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 batch 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 be definitely 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. Usage of creative thinking tools is necessary for the generation of innovative ideas