Ex parte Lee et al.

Board of Patent Appeals and Interferences

Jul 29, 1998

07707365 (B.P.A.I. Jul. 29, 1998)

Application for patent filed May 30, 1991.1
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THIS OPINION WAS NOT WRITTEN FOR PUBLICATION
The opinion in support of the decision being entered today
(1) was not written for publication in a law journal and
(2) is not binding precedent of the Board.
Paper No. 16
UNITED STATES PATENT AND TRADEMARK OFFICE
____________
BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________
Ex parte KUO-HUA LEE and JANMYE SUNG
____________
Appeal No. 94-0809
Application 07/707,3651
____________
ON BRIEF
____________
Before GRON, PAK and OWENS, Administrative Patent Judges.
GRON, Administrative Patent Judge.
DECISION ON APPEAL UNDER 35 U.S.C. § 134
1. Introduction
This is an appeal from an examiner’s rejection of Claims 1-3
and 6, all claims pending in this application. Claims 4 and 5
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were canceled by amendment filed July 16, 1992 (Paper No. 7).
Claims 1-3 and 6 stand finally rejected under 35 U.S.C. § 103
over the teaching of Nishizaka, U.S. 4,981,812, patented
January 1, 1991, in view of the combined teachings of Godejahn,
U.S. 4,506,437, patented March 26, 1985, and O’Mara et al.
(O’Mara), U.S. 5,027,187, patented June 25, 1991, based on an
application filed Nov. 6, 1990. Claim 1 reads:
1. A method of semiconductor integrated circuit
manufacturing comprising the steps of:
forming insulating regions on a substrate;
fabricating gate structures on said substrate between
the insulating regions thereby forming regions between
said gate structure and said insulating regions, said gate
structures having insulating sidewalls, a conducting layer,
and an insulating top layer comprising a first material;
making polysilicon plugs between said gate structure
and said insulating regions;
implanting impurities into said plugs;
oxidizing the surfaces of said plugs and said first
material thereby causing said impurities to diffuse into
the substrate to form source/drain regions of a field
effect transistor, said gate structure being between said
source and said drain regions;
patterning to expose at least selected portions of
the gate structure;
etching to remove both the oxide on top of the first
material and said first material, thereby exposing portions
of said conducting layer but leaving oxide on top of the
polysilicon plugs; and
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forming an electrical contact to said gate structure,
said contact extending over said source/drain regions and
extending to said insulating regions.
2. Discussion
When comparing the invention appellants claim to the subject
matter the prior art disclosed or would have reasonably suggested
to a person having ordinary skill in the art, both the examiner
and appellants have in this case overemphasized the semiconductor
integrated circuits depicted in Figs. 1-6 of this specification,
which were manufactured in accordance with the method appellants
claim, and the integrated circuits depicted in Figs. 3(A-L)-5 of
Nishizaka. We believe their focus on the differences between the
structures of the integrated circuits depicted in appellants’ and
Nishizaka’s figures rather than on the steps of the methods of
manufacturing the integrated circuits broadly claimed and
described by the cited prior art has brought confusion to this
case. We remind both appellants and the examiner that the
patentability of the claimed method and its scope and content is
the issue on appeal. Just as a product’s patentability may not
be determined by the patentability of the method by which the
product is made, In re Thorpe, 777 F.2d 695, 697, 227 USPQ 964,
966 (Fed. Cir. 1985) and In re Pilkington, 411 F.2d 1345, 1348,
Appeal No. 94-0809
Application 07/707,365
Polysilicon is another name for polycrystalline silicon. 2
See Godejahn, col. 2, l. 7-9 (“A doped polycrystalline silicon
layer is applied to such a wafer and a silicon nitride layer is
then applied atop the polysilicon layer.”)
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162 USPQ 145, 147 (CCPA 1969), so the patentability of a novel
method of manufacturing a product may not be limited by the
patentability of the product made.
