Ex Parte Baluswamy

Board of Patent Appeals and Interferences

Sep 11, 2007

10651351 (B.P.A.I. Sep. 11, 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The opinion in support of the decision being entered today is not binding
precedent of the Board.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 PARY BALUSWAMY
____________

Appeal 2007-3372
Application 10/651,351
Technology Center 1700
____________

Decided: September 11, 2007
____________

Before BRADLEY R. GARRIS, CHARLES F. WARREN, and
PETER F. KRATZ, Administrative Patent Judges.

KRATZ, Administrative Patent Judge.

DECISION ON APPEAL
This is a decision on an appeal from the Examiner’s final rejection of
claims 1-4, 6-12, 14-22, and 24-30, the only claims that remain pending in
this application. We have jurisdiction pursuant to 35 U.S.C. §§ 6 and 134.

Appeal 2007-3372
Application 10/651,351

Appellant’s claimed invention is directed to a method for producing a
pattern on a photoresist disposed on a substrate using a mask and wherein a
mask pattern image is altered with a nonzero spherical aberration value.1
The altered mask pattern image is focused at approximately mid-depth of the
photoresist. Claims 1 and 11 are illustrative and reproduced below:
1. A method of producing a pattern on a photoresist,
comprising:
providing a mask having a pattern defined thereon;

disposing the mask between an illumination source and a substrate having a
photoresist disposed thereon;

irradiating the mask with light from the illumination source to produce a
mask pattern image;

altering the mask pattern image with nonzero spherical aberration value
selected to at least partially compensate for spherical aberration
induced by the photoresist; and

focusing the altered mask pattern image at approximately a mid-depth of the
photoresist on the substrate.

11. A method of producing a pattern on a photoresist,
comprising:

disposing a mask having a pattern defined thereon between an illumination
source and a substrate having a photoresist disposed thereon;

irradiating the mask with light from the illumination source to produce a
mask pattern image;

1 Appellant explains that “[s]pherical aberration is caused by using
spherically shaped lenses and mirrors because truly spherical surfaces do not
form sharp images” (Specification ¶ 0005). Appellant’s drawing Figure 2
illustrates a prior art Example of a spherical aberration.
2
Appeal 2007-3372
Application 10/651,351

selecting a nonzero spherical aberration value using the equation:

where a is the nonzero spherical aberration value of the mask pattern
image, n is a refractive index of the photoresist, t is a thickness of
photoresist, and s is a focal distance into the photoresist;

introducing the nonzero spherical aberration value to the mask pattern
image; and

irradiating the photoresist with the mask pattern image including the nonzero
spherical aberration value.

The Examiner relies on the following prior art references as evidence
in rejecting the appealed claims:
Takahashi US 5,831,715 Nov. 3, 1998
Yasuzato US 5,935,738 Aug. 10, 1999
Nozue US 5,432,587 Jul. 11, 1995

Claims 1-4, 9-12, 14, 15, 19-22, 24, 25, 29, and 30 stand rejected
under 35 U.S.C. § 103(a) as being unpatentable over Takahashi in view of
Yasuzato. Claims 6-8, 16-18, and 26-28 stand rejected under 35 U.S.C. §
103(a) as being unpatentable over Takahashi in view of Yasuzato and
Nozue.
We affirm the Examiner’s rejections. Our reasoning follows.
Under 35 U.S.C. § 103, the factual inquiry into obviousness requires a
determination of: (1) the scope and content of the prior art; (2) the
differences between the claimed subject matter and the prior art; (3) the level
of ordinary skill in the art; and (4) secondary considerations. See Graham v.
John Deere of Kansas City, 383 U.S. 1, 17-18, 148 USPQ 459, 467 (1966).
3
Appeal 2007-3372
Application 10/651,351

