Appeal No. 1999-1871 Page 5
Application No. 08/688,337
Appellant acknowledges that thermal oxides such as silicon dioxide were utilized in the
semiconductor processing arts at the time of Higashi’s invention (Brief at 4). However,
Appellant argues that if were obvious to substitute a high temperature oxide for the aluminum
sacrificial layer taught in Higashi, Higashi would have utilized such an oxide yet nowhere does
Higashi mention the use of alternative sacrificial layer material to provide higher process latitude
(Brief at 4-5).
Appellant’s argument misses the mark. The fact that Higashi does not expressly describe
the use of thermal silicon dioxide does not necessarily mean that its use was not obvious to those
of ordinary skill in the art at the time of the invention. An express suggestion to substitute one
equivalent for another need not be present to render such substitution obvious. In re Fout, 675
F.2d 297, 301, 213 USPQ 532, 536 (CCPA 1982). Here, Higashi suggests that other selectively
etchable layers can be used as the sacrificial layer and the Examiner has established that silicon
dioxide was just such a known sacrificial layer. That is enough to establish a prima facie case of
obviousness.
Claim 2
Claim 2 further limits the sacrificial layer composition to phosphosilicate glass (PSG).
The Examiner has established that the use of PSG as a sacrificial layer was known in the prior art
at the time of invention as evidenced by Mastrangelo and Fan (Answer at 4). Appellant argues
that none of the prior art discusses the importance of certain advantages associated with using
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