U.S. patent application number 14/145901 was filed with the patent office on 2014-05-01 for systems for surface treatment of semiconductor substrates using sequential chemical applications.
This patent application is currently assigned to Lam Research Corporation. The applicant listed for this patent is Lam Research Corporation. Invention is credited to Katrina Mikhaylichenko, Dragan Podlesnik, Yizhak Sabba.
Application Number | 20140116476 14/145901 |
Document ID | / |
Family ID | 41567545 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140116476 |
Kind Code |
A1 |
Mikhaylichenko; Katrina ; et
al. |
May 1, 2014 |
Systems for Surface Treatment of Semiconductor Substrates using
Sequential Chemical Applications
Abstract
Systems for removing post etch polymer residue from etched
surface includes a first proximity head to introduce a first
cleaning chemistry as a first meniscus to a portion of the surface
of the substrate so as to cover a length that extends to at least a
diameter of the substrate and a first width that is less than the
diameter of the substrate. A second proximity head is configured to
introduce a second cleaning chemistry as a second meniscus to the
portion so as to cover the length that extends to the diameter and
a second width that is less than the diameter of the substrate. A
substrate supporting device equipped with a motor coupled to a
computing system is used to move the substrate supporting device
under the first proximity head at a first linear speed and under
the second proximity head at a second linear speed.
Inventors: |
Mikhaylichenko; Katrina;
(San Jose, CA) ; Sabba; Yizhak; (Castro Valley,
CA) ; Podlesnik; Dragan; (Palo Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lam Research Corporation |
Fremont |
CA |
US |
|
|
Assignee: |
Lam Research Corporation
Fremont
CA
|
Family ID: |
41567545 |
Appl. No.: |
14/145901 |
Filed: |
December 31, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12212559 |
Sep 17, 2008 |
8652266 |
|
|
14145901 |
|
|
|
|
61083498 |
Jul 24, 2008 |
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Current U.S.
Class: |
134/95.2 ;
134/95.1 |
Current CPC
Class: |
H01L 22/20 20130101;
H01L 21/6704 20130101; H01L 21/67075 20130101; H01L 22/12 20130101;
H01L 21/02071 20130101; H01L 21/67051 20130101; H01L 21/67253
20130101 |
Class at
Publication: |
134/95.2 ;
134/95.1 |
International
Class: |
H01L 21/67 20060101
H01L021/67 |
Claims
1. A system for preparing a surface of a substrate by removing post
etch polymer residue from etched surfaces that define a gate
structure formed from at least one layer of tungsten metal,
comprising: a first proximity head configured to introduce a first
cleaning chemistry as a first meniscus to a portion of the surface
of the substrate, when present, the first meniscus is introduced to
cover a length that extends to at least a diameter of the substrate
and a first width that is less than the diameter of the substrate,
when present; a second proximity head configured to introduce a
second cleaning chemistry as a second meniscus to the portion of
the surface of the substrate, the second meniscus is introduced to
cover the length that extends to at least the diameter of the
substrate and a second width that is less than the diameter of the
substrate, when present, the first and the second cleaning
chemistries introduced sequentially; and a substrate support to
receive and transport the substrate, the substrate support
controlled by a motor that is coupled to a computing system to
actuate movement of the substrate support, the substrate support
controlled to move under the first proximity head at a first linear
speed so as to expose the portion of the surface of the substrate
to the first cleaning chemistry for a pre-defined exposure time and
move under the second proximity head at a second linear speed.
2. The system of claim 1, wherein one or both of the first and the
second proximity heads is further designed to apply a rinsing
chemistry to the surface of the substrate after the application of
the first and/or the second cleaning chemistries to the surface of
the substrate.
3. The system of claim 2, wherein the first and the second
proximity heads each are configured to apply the rinsing chemistry
and the corresponding first or second cleaning chemistries as
distinct menisci.
4. The system of claim 2, wherein one of the first proximity head
or the second proximity head is further designed to perform a
drying operation following the rinsing operation, the drying
operation performed at the end of the cleaning process.
5. The system of claim 1, wherein the first linear speed is
different from the second linear speed.
6. The system of claim 1, wherein the first linear speed is same as
the second linear speed.
7. The system of claim 1, wherein the pre-defined exposure time is
defined as a function of the first linear speed and the first width
of the first meniscus.
8. The system of claim 1, wherein the first cleaning chemistry is
ammonium peroxide mixture and the second cleaning chemistry is
diluted hydrofluoric acid.
9. A system for preparing a surface of a substrate by removing post
etch polymer residue from etched surfaces that define a gate
structure formed from at least one layer of tungsten metal,
comprising: a first proximity head configured to introduce a first
cleaning chemistry as a first meniscus to a portion of the surface
of the substrate, the first meniscus is introduced to cover a
length that extends to at least a diameter of the substrate and a
first width that is less than the diameter of the substrate, when
present; a second proximity head configured to introduce a second
cleaning chemistry as a second meniscus to the portion of the
surface of the substrate, the second meniscus is introduced to
cover the length that extends to at least the diameter of the
substrate and a second width that is less than the diameter of the
substrate, when present, the first and the second cleaning
chemistries introduced sequentially; and a substrate support to
receive and transport the substrate, when present, the substrate
support controlled by a motor that is coupled to a computing system
to actuate movement of the substrate support, the substrate support
controlled to move under the first proximity head at a first linear
speed so as to expose the portion of the surface of the substrate
to the first cleaning chemistry for a first pre-defined exposure
time, wherein the first pre-defined exposure time is defined by the
first linear speed and the first width of the first meniscus and
move under the second proximity head at a second linear speed so as
to expose the portion of the surface of the substrate to the second
cleaning chemistry for a second pre-defined exposure time, the
second pre-defined exposure time defined by the second linear speed
and the second width of the second meniscus.
