April 9, 2021
MIT.nano's Assistant Director for User Services at Fab.nano Jorg Scholvin has put together this list of helpful tips and tricks for MLA-150 users.
1. MLA-150 quick steps for avoiding write slowdowns:
- During writes of complex patterns, the MLA software can have leftover data in memory after a write.
- Eventually that leads to Windows running out of memory as it clogs up its 32 GB of space. That in turn will lead to heavy off-loading into virtual memory, which slows the computer down, and results in a slow write.
- This happens quickly when writing complex patterns (e.g. my wafer needed 20 GB of peak memory use, and after completion about 6 GB of memory debris remained—writing just two or three of such patterns would fill up the memory).
- You can monitor this in the windows task manager (look at Memory usage under “performance” tab).
- When you close the MLA software, the memory debris is cleaned up. You don’t need to restart the PC. Simply close the MLA software and start it again.
- You don’t need to restart the software every time. Here’s what I do: (1) Open task manager to check out the memory used. (2) If it’s >10 GB, I close the MLA software and restart it. If it’s <10 GB used, I keep going as there’s enough memory to avoid running into issues.
2. The depth-of-focus on the MLA optics is about 3 um. The defocus steps are about 3 um step sizes.
3. The air autofocus does not adjust when you get within ~5 mm or thereabout of the sample edge.
- That’s because the air doesn’t work close to the edge, since the air pressure gets messed up by the edge, which prevents focusing with air.
- Thus, if you’re running on <1 cm pieces, you get no autofocus if you use air (so that means your features will be all over the place, as you’re likely out of focus). If your samples are much smaller than 1 cm, I would imagine the air autofocus will not always repeatable.
- Running a dose-defocus matrix on small pieces (<1cm) using air autofocus thus makes not much sense (as you never get the same focus across your matrix and between samples)
- To resolve this, either (trivial solution) use larger samples, or (practical solution) use the optical autofocus on the Lv1 MLA, as it can continue focusing closer to the edge.
- IMPORTANT: To use the optical autofocus on the Lv1 MLA, you may need to manually select it when running your sample—it is not always set it by default.
- We've received feedback on users running pieces that their lithography repeatability and accuracy significantly improved when using the optical autofocus.
As always, email mitnano-feedback@mit.edu with any questions or suggestions!