U.S. patent application number 16/515526 was filed with the patent office on 2021-01-21 for nanosheet transistors with inner airgaps.
The applicant listed for this patent is INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Alexander Reznicek, Heng Wu, Ruilong Xie, Lan Yu.
Application Number | 20210020741 16/515526 |
Document ID | / |
Family ID | 1000004260005 |
Filed Date | 2021-01-21 |
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United States Patent
Application |
20210020741 |
Kind Code |
A1 |
Wu; Heng ; et al. |
January 21, 2021 |
NANOSHEET TRANSISTORS WITH INNER AIRGAPS
Abstract
A method is presented for constructing a nanosheet transistor.
The method includes forming a nanosheet stack including alternating
layers of a first material and a second material over a substrate,
forming a dummy gate over the nanosheet stack, forming sacrificial
spacers adjacent the dummy gate, and selectively etching the
alternating layers of the first material to define gaps between the
alternating layers of the second material. The method further
includes filling the gaps with inner spacers, epitaxially growing
source/drain regions adjacent the nanosheet stack, selectively
removing the sacrificial spacers and the inner spacers to define
cavities, and filling the cavities with a spacer material to define
first airgaps adjacent the dummy gate and second airgaps adjacent
the etched alternating layers of the first material.
Inventors: |
Wu; Heng; (Guilderland,
NY) ; Xie; Ruilong; (Niskayuna, NY) ;
Reznicek; Alexander; (Troy, NY) ; Yu; Lan;
(Voorheesville, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTERNATIONAL BUSINESS MACHINES CORPORATION |
Armonk |
NY |
US |
|
|
Family ID: |
1000004260005 |
Appl. No.: |
16/515526 |
Filed: |
July 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/0653 20130101;
H01L 29/78696 20130101; H01L 29/068 20130101; H01L 29/66545
20130101 |
International
Class: |
H01L 29/06 20060101
H01L029/06; H01L 29/66 20060101 H01L029/66; H01L 29/786 20060101
H01L029/786 |
Claims
1. A method for constructing a nanosheet transistor, the method
comprising: forming a nanosheet stack including alternating layers
of a first material and a second material over a substrate; forming
a dummy gate over the nanosheet stack; forming sacrificial spacers
adjacent the dummy gate; selectively etching the alternating layers
of the first material to define gaps between the alternating layers
of the second material; filling the gaps with inner spacers;
epitaxially growing source/drain regions adjacent the nanosheet
stack; selectively removing the sacrificial spacers and the inner
spacers to define cavities; and filling the cavities with a spacer
material to define first airgaps adjacent the dummy gate and second
airgaps adjacent the etched alternating layers of the first
material.
2. The method of claim 1, wherein the first airgaps are vertically
aligned with the second airgaps.
3. The method of claim 1, wherein the first airgaps are larger than
the second airgaps.
4. The method of claim 1, wherein the second airgaps are positioned
between the source/drain regions and the etched alternating layers
of the first material.
5. The method of claim 1, further comprising forming metal gates
after formation of the first and second airgaps.
6. The method of claim 1, wherein the first and second airgaps are
formed after the epitaxial growth of the source/drain regions.
7. The method of claim 1, wherein the inner spacers include silicon
germanium (SiGe) with a germanium (Ge) concentration of greater
than 70%.
8. The method of claim 1, wherein the source/drain regions directly
contact an entire length of the nanosheet stack.
9. A method for constructing a nanosheet transistor, the method
comprising: forming a nanosheet stack including alternating layers
of a first material and a second material over a substrate; forming
a dummy gate over the nanosheet stack; selectively etching the
alternating layers of the first material to define gaps between the
alternating layers of the second material; filling the gaps with
inner spacers; epitaxially growing source/drain regions in direct
contact with sidewalls of the inner spacers; selectively removing
an entirety of the inner spacers to define first cavities; and
filling the first cavities with a spacer material to define first
airgaps adjacent the etched alternating layers of the first
material.
10. The method of claim 9, further comprising forming sacrificial
spacers adjacent the dummy gate before selectively etching the
alternating layers of the first material to define the gaps.
11. The method of claim 10, further comprising selectively removing
the sacrificial spacers adjacent the dummy gate before removal of
the inner spacers to define second cavities.
12. The method of claim 11, further comprising filling the second
cavities with the spacer material to define second airgaps adjacent
the dummy gate.
13. The method of claim 12, wherein the first airgaps are
vertically aligned with the second airgaps.
