Mathew,

As to your data, your KOH concentration is not 30% (wt), it is about 20% (wt).
The etched silicon surface will be rough in this concentration. Increasing KOH
concentration to 45% may help.

Thomas

sheeja mathew  wrote:
Hi all,

  Sub: Precipitate during KOH etching

We have a problem of black precipitate formation

during KOH etching of Si. SiO2 is masking layer,

Si is being etched in 30% KOH(30g KOH and 100ml

 DI water)   solution with 30ml tert-butanol*.

The thickness of Si to be etched   is 10-12um.

The tert butanol is added to avoid undercuts which

will destroy   the right-angled beams.

The etching solution is kept at 80C and once the

 solution stabilizes at the temperature the sample is

 put. A black deposition   is found on the sample especially on

the pattern. Once the black precipitate   comes, further etching doesn’t take
place.

Can anyone please suggest a solution?

Thank you

Sheeja  * Reference : I Zubel, M Kramkowska(2002) The effect of alcohol
additives on   etching characteristics in KOH solutions. Sensor and Actuators A,
101 255-261