A Study Of TTV Control Of The Multi-wire Sawn Multicrystalline Wafers

Currently,multicrystalline silicon(mc-Si)wafers are the most important materials used for photovoltaic solar cells.With the rapid development of photovoltaic industry,the demands of market for the technical requirements of mc-Si are increasing,while the development of multi-wire cutting technology also needs to quickly adapt to the market demand.TTV refers to Total Thickness Variation of a wafer,which is an important parameter for quality of a wafer.It strongly affects breakage rate in solar cell fabrication processes,and the quality of the solar cells.In the present paper,we researched the trend of TTV of mc-si wafer in the process of the multi-wire cutting.TTV value was measured by wafer sorting machine with different cutting processes,and the relationship between the main process parameters and TTV was determined.The main conclusions are as following:1.The particle size of silicon carbide is an important factor influencing the TTV in the process of multi-wire cutting,the TTV value increases with the particle size increase,TTV value with 1500~#SiC is 1.4?m smaller than that of with 1200~#SiC,and 0.8?m larger than that of with 1800~#SiC.2.Rational utilization and modification of sand slurry can effective control TTV.Removing the iron impurity in sand slurry by the way of removing iron online can reduce the harmful effects of iron impurity on sand slurry cutting,consequently decreases TTV value 3?m.Add sand slurry by stages can changes the density and viscosity of sand slurry in the process of multi-wire cutting,decrease the performance changes of the whole process,and decreases TTV value 1.5?m.Additives can reduce abrasion of steel wire in the process of cutting,and stable the amount of sand-carrying,result in reducing TTV value.The abrasion loss of steel wire with straight line cutting is less than that of with wave line cutting,which result in the TTV value with straight line cutting is 1.5?m smaller than that of with wave line cutting.3.Table speed and wire speed are the two most important factors in the process of cutting,which influence the cutting quality directly.The influence of TTV were different with different ratios between table speed and wire speed(Vt/Vw),and the overall trend of TTV value is increase with improvement of Vt/Vw,and the bigger with higher table speed,the larger of TTV value.4.Groove profile of guide wheel has a great effect on the distribution of TTV value.The distribution of wafer thickness is more concentrated and the TTV value is smaller with deeper on the both ends of guide wheel.Stabilization of equipment affects TTV directly,and after maintenance and replace of key driving parts,the jump displacement of guide wheel drops,and the wire line stables,which improve TTV obviously.5.The breakage rate and the yield of TTV mean value with 13.86?m is 0.16%less than and 0.65 higher than that of with 16.53?m,respectively.