Photolithography - Improving Adhesion Photoresist Adhesion
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Don't forget that, for lift-off processes, the Imaging (top) Photoresist will lift-off as well if you undercut it too much during develop!
Underlayers for improving PR adhesion
High-temperature (>150°C) underlayers, such as LOL1000/2000, BARC layers tend to improve adhesion of the imaging resist.
- Substrate prep: O2 plasma (PEii Technics), 10sec
- Apply high-temp underlayer, eg. LOL1000/2000, PMGI, DSK101 (DUV), DSK42P (DUV)
- Beware of underlayers that have a develop-rate - undercutting the imaging PR fully can also cause delamination)
- Apply your Imaging photoresist as normal.
HMDS Process for PR Improving Adhesion
This process tends to improve adhesion between the substrate and subsequent photoresist layers. Use this procedure if you are finding poor adhesion (resist delaminating during develop etc.), or for chemicals (like BHF) that attack the PR adhesion interface strongly.
- 150°C bake ~2min (Dehydration step)
- Optionally could instead do Dehydration of: O2 plasma (PEii Technics), 10sec; however this could create more surface SiO2 on silicon.
- HMDS application & soak 40s
- Do this with sample loaded on the PR spinner.
- Spin-dry - any spin speed, ~15-30sec
- HMDS bake at 100-110°C for 90s.
- Then your normal PR process on top.