U.S. patent application number 14/942678 was filed with the patent office on 2017-05-18 for method and structure for semiconductor mid-end-of-line (meol) process.
The applicant listed for this patent is Taiwan Semiconductor Manufacturing Company, Ltd.. Invention is credited to Zhao-Cheng Chen, Chien-Hua Huang, Chung-Ju Lee, Chih Wei Lu, Hsiang-Ku Shen.
Application Number | 20170141104 14/942678 |
Document ID | / |
Family ID | 58546584 |
Filed Date | 2017-05-18 |
United States Patent
Application |
20170141104 |
Kind Code |
A1 |
Lu; Chih Wei ; et
al. |
May 18, 2017 |
METHOD AND STRUCTURE FOR SEMICONDUCTOR MID-END-OF-LINE (MEOL)
PROCESS
Abstract
A method of forming a semiconductor device provides a precursor
that includes a substrate having first and second regions, wherein
the first region includes an insulator and the second region
includes source, drain, and channel regions of a transistor. The
precursor further includes gate stacks over the insulator, and gate
stacks over the channel regions. The precursor further includes a
first dielectric layer over the gate stacks. The method further
includes partially recessing the first dielectric layer; forming a
second dielectric layer over the recessed first dielectric layer;
and forming a contact etch stop (CES) layer over the second
dielectric layer. In an embodiment, the method further includes
forming gate via holes over the gate stacks, forming source and
drain (S/D) via holes over the S/D regions, and forming vias in the
gate via holes and S/D via holes.
Inventors: |
Lu; Chih Wei; (Hsinchu City,
TW) ; Lee; Chung-Ju; (Hsinchu City, TW) ;
Huang; Chien-Hua; (Miaoli County, TW) ; Shen;
Hsiang-Ku; (Hsinchu City, TW) ; Chen; Zhao-Cheng;
(New Taipei City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Company, Ltd. |
Hsin-Chu |
|
TW |
|
|
Family ID: |
58546584 |
Appl. No.: |
14/942678 |
Filed: |
November 16, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 23/5286 20130101;
H01L 21/76832 20130101; H01L 21/823475 20130101; H01L 23/485
20130101; H01L 21/76807 20130101; H01L 23/5226 20130101; H01L
21/76816 20130101; H01L 29/66545 20130101; H01L 21/76834 20130101;
H01L 27/088 20130101; H01L 29/66515 20130101; H01L 27/0207
20130101; H01L 21/467 20130101; H01L 29/0649 20130101; H01L 29/665
20130101; H01L 21/31055 20130101; H01L 21/7684 20130101; H01L
23/528 20130101; H01L 21/76877 20130101 |
International
Class: |
H01L 27/088 20060101
H01L027/088; H01L 23/528 20060101 H01L023/528; H01L 21/8234
20060101 H01L021/8234; H01L 27/02 20060101 H01L027/02; H01L 21/768
20060101 H01L021/768; H01L 21/3105 20060101 H01L021/3105 |
Claims
1. A method of forming a semiconductor device, the method
comprising: providing a device that includes: a substrate having
first and second regions, wherein the first region includes an
insulator and the second region includes source, drain, and channel
regions of a transistor; first and second gate stacks over the
insulator; a third gate stack over the channel region; and a first
dielectric layer over the first, second, and third gate stacks;
partially recessing the first dielectric layer, resulting in a
recessed first dielectric layer; forming a second dielectric layer
over the recessed first dielectric layer; and forming a contact
etch stop (CES) layer over the second dielectric layer.
2. The method of claim 1, further comprising: forming an
inter-layer dielectric (ILD) layer over the CES layer; etching
first and second holes in the ILD layer over the second and third
gate stacks respectively; etching the CES layer and the second
dielectric layer through the first and second holes to expose the
recessed first dielectric layer over the second and third gate
stacks; etching the ILD layer in the first region to expose the CES
layer; etching the CES layer in the first region to expose the
second dielectric layer; and etching the recessed first dielectric
layer to expose the second and third gate stacks, while the first
gate stack remains covered by the recessed first dielectric layer
and the second dielectric layer over the recessed first dielectric
layer.
3. The method of claim 2, wherein the first hole is etched in an
area of the semiconductor device that has a smaller gate via pitch
than where the second hole is etched.
4. The method of claim 2, wherein the first hole is etched in an
area of the semiconductor device that has a greater gate via pitch
than where the second hole is etched.
5. The method of claim 2, wherein the etching of the CES layer and
the second dielectric layer includes an etching process that is
tuned to remove the second dielectric layer while the recessed
first dielectric layer remains substantially unchanged.
6. The method of claim 2, wherein the etching of the recessed first
dielectric layer includes an etching process that is tuned to
remove the recessed first dielectric layer while the second
dielectric layer remains substantially unchanged.
