U.S. patent application number 16/390473 was filed with the patent office on 2020-10-22 for metal gate for a field effect transistor and method.
This patent application is currently assigned to GLOBALFOUNDRIES INC.. The applicant listed for this patent is GLOBALFOUNDRIES INC.. Invention is credited to Tao Chu, Rongtao Lu, Wei Ma, Ayse M. Ozbek, Haiting Wang.
Application Number | 20200335602 16/390473 |
Document ID | / |
Family ID | 1000004067319 |
Filed Date | 2020-10-22 |
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United States Patent
Application |
20200335602 |
Kind Code |
A1 |
Chu; Tao ; et al. |
October 22, 2020 |
METAL GATE FOR A FIELD EFFECT TRANSISTOR AND METHOD
Abstract
Disclosed is a metal gate (e.g., a replacement metal gate (RMG)
for a field effect transistor (FET) and a method of forming the
metal gate. The method includes depositing a conformal dielectric
layer to line a gate opening and performing a series of unclustered
and clustered conformal metal deposition and chamfer processes to
selectively adjust the heights of conformal metal layers within the
gate opening. By selectively controlling the heights of the
conformal metal layers, the method provides improved overall gate
height control and gate quality particularly when the metal gate
has a small critical dimension (CD) and/or a high aspect ratio
(AR). The method can also include using different etch techniques
during the different chamfer processes and, particularly, when
different materials and/or different material interfaces are
exposed to an etchant in order to ensure an essentially uniform
etch rate of the conformal metal layer(s) at issue in a direction
that is essentially vertical.
Inventors: |
Chu; Tao; (Clifton Park,
NY) ; Lu; Rongtao; (Rexford, NY) ; Ozbek; Ayse
M.; (Malta, NY) ; Ma; Wei; (Clifton Park,
NY) ; Wang; Haiting; (Clifton Park, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES INC. |
GRAND CAYMAN |
|
KY |
|
|
Assignee: |
GLOBALFOUNDRIES INC.
GRAND CAYMAN
KY
|
Family ID: |
1000004067319 |
Appl. No.: |
16/390473 |
Filed: |
April 22, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/66795 20130101;
H01L 29/66545 20130101; H01L 21/3213 20130101; H01L 29/785
20130101; H01L 21/3212 20130101; H01L 21/31055 20130101; H01L
29/42376 20130101; H01L 21/32055 20130101; H01L 21/31116 20130101;
H01L 29/42364 20130101; H01L 29/6653 20130101; H01L 29/401
20130101 |
International
Class: |
H01L 29/66 20060101
H01L029/66; H01L 29/40 20060101 H01L029/40; H01L 29/423 20060101
H01L029/423; H01L 29/78 20060101 H01L029/78; H01L 21/3105 20060101
H01L021/3105; H01L 21/311 20060101 H01L021/311; H01L 21/3205
20060101 H01L021/3205; H01L 21/3213 20060101 H01L021/3213 |
Claims
1. A metal gate comprising: a conformal dielectric layer
immediately adjacent to a channel region of a field effect
transistor, wherein the field effect transistor comprises
source/drain regions, the channel region positioned laterally
between the source/drain regions, the metal gate adjacent to the
channel region, and gate sidewall spacers between the metal gate
and the source/drain regions, and wherein the conformal dielectric
layer is further positioned laterally immediately adjacent to
vertical surfaces of the gate sidewall spacers; and multiple
conformal metal layers comprising: a first conformal metal layer
immediately adjacent to the conformal dielectric layer opposite the
channel region and further opposite lower portions of the vertical
surfaces of the gate sidewall spacers, wherein a top end of the
first conformal metal layer is at a height above a level of a top
surface of the channel region and further below a level of a top
end of the conformal dielectric layer; and additional conformal
metal layers above the first conformal metal layer, wherein one of
the additional conformal metal layers is extends over the top end
of the first conformal metal layer and is further positioned
laterally immediately adjacent to the conformal dielectric layer
opposite upper portions of the vertical surfaces of the gate
sidewall spacers, and wherein top ends of the additional conformal
metal layers are at a height above the height of the top end of the
first conformal metal layer.
2. The metal gate of claim 1, further comprising conductive fill
material on the additional conformal metal layers.
3. The metal gate of claim 1, wherein the conformal dielectric
layer comprises a high-K dielectric layer, wherein the first
conformal metal layer comprises a p-type work function metal layer,
and wherein the additional conformal metal layers comprises an
n-type work function metal layer and a barrier metal layer on the
n-type work function metal layer.
4. The metal gate of claim 3, wherein the p-type work function
metal layer and the barrier metal layer comprise titanium nitride
layers, and wherein the n-type work function metal layer comprises
a titanium aluminum carbide layer.
5. The metal gate of claim 1, wherein the multiple conformal metal
layers further comprise a second conformal metal layer between the
first conformal metal layer and the additional conformal metal
layers such that the second conformal metal layer is positioned
laterally immediately adjacent to the conformal dielectric layer
opposite middle portions of the vertical surfaces of the gate
sidewall spacers and further such that a height of a top end of the
second conformal metal layer is between the height of the top end
of the first conformal metal layer and the height of the top ends
of the additional conformal metal layers.
6. The metal gate of claim 5, wherein the first conformal metal
layer and the second conformal metal layer comprise a same p-type
work function metal.
7-20. (canceled)
21. The metal gate of claim 1, wherein a top end of the conformal
dielectric layer is at approximately a same level as the top ends
of the additional conformal metal layers.
22. A metal gate comprising: a conformal dielectric layer
immediately adjacent to a channel region of a field effect
transistor, wherein the field effect transistor comprises
source/drain regions, the channel region positioned laterally
between the source/drain regions, the metal gate adjacent to the
channel region, and gate sidewall spacers between the metal gate
and the source/drain regions, and wherein the conformal dielectric
layer is further positioned laterally immediately adjacent to
vertical surfaces of the gate sidewall spacers; and multiple
conformal metal layers comprising: a first conformal metal layer
immediately adjacent to the conformal dielectric layer opposite the
channel region and further opposite lower portions of the vertical
surfaces of the gate sidewall spacers, wherein a top end of the
first conformal metal layer is at a height above a level of a top
surface of the channel region; and additional conformal metal
layers above the first conformal metal layer and further positioned
laterally immediately adjacent to the conformal dielectric layer
opposite upper portions of the vertical surfaces of the gate
sidewall spacers, wherein top ends of the additional conformal
metal layers are at a height above the height of the top end of the
first conformal metal layer, and wherein the multiple conformal
metal layers further comprise a second conformal metal layer
between the first conformal metal layer and the additional
conformal metal layers such that the second conformal metal layer
is positioned laterally immediately adjacent to the conformal
dielectric layer opposite middle portions of the vertical surfaces
of the gate sidewall spacers and further such that a height of a
top end of the second conformal metal layer is between the height
of the top end of the first conformal metal layer and the height of
the top ends of the additional conformal metal layers.
23. The metal gate of claim 22, further comprising conductive fill
material on the additional conformal metal layers.
24. The metal gate of claim 22, wherein the conformal dielectric
layer comprises a high-K dielectric layer, wherein the first
conformal metal layer comprises a p-type work function metal layer,
and wherein the additional conformal metal layers comprises an
n-type work function metal layer and a barrier metal layer on the
n-type work function metal layer.
25. The metal gate of claim 24, wherein the p-type work function
metal layer and the barrier metal layer comprise titanium nitride
layers, and wherein the n-type work function metal layer comprises
a titanium aluminum carbide layer.