14. The method of claim 12, wherein the first airgaps are larger
than the second airgaps.
15. The method of claim 12, wherein the second airgaps are
positioned between the source/drain regions and the etched
alternating layers of the first material.
16. The method of claim 12, further comprising forming metal gates
after formation of the first and second airgaps.
17. The method of claim 12, wherein the first and second airgaps
are formed after the epitaxial growth of the source/drain
regions.
18. The method of claim 9, wherein the inner spacers include
silicon germanium (SiGe) with a germanium (Ge) concentration of
greater than 70%.
19. A nanosheet transistor comprising: a nanosheet stack including
alternating layers of a recessed first material and a second
material; source/drain regions disposed adjacent the nanosheet
stack; a conductive material disposed over the source/drain
regions; first airgaps defined between the source/drain regions and
the recessed alternating layers of the first material; and second
airgaps defined adjacent the conductive material, wherein the first
airgaps are vertically aligned with the second airgaps.
20. The nanosheet transistor of claim 19, wherein the first airgaps
are larger than the second airgaps.
Description
BACKGROUND
[0001] The present invention relates generally to semiconductor
devices, and more specifically, to nanosheet transistors with inner
airgaps.
[0002] As semiconductor integrated circuits (ICs) or chips become
smaller, stacked nanosheets, which are two-dimensional
nanostructures with a thickness range on the order of 1 to 100
nanometers, are increasingly used. Nanosheets and nanowires are
seen as a feasible device option for 7 nanometer and beyond scaling
of semiconductor devices. The general process flow for nanosheet
formation involves removing sacrificial layers of silicon germanium
(SiGe) between the silicon (Si) sheets.
SUMMARY
[0003] In accordance with an embodiment, a method is provided for
constructing a nanosheet transistor. The method includes forming a
nanosheet stack including alternating layers of a first material
and a second material over a substrate, forming a dummy gate over
the nanosheet stack, forming sacrificial spacers adjacent the dummy
gate, selectively etching the alternating layers of the first
material to define gaps between the alternating layers of the
second material, filling the gaps with inner spacers, epitaxially
growing source/drain regions adjacent the nanosheet stack,
selectively removing the sacrificial spacers and the inner spacers
to define cavities, and filling the cavities with a spacer material
to define first airgaps adjacent the dummy gate and second airgaps
adjacent the etched alternating layers of the first material.
[0004] In accordance with another embodiment, a method is provided
for constructing a nanosheet transistor. The method includes
forming a nanosheet stack including alternating layers of a first
material and a second material over a substrate, forming a dummy
gate over the nanosheet stack, selectively etching the alternating
layers of the first material to define gaps between the alternating
layers of the second material, filling the gaps with inner spacers,
epitaxially growing source/drain regions adjacent the nanosheet
stack, selectively removing the inner spacers to define first
cavities, and filling the first cavities with a spacer material to
define first airgaps adjacent the etched alternating layers of the
first material.
[0005] In accordance with yet another embodiment, a nanosheet
transistor is provided. The nanosheet transistor includes a
nanosheet stack including alternating layers of a recessed first
material and a second material, source/drain regions disposed
adjacent the nanosheet stack, a conductive material disposed over
the source/drain regions, first airgaps defined between the
source/drain regions and the recessed alternating layers of the
first material, and second airgaps defined adjacent the conductive
material, wherein the first airgaps are vertically aligned with the
second airgaps.
[0006] It should be noted that the exemplary embodiments are
described with reference to different subject-matters. In
particular, some embodiments are described with reference to method
type claims whereas other embodiments have been described with
reference to apparatus type claims. However, a person skilled in
the art will gather from the above and the following description
that, unless otherwise notified, in addition to any combination of
features belonging to one type of subject-matter, also any
combination between features relating to different subject-matters,
in particular, between features of the method type claims, and
features of the apparatus type claims, is considered as to be
described within this document.
