Ex Parte Wang

Board of Patent Appeals and Interferences

Jan 24, 2006

10071809 (B.P.A.I. Jan. 24, 2006)

The opinion in support of the decision being entered today was not
written for publication and is not binding precedent of the Board.

UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________

Ex parte TINGHAO F. WANG
____________

Appeal No. 2006-0293
Application No. 10/071,809
____________

ON BRIEF
____________

Before OWENS, WALTZ and TIMM, Administrative Patent Judges.
WALTZ, Administrative Patent Judge.

DECISION ON APPEAL
This is a decision on an appeal from the primary examiner’s final rejection of
claims 1, 3 through 12, 14, 15, 21 through 23, 25 and 27, which are the only claims
pending in this application. We have jurisdiction pursuant to 35 U.S.C. § 134.
According to appellant, the invention is directed to a method of etching a metal
silicide layer while fabricating an integrated circuit using a chlorine/oxygen gas
environment at a pressure of approximately 2 to 40 mili-Torr and an oxygen

concentration of greater than or equal to 25% by volume (Brief, page 2).
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Representative independent claim 1 is reproduced below:
1. A method comprising, etching a metal silicide layer during fabrication of an
integrated circuit in a Cl2/02 environment having an 02 concentration of greater than or
equal to 25% by volume,

wherein the Cl2/02, environment is provided at a pressure of approximately 2-40
mili-Torr, and wherein the etching is a metal silicide etch that is selective to poly-silicon
with a ratio of etch rates of at least 30.

The examiner has relied upon the following references as evidence of
obviousness:
Tsai 5,880,033 Mar. 09, 1999
Langley et al. (Langley), “One-Chamber Polycide Sandwich Etching,” Semiconductor
International, pp. 95-97, October 1989.

Appellant relies upon the following reference as evidence of non-obviousness:
Nojiri et al. (Nojiri), J. Vac. Sci. Technol., B14(3), May/June 1996, pp. 1791-1795.