26. The metal gate of claim 22, wherein the first conformal metal
layer and the second conformal metal layer comprise a same p-type
work function metal.
27. The metal gate of claim 22, wherein a top end of the conformal
dielectric layer is at approximately a same level as the top ends
of the additional conformal metal layers.
28. A metal gate comprising: a conformal dielectric layer
immediately adjacent to a channel region of a field effect
transistor, wherein the field effect transistor comprises
source/drain regions, the channel region positioned laterally
between the source/drain regions, the metal gate adjacent to the
channel region, and gate sidewall spacers between the metal gate
and the source/drain regions, and wherein the conformal dielectric
layer is further positioned laterally immediately adjacent to
vertical surfaces of the gate sidewall spacers; and multiple
conformal metal layers comprising: a first conformal metal layer
immediately adjacent to the conformal dielectric layer opposite the
channel region and further opposite lower portions of the vertical
surfaces of the gate sidewall spacers, wherein a top end of the
first conformal metal layer is at a height above a level of a top
surface of the channel region and further below a level of a top
end of the conformal dielectric layer; and additional conformal
metal layers above the first conformal metal layer, wherein one of
the additional conformal metal layers extends over and is
immediately adjacent to the top end of the first conformal metal
layer and is further positioned laterally immediately adjacent to
the conformal dielectric layer opposite upper portions of the
vertical surfaces of the gate sidewall spacers, and wherein top
ends of the additional conformal metal layers are approximately
level with the top end of the first conformal metal layer.
29. The metal gate of claim 28, further comprising conductive fill
material on the additional conformal metal layers.
30. The metal gate of claim 28, wherein the conformal dielectric
layer comprises a high-K dielectric layer, wherein the first
conformal metal layer comprises a p-type work function metal layer,
and wherein the additional conformal metal layers comprises an
n-type work function metal layer and a barrier metal layer on the
n-type work function metal layer.
31. The metal gate of claim 30, wherein the p-type work function
metal layer and the barrier metal layer comprise titanium nitride
layers, and wherein the n-type work function metal layer comprises
a titanium aluminum carbide layer.
Description
BACKGROUND
Field of the Invention
[0001] The present invention relates to field effect transistors
(FETs) and, more particularly, to a metal gate (e.g., a replacement
metal gate (RMG)) for a FET and a method for forming the metal gate
during FET formation.
Description of Related Art
[0002] Integrated circuit (IC) design innovations are often driven
by device performance, scalability, and manufacturability. For
example, prior to the development of the 45 nm technology node,
gate-first processing was used. With the 45 nm technology node came
the development of high-K/metal gates to reduce leakage current and
increase drive current. Currently, the preferred technique for
forming high-K/metal gates is referred to as replacement metal gate
processing and the resulting gates are referred to as replacement
metal gates (RMGs). RMG processing can include, for example:
forming a sacrificial gate structure with gate sidewall spacers on
a semiconductor body adjacent to the channel region; forming the
source/drain regions, etc.; subsequently removing the sacrificial
gate to form a gate opening and forming a RMG in the gate opening.
However, with each new technology node, the gate critical dimension
(CD) (i.e., the gate length as measured across the channel region
from one source/drain region to the other gets gets smaller) is
shrinking. Furthermore, with the development of non-planar devices
(e.g., fin-type field effect transistors (FINFETs) and
gate-all-around field effect transistors (GAAFETs)), gate heights
have increased and, thus, so have gate aspect ratios (ARs) (i.e.,
the ratio of gate length to gate height). These smaller gate CDs
and/or the larger gate ARs have made forming quality RMGs more
challenging because of problems associated with depositing material
into or removing material from a gate opening with a small CD
and/or a high AR.
SUMMARY
[0003] Disclosed herein are embodiments of a metal gate (e.g., a
replacement metal gate (RMG)) for a field effect transistor (FET).
The FET can include source/drain regions, a channel region that
extends laterally between the source/drain regions, the metal gate
adjacent to the channel region, and gate sidewall spacers between
the metal gate and the source/drain regions. The metal gate can
include a conformal dielectric layer immediately adjacent to the
channel region of the FET and further positioned laterally
immediately adjacent to vertical surfaces of the sidewall spacers.
The metal gate can further include multiple conformal metal layers.
These conformal metal layers can include a first conformal metal
layer immediately adjacent to the conformal dielectric layer
opposite the channel region and further opposite lower portions of
the vertical surfaces of the gate sidewall spacers. A top end of
the first conformal metal layer can be at some predetermined height
above the level of the top surface of the channel region. The
conformal metal layers can also include multiple additional
conformal metal layers above the first conformal metal layer and
further positioned laterally immediately adjacent to the conformal
dielectric layer opposite upper portions of the vertical surfaces
of the gate sidewall spacers. Top ends of the additional conformal
metal layers can at a height above the height of the top end of the
first conformal metal layer.
[0004] Also disclosed herein are embodiments of a method of forming
a metal gate (e.g., a replacement metal gate (RMG)) for a field
effect transistor (FET).
[0005] A first embodiment of the method can include depositing a
conformal dielectric layer so as to line a gate opening, which
exposes a channel region of a field effect transistor (FET). The
method can further include depositing a first conformal metal layer
over the conformal dielectric layer so as to further line the gate
opening. Next, a first chamfer process can be performed in order to
etch back the first conformal metal layer within the gate opening
to a first height above the level of the top surface of the channel
region, thereby exposing a portion of the conformal dielectric
layer that is above the first height. Additional conformal metal
layers can then be deposited over the exposed portion of conformal
dielectric layer and over the first conformal metal layer so as to
further line the gate opening. Next, a second chamfer process can
be performed to etch back the additional conformal metal layers
within the gate opening to a second height (which is greater than
the first height) above the level of the top surface of the channel
region, thereby exposing a portion of the conformal dielectric
layer above the second height (i.e., a smaller portion than was
exposed after the first chamfer process).
[0006] A second embodiment of the method can similarly include
depositing a conformal dielectric layer so as to line a gate
opening, which exposes a channel region of a field effect
transistor (FET). Then, a first conformal metal layer can be
deposited over the conformal dielectric layer so as to further line
the gate opening and a first chamfer process can be performed in
order to etch back the first conformal metal layer within the gate
opening to a first height above the level of the top surface of the
semiconductor body, thereby exposing a portion of the conformal
dielectric layer that is above the first height. In this
embodiment, instead of forming the additional conformal metal
layers immediately following the first chamfer process, a second
conformal metal layer can be deposited over the exposed portion of
conformal dielectric layer and over the first conformal metal layer
so as to further line the gate opening. A second chamfer process
can be performed in order to etch back the second conformal metal
layer within the gate opening to a second height (which is greater
than the first height) above the level of the top surface of the
channel region, thereby exposing an upper portion of the conformal
dielectric layer above the second height (i.e., a smaller portion
than was exposed after the first chamfer process). After the second
chamfer process is performed, additional conformal metal layers can
be deposited over the exposed portion of the conformal dielectric
layer and over the second conformal metal layer so as to further
line the gate opening. Then, a third chamfer process can be
performed in order to selectively etch back the additional
conformal metal layers within the gate opening to a third height
(which is greater than the second height) above the level of the
top surface of the channel region, thereby exposing an upper
portion of the conformal dielectric layer above the third height
(i.e., a smaller upper portion than was exposed after the second
chamfer process).
