Ex Parte Ahn et al

Board of Patent Appeals and Interferences

Jul 30, 2007

10109713 (B.P.A.I. Jul. 30, 2007)

The opinion in support of the decision being entered today
is not binding precedent of the Board.

UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________

Ex parte KIE Y. AHN and LEONARD FORBES
____________

Appeal 2007-1295
Application 10/109,713
Technology Center 2800
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Decided: July 30, 2007
____________

Before BRADLEY R. GARRIS, THOMAS A. WALTZ, and
JEFFREY T. SMITH, Administrative Patent Judges.

SMITH, Administrative Patent Judge.

DECISION ON APPEAL
Statement of the Case
This is an appeal under 35 U.S.C. § 134 from a final rejection of
claims 31-45. We have jurisdiction under 35 U.S.C. § 6.
Appellants’ invention relates to the field of semiconductors and, in
particular, to a copper damascene structure. Representative independent
claim 31, as presented in the Brief, appears below:
Appeal 2007-1295
Application 10/109,713

31. A dual damascene structure comprising:
a substrate;
a metal layer provided within said substrate;
a methylsilsequiazane layer located over said substrate;
a via situated within said methylsilsequiazane layer and extending
to at least a portion of said metal layer, said via being lined with a
tungsten nitride layer and filled with a copper material; and
a trench situated within said methylsilsequiazane layer and
extending to said via, said trench being lined with said tungsten
nitride layer and filled with said copper material.

The Examiner relies on the following references in rejecting the
appealed subject matter:
Chen US 6,352,938 B2 Mar. 5, 2002
Lopatin US 6,368,954 B1 Apr. 9, 2002
Farrar US 6,395,632 B1 May 28, 2002

T. Kikkawa, Current and Future Low-K Dielectrics for Cu Interconnects,”
IEDM Tech. Digest, 253-256 (2000).

J.W. Klaus, S.J. Ferro, and S. M. George, Atomic Layer Deposition of
Tungsten Nitride Films Using Sequential Surface Reactions, Journal of the
Electrochemical Society, 2000, 147, no. 3, 1175-1181 (2000).

Claims 31-43 stand rejected under 35 U.S.C. $ 103 as unpatentable
over Chen in view of Lopatin and the "Admitted Prior Art" or Kikkawa;
claims 34 and 40 stand rejected under 35 U.S.C. § 103 as unpatentable over
of Lopatin et al. and the "Admitted Prior Art" or Kikkawa, further in view of
Klaus; and claims 44 and 45 stand rejected under 35 U.S.C. § 103 as
unpatentable over of Lopatin and the "Admitted Prior Art" or Kikkawa,
further in view of Farrar or the "Admitted Prior Art."

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The issue presented for review is as follows:
Has the Examiner reasonably determined that a person having
ordinary skill in the art would have been led to form a dual damascene
structure comprising a substrate having a metal layer provided within the
substrate, a methylsilsequiazane layer located over the substrate and a via
situated within the methylsilsequiazane layer and lined with a tungsten
nitride layer and filled with a copper material within the meaning of
35 U.S.C. § 103? On this record, we answer this question in the affirmative.
Under 35 U.S.C. § 103, the factual inquiry into obviousness requires a
determination of: (1) the scope and content of the prior art; (2) the
differences between the claimed subject matter and the prior art; (3) the level
of ordinary skill in the art; and (4) secondary considerations (e.g., the
problem solved). Graham v. John Deere Co. of Kansas City, 383 U.S. 1,
17-18, 148 USPQ 459, 467(1966). “[A]nalysis [of whether the subject
matter of a claim is obvious] need not seek out precise teachings directed to
the specific subject matter of the challenged claim, for a court can take
account of the inferences and creative steps that a person of ordinary skill in
the art would employ.” KSR Int’l Co. v. Teleflex, Inc., 127 S. Ct. 1727,
1740-41, 82 USPQ2d 1385, 1396 (2007) quoting In re Kahn, 441 F.3d 977,
988, 78 USPQ2d 1329, 1336-37 (Fed. Cir. 2006); see also DyStar
Textilfarben GmBH & Co. Deutschland KG v. C.H. Patrick Co., 464 F.3d
1356, 1361, 80 USPQ2d 1641, 1645 (Fed. Cir. 2006)(“The motivation need
not be found in the references sought to be combined, but may be found in
any number of sources, including common knowledge, the prior art as a
whole, or the nature of the problem itself.”); In re Bozek, 416 F.2d 1385,
1390, 163 USPQ 545, 549 (CCPA 1969)(“Having established that this
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Application 10/109,713

