Ex Parte Tran

Board of Patent Appeals and Interferences

Oct 2, 2007

09848846 (B.P.A.I. Oct. 2, 2007)

The opinion in support of the decision being entered today is not binding
precedent of the Board.

UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________

Ex parte LUAN C. TRAN
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Appeal 2007-2035
Application 09/848,8461
Technology Center 2800
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Decided: October 2, 2007
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Before KENNETH W. HAIRSTON, ROBERT E. NAPPI,
and JOHN A. JEFFERY, Administrative Patent Judges.

JEFFERY, Administrative Patent Judge.

DECISION ON APPEAL
Appellant appeals under 35 U.S.C. § 134 from the Examiner’s
rejection of claims 11, 12, and 14. We have jurisdiction under 35 U.S.C.
§ 6(b). We reverse.

1 This application is a divisional of Application Serial No. 09/388,856, filed
Sept. 1, 1999, now U.S. Pat. 6,579,751.
Appeal 2007-2035
Application 09/848,846

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STATEMENT OF THE CASE
Appellant invented a method for forming integrated circuitry. In
particular, memory and peripheral circuitry are formed over a semiconductor
substrate. Using a common mask, a halo implant2 is conducted so as to
impart to at least three of the devices three different respective threshold
voltages. To this end, the common masking step involves masking only
portions of some of the devices which receive the halo implant.3 Claim 11 is
illustrative with the key limitation in dispute emphasized:

11. A semiconductor processing method comprising:

a masking step providing a common mask; and

an implant step carried out through the common mask, comprising
conducting a halo implant of devices formed over a substrate comprising
memory circuitry and peripheral circuitry sufficient to impart to at least
three of the devices three different respective threshold voltages, wherein the
common masking step comprises masking only portions of some of the
devices which receive the halo implant, said portions comprising portions of
peripheral circuitry devices.

(Emphasis added.)

2 “Halo implants” are formed in MOSFETs by implanting dopants within a
substrate proximate the source and drain regions, and are typically
underneath the channel region. The implanted halo dopant raises the doping
concentration only on the inside walls of the source/drain junctions, so that
the channel length can be decreased without needing to use a higher doped
substrate. As a result, deleterious effects of “punchthrough” (i.e., merging
of the source and drain depletion regions) are minimized (Specification 2:2-
18)
3 See generally Specification P. 9, l. 1 - P. 10, l. 16.
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The Examiner relies on the following prior art reference to show
unpatentability:
Lowrey US 5,252,504 Oct. 12, 1993

Claims 11, 12, and 14 stand rejected under 35 U.S.C. § 103(a) as
unpatentable over Lowrey.
Rather than repeat the arguments of Appellant or the Examiner, we
refer to the Brief and the Answer for their respective details. In this
decision, we have considered only those arguments actually made by
Appellant. Arguments which Appellant could have made but did not make
in the Brief have not been considered and are deemed to be waived. See 37
C.F.R. § 41.37(c)(1)(vii).