10. The system of claim 9, wherein the first width is different
from the second width.
11. The system of claim 9, wherein the first width is same as the
second width.
12. The system of claim 9, wherein the first linear speed is
different from the second linear speed.
13. The system of claim 9, wherein the first linear speed is same
as the second linear speed.
14. A system for removing post etch polymer residue from etched
surfaces that define a metal gate structure formed on a surface of
a substrate, comprising: a carrier for receiving and transporting
the substrate; a first proximity head configured to introduce a
first cleaning chemistry to a portion of the surface of the
substrate as a first meniscus; a second proximity head configured
to introduce a second cleaning chemistry to the portion of the
surface of the substrate as a second meniscus, the first and the
second cleaning chemistries introduced sequentially; and a motor
for moving the carrier under the first and the second proximity
heads so as to enable application of the first and the second
cleaning chemistries to the portion of the surface of the
substrate, the motor coupled to a computing system to control a
linear speed of the carrier moving under the first proximity head
and the second proximity head so as to expose the portion of the
substrate to the first and the second cleaning chemistries for an
exposure time defined by the linear speed.
15. The system of claim 14, wherein the linear speed of the carrier
under the first proximity head is different from the linear speed
of the carrier under the second proximity head, wherein the
exposure time under the first and the second menisci varying in
accordance with the linear speed of the carrier under the first and
the second menisci.
16. The system of claim 14, wherein each of the first and the
second proximity heads is further configured to introduce a rinsing
chemistry to the portion of the surface of the substrate, the
rinsing chemistry is applied after the application of the first and
the second cleaning chemistries.
17. The system of claim 16, wherein the first and the second
proximity heads are configured to apply the rinsing chemistry and
the corresponding first or second cleaning chemistries as distinct
menisci.
18. The system of claim 16, wherein one of the first proximity head
or the second proximity head is further configured to perform a
drying operation following the rinsing operation, the drying
operation performed at the end of a cleaning process based on the
sequence of application of the first and the second cleaning
chemistries to the surface of the substrate.
Description
CLAIM OF PRIORITY
[0001] This application claims priority under 35 U.S.C. .sctn.120
as a divisional application to co-pending U.S. patent application
Ser. No. 12/212,559, filed Sep. 17, 2008, entitled "Method and
Apparatus for Surface Treatment of Semiconductor Substrates using
Sequential Chemical Applications," which claims priority under 35
U.S.C. 119(e) to U.S. Provisional application No. 61/083,498, filed
on Jul. 24, 2008, and entitled "Method and Apparatus for Surface
Treatment of Semiconductor Substrates using Sequential Chemical
Applications," contents of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to semiconductor
substrate processing, and more particularly, to systems and methods
for treating a surface of a semiconductor substrate using
sequential chemical applications.
DESCRIPTION OF THE RELATED ART
[0003] Semiconductor devices are obtained through various
fabrication operations. The fabrication operations define a
plurality of features, such as gate structures, on semiconductor
wafers (wafers or substrates) that span multi-levels. During the
various fabrication operations, the substrate is exposed to various
contaminants. Any material or chemical used in the fabrication
operations to which the substrate is exposed is a potential source
of contamination. Chemicals used in the various fabrication
operations, such as etching, deposition, etc., leave deposit, such
as process gases, etching chemicals, deposition chemicals, etc., on
and around features, such as gate structures, formed on the surface
of the substrate, as particulates or polymer residue contaminants.
The sizes of the particulate contaminants are in the order of the
critical dimensions of the features being fabricated on the
substrate. These contaminants lodge on the top, along the side
walls and in between the features in hard-to-reach areas, such as
in a trench surrounding the delicate features, and may likely cause
damage to the features within the vicinity of the contaminant
particles.
[0004] A typical gate structure formed on a substrate may include a
stack of layers made of different materials defining the gate
structure. The gate structure may include a layer of gate oxide
over which an electrode is fabricated using one or more layers of
metal, such as tungsten, tungsten compounds, etc. The metal that
may be used in fabricating the electrode may include tungsten,
tungsten silicide, tungsten nitride, tantalum, polysilicon, silicon
oxide, aluminum oxide, hafnium oxide, silicon oxynitride, tantalum
nitride, etc. A layer of polysilicon is formed on top of the metal
layer and a hardmask layer is fabricated over the top of the
polysilicon layer. The hardmask layer is fabricated as a
photoresist layer and is used to pattern the gate stack and
preserve the underlying layers. During an etching operation,
etching chemicals used in patterning the hardmask and the
underlying layers leave polymer residue on top and along the
sidewalls of the gate structure. Conventional polymer residue
cleaning methods have relied on batch tools that expose the polymer
residues to cleaning chemistries for a prolonged period of time.
When a less aggressive cleaning chemistry is used, the exposure
results in inefficient removal of polymer residues and other
contaminants. On the other hand, when a more aggressive chemistry
is used, the exposure using the batch tools leads to high material
loss rates at the gate structure rendering the cleaning process
undesirable. The material loss includes pullback of the hardmask
layer and/or undercut of gate oxide and other layers of the gate
structure formed on the substrate. FIG. 1 illustrates a typical
gate structure and FIG. 2 illustrates an example of some of the
negative effects experienced at various layers of the gate
structure.
