Appeal No. 1998-1578
Application No. 08/543,827
Neither Larson nor Scott describes a step of annealing
the titanium nitride barrier layer under the condition recited
in appealed claim 1 or 14 before depositing the platinum
layer. However, Ho teaches as follows:
Titanium nitride (TiN) is used as a barrier
layer. However, TiN as sputtered suffers from two
defects. First, TiN has a columnar structure. If a
transmission electron micrograph were taken of the
TiN, the TiN would appear as groups of columns or
grains. The gaps between the columns are referred
to as grain boundaries. Grain boundaries cause
problems with barrier layers. The grain boundaries
form a path through which the metal can migrate to
reach the underlying substrate. If the metal
migrates through the barrier layer, spike formation
or metal diffusion into the substrate can occur.
Second, sputtering TiN itself causes a problem.
A simple overview of sputtering techniques will
indicate how the problem develops. A sputtering
chamber is comprised of the following parts: a
substrate, a target, the sputtering chamber itself,
gases, and a power generator. The power generated
can be direct current (DC), radio frequency (RF),
etc. The generator ionizes the gas to form a
plasma. The plasma is directed toward the target.
In this case, reactive sputtering is utilized. The
nitrogen in the plasma reacts with the surface of a
titanium target to form a thin layer of TiN. In
addition, the plasma hits the target causing the TiN
to be stripped away from the target. The TiN coats
the substrate and the walls of the sputtering
chamber.
Sputtering has problems. If the sputtering
occurs faster than the plasma reaction at the target
(converting the surface titanium to TiN), some
titanium will be sputtered form [sic, from] the
target before it si [sic, is] converted to TiN. The
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