knowledge was in the art, the examiner could then properly rely, as put forth
by the solicitor, on a conclusion of obviousness ‘from common knowledge
and common sense of the person of ordinary skill in the art without any
specific hint or suggestion in a particular reference.’”); In re Hoeschele,
406 F.2d 1403, 1406-07, 160 USPQ 809, 811-812 (CCPA 1969) (“[I]t is
proper to take into account not only specific teachings of the references but
also the inferences which one skilled in the art would reasonably be
expected to draw therefrom...”). The analysis supporting obviousness,
however, should be made explicit and should “identify a reason that would
have prompted a person of ordinary skill in the art to combine the elements”
in the manner claimed. KSR, 127 S.Ct. at 1731, 82 USPQ2d at 1389.
As evidence of obviousness of the claimed subject matter under § 103,
the Examiner has relied on the disclosures of Chen in view of Lopatin, the
APA and Kikkawa (Answer 3-6).
Chen teaches forming low dielectric layer 204 on copper line 202,
forming dual damascene including barrier 212 and copper 214/216. (See col.
3, l. 32 to col. 5, l. 35 and Fig. 2D). Chen discloses the barrier layer 212 is
formed using a material that can prevent copper atoms from diffusing into
the inter-metal dielectric layer 204 (Col. 3, ll. 47-51). Chen does not
describe the use of methylsilsesquiazane as dielectric material and tungsten
nitride as the barrier layer.
Lopatin describes an improved interconnect structure including
improved barrier and seed layers as well as the method of forming these
structures and layers to overcome recognized drawbacks existing in the
processing of copper interconnect formation. These drawbacks include
difficulties in forming seed and barrier layers in vias and trenches having
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high aspect ratios (i.e., deep trenches having narrow trench widths), poor
step coverage (non-uniform surface coverage), and void formation in the
barrier, seed, and bulk interconnect layers of the damascened process (col. 2,
ll. 52-65).
Lopatin teaches the interconnect structure comprising a tungsten
nitride barrier layer 401, formed using atomic layer deposition (ALD),
which has excellent step coverage and adhesion characteristics to the
underlying low dielectric constant layer (col. 5, ll. 19-40). Lopatin discloses
that typically, the ALD process is performed using a Chemical Vapor
Deposition (CVD) process tool (col. 4, ll. 32-34).
Kikkawa describes multilevel Cu interconnect including a
methylsilsesquiazane (MSZ) layer having a low dielectric constant. MSZ is
disclosed to be directly patterned by use of electron beam lithograph or
ultraviolet lithography. This lithography permits a small feature size of 50
nm for damascene lines and provides that via holes could be directly
patterned without using photoresist and dry etching for interlayer dielectric
formation (See p. 253, left column, p. 254, third paragraph).
APA, specification page 8, line 13 to page 9, line 11, teaches the low
k dielectric constant material, methylsilsesquiazane (MSZ), which can be
conveniently patterned by direct patterning, e.g., by direct EB or UV
lithography. Thus, need for using a photoresist and dry etching is
eliminated. Appellants assert that the teaching of the APA is the same as
Kikkawa (Br. 11).

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The Examiner concluded that
“it would have been obvious to one skilled
in the art in practicing the Chen invention to
have employed the suitable and conventional low-k
dielectric materials including MSZ since such is
conventional and advantageous as evidenced by
APA or Kikkawa wherein the use of MSZ as the
low dielectric constant films would have been
advantageous in eliminating photoresist coating, dry
etching and etchstop layer as delineated in the
instant specification page 8 lines 18-20 and as in
Kikkawa as delineated above. It would have been
obvious to one skilled in the art to have ALD
tungsten nitride as the barrier material since such
would have good step coverage and adhesion
characteristics as taught by Lopatin. The selection
of desired and suitable layer thicknesses for the
dielectric and nitride barrier is matter of routine
optimization well within the purview of one skilled
in the art and as such would have been obvious”
(Answer 4-5).

