U.S. patent application number 13/797001 was filed with the patent office on 2014-09-18 for methods of increasing space for contact elements by using a sacrificial liner and the resulting device.
This patent application is currently assigned to GLOBALFOUNDRIES INC.. The applicant listed for this patent is GLOBALFOUNDRIES INC.. Invention is credited to Xiuyu Cai, Kangguo Cheng, Ali Khakifirooz, Ruilong Xie.
Application Number | 20140264479 13/797001 |
Document ID | / |
Family ID | 51523661 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140264479 |
Kind Code |
A1 |
Cai; Xiuyu ; et al. |
September 18, 2014 |
METHODS OF INCREASING SPACE FOR CONTACT ELEMENTS BY USING A
SACRIFICIAL LINER AND THE RESULTING DEVICE
Abstract
One method includes forming a sidewall spacer adjacent a gate
structure, forming a first liner layer on the sidewall spacer,
forming a second liner layer on the first liner layer, forming a
first layer of insulating material above the substrate and adjacent
the second liner layer, selectively removing at least portions of
the second liner layer relative to the first liner layer, forming a
second layer of insulating material above the first layer of
insulating material, performing at least one second etching process
to remove at least portions of the first and second layers of
insulating material and at least portions of the first liner layer
so as to thereby expose an outer surface of the sidewall spacer,
and forming a conductive contact that contacts the exposed outer
surface of the sidewall spacer and a source/drain region of the
transistor.
Inventors: |
Cai; Xiuyu; (Niskayuna,
NY) ; Xie; Ruilong; (Niskayuna, NY) ;
Khakifirooz; Ali; (Mountain View, CA) ; Cheng;
Kangguo; (Schenecdtady, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES INC. |
Grand Cayman |
|
KY |
|
|
Assignee: |
GLOBALFOUNDRIES INC.
Grand Cayman
KY
|
Family ID: |
51523661 |
Appl. No.: |
13/797001 |
Filed: |
March 12, 2013 |
Current U.S.
Class: |
257/288 ;
438/586 |
Current CPC
Class: |
H01L 29/41783 20130101;
H01L 29/41775 20130101; H01L 29/401 20130101; H01L 29/66636
20130101; H01L 29/66545 20130101; H01L 21/76832 20130101; H01L
21/76897 20130101; H01L 21/7682 20130101; H01L 29/66575
20130101 |
Class at
Publication: |
257/288 ;
438/586 |
International
Class: |
H01L 29/40 20060101
H01L029/40; H01L 29/417 20060101 H01L029/417 |
Claims
1. A method of forming a transistor, comprising: forming a gate
structure above a semiconductor substrate; forming a sidewall
spacer adjacent said gate structure; forming a first liner layer on
at least said sidewall spacer; forming a second liner layer on said
first liner layer; forming a first layer of insulating material
above said substrate and adjacent said second liner layer;
performing at least one etching process to selectively remove at
least portions of said second liner layer relative to said first
liner layer and said first layer of insulating material so as to
thereby form a space between said first layer of insulating
material and said first liner layer; and forming a second layer of
insulating material above said first layer of insulating
material.
2. The method of claim 1, wherein said sidewall spacer and said
second liner layer are comprised of silicon nitride and said first
liner layer and said first layer of insulating material are
comprised of silicon dioxide.
3. The method of claim 2, wherein said second layer of insulating
material is comprised of silicon dioxide.
4. The method of claim 1, wherein said gate structure comprises a
sacrificial gate electrode.
5. The method of claim 1, wherein, after forming said second layer
of insulating material, said space between said first layer of
insulating material and said first liner layer remains
substantially unfilled.
6. The method of claim 1, further comprising: performing at least
one etching process to remove at least portions of said first and
second layers of insulating material and at least portions of said
first liner layer so as to thereby expose an outer surface of said
sidewall spacer; and forming a conductive contact that is in
physical contact with said exposed outer surface of said sidewall
spacer and conductively coupled to a source/drain region of said
transistor.
7. The method of claim 1, wherein said first and second layers of
insulating material are comprised of silicon dioxide or a material
having a dielectric constant less than 3.
8. A method of forming a transistor, comprising: forming a gate
structure above a semiconductor substrate; forming a sidewall
spacer adjacent said gate structure; forming a first liner layer on
at least said sidewall spacer; forming a second liner layer on said
first liner layer; forming a first layer of insulating material
above said substrate and adjacent said second liner layer;
performing at least one first etching process to selectively remove
at least portions of said second liner layer relative to said first
liner layer; forming a second layer of insulating material above
said first layer of insulating material; performing at least one
second etching process to remove at least portions of said first
and second layers of insulating material and at least portions of
said first liner layer so as to thereby expose an outer surface of
said sidewall spacer; and forming a conductive contact that is in
physical contact with said exposed outer surface of said sidewall
spacer and conductively coupled to a source/drain region of said
transistor.
9. The method of claim 8, wherein said sidewall spacer and said
second liner layer are comprised of silicon nitride and said first
liner layer and said first layer of insulating material are
comprised of silicon dioxide.
10. The method of claim 9, wherein said second layer of insulating
material is comprised of silicon dioxide.
