Ex Parte TWU et al

Board of Patent Appeals and Interferences

Sep 17, 2003

09298879 (B.P.A.I. Sep. 17, 2003)

The opinion in support of the decision being entered today was not
written for publication and is not binding precedent of the Board.
Paper No. 12
UNITED STATES PATENT AND TRADEMARK OFFICE
____________
BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________
Ex parte JIH-CHURNG TWU, SYUN-MING JANG, and CHEN-HUA YU
____________
Appeal No. 2002-0102
Application No. 09/298,879
____________
ON BRIEF
____________
Before KIMLIN, LIEBERMAN, and POTEATE, Administrative Patent
Judges.
POTEATE, Administrative Patent Judge.
DECISION ON APPEAL
This is an appeal under 35 U.S.C. § 134 from the examiner's
refusal to allow claims 1-8, 10-15 and 18-22, which are all of
the claims pending in the application.
Claim 1 is representative of the subject matter on appeal
and is reproduced below:
1. The method of simultaneously forming both a high voltage and
a low voltage transistor in the manufacture of an integrated
circuit comprising:
providing a semiconductor substrate wherein active areas of
said substrate are isolated from other active areas and wherein
there is at least one low voltage area in which said low voltage
transistor will be formed and at least one high voltage area in
Appeal No. 2002-0102
Application No. 09/298,879
2
which said high voltage transistor will be formed wherein said
high voltage transistor as a voltage higher than said low voltage
transistor;
first wet oxidizing the surface of said semiconductor
substrate to form a first layer of gate oxide on the surface of
said semiconductor substrate in said active areas;
covering said low voltage active area with a mask;
second wet oxidizing the surface of said semiconductor
substrate where it is not covered by said mask to form a second
layer of gate oxide underlying said first gate oxide layer in
said high voltage active area wherein said second wet oxidizing
comprises H2 and O2 in a N2 atmosphere in the ratio of H2 : O2 : N2
of 1 : 2 : more than 20;
thereafter removing said mask;
depositing a layer of polysilicon overlying said first gate
oxide layer in said low voltage active area and overlying said
first and second gate oxide layers in said high voltage active
area; and
patterning said polysilicon layer to form gate electrodes
for said low voltage and said high voltage transistors in the
fabrication of said integrated circuit.
The references relied upon by the examiner are:
Pong et al. (Pong) 5,210,056 May 11, 1993
Lin 5,502,009 Mar. 26, 1996
Sun et al. (Sun) 5,920,779 Jul. 6, 1999
El-Diwany 5,953,599 Sep. 14, 1999
Grounds of Rejection
1. Claims 1-5, 8, 11-14 and 18-22 stand rejected under
35 U.S.C. § 103 as unpatentable over El-Diwany and Lin and
further in view of Pong.
Appeal No. 2002-0102
Application No. 09/298,879
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2. Claims 6, 7, 10 and 15 stand rejected under 35 U.S.C.
§ 103 as unpatentable over El-Diwany in view of Lin and Sun and
further in view of Pong.
We reverse.
Background
The invention relates to a method of simultaneously forming
both a high voltage and a low voltage transistor in the
manufacture of an integrated circuit. Claims 1, 10 and 18. The
method involves a two-step wet oxidation using H2, O2 and N2 in
specified ratios. Id. The claims require that the second gate
oxide layer underlies the first gate oxide layer. Id. According
to appellants,
[t]he significance of forming the second gate oxide
under the first gate oxide is that the substrate in
this area is not damaged by the process of removing the
first gate oxide and then regrowing a second gate
oxide. The substrate is protected by the first gate
oxide, thus maintaining high quality.

