Ex Parte Lin et al

Board of Patent Appeals and Interferences

Mar 16, 2011

10814682 - (D) (B.P.A.I. Mar. 16, 2011)

UNITED STATES PATENT AND TRADEMARK OFFICE
____________________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________________

Ex parte WEN LIN and CHARLES W. PEARCE
____________________

Appeal 2009-013362
Application 10/814,682
Technology Center 2800
____________________

Before JOSEPH F. RUGGIERO, MAHSHID D. SAADAT, and
ALLEN R. MacDONALD, Administrative Patent Judges.

MacDONALD, Administrative Patent Judge.

DECISION ON APPEAL1

1 The two-month time period for filing an appeal or commencing a civil
action, as recited in 37 C.F.R. § 1.304, or for filing a request for rehearing,
as recited in 37 C.F.R. § 41.52, begins to run from the “MAIL DATE”
(paper delivery mode) or the “NOTIFICATION DATE” (electronic delivery
mode) shown on the PTOL-90A cover letter attached to this decision.
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STATEMENT OF CASE
Introduction
Appellants appeal under 35 U.S.C. § 134 from a final rejection of
claims 41-53. Claims 1-40 have been canceled. We have jurisdiction under
35 U.S.C. § 6(b).
We affirm.
Exemplary Claim
Exemplary independent claim 41 under appeal, with emphases added,
reads as follows:
41. A semiconductor device, comprising:
a co-doped germanium buried layer located over a doped substrate;
a doped epitaxial layer located over said co-doped germanium buried
layer
a gate structure located over said doped epitaxial layer, said gate
structure including a gate dielectric and gate electrode; and
source/drain regions located within said doped epitaxial layer
proximate said gate structure, wherein said source/drain regions do not
extend into said co-doped germanium buried layer.
Rejections
1. The Examiner rejected claims 41-52 as being unpatentable
under 35 U.S.C. § 103(a) over the combination of Bevk (US 5,500,391) and
Liaw (US 5,891,769).
2. The Examiner rejected claim 53 as being unpatentable under
35 U.S.C. § 103(a) over the combination of Bevk, Liaw, and Ramdani (US
7,067,856 B2).
Appellants’ Contentions
1. Appellants contend (App. Br. 5-16; Reply Br. 2) that the
Examiner erred in rejecting claims 41-52 under 35 U.S.C. § 103(a) for
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numerous reasons, including: (1) Liaw fails to teach or suggest source/drain
regions that do not extend into a co-doped germanium buried layer; (2)
Liaw’s Figure 4 and column 6, lines 17-39, do not teach or suggest such a
feature because the cited portions of Liaw describe an SiC, and not a co-
doped germanium, buried layer; (3) Liaw’s Figure 1 does not disclose
source/drain regions that are not extended into a co-doped germanium buried
layer; (4) column 5, lines 36-51, of Liaw is a description of Figure 3, not
Figure 4, and although this citation might teach or suggest other materials
useful in doping a buried layer, the citation does not teach or suggest a co-
doped germanium buried layer; and (5) the Examiner has misapplied the law
relating to dimensional limitations since claim 41 concerns the location of
recited elements.
2. Appellants contend (App. Br. 16-17) that the Examiner erred in
rejecting claim 53 under 35 U.S.C. § 103(a) because Ramdani fails to cure
the deficiencies of Bevk and Liaw as discussed supra as to Appellants’ first
contention.
Issue on Appeal
Did the Examiner err in rejecting claims 41-53 as being obvious
because Liaw fails to teach or suggest source/drain regions that do not
extend into a co-doped germanium buried layer, as set forth in independent
claim 41?

