mtang at stanford.edu
Tue Jul 8 09:06:49 PDT 2008
Hi Houbi --
I would suggest looking into HCl. It's similar in many ways to HF and I
think has some etching effect on oxide, but I am not sure how much -- I
think it is quite slow. But if you are only removing native oxide, then
time is less of a concern. The nice thing about it is that it also is
pretty effective at decontaminating. The normal prediffusion clean
includes a 5:1:1 water:H2O2:HCl dip -- I suspect the H2O2 might oxidize
the silicon surface, so an additional HCl dip without H2O2 might be in
I would suggest checking in the literature -- there was a lot published
in the 60's-70's on various cleans (most notably by "Kern" of "Vossen
and Kern" fame published the definitive articles in the "RCA Review" in
1970 -- the library has bound copies.) They investigated a lot of
different chemicals before deciding on the famous RCA clean.
If you do decide to change the clean, please submit a SpecMat request,
so we can ensure that your process is compatible with the wet bench and
furnace you will be using.
Houbi Nguyen wrote:
> Hi Mary. Yes, I may have mentioned this to you before, but I wasn't
> sure of my analysis plans back then either.
> Now, my process is to clean the native oxide off new wafers, grow
> roughly 10 nm of oxide on the surface, then go through a very simple
> photolithography procedure resulting in a chrome or chrome/aluminum
> grid pattern on the surface of the wafer. At the end of my
> processing, I'll have a 5 x 5 mm substrate with ~10 nm of oxide
> exposed on the surface and divided into squares, where the lines of
> the squares are the chrome or chrome/aluminum (I try to evaporate on
> 5-10 nm of metal using the Innotec).
> I typically use Tylan 1 or 2.
> The only requirements for my interface are a very thin layer of oxide
> (although not as thin as native oxide) and as little fluorine as I can
> possibly have on the surface. I've been told that fluorine, once it
> gets on the surface and stays on the surface, can become embedded in
> the oxide layer grown on the surface of wafers and I would like to
> prevent that from happening.
> The reason why I even care about how much fluorine is on the surface
> is that I am conducting mass spectrometry experiments on organic
> samples that I will later deposit onto these substrates. Fluorine is
> a potential label for some of the molecules I'm looking at, but the
> instrument I'm using is so sensitive that it is giving me background
> counts of fluorine, even in the very minute amounts coming from an HF
> dip during pre-diffusion cleaning. I know this because I've examined
> an empty substrate (no sample deposition yet) and I am getting
> fluorine counts (and counts that can vary by quite a bit from one
> substrate to another). I'd like to minimize these counts as much as
> possible and right now, for lack of a better source of contamination
> or background, I think the HF dip is responsible for the presence of
> fluorine on the wafers.
> It's my understanding that the HF dip removes chemical oxides on the
> wafer surface during pre-diffusion cleaning. If I could find an
> alternative to HF or any solvent normally used for cleaning, that
> would be excellent. Thanks for the help Mary.
> On Jul 8, 2008, at 8:24 AM, Mary Tang wrote:
>> Hi Houbi --
>> I think we talked about this before, but I don't remember the
>> outcome... I remember you did not want any fluorine on your wafer
>> surface. What is on your wafer at this point? And what is your next
>> step in your process? (i.e., which furnace?) And what is critical
>> for your interface, other than excluding fluorine? What kind of
>> analysis are you planning to do?
>> I ask, because there are alternatives to HF -- not so much for
>> removing native oxide, but for decontamination. So, it would be good
>> to get a better idea of what your objective or experimental plan is....
>> Houbi Nguyen wrote:
>>> Hello everyone. I have a question regarding native oxide etching.
>>> Does anyone know of a method by which I can strip off native oxide
>>> (i.e., for a pre-diffusion cleaning) without using a
>>> fluorine-containing mixture, specifically HF? Thanks for the help.
>> Mary X. Tang, Ph.D.
>> Stanford Nanofabrication Facility
>> CIS Room 136, Mail Code 4070
>> Stanford, CA 94305
>> mtang at stanford.edu
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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