The analysis supporting obviousness should be made explicit and should
“identify a reason that would have prompted a person of ordinary skill in the
art to combine the elements” in the manner claimed. KSR Int’l Co. v.
Teleflex, Inc., 127 S. Ct. 1727, 1731, 82 USPQ2d 1385, 1389 (2007).
§ 103(a) Rejection over Takahashi taken with Yasuzato.
Appellant argues claims 1, 2, 4, 9 and 10 together as a group. We
select claim 1 as the representative claim for this claim grouping.
The Examiner has determined that Takahashi discloses much of the
representative claim 1 method step requirements but that “[t]he difference
between the claims and Takahashi is that Takahashi does not disclose that
the projected pattern image is focused at approximately mid-depth of the
photoresist on the substrate” (Answer 4 and 5).
The Examiner further relies on Yasuzato as evidence of the
obviousness of the subject matter of representative claim 1. The Examiner
contends that it would have been obvious to one of ordinary skill in the art at
the time of the invention “to modify Takahashi by employing the method of
focusing the light to ... mid-depth of the photoresist as suggested by
Yasuzato because Yasuzato, in col. 5, lines 46-54, and in col. 6, lines 1-13,
discloses that increasing the depth of focus enables the precision of the
pattern dimension to be enhanced” (Answer 5).
Appellant does not dispute that Takahashi taught or would have
suggested the representative claim 1 method but for the focus location
(approximately mid-depth of the photoresist) of the step of focusing the
altered image pattern as required by appealed claim 1 (Br. 5-9; Reply Br. 2-
4
Appeal 2007-3372
Application 10/651,351

4).2 Appellant contends that Takahashi alone or together with Yasuzato
would not have taught or suggested the method of representative claim 1 to
one of ordinary skill in the art at the time of the invention in light of the
required approximately mid-depth photoresist focus location of the focus
step.
Thus, the principal issue before us with respect to the propriety of the
Examiner’s obviousness rejection of claims 1, 2, 4, 9 and 10 is: Has
Appellant identified reversible error in the Examiner’s obviousness rejection
of claims 1, 2, 4, 9, 10 by the assertions in the Briefs that Takahashi taken
alone or with Yasuzato would not have taught or suggested the photoresist
approximate mid-depth location for the focusing of the altered mask pattern
image?
We answer this question in the negative and affirm the Examiner’s
obviousness rejection of claims 1, 2, 4, 9, and 10 over Takahashi taken with
Yasuzato for substantially the reasons stated in the Answer. We offer the
following for emphasis.
Appellant acknowledges that Yasuzato teaches a depth of focus for
focusing a mask pattern image on a photoresist that is “the range in which
the deviation from the focus position is permissible.” (Reply Br. 3 quoting
from Yasuzato, col. 1, ll. 45-49). In other words, Yasuzato teaches an
increased range of deviation from an ideal focus position of a mask pattern
image on a photoresist for permissible or acceptable results that allows for
the precision of the pattern dimensions to be enhanced (Yasuzato, col. 5, l.
25 - col. 6, l. 7). Consequently, we are not persuaded by Appellant’s

2 Arguments not made in the Briefs are considered to be waived. See 37
C.F.R. § 41.37(c)(vii) (2006).
5
Appeal 2007-3372
Application 10/651,351

argument that one of ordinary skill in the art would not have been led to
combine Yasuzato with Takahashi in a manner to arrive at the subject matter
of representative claim 1 for substantially the reasons stated by the Examiner
(Answer 6-8). Indeed, Takahashi’s disclosure of a focus position correction
means to allow for adjustment of the focus position to a best (optimum)
focus position would have reasonably led one of ordinary skill in the art to
an approximately mid-depth of the photoresist layer focus position upon
routine experimentation by itself, much less as a result of the combined
teachings of Yasuzato therewith. In this regard, we note that Takahashi
recognized that the resist material should be taken into account in adjusting
the spherical aberration (Takahashi, col. 1, ll. 27-48).3 This would
reasonably have suggested adjusting to a focus position for the altered image
projection at the photoresist that would include focus positions in the
photoresist layer, including positions proximate the middle of the
photoresist. After all, Takahashi’s purpose in adjusting the focus position is
to produce a mask pattern image in a photoresist via projection exposure.
Hence, one of ordinary skill in the art would have recognized that the
photoresist location of Takahashi, including a mid-depth location thereof, is
clearly within the locus where the focus position of the altered mask pattern

3 Also, we note Appellant’s admissions in the Specification and drawing
Figures with regard to the prior art projection (focus) of an altered mask
image at a resist coated substrate for compensating for spherical aberration
(Specification ¶¶ 0004 -0007; Figs, 1 and 2). It is axiomatic that admitted
prior art in an applicant's Specification may be used in determining the
patentability of a claimed invention and that consideration of the prior art
cited by the Examiner may include consideration of the admitted prior art
found in an applicant's Specification. In re Nomiya, 509 F.2d 566, 570-571,
184 USPQ 607, 611-612 (CCPA 1975).
6
Appeal 2007-3372
Application 10/651,351