FINDINGS OF FACT (FF)
1. Appellants describe known problems with cross-talk in semiconductor
devices and methods of making such devices, due in part to an
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increase in device packing density and a decrease in device size (Spec.
¶ [0005]).
2. Appellants admit that one solution to the cross-talk problem (see FF 1
supra), is to position a highly doped buried layer between an epitaxial
layer and a substrate, and that the high dose of ion implantation used
in forming the highly doped buried layer causes high stress between
the epitaxial layer and the substrate (Spec. ¶ [0006]). Appellants
further describe that the high stress at the interface of the epitaxial
layer and the substrate causes defects and lattice strain (Spec. ¶
[0007]). Appellants admit that adding boron to silicon causes lattice
contraction, mismatch, and defects (Spec. ¶ [0007]).
3. Bevk describes a doped epitaxial silicon layer 30 over a boron doped
buried layer 20 which is over a substrate 10 (Abs.; Figs. 4-6; col. 3, ll.
5-10). Bevk discloses that “[i]t has long been known that the presence
of germanium as a co-dopant will retard the diffusion of boron” (col.
1, ll. 20-21), and boron is known to diffuse during the manufacture of
metal oxide semiconductors (col. 1, ll. 14-19).
4. Liaw describes an embodiment (Figs. 1-3; col. 2, l. 36 to col. 6, l. 5)
of a semiconductor device 10, and method of making the device (Fig.
2), including (i) starting with a substrate 11 (step 31; col. 3, ll. 4-13),
(ii) forming a strained SiGe layer over the substrate (step 33) and
doping the SiGe layer with boron to adjust the degree of film stress
(col. 3, ll. 17-26), (iii) thermally inducing relaxation of the strained
layer (step 36; col. 3, ll. 45-63), and (iv) forming a strained layer 14
over the relaxed layer 12 (step 38; col. 4, ll. 30-31).
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5. Liaw describes another embodiment (Figs. 4, 5; col. 6, l. 17 to col. 8,
l. 19) of a semiconductor device 50, and method of making the device
(Fig. 5), including (i) starting with a substrate 51 (step 44; col. 6, ll.
40-43), (ii) forming a strained heteroepitaxy layer over the substrate
(step 46; col. 6, ll. 57-61) and adjusting the degree of film stress and
lattice strain with a thermal process (col. 7, ll. 28-65), (iii) thermally
inducing relaxation of the heteroepitaxy layer (step 47; col. 7, l. 28 to
col. 8, l. 11), and (iv) forming a device layer 54 over the relaxed
heteroepitaxy layer 53 (step 48; col. 8, ll. 12-29). Source and drain
regions 56/57 are formed in device layer 54 (col. 6, ll. 30-31) and do
not extend into the relaxed heteroepitaxy (i.e., buried) layer 53 (see
Fig. 5).
6. By way of example, Liaw describes using SiC for relaxed
heteroepitaxy layer 53 (col. 5, ll. 46-48; col. 6, ll. 28-29). However,
Liaw recognizes that SiC films are very difficult to grow epitaxially
due to the large lattice mismatch between SiC and silicon (col. 5, ll.
55-59), and SiC films have unacceptably high levels of defects (col. 6,
ll. 1-3). Liaw discloses that other materials are suitable for forming
low defect heteroepitaxial films (col. 5, ll. 35-50). One other material
disclosed by Liaw in the first embodiment (see FF 4 supra) for use in
forming relaxed layers is SiGe (col. 1, ll. 30-31; col. 2, ll. 47-49; col.
3, ll. 17-44; col. 5, ll. 1-14; claim 22 at col. 10, ll. 19-21).
7. Liaw describes the use of boron doping to lower melting points and
reduce stress (i.e., increase relaxation or reduce lattice strain) in
germanium by forming a strained SiGe layer on a silicon substrate and
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then relaxing the SiGe by thermal stress and external high temperature
thermal treatments (col. 1, l. 63 to col. 2, l. 36; col. 3, ll. 25-26).
8. Liaw’s claim 21 describes a method for forming a semiconductor
device including:
providing a substrate comprising a first material
having a first lattice constant, the substrate further
including a relaxed layer comprising a second material
having a second lattice constant different than the first
lattice constant, and a first layer comprising a third
material having a third lattice constant different than the
second lattice constant formed over the relaxed layer,
wherein the relaxed layer is formed by forming a strained
layer over the substrate and relaxing the strained layer by
thermal stress without exposing the strained layer to an
oxidizing ambient;
. . . ; and
forming a source and a drain region in the first
layer.
Column 10, lines 5-18.
9. Liaw’s claim 22 further describes that the method for forming the
substrate in the semiconductor device includes providing a relaxed
layer comprising germanium (col. 10, ll. 19-21).