7. The method of claim 2, further comprising, before the etching of
the ILD layer in the first region: etching via holes in the ILD
layer over the source and drain (S/D) regions.
8. The method of claim 7, wherein: the device further includes: S/D
contacts over the S/D regions; and a third dielectric layer over
the S/D contacts; and the etching of the CES layer in the first
region includes etching the CES layer and the third dielectric
layer through the via holes to expose the S/D contacts.
9. The method of claim 8, further comprising: depositing a metal
layer over the first and second regions, wherein the metal layer is
in electrical communication with the second and third gate stacks
and the S/D contacts, and wherein the metal layer is isolated from
the first gate stack by at least the recessed first dielectric
layer and the second dielectric layer.
10. The method of claim 9, further comprising: performing a
chemical mechanical planarization (CMP) process to remove portions
of the metal layer and the ILD layer until the CES layer is exposed
over the second region.
11. The method of claim 1, wherein the partially recessing of the
first dielectric layer reduces a thickness of the first dielectric
layer by about 10% to about 90%.
12. A method of forming a semiconductor device, the method
comprising: providing a device that includes: a substrate having a
first region; first and second gate stacks over the first region;
and a first dielectric layer over the first and second gate stacks;
partially recessing the first dielectric layer, resulting in a
recessed first dielectric layer; forming a second dielectric layer
over the recessed first dielectric layer; forming a patterning
layer over the second dielectric layer; etching a hole in the
patterning layer over the second gate stack; etching a first
portion of the second dielectric layer through the hole to expose a
first portion of the recessed first dielectric layer; removing the
patterning layer over the first region; and etching the first
portion of the recessed first dielectric layer to expose the second
gate stack, while the first gate stack remains covered by a second
portion of the recessed first dielectric layer and a second portion
of the second dielectric layer.
13. The method of claim 12, further comprising: forming a metal
layer over the first and second gate stacks, wherein the metal
layer is in electrical communication with the second gate stack and
is isolated from the first gate stack by at least the second
portion of the recessed first dielectric layer and the second
portion of the second dielectric layer.
14. The method of claim 12, wherein the first and second gate
stacks are disposed over an insulator in the first region.
15. The method of claim 12, wherein the etching of the first
portion of the second dielectric layer includes an etching process
that is tuned to remove the first portion of the second dielectric
layer while the first portion of the recessed first dielectric
layer remains substantially unchanged.
16. The method of claim 12, wherein the etching of the first
portion of the recessed first dielectric layer includes an etching
process that is tuned to remove the first portion of the recessed
first dielectric layer while the second portion of the second
dielectric layer remains substantially unchanged.
17. The method of claim 12, wherein the partially recessing of the
first dielectric layer reduces a thickness of the first dielectric
layer by about 10% to about 90%.
18-20. (canceled)
21. A method, comprising: providing a device that includes: a
substrate having first and second regions; first and second gate
stacks over an insulator in the first region; a third gate stack
over an active region in the second region; and a first dielectric
layer over the first, second, and third gate stacks; partially
recessing the first dielectric layer, resulting in a recessed first
dielectric layer; forming a second dielectric layer over the
recessed first dielectric layer; forming a contact etch stop (CES)
layer over the second dielectric layer; forming an inter-layer
dielectric (ILD) layer over the CES layer; etching holes over the
second and third gate stacks through the ILD layer, the CES layer,
and the second dielectric layer, thereby exposing the recessed
first dielectric layer over the second and third gate stacks; after
the etching of the holes, removing the ILD layer in the first
region; and after the removing of the ILD layer in the first
region, removing the CES layer in the first region to expose the
second dielectric layer over the first gate stack.
22. The method of claim 21, wherein the removing of the ILD layer
in the first region further includes: etching another hole over a
source/drain region adjacent the third gate stack, wherein the
another hole exposes the CES layer in the second region.
23. The method of claim 22, wherein the removing of the CES layer
in the first region further includes: extending the another hole to
expose a contact feature over the source/drain region.
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 and, for these
advancements to be realized, similar developments in IC processing
and manufacturing are needed.
[0002] For example, in the mid-end-of-line (MEOL) processes, it is
typical that gate via holes are etched in some areas that have
dense vias and in some areas that have isolated vias. It is
difficult to control via etching depth in both the dense and
isolated via areas when the vias are partially etched. As a result,
the via depth varies from one area to another. The via depth
variation may cause issues in subsequent fabrication. For example,
it may cause a leakage concern when gate contacts and source/drain
(S/D) contacts are formed in a later step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] Aspects of the present disclosure are best understood from
the following detailed description when read with the accompanying
figures. It is emphasized that, in accordance with the standard
practice in the industry, various features are not drawn to scale.
In fact, the dimensions of the various features may be arbitrarily
increased or reduced for clarity of discussion.
