The Impact of Recycling Silicon Carbide on the Quality of Silicon Wafers (1)
Summary:
Silicon carbide micropowder is a key abrasive used in multi-wire cutting for silicon wafers, especially for materials that are hard and brittle. Multi-line cutting involves a steel wire driven by a guide wheel at high speed, carrying a grinding slurry composed of polyethylene glycol (PEG) and silicon carbide (SiC). After the cutting process, this slurry becomes waste, which can lead to severe environmental pollution if not properly managed. Moreover, discarding it increases production costs. Therefore, recycling silicon carbide has become a growing trend in the photovoltaic industry. This paper explores how different ratios of recycled silicon carbide affect the quality of silicon wafers.
Introduction:
The slurry used in cutting consists of PEG and SiC. The waste slurry from the cutting process contains impurities such as iron powder and silicon dust, and many SiC particles become damaged during the process. These damaged particles may lose their cutting efficiency, directly impacting the quality of the resulting silicon wafers. To address this, the waste slurry must be refined, and the SiC and PEG must be reprocessed before being mixed with new material. In practice, the industry commonly recycles 60%–80% of SiC, while up to 90% or even 100% of the cutting fluid may be reused.
1. Parameters Affecting Quality in Silicon Carbide
During silicon wafer cutting, the steel wire carries the slurry and performs rolling cuts. The silicon carbide within the slurry plays a central role. As the SiC particles rub against the silicon, they gradually wear down and break, affecting the cutting performance. Key parameters that influence the quality include hardness, grain size, particle size distribution, circularity, and fine powder content. The hardness of SiC depends on the raw material and smelting time. If the hardness is too low, the particles may flatten and become inactive during cutting, leading to saw marks on the wafer. Additionally, if the particles have irregular shapes—such as long strips or flat fragments—they may not roll effectively, reducing cutting efficiency and causing misalignment or uneven cuts.
During production, it's challenging to achieve uniform particle sizes. Larger or smaller particles can both negatively impact cutting quality, so the median particle size must be carefully controlled. Circularly shaped SiC particles are more effective for cutting. If the circularity is poor, the edges may become rounded, reducing sharpness and cutting ability, which again leads to visible saw marks. In the recycling process, fine powders—particles smaller than 2 μm—are particularly difficult to remove. These fine particles can coat the SiC during cutting, reducing its effectiveness and ultimately degrading the quality of the silicon wafer.
2. Machine Testing Part
To evaluate the effects of different recycled SiC ratios, we conducted tests using the same equipment to cut 156x156 mm polycrystalline silicon blocks. We compared the cutting quality under various SiC recovery rates: 50%, 60%, 65%, and 90%. The steel wire used was 0.13 mm in diameter, and all other process parameters were kept consistent, including the amount of mortar used. We analyzed the results using scanning electron microscopy, a Beckman particle size analyzer, and a Malvern 3000 roundness meter to assess particle size, circularity, and fine powder content. We also compared the presence of silicon powder, iron powder, and overall wafer quality in waste slurry from different recycling ratios.
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