[0007] These and other features and advantages will become apparent
from the following detailed description of illustrative embodiments
thereof, which is to be read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention will provide details in the following
description of preferred embodiments with reference to the
following figures wherein:
[0009] FIG. 1 is a cross-sectional view of a semiconductor
structure including a nanosheet stack formed over a substrate, in
accordance with an embodiment of the present invention;
[0010] FIG. 2 is a cross-sectional view of the semiconductor
structure of FIG. 1 where a dummy spacer is formed over the
nanosheet stack, in accordance with an embodiment of the present
invention;
[0011] FIG. 3 is a cross-sectional view of the semiconductor
structure of FIG. 2 where the dummy spacer is etched, in accordance
with an embodiment of the present invention;
[0012] FIG. 4 is a cross-sectional view of the semiconductor
structure of FIG. 3 where layers of a first material of the
nanosheet structure are etched to define voids or gaps or
indentations for subsequent inner spacer formation, in accordance
with an embodiment of the present invention;
[0013] FIG. 5 is a cross-sectional view of the semiconductor
structure of FIG. 4 where inner spacers are formed in the
indentations of the nano sheet structure, in accordance with an
embodiment of the present invention;
[0014] FIG. 6 is a cross-sectional view of the semiconductor
structure of FIG. 5 where source/drain regions are formed, in
accordance with an embodiment of the present invention;
[0015] FIG. 7 is a cross-sectional view of the semiconductor
structure of FIG. 6 where an inter-layer dielectric (ILD) is
deposited and planarized by chemical-mechanical polishing (CMP), in
accordance with an embodiment of the present invention;
[0016] FIG. 8 is a cross-sectional view of the semiconductor
structure of FIG. 7 where the dummy spacer is removed, in
accordance with an embodiment of the present invention;
[0017] FIG. 9 is a cross-sectional view of the semiconductor
structure of FIG. 8 where the inner spacers are removed, in
accordance with an embodiment of the present invention;
[0018] FIG. 10 is a cross-sectional view of the semiconductor
structure of FIG. 9 where a spacer is deposited and airgaps are
formed, in accordance with an embodiment of the present
invention;
[0019] FIG. 11 is a cross-sectional view of the semiconductor
structure of FIG. 10 where a CMP polish takes place, in accordance
with an embodiment of the present invention; and
[0020] FIG. 12 is a cross-sectional view of the semiconductor
structure of FIG. 11 where a high-k metal gate (HKMG), a conductive
material, and a self-aligned contact (SAC) cap are formed, in
accordance with an embodiment of the present invention.
[0021] Throughout the drawings, same or similar reference numerals
represent the same or similar elements.
DETAILED DESCRIPTION
[0022] Embodiments in accordance with the present invention provide
methods and devices for enabling a later inner spacer process in
nanosheets with improved epi growth and strain introduction.
Nanosheets provide for viable device architectures for scaling
complementary metal oxide semiconductors (CMOS) beyond the 7nm
node. Thin gate dielectric nanosheet transistors can be used, e.g.,
for logic and static random access memory (SRAM) applications,
whereas thick gate dielectric nanosheet transistors can be used,
e.g., for high voltage and analog applications.
[0023] Embodiments in accordance with the present invention provide
methods and devices for forming a nanosheet structure with
source/drain regions before the device spacer formation to enable
improved epi quality and strain introduction. With the sacrificial
spacer modification, airgap spacers are realized for both the gate
spacers and the inner spacers in the nanosheet structure.
[0024] Embodiments in accordance with the present invention provide
methods and devices for constructing nanosheet devices having
channel strain with high quality embedded source/drain epitaxy
grown at the end of the entire nanosheet stack, instead of the Si
tip, employing a sacrificial spacer process with inner spacer/gate
spacer formed after epi growth, enabling growth of a sacrificial
high content germanium (Ge) silicon germanium (SiGe) layer after
indentation to serve as a placeholder for the inner spacers, and
forming airgaps in regions where the sacrificial spacers are
removed. The airgaps can be thus constructed in both the gate
spacer region and the inner spacer region of the nanosheet
transistor.
[0025] Examples of semiconductor materials that can be used in
forming such nanosheet structures include silicon (Si), germanium
(Ge), silicon germanium alloys (SiGe), silicon carbide (SiC),
silicon germanium carbide (SiGeC), III-V compound semiconductors
and/or II-VI compound semiconductors. III-V compound semiconductors
are materials that include at least one element from Group III of
the Periodic Table of Elements and at least one element from Group
V of the Periodic Table of Elements. II-VI compound semiconductors
are materials that include at least one element from Group II of
the Periodic Table of Elements and at least one element from Group
VI of the Periodic Table of Elements.
[0026] It is to be understood that the present invention will be
described in terms of a given illustrative architecture; however,
other architectures, structures, substrate materials and process
features and steps/blocks can be varied within the scope of the
present invention. It should be noted that certain features cannot
be shown in all figures for the sake of clarity. This is not
intended to be interpreted as a limitation of any particular
embodiment, or illustration, or scope of the claims.