[0005] FIG. 1 illustrates a typical metal gate structure formed on
a substrate 100 by various fabrication operations. An etching
operation is used to form various layers of the gate structure
thereby defining a gate stack. The gate structure includes a layer
of gate oxide 115 formed on the substrate 100. The substrate 100
includes a source/drain region 105 over which the layer of gate
oxide 115 (usually of high dielectric constant) is formed. A metal
electrode is fabricated over the gate oxide 115 using one or more
layers of metal. In the metal gate structure illustrated in FIG. 1,
the metal electrode is formed using a layer of metal 1 120 and a
layer of metal 2 122. A polysilicon layer 125 is formed over the
metal layer and a hardmask layer is formed over the polysilicon
layer. The hardmask layer may further include one or more layers of
hardmask. As depicted in FIG. 1, the hardmask layer includes 3
layers of hardmask, mask 1 130, mask 2 132, and mask 3 134. The
etched materials and the etching chemicals used in the etching
operation to define the stack deposit metallic or polymer
contaminants on the top and sidewalls of the gate structure.
Typical contaminants include polymer residues 140 and metal
containing polymer residues 142.
[0006] FIG. 2 illustrates some of the potential issues experienced
at the gate structure as a result of a cleaning process using a
traditional batch tool. The prolonged exposure of the gate
structure to aggressive cleaning chemistry used in the batch tool
results in the erosion of the hardmask, otherwise known as hardmask
pullback. The hardmask erosion results in the premature exposure of
the underlying layers leading to potential damage and/or further
contamination of the gate features. The prolonged exposure to the
cleaning chemistry may further result in the undercut of the metal
layer, such as tungsten, tungsten silicide, etc., used in forming
the metal electrode over the gate oxide eventually exposing the
gate oxide to the cleaning chemistry. The pullback of the hardmask
and the undercut of the metal and other layers of the gate
structure including the gate oxide pose the greatest problems in
the cleaning process. The premature exposure of the various layers
of a gate stack to chemistries used in subsequent fabrication
operations may result in further damage of the layers lending the
gate structure inoperable. Efficient and non-damaging removal of
contaminants during fabrication poses a great challenge in the
cleaning process.
[0007] In view of the foregoing, a more effective cleaning
technology is needed in removing the contaminants from the surface
of the substrate while preserving the structural integrity of the
gate structure. It is in this context embodiments of the invention
arise.
SUMMARY
[0008] The present invention fills the need by providing improved
methods and apparatus for efficiently removing polymer residue
contaminants formed around a metal gate structure on the surface of
the substrate. It should be appreciated that the present invention
can be implemented in numerous ways, including an apparatus and a
method. Several inventive embodiments of the present invention are
described below.
[0009] In one embodiment, a system for preparing a surface of a
substrate by removing post etch polymer residue from etched
surfaces that define a gate structure formed from at least one
layer of tungsten metal, is defined. The system includes a first
proximity head configured to introduce a first cleaning chemistry
as a first meniscus to a portion of the surface of the substrate,
when present. The first proximity head is designed to cover a
length that extends to at least a diameter of the substrate and a
first width that is less than the diameter of the substrate, when
present. The system includes a second proximity head configured to
introduce a second cleaning chemistry to the portion of the surface
of the substrate as a second meniscus. The second proximity head is
designed to cover a length that extends to at least a diameter of
the substrate and a second width that is less than the diameter of
the substrate, when present. The first and second cleaning
chemistries are introduced sequentially. The system also includes a
substrate supporting device to receive and transport the substrate.
The substrate supporting device is equipped with a motor that is
coupled to a computing system to control movement of the substrate
supporting device to, (a) move under the first proximity head at a
first linear speed so as to expose the portion of the surface of
the substrate to the first cleaning chemistry for a pre-defined
exposure time, and (b) move under the second proximity head at a
second linear speed.
[0010] In another embodiment, a system for preparing a surface of a
substrate by removing post etch polymer residue from etched
surfaces that define a gate structure formed from at least one
layer of tungsten metal, is disclosed. The system includes a first
proximity head configured to introduce a first cleaning chemistry
as a first meniscus to a portion of the surface of the substrate,
when present. The first proximity head is designed to introduce the
first meniscus to cover a length that extends to at least a
diameter of the substrate and a first width that is less than the
diameter of the substrate, when present. The system includes a
second proximity head configured to introduce a second cleaning
chemistry to the portion of the surface of the substrate as a
second meniscus. The second proximity head is designed to introduce
the second meniscus to cover the length that extends to at least
the diameter of the substrate and a second width that is less than
the diameter of the substrate, when present. The first and second
cleaning chemistries are introduced sequentially. The system also
includes a substrate supporting device to receive and transport the
substrate, when present. The substrate supporting device includes a
motor that is coupled to a computing system to control movement of
the substrate supporting device to, (a) move under the first
proximity head at a first linear speed so as to expose the portion
of the surface of the substrate, when present, to the first
cleaning chemistry for a first pre-defined exposure time, wherein
the first pre-defined exposure time is defined by the first linear
speed and the first width of the first meniscus, and (b) move under
the second proximity head at a second linear speed so as to expose
the portion of the surface of the substrate to the second cleaning
chemistry for a second pre-defined exposure time, wherein the
second pre-defined exposure time is defined by the second linear
speed and the second width of the second meniscus.
