[Fwd: Re: Etching Nitride layers - P5000]

Mary Tang mtang at snf.stanford.edu
Mon Feb 14 07:05:28 PST 2005

-------- Original Message --------
Subject: 	Re: Etching Nitride layers - P5000
Date: 	Fri, 11 Feb 2005 17:35:43 -0800
From: 	Ofer Levi <levi at snowmass.stanford.edu>
To: 	Jim McVittie <mcvittie at snf.stanford.edu>
CC: 	Mary Tang <mtang at snf.stanford.edu>, James Harris 
<harris at snowmass.stanford.edu>, James Conway <jwc at snf.stanford.edu>
References: 	< at snow.stanford.edu> 
<420D332A.B1B20 at snf.stanford.edu>

Dear Jim,
I am using a ZEP E-beam resist for my patterns to create the Photonic 
crystal sensor. The thickness of the ZEP resist layer after development 
is  ~ 3000-3500 Ang. over silicon. I am evaluating the resist thickness 
over my Quartz/SiNx samples now, but assume similar thickness.

I talked to Gigi today about etching in Pquest. He suggests that his data 
shows 400/500 A/min. for etching SiNx using the Chlorine based recipe we 
use for GaAs in Pquest. He estimated that the resist etch rate for the ZEP 
resist will be ~ 1000 A/min. This is also what I get for the ZEP resist 
etch rate at Drytek 1, using the Nitride etch recipe (F13/SF6 etch).
It is still ~ 2x better then PMMA for this ZEP resist etch rate but when 
you try to etch the Nitride layer to a depth of 2500 Ang. you need ~ 5 
minutes of etch for this Chlorine based recipe, and by that time the E-beam 
resist will be long gone.

Gigi suggests to keep looking for a solution that will have good etching 
performance with good side wall roughness using Fluorine based chemistry. 
This is why I chose to look into using the P5000 machine for 
etching.  Please also note that before deposition of any materials on my 
sample in the PECVD, I overcoat the walls twice with a 2500 Ang. of Nitride 
(one conditioning coat, and one calibration coat on Silicon wafer) so there 
is not much that can come off the walls onto my sample at that point.
I can also further clean the sample after dicing (I am already using a 
solvent clean, and an Piranha clean to the samples after dicing) to make 
them clean. So, I see no major issue aside from the Chrome layer deposition 
that may prevent my process from etching at the P5000 system. This Chrome 
layer deposition is a common feature for people who use e-beam lithography 
to get better writing performance and image resolution so it is a common 
material in our process. At the moment I do remove this very thin (5 nm) 
layer before etching.

I will be happy to further discuss this issue with you on Monday to look 
into issues with my process, and finding good solutions to them. I will be 
in the clean room most of the day since I write e-beam patterns on the 
Raith from the morning.


At 02:35 PM 2/11/2005, Jim McVittie wrote:
>There are a number issues with your process which are going to be a 
>problem in getting your samples into
>the P5000. I did not realize it until recently but the GaAs etch process 
>in the PQuest has a high nitride
>etch rate (400 to 500 A/min). I think you should look at doing your etch 
>in the PQuest.
>     Jim
>Ofer Levi wrote:
> > Dear Mary,
> > Following our discussion yesterday, I attach hereby a revised run sheet for
> > our sensor wafer that describes the processing I do so far. I can clean the
> > sample as needed before coating the sample with E-beam resist and Chrome.
> > At the moment I am using Innotec for chrome layer, but if needed I can
> > consider doing clean Cr. deposition. After e-beam writing, I remove the
> > Chrome layer using the wet Chrome etch, and develop the resist.
> > I would like to try using the P-5000 etch tool, by mounting my sample onto
> > a 4 inch Silicon wafer and etching the Nitride layer.
> > Thanks,
> > Ofer
> >
> > ______________________________________________
> >
> > Ofer Levi,      Ph.D.
> > Department of Electrical Engineering, Stanford University
> > CIS-X Rm 310,  Stanford, CA 94305-4075
> >
> > Phone:                             (650)723-0464 or 725-6907
> > Fax:                                              (650)723-4659
> > Adm. Asst.: Gail Chun-Creech                  Ph:  (650)723-0983
> > E-Mail:                          levi at snow.stanford.edu
> > Web page:               http://snow.stanford.edu/~levi/
> > ______________________________________________
> >
> >   ------------------------------------------------------------------------
> >                                                     Name: PC sensor run 
> sheet_February_10_05.doc
> >    PC sensor run sheet_February_10_05.doc           Type: Microsoft 
> Word Document (application/msword)
> >                                                 Encoding: base64
> >                                          Download Status: Not 
> downloaded with message

Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
mtang at stanford.edu

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