Dear Ahmed,
If you want to etch a zone of your chip in order to make your custom sensor or device you must be sure of this:
First, your design must include an open window in the passivation layer. This provides an access to the volume of oxide or metal that you need to etch before reaching the substrate.
Second, as the open window in the passivation layer, it is important to define a "no-fill area" for the metal dummies, it is usually called "no fill" layer.
If the design does not achieve the design rules you have to inform the foundry that you accept all the risks of fabricating your chip section.
Greetings.