For example, appellants argue that Nishizaka forms trenches
and fills them with polycrystalline silicon which “may be doped
with impurities to be the same conduction type as that of the
substrate” (col. 4, l. 16-18) and emphasize that Nishizaka’s
trenches are not identical in “structure” to the polysilicon2
plugs depicted in their drawings (Reply Brief (RB.), p. 1,
third para.; emphasis added):
There is a fundamental reason why Nishizaka does not
teach or suggest these steps, and this reason is founded
in the details of the structure taught by Nishizaka. The
polysilicon plugs 10 (i.e., the buried polycrystalline
silicon layer) of Nishizaka are not part of or over the
source/drain regions of Nishizaka. Nor are they part of
the device; rather, the trenches are used to separate
elements.
Appellants argue that because of this different “structure”
(id.), “Nishizaka refers to the function of these trenches as
‘element separating trenches.’ Thus, the trenches serve no
purpose other than to isolate elements; that is, they do not
function as source/drain regions” (Brief on Appeal, p. 3, first
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para.). Some confusion appears to stem from appellants’ apparent
acknowledgment thereafter that Nishizaka does make polysilicon
plugs and may implant impurities into said plugs at least within
the meaning of the terms in their claims. Appellants state,
“[t]he polysilicon plugs 10 (i.e., the buried polycrystalline
silicon layer) of Nishizaka are not part of or over the
source/drain regions of Nishizaka” (RB., p. 1, third para.;
emphasis added). Had appellants emphasized comparative function
rather than comparative “structure,” this appeal might not have
been necessary.
That the examiner’s ultimate decision on the patentability
of the claimed subject matter is erroneous in this case is not
readily apparent from the respective analyses of Nishizaka’s
disclosure in the Examiner’s Answer (Ans.) and Appellants’ Brief
on Appeal (Br.). However, because we find that the impurities
with which Nishizaka’s buried polycrystalline silicon layer 10
may be doped would not “diffuse into the substrate to form
source/drain regions of a field effect transistor” (emphasis
added), we are constrained to reverse the examiner’s holding of
unpatentability under 35 U.S.C. § 103 over the combined teachings
of Nishizaka, Godejahn, and O’Mara.
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The examiner finds (Ans., pp. 4-5, bridging para.):
Nishizaka teaches a process of forming an integrated
circuit substantially as claimed including forming an
oxide layer 3 and insulation regions 2 on a substrate 1,
depositing a polysilicon layer 4 on said oxide film 3,
forming an oxidation film 5 and a silicon nitride layer 6 on
said polysilicon layer 4 (Fig. 3(A)), etching said layers 4,
5, and 6 to form gate structure having insulation sidewalls
9, a gate electrode 4, and insulation layers 5 and 6 on top
of said gate electrode 4 (Fig. 3(C)), forming polysilicon
plugs 10 between gate electrode 4 and insulation region 2
(Fig) 3(E)), doping impurities into said polysilicon
plugs 10 (col.4, lines 10-20), oxidizing surface of said
polysilicon plugs 10 to form an oxidation layer 11 on top
of said plugs 10, connecting a source electrode 16 to said
polysilicon plugs 10 (col. 5, lines 1-4 and Fig. 3(L)),
etching said oxidation film 5 and said nitride layer 6
to expose a portion of gate electrode 4, and forming
an interconnection layer 12 connected to said exposed
electrode 4.
Appellants do not contest these findings. Moreover, after
examining Nishizaka’s disclosure, we cannot conclude with
confidence that the examiner’s findings are clearly erroneous.
Fig. 3A shows that “a p-semiconductor substrate 1 is
selectively oxidized on a predetermined region to provide
a field oxidation film 2" (col. 3, l. 53-55), “a gate oxidation
film 3 . . . is formed . . .” (col. 3, l. 55-56), “a poly-
crystalline silicon layer 4 . . . is grown on the substrate 1
having the gate oxidation film 3 thereon” (col. 3, l. 57-60),
“a mask oxidation film 5 . . . is formed on the polycrystalline
silicon layer 4" (col. 3, l. 60-62), and “a silicon nitride film
6 is formed on the mask oxidation film 5" (col. 3, l. 63-65).
