Tantalum pentoxide, a non conventional gate insulator for MOS devices

Non conventional gate insulators for MOS devices are generally dielectrics that depart considerably from the classic Si0₂ used extensively in this technology. The work presented here reflects the research and development of an existing compound, Ta₂0₅, and its application as a gate insulator for both MOS capacitors and transistors. The oxide is grown both thermally and anodically from pure sputtered tantalum metal over silicon wafers. Succesful dielectrics suitable for gate insulators were obtained using both methods. High relative permittivity (≃26-28) being characteristic of tantalum pentoxide, offers considerable advantage over classic silicon dioxide gate insulators, however higher leakage currents (100 to 1000 times greater) were encountered in MOS Capacitor samples at room temperature. A method for processing the tantalum metal was developed using the liftoff technique, and it was successfully applied to both MOS capacitors and field effect transistors. Furthermore, devices were fabricated in the form of MOS Transistors, which exhibited good Id vs. Vds characteristics, with Vgs as a parameter. Gate leakage currents were low, as a double dielectric Ta₂0₅ over Si0₂ structure was used as gate insulator. A small signal model of this class of devices is presented, that takes into account the non zero gate leakage current. Another successful technique, interfacial oxidation of Ta₂0₅ over Si, was used in fabricating MOS Capacitors that yielded also low leakage currents and high specific capacitances. The purpose of this Thesis is to report the development at the University of British Columbia of the double gate insulator MOSFET technology based on the Tantalum Pentoxide-Silicon Dioxide (Ta₂0₅/Si0₂) heteromorphic structure.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat