Hi,

You may try for Tetra Methyl Ammonium Hydroxide (TMAH). To get smooth walls
you may need to try different concentartions of TMAH in water. This etchant
is not as anisotropic as KOH and can produce little wider undercut.

regards,

Samadhan



----- Original Message -----
From: "Xiaoguang Liu" 
To: "General MEMS discussion" 
Sent: Tuesday, August 18, 2009 8:56 PM
Subject: Re: [mems-talk] KOH etch


Given his requirement of vertical sidewalls with >12:1 aspect ratio,
I don't think HNA is even an option. KOH etch is pretty much the
only reasonable choice.

However, he needs to be reminded that he will have to align the
crystalline faces well with the features on his mask and that he will
only get vertical walls in one direction.

Best
Leo