image best focusing position and corrections thereof taught or suggested by
Takahashi would have been directed at.
Moreover, we are not persuaded by Appellant’s contention that
Yasuzato is not combinable with Takahashi because Yasuzato alters the
wavelength of light using a mask whereas Takahashi alters the light source
to modify the wave length of the light employed (Reply Br. 4; Br. 8 and 9).
Appellant has not buttressed this argument with persuasive evidence
establishing that one of ordinary skill in the art would have possessed less
than the level of skill required to select either one or both of these known
methods of light wavelength adjustment for use in photoresist pattern
formation wherein the mask pattern image applied to the photoresist is
adjusted for spherical aberration given the combined teachings of these
references. In this regard, Yasuzato discloses that the phase shifting mask
embodiments thereof are “applicable with no restriction on the exposure
light and the exposing system” (Yasuzato, col. 12, ll. 38-40).
On balance, we determine that the evidence of obviousness presented
by the Examiner outweighs the arguments in favor of an unobviousness
holding furnished in the Briefs for the rejected claims 1, 2, 4, and 6-10.
Concerning claims 3, 11, 12, 14, 15, 19-22, 24, 25, 29, and 30,
Appellant presents substantially the same argument against the Examiner’s
obviousness holding.4 Hence, we select claim 11 as the representative claim
for rejected claims 11, 12, 14, 15, 19-22, 24, 25, 29, and 30 with claim 3
being separately considered in so far as the arguments made for claim 1.
However, we do not find the arguments made against the Examiner’s

4 For dependent claims 3, this argument is in addition to the arguments made
with regard to the Examiner’s rejection of claim 1, the claim from which
claim 3 depends.
7
Appeal 2007-3372
Application 10/651,351

rejection of claim 3, which are based on the features thereof common with
claim 1, to be persuasive for the reasons we stated above with respect to the
rejection of claim 1. Thus, we focus on representative claim 11 in
considering Appellant’s arguments regarding rejected claims 3, 11, 12, 14,
15, 19-22, 24, 25, 29, and 30. These arguments are directed at the alleged
non-obviousness of the claimed process based on the use of a specified
equation for selection of a nonzero spherical aberration value that is
introduced or added to the mask pattern image used in treating the
photoresist (Br. 10-16; Reply Br. 4-8). This equation can be found in claim
11, reproduced above.
Regarding representative claim 11, the Examiner basically takes the
position that the equation is an expression of an optimization of three known
result effective factors or variables; that is, the photoresist refractive index
(n), the thickness of the photoresist layer (t), and the focal distance into the
photoresist (s) with the equation representing an optimization expression for
assessing the spherical aberration value to be applied or introduced into the
mask pattern image as a correction to the image so as to take spherical
aberration of the projected mask image into account (Answer 5, 9, and 10,
Takahashi, col. 3, l. 34 –col. 4, l. 5 and col. 6, ll. 25-30).
Appellant does not dispute that the photoresist refractive index and
thickness would have been known or suggested to one of ordinary skill in
the art as result effective variables for determining a nonzero spherical
aberration correction value based on the disclosure of Takahashi. Nor does
Appellant dispute that it would have been obvious for one of ordinary skill
in the art to derive a nonzero spherical aberration adjustment formula, as
required by representative claim 11, if the focal distance into the photoresist
8
Appeal 2007-3372
Application 10/651,351

was a known result effective variable like the other two result effective
variables used in the equation. Rather, Appellant contends that the focal
distance (amount of defocus, or focal depth) into the substrate (s) is not
recognized as a result effective variable by Takahashi (Br. 10-16; Reply Br.
4-8). We are not persuaded of reversible error in the Examiner’s
obviousness determination based on this line of argument, as furnished in
the Briefs.
At the outset, we note that the question raised by this line of argument
as presented in the Briefs may be more properly asked as follows. Has
Appellant established reversible error in the Examiner’s obviousness
rejection of representative claim 11 (as well as separately considered claim
3) by the contention that the applied references, including Takahashi, would
not have taught, suggested or otherwise led one of ordinary skill in the art to
the determination or recognition that the focal distance into the substrate is a
result effective variable (in addition to the other two claimed factors) for
optimizing the amount of correction to be applied to the mask pattern image
of Takahashi that is to be projected into a photoresist. We answer this
question in the negative on this record.
Here, the thrust of Appellant’s argument is that:
The Final Action argues that Takahashi recognizes a
relationship between the line width change relative to the
degree of defocus, which allegedly satisfies the requirement
that the focal distance is recognized by Takahashi as a result-
effective variable. This is not the case. In particular, the graph
in Figure 2 of Takahashi represents "a relationship between a
line width of the resist image and the focus position provided as
a result of projecting the reticle 6 pattern onto the wafer 8 with
a certain spherical aberration." See, Takahashi at col. 3, lines
44-47 (emphasis added). The focus position has no effect on
the line width; rather, the spherical aberration applied to the
9
Appeal 2007-3372
Application 10/651,351

