Inconsistent Teachings Weigh Against a Reason to Modify or Combine Prior Art References

A prima facie obviousness rejection combining multiple disclosures requires a reason to modify or combine the prior art to achieve the claimed invention with a reasonable expectation of success.  In Ex parte Liu (Appeal No. 2018-001645), the Patent Trial and Appeal Board (“Board”) reversed the Examiner’s obviousness rejections because the Board found teachings in the prior art references to be inconsistent such that there would not have been a reason to modify or combine the prior art in the manner as set forth in Appellant’s claims.

The claimed invention at issue was directed to a method for forming a metal gate in a semiconductor device.  The method included a step of “de-oxidizing, using a reducing agent, an oxidation layer formed on the metal gate.”

The Examiner rejected the claimed method as obvious over the combination of Chiang and Wood and also over the combination of Chiang and Ngo.  Although the Examiner acknowledged that the primary reference, Chiang, did not disclose the step of de-oxidizing the oxidation layer formed on the metal gate, she asserted Wood and Ngo, both of which taught the missing step, would be proper to modify Chiang.  In particular, the Examiner asserted it would have been obvious to modify Chiang by Wood “to remove the oxidation layer without damaging the surrounding layers” and it would have been obvious to modify Chiang by Ngo “[to de-oxidize] the oxidation layer … to clean the exposed surface of the metal.”

The Board disagreed and found no evidence of record supported the contention that a person of ordinary skill in the art would wish to remove the oxidation layer described in Chiang.  The Board noted Chiang taught intentionally performing an oxygen treatment to form an oxidized protective layer in a preferred embodiment and Chiang further described that the oxidized protective layer prevented the transistor from being damaged due to etching selectivity.  Wood, on the other hand, taught a de-oxidation process to remove an “undesired” oxide film from a surface of a conductor.  The Board thus held “although described in the context of a preferred embodiment of Chiang’s gate structure, Wood’s teachings … are inapt for Chiang’s gate in which an oxide film is disclosed as protective film, not an undesired deposited film.”  As to the combination of Chiang and Ngo, the Board similarly found the Examiner failed to show Ngo provided a reason for removing Chiang’s protective layer by de-oxidizing using a reducing agent because “such a removal is inconsistent with Chiang’s stated goal.”

The Board emphasized “[the] mere fact that the prior art may be modified in the manner suggested by the Examiner does not make the modification obvious unless the prior art suggested the desirability of the modification.”  Because both Wood and Ngo failed to suggest the desirability of the alleged modification in that their teachings were inconsistent with Chiang’s, the Board did not find the Examiner properly identified a reason to modify or combine the prior art to achieve Appellant’s claimed invention.  Accordingly, the Examiner’s obviousness rejections were reversed.

Takeaway:  When faced with an obviousness rejection in which the examiner modifies a primary reference based on the teachings of one or more secondary references, it is important to scrutinize the examiner’s reason for the modification.  It is worth analyzing whether the identified reason finds support in the evidence of record.  As illustrated by Liu, an examiner’s allegation that there would be a reason to modify or combine the prior art can be rebutted by showing that a secondary reference contains teachings that are inconsistent with the primary reference such that the alleged combination would not work.

Judges:  R. H. Delmendo, J. T. Moore, and M. T. Squire