U.S. patent application number 15/714271 was filed with the patent office on 2018-04-26 for bottom spacer formation for vertical transistor.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Oleg Gluschenkov, Sanjay C. Mehta, Shogo Mochizuki, Alexander Reznicek.
Application Number | 20180114860 15/714271 |
Document ID | / |
Family ID | 59886758 |
Filed Date | 2018-04-26 |
United States Patent
Application |
20180114860 |
Kind Code |
A1 |
Gluschenkov; Oleg ; et
al. |
April 26, 2018 |
BOTTOM SPACER FORMATION FOR VERTICAL TRANSISTOR
Abstract
A bilayer of silicon dioxide and silicon nitride is formed on
exposed surfaces of at least one semiconductor fin having a bottom
source/drain region located at the footprint, and on each side, of
the at least one semiconductor fin. An upper surface of each
horizontal portion of the silicon nitride layer is then carbonized,
and thereafter non-carbonized vertical portions of the silicon
nitride layer are removed. Next, the carbonized portions of the
silicon nitride layer are removed, and thereafter the vertical
portions of the silicon dioxide layer are removed from sidewalls of
the at least one semiconductor fin utilizing each remaining portion
of the silicon nitride layer as an etch mask A bottom spacer
structure is provided on each bottom source/drain region in which
each bottom spacer structure includes a remaining portion of the
silicon dioxide layer and the remaining portion of the silicon
nitride layer.
Inventors: |
Gluschenkov; Oleg;
(Tannersville, NY) ; Mehta; Sanjay C.; (Niskayuna,
NY) ; Mochizuki; Shogo; (Clifton Park, NY) ;
Reznicek; Alexander; (Troy, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
59886758 |
Appl. No.: |
15/714271 |
Filed: |
September 25, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15335105 |
Oct 26, 2016 |
9773901 |
|
|
15714271 |
|
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/7827 20130101;
H01L 29/6656 20130101; H01L 29/0653 20130101; H01L 29/0847
20130101; H01L 29/66666 20130101 |
International
Class: |
H01L 29/78 20060101
H01L029/78; H01L 29/66 20060101 H01L029/66; H01L 29/06 20060101
H01L029/06 |
Claims
1. A semiconductor structure comprising: at least one semiconductor
fin extending upward from a surface of a substrate; a bottom
source/drain region located at the footprint, and on each side, of
the at least one semiconductor fin; a bottom spacer structure
located on each bottom source/drain region, each bottom spacer
structure comprising a silicon dioxide spacer and a silicon nitride
spacer, wherein the silicon nitride spacer is entirely separated
from the at least one semiconductor fin by a first portion of the
silicon dioxide spacer and entirely separated from the bottom
source/drain region by a second portion of the silicon dioxide
spacer; a functional gate structure located on each side of the at
least one semiconductor fin and above the bottom spacer structure;
a top spacer located on each functional gate structure and
contacting a sidewall of a portion of the at least one
semiconductor fin; and a top source/drain structure extending from
each sidewall of an upper portion of the at least one semiconductor
fin.
2. The semiconductor structure of claim 1, wherein a topmost
surface of each silicon nitride spacer is coplanar with a topmost
surface of each silicon nitride spacer.
3. The semiconductor structure of claim 2, wherein a portion of
each functional gate structure directly contacts the topmost
surface of the silicon dioxide spacer and the topmost surface of
the silicon nitride spacer.
4. The semiconductor structure of claim 2, wherein a bottommost
surface of each silicon dioxide spacer is located directly on a
topmost surface of the bottom source/drain region.
5. The semiconductor structure of claim 2, wherein a bottommost
surface of the silicon nitride spacer is present on a surface of
the silicon dioxide spacer.
6. The semiconductor structure of claim 1, wherein said substrate
comprises a remaining portion of a bulk semiconductor
substrate.
7. The semiconductor structure of claim 1, wherein the at least one
semiconductor fin and the substrate comprise a same semiconductor
material.
8. The semiconductor structure of claim 1, wherein each top
source/drain structure has a faceted surface.
9. The semiconductor structure of claim 1, wherein each top
source/drain structure has a non-faceted surface.
10. The semiconductor structure of claim 1, wherein each top
source/drain structure is diamond shaped.
11. The semiconductor structure of claim 1, wherein each top
source/drain structure is triangularly shaped, and is present only
on the sidewall of the at least one semiconductor fin.
12. The semiconductor structure of claim 1, wherein each functional
gate structure comprises a U-shaped gate dielectric liner portion,
a U-shaped gate conductor liner portion, and a gate conductor
portion.
13. The semiconductor structure of claim 12, wherein the U-shaped
gate dielectric liner portion, the U-shaped gate conductor liner
portion, and the gate conductor portion have topmost surfaces that
are coplanar with each other.
14. The semiconductor structure of claim 1, wherein the top spacer
has a height that is less than a height of the at least one
semiconductor fin.
15. The semiconductor structure of claim 1, wherein the at least
one semiconductor fin, the bottom source/drain structure and the
top source/drain structure comprise a same semiconductor
material.
16. The semiconductor structure of claim 1, wherein the bottom
source/drain region and the top source/drain structure have a
dopant concentration from 2.times.10.sup.20 atoms/cm.sup.3 to
1.times.10.sup.21 atoms/cm.sup.3.
