Ex Parte Rahimo et al

Patent Trial and Appeal Board

Jan 16, 2018

14477229 (P.T.A.B. Jan. 16, 2018)

United States Patent and Trademark Office
UNITED STATES DEPARTMENT OF COMMERCE
United States Patent and Trademark Office
Address: COMMISSIONER FOR PATENTS
P.O.Box 1450
Alexandria, Virginia 22313-1450
www.uspto.gov
APPLICATION NO. FILING DATE FIRST NAMED INVENTOR ATTORNEY DOCKET NO. CONFIRMATION NO.
14/477,229 09/04/2014 MunafRAHIMO ABBCH-00140 7985
129925
ARR Tno
7590 01/18/2018 EXAMINER
Taft, Stettinius & Hollister LLP
One Indiana Square
GHEYAS, SYED I
Suite 3500 ART UNIT PAPER NUMBER
Indianapolis, UN 4b2U4-2U23 2812
NOTIFICATION DATE DELIVERY MODE
01/18/2018 ELECTRONIC
Please find below and/or attached an Office communication concerning this application or proceeding.
The time period for reply, if any, is set in the attached communication.
Notice of the Office communication was sent electronically on above-indicated "Notification Date" to the
following e-mail address(es):
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PTOL-90A (Rev. 04/07)
UNITED STATES PATENT AND TRADEMARK OFFICE
BEFORE THE PATENT TRIAL AND APPEAL BOARD
Ex parte MUNAF RAHIMO, CHIARA CORVASCE,
JAN VOBECKY, and YOICHI OTANI
Appeal 2017-002492
Application 14/477,229
Technology Center 2800
Before CATHERINE Q. TIMM, WESLEY B. DERRICK, and
DEBRA L. DENNETT, Administrative Patent Judges.
TIMM, Administrative Patent Judge.
DECISION ON APPEAL1
STATEMENT OF CASE
Pursuant to 35 U.S.C. § 134(a), Appellant2 appeals from the
Examiner’s decision to reject claims 1—3, 6—8, 10-13, and 16—18 under
1 In explaining our Decision, we cite to the Specification dated September 4,
2014 (Spec.), Final Office Action dated September 8, 2015 (Final), Appeal
Brief dated March 8, 2016 (Appeal Br.), Examiner’s Answer dated
September 29, 2016 (Ans.), and Reply Brief dated November 23, 2016
(Reply Br.).
2 Appellant is the Applicant, ABB Technology AG, which, according to the
Appeal Brief, is the real party in interest. Appeal Br. 2.
Appeal 2017-002492
Application 14/477,229
35 U.S.C. § 103(a) as obvious over Suzuki3 in view of Miyazaki,4 Miyairi,5
and Hawryluk6 and the rejection of claims 4, 5, 9, 14, 15, 19, and 20 as
obvious over those references in view of further prior art. We have
jurisdiction under 35 U.S.C. § 6(b).
We AFFIRM.
In arguing against the Examiner’s rejections, Appellant focuses on the
rejection of claim 1 (Appeal Br. 6—12). Thus, the question on appeal is
whether Appellant has identified a reversible error in the Examiner’s
rejection of claim 1.
Claim 1 is directed to a method for manufacturing a power
semiconductor device including steps of depositing a titanium deposition
layer on the second main side of a doped wafer and laser annealing the
titanium deposition layer at a temperature higher than 1200 °C. The result is
an intermetal compound layer, such as titanium silicide, at an interface
between the titanium deposition layer and the wafer. Annealing also causes
diffusion of the dopant into the wafer. Claim 1 reads:
1. A method for manufacturing a power semiconductor
device, comprising:
providing a wafer of a first conductivity type, which
wafer has a first main side and a second main side opposite to
the first main side, part of the wafer having an unamended
doping concentration forming a drift layer;
applying on the second main side at least one of a dopant
of the first conductivity type for forming a layer of the first
3 Suzuki et al., US 2008/0102576 Al, published May 1, 2008.
4 Miyazaki et al., US 5,623,157, issued Apr. 22, 1997.
5 Miyairi, US 2008/0299743 Al, published Dec. 4, 2008.
6 Hawryluk et al., US 6,303,476 Bl, issued Oct. 16, 2001.
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Application 14/477,229
conductivity type and a dopant of a second conductivity type,
which is different from the first conductivity type, for forming a
layer of the second conductivity type;
depositing a Titanium deposition layer on the second
main side after the applying of the dopant;
laser annealing the Titanium deposition layer at a
temperature higher than 1200 °C so that simultaneously (i) an
intermetal compound layer is formed at an interface between
the Titanium deposition layer and the wafer (ii) and the at least
one dopant is diffused into the wafer, and so that the Titanium
deposition layer will act as a light absorber to achieve an
increased temperature in the wafer below the Titanium
deposition layer; and
creating a first metal electrode layer on the second side.
