No success with UV Ozone Bonding at 100C with High Humidity
Following the advice of Dave and Chris I ran a UV Ozone bonding trial yesterday with the stage temperature set to 100C (instead of the usual 25C). The idea behind the elevated stage temperature is to drive off any water vapor that might be within the UV Ozone chamber during the treatment process.
At the time I ran this trial the humidity level in the third floor equipment room was 62%. When I checked the systems this morning I found that not a single one (n=4) had successfully bonded. I think the problem with the humidity is not occurring within the UV Ozone chamber during the treatment. Rather I think that the issue is when the chamber is opened just prior to flipping the PDMS onto the pncSi membrane chips. Even though this “flipping” process is done as quickly as possible once the chamber is opened I feel that at a higher humidity the now hydrophilic surfaces of the PDMS and pncSi will need less time to “react” with water molecules in the environment. At a lower humidity less atmospheric water vapor is able to “react” with the two surfaces prior to flipping, enabling them to remain hydrophilic and thus for the bond between them. When the humidity is increased it might take a very short time for the atmospheric water vapor to nullify the hydrophilic surface properties of the two surfaces. As a result when they are introduced no bonds are formed.
Based on what I have seen so far I think this is a plausible explination for the lack of bonding we have seen at high humidity. If this is truly the case then I think a possible solution would be to look into some sort of dehumidifier for the third floor clean room. I had talked with Jess and she has heard of people doing this and reporting improvements in their bonding efficiencies.
Dehumidifiers don’t work unless you place them in a contained area, like a closed box. Buildings have too many air changes per hour for the dehumidifier to keep up. A real science building would have HVAC humidity control. You could try buying a large “glove bag” from Aldrich that you could purge with dry nitrogen. You would put the whole ozone system in the bag and run the process dry.
I have doubts about whether this is necessary though. There are probably simpler measures that could be tried first. Is the actual bonding done in a desiccator? I don’t think water would coat the surfaces in seconds – you should have minutes anyway…
I agree with Chris. I mentioned to Jim last week that it seemed to me that you guys proved that the bonding occurred in the subsequent 12-24 hrs. A simple test would be to flip and then put the pieces in one of the desiccators that Dave bought for the 12-24 hr bonding period. If you already tried this and I missed it, I apologize.
On Wednesday I ran a trial of UV Ozone bonding with the system now placed within the hood on the third floor clean room. The stage temperature was set to 100C and the humidity during the bonding was 59%. As Tom suggested I placed the samples in one of the desiccators that Dave bought for the 12-24 hr bonding period. When I checked the samples yesterday no bonding had occurred.
I’m not sure what the 3rd floor cleanroom is or how using a hood helps, but I’ve also lost track of what you have tried to do – let’s discuss on Tuesday…