Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


KOH - backside etch - frontside protection

KOH - backside etch - frontside protection

KOH - backside etch - frontside protection

Hi all,

I'm planning on a process where I want to create membranes in a KOH etch from the back side but the front-side is already structured and must remain dry. I want to control the membrane thickness (~18µ) optically. Does anyone
have experience with such a process or knowledge on the equipment I would need?


RE: KOH - backside etch - frontside protection

You will need front side (and back side is masking required) polyimide spin on coater and cure oven.
You will need a solvent bench to remove polyimide and possibly a oxygen plasma resist strip system.
Do you need to remove backside silicon and stop 18um from the surface? Without an etch stop this will be difficult to do accurately with just KOH.
There are semiconductor step prifiler measurement systems that use a probe needle to detect step heights which would work. They are expensive but available on the 2nd hand market.
Another less accurate way is that KOH will etch along the crystal plane so you can measure the width of the slope under a microscope and calculate the depth.

RE: KOH - backside etch - frontside protection

A further comment to the crystal plane preference, it also means that you'll lose roughly the thickness of the wafer laterally because of the etch slope.  

So, a 0x0 um finished feature on the frontside will occupy about 500x500um on the backside, assuming a 19 mil etch depth.  This can result in structural problems with the circuitry if you haven't allowed for that.  Flexing of the membrane can could generate unforeseen leakage currents in the surrounding circuitry.


FAQ731-376: Eng-Tips.com Forum Policies

RE: KOH - backside etch - frontside protection

Thanks guys, I found a company which provides mechanical fixtures for wafers. These fixtures keep one side dry while exposing the other to KOH. They also offer systems for electrochemical etch-stop to control the membrane thickness.
(check ammt.com)

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close