Most likely your oxide mask was consumed in the first 100 um etch. After
that the wafer was etched uniformly across the wafer that is why you would
measure a step of constant depth.  If so use thicker oxide for mask.
Wen Ko



At 02:17 PM 10/22/98 -0500, you wrote:
>Hello,
>
>   I am trying to anisotropically etch a 200 um well in a silicon wafer
>coated with 1 um of oxide. I'm using KOH mixed at 30% concentration and
>have tried temperatures at 60 C and 70 C. Both trials the etch worked fine
>all the way up to about 90-100 um, and then it just stopped. Even if I
>leave the wafer in for extra hours, the etch still remains at 90-100 um.
>Nothing else has been done to the wafer before this except a BOE etch to
>pattern the oxide. Any ideas would be greatly appreciated.
>
>---Chris
>
>
>
>
Wen H. Ko
Phone: 1-216-368-2071
FAX: 1-216-368-0346
e mail: whk@po.cwru.edu