U.S. patent application number 16/571715 was filed with the patent office on 2021-03-18 for gate spacer with air gap for semiconductor device structure and method for forming the same.
The applicant listed for this patent is Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Chia-Hao Chang, Cheng-Chi Chuang, Chia-Lin Chuang, Lin-Yu Huang, Yu-Ming Lin, Chih-Hao Wang, Sheng-Tsung Wang.
Application Number | 20210083067 16/571715 |
Document ID | / |
Family ID | 1000005430129 |
Filed Date | 2021-03-18 |
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United States Patent
Application |
20210083067 |
Kind Code |
A1 |
Wang; Sheng-Tsung ; et
al. |
March 18, 2021 |
GATE SPACER WITH AIR GAP FOR SEMICONDUCTOR DEVICE STRUCTURE AND
METHOD FOR FORMING THE SAME
Abstract
A semiconductor device structure includes a gate stack and an
adjacent source/drain contact structure formed over a semiconductor
substrate. The semiconductor device structure includes a first gate
spacer structure extending from a sidewall of the gate stack to a
sidewall of the source/drain contact structure, and a second gate
spacer structure formed over the first gate spacer structure and
between the gate stack and the source/drain contact structure. The
second gate spacer structure includes first and second gate spacer
layers adjacent to the sidewall of the gate stack and the sidewall
of the source/drain contact structure, respectively, and a third
gate spacer layer separating the first gate spacer layer from the
second gate spacer layer, so that an air gap is sealed by the
first, second, and the third gate spacer layers and the first gate
spacer structure.
Inventors: |
Wang; Sheng-Tsung; (Hsinchu,
TW) ; Huang; Lin-Yu; (Hsinchu, TW) ; Chuang;
Chia-Lin; (Taoyuan City, TW) ; Chang; Chia-Hao;
(Hsinchu City, TW) ; Chuang; Cheng-Chi; (New
Taipei City, TW) ; Lin; Yu-Ming; (Hsinchu City,
TW) ; Wang; Chih-Hao; (Baoshan Township, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Co., Ltd. |
Hsinchu |
|
TW |
|
|
Family ID: |
1000005430129 |
Appl. No.: |
16/571715 |
Filed: |
September 16, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/45 20130101;
H01L 29/4991 20130101; H01L 29/66545 20130101; H01L 21/764
20130101; H01L 21/28123 20130101; H01L 29/6656 20130101; H01L
29/7851 20130101; H01L 29/66795 20130101 |
International
Class: |
H01L 29/49 20060101
H01L029/49; H01L 29/45 20060101 H01L029/45; H01L 29/78 20060101
H01L029/78; H01L 21/28 20060101 H01L021/28; H01L 21/764 20060101
H01L021/764; H01L 29/66 20060101 H01L029/66 |
Claims
1. A semiconductor device structure, comprising: a gate stack
formed over a semiconductor substrate; a source/drain contact
structure formed over the semiconductor substrate and laterally
adjacent to the gate stack; a first gate spacer structure formed
over the semiconductor substrate and continuously extending from a
sidewall of the gate stack to a sidewall of the source/drain
contact structure; and a second gate spacer structure formed over
the first gate spacer structure and interposed between the sidewall
of gate stack and the sidewall of the source/drain contact
structure; wherein the second gate spacer structure comprises: a
first gate spacer layer adjacent to the sidewall of the gate stack;
a second gate spacer layer adjacent to the sidewall of the
source/drain contact structure; and a third gate spacer layer
separating the first gate spacer layer from the second gate spacer
layer, wherein an air gap is formed between the first gate spacer
layer and the second gate spacer layer and has a top below a top
surface of the gate electrode layer in the gate stack.
2. The semiconductor device structure as claimed in claim 1,
wherein the third gate spacer layer has a top width that is greater
than a top width of the air gap.
3. The semiconductor device structure as claimed in claim 1,
wherein the second gate spacer structure further comprises a fourth
gate spacer layer formed in the third gate spacer layer.
4. The semiconductor device structure as claimed in claim 3,
wherein the third gate spacer layer extends in the air gap to
conformally cover a bottom and sidewalls of the air gap.
5. The semiconductor device structure as claimed in claim 3,
wherein the fourth gate spacer layer has a seam formed therein.
6. The semiconductor device structure as claimed in claim 3,
wherein a bottom and sidewalls of the fourth gate spacer layer are
surrounded by the third gate spacer layer.
7. The semiconductor device structure as claimed in claim 1,
wherein the third gate spacer layer extends in the air gap to
conformally cover a bottom and sidewalls of the air gap.
8. The semiconductor device structure as claimed in claim 1,
wherein the third gate spacer layer has a seam formed therein.
9. The semiconductor device structure as claimed in claim 1,
wherein the first gate spacer structure has a dielectric constant
that is different from a dielectric constant of the second gate
spacer structure.
10. A semiconductor device structure, comprising: a fin structure
over a semiconductor substrate; a gate stack across the fin
structure, comprising: a gate electrode layer; a gate dielectric
layer surrounding a bottom and sidewalls of the gate electrode
layer; and a first capping feature covering the gate electrode
layer and the gate dielectric layer; a source/drain feature
adjacent to the fin structure; a conductive contact structure
formed over and electrically connected to the source/drain feature;
a first gate spacer structure separating the gate dielectric layer
from the source/drain feature; and a second gate spacer structure
formed over the first gate spacer structure and interposed between
a sidewall of gate stack and a sidewall of the conductive contact
structure; wherein the second gate spacer structure comprises: a
first gate spacer layer adjacent to the sidewall of the gate stack;
a second gate spacer layer adjacent to the sidewall of the
conductive contact structure; and a third gate spacer layer
separating an upper portion of the first gate spacer layer from an
upper portion of the second gate spacer layer, so as to define an
air gap separating a lower portion of the first gate spacer layer
from a lower portion of the second gate spacer layer, wherein the
first gate spacer structure has a dielectric constant that is
higher than a dielectric constant of the second gate spacer
structure.
11. The semiconductor device structure as claimed in claim 10,
wherein the third gate spacer layer has a top width that is greater
than a top width of the air gap.
12. The semiconductor device structure as claimed in claim 10,
wherein the second gate spacer structure further comprises a fourth
gate spacer layer formed in the third gate spacer layer.
13. The semiconductor device structure as claimed in claim 12,
wherein the third gate spacer layer extends in the air gap to
conformally cover a bottom and sidewalls of the air gap.
