U.S. patent application number 14/951660 was filed with the patent office on 2017-03-02 for semiconductor device including dual spacer and uniform epitaxial buffer interface of embedded sige source/drain.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Veeraraghavan S. Basker, Zuoguang Liu, Tenko Yamashita, Chun-Chen Yeh.
Application Number | 20170062588 14/951660 |
Document ID | / |
Family ID | 58095902 |
Filed Date | 2017-03-02 |
United States Patent
Application |
20170062588 |
Kind Code |
A1 |
Basker; Veeraraghavan S. ;
et al. |
March 2, 2017 |
SEMICONDUCTOR DEVICE INCLUDING DUAL SPACER AND UNIFORM EPITAXIAL
BUFFER INTERFACE OF EMBEDDED SIGE SOURCE/DRAIN
Abstract
A semiconductor device includes at least one semiconductor fin
on an upper surface of a semiconductor substrate. The semiconductor
fin includes a channel region formed of a first semiconductor
material interposed between opposing embedded source/drain regions
formed of a second semiconductor material different from the first
semiconductor material. At least one gate stack is formed on the
upper surface of the semiconductor substrate and wraps around the
channel region. The embedded source/drain regions have a
symmetrical shape and a uniform embedded interface.
Inventors: |
Basker; Veeraraghavan S.;
(Schenectady, NY) ; Liu; Zuoguang; (Schenectady,
NY) ; Yamashita; Tenko; (Schenectady, NY) ;
Yeh; Chun-Chen; (Clifton Park, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
58095902 |
Appl. No.: |
14/951660 |
Filed: |
November 25, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14834481 |
Aug 25, 2015 |
|
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14951660 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/66795 20130101;
H01L 29/167 20130101; H01L 29/6656 20130101; H01L 21/823431
20130101; H01L 29/785 20130101; H01L 21/3065 20130101; H01L
29/66636 20130101; H01L 29/7848 20130101; H01L 29/41791 20130101;
H01L 21/30604 20130101; H01L 29/165 20130101; H01L 29/0847
20130101; H01L 29/7851 20130101; H01L 21/823418 20130101; H01L
29/41783 20130101; H01L 21/02381 20130101; H01L 21/02532
20130101 |
International
Class: |
H01L 29/66 20060101
H01L029/66; H01L 21/3065 20060101 H01L021/3065 |
Claims
1. A method of fabricating a semiconductor device, the method
comprising: forming at least one semiconductor fin on an upper
surface of a semiconductor substrate, the at least one
semiconductor fin including a channel region interposed between
opposing source/drain regions; recessing a portion of the
source/drain regions with respect to the channel region;
epitaxially growing a first semiconductor material from opposing
sidewalls of the channel region and from the recessed source/drain
regions, and selectively removing a base portion of the first
semiconductor material formed on the recessed source/drain regions
while maintaining a side portion of the first semiconductor
material formed on respective sidewalls of the channel region; and
epitaxially growing a second semiconductor material from the side
portions and from the recessed source/drain regions so as to form
embedded source/drain regions having a substantially symmetrical
shape.
2. The method of claim 1, wherein the first semiconductor material
has a first doping concentration so as to define a buffer layer and
the second semiconductor material has a second doping concentration
different from the first doping concentration to define a raised
source/drain layer.
3. The method of claim 2, wherein each embedded source/drain region
includes an embedded interface at which the buffer layer entirely
contacts the raised source/drain layer.
4. The method of claim 3, wherein each embedded interface extends
completed from a respective recessed source drain/region to a lower
surface of at least one gate structure.
5. The method of claim 4, wherein the embedded interface is
entirely uniform.
6. The method of claim 5, wherein a first total height of the
buffer layer is approximately equal to a second total height of the
raised source/drain layer.
7. The method of claim 2, further comprising forming the at least
one gate structure on an upper surface of the substrate, the at
least one gate structure wrapping around the channel region of the
fin, wherein the at least one gate structure serves as a mask to
protect the channel region when recessing the portion of the
source/drain regions.
