U.S. patent application number 15/827709 was filed with the patent office on 2019-05-30 for cut metal gate process for reducing transistor spacing.
The applicant listed for this patent is Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Chang-Yun Chang, Hung-Kai Chen, Hsien-Chin Lin, Ming-Chang Wen.
Application Number | 20190164741 15/827709 |
Document ID | / |
Family ID | 66632780 |
Filed Date | 2019-05-30 |
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United States Patent
Application |
20190164741 |
Kind Code |
A1 |
Wen; Ming-Chang ; et
al. |
May 30, 2019 |
Cut Metal Gate Process for Reducing Transistor Spacing
Abstract
A method includes providing a structure having a substrate and
first and second fins over the substrate and oriented lengthwise
generally along a first direction; epitaxially growing
semiconductor source/drain (S/D) features over the first and second
fins, wherein a first semiconductor S/D feature over the first fin
merges with a second semiconductor S/D feature over the second fin;
and performing a first etching process to an area between the first
and second fins, wherein the first etching process separates the
first and second semiconductor S/D features.
Inventors: |
Wen; Ming-Chang; (Kaohsiung
City, TW) ; Chang; Chang-Yun; (Taipei, TW) ;
Lin; Hsien-Chin; (Hsinchu City, TW) ; Chen;
Hung-Kai; (Taichung City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Co., Ltd. |
Hsinchu |
|
TW |
|
|
Family ID: |
66632780 |
Appl. No.: |
15/827709 |
Filed: |
November 30, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/76224 20130101;
H01L 27/0924 20130101; H01L 27/0207 20130101; H01L 29/0649
20130101; H01L 21/0214 20130101; H01L 29/66545 20130101; H01L
21/02164 20130101; H01L 21/31056 20130101; H01L 21/823814 20130101;
H01L 21/823821 20130101; H01L 29/785 20130101; H01L 21/32155
20130101; H01L 27/1104 20130101; H01L 29/7848 20130101; H01L
21/8258 20130101 |
International
Class: |
H01L 21/02 20060101
H01L021/02; H01L 21/3215 20060101 H01L021/3215; H01L 21/3105
20060101 H01L021/3105; H01L 21/8258 20060101 H01L021/8258; H01L
29/66 20060101 H01L029/66; H01L 21/762 20060101 H01L021/762; H01L
29/78 20060101 H01L029/78; H01L 29/06 20060101 H01L029/06 |
Claims
1. A method comprising: providing a structure having a substrate
and first and second fins over the substrate and oriented
lengthwise generally along a first direction; epitaxially growing
semiconductor source/drain (S/D) features over the first and the
second fins, wherein a first semiconductor S/D feature over the
first fin merges with a second semiconductor S/D feature over the
second fin; and performing a first etching process to an area
between the first and the second fins, wherein the first etching
process removes portions of the first and the second semiconductor
S/D features and portions of a dielectric layer disposed
therebetween.
2. The method of claim 1, further comprising, before the performing
of the first etching process: forming gate structures over the
substrate and the first and the second fins, wherein the gate
structures are oriented lengthwise generally along a second
direction perpendicular to the first direction, wherein the first
etching process is tuned to selectively etch the first and the
second semiconductor S/D features but not the gate structures.
3. The method of claim 2, wherein the forming of the gate
structures includes: forming temporary gate structures over the
substrate and the first and the second fins; depositing the
dielectric layer over the temporary gate structures and the
semiconductor S/D features; removing the temporary gate structures,
resulting in gate trenches in the dielectric layer; and depositing
the gate structures in the gate trenches.
4. The method of claim 3, wherein the depositing of the gate
structures includes forming a high-k dielectric layer and a metal
gate electrode over the high-k dielectric layer.
5. The method of claim 4, wherein the performing of the first
etching process results in a trench in the dielectric layer in the
area between the first and the second fins, further comprising:
depositing one or more dielectric materials in the trench.
6. The method of claim 5, further comprising: etching a contact
hole that exposes both the first and the second semiconductor S/D
features; depositing a conductive material in the contact hole; and
performing a chemical mechanical planarization (CMP) process to
separate the conductive material into a first portion and a second
portion, wherein the first and the second portions are electrically
connected to the first and the second semiconductor S/D features,
respectively, and are isolated from each other by the one or more
dielectric materials.
7. The method of claim 2, wherein: the structure further includes a
third fin over the substrate and oriented lengthwise generally
along the first direction; the gate structures are also formed over
the third fin; and the first etching process is also performed to
an area between the second and the third fins.
8. The method of claim 7, wherein the performing of the first
etching process results in a first trench in the dielectric layer,
further comprising: performing a second etching process to the area
between the second and the third fins to form a second trench,
wherein the second etching process is tuned to selectively etch the
gate structures but not the dielectric layer.
9. The method of claim 1, wherein the first and the second
semiconductor S/D features include p-type doped silicon
germanium.
10. The method of claim 8, further comprising: depositing one or
more dielectric materials in the second trench.
11. A method comprising: providing a structure having: a substrate;
a first fin, a second fin, and a third fin over the substrate and
oriented lengthwise generally along a first direction; metal gate
structures over the first, the second, and the third fins and
oriented lengthwise generally along a second direction
perpendicular to the first direction, wherein each gate structure
includes a high-k dielectric layer and a metal gate electrode;
first and second epitaxial semiconductor source/drain (S/D)
features over the first and the second fins respectively, wherein
the first and the second epitaxial semiconductor S/D features merge
along the second direction; and a first dielectric layer over the
substrate, the first, the second, and the third fins, and the first
and the second epitaxial semiconductor S/D features, the first
dielectric layer filling space between the metal gate structures;
performing a first etching process to a first area between the
first and the second fins and to a second area between the second
and the third fins, wherein the first etching process is tuned to
selectively etch the first and the second epitaxial semiconductor
S/D features and the first dielectric layer but not the metal gate
structures; performing a second etching process to the second area,
wherein the second etching process is tuned to selectively etch the
metal gate structures to form a trench in the metal gate
structures; and forming a second dielectric layer in the
trench.
12. The method of claim 11, wherein the first etching process
removes portions of the first and the second epitaxial
semiconductor S/D features and portions of the first dielectric
layer disposed therebetween.
13. The method of claim 11, wherein the trench is a first trench,
and wherein the first etching process results in a second trench
between the first and the second epitaxial semiconductor S/D
features, further comprising: depositing one or more dielectric
materials in the second trench to form a third dielectric layer,
wherein the third dielectric layer is separated from the first and
the second epitaxial semiconductor S/D features by two continuous
interfaces.
