mask for KOH etching

[Yahong Yao]

Dear All,

Recently, I always met problems when I conducted the KOH through wafer
etching.  Film stack is: Nitride (4000A)/PolySi(3000A)/Nitride(4000A).
Backside has the same stack.  I opened the backside for KOH etching.
Front side is covered by Nitride (no KOH openings).  After two hours KOH
etching, the front side had a lot of blisters.  It seems Nitride was
broken therefore the underlying PolySi was etched rapidly and worsened
the situation.   More interesting thing was when I didn't open the
backside, just threw a wafer with film stack in KOH, after two hours,
the front side was good.  No blisters were observed.

I tried different Nitride recipe: LONH378 and NITRIDE2.  Both had the
problem.  I changed to TMAH solution, problem was still there.  Any
suggestion?  Thank you in advance.

Yahong
--
Yahong Yao, Ph. D.
Phone:  (408) 252-6410 x. 407
Mobile:(408) 718-8831
Fax:      (408) 252-6430