PQuest

Nickolai Belov nbelov at nanochip.com
Thu Sep 29 14:50:24 PDT 2005


Hello Michael,

Thank you for your response.

I'll be happy to meet and discuss the proposed "no CF4 without O2" rule.

Process/tools related restrictions usually require either executive
decision or have to be proven experimentally.

You are trying to solve the CF4 etching issue using executive decision.
If the decision will be made then I'll follow it. 

I believe that experimental comparison of results of Cl2 etching versus
(CF4 etching - oxygen cleaning - Cl2 etching) should be the main
argument in the discussion. It is likely that we'll be able to find a
"common ground".

Please, suggest meeting time and I'll try to be there. I hope that some
other PQuest users will join us as well.

I'll be out of area this Friday (09/30).
I have several regular meetings in my schedule (Monday 1 p.m. - 3 p.m.;
Wednesday, Friday 9-10 a.m.).

With respect

Nickolai Belov
Tel: (510)-770-2516

-----Original Message-----
From: Michael Wiemer [mailto:mwiemer at stanford.edu] 
Sent: Thursday, September 29, 2005 1:54 PM
To: Nickolai Belov
Cc: 'Rafael Aldaz'
Subject: PQuest

Hi Nickolai,

First, I am sorry this has taken so long. And second, I brought up the
issue
of testing the CF4 etching in the Pquest with other GaAs users. As you
can
see below, it did was not met with much enthusiasm. I am sure you do not
like this proposal (see below). So perhaps the best thing at this point
is
to get you together with some of the strongest opponents to this etch,
along
with Jim McVittie, and we can discuss.  If you are interested, when are
you
going to be on Campus?

Please read below. This was sent out to the Pquest list. Im not sure if
you
are on the pquest list and I wanted to make sure this got to you.

Pquest Users,

Over the last couple of weeks GaAs users - mostly Harris group people
who
are by far the group with the most people using the tool - have
discussed
the question of opening the tool for CF4 etching. The question was
basically, "Should CF4 etching of SiO2 and other materials widely used
in
the lab be allowed in the Pquest and if so, under what circumstances".
Nickolai Belov proposed a test to investigate the effects of CF4 on GaAs
etching to help answer this question. In the end, little support was
voiced
for the tests proposed by Nickolai Belov (test CF4 effect on GaAs
etching),
or for Flourine etching in the Pquest in general. I will try to
summarize
the main points which came out in the discussion in this email.

Currently, O2 with small amounts of CF4 is used to clean the chamber as
well
as etch some polymers (BCB for example). No one really had a problem
with
this as it is a necessary cleaning procedure, nor with the BCB etch,
being
so similar to the clean. 

The issues, as well as I can summarize them here, follow below. While
reading, keep in mind that this is not a "etch anything" tool. It is the
only III-V etch tool in the lab and its integrity as a III-V etch tool
must
be maintained. This can only be done with good policy (I fully recognize
that policy on this tool has not always been stellar). And any good
policy
is simple, so here we go....

1.) CF4 polymerization

Instead of using an oxygen rich plasma like the CF4/O2 clean, the
proposed
etching would involve little to *no* O2 and 100% CF4. With this kind of
etch, there is the concern that this etch will deposit/build up a
teflon-like polymer film in the chamber. 

2.) F affects the GaAs (and, more dramatically, the AlGaAs) etch rate.

This this is well documented. There is no desire among the users to
re-prove
this. Conditioning the chamber after a F etch can return the chamber to
good
Cl2/BCl3 GaAs etching condition. The question is what kind of
conditioning
and how long should the conditioning be. However, there was little
desire to
put the effort into researching this. Just like tests which may address
problem 1 above, the test to address this problem is time consuming and
may
ultimately be inconclusive. And any test only tests 1 particular
condition -
other CF4 users in the future would surely want to alter the process a
little and then we can be faced with the same problems all over again -
this
leads to the next problem....

3.) What about other people and the future? 

One of the biggest problems which came out during the discussion is that
etching of SiO2 opens the door to more SiO2 etching. 90% of the lab
users
are Silicon people and if the word gets out that the Pquest can be used
for
SiO2 etching, there would probably be significantly more interest in the
future. Considering there are at least 6 SiO2 etch tools in the fab, why
do
we have to make the Pquest another one? People do not want to open this
tool
to SiO2 (Fluorine) etching and then deal with these issues above
continually
as the next and then the next person decides that Pquest is their
best-bet
tool for their Fluorine etch. If we make an exception here, or there, we
will CONSTANTLY have to deal with issues of process compatibility. The
tool
must be maintained as a III-V etch tool. Why do these questions never
come
up with the P5000? Answer: because there is a strong policy on that tool
about what gases/materials can be run in each chamber. 

Proposal:
We propose that CF4 etching is eliminated from the "list" of possible
Pquest
etches. High O2-low CF4 flow etches will still be OK. And the week will
stay
split: GaAs etching Wed-Sat, non-GaAs etching Sun-Tues. If you want to
use
CF4 in the Pquest and are unhappy by this, perhaps the best way to
communicate is to get together (email is so difficult and time
consuming).
Contact people: Rafael Aldaz (aldaz at stanford.edu) and Mike Wiemer
(mwiemer at stanford.edu). We are in contact with other GaAs users.










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