Ex Parte Ng

Board of Patent Appeals and Interferences

Jun 15, 2005

09821478 (B.P.A.I. Jun. 15, 2005)

The opinion in support of the decision being entered today was
not written for publication and is not precedent of the Board.

UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES

____________

Ex parte HUNG YIP NG
___________

Appeal No. 2005-0585
Application No. 09/821,478

____________

ON BRIEF
____________

Before GARRIS, OWENS, and PAWLIKOWSKI, Administrative Patent
Judges.
PAWLIKOWSKI, Administrative Patent Judge.

DECISION ON APPEAL
This is a decision under 35 U.S.C. § 134 from the
examiner’s final rejection of claims 1, 3, 4-8, 10-14, and 16-
20.
Claims 1 and 4 are representative of the subject matter on
appeal, and are set forth below:
1. A method of forming a semiconductor device,
comprising:
lithographically patterning a structure having a
first critical dimension, wherein said structure
includes nested features and an isolated feature;
etching said structure with an O2-containing
material to trim said first critical dimension to a
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second critical dimension to correct an offset between
said nested features and said isolated feature created
by said lithographic patterning.

4. The method of claim 1, wherein said structure
comprises a negative photoresist; and
wherein said etching comprises a surface charging
technique in combination with a plasma etch, such that
said nested feature is etched faster than said
isolated feature.

On page 5 of the brief, appellant states that there are two
groups of claims, and that one of the groups of claims stands or
falls with claim 1, and the other group of claims stands or
falls with claim 4. We therefore consider claims 1 and 4 in
this appeal.
Claims 1, 3-8, 10-14, and 16-20 stand rejected under 35
U.S.C. § 103 as being unpatentable over Tao in view of Ma, and
further view of Horak.1
The examiner relies upon the following references as
evidence of unpatentability:
Ma et al. (Ma) 5,783,101 Jul. 21, 1998
Tao et al. (Tao) 6,147,818 Jan. 16, 2001
Horak et al. (Horak) 6,297,166 Oct. 21, 2001

1 We note that on page 5 of the answer, the examiner indicates that
claims 1-20 are rejected in this rejection. However, we believe that
the examiner intended to indicate that claims 1, 3-8, 10-14, and 16-20
stand rejected under this rejection because appellants indicate that
these claims are the only claims pending (brief, page 3), and the
examiner agreed with appellants’ summary of the status of the claims
(answer, page 2).
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OPINION
I. The rejection of claims 1, 3-8, 10-14, and 16-20 under 35
U.S.C. § 103 as being unpatentable over Tao in view of Ma
and further view of Horak

