Electron Beam Lithography (EBL) and how I lost hours due to a'\W'
Will I ever post anything here without a push from Erika? I don't know (sorry and thank you Erika for the constant reminders). But believe me or not this post has been in the making for more than a month now. The initial idea was to share the news of me getting the license to use EBL system at Chalmers on 14th February 2019. But I had to let it evolve into a much more interesting anecdote.
The Joel JBX 9300 FS EBL system at Chalmers looks like a beast. In fact the first time I saw it, everything looked so complicated that I was pretty sure I would not be operating it alone anytime in the near future. But, like I mentioned in my previous post, when you work with Domenico you learn things fast (or you get kicked, just kidding). He taught me so well that during my first training session with the tool responsible, Bengt exclaimed, 'you seem to understand what I am telling you, usually that's not the case!'. During the rest of training sessions, I learned a few new tricks from Bengt and we even had some disagreements between 'Domenico's way things' and 'Bengt's way of doing things' (as one of them works with small sized chips and the other does wafer scale process). After 3 training session with Bengt, I got the license to operate the tool. Since I had to work with small chips, I continued to use Domenico's method.
We decided to make a 4 inch wafer with alignment mark so that I will have enough substrates. We tried long exposures (which can only be done during the weekends) twice and both time the wafer came out clean without any pattern. Neither me nor Domenico had a clue as to what is happening. We checked and everything looked fine. So then we mailed Bengt with all the details and his solution to this 'oh, just add a \W in the beginning of your script'. We were like, 'What?'. Then we tried and it worked for sure! (thanks to David for helping in imaging the wafer with less reflection). Now I have enough substrates with alignment marks for a year or so. Apparently no one in our group had a clue about this '\W', which tells the machine if it is a mask cassette or wafer cassette. But everyone in our group use 3 inch cassette and for 3 inch cassette it does not matter if you include or don't include the '\W'.
During my first month as an independent user, I tried various things with scripting to make the process easier. Also, taking Bengt's advice, I started using 'jdi files' instead of 'doses file' and our recipes began to fail. I lost close to a month doing the dose re-calibrations. But in the end we came up with some thick resist recipes (required due to the thickness of the nano belts) which allows to write patterns as low as 25-35 nm (previously we could only go till 50-70 nm). During the whole process, we asked various questions to Bengt and suggested that it would have been better if we had some reference for making scripts to run the EBL. Few weeks ago such a page was created by Bengt in the LIMS webpage with detailed information about JOEL script writing and file conversions. So, even though we spend sometime without success, it turned out to be useful for all the EBL users.