Ex parte TSUKAMOTO

Board of Patent Appeals and Interferences

Aug 25, 1998

08296988 (B.P.A.I. Aug. 25, 1998)

Application for patent filed August 26, 1994. According1
to Appellant, the application is a continuation of Application
07/738,648, filed July 31, 1991 (now abandoned), which is a
continuation of Application 07/662,989, filed February 28, 1991
(now Patent No. 5,047,818), which is a continuation of
Application 07/146,686, filed January 20, 1988 (now abandoned).
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(2) is not binding precedent of the Board.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. 37
UNITED STATES PATENT AND TRADEMARK OFFICE
_____________
BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
_____________
Ex parte KATSUHIRO TSUKAMOTO
_____________
Appeal No. 96-1549
Application 08/296,9881
______________
ON BRIEF
_______________
Before THOMAS, MARTIN, and BARRETT, Administrative Patent Judges.
MARTIN, Administrative Patent Judge.
DECISION ON APPEAL
This is an appeal under 35 U.S.C. § 134 from the examiner's
final rejection of claim 10, Appellant's sole pending claim,
Appeal No. 96-1549
Application 08/296,988
This is the second § 134 appeal in this application. In2
the first appeal (Appeal No. 93-3432), the Board affirmed the
§ 103 rejection of a different claim, i.e., claim 9.
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under 35 U.S.C. § 103 for obviousness over the prior art. We2
reverse.
The invention is a semiconductor memory device which
includes a continuous buried layer which serves as a barrier
against "-ray induced carriers.
Claim 10, the sole appealed claim, reads as follows:
10. A semiconductor memory device including a memory sell
having a write/read transistor and a charge storage capacitor
comprising:
a semiconductor substrate formed of a material having a
first conductivity type and first impurity concentration, said
substrate having a main surface;
a field oxide isolation film formed on said main surface for
isolating semiconductor elements from each other;
a pair of regions of a second conductivity type of said
write/read transistor formed on said main surface, a first region
of said pair of regions being connected with a bit line and the
second region of said pair of regions being connected with one
electrode of said charge storage capacitor;
a gate formed on said main surface between said pair of
regions of said write/read transistor; and
a continuous buried layer of the first conductivity type
formed to stop " particles having a second impurity concentration
higher than said first impurity concentration of said substrate
and being continuously formed in said substrate beneath said gate
and said pair of regions of said write/read transistor as well as
beneath said field oxide isolation film,
Appeal No. 96-1549
Application 08/296,988
Bakeman was relied on in the previous appeal, in which3
the Board affirmed a rejection of claim 9 for obviousness over
Wordeman in view of Bakeman.
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wherein said continuous buried layer has a first peak
position of impurity concentration beneath said field oxide
isolation film and a second peak position of impurity
concentration beneath said gate and said first region of said
pair of regions, a first depth from said main surface to said
first peak position being less than a second depth from said main
surface to said second peak position, and
said continuous buried layer has a lower surface arranged so
that the entire lower surface is in contact with said substrate
material.
The only reference relied on by the examiner in the Answer
is:
Wordeman et al. (Wordeman), A Buried N-Grid for Protection
Against Radiation Induced Charge Collection in Electronic
Circuits, IEDM Tech. Dig., pp. 40-43, 1981.
Although the final Office action (at 3) additionally
mentions Bakeman, Jr., et al. U.S. Patent 4,506,436 (Bakeman) in
response to Appellant's arguments, the Answer specifically states
(at 5) that Bakeman is not used in the rejection. Accordingly,3
Bakeman has not been considered.
Claim 10 stands rejected for obviousness over the DRAM cell
structure shown in Figure 6 of Wordeman, which includes, inter
alia, a buried grid of n-type material (labeled "BURIED n-LAYER")
and a buried continuous layer of p-type material (labeled "BURIED
Appeal No. 96-1549
Application 08/296,988
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p-LAYER)." As best shown in Figure 3b, the buried p-type layer
has deeper portions or dimples which fill in the holes in the n-
type grid and has shallower portions which overlie the n-type
material of the grid. Figure 6 shows that when this arrangement
is used in a DRAM cell, the n-type grid and p-type layer are
positioned such that the deeper portions or dimples of the p-type