14. The method of claim 13, wherein the first and the second
etching processes collectively form a third trench between the
second and the third fins, further comprising depositing the one or
more dielectric materials in the third trench.
15. The method of claim 11, wherein the first etching process
includes dry etching with an etchant having hydrogen fluoride and
ammonia.
16. The method of claim 11, wherein the second etching process uses
a chlorine-containing etchant.
17. A semiconductor structure, comprising: a substrate; first and
second fins over the substrate and oriented lengthwise generally
along a first direction, wherein bottom portions of the first and
the second fins are separated by an isolation feature; first and
second epitaxial semiconductor source/drain (S/D) features over the
first and second fins, respectively; and a first dielectric layer
disposed between and in physical contact with the first and the
second epitaxial semiconductor S/D features, wherein the first
dielectric layer is defined by a first interface between the first
dielectric layer and the first epitaxial semiconductor S/D feature,
and a second interface between the first dielectric layer and the
second epitaxial semiconductor S/D feature, and wherein a bottom
surface of the first dielectric layer is disposed below a top
surface of the isolation feature.
18. The semiconductor structure of claim 17, further comprising:
gate structures over the first and second fins and oriented
lengthwise generally along a second direction perpendicular to the
first direction; and a second dielectric layer over the substrate,
the first and second fins, and the first and second epitaxial
semiconductor S/D features, the second dielectric layer filling
space between the gate structures, wherein the first and the second
dielectric layers include different dielectric materials.
19. The semiconductor structure of claim 18, further comprising a
contact etch stop layer between the second dielectric layer and the
first and second epitaxial semiconductor S/D features.
20. The semiconductor structure of claim 17, further comprising: a
first conductive feature over the first epitaxial semiconductor S/D
feature; and a second conductive feature over the second epitaxial
semiconductor S/D feature, wherein the first dielectric layer is
disposed between the first and the second conductive features.
Description
BACKGROUND
[0001] The semiconductor integrated circuit (IC) industry has
experienced exponential growth. Technological advances in IC
materials and design have produced generations of ICs where each
generation has smaller and more complex circuits than the previous
generation. In the course of IC evolution, functional density
(i.e., the number of interconnected devices per chip area) has
generally increased while geometry size (i.e., the smallest
component (or line) that can be created using a fabrication
process) has decreased. This scaling down process generally
provides benefits by increasing production efficiency and lowering
associated costs. Such scaling down has also increased the
complexity of processing and manufacturing ICs.
[0002] For example, when designing and manufacturing SRAM (static
random access memory) cells having pull-up (PU) devices, pull-down
(PD) devices, and pass-gate (PG) devices, it is common to form PU
devices (e.g., PMOS) in one device region (e.g., in an n-well), and
form PD and PG devices in another device region (e.g., in a
p-well). However, at least for the PU devices, there is a concern
that the spacing among them needs to be sufficiently large so that
epitaxial source/drain (S/D) features of the PU devices do not
merge to cause short defects. On the one hand, having large
epitaxial S/D features are generally desirable for reducing S/D
contact resistance. On the other hand, having large epitaxial S/D
features also increases the spacing requirements among the PU
devices, thereby undesirably reducing device integration. An object
of the present disclosure seeks to resolve this issue, among
others.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] The present disclosure is best understood from the following
detailed description when read with the accompanying figures. It is
emphasized that, in accordance with the standard practice in the
industry, various features are not drawn to scale and are used for
illustration purposes only. In fact, the dimensions of the various
features may be arbitrarily increased or reduced for clarity of
discussion.
[0004] FIG. 1A shows a top view of a semiconductor structure
implemented with a cut metal gate process, according to aspects of
the present disclosure.
[0005] FIGS. 1B, 1C, and 1D show cross-sectional views of the
structure in FIG. 1A, in accordance with some embodiments.
[0006] FIGS. 2A, 2B, and 2C show a flow chart of a method for
forming the structure shown in FIGS. 1A-1D, according to aspects of
the present disclosure.
[0007] FIGS. 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B, 9A,
9B, 10, 11, 12A, 12B, 13, 14A, 14B, 15, 16, 17, and 18 illustrate
cross-sectional views of a semiconductor structure during a
fabrication process according to the method of FIGS. 2A-2C, in
accordance with some embodiments.
DETAILED DESCRIPTION
[0008] The following disclosure provides many different
embodiments, or examples, for implementing different features of
the provided subject matter. Specific examples of components and
arrangements are described below to simplify the present
disclosure. These are, of course, merely examples and are not
intended to be limiting. For example, the formation of a first
feature over or on a second feature in the description that follows
may include embodiments in which the first and second features are
formed in direct contact, and may also include embodiments in which
additional features may be formed between the first and second
features, such that the first and second features may not be in
direct contact. In addition, the present disclosure may repeat
reference numerals and/or letters in the various examples. This
repetition is for the purpose of simplicity and clarity and does
not in itself dictate a relationship between the various
embodiments and/or configurations discussed.
[0009] Further, spatially relative terms, such as "beneath,"
"below," "lower," "above," "upper" and the like, may be used herein
for ease of description to describe one element or feature's
relationship to another element(s) or feature(s) as illustrated in
the figures. The spatially relative terms are intended to encompass
different orientations of the device in use or operation in
addition to the orientation depicted in the figures. The apparatus
may be otherwise oriented (rotated 90 degrees or at other
orientations) and the spatially relative descriptors used herein
may likewise be interpreted accordingly.
[0010] The present disclosure is generally related to semiconductor
devices and fabrication methods, and more particularly to
fabricating FinFET semiconductor devices using a cut metal gate
process that beneficially reduces the spacing requirements between
adjacent fins such as fins for forming p-type FinFETs. A cut metal
gate (CMG) process refers to a fabrication process where after a
metal gate (e.g., a high-k metal gate or HK MG) replaces a dummy
gate structure (e.g., a polysilicon gate), the metal gate is cut
(e.g., by an etching process) to separate the metal gate into two
or more portions. Each portion functions as a metal gate for an
individual transistor. An isolation material is subsequently filled
into trenches between adjacent portions of the metal gate. These
trenches are referred to as cut metal gate trenches, or CMG
trenches, in the present disclosure. A CMG process according to the
present disclosure includes two exposure steps and two etching
steps (so-called 2P2E). The first exposure step and the first
etching step are designed for etching dielectric layers and those
merged epitaxial S/D features that need to be separated, without
etching the metal gates. The second exposure step and the second
etching step are designed for etching the metal gates. By utilizing
this 2P2E process, semiconductor fins can be arranged closer and
epitaxial S/D features can be grown larger than traditional
devices. This simultaneously serves two purposes: increasing device
integration by reducing spacing between semiconductor fins, and
growing large epitaxial S/D features for reducing S/D contact
resistance.