[0004] FIGS. 1A and 1B are a flow chart of a method of forming a
semiconductor device according to various aspects of the present
disclosure.
[0005] FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H, 2I, 2J, 2K, and 2L are
cross-sectional views of a portion of a semiconductor device
constructed according to the method in FIGS. 1A and 1B, in
accordance with an embodiment.
[0006] FIG. 3 illustrates areas of an IC that have different gate
pitches.
[0007] FIG. 4 illustrates areas of an IC that have different via
pitches.
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 methods of forming the same. More particularly, the
present disclosure is related to MEOL processes in semiconductor
manufacturing. One object of the present disclosure is to provide
methods and structures for improving the MEOL processes in view of
via depth loading issues associated with unevenly distributed vias
in different areas of an IC.
[0011] FIGS. 1A and 1B show a flow chart of a method 10 of forming
a semiconductor device 100, according to various aspects of the
present disclosure. The method 10 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 10, and some operations
described can be replaced, eliminated, or moved around for
additional embodiments of the method. The method 10 is described
below in conjunction with FIGS. 2A-2L which are cross-sectional
views of the semiconductor device 100 in various stages of a
manufacturing process.
[0012] The semiconductor device 100 is provided for illustration
purposes and does not necessarily limit the embodiments of the
present disclosure to any number of devices, any number of regions,
or any configuration of structures or regions. Furthermore, the
semiconductor device 100 as shown in FIGS. 2A-2L may be an
intermediate device fabricated during processing of an IC, or a
portion thereof, that may comprise static random access memory
(SRAM) and/or logic circuits, passive components such as resistors,
capacitors, and inductors, and active components such as p-type
field effect transistors (PFETs), n-type FETs (NFETs), multi-gate
FETs such as FinFETs, metal-oxide semiconductor field effect
transistors (MOSFETs), complementary metal-oxide semiconductor
(CMOS) transistors, bipolar transistors, high voltage transistors,
high frequency transistors, other memory cells, and combinations
thereof.
[0013] At operation 12, the method 10 (FIG. 1A) provides a
precursor of the device 100 as shown in FIG. 2A. For the
convenience of discussion, the precursor of the device 100 is also
referred to as the device 100. Referring to FIG. 2A, the device 100
includes a substrate 102 and various features formed therein or
thereon. The substrate 102 includes two substrate regions 102A and
102B. In the present embodiment, the substrate region 102A includes
an insulator such as a shallow trench isolation (STI), while the
substrate region 102B includes active regions for forming
transistors. In the present embodiment, the two substrate regions
102A and 102B serve for different purposes for the device 100. For
example, the substrate region 102A may be used for forming power
rails such as voltage supply and/or ground plane, while the
substrate region 102B may be used for forming logic circuits. As
shown in FIG. 1A, the substrate region 102B includes various source
and drain (S/D) regions 104 and channel regions 106 between the S/D
regions 104.
[0014] Still referring to FIG. 1A, the device 100 further includes
a plurality of gate stacks 108A, 108B, 108C, 108D, 108E, 108F, and
108G, wherein the gate stacks 108A-C are disposed over the
substrate region 102A, and the gate stacks 108D-G are disposed
adjacent to the channel regions 106 in the substrate region 102B.
The device 100 further includes a dielectric layer 110 disposed
over each gate stack 108A-G, and a gate spacer 112 on sidewalls of
each gate stack 108A-G and on sidewalls of the respective
dielectric layer 110. In the present embodiment, the device 100
includes a contact etch stop (CES) layer 114 over the substrate 102
and on sidewalls of the gate spacer 112, and further includes an
inter-layer dielectric (ILD) layer 116 over the CES layer 114. The
device 100 further includes contacts 118A and 118B over the
substrate regions 102A and 102B respectively. Over the substrate
region 102A, the contacts 118A are disposed over the CES layer 114
between some of the gate stacks (e.g., between the gate stacks 108A
and 108B). In the present embodiment, the contacts 118A are used
for forming power rails. Therefore, they are also referred to as
power contacts 118A. Over the substrate region 102B, the contacts
118B are disposed over the S/D regions 104 and in electrical
communication with the respective S/D regions 104. Therefore, they
are also referred to as S/D contacts 118B. The device 100 further
includes a dielectric layer 120 over the contacts 118A-B. The
various features (or components) of the device 100 are further
described below.
[0015] The substrate 102 is a silicon substrate in the present
embodiment. In alternative embodiments, the substrate 102 includes
other elementary semiconductors such as germanium; a compound
semiconductor such as silicon carbide, gallium arsenide, indium
arsenide, and indium phosphide; or an alloy semiconductor, such as
silicon germanium carbide, gallium arsenic phosphide, and gallium
indium phosphide. In embodiments, the substrate 102 may include
silicon on insulator (SOI) substrate, be strained and/or stressed
for performance enhancement, include epitaxial regions, include
isolation regions, include doped regions, and/or include other
suitable features and layers.