We limit our consideration to claims 1 and 4, as stated
supra.
A. The Examiner’s Position
The examiner’s position for this rejection is set forth on
pages 5-8 of the answer. The examiner’s position is summarized
below.
The examiner states that the claimed subject matter is
directed to a method of compensating for nested-to-isolated
pattern bias. Answer, pages 5-6. The examiner states that
positive bias is compensated for by adding a sputtering
component to the etch chemistry, while negative bias is adjusted
for by the electrical bias on the substrate (“space charge”
effect). Answer, pages 5-6.
The examiner states that the instant claims recite
providing a structure with a first critical dimension (CD) and
lithographically reducing the CD by an O2-containing trimming
etch. The claims further recite correcting the CD-bias between
nested and isolated features during a plasma-etch, and also the
etching parameters for the process. Answer, page 6.
The examiner finds that Tao teaches a method for narrowing
gate electrodes on a device. The steps comprise (a) forming a
stack layer and patterning the photoresist, (b) optionally
trimming the resist pattern, (c) etching the anti-reflection
coating (ARC) and hardmask and trimming the hard mask to a sub-
lithographic dimension (if not trimmed by the photoresist), and
(d) etching the gate to the desired sub-lithographic dimension.
These steps are shown in Figs. 2-6. The examiner finds that Tao
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uses an O2-containing gas in the plasma etching process (col. 3,
lines 43-52). Answer, page 6.
The examiner states that Tao does not teach correcting for
the CD-bias, and does not specify positive or negative resists.
Answer, page 7. The examiner states that Tao’s layers include
an oxide layer, and an ARC, but not TEOS. Answer, page 7.
The examiner finds that Ma teaches that CD-bias or “profile
microloading” is known (col. 1, lines 60- col. 2, line 21). The
examiner states this prior art process corrects for the
microloading effect by adjusting the RF power (and hence the
space charge). The examiner states that the resist sputtering
effect is also adjustable by adjusting the frequency of the RF
power (col. 2, lines 32-64). Answer, page 7.
The examiner also finds that Ma discloses further adjusting
the etch parameters to correct for the CD bias. These include
lowering the frequency (Fig. 5) and increasing the RF power
(col. 3, lines 10-27). The system is operated at 0-100mT (col.
5, lines 45-49). Answer, page 7.
The examiner states that Ma does not specify positive or
negative photoresists (claim 4). However, the examiner states
that the choice of a type of photoresist is uniquely determined
by the process.2 Answer, page 7.
With respect to the claimed “trim” aspect of the etching
step of claim 1, the examiner finds that Horak teaches the
concept of trimming the resist and ARC (anti-reflective coating)
to compensate for a nested-isolated etching bias of the gate
(col. 6, lines 49-col. 7, lines 44). The examiner also finds
that Horak teaches that nested-iso print bias is also corrected

2 We find that Horak specifically teaches that the type of resist chosen
is a design variable. See column 10, lines 7-10 of Horak. Hence, we
agree with this statement made by the examiner.
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by this process (col. 7, lines 45-67). The etch chemistries are
adjusted between the sputtering and etching species to bring
about the variable etch rates (fig. 5-8). Answer, page 7.
The examiner states that Horak, Ma and Tao solve the
problem of etch bias, and attempt to form narrow gates with
consistent CDs. Answer, pages 7-8.
The examiner concludes that it would have been obvious to
one of ordinary skill in the art to have compensated for the
etch bias of nested and isolated lines by biasing the etch-
masks, as taught by Horak, using the teachings of Ma and Horak,
to set the etching parameters in Tao’s trimming process, because
Ma teaches that varying the above-discussed parameters reduces
microloading, and increases the process window (col. 3, lines
15-27), while Horak teaches that this facilitates the design
process for producing consistent products (col. 2, lines 45-65).
Answer, pages 7-8.

B. Appellant’s Position
Appellant’s position regarding the examiner’s rejection is
set forth on pages 4-12 of the brief.
Appellant first argues that Tao, Ma, and Horak would not
have been combined as alleged by the examiner because the
references are directed to completely different matters and
problems. Brief, page 8.
Appellant argues that Tao is directed to forming a very
narrow polysilicon gate line (col. 1, lines 65-67) using a
consumable hard mask of silicon oxynitride covered by a thin
layer of silicon oxide during the etching of the polysilicon
(col. 2, lines 6-9). Appellant states that Tao combines the
functions of the anti-reflection coating function, and the
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substitution of a hard mask, during the etching step (col. 2,
lines 8-12). Brief, page 8.
Appellant states that, in contrast, Ma is specifically
directed to reducing a power frequency in a plasma etch reactor
so that the plasma source power level may be increased which
provides complete residue removal and prevents etch microloading
(col. 3, lines 10-28). Appellant states that, thus, Tao and Ma
would not have been combined, absent hindsight. Brief, page 8.
Appellant also argues that Horak is specifically directed
to performing a reactive ion etching process which compensates
for a subsequent normal etching process, to prevent a
nested/isolated feature offset (col. 6, line 49-col. 7, line 2).
Appellant states that Ma teaches entirely avoiding any such
“profile microloading.” Appellant concludes that one of
ordinary skill in the art would not have been motivated to
modify the teachings of Ma with a reactive ion etching process
which compensates for a subsequent etching process, as disclosed
by Horak, because Ma discloses a method which entirely avoids
any such problem. Brief, pages 8-9.
Appellant also argues that the combination of applied
references does not teach or suggest each and every element of
the claimed invention. Brief, page 9.
Appellant argues that the present invention recites etching
a structure to correct an offset between isolated and nested
structures which were created by a lithographic process.
Appellant states that, in other words, his invention corrects
for the isolated/nested offset from a previous lithographic
formation, as opposed to correcting for any isolated-feature,
nested-feature offset, which would otherwise result from a
subsequent lithographic formation. Brief, page 9. Appellant
discusses his assertions as to why the applied references do not
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teach this claimed feature, and we refer to the discussion in
the brief, therein. Brief, pages 10-12.
In summary, appellant states that none of the applied
references acknowledge correcting an existing offset. Appellant
states that the applied references concentrate on preventing any
offset which may occur from a subsequent etching. Appellant
states that clearly the applied references are incapable of
teaching or suggesting compensating for an existing offset.
Brief, pages 11-12.