17. The semiconductor structure of claim 1, wherein each functional
gate structure comprises a U-shaped gate dielectric liner portion,
wherein a bottommost surface of the U-shaped gate dielectric liner
portion is in direct physically contact with topmost surfaces of
both the silicon dioxide spacer and the silicon nitride spacer of
the bottom spacer structure.
18. The semiconductor structure of claim 1, wherein the at least
one semiconductor fin has a height from 20 nm to 200 nm, and a
width from 2 nm to 30 nm.
19. The semiconductor structure of claim 1, wherein the at least
one semiconductor fin comprises a plurality of spaced apart
semiconductor fins, and each semiconductor fin has a height from 20
nm to 200 nm, and a width from 2 nm to 30 nm.
20. The semiconductor structure of claim 19, wherein a pitch
between each adjacent semiconductor fin of the plurality of spaced
apart semiconductor fins is from 20 nm to 100 nm.
Description
BACKGROUND
[0001] The present application relates to a semiconductor structure
and a method of forming the same. More particularly, the present
application relates to a semiconductor structure including a
vertical transistor having a bottom spacer structure that is
present on a bottom source/drain region, wherein the bottom spacer
structure includes a silicon dioxide spacer and a silicon nitride
spacer. The present application also provides a method of forming
such a semiconductor structure.
[0002] Conventional vertical transistors are devices where the
source-drain current flows in a direction normal, i.e., vertical,
to the substrate surface. In such devices, a vertical semiconductor
pillar defines the channel with the source and drain located at
opposing ends of the semiconductor pillar. One advantage of a
vertical transistor is that the channel length is not defined by
lithography, but by methods such as epitaxy or layer deposition,
which enable precise dimensional control. As such, vertical
transistors are an attractive option for technology scaling for 5
nm and beyond.
[0003] In conventional vertical transistor device architecture, it
is difficult to remove the bottom spacer material from the
sidewalls of the vertical semiconductor pillar without removing
portions of the bottom spacer material that are present above the
bottom source/drain region that is formed at the footprint of the
vertical semiconductor pillar. Instead, conventional vertical
transistors typically have a step coverage of the bottom spacer
material along the sidewalls of the vertical semiconductor pillar.
Such step coverage may lead to variation in channel length and
junction location. As such, there is a need for providing a
semiconductor structure including a vertical transistor in which
the step coverage of the bottom spacer is minimized thus reducing
the variation in channel length and junction location of the
vertical transistor.
SUMMARY
[0004] A bilayer of silicon dioxide and silicon nitride is formed
on exposed surfaces of at least one semiconductor fin having a
bottom source/drain region located at the footprint, and on each
side, of the at least one semiconductor fin. An upper surface of
each horizontal portion of the silicon nitride layer is then
carbonized, and thereafter non-carbonized vertical portions of the
silicon nitride layer are removed. Next, the carbonized portions of
the silicon nitride layer are removed, and thereafter the vertical
portions of the silicon dioxide layer are removed from sidewalls of
the at least one semiconductor fin utilizing each remaining portion
of the silicon nitride layer as an etch mask. A bottom spacer
structure is provided on each bottom source/drain region in which
each bottom spacer structure includes a remaining portion of the
silicon dioxide layer and the remaining portion of the silicon
nitride layer. In the present application, step coverage of the
bottom spacer is minimized thus reducing the variation in channel
length and junction location of the vertical transistor.
[0005] In one aspect of the present application, a semiconductor
structure is provided. In one embodiment of the present
application, the semiconductor structure includes at least one
semiconductor fin extending upward from a surface of a substrate. A
bottom source/drain region is located at the footprint, and on each
side, of the at least one semiconductor fin. A bottom spacer
structure is located on each bottom source/drain region. Each
bottom spacer structure comprises a silicon dioxide spacer and a
silicon nitride spacer, wherein the silicon nitride spacer is
entirely separated from the at least one semiconductor fin by a
first portion of the silicon dioxide spacer and entirely separated
from the bottom source/drain region by a second portion of the
silicon dioxide spacer. The structure of the present application
further includes a functional gate structure located on each side
of the at least one semiconductor fin and above the bottom spacer
structure, a top spacer located on each functional gate structure
and contacting a sidewall of a portion of the at least one
semiconductor fin, and a top source/drain structure extending from
each sidewall of an upper portion of the at least one semiconductor
fin.
[0006] In another aspect of the present application, a method of
forming a semiconductor structure is provided. In one embodiment of
the present application, the method includes forming at least one
semiconductor fin extending upward from a surface of a substrate,
wherein a bottom source/drain region is located at the footprint,
and on each side, of the at least one semiconductor fin. Next, a
dielectric material stack of, from bottom to top, a silicon dioxide
layer and a silicon nitride layer is formed on exposed surfaces of
each bottom source/drain region and the at least one semiconductor
fin. An upper surface of each horizontal portion of the silicon
nitride layer is then carbonized, and thereafter non-carbonized
vertical portions of the silicon nitride layer are removed. Next,
the carbonized portions of the silicon nitride layer are removed,
and thereafter the vertical portions of the silicon dioxide layer
are removed from sidewalls of the at least one utilizing each
remaining portion of the silicon nitride layer as an etch mask to
provide a bottom spacer structure located on each bottom
source/drain region, each bottom spacer structure comprises a
remaining portion of the silicon dioxide layer and the remaining
portion of the silicon nitride layer.
