Patent Prosecution Tip: Challenging § 103 Obviousness Rejections Based on Markush Groups

DEREK FAHEY, ESQ.

A recent Patent Trial and Appeal Board decision provides patent attorneys and applicants with a useful strategy for challenging obviousness rejections under 35 U.S.C. § 103: check whether the Examiner’s characterization of the prior art matches what the reference actually teaches.

In Ex parte Minfeng Chen and Shuo-Yen Chou, Appeal 2025-002620, the PTAB reversed an obviousness rejection involving claims directed to an extreme ultraviolet (“EUV”) mask. The claims required an absorber comprising “an alloy of two or more of Sn, Ni, Te, Co, In, and Sb.”

The Examiner relied on a prior art reference US 2018/0031964 A1 to Jindal (“Jindal” to supply the missing alloy limitation, characterizing the reference as teaching “at least one of” certain listed metals. But Jindal actually used the closed Markush language “selected from the group consisting of.” The PTAB found that the Examiner had “misquote[d] Jindal” and emphasized that “Jindal nowhere states that an absorber layer may comprise more than one material.”

I. Why This Matters in Patent Prosecution

For patent practitioners, the distinction can be critical. A prior-art reference identifying A, B, C, or D as alternative materials does not necessarily teach combining A+B, A+C, or another combination. An Examiner may still establish obviousness with appropriate evidence and reasoning, but the mere disclosure of individual alternatives does not necessarily supply the claimed combination.

The PTAB also rejected reliance on generic language stating that features, structures, materials, or characteristics “may be combined in any suitable manner.” The Board characterized that language as “boilerplate” and found that it did not teach combining two absorber materials into an alloy. Similarly, defining what constitutes an “alloy” did not explain why a person of ordinary skill would have made the particular claimed combination.

II. Practitioner Takeaway

When evaluating a § 103 obviousness rejection, patent counsel should look beyond whether every claim element can somehow be found among the cited references. The more important questions may be: Does the prior art actually teach the claimed combination? Has the Examiner converted a list of alternatives into a disclosure of multiple selections? Does generic “may be combined” language genuinely support the proposed modification? And is there evidence explaining why a person of ordinary skill would have made the claimed combination without using the applicant’s disclosure as a roadmap?

These questions can be particularly important in patent applications involving chemical compositions, semiconductor materials, pharmaceuticals, polymers, alloys, and other technologies where the distinction between selecting individual alternatives and combining them is technically significant.

In Ex parte Chen, the PTAB ultimately concluded that the Examiner’s analysis “improperly relies upon hindsight reconstruction of the claimed invention” and reversed the § 103 rejection of all 20 claims.

For patent applicants and counsel facing similar obviousness rejections, the decision is a reminder that effective patent prosecution often turns on the details. Carefully testing an Examiner’s characterization of the prior art - and identifying where the rejection moves from what a reference actually teaches to what it arguably could be modified to teach - can expose an important weakness in an obviousness rejection.