8. The method of claim 7, wherein selectively removing the base
portion of the first semiconductor material comprises: depositing
an outer spacer layer that conforms to outer surfaces of the at
least one gate structure and each buffer layer; performing a first
anisotropic etching process selective to the first semiconductor
material so as to remove a first portion of the outer spacer layer
and expose the underlying base portions while maintaining a second
portion of the outer spacer layer to cover the side portions; and
performing a second anisotropic etching process selective to the
outer spacer layer so as to remove the base portions and expose the
recessed source/drain regions while maintaining the side
portions.
9. The method of claim 2, wherein the first doping concentration is
less than the second doping concentration.
10. A method of forming a finFET device having symmetrically-shaped
embedded source/drain regions, the method comprising: recessing
source/drain regions of at least one semiconductor fin with respect
to channel region of the at least one semiconductor fin;
epitaxially growing a first semiconductor material from the at
least one semiconductor fin, the first semiconductor material
including a side portion grown from opposing sidewalls of the
channel region and a base portion grown from recessed portions of
the source/drain regions; selectively removing the base portion
while maintaining the side portion to define a first height of the
side portion; and epitaxially growing a second semiconductor
material from the side portion and from the recessed source/drain
regions so as to form embedded source/drain regions having a second
height, the second height substantially matching the first height
so as to form the symmetrically-shaped embedded source/drain
regions.
11. The method of claim 10, wherein the at least one semiconductor
fin comprises silicon (Si) and each of the first and second
semiconductor materials comprise silicon germanium (SiGe).
12. The method of claim 11, wherein the second semiconductor
material is doped with boron (B).
13. The method of claim 10, wherein the at least one semiconductor
fin comprises silicon germanium (SiGe) and each of the first and
second semiconductor materials comprise silicon (Si).
14. The method of claim 10, wherein a first doping concentration of
the first semiconductor material is different than a second doping
concentration of the second semiconductor material.
Description
DOMESTIC PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/834,481, filed Aug. 25, 2015, the
disclosure of which is incorporated by reference herein in its
entirety.
BACKGROUND
[0002] The present invention relates to semiconductor devices, and
more specifically, to three-dimensional (3D) transistor
devices.
[0003] Recent semiconductor fabrication methods have been developed
to replace all or a portion of pure silicon (Si) fins with silicon
germanium (SiGe) material, especially in p-type finFET devices.
SiGe material reduces the threshold voltage (Vt) of a p-type
semiconductor device, thereby increasing the drive current that
flows through the channel. Further, SiGe material provides higher
carrier mobility than fins consisting of only Si. Accordingly, SiGe
fins typically have improved hole mobility performance compared to
Si fins. The benefits of SiGe material described above have led to
design trends that form fins with embedded SiGe (eSiGe)
source/drain regions.
[0004] Referring to FIGS. 1-2, a conventional method of forming a
finFET device 100 including eSiGe source/drain regions is
illustrated. Conventional methods typically utilize only a single
spacer layer followed by a directional etch to expose the
underlying Si source/drain regions 102 of the fin while forming a
single pair of spacers 104 on opposing sidewalls of the gate
structure 106 (see FIG. 1). The exposed Si source/drain regions 102
are utilized as seed regions capable of epitaxially growing a
semiconductor material therefrom.
[0005] Conventional eSiGe source/drain regions 108 typically
include an epitaxially grown SiGe buffer layer 110 interposed
between the original Si source/drain regions 102 and a subsequently
grown highly-doped main SiGe layer 112 as further shown in FIG. 2.
When performing a thermal anneal process to activate dopants of the
main SiGe layer 112, for example, the buffer layer 110 serves to
inhibit dopants of the highly-doped main SiGe layer 112 from
diffusing into the fin channel region to prevent
source/drain-channel shorting.
