The electrical properties of Hg-sensitized "photox"-oxide layers deposited at 80°C

This paper deals with the electrical properties of low-pressure CVD SiO₂ deposited at 80°C. The deposition rate is enhanced by UV radiation in the presence of Hg vapor. The photo-enhanced low-pressure chemical-vapor-deposited oxide, known also as "photox," offers a good quality oxide deposited at temperatures as low as 80°C. The films are deposited in a batch-load "photox" barrel reactor and subsequently annealed at 950°C for 30 min in a conventional hot-wall furnace. Cold-sputtered aluminum-gate guard-ring capacitors are fabricated on the oxide films. High-frequency and quasi-static capacitance measurements indicate the interfacial properties of "photox" are comparable to those of thermal oxide. Fast interface states density are less than 2 × 10¹⁰ cm^-2 eV^-1 and a light negative interfacial charge could just be detected. The dielectric breakdown field is typically 4-5 MV/cm. Deep-depletion transient-capacitance measurements were performed at temperatures between 20 and 100°C to investigate the possible impact of "photox" processing on the generation lifetime. The Hg in particular might be suspected as a heavy-metal contaminant. Typical recovery times observed at 20°C were in the range of 10-15 min. The generation lifetime derived from such measurements ranges from 140 to 200 μs which is comparable to values for control samples made with standard thermal oxide. The magnitude and temperature dependence of the generation lifetime suggest that the same G-R centers are present in both "photox" and thermal oxide devices. The only apparent electrical effect of the Hg vapors used in the deposition process is a small negative fixed interface charge, 2 × 10¹⁰ cm^-2.