Ex Parte Frohberg et al

Patent Trials and Appeals Board

Sep 26, 2014

12359839 - (D) (P.T.A.B. Sep. 26, 2014)

UNITED STATES PATENT AND TRADEMARK OFFICE
____________________

BEFORE THE PATENT TRIAL AND APPEAL BOARD
____________________

Ex parte KAI FROHBERG, VOLKER GRIMM,
HEIKE SALZ, and HEIKE BERTHOLD
____________________

Appeal 2012-007144
Application 12/359,839
Technology Center 2800
____________________

Before ADRIENE LEPIANE HANLON, CATHERINE Q. TIMM, and
JAMES C. HOUSEL, Administrative Patent Judges.

TIMM, Administrative Patent Judge.

DECISION ON APPEAL

STATEMENT OF CASE
Appellants seek review of the Examiner’s decision to reject claims 1–
3, 5–12, and 24–34. We have jurisdiction under 35 U.S.C. §§ 6(b) and
134(a).
We REVERSE.
Representative claim 1, with the limitation at issue italicized, is
reproduced below:
1. A method, comprising:
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Application 12/359,839

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forming a dielectric layer stack above a first transistor
and a second transistor, said dielectric layer stack comprising a
first stress-inducing layer and an etch control layer formed
above said first stress-inducing layer;
performing an etch sequence for selectively removing a
portion of said dielectric layer stack from above said second
transistor;
concurrently recessing metal silicide regions in the
second transistor and reducing a size of a sidewall spacer
structure formed on sidewalls of a gate electrode structure of
said second transistor, while maintaining a sidewall spacer
structure formed on sidewalls of a gate electrode structure of
said first transistor;
forming a second stress-inducing layer above said first
and second transistors; and
removing a portion of said second stress-inducing layer
from above said first transistor by using said etch control layer
as an etch stop material.
(Claims Appendix at Appeal Br. A-1 (emphasis added).) Claim 24, the only
other independent claim on appeal, similarly requires “said reducing being
concurrent with forming recesses in metal silicide regions in the first
transistor.” (Claims Appendix at Appeal Br. A-3.)
The Examiner rejects claims 1 and 24, along with various dependent
claims, under 35 U.S.C. § 103(a) as obvious over Yang1 in view of Smith2
(Ans. 4–6). The Examiner further refers to Choi3 in responding to
Appellants’ arguments (Ans. 9–10).

1 Yang et al., US 2007/0108525 A1, pub. May 17, 2007.
2 Smith, US 6,255,180 B1, patented July 3, 2001.
3 Choi et al., US 6,437,411 B1, patented Aug. 20, 2002. Although the
Examiner did not include Choi in the statement of the rejection, Appellants’
arguments evince an understanding of the Examiner’s reliance upon Choi.
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The Examiner finds that Yang teaches a method including the claimed
steps of forming, performing, forming and removing, and further finds that
Yang teaches reducing the size of a sidewall spacer structure formed on
sidewalls of the gate electrode structure of the second transistor as also
required by claim 1 (Ans. 5). There is no question that Yang does not
expressly disclose recessing metal silicide regions in the second transistor
concurrently with the step of reducing the size of the sidewall spacer
structure (Ans. 5). Rather, the Examiner finds this recessing step to be
inherent in the process of Yang in view of Smith (Ans. 5–6).
The Examiner’s inherency finding is based upon the fact that Yang
teaches reducing the size of the sidewall spacer structure by etching with
CHF3 (Ans. 5, citing Yang ¶ 59). According to the Examiner, Smith teaches
that a plasma provided with CHF3 can be used (Ans. 5). The Examiner
concludes that it would have been obvious to one of ordinary skill in the art
at the time the invention was made to reduce the size of the nitride sidewall
spacer structure of Yang by etching with plasma provided with CHF3 as
taught by Smith and so etching would concurrently recess the metal silicide
regions of Yang at least to a certain degree (Ans. 5–6). To support the
inherent nature of the metal silicide etching, the Examiner also points out
that Choi teaches using a plasma etching technique with, for instance, CHF3
gas, to etch a metal silicide layer (Ans. 9).
In general, a limitation is inherent “if it is the ‘natural result flowing
from’ the explicit disclosure of the prior art.” Schering Corp. v. Geneva
Pharms., 339 F.3d 1373, 1379 (Fed. Cir. 2003) (quoting Eli Lilly & Co. v.