C. The Examiner’s Rebuttal
The examiner’s response to appellant’s arguments is set
forth below, and is found on pages 8-16 of the answer.
With regard to appellants’ first line of argument
(references would not have been combined), the examiner states
that Tao, Ma, and Horak are analogous art, and solve the same
problem as the appellant’s, i.e., using resist trimming (Tao and
Horak) and space charge effect (Horak and Ma). Answer, page 8.
The examiner explains that appellant recognizes (instant
specification: p.1-p.2, line 8) the criticality of controlling
gate “length” (the width of the polysilicon conductive line
below the gate oxide) of a transistor, and notes that in
achieving a higher density of transistors on a substrate with
smaller dimensions (referred to as “scaling path”), this is even
more critical (instant specification: p.4, line 11-14). The
examiner states that appellant’s invention is directed to a
process to reduce variations in the gate CD in nested and
isolated areas. Answer, page 8-9.
The examiner finds that Tao addresses the same problem of
gate CD control (col. 1, lines 9-14), and teaches that as device
density increases, the criticality of controlling the gate CD
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increases (col. 1, lines 15-20). The examiner states that Tao
teaches that photoresist trimming to achieve gate CD control
becomes difficult to implement (col. 1, lines 26-29). The
examiner states that Tao teaches that the prior art shows that
polymer deposition during etching (from organic materials such
as photoresists and anti-reflective coatings (ARC)) contributes
to etch rate differences (col. 1, lines 44-51). Tao's solution
comprises an inorganic ARC, which also serves as one layer of a
hard mask (col. 2, lines 6-9), and trimming the photoresist with
an O-plasma (col. 2, lines 14-17). The photoresist is removed
after transferring the trimmed pattern to the hard mask layers.
The examiner states that, thus, Tao clearly addresses gate CD
control in nested features. Answer, page 9.
The examiner states that Tao does not explicitly address
differential etching between nested and isolated features. The
examiner states, however, that the CD of isolated features is
controlled by the same etch as used for nested features, and it
would be illogical to control one feature dimension at the
expense of another. The examiner states that one of ordinary
skill in the art would recognize the inconsistency of the logic.
The examiner states that this has also been explicitly stated by
Horak. The examiner states that Horak teaches that it would be
deleterious to the device to trim only isolated features without
considering nested features (col. 6, lines 31-35). This is
further explained, stating “the nested to isolated etch bias
cannot be adjusted without causing the nested etch bias to also
decrease” (col. 6, lines 43-46). The examiner finds that Horak
states “In addition, both nested and isolated lines will be
etched at the same time the isolated lines are etched faster
than are nested lines, but both are etched” (col. 2, lines 17-
20). Answer, pages 9-10.
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The examiner further states that appellant’s argument that
Tao does not teach reducing the bias between nested and isolated
features, is unconvincing because it is not possible to etch one
without etching the other. The examiner states that appellant’s
selective reading of Tao’s teachings leads to incorrect
conclusions, and states that Tao’s Figs. 3-5 are similar to
instant Figs. 2A-2B. The examiner states that it would be
misleading to suggest that the instant invention is directed to
the trimming of an isolated line based on instant Figs. 2A-2B.
Answer, page 10.
The examiner states that Ma, admittedly, does not address
gate CD control; but is directed to an analogous problem;
namely, linewidth variations in conductor lines in nested and
isolated features, when using photoresist masks. The examiner
states that the etching process is the same as that of the
instant invention, using oxygen reactive ion etching (O-RIE).
The examiner states that the phenomenon of space charge effect
in etching a metal and polysilicon are the same is evidenced by
