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Surface characteristics and mechanical properties of diamond wire cut silicon wafer

Diamond wire cutting is a new alternative cutting technology. Diamond wire cutting not only has high cutting speed, long service life of cutting line and low environmental pollution, but also can recover silicon waste, so it has attracted great attention. Many research companies are developing relevant supporting equipment and technology.

Diamond wire cutting has been initially applied to the cutting of monocrystalline silicon materials, but it has not been used for monocrystalline like and polycrystalline cutting. As the silicon crystal material and cutting process account for about 35% of the total cost of solar photovoltaic cells, people hope to further reduce the thickness of silicon wafer on the one hand, and improve the cutting efficiency and quality on the other hand, so as to reduce the cost. Diamond wire cutting technology is a new technology, which still faces many challenges in development and application.

Because the thickness of the silicon wafer changes very little, the overall size is between 185-195 microns, and it is relatively thick only at the edge of the silicon wafer (about 200 microns). There is no gradual change in the thickness of free abrasive cutting in WEDM, but there will be local sideshift or thinning of silicon wafer thickness. The reasons for the two thickness changes are related to the vibration of the cutting line. The opposite and opposite movement of the adjacent cutting lines can lead to the lateral movement and thinning of the silicon wafer thickness respectively. Generally speaking, the former usually has little effect on the properties of silicon wafer, while the latter will reduce the fracture strength of silicon wafer. When perpendicular, the silicon wafer shows high fracture strength, about 200-300mpa. However, when the bending direction is parallel to the groove, the fracture strength of the silicon wafer is low, about 80-180mpa. The difference of fracture strength between the two directions is about 1 time, showing obvious anisotropy.

The observation shows that the anisotropy of fracture strength of silicon wafer is closely related to the cutting morphology, especially the surface crack. Diamond wire cutting can lead to surface cracks on silicon wafers, which are usually unidirectional, parallel to the scratch direction, and the crack size is large. Under the joint influence of scratch groove and crack, the fracture strength of silicon wafer decreases significantly in the parallel direction of crack. This phenomenon shows that the fracture strength of silicon wafer is greatly affected by surface factors. In order to improve the performance of silicon wafer, it is necessary to reduce surface defects while reducing bulk defects.

The design of diamond cutting line mainly involves the preparation of abrasive particles. Although the abrasive particles are fixed on the diamond line and are in direct contact with the workpiece in the cutting process, this contact mode is different from the traditional rigid body contact. Because of the elasticity of the cutting line, it is actually a semi flexible contact mode. Therefore, the feed rate and cutting depth in the cutting process will change with the change of elasticity. In addition, there are differences in the shape, size and distribution of diamond abrasive particles, and the cutting depth of each abrasive particle will be different.

Diamond wire cutting is a new alternative cutting technology. Diamond wire cutting not only has high cutting speed, long service life of cutting line and low environmental pollution, but also can recover silicon waste, so it has attracted great attention. Many research companies are developing relevant supporting equipment and technology.

Diamond wire cutting has been initially applied to the cutting of monocrystalline silicon materials, but it has not been used for monocrystalline like and polycrystalline cutting. As the silicon crystal material and cutting process account for about 35% of the total cost of solar photovoltaic cells, people hope to further reduce the thickness of silicon wafer on the one hand, and improve the cutting efficiency and quality on the other hand, so as to reduce the cost. Diamond wire cutting technology is a new technology, which still faces many challenges in development and application.

Because the thickness of the silicon wafer changes very little, the overall size is between 185-195 microns, and it is relatively thick only at the edge of the silicon wafer (about 200 microns). There is no gradual change in the thickness of free abrasive cutting in WEDM, but there will be local sideshift or thinning of silicon wafer thickness. The reasons for the two thickness changes are related to the vibration of the cutting line. The opposite and opposite movement of the adjacent cutting lines can lead to the lateral movement and thinning of the silicon wafer thickness respectively. Generally speaking, the former usually has little effect on the properties of silicon wafer, while the latter will reduce the fracture strength of silicon wafer. When perpendicular, the silicon wafer shows high fracture strength, about 200-300mpa. However, when the bending direction is parallel to the groove, the fracture strength of the silicon wafer is low, about 80-180mpa. The difference of fracture strength between the two directions is about 1 time, showing obvious anisotropy.

The observation shows that the anisotropy of fracture strength of silicon wafer is closely related to the cutting morphology, especially the surface crack. Diamond wire cutting can lead to surface cracks on silicon wafers, which are usually unidirectional, parallel to the scratch direction, and the crack size is large. Under the joint influence of scratch groove and crack, the fracture strength of silicon wafer decreases significantly in the parallel direction of crack. This phenomenon shows that the fracture strength of silicon wafer is greatly affected by surface factors. In order to improve the performance of silicon wafer, it is necessary to reduce surface defects while reducing bulk defects.

The design of diamond cutting line mainly involves the preparation of abrasive particles. Although the abrasive particles are fixed on the diamond line and are in direct contact with the workpiece in the cutting process, this contact mode is different from the traditional rigid body contact. Because of the elasticity of the cutting line, it is actually a semi flexible contact mode. Therefore, the feed rate and cutting depth in the cutting process will change with the change of elasticity. In addition, there are differences in the shape, size and distribution of diamond abrasive particles, and the cutting depth of each abrasive particle will be different.

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