Study On Copper Precipitation Behaviors In Metallurgical Polycrystalline Silicon

Silicon prepared by metallurgical method is a promising craft in solar cell field, copper (Cu) as a common contaminat during the fabrication of silicon wafers and devices. Therefore, the study on copper behaviors in silicon prepared metallurgical method was proposed, which has huge practical significance and application value for the development and application of silicon solar cells.The laboratory-made metallurgical polysilicon were used as a silicon-based material in this thesis, and copper precipitation experiments were studied on the polysilicon. The different states of copper impurities was investigated during copper precipition, as well as the different heat treatment conditions such as heat treatment temperature, annealing time, cooling rate and annealing atmosphere were studied during copper precipition procedure. The phosphrous diffusion was investigated as well. The four probe resistance tester was used to measure the resistivity and the microwave photoconductivity decay measurement was used to measure the minority carrier lifetime, scanning electron microscopy was used to measure surface morphology and distribution of impurities in silicon.The unpolished surface of the polycrystalline silicon was covered with copper elemental and copper compounds by magnetron sputtering and solution impregnation method respectively, which were heated in a tubular furnace. The electrical properties of the samples after copper precipitation procedure declined. Different sources of copper impurities have different copper precipitation behaviors in polycrystalline silicon, and that the elemental copper impurities were introduced directly into the copper is easier to form a copper precipitate. In this process, the copper was precipitated when the temperature is higher than700℃. And it is easier to form copper precipitation in a RTP furnace compared to tubular furnace, which will affect the electrical properties of polycrystalline silicon a lot.Copper precipitation experiments were conducted at different heat treatment conditions. As the annealing temperature became higher, it is easier to form a copper precipitation in the polysilicon; And it were found obviously in5min on polysilicon surface that copper precipitate formed when the annealing time varied from0.5min to10min; under slow cooling conditions, since there is enough time for copper to diffuse into the precipitation zone, it is easier to form copper precipitate in polycrystalline silicon compared to in the rapid cooling conditions; the polysilicon will be generated holes and other related defects to promot the formation of copper precipitation under an argon atmosphere more than in air, which affected the performance of silicon.Repeated annealing was done in the thesis. When the temperature is higher, the precipitation formation driven is lower which could promote the formation of copper precitation; and extended the annealing time, the contents of copper precipitation is larger and more before5min when the annealing time varied from0.5min to10min,then in10min the surface morphololy changed little compared in5min.During the production and application of polysilicon, it is need to avoid polysilicon and devices using and contacting with the copper impurities for a long time at high temperature, and in the actual process phosphorus gettering layer can be formed by phosphrous diffusion, to improve the performance of the polysilicon.