Hi,

I would like to seek help from anybody who has experience in the wet
etching.

The followings are what I have done.
First, I have a patterned polysilicon structure covered with undoped TEOS
oxide around the sidewall of the moving beams. Next, I am going to use
buffered HF (BOE) to remove part of the undoped TEOS with photoresist as the
mask. My objective is to wet etch until certain remaining oxide thickness.
So, what I have done is I checked the remaining oxide thickness after a
certain time. If it is not etched until the desired oxide thickness, I will
repeat the wet etch a few times. However, the uniformity of the wafer did
not look very good. My question is whether I can repeat the wet etch for a
few time or I should do it only once but using a monitoring wafer as a
reference? I suspect there is something that might have formed on top of the
oxide and block the oxide from being etched further. Can somebody help to
answer my queries? Thanks.

Dr Ruan Aiwu

Microfabrication Lab
School of Electronical &Electronic Engineering
Nanyang Technological University
Nanyang Avenue
Singapore 639798
Tel: (65)7906387