14. The semiconductor device structure as claimed in claim 10,
wherein the third gate spacer layer extends in the air gap to
conformally cover a bottom and sidewalls of the air gap.
15-20. (canceled)
21. A semiconductor device structure, comprising: a gate electrode
layer formed over a fin structure over semiconductor substrate; a
gate dielectric layer comprising a first portion formed between the
fin structure and the gate electrode layer and a second portion
extending along a sidewall of the gate electrode layer and; a first
gate spacer structure formed over the fin structure and adjoining
to the first portion of the gate dielectric layer; and a second
gate spacer structure extending from an upper surface of the first
gate spacer structure, comprising: a first gate spacer layer
adjoining to and extending along the second portion of the gate
dielectric layer; a second gate spacer layer opposite and spaced
apart from the first gate spacer layer; and a third gate spacer
layer adjoining between an upper portion of the first gate spacer
layer and an upper portion of the second gate spacer layer, wherein
top surfaces of the first, second, and third gate spacer layers are
substantially level with each other.
22. The semiconductor device structure as claimed in claim 21,
wherein the third gate spacer layer conformally extends along a
sidewall of the first gate spacer layer and a sidewall of the
second gate spacer layer to the upper surface of the first gate
spacer structure.
23. The semiconductor device structure as claimed in claim 22,
wherein the third gate spacer layer has a seam formed therein.
24. The semiconductor device structure as claimed in claim 21,
wherein the second gate spacer structure further comprises a fourth
gate spacer layer formed in the third gate spacer layer.
25. The semiconductor device structure as claimed in claim 24,
wherein the third gate spacer layer conformally extends along a
sidewall of the first gate spacer layer and a sidewall of the
second gate spacer layer to the upper surface of the first gate
spacer structure, and wherein the fourth gate spacer layer has a
seam formed therein.
26. The semiconductor device structure as claimed in claim 10,
wherein a top surface of the third gate spacer is substantially
level with a top surface of the first capping feature.
Description
BACKGROUND
[0001] The semiconductor integrated circuit (IC) industry has
experienced rapid growth. Technological advances in IC materials
and design have produced generations of ICs. Each generation has
smaller and more complex circuits than the previous generation.
However, as the semiconductor industry has progressed into
nanometer technology process nodes in pursuit of higher device
density, higher performance, and lower costs, challenges from both
fabrication and design issues have resulted in the development of
three-dimensional designs, such as the fin field effect transistor
(FinFET).
[0002] Although existing FinFETs and the manufacturing processes
thereof have generally been adequate for their intended purposes,
they have not been entirely satisfactory in all respects,
especially as device scaling-down continues. For example, it is a
challenge to form gate spacer structures at smaller and smaller
sizes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] Aspects of the present disclosure are best understood from
the following detailed description when read with the accompanying
figures. It should be noted that, in accordance with standard
practice in the industry, various features are not drawn to scale.
In fact, the dimensions of the various features may be arbitrarily
increased or reduced for clarity of discussion.
[0004] FIGS. 1A to 1F illustrate perspective views of various
stages of manufacturing a semiconductor device structure in
accordance with some embodiments.
[0005] FIGS. 2A to 2P illustrate cross-sectional representations of
various stages of manufacturing the semiconductor device structure
in accordance with some embodiments.
[0006] FIG. 3 illustrates a cross-sectional representation of a
semiconductor device structure in accordance with some
embodiments.
[0007] FIG. 4 illustrates a cross-sectional representation of a
semiconductor device structure in accordance with some
embodiments.
[0008] FIG. 5 illustrates a cross-sectional representation of a
semiconductor device structure in accordance with some
embodiments.
[0009] FIG. 6 illustrates a cross-sectional representation of a
semiconductor device structure in accordance with some
embodiments.
[0010] FIG. 7 illustrates a cross-sectional representation of a
semiconductor device structure in accordance with some
embodiments.
DETAILED DESCRIPTION
[0011] The following disclosure provides many different
embodiments, or examples, for implementing different features of
the subject matter provided. Specific examples of components and
arrangements are described below to simplify the present
disclosure. These are, of course, merely examples and are not
intended to be limiting. For example, the formation of a first
feature over or on a second feature in the description that follows
may include embodiments in which the first and second features are
formed in direct contact, and may also include embodiments in which
additional features may be formed between the first and second
features, such that the first and second features may not be in
direct contact. In addition, the present disclosure may repeat
reference numerals and/or letters in the various examples. This
repetition is for the purpose of simplicity and clarity and does
not in itself dictate a relationship between the various
embodiments and/or configurations discussed.
[0012] Furthermore, spatially relative terms, such as "beneath,"
"below," "lower," "above," "upper" and the like, may be used herein
for ease of description to describe one element or feature's
relationship to another element(s) or feature(s) as illustrated in
the figures. The spatially relative terms are intended to encompass
different orientations of the device in use or operation in
addition to the orientation depicted in the figures. The apparatus
may be otherwise oriented (rotated 90 degrees or at other
orientations) and the spatially relative descriptors used herein
may likewise be interpreted accordingly. It should be understood
that additional operations can be provided before, during, and
after the method, and some of the operations described can be
replaced or eliminated for other embodiments of the method.
[0013] Embodiments for semiconductor device structures and the
fabrication thereof are provided. The semiconductor device
structures may include an active gate stack and an adjacent
conductive contact structure (which is also referred to as a
source/drain contact structure) over a fin structure of the
semiconductor substrate. A first gate spacer structure and a second
gate spacer structure over the first gate spacer structure are
successively formed between the active gate stack and the
conductive contact structure. During the formation of the second
gate spacer structure, a first gate spacer layer is formed adjacent
to the sidewall of the active gate stack, a second gate spacer
layer is formed adjacent to the sidewall of the conductive contact
structure, and a third gate spacer layer is formed to separate an
upper portion of the first gate spacer layer from an upper portion
of the second gate spacer layer, so as to define an air gap that
separates a lower portion of the first gate spacer layer from a
lower portion of the second gate spacer layer. The existence of the
air gap reduces the dielectric constant (k) of the second gate
spacer structure, thereby reducing the parasitic capacitance
between the source/drain contact structure and the gate electrode
layer of the active gate stack. Moreover, the second gate spacer
structure can be formed with a material that is different form a
material of the first gate spacer structure, so that the total
dielectric constant (k) of the first and second gate spacer
structures can be lowered further. As a result, the device
performance can be effectively increased.
