Precipitation Behavior Of Transitional Metals In Crystalline Silicon

In microelectronic or photovoltaic industry, crystalline silicon is the main material in which impurities or defects can remarkably influence on the properties of silicon-based devices. Transitional metals are some of important impurities in silicon. During wafer preparation or device processes, they can easily contaminate crystalline silicon and exist in silicon as the form of elements, complexes or silicide precipitates. Generally speaking, each form of transitional metals is detrimental to silicon-based devices, especially silicide precipitate. Therefore, it is very important to investigate the precipitation behavior of transitional metals in crystalline silicon from the view of engineering. Furthermore, it is also necessary to research the influence of intrinsic point defects, dislocations or grain boundaries on the transitional-metal precipitation in crystalline silicon for enriching the defect engineering from the scientific point. Copper, nickel and iron are the most common and important transitional metals in silicon-based device fabrication. In the past decades, the precipitation behavior of transitional metals or their effects on electrical properties in monocrystalline silicon with small diameter have been exhaustively investigated, while the precipitation behavior of transitional metals in large-diameter Cz silicon or cast multicrystalline silicon are still poorly understood.Thereby, on the basis of reviewing previous work, precipitation behaviors of copper, nickel or iron in Cz silicon with deferent diameters and in cast mulitcrystalline silicon treated at different temperatures under air-cooling or slowly cooling were systemically studied by Scanning Infrared Microscopy (SIRM), Scanning Electron Microscopy (SEM) combined with Electron Beam Induced Current (EBIC), Optical Microscopy following Defect Etching, Surface Photo Voltage (SPY) and Transmission Electron Microscopy (TEM). Additional, the influence of transitional-metal precipitation on electrical properties and oxygen precipitation subsequently was also researched in this dissertation.In crystalline silicon, not only intrinsic point defects but also dislocations orgrain boundaries can remarkably influence on the precipitation behavior of copper. High density of tiny copper-precipitate colony occurred in the D-defect zone of the specimen annealed at 1100℃ under air-cooling, while in the A-defect zone the result was inverse. For the specimen annealed at the same temperature under slowly cooling, large star-like copper-precipitate colonies formed both in the D-defect zone and A-defect zone generated great stress on the silicon matrix. However, in spite of different kind of cooling way, the diffusion length of minority carrier in the D-defect zone was always lower than that in the A-defect zone. These results indicated that vacancies in the D-defect zone enhanced the nucleation of copper-precipitates colony but hindered their growth. The copper-precipitation temperature in as-pown Cz silicon was about 800℃, agreeing well with the deduced results from the givenby previous researchers. But in cast multicrystalline silicon, the copper-precipitationtemperature was about 700℃, much lower than that in as-grown Cz silicon.Although both nickel and copper have the highest diffusivity in silicon, theprecipitation behavior of nickel is largely different form that of coppr. Nickel precipitation took place only in the bulk and nickel-precipitate-free formei near thesurface for small-diameter Cz silicon annealed at 1100℃ under air-cooling, And for the specimen annealed at the same temperature but under slowly cooling, it was so difficult to precipitate in the whole specimen for nickel. However, in the large-diameter Cz silicon, nickel precipitation could happen in the bulk notwithstanding different cooling rate, which should be correlated with void in as-grown materials. Nickel-precipitation temperature in Cz silicon was above 800℃ and also did depend on materials quality and cooling rate. In cast multicrystalline silicon...