[0011] FIG. 1A illustrates a top view of a semiconductor device (or
semiconductor structure) 100. FIG. 1B illustrates a cross-sectional
view of the device 100 along the B-B line of FIG. 1A. FIG. 1C
illustrates a cross-sectional view of the device 100 along the C-C
line of FIG. 1A. FIG. 1D illustrates a cross-sectional view of the
device 100 along the D-D line of FIG. 1A.
[0012] Referring to FIGS. 1A-1B, the device 100 includes a
substrate 102, a plurality of fins 104 protruding out of the
substrate 102 including fins 104a in a first device region 103a and
fins 104b in a second device region 103b, an isolation structure
106 over the substrate 102 and between the fins 104, and a
plurality of gate structures 112 disposed over the fins 104 and the
isolation structure 106.
[0013] The fins 104 are oriented lengthwise along X direction and
spaced from each other along Y direction perpendicular to the X
direction. In the present embodiment, the fins 104a are designed
for forming p-type FinFETs; and the fins 104b are designed for
forming n-type FinFETs. The fins 104a have an edge-to-edge spacing
P1 along the Y direction. In an embodiment, P1 ranges from 20 to 30
nm, which is smaller than traditional fin configurations where
adjacent epitaxial S/D features are formed separately (not merged).
In a particular embodiment, P1 is designed to be few nanometers
greater than a resolution of a lithography exposure tool, such as
an extreme ultraviolet (EUV) exposure tool whose resolution is
about 13.3 nm in an embodiment. The smaller spacing P1
advantageously increases device integration. Some of the fins 104b
are placed close to each other for forming multi-fin transistors
for boosting device performance. In the embodiment shown in FIG.
1A, there are two groups of dual fins 104b. The spacing between the
fin 104a and a nearby fin 104b is P2, which ranges from 40 to 50 nm
in an embodiment. The spacing between two groups of fins 104b is
P3, which ranges from 40 to 50 nm in an embodiment. In various
embodiments, a group of fins 104b may include two (as shown),
three, or more fins for forming multi-fin transistors.
[0014] The gate structures 112 are oriented lengthwise along the Y
direction, and are spaced from each other along the X direction.
The gate structures 12 engage the fins 104a and 104b in their
respective channel regions to thereby form FinFETs. In the present
embodiment, the gate structures 112 engage the fins 104a to form
p-type FinFETs, which may be used for pull-up (PU) devices in SRAM
cells; and the gate structures 112 engage the fins 104b to form
n-type FinFETs, which may be used for pull-down (PD) devices or
pass-gate (PG) devices in SRAM cells. Due to the reduced spacing
P1, the SRAM cells configured with the present PU, PD, and PG
devices have a smaller area than traditional SRAM cells.
[0015] Still referring to FIGS. 1A-1B, the device 100 further
includes S/D features 162, including S/D features 162a and 162b
disposed over the fins 104a and 104b respectively. It is noted that
not all of the S/D features 162 are illustrated in FIG. 1A for the
sake of simplicity. Generally, S/D features 162 are disposed on
each of the fins 104 in their respective S/D regions. In an
embodiment, the S/D features 162a include p-type doped silicon
germanium, while the S/D features 162b include n-type doped
silicon.
[0016] The device 100 further includes a dielectric layer 114,
including dielectric features 114a, 114b, and 114c. Particularly,
the dielectric features 114a are disposed between two rows of fins
104a in the device region 103a, and the dielectric features 114b
and 114c are disposed between two groups of fins 104b in the device
region 103b, as well as between the device regions 103a and 103b.
The dielectric layer 114 fills in CMG trenches, and is therefore
referred to as CMG dielectric layer 114. The CMG dielectric layer
114 is arranged lengthwise along the X direction and separates some
of the gate structures 112 into at least two portions. In the
present embodiment, the areas indicated by the dashed boxes 113a
and 113b are processed by one exposure and etching process, while
the areas indicated by the dashed boxes 113c are process by another
exposure and etching process. This aspect will be discussed in
detail later. The dielectric features 114a are disposed within the
dashed box 113a and expand from one edge of a gate structure 112 to
an adjacent edge of the gate structure 112 along the X direction.
The dielectric features 114b are disposed within the dashed boxes
113b and expand from one edge of a gate structure 112 to an
adjacent edge of the gate structure 112 along the X direction. The
dielectric features 114c are disposed within the dashed boxes 113c
and expand from one edge of a gate structure 112 to an adjacent
edge of the gate structure 112 along the Y direction. In the
present embodiment, the dielectric features 114b are wider than the
dielectric features 114c along the Y direction. The dielectric
features 114a, 114b, and 114c include the same dielectric
material(s) in the present embodiment. The width W1 of the
dielectric features 114a along the Y direction is smaller than P1
and ranges from 16 to 18 nm in an embodiment. In an embodiment, the
width W1 is designed to be the same or slightly greater than the
resolution of the lithography exposure tool, such as an EUV
exposure tool whose resolution is about 13.3 nm.
[0017] Referring to FIG. 1B, the CMG dielectric feature 114a is
disposed between and in physical contact with two S/D features
162a. In an embodiment, the interfaces 115 between the CMG
dielectric feature 114a and the two S/D features 162a are two
generally straight lines in this cross-sectional view, whose
straightness depends on the etching and deposition processes that
form the CMG dielectric features 114a as will be discussed later.
In an embodiment, each of the interfaces 115 forms an angle ranging
from 0 to 5 degrees with normal (Z direction) of a top surface of
the substrate 102. In an embodiment, the horizontal (along the Y
direction) distances between the two interfaces 115 at different
heights (along the Z direction) are about the same or linearly and
monotonically decrease from top to bottom. In another embodiment,
the two interfaces 115 are tilted toward each other from top to
bottom regardless whether or not they are generally straight lines.
The interfaces 115 are different from other facets of the S/D
features 162a. The other facets are formed by epitaxial growth
process and generally follow the crystalline orientation of the
semiconductor material(s) of the S/D features 162a, while the
interfaces 115 are formed by etching the S/D features 162a
regardless of the underlying crystalline orientation.
[0018] Referring to FIG. 1C, each gate structure 112 includes a
high-k dielectric layer 108 and a conductive layer 110 over the
high-k dielectric layer 108. The conductive layer 110 includes one
or more layers of metallic materials. Therefore, each gate
structure 112 is also referred to as a high-k metal gate (or HK MG)
112. The gate structures 112 may further include an interfacial
layer (not shown) under the high-k dielectric layer 108. The CMG
dielectric feature 114c separates the gate structure 112 into left
and right portions. The left portion engages a fin 104a to form a
transistor, and the right portion engages two fins 104b to form
another transistor.