[0007] The method may further include: forming a functional gate
structure located on each side of the at least one semiconductor
fin and above the bottom spacer structure, forming a top spacer
located on each functional gate structure and contacting a sidewall
of a portion of the at least one semiconductor fin, and forming a
top source/drain structure extending from each sidewall of an upper
portion of the at least one semiconductor fin.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0008] FIG. 1 is a cross sectional view of an exemplary
semiconductor structure including a plurality of semiconductor fins
located on a surface of a substrate, wherein a bottom source/drain
region is present at the footprint, and on each side of, the
semiconductor fins.
[0009] FIG. 2 is a cross sectional view of the exemplary
semiconductor structure of FIG. 1 after forming a dielectric
material stack of, from bottom to top, a silicon dioxide layer and
a silicon nitride layer.
[0010] FIG. 3 is a cross sectional view of the exemplary
semiconductor structure of FIG. 2 after carbonizing an upper
surface of the horizontal portions of the silicon nitride
layer.
[0011] FIG. 4 is a cross sectional view of the exemplary
semiconductor structure of FIG. 3 after removing the non-carbonized
vertical portions of the silicon nitride layer.
[0012] FIG. 5 is a cross sectional view of the exemplary
semiconductor structure of FIG. 4 after removing the carbonized
portions of the silicon nitride layer.
[0013] FIG. 6 is a cross sectional view of the exemplary
semiconductor structure of FIG. 5 after removing vertical portions
of the silicon dioxide layer from sidewalls of each semiconductor
fin utilizing the remaining portions of the silicon nitride layer
as an etch mask.
[0014] FIG. 7 is a cross sectional view of the exemplary
semiconductor structure of FIG. 6 after forming a functional gate
structure on each side of the semiconductor fins.
[0015] FIG. 8 is a cross sectional view of the exemplary
semiconductor structure of FIG. 7 after recessing each functional
gate structure.
[0016] FIG. 9 is a cross sectional view of the exemplary
semiconductor structure of FIG. 8 after forming a top spacer.
[0017] FIG. 10 is a cross sectional view of the exemplary
semiconductor structure of FIG. 9 after forming a top source/drain
structure from exposed surfaces of an upper portion of each
semiconductor fin in accordance with one embodiment of the present
application.
DETAILED DESCRIPTION
[0018] The present application will now be described in greater
detail by referring to the following discussion and drawings that
accompany the present application. It is noted that the drawings of
the present application are provided for illustrative purposes only
and, as such, the drawings are not drawn to scale. It is also noted
that like and corresponding elements are referred to by like
reference numerals.
[0019] In the following description, numerous specific details are
set forth, such as particular structures, components, materials,
dimensions, processing steps and techniques, in order to provide an
understanding of the various embodiments of the present
application. However, it will be appreciated by one of ordinary
skill in the art that the various embodiments of the present
application may be practiced without these specific details. In
other instances, well-known structures or processing steps have not
been described in detail in order to avoid obscuring the present
application.
[0020] It will be understood that when an element 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 may 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 "beneath"
or "under" another element, it can be directly beneath or under the
other element, or intervening elements may be present. In contrast,
when an element is referred to as being "directly beneath" or
"directly under" another element, there are no intervening elements
present.
[0021] Referring first to FIG. 1, there is illustrated an exemplary
semiconductor structure that can be employed in one embodiment of
the present application. The exemplary semiconductor structure of
FIG. 1 includes a plurality of semiconductor fins 12 (two of which
are shown by way of one example) located on a surface of a
substrate 10, wherein a bottom source/drain region 16 is present at
the footprint, and on each side, of the semiconductor fins 12. Each
semiconductor fin 12 may be capped with a hard mask cap 14.
Although the present application describes and illustrates the
formation of a plurality of semiconductor fins 12 extending upwards
from substrate 10, the present application can be employed when
only a single semiconductor fin is formed. The semiconductor fins
12 may also be referred to a vertical semiconductor pillar.
[0022] The exemplary semiconductor structure that is shown in FIG.
1 can be formed by first providing a bulk semiconductor substrate
(not shown). The term "bulk" when used in conjunction with the term
"semiconductor substrate" denotes a substrate that is entirely
composed of one or more semiconductor materials having
semiconducting properties; no insulator materials or conductive
materials are present in a bulk semiconductor substrate.
[0023] Examples of semiconductor materials that may provide at
least a portion of the bulk semiconductor substrate include silicon
(Si), germanium (Ge), silicon germanium alloys (SiGe), silicon
carbide (SiC), III-V compound semiconductors 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. In one example, the bulk semiconductor substrate
may be entirely composed of silicon. In another example, the bulk
semiconductor substrate may include a multilayered semiconductor
material stack of, and in any order, Si and a silicon germanium
alloy.
[0024] The semiconductor material that provides the bulk
semiconductor substrate may be a single crystalline semiconductor
material. The semiconductor material that provides the bulk
semiconductor substrate may have any of the well known crystal
orientations. For example, the crystal orientation of the bulk
semiconductor substrate may be {100}, {110}, or {111}. Other
crystallographic orientations besides those specifically mentioned
can also be used in the present application.
