균등론과 출원경과금반언

The Doctrine of Equivalents and the Prosecution History Estoppel

The Doctrine of Equivalents(DOE) is a judicial creation that allows patentees to establish infringement liability beyond the textual scope of a patent’s claims where the accused product or process is insubstantially different from the patented invention. The most commonly asserted legal limitation on the DOE is the Prosecution History Estoppel(PHE), which provides that a patentee may not seek to ensnare under DOE any subject matter that it surrendered in order to obtain the patent. The most difficult issue regarding PHE is whether the patentee may narrow its claim via amendment in response to the patent office rejections and yet still retain some scope of equivalents beyond the literal scope of the amended claim, that is the scope of the estoppel. In the U.S., there have been a few different approaches regarding this issue. Although the Court of Appeals for the Federal Circuit(CAFC) adopted a flexible approach in its early decisions, the CAFC announced a complete bar rule in 2000. However, the U.S. Supreme Court flatly rejected the complete bar rule and adopted a rebuttable presumptive bar rule in its 2002 Festo decision. In a few post-Festo CAFC decisions, patentees successfully rebutted the Festo presumption where the amendment was merely tangential to the contested element in the accused device. In Japan, several commentators and a few lower court decisions seem to apply flexible bar rule. Examination of 10 Supreme Court cases which dealt with PHE shows that there is no hard and fast rule in Korea. This article points out that the flexible bar approach should be applied when examining the subject matter surrendered by the narrowing amendment because, under the complete bar rule, narrowing amendments automatically destroy all possible scope of equivalents.