[0014] FIGS. 1A to 1F illustrate perspective views of various
stages of manufacturing a semiconductor device structure 10 and
FIGS. 2A to 2P illustrate cross-sectional representations of
various stages of manufacturing a semiconductor device structure 10
in accordance with some embodiments. In addition, FIGS. 2A to 2F
illustrate the cross-sectional representations of the semiconductor
device structure 10 shown along line 2-2' in FIGS. 1A to 1F in
accordance with some embodiments. In some embodiments, the
semiconductor device structure 10 is implemented as a fin field
effect transistor (FinFET) structure.
[0015] As shown in FIGS. 1A and 2A, a substrate 100 is provided. In
some embodiments, the substrate 100 is a semiconductor substrate,
such as a bulk semiconductor, a semiconductor-on-insulator (SOI)
substrate, or the like, which may be doped (e.g. with a P-type or
an N-type dopant) or undoped. Generally, the SOI substrate is
fabricated using a wafer bonding process, a silicon film transfer
process, a separation by implantation of oxygen (SIMOX) process,
another applicable method, or a combination thereof. In some
embodiments, the substrate 100 is a silicon wafer. The substrate
100 may include silicon or another elementary semiconductor
material such as germanium. In some other embodiments, the
substrate 100 includes a compound semiconductor. The compound
semiconductor may include gallium arsenide, silicon carbide, indium
arsenide, indium phosphide, another suitable compound
semiconductor, or a combination thereof.
[0016] Afterwards, multiple recesses (or trenches) are formed in
the substrate 100 to successively form fin structures over the
substrate 100, in accordance with some embodiments. As a result,
multiple fin structures 100a are formed between the recesses. As
shown in FIGS. 1A and 2A, one of the fin structures 100a is shown.
In some embodiments, one or more photolithography and etching
processes are used to form the fin structures 100a between the
recesses.
[0017] Isolation features 104 are then formed in the recesses to
surround lower portions of the fin structures 100a, as shown in
FIGS. 1A and 2A in accordance with some embodiments. The isolation
features 104 are used to define and electrically isolate various
device elements formed in and/or over the substrate 100. In some
embodiments, the isolation features 104 include shallow trench
isolation (STI) features, local oxidation of silicon (LOCOS)
features, other suitable isolation features, or a combination
thereof. The insulating layer for the formation of the isolation
features 104 may be made of silicon oxide, silicon nitride, silicon
oxynitride, fluorosilicate glass (FSG), low-k dielectric materials,
and/or another suitable dielectric material and may be deposited by
a flowable chemical vapor deposition (FCVD) process, a chemical
vapor deposition (CVD) process, an atomic layer deposition (ALD)
process, or another applicable process.
[0018] Afterwards, dummy gate stacks 110a are formed across the fin
structure 100a over the substrate 100 to cover the isolation
features 104 by deposition, photolithography, and etching
processes, as shown in FIGS. 1A and 2A in accordance with some
embodiments. In such an etching process, a capping feature 101 is
used as an etch mask. Each of the dummy gate stacks 110a includes
an optional dummy gate dielectric layer (not shown) and a dummy
gate electrode layer 106 formed over the dummy gate dielectric
layer and capped by the capping feature 101. The dummy gate
dielectric layer and the dummy gate electrode layer 106 may be made
of silicon oxide and polysilicon, respectively.
[0019] Afterwards, multilayer gate spacers are formed on the
opposite sidewalls of the dummy gate stacks 110a, respectively, as
shown in FIGS. 1A and 2A in accordance with some embodiments. Each
of the multilayer gate spacers includes a gate spacer layer 103
covering the sidewall of the corresponding dummy gate electrode
layer 106, a gate spacer layer 105 covering the sidewall of the
gate spacer layer 103, and a gate spacer layer 107 covering the
sidewall of the gate spacer layer 105, as shown in FIGS. 1A and 2A
in accordance with some embodiments. In some embodiments, the gate
spacer layers 103, 105, and 107 have a top surface that is
substantially level with the top surface of the capping feature
101.
[0020] In some embodiments, the gate spacer layers 103, 105, and
107 are made of different materials so that their etch selectivity
is different. For example, the gate spacer layers 103, 105, or 107
may be made of SiO, SiN, SiC, SiCN, SiOC, SiON, SiCN, SiOCN, ZrO,
HfO.sub.2, AlO, AlON, or a high-k material or another applicable
dielectric material. Moreover, the gate spacer layers 103, 105, and
107 may be formed by a deposition process, such as such as a
chemical vapor deposition (CVD) process, a plasma enhanced CVD
(PECVD) process, an atomic layer deposition (ALD) process, or
another applicable deposition process. In some embodiments, the
gate spacer layers 103, 105, and 107 have a width (which is also
referred to as critical dimension (CD)) in a range from about 0.5
nm to about 10 nm.
[0021] After formation of the multilayer gate spacers, source/drain
features 112 are formed in and laterally adjacent to the fin
structure 100a, and exposed from the dummy gate stacks 110a, as
shown in FIGS. 1A and 2A in accordance with some embodiments. In
some embodiments, each multilayer gate spacer separates the
corresponding dummy gate electrode layer 106 from the corresponding
source/drain feature 112. In some embodiments, each of the
source/drain features 112 (which are also referred to as
source/drain regions) is formed by recessing the portions of the
fin structure 100a laterally adjacent to the dummy gate stacks 110a
and growing semiconductor materials in the formed recesses in the
fin structure 100a by epitaxial (epi) growth processes. For
example, the semiconductor device structure 10 may be an NMOS
device, and the source/drain structure 120 may include Si, SiP,
SiC, SiPC, or an III-V group semiconductor material (such as InP,
GaAs, AlAs, InAs, InAlAs, or InGaAs), or the like. Alternatively,
the semiconductor device structure 10 may be a PMOS device, and the
source/drain feature 120 may include Si, SiGe, SiGeB, or an III-V
group semiconductor material (such as InSb, GaSb, or InGaSb), or
the like. The source/drain features 112 protrude above the
isolation feature 104, as shown in FIG. 1A. For example, the
source/drain features 112 have a height (which is also referred to
as thickness) in a range from about 1 nm to about 30 nm.
