Hi Martyna and everyone,

Yes, I have the same problem. Basically, I want to do deep TMAH
etching (20wt%, 90C, magnetic stirrer 250rpm) on one side of the Si
chip (300um thickness) while the other side is protected since it has
Al patterns. At this moment, I am using a Teflon jig with two O-rings
(Aflas, alkali-resistant O-rings) to protect back side while exposing
front side for the etching. The etching is stable. However, the
problem is TMAH still leak into the back side of the chip and attack
my Al pattern.

I also tried to cast a thin layer of PDMS between the chip and the jig
to enhance the sealing. It is getting a little bit better but still Al
was attacked. So as what Martyna mentioned, I would appreciate it very
much if anyone suggest me a special coating (wax, resins...) or a
protection fixture configuration that eliminate the TMAH leaking.

@: Martyna: I don't know if you can try a jig with your Si etching. If
you like I will send you the design of my Teflon jig. My email is:
[email protected]

Best regards,
Le Nam, Graduate student
Ritsumeikan University, Japan

On 9/28/06, Martyna Grydlik  wrote:
> Hello,
>
> Does anybody know any product (polymer, photoresist, protective coating)
> that could protect my metal contacts (Au/Al) while long time Si etching
> of the backside? For etching I use TMAH at 80°C.  I tried already
> several products including BCB, SU8, ProTek etc., but all of them simply
> peel off from Au surface. I would appreciate any hint or suggestion.