[0011] In yet another embodiment, a system for removing post etch
polymer residue from etched surfaces that define a metal gate
structure formed from at least one layer of tungsten metal, is
disclosed. The system includes a carrier, a first proximity head, a
second proximity head and a motor. The carrier is configured to
receive and transport the substrate. The first proximity head is
configured to introduce a first cleaning chemistry to a portion of
the surface of the substrate as a first meniscus. The second
proximity head is configured to introduce a second cleaning
chemistry to the portion of the surface of the substrate as a
second meniscus. The first and the second cleaning chemistries are
introduced sequentially. The motor is configured to move the
carrier under the first and the second proximity heads to enable
application of the first and the second cleaning chemistries to the
portion of the surface of the substrate. The motor is coupled to a
computing system to control a linear speed of the carrier moving
under the first proximity head and the secondary proximity head so
as to expose the portion of the substrate to the first and the
second cleaning chemistries for an exposure time defined by the
linear speed.
[0012] Other aspects and advantages of the invention will become
more apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention may best be understood by reference to the
following description taken in conjunction with the accompanying
drawings. These drawings should not be taken to limit the invention
to the preferred embodiments, but are for explanation and
understanding only.
[0014] FIG. 1 illustrates a simplified schematic diagram of a
typical post-etch metal gate structure, in one embodiment of the
invention.
[0015] FIG. 2 illustrates a simplified schematic diagram of
potential issues and damages experienced at the post-etch metal
gate structure illustrated in FIG. 1 during cleaning operation, in
one embodiment of the invention.
[0016] FIGS. 3A-3D illustrate simplified schematic diagrams of
various gate structures after etching operation. FIG. 3A
illustrates a simplified DRAM gate structure after full etch, in
one embodiment of the invention. FIG. 3B illustrates a simplified
DRAM gate structure after partial etch, in another embodiment of
the invention. FIG. 3C illustrates a simplified Flash tungsten gate
structure after an etching operation, in another embodiment of the
invention. FIG. 3D illustrates a simplified tungsten gate Logic
structure after an etching operation, in another embodiment of the
invention.
[0017] FIG. 3E illustrates a simplified schematic diagram of a
tungsten metal gate structure after a typical tank cleaning
operation, in one embodiment of the invention.
[0018] FIGS. 4A-4C illustrate simplified schematic diagrams of
desired cleaning results expected for various gate structures
illustrated in FIGS. 3A-3C after a cleaning operation.
[0019] FIG. 4D illustrates a resultant metal gate structure after a
cleaning operation using a first cleaning chemistry and second
cleaning chemistry, in one embodiment of the invention.
[0020] FIG. 5 illustrates a simplified schematic diagram of a
system used in the application of first and second application
chemistry to the surface of the substrate, in one embodiment of the
invention.
[0021] FIGS. 6A and 6B illustrate graphs identifying effective
removal rate of polymer residue using the first and second cleaning
chemistry, in one embodiment of the invention.
[0022] FIG. 7 illustrates the optimal exposure time and carrier
speed required for effective removal of metal containing polymer
residue removal, in one embodiment of the invention.
[0023] FIG. 8 illustrates the optimum concentration for effective
metal containing polymer residue removal rate, in one embodiment of
the invention.
[0024] FIG. 9 illustrates various method operations involved in
removing polymer residue from around a metal gate structure during
post-etch cleaning operation, in one embodiment of the
invention.
DETAILED DESCRIPTION
[0025] Several embodiments for effectively removing polymer
residues, including metal containing polymer residues, from around
a metal gate structure formed on a surface of a substrate will now
be described. It will be obvious, however, to one skilled in the
art, that the present invention may be practiced without some or
all of these specific details. In other instances, well known
process operations have not been described in detail in order not
to unnecessarily obscure the present invention.
[0026] Effective removal of contaminants, such as polymer residues
and metal containing polymer residues, from the surface of a
substrate helps in retaining the functionality of the features
formed on the substrate and the resulting devices, such as
microchips. In one embodiment of the invention, the polymer
residues formed around a metal gate structure are removed by
sequentially applying aggressive chemistries to the surface of the
substrate. The aggressive chemistries are applied in a very
controlled manner so as to enable optimal removal of the polymer
residue contaminants from around the gate structure while
preserving the structural integrity of the gate structure. In order
to apply the aggressive chemistries in a very controlled manner, a
plurality of process parameters associated with the gate structure
and the polymer residue are determined. The process parameters are
obtained by analyzing the plurality of fabrication layers forming
the gate structure and the various types of polymer residues formed
around the gate structure feature. The process parameters define
one or more characteristics associated with the different layers of
the gate structure and the polymer residue. A first and a second
aggressive chemistry are identified and one or more application
parameters are defined for the identified aggressive chemistries
based on the process parameters. The application parameters are
used in applying the aggressive chemistries sequentially in a
controlled manner so that optimal removal of polymer residues is
enabled without losing the structural integrity of the gate
structure.
[0027] The advantages of the various embodiments include use of
simple, common chemistries to effectively remove the unwanted
polymer residue resulting in a substantially clean device. The
controlled application of the aggressive chemistries effectuates
removal of polymer residue with precise control of critical
dimension.
