Subject: Re: Problems with PMMA as a mask -- Try this!
From: James Conway <>
Date: Fri, 03 Oct 2003 18:17:11 -0700


Two things that will help you:

1- NO Oxygen during the etch process,  and be sure to pump the system to base
pressure before back filling and flowing your process gases for several
minutes.  PMMA and most of the ebeam resist materials (ZEP-520 for example)
will quickly be removed with even the slightest trace of Oxygen in the process
gases. My old descum process was 15 W 30 sec. 0.200 mT O2 in a March Mini-80
RIE system.  This will rapidly decompose the ZEP-520 material.

2. Post develop bake on hot plate or preferably in N2 oven for 10 - 30
minutes. I recommend 90 - 110 degrees C.
 This will assist cure and cross linking of the resist material making it more
resistant to the RIE process.

Please reply with your notes and results when you have tried this to add to
our knowledge base.


James Conway

"Scott D. Andrews" wrote:

> Has anyone tried using PMMA as a mask when etching SiO2?  I need to etch
> 10 nm of SiO2 with 100 nm of PMMA as the mask layer.  However, when I use
> the mrc with O2 and freon 23, the PMMA does not survive.  Ideally, I would
> like an anisotropic etch, but if necessary, I would accept a wet process
> that undercuts slightly.
> Thanks,
> Scott Andrews