Dear Kamlesh;

As you know (Maybe you don't know) all wet etchents etches at equal rate in
all directions. So wet etch is ISOTROPIC ETCH TECHNIQUE. Even if you increased
the water percent of the etchent you will not obtain the shape that you have
explained in your mail.
I guess, DRY ETCH is very suitable for your fabrication.. You can try it.
Regards.

Tolga YELBOGA
Project Engineer
Nanotechnology Researh Center
Bilkent University
Bilkent, Ankara 06800 TURKEY
Voice: 90-312-290-1020
http://www.nanointurkey.com
http://www.nanotam.bilkent.edu.tr

-----Original Message-----
From: Jaibir sharma [mailto:jaibirs@rediffmail.com]
Sent: Tuesday, September 16, 2008 7:24 PM
To: General MEMS discussion
Subject: Re: [mems-talk] problem in BHF etching

dear kamlesh,

               I agree with Mr sinha.if you have facility you can use
thermal oxide in place of PECVD or LPCVD.We use the following recipe for BHF
(30gm NH4OH in 45 ml of DI water)-after filtering one ninth of filtered
solution we add HFto it.

I hope this may work.


On Tue, 16 Sep 2008 kamlesh_engg@iitb.ac.in wrote :
>hi
>i am doing BHF etch on silicon dioxide deposited on silicon wafer.
>i am using 5:1 BHF etchant
>etch rate 120 nm/min
>i want to etch 1 micron deeep channel with 200 micron width. there are
>multiple channels in parallel each seprated by 6 micron. so i diped my
>sample in BHF for 8.33 min
>but after the etch no channels was formed and everything is etched away.
>can anyone tell me what could be the problem ???