[0028] In order to understand the effectiveness of controlled
application of the aggressive chemistries, the negative effects
experienced at the gate structure will be first described with
reference to FIGS. 1 and 2. FIG. 1 illustrates a simplified
schematic diagram of a gate structure, in one embodiment of the
invention. The gate structure is formed using a plurality of
fabrication layers where fabrication materials are deposited over a
surface of a substrate 100. The fabrication layers may include one
or more layers of metal 120, 122 formed over a layer of gate oxide
115 on the surface of a substrate 100. The gate oxide layer 115 is
usually a high dielectric constant film layer formed over the
source/drain 105. Layers of metals are used to form a metal
electrode. In FIG. 1, two layers of metal, Metal 1 120 and Metal 2
122, are used in forming the metal electrode. Some of the metals
that are used for forming the metal electrode include Tungsten (W),
Tungsten Silicide, Tungsten Nitride, Tantalum, poly-silicon (doped
or undoped), Silicon Oxide (SiO.sub.2) Tantalum Nitride (TaN),
Hafnium Oxide, Aluminum Oxide, Nitrided Hafnium-silicate (HfSiON),
etc. A polysilicon layer 125 is formed over the metals. A hardmask
layer 130 is formed over the polysilicon layer 130. The hardmask
layer 130 may be made up of a plurality of layers of hardmask 130,
132, 134. Typical materials used to form hardmask layers include
Silicon Nitride, Silicon Oxide, etc. The hardmask layer is formed
as a photoresist layer and is used to protect the underlying layers
during an etching operation. During the etching operation, the
etching chemicals used to define the metal gate structure will
leave polymer residue contaminants 140 and metal containing polymer
residue contaminants 142 on top and along the sidewalls of the
metal gate structure. It is essential to remove the unwanted
polymer residue contaminants 140, 142 while preserving the
characteristics of the metal gate structure.
[0029] The gate structure illustrated in FIG. 1 is one example of a
gate structure formed over the substrate. Variations of the gate
structure are possible. FIGS. 3A-3D illustrate some variations of
the gate structure illustrated in FIG. 1. FIG. 3A illustrates a
DRAM gate structure after a full etch. A gate stack of the gate
structure includes a gate oxide 115 formed over a silicon substrate
100. A poly silicon layer 125 is formed over the gate oxide 115
followed by a layer of metal 1 120 and a layer of metal 2 122. A
hardmask layer 130 is formed over the metal 2 layer. As can be
seen, after the etching operation post-etch polymer residues 140
and metal containing polymer residues 142 form around the gate
structure. It is a challenge to get rid of the polymer residues
formed around the gate structure without actually damaging the
various layers of the gate structure.
[0030] FIG. 3B illustrates a variation of the gate structure shown
in FIG. 3A. The gate structure in FIG. 3B is formed as a result of
an open etch process with the poly silicon layer 125 formed over
the entirety of the gate oxide 115 and the gate stack is formed
over a portion of the poly silicon layer 125.
[0031] FIG. 3C illustrates an embodiment of a flash tungsten metal
gate structure formed over the silicon substrate 100. The gate
stack of the gate structure includes a gate oxide 115 formed over
the substrate. A protective layer of silicon nitride 152 is formed
over the gate oxide 115. Layers of metal 1, 120, metal 2, 122 and
metal 3, 124, are formed on top of the silicon nitride layer 152. A
hardmask layer 130 is formed on top of the metal layer 124.
[0032] FIG. 3D illustrates a post-etch gate structure formed over
the silicon substrate 100, in one embodiment of the invention. As
mentioned earlier with other gate structures, a high dielectric
constant film layer 115 is formed over the silicon substrate, a
plurality of metal layers, such as a layer of metal 2, 122, and
metal 1, 120, are formed over the high dielectric constant film
layer 115. The metal layers may be tungsten or tantalum based metal
layers, such as tungsten, tungsten silicide, tantalum, tantalum
nitride, etc. On top of the metal layers, a layer of poly silicon
125 is formed. On top of the poly silicon 125, a hardmask layer is
formed. The various chemicals used in the etching operation deposit
around the gate features as polymer residues 140. Removal of the
post-etch polymer residues 140 including metal containing polymer
residues 142 are challenging as the chemicals used to remove these
residues during a cleaning operation, tend to damage one or more
layers of the gate structure. FIG. 2 illustrates one such example
of potential cleaning issues of mask pullback and undercut to the
metal layers due to metal corrosion, when the traditional cleaning
tools were used.
[0033] FIG. 3E illustrates another potential cleaning issue when a
batch tool is used during cleaning operation. A batch tool, such as
an immersion tank tool, (for example, Process of Record (POR) tank
tool, is used to effectively remove the polymer residue
contaminants. The batch tool exposes the substrate with the
associated gate structure to the cleaning chemistry for effective
removal of the polymer residue. Using a less aggressive chemistry
in the tank tool leads to inefficient cleaning process. When a more
aggressive chemistry is used in the tank tool, the gate structure
experiences high material loss, as illustrated in FIG. 3E. The
aggressive chemistry used to dissolve the metal containing polymer
residue contaminant will also react with the hardmask layer
severely eroding the hardmask layer thereby exposing the underlying
layers of the gate structure to the aggressive cleaning chemistries
during cleaning and post-cleaning process. The exposed layers of
the gate structure may undergo severe damage from the aggressive
cleaning and other fabrication chemicals resulting in a damaged or
inoperable gate structure.
[0034] Conventional methods used an immersion tool to expose the
surface of the substrate to cleaning chemistries. When a less
aggressive cleaning chemistry is used in the immersion tool, the
cleaning was inefficient with very poor profile control. On the
other hand, when a more aggressive chemistry is used to treat the
surface of the substrate, substantial damage to the fabrication
layers occurs including pullback of the hardmask layer and undercut
of the various fabrication layers, as illustrated in FIG. 2. This
is due to the fact that the polymer residues on the sidewalls and
on top of the gate structure contain metal. In order to effectively
remove the metal containing polymer residues, aggressive
chemistries are chosen such that the aggressive chemistries are
capable of dissolving and/or removing the metal containing polymer
residue during the cleaning operation. These aggressive
chemistries, however, also react with the metal containing
fabrication layers and the hardmask layers resulting in removing
portions of hardmask layers (hardmask pull back) and undercutting
portions of the metal containing fabrication layers of the gate
structure. When there is a pullback in the hardmask layer, the
underlying fabrication layers that form the gate structure are
prematurely exposed to ambient environment which includes chemicals
used in subsequent fabrication operations, leading to contamination
or damage of the underlying layers. The contaminated/damaged
underlying layers may render the resulting device inoperative. It
is, therefore, beneficial to prevent the hardmask pullback while
preserving the underlying fabrication layers that may otherwise
prematurely expose the gate oxide layer to fabrication
chemicals.
