Ex Parte Ward et al

Board of Patent Appeals and Interferences

Jun 18, 2009

10884930 (B.P.A.I. Jun. 18, 2009)

UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________

Ex parte ALLAN WARD III, JASON PATRICK HENNING,
HELMUT HAGLEITNER, and KEITH DENNIS WIEBER
____________

Appeal 2009-002256
Application 10/884,930
Technology Center 2800
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Decided:1 June 18, 2009
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Before JOSEPH F. RUGGIERO, MAHSHID D. SAADAT,
and ROBERT E. NAPPI, Administrative Patent Judges.

SAADAT, Administrative Patent Judge.

DECISION ON APPEAL

1 The two-month time period for filing an appeal or commencing a civil
action, as recited in 37 C.F.R. § 1.304, begins to run from the decided date
shown on this page of the decision. The time period does not run from the
Mail Date (paper delivery) or Notification Date (electronic delivery).
Appeal 2009-002256
Application 10/884,930

Appellants appeal under 35 U.S.C. § 134(a) from a Final Rejection of
claims 34 and 35. We have jurisdiction under 35 U.S.C. § 6(b).
We affirm.

STATEMENT OF THE CASE
The invention
Appellants’ invention relates to an improved ohmic contact to a layer
of silicon carbide (SiC), wherein the contact is made of a deposited film of
silicon and nickel. (Spec. 3.) According to Appellants, the composition of
the contact film has the formula Ni1-xSix where 0.5 < x < 0.67. (Id.)
Independent claim 34 is representative and reads as follows:
34. A semiconductor device comprising:

a layer of silicon carbide;

a contact on said silicon carbide layer and demonstrating ohmic
character, said contact being formed of a composition having the
atomic percentage formula Ni1-xSix where 0.5 < x < 0.67;

said ohmic contact having a resistivity of at least about 10-4
ohm-cm2; and

a metallization layer on said ohmic contact.

The Rejections
The Examiner relies on the following prior art references in rejecting
the claims:
Cole US 6,759,683 B1 Jul. 6, 2004
(filed Aug. 27, 2001)
Ogino JP 07-099169 A Apr. 11, 1995

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Claims 34 and 35 stand rejected as being unpatentable under
35 U.S.C. § 103(a) over Ogino and Cole.
Claims 34 and 35 stand rejected as being unpatentable under
35 U.S.C. § 103(a) over Ogino.
Rather than repeat the arguments here, we make reference to the
Appeal Brief (filed Feb. 19, 2008) and the Answer (mailed May 14, 2008)
for the respective positions of Appellants and the Examiner.2 Only those
arguments actually made by Appellants have been considered in this
decision. Arguments which Appellants did not make in the Brief have not
been considered and are deemed waived. See 37 C.F.R. § 41.37(c)(1)(vii).

ISSUES
Rejection of claims over Ogino and Cole
The Examiner found that Ogino discloses all the limitations of claim
34, with the exception of a metallization layer on the ohmic contact (Ans. 4).
The Examiner reasoned that a person of ordinary skill in the art would
reasonably have been expected to use the known structure of metallization
over an ohmic contact disclosed in Cole to arrive at the claimed invention
(id.). Appellants argue that Cole describes a nickel-silicon contact on silicon
carbide to be undesirable and therefore, teaches away from combining
Cole’s metallization layer with the ohmic contact of Ogino (Br. 3-4).
Accordingly, the first issue is as follows:
1. Have Appellants shown that the Examiner erred in rejecting
claims 34 and 35 under 35 U.S.C. § 103(a) based on combining Ogino and

2 An oral hearing was held for this appeal on Jun. 9, 2009.
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Cole to teach or suggest the claimed subject matter related to a metallization
over a nickel-silicon ohmic contact?
Rejection of claims over Ogino
Regarding the claim rejection over Ogino alone, the Examiner reasons
that Ogino teaches the claimed nickel-silicon composition ratio while the
specific claimed resistivity results from using the same contact material as
recited in the claims (Ans. 5-6). Appellants respond that the composition
ratio disclosed in Ogino covers a larger range than what the claims require
and therefore, does not render the claims obvious since the parameter to be
optimized was not recognized to be a result-effective variable (Br. 5).
Therefore, the following question is the second issue before this panel:
2. Have Appellants demonstrated error in the Examiner’s
reasoning as to whether the claimed range of nickel-silicon composition
ratio reads on the larger range disclosed by Ogino?