Because the Examiner’s error was harmless, we consider Choi in rendering
our Decision.
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Barr Labs., Inc., 251 F.3d 955, 970 (Fed. Cir. 2001)). “Inherency ... may
not be established by probabilities or possibilities. The mere fact that a
certain thing may result from a given set of circumstances is not sufficient.”
MEHL/Biophile Int’l Corp. v. Milgraum, 192 F.3d 1362, 1365 (Fed. Cir.
1999) (quoting In re Oelrich, 666 F.2d 578, 581 (CCPA 1981)). This is not
to say that the step of recessing must always occur in every embodiment of
the method taught by Yang in order to be inherent; it is possible to establish
inherency by establishing that it would have been obvious to select plasma
etching using CHF3 as taught by Smith, but the Examiner must establish that
once this selection is made, recessing the metal silicide regions will always
occur. See Hewlett-Packard Co. v. Mustek Sys., Inc., 340 F.3d 1314, 1326
(Fed. Cir. 2003) (the fact that changing one setting on a prior art scanner
would cause the scanner to behave in a different manner than claimed did
not defeat a finding of inherency given there was no dispute that another
setting resulted in the claimed operation).
Yang is particularly concerned with the effects of etching with
chemicals such as CHF3 on the metal silicide contact 28. According to
Yang, some damage may take place within silicide contact 28 when etching
away the nitride stress inducing liner 30 using etching chemicals such as
CHF3 (Yang ¶ 58). According to Yang, this damage consists of at least
some part, particularly a surface region, of the silicide becoming
amorphorized (id.). As pointed out by Appellants, amorphorization involves
a change in phase from crystalline to amorphous (Appeal Br. 6). The
Examiner provides no evidence that such a phase transition results in
recessing of the metal silicide regions.
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Even though Yang points out a concern with damaging the metal
silicide contact, and further teaches a step of etching the nitride spacers with
similar etchants as used to etch the nitride liner 30, Yang is completely silent
with regard to any etching or recessing of the silicide contact (Yang ¶¶ 58–
59). This is some evidence that recessing it not necessarily occurring, but
not a level of evidence that indicates the Examiner’s inherency finding is
unreasonable.
More importantly, the evidence as a whole supports Appellants’
argument that recessing does not necessarily occur when plasma etching a
nitride spacer with CHF3 as taught by Smith because
the ability of an etching process to remove one type of material,
and the selectivity of the etching process to this type of material
in relation to other types of material, is determined by the
parameters of the etching process such as the type of etchant,
the flow rate of the etching gas, the temperature, and the
pressure.

(Appeal Br. 7.)
Yang is not specific as to the type of etching used to etch the spacers,
but discloses a number of chemicals typically used when the spacer is
comprised of a nitride (Yang ¶ 59). Specifically, Yang lists CH2F2, CHF3,
CH3F, and O2 (id.). Again, Yang does not disclose any removal or recessing
of the metal silicide contact (id.).
Smith teaches anisotropic etching a nitride layer to form sidewall
spacers using a plasma provided with a carbon-containing species, e.g.,
CHF3, C2H2F4, and/or a fluorocarbon, e.g., C2F6 (Smith, col. 6, ll. 53–57).
Smith also is silent with respect to any etching of metal silicide.
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Choi teaches an isotropic dry etching of a metal silicide layer by a
plasma etching technique used with at least one of CF4, C2F6, CHF3, CO, Ar,
O2, N2, and He-O2 gas in, for instance, a transformer coupled plasma source
type apparatus or a decoupled plasma source type apparatus (Choi, col. 13,
ll. 3–8). Choi discloses specific gas mixtures, flow rates, temperatures, and
pressures and sets conditions to obtain specific etching rates in lateral and
vertical directions (Choi, col. 13, ll. 9–23).
Given that Yang selects the etching parameters to etch the nitride of
the spacers and is silent with respect to any etching of the silicide, it follows
that one of ordinary skill in the art would have selected the etching
parameters to etch the nitride rather than the silicide and Smith and Choi do
not provide evidence that, despite those efforts to limit etching to the nitride,
etching of the silicide would still occur. We cannot say that the Examiner
has provided the level of evidence required to support the finding of
inherency.
The Examiner applies further prior art references to reject other
dependent claims, but the Examiner does not rely upon those references in a
way that overcomes the deficiency discussed above.
Therefore, we do not sustain the Examiner’s rejections.

DECISION
The Examiner’s decision is reversed.

REVERSED

cdc