[0016] The substrate region 102A includes an insulator (or an
isolation structure), and may be formed of silicon oxide, silicon
nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), a
low-k dielectric material, and/or other suitable insulating
material. The insulator may be STI features. In an embodiment, the
insulator is formed by etching trenches in the substrate 102,
filling the trenches with an insulating material, and performing a
chemical mechanical planarization (CMP) process to the substrate
102 including the insulating material. The substrate region 102A
may include other isolation structure(s) such as field oxide and
LOCal Oxidation of Silicon (LOCOS). The substrate region 102A may
include a multi-layer isolation structure.
[0017] The substrate region 102B may include n-type doped regions
and/or p-type doped regions for forming active devices such as
transistors. The S/D regions 104 may include heavily doped S/D
(HDD), lightly doped S/D (LDD), raised regions, strained regions,
epitaxially grown regions, and/or other suitable features. The S/D
regions 104 may be formed by etching and epitaxial growth, halo
implantation, S/D implantation, S/D activation, and/or other
suitable processes. In an embodiment, the S/D regions 104 further
include silicidation or germanosilicidation. For example,
silicidation may be formed by a process that includes depositing a
metal layer, annealing the metal layer such that the metal layer is
able to react with silicon to form silicide, and then removing the
non-reacted metal layer. In an embodiment, the substrate region
102B includes fin-like active regions for forming multi-gate FETs
such as FinFETs. To further this embodiment, the S/D regions 104
and the channel regions 106 may be formed in or on the fins. The
channel regions 106 are sandwiched between a pair of S/D regions
104. The channel region 106 conducts currents between the
respective S/D regions 104 when the semiconductor device 100 is in
use.
[0018] Each of the gate stacks 108A-G may be a multi-layer
structure. Further, the gate stacks 108A-G may have the same or
different structures and materials among them. The following
description applies to any one of the gate stacks 108A-G. In an
embodiment, the gate stacks 108A-G include an interfacial layer and
a polysilicon (or poly) layer over the interfacial layer. In some
embodiments, the gate stacks 108A-G may further include a gate
dielectric layer and a metal gate layer disposed between the
interfacial layer and the poly layer. In some embodiments, the gate
stacks 108A-G include one or more metal layers in place of the poly
layer. In various embodiments, the interfacial layer may include a
dielectric material such as silicon oxide (SiO.sub.2) or silicon
oxynitride (SiON), and may be formed by chemical oxidation, thermal
oxidation, atomic layer deposition (ALD), chemical vapor deposition
(CVD), and/or other suitable methods. The poly layer can be formed
by suitable deposition processes such as low-pressure chemical
vapor deposition (LPCVD) and plasma-enhanced CVD (PECVD). The gate
dielectric layer may include a high-k dielectric layer such as
hafnium oxide (HfO.sub.2), 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), other suitable
metal-oxides, or combinations thereof; and may be formed by ALD
and/or other suitable methods. The metal gate layer may include a
p-type work function metal layer or an n-type work function metal
layer. The p-type work function metal layer comprises a metal
selected from, but not limited 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 metal layer comprises a metal selected from, but not
limited to, the group of titanium (Ti), aluminum (Al), tantalum
carbide (TaC), tantalum carbide nitride (TaCN), tantalum silicon
nitride (TaSiN), or combinations thereof. The p-type or n-type work
function metal layer may include a plurality of layers and may be
deposited by CVD, PVD, and/or other suitable process. The one or
more metal layers may include aluminum (Al), tungsten (W), cobalt
(Co), copper (Cu), and/or other suitable materials, and may be
formed by CVD, PVD, plating, and/or other suitable processes. The
gate stacks 108A-G may be formed in a gate-first process or a
gate-last process (i.e., a replacement gate process).
[0019] The dielectric layer 110 is disposed over the gate stacks
108A-G. In an embodiment, the dielectric layer 110 includes a metal
oxide, a metal nitride, or other suitable dielectric materials. For
example, the metal oxide may be titanium oxide (TiO.sub.2),
aluminum oxide (Al.sub.2O.sub.3), or other metal oxides. For
example, the metal nitride may be titanium nitride (TiN), aluminum
nitride (AlN), aluminum oxynitride (AlON), tantalum nitride (TaN),
or other metal nitrides. The dielectric layer 110 may be formed
over the gate stacks 108A-G by one or more deposition and etching
processes.
