In accordance with an embodiment of the present invention, a semiconductor device
is formed as follows. An exposed surface area of a silicon layer where silicon
can be removed is defined. A portion of the silicon layer is removed to form a
middle section of a trench extending into the silicon layer from the exposed surface
area of the silicon layer. Additional exposed surface areas of the silicon layer
where silicon can be removed are defined. Additional portions of the silicon layer
are removed to form outer sections of the trench such that the outer sections of
the trench extend into the silicon layer from the additional exposed surface areas
of the silicon layer. The middle section of the trench extends deeper into the
silicon layer than the outer sections of the trench.