[0019] Referring to FIG. 1D, in this cross-sectional view, the CMG
dielectric feature 114a is in physical contact with only one S/D
feature 162a. The above discussion of the S/D feature 162a, the
interface 115, and the CMG dielectric feature 114a also applies to
FIG. 1D.
[0020] The device 100 further includes one or more dielectric
layers, such as a contact etch stop layer (CESL) 164 disposed over
the S/D features 162 and the isolation structure 106, and an
inter-layer dielectric (ILD) layer 166 disposed over the isolation
structure 106, the fins 104, the gate structures 112, and the CESL
164. The components of the device 100 are further described
below.
[0021] The substrate 102 is a silicon substrate in the present
embodiment. Alternatively, the substrate 102 may comprise another
elementary semiconductor, such as germanium; a compound
semiconductor including silicon carbide, gallium arsenide, gallium
phosphide, indium phosphide, indium arsenide, and indium
antimonide; an alloy semiconductor including silicon germanium,
gallium arsenide phosphide, aluminum indium phosphide, aluminum
gallium arsenide, gallium indium arsenide, gallium indium
phosphide, and gallium indium arsenide phosphide; or combinations
thereof.
[0022] The fins 104 may comprise one or more semiconductor
materials such as silicon, germanium, silicon carbide, gallium
arsenide, gallium phosphide, indium phosphide, indium arsenide,
indium antimonide, silicon germanium, gallium arsenide phosphide,
aluminum indium phosphide, aluminum gallium arsenide, gallium
indium arsenide, gallium indium phosphide, and gallium indium
arsenide phosphide. In an embodiment, the fins 104 may include
alternately stacked layers of two different semiconductor
materials, such as layers of silicon and silicon germanium
alternately stacked. The fins 104 may additionally include dopants
for improving the performance of the device 100. For example, the
fins 104 may include n-type dopant(s) such as phosphorus or
arsenic, or p-type dopant(s) such as boron or indium.
[0023] The isolation structure 106 may comprise silicon oxide,
silicon nitride, silicon oxynitride, fluoride-doped silicate glass
(FSG), a low-k dielectric material, and/or other suitable
insulating material. The isolation structure 106 may be shallow
trench isolation (STI) features. Other isolation structure such as
field oxide, LOCal Oxidation of Silicon (LOCOS), and/or other
suitable structures are possible. The isolation structure 106 may
include a multi-layer structure, for example, having one or more
thermal oxide liner layers adjacent to the fins 104.
[0024] The high-k dielectric layer 108 may include one or more
high-k dielectric materials (or one or more layers of high-k
dielectric materials), such as hafnium silicon oxide (HfSiO),
hafnium oxide (HfO.sub.2), alumina (Al.sub.2O.sub.3), zirconium
oxide (ZrO.sub.2), lanthanum oxide (La.sub.2O.sub.3), titanium
oxide (TiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), strontium
titanate (SrTiO.sub.3), or a combination thereof.
[0025] The conductive layer 110 includes one or more metal layers,
such as work function metal layer(s), conductive barrier layer(s),
and metal fill layer(s). The work function metal layer may be a
p-type or an n-type work function layer depending on the type (PFET
or NFET) of the device. The p-type work function layer comprises a
metal selected from but not restricted to the group of titanium
nitride (TiN), tantalum nitride (TaN), ruthenium (Ru), molybdenum
(Mo), tungsten (W), platinum (Pt), or combinations thereof. The
n-type work function layer comprises a metal selected from but not
restricted to the group of titanium (Ti), aluminum (Al), tantalum
carbide (TaC), tantalum carbide nitride (TaCN), tantalum silicon
nitride (TaSiN), titanium silicon nitride (TiSiN), or combinations
thereof. The metal fill layer may include aluminum (Al), tungsten
(W), cobalt (Co), and/or other suitable materials.
[0026] The CMG dielectric layer 114 may include one or more
dielectric materials, such as silicon nitride, silicon oxide,
silicon oxynitride, fluoride-doped silicate glass (FSG), a low-k
dielectric material, and/or other suitable insulating material; and
may be formed by CVD (chemical vapor deposition), PVD (physical
vapor deposition), ALD (atomic layer deposition), or other suitable
methods.
[0027] The CESL 164 may comprise silicon nitride, silicon
oxynitride, silicon nitride with oxygen (O) or carbon (C) elements,
and/or other materials; and may be formed by CVD, PVD, ALD, or
other suitable methods. The ILD layer 166 may comprise
tetraethylorthosilicate (TEOS) oxide, un-doped silicate glass, or
doped silicon oxide such as borophosphosilicate glass (BPSG), fused
silica glass (FSG), phosphosilicate glass (PSG), boron doped
silicon glass (BSG), and/or other suitable dielectric materials.
The ILD layer 166 may be formed by PECVD (plasma enhanced CVD),
FCVD (flowable CVD), or other suitable methods.
[0028] FIGS. 2A, 2B, and 2C illustrate a flow chart of a method 200
for forming the semiconductor device 100 in accordance with an
embodiment. The method 200 is merely an example, and is not
intended to limit the present disclosure beyond what is explicitly
recited in the claims. Additional operations can be provided
before, during, and after the method 200, and some operations
described can be replaced, eliminated, or moved around for
additional embodiments of the method. The method 200 is described
below in conjunction with FIGS. 3A-18, which illustrate various
cross-sectional views of the semiconductor device 100 during
fabrication steps according to the method 200.
[0029] At operation 202, the method 200 (FIG. 2A) provides, or is
provided with, a device structure 100 having a substrate 102, fins
104 (including fins 104a and 104b) protruding out of the substrate
102, and an isolation structure 106 over the substrate 102 and
between the fins 104, such as shown in FIGS. 3A and 3B.
Particularly, FIGS. 3A and 3B show cross-sectional views of the
device structure 100 along the B-B line and the C-C line of FIG.
1A, respectively. The various materials for the substrate 102, the
fins 104, and the isolation structure 106 have been discussed above
with reference to FIGS. 1A-1D.
[0030] In an embodiment, the substrate 102 may be a wafer, such as
a silicon wafer. The fins 104 can be formed by epitaxially growing
one or more semiconductor layers over the entire area of the
substrate 102 and then patterned to form the individual fins 104.
