Ex Parte Pawloski et al

Board of Patent Appeals and Interferences

Feb 3, 2010

10790457 (B.P.A.I. Feb. 3, 2010)

UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________

Ex parte ADAM R. PAWLOSKI, AMR Y. ABDO,
GILLES R. AMBLARD, BRUNO M. LAFONTAINE,
IVAN LALOVIC, HARRY J. LEVINSON,
JEFFREY A. SCHEFSKE, CYRUS E. TABERY,
and FRANK TSAI
____________

Appeal 2009-000205
Application 10/790,457
Technology Center 1700
____________

Decided: February 3, 2010
____________

Before ALLEN R. MACDONALD, Vice Chief Administrative Patent Judge,
PETER F. KRATZ, and MARK NAGUMO, Administrative Patent Judges.

KRATZ, Administrative Patent Judge.

DECISION ON APPEAL
This is a decision on an appeal under 35 U.S.C. § 134 from the
Examiner’s final rejection of claims 1-6, 8-13, 15-21, and 23. We have
jurisdiction pursuant to 35 U.S.C. § 6.

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Appellants’ claimed invention is directed to a method of removing an
immersion lithography medium from the surfaces of semiconductor wafers
as part of an immersion lithography process. As explained by Appellants,
“[i]n immersion lithography, an immersion lithography medium is placed
between the final lens of the imaging system and a photosensitive material
(e.g., a photoresist) on the surface of a nascent semiconductor device” (Spec.
2: 2-5). Appellants note that “the immersion lithography medium needs to
be removed from the semiconductor wafer with which it has been used” in a
non-deleterious manner to avoid contamination of subsequent processing
steps and the semiconductor device itself (Spec. 2: 18-23). As one
embodiment, Appellants note that “polyfluoroethers can be used as the
immersion lithography medium in conjunction with a 157 nm light source
14” (Spec. 6: 4-5) and that supercritical carbon dioxide can be used to
remove the immersion lithography medium from the wafer surfaces (Spec.
3: 5-12). The separated immersion lithography medium and carbon dioxide
can be recovered and reused (Spec. 3: 13-29).
Claim 1 is illustrative and reproduced below:
1. A process for fabricating a semiconductor device, comprising:

applying an immersion lithography medium to a surface of a
semiconductor wafer;

exposing a material on the surface of the semiconductor wafer to
electromagnetic radiation having a selected wavelength;

applying supercritical carbon dioxide to the semiconductor wafer to
remove the immersion lithography medium from the surface of the
semiconductor wafer; and

following the step of applying supercritical carbon dioxide to the
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wafer, obtaining a mixture of the immersion lithography medium removed
from the surface and carbon dioxide and recovering and purifying the
immersion lithography medium from the mixture.

The Examiner relies on the following prior art references as evidence
in rejecting the appealed claims:
Wallace 6,024,801 Feb. 15, 2000
Costantini US 6,612,317 B2 Sep. 2, 2003

Switkes, “Immersion Lithography at 157nm” J. Vac. Sci. Technol. B. 19(6),
Nov./Dec. 2001, pp. 2353-2356