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0007] The present invention will be better understood from the
following detailed description with reference to the drawings,
which are not necessarily drawn to scale and in which:
[0008] FIG. 1 is a flow diagram illustrating method embodiments for
forming a field effect transistor (FET) having a replacement metal
gate (RMG);
[0009] FIGS. 2A-2B to FIGS. 10A-10B are cross-section diagrams
illustrating partially completed structures formed according to the
flow diagram of FIG. 1 and using optional process flow A;
[0010] FIGS. 11A-11B are cross-section diagrams illustrating an
embodiment of a FET having a RMG;
[0011] FIGS. 2A-2B to FIGS. 7A-7B and FIGS. 12A-12B to FIGS.
17A-17B are cross-section diagrams illustrating partially completed
structures formed according to the flow diagram of FIG. 1 and using
optional process flow B; and
[0012] FIGS. 18A-18B are cross-section diagrams illustrating
another embodiment of a FET having a RMG.
DETAILED DESCRIPTION
[0013] As mentioned above, replacement metal gates (RMGs) can be
employed in field effect transistors (FETs) to reduce leakage
current and increase drive current. However, with each new
technology node, the gate critical dimension (CD) (i.e., the gate
length as measured across the channel region from one source/drain
region to the other gets gets smaller) is shrinking. Furthermore,
with the development of non-planar devices (e.g., fin-type field
effect transistors (FINFETs) and gate-all-around field effect
transistors (GAAFETs)), gate heights have increased and, thus, so
have gate aspect ratios (ARs) (i.e., the ratio of gate length to
gate height). The smaller gate CDs and/or the larger gate ARs have
made forming quality RMGs (i.e., essentially defect-free RMGs with
uniform gate heights across a semiconductor wafer) more challenging
because of problems associated with depositing material into or
removing material from a gate opening with a small CD and/or a high
AR. Additionally, adjusting metal layer thicknesses within an RMG
in order to fine tune performance parameters (e.g., threshold
voltage) can be challenging due to the limited amount of space
within the gate opening.
[0014] In view of the foregoing, disclosed herein are embodiments
of a metal gate (e.g., a replacement metal gate (RMG)) for a field
effect transistor (FET) and a method of forming the metal gate.
Specifically, the method can include depositing a conformal
dielectric layer to line a gate opening and then performing a
series of conformal metal deposition and chamfer processes to
selectively adjust the heights of the conformal metal layers within
the gate opening. By selectively controlling the heights of these
metal layers, the method provides improved gate quality and
improved gate height control particularly for RMGs having a small
critical dimension (CD) (e.g., a gate length of 20 nm or less)
and/or a high aspect ratio (AR) (e.g., an AR of 1:4 or higher, such
as gate length of 20 nm or less to a gate height of 80 nm or more).
The method also, optionally, includes using different etch
techniques during the different chamfer processes and,
particularly, when different materials are etched in order to
ensure a controlled and essentially uniform etch rate in a downward
vertical direction.
[0015] More particularly, FIG. 1 is a flow diagram illustrating
embodiments of a method of forming a replacement metal gate (RMG)
during formation of a field effect transistor (FET).
[0016] Each of the method embodiments can include providing a
semiconductor wafer 204 and performing front end of the line (FEOL)
and some middle of the line (MOL) processing in order to form, on
the semiconductor wafer, one or more partially completed FET
structures 201 (see process steps 102-104 and FIGS. 2A-2B). The
semiconductor wafer 204 can be, for example, a bulk semiconductor
wafer (e.g., a bulk silicon wafer or other suitable bulk
semiconductor wafer). Alternatively, the semiconductor wafer can be
a semiconductor-on-insulator wafer (e.g., a silicon-on-insulator
(SOI) wafer), which includes a semiconductor substrate (e.g., a
silicon substrate), an insulator layer (e.g., a buried oxide (BOX)
layer or other suitable insulator layer) on the semiconductor
substrate and a semiconductor layer (e.g., a silicon layer or other
suitable semiconductor layer) on the insulator layer.
[0017] Each partially completed FET structure 201 can include at
least one semiconductor body 210 and a channel region 211, which is
within the semiconductor body 210 and which is positioned laterally
between source/drain regions 213. Each partially completed FET
structure 201 can further include a shallow trench isolation (STI)
region 205.
[0018] For purposes of illustration, each partially completed FET
structure 201 can be a partially completed single-fin fin-type
field effect transistor (FINFET) (as illustrated), where the
semiconductor body 210 is a semiconductor fin (e.g., a silicon
fin), where multiple FINFETs are formed along the same
semiconductor fin, where adjacent FINFETs share a source/drain
region therebetween, and where the STI region 205 laterally
surrounds a lower portion of the semiconductor fin. However, it
should be understood that the specification and drawings are not
intended to be limiting. Alternatively, each partially completed
FET structure 201 can have a different FINFET configuration. For
example, each partially completed FET structure 201 could be a
multi-fin FINFET with multiple semiconductor bodies (i.e., multiple
semiconductor fins) and the lower portion of each fin can be
laterally surrounded by STI. Alternatively, each partially
completed FET structure 201 could be a partially completed planar
FET, where the STI laterally surrounds and defines the shape of a
planar semiconductor body. Alternatively, each partially completed
FET structure 201 could be a partially completed gate-all-around
FET (GAAFET), where, after sacrificial gate removal and before RMG
formation, the semiconductor body is processed into nanowire(s) or
nanosheet(s) (e.g., silicon nanowire(s) or nanosheet(s)) and where
the STI is below the nanowire(s) or nanosheet(s). Thus, it should
be understood that each partially completed FET structure 201 could
be any suitable partially completed FET structure for which RMG
processing can be performed.
[0019] In any case, each partially completed FET structure 201 can
include a sacrificial gate 260 with a sacrificial gate cap 262. The
sacrificial gate 260 can be above and immediately adjacent to the
STI region 205 and can further be adjacent to the channel region
211 (e.g., adjacent to the top surface and opposing sides of the
semiconductor fin at the channel region 211 in the case of the
single-fin FINFET shown). The sacrificial gate 260 can include an
optional first sacrificial gate layer adjacent to the channel
region 211 and a second sacrificial layer on the first sacrificial
gate layer. The first sacrificial gate layer can be, for example, a
thin silicon dioxide layer. The second sacrificial gate layer can
be, for example, a polysilicon layer, an amorphous silicon layer or
any other suitable sacrificial gate material, which is different
from the semiconductor body material at the channel region 211 and
which can be selectively and isotropically etched away from the
semiconductor body at the channel region during subsequent
processing. The sacrificial gate cap can be, for example, a silicon
nitride cap layer. During processing these layers can be deposited
over the channel region 211 and then lithographically patterned and
etched to form the sacrificial gate 260 with the sacrificial gate
cap 262.
[0020] Each partially completed FET structure 201 can further
include dielectric gate sidewall spacers 261 positioned laterally
adjacent to the sidewalls of the sacrificial gate 260.
Specifically, gate sidewall spacers 261 can be positioned laterally
adjacent to opposing sidewalls of the sacrificial gate 260 such
that they are positioned laterally between the sacrificial gate 260
and the source/drain regions 213 and, thus, such that they traverse
the semiconductor body 210 on either side of the channel region 211
(as shown in FIG. 2A). Additional gate sidewall spacers 261 could
be positioned laterally adjacent to other sidewalls of the
sacrificial gate such that they are parallel to and on either side
of the semiconductor body 210 at the channel region 211 (as shown
in FIG. 2B). The gate sidewall spacers 261 can be formed using
conventional gate sidewall spacer formation techniques. The gate
sidewall spacers 261 can, for example, be made of silicon nitride,
silicon carbon nitride, silicon boron carbon nitride or any other
suitable gate sidewall spacer material that is different from the
material used for the sacrificial gate 260.
