Subject: Re: Questions about the ZEP-520A
From: "James W. Conway" <>
Date: Tue, 16 Feb 2010 09:29:42 -0800

Hello Don

Great questions which I will share with the Raith On Line Community...

ZEP-520A makes a great liftoff structure when exposed at below 10 kV.  
It is very high contrast material and about three times faster than our 
normal PMMA materials.  It also has suitable etch resistance and 
selectivity for RIE using the normal process gases with the exception of 

In normal careful dose determination you should see a clearing dose 
threshold of 37 to 40 ┬ÁC/cm**2 at 10 keV for areas above 100 nm in 
size.  At the lower dose you may see some resist residues visible as 
small fringes in the corners of the area test boxes.  This is normal and 
a slight increase in dose should clear these edges well.  Always employ 
the very slightest of agitation during development and be sure to not 
over-develop your patterns.

In the past have employed very gentle descum processing in the past for 
Ohmic contacts and and dots using very low powers applied with Oxygen -- 
but only for 5 - 15 second descum cycles at less than 50 W of power.  
(My old etcher was a MARCH Mini-80 tabletop RIE system when I used 5O W 
for 15 seconds at 0.200 T O2 pressure and after a complete pump down and 
2 Ar purge cycle to remove water vapor and O2 from the chamber walls.)

The issue with descum processing of lift off structures is you may 
simply sputter away some of your reentrant profile in the resist and 
that will make it more difficult to lift off cleanly.

Please see me if you need any assistance in your inspections or to 
develop your process parameters as I have lots of experience working 
with ZEP-520A.
Other Users care to report their doses used or add you comments to this 
thread?  I am reiterating our process for a new process sheet to come 
out in March. 
Your comments are welcomed.

Thank you,


Donkoun Lee wrote:
> Hi all:
> I have some questions about the ZEP-520A. Now, I do my e-beam process with ZEP-520A.
After exposure, I deposit metal layers and do lift-off process in order to make an electrical
contact. However, I am wondering if there are residues(scum) after developing process
with Xylenes and Iso-propanol or not.
> If there are residual layers (scum) after developing process, do I need to do oxygen
plasma process (descum process) to remove the residues? If I need to do the O2 plasma
process, can I share the recipe?
> Thank you.
> Kind Regards,
> Donkoun Lee