11. The method of claim 8, wherein said gate structure comprises a
sacrificial gate electrode.
12. The method of claim 8, wherein said first and second layers of
insulating material are comprised of silicon dioxide or a material
having a dielectric constant less than 3.
13. A transistor device, comprising: a gate structure positioned
above a semiconductor substrate; a sidewall spacer positioned
adjacent opposite sides of said gate structure; a first layer of
insulating material positioned above said substrate, said first
layer of insulating material being laterally spaced apart from and
not in contact with said sidewall spacer; a second layer of
insulating material positioned above said first layer of insulating
material, said second layer of insulating material contacting said
sidewall spacer; and first and second air gaps positioned on
opposite sides of said gate structure, wherein each of said first
and second air gaps is defined, in part, by an outer surface of
said sidewall spacer, said first layer of insulating material and
said second layer of insulating material.
14. The device of claim 13, wherein each of said first and second
air gaps is further defined by an upper surface of said
substrate.
15. The device of claim 13, wherein each of said first and second
air gaps is further defined by at least one additional layer of
insulating material positioned between said first layer of
insulating material and said substrate, said at least one
additional layer of insulating material being laterally spaced
apart from and not in contact with said sidewall spacer.
16. The device of claim 13, wherein said device further comprises
first and second conductive contacts that are positioned on
opposite sides of said gate structure, each of said first and
second conductive contacts being conductively coupled to a
source/drain region of said transistor, wherein said first air gap
is positioned between said first conductive contact and said gate
structure and said second air gap is positioned between said second
conductive structure and said gate structure.
17. A transistor device, comprising: a gate structure positioned
above a semiconductor substrate; a sidewall spacer positioned
adjacent opposite sides of said gate structure; a first layer of
insulating material positioned above said substrate, said first
layer of insulating material being laterally spaced apart from and
not in contact with said sidewall spacer; a second layer of
insulating material positioned above said first layer of insulating
material, said second layer of insulating material contacting said
sidewall spacer; and first and second air gaps positioned on
opposite sides of said gate structure, wherein each of said first
and second air gaps is defined, in part, by an outer surface of
said sidewall spacer, said first layer of insulating material, said
second layer of insulating material and an upper surface of said
substrate.
18. The device of claim 17, wherein each of said first and second
air gaps is further defined by at least one additional layer of
insulating material positioned between said first layer of
insulating material and said substrate, said at least one
additional layer of insulating material being laterally spaced
apart from and not in contact with said sidewall spacer.
19. The device of claim 17, wherein said device further comprises
first and second conductive contacts that are positioned on
opposite sides of said gate structure, each of said first and
second conductive contacts being conductively coupled to a
source/drain region of said transistor, wherein said first air gap
is positioned between said first conductive contact and said gate
structure and said second air gap is positioned between said second
conductive structure and said gate structure.
20. A transistor device, comprising: a gate structure positioned
above a semiconductor substrate; a source/drain region; a sidewall
spacer positioned adjacent opposite sides of said gate structure;
and a conductive contact that is in physical contact with an outer
surface of said sidewall spacer and conductively coupled to said
source/drain region of said transistor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present disclosure generally relates to the fabrication
of integrated circuits, and, more particularly, to various methods
of increasing the available space for contact elements, such as
self-aligned contacts for a semiconductor device, by use of a
sacrificial liner layer.
[0003] 2. Description of the Related Art
[0004] In modern integrated circuits, such as microprocessors,
storage devices and the like, a very large number of circuit
elements, especially transistors, are provided and operated on a
restricted chip area. Immense progress has been made over recent
decades with respect to increased performance and reduced feature
sizes of circuit elements, such as transistors. However, the
ongoing demand for enhanced functionality of electronic devices
forces semiconductor manufacturers to steadily reduce the
dimensions of the circuit elements and to increase the operating
speed of the circuit elements. The continuing scaling of feature
sizes, however, involves great efforts in redesigning process
techniques and developing new process strategies and tools so as to
comply with new design rules. Generally, in complex circuitry
including complex logic portions, MOS technology is presently a
preferred manufacturing technique in view of device performance
and/or power consumption and/or cost efficiency. In integrated
circuits including logic portions fabricated by MOS technology,
field effect transistors (FETs) are provided that are typically
operated in a switched mode, that is, these devices exhibit a
highly conductive state (on-state) and a high impedance state
(off-state). The state of the field effect transistor is controlled
by a gate electrode, which controls, upon application of an
appropriate control voltage, the conductivity of a channel region
formed between a drain region and a source region.
[0005] To improve the operating speed of FETs, and to increase the
density of FETs on an integrated circuit device, device designers
have greatly reduced the physical size of FETs over the years. More
specifically, the channel length of FETs has been significantly
decreased, which has resulted in improving the switching speed of
FETs. However, decreasing the channel length of a FET also
decreases the distance between the source region and the drain
region. In some cases, this decrease in the separation between the
source and the drain makes it difficult to efficiently inhibit the
electrical potential of the source region and the channel from
being adversely affected by the electrical potential of the drain.
This is sometimes referred to as a so-called short channel effect,
wherein the characteristic of the FET as an active switch is
degraded.