[0021] Each partially completed FET structure 201 can further
include, for example: metal plugs 248 on the source/drain regions
213 and dielectric plug caps 249 on the metal plugs 248. Interlayer
dielectric (ILD) material 250 can be positioned laterally adjacent
to each partially completed FET structure 201. Such features are
well known in the art and, thus, the details thereof have been
omitted from this specification in order to allow the reader to
focus on the salient aspects of the disclosed embodiments. In any
case, the top surfaces of the ILD material 250, gate sidewall
spacers 261, the dielectric plug caps 249 and the sacrificial gate
cap(s) 262 can be essentially co-planar (e.g., due to chemical
mechanical polishing (CMP)).
[0022] The following process steps are described below with respect
to one of the partially completed FET structures (e.g., partially
completed FET structure 201). However, it should be understood that
these process steps could be performed with respect to each of the
partially completed FET structures.
[0023] The method embodiments can include removing the sacrificial
gate 260 (see process step 106 and FIGS. 3A-3B). For example, a
polishing process (e.g., a CMP process) can be performed to remove
the sacrificial gate cap 262 and expose the top surface of the
sacrificial gate 260. Then, a selective etch process can be
performed to selectively etch away the material of the second
sacrificial gate layer without impacting the semiconductor body or
exposed dielectric material (e.g., the gate sidewall spacers 261,
the plug caps 249, the ILD material 250, etc.). As mentioned above,
formation of the sacrificial gates 260 can include an optional
first sacrificial gate layer (e.g., a thin conformal silicon
dioxide layer). This thin silicon dioxide layer can protect the
semiconductor material of the semiconductor body during removal of
the second sacrificial gate layer and can be removed, for example,
by buffered hydrofluoric acid (BHF). Removal of the sacrificial
gate 260 creates a gate opening 265, which exposes the channel
region 211 extending laterally through the gate opening (e.g.,
exposes the top surface and opposing sides of the semiconductor fin
at the channel region 211 in the case of a single-fin FINFET, as
illustrated), which exposes the STI region 205 at the bottom of the
gate opening (e.g., on either side of the channel region 211 as
shown in FIG. 3B) and, which exposes vertical surfaces of the
sidewalls spacers 261 at the outside edges of the gate opening.
[0024] It should be noted that the FET design can be such that the
RMG in the final FET structure has a small critical dimension (CD)
(e.g., a gate length of 20 nm or less) and/or a high aspect ratio
(AR) (e.g., an AR of 1:4 or higher, such as gate length of 20 nm or
less to gate height of 80 nm or more). Thus, the gate opening 265
will have similar dimensions.
[0025] The method embodiments can further include forming a RMG
within gate opening 265 (see process step 108). Each of the method
embodiments includes depositing a conformal dielectric layer to
line the gate opening 265 and then performing a series of conformal
metal deposition and chamfer processes to selectively adjust the
heights of the conformal metal layers within the gate opening
265.
[0026] In one embodiment of the method, the RMG can be formed at
process step 108 using process flow A. Process flow A includes an
unclustered metal deposition process, a chamfer process, a
clustered metal deposition process and another chamfer process. In
another embodiment of the method, the RMG can be formed at process
step 108 using process flow B. Process flow B includes an
unclustered metal deposition process, a chamfer process, an
additional unclustered metal deposition process, another chamfer
process, a clustered metal deposition process, and yet another
chamfer process. As discussed below the additional unclustered
deposition process can be employed to increase the thickness of a
particular metal material at the bottom of the gate opening and,
thereby selectively adjust the threshold voltage (Vt) of the FET
being formed.
[0027] More particularly, process flow A and process flow B can
both include depositing a conformal dielectric layer 271 into the
gate opening 265 so as to line the gate opening 265 (see process
step 110 of process flow A or process step 120 of process flow B
and FIGS. 4A-4B). The conformal dielectric layer 271 can be a
conformal high-K dielectric layer. Exemplary high-K dielectric
materials include, but are not limited to, hafnium (HO-based
dielectrics (e.g., hafnium oxide, hafnium silicon oxide, hafnium
silicon oxynitride, hafnium aluminum oxide, etc.) or other suitable
high-k dielectrics (e.g., aluminum oxide, tantalum oxide, zirconium
oxide, etc.). As a result of this conformal deposition process, the
conformal dielectric layer 271 will have a portion covering the
channel region 211 (i.e., immediately adjacent to the exposed
surfaces of the channel region within the gate opening), a portion
covering the STI region 205 at the bottom of the gate opening 265,
a portion covering the vertical surfaces of the gate sidewall
spacers 261 at the outer edges of the gate opening and a portion
covering the top surface of the partially completed FET structure
outside the gate opening (i.e., extending laterally over the gate
sidewall spacers 261, plug caps 249, and ILD material 250).
[0028] Process flow A and process flow B can both include
depositing a first conformal metal layer 272 on the conformal
dielectric layer 271 so as to further line the gate opening 265
(see process step 111 of process flow A or process step 121 of
process flow B and FIGS. 5A-5B). The first conformal metal layer
272 can be, for example, a p-type work function metal layer. For
purposes of this disclosure, "a p-type work function metal" refers
to a metal that has an optimal gate conductor work function for a
p-type FET (PFET) and, particularly, a work function between about
4.9 eV and about 5.2 eV. Exemplary metals (and metal alloys) having
a work function within this range include, but are not limited to,
ruthenium, palladium, platinum, cobalt, and nickel, as well as
metal oxides (aluminum carbon oxide, aluminum titanium carbon
oxide, etc.) and metal nitrides (e.g., titanium nitride, titanium
silicon nitride, tantalum silicon nitride, titanium aluminum
nitride, tantalum aluminum nitride, etc.). In one exemplary
embodiment, the first conformal metal layer can be a titanium
nitride (TiN) layer.
[0029] In any case, deposition of the first conformal metal layer
271 at process step 111 or 121 can be unclustered. Specifically,
deposition of the first conformal metal layer can be performed in a
deposition chamber. The wafer can then be removed from the
deposition chamber (i.e., exposed to ambient air) following the
deposition process and, particularly, prior to deposition of any
other materials onto the first conformal metal layer. Since only
the one layer is deposited, it is referred to as an "unclustered"
layer.
[0030] Process flow A and process flow B can include preforming a
chamfer process in order to etch back the first conformal metal
layer 272 within the gate opening 265 to a height 10 above the
level of the top surface of the channel region 211, thereby
exposing a portion of the conformal dielectric layer 271 that is
above the height 10 (see process step 112 of process flow A or
process step 122 of process flow B and FIGS. 6A-6B and 7A-7B).
Specifically, this chamfer process can include depositing a first
planarization layer 279a on the first conformal metal layer 272 to
fill the gate opening 265. The first planarization layer 279a can
be, for example, an organic planarization layer (e.g., an amorphous
carbon layer, an amorphous silicon layer, a polymer layer or any
other suitable planarization layer). The first planarization layer
279a can then be recessed within the gate opening so that the top
surface of the first planarization layer 279a is at the desired
height 10 (see FIGS. 6A-6B). Next, the exposed metal of the first
conformal metal layer 272 above the top surface of the first
planarization layer 279a (i.e., above the height 10) can be
selectively removed using a first selective isotropic etch process.
