What is Edge Die?

Edge die refers to chips located at the edge of the wafer that may have defects in design or incomplete dimensions due to mask alignment errors or wafer dicing during the wafer manufacturing process. Here's a detailed explanation of the edge chip:

1.Cause of Edge Die

In the wafer manufacturing process, the role of processes such as lithography, deposition, etching is usually concentrated in the center of the wafer because of the higher alignment accuracy and more stable process conditions. The edge area of the wafer is far away from the alignment reference of the process equipment, which is greatly affected by optical diffraction effect, mechanical stress, temperature and other factors, resulting in poor chip quality at the edge part. Especially in wafer dicing, due to the uneven mechanical force of the wafer, the edge part is prone to the formation of defective or incomplete diced chips.

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2. Features of edge die

Incomplete dimensions: Due to the fact that the Edge dies may not fully meet the design requirements during the cutting process, the dimensions may be irregular, or even incomplete. This means that chips in the edge region have lower yields during production. Increased defects: Due to the low alignment accuracy of lithography and etching, Edge dies are prone to some minor defects or failures, which affect the function of the chip.

Waste and loss: Edge dies are often considered waste areas because they are of poor quality and performance and do not meet standard requirements. The presence of these chips means that there is a certain amount of waste in the wafer processing process.

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3. The impact of edge die on wafer utilization

Edge dies for wafers are mainly wasted area due to physical constraints in fabrication and dicing. In order to improve the efficiency of wafer utilization, the semiconductor industry is constantly pushing for the use of larger diameter wafers (such as 300mm wafers) to reduce the area occupied by Edge dies. This is because large-diameter wafers provide more active area and less waste at the edges that cannot be used.

4. How to mitigate the impact of edge die

Improve process accuracy: Reduce chip defects in edge areas by improving the accuracy of lithography, etching, and other processes. This is a fundamental way to improve yield and reduce the number of Edge dies. Optimized dicing method: Finer wafer dicing technology is used to minimize the loss of edge parts during dicing. Increased wafer size: Increasing the size of the wafer (e.g., using larger 300mm or 450mm wafers) can reduce the area ratio of Edge dies, which in turn increases the number of chips per unit area.

5. Analogy and metaphor

A wafer can be compared to a big cake, with chips being cut into small pieces. And Edge dies are like some crumbs on the edge of a cake, although they are originally part of the cake, these crumbs are usually inedible due to imperfect edge cutting. To reduce these crumbs, manufacturers try to improve the cutting tools or opt for larger cakes, which ensures a higher quality cake in the center area, even if some of the corners are wasted.

Summary

Edge dies are an inevitable product in wafer production, mainly caused by photoli-thography, dicing and other processes. Although Edge dies do not meet the standards and cannot be used as qualified products, by improving process accuracy, optimizing dicing technology, and using larger diameter wafers, the area waste of Edge dies can be effectively reduced, and the overall wafer utilization rate and yield can be improved.