Appeal No. 2004-0859
Application 08/866,456
to substantially uniformly enlarge and taper the opening in the
insulating layer, and 3) anisotropically etches the opening in
the insulating layer through to the source/drain regions (col. 2,
line 61 - col. 3, line 4; col. 4, line 66 - col. 5, line 27).
Liu states that this method forms a tapered opening with a metal
step coverage improvement over the state of the art of about 20-
60%, where metal step coverage is “the ratio of thickness of the
thinnest metal in the contact hole to the metal thickness on the
horizontal area” (col. 3, lines 5-9). This step coverage is
shown in Liu’s figures 4-6 wherein metal layer 36 fills the lower
portion of the opening and covers metal layer 34 which lines the
opening, but does not fill the opening’s upper portion.
The examiner argues that it would have been obvious to one
of ordinary skill in the art to use Liu’s method to form the
lower and upper portions of Sato’s opening to improve step
coverage of a metal wiring layer at the opening (answer, pages 6,
8, 13 and 15-16). Unlike Liu, however, Sato completely fills the
opening with metal and then etches back the metal to the
insulating layer upper surface (col. 5, lines 10-17). The
examiner has not established that one of ordinary skill in the
art would have been led by the applied references to use Liu’s
technique, which only partially fills the opening with metal, to
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