A method for etching to form a planarized surface is disclosed.
Spaced-apart features are formed of a first material, the first material
either conductive or insulating. A second material is deposited over and
between the first material. The second material is either insulating or
conductive, opposite the conductivity of the first material. The second
material is preferably self-planarizing during deposition. An unpatterned
etch is performed to etch the second material and expose the top of the
buried features of the first material. The etch is preferably a two-stage
etch: The first stage is selective to the second material. When the
second material is exposed, the etch chemistry is changed such that the
etch is nonselective, etching the first material and the second material
at substantially the same rate until the buried features are exposed
across the wafer, producing a substantially planar surface.