Appeal No. 2000-1810
Application No. 09/148,556
trichloride, the examiner has not established why one of
ordinary skill in the art would have considered Cote's etchant
composition for tungsten to be suitable for the silicon oxide
etchable layer of Huang. Moreover, as emphasized by
appellants, Cote actually teaches a plasma gas mixture
comprising chlorine gas and oxygen as the etchant composition
which provides "a combination of high tungsten etch rate, high
etch selectivity to silicon oxide, and an anisotropic etch
profile" (column 4, lines 66-68). Indeed, Cote gives no
indication that an etchant comprising an oxygen containing gas
and boron trichloride is even a non-preferred embodiment of
the invention. While Cote teaches that chlorine-based plasmas
reduce the non-uniformity problem and undercut problem of
fluorine-based plasmas, the reference also discloses that "the
other chlorine-based chemistries provided a fairly low
tungsten to BPSG etch rate ratio . . . [and] the maximum
tungsten etch rate achieved by these chlorine-based plasmas
was on the order of 600 angstroms per minute" (column 5, lines
40-45). Consequently, we find that Cote fails to teach the
use of the claimed etchant composition for tungsten, let alone
the silicon oxide material of Huang. Moreover, Cote only
-4-
Page: Previous 1 2 3 4 5 6 7 Next
Last modified: November 3, 2007