Appeal Br., Claims Appendix 1.
OPINION
The Examiner finds Suzuki teaches a method of manufacturing a
power semiconductor including providing a wafer, applying dopants,
depositing a titanium deposition layer, and creating a first metal electrode as
required by claim 1. Final 3.
The Examiner further finds Suzuki teaches a laser annealing step, but
acknowledges that Suzuki does not disclose the temperature or the intent to
form an intermetal compound layer while simultaneously diffusing dopant
into the wafer, and also does not disclose the titanium layer as acting as a
light absorber. Final 3^4. Thus, the Examiner turns to Miyazaki’s teaching
of laser annealing a titanium deposition layer overlying a doped silicon layer
to show that it was known in the art to laser anneal after depositing the
titanium layer to diffuse the dopant and to simultaneously achieve low
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Application 14/477,229
contact resistance by forming titanium silicide at the interface between the
titanium and silicon. Final 4.
As to the temperature, the Examiner determines that Miyazaki teaches
the general conditions of the annealing process such that discovering the
optimum or workable ranges of annealing temperature would have involved
only routine skill in the art and provides an evidentiary basis and reasoning
indicating that temperatures above 1200 °C would have been within the
optimal or workable ranges. Final 5—6.
The Examiner further finds that the titanium layer inherently acts as a
light absorber to achieve an increased temperature in the wafer below the
titanium deposition layer and provides Miyairi to support this finding. Final
6. The Examiner also relies upon Hawryluk to support the finding that the
use of temperatures above 1200 °C was known in the art for laser annealing
titanium deposition layers to diffuse dopant into wafers and it was known
that the titanium layer acts as a light absorber. Final 6—7.
Appellant contends that the Examiner’s proposed combination of prior
art fails to disclose or suggest the combination of features (B)-(D) as recited
in claim 1. Appeal Br. 9. Appellant further contends that “the Examiner
has, in several cases, disregarded the express teachings of the applied
references in an attempt to piece together incongruous teachings of the
applied references to arrive at the features of the claimed invention.” Appeal
Br. 10. Appellant specifically finds fault with the Examiner’s determination
that Miyazaki teaches the general conditions of laser annealing and tries to
differentiate Miyairi and Hawryluk from the method of the claims based on
a teaching in those references that the heating method is indirect. Appeal Br.
10-11.
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We determine a preponderance of the evidence supports the
Examiner’s well-presented and detailed findings of fact, analysis, and
conclusions of law. We agree with the Examiner that Appellant has
misinterpreted the prior art and we incorporate by reference the Examiner’s
thorough response to Appellant’s arguments. Ans. 3—15. We add the
following for emphasis.
The Examiner finds that Suzuki teaches manufacturing a power
semiconductor device including steps of providing a wafer and doping it,
depositing a titanium layer, and creating a first metal electrode as required
by claim 1. Final 3. These findings are supported by Suzuki. Suzuki
teaches a power semiconductor device with a silicon substrate 20, doped
regions 9 and 10, and a back electrode 14 with a titanium layer 11 in contact
with the doped regions 9 and 10. Suzuki H 25, 28—31.
The Examiner further finds that Suzuki teaches laser annealing to
diffuse the dopant into the wafer. Final 3. Suzuki supports this finding as
well. Suzuki teaches activating dopant regions 9 and 10 by laser annealing.
Suzuki 147. Laser annealing is used to control diffusion depth and peak
concentration in region 9 so that excellent ohmic contact between back
electrode 14 and semiconductor substrate 20 is achieved and an increase in
the ON voltage can be further prevented. Suzuki 135.
The Examiner acknowledges that Suzuki does not teach laser
annealing the titanium layer at a temperature higher than 1200 °C to form an
intermetal compound layer at the interface with the wafer and diffuse the
dopant. Final 3^4. Suzuki teaches laser annealing the doped wafer before
depositing the titanium layer in order to use high temperatures, i.e.,
temperatures higher than the melting point of the back electrode, to activate
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the dopants. Suzuki | 55. Performing the laser anneal before depositing the
titanium layer reduces warping between the silicon wafer and back electrode
due to the difference in thermal coefficient of expansion between these
materials. Suzuki || 11, 13. However, Suzuki also indicates that heat
treatment after forming back electrodes was known in the art for achieving
excellent ohmic contact albeit with back electrodes of a different
composition such as Al/Mo/Ni/Au back electrodes. Suzuki 110. Although
Suzuki laser anneals before depositing the titanium layer, Suzuki discloses
that the timing of the laser anneal has little effect on ON voltage properties
VcE(sat) and V/ when using a Ti/Ni/Au back electrode. Suzuki || 63, 65. As
a whole, Suzuki provides evidence that performing laser annealing after
depositing the titanium layer would have been known in the art although
those of ordinary skill would have expected some product loss due to
warpage.
