Correlations Between Optical, Electrical, and Structural Properties of In-Situ Phosphorus-Doped Hydrogenated Microcrystalline Silicon - Effects of Rapid Thermal Annealing on Material Properties

Abstract

AbstractFilms of in-situ phosphorus-doped hydrogenated microcrystalline silicon (n--μc-Si:H) were deposited by plasma enhanced chemical vapor deposition (PECVD) on Si(100) and fused quartz substrates over a range of substrate temperatures (100 - 500°C) and reactant gas dilutions (I - 100% of 1% PH3/SiH4 in H2) while maintaining a constant RF power density (0.1 W-cm−2) and total gas pressure (1 Torr). Some of the films were subjected to a rapid thermal anneal (RTA) at temperatures between 600- 1000°C for a duration of 10 seconds. The μ-Mc-Si:H films were characterized, before and after RTA, in terms of their microstructure, optical band-gap, electrical conductivity, and hydrogen and phosphorus content. The deposition rate was determined to be insensitive to substrate temperature and to decrease with increasing H2 gas dilution indicating that deposition kinetics are dominated by plasma chemistry and are not thermally activated. For pre-annealed films, cross-sectional TEM confirmed the presence of a mixed phase material at all deposition temperatures with gas dilutions ≤10%. The surfaces of thick films (>0.15 μm) were rough, giving them a hazy appearance, while thin μic-Si:H films (<0.15 μm) were smooth and mirror-like. The rough surfaces were correlated with voids and microcracks in the μuc-Si:H films observed by TEM. The optical band-gap of all pre-annealed films was 11.8eV and the electrical conductivity varied between 1 and 20 (Δ-cm)−l. The H content was found to be independent of gas dilution but decreased with increasing substrate temperature; the P content depended on both the gas dilution and substrate temperature, decreasing at high deposition temperatures. RTA was observed to significantly alter film morphology and microstructure, increase electrical conductivity, and decrease the optical band-gap.