[0035] FIGS. 4A-4C illustrate the cleaning results desired from a
cleaning operation for various gate structures depicted in FIGS.
3A-3C. The expected desired result preserves the various
fabrication layers of the gate structure while effectively removing
the polymer residue contaminants from around the gate structure.
Towards this end, FIG. 4A illustrates the desired result expected
after a cleaning operation for a full-etch gate structure
illustrated in FIG. 3A, FIG. 4B illustrates the desired cleaning
result for a open-etch gate structure illustrated in FIG. 3B and
FIG. 4C illustrates the desired cleaning result for a tungsten
metal gate structure illustrated in FIG. 3C. As can be seen, the
desired results require effective removal of the polymer residue
contaminants, including the metal containing residues, without
damaging any of the fabrication layers.
[0036] FIG. 5 illustrates a system 500 within a clean room used to
introduce a first cleaning chemistry and a second cleaning
chemistry to a surface of a substrate 100 in a controlled manner to
substantially remove polymer residues deposited around metal gate
structures, in one embodiment of the invention. The system 500
includes a housing chamber 510 having a substrate supporting
device, such as a carrier 550, to receive, support and transport a
substrate through the housing chamber 510 on a selected plane. The
substrate 100 is received at the substrate input region 515,
transported through a region with one or more sets of proximity
heads 545 and 555 and delivered to the substrate output region 560.
The embodiment of FIG. 5 shows a pair of proximity heads positioned
on either side of the selected plane through which the substrate
100 is transported, to deliver the first and second cleaning
chemistries to both sides of the substrate 100. It should be noted
that this configuration of proximity heads is exemplary and should
not be construed as limiting. As a result, other combinations and
configurations of proximity heads may also be considered for
effective cleaning of the substrate 100.
[0037] The first set of proximity heads 545 are used to apply a
first cleaning chemistry and the second set of proximity heads 555
are used to apply a second cleaning chemistry, respectively, as
menisci to the surface of the substrate during a post-etch cleaning
operation. The term, "meniscus," as used herein, refers to a volume
of liquid bounded and contained in part by surface tension of the
liquid. The meniscus, defining a contained chemical region, is
controllable and can be moved over a surface in the contained
shape. Furthermore, the meniscus shape can be controlled through a
computing system 505 connected to the proximity heads 545 and 555.
The system 510 may include reservoirs 525 and 530 to receive, hold
and supply the first and second cleaning chemistries to the
proximity heads, 545 and 555. A chemistry application mechanism 520
connected to the reservoirs 525 and 530 control the flow of the
first and second cleaning chemistries through the proximity heads
545 and 555. The chemistry application mechanism 520 may include
one or more precision controls to enable controlled delivery of the
first and second cleaning chemistries to the proximity heads 545
and 555. The precision controls may be remotely controlled by the
computing system 505. Software in the computing system 505 may be
used to manipulate the precision controls such that proper amount
of first and second application chemistries are supplied to the
proximity heads at appropriate stages of the cleaning process. A
plurality of process parameters associated with the various
fabrication layers and the polymer residue contaminants is used to
manipulate the delivery controls so that adequate amounts of the
first and second cleaning chemistries are delivered to the
proximity heads.
[0038] The application of the first and second cleaning chemistries
is based on the plurality of process parameters. The process
parameters are obtained by analyzing various fabrication layers
that form the gate structure and the polymer residues that need to
be removed. The process parameters define characteristics of each
of the fabrication layers and the polymer residue. Some of the
process parameters associated with each of the fabrication layers
at the gate structure include one or more of type, size, and
composition. Some of the process parameters associated with the
polymer residue removal may include chemistry type, concentration,
temperature, exposure time, and target removal rate on
semiconductor materials used in the process of gate manufacturing.
Some of the semiconductor materials used in the process of gate
manufacturing may include Silicon oxide (SiO.sub.2), Tungsten (W),
Tungsten silicide, Tungsten Nitride, Tantalum Nitride, Tantalum,
and others. The first cleaning chemistry and second cleaning
chemistry are selected based on the process parameters so that the
polymer residue contaminants are effectively and substantially
removed without damaging the gate structure feature. The process
parameters associated with the fabrication layers and polymer
residues may vary from one substrate to the next. It is essential
to preserve the gate structure formed on the surface of the
substrate during the cleaning operation so that the functionality
of the gate structure and that of the semiconductor device is
maintained.
[0039] The first and second cleaning chemistries that are selected
based on process parameters are aggressive chemistries that are
normally not used in traditional tools during the cleaning
operation. These aggressive chemistries are known to cause
considerable damage to the features formed on the substrate 100
when exposed over an extended period of time. However, these
aggressive chemistries facilitate effective removal of polymer
residues formed around the gate structures when applied in a
controlled manner for a limited amount of time. In one embodiment,
the first cleaning chemistry is ammonium peroxide mixture (APM) and
the second cleaning chemistry is diluted Hydrofluoric acid (dHF).