[0022] In some embodiments, after the source/drain features 112 are
formed, optional capping features 114 are formed to cover the
source/drain features 112, respectively. The capping feature 114
may be made of Si, SiO, SiN, SiC, SiCN, SiOC, SiON, SiCN, SiOCN,
ZrO, HfO.sub.2, AlO, AlON, or a high-k material or another
applicable dielectric material. Moreover, the capping features 114
may be formed by a deposition process, such as such as a chemical
vapor deposition (CVD) process, a plasma enhanced CVD (PECVD)
process, an atomic layer deposition (ALD) process, or another
applicable deposition process. The formed capping features 114 may
have a height (i.e., thickness) less than or equal to about 10
nm.
[0023] Afterward, the gate spacer layers 107 are recessed, as shown
in FIGS. 1B and 2B in accordance with some embodiments. In some
embodiments, the gate spacer layers 107 are recessed by an etching
process (e.g., a dry etching process) using the capping features
114 as an etch stop layer. After the etching process, the remaining
gate spacer layers 107 have a top surface that is substantially
level with the uppermost surface of the capping features 107.
[0024] Afterward, the gate spacer layers 105 and the gate spacer
layer 103 are successively or simultaneously recessed, as shown in
FIGS. 1C and 2C in accordance with some embodiments. In some
embodiments, the gate spacer layers 105 and the gate spacer layer
103 are recessed by one or more etching processes using the capping
features 114 as an etch stop layer. After the gate spacer layers
105 and the gate spacer layer 103 are recessed, the sidewalls of
each capping feature 101 and each dummy gate electrode layer 106
are exposed. The remaining gate spacer layer 105 and the remaining
gate spacer layer 103 have a top surface that is substantially
level with the top surface of the remaining gate spacer layer 107.
Moreover, the remaining gate spacer layers 103, 105, and 107 form a
first gate spacer structure that has a top surface below the top
surface of the dummy gate electrode layer 106.
[0025] After the gate spacer layers 103, 105, and 107 are recessed,
spacer layers 113 are formed to cover the exposed sidewalls of each
capping feature 101 and each dummy gate electrode layer 106,
respectively, as shown in FIGS. 1D and 2D in accordance with some
embodiments. In some embodiments, the gate spacer layer 113 is
formed directly over and in direct contact with the corresponding
remaining gate spacer layer 103 and has a top surface that is
substantially level with the top surface of the capping feature
101. The gate spacer layers 113 may be made of Si, SiO, SiN, SiC,
SiCN, SiOC, SiON, SiCN, SiOCN, ZrO, HfO.sub.2, AlO, AlON, or a
high-k material or another applicable dielectric material.
Moreover, the gate spacer layers 113 may be formed by a deposition
process, such as such as a chemical vapor deposition (CVD) process,
a plasma enhanced CVD (PECVD) process, an atomic layer deposition
(ALD) process, or another applicable deposition process. In some
embodiments, the gate spacer layers 113 have a width (i.e., CD) in
a range from about 0.5 nm to about 10 nm and a thickness (i.e.,
height) in a range from about 1 nm to about 30 nm.
[0026] Afterward, spacer layers 115 are formed to cover the
sidewalls of the gate spacer layer 113, respectively, as shown in
FIGS. 1E and 2E in accordance with some embodiments. In some
embodiments, the gate spacer layer 115 is formed directly over and
in direct contact with the corresponding remaining gate spacer
layer 105 and has a top surface that is substantially level with
the top surface of the gate spacer layer 113.
[0027] In some embodiments, the gate spacer layers 115 are made of
a material that is different from that of the gate spacer layer 113
so that they have a different etch selectivity. The gate spacer
layers 115 may be made of Si, SiO, SiN, SiC, SiCN, SiOC, SiON,
SiCN, SiOCN, ZrO, HfO.sub.2, AlO, AlON, or a high-k material or
another applicable dielectric material. Similarly, the gate spacer
layers 115 may be formed by a deposition process that is the same
or similar to the deposition process for forming the gate spacer
layer 113. In some embodiments, the gate spacer layers 115 have a
width (i.e., CD) in a range from about 0.5 nm to about 10 nm and a
thickness (i.e., height) in a range from about 1 nm to about 30
nm.
[0028] After the gate spacer layer 115 is formed, an insulating
liner layer 117 and an insulating layer 120 are successively formed
over the substrate 100 to cover the isolation feature 104 and the
capping features 114, as shown in FIGS. 1F and 2F in accordance
with some embodiments. In some embodiments, the insulating liner
layer 117 conformally covers the top surface of each capping
feature 101, the sidewall of each gate spacer layer 115 and the top
surface of each capping feature 114. Moreover, the insulating layer
120 covers the insulating liner layer 117. Afterwards, a polishing
process, such as a chemical mechanical polishing (CMP) process, is
performed to remove the excess insulating layer 120 and the excess
insulating liner layer 117 above the capping feature 101a, as shown
in FIGS. 1F and 2F in accordance with some embodiments. The
remaining insulating liner layer 117 is formed for serving as a
gate spacer layer 117a (indicated in FIG. 2J) after subsequent
etching process. In other words, the remaining insulating liner
layer 117, and the gate spacers 113 and 115 form a multilayer gate
spacer. In some embodiments, the insulating liner layer 117 is made
of a different material than the gate spacer layer 115 so that it
may have a different etch selectivity. Alternatively, the
insulating liner layer 117 may be made of the same material as the
gate spacer layer 113. For example, the insulating liner layer 117
may be made of Si, SiO, SiN, SiC, SiCN, SiOC, SiON, SiCN, SiOCN,
ZrO, HfO.sub.2, AlO, AlON, or a high-k material or another
applicable dielectric material. Similarly, the insulating liner
layer 117 may be formed by a deposition process that is the same or
similar to the deposition process used for forming the gate spacer
layer 113 or 115. In some embodiments, the remaining insulating
liner layer 117 has a width (i.e., CD) in a range from about 0.5 nm
to about 10 nm and a top surface that is substantially level with
the top surface of the gate spacer layer 115.
[0029] The remaining insulating layer 120 may serve as an
interlayer dielectric (ILD) layer. In some embodiments, the
insulating layer 120 is a single layer made of silicon oxide,
tetraethyl orthosilicate (TEOS), phosphosilicate glass (PSG),
borosilicate glass (BSG), boron-doped phosphosilicate Glass (BPSG),
fluorosilicate glass (FSG), undoped silicate glass (USG), or the
like. The insulating layer 120 is deposited using any suitable
method, such as a chemical vapor deposition (CVD) process, a plasma
enhanced CVD (PECVD) process, flowable CVD (FCVD) process, the
like, or a combination thereof.