For example, in the case of a titanium nitride first conformal
metal layer 272, the first selective isotropic etch process can be
a wet etch process performed with a standard cleaning solution
number one (SC1), which consists of hydrogen peroxide
(H.sub.2O.sub.2), ammonia, and water with a ratio of 1:1.5:50, at
an elevated temperature (e.g., 50-70.degree. C.) in order to
improve etch rate. The first selective isotropic etch process can
be followed by selective removal of the first planarization layer
279a so as to expose the remaining portion of the first conformal
metal layer 271 in the lower portion of the gate opening 265 (see
FIGS. 7A-7B).
[0031] Referring specifically to process flow A of the flow diagram
of FIG. 1, after the first conformal metal layer 272 is chamfered,
additional conformal metal layers 273-274 can be deposited over the
exposed upper portion of the conformal dielectric layer 271 and
over the first conformal metal layer 272 so as to further line the
gate opening 265 (see process step 113 of process flow A and FIGS.
8A-8B). These additional conformal metal layers can include, for
example, an n-type work function metal layer. For purposes of this
disclosure, "an n-type work function metal" refers to a metal that
has an optimal gate conductor work function for an n-type FET
(NFET) and, particularly, a work function between about 3.9 eV and
about 4.2 eV. Exemplary metals (and metal alloys) having a work
function within this range include, but are not limited to,
hafnium, zirconium, titanium, tantalum, aluminum, and alloys
thereof, such as, hafnium carbide, zirconium carbide, titanium
carbide, tantalum carbide, aluminum carbide, and titanium aluminum
carbide. In one exemplary embodiment, this n-type work function
metal layer 273 can be a titanium aluminum carbide (TiAlC) layer.
These additional conformal metal layers can further include a
barrier metal layer 274 on the n-type work function metal layer
273. The barrier metal layer 274 can be, for example, a titanium
nitride layer, a fluorine-free tungsten layer or any other suitable
barrier metal layer 274. In one exemplary embodiment, the barrier
metal layer 274 is a titanium nitride (TiN) layer. In any case,
deposition of the additional conformal metal layers 273-274 can be
clustered. That is, the additional conformal metal layers can be
deposited in succession within a deposition chamber without
removing the wafer from the deposition chamber and, thus, without
exposing any of the additional conformal metal layers to ambient
air between deposition processes. Clustering of these layers is
particularly important when oxygen in the air would react with the
n-type work function metal layer and alter its electrical
properties (i.e., its work function). For example, the aluminum in
some n-type work function metal layers (e.g., in TiAlC) can react
with oxygen.
[0032] After the additional conformal metal layers have been
deposited, another chamfer process can be performed to etch back
the additional conformal metal layers 273-274 within the gate
opening 265 to a height 30 (which is greater than the height 10)
above the level of the top surface of the channel region 211,
thereby exposing an upper portion of the conformal dielectric layer
271 above the height 30 (i.e., a smaller upper portion than was
exposed after the earlier chamfer process) (see process step 114 of
process flow A and FIGS. 9A-9B and 10A-10B). Specifically, this
chamfer process can include depositing a second planarization layer
279b on the uppermost additional conformal layer (i.e., on the
barrier metal layer 274) to fill the gate opening 265. The second
planarization layer 279b, like the first planarization layer 279a,
can be an organic planarization layer (e.g., an amorphous carbon
layer, an amorphous silicon layer, a polymer layer or any other
suitable planarization layer). The second planarization layer 279b
can then be recessed within the gate opening so that the top
surface of the second planarization layer 279b is at the desired
height 30 (see FIGS. 9A-9B). Next, the exposed metal of the
additional conformal metal layers 273-274 above the top surface of
the second planarization layer 279b (i.e., above the height 30) can
be selectively removed using a second selective isotropic etch
process.
[0033] It should be noted that the second selective isotropic etch
process used on the additional conformal metal layers 273-274
during this chamfer process can be different from the first
selective isotropic etch process used on the first conformal metal
layer 272 during the earlier chamfer process. Specifically, the
specifications of this second selective isotropic etch process can
be predetermined and tuned, based on the different metal materials
of the additional conformal metal layers and also based on
reactivity at the interface between the conformal dielectric layer
271 and the lowermost additional conformal metal layer (i.e., the
n-type work function metal layer 274).
[0034] For example, consider the exemplary embodiment where the
conformal dielectric layer is a high-k dielectric layer, where the
first conformal metal layer 272 is a titanium nitride p-type work
function metal layer and where the additional conformal metal
layers are a titanium aluminum carbide n-type work function metal
layer 273 and a titanium nitride barrier layer 274. In this case,
if the first selective isotropic etch process, described above,
were to be used when etching the additional conformal metal layers,
the etch rate of the titanium aluminum carbide (particularly at the
interface with the high-k dielectric) in a downward vertical
direction (e.g., toward the STI region 205) will be significantly
faster than the etch rate of the titanium nitride. Thus, the top
ends these materials would be at different heights following the
etch process. Consequently, a different selective isotropic etch
process is required where the etch rate of the exposed metal
material of all the additional conformal metal layers, including at
the interface between the titanium aluminum carbide n-type work
function metal layer 273 and the high-K dielectric layer 271, is
controlled and essentially uniform in the downward vertical
direction.
[0035] In one exemplary embodiment, this controlled and essentially
uniform etch of titanium aluminum carbide and titanium nitride in
the downward vertical direction can be achieved with a wet etch
process that includes, for example, using the standard cleaning
solution number one (SC1), discussed above with regard to the first
selective isotropic etch process, but with a higher concentration
of the ammonia base (e.g., more than 1.5 parts ammonia) and at
lower temperature (e.g., at room temperature) for a first clean
step and further using diluted hydrofluoric acid (DHF) for an oxide
strip step. By ensuring that the etch rate is controlled and
essentially uniform in the downward vertical direction, this wet
etch process further ensures that top ends of the additional
conformal metal layers 273 and 274 at about the same desired height
30 (e.g., essentially co-planar).
[0036] The second selective isotropic etch process can be followed
by selective removal of the second planarization layer 279b so as
to expose top ends of the additional conformal metal layers 273 and
274 as well the entire top surface of the barrier metal layer 274
(see FIGS. 10A-10B).
[0037] Additional RMG processing can then be performed in order to
complete each RMG 280 and, thereby to complete each FET 291 (see
process step 115 of process flow A and FIGS. 11A-11B). The
additional RMG processing can include, but is not limited to,
depositing a conductive fill material 275 onto the barrier metal
layer 274 so as to fill the gate opening. The conductive fill
material 275 can be, for example, tungsten, cobalt, aluminum,
nickel, copper, doped polysilicon, or any other suitable low
resistance conductive fill material. Optionally, the conductive
fill material 275 can be polished (e.g., an optional CMP can be
performed). Then, the conductive fill material 275 can be etched
back within the gate opening to a height 50, which is higher than
the height 30 of the top ends of the additional conformal metal
layers 273-274 discussed above. This height 50 of the conductive
fill material 275 can specifically be some predetermined/desired
overall gate height above the level of the top surface of the
channel region 211. It should be noted that the etch process used
to etch back the conductive fill material 275 can also result in
etching back of the exposed upper portion of the conformal
dielectric layer 271 (e.g., to about the same height 30 as the top
ends of the additional conformal metal layers). Alternatively, an
additional etch process could be used to remove the exposed upper
portion of the conformal dielectric layer 271 (e.g., so that the
top end of the conformal dielectric layer is at about the same
height 30 of the top ends of the additional conformal metal
layers). Next, a dielectric gate cap material can be deposited so
as to fill the gate opening and a polishing process (e.g., a CMP
process) can be perform so as to remove the dielectric gate cap
material from above the top surface of the ILD material 250,
thereby forming a dielectric gate cap 276 on each RMG 280'.
