Fabrication Of Cast Quasi-crystal Silicon And Dislocation Elimination Technology

The traditional production technology and products of wafers in the photovoltaic market are mainly polycrystalline silicon produced by casting method and monocrystalline silicon produced by Cz method.The casting polycrystalline silicon has low conversion efficiency and high productivity,and the low-efficiency of the Cz single crystal silicon is high.Their respective advantages and disadvantages,in the last 10 years,developed a new crystal growth technology,namely the casting quasi-single crystal technology,which is the growth of cast quasi-single crystal by directional solidification.The performance and cost of the quasi-single silicon ingots are between the cast polycrystalline and the Cz single crystal,and have the advantages of high production efficiency,low production cost,low raw material requirements,and high photoelectric conversion efficiency.However,the current quasi-single crystal preparation technology still has problems in the process of industrial production and needs to be solved.In this paper,two kinds of different heat dissipation methods of polycrystalline ingot furnace were used to prepare quasi-single silicon ingots.At the same time,PL detector integrated machine,minority carrier life tester,IRB infrared flaw detector and other instruments were used to separate the impurities of the quasi-single crystal.The minority carrier lifetime and dislocation defects were studied.The morphology of dislocation defects in the cast quasi-single crystal was analyzed by corrosion method.The results show that the side heat dissipation mode is “W” type in the crystal growth process,and the bottom heat dissipation mode is a stable solid-liquid interface with a slightly convex surface on both sides.The minority life of the two heat dissipation methods is intermediate ingot > edge > angle.In general,the heat dissipation method at the bottom is higher than that of the quasi-single crystal ingot in the side heat dissipation mode.The quasi-single-crystal small ingot produced by the ingot furnace with the bottom heat dissipation method has a more uniform distribution of minority life and better quality.The life of the minority carrier is affected by defects and impurities.The life of the sub-single crystal ingot is lower at the top,bottom and contact with the crucible,and the life of the ingot is less uniform and higher.The bottom-heat-dissipating ingot furnace is difficult to diffuse inward due to the stable solid-liquid interface of the flattened sides on both sides,and the side nucleation and dislocation defects are not easily diffused inward,which increases the single crystal area of the quasi-single-crystal whole ingot.Ingot 100% single crystal;stable solid-liquid interface ensures that dislocation defects do not spread quickly,avoiding the generation of large-area dislocation defects.For this reason,the bottom heat-dissipating ingot furnace is more suitable for the production of cast quasi-single crystals.Promotion.By chemically polishing the seed crystal,the surface defects of the seed crystal can be removed,and the polishing surface can also increase the tightness of the bonding between the seed crystals,preventing leakage of the silicon liquid from the seed crystal slit,and avoiding dislocation defects.Formed from the gap between the seed crystals;By increasing the buffer layer and increasing the temperature of TC2 in the initial stage of crystal growth,in the process of casting quasi-single crystal nucleation and crystal growth,fine process control is carried out,and the cooling rate of TC2 is controlled at 8 °C/h,which is beneficial to the growth of quasi-single crystal.Eliminate seed crystal-derived dislocation defects.The paper has 42 pictures,2 tables,and 67 references.