Dear Friend,
Are you filtering the NH4F and DI water solution or not?
We are filtering the solution and then mixing the resultant soln. with HF acc.
to our concen. requirement. We have not faced any problems.
Try it.
With good luck,
Sujatha


---------- Original Message -----------
From: "Qiao Dayong" 
To: mems-talk@memsnet.org
Sent: Mon, 25 Dec 2006 10:12:12 +0800
Subject: Re:[mems-talk] BHF precipitates ?

> I have the similiar problems as you. I guess it is because of the
> NH4F. To get rid of this problem, be sure that the container of the
> BHF ethant is good covered to prevent the solution from evaporation.
>
> >Hi all, i prepared 500ml of fresh BHF 1:4 and etched 50 nm of silicon
> > nitride from the entire surface of a 4'' silicon wafer. At the end of the
> > etch i noticed the formation of a salt which covered the entire silicon
> > wafer. In previous etch in the same conditions it never appared. What could
> > it be :o ?