Copper contamination update
Dave and I tested 8 wafers (187, 189, 310, 316, 318, 325, 327, 329) from the last 3 runs and traces of copper can be found within all the wells. However, the amount and position of this contamination varies greatly, with the most particles being located near the top of the well, away from the membrane.
Some general observations:
-There is generally more contamination found on samples near the wafer edge
-Wafers with higher pinhole density also tend to have more copper, although exceptions have been found
-Copper does not always form the characteristic CB pinholes
JP, Dave, and I believe that both the pinholes and Cu contamination are arising somewhere at RIT, and we will be trying to pinpoint the cause over the next few runs. We have much more control over the UR equipment, and it seems unlikely that such variability (especially pinholes) could be coming from these facilities. The last wafer run was nearly unusable due to pinhole density….
To give you a feeling for what we are looking at, here is an SEM image from within the well of wafer 316. When we focus on any of these particles (typically the largest clumps for improved signal), the characteristic Cu peak signatures show up. From past work on the membranes, these appear to be copper silicide, not pure copper.