FINDINGS OF FACT
The following findings of fact (FF) are relevant to the issues involved
in the appeal.
Ogino
1. Ogino relates to a method for depositing a nickel-silicon (Ni-Si)
alloy layer for forming an ohmic electrode on a silicon carbide substrate,
wherein the nickel composition is at a specific atomic %. (Abstract.)
2. Ogino conducts a heat treatment process at a low temperature in
order to prevent graphite from being precipitated on the surface of the ohmic
contact. (Id.)
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3. The Ni-Si alloy is formed in such a way that Ni and Si have an
atomic ratio of 38:62 followed by annealing in a vacuum at 600°C for 30
minutes. (Id.)
4. Ogino further discloses that a good ohmic property is displayed
when the composition of Ni is at an atomic ratio between 33% and 67%.
Such ratio is disclosed to result in an ohmic contact without the need for
high temperature heat treatment and without the problem of precipitating
graphite on the face of the electrode. (Id.)
Cole
5. Cole relates to a metallization scheme and fabrication process
for forming a low resistance, thermally stable ohmic contact on an n-type
silicon carbide (SiC) substrate using post-deposition annealing. (Col. 1, ll.
19-24.)
6. Cole describes nickel ohmic contacts to silicon carbide, in the
form of a Ni2Si-SiC contact as the standard contact to SiC substrates that
demonstrates a resistivity of less than 5.0x10-6 ohm-cm2. (Col. 2, ll. 12-17,
41-47.)
7. However, Cole identifies certain problems with the nickel
ohmic contact resulting from the high temperature annealing process used in
forming the contact, such as broadening of the contact layer thickness or
metal-SiC interface expansion, rough interface morphology, carbon
segregation at the metal SiC interface, and roughening of the contact surface.
(Col. 2, ll. 44-48.)
8. Cole provides for a more stable interface by using a
Platinum/Titanium/Tungstensilicide/Nickel (Pt/Ti/WSi/Ni) stack on the n-
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type Silicon carbide (n-SiC) substrate for forming an improved ohmic
contact. (Col. 7, ll. 51-58.)
9. Cole’s Figure 5 is reproduced below:

10. Cole shows the 850°C isothermal section of the Ni-SiC-C
ternary phase diagram in Figure 5, which is characterized by the absence of
Ni-C compounds and therefore determined by the nickel-silicide, δNi2Si
(orthorhombic phase), which is in equilibrium with both, C and SiC. In this
ternary phase diagram, no tie line Ni-SiC exists indicating that Ni is not in
thermodynamic equilibrium with SiC and demonstrating the existence of the
Ni-Si reaction product, Ni2Si, spatially adjacent to the SiC substrate. (Col.
10, ll. 10-20.)

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PRINCIPLES OF LAW
Section 103 forbids issuance of a patent when “the differences
between the subject matter sought to be patented and the prior
art are such that the subject matter as a whole would have been
obvious at the time the invention was made to a person having
ordinary skill in the art to which said subject matter pertains.”
KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398, 406 (2007).
When a work is available in one field of endeavor, design
incentives and other market forces can prompt variations of it,
either in the same field or a different one. If a person of
ordinary skill can implement a predictable variation, § 103
likely bars its patentability. For the same reason, if a technique
has been used to improve one device, and a person of ordinary
skill in the art would recognize that it would improve similar
devices in the same way, using the technique is obvious unless
its actual application is beyond his or her skill.

