Ex parte Shibib

Board of Patent Appeals and Interferences

Mar 26, 1999

08163967 (B.P.A.I. Mar. 26, 1999)

Application for patent filed December 8, 1993.1
1
THIS OPINION WAS NOT WRITTEN FOR PUBLICATION
The opinion in support of the decision being entered today
(1) was not written for publication in a law journal and
(2) is not binding precedent of the Board.
Paper No. 24
UNITED STATES PATENT AND TRADEMARK OFFICE
_____________
BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
_____________
Ex parte MUHAMMED A. SHIBIB
_____________
Appeal No. 95-5041
Application 08/163,9671
______________
ON BRIEF
_______________
Before HAIRSTON, BARRETT, and GROSS, Administrative Patent
Judges.
HAIRSTON, Administrative Patent Judge.
DECISION ON APPEAL
This is an appeal from the final rejection of claims 1, 4
and 5.
Appeal No. 95-5041
Application No. 08/163,967
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The disclosed invention relates to a high voltage
semiconductor device having an improved junction termination
extension for increasing the surface breakdown junction
voltage.
Claim 1 is the only independent claim on appeal, and it
reads as follows:
1. A high voltage semiconductor device having an
improved junction termination extension for increasing the
surface breakdown junction voltage, comprising:
a semiconductor substrate of a first electrical
conductivity type, said substrate defining a major surface
having an edge;
a first impurity region of a second electrical
conductivity type formed in said substrate and having a first
doping concentration;
a second impurity region formed in said substrate between
said first impurity region and said edge and in contact with
said first impurity region and extending on said major surface
from said first impurity region to a junction extension remote
from said first impurity region, said second impurity region
being of said second electrical conductivity type and having a
second doping concentration less than said first doping
concentration;
a first field shield plate disposed on said major surface
directly above and in electrical contact with said first
impurity region, said first field shield plate having an outer
edge terminating directly above said second impurity region
before said junction extension;
a first layer of insulating material disposed on said
major surface of said substrate and separating said first
Appeal No. 95-5041
Application No. 08/163,967
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field shield plate from said second impurity region;
a second layer of insulating material disposed directly
above said first field shield plate; and
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a second field shield plate disposed on said second layer
of insulating material, directly above and in electrical
contact with said first impurity region, and having an outer
edge terminating directly above said substrate beyond said
junction extension so that said junction extension is
positioned on said major surface between the outer edge of
said first field shield plate and the outer edge of said
second field shield plate.
The reference relied on by the examiner is:
Terashima 5,204,545 Apr.
20, 1993
Claims 1, 4 and 5 stand rejected under 35 U.S.C. § 103 as
being unpatentable over the admitted prior art in Figures 2A
and 3A in view of Terashima. According to the examiner
(Answer, page 4):
Appellant’s prior art figures 2A and 3A disclose
all the claimed subject matter except for the first
field shield plate having an outer edge terminating
before the PN junction. However, Terashima teaches
from line 38 of column 2 that it is “possible to
prevent concentration of electric fields caused in
the end region 7a of the island 7" by applying
electric fields from interconnection 15 (equivalent
to layer 34 in figure[s] 2A to 3B of Appellant’s
drawings) with a fixed potential[s] (note line 31 of
column 2) at plates 16b, 16c, and 16d (equivalent to
layer 30 in figure[s] 2A to 3B of Appellant’s
drawings) so that “the equipotential lines in the
depletion layers are not concentrated toward the p-
type isolating diffusion region 13" (note line 43 of
column 2) to increase “breakdown voltage” (note line
49 of column 2). Therefore, it would have been
obvious to one of ordinary skill in the art to form
the first field shield plate 30 in Appellant’[s]
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prior art figure[s] 2A and 3A before the PN junction
to form the depletion layer in region 28 to increase
the surface breakdown voltage as taught by
Terashima.
Appellant argues that the claimed invention, like
Terashima, reduces “the concentration of electric field that
occurs at the major surface between the high voltage and low
voltage terminals of semiconductor devices, thereby increasing
the effective breakdown voltage of such devices” (Brief, page
5). Despite the functional similarities between the claimed
invention and Terashima, appellant argues that “the present
invention attains such functionality in an entirely different
manner than does Terashima” (Brief, pages 5 and 6). Appellant
also argues (Brief, pages 8 and 9) that the teaching or
suggestion to combine the admitted prior art with Terashima is
only apparent from appellant’s disclosure.
Reference is made to the brief and the answer for further
detailed positions of the appellant and the examiner.
OPINION
We have carefully considered the entire record before us,
and we will reverse the obviousness rejection of claims 1, 4
and 5.
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Application No. 08/163,967
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As indicated supra, Terashima is concerned with
preventing field concentration in an end portion of a