The Examiner maintains the following ground of rejection:
Claims 1-6, 8-13, 15-21, and 23 stand rejected under 35 U.S.C. §
103(a) as being unpatentable over Switkes in view of Wallace and
Costantini.
We reverse the stated rejection. Our reasoning follows.
All of the appealed claims require a process including at least the
following steps: (1) applying immersion lithography medium to a
semiconductor surface; (2) exposing material on the wafer surface to a
selected wavelength of electromagnetic radiation; (3) applying supercritical
carbon dioxide to the wafer to remove the immersion lithography medium
from the wafer surface; and (4) obtaining a mixture of removed immersion
lithography medium and carbon dioxide following step (3) and recovering
and purifying immersion lithography medium from the admixture (claims 1,
10, and 16).
The Examiner relies on Switkes for teaching steps corresponding to
the first two steps of Appellants’ claimed process, as noted above (Ans. 4;
Switkes, pp. 2353-2355). The Examiner acknowledges that Switkes, the
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primary reference, does not disclose the use of supercritical carbon dioxide
to remove immersion lithography medium, such as the perflouropolyether of
Switkes, from a semiconductor wafer, as Appellants’ process requires (Ans.
4 and 5). Consequently, Switkes fails to disclose the subsequent steps of
obtaining a mixture of carbon dioxide and removed immersion lithography
fluid, and recovering and purifying the medium from the admixture, as
Appellants’ process requires (Ans. 5).
However, based on additional alleged teachings attributed to Wallace
and Costantini, the Examiner takes the position that:
[i]t would have been obvious to one of ordinary skill in
the art at the time of invention by applicant to modify the
teachings of Switkes et al in view of Wallace ('801) and further
in view of Costantini ('317), in order to recover the immersion
lithography medium that is removed by applying supercritical
CO2 to the wafer, because Wallace ('801) teaches that
supercritical fluids such as supercritical CO2 can be use[d] to
remove substances such [as] fluorocarbons from the surface [of]
a semiconductor wafer, and Costantini ('317) teaches that one
can recover and then purify effluent from a semiconductor
wafer processing chamber in order to recycle the immersion
lithography medium that is recovered back to the
semiconductor wafer processing chamber for re-use, resulting
in a more economically efficient semiconductor wafer
processing method.
Ans. 6-7
Appellants contrarily urge that while Wallace teaches the use of
fluids, such as carbon dioxide, in a supercritical state, for removal of
substances from a semiconductor wafer prior to a passivation treatment,
Wallace has nothing to do with immersion lithography (App. Br. 7).
Appellants contend that Wallace’s disclosure of fluorocarbon, as referred to
by the Examiner has little to do with their claimed process and that the
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teachings of Costantini, as relied upon by the Examiner, are not directed to
an immersion lithography process wherein the immersion medium is
recovered and purified after using carbon dioxide for extraction thereof from
a wafer (App. Br. 7-8). Rather, Appellants urge that Costantini is directed to
the recovery and reuse of a co-solvent and solvent (carbon dioxide) used as
part of the cleaning medium, a part of a super critical fluid, used in a wafer
cleaning process. Id.
Consequently, Appellants argue, in essence, that the Examiner has
read too much into the applied references and has failed to discharge the
burden of establishing an adequate factual basis and provide a rationale
reason that supports the Examiner’s proposed modification of Switkes’s
immersion lithography process such that it would have been reasonable to
expect that an ordinarily skilled artisan would have arrived at Appellants’
claimed process with a reasonable expectation of success based on the
applied teachings of the combined references (App. Br. 7-15; see generally
Reply Br.).

DISPOSITIVE ISSUE
Have Appellants shown error in the Examiner’s obviousness
determination because the Examiner has not supplied an adequate factual
basis and reasoning to establish, prima facie, that one of ordinary skill in the
art would have been led to modify the immersion lithography process of
Switkes so as to arrive at a process corresponding to the claimed process
with a reasonable expectation of success in so doing, by including a step of
applying supercritical carbon dioxide to remove the immersion medium of
Switkes from a semiconductor wafer and steps of subsequently recovering
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and purifying the immersion medium from an admixture with carbon
dioxide based on the combined teachings of Switkes, Wallace and
Costantini, as applied by the Examiner?

PRINCIPLES OF LAW
The Examiner bears the initial burden, on review of prior art or on any
other ground, of presenting a prima facie case of unpatentability. In re
Oetiker, 977 F.2d 1443, 1445 (Fed. Cir. 1992). However, on appeal to this
Board, Appellants must present argument to show that the Examiner erred in
rejecting the claims. See 37 C.F.R. § 41.37(c)(1)(vii).
“[R]ejections on obviousness grounds cannot be sustained by mere
conclusory statements; instead, there must be some articulated reasoning
with some rational underpinning to support the legal conclusion of
obviousness.” KSR Int’l v. Teleflex, Inc., 550 U.S. 398, 418 (2007) (quoting
In re Kahn, 441 F.3d 977, 988 (Fed. Cir. 2006)). In this regard, “a patent
composed of several elements is not proved obvious merely by
demonstrating that each of its elements was, independently, known in the
prior art.” Id.
Rejections based on § 103(a) must rest on a factual basis with these facts
being interpreted without hindsight reconstruction of the invention from the
prior art. See In re Warner, 379 F.2d 1011, 1017 (CCPA 1967), cert.
denied, 389 U.S. 1057 (1968).