[0020] The gate spacer 112 may be a single layer or multi-layer
structure. In an embodiment, the gate spacer 112 includes a low-k
(e.g., k<7) dielectric material. In some embodiments, the gate
spacer 112 includes a dielectric material, such as silicon oxide
(SiO.sub.2), silicon nitride (SiN), silicon oxynitride (SiON),
other dielectric material, or combination thereof. In an example,
the gate spacer 112 is formed by blanket depositing a first
dielectric layer (e.g., a SiO.sub.2 layer having a uniform
thickness) as a liner layer over the device 100 and a second
dielectric layer (e.g., a SiN layer) as a main D-shaped spacer over
the first dielectric layer, and then, anisotropically etching to
remove portions of the dielectric layers to form the gate spacer
112. In the present embodiment, the gate spacer 112 is disposed on
sidewalls of the gate stacks 108A-G and on sidewalls of the
dielectric layer 110.
[0021] The CES layer 114 may include a dielectric material such as
silicon nitride (SiN), silicon oxide (SiO.sub.2), silicon
oxynitride (SiON), and/or other materials. The CES layer 114 may be
formed by PECVD process and/or other suitable deposition or
oxidation processes. The ILD layer 116 may include materials such
as 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 116 may be deposited by a PECVD process, a flowable
CVD (FCVD) process, or other suitable deposition technique. In an
embodiment, the CES layer 114 is deposited as a blanket layer over
the substrate 102 covering various structures thereon, and the ILD
layer 116 is deposited over the CES layer 114. Subsequently,
portions of the ILD layer 116 and the CES layer 114 are etched back
to form trenches for depositing the contacts 118A-B. Over the
substrate region 102A, portions of the ILD layer 116 are etched
(e.g., between the gate stacks 108A and 108B) until the CES layer
114 is exposed. As a result, portions of the CES layer 114 remain
over the substrate region 102A between adjacent gate spacers 112.
Over the substrate region 102B, portions of the ILD layer 116 and
the CES layer 114 are etched (e.g., between the gate stacks 108E
and 108F) to expose the S/D regions 104 underneath.
[0022] The contacts 118A-B are separated by the structures
including the respective gate stacks 108A-G, the gate spacer 112,
and the CES layer 114. In an embodiment, the contacts 118A-B
include a metal such as aluminum (Al), tungsten (W), copper (Cu),
cobalt (Co), combinations thereof, or other suitable conductive
material. In an embodiment, the contact metal is deposited using a
suitable process, such as CVD, PVD, plating, and/or other suitable
processes. After the contact metal is deposited, it may be etched
back to leave room for depositing the dielectric layer 120.
[0023] The dielectric layer 120 may include a metal oxide (e.g.,
TiO.sub.2 and Al.sub.2O.sub.3), a metal nitride (e.g., TiN, AlN,
AlON, and TaN), or other suitable dielectric materials. In various
embodiments, the dielectric layers 110 and 120 may be of the same
or different materials. The dielectric layer 120 may be deposited
using PVD, CVD, or other deposition methods. In an embodiment,
after the dielectric layer 120 is deposited, a CMP process is
performed to planarize a top surface the device 100. As a result,
top surfaces of the various layers, 110, 112, 114, 116, and 120,
become co-planar.
[0024] At operation 14, the method 10 (FIG. 1A) partially recesses
the dielectric layer 110. Referring to FIG. 2B, the dielectric
layer 110 over each of the gate stacks 108A-G is recessed. In an
embodiment, the operation 14 includes an etching process that is
tuned to etch the dielectric layer 110 while the other layers, 112,
114, 116, and 120, remain substantially unchanged in the etching
process. In embodiments, the operation 14 may use a dry etching, a
wet etching, or other suitable etching 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.
[0025] In an embodiment, there are different gate pitches (or gate
densities) in different areas (or portions) of the device 100. Some
examples are illustrated in FIG. 3 as a top view of two areas 302
and 304 of the device 100. Referring to FIG. 3, the area 302
includes gate stacks 306 having a gate pitch P1 and the area 304
includes gate stacks 308 having a gate pitch P2 that is greater
than P1. The gate pitches P1 and P2 may be given as center-line to
center-line pitches (as shown) or edge to edge pitches. As
illustrated, the area 302 has a smaller gate pitch, hence a higher
gate density, than the area 304. In embodiments, the substrate
regions 102A and 102B may correspond to areas of the device 100
that have the same or different gate pitches. For example, the
substrate region 102A may correspond to a higher gate pitch area
and the substrate region 102B may correspond to a lower gate pitch
area, or vice versa. When the dielectric layer 110 is partially
etched (FIG. 2B), which is usually controlled by a timer, the
different gate pitches in different areas of the device 100 create
different etch loadings. As a result, the dielectric layer 110 is
etched more (or deeper) in some areas and less (or shallower) in
some other areas. In the present embodiment, another dielectric
layer will be formed over the recessed dielectric layer 110, as
will be discussed below. Therefore, the different thicknesses of
the recessed dielectric layer 110 will not cause issues for
subsequent manufacturing processes. In the present embodiment, the
operation 14 may reduce a thickness of the dielectric layer 110 by
about 10% to about 90%, which provides a broad process window.