[0030] After the polishing process is performed, each of the dummy
gate stacks 110a is replaced by an active gate stack, as shown in
FIGS. 2G to 21 in accordance with some embodiments. In some
embodiments, the capping features 101 and the underlying dummy gate
stacks 110a are successively removed by etching, so as to form
trench openings 122, as shown in FIG. 2G. Afterwards, the an active
gate stack fills each of the trench openings 122, as shown in FIGS.
2H and 21 in accordance with some embodiments. Each of the active
gate stacks includes a gate dielectric layer 124, a gate electrode
layer 126, and a capping feature 130.
[0031] The gate dielectric layer 124 may be made of a high-K
dielectric material. Examples of high-K dielectric materials
include hafnium oxide, zirconium oxide, aluminum oxide, silicon
oxynitride, hafnium dioxide-alumina alloy, hafnium silicon oxide,
hafnium silicon oxynitride, hafnium tantalum oxide, hafnium
titanium oxide, hafnium zirconium oxide, another suitable high-K
material, or a combination thereof. In some embodiments, the gate
electrode layer 126 is made of a conductive material, such as
copper, tungsten, aluminum, titanium, tantalum, or another
applicable material.
[0032] Each of the active gate stacks may further include a work
functional metal layer (not shown) between the gate dielectric
layer 124 and the gate electrode layer 126. The work function metal
layer may be made of TiN, TaN, Ru, Mo, Al, WN, ZrSi.sub.2,
MoSi.sub.2, TaSi.sub.2, NiSi.sub.2, WN, or a combination thereof.
Alternatively, the work function metal layer may be made of Ti, Ag,
TaAl, TaAlC, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, or a combination
thereof.
[0033] Afterwards, the gate dielectric layer 124 and the gate
electrode layer 126 are recessed to form recessing openings (not
shown), and each of the recessing openings is filled with the
capping feature 130, as shown in FIG. 21 in accordance with some
embodiments. For example, an insulating or semiconductor layer (not
shown) is formed over the insulating layer 120 and fills the
recessing openings. Afterwards, a polishing process, such as a
chemical mechanical polishing (CMP) process, is performed to remove
the excess insulating or semiconductor layer above the insulating
layer 120. As a result, the remaining insulating or semiconductor
layer forms the capping features 130 respectively in the recessing
openings.
[0034] The capping feature 130 may be made of Si, SiO, SiN, SiC,
SiCN, SiOC, SiON, SiCN, SiOCN, ZrO, HfO.sub.2, AlO, AlON, or a
high-k material or another applicable material. The capping feature
130 may be formed by performing a chemical vapor deposition (CVD)
process, a plasma enhanced CVD (PECVD) process, low-pressure CVD
(LPCVD) process, an atomic layer deposition (ALD) process, or
another applicable process.
[0035] The top surfaces of the capping features 130 are
substantially level with the top surface of the insulating layer
120, as shown in FIG. 21. The capping features 130 may serve as
etch masks and protect the gate dielectric layer 124 and the gate
electrode layer 126 from damage in the subsequent manufacturing
processes (e.g., etching processes). In some embodiments, the
capping features 130 have a thickness (i.e., height) in a range
from about 1 nm to about 30 nm and a top surface that is
substantially level with the top surface of the gate spacer layers
113 and 115, and the insulating liner layer 117.
[0036] After each of the recessed gate electrode layers 126 is
capped with the capping feature 130, portions of the insulating
layer 120, the insulating liner layer 117, and the capping feature
114 above each of the source/drain features 112 are removed, as
shown in FIG. 2J in accordance with some embodiments. In some
embodiments, the portions of the insulating layer 120, the
insulating liner layer 117, and the capping feature 114 above each
of the source/drain features 112 are successively removed by one or
more etching processes, so as to form contact openings 132. Each of
the contact openings 132 exposes a portion of the corresponding
source/drain features 112. The remaining insulating liner layer 117
forms a gate spacer layer 117a adjacent to the corresponding gate
spacer layer 115, so that the gate spacer layers 113, 115, and 117a
form a multilayer gate spacer. Moreover, the remaining capping
feature 114 may form a portion of the first gate spacer structure.
In the contact opening 132, a conductive contact structure (which
is also referred to as a source/drain contact structure) is formed
therein in the subsequent manufacturing processes, so that the
first gate spacer structure formed over the substrate 100
continuously extends from the sidewall of the corresponding active
gate stack (e.g., the sidewall of the gate dielectric layer 124) to
a sidewall of the corresponding conductive contact structure.
[0037] Afterwards, a deposition process is performed on the
structure in FIG. 2J to form a conformal metal layer (not shown)
over a sidewall and the bottom of each of the contact openings 132
in accordance with some embodiments. The conformal metal layer may
be formed of Ti, Al, Zr, Hf, Ta, Co, Ni, Y, and may be formed by,
for example, a CVD, ALD or electrochemical plating (ECP) process.
Afterwards, an annealing process may be performed at a temperature
of about 350.degree. C. to about 500.degree. C. While the annealing
process is being performed, the conformal metal layer reacts with
the exposed source/drain features 112, so as to form a metal
silicide or germanide layer 136 on each of the exposed the
source/drain features 112. The metal silicide or germanide layer
136 is employed to reduce the contact resistance between the
source/drain features 112 and the subsequently formed conductive
contact structure.
[0038] Afterwards, each of the remaining contact openings 132 is
filled with a conductive contact structure 140 laterally adjacent
to the corresponding active gate stack to serve as a source/drain
contact structure, as shown in FIG. 2K in accordance with some
embodiments. For example, a metal layer (not shown) is formed over
the gate spacer layers 113, 115, and 117a and the capping features
130 and fills the remaining contact openings 132. Afterwards, a
polishing process, such as a chemical mechanical polishing (CMP)
process, is performed to remove the excess metal layer above the
gate spacer layers 113, 115, and 117a and the capping features 130.
As a result, the remaining metal layers form the conductive contact
structures 140 respectively in the remaining contact openings 132,
so as to electrically connect the corresponding source/drain
features 112, respectively, via the corresponding metal silicide or
germanide layer 136.