comparing Ma (col. 2, lines 8-21) and the instant specification
(instant specification: p.13, lines 9-18). The examiner states
that both describe the charge build up and lateral etching of
the layers above the conductor layer. The examiner states that
Ma compensates for the space charge effect by adjusting the RF
frequency of the RIE unit (Ma: abstract). The examiner states
that a person of ordinary skill in the art would recognize that
etching conductive underlayers such as polysilicon gates, would
pose the same problems as Ma’s etching of nested and isolated
metal lines. The examiner points out that Ma and Tao are both
related to device fabrication by the same lithographic
processes, and states that appellant has selectively interpreted
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Ma’s teachings to suggest divergent subject matter. Answer,
page 10.
The examiner states that Horak deals with the same problems
as Tao and Ma: etching nested and isolated lines on
semiconductor devices (col. 2, lines 51-65). The examiner
states that Horak teaches the basic phenomenon of etching bias
in Tao’s plasma etching (col. 1, lines 34-54) as well as Ma’s
RIE-etching (col. 1, lines 55-col.2, line 20). The examiner
states that Horak uses Ma’s O-RIE etching to trim the etch masks
prior to etching the underlying polysilicon layer (col. 3, lines
11-15). The examiner states that the space charge effect is
mitigated by adjusting the “etching” and “sputtering” species in
the gases (col. 3, lines 20-27). The examiner states that this
is the same technique used in the instant invention. The
examiner notes further that Horak teaches the equivalence of
metal conductor etching and polysilicon etching to control gate
CD using O-RIE (col. 8, lines 44-50). Answer, pages 10-11.
The examiner also states that appellant argues (instant
brief: p.8) that Ma teaches “avoiding microloading” (col. 3,
lines 10-28), while Horak teaches “compensating for subsequent
normal etching process to prevent a nested/isolated offset-
effect” (col. 6, lines 49-col. 7, line 2), and thus, the two
references are incompatible. The examiner disagrees for the
following reasons.
The examiner states that Ma solves the problem of
nested/isolated offset in etching a conductor layer using a
photoresist mask. The examiner states that Ma does so by
adjusting the RF power and frequency such that the sputtering
phenomenon and etching phenomenon are balanced (“space charge
effect”). This leads to little or no re-deposition of the
photoresist (“profile microloading”) during the conductor etch.
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The reduction of microloading permits faster etching of nested
features. Answer, page 11.
The examiner states that Horak similarly solves the problem
of nested/isolation offset in etching an underlayer using a
photoresist mask (the resist mask is not shown in figures; see
col. 5, lines 3-4). The examiner states that Horak uses the
space charge effect in O-RIE similar to Ma and the instant
invention. The examiner states that Horak adjusts the reactive
components to balance the sputtering and etching phenomenon;
this adjustment is similar to the instant invention. This
etching step provides a mask layer with no print bias and thus
subsequent normal etching of the conductor layer becomes
feasible (col. 6, lines 49-col. 7, line 2); this serves the same
function as mask trimming. The examiner states that Horak
clarifies the term “normal etching” to include differential
etching of nested/iso features under the mask (col. 6, lines 21-
36 & col. 9, lines 6-33). Answer, page 12.
The examiner ultimately concludes that appellant’s argument
that the references teach unrelated subject matters, and are
therefore not combinable, is not convincing. Answer, page 12.
With regard to appellant’s contention that the applied
references do not teach each and every element of the instant
claims, on page 13 of the answer, the examiner states that it
has been shown, supra, that the combination of references
teaches each and every element of the instant claims. We refer
to pages 13-16 of the answer regarding the examiner’s additional
statements in this regard.