[0026] At operation 16, the method 10 (FIG. 1A) forms a dielectric
layer 122 over the recessed dielectric layer 110. Referring to FIG.
2C, the dielectric layer 122 is disposed over the recessed
dielectric layer 110 over each of the gate stacks 108A-G. In an
embodiment, the operation 16 includes depositing a dielectric
material over the device 100 and filling in the trenches, followed
by a CMP process to remove excessive dielectric materials. Due to
the different thicknesses of the recessed dielectric layer 110 as
discussed above, the dielectric layer 122 may have different
thicknesses over different gate stacks. For example, the dielectric
layer 122 over the gate stacks 108A and 108D may be of different
thicknesses. The dielectric layer 122 may include a metal oxide, a
metal nitride, or other suitable dielectric materials. For example,
the metal oxide may be TiO.sub.2, Al.sub.2O.sub.3, or other metal
oxides. For example, the metal nitride may be TiN, AlN, AlON, TaN,
or other metal nitrides. In various embodiments, the dielectric
layer 122 includes a material different from that of the dielectric
layer 110. The dielectric layer 122 may be formed by ALD, PVD, CVD,
spin-on coating, or other suitable deposition methods.
[0027] At operation 18, the method 10 (FIG. 1A) forms another CES
layer 124 over the various layers 112, 114, 116, 120, and 122. At
operation 20, the method 10 (FIG. 1A) forms another ILD layer 126
(also referred to as a patterning layer 126) over the CES layer
124. Referring to FIG. 2D, the CES layer 124 may include a
dielectric material such as SiN, SiO.sub.2, and SiON. The ILD layer
126 may include an oxide such as TEOS, BPSG, FSG, PSG, and BSG. The
ILD layer 126 and the CES layer 124 may include the same materials
as the ILD layer 116 and the CES layer 114 respectively, or include
different materials. Furthermore, in the present embodiment, the
CES layer 124 may include the same material as the dielectric layer
110 and/or the dielectric layer 120. The CES layer 124 may be
formed by a PECVD process or other suitable deposition or oxidation
processes. The ILD layer 126 may be deposited by a PECVD process, a
FCVD process, or other suitable deposition processes.
[0028] At operation 22, the method 10 (FIG. 1A) etches the ILD
layer 126 to form gate via holes 128 over some of the gate stacks
108A-G. Referring to FIG. 2E, gate via holes 128 are formed in the
ILD layer 126 over the gate stacks 108B, 108E, 108F, and 108G, but
not over the gate stacks 108A and 108C in this cross-sectional
view. In an embodiment, operation 22 includes a photolithography
process and an etching process. The photolithography process may
include forming a photoresist (or resist) over the ILD layer 126,
exposing the resist to a pattern that defines various geometrical
shapes for the gate via holes 128, performing post-exposure bake
processes, and developing the resist to form a masking element
including the resist. The masking element, or a derivative thereof,
is then used for etching recesses into the ILD layer 126. The
masking element (e.g., a patterned resist) is subsequently removed.
The etching processes may include one or more dry etching
processes, wet etching processes, and other suitable etching
techniques. The CES layer 124 has sufficient etch selectivity with
respect to the ILD layer 126, and serves as an etch stop in the
etching process.
[0029] Similar to the scenario with different gate pitches
discussed above, there may be different gate via pitches in
different areas of the device 100. Some examples are illustrated in
FIG. 4 as a top view of four areas 402, 404, 406, and 408 of the
device 100. Referring to FIG. 4, the area 402 has a gate via pitch
P3, the area 404 has a gate via pitch P4 that is greater than P3,
the area 406 has a gate via pitch P5 that is greater than P4, and
the area 408 has a gate via pitch (not labeled) that is greater
than P5. In embodiments, the substrate regions 102A and 102B may
each correspond to a dense via area (having a smaller gate via
pitch) or an isolated via area (having a greater gate via pitch).
However, since the ILD layer 126 is fully etched in the operation
22 and the two layers 126 and 124 have sufficient etch selectivity,
the difference in gate via pitches does not create much difference
in the structure so formed.
[0030] At operation 24, the method 10 (FIG. 1B) etches the CES
layer 124 and the dielectric layer 122 through the gate via holes
128, thereby exposing a portion of the recessed dielectric layer
110 over the respective gate stacks 108B, 108E, 108F, and 108G
(FIG. 2F). The etching processes may include one or more dry
etching processes, wet etching processes, and other suitable
etching techniques. In the present embodiment, the operation 24
includes a selective etching process, i.e., an etching process that
is tuned to remove the dielectric layer 122 while the dielectric
layer 110 remains substantially unchanged in the etching process.