[0006] However, due to the natural asymmetrical directional growth
of SiGe from Si, the SiGe buffer layer 110 is formed having an
asymmetrical shape as further illustrated in FIG. 2. For example,
the side portions 114a of the SiGe buffer layer 110 (i.e., grown
from the Si sidewalls of the fin 102) are thinner than the base
portions 114b (i.e., grown on the lower portion of Si source/drain
regions of the fin 102). This asymmetrical shape (i.e., thickness
delta) causes a non-uniform extension junction profile from the top
of the fin channel to the bottom of the fin channel which can
potentially affect the overall performance of the finFET device.
For instance, the side portions 114a of the buffer layer 110 have a
first total height (H.sub.1) while the highly-doped main SiGe layer
112 has a second total height (H.sub.2) that is less than H.sub.1.
Consequently, a non-uniform eSiGe junction is formed, particularly
at the corner region 116 of the buffer layer 110.
SUMMARY
[0007] According to a non-limiting embodiment of the present
invention, a semiconductor device includes at least one
semiconductor fin on an upper surface of a semiconductor substrate.
The semiconductor fin includes a channel region formed of a first
semiconductor material interposed between opposing embedded
source/drain regions formed of a second semiconductor material
different from the first semiconductor material. At least one gate
stack is formed on the upper surface of the semiconductor substrate
and wraps around the channel region. The embedded source/drain
regions have a symmetrical shape, and a uniform embedded
interface.
[0008] According to another non-limiting embodiment, a method of
forming a finFET device having symmetrically-shaped embedded
source/drain regions comprises recessing source/drain regions of at
least one semiconductor fin with respect to channel region of the
semiconductor fin. The method further includes epitaxially growing
a first semiconductor material from the at least one semiconductor
fin. The first semiconductor material includes a side portion grown
from opposing sidewalls of the channel region and a base portion
grown from recessed portions of the source/drain regions. The
method further includes selectively removing the base portion while
maintaining the side portion to define a first height of the side
portion. The method further includes epitaxially growing a second
semiconductor material from the side portion and from the recessed
source/drain regions so as to form embedded source/drain regions
having a second height. The second height substantially matches the
first height so as to form the symmetrically-shaped embedded
source/drain regions
[0009] According to still another non-limiting embodiment, a method
of fabricating a semiconductor device comprises forming at least
one semiconductor fin on an upper surface of a semiconductor
substrate. The at least one semiconductor fin includes a channel
region interposed between opposing source/drain regions. The method
further includes recessing a portion of the source/drain regions
with respect to the channel region. The method further includes
epitaxially growing a first semiconductor material from opposing
sidewalls of the channel region and from the recessed source/drain
regions. The method further includes selectively removing a base
portion of the first semiconductor material formed on the recessed
source/drain regions while maintaining a side portion of the of the
first semiconductor material formed on respective sidewalls of the
channel region. The method further includes epitaxially growing a
second semiconductor material from the side portions and from the
recessed source/drain regions so as to form embedded source/drain
regions having a symmetrical shape.
[0010] Additional features are realized through the techniques of
the present invention. Other embodiments are described in detail
herein and are considered a part of the claimed invention. For a
better understanding of the invention with the features, refer to
the description and to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIGS. 1-2 illustrate a conventional method of fabricating a
finFET device including eSiGe source/drain regions.
