Appeal No. 95-1487
Application 07/813,387
the mask and method of making it" as disclosed by Kawabata
differs from the claimed construction and method only by the use
of MgO as an etch stop layer instead of the aluminum oxide etch
stop layer of Kawabata (main answer, page 3). Appellants do not
contest these findings (main brief, page 3).
The examiner states that Nakagawa "teaches the use of
magnesium oxide as an etching stop layer arranged between the
layer to be subjected to etching" (main answer, page 4). The
examiner alleges that magnesium oxide and aluminum oxide are used
"interchangeably" as is well known in the art and, "because the
transmittance properties of the materials used for the etch stop
layers is [sic, are] known," it would have been obvious to adjust
the material composition to achieve the desired result of
transmittance in a known region (main answer, page 4).
Appellants contend that Nakagawa is not related to optical
devices and provides no description or suggestion regarding the
optical properties of the MgO etching stopper (main brief, page
3). As appellants argue, it is essential that the material
forming the mask be substantially transparent to the optical
beam. Appellants further argue that, in the absence of the
knowledge that MgO has a high transparency for ultraviolet
radiation, one of ordinary skill in the art would never be led to
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