[0025] After providing the bulk semiconductor substrate, a layer of
hard mask material (not shown) is formed upon the topmost surface
of the bulk semiconductor substrate. The layer of hard mask
material is a continuous layer that is formed on the entirety of
the bulk semiconductor substrate. The layer of hard mask material
may be composed of a dielectric oxide, a dielectric nitride, a
dielectric oxynitride or a multilayered combination thereof. The
uppermost portion of the layer of hard mask material is composed of
a different dielectric material than the bottom layer of the
dielectric material stack (18, 20) to be subsequently formed on the
exemplary semiconductor structure shown in FIG. 1. In one example,
the layer of hard mask material may be composed of silicon nitride
and/or silicon oxynitride. In one embodiment, the layer of hard
mask material may be formed by a deposition process such as, for
example, chemical vapor deposition (CVD) or plasma enhanced
chemical vapor deposition. In another embodiment, the layer of hard
mask material may be formed by a thermal growth process such as,
for example, thermal oxidation and/or thermal nitridation. In yet
another embodiment, the layer of hard mask material may be formed
utilizing a combination of a deposition process and thermal growth.
The layer of hard mask material that is formed on the bulk
semiconductor substrate may have a thickness from 5 nm to 20 nm;
although other thicknesses that are lesser than, or greater than,
the aforementioned thickness range can also be used as the
thickness of the layer of hard mask material.
[0026] After providing the bulk semiconductor substrate and the
layer of the hard mask material, the layer of hard mask material
and the bulk semiconductor substrate are patterned to provide a
plurality of fin structures that include a semiconductor fin 12 and
a hard mask cap 14 extending upward from substrate 10. Each hard
mask cap 14 constitutes a remaining portion of the layer of hard
mask material, each semiconductor fin 12 constitutes a remaining
upper portion of the bulk semiconductor substrate, and substrate 10
constitutes a remaining portion of the bulk semiconductor
substrate. In some embodiments (and as illustrated in the drawings
of the present application), no material interface exists between
the semiconductor fins 12 and the substrate 10. In other
embodiments (not specifically illustrated), a material interface
exists between the semiconductor fins 12 and the substrate 10.
[0027] In one embodiment, patterning may include lithography and
etching. The lithographic process includes forming a photoresist
(not shown) atop a material or material stack to be patterned,
exposing the photoresist to a desired pattern of radiation and
developing the exposed photoresist utilizing a conventional resist
developer. The photoresist may be a positive-tone photoresist, a
negative-tone photoresist or a hybrid-tone photoresist. The
photoresist may be formed utilizing a deposition process such as,
for example, spin-on coating. The etching process includes a dry
etching process (such as, for example, reactive ion etching, ion
beam etching, plasma etching or laser ablation), and/or a wet
chemical etching process. Typically, reactive ion etching is used
in providing the fin structures (12, 14) shown in FIG. 1 of the
present application. In some embodiments, the etching process
includes a first pattern transfer step in which the pattern
provided to the photoresist is transferred to the layer of hard
mask material, the patterned photoresist is then removed by an
ashing step, and thereafter, a second pattern transfer step is used
to transfer the pattern from the patterned layer of hard mask
material (i.e., hard mask caps 14) into the underlying bulk
semiconductor substrate.
[0028] In another embodiment, patterning may include a sidewall
image transfer (SIT) process. The SIT process includes forming a
mandrel material layer (not shown) atop the material or material
layers that are to be patterned. The mandrel material layer (not
shown) can include any material (semiconductor, dielectric or
conductive) that can be selectively removed from the structure
during a subsequently performed etching process. In one embodiment,
the mandrel material layer (not shown) may be composed of amorphous
silicon or polysilicon. In another embodiment, the mandrel material
layer (not shown) may be composed of a metal such as, for example,
Al, W, or Cu. The mandrel material layer (not shown) can be formed,
for example, by chemical vapor deposition or plasma enhanced
chemical vapor deposition. Following deposition of the mandrel
material layer (not shown), the mandrel material layer (not shown)
can be patterned by lithography and etching to form a plurality of
mandrel structures (also not shown) on the topmost surface of the
structure.
[0029] The SIT process continues by forming a spacer (not shown) on
each sidewall of each mandrel structure. The spacer can be formed
by deposition of a spacer material and then etching the deposited
spacer material. The spacer material may comprise any material
having an etch selectivity that differs from the mandrel material.
Examples of deposition processes that can be used in providing the
spacer material include, for example, chemical vapor deposition
(CVD), plasma enhanced chemical vapor deposition (PECVD), or atomic
layer deposition (ALD). Examples of etching that be used in
providing the spacers include any etching process such as, for
example, reactive ion etching.
[0030] After formation of the spacers, the SIT process continues by
removing each mandrel structure. Each mandrel structure can be
removed by an etching process that is selective for removing the
mandrel material. Following the mandrel structure removal, the SIT
process continues by transferring the pattern provided by the
spacers into the underlying material or material layers. The
pattern transfer may be achieved by utilizing at least one etching
process. Examples of etching processes that can used to transfer
the pattern may include dry etching (i.e., reactive ion etching,
plasma etching, and ion beam etching or laser ablation) and/or a
chemical wet etch process. In one example, the etch process used to
transfer the pattern may include one or more reactive ion etching
steps. Upon completion of the pattern transfer, the SIT process
concludes by removing the spacers from the structure. Each spacer
may be removed by etching or a planarization process.
[0031] As used herein, a "semiconductor fin" refers to a
semiconductor material that includes a pair of vertical sidewalls
that are parallel to each other. As used herein, a surface is
"vertical" if there exists a vertical plane from which the surface
does not deviate by more than three times the root mean square
roughness of the surface. In one embodiment of the present
application, each semiconductor fin 12 has a height from 20 nm to
200 nm, and a width from 5 nm to 30 nm. Other heights and/or widths
that are lesser than, or greater than, the ranges mentioned herein
can also be used in the present application. Each semiconductor fin
12 is spaced apart from its nearest neighboring semiconductor fin
12 by a pitch of from 20 nm to 100 nm. Also, each semiconductor fin
12 is oriented parallel to each other.