[0012] FIGS. 3A-9B are a series of diagrams illustrating a method
of fabricating a semiconductor device including eSiGe source/drain
regions according to a non-limiting embodiment, in which:
[0013] FIG. 3A is a perspective view of an intermediate
semiconductor device including a semiconductor fin formed atop a
substrate, and a gate structure wrapping around a channel region of
the semiconductor fin;
[0014] FIG. 3B is cross-sectional view of the intermediate
semiconductor device taken along the line A-A showing initial
source/drain regions of the fin abutting gate spacers formed on
sidewalls of the gate structure;
[0015] FIG. 4A is a perspective view of the semiconductor device
illustrated in FIGS. 3A-3B following a first directional etch
process that stops on the upper surface of the substrate so as to
recesses the initial source/drain regions;
[0016] FIG. 4B is a cross-sectional view of the semiconductor
device illustrated in FIG. 4A showing the recessed source/drain
regions being flush with the upper surface of the substrate;
[0017] FIG. 5A is a perspective view of the semiconductor device
illustrated in FIGS. 4A-4B after epitaxially growing a
semiconductor buffer layer from exposed portions of the recessed
source/drain regions and sidewalls of the fin;
[0018] FIG. 5B is a cross-sectional view of the semiconductor
device illustrated in FIG. 5A showing the buffer layer having a
thin side portion formed against the sidewall of the fin and
extending from the recessed source/drain region to a bottom portion
of the gate spacers, and a thick base portion formed on the
recessed source/drain regions;
[0019] FIG. 6A is a perspective view of the semiconductor device
illustrated in FIGS. 5A-5B after depositing an outer conformal
spacer layer on an upper surface of the substrate so as to cover
the buffer layer, the gate spacers and the upper surface of the
gate structure;
[0020] FIG. 6B is a cross-sectional view of the semiconductor
device illustrated in FIG. 6A showing the outer spacer layer
conforming to an upper surface of the buffer layer such that the
buffer layer is interposed between the outer spacer layer and the
fin;
[0021] FIG. 7A is a perspective view of the semiconductor device
illustrated in FIGS. 6A-6B following a second directional etch
process selective to the buffer layer so as to form outer spacers
on the sidewalls of the gate spacers;
[0022] FIG. 7B is a cross-sectional view of the semiconductor
device illustrated in FIG. 7A showing the side portion of the
buffer layer covered by the outer spacer while the base portion of
the buffer layer is exposed;
[0023] FIG. 8A is a perspective view of the semiconductor device
illustrated in FIGS. 7A-7B following a third directional etch
process selective to the substrate and the fin such that the base
portion of the buffer layer is removed while the side portion of
the buffer layer located beneath the outer spacers is
preserved;
[0024] FIG. 8B is a cross-sectional view of the semiconductor
device illustrated in FIG. 8A showing the preserved side portion
extended from the outer spacer to the recessed source drain region
of the fin to define a first total height;
[0025] FIG. 9A is a perspective view of the semiconductor device
illustrated in FIGS. 8A-8B after epitaxially growing a highly-doped
raised source/drain region from the preserved side portion of the
buffer layer and the recessed source/drain regions of the fin;
[0026] FIG. 9B is a cross-sectional view of the semiconductor
device illustrated in FIG. 9A showing the highly-doped raised
source/drain region having an upper surface that is flush with an
upper surface of the preserved side portion and has a second total
height equal to the first height of the preserved side portion so
as to define a uniform epitaxially grown source/drain region.
DETAILED DESCRIPTION
[0027] Various non-limiting embodiments of the invention provide a
semiconductor device including a dual spacer that defines an
epitaxial buffer interface of an embedded SiGe source/drain region.
The dual spacer protects the buffer layer during a second
directional etch process that selectively removes a portion of the
buffer layer from the original Si source/drain region of the fin.
In this manner, the buffer layer is formed on only the sidewall of
the fin channel region, while the lower etched region of original
Si source/drain region is re-exposed. Accordingly, the highly-doped
main SiGe portion can be grown directly from the Si source/drain
region and sidewalls of the buffer layer such that the base portion
of the buffer layer is formed uniform with respect to the
highly-doped main SiGe portion from top of the fin channel to the
bottom of the fin channel.
[0028] With reference now to FIGS. 3A-3B, a semiconductor structure
200 which serves as a starting point for fabricating a finFET
device in accordance with an exemplary embodiment is shown. In
exemplary embodiments, the semiconductor structure 200 includes a
semiconductor substrate 202 including one or more isolation regions
204 formed therein. The semiconductor substrate 202 extends along a
first axis (e.g., an X-axis) to define a length, a second axis
(e.g., a Y-axis) to define a width, and a third axis (e.g., a
Z-axis) to define a height. According to a non-limiting embodiment,
the substrate 202 is a bulk substrate formed from, for example,
silicon (Si). The isolation region 204 is a shallow trench
isolation (STI) region formed by depositing one or more dielectric
materials such as silicon dioxide (SiO.sub.2) in the bulk substrate
202 as understood by one of ordinary skill in the art. Although a
bulk substrate 202 including an isolation region 204 is discussed
going forward, it should be appreciated that the semiconductor
substrate 202 may also be formed as a semiconductor-on-insulator
(SOI) substrate without departing from the scope of the
invention.