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FINDINGS OF FACT
In addition to findings of fact set forth elsewhere in this Opinion, we
determine the following relevant findings of fact by a preponderance of the
evidence standard.
Switkes discloses and/or suggests a method of forming a
semiconductor device wherein: (1) a non-toxic, chemically inert, clean room
environment compatible immersion lithography medium, such as
perfluoropolyether (PFPE, commercially available as Fomblin®Y or Z) , is
applied to a semiconductor wafer surface; (2) the wafer surface is exposed to
electromagnetic radiation of a specified wavelength, such as at a wavelength
of 157 nm, and (3) the lithography medium is separated from the wafer with
a low molecular weight PFPE solvent (Fomblin PFS-1) (pp. 2353-2355; see
Ans. 4).
Wallace discloses and/or suggests that it is well known to employ a
method of processing semiconductor wafers or micromechanical devices of
the semiconductor-type wherein the wafers are treated with a supercritical
fluid (SCF), such as carbon dioxide, to clean the wafers, such as by
removing various liquids (ambient), contaminants, and/or organic
compounds therefrom via SCF treatment (col. 3, l. 21- col. 4, l. 37). Wallace
further teaches or suggests that SCF can be used to remove soluble chemical
compounds prior to passivation treatment to preserve the surface integrity of
a part. Finally, Wallace teaches that PFPE can be used for the passivation
treatment that follows the SCF treatment (col. 4, l. 65- col. 5, l. 5 and col. 9,
ll. 23-27).
While Wallace discloses that “fluorocarbon removal would be
facilitated by exposure to UV light in the course of the CO2 SCF process,”
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the Examiner has not pointed out where Wallace explicitly discloses that
perfluoropolyether or any specified immersion lithography fluid is
dissolvable and removed from a wafer by SCF treatment with carbon
dioxide (Wallace, col. 8, ll. 55-57; see generally the Examiner’s Answer).
Costantini teaches or suggests a fluid delivery and recovery system for
use in supercritical fluid (SCF) treatment of semi-conductor wafers wherein,
after the wafer cleaning, the effluent materials separated from the wafer can
be processed by separation for recovery, purification, recycle, and/or
disposal of the various materials found in the effluent obtained from the
supercritical fluid treatment of the wafer (see generally Costantini).
Costantini refers to the SCF fluid as “solvent” (col. 5, ll. 7-14).
While Costantini discloses recovery and purification of the SCF
solvent (carbon dioxide) and an optional SCF co-solvent after treating a
wafer therewith in the disclosure of Costantini relied upon by the Examiner,
the Examiner has not shown where Costantini teaches that a material useful
as a lithography immersion medium, such as the PFPE of Switkes, is
removed from a wafer by a carbon dioxide-containing SCF fluid followed by
recovery and purification of such a lithography immersion medium from an
admixture with carbon dioxide (Costantini, col. 2, ll. 7-11, col. 3, ll. 24-32,
col. 4, ll. 1-10, and col. 6, ll. 6-56; Ans., 5, 6, and 8-12).