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Fig. 3A does not show a plurality of “insulating regions on
a substrate.” However, Nishizaka teaches at col. 1, l. 18-24:
In a conventional process for providing the
trench separation, field oxidation films are formed
at predetermined regions on a p-semiconductor substrate
by use of a selective oxidation method at a first stage.
Although plural field oxidation films are provided on
plural regions of the substrate, a limited section
including only one field oxidation film will be
explained hereinafter.
Fig. 3B shows that all the aforementioned films and layers
“and an upper portion of the substrate 1 are selectively etched
to provide element separating trenches 8" (col. 3, l. 66, to
col. 4, l. 2).
Fig. 3C shows that the “inner surface of the element
separating trenches 8 is oxidized to provide trench oxidation
films 9" (col. 4, l. 3-5).
Fig. 3D shows that “the trench oxidation films 9 are removed
on the bottom surface” (col. 4, l. 10-11), “a polycrystalline
silicon layer 10 is grown on an overall surface . . . so that the
element separating trenches 8 are buried with polycrystalline
silicon layer 10" (col. 4, l. 12-16) which “may be doped with
impurities to be the same conduction type as that of substrate 1"
(col. 4, l. 17-18), and “the polycrystalline silicon layer 10 is
etched back on the silicon nitride film 6" (col. 4, l. 18-20).
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Figs. 3B-C depict gate structures fabricated when the
structure of Fig. 3A is selectively etched to form a repeat of
gate structures and separating trenches positioned between
insulating regions (not depicted).
Fig. 3D depicts “polysilicon plugs” made by applying
polycrystalline silicon over the entire substrate and filling the
trenches. Nishizaka’s polycrystalline silicon-filled trenches
may be implanted or “doped with impurities to be the same
conduction type as that of the substrate 1” (Nishizaka, col. 4,
l. 16-18).
Figs. 3E-F show that “the polycrystalline silicon layer 10
is etched back . . . by use of the silicon nitride 6 as a mask”
for the gate structure (col. 4, l. 21-23) and “insulating
oxidation films 11 are formed on the top surface of the
polycrystalline silicon layer 10 and on the sides of the
polycrystalline silicon layer 4" (col. 4, l. 23-26) and on the
silicon nitride 6 used as a mask.
However, we can and do find that Nishizaka’s formation of
insulating oxidation films 11 on the top surface of the
polycrystalline silicon layers 10 and on the silicon nitride 6
mask does not cause the impurities with which polycrystalline
silicon layer 10 may be doped “to diffuse into the substrate to
form source/drain regions of a field effect transistor.” We note
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that this finding is entirely consistent with the examiner’s
finding that Nishizaka “fails to show forming source and drain
regions by implanting dopants into silicon plugs and diffusing
impurities from the doped polysilicon plugs into the substrate”
(Ans., p. 5, first full para.).
Our finding appears also to be consistent with the
conventional processes of making the integrated circuits which
Nishizaka describes in the BACKGROUND OF THE INVENTION, cols. 1-
2. Nishizaka teaches that conventionally (col. 1, l. 31-51;
emphasis added):
. . . a trench oxidation film is formed on the
inner surface of the element separating trenches, and
an oxidation film is then formed on the silicon nitride
film and the trench oxidation films by providing an oxide
having a high re-flow property such as BPSG, etc. After
this, the high re-flow property oxidation film is re-flowed
by a heat treatment of approximately 900 to 1000 C.O O
At the following stage, the re-flowed oxidation
film is etched back to be left in the element separating
trenches, so that the top surface of the film is above
the top surface of the p-semiconductor substrate, and
the silicon nitride film and pad oxidation film are
successively removed. Then, a gate oxidation film is
formed on the p-semiconductor substrate thus processed,
and a polycrystal silicon layer and a WSi layer are
successively grown on the gate oxidation film.