[0027] FIG. 1 is a cross-sectional view of a semiconductor
structure including a nanosheet stack formed over a substrate, in
accordance with an embodiment of the present invention.
[0028] In various example embodiments, a semiconductor structure 5
includes shallow trench isolation (STI) regions 12 formed within a
substrate 10. Multiple field effect transistor (FET) devices can be
formed over the substrate 10. In one example, a single FET device
can be formed over the substrate 10. The FET device can be formed
by constructing a nanosheet stack.
[0029] The nanosheet stack 20 of structure 5 can include
alternating layers of a first semiconductor layer 22 and a second
semiconductor layer 24. The first semiconductor layer 22 can be,
e.g., silicon germanium (SiGe) and the second semiconductor layer
24 can be, e.g., silicon (Si). Structure 5' is a cross-sectional
view along line A-A'. Structure 5' illustrates the STI 12 formed
over the substrate 10. A dummy gate 26 can also be formed over the
nanosheet stack 20.
[0030] In one or more embodiments, the substrate 10 can be a
semiconductor or an insulator with an active surface semiconductor
layer. The substrate 10 can be crystalline, semi-crystalline,
microcrystalline, or amorphous. The substrate 10 can be essentially
(e.g., except for contaminants) a single element (e.g., silicon),
primarily (e.g., with doping) of a single element, for example,
silicon (Si) or germanium (Ge), or the substrate 10 can include a
compound, for example, Al.sub.2O.sub.3, SiO.sub.2, GaAs, SiC, or
SiGe. The substrate 10 can also have multiple material layers, for
example, a semiconductor-on-insulator substrate (SeOI), a
silicon-on-insulator substrate (SOI), germanium-on-insulator
substrate (GeOI), or silicon-germanium-on-insulator substrate
(SGOI). The substrate 10 can also have other layers forming the
substrate 10, including high-k oxides and/or nitrides. In one or
more embodiments, the substrate 10 can be a silicon wafer. In an
embodiment, the substrate 10 is a single crystal silicon wafer.
[0031] The shallow trench isolation (STI) regions 12 can be formed
by etching a trench in doped bottom source/drain (S/D) regions (not
shown) utilizing a conventional dry etching process such as
reactive ion etching (RIE) or plasma etching. The trenches can
optionally be lined with a conventional liner material, e.g.,
silicon nitride or silicon oxynitride, and then chemical vapor
deposition (CVD) or another like deposition process is used to fill
the trench with silicon oxide or another like STI dielectric
material. The STI dielectric can optionally be densified after
deposition. A conventional planarization process such as
chemical-mechanical polishing (CMP) can optionally be used to
provide a planar structure.
[0032] Referring to, e.g., the nanosheet stack 20, the first
semiconductor layer 22 can be the first layer in a stack of sheets
of alternating materials. The first nanosheet stack 20 includes
first semiconductor layers 22 and second semiconductor layers 24.
Although it is specifically contemplated that the first
semiconductor layers 22 can be formed from silicon germanium and
that the second semiconductor layers 24 can be formed from silicon,
it should be understood that any appropriate materials can be used
instead, as long as the two semiconductor materials have etch
selectivity with respect to one another. As used herein, the term
"selective" in reference to a material removal process denotes that
the rate of material removal for a first material is greater than
the rate of removal for at least another material of the structure
to which the material removal process is being applied. The
alternating semiconductor layers 22/24 can be deposited by any
appropriate mechanism. It is specifically contemplated that the
semiconductor layers 22/24 can be epitaxially grown from one
another, but alternate deposition processes, such as chemical vapor
deposition (CVD), physical vapor deposition (PVD), atomic layer
deposition (ALD), or gas cluster ion beam (GOB) deposition, are
also contemplated.
[0033] FIG. 2 is a cross-sectional view of the semiconductor
structure of FIG. 1 where a dummy spacer is formed over the
nanosheet stack, in accordance with an embodiment of the present
invention.
[0034] In various example embodiments, in structures 30, 30', a
dummy spacer 28 is deposited.
[0035] The dummy spacer 28 can include any known spacer material.
In one embodiment, the dummy spacer 28 includes a low-k dielectric
material.
[0036] FIG. 3 is a cross-sectional view of the semiconductor
structure of FIG. 2 where the dummy spacer is etched, in accordance
with an embodiment of the present invention.
