Appeal No. 95-2454
Application No. 07/396,733
dioxide. Doo, col. 2, lines 30-32. Doo teaches that channels partially filled with silicon dioxide with the
remainder a high temperature material such as polycrystalline silicon will also act as an insulator. Doo, col.
5, lines 12-15.
The person having ordinary skill in the art would have recognized that the incorporation of
Murphy’s depression filling technique into Frouin’s process would eliminate (1) the need to fill the
depressions with polycrystalline silicon material and (2) the subsequent grinding to remove the
polycrystalline silicon material from the surface while still providing the necessary insulation. The person
having ordinary skill in the art would have had a reasonable expectation that silicon oxide alone could be
substituted for polycrystalline silicon and silicon oxide layer in light of Doo’s teaching that silicon oxide and
a combination of silicon oxide and polycrystalline silicon are interchangeable for the purpose of electrical
isolation. Doo, col. 5, lines 12-16. Accordingly, we conclude that the subject matter of claims 14 and
36 would have been prima facie obvious.
Applicant argues that it would not be commercially practical to apply Murphy’s teaching relating
to the filling depressions with oxide to the process described by Frouin. Brief, p. 12-14. The basis for
this assertion is that Murphy relates to a thin epitaxial layer of the order of 1 micron and Frouin relates to
an epitaxial layer of about 10 microns. Brief, pp. 12-13. Applicant asserts that “it is extremely unlikely
that it would be commercially feasible to grow a thermal recessed oxide to a thickness in the vicinity of 10
microns.” Brief, p. 12.
In our view, the argument relating to commercial feasibility is not relevant to the obviousness issue
before us. First, nothing in applicant’s claims limits the claims to (1) any particular thickness of the epitaxial
layer or (2) to a commercially feasible process. Second, as noted by the Federal Circuit:
That a given combination would not be made by businessmen for economic
reasons does not mean that persons skilled in the art would not make the
combination because of some technological incompatibility. Only the latter fact
would be relevant.
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