[0006] In contrast to a FET, which has a planar structure, a
so-called FinFET device has a three-dimensional (3D) structure.
More specifically, in a FinFET, a generally vertically positioned
fin-shaped active area is formed and a gate electrode encloses both
sides and an upper surface of the fin-shaped active area to form a
tri-gate structure so as to use a channel having a
three-dimensional structure instead of a planar structure. In some
cases, an insulating cap layer, e.g., silicon nitride is positioned
at the top of the fin and the FinFET device only has a dual-gate
structure. Unlike a planar FET, in a FinFET device, a channel is
formed perpendicular to a surface of the semiconducting substrate
so as to reduce the physical size of the semiconductor device.
Also, in a FinFET, the junction capacitance at the drain region of
the device is greatly reduced, which tends to reduce at least some
short channel effects. When an appropriate voltage is applied to
the gate electrode of a FinFET device, the surfaces (and the inner
portion near the surface) of the fins, i.e., the substantially
vertically oriented sidewalls and the top upper surface of the fin
with inversion carriers, contributes to current conduction. In a
FinFET device, the "channel-width" is approximately two times
(2.times.) the vertical fin-height plus the width of the top
surface of the fin, i.e., the fin width. Multiple fins can be
formed in the same foot-print as that of a planar transistor
device. Accordingly, for a given plot space (or foot-print),
FinFETs tend to be able to generate significantly stronger drive
currents than planar transistor devices. Additionally, the leakage
current of FinFET devices after the device is turned "OFF" is
significantly reduced as compared to the leakage current of planar
FETs due to the superior gate electrostatic control of the "fin"
channel on FinFET devices. In short, the 3D structure of a FinFET
device is a superior MOSFET structure as compared to that of a
planar FET, especially in the 20 nm CMOS technology node and
beyond.
[0007] By using such field effect transistors, more complex circuit
components may be composed, such as inverters and the like, thereby
forming complex logic circuitry, embedded memories and the like.
Over the recent years, due to the reduced dimensions of the
transistor devices, the operating speed of the circuit components
has been increased with every new device generation and the
"packing density" in such products has been increased over the
recent years. i.e., there are an increased number of devices per
unit area. Such improvements in the performance of transistor
devices has reached the point where the limiting factor of the
ultimate operating speed of complex integrated circuit products is
no longer the individual transistor element but the electrical
performance of the complex wiring system that is formed above the
semiconductor-based circuit elements. Typically, due to the large
number of circuit elements and the required complex layout of
modern integrated circuits, the electrical connections of the
individual circuit elements cannot be established within the same
device level on which the circuit elements are manufactured, but
require one or more additional metallization layers, which
generally include metal-containing lines providing the intra-level
electrical connection, and also include a plurality of inter-level
connections or vertical connections, which are also referred to as
vias. These vertical interconnect structures comprise an
appropriate metal and provide the electrical connection of the
various stacked metallization layers.
[0008] Furthermore, in order to actually connect the circuit
elements formed in the semiconductor material with the
metallization layers, an appropriate vertical contact structure is
provided, a first end of which is connected to a respective contact
region of a circuit element, such as a gate electrode and/or the
drain and source regions of transistors, and a second end that is
connected to a respective metal line in the metallization layer. In
some applications, the second end of the contact structure may be
connected to a contact region of a further semiconductor-based
circuit element, in which case the interconnect structure in the
contact level is also referred to as a local interconnect. The
contact structure may comprise contact elements or contact plugs
having a generally square-like or round shape that are formed in an
interlayer dielectric material, which in turn encloses and
passivates the circuit elements. As the critical dimensions of the
circuit elements in the device level decreased, the dimensions of
metal lines, vias and contact elements were also reduced. In some
cases, the increased packing density has mandated the use of
sophisticated metal-containing materials and dielectric materials
in order to reduce the parasitic capacitance in the metallization
layers and provide a sufficiently high conductivity of the
individual metal lines and vias. For example, in complex
metallization systems, copper in combination with low-k dielectric
materials, which are to be understood as dielectric materials
having a dielectric constant of approximately 3.0 or less, are
typically used in order to achieve the required electrical
performance and the electromigration behavior as is required in
view of reliability of the integrated circuits. Consequently, in
lower-lying metallization levels, metal lines and vias having
critical dimensions of approximately 100 nm and significantly less
may have to be provided in order to achieve the required packing
density in accordance with the density of circuit elements in the
device level.
[0009] As device dimensions have decreased, e.g., transistors with
gate lengths of 50 nm and less, the contact elements in the contact
level have to have critical dimensions on the same order of
magnitude. The contact elements typically represent plugs, which
are formed of an appropriate metal or metal composition, wherein,
in sophisticated semiconductor devices, tungsten, in combination
with appropriate barrier materials, has proven to be a viable
contact metal. When forming tungsten-based contact elements,
typically the interlayer dielectric material is formed first and is
patterned so as to receive contact openings, which extend through
the interlayer dielectric material to the corresponding contact
areas of the circuit elements. In particular, in densely packed
device regions, the lateral size of the drain and source areas and
thus the available area for the contact regions is 100 nm and
significantly less, thereby requiring extremely complex lithography
and etch techniques in order to form the contact openings with
well-defined lateral dimensions and with a high degree of alignment
accuracy.