[0037] In various example embodiments, the dummy spacer 28 is
etched to form spacers 32 adjacent the dummy gate 26. Any etching
technique known in the art can be used. In structure 35, an opening
34 is formed between two portions of the nanosheet stack. A top
surface 11 of the substrate 10 is also exposed. Structure 35' is a
cross-sectional view along line A-A' and illustrates the spacers 32
adjacent the dummy gate 26 and the nanosheet stack 20.
[0038] FIG. 4 is a cross-sectional view of the semiconductor
structure of FIG. 3 where layers of a first material of the
nanosheet structure are etched to define voids or gaps or
indentations for subsequent inner spacer formation, in accordance
with an embodiment of the present invention.
[0039] In various example embodiments, layers of a first material
of the nanosheet structure are etched to create or define voids or
gaps or indentations 42 for subsequent inner spacer formation.
[0040] The etching can include a dry etching process such as, for
example, reactive ion etching, plasma etching, ion etching or laser
ablation. The etching can further include a wet chemical etching
process in which one or more chemical etchants are used to remove
portions of the blanket layers that are not protected by the
patterned photoresist.
[0041] In some examples, the selective wet etch or the selective
dry etch can selectively remove the portions of first semiconductor
layer 22 (e.g., the SiGe layer) and leave the entirety or portions
of the second semiconductor layer 24. The removal creates gaps or
openings or indentations 42 between the second semiconductor layers
24 of the FET device in structure 40 and gaps or openings 42
between the second semiconductor layers 24 of the FET device in
structure 40'', which is a cross-sectional view along line B-B'.
Structure 40' is the same as structure 35' in FIG. 3.
[0042] The dry and wet etching processes can have etching
parameters that can be tuned, such as etchants used, etching
temperature, etching solution concentration, etching pressure,
source power, RF bias voltage, RF bias power, etchant flow rate,
and other suitable parameters. Dry etching processes can include a
biased plasma etching process that uses a chlorine-based chemistry.
Other dry etchant gasses can include Tetrafluoromethane (CF.sub.4),
nitrogen trifluoride (NF.sub.3), sulfur hexafluoride (SF.sub.6),
and helium (He), and Chlorine trifluoride (ClF.sub.3). Dry etching
can also be performed anisotropically using such mechanisms as DRIE
(deep reactive-ion etching). Chemical vapor etching can be used as
a selective etching method, and the etching gas can include
hydrogen chloride (HCl), Tetrafluoromethane (CF.sub.4), and gas
mixture with hydrogen (H.sub.2). Chemical vapor etching can be
performed by CVD with suitable pressure and temperature.
[0043] FIG. 5 is a cross-sectional view of the semiconductor
structure of FIG. 4 where inner spacers are formed in the
indentations of the nano sheet structure, in accordance with an
embodiment of the present invention.
[0044] In various example embodiments, in structures 50, 50'',
inner spacers 52 are formed in the indentations 42 of the nanosheet
structure 20. The inner spacers 52 can be e.g., SiGe with a high
concentration of Ge. In one example, the Ge content can be about
70%. One skilled in the art can contemplate higher concentrations
of Ge. The inner spacer material 52 seals the voids or gaps or
indentations formed from the selective etching of the first
semiconductor layer 22. Structure 50' remains the same as structure
40' depicted in FIG. 4.
[0045] It is further noted that the recessed SiGe layers 22 have a
low concentration of Ge (less than 50%), whereas the inner spacers
52 have a high concentration of Ge (greater than 70%).
[0046] FIG. 6 is a cross-sectional view of the semiconductor
structure of FIG. 5 where source/drain regions are formed, in
accordance with an embodiment of the present invention.
[0047] In various example embodiments, in structure 60,
source/drain regions 62 are formed. Structures 60' and 60'' remain
the same as structures 50' and 50'' depicted in FIG. 5.
[0048] The source/drain regions 62 can contact the inner spacers
52. The source/drain regions 62 can contact a portion of the second
material 24 (e.g., Si). The source/drain regions 62 can have a
height approximately equal to or greater than a height of the
nanosheet stack 20.
[0049] Source/drain regions 62 are fabricated using CMOS process
steps (e.g., epitaxial growth of doped semiconductor
materials).
[0050] FIG. 7 is a cross-sectional view of the semiconductor
structure of FIG. 6 where an inter-layer dielectric (ILD) is
deposited and planarized by chemical-mechanical polishing (CMP), in
accordance with an embodiment of the present invention.
[0051] In various example embodiments, in structures 70, 70', 70'',
an inter-layer dielectric (ILD) 72 is deposited and planarized by
chemical-mechanical polishing (CMP).
