SURFACE DAMAGE FROM MULTIWIRE SAWING AND MECHANICAL PROPERTIES OF SILICONWAFERS

摘要

Multi wire sawing is the main slicing technique for large multi- and monocrystalline silicon crystals in the photovoltaic and microelectronic industry. While in the last years the cost of solar cell processing and modulefabrication could be reduced considerably the sawing cost remains high. Thus the incentive to optimize the sawingtechnique has great power. In terms of high throughput, low material losses, reduction of supply material andimproved wafer quality several variable parameters play an important role. Basic knowledge about the microscopicdetails of the sawing process is required to understand the influence of these parameters and their interactions.The aim of our work is to relate the sawing parameters throughput, material loss, supply material and wafer qualityby understanding of the basic mechanisms. Therefore a model of the wire sawing mechanism has been designed.Finite element calculations of elasto-hydrodynamic slurry flow in the sawing channel are part of the sawing model. Inaddition, the interaction between abrasive particles and crystal yields a typical damage pattern of microcracks on thesurface of the Si-wafers. These microcracks together with microcracks resulting from ingot-sawing process determinethe mechanical strength of wafers and solar cells. The microcrack distribution was investigated on beveled polishedsurfaces, the corresponding fracture strength by mechanical fracture test. Both distributions are correlated through theGriffith criteria. In this way, it has been possible to calculate the fracture stress distribution of silicon wafers with increasing etch removal.