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

Mary Tang mtang at
Wed Feb 18 08:09:07 PST 2004

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


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>
> To: specmat at
> Cc: sher at
> 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
mtang at

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