C. Our Analysis
With regard to appellant’s assertions that (1) the applied
references are not combinable, and (2) the combination does not
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teach the claimed invention, we note that “the consistent
criterion for determination of obviousness is whether the prior
art would have suggested to one of ordinary skill in the art
that this process should be carried out and would have a
reasonable likelihood of success, viewed in the light of the
prior art.” In re Dow Chemical Co., 837 F.2d 469, 5 USPQ2d
1529, 1531 (Fed. Cir. 1988) (citing Burlington Industries v.
Quigg, 822 F.2d 1581, 583, 3 USPQ2d 1436, 1438 (Fed. Cir.
1987); In re Hedges, 783 F.2d 1038, 1041, 228 USPQ 685, 687
(Fed. Cir. 1987)); Orthopedic Equipment Co. v. United States,
702 F.2d 1005, 1013, 217 USPQ 193, 200 Fed. Cir. 1983); In re
Rinehart, 531 F.2d 1048, 1053-54, 189 USPQ 143, 148 (CCPA
1976). It is thus the position of the court that, where
claimed subject matter has been rejected as obvious in view of
a combination of prior art references, a proper analysis under
§ 103 requires, inter alia, consideration of two factors: (1)
whether the prior art would have suggested to those of ordinary
skill in the art that they should make the claimed composition
or device, or carry out the claimed process; and (2) whether
the prior art would also have revealed that in so making or
carrying out, those of ordinary skill would have a reasonable
expectation of success. Both the suggestion and the reasonable
expectation of success must be founded in the prior art, not in
the applicant’s disclosure. Dow Chem., supra.
In the instant case, the examiner has explained, in detail,
(1) how the applied art suggests carrying out appellant’s
claimed process, and (2) how the applied art reveals a
reasonable expectation of success in carrying out the claimed
process. We refer to the above-described examiner’s position in
this regard.
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With specific regard to appellant’s repeated and emphasized
argument that the claimed invention corrects offset from a
previous lithographic formation [emphasis added], and that the
applied art does not do so, we find that Horak discusses the
formation of a lithographic film (col. 7, lines 4-5) that is
subsequently subjected to a special etch (col. 7, lines 3-10).
Hence, Horak teaches etching a structure from a previous
lithographic formation. Hence, we agree with the examiner’s
statement, made on page 16 of the Answer, that the applied art
teaches every element of the claims.
We also add that Horak explains that “the amount of
lithographic film or other etch mask added” to a nested line
will decrease angle 2002 (depicted in Figure 10 of Horak).
Horak thus recognizes how offsets, created [emphasis added] by a
lithographic film, are formed. In this manner, the art has
recognized the need to compensate for an offset created by a
lithographic film or other etch mask.
In view of the above, we therefore affirm the rejection of
claims 1, 3-8, 10-14, and 16-20 under 35 U.S.C. § 103 as being
obvious over Tao in view of Ma, and further view of Horak.

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No time period for taking any subsequent action in
connection with this appeal may be extended under 37 CFR
§ 1.136(a)(1)(iv)(effective September 13, 2004; 69 Fed. Reg.
49960 (August 12, 2004); 1286 Off. Gaz. Pat. Office 21
(September 7, 2004)).

AFFIRMED

BRADLEY R. GARRIS )
Administrative Patent Judge )
)
)
)BOARD OF PATENT
) APPEALS AND
TERRY J. OWENS ) INTERFERENCES
Administrative Patent Judge )
)
)
)
)
)
BEVERLY A. PAWLIKOWSKI )
Administrative Patent Judge )

BAP/sld
Appeal No. 2005-0585
Application No. 09/821,478

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