Appeal brief, Paper No. 10, received April 23, 2001, page 8.
Discussion
The initial burden of presenting a prima facie case of
obviousness rest on the examiner. In re Oetiker, 977 F.2d 1443,
1445, 24 USPQ2d 1443, 1444 (Fed. Cir. 1992). Where an
obviousness determination is based on a combination of prior art
Appeal No. 2002-0102
Application No. 09/298,879
4
references, there must be some "teaching, suggestion or incentive
supporting the combination." In re Geiger, 815 F.2d 686, 688, 2
USPQ2d 1276, 1278 (Fed. Cir. 1987). "The factual inquiry whether
to combine references must be thorough and searching." McGinley
v. Franklin Sports, Inc., 262 F.3d 1339, 1351-52, 60 USPQ2d 1001,
1008 (Fed. Cir. 2001).
In rendering a decision on appeal, the Board must ensure
that the requisite findings are made based on the evidence of
record. See In re Lee, 277 F.3d 1338, 1342, 61 USPQ2d 1430, 1432
(Fed. Cir. 2002). The Board must set forth its findings and the
grounds thereof as supported by the agency record and explain its
application of the law to the facts. Id. the Board's decision
must be supported by substantial evidence. In re Zurko, 258 F.3d
1379, 1381, 59 USPQ2d 1693, 1694 (Fed. Cir. 2001).
For the reasons discussed below, we find that the examiner
has failed to meet his burden of establishing a prima facie case
of obviousness. In particular, the examiner has failed to make
the requisite findings of fact and we are constrained to reverse
the examiner's final rejection of the claims.
As noted above in the background section, each of
independent claims 1, 10 and 18 requires that during the second
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Application No. 09/298,879
5
wet oxidizing step, the second layer of gate oxide be formed
underlying the first gate oxide layer. In their arguments on
appeal, appellants repeatedly assert that none of the cited
references disclose or suggest forming the second gate oxide
underlying the first gate oxide. See, e.g., appeal brief, pages
8-12. Our discussion regarding the step of forming the second
oxide layer under the first oxide layer is provided on pages 9-10
and 11 in connection with figures 3-4 and 6-7.
The examiner concedes that El-Diwany does not specifically
teach a second wet oxidizing step to form a second gate oxide
underlying the first gate oxide layer. See examiner's answer,
Paper No. 11, mailed July 5, 2001, page 3, penultimate paragraph.
The examiner relies on Lin as disclosing a second wet oxidation
step. See Id., page 4. However, the examiner does not identify
in Lin or any of the other references, a specific teaching as to
forming the second gate oxidation layer under the first layer.
Rather, the examiner's response to appellants' argument that such
a step is not taught or suggested by the cited references by
stating that,
[f]urther it is a well known fact that any time
oxidation step is under taken a portion of the oxide
grows below the surface of the existing layer
(generally about 40%) and the rest grows above thus at
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Application No. 09/298,879
6
least about 40% of the second oxide layer 146 is grown
below (underlying) the layer 134.

Examiner's answer, page 8 (referencing figures 1C and D of El-
Diwany).
However, the examiner's mere assertion that it is well known
that a portion of oxide grows below the surface of an existing
layer is simply insufficient to establish a prima facie case of
obviousness. The Federal Circuit has held that it is
impermissible for the Board to reach conclusions based on what
the examiner believes to be basic knowledge or common sense.
In re Zurko, 258 F.3d 1379, 1386, 59 USPQ2d 1693, 1697 (Fed. Cir.
2001). Rather, it is necessary for the examiner to identify
concrete evidence in the record in support of its findings, see
Id., such that the Board may examine the relevant data and
articulate a thorough explanation for its decision. See In re
Lee, 277 F.3d 1338, 1344, 61 USPQ2d 1430, 1434 (Fed. Cir. 2002).
Appeal No. 2002-0102
Application No. 09/298,879
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Accordingly, the rejections of the claims under 35 U.S.C.
§ 103 are reversed.
REVERSED
EDWARD C. KIMLIN )
Administrative Patent Judge )
)
)
)
) BOARD OF PATENT
PAUL LIEBERMAN ) APPEALS
Administrative Patent Judge ) AND
) INTERFERENCES
)
)
)
LINDA R. POTEATE )
Administrative Patent Judge )
LRP/lbg
Appeal No. 2002-0102
Application No. 09/298,879
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STEPHEN B. ACKERMAN
20 MCINTOSH DRIVE
NEW YORK, NY 12603