The effect of recycling silicon carbide on the quality of silicon wafers (1)

Summary:

Silicon carbide micropowder is the most important abrasive in multi-wire cutting silicon wafers, suitable for cutting hard and brittle materials. Multi-line cutting is a cutting method in which a steel wire is driven by a guide wheel to perform high-speed movement, and a steel wire carries a mortar for grinding. The mortar is a mixture of a suspension (PEG) and silicon carbide (SiC), and when the cutting is completed, the new mortar becomes Waste mortar, if the waste mortar is discarded, it will cause great environmental pollution and is also unfavorable for cost reduction. Therefore, the current development trend of the photovoltaic industry is to use recycled silicon carbide. This paper discusses the effect of different proportions of recycled silicon carbide on the quality of silicon wafers. .

introduction:

Mortar is a mixture of suspension (PEG) and silicon carbide (SiC). The cut waste mortar contains more impurities such as iron powder and silicon powder, and many silicon carbide particles involved in cutting are damaged, and then directly involved in cutting. It will have a great influence on the cutting ability, thus affecting the quality of the silicon wafer. Therefore, it is necessary to refine the waste mortar, reprocess the silicon carbide and suspension inside, and then reprocess the silicon carbide and suspension with new silicon carbide. The new suspension is compounded and cut again in a certain proportion. At present, the proportion of silicon carbide generally recovered in the industry is 60%-80%, and the proportion of recycled cutting fluid is 40%-90% or even 100%.

1. Parameters affecting quality in silicon carbide

The silicon wafer cutting is mainly the rolling cutting of the steel wire carrying the mortar for grinding. The leading role is the silicon carbide in the mortar. Since the silicon carbide in the cutting will collide with the silicon and rub, the SiC particles will wear continuously and Broken, which affects the quality of wafer cutting. Among the main parameters of silicon carbide, hardness, grain size, particle size, circularity and fine powder content play a crucial role in the cutting. The hardness of silicon carbide is determined by the hardness of the raw material produced by silicon carbide. The length of smelting time determines the hardness of silicon carbide. If the hardness is too low, it will collide with silicon during the cutting process, which will cause the particles to be flattened and passivated, resulting in insufficient cutting ability, which will eventually cause saw marks on the silicon wafer; In connection with the crushing process, if there are many long strips and flat particles in the granules, the rolling friction of the silicon will not occur during the cutting process, so that the cutting ability is lowered, resulting in the occurrence of sawing and skewing of the silicon wafer; In the process of silicon carbide production, it is impossible to concentrate the particles of the same particle size, but the larger the particles and the smaller silicon carbide have adverse effects on the cutting quality, so the median particle size is required to be within a certain range; The degree and fine powder content are particularly evident in the recovery of silicon carbide. The circularity characterizes the sharpness of the edge of the silicon carbide. When the silicon wafer is cut, if the circularity is large, that is, the edge Smoothing will result in insufficient cutting ability and lead to the occurrence of saw marks in silicon wafers. In the process of silicon carbide production, especially in the process of recycling silicon carbide from waste mortar, the fine powder is difficult to be cleaned, generally refers to particles with a particle size of less than 2 μm. If more, the micro-powder will form a wrap to the silicon carbide during the cutting process, thereby reducing the cutting ability of the silicon carbide and affecting the quality of the silicon wafer.

Second, the machine test part

Using the same equipment to cut 156*156mm polycrystalline silicon block, compare the cutting quality of silicon wafer under different recycled silicon carbide ratio, recover 50%, 60%, 65% of silicon carbide ratio, recover 90% of cutting fluid ratio, steel wire model 0.13mm, the same process parameters, the same amount of mortar update, and the use of scanning electron microscopy, Beckman particle size analyzer, Malvern 3000 roundness meter for the circularity, particle size and The detection of micronized content, etc., and the comparison of the quality of silicon powder, iron powder and silicon wafer in the waste mortar of different recycled silicon carbide ratios.

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