The project team needed to analyze the reasons for the large variation of the film thickness and screen out the possible factors
FINDING THE ROOT CAUSE ALONG THE PRODUCTION LINE
The team wanted to determine whether the measurement system or process errors were causing the discrepancies in film thickness. They used the Topcon product testing platform, an industry-standard testing equipment, to measure the film thickness and refractive index.
The team then used Minitab’s Gage R&R measurement system analysis to see if the variability was caused by the measurement system itself. The analysis value of the measurement, Gage R&R, is 9.16, which is less than 10%, indicated that the Topcon measurement system met the requirements and was therefore not causing the issues.
NARROWING DOWN POSSIBILITIES WITH MINITAB BRAINSTORMING TOOLS
Still looking for possible influencing factors, the team used the fishbone diagram (also known as a cause-and-effect diagram) in Minitab Engage to brainstorm. Based on the fishbone diagram and the leader’s previous experience, the team identified two possible reasons why a malfunction in the equipment or a process issue may cause a variation of the silicon nitride film thickness:
- Frequency of which the butterfly valve, which is a valve that regulates the flow of fluid, in the coating equipment is cleaned
- Furnace temperature and position of the silicon in the furnace
First, the team investigated whether the butterfly valve in the coating equipment cleaning was an issue. The team created a two-sample t-test in Minitab to confirm whether the frequency of the butterfly valve cleaning makes a significant difference to the film thickness.