[0010] For this reason, contact technologies have been developed in
which contact openings are formed in a self-aligned manner by
removing dielectric material, such as silicon dioxide, selectively
from the spaces between closely spaced gate electrode structures.
That is, after completing the transistor structure, the gate
electrode structures are used as etch masks for selectively
removing the silicon dioxide material in order to expose the
contact regions of the transistors, thereby providing self-aligned
trenches which are substantially laterally delineated by the liner
structures that are formed on the sidewall spacers positioned
adjacent the gate electrode structures. Consequently, a
corresponding lithography process only needs to define a global
contact opening above an active region, wherein the contact
trenches then result from the selective etch process using the gate
electrode structures (including spacers plus liners), i.e., the
portions exposed by the global contact opening, as an etch mask.
Thereafter, an appropriate contact material, such as tungsten and
the like, may be filled into the contact trenches.
[0011] However, the reduction in feature sizes as well and the
pitch between adjacent transistor devices has reached the point
where there is simply very little space available for the contact
element to make electrical contact to source/drain regions of a
transistor device. FIG. 1 schematically illustrates a
cross-sectional view of an illustrative prior art integrated
circuit product 10 at an advanced manufacturing stage. As
illustrated, the product 10 comprises a plurality of illustrative
gate structures 11 that are formed above a substrate 12, such as a
silicon substrate. The gate structures 11 are comprised of an
illustrative gate insulation layer 13 and an illustrative gate
electrode 14. An illustrative gate cap layer 16, liner layer 17 and
sidewall spacers 18 encapsulate and protect the gate structures 11.
The gate cap layer 16, liner layer 17 and sidewall spacers 18 are
typically made of silicon nitride. Also depicted in FIG. 1 are a
plurality of raised source/drain regions 20 and a layer of
insulating material 22, e.g., silicon dioxide. The liner layer 17
is provided as a means of protecting the source/drain regions 20
when an etching process is performed to define contact openings for
the contacts that will be formed in such openings to establish
electrical connection to the source/drain region 20. Typically,
after the contact opening is formed, a brief "punch-through"
etching process is performed to remove or clear the liner material
from above the source/drain region 20 just prior to forming the
conductive contact in the contact opening. As mentioned above,
there is very little space available in the region 19 for a contact
to land and make contact to the underlying source/drain region 20.
Moreover, even if contact can be made, the small contact area
results in an undesirable localized increase in electrical
resistance and heating of the device 10.
[0012] The present disclosure is directed to various methods of
increasing the available space for contact elements, such as
self-aligned contacts for a semiconductor device, by use of a
sacrificial liner layer, that may avoid, or at least reduce, the
effects of one or more of the problems identified above.
SUMMARY OF THE INVENTION
[0013] The following presents a simplified summary of the invention
in order to provide a basic understanding of some aspects of the
invention. This summary is not an exhaustive overview of the
invention. It is not intended to identify key or critical elements
of the invention or to delineate the scope of the invention. Its
sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is discussed
later.
[0014] Generally, the present disclosure is directed to various
methods of increasing the available space for contact elements,
such as self-aligned contacts for a semiconductor device, by use of
a sacrificial liner layer. One method disclosed includes forming a
gate structure above a semiconductor substrate, forming a sidewall
spacer adjacent the gate structure, forming a first liner layer on
the sidewall spacer, forming a second liner layer on the first
liner layer, forming a first layer of insulating material above the
substrate and adjacent the second liner layer, performing at least
one etching process to selectively remove at least portions of the
second liner layer relative to the first liner layer and the first
layer of insulating material so as to thereby form a space between
the first layer of insulating material and the first liner layer,
and forming a second layer of insulating material above the first
layer of insulating material.
[0015] A further illustrative method disclosed herein includes
forming a gate structure above a semiconductor substrate, forming a
sidewall spacer adjacent the gate structure, forming a first liner
layer on the sidewall spacer, forming a second liner layer on the
first liner layer, forming a first layer of insulating material
above the substrate and adjacent the second liner layer, performing
at least one first etching process to selectively remove at least
portions of the second liner layer relative to the first liner
layer, forming a second layer of insulating material above the
first layer of insulating material, performing at least one second
etching process to remove at least portions of the first and second
layers of insulating material and at least portions of the first
liner layer so as to thereby expose an outer surface of the
sidewall spacer, and forming a conductive contact that is in
physical contact with the exposed outer surface of the sidewall
spacer and conductively coupled to a source/drain region of the
transistor.
[0016] One illustrative example of a novel transistor device
disclosed herein includes a gate structure positioned above a
semiconductor substrate, a sidewall spacer positioned adjacent
opposite sides of the gate structure, a first layer of insulating
material positioned above the substrate, wherein the first layer of
insulating material is laterally spaced apart from and not in
contact with the sidewall spacer, a second layer insulating
material positioned above the first layer of insulating material,
wherein the second layer of insulating material contacts the
sidewall spacer, and first and second air gaps positioned on
opposite sides of the gate structure, wherein each of the first and
second air gaps is defined, in part, by an outer surface of the
sidewall spacer, the first layer of insulating material, the second
layer of insulating material and an upper surface of the
substrate.