Id. at 417. In order to be patentable, the improvement must be more than the
predictable use of prior art elements according to their established functions.
Id.
Such a showing requires
‘some articulated reasoning with some rational underpinning to
support the legal conclusion of obviousness’ . . . [H]owever, the
analysis 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.

Id. at 418 (quoting In re Kahn, 441 F.3d 977, 988 (Fed. Cir. 2006)). The
proper inquiry is whether a person of ordinary skill in the art would have
seen a benefit to combining the prior art teachings. Id. at 424.
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Discovery of an optimum value of a result effective variable is
ordinarily within the skill of the art. See In re Boesch, 617 F.2d 272, 276
(CCPA 1980) and In re Aller, 220 F.2d 454, 456 (CCPA 1955).
When ranges recited in a claim overlap with ranges disclosed in the
prior art, a prima facie case of obviousness typically exists and the burden of
proof is shifted to applicant to show that the claimed invention would not
have been obvious. In re Peterson, 315 F.3d 1325, 1329-30 (Fed.Cir.2003);
In re Woodruff, 919 F.2d 1575, 1578 (Fed.Cir.1990). Where the difference
between the prior art and a claimed invention is some range or variable with
in the claims, “the applicant must show that the particular range is critical,
generally by showing that the claimed range achieves unexpected results
relative to the prior art range.” Woodruff, 919 F.2d at 1578.
Additionally, where the ranges involve variables that were known to
be result-effective, it is not inventive to discover optimum values. Peterson,
315 F.3d at 1330 (“The normal desire of scientists or artisans to improve
upon what is already generally known provides the motivation to determine
where in a disclosed set of percentage ranges is the optimum combination of
percentages.”). That is, it is not enough to merely establish a difference in
results - the results must be shown to be unexpected to a person having
ordinary skill in the art. In re Harris, 409 F.3d 1339, 1344 (Fed. Cir. 2005)
(“The 32-43 % increase in stress-rupture life, however, does not represent a
‘difference in kind’ that is required to show unexpected results.”).
Even where an applicant’s modification results in great improvement
and utility over the prior art, it may still not be patentable if the modification
was within the capabilities of one skilled in the art, unless the modification
produces a new and unexpected result that differs in kind and not merely in
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degree from the results of the prior art. In re Huang, 100 F.3d 135, 139
(Fed. Cir. 1996).

