How to etch silicon on pieces

S. Ekin Kocabas kocabas at
Wed Nov 28 15:44:30 PST 2007

Hi Josh, and members of SNF,

I forgot to follow up on my previous email which was sent on June 10. Here's
what I do to etch pieces of SOI wafers

   1. Thin down the Silicon thickness of the SOI wafer to desired value
   via cyclic oxidation, wet etching and ellipsometric thickness measurement of
   2. Cleave the wafer into pieces
   3. Coat the piece with with 5% PMMA ( 4000rpm at Headway, gives around
   220nm thickness measured by Woolam ellipsometer. To be able to measure PMMA
   thickness with Woolam first use a dummy Si wafer, coat it with PMMA, extract
   PMMA characteristics and save it as a Cauchy material. Then create a stack
   of Silicon-Oxide-Silicon-PMMA model, do spectroscopic scans and normal fits)
   4. Do e-beam lithography with Raith
   5. Develop using standard recipe (30 sec in 1:3 MIBK:IPA , 30 sec in
   IPA, blow dry)
   6. Stick the piece at the center of a clean dummy wafer using Kapton
   tape that can be purchased from the stock room. Have separate sharp pointed
   tweezers for this purpose. In more detail (thanks to Rohan for showing all
   this to me)
   1. Stick strips of tape cut by scissors on the outside of a tweezer
      2. Use a razor blade to cut the strips into fine lines of
      desired width&length while the strips are stuck on the box
      3. Use a fine pointed tweezer to pick up the cut strips
      4. Stick the sample to the carrier wafer with tape on all four
      corners. Use one tweezer to stabilize the piece, another to pick
up a strip
      of tape from the top of the tweezer box and stick the sample
      7. Use P5000 Chamber C, standard poly etch recipe (always double
   check that the recipe is not modified by comparing against the printed copy
   in the Chamber C folder at P5000) with BT=10 sec, ME=10 sec, OE = 0 sec,
   Pump=120 sec . This etches away 60-70nm Si while not etching all the way
   through the PMMA
   8. Get rid of the PMMA by dipping it in heated Remover PG (around 40
   celcius) for 10mins at the solvent wet bench. The ultrasonic takes forever
   to heat, so use the hot plate with a thermometer. Use a long beaker that can
   be found next to wbgeneral. Use acetone, methanol, IPA to finish off.

I hope this helps. It's always best to double check stuff, so if you'd like
to do this yourself, I'd suggest you start with a sample that does not have
a lot of time invested on it.


On Nov 28, 2007 3:08 PM, Josh Ratchford <joshuar at> wrote:

> Hi Ekin,
> I searched my email account to find information from lab users about
> silicon etching.  Do you mind forwarding me the information you recieved
> from your inquiry about silicon etching.
> Thank you,
> Josh
> On Jun 10, 2007 3:30 PM, S. Ekin Kocabas <kocabas at> wrote:
> > Dear Labmembers,
> >
> > I would like to be able to etch silicon on SOI pieces. While I'm waiting
> > for the SOI wafers to arrive, I'm testing the process flow with full
> > silicon wafers. I have used P5000 to etch silicon on full wafers, and
> > the results look alright. Which tools do you use to do silicon etching
> > on pieces with PMMA on them? What kind of problems do/did you face?
> >
> > I'd appreciate any information you can provide. If you could reply to my
> > email ( kocabas at ), I'll compile the answers in a nice form
> > and send it to the labmembers list.
> >
> > Thank you,
> >
> > Ekin
> >
> > PS: I sent a very similar email to the Raith list earlier today. It was
> > recommended that I send the email to the general labmembers email list.
> > I'm sorry for the duplicate emails that raith at snf members received.
> >
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