The fins 104 may be patterned by any suitable method. For example,
the fins 104 may be patterned using one or more photolithography
processes, including double-patterning or multi-patterning
processes. Generally, double-patterning or multi-patterning
processes combine photolithography and self-aligned processes,
allowing patterns to be created that have, for example, pitches
smaller than what is otherwise obtainable using a single, direct
photolithography process. For example, in one embodiment, a
sacrificial layer is formed over a substrate and patterned using a
photolithography process. Spacers are formed alongside the
patterned sacrificial layer using a self-aligned process. The
sacrificial layer is then removed, and the remaining spacers, or
mandrels, may then be used to pattern the fins 104 by etching the
initial epitaxial semiconductor layers. The etching process can
include dry etching, wet etching, reactive ion etching (RIE),
and/or other suitable processes. For example, a dry etching process
may implement an oxygen-containing gas, a fluorine-containing gas
(e.g., CF.sub.4, SF.sub.6, CH.sub.2F.sub.2, CHF.sub.3, and/or
C.sub.2F.sub.6), a chlorine-containing gas (e.g., Cl.sub.2,
CHCl.sub.3, CCl.sub.4, and/or BCl.sub.3), a bromine-containing gas
(e.g., HBr and/or CHBR.sub.3), an iodine-containing gas, other
suitable gases and/or plasmas, and/or combinations thereof. For
example, a wet etching process may comprise etching in diluted
hydrofluoric acid (DHF); potassium hydroxide (KOH) solution;
ammonia; a solution containing hydrofluoric acid (HF), nitric acid
(HNO.sub.3), and/or acetic acid (CH.sub.3COOH); or other suitable
wet etchant.
[0031] The isolation structure 106 may be formed by one or more
deposition and etching methods. The deposition methods may include
thermal oxidation, chemical oxidation, and chemical vapor
deposition (CVD) such as flowable CVD (FCVD). The etching methods
may include dry etching, wet etching, and chemical mechanical
planarization (CMP).
[0032] At operation 204, the method 200 (FIG. 2A) forms gate
structures 112 engaging the fins 104. In an embodiment, the
operation 204 includes depositing the various layers of the gate
structures 112 including the gate dielectric layer 108 and the
conductive layer 110, and patterning the various layers to form the
gate structures 112 as illustrated in FIGS. 1A and 1C. In a
particular embodiment, the operation 204 uses a replacement gate
process where it first forms temporary (or dummy) gate structures
and then replaces the temporary gate structures with the gate
structures 112. An embodiment of the replacement gate process is
illustrated in FIG. 2B including operations 204a, 204b, and 204c,
which are further discussed below.
[0033] At operation 204a, the method 200 (FIG. 2B) forms temporary
gate structures 149 engaging the fins 104 such as shown in FIGS. 4A
and 4B, which show cross-sectional views of the device 100 cut
along the A-A line and the C-C line of FIG. 1A, respectively.
Referring to FIGS. 4A and 4B, each temporary gate structure 149
includes an interfacial layer 150, an electrode layer 152, and two
hard mask layers 154 and 156. The operation 204a further forms gate
spacers 160 on sidewalls of the temporary gate structures 149.
[0034] The interfacial layer 150 may include a dielectric material
such as silicon oxide layer (e.g., SiO.sub.2) or silicon oxynitride
(e.g., SiON), and may be formed by chemical oxidation, thermal
oxidation, atomic layer deposition (ALD), CVD, and/or other
suitable methods. The gate electrode 152 may include
poly-crystalline silicon (poly-Si) and may be formed by suitable
deposition processes such as low-pressure chemical vapor deposition
(LPCVD) and plasma-enhanced CVD (PECVD). Each of the hard mask
layers 154 and 156 may include one or more layers of dielectric
material such as silicon oxide and/or silicon nitride, and may be
formed by CVD or other suitable methods. The various layers 150,
152, 154, and 156 may be patterned by photolithography and etching
processes. The gate spacers 160 may comprise a dielectric material,
such as silicon oxide, silicon nitride, silicon oxynitride, silicon
carbide, other dielectric material, or combinations thereof, and
may comprise one or multiple layers of material. The gate spacers
160 may be formed by depositing a spacer material as a blanket over
the isolation structure 106, the fins 104, and the temporary gate
structures 149. Then the spacer material is etched by an
anisotropic etching process to expose the isolation structure 106,
the hard mask layer 156, and a top surface of the fins 104.
Portions of the spacer material on the sidewalls of the temporary
gate structures 149 become the gate spacers 160. Adjacent gate
spacers 160 provide trenches 158 that expose the fins 104 in the
S/D regions of the device 100.
[0035] At operation 206, the method 200 (FIGS. 2A and 2B) forms
source/drain (or S/D) features 162, such as shown in FIGS. 5A and
5B, which are cross-sectional views of the device 100 along the A-A
line and the B-B line of FIG. 1A, respectively. For example, the
operation 206 may etch recesses into the fins 104 exposed in the
trenches 158, and epitaxially grow semiconductor materials in the
recesses. The semiconductor materials may be raised above the top
surface of the fins 104, as illustrated in FIGS. 5A and 5B. The
operations 206 may form the S/D features 162 separately for NFET
and PFET devices. For example, the operations 206 may form the S/D
features 162b with n-type doped silicon for NFET devices and form
the S/D features 162a with p-type doped silicon germanium for PFET
devices. In the present embodiment, some of the S/D features 162
merge together, such as shown in FIG. 5B. Particularly, two S/D
features 162a that are designed for two individual PFETs merge, and
two S/D features 162b that are designed for a multi-fin NFET also
merge. Typically, two S/D features that are designed for two
individual transistors (as opposed to a multi-fin transistor) are
not allowed to merge together. To avoid the merging, the spacing
between the two fins 104a is typically designed to be greater than
the lateral size of the S/D feature 162a. This typically requires
either greater spacing (more area) for the two individual
transistors or smaller epitaxial S/D features. Neither is ideal
because the former would reduce device integration and the latter
would increase S/D contact resistance. The present disclosure
improves over the typical approaches by initially growing S/D
features 162a large enough to merge and then etches the merged S/D
feature to separate them, which will be discussed in details
later.
[0036] At operation 208, the method 200 (FIGS. 2A and 2B) forms
various features including a contact etch stop layer (CESL) 164
over the S/D features 162, and an interlayer dielectric (ILD) layer
166 over the CESL 164, such as shown in FIGS. 6A and 6B, which are
cross-sectional views of the device 100 along the A-A line and the
B-B line of FIG. 1A, respectively. The CESL 164 may comprise
silicon nitride, silicon oxynitride, silicon nitride with oxygen
(O) or carbon (C) elements, and/or other materials; and may be
formed by CVD, PVD (physical vapor deposition), ALD, or other
suitable methods. The ILD layer 166 may comprise
tetraethylorthosilicate (TEOS) oxide, un-doped silicate glass, or
doped silicon oxide such as borophosphosilicate glass (BPSG), fused
silica glass (FSG), phosphosilicate glass (PSG), boron doped
silicon glass (BSG), and/or other suitable dielectric materials.