[0017] Yet another example of a novel transistor device disclosed
herein includes a gate structure positioned above a semiconductor
substrate, a source/drain region, a sidewall spacer positioned
adjacent opposite sides of the gate structure and a conductive
contact that is in physical contact with an outer surface of the
sidewall spacer and conductively coupled to the source/drain region
of the transistor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The disclosure may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0019] FIG. 1 schematically illustrates a cross-sectional view of
an illustrative prior art integrated circuit product that employs
self-aligned contacts; and
[0020] FIGS. 2A-2K depict various methods disclosed herein for
increasing the available space for contact elements, such as
self-aligned contacts for a semiconductor device, by use of a
sacrificial liner layer, and various novel device structures.
[0021] While the subject matter disclosed herein is susceptible to
various modifications and alternative forms, specific embodiments
thereof have been shown by way of example in the drawings and are
herein described in detail. It should be understood, however, that
the description herein of specific embodiments is not intended to
limit the invention to the particular forms disclosed, but on the
contrary, the intention is to cover all modifications, equivalents,
and alternatives falling within the spirit and scope of the
invention as defined by the appended claims.
DETAILED DESCRIPTION
[0022] Various illustrative embodiments of the invention are
described below. In the interest of clarity, not all features of an
actual implementation are described in this specification. It will
of course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0023] The present subject matter will now be described with
reference to the attached figures. Various structures, systems and
devices are schematically depicted in the drawings for purposes of
explanation only and so as to not obscure the present disclosure
with details that are well known to those skilled in the art.
Nevertheless, the attached drawings are included to describe and
explain illustrative examples of the present disclosure. The words
and phrases used herein should be understood and interpreted to
have a meaning consistent with the understanding of those words and
phrases by those skilled in the relevant art. No special definition
of a term or phrase, i.e., a definition that is different from the
ordinary and customary meaning as understood by those skilled in
the art, is intended to be implied by consistent usage of the term
or phrase herein. To the extent that a term or phrase is intended
to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be
expressly set forth in the specification in a definitional manner
that directly and unequivocally provides the special definition for
the term or phrase.
[0024] The present disclosure generally relates to various methods
of increasing the available space for contact elements, such as
self-aligned contacts for a semiconductor device, by use of a
sacrificial liner layer. Moreover, as will be readily apparent to
those skilled in the art upon a complete reading of the present
application, the present method is applicable to a variety of
devices, including, but not limited to, logic devices, memory
devices, etc., and the methods disclosed herein may be employed to
form N-type or P-type semiconductor devices. The methods and
devices disclosed herein may be employed in manufacturing products
using a variety of technologies, e.g., NMOS, PMOS, CMOS, etc., and
they may be employed in manufacturing a variety of different
devices, e.g., memory devices, logic devices, ASICs, etc. With
reference to the attached figures, various illustrative embodiments
of the methods and devices disclosed herein will now be described
in more detail. As will be appreciated by those skilled in the art
after a complete reading of the present application, the inventions
disclosed herein may be employed in forming planar transistor
devices (NFET or PFET devices), as well as so-called 3-D devices,
such as FinFETs. For purposes of disclosure, reference will be made
to an illustrative process flow for forming an integrated circuit
product comprised of planar transistor devices. However, the
inventions disclosed herein should not be considered to be limited
to such an illustrative example.
[0025] FIG. 2A is a simplified view of an illustrative integrated
circuit device or product 100 at an early stage of manufacturing.
Illustrative transistors 106A-C will be formed in and above the
semiconductor substrate 102. The pitch between the transistors
106A-B is tighter (smaller) than the pitch between the transistors
106B-C. So as not to obscure the inventions disclosed herein,
isolation regions that are formed in the substrate to define active
regions where the transistors 106A-C will be formed are not
depicted in the attached drawings. The substrate 102 may have a
variety of configurations, such as the depicted bulk silicon
configuration. The substrate 102 may also have a
silicon-on-insulator (SOI) configuration that includes a bulk
silicon layer, a buried insulation layer and an active layer,
wherein semiconductor devices are formed in and above the active
layer. The substrate 102 may be made of silicon or it may be made
of materials other than silicon. Thus, the terms "substrate,"
"semiconductor substrate" or "semiconducting substrate" should be
understood to cover all semiconducting materials and all forms of
such materials.