OPINION
In rejecting claims under 35 U.S.C. § 103, it is incumbent upon the
Examiner to establish a factual basis to support the legal conclusion of
obviousness. See In re Fine, 837 F.2d 1071, 1073, 5 USPQ2d 1596, 1598
(Fed. Cir. 1988). In so doing, the Examiner must make the factual
determinations set forth in Graham v. John Deere Co., 383 U.S. 1, 17, 148
USPQ 459, 467 (1966).
Discussing the question of obviousness of a patent that claims a
combination of known elements, KSR Int’l v. Teleflex, Inc., 127 S. Ct. 1727,
82 USPQ2d 1385 (2007) explains:
When a work is available in one field of endeavor, design
incentives and other market forces can prompt variations of it,
either in the same field or a different one. If a person of
ordinary skill can implement a predictable variation, §103
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likely bars its patentability. For the same reason, if a technique
has been used to improve one device, and a person of ordinary
skill in the art would recognize that it would improve similar
devices in the same way, using the technique is obvious unless
its actual application is beyond his or her skill. Sakraida [v. AG
Pro, Inc., 425 U.S. 273, 189 USPQ 449 (1976)] and
Anderson's-Black Rock[, Inc. v. Pavement Salvage Co.,
396 U.S. 57, 163 USPQ 673 (1969)] are illustrative—a court
must ask whether the improvement is more than the predictable
use of prior art elements according to their established
functions.
KSR, 127 S. Ct. at 1740, 82 USPQ2d at 1396. If the claimed subject matter
cannot be fairly characterized as involving the simple substitution of one
known element for another or the mere application of a known technique to
a piece of prior art ready for the improvement, a holding of obviousness can
be based on a showing that “there was an apparent reason to combine the
known elements in the fashion claimed.” Id., 127 S. Ct. at 1740-41,
82 USPQ2d at 1396. Such a showing requires “some articulated reasoning
with some rational underpinning to support the legal conclusion of
obviousness. . . . [H]owever, the analysis need not seek out precise teachings
directed to the specific subject matter of the challenged claim, for a court
can take account of the inferences and creative steps that a person of
ordinary skill in the art would employ.” Id., 127 S. Ct. at 1741, 82 USPQ2d
at 1396 (quoting In re Kahn, 441 F.3d 977, 987, 78 USPQ2d 1329, 1336
(Fed. Cir. 2006)).
If the Examiner’s burden is met, the burden then shifts to the
Appellant to overcome the prima facie case with argument and/or evidence.
Obviousness is then determined on the basis of the evidence as a whole and
the relative persuasiveness of the arguments. See In re Oetiker, 977 F.2d
1443, 1445, 24 USPQ2d 1443, 1444 (Fed. Cir. 1992).
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The Examiner's rejection indicates that Lowrey teaches a
semiconductor processing method with every claimed feature including
conducting a halo implant to devices formed over a substrate that is
sufficient to impart two different threshold voltages to two different
respective threshold voltages. According to the Examiner, Lowrey teaches
every claimed feature except for three different devices having three
different threshold voltages. The Examiner, however, concludes that such a
feature merely duplicates parts and therefore is an obvious variation of
Lowrey’s teachings (Answer 3-4).
Appellant argues that the Examiner has simply not provided any
reason or evidence as to why the skilled artisan would have included three
different transistors with three different threshold voltages in Lowrey rather
than two transistors (Br. 4-6).
The Examiner responds that it would have been obvious to form a
third transistor with a third threshold voltage because DRAM devices may
include hundreds of transistors, such as read-out transistors, which would
have a third threshold voltage different from the peripheral and access
transistors (Answer 6).
The sole issue before us, then, is whether it would have been obvious
to the skilled artisan at the time of the invention to form a third device with a
third threshold voltage in Lowrey via the claimed processing method. For
the following reasons, we answer this question “no.”
Lowrey discloses a CMOS integrated circuit (e.g., a DRAM) where a
first layer of polysilicon 45 is deposited on a wafer 11 that forms transistor
gates (Lowrey, col. 6, ll. 44-48; Fig. 6). The polysilicon 45 is patterned only
in the n channel areas which are over p type material. A halo implant (or
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“blanket implant”) consisting of boron is applied. Because the polysilicon
completely covers the n wells 21, the halo implant is effectively only applied
to the p type material (Lowrey, col. 6, ll. 57-66; Fig. 6).
Although Lowrey does not actually show the halo implants in Figure
6, we presume that they would be implanted to the p type material in areas
which are not directly underneath the polysilicon layer 45 (i.e., in the areas
adjacent the n-wells 21). In this regard, we presume that the polysilicon
layer 45 functions as the “common mask” as claimed.
It is undisputed that implanting this boron halo implant directly affects
the device’s threshold voltage. Furthermore, Lowrey discusses in the
Background section that in DRAM applications, access devices generally
need a higher threshold than the periphery to optimize dynamic refresh
characteristics. Peripheral transistors are optimized at reduced threshold
values for maximum high speed performance. The conventional solution,
therefore, is to separately adjust the threshold of these two groups of
transistors using a photomasking level (Lowrey, col. 2, ll. 4-13).
When these two teachings are read together, we generally agree with
the Examiner that the skilled artisan would have readily adjusted the
threshold of two different devices (i.e., access and peripheral devices) by
selectively implanting a halo implant using a common mask (i.e., the
polysilicon layer noted above). But we fail to see how these teachings
reasonably suggest providing three or more of such devices with respective
different threshold values using the claimed technique.
At best, Lowrey teaches masking n-channel areas (i.e., areas over n-
wells 21) to selectively apply a halo implant to p-type material. While we
can see how such a technique would achieve two different threshold voltages
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resulting from the presence or absence of a halo implant, we fail to see how
such a technique would result in three or more threshold voltages for three
different devices. Nor has the Examiner explained on this record how this
can be achieved.
In our view, using the claimed technique to conduct halo implants
using a common mask to impart to at least three different devices three
different threshold voltages goes well beyond mere duplication of parts. The
claimed invention uses a common mask for three different devices to vary
the degree of masking which dictates the resulting halo implant. In short,
the type of mask dictates the type of halo implant. The particular type of
halo implant that is formed, in turn, dictates the resulting threshold voltage
for that particular device. That is the essence of the claimed invention.
As shown in Figure 6 of the present application, partial masking
(partial exposure) for transistor 26 results in only one halo region 41.
Complete masking (no exposure) for transistor 26a results in no halo region
at all. But no masking (full exposure) for transistor 26b results in two halo
regions 41. As a result, transistor 26b has the highest threshold voltage and
transistor 26a has the lowest threshold voltage. The threshold voltage of
transistor 26 is between that of the other transistors. See Specification 9, l. 1
- 10, l. 16.
To render the claimed invention obvious over Lowrey, the skilled
artisan would have to recognize that the common mask (polysilicon 45)
could somehow be altered to provide at least three different exposure levels
that would result in at least three different types of halo implants for three or
more discrete devices respectively. Such an alteration of the structure of
Lowrey, in our view, simply strains reasonable limits and amounts to
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impermissible hindsight reconstruction of the invention using Appellant’s
own disclosure as a blueprint.
Although the Examiner contends that DRAMs typically include
hundreds of different transistors with different threshold voltages, such as
read-out transistors (Answer 6), the Examiner has provided absolutely no
evidence on this record to support this assertion apart from mere conclusory
statements. In any event, even if we assume that DRAM devices include
numerous devices distinct from the peripheral and access devices as the
Examiner asserts, Lowrey still falls well short of teaching providing
different threshold voltages for these other devices using the particular
common mask technique recited in the claims.
In sum, Lowrey reasonably suggests adjusting the threshold voltage of
two devices by selectively applying a halo implant via masking. But this
teaching merely suggests that the implant is either applied or it is not -- a
binary implantation that provides, at best, two different threshold voltages.
Lowrey does not, however, reasonably teach or suggest varying the degree
of masking to vary the degree of resulting halo implant regions (and the
resulting threshold voltages) to achieve three or more threshold voltages, let
alone associating each such threshold voltage with a different device
respectively.
For the foregoing reasons, we will not sustain the Examiner’s
rejection of claims 11, 12, and 14.

Appeal 2007-2035
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DECISION
We have not sustained the Examiner's rejection with respect to all
claims on appeal. Therefore, the Examiner’s decision rejecting claims 11,
12, and 14 is reversed.

REVERSED

KIS

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