[0029] One or more semiconductor fins 206 are formed on an upper
surface of the substrate 202. The fin 206 extends along the length
(e.g., X-axis) of the substrate 202 to define a fin length.
According to a non-limiting embodiment, the fin is formed
semiconductor material such as, for example, Si.
[0030] Various patterning techniques may be used to form the
semiconductor fin 206. For example, a suitable hardmask blocking
layer (not shown) formed of silicon dioxide (SiO.sub.2), for
example, can be initially deposited on an upper surface of the bulk
substrate 202. Next, a suitable hardmask cap layer (not shown)
formed of silicon nitride (SiN), for example, is deposited atop the
hardmask blocking layer. The hardmask cap layer and the hardmask
blocking layer will be used to pattern the underlying bulk
substrate 202 while serving to protect the fin 206 during the
formation of the isolation region 204.
[0031] Next, the hardmask blocking layer and the hardmask cap layer
are etched to define the desired fin pattern. A developed
photoresist mask (not shown) is typically used to define the
desired fin pattern. The hardmask blocking layer and hardmask cap
layer can then be patterned selective to the developed photoresist
mask according to a reactive ion etch (RIE) process. The patterned
hardmask layers will then be used to transfer the desired fin
pattern into the underlying bulk substrate layer 202 according to a
RIE process to define one or more of the semiconductor fins 206. It
should be appreciated that the length and width of the patterning
can be determined according to the desired fin dimensions for the
particular application.
[0032] The semiconductor structure 200 further includes one or more
gate structures 208 formed atop the isolation region 206. The gate
structure 208 extends along a width (e.g. Y-axis) of the substrate
202 so as to wrap around the sidewalls and upper surface of the fin
206. The arrangement of the gate structure 208 and the fin 206
defines a covered channel region 210 interposed between a pair of
exposed fin regions 212a-212b which are reserved for the
source/drain regions of the semiconductor device 200 (see FIG. 3B).
Going forward, these reserved fin regions 212a-212b will be
referred to as initial source/drain regions 212a-212b.
[0033] The gate structure 208 includes a gate stack 214 and gate
spacers 216 formed on opposing sidewalls of the gate stack 214. The
gate stack 214 is formed from various conductive gate materials
understood by those of ordinary skill in the art, and has a length
ranging from approximately X nm to approximately Y nm. The gate
spacers 216 are formed from a low-k material such as, for example,
silicon nitride (SiN), and have a thickness (e.g., along the
X-axis) ranging from approximately 8 nm to approximately 10 nm.
Although not illustrated, a gate dielectric layer (e.g., a high-k
gate dielectric layer) and one or more work function metal layers.
The gate dielectric layer may be interposed between the fin 206 and
the gate stack 214. The work function metal layers include, but are
not limited to, a titanium nitride (TiN) liner and a tantalum
nitride (TaN) liner, which are formed on sidewalls of the gate
stack 214 as understood by one of ordinary skill in the art. In
this case, it should be appreciated that the gate structure 208
includes the gate stack 214, the gate dielectric layer, the work
function metals, and the gate spacers 216.
[0034] Referring to FIGS. 4A-4B, the semiconductor device 200 is
illustrated following a first anisotropic directional etching
process. A reactive ion etch (RIE), for example, that is selective
to the material of the gate spacers 216 (e.g., SiN) and the
material of the isolation region 204 (e.g., SiO.sub.2) may be
performed so as to etch the reserved fin regions 212a-212b (i.e.,
the uncovered portions of the fin 206) while stopping on the
isolation region 204. Moreover, the gate structure 208 serves as a
mask to protect the channel region 210 when recessing the
source/drain regions 212a-212b. In this manner, remaining fin base
portions 218a-218b are formed flush with the upper surface of the
isolation region 204, while remaining fin side portions 220a-220b
are formed flush with sidewalls of the gate spacers 216.
