A Electrical Characterization of Low Temperature, High Pressure Thermal Silicon Dioxide

High quality thermal oxides of silicon have been fabricated using elevated pressures of dry oxygen. This technique allows the growth of oxides at temperatures several hundred degrees below those used in conventional processing. MOS capacitor structures fabricated from these oxides have been characterized using capacitance-voltage, current-voltage and avalanche hole and electron injection techniques. In general, the results of such characterization indicate that thermal oxides grown at temperatures as low as 635(DEGREES)C using high pressure oxidation are of a quality comparable to those fabricated using conventional, higher temperature technologies. A requirement for longer post-oxidation -anneal time is noted for the low temperature oxides. In addition, an increase in electron trap density and trapping efficiency is observed. Avalanche hole injection techniques were used to characterize the low temperature oxides, as well as to explore the nature of the trapped hole in SiO(,2). A minimum in the density of hole traps is observed to occur for an oxidation temperature between 800(DEGREES)C and 900(DEGREES)C. This phenomenon is interpreted according to a model in which Si-SiO(,2) interface stress increases outside this temperature range. No other dependence of hole trapping on process variables is observed. A model is proposed according to which hole traps are located spatially within about 3 nm of the Si-SiO(,2) interface and energetically within about 4 eV of the oxide valence band. Evidence for this model is based on the electrical behavior of trapped holes in MOS oxides. A distinction is made between the positive charging observed in this work and the so-called "anomalous positive charge" generated during avalanche electron injection experiments.