APM is an effective cleaning chemistry as it is known to interact
with metal containing polymer residues effectively removing them
from around features formed on the substrate. However, as mentioned
earlier, APM is also known to be an aggressive chemistry with high
removal rates for tungsten and tungsten containing compounds making
it difficult to use it as an effective cleaning chemistry for
cleaning tungsten containing device stacks, such as the gate
structures, in conventional batch cleaning tools. In order to avoid
damage to the fabrication layers of the gate structure, especially
the ones that contain tungsten/tungsten compounds, the first and
second cleaning chemistries are applied in a very controlled manner
using the proximity heads 545 and 555, respectively, so as to limit
the exposure of the surface of the substrate to the cleaning
chemistries. The length and precise exposure time using proximity
heads may be driven by a desired target removal rate of the polymer
residue so as to enable one to define acceptable amount of metal
film loss in the fabrication layers of the feature during APM
application.
[0040] To assist in limiting the exposure of the substrate surface
to the cleaning chemistries, one or more application parameters are
defined for each of the first and second cleaning chemistries based
on the process parameters associated with the various fabrication
layers of the features, such as gate structures, and the polymer
residue contaminants. Some of the application parameters that may
be defined for each of the first and second cleaning chemistries
may include chemistry type, the order of application of first and
second cleaning chemistry, concentration, exposure time,
temperature, pressure, and flow rate. In one embodiment, exposure
time may be further defined as a function of linear speed at which
the substrate is transported under the proximity heads and the
width of the meniscus that may be applied to the surface of the
substrate. Accordingly, F(t.sub.exposure time)=f (Meniscus
Width/surface area, substrate linear speed). The linear speed of
the wafer may be controlled using mechanical devices such as a
motor. For instance, if the proximity head 545 is capable of
applying a meniscus that is about 20 mm wide, then the linear speed
of the substrate may be adjusted to about 20 mm/sec to give an
exposure time for the application of first cleaning chemistry of 1
second. Depending on the exposure time desired for each of the
first and second cleaning chemistries, the linear speed of the
substrate under the proximity heads may be adjusted accordingly
using the motor.
[0041] Upon establishing the application parameters for the
cleaning chemistries, the first and second cleaning chemistries are
applied to the surface of the substrate sequentially in a
controlled manner using the first and second proximity heads, 545
and 555, based on the application parameters. The order of the
application of the cleaning chemistries is not rigid. In one
embodiment, first cleaning chemistry (APM) is applied using the
first proximity head 545 followed by the application of the second
cleaning chemistry (dHF) using the second proximity head 555. In
another embodiment, the first cleaning chemistry (APM) is applied
using the second proximity head 555 sequentially after the
application of the second cleaning chemistry (dHF) using the first
proximity head 545. The order of application of the cleaning
chemistries might be based on desired outcomes, such as the amount
of metal oxide to be preserved. The controlled sequential
application of the first and second cleaning chemistries aid in
substantial removal of the polymer residue from around features,
such as gate structures, without damaging the features. As
mentioned earlier, the exposure time of each of the cleaning
chemistries is controlled by controlling the linear speed of the
substrate under the corresponding proximity heads.
[0042] The application of each of the first and second cleaning
chemistries may be followed by a rinsing operation using a rinsing
chemistry. The rinsing chemistry is used to remove any residual
cleaning chemistry applied to the substrate surface after the
respective cleaning operation. Consequently, the order of treatment
of various chemistries, in one embodiment of the invention, may
include application of first cleaning chemistry, rinsing operation
with a rinsing chemistry, application of second cleaning chemistry
and rinsing operation with a rinsing chemistry. The rinsing
operation following the application of each of the first and second
cleaning chemistries may use the same rinsing chemistry or
different rinsing chemistries.
[0043] The first and second proximity heads (545, 555) are
configured to deliver the cleaning chemistry and the rinsing
chemistry as menisci to clean and rinse the surface of the
substrate. The cleaning chemistry and rinsing chemistry menisci may
be connected or separated. In one embodiment, the cleaning
chemistries and rinsing chemistry menisci are connected. The
proximity heads (545, 555) are configured to enable connection
between the cleaning chemistry meniscus and rinsing chemistry
meniscus. In this embodiment, the applied cleaning chemistries are
used once and not reclaimed after the application. In another
embodiment, the cleaning chemistries and rinsing chemistry menisci
are separate. In this embodiment, each of the proximity heads (545,
555) is configured such that the cleaning chemistry meniscus is
kept distinct from the rinsing chemistry meniscus. Accordingly, in
this embodiment, the applied cleaning chemistry can be reclaimed
after application for re-use in subsequent cleaning operations.
[0044] Each of the first and second proximity heads, 545, 555, is
further configured to provide a drying operation to dry the surface
of the substrate after the cleaning and rinsing operations, in one
embodiment of the invention. The drying operation may include
application of a drying chemistry, such as isopropyl alcohol (IPA)
vapor, to the substrate surface. In one embodiment, the drying
operation is optional after the first cleaning and rinsing
operation. In the embodiment, where the drying operation is not
performed after the application of the first cleaning chemistry and
rinsing chemistry, a film of de-ionized water (DIW) is left on the
surface of the substrate so as to prevent premature drying and/or
further contamination. The drying operation is, however, included
after the second cleaning and rinsing operation.
[0045] During the cleaning process, the substrate is made to move
radially under the proximity heads (545, 555), to ensure even
application of various chemistries to all portions of the substrate
surface. In this embodiment, the size of the proximity heads is
smaller than the width of the substrate. The speed of rotation of
the substrate underneath the proximity heads is adjusted based on
desired exposure time and the target removal rate of the polymer
residue.