[0026] In the example disclosed herein, the transistors 106A-C will
be formed using a replacement gate technique. However, as will be
appreciated by those skilled in the art after a complete reading of
the present application, the novel inventions disclosed herein may
also be employed in the context of using so-called "gate-first"
manufacturing techniques. Accordingly, with continuing reference to
FIG. 2A, the process begins with the formation of a sacrificial
gate insulation layer 104, such as silicon dioxide (sometimes
referred to as a "dummy oxide") on the substrate 102. The
sacrificial gate insulation layer 104 may be formed by performing a
thermal growth process or a deposition process. Also depicted in
FIG. 2A are schematically depicted sacrificial gate electrodes 108
with a gate cap layer 110 formed thereabove. Such structures and
layers may be formed using a variety of different materials and by
performing a variety of known techniques. For example, the
sacrificial gate electrodes 108 may be comprised of polysilicon or
amorphous silicon and the gate cap layers 110 may be comprised of
silicon nitride. The sacrificial gate insulation layer 104,
sacrificial gate electrodes 108 and the gate cap layer 110 may be
of any desired thickness or configuration. Of course, those skilled
in the art will recognize that there are other features of the
transistors 106A-C that are not depicted in the drawings so as not
to obscure the present invention. For example, so-called halo
implant regions and various layers or regions of silicon/germanium
that are typically found in high performance PFET transistors are
not depicted in the drawings. The sacrificial gate electrodes 108
and the gate cap layers 110 may be formed by depositing the
appropriate layers of material using any of a variety of different
known techniques, e.g., a chemical vapor deposition (CVD) process,
an atomic layer deposition (ALD) process, a thermal growth process,
etc. Thereafter, one or more patterning and etching processes are
performed on the deposited layers of material to define the
sacrificial gate electrodes 108 and the gate cap layers 110.
Typically, the gate cap layers 110 are patterned using known
photolithography and etching techniques to thereby define a
patterned gate cap layer. Thereafter, one or more etching processes
are performed through the patterned gate cap layer to remove
exposed portions of the sacrificial gate electrode material layer
to thereby define the depicted sacrificial gate electrodes 108.
[0027] FIG. 2B depicts the device 100 after an illustrative
sidewall spacer 112 was formed adjacent the sacrificial gate
electrodes 108. The sidewall spacer 112 may be formed by depositing
a layer of spacer material and thereafter performing an anisotropic
etching process. The sidewall spacer 112 may be comprised of a
variety of different materials, e.g., silicon nitride, silicon
oxynitride, etc. The base thickness of the sidewall spacer 112 may
vary depending upon the particular application. In one illustrative
embodiment, the sidewall spacer 112 may have a thickness at its
base of about 5-10 nm.
[0028] FIG. 2C depicts the device 100 after several process
operations have been performed. First, various known process
operations are performed to form illustrative raised source/drain
regions 114 in the substrate 102 adjacent the sidewall spacers 112.
However, such raised source/drain regions 114 need not be formed in
all applications, and the disclosed inventions should not be
considered to be limited to such an illustrative configuration.
That is, the inventions disclosed herein may be employed with
transistor devices that have traditional, planar source/drain
regions. The raised source/drain regions 114 may be formed by
forming cavities in the substrate 102 and thereafter performing an
epitaxial deposition process to thereby form doped semiconductor
material in the cavities. Although not depicted in the drawings, an
extension implantation process may be performed to form extension
implant regions (not shown) in the substrate 102 prior to or after
the formation of the sidewall spacers 112. After the formation of
the source/drain regions 114, a conformably deposited first liner
layer 116 (comprised of an insulating material) having a thickness
of about 2-5 nm is formed on the device 100. In one illustrative
embodiment, the first liner layer 116 is deposited on the sidewall
spacers 112. The first liner layer 116 should be comprised of a
material that exhibits good etch selectivity relative to the
material selected for the sidewall spacers 112. In one illustrative
embodiment, where the sidewall spacers 112 are made of silicon
nitride, the first liner layer 116 may be comprised of silicon
dioxide, etc., and it may be formed by performing an ALD or CVD
process.
[0029] FIG. 2D depicts the device 100 after a conformably deposited
second liner layer 118 (comprised of an insulating material) having
a thickness of about 2-5 nm is formed on the device 100. As will be
discussed more fully below, the second liner layer 118 is
sacrificial in nature as most, if not all, of the second liner
layer 118 will be removed as fabrication continues. In one
illustrative embodiment, the second liner layer 118 is deposited on
the first liner layer 116. The second liner layer 118 should be
comprised of a material that exhibits good etch selectivity
relative to the material selected for the first liner layer 116. In
one illustrative embodiment, where the first liner layer 116 is
made of silicon dioxide, the second liner layer 118 may be
comprised of silicon nitride, etc., and it may be formed by
performing an ALD or CVD process.
[0030] Then, as shown in FIG. 2E, a layer of insulating material
120 is blanket-deposited over the device 100. In one illustrative
example, the layer of insulating material 120 may be a silicon
dioxide material, such as a flowable oxide material, and it may be
formed using traditional techniques, e.g., CVD, spin-on/cure, etc.
In one particular example, the layer of insulating material 120 is
formed such that its upper surface 120S is positioned slightly
below the upper surface 108S of the sacrificial gate electrodes
108. This may be accomplished by initially depositing the layer of
insulating material 120 such that it overfills the spaces between
the gate structures, performing a chemical mechanical polishing
(CMP) process that stops on the second liner layer 118, and
thereafter performing a timed, recess etching process (sometimes
referred to as an etch-back process) until such time as the upper
surface 120S of the layer of insulating material 120 is at the
desired height level.
