Ex Parte Hsu et al

Patent Trial and Appeal Board

Jan 9, 2015

11684830 (P.T.A.B. Jan. 9, 2015)

UNITED STATES PATENT AND TRADEMARK OFFICE
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BEFORE THE PATENT TRIAL AND APPEAL BOARD
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Ex parte CHIA-LUN HSU, MU-YI LIU, TAO-CHENG LU,
ICHEN YANG, and KUAN-PO CHEN
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Appeal 2012-011155
Application 11/684,8301
Technology Center 2800
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Before ADRIENE LEPIANE HANLON, CATHERINE Q. TIMM, and
JAMES C. HOUSEL, Administrative Patent Judges.

HOUSEL, Administrative Patent Judge.

DECISION ON APPEAL

Pursuant to 35 U.S.C. § 134, Appellants appeal from the Examiner’s
decision rejecting claims 1–3 and 5–14 as unpatentable under 35 U.S.C.
§ 103(a). We have jurisdiction over the appeal under 35 U.S.C. § 6(b).
We AFFIRM.2

1 According to Appellants, the Real Party in Interest is Macronix
International Co., Ltd. (App. Br. 4).
2 Our decision refers to Appellants’ Appeal Brief (Appeal Br.) filed February
9, 2012, the Examiner’s Answer (Ans.) mailed May 24, 2012, and
Appellants’ Reply Brief (Reply Br.) filed July 23, 2012.
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STATEMENT OF THE CASE
The invention is directed to a lateral double diffused metal oxide
semiconductor (LDMOS) device including a well region with a super steep
retrograde (SSR) well profile having a lighter doping concentration in a
surface region of the well region and heavier sub-surface doping
concentration below the surface region. Spec. ¶¶ 2 and 10. According to
Appellants, the lighter surface doping enables a higher breakdown voltage,
whereas the heavier sub-surface doping decreases the low on-resistance
(Ron). Id. at 10.
Claim 1, reproduced below from the Claims Appendix to Appellants’
Appeal Brief, is illustrative of the subject matter on appeal:
1. A lateral double diffused metal oxide semiconductor (LDMOS)
device, comprising:
a substrate of a first conductivity type;
a well region of a second conductivity type formed in the
substrate, the well region having a super steep retrograde (SSR)
well profile in which a doping concentration changes with
depth so as to provide a lighter doping concentration in a
surface region of the well region than in a region below the
surface region of the well region;
a gate which partly overlies a portion of the substrate of
the first conductivity type adjacent to the well region, said
portion including a channel for the LDMOS device, and the
gate partly overlying the well region; and
one of a source region and a drain region having said
second conductivity type and located in the well region, and the
other of the source region and the drain region in said portion of
the substrate.
The Rejections
The Examiner maintains, and Appellants request review of, the
following grounds of rejection under 35 U.S.C. § 103(a):
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(1) Claims 1, 6–9, and 11–14 as unpatentable over Chen in view of
Williams ʼ818;
(2) Claims 2, 3, and 5 as unpatentable over Chen and Williams
ʼ818, and further in view of Williams ʼ228; and
(3) Claim 10 as unpatentable over Chen and Williams ʼ818, and
further in view of Huster.
We sustain the above rejections based on the findings of fact,
conclusions of law, and rebuttals to arguments well expressed by the
Examiner in the Final Office Action and the Answer. The following
comments are added for emphasis.