[0039] The conductive contact structure 140 may be made of W, Co,
Ru, Ti, Ni, Cu, Au, Ag, Pt, Pd, Ir, Os, Rh, Al, Mo, or another
applicable metal material. The conductive contact structure 140 may
be formed by performing a chemical vapor deposition (CVD) process,
a plasma enhanced CVD (PECVD) process, low-pressure CVD (LPCVD)
process, an atomic layer deposition (ALD) process, or another
applicable process. In some other embodiments, a metal barrier
layer (not shown) is conformally formed on the bottom and sidewalls
of each remaining contact openings 132 prior to the formation of
the conductive contact structure 140. The metal barrier layer may
be made of Ti, Ta, TiN, TaN, W, Co, Ru, or a combination thereof,
or another applicable metal material. In some embodiments, the
metal barrier layer has a thickness that is less than or
substantially equal to 10 nm.
[0040] Afterwards, the metal barrier layer (if presented) and
conductive contact structure 140 are recessed to form recessing
openings (not shown), and each of the recessing openings is filled
with an optional capping feature 142, as shown in FIG. 2L in
accordance with some embodiments. In some embodiments, the method
and the material used in the optional capping feature 142 is the
same as or similar to those of the capping feature 130. For
example, the optional capping feature 142 may be made of Si, SiO,
SiN, SiC, SiCN, SiOC, SiON, SiCN, SiOCN, ZrO, HfO.sub.2, AlO, AlON,
or a high-k material or another applicable material. The top
surfaces of the optional capping features 142 are substantially
level with the top surfaces of the capping features 130 and the
gate spacer layers 113, 115, and 170a. The optional capping feature
142 may serve as etch masks and protect the metal barrier layer (if
presented) and conductive contact structure 140 from damage in the
subsequent manufacturing processes (e.g., etching processes). In
some embodiments, the capping features 130 has a thickness (i.e.,
height) less than or substantially equal to 30 nm.
[0041] After each of the recessed conductive contact structures 140
is capped with the capping feature 142, an opening 154 is formed in
each of the multilayer gate spacer (which includes the gate spacer
layers 113, 115, and 117a to expose a portion of the first gate
spacer structure (which includes the remaining gate spacer layers
103, 105, and 107 and the remaining capping feature 114), as shown
in FIGS. 2M to 2O in accordance with some embodiments. In some
embodiments, the gate spacer layers 115 are recessed, so that
openings 150 are formed above the recessed gate spacer layers 115,
respectively, as shown in FIG. 2M. In some embodiments, the
openings 150 are formed by removing the upper portion of the gate
spacer layers 115 using an etching process (e.g., a dry etching
process). The etching process is performed using an fluorine
(F)-based gas, a chlorine (Cl)-based gas, or a combination thereof
as a process gas. Moreover, the process temperature for etching is
less than or substantially equal to about 200.degree. C. In
addition, the process pressure for etching is in a range from about
0.1 Torr to about 10 Torr.
[0042] Afterwards, openings 152 are formed above the recessed gate
spacer layers 115, respectively, as shown in FIG. 2N in accordance
with some embodiments. In some embodiments, the exposed sidewall of
gate spacer layers 113 and 117a above the recessed gate spacer
layers 115 and the top surface of the recessed gate spacer layers
115 are partially etched, so that openings 150 are widened to form
openings 152 above the recessed gate spacer layers 115. In some
embodiments, the openings 152 are formed using an etching process
(e.g., a dry etching process). The etching process is performed
using an F-based gas, a Cl-based gas, or a combination thereof as a
process gas. Moreover, the process temperature for etching is less
than or substantially equal to about 200.degree. C. In addition,
the process pressure for etching is in a range from about 0.1 Torr
to about 10 Torr.
[0043] Afterwards, the remaining gate spacer elements 115
respectively under the openings 152 are entirely removed and the
sidewalls of the openings 154 are partially removed to form the
openings 154, as shown in FIG. 2O in accordance with some
embodiments. In some embodiments, the opening 154 that exposes a
portion of the first gate spacer structure are formed using an
etching process (e.g., a dry etching process). The etching process
is performed using an F-based gas, a Cl-based gas, or a combination
thereof as a process gas. Moreover, the process temperature for
etching is less than or substantially equal to about 200.degree. C.
In addition, the process pressure for etching is in a range from
about 0.1 Torr to about 10 Torr. In some embodiments, the top width
of the upper portion of the opening 154 is greater than the top
width of the lower portion of the opening 154, so that the opening
154 has a T-shaped cross-sectional contour, as shown in FIG. 2O.
Moreover, the upper portion of the opening 154 and the lower
portion of the opening 154 may have tapered sidewalls.
[0044] After the openings 154 are formed, the upper portion of each
of the openings 154 is capped with an insulating sealing layer 156
to form air gap 160, as shown in FIG. 2P in accordance with some
embodiments. In some embodiments, the insulating sealing layer 156
is formed to separate the upper portion of the corresponding gate
spacer layer 113 from the upper portion of the corresponding gate
spacer layer 117a, so as to define the air gap 160 separating the
lower portion of the corresponding gate spacer layer 113 from the
lower portion of the corresponding gate spacer layer 117a. Namely,
the air gap 160 is formed between the corresponding gate spacer
layer 113 and the corresponding gate spacer layer 117a and between
the insulating sealing layer 156 and the first gate spacer
structure. The insulating sealing layer 156, the corresponding gate
spacer layer 113 and 117a, and the corresponding air gap 160 form a
second gate spacer structure. Therefore, the insulating sealing
layer 156 may be referred to as a gate spacer layer and the air gap
160 may be referred to as an air spacer. The insulating sealing
layer 156 may be made of Si, SiO, SiN, SiC, SiCN, SiOC, SiON, SiCN,
SiOCN, ZrO, HfO.sub.2, AlO, AlON, or a high-k material or another
applicable dielectric material. Moreover, the insulating sealing
layer 156 may be formed by a deposition process, such as such as a
chemical vapor deposition (CVD) process, a plasma enhanced CVD
(PECVD) process, an atomic layer deposition (ALD) process, or
another applicable deposition process. In some embodiments, the
insulating sealing layer 156 has a width (i.e., CD) in a range from
about 0.5 nm to about 10 nm and a thickness (i.e., height) not less
than about 1 nm and less than about 30 nm.
[0045] In some embodiments, the air gap 160 has a width (i.e., CD)
in a range from about 0.5 nm to about 10 nm and a height in a range
from about 1 nm to about 30 nm. In some embodiments, the first gate
spacer structure and the second gate spacer structure are made of
different materials and have different dielectric constant (k). In
some embodiments, the first gate spacer structure has a dielectric
constant (k) higher than that of the second gate spacer structure
due to the existence of the air gap 160 in the second gate spacer
structure.
