PHOSPHORUS DOPING OF LOW-PRESSURE CHEMICALLY VAPOR-DEPOSITED SILICON FILMS

Conduction in polycrystalline-silicon films deposited by low pressure chemical vapor deposition has been investigated and compared to that in films deposited at atmospheric pressure. Low pressure films were deposited at 580° and 620°C and doped with phosphorus by ion implantation. Films deposited at 620°C were polycrystalline while those deposited at 580°C were initially amorphous but crystallized readily on further heat-treatment. The effect of annealing temperature on resistivity was studied in the low pressure films for two phosphorus doses, and the resistivity was found to decrease with increasing annealing temperature. After annealing, the films deposited at 580 °C always had lower resistivity than did those deposited at 620°C, with the most marked differences seen at lower annealing temperatures. In a second set of experiments, phosphorus was implanted with a wide range of doses corresponding to average dopant concentrations of 2 × 1015 to 2 × 1020/cm3. The resistivity was only a slow function of dopant concentration below 6 × 1016/cm3 and above 2 × 1018/cm3, while in the intermediate range slight changes in concentration caused large changes in resistivity. As before, films deposited at 580°C always had the lowest resistivity, especially in the intermediate doping range. The Hall mobility was measured and found to be maximum near a dopant concentration of 6 × 1018/cm3 and to decrease rapidly at lower dopant concentrations. The observed behavior is consistent with that expected from a film composed of small crystallites surrounded by grain boundaries containing large numbers of carrier traps. © 1979, The Electrochemical Society, Inc. All rights reserved.