太阳能硅片游离磨料电解磨削多线切割表面完整性研究

Study on Surface Integrity of Solar Cell Wafers by Using Free Abrasive Electrochemical Multi-wire Sawing Method

游离磨料多线切割是目前加工太阳能硅片的主要方法。然而,该方法切痕较深,损伤层较厚,进一步增大硅片尺寸、减小硅片厚度难度很大。游离磨料电解磨削多线切割,复合了机械磨削和电化学加工方法,通过在加工过程中给硅锭和切割线施加电场产生阳极钝化或腐蚀,可以有效降低切割负载,提高切割效率,改善硅片的表面质量。以156 mm×56 mm（8寸）、电阻率（1~3？·cm）P型多晶硅片切割为例,初步试验结果表明,采用相同的切割参数和原材料,相对于游离磨料多线切割,电解磨削多线切割硅片的弯曲度降低了3μm,分布区间集中在0~9μm之间;采用20%的Na OH溶液腐蚀硅片,表面的隐裂和深沟槽较少出现,说明硅片的表面损伤程度减轻,有利于减少后续制绒减薄量。该方法和现有游离或固结磨料多线切割技术兼容性好,设备改造成本低,工程应用前景十分广阔。

Currently,free abrasive multi-wire sawing（FAMS） is adopted as the primary wafering technique in China.However,its main drawbacks are generating deep saw marks and thick damage layer as well,which cannot meet the further demand of large scale and ultra thin wafers.Free abrasive electrochemical multi-wire sawing（FAEMS） is a new grinding method of which combines with electrochemical machining,i.e.,the silicon ingot and the cutting wire are served as anode and cathode,respectively,and the anodic passivation（or erosion） on silicon can be controlled by applying an anodic potential during the mechanical sawing process.Hereby,cutting load can be effectively reduced.And cutting efficiency as well as surface quality of wafers will be significantly improved.In this work,156 mm×156 mm（8″） p-type（boron-doped） polycrystalline silicon ingots with a resistivity of 1-3？·cm are selected as raw materials,and in order to explore the difference of surface integrity between FAMS and FAEMS methods,all machining parameters are fixed with no change.The experimental results show that the profile bending rate（BOW） of FAEMS is 3 μm lower than that of FAMS,and is quite centered on narrow size distribution ranging from 0 to 9 μm.Further,hidden cracks and deep grooves on the sub-surface of FAEMS wafer are relatively rare to be observed after being etched by 20% Na OH solution,which indicates that surface damage is less than that of FAMS,and the thickness reduction of wafer for subsequent texturing process will be thinner too.For free abrasive and fixed abrasive multi-wire sawing techniques,this new method is totally compatible to be adopted with low cost of equipment improvement,which has a bright future for industry applications.