Appeal No. 2001-2540
Application No. 09/240,395
However, as pointed out by appellants, the disclosed
function of the diffusion barrier layer 16 in Lur is “to minimize
the diffusion of fluorine atoms from the tungsten silicide to the
gate oxide layer” [column 2, lines 50-51]. Yet, Thomas
specifically discloses, at column 7, lines 42-45, that the
“barrier metal layer is then dry etched with a fluorine or
chloride based plasma which selectively attacks the barrier layer
material.”
If Lur seeks to minimize the diffusion of fluorine atoms,
then it seems reasonable to us that the artisan would not employ
a material in Lur that is taught to be etchable with a fluorine
based plasma, i.e., a material that is to act as a barrier for a
particular thing should not, reasonably, be etchable by that
thing since etchability implies a poor barrier. Now, it may be
that the fluorine etch in an uncontrolled environment will etch
entirely through the “barrier” layer in which case it appears
clear that this layer is not a barrier to fluorine. But Lur
wants to minimize the diffusion of fluorine. Accordingly, it
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