Appellants contend that a person of ordinary skill in the art would not
have been motivated to combine Chen, which teaches photoresist removal
employing a specific chemistry, with Lopatin, which teaches an ALD/ALE
process for copper structure formation (Br. 9).
We do not agree. As stated above, Lopatin describes an improved
interconnect structure including improved barrier and seed layers as well as
the method of forming these structures and layers to overcome recognized
drawbacks existing in the processing of copper interconnect formation.
Thus, a person of ordinary skill in the art would have used the process of
Lopatin for copper structure formation to overcome the drawbacks
recognized in the art. A person of ordinary skill in the art would have
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reasonably expected that the process as disclosed by the prior art would have
been suitable for the formation of damascene structures.
Appellants contend a person skilled in the art would not have been
motivated to combine the teachings of Chen and Lopatin with Kikkawa
because Kikkawa teaches the direct patterning of MSZ, without using
photoresist and dryetching (See Kikkawa at 2). (Br. 9).
Appellants’ contention is not persuasive. As acknowledged by
Appellants (Br. 9-10), Kikkawa specifically emphasizes that direct
patterning of low-k dielectric films is one of the most promising solutions
for reducing the process cost of future Cu interconnects" (Kikkawa at 2).
Thus, a person of ordinary skill in the art would have used the process of
Kikkawa to gain the advantages disclosed therein. Further, a person of
ordinary skill in the art would have recognized that MSZ could serve as the
barrier layer as disclosed by Kikkawa (Kikkawa at 2).
Claims 34 and 40 stand rejected under 35 U.S.C. 103(a) as being
unpatentable over Chen, Lopatin and APA or Kikkawa as applied to claims
31-43 above, and further in view of Klaus.
The Examiner contends that sequential ALD tungsten nitride would
have been obvious over the teachings of over Chen taken with Lopatin and
APA or Kikkawa, and alternatively, such would have been further obvious
over the teaching of Klaus. According to the Examiner, Klaus describes the
application of tungsten nitride using sequential ALD (Answer 5).
Appellants contend that a person of ordinary skill in the art would also
not have been motivated to combine the references because of the specific
chemistry of each reference (Br. 12).
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This is the same contention that Appellants raised in the discussion of
the previous rejection. As previously discussed, the Lopatin and APA,
Kikkawa references described advances in the formation of damascene
structures. This is also the case for the Klaus reference. As previously
stated, a person of ordinary skill in the art would have viewed the techniques
of the identified prior art references to obtain the advances described therein.
A person of ordinary skill in the art would have reasonably expected that the
process as disclosed by the prior art would have been suitable for the
formation of damascene structures.
Claims 44 and 45 stand rejected under 35 U.S.C. §103(a) as
unpatentable over Chen, Lopatin and the APA or Kikkawa and further in
view of Farrar or the APA (Specification 14, l. 23 to p. 15, l. 3).
The Examiner cites the APA and the Farrar reference as evidence that
it was conventional to couple a damascene structure and an integrated circuit
with a processor (Answer 6).
Appellants’ argument, Br. 14, regarding the suitability of the Farrar
reference as appropriate prior art is noted. The Examiner relied on this
reference as further evidence of the position that the APA described that it
was known to incorporate damascene structures into integrated circuits.
Even assuming the Appellants’ argument is correct, the exclusion of this
reference from the rejection does not detract from the Examiner's position
that a person of ordinary skill in the art would have recognized that
damascene structures could be incorporated into integrated circuits. In fact,
Lopatin describes, in the Background of the Invention portion of the patent,
the suitability of incorporating damascene structures in circuit patterns (See
columns 1-2).
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As a final point with respect to the § 103 rejections, we note that
Appellants base no argument upon objective evidence of nonobviousness,
such as unexpected results.

ORDER
The Examiner's rejection of claims 31-45 under 35 U.S.C. § 103(a) is
affirmed.
No time period for taking any subsequent action in connection with
this appeal may be extended under 37 C.F.R. § 1.136(a)(1)(iv)(2006).
AFFIRMED

TLC/ls

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