Time after RTP – Discoloration
Last week in lab meeting, someone wondered if there the time after RTP affects the rate of discoloration. To test this, I RTP’ed chips from w638 in Ar at 800C for 5 minutes. I then followed discoloration in DMEM+10%FBS in the incubator with untreated w638 chips as controls.
All of the chips discolored within a day, and the RTP doesn’t prevent discoloration. Since RTP typically prevents discoloration at least for a day or 2, I looked at w638 with Brian’s microscope. As shown on the right frame, there was diffuse contamination all over this wafer. I’m not sure what these spots are, but it’s possible that they are affecting the rate of discoloration. I stopped this experiment, RTP’ed a different wafer and am currently repeating this experiment with DMEM/F12 instead of DMEM.
Regarding contaminants – I tried re-washing and cleaning some of the old chips (w/ pentane and methane) that had the several micron sized features on them. I had no success in getting any of them off. I am no expert on bacterial contamination, but it certainly looked like bugs were on that surface. Can we have some samples of the DI water that you guys are using to wash/rinse your wafers? Particularly the last step before the pentane rinse. Which building and water supply is this from?
The spots in the image are most likely some type of silicon deposit left from the etch. The wafers are cleaned in 18M Sulfuric acid, so I can’t imagine there would be anything organic left on the surface. The DI water in Hopemen is probably the cleanest on campus, going through multiple particle filters down to 0.2 micron and there is an in-line UV irradiation system to break down organics molecules. The system is also a continuous flowing loop (~8 gal/min) to prevent any biofilm growth.I have not seen anything that will remove these features without attacking the membranes. I suppose the good news is that these features are stable, so they should not affect experiments, but we still want to get rid of them.