors with gauge factor of 76 can be formed at low thermal budget. This is the highest gauge factor reported for polysilicon films and remarkable that it is achieved at low thermal budget. The results also show that AIC UHVEE polysilicon films displays low stress, lower stress-gradient than other thin polysilicon films, and Young’s modulus of 120 GPa, demonstrating the potential of AIC-UHVEE as a structural material for MEMS integration on CMOS. |
