I am looking for service provider for following oxid spec:

Oxid on 4" Si-wafer:
2 layers of oxide (core layer wafer)
Substrate thickness will be 525+/-25 µm
First layer of oxid should have thickness of 15 - 20 µm (micro meter) !!! Very
thick layer
Second layer: Delta 0.75% and layer thickness of 6µm (micro meter)
Please note the exact thickness of 2nd layer and the distributed condition of
refractive index (n)...

If any body has a idea who can supply such service?

Thanks.

Marcus