[0032] At this point of the present application, bottom
source/drain regions 16 can be formed at the footprint, and on each
side, of the semiconductor fins 12. Each bottom source/drain region
16 includes a semiconductor material and a p-type or n-type dopant;
stated in other terms, each bottom source/drain region 16 is
composed of a doped semiconductor material. The term "p-type"
refers to the addition of impurities to an intrinsic semiconductor
that creates deficiencies of valence electrons. In a
silicon-containing semiconductor material, examples of p-type
dopants, i.e., impurities, include, but are not limited to, boron,
aluminum, gallium and indium. "N-type" refers to the addition of
impurities that contributes free electrons to an intrinsic
semiconductor. In a silicon containing semiconductor material,
examples of n-type dopants, i.e., impurities, include, but are not
limited to, antimony, arsenic and phosphorous. The semiconductor
material that provides each bottom source/drain region 16 may
include one of the semiconductor materials mentioned above for the
bulk semiconductor substrate. In one embodiment, each bottom
source/drain region 16 is composed of a same semiconductor material
as substrate 10. In another embodiment, each bottom source/drain
region 16 can be composed of a different semiconductor material
than substrate 10. Each bottom source/drain region 16 may have a
dopant concentration that can be within a range from
2.times.10.sup.20 atoms/cm.sup.3 to 1.times.10.sup.21
atoms/cm.sup.3.
[0033] In one embodiment, the bottom source/drain regions 16 can be
formed by introducing a p-type or n-type dopant into the substrate
10. In one example, ion implantation be used to introduce the
dopant into the substrate 10, followed by an anneal. In such an
embodiment, the semiconductor material that provides each bottom
source/drain region 16 is the same as the substrate 10.
[0034] In another embodiment, the bottom source/drain regions 16
can be formed by epitaxially growing a doped semiconductor material
on the substrate 10 or within a trench formed into the substrate
10. In this embodiment, the semiconductor material that provides
the source/drain regions 16 may be the same as, or different from,
the semiconductor material that provides substrate 10.
[0035] The terms "epitaxial growth and/or deposition" and
"epitaxially formed and/or grown" mean the growth of a
semiconductor material on a deposition surface of a semiconductor
material, in which the semiconductor material being grown has the
same crystalline characteristics as the semiconductor material of
the deposition surface. In an epitaxial deposition process, the
chemical reactants provided by the source gases are controlled and
the system parameters are set so that the depositing atoms arrive
at the deposition surface of the semiconductor substrate with
sufficient energy to move around on the surface and orient
themselves to the crystal arrangement of the atoms of the
deposition surface. Therefore, an epitaxial semiconductor material
has the same crystalline characteristics as the deposition surface
on which it is formed. For example, an epitaxial semiconductor
material deposited on a {100} crystal surface will take on a {100}
orientation. Thus, each bottom source/drain regions 16 has as an
epitaxial relationship with the growth surface of substrate 10.
[0036] Examples of various epitaxial growth process apparatuses
that can be employed in the present application include, e.g.,
rapid thermal chemical vapor deposition (RTCVD), low-energy plasma
deposition (LEPD), ultra-high vacuum chemical vapor deposition
(UHVCVD), atmospheric pressure chemical vapor deposition (APCVD)
and molecular beam epitaxy (MBE). The temperature for epitaxial
deposition typically ranges from 500.degree. C. to 900.degree. C.
Although higher temperature typically results in faster deposition,
the faster deposition may result in crystal defects and film
cracking. The epitaxial growth can be performed utilizing any well
known precursor gas or gas mixture including for example, a silicon
containing precursor gas (such as silane) and/or a germanium
containing precursor gas (such as a germane). Carrier gases like
hydrogen, nitrogen, helium and argon can be used. A dopant can be
introduced into the precursor gas during the epitaxial growth
process. In other embodiments, the dopant can be introduced after
the epitaxial growth process.
[0037] Referring now to FIG. 2, there is illustrated the exemplary
semiconductor structure of FIG. 1 after forming a dielectric
material stack (18, 20) of, from bottom to top, a silicon dioxide
layer 18 and a silicon nitride layer 20. The silicon dioxide layer
18 and the silicon nitride layer 20 are both conformal layers. By
"conformal" it is meant that a material has a vertical thickness
(as measured from a bottom surface to a top surface) along a
horizontal surface of another material that is equal to a lateral
thickness (as measured from one sidewall to another sidewall) along
sidewall surfaces of another material. As is shown, the dielectric
material stack (18, 20) is continuously present on the exemplary
semiconductor structure shown in FIG. 1. Notably, the dielectric
material stack (18, 20) is present on horizontal surfaces of the
substrate 10 and hard mask cap 14, and along the sidewalls of the
semiconductor fins 12 and hard mask caps 14.
[0038] The silicon dioxide layer 18 can be formed utilizing a
deposition process such as, for example, chemical vapor deposition,
plasma enhanced chemical vapor deposition or atomic layer
deposition. The thickness of the silicon dioxide layer 18 can be
from 5 nm to 20 nm; although other thicknesses that are lesser
than, or greater than, the aforementioned thickness range may also
be used as the thickness of the silicon dioxide layer 18.
