CHARACTERIZATION OF INTERFACE DEFECTS IN OXYGEN-IMPLANTED SILICON FILMS

Defects in ungated n- or p-type and gated p-type resistors have been characterized by photoinduced transient spectroscopy (PITS). These resistors were fabricated with p-type separation by implanted oxygen (SIMOX) wafers with a single-energy 200-keV oxygen implant to a total fluence of 1.8 X 10(18) cm-2. One wafer, used for gated resistor fabrication was implanted at 595-degrees-C and sequentially annealed at 1325-degrees-C for 4 h in argon (plus 0. 5% oxygen) followed by 4 h in nitrogen (plus 0.5% oxygen). Another wafer, used for ungated resistor fabrication, was implanted at 650-degrees-C and annealed at 1275-degrees-C for 2 h in nitrogen (plus 0.5% oxygen). The photoconductive response of these resistors to a 1-mus long visible light pulse, measured at temperatures in the 80- to 170-K range, shows different persistent photoconductive effects due to trapped minority carriers that are somewhat linked to the thermal anneal given to the SIMOX wafers. Our results indicate that more damage is present in the wafer annealed at 1275-degrees-C than in the one annealed at 1325-degrees-C. We model the photoconductive response in terms of a perpendicular built-in field created in the conductive film by trapped charge located at or near the interface with the buried oxide. Defects distributed throughout the conductive film body or located at the interface with the gate oxide are not expected to contribute significantly to the PITS signature, because of the fabrication of the gate oxide with standard metal-oxide semiconductor technology. We estimate the average trap density at the back interface to be in the 10(11) cm-2 range.