Hi,
I have a need to determine how well a curve meets specification.
This simulated case is from wafer manufacturing where there is a targeted wafer bow profile. A flat wafer is not good. Neither is a profile having excessive bow.
Having processed a wafer I would like to determine how well the profile meets my specification, in this case a template created using natural tolerance limits set at +/- 2 sigma (0.025 and 97.5 percentiles).
Profiles for 500 wafers processed in the past look like this:
I calculate from these profiles (aggregating over every 10 mm across the wafer), an ideal profile (Median) and Upper and Lower tolerances (0.025 and 97.5 percentiles) resp.. to get the following:
So, having determined my tolerance window, I would like to measure how well a wafer's bow profile meets spec.
The best case would be that the just measured bow profile would be exactly the same as the "ideal" profile, however this is not typically the case. I would like to know how well the latest bow profile sits inside the tolerance window, indicating distance from tolerance limit(s) and distance from ideal. Something like a Ppk value.
I would expect the best value for wafer '257' above and worst for wafers '263' and '260'
Can this be done using FDE perhaps?
Your comments and suggestions are most welcome.
Data and Table Script attached
- Philip