Thereafter, a gate electrode is provided by
defining the polycrystalline silicon layer and the
WSi layer to be a predetermined pattern, and impurities
are then injected to provide a source and a drain of a
transistor . . . .
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Nishizaka teaches that by burying polycrystalline silicon
layer 10 in trenches encased by an oxidation film 9, substrate 20
is effectively held at the ground potential in a stable manner
(Nishizaka, col. 5, l. 28-33). Nishizaka nowhere suggests that
his process causes the impurities with which the polycrystalline
silicon layer 10 “may be doped” to diffuse into the substrate
to form source/drain regions of a field-effect transistor (Ans.,
p. 5, first full para.). To the contrary, Nishizaka expressly
states (col. 5, l. 44-58):
Therefore, [the (sic)] following advantages are obtained
in the invention.
. . . . .
(2) A short circuit is avoided between digit lines,
because no charge is accumulated in a polycrystalline
silicon layer which is buried into element separating
trenches. Furthermore, if the polycrystalline silicon
layer is connected to a semiconductor substrate, and
connected through a source electrode to the ground
potential, the semiconductor substrate is easily connected
to the ground potential, so that the transistor operates
with a stable characteristic.
It is difficult for this panel to understand how the
polycrystalline silicon layers buried into the separating
trenches can “form source/drain regions of a field effect
transistor” and impart the advantage of functional stability to
Nishizaka’s invention when doping the buried polycrystalline
silicon layers with impurities is entirely optional.
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We have given the language of appellants’ claimed process
its broadest reasonable interpretation consistent with the
description of the invention in the specification. In re Zletz,
893 F.2d 319, 321, 13 USPQ2d 1320, 1322 (Fed. Cir. 1989). We
have reviewed the examiner’s findings with regard to the
teachings of the cited prior art. While we cannot agree with
appellants’ view that the “element separating trenches . . .
serve no purpose other than to isolate elements” (Br., p. 3,
first para.), we hold that the examiner’s rejection is neither
supported by objective evidence nor reasonable. We restate here
that the examiner has the initial burden to establish a prima
facie case of obviousness under 35 U.S.C. § 103. In re Fine,
837 F.2d 1071, 1073, 5 USPQ2d 1596, 1598 (Fed. Cir. 1988).
Appellants argue that (1) the examiner is reading Nishizaka
too broadly and (2) Nishizaka’s polysilicon plugs 10, i.e., the
buried polycrystalline silicon layers 10, are not part of or over
the source/drain regions (RB, p. 1, third para.). Appellants’
argument is supported by the greater weight of evidence in this
record. However, our deliberations are not therefore put to
rest. Appellants’ claims stand rejected under 35 U.S.C. § 103 in
view of the combined teachings of Nishizaka, Godejahn and O’Mara.
The examiner seems to rely upon the teachings of Godejahn
and O’Mara for motivation to form a field effect transistor
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having source and drain regions by oxidizing doped polysilicon
plugs and/or by implanting dopant impurities into polysilicon
plugs and diffusing impurities from polysilicon plugs into a
substrate (Ans., p. 5, final two para.). What the examiner has
not explained and we do not find apparent is a reason why a
person having ordinary skill in the art would have sought to
alter Nishizaka’s device in a manner inconsistent with its design
to function in a manner which undermines its advantages.
3. Conclusion
Accordingly, we reverse the examiner’s rejection of
Claims 1-3 and 6 under 35 U.S.C. § 103 in view of the combined
teachings of Nishizaka, Godejahn and O’Mara.
REVERSED
Teddy S. Gron )
Administrative Patent Judge )
)
)
)
Chung K. Pak ) BOARD OF PATENT
Administrative Patent Judge ) APPEALS AND
) INTERFERENCES
)
)
Terry J. Owens )
Administrative Patent Judge )
Appeal No. 94-0809
Application 07/707,365
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Mr. P.V.D. Wilde
General Attorney
AT&T Bell Laboratories
600 Mountain Avenue
Murray Hill, NJ 07974-0636