layer lie under the n-type bit lines and FET channels, where
capacitance is to be minimized, and the shallower portions of the
p-type layer lie under the storage nodes, where an increase in
capacitance is desirable (Wordeman at 42-43).
Appellant argues that Wordeman's buried p-type layer fails
to satisfy the claim in two respects, the first being that
Wordeman does not teach that the buried p-layer by itself "would
be adequate to substantially reduce the soft-error rate, as
taught by the present invention" (Br. at 7). This argument fails
because the claim language "formed to stop " particles" does not
require that substantially all " particles be stopped and because
Wordeman discloses (at 41, 2d col., item 3) that the p-type layer
. . . blocks the radiation-generated minority carriers from
diffusing up through the [grid] holes (due to the field in
the high-low junction formed between the low doped substrate
and the high p-doping in the hole). These carriers diffuse
sideways to be collected in the n-grid.
Appeal No. 96-1549
Application 08/296,988
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Appellant's second argument is that the buried p-type layer
does not "ha[ve] a lower surface arranged so that the entire
lower surface is in contact with said substrate material," as
required by the claim. The examiner argues that this limitation
is satisfied because the n-type grid material that underlies the
p-type layer is part of the substrate material (Answer at 3). We
agree with Appellant that after the substrate material is
converted to n-type grid material, it is no longer part of the
substrate in the sense of the claim (Reply Br. at 1-2), which
recites a "substrate formed of a material having a first
conductivity type and first impurity concentration." We
therefore agree with Appellant that the entire lower surface of
Wordeman's buried p-type layer is not in contact with the
substrate material, as required by the claim.
The examiner alternatively notes (Answer at 4-5) that the
Board in the previous appeal determined that it would have been
obvious to omit Wordeman's n-type grid altogether, in which case
the p-type layer would have its entire lower surface in contact
with the substrate. Claim 9 in that appeal included a limitation
("wherein the entire buried layer has a lower surface in contact
with said substrate") which is similar to the limitation of
Appeal No. 96-1549
Application 08/296,988
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claim 10 at issue in this appeal. In affirming a rejection of
claim 9 for obviousness over Wordeman in view of Bakeman, the
Board stated:
. . . [W]e note that it is the upper surface of the
buried P layer that provides all of the advantages described
by appellant in the specification. As indicated supra, the
upper surface of the buried P layer is located at one
distance from the capacitor region, and is located at
another distance from the transistor region. The
specification is completely silent concerning any advantage
that is gained by having the entire lower surface of the
buried P layer in contact with the substrate. For this
reason, we find that it would have been manifestly obvious
to one of ordinary skill in the art to eliminate the N layer
that lies buried under a portion of the buried P layer in
Figure 6 of Wordeman. [Paper No. 24, at 5.]
Appellant argues that when considered without reference to
Appellant's specification, Wordeman fails to suggest that the n-
type grid can be omitted and the p-type layer used alone to
collect radiation-generated minority carriers. We agree. In
Wordeman, the function of collecting the radiation-generated
minority carriers is performed primarily by the n-type buried
grid (Wordeman at 40, 2d col.); the primary function of
Wordeman's p-type layer is to prevent "punch through" to the n-
type grid from reverse-biased surface elements (Wordeman at 41,
1st col.). Although, as noted above, Wordeman discloses that the
p-type layer additionally prevents minority carriers from passing
through the grid openings and diffuses them sideways to be
Appeal No. 96-1549
Application 08/296,988
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collected by the grid, Wordeman does not suggest that the p-type
layer would be capable, in the absence of the n-type grid, of
blocking enough minority carriers to make it feasible to omit the
n-type grid.
For the foregoing reasons, the rejection of claim 10 under
35 U.S.C. § 103 as unpatentable over Wordeman is reversed.
REVERSED
)
JAMES D. THOMAS )
Administrative Patent Judge )
)
)
) BOARD OF PATENT
JOHN C. MARTIN )
Administrative Patent Judge ) APPEALS AND
)
) INTERFERENCES
)
LEE E. BARRETT )
Administrative Patent Judge )
Appeal No. 96-1549
Application 08/296,988
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