[0031] Next, as shown in FIG. 2F, a wet etching process is
performed to remove at least portions of the sacrificial second
liner layer 118 relative to the first liner layer 116 and the layer
of insulating material 120. In the case where the first liner layer
116 and the layer of insulating material 120 are comprised of
silicon dioxide and the sacrificial second liner layer 118 is
comprised of silicon nitride, the wet etching process may be
performed using, for example, an etching chemistry comprised of hot
phosphoric acid. This etching process results in the formation of
gaps or pockets 122 that were formerly occupied by the removed
portions of the sacrificial second liner layer 118. Note that, in
the depicted example, the above-described etching process does not
remove the entire sacrificial second liner layer 118 as remaining
portions 118A of the sacrificial second liner layer 118 may still
be present under portions of the layer of insulating material
120.
[0032] FIG. 2G depicts the product 100 after several process
operations have been performed. First, a layer of insulating
material 124 was blanket-deposited across the product 100. The
layer of insulating material 124 may be comprised of a variety of
different materials, such as silicon dioxide, a low-k (k value less
than 3.3) material, etc., and it may be formed by performing a
variety of techniques, e.g., CVD, etc. The thickness of the layer
of insulating material 124 may vary depending upon the particular
application. Thereafter, one or more CMP processes were performed
on the layer of insulating material 124. The CMP process stopped on
the upper surface 110S of the gate cap layers 110, i.e., the gate
cap layers 110 were used as a polish stop. In this example, the CMP
process also removes portions of the first liner layer 116 that
were positioned above the gate cap layers 110. Note that, given the
relatively high aspect ratio of the gaps or pockets 122, they may
remain substantially unfilled, i.e., they may effectively become
air gaps, when the layer of insulating material 124 is deposited on
the device 100.
[0033] FIG. 2H depicts the device after several process operations
were performed that involved removing the sacrificial gate
electrodes 108 and the sacrificial gate insulation layer 106, and
the formation of a replacement gate structure 130 for the
transistors 106A-C. The process used to remove the sacrificial gate
materials and replace them with desired final gate materials are
well known to those skilled in the art, and thus should not be
considered to be limitations of the presently disclosed inventions.
Nevertheless, a brief description of at least some of the
activities that may be performed to accomplish this objective will
now be discussed.
[0034] Initially, one or more etching processes were performed to
remove the gate cap layers 110, the sacrificial gate electrodes 108
and portions of the sacrificial gate insulation layer 104 exposed
by the removal of the sacrificial gate electrodes 108 to thereby
define a plurality of gate cavities 119 where the replacement gate
structures 130 will subsequently be formed. Note that the gate
cavities 119 are each laterally defined by the sidewall spacers 112
at this point in the process flow. Typically, the sacrificial gate
insulation layer 104 is removed as part of the replacement gate
technique, as depicted herein. However, the sacrificial gate
insulation layer 104 may not be removed in all applications. Even
in cases where the sacrificial gate insulation layer 104 is
intentionally removed, there will typically be a very thin native
oxide layer (not shown) that forms on the substrate 102 within the
gate cavities 119.
[0035] As shown in FIG. 2H, schematically depicted replacement gate
structures 130 for the transistors 106A-C were formed in the gate
cavities 119. The schematically depicted gate structure 130
includes a gate insulation layer and one or more layers of
conductive material that act as the gate electrode for the
transistor. As will be recognized by those skilled in the art after
a complete reading of the present application, the gate structure
130 of the devices 100 depicted in the drawings, i.e., the gate
insulation layer and the gate electrode, is intended to be
representative in nature. For example, the gate insulation layer
may be comprised of a variety of different materials, such as, for
example, silicon dioxide, a so-called high-k (k greater than 10)
insulation material (where k is the relative dielectric constant),
etc. The gate electrode may be comprised of one or more layers of
conductive material, e.g., polysilicon, tungsten, aluminum, one or
more layers of metal, etc. As noted above, in some cases, if
desired, a metal layer (not shown), such as a very thin work
function adjusting metal (e.g., a layer of titanium nitride), may
be formed on a high-k gate insulation layer. As will be recognized
by those skilled in the art after a complete reading of the present
application, the insulating materials and the metal layer(s) that
are part of the replacement gate structure 130 may be of any
desired construction and comprised of any of a variety of different
materials. Additionally, the replacement gate structure 130 for an
NFET device may have different material combinations as compared to
a replacement gate structure 130 for a PFET device. Thus, the
particular details of construction of replacement gate structure
130, and the manner in which such a replacement gate electrode
structure 130 is formed, should not be considered a limitation of
the present invention unless such limitations are expressly recited
in the attached claims.
[0036] In one illustrative example, the replacement gate formation
process begins with performing a conformal deposition process to
form a high-k gate insulation layer (not shown) in the gate
cavities 119 and above the layer of insulating material 124
followed by performing a high temperature anneal process in an
attempt to anneal out or repair any defects in the high-k gate
insulation layer. Thereafter, the conductive materials that will be
used for the gate electrode, e.g., one or more metal layers, will
be deposited across the devices by performing one or more conformal
deposition processes and/or one or more blanket-deposition
processes so as to substantially overfill the gate cavities 119
with conductive gate electrode material(s). At that point, one or
more CMP processes are performed to remove excess portions of the
gate insulation layer and the layers of conductive material that
will be used to form the gate electrode positioned above the layer
of insulating material 124. This CMP process essentially planarizes
the upper surface of the materials of the gate structure 130 with
the upper surface of the layer of insulating material 124.