The ILD layer 166 may be formed by PECVD, FCVD, or other suitable
methods. The operation 208 may perform one or more CMP processes to
planarize the top surface of the device 100, remove the hard mask
layers 154 and 156, and expose the electrode layer 152.
[0037] At operation 204b, the method 200 (FIG. 2B) removes the
temporary gate structures 149 to form gate trenches 169, such as
shown in FIGS. 7A and 7B, which are cross-sectional views of the
device 100 along the A-A and C-C lines of FIG. 1A, respectively.
The gate trenches 169 expose surfaces of the fins 104 and sidewall
surfaces of the gate spacers 160. The operation 204b may include
one or more etching processes that are selective to the material in
the electrode layer 152 and the interfacial layer 150. The etching
processes may include dry etching, wet etching, reactive ion
etching, or other suitable etching methods.
[0038] At operation 204c, the method 200 (FIG. 2B) deposits gate
structures (e.g., high-k metal gates) 112 in the gate trenches 169,
such as shown in FIGS. 8A and 8B which are cross-sectional views of
the device 100 along the A-A and C-C lines of FIG. 1A,
respectively. The gate structures 112 include the high-k dielectric
layer 108 and the conductive layer 110. The gate structures 112 may
further include an interfacial layer (e.g., SiO.sub.2) (not shown)
between the high-k dielectric layer 108 and the fins 104. The
interfacial layer may be formed using chemical oxidation, thermal
oxidation, ALD, CVD, and/or other suitable methods. The materials
of the high-k dielectric layer 108 and the conductive layer 110
have been discussed above with reference to FIGS. 1A-1D. The high-k
dielectric layer 108 may include one or more layers of high-k
dielectric material, and may be deposited using CVD, ALD, and/or
other suitable methods. The conductive layer 110 may include one or
more work function metal layers and a metal fill layer, and may be
deposited using methods such as CVD, PVD, plating, and/or other
suitable processes.
[0039] At operation 210, the method 200 (FIGS. 2A and 2B) forms one
or more patterned hard mask layers over the device 100, such as
shown in FIGS. 9A and 9B which are cross-sectional views of the
device 100 along the B-B line and the C-C line of FIG. 1A,
respectively. One hard mask layer 170 is illustrated in this
example. The hard mask layer 170 may include titanium nitride,
silicon nitride, amorphous silicon, yttrium silicate (YSiO.sub.x),
or other suitable hard mask material(s). In an embodiment, the
operation 210 deposits the hard mask layer 170 using CVD, PVD, ALD,
or other suitable methods, and subsequently patterns the hard mask
layer 170 to form openings 171. The openings 171 correspond to the
dashed boxes 113a and 113b of FIG. 1A. The openings 171 expose the
conductive layer 110 and the ILD layer 166. In an example, the
operation 210 may form a patterned photoresist over the hard mask
layer 170 by photoresist coating, exposing, post-exposure baking,
and developing. The patterned photoresist provides openings
corresponding to the boxes 114a and 114b of FIG. 1A. In a
particular embodiment, the operation 210 uses a single exposure
process (e.g., using EUV exposure) to expose the photoresist layer
to have a latent image that includes the dashed boxes 113a and
113b, and then develops the photoresist layer to provide the
openings. Then, the operation 210 etches the hard mask layer 170
using the patterned photoresist as an etch mask to form the opening
171. The etching process may include wet etching, dry etching,
reactive ion etching, or other suitable etching methods. The
patterned photoresist is removed thereafter, for example, by resist
stripping.
[0040] At operation 212, the method 200 (FIG. 2A) etches the device
100 through the openings 171. The patterned hard mask layer 170
protects the rest of the device 100 from the etching process. In
the present embodiment, the operation 212 uses an etching process
that is tuned to selectively etch the ILD layer 166 and the S/D
features 162a without (or insignificantly) etching the gate
structures (e.g., HK MG) 112. For example, the operation 212 may
perform a dry etching process using hydrogen fluoride (HF) and
ammonia, and may use argon gas as a carrier gas. These etchants are
selective to oxide (in the ILD layer 166) and silicon or
silicon-germanium (in the S/D features 162), and do not etch well
the conductive layer 110 in the gate structures 112. Referring to
FIG. 10 which is a cross-sectional view of the device 100 along the
B-B line of FIG. 1A, the operation 212 extends the openings 171
down and through the ILD layer 166 and the S/D features 162a and
may extend the openings 171 into the isolation structure 106. In
the cross-sectional view of the device 100 along the C-C line of
FIG. 1A, the device 100 remains about the same as shown in FIG. 9B
because the etching process is tuned to not etch the conductive
layer 110.
[0041] At operation 214, the method 200 (FIG. 2A) fills the
trenches 171 with one or more dielectric materials to form the
dielectric layer 114 including the dielectric features 114a and
114b, and performs a chemical mechanical polishing (CMP) process to
remove the patterned hard mask 170 and to planarize the top surface
of the device 100. The resultant device 100 is illustrated in FIG.
11. Since the sidewalls of the gate structures 112 contain metallic
materials, at least the outer portion of the dielectric layer 114
(that is in direct contact with the sidewalls of the gate
structures 112) is free of active chemical components such as
oxygen. For example, the outer portion of the dielectric layer 114
may include silicon nitride and is free of oxygen or oxide. The
dielectric layer 114 may include some oxide in the inner portion
thereof in some embodiments. Alternatively, the dielectric layer
114 may include one uniform layer of silicon nitride and is free of
oxide. The dielectric layer 114 may be deposited using CVD, PVD,
ALD, or other suitable methods. In the present embodiment, the
dielectric layer 114 is deposited using ALD to ensure that it
completely fills the trenches 171.
[0042] At operation 216, the method 200 (FIG. 2C) forms another
patterned mask 172 over the device 100. The patterned mask 172
provides openings 173 such as shown in FIGS. 12A and 12B, which are
cross-sectional views of the device 100 along the B-B line and the
C-C line of FIG. 1A, respectively. The openings 173 correspond to
the dashed boxes 113c of FIG. 1A. Particularly, the openings 173
expose portions of the gate structures 112 that are to be cut. The
openings 173 may be formed by a single patterning process or
multiple patterning processes. The hard mask layer 172 may include
titanium nitride, silicon nitride, amorphous silicon, yttrium
silicate (YSiO.sub.x), or other suitable hard mask material(s); and
may be deposited using CVD, PVD, ALD, or other suitable methods. In
an example, the operation 216 may form a patterned photoresist over
the hard mask layer 172 by photoresist coating, exposing,
post-exposure baking, and developing. Then, the operation 216
etches the hard mask layer 172 using the patterned photoresist as
an etch mask to form the opening 173. The etching process may
include wet etching, dry etching, reactive ion etching, or other
suitable etching methods. The patterned photoresist is removed
thereafter, for example, by resist stripping.