Rejection (1): Obviousness over Chen and Williams ʼ818
Appellants do not separately argue the claims on appeal in this
rejection. Accordingly, we select independent claim 1 as representative and
address Appellants’ arguments by reference to this claim. 37 C.F.R.
§ 41.37(c)(iv). The remaining claims stand or fall with claim 1.
The Examiner finds Chen, Figure 15, discloses an LDMOS device
comprising a substrate 202 of a first conductivity type, a well region 236 of a
second conductivity type, and a gate 212 partly overlying a portion of the
substrate adjacent the well region including a channel and partly overlying
the well region, wherein one of a source and drain regions having the second
conductivity located in the well region and the other of the source and drain
regions located in the portion of the substrate. Ans. 5. The Examiner
acknowledges that Chen does not disclose the well region having an SSR
well profile in which doping concentration changes with depth. Id.
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However, the Examiner finds Williams ʼ818 discloses a bipolar-CMOS-
DMOS integrated circuit having well regions with a retrograde profile
having lighter doped portion NW5 to maintain a low threshold against
surface punch-through and higher doped portion NW5B to prevent bulk
punch-through breakdown. Id. at 5–6. The Examiner concludes it would
have been obvious to incorporate such a retrograde profile in Chen to
prevent bulk punch-through breakdown while maintaining a low threshold
against surface punch-through. Id. at 6.
Appellants argue that Williams ʼ818 teaches the retrograde is a
sidewall extending to an underlying region of the same conductivity type to
form a pocket-shaped isolation region. App. Br. 17. As such, Appellants
urge that applying Willliams ʼ818’s teaching to Chen would lead one to
replace Chen’s guard ring structure with pocket-shaped isolation regions
having retrograde sidewalls, and not to include a super steep retrograde well
and gate that overlies that well and the channel of the LDMOS. Id.
We disagree. The Examiner finds that Williams ʼ818 teaches placing
the retrograde profile “in or adjacent the location of the N-well.” Ans. 12.
Further, the Examiner notes Williams ʼ818 teaches a plurality of
embodiments some of which provide the retrograde profile with the high
doping concentration region NW5B extending “the majority if not the entire
length of the substrate.” Id. at 12; e.g., Figs. 9B and 15A. In this regard, we
note Appellants’ claim 1, while requiring the well region partly underlies the
gate, does not limit the retrograde profile to be under only one of the source
and the drain regions. Further, in still other embodiments, we note Williams
ʼ818 teaches retrograde profiles in the well region of a second conductivity
type formed in a substrate of a first conductivity type. See, for example,
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Williams ʼ818, Fig. 15A. In both instances, applying these retrograde
profile embodiments to Chen would result in a well region having a
retrograde profile with the gate partly overlying this well region and partly
overlying the channel. Ans. 12. Also, we are not persuaded that Williams
ʼ818’s teaching of forming a pocket-shaped isolation region between the
field oxide (FOX) structures, for example, demonstrates reversible error
since Appellants’ claims are broad and do not prevent inclusion of such
isolation structure. Moreover, we note that Chen, Figure 15, provides a
pocket-shaped isolation region under the LDMOS using the deep wells 232
and layer 204. Accordingly, Appellants have not shown that the Examiner’s
combination would not result in the claimed structure.
Appellants also contend that the combination of the teachings of Chen
and Williams ʼ818 would render the devices inoperable. Id. at 17–18.
Appellants assert that Williams ʼ818 does not discuss locating the retrograde
well in the active region beneath the gate and adjacent the channel of the
device, but instead locates it away from the channel and gate being isolated.
Id. at 18. Further, Appellants argue that Williams ʼ818’s placement of the
pocket-shaped isolation region in the active region of an LDMOS device
would be inoperable. Id.
We do not find this argument persuasive of reversible error in the
Examiner’s obviousness conclusion. Although Appellants assert the
combination of Chen and Williams ʼ818 would be inoperable, Appellants
have not persuasively established inoperability of the Examiner’s proposed
combination. Appellants do not explain why providing a retrograde profile
in the underlying well of Chen’s device as the Examiner proposes would
short out the drain contact of an LDMOS device.
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Appellants next argue the combination of Chen and Williams ʼ818
would render Williams ʼ818 unsatisfactory for its intended purpose. Id. at
19. Appellants assert that applying Williams ʼ818 for its intended purpose in
Chen would block current flow. Id. Moreover, Appellants also asset
arranging a drift well in the manner as taught by Williams ʼ818 would short
out the drain contact of the LDMOS device. Id.
We do not find this final argument persuasive. The focus in
evaluating the propriety of this obviousness rejection is whether the ordinary
artisan modifying Chen in accord with the teaching of Williams ʼ818 would
have rendered Chen’s device unsatisfactory for its intended purpose. See In
re Gordon, 733 F.2d 900, 902 (Fed. Cir. 1984) (question was whether the
proposed modification, turning the prior art device upside down, would
render the device inoperable for its intended purpose.) Here, the Examiner
has established that modification of Chen’s device to include a retrograde
well in the active region of the LDMOS device in view of Williams ʼ818
would not render Chen inoperable, but would enhance its performance.
Appellants have not argued that Chen’s device so modified would be
rendered inoperable.
It follows that we will sustain the Examiner’s obviousness rejection of
claim 1.

Rejection (2): Obviousness over Chen, Williams ʼ818, and Williams ʼ228
Appellants argue that Williams ʼ228 suffers from the same deficiency
as Chen and Williams ʼ818 in describing use of retrograde profile well
regions for isolation, rather than for improving performance of an LDMOS
device by using a drift well with the retrograde profile. App. Br. 21. For the
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reasons given above, we do not find this argument persuasive. Appellants’
claims do not exclude use of a retrograde profile for isolation. The
Examiner has provided rationale for combining the respective teachings of
the Williams references with the Chen device. Ans. 7–9. Appellants have
not persuasively identified error in this rationale. Accordingly, we will also
sustain this rejection.

Rejection (3): Obviousness over Chen, Williams ʼ818, and Huster
Appellants argue that Huster suffers from the same deficiency as Chen
and Williams ʼ818 in describing use of retrograde profile well regions for
isolation, rather than for improving performance of an LDMOS device by
using a drift well with the retrograde profile. App. Br. 22. For the reasons
given above, we do not find this argument persuasive. Appellants’ claims
do not exclude use of a retrograde profile for isolation. The Examiner has
provided rationale for combining the respective teachings of the Williams
references with the Chen device. Ans. 10–11. Appellants have not
persuasively identified error in this rationale. Accordingly, we will also
sustain this rejection.

CONCLUSION
Upon consideration of the record, and for the reasons given in the
Answer and above, the decision of the Examiner rejecting claims 1–3 and 5–
14 under 35 U.S.C. § 103(a) as unpatentable over Chen and Williams ʼ818,
alone or further in view of Williams ’228 or Huster is affirmed; and
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FURTHER ORDERED that 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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