Wafer cleaning issues at the wet process
Process description
The wet cleaning process is performed with single wafer equipment, one by one.
The wafer rotates, and the chemistry or rinsing water is poured from the nozzle to the central area of the wafer but can also move from the center to the periphery of the wafer.
Equipment:
Failure and possible trigger:
- Defects were found on the wafer after the wet cleaning.
- The defects started appearing after the introduction of a new batch of chemistry (tourn-on date):
- The comparative chemical analyses of the previous and suspected batches showed that all parameters for both batches are within specification limits.
- The only difference found is that the concentration of one of the components is slightly elevated in the suspected batch.
- Nevertheless, it is important to highlight that the elevated component remained well within the specification limits. See the chart below:
The traditional approach to problem-solving
The Problem
The new batch of chemistry is contaminated. The chemical content of the suspected batch does not match the typical composition of the chemistry.
Direction to solve this problem
- Remove the batch from the production line. Dispose or return it to the vendor and ask to prepare another batch with a purity that matches the typical batches.
- Change the specification limits to be tighter than the current to avoid similar excursions in the future.
The disadvantages of the traditional approach
- Cost increase – production cost will definitely be elevated
- Recurring excursions – similar excursions may occur again with the same or other components
- Lack of innovation – this solution is not improving the process or development of the technology
A systematic approach is needed. The usage of creative thinking tools is necessary for the generation of innovative ideas
Similar projects
The process is related to microelectronics - microchip manufacturing. The purpose of the process is to create a SiO2 layer on the surface of a Si wafer. Equipment: Vertical furnace to heat the wafers in the Q2 atmosphere and perform oxidation on the wafer surface. Process: The oxidation occurs on the front side and on the back side of the wafer Requirements: Create a SiO2 thin layer with a certain thickness and low sigma - low standard deviation of the thickness between the wafers and within the wafer Failure: Wafers from the lower zone have higher thickness and significantly higher within wafer sigma (standard deviation of the thickness within the wafer)
The project was dedicated to production yield improvement in microchip manufacturing. The bumps are created on the top of a wafer and used for the final test of all dies. Only good dies are taken for the packaging. All dies that fail the test will be scrapped. The process yield depends on the amount of "good" and "bad" dies. It was revealed that in some cases, the time between the end of the process and the final test impacts the yield. The longer the dwelling, the more dies fail the final test. If the dwelling exceeds hundreds of hours, the amount of failed dies becomes dramatically high, which results in the scrapping of the whole wafer. The problem was analyzed and solved.
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