Claims 1, 3-12, 14, 15, 21 and 27 stand rejected under
35 U.S.C. § 103(a) as unpatentable over Tsai (Answer, page 3). Claims 22, 23 and 25
stand rejected under 35 U.S.C. § 103(a) as unpatentable over Tsai in view of Langley
(Answer, page 4). We reverse both rejections on appeal essentially for the reasons
stated in the Brief and those reasons set forth below. Pursuant to our authority under
37 CFR § 41.50(a)(1)(2004), we also remand this application to the examiner for action
consistent with our remarks below.
OPINION
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A. The Rejections on Appeal
The examiner finds that Tsai discloses a method of etching metal silicide using
chlorine and oxygen under the same pressure and power ranges as disclosed and
claimed by appellant, with flow rates of 20-800 sccm of chlorine and 1-50 sccm for
oxygen (Answer, page 3). The examiner recognizes that Tsai does not disclose the
claimed oxygen concentration of greater than or equal to 25% by volume (id.).
However, the examiner finds that Tsai teaches that a high concentration of oxygen is
desirable and etches the metal silicide at a much greater rate (Answer, sentence
bridging pages 3-4). The examiner also finds that Tsai teaches that the power ratio may
be optimized (Answer, page 4). From these findings, the examiner concludes that it
would have been obvious to one of ordinary skill in this art to determine the optimum
parameters through routine experimentation to etch
the metal silicide at a high rate and selectivity with respect to the underlying polysilicon
layer (id.). We disagree.
As correctly argued by appellant (Brief, page 4, footnote 2, and page 9, footnote
6), and apparently overlooked by the examiner (Answer, page 5), the disclosure of Tsai
mistakenly recites that the etching selectivity “increases” with increasing flow rates of
oxygen while in fact the data of Tsai establish that etching selectivity decreases with
higher flow rates of oxygen since the polysilicon etch rate increases with increasing flow
rates of oxygen (compare Tsai, col. 7, ll. 63-66, with Figure 4, and also compare Tsai,
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col. 8, ll. 5-7, with Figure 5). It is clear from Figure 5 of Tsai that the selectivity
decreases when the oxygen flow rate is increased from 0 to 10 sccm, although the
selectivity increases at a constant oxygen flow rate when the flow rate of nitrogen
increases. It is also clear from Figure 4 of Tsai that, at any nitrogen flow rate, the
polysilicon etching rate undesirably increases with increasing oxygen flow rates from 0
to 10 sccm.
Additionally, as correctly argued by appellant (Brief, page 6), Tsai teaches away
from the use of “excessively high” flow rates of oxygen (Tsai, col. 7, ll. 15-20).
Furthermore, Tsai teaches preferred volume flow ratios where the maximum volume
flow of oxygen could be 13.89% (col. 8, ll. 17-22, where the oxygen/nitrogen ratio is 5:1
and the chlorine to oxygen+nitrogen ratio is 5:1). Finally, Tsai exemplifies about a 3%
by volume oxygen plasma gas to achieve a selectivity of about 4-5 (col. 9, ll. 23-45).
“Under the proper legal standard, a reference will teach away when it suggests
that the developments flowing from its disclosures are unlikely to produce the objective
of the applicant’s invention. In re Gurley, 27 F.3d 551, 553 (Fed. Cir. 1994).” Syntex v.
Apotex, 407 F.3d 1371, 1380, 74 USPQ2d 1823, 1830 (Fed. Cir. 2005). General
skepticism of those in the art is relevant and persuasive evidence of non-obviousness.
See Gillette Co. v. S.C. Johnson & Son, Inc., 919 F.2d 720, 726, 16 USPQ2d 1923,
1929 (Fed. Cir. 1990). The disclosures of Tsai, as discussed above and in the Brief,
certainly suggests developments that are unlikely to produce the objective of appellant’s
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invention, namely the ratio of etch rates of at least 30. Furthermore, the examiner has
not commented on the Nojiri article cited by appellant (Brief, page 2), which teaches that
the etch rate of tungsten silicide increases up to an oxygen concentration of 10% but
etching suddenly stops when the oxygen concentration exceeds 25% (page 1792, left
column and Figure 2).
For the foregoing reasons and those stated in the Brief, we determine that the
examiner has failed to establish a prima facie case of obviousness with respect to the
reference evidence. Therefore we cannot sustain the examiner’s rejection of claims 1,
3-12, 14, 15, 21 and 27 under section 103(a) over Tsai.
With regard to the rejection of claims 22, 23 and 25 (Answer, page 4), the
examiner applies Langley to show use of a “breakthrough” etch. Therefore, Langley
fails to remedy the deficiencies in the rejection discussed above. Accordingly, this
rejection is also reversed.
B. The Remand
Pursuant to our authority under 37 CFR § 41.50(a)(1)(2004), we remand this
application to the jurisdiction of the examiner for actions consistent with our remarks
below.
The examiner and appellant should consider the patentability of the claimed
subject matter in view of the requirements of
35 U.S.C. § 112, first paragraph, regarding the scope of the enabling disclosure.
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Appellant is claiming a method that is the same or substantially the same as disclosed
by Nojiri, as discussed above. Nojiri discloses an etching method for the same tungsten
silicide/polysilicon layers as here claimed, under the same pressure and other reaction
parameters, and tests the process at oxygen concentrations of 25% as per appellant’s
claim 1 (pages 1791-1792). However, as noted by appellant (specification, page 7, ll.
15-17), appellant discloses and claims a selectivity ratio of at least 30 while Nojiri
discloses that the “etching suddenly stops” at an oxygen concentration of 25% (page
1792, left column). The only difference between the method of Nojiri and appellant’s
disclosure is the teaching of using a “breakthrough” etch using carbon tetrafluoride
(specification, page 7, ll. 17-20). Accordingly, the enabling disclosure appears to be
lacking any teachings of how to achieve the desired result as compared to the
undesired results of the prior art method, absent the use of a breakthrough etch using
carbon tetrafluoride. This “breakthrough” etch is only specifically claimed in claim 23 on
appeal. Therefore it would appear that the remaining claimed subject matter is not
supported by an enabling disclosure, since Nojiri is evidence that the claimed objective
cannot be met by following the process as claimed. See In re Mayhew, 527 F.2d 1229,
1233, 188 USPQ 356, 358 (CCPA 1976).
Accordingly, we remand this application to the jurisdiction of the examiner for
consideration of the issue raised above.

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This application, by virtue of its “special” status, requires an immediate action,
MPEP § 708.01 (D).
REVERSED & REMANDED

TERRY J. OWENS )
Administrative Patent Judge )
)
)
)
) BOARD OF PATENT
THOMAS A. WALTZ ) APPEALS
Administrative Patent Judge ) AND
) INTERFERENCES
)
)
)
CATHERINE TIMM )
Administrative Patent Judge )

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