[0039] The silicon nitride layer 20 can be formed utilizing a
deposition process such as, for example, chemical vapor deposition,
plasma enhanced chemical vapor deposition or atomic layer
deposition. The thickness of the silicon nitride layer 20 can be
from 5 nm to 20 nm; although other thicknesses that are lesser
than, or greater than, the aforementioned thickness range may also
be used as the thickness of the silicon nitride layer 20.
[0040] As is shown, the silicon oxide layer 18 and the silicon
nitride layer 20 include horizontal portions and vertical portions.
The horizontal portions are present directly above the horizontal
surfaces of the source/drain regions 16 and the hard mask cap 14,
while the vertical portions are present along the sidewalls of the
each semiconductor fin 12 and each hard mask cap 14.
[0041] Referring now to FIG. 3, there is illustrated the exemplary
semiconductor structure of FIG. 2 after carbonizing an upper
surface of the horizontal portions of the silicon nitride layer 20.
In the drawings, element 20C represents the carbonized portions of
the silicon nitride layer 20; the non-carbonized portions of the
silicon nitride layer remain labeled as element 20 in the drawings
of the present application The carbonized portions 20C of the
silicon nitride layer 20 may also be referred to as a C enriched
dielectric surface layer. The term "C enriched dielectric surface
layer" denotes that the surfaces of the silicon nitride layer 20
that are exposed to carbonization have a higher carbon content
therein as compared to the originally deposited silicon nitride
layer 20. The carbonizing step may also be referred to as a carbon
surface treatment (or plasma implantation) process.
[0042] Carbonization (i.e., carbon surface treatment process or
plasma implantation) is performed utilizing a directional plasma
carbon deposition process in which the energy of the deposition is
100 eV (electron volts) or less. The carbonization is performed by
generating a plasma from a carbon-containing ambient such as, for
example, methane. In one embodiment, the carbonization employed in
the present application is performed at a temperature from
50.degree. C. to 450.degree. C. The carbonization can be performed
by applying a bias (from 50 V to 330) to the exemplary
semiconductor structure of FIG. 2.
[0043] The depth of carbonization of the horizontal portions of the
silicon nitride layer 20 may vary. Typically, the depth of
carbonization of the horizontal portions of the silicon nitride
layer 20, as measured from the exposed surface of the silicon
nitride layer 20 inward, is from 0.5 nm to 5 nm.
[0044] Each carbonized portion 20C of the silicon nitride layer 20
is composed of silicon nitride with added carbon. In some
embodiments, the carbon content of each carbonized portion 20C of
the silicon nitride layer 20 is 5 atomic percent or greater. In one
embodiment, the carbon content of each carbonized portion 20C of
the silicon nitride layer 20 can be from 10 atomic percent nitrogen
to 50 atomic percent carbon. Carbon contents of less than 5 atomic
percent are also contemplated.
[0045] Referring now to FIG. 4, there is illustrated the exemplary
semiconductor structure of FIG. 3 after removing the non-carbonized
vertical portions of the silicon nitride layer 20; the carbonized
portions 20C of the silicon nitride layer 20 serve as an etch mask
during this step of the present application. The removal of the
non-carbonized vertical portions of the silicon nitride layer 20
occurs adjacent to each semiconductor fin 12 and exposes a surface
of the silicon dioxide layer 18 that is present along the sidewalls
of each semiconductor fin 12. After removing the non-carbonized
vertical portions of the silicon nitride layer 20, a portion of the
original silicon nitride layer 20 remains beneath each carbonized
portion 20C. Each remaining portion of the original silicon nitride
layer that remains beneath a carbonized portion 20C may be referred
to herein a silicon nitride spacer 20P.
[0046] The non-carbonized vertical portions of the silicon nitride
layer 20 can be removed utilizing an etching process that is
selective in removing the non-carbonized vertical portions of the
silicon nitride layer 20 selective to the carbonized portions 20C
of the silicon nitride layer 20. In one example, the non-carbonized
vertical portions of the silicon nitride layer 20 can be removed
utilizing phosphoric acid.
[0047] Referring now to FIG. 5, there is illustrated the exemplary
semiconductor structure of FIG. 4 after removing the carbonized
portions 20C of the silicon nitride layer 20. The removal of the
carbonized portions 20C of the silicon nitride layer 20 exposes the
underlying silicon nitride spacer 20P.
[0048] The carbonized portions 20C of the silicon nitride layer 20
can be removed utilizing an etching process that is selective in
removing the carbonized portions 20C selective to each silicon
nitride spacer 20P. In one example, the carbonized portions 20C of
the silicon nitride layer 20 can be removed utilizing oxygen
ashing.
[0049] Referring now to FIG. 6, there is illustrated the exemplary
semiconductor structure of FIG. 5 after removing vertical portions
of the silicon dioxide layer 18 from sidewalls of each
semiconductor fin 12 utilizing the remaining portions of the
silicon nitride layer (i.e., silicon nitride spacer 20P) as an etch
mask. The removal of the vertical portions of the silicon dioxide
layer 18 may be performed utilizing a dry isotopic etch. The dry
isotropic etch may include CF.sub.4, SF.sub.6 or NF.sub.3 as an
etchant.