As a result, the operation 24 successfully exposes and stops at the
recessed dielectric layer 110 over the respective gate stacks,
despite that the dielectric layer 122 may be of different
thicknesses over the respective gate stacks and/or there may be
different via pitches over the substrate regions 102A and 102B.
[0031] At operation 26, the method 10 (FIG. 1B) etches the ILD
layer 126 over some of the S/D contacts 118B to form S/D via holes
130 in the ILD layer 126 (FIG. 2G). In an embodiment, the operation
26 includes a photolithography process and an etching process. For
example, the photolithography process forms a masking element
(e.g., a patterned resist) over the device 100, which defines the
S/D via holes 130; and the etching process etches the ILD layer 126
with the masking element as an etch mask. The etching processes may
include one or more dry etching processes, wet etching processes,
and other suitable etching techniques. The CES layer 124 has
sufficient etch selectivity with respect to the ILD layer 126, and
serves as an etch stop in the etching process. The masking element
is subsequently removed.
[0032] At operation 28, the method 10 (FIG. 1B) etches the ILD
layer 126 over the substrate region 102A. Referring to FIG. 2H, in
the present embodiment, the operation 28 includes a
photolithography process and an etching process. The
photolithography process forms a masking element (e.g., a patterned
resist) over the device 100, defining trenches for forming power
rails over the first substrate region 102A. The etching process
etches the ILD layer 126 through the masking element. The etching
process may include one or more dry etching processes, wet etching
processes, and other suitable etching techniques. The etching
process is tuned to remove the ILD layer 126 while the CES layer
124 and the recessed dielectric layer 110 remain substantially
unchanged. The masking element is subsequently removed.
[0033] At operation 30, the method 10 (FIG. 1B) etches the CES
layer 124 and the dielectric layer 120 over the device 100.
Referring to FIG. 2I, over the substrate region 102A, the CES layer
124 and the dielectric layer 120 (see FIG. 2H) are etched. The
recessed dielectric layer 110 and the dielectric layer 122 protect
the gate stacks 108A-C from the etching process. As a result, the
power contacts 118A and the ILD layer 116 are exposed. Still
referring to FIG. 2I, over the substrate region 102B, the CES layer
124 and the dielectric layer 120 are etched through the S/D via
holes 130, thereby exposing the S/D contacts 118B thereunder. The
ILD layer 126 and the recessed dielectric layer 110 protect other
structures, including the gate stacks 108D-G, from the etching
process. The etching process may include one or more dry etching
processes, wet etching processes, and other suitable etching
techniques.
[0034] At operation 32, the method 10 (FIG. 1B) etches the portions
of the recessed dielectric layer 110 that are exposed in the gate
vias 128. The etching process may include one or more dry etching
processes, wet etching processes, and other suitable etching
techniques. In the present embodiment, the etching process is tuned
to remove the recessed dielectric layer 110 while the dielectric
layer 122 remains substantially unchanged. Furthermore, other
layers of material, including the gate spacer 112, the CES layers
114 and 124, the ILD layers 116 and 126, and the contacts 118A and
118B, remain substantially unchanged in the etching process in the
present embodiment. Referring to FIG. 2J, top surfaces of the gate
stacks 108A, 108E, 108F, and 108G are exposed as a result of the
etching process, while the gate stacks 108A and 108C are still
covered by a stack of the dielectric layer 122 over the recessed
dielectric layer 110. In the present embodiment, the dielectric
layer 122 serves as a protection layer for the recessed dielectric
layer 110. Without the dielectric layer 122, the recessed
dielectric layer 110 over the gate stacks 108A and 108C would also
be etched in the operation 32. In some cases, the depth of etching
is difficult to control in view of different via pitches in
different areas of the device 100. Consequently, the gate stacks
108A and 108C might be inadvertently exposed, causing leakage
concerns or device defects. In the present embodiment, the
dielectric layers 110 and 122 have sufficient etch selectivity such
that the recessed dielectric layer 110 over the gate stacks 108B,
108E, 108F, and 108G are fully etched while the gate stacks 108A
and 108C remain protected by the dielectric layer 122 over the
recessed dielectric layer 110.
[0035] At operation 34, the method 10 (FIG. 1B) deposits a metal
layer 132 over the device 100, filling in the various trenches and
via holes thereon. Referring to FIG. 2K, the metal layer 132 is in
electrical communication with: the gate stacks 108A, 108E, 108F,
and 108G; the power contacts 118A (between the gate stacks 108A and
108B and between the gate stacks 108C and 108D); and the S/D
contacts 118B (between the gate stacks 108E and 108F and between
the gate stacks 108F and 108G). The metal layer 132 is electrically
isolated from the gate stacks 108A, 108C, and 108D by at least the
recessed dielectric layer 110 and the dielectric layer 122. In the
present embodiment, the metal layer 132 may include aluminum (Al),
tungsten (W), cobalt (Co), copper (Cu), and/or other suitable
materials, and may be formed by CVD, PVD, plating, and/or other
suitable processes.
