Dear colleagues,

We have the following problem here. The underetching rate of SiON (silicon
oxinitride) during the etching with BOE at room temperature is too high.
Normally, it must be in the range of 1:1 or minimally 1:2 with respect to
the profile depth, but we have 1:6. And the slope shape is very unstable,
always different.

We suspect that our photoresist (HIPR) has bad adhesion to the SiON. We use
HMDS for better adhesion, but it seem to be of very little help.

Does anyone know how to solve the problem?

Many thanks in advance!

Best regards,

--
M.Sc. Denis Petrov

MEMS Foundry Itzehoe GmbH