EFFECTS OF VARIOUS PRE-INTRINSIC AND PHOSPHORUS DIFFUSION GETTERING TREATMENTS UPON QUALITY OF CZOCHRALSKI SILICON-WAFER SURFACE DURING A SIMULATED 4-MEGABIT DYNAMIC RANDOM-ACCESS MEMORY PROCESS

Effects of various preintrinsic and phosphorus diffusion gettering treatments upon quality of near-surface region in Czochralski silicon wafers are studied during a simulated 4 Mb dynamic random access memory process. Denuded zone depth and bulk microdefect density are determined by synchrotron radiation section topography. Minority carrier life-time and junction characteristics from test device structures were measured to determine overall gettering efficiency. A two-step thermal anneal cycle before actual device processing resulted in formation of precipitates, dislocations, stacking faults, and a well-defined denuded zone in samples with medium oxygen content only when a low-temperature cycle at 775-degrees-C was followed by a high-temperature one at 1150-degrees-C. The longest minority carrier lifetimes are observed in samples where very few or no defects are visible in the bulk of the wafer in the section topographs. Phosphorus gettering, however, was found to be effective for improving both minority carrier lifetime and junction properties.