I want to do some nanostructures with resist of PMMA by electron beam lithography, but the nanostructure always leave the quartz substrate when I developer. so, I think the reason is PMMA have very weak adhesive with quartz substrate ? Is there anyone can give me some suggestions to help me dealing with this problem? Thanks
1. Be sure to thoroughly clean the quartz substrate with piranha solution or strong UV/ozone/oxygen plasma cleaning before applying PMMA.
2. Thoroughly bake out solvent before doing lithography. I suggest 160 deg C film temperature for 5-10 minutes as a starting point.
3. PMMA and quartz actually possess very strong adhesion between one another when processed this way.
thanks for you answer.
1. I have clean the quartz substrate with acetone and IPA solution before applying PMMA
2. Clean the substrate with strong oxygen plasma before applying PMMA
3. Thoroughly bake out solvent with 180 deg C film temperature for 10 minutes before doing lithography
4. All of the methods above I have tried, but the nanostructure of PMMA still leave the quartz substrate
Dear Qing Li,
Before spin coating of PMMA, try HMDS -surface treatment. It will increase the adhesion of resist.
Good Luck.
Adnan
Dear Qing Liu,
Quartz is an insulating substrate. You did not mention any conductive layer coating onto resist or susbstrate prior to e-beam exposure. Surface charging built up during e-beam exposure makes pattern definition using e-beam on insulating substrates almost impossible. Without conductive coating, I believe this is one of the surface charging effect.
try to piranha clean quartz substrate instead of oxygen plasma. Try higher bake temperatures or longer bake times. PMMA adsorbs to quartz under deposition conditions described in papers such as this one: Article Adsorption of Poly(methyl methacrylate) Melts on Quartz
Qing,
According to my experience in nanolithography and patterning, working with Quartz is not easy at all. As Khairudin said, e-beam is based on electron exposure patterning and since your substrate is a perfect insulator you will have charge accumulation between resist and substrate, results in backing resist from the bottom. However, I have some suggestion to for you to get a better resolution:
1- After cleaning (Piranha-Acetone-IPA-DI water-Nitrogen gun), bake your sample at 200 C for 2 min.
2- Don't do oxygen plasma.
3- Use HMDS right after part (1) and bake it at 150 for 30 s, then spin coat your resist.
4- During exposing, use smaller current and voltage, but longer time.
5- If that is possible, do a post bake at low temperature (below 110 C) before developing.
Hope it works for you to emerge you structure.
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