semiconductor region caused by p-n junction isolation on a
semiconductor substrate (column 1, lines 11 through 14).
Terashima discloses (Figure 3) a semiconductor substrate 12 of
a first electrical conductivity type, a first impurity region
11 of a second electrical conductivity type formed in the
substrate and having a first doping concentration, a second
impurity region 7a formed in the substrate between the first
impurity region 11 and the edge of the substrate and in
contact with the first impurity region and extending on a
major surface from the first impurity region to form a
junction extension remote from the first impurity region. The
second impurity region 7a is of the second electrical
conductivity type, and the doping concentration thereof is
less than the doping concentration of the first impurity
region 11. A first field shield plate 16e is disposed on the
major surface directly above and in electrical contact with
the first impurity region 11 (column 2, lines 5 through 12).
A layer of insulating material 14 is disposed on the major
surface of the substrate, and it separates the first field
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shield plate 16e from the second impurity region 7a, and it
also separates the first field shield plate 7a from a second
field shield plate 15 (column 1, line 67 through column 2,
line 8). The second field shield plate 15 is located directly
above and in electrical contact with the first impurity region
11, and has an outer edge terminating directly
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above the substrate but beyond the junction extension 7a
(column 2, lines 1 through 5).
The first field shield plate 16e is linked to conductive
plates 16a through 16d (column 2, lines 5 through 15).
According to Terashima (column 2, lines 27 through 50):
The conductive plate 16a is fixed at the low
potential of the p-type separation diffusion region
13, and the conductive plate 16e is fixed at the
high potential of the n-type diffusion region 11.
The floating conductive plates 16b, 16c and 16d are
fixed at certain potentials by a first capacitance
between the conductive plates 16a to 16e and a
second capacitance between the aluminum wiring 15
and the respective conductive plates 16a to 16e . .
. . Thus, it is possible to prevent concentration
of electric fields caused in the end region 7a of
the island 7, particularly on its surface, through
influence exerted by an electric field from the
high-potential aluminum interconnection 15 . . . .
Thus, the island 7 . . . is increased in breakdown
voltage.
Appellant argues (Brief, pages 7 and 8) that:
With respect to the Examiner’s rejection of the
claims . . . , the Examiner appears to have combined
Terashima plates 16b, 16c and 16d, i.e. the
“floating plates”, with fixed conductive plate (16e)
to create a “combination plate”, and has treated
this “combination plate” as an equivalent to
applicant’s first field shield plate 30 in an effort
to show that the junction extension region of
Terashima extends beyond the far edge of the
“combination plate”, i.e. beyond the left edge of
plate 16b in FIG. 3 of the reference. However,
there is absolutely no support or teaching for the
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Examiner’s proffered combination. If a “combination
plate” is to be envisioned in accordance with the
Examiner’s reasoning, all of the Terashima plates
(16a through 16e) should be combined, thereby
resulting in a bridging of the entire region from
the high voltage diffusion region (11) to the low
voltage diffusion region (13). In other words, and
with reference to the terminology of the present
invention, this “combination plate” would create a
first field shield plate having one end in
electrical contact with the high voltage region and
the other end in electrical contact with the low
voltage region and extending above the major surface
over the entire junction extension region. Such a
result is exactly the configuration shown in
applicant’s prior art FIGS. 2A and 3A. There is no
teaching whatsoever, nor any suggestion in Terashima
or in any of the prior art to either shorten the
first field shield plate 30 or, in the alternative,
to extend the junction extension region 28 “so that
the junction extension (29) is positioned on the
major surface between the outer edge of the first
field shield plate and the outer edge of the second
field shield plate” as is expressly recited in
applicant’s claim 1.
It is respectfully submitted that the Examiner
has simply exercised impermissible hindsight in
applying the Terashima reference in combination with
applicant’s prior art FIGS. 2A and 3A to reject
applicant’s claims.
We agree. In the absence of a teaching or suggestion in
the applied prior art or a convincing line of reasoning by the
examiner, the examiner cannot pick and choose among the
conductive plates 16a through 16e in Terashima to select only
those conductive plates (i.e., 16b through 16e) that terminate
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before the junction extension 7a (Brief, page 8).
In summary, the obviousness rejection of claims 1, 4 and
5 is reversed.
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Application No. 08/163,967
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DECISION
The decision of the examiner rejecting claims 1, 4 and 5
under 35 U.S.C. § 103 is reversed.
REVERSED
KENNETH W. HAIRSTON )
Administrative Patent Judge )
)
)
) BOARD OF PATENT
LEE E. BARRETT ) APPEALS AND
Administrative Patent Judge ) INTERFERENCES
)
)
)
ANITA PELLMAN GROSS )
Administrative Patent Judge )
KWH:svt
Appeal No. 95-5041
Application No. 08/163,967
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Docket Administrator
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