[0052] The ILD 72 can be any suitable material, such as, for
example, porous silicates, carbon doped oxides, silicon dioxides,
silicon nitrides, silicon oxynitrides, or other dielectric
materials. Any known manner of forming the ILD 72 can be utilized.
The ILD 72 can be formed using, for example, CVD, PECVD, ALD,
flowable CVD, spin-on dielectrics, or PVD. In some embodiments, the
ILD 72 is planarized to a top surface of the dummy gate 26, using,
for example, a CMP operation.
[0053] FIG. 8 is a cross-sectional view of the semiconductor
structure of FIG. 7 where the dummy spacer is removed, in
accordance with an embodiment of the present invention.
[0054] In various example embodiments, in structures 80, 80', 80'',
the spacers 32 are removed, thus creating openings 82 adjacent the
dummy gate 26, as well as adjacent the nanosheet stack 20. The
removal can be accomplished by etching, such as, e.g., RIE.
[0055] FIG. 9 is a cross-sectional view of the semiconductor
structure of FIG. 8 where the inner spacers are removed, in
accordance with an embodiment of the present invention.
[0056] In various example embodiments, in structures 90, 90', 90'',
the inner spacers 52 are removed, thus creating openings 92 between
the recessed SiGe layers 22 and the source/drain regions 62. The
openings 92 are further visible in structure 90'', which is a
cross-sectional view taken along line B-B'. The removal can be
accomplished by etching, such as, e.g., RIE.
[0057] FIG. 10 is a cross-sectional view of the semiconductor
structure of FIG. 9 where a spacer is deposited and airgaps are
formed, in accordance with an embodiment of the present
invention.
[0058] In various example embodiments, in structures 100, 100',
100'', a spacer 102 is deposited by, e.g. ALD, and airgaps 104,
104' are formed or defined. The airgaps 104' are formed in the
openings 82 (defined by the removal of the spacers 32) and the
airgaps 104 are formed in the openings 92 (defined by the removal
of inner spacers 52). Thus, two types of airgaps are formed.
Airgaps 104' adjacent the dummy gate 26 and airgaps 104 adjacent
the recessed SiGe layers 24. Airgaps 104' can be referred to as
gate airgaps, whereas airgaps 104 can be referred to as inner
spacer airgaps. The airgaps 104, 104' have a substantially circular
or substantially oval configuration. The airgaps 104, 104' are
completely enclosed within spacer material 102. The airgaps 104,
104' are thus formed by removing sacrificial materials or layers,
and then filling them back in. Also, the airgaps 104, 104' are
formed after formation of the source/drain regions 62.
[0059] The airgaps 104 are defined between the recessed SiGe layers
22 of the nanosheet stack and the source/drain regions 62. In other
words, the airgaps 104 are defined between the source/drain regions
62 and the channel. The airgaps 104 are substantially aligned in a
vertical manner. Stated differently, the airgaps 104 are aligned
perpendicular to the substrate 10. The airgaps 104 are horizontally
offset from the Si layers 24 of the nanosheet stack. The airgaps
104, 104' are substantially vertically aligned with respect to each
other.
[0060] Moreover, the airgaps 104 are formed within the nanosheet
stack, whereas airgaps 104' are formed over the nanosheet stack.
Thus, the airgaps 104 are formed in a different region than the
airgaps 104'. The airgaps 104' also occupy a space that is greater
than the space occupied by the airgaps 104. In other words, the
airgaps 104' are bigger than the airgaps 104. Also, the airgaps
104, 104' are formed before the gate formation.
[0061] It is also noted that the airgaps 104, 104' reduce parasitic
capacitance. Embodiments in accordance with the present invention
provide methods and devices for reducing parasitic capacitance
between, e.g., gate structures and source/drain regions. In
electrical circuits, parasitic capacitance is unwanted capacitance
that exists between parts of an electronic component or circuit
simply because of their proximity to each other. When two
electrical conductors at different voltages are close together, the
electric field between them causes electric charge to be stored
thereon, which is referred to as parasitic capacitance. Therefore,
reducing front end of line (FEOL) parasitic capacitance remains a
focus for advanced technology node development. The exemplary
embodiments provide for air-gaps that can be created and
incorporated into semiconductor manufacturing technology to reduce
parasitic capacitance.
[0062] FIG. 11 is a cross-sectional view of the semiconductor
structure of FIG. 10 where a CMP polish takes place, in accordance
with an embodiment of the present invention.