[0046] Compared to a single type gate spacer structure between the
active gate stack and the dielectric constant (k) structure 140,
the dielectric constant of the first and second gate spacer
structures can be adjusted by the selection of the materials
thereof, thereby lowering the dielectric constant (k) of the first
and second gate spacer structures. As a result, the parasitic
capacitance between the gate electrode layer of the active gate
stack and the corresponding conductive contact structure(s).
[0047] In some embodiments, the insulating sealing layer (or the
gate spacer layer) 156 has a wider top width W1 than the top width
W2 of the air gap 160, so that the air gap 160 is easier to form.
In some embodiments, the insulating sealing layer 156 has a seam
156a formed therein, thereby lowering further the dielectric
constant (k) of the second gate spacer structure.
[0048] Many variations and/or modifications can be made to
embodiments of the disclosure. FIG. 3 shows a cross-sectional
representation of a semiconductor device structure 20, in
accordance with some embodiments. The semiconductor device
structure 20 shown in FIG. 3 is similar to the semiconductor device
structure 10 shown in FIG. 2P. In some embodiments, the materials,
formation methods, and/or benefits of the semiconductor device
structure 10 shown in FIGS. 2A to 2P may also be applied in the
embodiments illustrated in FIG. 3, and are therefore not
repeated.
[0049] Unlike the single insulating sealing layer 156 in the
semiconductor device structure 10 shown in FIG. 2P, the
semiconductor device structure 20 includes multiple insulating
layers to serves as a multilayer insulating sealing structure, in
accordance with some embodiments. In some embodiments, the second
gate spacer structure further includes another gate spacer layer
(i.e., insulating sealing layer 170) formed in the insulating
sealing layer 156. In some embodiments, the bottom and the
sidewalls of the insulating sealing layer 170 are surrounded by the
insulating sealing layer 156. In some embodiments, the insulating
sealing layer 170 and the insulating sealing layer 156 are made of
different materials. For example, the insulating sealing layer 170
is made of Si, SiO, SiN, SiC, SiCN, SiOC, SiON, SiCN, SiOCN, ZrO,
HfO.sub.2, AlO, AlON, or a high-k material or another applicable
dielectric material. Moreover, the insulating sealing layer 170 may
be formed by a deposition process, such as such as a chemical vapor
deposition (CVD) process, a plasma enhanced CVD (PECVD) process, an
atomic layer deposition (ALD) process, or another applicable
deposition process. In some embodiments, the insulating sealing
layer 170 has a width (i.e., CD) in a range from about 0.5 nm to
about 10 nm and a thickness (i.e., height) less than that of the
insulating sealing layer.
[0050] Many variations and/or modifications can be made to
embodiments of the disclosure. FIG. 4 shows a cross-sectional
representation of a semiconductor device structure 30, in
accordance with some embodiments. The semiconductor device
structure 30 shown in FIG. 4 is similar to the semiconductor device
structure 20 shown in FIG. 3 and the semiconductor device structure
10 shown in FIG. 2P. In some embodiments, the materials, formation
methods, and/or benefits of the semiconductor device structure 10
shown in FIGS. 2A to 2P may also be applied in the embodiments
illustrated in FIG. 4, and are therefore not repeated.
[0051] Unlike the insulating sealing layer 170 in the semiconductor
device structure 20 shown in FIG. 3 and similar to insulating
sealing layer 156 in the semiconductor device structure 10 shown in
FIG. 2P, the insulating sealing layer 170 in the semiconductor
device structure 30 shown in FIG. 4 has a seam 170a formed therein,
in accordance with some embodiments. The dielectric constant (k) of
the second gate spacer structure can be lowered further via the
seam 170a.
[0052] Many variations and/or modifications can be made to
embodiments of the disclosure. FIG. 5 shows a cross-sectional
representation of a semiconductor device structure 40, in
accordance with some embodiments. The semiconductor device
structure 40 shown in FIG. 5 is similar to the semiconductor device
structure 10 shown in FIG. 2P. In some embodiments, the materials,
formation methods, and/or benefits of the semiconductor device
structure 10 shown in FIGS. 2A to 2P may also be applied in the
embodiments illustrated in FIG. 5, and are therefore not
repeated.
[0053] Unlike the semiconductor device structure 10 shown in FIG.
2P, the insulating sealing layer 156 in the semiconductor device
structure 40 shown in FIG. 5 further extends in the corresponding
air gap 160 to conformally cover the bottom and sidewalls of the
air gap 160, in accordance with some embodiments. In those cases,
the air gap 160 is entirely sealed by the insulating sealing layer
156 with a conformal liner portion. The conformal liner portion may
have a thickness that is in a range from about 0.5 nm to about 5
nm.
[0054] Many variations and/or modifications can be made to
embodiments of the disclosure. FIG. 6 shows a cross-sectional
representation of a semiconductor device structure 50, in
accordance with some embodiments. The semiconductor device
structure 50 shown in FIG. 5 is similar to the semiconductor device
structure 20 shown in FIG. 3, the semiconductor device structure 40
shown in FIG. 5, and the semiconductor device structure 10 shown in
FIG. 2P. In some embodiments, the materials, formation methods,
and/or benefits of the semiconductor device structure 10 shown in
FIGS. 2A to 2P may also be applied in the embodiments illustrated
in FIG. 6, and are therefore not repeated.
[0055] Unlike the semiconductor device structure 20 shown in FIG.
3, the top of the air gap 160 in the semiconductor device structure
50 shown in FIG. 6 is capped by and in direct contact with the
insulating sealing layer 170, in accordance with some embodiments.
In addition, similar to insulating sealing layer 156 in the
semiconductor device structure 40 shown in FIG. 5, the insulating
sealing layer 156 in the semiconductor device structure 50 shown in
FIG. 6 also extends in the corresponding air gap 160 to conformally
cover the bottom and sidewalls of the air gap 160, in accordance
with some embodiments. In those cases, the air gap 160 is entirely
sealed by the insulating sealing layer 156 with a conformal liner
portion.