[0050] After removal of the vertical portions of the silicon
dioxide layer 18 from the sidewalls of each semiconductor fin 12,
portions of the silicon dioxide layer 18 remain beneath each
silicon nitride spacer 20P. Each remaining portion of the silicon
dioxide layer 18 can be referred to herein as silicon dioxide
spacer 18P. At this point of the present application and as is
shown in FIG. 6, a silicon dioxide spacer 18P and a silicon nitride
spacer 20P remain atop each source/drain region 16, while another
silicon dioxide spacer 18P and another silicon nitride spacer 20P
remain atop each hard mask cap 14. The another silicon dioxide
spacer 18P and the another silicon nitride spacer 20P that remain
atop each hard mask cap 14 are removed in a subsequent processing
step of the present application.
[0051] The silicon dioxide spacer 18P and the silicon nitride
spacer 20P that remain atop each source/drain region 16 can be
referred to here as a bottom spacer structure 21.
[0052] As is shown in FIG. 6, the silicon nitride spacer 20P of
each bottom spacer structure 21 is entirely separated from a bottom
sidewall portion of each semiconductor fin 12 by a first portion of
the silicon dioxide spacer 18P as well as being entirely separated
from a topmost surface of the bottom source/drain regions 16 by a
second portion of the silicon dioxide spacer 18P; each silicon
dioxide spacer 18P has a bottommost surface that is located
directly on a topmost surface of one of the source/drain regions
16. As is further shown, the silicon dioxide spacer 18P of each
bottom spacer structure 21 has a topmost surface that is coplanar
with a topmost surface of the silicon nitride spacer 20P. As is
even further shown, a bottommost surface of each silicon nitride
spacer 20P of the bottom spacer structure 21 is present on a
surface of one of the underlying silicon oxide spacer portions 18P
of the bottom spacer structure 21. In the present application, the
bottom spacer structure 21 is present beneath the topmost surface
of each semiconductor fin 12 and a portion of the bottom spacer
structure 21, i.e., the first portion of the silicon oxide spacer
18P mentioned above, directly contacts a lower sidewall of each
semiconductor fin 12.
[0053] Referring now to FIG. 7, there is illustrated the exemplary
semiconductor structure of FIG. 6 after forming a functional gate
structure (22, 24, 26) on each side of the semiconductor fins 12.
Each functional gate structure (22, 24, 26) is formed above the
bottom spacer structure 21. At this point of the present
application, each functional gate structure (22, 24, 26) has a
topmost surface that is coplanar with a topmost surface of the hard
mask cap 14. As is shown, a portion of each functional gate
structure directly contacts the topmost surface of the silicon
dioxide spacer 18P of the bottom spacer structure 21 and the
topmost surface of the silicon nitride spacer portion 20P of the
bottom spacer structure 21.
[0054] By "functional gate structure" it is meant a permanent gate
structure used to control output current (i.e., flow of carriers in
the channel) of a semiconducting device through electrical or
magnetic fields. Each functional gate structure may include a gate
dielectric liner 22, a gate conductor liner 24, and a gate
conductor structure 26. In some embodiments, the gate conductor
liner 24 may be omitted. The gate dielectric liner 22 and the gate
conductor liner 24 may be U-shaped. By "U-shaped" it is meant a
material that has a horizontal portion and two vertical portions
extending upward from each end of the horizontal portion.
[0055] Each gate dielectric liner 22 is composed of a gate
dielectric material such as, for example, a dielectric oxide,
nitride, and/or oxynitride. In one example, the gate dielectric
material that provides each gate dielectric liner 22 can be a
high-k material having a dielectric constant greater than silicon
dioxide. Exemplary high-k dielectrics include, but are not limited
to, HfO.sub.2, ZrO.sub.2, La.sub.2O.sub.3, Al.sub.2O.sub.3,
TiO.sub.2, SrTiO.sub.3, LaAlO.sub.3, Y.sub.2O.sub.3,
HfO.sub.xN.sub.y, ZrO.sub.xN.sub.y, La.sub.2O.sub.xN.sub.y,
Al.sub.2O.sub.xN.sub.y, TiO.sub.xN.sub.y, SrTiO.sub.xN.sub.y,
LaAlO.sub.xN.sub.y, Y.sub.2O.sub.xN.sub.y, SiON, SiN.sub.x, a
silicate thereof, and an alloy thereof. Each value of x is
independently from 0.5 to 3 and each value of y is independently
from 0 to 2. In some embodiments, a multilayered gate dielectric
structure comprising different gate dielectric materials, e.g.,
silicon dioxide, and a high-k gate dielectric, can be formed and
used as the gate dielectric material of each gate dielectric liner
22. The gate dielectric material that provides each gate dielectric
liner 22 can be formed by any deposition process including, for
example, chemical vapor deposition (CVD), plasma enhanced chemical
vapor deposition (PECVD), physical vapor deposition (PVD),
sputtering, or atomic layer deposition. In one embodiment of the
present application, the gate dielectric material that can provide
each gate dielectric liner 22 can have a thickness in a range from
1 nm to 10 nm. Other thicknesses that are lesser than, or greater
than, the aforementioned thickness range can also be employed for
the gate dielectric material of each gate dielectric liner 22.
[0056] Each gate conductor liner 24, which is contact with an
exposed surface of a respective gate dielectric liner 22, can
include a gate conductor material. The gate conductor material used
in providing each gate conductor liner 24 can include any
conductive material including, for example, doped polysilicon, an
elemental metal (e.g., tungsten, titanium, tantalum, aluminum,
nickel, ruthenium, palladium and platinum), an alloy of at least
two elemental metals, an elemental metal nitride (e.g., tungsten
nitride, aluminum nitride, and titanium nitride), an elemental
metal silicide (e.g., tungsten silicide, nickel silicide, and
titanium silicide) or multilayered combinations thereof.