[0035] Referring to FIGS. 5A-5B, buffer layers 222a-22b are formed
on exposed portions of the fin 206. For instance, various
well-known epitaxy processes may be used to grow a semiconductor
material from the base portions 218a-218b and the fin side portions
220a-220b, respectively. The epitaxial grown semiconductor material
includes, for example, undoped silicon germanium (SiGe) or SiGe
having a low concentration of dopants including, but not limited
to, boron (B). The dopant concertation of the buffer layers
222a-222b may range from approximately 0/cm.sup.3 (i.e., un-doped)
to approximately 10.sup.19/cm.sup.3. In this manner, the buffer
layers 222a-222b may serve to inhibit diffusion of dopants into the
channel region when exposing the semiconductor device 200 to
various thermal anneal processes understood by one of ordinary
skill in the art. Although a p-FET device is described going
forward, it should be appreciated that an n-FET device may be
formed in a similar manner as described above. When forming an
n-FET device, the epitaxial grown semiconductor material is undoped
Si, or Si having a low concentration of dopants including, but not
limited to, phosphorous (P).
[0036] The buffer layers 222a-222b each include a side portion
224a-224b and a base portion 226a-226b as further illustrated in
FIG. 5B. The side portions 224a-224b extend from the recessed
surface of the reserved source/drain regions 218a-218b to an upper
surface of the preserved fin 204 (i.e., the portion of the fin 206
defining an interface between the gate structure 208 and the fin
204) to thereby defining a first total height (H.sub.1) equal or
approximately equal to the fin 206 and a first total thickness
(T.sub.1) ranging from approximately 3 nm to approximately 5 nm.
During the epitaxy process, however, crystal growth of the buffer
layers 222a-222b naturally grows slower in the lateral direction
(e.g., along the X-axis) compared to the vertical direction (e.g.,
along the Z-axis). Therefore, the base portions 226a-226b extend
from the recessed surface at a second total height (H.sub.2)
ranging from approximately 8 nm to approximately 10 nm. A second
total thickness (T.sub.2) depends on the lateral dimension of
source/drain. Accordingly, T.sub.2 may range from approximately 20
nm to approximately 40 nm.
[0037] Referring to FIGS. 6A-6B, a conformal outer spacer layer 228
is deposited on the upper surface of the substrate 202 so as to
cover the buffer layers 222a-222b, the sidewalls of the gate
spacers 216 and an upper surface of the gate stack 214. Various
disposition processes may be used to deposit the outer spacer layer
229 such as, for example, chemical vapor deposition (CVD). The
outer spacer layer 228 has a thickness ranging for example, from
approximately 4 nm to approximately 8 nm, and is formed from
various nitride-based materials including, but not limited to,
silicon nitride (SiN).
[0038] Turning to FIGS. 7A-7B, the semiconductor device 200 is
illustrated following a second selective directional etch process
that etches the outer spacer layer 220 to form outer spacers 230 on
the sidewalls of the gate spacers 216. According to a non-limiting
embodiment, the second directional etch process includes a dry RIE
process that is selective to the material of the buffer layers
222a-222b and the isolation region 204. Further, the portion of the
outer spacer material covering the base portions 226a-226b is
etched at a faster rate than the portion of the outer spacer layer
229 covering the side portions 224a-224b. Accordingly, the side
portions 224a-224b are preserved and remain covered by respective
outer spacers 230 while the base portions 226a-226b are
exposed.
[0039] Referring to FIGS. 8A-8B, the semiconductor device is
illustrated following a third selective directional etch process
that removes the base portion 226a-226b of the buffer layers
222a-222b from the upper surface of the recessed source/drain
regions 218a-218b. The third etch process includes, for example, a
dry anisotropic RIE process selective to the material of the
isolation region 204, the fin 206 and the outer spacers 230 can be
performed such that the base portions 226a-226b are removed while
the side portions 224a-224b located beneath respective outer
spacers 230 are preserved. In this manner, the side portions
224a-224b are formed flush with the respective outer spacers 230,
while the recessed source/drain regions 218a-218b are
re-exposed.