[0063] In various example embodiments, in structures 110, 110',
110'', a CMP polish takes place to recess the spacer 102 to expose
a top surface of the dummy gate 26, as well as a top surface of the
ILD 72.
[0064] FIG. 12 is a cross-sectional view of the semiconductor
structure of FIG. 11 where a high-k metal gate, a conductive
material, and a self-aligned contact (SAC) cap are formed, in
accordance with an embodiment of the present invention.
[0065] In various example embodiments, in structures 120, 120',
120'', a high-k metal gate (HKMG) 126, a conductive material 122,
and a self-aligned contact (SAC) 124 are deposited.
[0066] In various embodiments, the HKMG 126 can include but is not
limited to work function metals such as titanium nitride, titanium
carbide, titanium aluminum carbide, tantalum nitride and tantalum
carbide; conducting metals such as tungsten, aluminum and copper;
and oxides such as silicon dioxide (SiO.sub.2), hafnium oxide
(e.g., HfO.sub.2), hafnium silicon oxide (e.g., HfSiO.sub.4),
hafnium silicon oxynitride (Hf.sub.wSi.sub.xO.sub.yN.sub.z),
lanthanum oxide (e.g., La.sub.2O.sub.3), lanthanum aluminum oxide
(e.g., LaAlO.sub.3), zirconium oxide (e.g., ZrO.sub.2), zirconium
silicon oxide (e.g., ZrSiO.sub.4), zirconium silicon oxynitride
(Zr.sub.wSi.sub.xO.sub.yN.sub.z), tantalum oxide (e.g., TaO.sub.2,
Ta.sub.2O.sub.5), titanium oxide (e.g., TiO.sub.2), barium
strontium titanium oxide (e.g., BaTiO.sub.3--SrTiO.sub.3), barium
titanium oxide (e.g., BaTiO.sub.3), strontium titanium oxide (e.g.,
SrTiO.sub.3), yttrium oxide (e.g., Y.sub.2O.sub.3), aluminum oxide
(e.g., Al.sub.2O.sub.3), lead scandium tantalum oxide
(Pb(Sc.sub.xTa.sub.1-x)O.sub.3), and lead zinc niobate (e.g.,
PbZn.sub.1/3Nb.sub.2/3O.sub.3).
[0067] The conductive material 122, can be, e.g., tungsten (W)
deposited over and in direct contact with the source/drain regions
62. A self-aligned contact (SAC) cap 64 is then formed over the
HKMG 126.
[0068] Regarding FIGS. 1-12, deposition is any process that grows,
coats, or otherwise transfers a material onto the wafer. Available
technologies include, but are not limited to, thermal oxidation,
physical vapor deposition (PVD), chemical vapor deposition (CVD),
electrochemical deposition (ECD), molecular beam epitaxy (MBE) and
more recently, atomic layer deposition (ALD) among others. As used
herein, "depositing" can include any now known or later developed
techniques appropriate for the material to be deposited including
but not limited to, for example: chemical vapor deposition (CVD),
low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD),
semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD),
rapid thermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited
reaction processing CVD (LRPCVD), metal-organic CVD (MOCVD),
sputtering deposition, ion beam deposition, electron beam
deposition, laser assisted deposition, thermal oxidation, thermal
nitridation, spin-on methods, physical vapor deposition (PVD),
atomic layer deposition (ALD), chemical oxidation, molecular beam
epitaxy (MBE), plating, evaporation.
[0069] The term "processing" as used herein includes deposition of
material or photoresist, patterning, exposure, development,
etching, cleaning, stripping, implanting, doping, stressing,
layering, and/or removal of the material or photoresist as needed
in forming a described structure.
[0070] It is to be understood that the present invention will be
described in terms of a given illustrative architecture; however,
other architectures, structures, substrate materials and process
features and steps/blocks can be varied within the scope of the
present invention.
[0071] It will also be understood that when an element such as a
layer, region or substrate is referred to as being "on" or "over"
another element, it can be directly on the other element or
intervening elements can also be present. In contrast, when an
element is referred to as being "directly on" or "directly over"
another element, there are no intervening elements present. It will
also be understood that when an element is referred to as being
"connected" or "coupled" to another element, it can be directly
connected or coupled to the other element or intervening elements
can be present. In contrast, when an element is referred to as
being "directly connected" or "directly coupled" to another
element, there are no intervening elements present.
