Appeal No. 1997-3734 Page 5
Application No. 08/329,806
Turning to page 246 of Wolf, we note that silicon reduction in which WF reacts with solid silicon to
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form tungsten (W) is described as a process of selectively depositing W (p. 246, lines 29-31). On
pages 247 and 248, Wolf describes the blanket CVD W and etchback process as a process involving
hydrogen or silane gas reduction of WF . Therefore, Wolf suggests etching a CVD W layer deposited
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by hydrogen or silane gas reduction to form plugs and runners simultaneously. Wolf does not describe
using a process of silicon reduction to form plugs and runners simultaneously. Looking at the prior art
as a whole, we cannot say that it would have been obvious to one of ordinary skill in the art to eliminate
the step of etching the silicon material of any of the Tadaki, Fujita, Kobayashi or Shioya processes,
convert a silicon layer covering the dielectric to tungsten and then etch the tungsten. There is simply no
reason, suggestion, or motivation in the prior art, as applied by the Examiner, to perform the process in
the claimed sequence.
While, after knowing the direction in which the inventor proceeded, the invention may seem like a
logical step forward, it cannot be said to have been obvious based solely on the information known
prior to the invention. We conclude that the Examiner has not established a prima facie case of
obviousness with respect to the subject matter of claims.
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