Ahmad:
Typical etch chemistries for SiN will attack the PR as well. You are seeing
profilometry step heights of <2.4um because you are removing some of the PR as
well as the 0.4um SiN layer. You would need to strip the remaining PR and take
another profilomtery measurement to get an accurate measure of the SiN/Si step
height. (The SiN etch will likely etch the underlying Si as well as the SiN.)
Typical etch selectivites for fluorine-based SiN-etch chemistries are in the
range of 1-2:1, so you'd expect to remove about 2600-5200A of the PR for a 130%
etch.
To address your original question about how much PR is required, the 2um PR
thickness should be sufficient. For the typical SiN/PR selectivities in the
range of 1-2:1 (SiN/PR), the 2um thickness gives you some overhead to maintain
your edge profile. At some point though, you may need to include other
characteristics of your etch, such as profile angle and residues to determine if
your process is acceptable.
Robert
-----Original Message-----
From: mems-talk-bounces+rditizio=tegal.com@memsnet.org [mailto:mems-talk-
bounces+rditizio=tegal.com@memsnet.org] On Behalf Of Haider, Ahmad M
Sent: Wednesday, May 08, 2013 9:15 PM
To: Lou Chomas
Cc: mems-talk@memsnet.org
Subject: [!! SPAM] Re: [mems-talk] Resist thickness for nitride etch
Thanks Lou, I got that.
The thing is that my Si wafer has a SiN layer on top of which 2 um resist acts a
mask. I want to do a plasma(Oxford endpoint RIE) etch exposed portions of SiN
(and not Si beneath it). The exposed SiN layer is 400 nm thick and consists of a
series of 25 um squares. Overall, if the whole exposed SiN is etched, I should
get a step depth of 2.4 um on the profilometer. I etch for 130% of the required
etch time to etch all 400 nm of nitride. However, when I measure the step depth
on profilometer, it always shows me that the depth is less than 2.4 um. I can't
fathom the reason behind it. Could it be because my features are very small?
Thanks
Ahmad
----- Original Message -----
From: "Lou Chomas"
To: "Ahmad M Haider"
Sent: Thursday, May 9, 2013 12:00:18 AM
Subject: RE: [mems-talk] Resist thickness for nitride etch
Hi Ahmad, If the layer under the nitride or resist that you are measuring is
also etched (silicon, oxide, etc.) you will measure a step that is the etch
through the material plus the etch into the substrate. So, if you etch just
resist and then measure the thickness before and after, you will need to then
strip the resist and measure the amount of etch into the substrate and subtract
it.
-Lou
> Date: Wed, 8 May 2013 23:33:17 -0400
> From: ahaider3@gatech.edu
> To: mems-talk@memsnet.org; lchomas@hotmail.com
> Subject: Re: [mems-talk] Resist thickness for nitride etch
>
> Hi Lou,
>
> What do you mean by "Be careful to account for any etching into the substrate
if you are using a profilometer to measure the thickness." I use the dektak
profilometer to measure the thickness in order to verify if the RIE plasma
etcher was able to remove all exposed silicon nitride.
>
> Thanks,
> Ahmad
>
> ----- Original Message -----
> From: "Lou Chomas"
> To: "General MEMS discussion"
> Sent: Wednesday, May 8, 2013 5:09:30 PM
> Subject: Re: [mems-talk] Resist thickness for nitride etch
>
> Ahmad, That depends a lot on your process. I would recommend putting some
resist down with your pattern on a test wafer and etching for some amount of
time. Pick something less than your total etch, but not too short. Measure the
thickness of the resist before and after and then you can calculate whether the
thickness will be sufficient. Be careful to account for any etching into the
substrate if you are using a profilometer to measure the thickness. If your
recipe has a lot of oxygen, the rate against the resist will likely be very
high.
> -Lou
> > Date: Wed, 8 May 2013 16:29:49 -0400
> > From: ahaider3@gatech.edu
> > To: mems-talk@memsnet.org
> > Subject: [mems-talk] Resist thickness for nitride etch
> >
> > Hi
> >
> > I am trying to do an anisotropic etch of 400 nm nitride layer in a RIE
machine. A portion of the nitride is protected by a resist layer on top of it.
Can you tell approximate how much thickness of resist would I need so that the
resist doesn't get stripped off during the nitride etch?
> >
> > Thanks,
> > Ahmad
> >
> > _______________________________________________
> > Hosted by the MEMS and Nanotechnology Exchange, the country's leading
> > provider of MEMS and Nanotechnology design and fabrication services.
> > Visit us at http://www.mems-exchange.org
> >
> > Want to advertise to this community? See http://www.memsnet.org
> >
> > To unsubscribe:
> > http://mail.mems-exchange.org/mailman/listinfo/mems-talk
>
> _______________________________________________
> Hosted by the MEMS and Nanotechnology Exchange, the country's leading
> provider of MEMS and Nanotechnology design and fabrication services.
> Visit us at http://www.mems-exchange.org
>
> Want to advertise to this community? See http://www.memsnet.org
>
> To unsubscribe:
> http://mail.mems-exchange.org/mailman/listinfo/mems-talk
>
> --
> Ahmad Haider
> PhD Student, School of Mechanical Engineering
> Georgia Institute of Technology, Atlanta
--
Ahmad Haider
PhD Student, School of Mechanical Engineering
Georgia Institute of Technology, Atlanta
_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org
Want to advertise to this community? See http://www.memsnet.org
To unsubscribe:
http://mail.mems-exchange.org/mailman/listinfo/mems-talk
_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org
Want to advertise to this community? See http://www.memsnet.org
To unsubscribe:
http://mail.mems-exchange.org/mailman/listinfo/mems-talk