The cutting of silicon wafers using multi-diamond wire sawing is a critical stage in solar cell manufacturing due to brittleness of silicon. Improving the cutting process output requires an in-depth understanding of phenomena associated with cutting parameters. In order to investigate the influence of diamond wire sawing on surface integrity of monocrystalline silicon, a looped diamond wire was used and cutting parameters wire cutting speed, feed rate and wire tension were varied. The surface morphology was observed by scanning electron microscopy. Surface roughness S a was measured with a non-contact profilometer. The brittle-ductile transition was identified by presence of residual phases on sawn surface. A bevel-polishing method was employed to determine the microcrack depth. The results show that with higher feed rate the surface presents deeper and wider craters because of deeper penetration of diamond grain. On increasing wire cutting speed, there were more regions formed in ductile mode. The higher S a values was observed on increasing both feed rate and wire tension, while S a decreased with an increase in wire cutting speed. The brittle mode was predominant with an increase in feed rate, resulting in Si-I phase in regions formed in fragile mode. Material removal in ductile mode led to appearance of a-Si phase at high wire cutting speed. No significant effect was observed on increasing wire tension. Subsurface microcracks mainly initiating from bottom of grooves generated by cutting mechanism. The most appropriate set of cutting parameters is the lowest feed rate and wire tension and highest wire cutting speed.

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This study aimed to evaluate and better understand the mechanical and crystalline responses of polycrystalline silicon sawn by diamond wire sawing. To simplify the multi-wire sawing kinematic, an endless wire saw with a single looped diamond wire was used. The wire cutting speed and feed rate of the sawing process were varied in order to evaluate the characteristics of sawn surface morphology, surface roughness and subsurface damage. The analysis of brittle-ductile transition and residual stress of the sawn surface and silicon chips were performed with Raman spectroscopy. The wear and failure mechanism of the diamond wire were analyzed. The results show that sawn surface is composed of brittle and ductile regions and the predominance of one of these directly affected the surface roughness R a . The ductile cutting mode induced the predominance of microgrooves and ploughing over the sawn surface and led to formation of an amorphous layer with residual compressive stress of up to -192.3 MPa. Micro-cracks in subsurface were identi ed and it reached a minimum depth of 7.2±1.6 µm.Chip fragments and elongated chips were observed and Raman spectra showed that the latter are amorphous. The wire wear analysis indicated that during the cutting there is deformation of the Ni-layer, exposed grits and grit pullout. The main wear mechanisms are Ni-matrix removal and abrasive wear of the diamond grit. A better surface quality of polycrystalline silicon was obtained on increasing wire cutting speed and decreasing feed rate. The results found in this study can help to reach a high quality surface of silicon wafer for photovoltaic application. HighlightsAnisotropy of poly-Si induces to sawn surface composed of brittle and ductile regions and it affected the surface roughness Ductile cutting leads to surface formation with amorphous phases and residual compressive stress On increasing wire cutting speed and decreasing feed rate was obtained a minimum micro-crack depth Chip fragments and elongated chips were observed and Raman spectra showed that the latter are amorphous Wear mechanisms of the diamond wire were Ni-matrix deformation and removal, abrasive wear and grits pullout

The aim of this study was to investigate the influence of the cutting parameters on monocrystalline silicon cut by diamond wire sawing. The sawn surface was analyzed in terms of surface morphology, surface roughness, material removal mechanism and residual stress (by Raman spectroscopy). The surface morphology exhibited evidence of both material removal mechanisms: the brittle mode and the ductile mode. The surface roughness increased with a high v f , which promoted the formation of craters on the sawn surface. On applying a higher v c , the surface roughness reduced, since this favored the formation of damage-free grooves. The Raman spectrum showed evidence of different residual crystalline phases on the sawn surface, which confirms the material removal mechanisms. An increase in v f , for the same v c , caused at reduction in the compressive stress, since the brittle mode predominated as the material removal mechanism. Maintaining v f constant and increasing v c results in higher compressive stress, caused by plastic deformation of the silicon during chip formation.

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