[0036] At operation 36, the method 10 (FIG. 1B) recesses the metal
layer 132. Referring to FIG. 2L, in the present embodiment, the
operation 36 also recesses the ILD layer 126 over the substrate
region 102B. In an embodiment, the operation 36 includes a CMP
process that removes the metal layer 132 and the ILD layer 126
until the CES layer 124 is exposed over the substrate region 102B.
As a result, various metal features are formed in the device 100.
Over the substrate region 102A, a power rail 134 is formed, which
includes a portion of the metal layer 132 and the power contacts
118A. The power rail 134 is in electrical communication with the
gate stack 108B, but is electrically isolated from the gate stacks
108A and 108C by at least the dielectric layer 122 and the recessed
dielectric layer 110. Over the substrate region 102B, gate vias (or
gate plugs) 136 are formed and are electrically connected to the
gate stacks 108E, 108F, and 108G; and S/D vias (or S/D plugs) 138
are formed and are electrically connected to the S/D regions 104
through the S/D contacts 118B.
[0037] At operation 38, the method 10 (FIG. 1B) proceeds to further
steps to complete the fabrication of the device 100. For example,
the method 10 may form multi-layer interconnect structure that
connects the gate vias 136 and the S/D vias 138 with other parts of
the device 100 to form a complete IC.
[0038] Although not intended to be limiting, one or more
embodiments of the present disclosure provide many benefits to a
semiconductor device and a formation process thereof. For example,
when forming gate and S/D vias in an MEOL process, embodiments of
the present disclosure can reliably connect some, but not all, gate
stacks to a power rail, despite of different via pitches (or via
densities) in different areas of the semiconductor device. Those
gate stacks that are not intended to be connected to the power rail
are fully protected by at least two dielectric layers. This
prevents power punch-through issues as well as gate and contact
leakage issues. The provided subject matter can be easily
integrated into existing IC fabrication flow.
[0039] In one exemplary aspect, the present disclosure is directed
to a method of forming a semiconductor device. The method includes
providing a precursor that includes a substrate having first and
second regions, wherein the first region includes an insulator and
the second region includes source, drain, and channel regions of a
transistor. The precursor further includes first and second gate
stacks over the insulator; a third gate stack over the channel
region; and a first dielectric layer over the first, second, and
third gate stacks. The method further includes partially recessing
the first dielectric layer, forming a second dielectric layer over
the recessed first dielectric layer, and forming a contact etch
stop (CES) layer over the second dielectric layer. In an
embodiment, the method further includes forming an inter-layer
dielectric (ILD) layer over the CES layer, etching first and second
holes in the ILD layer over the second and third gate stacks
respectively, etching the CES layer and the second dielectric layer
through the first and second holes to expose the recessed first
dielectric layer over the second and third gate stacks, etching the
ILD layer in the first region to expose the CES layer, and etching
the CES layer in the first region to expose the second dielectric
layer. The method further includes etching the recessed first
dielectric layer to expose the second and third gate stacks, while
the first gate stack remains covered by the recessed first
dielectric layer and the second dielectric layer over the recessed
first dielectric layer.
[0040] In another exemplary aspect, the present disclosure is
directed to a method of forming a semiconductor device. The method
includes providing a precursor that includes a substrate having a
first region, first and second gate stacks over the first region,
and a first dielectric layer over the first and second gate stacks.
The method further includes partially recessing the first
dielectric layer, forming a second dielectric layer over the
recessed first dielectric layer, forming a patterning layer over
the second dielectric layer, etching a hole in the patterning layer
over the second gate stack, etching a first portion of the second
dielectric layer through the hole to expose a first portion of the
recessed first dielectric layer, and removing the patterning layer
over the first region. The method further includes etching the
first portion of the recessed first dielectric layer to expose the
second gate stack, while the first gate stack remains covered by a
second portion of the recessed first dielectric layer and a second
portion of the second dielectric layer.
[0041] In yet another exemplary aspect, the present disclosure is
directed to a semiconductor device. The semiconductor device
includes a substrate having first and second regions, wherein the
first region includes an insulator and the second region includes
source, drain, and channel regions of a transistor. The
semiconductor device further includes first and second gate stacks
over the insulator, a third gate stack over the channel region. The
semiconductor device further includes a first dielectric layer over
the first, second, and third gate stacks; and a second dielectric
layer over the first dielectric layer. The semiconductor device
further includes a metal layer over the first and second gate
stacks, wherein the metal layer is in electrical communication with
the second gate stack and is isolated from the first gate stack by
at least the first and second dielectric layers.
[0042] 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.
* * * * *