Wafer Crafts Yield in Chip Manufacturing

Usually wafer fabrication and packaging steps are designed to several hundred process steps, which are quite long and complex. These processes cannot be perfect every time, so the yield control of wafers is particularly important, and yield also has a significant impact on the cost of products.

Wafer Crafts Yield in Chip Manufacturing

Yield monitoring point

For the wafer processing process, there are two factors that affect the overall yield of the wafer. First, the wafer production process is very long and complex. We need to make millions of micron-sized components in the plane structure and three-dimensional layer side in an extremely harsh clean space within a chip range of 0.5 square feet. Thinking is a very difficult thing; the second is that most of the defects can not be repaired. And for manufacturing, the more defects are detected later, the higher the cost. Therefore, there are three main inspection points for wafer production:

1. Wafer manufacturing: yield = number of wafers output / number of wafers input

2. In-wafer measurement: yield = number of qualified chips/total number of chips on the wafer

3. Packaging: Yield rate = the number of packaged chips that passed the final test / the number of qualified chips put into the package

Wafer yield calculation

Successful wafer fabrication must have an overall wafer yield of greater than 90% to remain profitable and competitive. The yield of wafers is divided into site yield and overall yield.

Among them, the site yield is the yield rate of each process to be counted separately, and the formula is:

Station yield = number of wafers leaving the process station / number of wafers entering the process

Then the total yield rate of the wafer = yield rate (process station 1) × yield rate (process station 2) × ... × product rate (process station n).

According to this, we may make a small calculation, assuming that a wafer needs to go through 10 process stations, and the yield rate of each process station is 99%, then the overall yield rate of the wafer is 90.4% (10 99 % multiplied), it can be seen that it is challenging to control the overall wafer yield above 90%.

Factors Affecting Wafer Yield

The yield rate of wafer production is restricted by many aspects. This article mainly introduces four constraints. The combined effect of these four basic factors determines the overall yield rate of a factory.

1. Number of process steps

2. Wafer cracking and bending

3. Process variation and defects

4. Photolithography Mask Defects

Elements of wafer electrical measurement yield

After the wafer production process is completed, the wafer is sent to an electrical testing machine, and each chip on the wafer is electrically tested according to device standards and functionality.

Conclusion

Wafer electrical testing is a very complex test, and many factors will affect the yield. For example: wafer diameter; chip size (area); number of process steps; circuit density; defect density; wafer crystal defect density; process cycle time.

Wafer Crafts Yield in Chip Manufacturing

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