[0038] Referring now to process flow B of the flow diagram of FIG.
1, after chamfering the first conformal metal layer 272, an
optional second conformal metal layer 278 can be deposited over the
exposed upper portion of the conformal dielectric layer 271 and
over the first conformal metal layer 272 so as to further line the
gate opening 265 (see process step 123 of process flow B and FIGS.
12A-12B). The second conformal metal layer 278 can, like the first
conformal metal layer 272, be a p-type work function metal layer.
For example, the second conformal metal layer 278 can be made of
the same p-type work function metal as the first conformal metal
layer. In one exemplary embodiment, this p-type work function metal
can be titanium nitride. The second conformal metal layer 278 can,
for example, be deposited so as to increase the thickness of the
p-type work function metal adjacent to the channel region 211 and,
thereby to selectively adjust (i.e., tune) the threshold voltage
(Vt) of the FET being formed. In any case, deposition of the second
conformal metal layer 278 at process step 123 can be
unclustered.
[0039] Next, another chamfer process can be performed in order to
etch back the second conformal metal layer 278 within the gate
opening 265 to a height 20 (which is greater than the height 10)
above the level of the top surface of the channel region 211,
thereby exposing an upper portion of the conformal dielectric layer
271 that is above the height 20 (i.e., a smaller upper portion than
was exposed after the earlier chamfer process) (see process step
124 of process flow B and FIGS. 13A-13B and 14A-14B). Specifically,
this chamfer process can include depositing a second planarization
layer 279b on the second conformal metal layer 278 to fill the gate
opening 265. Like the first planarization layer 279a, the second
planarization layer 279b can be an organic planarization layer
(e.g., an amorphous carbon layer, an amorphous silicon layer, a
polymer layer or any other suitable planarization layer). The
second planarization layer 279b can then be recessed within the
gate opening so that the top surface of the second planarization
layer 279b is at the desired height 20 (see FIGS. 13A-13B). Next,
the exposed metal of the second conformal metal layer 278 above the
top surface of the second planarization layer 279b (i.e., above the
height 20) can be selectively removed (e.g., using the same first
selective isotropic etch process used for chamfering the first
conformal meta layer 272, as discussed above). The second
planarization layer 279b can then be selectively removed so as to
expose the remaining portion of the second conformal metal layer
278 (see FIGS. 14A-14B).
[0040] Next, additional conformal metal layers 273-274 can be
deposited over the exposed upper portion of the conformal
dielectric layer 271 and over the second conformal metal layer 278
so as to further line the gate opening 265 (see process step 125 of
process flow B and FIGS. 15A-15B). As discussed in detail above
with regard to process step 113 of process flow A, the additional
conformal metal layers can include, for example, an n-type work
function metal layer 273 and a barrier metal layer 274 on the
n-type work function metal layer 273. In one exemplary embodiment,
this n-type work function metal layer 273 can be a titanium
aluminum carbide (TiAlC) layer and the barrier metal layer 274 can
be a titanium nitride (TiN) layer. In any case, deposition of the
additional conformal metal layers 273-274 can be clustered.
Clustering of these additional conformal metal layers is
particularly important when/if oxygen in the air can react with the
n-type work function metal layer and alter its electrical
properties (i.e., its work function). For example, the aluminum in
some n-type work function metal layers (e.g., in TiAlC) can react
with oxygen and so clustering protects the TiAlC.
[0041] After the additional conformal metal layers have been
deposited, yet another chamfer process can be performed to etch
back the additional conformal metal layers 273-274 within the gate
opening 265 to a height 30 (which is greater than the heights 10
and 20) above the level of the top surface of the channel region
211, thereby exposing an upper portion of the conformal dielectric
layer 271 above the height 30 (i.e., a smaller upper portion than
was exposed after the previous chamfer processes) (see process step
126 and FIGS. 16A-16B and 17A-17B). Specifically, this chamfer
process can include depositing a third planarization layer 279c on
the uppermost additional conformal layer (i.e., on the barrier
metal layer 274) to fill the gate opening 265. Like the first and
second planarization layers, the third planarization layer 279c can
be an organic planarization layer (e.g., an amorphous carbon layer,
an amorphous silicon layer, a polymer layer or any other suitable
planarization layer). The third planarization layer 279c can then
be recessed within the gate opening so that the top surface of the
third planarization layer 279c is at the desired height 30 (see
FIGS. 16A-16B). Next, the exposed metal of the additional conformal
metal layers 273-274 above the top surface of the third
planarization layer 279c (i.e., above the height 30) can be
selectively removed using a second selective isotropic etch
process. The second selective isotropic etch process used on the
additional conformal metal layers 273-274 can be different from the
first selective isotropic etch process used on the first conformal
metal layer 272 and the second conformal metal layer 278.
Specifically, the specifications of this second selective isotropic
etch process can be predetermined and tuned, based on the different
metal materials of the additional conformal metal layers and also
based on reactivity at the interface between the conformal
dielectric layer 271 and the lowermost additional conformal metal
layer (i.e., the n-type work function metal layer 274).
[0042] It should also be noted that the second selective isotropic
etch process used on the additional conformal metal layers 273-274
at process step 126 can be the same as that used on the additional
conformal metal layers at process step 114 of process flow A
(discussed in detail above). For example, in one exemplary
embodiment, a controlled and essentially uniform etch of titanium
aluminum carbide and titanium nitride in the downward vertical
direction can be achieved with a wet etch process that includes,
for example, using the standard cleaning solution number one (SC1),
discussed above with regard to the first selective isotropic etch
process, but with a higher concentration of the ammonia base (e.g.,
more than 1.5 parts ammonia) and at lower temperature (e.g., room
temperature) for a first clean step and further using diluted
hydrofluoric acid (DHF) for an oxide strip step. Again, by ensuring
that the etch rate is controlled and essentially uniform in the
downward vertical direction, this wet etch process further ensures
that top ends of the additional conformal metal layers 273 and 274
are at about the desired height 30 (e.g., essentially co-planar).
The second selective isotropic etch process can be followed by
selective removal of the third planarization layer 279c so as to
expose top ends of the additional conformal metal layers 273 and
274 as well the entire top surface of the barrier metal layer 274
(see FIGS. 17A-17B).
[0043] Additional RMG processing can then be performed in order to
complete each RMG 280' and, thereby each FET 291' (see process step
127 of process flow B and FIGS. 18A-18B). The additional processing
can be essentially the same as that described in detail above with
regard to process step 115 of process flow A. That is, the
additional processing can include, but is not limited to,
depositing a conductive fill material 275 onto the barrier metal
layer 274 so as to fill the gate opening. Optionally, the
conductive fill material 275 can then be polished (e.g., an
optional CMP can be performed). Then, the conductive fill material
275 can be etched back within the gate opening to a height 50,
which is, for example, slightly higher than the height 30 of the
top ends of the additional conformal metal layers 273-274 discussed
above. The height 50 can specifically be some predetermined/desired
gate height above the level of the top surface of the channel
region 211. It should be noted that the etch process used to etch
back the conductive fill material 275 can also result in etching
back of the exposed upper portion of the conformal dielectric layer
271 (e.g., to the same height 30 of the top ends of the additional
conformal metal layers). Alternatively, an additional etch process
could be used to remove the exposed upper portion of the conformal
dielectric layer 271 (e.g., so that the top end of the conformal
dielectric layer 271 is at about the same height 30 as the top ends
of the additional conformal metal layers). Next, a dielectric gate
cap material can be deposited so as to fill the gate opening and a
polishing process (e.g., a CMP process) can be perform so as to
remove the dielectric gate cap material from above the top surface
of the ILD material 250, thereby forming a dielectric gate cap 276
on each RMG 280'.
