Photolithography - Improving Adhesion Photoresist Adhesion

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)
• Bake at recommended temperature for the underlayer, typically >> 150°C.
• Apply & bake your Imaging photoresist as normal for that resist,
  • Bake temp should be lower than the underlayer bake temp.
• If your underlayer dissolves during the same develop step as the imaging resist, you will need to increase your develop time to go through both layers.
  • 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!

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.