[0040] Turning now to FIGS. 9A-9B, the semiconductor device 200 is
illustrated after epitaxially growing highly-doped raised
source/drain layers 232a-232b from the recessed source/drain
regions 218a-218b and the preserved buffer layer side portions
224a-224b, respectively. Accordingly, a lower portion of the raised
source/drain layers 232a-232b may be formed directly against a
surface of the initial fin 206 (i.e., the recessed source/drain
regions 218a-218b), while sides of the raised source/drain layers
232a-232b are formed directly against the buffer layer 222a-222b
(i.e., the side portions 224a-224b).
[0041] The combination of the remaining buffer layers 222a-222b
(i.e., the preserved side portions 224a-224b) and the highly-doped
raised source/drain layers 232a-232b can be viewed as embedded SiGe
(eSiGe) source/drain layers 234a-234b. As further illustrated in
FIG. 9B, the highly-doped raised source/drain layers 232a-232b have
an upper surface that is flush with an upper surface of a
respective preserved side portion 224a-224b. Accordingly, the
highly-doped raised source/drain layers 232a-232b have a total
height (H.sub.3) equal or substantially equal to the first height
of the preserved side portions 218a-218b (H.sub.1) so as to define
symmetrical eSiGe source/drain regions 234a-234b as further
illustrated in FIG. 9B. Further, each buffer layer 222a-222b
entirely contacts a respective raised source/drain layer 232a-232b
so as to define an embedded interface 233a-233b therebetween. The
embedded interface extends from the upper surface of substrate 202
(e.g., the surface of the recessed source/drain regions 218a-218b)
to an upper surface of the channel region 210. Accordingly,
embedded interface 233a-233b between the buffer layers 222a-222b
(i.e., the preserved side portions 224a-224b) and the raised
source/drain layers 232a-232b is uniform.
[0042] Various epitaxy processes may be used to grow the
highly-doped raised source/drain layers 232a-232b from the base
portions 218a-218b and the buffer layer side portions 224a-224b.
The epitaxial grown semiconductor material includes, for example,
in-situ doped silicon germanium (SiGe) having a high concentration
of dopants including, but not limited to, boron (B). The dopant
concertation of the raised source/drain layers 232a-232b may range
from approximately 5.times.10.sup.19/cm.sup.3 to approximately
10.sup.21/cm.sup.3. In this manner, uniform eSiGe source/drain
regions 234a-234b are formed including buffer layers 222a-222b
(i.e., the preserved buffer layer side portions 224a-224b) which
serve to inhibit diffusion of dopants into the channel region when
exposing the semiconductor device 200 to one or more well-known
subsequent thermal anneal processes. Although a p-FET device is
described going forward, it should be appreciated that an n-FET
device may be formed in a similar manner as described above. When
forming an n-FET device, the raised source/drain layers 232a-232b
may include in-situ doped epitaxial grown Si, having a high
concentration of dopants including, but not limited to, phosphorous
(P).
[0043] As described in detail above, the base portions 226a-226b of
each buffer layer 222a-222b is removed prior to forming the raised
source/drain layers 232a-232b. In this manner, the uniformity of
the eSiGe source/drain region 234a-234b is substantially improved
compared to conventional finFET devices that utilize eSiGe
source/drain regions. Accordingly, a finFET device having a uniform
eSiGe source/drain region profile is provided, thereby improving
the overall performance the semiconductor device 200.
[0044] The descriptions of the various embodiments of the present
invention have been presented for purposes of illustration, but are
not intended to be exhaustive or limited to the embodiments
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art without departing from the scope
and spirit of the described embodiments. The terminology used
herein was chosen to best explain the principles of the
embodiments, the practical application or technical improvement
over technologies found in the marketplace, or to enable others of
ordinary skill in the art to understand the embodiments disclosed
herein.
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