[0044] It should be noted that in each of the process flows A and B
described above, techniques for controlled recessing of
planarization layers and for subsequent removal of the
planarization layers are well known in the art. Thus, the details
of such techniques have been omitted from this specification in
order to allow the reader to focus on the salient aspects of the
disclosed methods.
[0045] Following the completion of the RMG(s) 280 (see process flow
A, shown in FIGS. 11A-11B) or the completion of the RMG(s) 280'
(see process flow B, shown in FIGS. 18A-18B), additional processing
(not shown) can be performed to complete the respective
semiconductor structures 200 and 200' (see process step 130). The
additional processing can include MOL processing including, but is
not limited to, gate and source/drain contact formation. The
additional processing can also include back end of the line (BEOL)
processing.
[0046] Regardless of the process flow used (i.e., A or B), due to
the unclustered deposition and subsequent chamfering of the first
conformal metal layer 272 (and, if applicable, the second conformal
metal layer 278), the disclosed method embodiments effectively
increase the volume of available space that is within the upper
part of the gate opening 265 during deposition and chamfering of
the additional conformal metal layers 273-274 and this is done
without having to increase the actual the size of the upper part of
that gate opening. By increasing the volume of available space in
the upper part of the gate opening, the method embodiments overcome
problems associated with deposition of material into and/or
removing material from a gate opening 265 with a small CD and/or
high AR. Thus, the heights of the top ends of the conformal metal
layers and, thereby the overall gate height 50 of the resulting RMG
280, 280' can be effectively controlled so that gate heights are
essentially uniform across the wafer and from wafer-to-wafer.
Furthermore, by clustering of the additional conformal metal layers
273-274, the disclosed method embodiments still protect the n-type
work function metal layer 273 from oxidizing (which as discussed
above can alter the work function).
[0047] Also disclosed herein are embodiments of a metal gate (e.g.,
a replacement metal gate (RMG)) for a field effect transistor (FET)
formed according to the above-described methods (e.g., see the RMG
280 in the FETs 291 in the semiconductor structure 200 shown in
FIGS. 11A-11B and the RMG 280' in the FETs 291' in the
semiconductor structure 200' of FIGS. 18A-18B).
[0048] The semiconductor structures 200, 200' can be formed on a
bulk or SOI semiconductor wafer, as discussed above with regard to
the method embodiments. Each FET 291, 291' can be, for example, a
single-fin fin-type field effect transistor (single fin FINFET) (as
illustrated). Alternatively, each FET 291, 291' could have
different FINFET configuration (e.g., can be a multi-fin FINFET).
Alternatively, each FET 291, 291' could be a planar FET, a
gate-all-around FET (GAAFET), or any other suitable type of FET
structure.
[0049] In any case, each FET 291, 291' can include a semiconductor
body 210 (e.g., a semiconductor fin for a FIFNET) and, in the
semiconductor body 210, a channel region 211 positioned laterally
between source/drain regions 213. Each FET 291, 291' can further
include a metal gate 280, 280' (e.g., a replacement metal gate
(RMG)) on the channel region 211 (as described in greater detail
below). Each FET 291, 291' can further include dielectric gate
sidewall spacers 261 positioned laterally adjacent to the sidewalls
of the RMG 280, 280' (e.g., a RMG) and a dielectric gate cap 276
above the RMG 280, 280'.
[0050] As discussed in detail above with regard to the method
embodiments, the gate sidewall spacers 261 define the limits of the
gate opening within which the RMG 280, 280' is formed. Gate
sidewall spacers 261 can be positioned laterally between sidewalls
of the RMG 280, 280' and the source/drain regions 213 such that
they traverse the semiconductor body 210 on either side of the
channel region 211 (as shown in FIGS. 11A and 18B, respectively).
Additional gate sidewall spacers 261 could be positioned laterally
adjacent to other sidewalls of the RMG 280, 280' such that they are
parallel to and on either side of the semiconductor body 210 at the
channel region 211 (as shown in FIGS. 11B and 18B,
respectively).
[0051] Each FET 291, 291' can further include metal plugs 248 on
the source/drain regions 213 and dielectric plug caps 249 on the
metal plugs 248. Interlayer dielectric (ILD) material 250 can
laterally surround the FETs. Such features are well known in the
art and, thus, the details thereof have been omitted from this
specification in order to allow the reader to focus on the salient
aspects of the disclosed embodiments. In any case, the top surfaces
of the ILD material 250, gate sidewall spacers 261, the dielectric
plug caps 249 and dielectric gate cap(s) 276 can be essentially
co-planar (e.g., due to chemical mechanical polishing (CMP)).
[0052] The RMG 280, 280' can, for example, have a small critical
dimension (CD) (e.g., a gate length of 20 nm or less) and/or a high
aspect ratio (AR) (e.g., an AR of 1:4 or higher, such as gate
length of 20 nm or less to gate height of 80 nm or more).
[0053] The RMG 280, 280' can include a conformal dielectric layer
271. The conformal dielectric layer 271 can be a conformal high-K
dielectric layer. Exemplary high-K dielectric materials include,
but are not limited to, hafnium (Hf)-based dielectrics (e.g.,
hafnium oxide, hafnium silicon oxide, hafnium silicon oxynitride,
hafnium aluminum oxide, etc.) or other suitable high-k dielectrics
(e.g., aluminum oxide, tantalum oxide, zirconium oxide, etc.). The
conformal dielectric layer 271 will have a portion immediately
adjacent to and covering the channel region 211 (e.g., adjacent to
the top surface and the opposing sidewalls of the semiconductor
body 210 at the channel region 211 in the case of a FINFET, as
shown in FIGS. 11B and 18B), a portion immediately adjacent to and
covering the STI region 205 at the bottom of the gate opening
(e.g., on opposing sides of the semiconductor body 211 at the
channel region 211, as shown in FIGS. 11B and 18B) and a portion
positioned laterally immediately adjacent to vertical surfaces of
the gate sidewall spacers 261 (e.g., as shown in FIGS. 11A-11B and
18A-18B).
[0054] The RMG 280, 280' can further include multiple conformal
metal layers, which, as discussed above, were formed through a
series of deposition and chamfer processes.
[0055] In each of the embodiments, the conformal metal layers can
include a first conformal metal layer 272 immediately adjacent to
the conformal dielectric layer 271 opposite the channel region 211,
opposite the STI 205 and further opposite lower portions of the
vertical surfaces of the gate sidewall spacers 261. As discussed
above with regard to the method, the first conformal metal layer
272 is an unclustered metal layer and, due to a chamfer process,
the top end of the first conformal metal layer 272 is at given
height 10 above the level of a top surface of the channel region
211 but below a level of a top end of the conformal dielectric
layer 171. The first conformal metal layer 272 can be, for example,
a p-type work function metal layer. For purposes of this
disclosure, "a p-type work function metal" refers to a metal that
has an optimal gate conductor work function for a p-type FET (PFET)
and, particularly, a work function between about 4.9 eV and about
5.2 eV. Exemplary metals (and metal alloys) having a work function
within this range include, but are not limited to, ruthenium,
palladium, platinum, cobalt, and nickel, as well as metal oxides
(aluminum carbon oxide, aluminum titanium carbon oxide, etc.) and
metal nitrides (e.g., titanium nitride, titanium silicon nitride,
tantalum silicon nitride, titanium aluminum nitride, tantalum
aluminum nitride, etc.). In one exemplary embodiment, the first
conformal metal layer can be a titanium nitride (TiN) layer.
