| Multi-crystalline silicon ingots have been dominant position in the photovoltaic industry for its low cost and high yield.The yield rate of the multi-crystalline silicon ingots cost is an important index to measure the factors that influence the effect of the maximum index for red zone.The red zone of the multi-crystalline silicon ingots is used to test the minority carrier lifetime by using the microwave photo electric conduction attenuation method.The red zone is mainly distributed in the silicon ingots head,the side wall,the tail part and the middle part of the silicon ingots.The red zone were in-depth study,fully understand the multi-crystalline silicon ingots red zone causes,is conducive to industrial production control and reduce the wafers of production cost,at the same time will also improve the quality of high efficiency multi-crystalline wafers.In the present paper,combined with large-scale production practice,from the production of a large number of samples to start a comprehensive analysis of the relationship between the tail red zone and oxygen,the red zone of the top and the bottom concentration,the formation of red zone drum package.By FTIR,?-PCD,PL tester,ICP-MS etc.testing means the analysis of the reasons of the multi-crystalline silicon ingots with different red zone,has achieved the following results:1?Through the comparison of the distribution of the oxygen distribution in the middle gap and the distribution of the red zone,it is found that there is an association between the oxygen and the bottom red zone,but the oxygen concentration is not the most important factor.Experimental results show that when the interstitial oxygen concentration lower than 4.5×1017cm-3,for the cast multi-crystalline low carrier lifetime,the effect is very small;when the interstitial oxygen concentration ranged from 4.5×1017cm-3 and 7×1017cm-3 between,will affect the cast multi-crystalline silicon minority carrier lifetime,an average reduction of minority carrier lifetime.5us.When the interstitial oxygen concentration is higher than 7×1017cm-3.Silicon ingots minority carrier lifetime received great impact,on average lifetime than 1.5us,forming red zone;therefore,only when the cast multi-crystalline silicon ingots tail interstitial oxygen concentration reached 7×1017cm-3,it may bottom formation in the red zone.2.Through the analysis of the metal impurities in the red zone of the silicon ingots,the main points of the red zone of the head are related to the segregation and diffusion of the metal impurities.The experimental results show that the length of the red zone of the head can be reduced obviously by accelerating the cooling rate of the silicon ingots,and the proportion of the length of the red zone of the head can be reduced to 35%.When the Fe concentration of the head reaches above 100ppbw,the silicon ingots will produce the red zone phenomenon.When the metal concentration is lower than 50ppbw,the silicon ingots is the best.3.Summary casting multi-crystalline silicon ingots except for the bottom and side wall red area outside the red zone of the abnormal performance,this kind of abnormal red zone is not flat,distribution has no specific location,usually for muster,spherical,called the red zone drum kits.Focus on the bottom of the red zone of the drum kits was dissected and element detection.The experiments show that there is no melting seed crystal in the center of the bulge in the red zone,and it is considered that the difference of the properties between the cast multi-crystalline silicon and the polysilicon produced by the SIEMENS method leads to the generation of local stress.In order to form the phenomenon of the red zone,which is the center of the seeds,which is not melted.By prolonging the melting time of the seed layer and increasing the melting temperature gradient,the difference of melting speed due to the different size and the crystal form of the silicon material is reduced,and the control of the drum kits in the bottom area is realized. |
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