How to remove only metal layer of IC chip not polysilicon layer?

[lakot18326]

Due to the presence of the metal layer on the IC chip, it is very difficult to determine how polysilicon layer is connected to the metal layer (first image).
I decided to remove the metal layer of the chip using a low concentration of hydrofluoric acid.
The second image provide useful information about the diffusion layer, but unfortunately, the polysilicon layer was also etched.
What material should I use to selectively etch only the metal layer?

[magic]

You need to remove some oxide that the metal is embedded in and you have just learned the hard way that stuff which attacks oxide attacks silicon too. I haven't done such things, but AFAIK people who do rely on careful timing to avoid overetching.

You could look here, but again, it's just one source I know about, I haven't done it.

[T3sl4co1l]

The metal is aluminum; anything which attacks it will do.  HCl and KOH are likely candidates, with KOH discouraged as it can attack SiO2.

If the full chip (minus bond pads, fuses, etc.) is passivated, this may not be very effective, and you'll have to carefully dose (time and concentration) HF to etch the passivation.

AFAIK, HF without oxidizing power (no excess nitrate, chlorine, O2, etc. dissolved) doesn't attack Si, or at least anywhere near as fast, so maybe you left it on much too long, or had too much oxidation available.  Doing a little bit at a time, and maybe adding a few granules of a reducing agent (sulfite, thiosulfate) to the solution, might help.

Tim

[lakot18326]

As expected, the right timing and concentration was the answer. Thank you for the good information.