Dear All,

 I have a 4" si wafer(Thickness=550um) and on the top of si surface, I have
7000A thermal SiO2. I need to pattern my oxide and open by BHF. After opening,
I need to do DRIE to etch all way,550um to make a gap inside my wafer. I am
using AZ 4620 as a mask for BHF as well as mask for DRIE. I got 11.35um with:

1- spin HMDS: 3000rpm for 30 sec,
2- Spin AZ 4620: 2000rpm for 30 sec,
3-wait for 15 min to get flat surface,
4- softbake in oven(90c) for 30min,
5- expose 30sec with 23mw/cm2,
6- develope AZ400:DI(1:3) ~4min,
7- Hardbake 120c for 30min.

After doing lithography, I get very good pattern but the problem I have is
that when I put my sample in BHF to open my oxide, it seems BHF attacks AZ
4620 from the border of my pattern. I really appreciate if anybody has a
solution.

Best regards
Hasan Sharifi

Best regards,
Hasan Sharifi