Thereafter, an etching process is performed to reduce the height of
the replacement gate structure 130 such that the upper surface of
the replacement gate electrode is positioned below the upper
surface of the layer of insulating material 124. Next, an
illustrative gate cap layer 132, comprised of, for example, silicon
nitride, was formed above the recessed gate structure 130. The gate
cap layer 132 may be formed by depositing a layer of the cap
material and thereafter performing a CMP process to remove excess
portions of the cap material positioned on top of the layer of
insulating material 124. These process operations result in the
structure depicted in FIG. 2H.
[0037] FIG. 2I depicts the product 100 after a layer of insulating
material 134 has been deposited across the product 100. The layer
of insulating material 134 may be comprised of a variety of
different materials, such as silicon dioxide, a low-k (k value less
than 3.3) material, etc., and it may be formed by performing a
variety of techniques, e.g., CVD, etc. The thickness of the layer
of insulating material 134 may vary depending upon the particular
application.
[0038] FIG. 2J depicts the product 100 after one or more etching
processes were performed on the product 100 through a patterned
etch mask (not shown), such as a patterned layer of photoresist
material, to define contact openings 138 where conductive contacts
will be formed to establish electrical connection to the
source/drain regions. As depicted, for closely spaced transistors,
e.g., transistors 106A-B, the etching process(es) performed to form
the contact openings 138 remove portions of the layer of insulating
material 134 and substantially all of the oxide materials, e.g.,
the layers of insulating materials 122, 124 and the first liner
layer 116 positioned between the gate structures of the transistors
106A-B. To the extent any residual portions 118A of the sacrificial
liner layer 118 remain, the etching process(es) may include a brief
etching process to insure that none of the remaining portions of
the sacrificial second liner layer 118 are positioned above the
source/drain regions 114. However, in the case of densely packed
transistors, such as the transistors 106A-B, there will be so
little of the sacrificial second liner layer 118 remaining between
such transistors such that the oxide etching process(es) will also
remove any such residual materials from the sacrificial second
liner layer 118. In the case where transistors are spaced
relatively far apart, such as the transistors 106B-C, it is likely
that there will be some remaining portions of the sacrificial
second liner layer 118 present above the source/drain regions 114.
In such an application, the etching process(es) used to form the
contact openings 138 may involve an initial etching process to
remove silicon dioxide materials, e.g., the layers 134, 124, 122
and 116, followed by a brief etching process that uses an etch
chemistry adapted to remove any residual portions of the
sacrificial second liner layer 118. Thereafter another etching
process may be performed to remove any remaining portions of the
first liner layer 116 within the contact opening 138 that may have
been positioned under remaining portions 118A of the sacrificial
second liner layer 118. For example, as depicted in FIG. 2J,
residual portions of both the first liner layer 116 and the second
sacrificial second liner layer 118 are positioned adjacent the air
gaps 122 of the transistor 106C. In contrast, given the densely
packed relationship of the transistors 106A-B, there is no such air
gap present, due to the consumption of the layers of insulating
material 120, 124 between the two transistors. In the drawings, it
is assumed that another densely packed transistor (not shown) is
present to the left of the transistor 106A and that another
non-densely packed transistor (not shown) is present to the right
of the transistor 106C.
[0039] FIG. 2K depicts the product 100 after conductive,
self-aligned contact structures 140 have been formed in the
self-aligned contact openings 138 such that they are conductively
coupled to the source/drain regions 114. The self-aligned contact
structures 140 are intended to be schematic and representative in
nature, as they may be formed using any of a variety of different
conductive materials and by performing traditional manufacturing
operations. The self-aligned contact structures 140 may also
contain one or more barrier layers (not depicted). In one
illustrative example, the self-aligned contact structures 140 may
be formed by depositing a liner, e.g., a titanium nitride liner,
followed by overfilling the self-aligned contact openings 138 with
a conductive material, such as tungsten. Thereafter, a CMP process
may be performed to planarize the upper surface of the layer of
insulating material 134 which results in the removal of excess
portions of the liner and the tungsten positioned above the layer
of insulating material 134 outside of the self-aligned contact
openings 138 and the formation of the self-aligned contact
structures 140. If desired, a metal silicide material (not shown)
may be formed on the source/drain regions 114 prior to forming the
self-aligned contact structures 140.
[0040] Note that the method disclosed herein involve effectively
removing the liner layer 17 discussed in the background section of
this application. As a result, there is physically more space
between the gate structures or, more precisely, between the
sidewall spacers on the transistors 106A-B than would be present if
the prior art liner layer 17 were still in position. Additionally,
in the case of less densely packed transistors, the methods
disclosed herein allow formation of the depicted air gaps 122
between the gate electrodes of the replacement gate structures 130
and the contacts 140. The presence of the air gaps 122 reduces the
parasitic capacitance between the gate electrode and the contact
140.
[0041] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. For example, the process steps
set forth above may be performed in a different order. Furthermore,
no limitations are intended to the details of construction or
design herein shown, other than as described in the claims below.
It is therefore evident that the particular embodiments disclosed
above may be altered or modified and all such variations are
considered within the scope and spirit of the invention.
Accordingly, the protection sought herein is as set forth in the
claims below.
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