[0056] In each of the embodiments, the conformal metal layers can
further include additional conformal metal layers 273-274, which
are above and cover first conformal metal layer 272. Furthermore,
the lowermost layer 273 of the additional conformal metal layers
can have a portion positioned laterally immediately adjacent to the
conformal dielectric layer 271 opposite upper portions of the
vertical surfaces of the gate sidewall spacer 261. As discussed
above with regard to the method, the additional conformal metal
layers 273-274 can be clustered metal layers and, due to a chamfer
process, the top ends of the additional conformal metal layers
273-274 can be at about a same height 30, which is greater than the
height 10 of the top end of the first conformal metal layer 272,
and, thus, essentially co-planar. As illustrated, the top end of
the conformal dielectric layer 272 can also be at about this height
30.
[0057] The additional conformal metal layers can include, for
example, an n-type work function metal layer 273. For purposes of
this disclosure, "an n-type work function metal" refers to a metal
that has an optimal gate conductor work function for an n-type FET
(NFET) and, particularly, a work function between about 3.9 eV and
about 4.2 eV. Exemplary metals (and metal alloys) having a work
function within this range include, but are not limited to,
hafnium, zirconium, titanium, tantalum, aluminum, and alloys
thereof, such as, hafnium carbide, zirconium carbide, titanium
carbide, tantalum carbide, aluminum carbide, and titanium aluminum
carbide. In one exemplary embodiment, this n-type work function
metal layer 273 can be a titanium aluminum carbide (TiAlC)
layer.
[0058] The additional conformal metal layers can further include a
barrier metal layer 274 on the n-type work function metal layer
273. The barrier metal layer 274 can be, for example, a titanium
nitride layer, a fluorine-free tungsten layer or any other suitable
barrier metal layer 274. In one exemplary embodiment, the barrier
metal layer 274 can be a titanium nitride (TiN) layer.
[0059] Optionally, as illustrated in the embodiment shown in FIGS.
18A-18B, the conformal metal layers can further include a second
conformal metal layer 278, which is sandwiched between the first
conformal metal layer 272 and the lowermost layer 273 of the
additional conformal metal layers. This second conformal metal
layer 278 can include a portion between vertical portions of the
first conformal metal layer 272 below and the layer 273 above and
positioned laterally immediately adjacent to the conformal
dielectric layer 271 opposite middle portions of the vertical
surfaces of the gate sidewall spacers 261 such that a height 20 of
a top end of the second conformal metal layer 278 is between the
height 10 of the top end of the first conformal metal layer 272 and
the height 30 of the top ends of the additional conformal metal
layers 273-274 and the conformal dielectric layer 271. The second
conformal metal layer 278 can be another unclustered layer and,
like the first conformal metal layer 272, can be a p-type work
function metal layer. For example, the second conformal metal layer
278 can be made of the same p-type work function metal as the first
conformal metal layer 272. In one exemplary embodiment, this p-type
work function metal can be titanium nitride and the second
conformal metal layer 278 can be employed to increase the thickness
of the p-type work function metal adjacent to the channel region
211 and, thereby to selectively adjust (i.e., tune) the threshold
voltage (Vt) of the FET. In any case, deposition of the second
conformal metal layer 278 at process step 123 can be
unclustered.
[0060] The RMG 280, 280' can further include a conductive fill
material 275 on the barrier metal layer 274. Narrow portions of the
conductive fill material 275 can be positioned laterally between
vertical portions of all the conformal metal layers 272-274 (and
278, if applicable) between those gate sidewall spacers 261 that
traverse the semiconductor body 210 (see FIGS. 11A and 18A) and/or
between the side(s) of the semiconductor body 210 at the channel
region 211 and the adjacent gate sidewall spacer(s) 261 that are
parallel to the semiconductor body 210 (see FIGS. 11B and 18B).
Wider portions of the conductive fill material 275 can be
positioned above the narrow portions and specifically between
vertical portions of only the additional conformal metal layers
above the top end of the first conformal metal layer 272 (see FIGS.
11A and 11B) and, if applicable, above the top end of the second
conformal metal layer 278 (see FIGS. 18A-18B). The conductive fill
material 275 can be, for example, tungsten, cobalt, aluminum,
nickel, copper, doped polysilicon, or any other suitable low
resistance conductive fill material. The conductive fill material
275 can be etched back, during processing, such that the height 50
of the conductive fill material 275 is higher than the height 30 of
the top ends of the additional conformal metal layers 273-274
discussed above. It should be noted that the height 50 of the
conductive fill material 275 will be some predetermined/desired
gate height above the level of the top surface of the channel
region 211.
[0061] Each RMG 280, 280' can further include a dielectric gate cap
276, which covers and is immediately adjacent to the conductive
fill material 275 and which further extends laterally onto the top
ends of the additional conformal metal layers 273-274. As discussed
above with regard to the method embodiments, an etch process that
is used to recess/adjust the height 50 of the conductive fill
material 275 prior to dielectric gate cap formation can also etch
away the conformal dielectric layer 271 from the upper vertical
surfaces of the gate sidewall spacers 261 above the level of the
height 30 (i.e., above the height of the top ends of the additional
conformal metal layers 273-274). Thus, the dielectric gate cap 276
may be immediately adjacent to upper vertical surfaces of the gate
sidewall spacer 261. In any case, as mentioned above, the top
surface of the ILD material 250, the dielectric gate cap 276 on
each RMG 280, 280', the gate sidewall spacers 261 and the
dielectric plug caps 249 can be essentially co-planar.
[0062] It should further be understood that the terminology used
herein is for the purpose of describing the disclosed structures
and methods and is not intended to be limiting. For example, as
used herein, the singular forms "a", "an" and "the" are intended to
include the plural forms as well, unless the context clearly
indicates otherwise. Additionally, as used herein, the terms
"comprises" "comprising", "includes" and/or "including" specify the
presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, integers, steps, operations, elements,
components, and/or groups thereof. Furthermore, as used herein,
terms such as "right", "left", "vertical", "horizontal", "top",
"bottom", "upper", "lower", "under", "below", "underlying", "over",
"overlying", "parallel", "perpendicular", etc., are intended to
describe relative locations as they are oriented and illustrated in
the drawings (unless otherwise indicated) and terms such as
"touching", "in direct contact", "abutting", "directly adjacent
to", "immediately adjacent to", etc., are intended to indicate that
at least one element physically contacts another element (without
other elements separating the described elements). The term
"laterally" is used herein to describe the relative locations of
elements and, more particularly, to indicate that an element is
positioned to the side of another element as opposed to above or
below the other element, as those elements are oriented and
illustrated in the drawings. For example, an element that is
positioned laterally adjacent to another element will be beside the
other element, an element that is positioned laterally immediately
adjacent to another element will be directly beside the other
element, and an element that laterally surrounds another element
will be adjacent to and border the outer sidewalls of the other
element. The corresponding structures, materials, acts, and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material, or
act for performing the function in combination with other claimed
elements as specifically claimed.
[0063] 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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