Re: How to etch silicon on pieces

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 Si
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 box
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.

Ekin

On Nov 28, 2007 3:08 PM, Josh Ratchford <joshuar@stanford.edu> 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@stanford.edu> 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@stanford.edu ), 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@snf members received.