Subject: Re: Metal Lift-off with PMMA
From: "James W. Conway" <jwc@snf.stanford.edu>
Date: Mon, 31 Jan 2011 11:30:29 -0800
Mon, 31 Jan 2011 11:30:29 -0800
Hello Byoungil Lee,

How thick is the metallization?  Normally in lift-off metallization you would not desire to fill the PMMA features more than about 50 - 60% of the resist thickness.
If you are depositing between 100 and 300 nm try the 5% 495K Single layer process with a PMMA resist thickness at 300 - 310 nm or 40 - 50 % thicker than your metal film.
If you are seeing significant line edge roughness in your PMMA features expose a new sample using a smaller aperture size which will also allow you to employ a smaller area or line step size.

You could also employ ZEP-520 process when exposed at 10 keV with the 10 or 20 µm aperture using a dose to clear of 35 - 40 µC/cm**2 for areas and 100 - 120 pC/cm for Single Pixel Lines.
This material has an inherent undercut suitable for most lift off structures when exposed at 10 keV and below.  It is also a very sensitive resist system that gives very reproducible results and your coated ZEP films on substrates will store for many months to years without a change in exposure characteristic.

Unless your metal deposition is really thick I would not recommend the dual layer process (JingKong1 process) as it will be hard to get 100 nm lines consistently due to aspect ratio of resist height ( typ. 1 - 1.5 µm) to feature size going beyond 10:1.  See me if you have more questions and I would be happy to examine your SEM's of these features together.

All the Best,

James Conway

Attachment:  Ebeam Resist Processing_Metal_liftoff.ppt 



Byoungil Lee wrote:
Dear James,

This is Byoungil (bilee), one of the Raith users.
Recently, I've been trying to get 100nm metal (Pt) lines by lift-off.
I tried the simplest process where I deposit Ti+Pt on 100nm thick PMMA pattern.
The 100nm wide metal lines look fine, but the edges are a little rough.
If I use double-layer resist, would it be better?   Could you give me any suggestion/comment/recipe on the metal lift-off process using PMMA?

By the way, the latex nano particles in the ebeam room are running out. Where could I get it when it runs out?

Thank you,
Byoungil Lee



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