| The detailed characterization of the physical and electrical properties of polycrystalline-silicon is essential to ensure the proper design and reliable performance of the devices in which this material is used. Modeling of electrical conduction in these films is critical for predicting the effects of the processing cycles on their electrical properties. In this research, the physical and electrical properties of low-pressure chemically-vapor-deposited silicon films are characterized and are then related to each other to develop a new model for electrical conduction.; The structure of the LPCVD films strongly depends on deposition conditions. Below the critical deposition temperature of (DBLTURN)580(DEGREES)C, the deposited films are amorphous, highly unstable, and recrystallize easily after high-temperature annealing. Enhanced grain growth is detected as a result of heavy doping and/or annealing at elevated temperatures.; The electrical properties of these films are only a weak function of deposition conditions. They strongly depend, however, on dopant concentration and species and processing.; Unlike boron, appreciable fractions of arsenic and phosphorus dopant atoms segregate to the grain boundaries in these films. Segregation is a function of doping, grain size, and high-temperature processing. A physical and quantitative model for the segregation mechanism is developed.; The earlier carrier-trapping and dopant-segregation models for electrical conduction are incapable of explaining all of the observed behavior of the electrical properties of these films. Carrier reflection at the grain boundaries (neglected in the above models) is demonstrated to be an important mechanism that, combined with carrier trapping and dopant segregation, controls electrical conduction in polycrystalline-silicon. A new conduction model is developed, therefore, based on these combined mechanisms. Carrier transport is believed to occur by thermionic emission over the potential barriers in the crystallines (created as a result of carrier trapping) and then by tunneling through the grain boundaries. |