[0043] At operation 218, the method 200 (FIG. 2C) etches the gate
structures 112 through the openings 173. Referring to FIG. 13, the
operation 218 extends the opening 173 down and through the gate
structures 112, and also into the isolation structure 106 in an
embodiment. The etching process may use one or more etchants or a
mixture of etchants that etch the various layers in the gate
structures 112. In an exemplary embodiment, the conductive layer
110 includes TiSiN, TaN, TiN, W, or a combination thereof. To etch
such a conductive layer and the high-k dielectric layer 108, the
operation 218 may apply a dry etching process with an etchant
having the atoms of chlorine, fluorine, bromine, oxygen, hydrogen,
carbon, or a combination thereof. For example, the etchant may have
a gas mixture of Cl.sub.2, O.sub.2, a carbon-and-fluorine
containing gas, a bromine-and-fluorine containing gas, and a
carbon-hydrogen-and-fluorine containing gas. In one example, the
etchant includes a gas mixture of Cl.sub.2, O.sub.2, CF.sub.4,
BCl.sub.3, and CHF.sub.3. To ensure the isolation between the
remaining portions of the gate structure 112, the operation 218
performs some over-etching to extend the openings 173 into the
isolation structure 106 in some embodiments. Such over-etching is
carefully controlled to not expose the substrate 102.
[0044] At operation 220, the method 200 (FIG. 2C) fills the
trenches 173 with one or more dielectric materials to form the
dielectric features 114c, and performs a chemical mechanical
polishing (CMP) process to remove the patterned hard mask 172 and
to planarize the top surface of the device 100.
[0045] The resultant structure is shown in FIGS. 14A and 14B which
are cross-sectional views of the device 100 along the B-B line and
the C-C line of FIG. 1A, respectively. Particularly, the one or
more dielectric materials in the trench 171 form the dielectric
features 114a and 114b, and the one or more dielectric materials in
the trenches 173 form the dielectric features 114c. Since the
sidewalls of the gate structures 112 contain metallic materials, at
least the outer portion of the dielectric layer 114 (that is in
direct contact with the sidewalls of the gate structures 112) is
free of active chemical components such as oxygen. For example, the
outer portion of the dielectric layer 114 may include silicon
nitride and is free of oxygen or oxide. The dielectric layer 114
may include some oxide in the inner portion thereof in some
embodiments. Alternatively, the dielectric layer 114 may include
one uniform layer of silicon nitride and is free of oxide. The
dielectric layer 114 may be deposited using CVD, PVD, ALD, or other
suitable methods. In the present embodiment, the dielectric layer
114 is deposited using ALD to ensure that it completely fills the
trenches 171 and 173.
[0046] At operation 222, the method 200 (FIG. 2C) deposits a
dielectric layer 180 over the device 100, such as shown in FIG. 15,
which is a cross-sectional view of the device along the B-B line of
FIG. 1A. In an embodiment, the dielectric layer 180 is another ILD
layer and may comprise TEOS oxide, un-doped silicate glass, or
doped silicon oxide such as BPSG, FSG, PSG, BSG, and/or other
suitable dielectric materials. The dielectric layer 180 may be
formed by PECVD, FCVD, or other suitable methods.
[0047] At operation 224, the method 200 (FIG. 2C) etches contact
holes 182 into the device 100, including contact holes 182a
exposing the S/D features 162a and contact holes 182b exposing the
S/D features 162b, such as shown in FIG. 16, which is a
cross-sectional view of the device along the B-B line of FIG. 1A.
In an embodiment, the operation 224 includes coating a photoresist
layer over the device 100, exposing and developing the photoresist
layer to form openings, and etching the various layers 180, 166,
and 164 through the openings to form the contact holes 182.
Particularly, the etching process is tuned to selectively etch the
layers 180, 166, and 164 but not the S/D features 162 and the
dielectric layer 114. The etching process is dry etching in an
embodiment.
[0048] At operation 226, the method 200 (FIG. 2C) deposits one or
more conductive materials 184 into the contact holes 182, such as
shown in FIG. 17, which is a cross-sectional view of the device
along the B-B line of FIG. 1A. In an embodiment, the method 200 may
form silicide features over the exposed surfaces of the S/D
features 162 before depositing the conductive materials 184. In an
embodiment, the conductive materials 184 includes a barrier layer
such as TaN or TiN and a metal fill layer such as Al, Cu, or W. The
conductive materials 184 may be deposited using CVD, PVD, plating,
or other suitable methods.
[0049] At operation 228, the method 200 (FIG. 2C) performs a CMP
process to remove excessive materials 184 and to expose the
dielectric layer 114, such as shown in FIG. 18, which is a
cross-sectional view of the device along the B-B line of FIG. 1A.
Referring to FIG. 18, in the present embodiment, the CMP process of
the operation 228 separates the conductive materials 184 above the
two S/D features 162a to thereby form two S/D contacts that are
isolated by the dielectric feature 114a. Due to the large surface
area of the S/D features 162a, each of the two S/D contacts has a
sufficiently large interface with the underlying S/D feature 162a
for reducing S/D contact resistance.
[0050] At operation 230, the method 200 (FIG. 2C) performs further
steps to complete the fabrication of the device 100. For example,
the method 200 may form metal interconnects electrically connecting
the source, drain, gate terminals of various transistors to form a
complete IC.
[0051] Although not intended to be limiting, one or more
embodiments of the present disclosure provide many benefits to a
semiconductor device and the formation thereof. For example,
embodiments of the present disclosure provide a two-step cut metal
gate process where the first step etches dielectric layers but not
the metal gate and the second step etches the metal gate.
Embodiments of the present disclosure then utilize the first
etching step to separate previously merged S/D features that are
designed for individual transistors. This allows semiconductor fins
for individual transistors to be arranged closer in embodiments of
the present disclosure than in traditional devices and the S/D
features to be grown larger than traditional devices. This not only
increases device integration, but also reduces S/D contact
resistance.
[0052] In one exemplary aspect, the present disclosure is directed
to a method. The method includes providing a structure having a
substrate and first and second fins over the substrate and oriented
lengthwise generally along a first direction; epitaxially growing
semiconductor source/drain (S/D) features over the first and second
fins, wherein a first semiconductor S/D feature over the first fin
merges with a second semiconductor S/D feature over the second fin;
and performing a first etching process to an area between the first
and second fins, wherein the first etching process separates the
first and second semiconductor S/D features.