projection of the reticle pattern alters the resist image
dimension for a given amount of defocus. The difference in the
two images in the graph of Figure 2 of Takahashi result from
differences in the spherical aberration applied to a projection
rather than to the focus position of a projection. Thus,
Takahashi does not recognize an amount of defocus, or focal
depth, as a result-effective variable which affects spherical
aberration of a projected image. The lack of such recognition
precludes a prima facie obviousness rejection because the
determination of an optimum working range for a variable is
not within one of ordinary skill in the art if the variable is not
recognized as a result-effective variable.
The combination of Takahashi with [Yasuzato] also fails
to make obvious claim 3 because [Yasuzato] does not teach or
suggest the equation recited in claim 3. See, In re Vaeck, 947
F.2d 488, 20 USPQ2d 1438 (Fed. Cir. 1991).
Br. 11 and 12 (emphasis omitted).
This argument is not persuasive of any reversible error. In particular,
Takahashi’s Figure 2 “is a graph showing a relationship between a line
width of the resist image and the focus position…” for a particular
photoresist (Takahashi; col. 3, ll. 44-52). The line width change (resist
image dimension change) at differing focus positions with a spherical
aberration of zero (solid line of Figure 2) is greater than the line width
change when a predetermined spherical aberration is applied (Takahashi;
col. 3, ll. 53-65; Fig. 2, broken line).
However, we note that the incident light would be expected to defocus
or experience differing refractions while traveling through the resist material
to a focal location or point therein as evidenced by the differing angles that
the incident light would be expected to arrive with (Admitted Prior Art, Fig.
2). Thus, the focal distance into the resist would have been recognized by
one of ordinary skill in the art as a result effective variable for determining a
10
Appeal 2007-3372
Application 10/651,351

nonzero spherical aberration correction value for the mask image to be
projected into a particular photoresist. This is in accord with the Examiner’s
position that Takahashi (with or without Yasuzato) reasonably teaches or
would have suggested that the focal distance to be traveled in a medium
(resist material) is a result effective variable for determining the optimum
corrective spherical aberration value to be applied to a mask image that is to
be projected into a particular photoresist (Answer 8-10). In this regard,
Appellant’s acknowledgement that refraction of incident light would occur
in differing amounts (defocusing) in correlation with Snell’s Law
(Specification ¶ 0008) appears to undercut Appellant’s argument for the
patentability of these claims based on an asserted lack of result effectiveness
of the focal distance into the photoresist (s) parameter. In other words, the
result effectiveness of this variable in setting a corrective spherical
aberration value would be predictable to one of ordinary skill in the art
familiar with Snell’s Law. Thus, the Examiner’s determination that the focal
distance (focal position in the resist) is a result effective variable for the
determination of an optimum corrective spherical aberration value appears to
be reasonable on this record.
It follows that we shall sustain the Examiner’s obviousness rejection
over Takahashi taken with Yasuzato.
As for the separate obviousness rejection of dependent claims 6-8, 16-
18, and 26-28 under 35 U.S.C. § 103(a) as being unpatentable over
Takahashi in view of Yasuzato and Nozue, we note that Appellant rests on
the arguments made with respect to the independent claims. Appellant does
not furnish any additional arguments against the Examiner’s additional
application of Nozue to these claims Br. 16-17; Reply Br. 9).
11
Appeal 2007-3372
Application 10/651,351

For the reasons set forth above, it follows that we shall sustain the
Examiner’s obviousness rejection as it pertains to the above-identified
dependent claims.
CONCLUSION
The decision of the Examiner to reject claims 1-4, 9-12, 14, 15, 19-22,
24, 25, 29, and 30 under 35 U.S.C. § 103(a) as being unpatentable over
Takahashi in view of Yasuzato; and to reject claims 6-8, 16-18, and 26-28
under 35 U.S.C. § 103(a) as being unpatentable over Takahashi in view of
Yasuzato and Nozue is affirmed.
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)(iv).

AFFIRMED

tc/ls

TRASK BRITT
P.O. BOX 2550
SALT LAKE CITY, UT 84110

12