Patent ID: 7531842

Claim:
A semiconductor wafer comprising; a device layer of silicon, a micro-machined mirror formed in the device layer, and a substrate layer supporting the device layer, the substrate layer comprising silicon, and having an access bore extending therethrough from a first face of the substrate layer remote from the device layer to a second face of the substrate layer adjacent the device layer for providing access to the micro-machined mirror, the access bore having a tapered lead-in portion tapering from the first face to a first depth to define a cone angle, and extending from the first depth to the second face, the tapered lead-in portion of the access bore being formed to the first depth by a first dry etch using the Bosch process whereby the substrate layer is sequentially subjected to alternating etch and deposition cycles through an etch opening formed in a masking layer formed on the first face thereof, the duration of the respective etch and deposition cycles being controlled for controlling the cone angle defined by the tapered lead-in portion, the access bore being formed from the first depth to the second face by subjecting the substrate layer to a second dry etch through the etch opening and the tapered lead-in portion of the access bore.