ANALYSIS
In formulating the stated rejection, the Examiner asserts that Wallace
discloses removal of soluble chemicals and/or a fluorocarbon, from a wafer
using SCF carbon dioxide (Ans. 5). However, the Examiner does not
reference evidence that substantiates a reasonable expectation of success in
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the proposed modification of Switkes’ process based on this disclosure of
Wallace. In this regard, the Examiner does not adequately explain why the
referenced disclosure of Wallace would have taught or suggested, to one of
ordinary skill in the art, that an immersion lithography medium
corresponding to the perfluoropolyether (PFPE) of Switkes, which is
chemically distinct from fluorocarbon, as referenced by the Examiner and
addressed by Wallace, would have been removed by SCF carbon dioxide
from the immersion lithography treated wafer of Switkes. For example, the
Examiner has not cited prior art evidence to establish that PFPE is soluble in
SCF carbon dioxide so as to be reasonably expected to be subject to removal
from a wafer followed by recovery. Nor has the Examiner otherwise
articulated why any other immersion lithography medium, that may have
been suggested as being useable in Switkes, would have been reasonably
expected to be subject to removal from a wafer by SCF carbon dioxide based
on the added teachings of Wallace.
We decline, in the first instance, to explore the record, make express
and detailed findings of fact as to the teachings of the references, weight
those various findings, and decide, on that basis, whether the Examiner’s
conclusions are well-founded.
In this appeal, the Examiner’s rejection falls short of furnishing a
persuasive rationale for the proposed modification of Switkes’ immersion
lithography process based on the use of SCF carbon dioxide by Wallace for
cleaning wafers or devices of materials that have not been shown to be
immersion lithography mediums prior to the passivation treatment of
Wallace.
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Moreover, the Examiner’s additional reliance on Costantini does not
remedy the aforementioned deficiency in the stated rejection because the
Examiner has not identified where Costantini, or any other prior art relied
upon in the rejection, teaches that a material useful as an immersion
lithography medium in accordance with the process of Switkes, such as
PFPE, would be subject to such a removal protocol. In this regard, we again
note, for example, that the Examiner does not furnish evidence to establish
that PFPE lithography medium would have been expected to be solvated by
SCF carbon dioxide.
Also, we note that the Examiner confounds the obviousness position
presented in the Answer by overstating and/or mischaracterizing the
teachings of the applied references in several locations and then
backtracking to seemingly incomplete and/or inconsistent alternative
obviousness positions in other locations.
For example, the Examiner maintains that:
Wallace ('801) claims a method of processing a wafer
comprising the steps of: placing the wafer have [sic] a wafer
surface in an enclosed and controlled environment; exposing
said wafer surface to a cleaning medium rendered as a
supercritical fluid; purging said environment of substance
including soluble chemical compound liberated from said wafer
surface by said cleaning medium. (See, claim 19). Wallace
('801) also discloses an example in which the supercritical fluid
used is carbon dioxide. (See, col.8, 31-42). Wallace ('801)
further discloses that removal of a material such as a
fluorocarbon from the surface of a wafer could be facilitated by
exposure to UV light during the exposure of the wafer to
supercritical CO2. These teachings in Wallace ('801) meet the
limitation of claims 1, 10 and 16 where supercritical carbon
dioxide is applied to a semiconductor wafer to remove
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immersion lithography medium from the surface of a
semiconductor wafer.
Ans. 5
In response to Appellants’ argument asserting that “Wallace has
nothing to do with immersion lithography” and that “[t]he Examiner’s
reference to the use of UV to remove a fluorocarbon from the surface is
completely irrelevant” (App. Br. 7), the Examiner retreats to an incompletely
formulated obviousness position based on several referenced “general”
teachings of Wallace that allegedly cure a deficiency in Switkes with respect
to the SCF carbon dioxide cleaning of a wafer (Ans. 8). However, as noted
above, the Examiner does not specifically cite to evidence to substantiate
that the generally referred to SCF carbon dioxide cleaning disclosure of
Wallace would have been reasonably expected to be applicable to the
removal of the PFPE immersion lithography fluid of Switkes by one of
ordinary skill in the art.
Similarly, the Examiner overstates the disclosure of Costantini in
asserting that, in Costantini “there is a recovery section (See, col. 3, 24-31)
that takes in a solvent, which is a mixture of immersion fluid and
supercritical CO2,, referred to as effluent, obtained from a semiconductor
processing chamber (See, col. 6, 6-18)” (Ans. 5-6). In response to argument
by Appellants highlighting this error, the Examiner follows with an
acknowledgement that Costantini does not explicitly disclose immersion
fluid as part of the effluent stream and resorts to reliance on alleged general
teachings of Costantini (Ans. 12). However, the Examiner again falls short
in furnishing reasoning establishing a sustainable prima facie case of
obviousness for the advocated modifications to the immersion lithography
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process of Switkes based on the properly interpreted teachings of Wallace
and Costantini.
On this record, we determine that Appellants have the better reasoned
position with respect to the obviousness question before us.

CONCLUSION
Appellants have shown that the Examiner’s obviousness
determination is founded on an inadequate factual basis and reasoning to
establish, prima facie, that one of ordinary skill in the art would have been
led to modify the immersion lithography process of Switkes by including the
application of supercritical carbon dioxide to remove the immersion medium
of Switkes from the semiconductor wafer and to include a subsequent
recovery and purification of the immersion medium from an admixture with
carbon dioxide so as to arrive at a process corresponding to the claimed
process, with a reasonable expectation of success in so doing, based on the
combined teachings of Switkes, Wallace, and Costantini, as referred to and
applied by the Examiner.

ORDER
The Examiner’s decision to reject claims 1-6, 8-13, 15-21, and 23
under 35 U.S.C. § 103(a) as being unpatentable over Switkes in view of
Wallace and Costantini is reversed.

REVERSED

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PL Initial:
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