Michael Wiemer mwiemer at stanford.edu
Mon Oct 3 16:27:56 PDT 2005


4:00pm Tomorrow (Tuesday) CISX Conference room 316 (on the 3rd floor).
Anyone interested in CF4 etching restrictions in the Pquest is welcome.


> -----Original Message-----
> From: Nickolai Belov [mailto:nbelov at nanochip.com] 
> Sent: Saturday, October 01, 2005 3:50 PM
> To: Michael Wiemer
> Cc: pquest at snf.stanford.edu
> Subject: RE: PQuest
> Hello Michael,
> Yes, I can come over to SNF Tuesday (October 4) at 4 p.m.
> I think it makes sense to invite to the meeting all PQuest users not
> only to opponents of fluorine etch. Would you, please, do 
> this when time
> and place of the meeting is finalized.
> With respect
> Nickolai Belov
> -----Original Message-----
> From: Michael Wiemer [mailto:mwiemer at stanford.edu] 
> Sent: Thursday, September 29, 2005 8:58 PM
> To: Nickolai Belov
> Subject: Re: PQuest
> Hi Nickolai,
> Im trying to see if some of the main opponents to the etch 
> are available
> next Tuesday at 4:00pm. They have not yet replied to my email I sent
> them 
> about this date/time so this is a very tentative date/time. 
> Would you be
> available then if they are as well?
> Ill keep you posted. Hopefully we can settle on a date tomorrow
> (Friday).
> Thanks,
> -Mike
> ----- Original Message ----- 
> From: "Nickolai Belov" <nbelov at nanochip.com>
> To: "Michael Wiemer" <mwiemer at stanford.edu>
> Cc: <pquest at snf.stanford.edu>
> Sent: Thursday, September 29, 2005 2:50 PM
> Subject: RE: PQuest
> 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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