[0053] In an embodiment, the method further includes, before the
performing of the first etching process, forming gate structures
over the substrate and the first and second fins, wherein the gate
structures are oriented lengthwise generally along a second
direction perpendicular to the first direction, wherein the first
etching process is tuned to selectively etch the first and second
semiconductor S/D features but not the gate structures. In a
further embodiment, wherein the forming of the gate structures
includes forming temporary gate structures over the substrate and
the first and second fins; depositing a dielectric layer over the
temporary gate structures and the semiconductor S/D features;
removing the temporary gate structures, resulting in gate trenches
in the dielectric layer; and depositing the gate structures in the
gate trenches. In a further embodiment, the first etching process
is tuned to also etch the dielectric layer. In a further
embodiment, wherein the performing of the first etching process
results in a trench in the dielectric layer in the area between the
first and second fins, the method further includes depositing one
or more dielectric materials in the trench. In a further
embodiment, the method further includes etching a contact hole that
exposes both the first and the second semiconductor S/D features;
depositing a conductive material in the contact hole; and
performing a chemical mechanical planarization (CMP) process to
separate the conductive material into first and second portions,
wherein the first and second portions are electrically connected to
the first and second semiconductor S/D features respectively, and
are isolated from each other by the one or more dielectric
materials.
[0054] In another embodiment, the structure further includes a
third fin over the substrate and oriented lengthwise generally
along the first direction; the gate structures are also formed over
the third fin; and the first etching process is also performed to
an area between the second and the third fins. In a further
embodiment, the method further includes performing a second etching
process to the area between the second and the third fins, wherein
the second etching process is tuned to etch the gate
structures.
[0055] In an embodiment of the method, the first and second
semiconductor S/D features include p-type doped silicon germanium.
In another embodiment, wherein the performing of the first etching
process results in a trench between the first and the second
semiconductors S/D features, the method further includes depositing
one or more dielectric materials in the trench.
[0056] In another exemplary aspect, the present disclosure is
directed to a method. The method includes providing a structure
having: a substrate; first, second, and third fins over the
substrate and oriented lengthwise generally along a first
direction; gate structures over the first, second, and third fins
and oriented lengthwise generally along a second direction
perpendicular to the first direction; first and second epitaxial
semiconductor source/drain (S/D) features over the first and second
fins respectively, wherein the first and second epitaxial
semiconductor S/D features merge along the second direction; and a
first dielectric layer over the substrate, the first, second, and
third fins, and the first and second epitaxial semiconductor S/D
features, and filling space between the gate structures. The method
further includes performing a first etching process to a first area
between the first and the second fins and to a second area between
the second and the third fins, wherein the first etching process is
tuned to selectively etch the first and second epitaxial
semiconductor S/D features and the first dielectric layer but not
the gate structures. The method further includes performing a
second etching process to the second area, wherein the second
etching process is tuned to selectively etch the gate
structures.
[0057] In an embodiment of the method, the first etching process
separates the first and second epitaxial semiconductor S/D
features. In another embodiment, wherein the first etching process
results in a first trench between the first and the second
epitaxial semiconductor S/D features, the method further includes
depositing one or more dielectric materials in the first trench. In
a further embodiment, the first and second etching processes
collectively form a second trench between the second and third
fins, and the one or more dielectric materials are also deposited
in the second trench.
[0058] In an embodiment of the method, the first etching process
includes dry etching with an etchant having hydrogen fluoride and
ammonia. In another embodiment of the method, the second etching
process uses a chlorine-containing etchant.
[0059] In yet another exemplary aspect, the present disclosure is
directed to a semiconductor structure. The semiconductor structure
includes a substrate; first and second fins over the substrate and
oriented lengthwise generally along a first direction; first and
second epitaxial semiconductor source/drain (S/D) features over the
first and second fins respectively; and a first dielectric layer
disposed between and in physical contact with the first and the
second epitaxial semiconductor S/D features, resulting in a first
interface between the first dielectric layer and the first
epitaxial semiconductor S/D feature, and a second interface between
the first dielectric layer and the second epitaxial semiconductor
S/D feature, wherein the first and second interfaces are tilted
toward each other from top to bottom.
[0060] In an embodiment, the semiconductor structure further
includes gate structures over the first and second fins and
oriented lengthwise generally along the second direction; and a
second dielectric layer over the substrate, the first and second
fins, and the first and second epitaxial semiconductor S/D
features, and filling space between the gate structures, wherein
the first and the second dielectric layers include different
dielectric materials. In a further embodiment, the semiconductor
structure further includes a contact etch stop layer between the
second dielectric layer and the first and second epitaxial
semiconductor S/D features.
[0061] In another embodiment, the semiconductor structure further
includes a first conductive feature over the first epitaxial
semiconductor S/D feature; and a second conductive feature over the
second epitaxial semiconductor S/D feature, wherein the first
dielectric layer is disposed between the first and the second
conductive features.
[0062] In an embodiment of the semiconductor structure, the first
and second interfaces are two generally straight lines in a
cross-sectional view cut along a second direction perpendicular to
the first direction. In a further embodiment, each of the two
generally straight lines forms an angle ranging from 0 to 5 degrees
with normal of a top surface of the substrate.
[0063] In another embodiment of the semiconductor structure, each
of the first and second epitaxial semiconductor S/D features
includes p-type doped silicon germanium.
[0064] In yet another embodiment, the semiconductor structure
further includes a third fin over the substrate and oriented
lengthwise generally along the first direction; and a third
epitaxial semiconductor S/D feature over the third fin, wherein the
first dielectric layer is also disposed between the second and the
third epitaxial semiconductor S/D features. In a further
embodiment, the first dielectric layer is not in direct contact
with the third epitaxial semiconductor S/D feature. In another
further embodiment, each of the first and second epitaxial
semiconductor S/D features includes p-type doped silicon germanium;
and the third epitaxial semiconductor S/D feature includes n-type
doped silicon.
[0065] The foregoing outlines features of several embodiments so
that those of ordinary skill in the art may better understand the
aspects of the present disclosure. Those of ordinary skill in the
art should appreciate that they may readily use the present
disclosure as a basis for designing or modifying other processes
and structures for carrying out the same purposes and/or achieving
the same advantages of the embodiments introduced herein. Those of
ordinary skill in the art should also realize that such equivalent
constructions do not depart from the spirit and scope of the
present disclosure, and that they may make various changes,
substitutions, and alterations herein without departing from the
spirit and scope of the present disclosure.
* * * * *