[0056] Many variations and/or modifications can be made to
embodiments of the disclosure. FIG. 7 shows a cross-sectional
representation of a semiconductor device structure 60, in
accordance with some embodiments. The semiconductor device
structure 60 shown in FIG. 7 is similar to the semiconductor device
structure 50 shown in FIG. 6 and the semiconductor device structure
10 shown in FIG. 2P. In some embodiments, the materials, formation
methods, and/or benefits of the semiconductor device structure 10
shown in FIGS. 2A to 2P may also be applied in the embodiments
illustrated in FIG. 7, and are therefore not repeated.
[0057] Unlike the insulating sealing layer 170 in the semiconductor
device structure 50 shown in FIG. 6, the insulating sealing layer
170 in the semiconductor device structure 60 shown in FIG. 7 has a
seam 170a formed therein, in accordance with some embodiments. The
dielectric constant (k) of the second gate spacer structure can be
lowered further via the seam 170a.
[0058] Embodiments of methods for forming a semiconductor device
structure are provided. The semiconductor device structure may
include a gate stack and a source/drain contact structure over a
fin structure of the semiconductor substrate. The formation of the
semiconductor device structure includes forming a first gate spacer
structure and a second gate spacer structure over the first gate
spacer structure are successively formed between the gate stack and
the source/drain contact structure. During the formation of the
second gate spacer structure, a first gate spacer layer is formed
adjacent to the sidewall of the gate stack, a second gate spacer
layer is formed adjacent to the sidewall of the conductive contact
structure, and a third gate spacer layer is formed to separate an
upper portion of the first gate spacer layer from an upper portion
of the second gate spacer layer, so as to define an air gap that
separates a lower portion of the first gate spacer layer from a
lower portion of the second gate spacer layer. As a result, the air
gap reduces the dielectric constant (k) of the second gate spacer
structure, thereby reducing the parasitic capacitance between the
source/drain contact structure and the gate electrode layer of the
gate stack. In addition, since the second gate spacer structure can
be formed with a material that is different form a material of the
first gate spacer structure, the total dielectric constant (k) of
the first and second gate spacer structures can be lowered further.
Therefore, the device performance can be effectively increased.
[0059] In some embodiments, a semiconductor device structure is
provided. The semiconductor device structure includes a gate stack
formed over a semiconductor substrate and a source/drain contact
structure formed over the semiconductor substrate and laterally
adjacent to the gate stack. The semiconductor device structure also
includes a first gate spacer structure formed over the
semiconductor substrate and continuously extending from a sidewall
of the gate stack to a sidewall of the source/drain contact
structure. In addition, the semiconductor device structure includes
a second gate spacer structure formed over the first gate spacer
structure and interposed between the sidewall of gate stack and the
sidewall of the source/drain contact structure. The second gate
spacer structure includes a first gate spacer layer adjacent to the
sidewall of the gate stack, a second gate spacer layer adjacent to
the sidewall of the source/drain contact structure, and a third
gate spacer layer separating the first gate spacer layer from the
second gate spacer layer. An air gap is formed between the first
gate spacer layer and the second gate spacer layer and between the
third gate spacer layer and the first gate spacer structure.
[0060] In some embodiments, a semiconductor device structure is
provided. The semiconductor device structure includes a fin
structure over a semiconductor substrate and a gate stack across
the fin structure. The gate stack includes a gate electrode layer,
a gate dielectric layer surrounding a bottom and sidewalls of the
gate electrode layer, and a first capping feature covering the gate
electrode layer and the gate dielectric layer. The semiconductor
device structure also includes a source/drain feature adjacent to
the fin structure and a conductive contact structure formed over
and electrically connected to the source/drain feature. In
addition, the semiconductor device structure includes a first gate
spacer structure separating the gate dielectric layer from the
source/drain feature, and a second gate spacer structure formed
over the first gate spacer structure and interposed between a
sidewall of gate stack and a sidewall of the conductive contact
structure. The second gate spacer structure includes a first gate
spacer layer adjacent to the sidewall of the gate stack, a second
gate spacer layer adjacent to the sidewall of the conductive
contact structure, and a third gate spacer layer separating an
upper portion of the first gate spacer layer from an upper portion
of the second gate spacer layer, so as to define an air gap
separating a lower portion of the first gate spacer layer from a
lower portion of the second gate spacer layer.
[0061] In some embodiments, a method for forming a semiconductor
device structure is provided. The method includes forming a dummy
gate electrode layer and a first multilayer gate spacer over a fin
structure of a semiconductor substrate. The first multilayer gate
spacer separates the dummy gate electrode layer from a source/drain
feature over the semiconductor substrate. The method also includes
recessing the first multilayer gate spacer, so as to form a first
gate spacer structure that has a top surface below a top surface of
the dummy gate electrode layer. The method also includes replacing
the dummy gate electrode layer with an active gate electrode layer,
and forming a second multilayer gate spacer over the first gate
spacer structure and adjacent to the active gate electrode layer.
In addition, the method includes forming a conductive contact
structure over and electrically connected to the source/drain
feature, and forming an opening in the second multilayer gate
spacer to expose a portion of the first gate spacer structure. The
method also includes capping an upper portion of the opening with
an insulating sealing layer to form a second gate spacer structure
over the first gate spacer structure. A lower portion of the
opening defines an air gap in the second gate spacer structure. The
second gate spacer structure includes the insulating sealing layer
and the air gap. The first gate spacer structure has a dielectric
constant different from a dielectric constant of the second gate
spacer structure.
[0062] The fins described above may be patterned by any suitable
method. For example, the fins may be patterned using one or more
photolithography processes, including double-patterning or
multi-patterning processes. Generally, double-patterning or
multi-patterning processes combine photolithography and
self-aligned processes, allowing patterns to be created that have,
for example, pitches smaller than what is otherwise obtainable
using a single, direct photolithography process. For example, in
one embodiment, a sacrificial layer is formed over a substrate and
patterned using a photolithography process. Spacers are formed
alongside the patterned sacrificial layer using a self-aligned
process. The sacrificial layer is then removed, and the remaining
spacers may then be used to pattern the fins.
[0063] The foregoing outlines features of several embodiments so
that those skilled in the art may better understand the aspects of
the present disclosure. Those skilled in the art should appreciate
that they may readily use the present disclosure as a basis for
designing or modifying other processes and structures for carrying
out the same purposes and/or achieving the same advantages of the
embodiments introduced herein. Those skilled in the art should also
realize that such equivalent constructions do not depart from the
spirit and scope of the present disclosure, and that they may make
various changes, substitutions, and alterations herein without
departing from the spirit and scope of the present disclosure.
* * * * *