[0057] Each gate conductor liner 24 may be composed of nFET gate
metal or a pFET gate metal. The gate conductor material used in
providing each gate conductor liner 24 can be formed utilizing a
deposition process including, for example, chemical vapor
deposition (CVD), plasma enhanced chemical vapor deposition
(PECVD), physical vapor deposition (PVD), sputtering, atomic layer
deposition (ALD) or other like deposition processes. When a metal
silicide is formed, a conventional silicidation process is
employed. In one embodiment, gate conductor liner 24 can have a
thickness from 20 nm to 100 nm. Other thicknesses that are lesser
than, or greater than, the aforementioned thickness range can also
be employed for the gate conductor liner 24.
[0058] Each gate conductor structure 26 comprises one of the
conductor materials mentioned above for the gate conductor liner
24. Typically, but not necessarily always, each gate conductor
structure 26 comprises a different gate conductor material than the
gate conductor liner 24. For example, each gate conductor liner 24
may include an nFET gate metal or a pFET gate metal and the gate
conductor structure 26 may comprise polysilicon or an elemental
metal such as tungsten. Each gate conductor structure 26 can be
formed by first depositing a gate conductor material utilizing one
of the deposition processes mentioned above in forming gate
conductor liner 24.
[0059] After providing each material layer of the functional gate
structure, a planarization process such as, for example, chemical
mechanical polishing (CMP), may be employed to provide the planar
structure shown in FIG. 7. During the planarization, the another
silicon dioxide spacer 18P and the another silicon nitride spacer
20P that remain atop each hard mask cap 14 are removed from atop
each hard mask cap 14.
[0060] Referring now to FIG. 8, there is illustrated the exemplary
semiconductor structure of FIG. 7 after recessing each functional
gate structure (22, 24, 26). The recessing, which removes an upper
portion of each functional gate structure (22, 24, 26) may be
performed utilizing a recess etch. The recess etch provides a
functional gate structure that now includes a remaining portion of
the gate dielectric liner 22, a remaining portion of the gate
conductor liner 24 (if present), and a remaining portion of the
gate conductor structure 26. The remaining portion of the gate
dielectric liner 22 may be referred to herein as a gate dielectric
liner portion 22P, the remaining portion of the gate conductor
liner 24, if present, may be referred to herein as a gate conductor
liner portion 24P, and the remaining portion of the gate conductor
structure 26 may be referred to herein as a gate conductor portion
26P.
[0061] Referring now to FIG. 9, there is illustrated the exemplary
semiconductor structure of FIG. 8 after forming a top spacer 28.
Top spacer 28 may be formed by deposition of a spacer dielectric
material. A recess etch may follow the deposition of the spacer
dielectric material. The spacer dielectric material that provides
the top spacer 28 may include for example, silicon dioxide, silicon
nitride and/or silicon oxynitride. The top spacer 28 has a height
that does not exceed the height of the semiconductor fin 12. Hence,
the topmost surface of the top spacer 28 is located beneath a
topmost surface of the semiconductor fin 12.
[0062] Referring now to FIG. 10, there is illustrated the exemplary
semiconductor structure of FIG. 9 after forming top source/drain
structures 30. Notably, FIG. 10 illustrates the exemplary
semiconductor structure of FIG. 9 after forming a top source/drain
structure 30 from exposed surfaces (top and sidewall) of an upper
portion of each semiconductor fin 12 in accordance with one
embodiment of the present application. In FIG. 10, each hard mask
cap 14 is removed from atop each semiconductor fin 12 to expose a
topmost surface of the semiconductor fin 12. Each hard mask cap 14
may be removed utilizing a planarization process.
[0063] The top source/drain structures 30 can be formed utilizing
an epitaxial growth (or deposition) as defined above. Each top
source/drain structure 30 includes a semiconductor material and a
dopant (n-type or p-type) as defined above. The dopant, which is of
the same conductivity type as the bottom source/drain region 16 can
be added during the epitaxial growth of the semiconductor material
that provides each top source/drain structure 30 or after
epitaxially depositing an intrinsic semiconductor material
utilizing a gas phase doping process. The dopant can be present in
each top source/drain structure 30 in a range as mentioned above
for the bottom source/drain region 16. The semiconductor material
that provides the each top source/drain structure 30 may be the
same as, or different from, the semiconductor material that
provides the semiconductor fin 12.
[0064] In some embodiments, and as shown, each top source/drain
structure 30 may have faceted surfaces, i.e., non-planar surfaces.
Such an embodiment is depicted in FIG. 10. In some embodiments and
as also shown in FIG. 10, each top source/drain structure 30 is
triangular in shape, wherein the base of the triangle directly
contacts one of the sidewalls of the upper portion of the
semiconductor fin 12 and a tip of the triangle extends outward from
the one sidewall of the upper portion of the semiconductor fin 12.
In some embodiments, and as shown in FIG. 10, each triangle may
merge above the topmost surface of the semiconductor fin 12. In
such an instance, the top source/drain structure 30 has a diamond
shape.
[0065] While the present application has been particularly shown
and described with respect to preferred embodiments thereof, it
will be understood by those skilled in the art that the foregoing
and other changes in forms and details may be made without
departing from the spirit and scope of the present application. It
is therefore intended that the present application not be limited
to the exact forms and details described and illustrated, but fall
within the scope of the appended claims.
* * * * *