PRINCIPLES OF LAW
On the issue of obviousness, the Supreme Court has stated that “[t]he
obviousness analysis cannot be confined by a formalistic conception of the
words teaching, suggestion, and motivation.” KSR Int’l Co. v. Teleflex Inc.,
550 U.S. 398, 419 (2007). Further, the Court stated “[t]he combination of
familiar elements according to known methods is likely to be obvious when
it does no more than yield predictable results.” Id. at 416. “One of the ways
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in which a patent’s subject matter can be proved obvious is by noting that
there existed at the time of invention a known problem for which there was
an obvious solution encompassed by the patent’s claims.” Id. at 419-20.

ANALYSIS
We have reviewed the Examiner’s rejections in light of Appellants’
contentions in the Appeal Brief and Reply Brief that the Examiner has erred.
We disagree with Appellants’ conclusions. We adopt as our own the
findings set forth by the Examiner in the action from which this appeal is
taken and as set forth by the Examiner in the Examiner’s Answer in response
to Appellants’ Appeal Brief. We disagree with Appellants’ contentions for
the following reasons.
Sole independent claim 41 recites source/drain regions that do not
extend into a co-doped germanium buried layer. As recited in dependent
claim 42 and 43, and disclosed at paragraph [0029] of Appellants’
Specification, the co-dopant can be boron.
Appellants, Bevk, and Liaw all recognize the usefulness of doping
with boron when making semiconductor devices (FF 2-4, 7). In addition,
Liaw teaches using boron to dope SiGe in semiconductor devices (FF 4).
Liaw, like Appellants, uses boron to reduce stress in a semiconductor device
layer and to compensate for lattice mismatch (FF 2, 4, 7).
With respect to claims 41-52, we disagree with Appellants’ first
contention, supra, that Liaw does not teach or suggest source/drain regions
that do not extend into a co-doped germanium buried layer. Because Liaw’s
two embodiments (see Figs. 1, 4) and claims 21 and 22 teach or suggest
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source/drain regions that do not extend into a co-doped germanium buried
layer, we concur with the conclusions reached by the Examiner.
Appellants admit that Liaw’s Figure 1 “teaches a co-doped
germanium buried layer” (App. Br. 6). Liaw’s Figure 4 teaches source and
drain regions that do not extend into a buried layer (FF 5). The issue before
us is whether or not Liaw teaches or suggests combining the SiGe feature of
one embodiment (first embodiment discussed in FF 4) with the non-
extension feature of the other embodiment (other embodiment discussed in
FF 5). Liaw’s claims 21 and 22 (FF 8, 9) are determinative.
Liaw’s claim 21 describes a substrate, a relaxed layer, a first layer, a
strained layer, and a gate structure, in that order (FF 8). Liaw’s Figure 4 and
claim 21 show and describe forming source and drain regions 56/57 in the
first layer (i.e., device layer 54), and not extending into the relaxed or buried
layer 53 (FF 5, 8). Liaw’s claim 22 discloses that the relaxed or buried layer
of claim 21, into which the source/drain regions do not extend (see FF 5), is
comprised of SiGe (FF 9). In other words, Liaw teaches or suggests using
doped germanium for the relaxed layer instead of SiC (which was used by
way of example in describing the embodiment of Figures 4 and 5, see FF 5).
Combining familiar elements (e.g., SiGe for a relaxed layer (see FF
6), using boron as a co-dopant in the SiGe layer to reduce stress (see FF 4,
7), and placing source and drain regions in a device layer and not the buried
relaxed layer located over the substrate (see FF 5, 8)) according to known
methods would have been obvious since it does no more than yield
predictable results. See KSR, 550 U.S. at 416.
Although we agree with Appellants’ assertion (App. Br. 7) that claim
41 concerns the location of recited elements, and not dimensional
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limitations, we agree with the Examiner (Ans. 4, 10) that Liaw teaches or
suggests the locations of the source/drain regions and co-doped germanium
buried layer recited in claims 41-52 for the foregoing reasons.
With respect to claim 53, Appellants’ second contention, supra, fails
for similar reasons as given above with respect to claims 41-52 (Appellants’
first contention, supra).

CONCLUSIONS
(1) The Examiner has not erred in determining that Liaw teaches or
suggests source/drain regions that do not extend into a co-doped germanium
buried layer, as set forth in claims 41-53.
(2) The Examiner has not erred in rejecting claims 41-53 as being
unpatentable under 35 U.S.C. § 103(a).
(3) Claims 41-53 are not patentable.

DECISION
The Examiner’s rejections of claims 41-53 are 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
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