The Examiner finds Miyazaki teaches laser annealing a titanium
deposition layer to form an intermetal compound layer and to diffuse dopant
into the wafer. Final 4. Miyazaki supports the Examiner’s finding. Like
Suzuki, Miyazaki seeks to form a good ohmic contact. Miyazaki, col. 3,
11. 15—45. Titanium silicide was known to form a good ohmic contact. Id.
Miyazaki teaches forming a titanium film 212 over doped regions 208, 209,
210, 211 of silicon that reside on a glass substrate 201. Miyazaki, col. 8,
11. 38—53; col. 9,11. 39-55; Figs. 7(C), 7(E), 7(F). Miyazaki irradiates the
structure with a KrF excimer laser of wavelength 248 nm and a pulse width
of 20 nsec to activate the implanted impurity (dopant) and to cause the
titanium film to react with the silicon to form regions 213 and 214 of
titanium silicide intermetal compound. Miyazaki, col. 9,11. 56—65;
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Fig. 7(G). Miyazaki does not disclose the temperature to which the titanium
layer is heated during the laser annealing. Id. Miyazaki merely provides
guidance regarding the temperature to which the glass substrate should be
heated. Id. According to Miyazaki, “[w]hen the laser light was illuminated,
if the substrate was heated to 200° to 500° C., then the peeling of the
titanium film could be suppressed.” Id. Miyazaki discloses an alternate
embodiment of irradiating with visible or near infrared light using a lamp to
heat the surface to about 800-1000°C. Miyazaki, col. 10,11. 16—29. Lamp
annealing at 800 °C requires a longer heating time of several minutes
whereas the higher temperature of 1000 °C can be conducted for a shorter
time period of tens of seconds. Id. Thus, the evidence supports the
Examiner’s finding that one of ordinary skill in the art would have
conducted the annealing to create a temperature gradient of high temperature
at the surface and lower temperature in the substrate to prevent peeling of
the titanium layer. Ans. 11—12.
Given that Miyazaki is silent with respect to the laser annealing
surface temperature and laser heating is more localized than lamp annealing
and Miyazaki teaches performing the annealing for the same purpose of
Appellant, i.e., to activate the dopant and form an intermetal compound of
titanium silicide, we agree with the Examiner that Miyazaki teaches the
general conditions of the process such that performing routine optimization
would have resulted in laser annealing temperatures higher than 1200 °C.
Ans. 11—13. The evidence is sufficient to shift the burden to Appellant to
show that they obtain some unexpected result from heating to above
1200 °C. See In re Alter, 220 F.2d 454, 456 (CCPA 1955) (explaining that
where the general conditions of a claimed process are disclosed in the prior
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Application 14/477,229
art, patentability does not lie in discovering the optimum or workable ranges
for process parameters such as temperature or concentration by routine
experimentation, instead the burden shifts to the applicant to show that the
particular ranges recited in the claim are critical for producing an unexpected
result).
Appellant contends that because Miyazaki does not disclose a range of
temperature overlapping Appellant’s higher than 1200 °C range, it cannot be
said that claim 1 is only directed to an optimal working range. Reply Br. 4.
Appellant oversimplifies the state of the law. The prior art need not disclose
an overlapping range; it need only disclose the general conditions the
ordinary artisan would use to experiment to discover the optimum
conditions. See In re Aller, 220 F.2d at 456 (upholding a conclusion of
obviousness where the prior art the general conditions of the process, but
exemplified the use of lower temperatures and higher sulphuric acid
concentrations); In re Kulling, 897 F.2d 1147, 1149 (Fed. Cir. 1990)
(upholding a finding that the amount of eluent to be used in a washing
sequence was a matter of routine optimization where the reference failed to
provide any numerical quantities).
The evidence also supports the Examiner’s finding that the titanium
layer inherently acts as a light absorber to achieve the increased temperature
in the wafer region below the titanium layer. Laser irradiation heats the
region under the titanium layer to cause the diffusion of the dopant in the
silicon layer and form the titanium silicide. Miyazaki, col. 9,11. 56—61.
CONCLUSION
We sustain the Examiner’s rejections.
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DECISION
The Examiner’s decision is affirmed.
TIME PERIOD FOR RESPONSE
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).
AFFIRMED
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