Hello;

This is a summary of responses regarding my deep RIE wafer mounting
question posed last week.  I have trimmed out headers and extraneous
information but have taken the liberty of leaving email contact
information for the people who kindly responded to my question.  I
sincerely appreciate all of your responses.

Best of luck with your work, Jack

ps. feel free to contact me with questions or additional suggestions
pps. Original posting:

> Hello;
>
> I'm having the classic problem of masking resist failure during Deep RIE
> etching (STS Etcher).  I have a 70um thick 4" Silicon substrate that must
> be mounted on a handle (carrier) wafer prior to photolith and Deep RIE
> etching.  I have experienced repeated failures with resist mounting
> (gluing) techniques (presumably from masking resist loss due to
> overheating) and am looking for a better mounting procedure or 'glue'.
> The wafer must be able to be released easily from the handle after etching
> and can not tolerate temperatures over ~170C.
>
> The generic recipe I have used for resist mounting of the thin substrate
> is to spin on ~1.6um resist on the handle and to bring the wafers in
> contact before baking.  Aluminum foil is placed over the wafer sandwich
> and a weight (2 pounds) is placed on the wafers.  The assembly is baked at
> 100C for 1-3 hours.  I notice significant resist flow (observed after
> failure) resulting in poor adhesion and likely poor cooling.
>
> Can you recommend a better glue or gluing technique to address the needs
> of thin substrate mounting for Deep RIE etching?
>
> Thank you very much, Jack
>
> Jack Kotovsky (H) (530) 758-6278
----------------
From: "Charles Ellis" 

Hello,

We use Aremco(phone# 914-268-0039) Crystal Bond 503, it is completely
removed in Acetone.  It will not hold up to temperatures much over 100C.

Charles Ellis...
Auburn University Microlab
---------------
From: Chua Bee Lee 

Hi,
I'm not too sure how important planarity of the wafer is to you, but have
you been able to remove your 70um wafer even you done with the DRIE ? From
the trial and error that we did, it seemed that the kind of resist you used
does matters. The thicker resist usually cracks up in the DRIE ( all the
flaked resist in the chamber) and they are almost impossible to remove after
that, no amount of acetone, IPA or methanol helps. I would think trying out
on drops of thinner resist (can't remember the Shipley whatever number)
might be an option worth trying. If planarity is not that critical, you may
want to use just  a couple of drops to hold them together. Otherwise it is
likely that there is will a certain amount of work involved in trying to
take them apart later on.

Good luck.
Beelee.
-------------------
From: Erik Jung 

You might try a material called "crystal bond" from Aremco
(www.aremco.com) or any type of hot wax used for polishing
applications. These materials typically melt around 1400C

Please post your findings!
MbR,
Erik

--------------------------
This has helped me in the past:

Spin the same photoresist on BOTH wafers before putting them together.
This way the surfaces of both wafers are wetted.

You can quantitatively tell how much this helps by
monitoring the wafer surface temperature.
This is easily done by putting temperature dots on the wafer
that turn dark when a certain temperature has been exceeded.
Temperature dots are available from Omega and come in many
temperature ranges. The STS is supposed to run at about 60 C,
so use that as your low end. I have seen wafers get well over 100 C,
so buy dots up to maybe 150 C.
I usually protect the dots with a piece of Kapton tape.
After taping, use a razor blade to make slices to let the air escape under
vacuum.

        --Kirt

*****************************************
Kirt R. Williams, Ph.D., P.E.
[email protected]
*****************************************
-------------
From: [email protected]

I have never used it but someone told me about a material called cool grease.
It must be a vacuum compatible lubricant that is a decent heat transfer
material. Maybe someone else has used it and can identify who makes it. Bob
Henderson
--------------

From: "Shivalik Bakshi" 

You can use Thermal Grease to attach the backing wafer.

The vendor is: AI Technology, NJ
(609) 799 9388

Its like toothpaste. And comes off easily in acetone.

Shivalik
-------------
From: Onnop Srivannavit 

Hi Jack

This is the recipe I use.

I spin HMDS first then

spin 1822 at 2000 rmp for 2 sec.  then put device
wafer on top of the mount wafers
I don;t really need to apply force.
then bake in oven at 110 c for 15-20 min.
If you have more questions, feel free to send me email

Onnop
Dept of Chem Eng.
University of Michigan