Dear Julie,

 From my past experiences, it is very likely that your passivation cycle
is a little aggressive. The yellow film you see is very likely to be
polymer deposits. The polymer deposits can also act as micro-mask and
create grass like silicon structures.

To adjust the sidewall profile, you have to deal with a combination of
parameters. In order for me to pin point exactly what you need, please
tell us your current process parameter, characteristics, and SEMs if you
have it available. I'll be more than happy to help you with your process.

Alternatively, our consulting firm (Nanoshift, LLC.) is currently
helping our clients developing next generation MEMS sensors and
actuators. For possible collaborations, please feel free to contact us.
You can also visit our company website at www.nanoshift.net

Cheers,

Ning Chen
Nanoshift, LLC.
www.nanoshift.net