Ex Parte Ryu et al

Patent Trial and Appeal Board

Sep 29, 2014

11331325 (P.T.A.B. Sep. 29, 2014)

UNITED STATES PATENT AND TRADEMARK OFFICE
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BEFORE THE PATENT TRIAL AND APPEAL BOARD
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Ex parte SEI-HYUNG RYU, ANANT K. AGARWAL, and
ALLAN WARD
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Appeal 2012-007912
Application 11/331,325
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–
8, 10, and 12–19 under 35 U.S.C. § 103(a) as obvious over Hideyuki1 in
view of Kinoshita2 and Havemann3 and claim 6 over those references further

1 JP3147331, pub. June 24, 1991. We rely upon the English Abstract and
Figures. Appellants state that they attached a machine translation of
Hideyuki (Appeal Br. 5), but the document attached to the Appeal Brief does
not appear to correspond to Hideyuki. Therefore, we do not rely upon that
document.
2 US 6,831,345 B2, patented Dec. 14, 2004.
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in view of Akiyama.4 We have jurisdiction under 35 U.S.C. §§ 6(b) and
134(a).
We AFFIRM.

The claims are directed to an edge termination structure for a silicon
carbide semiconductor device (see claims 1 and 13). Figure 14 illustrates
one embodiment of the device and is reproduced below:

Figure 14 is a cross-sectional illustration of a SiC Schottky diode having an
edge termination according to some embodiments of the invention

To further illustrate the invention and emphasize the limitations of the
claim at issue in the appeal, we reproduce claim 1 with reference numerals
from Figure 14, and important limitations italicized.
1. An edge termination structure for a silicon carbide
semiconductor device, comprising:
a plurality of spaced apart concentric floating guard rings
[34] in a silicon carbide layer [30], the plurality of spaced apart

3 US 5,565,384, patented Oct. 15, 1996.
4 US 5,994,189, patented Nov. 30, 1999.
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concentric floating guard rings [34] at least partially
surrounding a silicon carbide-based junction [52];
an insulating structure [56, 66] on a surface of the silicon
carbide layer [30]; and
a silicon carbide surface charge compensation region
[38] between the floating guard rings [34] and adjacent the
surface of the silicon carbide layer [30], wherein the surface
charge compensation region [38] has a dopant concentration
such that the surface charge compensation region [38] is
substantially depleted by surface charges of the insulating
structure [56, 66] and the surface charge compensation region
[38] is fully depleted when a reverse bias lower than the
blocking voltage of the device is applied to the device;
wherein the insulating structure [56, 66] comprises a
silicon nitride layer [56] on the silicon carbide layer [30], and
an organic protective layer [66] on the silicon nitride layer [56],
wherein the silicon nitride layer [56] is between the organic
protective layer [66] and the silicon carbide layer [30], and
wherein the organic protective layer [66] does not contact the
silicon carbide layer [30].
(Claims Appendix at Appeal Br. 10 (emphasis added).)

OPINION
As a first matter, with respect to the rejection of all the claims over
Hideyuki in view of Kinoshita and Havemann, Appellants do not argue any
claim apart from the others. Therefore, for that rejection we select claim 1
as representative to decide the issue on appeal. The issue on appeal is:
Have Appellants identified a reversible error in the Examiner’s
determination that one of ordinary skill in the art would have constructed an
edge termination structure including a silicon surface charge compensation
Appeal 2012-007912
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region having the dopant concentration required by claim 1 when following
the teachings of Hideyuki?
The Examiner relies upon Hideyuki’s Figure 2 as depicting the edge
termination structure. Figure 2 is reproduced below:

Figure 2 of Hideyuki is a cross-sectional view of a high-breakdown-strength
semiconductor device

Hideyuki discloses the device as having a substrate 1 of N-
conductivity, a first region 2 and second region (guard rings) 3 both having
P+ conductivity, and a third region 8 of P- conductivity.
The English Abstract of Hideyuki does not identify the composition of
layer 7, but given the similarities of Hideyuki’s device to other devices with
guard rings that have high breakdown strength, it was reasonable for the
Examiner to find that Hideyuki would have suggested to one of ordinary
skill in the art a device including an insulating layer at 7 (compare Hideyuki,
Fig. 2 with Appellants’ Figure 1A and with Kinoshita, Fig. 21 (showing
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oxide layer 106 above guard rings 108 as explained in col. 1, l. 49 to col. 2,
l. 27)).
Hideyuki discloses forming the third region 8, i.e., the region between
first region 2 and the second region (guard rings) 3, by a diffusion process
(Hideyuki, Abstract). The third region 8 has an impurity concentration
lower than that of the first region, i.e., region 2.5
Hideyuki states that “[b]y this structure, a breakdown strength can be
improved.” (Hideyuki, Abstract.)
Other than to say that the impurity (dopant) concentration is lower
than that of the first region 2, Hideyuki does not identify the level of
concentration of the dopant; nor does Hideyuki specifically state the
concentration results in the depletions recited in claim 1. But the Examiner
concludes that it would have been obvious to one of ordinary skill in the art
at the time of the invention to obtain the concentration as recited in claim “in
order to improve the device characteristics when operating the device.”
(Ans. 7.) The basis for the conclusion: The concentration level is a mere
matter of performing routine experimentation to optimize it for a desired
result (id.).
Indeed, parameters such as concentration are normally the type of
variable one of ordinary skill in the art would be expected to optimize
through routine experimentation. See In re Aller, 220 F.2d 454, 456 (CCPA
1955) (“Normally, it is to be expected that a change in temperature, or in
concentration, or in both, would be an unpatentable modification . . . where

5 At one location within the English Abstract, Hideyuki identifies the third
region with reference numeral 6; that is clearly a typographical error given
the third region connects the first region 2 and second region 3. It is region
8 that so connects first region 2 and second region 3.
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the general conditions of a claim are disclosed in the prior art, it is not
inventive to discover the optimum or workable ranges by routine
experimentation.”)
In the context of Hideyuki, one of ordinary skill in the art would have
performed routine experimentation to find the optimal or workable
concentrations that would result in a semiconductor device with the high
breakdown strength and excellent switching characteristics Hideyuki desires
(Hideyuki, Abstract). It appears that the low impurity concentrations
suggested by Hideyuki are in-line with the dopant concentrations sought by
Appellants to obtain the results they recite in claim 1 (compare Hideyuki,
Abstract (concentrations lower than that of the first region in a device with
guard rings) with Spec. ¶ 59 (concentration small enough so that the surface
charge compensation regions can be completely depleted at a lower voltage,
which may be required for the guard rings to function properly)).
A preponderance of the evidence supports the Examiner’s
determination that the dopant concentration required by claim 1 would have
been arrived at through routine experimentation by one of ordinary skill in
the art following the teachings of Hideyuki. This is sufficient to support a
prima facie case of obviousness and shift the burden to Appellants to show
that the concentration recited in the claim represents a range that is critical
for obtaining an unexpected result. See In re Boesch, 617 F.2d 272, 276
(CCPA 1980); In re Woodruff, 919 F.2d 1575, 1578 (Fed. Cir. 1990); Aller,
220 F.2d at 456. Appellants present no convincing evidence of unexpected
results on this record.
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Appellants present no persuasive arguments directed to the rejection
of claim 6 over Hideyuki, Kinoshita, Havemann, and Akiyama. We sustain
that rejection for the reasons presented above.
CONCLUSION
We sustain the Examiner’s rejections.

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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