ANALYSIS
Rejection of claims over Ogino and Cole
Appellants’ argument that Cole describes the nickel-silicon contact on
silicon carbide to be undesirable and, therefore, teaches away from
combining Coles and Ogino, is unpersuasive. This argument ignores the
overall teachings of Cole with respect to recognizing nickel-silicon as the
standard contact material to a silicon carbide substrate (FF 5-6). Although
Cole describes certain problems with Ni-Si contacts (FF 7), the disclosed
improvements are still made to the Ni-Si contacts whereby adding Pt, Ti,
and W metallization stabilizes the contact (FF 8). As depicted in Figure 5
(FF 9), Cole still focuses on the Ni-SiC-C ternary phase diagram and Ni-Si
ohmic contact (FF 10).
For the reasons discussed above, we disagree with Appellants’
assertion that Cole teaches the skilled artisan to avoid the Ni-Si contact
structure and find that Cole, in fact, suggests such contacts by disclosing
additional metal layers for stabilizing the contact. Accordingly, the
35 U.S.C. § 103 rejection of claims 34 and 35 over Ogino and Cole is
sustained.
Rejection of claims over Ogino
Appellants do not dispute the Examiner’s findings that Ogino
discloses all features of claim 34 with the exception that Ogino does not
specifically discuss the optimization of the nickel and silicon composition to
arrive at the claimed nickel-silicon composition ratios (Br. 4). Appellants
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rely on their Figure 4 and assert that the claimed composition ratios are more
than optimum or workable ranges and avoid some of the problems identified
with Ogino’s ratio (Br. 4-5). In that regard, Appellants point out that the
claimed invention operates within a smaller triangle on the phase diagram,
while the composition disclosed by Ogino covers a wider range of
possibilities (Br. 5; Oral Hearing). Appellants further acknowledge that the
phase diagram of Figure 4 is a standard diagram and well known to the
skilled artisan (Oral Hearing.)
In light of the concededly well known ternary phase diagram, the
optimum ratio for the Ni-Si composition would have been determinable by
selecting a range for Ni-Si composition with no carbon present in the
contact, and thus, easily predictable by a person of ordinary skill in the art.
As recognized by the Examiner (Ans. 7-8), Ogino is indeed concerned with
forming an ohmic contact on silicon carbide with no carbon precipitated on
its surface (FF 1-2). Ogino further discloses the range of atomic ratio of Ni-
Si alloy to be 38-62 for an ohmic contact without using high temperature
annealing process (FF 3-4). Therefore, Ogino’s ratio satisfies the
requirements of low temperature processing and the absence of carbon in the
contact.
We find that Appellants have not provided any evidence to the
contrary, that is, evidence showing that the particular Ni-Si composition
ratio selected by Appellants yielded results which could not have been
predicted by a person of ordinary skill in the art at the time of Appellants’
invention (FF 1-4). Moreover, a person of ordinary skill in the art (see also
FF 9-10), faced with the conventional engineering task of designing a
Nickel-Silicon ohmic contact on a Silicon-carbide substrate, as disclosed by
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Ogino to have low resistivity and be void of graphite precipitation (FF 1-3),
would select a Nickel-Silicon composition ratio from the ternary phase
diagram that provides the desired properties. There is nothing in the record
before us which indicates that the selection of such a composition ratio
would have been beyond the technical grasp of a person of ordinary skill in
the art. To the contrary, the record indicates that selection of such a ratio
would have been well within the grasp of a person of ordinary skill in the art
in the form of a Ni-SiC-Si ternary phase diagram showing the desired range
resulting in the absence of carbon in the contact layer as well as low contact
resistivity with respect to different composition ratios shown on the diagram.
Appellants’ contention that the claimed range is unobvious since
optimizing such result-effective variables were “unexpectedly good” (Br. 5)
does not persuade us that the selection of a known range of nickel-silicon
composition ratio from known ranges that result in good ohmic contact
without carbon presence, which are available to the skilled artisan in the
form of the Ni-SiC-Si ternary phase diagram, to achieve the required contact
resistivity, would have been beyond the technical grasp of a person of
ordinary skill in the art. A person of ordinary skill in the art (see FF 9-10)
would have been capable of determining the optimum composition ratio for
a silicon-nickel contact in accordance with the known ternary phase
diagram. Additionally, Appellants have not presented any evidence in
support of any unexpected advantages for their claimed range and how such
results were “unexpectedly good.” Such evidence must show difference in
kind for the unexpected results, not merely in degree. (See In re Huang.)
For the above reasons, Appellants’ arguments do not show that the
optimized ratio called for in claim 34 would have been beyond the technical
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grasp of a person of ordinary skill in the art or achieved unexpected results.
Consequently, Appellants’ arguments fail to convince us that the claimed
ratio patentably distinguishes claim 34 over Ogino.

CONCLUSIONS
1. Appellants have not demonstrated error in the Examiner’s
reasoning as to why combining Ogino and Cole to teach or suggest the
claimed subject matter related to a metallization over a nickel-silicon ohmic
contact would have been obvious.
2. Appellants have not demonstrated error in the Examiner’s
reasoning as to whether the claimed range of nickel-silicon composition
ratio reads on the larger range disclosed by Ogino.

DECISION
The decision of the Examiner rejecting claims 34 and 35 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).

AFFIRMED

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