Status? - DI/Ethanol/HF Request (fwd)

Mary Tang mtang at snf.stanford.edu
Wed Feb 18 10:31:50 PST 2004


Hi Chris --

Yes, I just received an email from Jim and as he was doing only a small
quantity, it was OK'ed to put the waste into the HF drain.  He indicated that
if this becomes a routine procedure, then we will need to reconsider the
ethanol issue.

So, consider this the official SpecMat go-ahead to proceed, with the proviso
that you are the only group doing this and that it is being done relatively
infrequently, with small quantities.


Thanks,

Mary

Chris Kenney wrote:

> Hi Mary,
>
> Thanks for your reply.
>
> I discussed all the details with Jim and Uli in December.
>
> My impression is that Jim has a permit form the county to
> dispose of a modest amount of ethanol down the HF drain.
>
> I was lacking official permission from specmat to proceed.
>
> I will talk to Uli and Jim again to make sure I understand
> the details of how I should do this before performing the etch.
>
> Thanks for your help.
>
> Chris
>
> On Wed, 18 Feb 2004, Mary Tang wrote:
>
> > Wups!  Sorry, I meant to follow up.  I believe Jim McVittie went through
> > this exercise and it was decided that this chemical mixture and the
> > first rinses of labware and wafers, should all go into the HF drain.
> > The only concern is that ethanol is a flammable solvent and that other
> > people using wbgeneral may put HNA (which contains nitric, an oxidizer
> > and a no-no with regard to flammables) into the sink as well.  It is
> > thought that the dilution from other HF tanks and such would make it a
> > non-issue, particularly if the volume and proportion of ethanol were
> > relatively small.  Alternatively, to be on the extra-safe side, it may
> > be better to simply collect the waste in a labelled hazardous waste
> > container and deal with it according to standard procedure.  I'll double
> > check with Jim and get back to you on this.
> >
> > As for the set up -- Uli and Jim Haydon have gone through this before
> > with another user in the last year or so.  Please work with them on the
> > logistics of scheduling, setup, etc. at wbgaas.
> >
> > Again, my apologies for the delay -- I'd forgotten about the SpecMat
> > files.
> >
> > Mary
> >
> >
> > Chris Kenney wrote:
> >
> > > Dear Specmat,
> > >
> > > Could you let me know the status of my request to perform
> > > photo-assisted, electrochemical etching using a DI/ethanol/HF
> > > solution?
> > >
> > > Do you need more information from me?
> > >
> > > Are there issues we should discuss?
> > >
> > > Thank you for your help.
> > >
> > > Chris
> > >
> > > ---------- Forwarded message ----------
> > > Date: Tue, 27 Jan 2004 01:07:38 -0800 (PST)
> > > From: Chris Kenney <kenney at slac.stanford.edu>
> > > To: specmat at snf.stanford.edu
> > > Cc: sher at slac.stanford.edu
> > > Subject: DI/Ethanol/HF Request
> > >
> > > Dear SpecMat,
> > >
> > > Our group would like to develop a photo-assisted, electro-
> > > chemical etch process for making high-aspect ratio holes
> > > in silicon substrates.
> > >
> > > The basic setup involves a container which holds the silicon
> > > wafer against a window on one side. This is sealed using
> > > an O-ring. One side of the wafer will be exposed to the
> > > etching solution and the other side to the ambient air and
> > > a light source.
> > >
> > > The entire apparatus will be set inside a secondary containment
> > > basin. This basin in turn would be inside the sink at the wet bench.
> > >
> > > So there would be 3 levels of nested containers for the solution.
> > >
> > > Electrical contact is also made to the air-side of the wafer.
> > >
> > > There are two platinum electrodes immersed in the solution iside
> > > the container: a reference electrode and a field electrode.
> > >
> > > In use, a potential of about 1 Volt will be applied between
> > > the field electrode and the silicon wafer. We expect total
> > > electrical currents used in the system to be less than
> > > 100 milliAmperes.  The power source will have current
> > > and Voltage limits set near these values for safety.
> > >
> > > The power source is a Keitheley 2400 source meter. It would
> > > be located away from the interior of the wet bench and close to
> > > the floor to avoid a fall hazard.
> > >
> > > The solution will consist of approximately 75% water and
> > > 25% ethanol with a small amount of HF. The typical HF concentration
> > > would be between 4% and 6% by weight.
> > >
> > > It seems that the unusual aspect of this request is the
> > > use of a mixture containing both an acid and a solvent.
> > >
> > > I'm unsure of the best method for disposing of this solution
> > > after use.
> > >
> > > We feel the most appropriate location for this set up is the
> > > GaAs wet bench. We would use less than half of the bench and
> > > would remove our set up when it wasn't in use to avoid
> > > getting in the way of other users.
> > >
> > > We welcome all suggestions and comments on the best way to proceed.
> > >
> > > Feel free to ask any questions.
> > >
> > > We would like permission to use the GaAs wet bench for this work.
> > >
> > > Thanks for your help.
> > >
> > > Chris
> >
> > --
> > Mary X. Tang, Ph.D.
> > Stanford Nanofabrication Facility
> > CIS Room 136, Mail Code 4070
> > Stanford, CA  94305
> > (650)723-9980
> > mtang at stanford.edu
> > http://snf.stanford.edu
> >
> >
> >

--
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
(650)723-9980
mtang at stanford.edu
http://snf.stanford.edu





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