Patent ID: 8791539

Claim:
A method of forming a die from a wafer stack, the wafer stack being comprised of a silicon device wafer having first and second sides and a silicon substrate wafer, the method comprised of: forming a cavity from the first side of the silicon device wafer, the cavity having an outer perimeter defined by a cavity wall and a cavity bottom surface; forming a tether layer on the bottom surface, the tether layer comprising at least one of silicon oxide, silicon nitride or poly silicon; attaching a silicon substrate wafer to the first side of the silicon device wafer, the silicon substrate wafer extending over the cavity and beyond the outer perimeter of the cavity; thinning the silicon device wafer by removing silicon from the second side of the silicon device wafer thereby forming a die top surface; forming a circuit on the die top surface; forming a trench from the die top surface to the tether layer and which surrounds a region having the circuit, the trench having an inner perimeter and an outer perimeter, the outer perimeter of the trench being less than the outer perimeter of the cavity, the trench having a width defined by its inner and outer perimeters and a depth extending from the die top surface to the tether layer.