[0072] The present embodiments can include a design for an
integrated circuit chip, which can be created in a graphical
computer programming language, and stored in a computer storage
medium (such as a disk, tape, physical hard drive, or virtual hard
drive such as in a storage access network). If the designer does
not fabricate chips or the photolithographic masks used to
fabricate chips, the designer can transmit the resulting design by
physical mechanisms (e.g., by providing a copy of the storage
medium storing the design) or electronically (e.g., through the
Internet) to such entities, directly or indirectly. The stored
design is then converted into the appropriate format (e.g., GDSII)
for the fabrication of photolithographic masks, which usually
include multiple copies of the chip design in question that are to
be formed on a wafer. The photolithographic masks are utilized to
define areas of the wafer (and/or the layers thereon) to be etched
or otherwise processed.
[0073] Methods as described herein can be used in the fabrication
of integrated circuit chips. The resulting integrated circuit chips
can be distributed by the fabricator in raw wafer form (that is, as
a single wafer that has multiple unpackaged chips), as a bare die,
or in a packaged form. In the latter case, the chip is mounted in a
single chip package (such as a plastic carrier, with leads that are
affixed to a motherboard or other higher level carrier) or in a
multichip package (such as a ceramic carrier that has either or
both surface interconnections or buried interconnections). In any
case, the chip is then integrated with other chips, discrete
circuit elements, and/or other signal processing devices as part of
either (a) an intermediate product, such as a motherboard, or (b)
an end product. The end product can be any product that includes
integrated circuit chips, ranging from toys and other low-end
applications to advanced computer products having a display, a
keyboard or other input device, and a central processor.
[0074] It should also be understood that material compounds will be
described in terms of listed elements, e.g., SiGe. These compounds
include different proportions of the elements within the compound,
e.g., SiGe includes Si.sub.xGe.sub.1-x where x is less than or
equal to 1, etc. In addition, other elements can be included in the
compound and still function in accordance with the present
embodiments. The compounds with additional elements will be
referred to herein as alloys.
[0075] Reference in the specification to "one embodiment" or "an
embodiment" of the present invention, as well as other variations
thereof, means that a particular feature, structure,
characteristic, and so forth described in connection with the
embodiment is included in at least one embodiment of the present
invention. Thus, the appearances of the phrase "in one embodiment"
or "in an embodiment", as well any other variations, appearing in
various places throughout the specification are not necessarily all
referring to the same embodiment.
[0076] It is to be appreciated that the use of any of the following
"/", "and/or", and "at least one of", for example, in the cases of
"A/B", "A and/or B" and "at least one of A and B", is intended to
encompass the selection of the first listed option (A) only, or the
selection of the second listed option (B) only, or the selection of
both options (A and B). As a further example, in the cases of "A,
B, and/or C" and "at least one of A, B, and C", such phrasing is
intended to encompass the selection of the first listed option (A)
only, or the selection of the second listed option (B) only, or the
selection of the third listed option (C) only, or the selection of
the first and the second listed options (A and B) only, or the
selection of the first and third listed options (A and C) only, or
the selection of the second and third listed options (B and C)
only, or the selection of all three options (A and B and C). This
can be extended, as readily apparent by one of ordinary skill in
this and related arts, for as many items listed.
[0077] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
example embodiments. 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. It will be further
understood that the terms "comprises," "comprising," "includes"
and/or "including," when used herein, 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.
[0078] Spatially relative terms, such as "beneath," "below,"
"lower," "above," "upper," and the like, can be used herein for
ease of description to describe one element's or feature's
relationship to another element(s) or feature(s) as illustrated in
the FIGS. It will be understood that 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
FIGS. For example, if the device in the FIGS. is turned over,
elements described as "below" or "beneath" other elements or
features would then be oriented "above" the other elements or
features. Thus, the term "below" can encompass both an orientation
of above and below. The device can be otherwise oriented (rotated
90 degrees or at other orientations), and the spatially relative
descriptors used herein can be interpreted accordingly. In
addition, it will also be understood that when a layer is referred
to as being "between" two layers, it can be the only layer between
the two layers, or one or more intervening layers can also be
present.
[0079] It will be understood that, although the terms first,
second, etc. can be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another element. Thus, a first
element discussed below could be termed a second element without
departing from the scope of the present concept.
[0080] Having described preferred embodiments of a method for
forming nanosheet transistors with inner airgaps (which are
intended to be illustrative and not limiting), it is noted that
modifications and variations can be made by persons skilled in the
art in light of the above teachings. It is therefore to be
understood that changes may be made in the particular embodiments
described which are within the scope of the invention as outlined
by the appended claims.
* * * * *