[0046] In another embodiment, the proximity heads are configured to
have a head that is slightly larger than the diameter of the
substrate so as to provide a more localized application of the
cleaning chemistries with short exposure time. In this embodiment,
the substrate is moving linearly under the proximity heads.
[0047] The short exposure time using proximity heads allows use of
concentrated and aggressive chemistries in the cleaning process.
The high flow conditions of the aggressive chemistries and the
subsequent displacement with rinsing chemistries enables faster
reaction with the polymer residue contaminants and faster
suspension of the reaction thereby enabling optimal removal of the
polymer residue contaminants while minimizing the exposure of the
features to the aggressive chemistries thereby preventing pullback
and undercut of fabrication layers of the features, such as the
gate structures during the cleaning process. Thus, for instance,
APM can be used to remove metal polymer residues around a metal
gate structure where tungsten/tungsten compound is used. Even
though APM is known to dissolve tungsten very quickly, the
controlled exposure time enables efficient removal of polymer
residue while preserving the features around which the polymer
residues are formed. FIGS. 6A, 6B and 7 illustrate charts 1, 2, and
3, respectively, depicting the residue cleaning rate with minimum
oxide layer loss. As can be seen in FIG. 6A, for instance, the
concentration of the APM may be adjusted to provide an etch rate of
about 1 .ANG./sec to about 10 .ANG./sec with an optimal etch rate
of about 5 .ANG./sec. The material loss in the gate structure can
be between about 5 .ANG. and about 10 .ANG. with about 5 second
exposure time. The concentration of the APM and the exposure time
may be adjusted to obtain acceptable range of polymer residue
removal while maintaining low material loss of the gate structure
material. The exposure time can be adjusted using precision
controls to fine tune the exposure time to an order of about
.+-.0.1 seconds. For instance, a typical range of the composition
of APM could be in the order of about 1:1:1 on the concentrated
side to about 1:4:50 on the diluted side with a standard
concentration of about 1:4:10. For dHF, the range of concentration
could be between about 1:10 on the concentrated side to about
1:1000 for diluted side with a standard concentration of about
1:100. The standard exposure time would be about 2 seconds with a
range between about 1 second to about 20 second. Depending on the
proximity head size, the speed of the substrate may be adjusted to
provide the required exposure time. The proximity head width could
be between about 10 mm to about 40 mm and the speed of the
substrate could be adjusted to the required exposure time. FIG. 8
illustrates a graph of the target exposure time to carrier speed
for effective removal of polymer residue contaminants.
[0048] The graph illustrated in FIG. 8 depicts the scanning speed
against exposure time for effective removal of the polymer residue
contaminants with two different proximity head widths. The graph
identifies the target removal rate of the polymer residue. Based on
the desired removal rate, the concentration of the first and second
application chemistries, speed of the substrate under the proximity
heads and exposure time can be adjusted. For instance, if it is
desired to remove 5 .ANG. of tungsten based residue, the graph
identifies the optimal exposure time and speed of the substrate to
achieve that goal.
[0049] As mentioned earlier, FIGS. 3D, 3E and 4D illustrate the
resultant metal gate structure before and after a cleaning
operation is performed, in one embodiment of the invention. As can
be seen in FIG. 3D illustrates a typical gate structure with
polymer residue contaminants formed around the gate structure. FIG.
3E illustrates the result of a traditional cleaning operation using
aggressive chemistries. The polymer residue on top of a hardmask
layer is stripped with severe erosion of hardmask layer, thereby
exposing the underlying layers. FIG. 4D illustrates the result
after a cleaning operation using the first and second cleaning
chemistries of the present invention. The precise delivery and
controlled exposure of the first and second cleaning chemistries to
the substrate surface enables efficient removal of the polymer
residue formed on top of the hardmask without causing any negative
effects on the hardmask layer. Additionally, the controlled
exposure of the cleaning chemistries enables removal of the polymer
residue formed on the sidewalls of the metal gate structure while
substantially preserving the metal layers of the gate
structure.
[0050] FIG. 9 illustrates the process operations involved in
removing polymer residue from around a metal gate structure during
post-etch cleaning operation, in one embodiment of the invention.
The process begins at operation 910, wherein a plurality of process
parameters associated with the metal gate structure and polymer
residue formed around the metal gate structure, are determined. The
metal gate structure may be a multi-layer structure formed using
various fabrication operations. The process parameters are obtained
by analyzing the fabrication layers that form the gate structure
and by analyzing the polymer residue formed around the gate
structure. The process parameters may include type, size,
composition, temperature associated with each of the fabrication
layers and of the polymer residue and target removal rate
associated with the polymer residue to be removed. The process
parameters define characteristics of each of the fabrication layers
that comprise the gate structure and the polymer residue to be
removed.
[0051] A first cleaning chemistry and second cleaning chemistry are
identified based on the process parameters, as illustrated in
operation 920. The first and second cleaning chemistry may be
aggressive cleaning chemistries and may include Ammonium peroxide
mixture (APM) and dilute Hydrofluoric acid (dHF). The examples for
first and second cleaning chemistry are exemplary and are not
restricted to APM and dHF but may include other aggressive
chemistries that are known to dissolve or effectively react to
substantially remove the metal polymer residues. Some of the other
aggressive chemistries that may be used as cleaning chemistries may
include, for example, a mixture of Hydrofluoric and Hydrochloric
acids (HF/HCl).
[0052] A plurality of application parameters associated with the
first and second cleaning chemistries are defined based on the
plurality of process parameters, as illustrated in operation 930.
Some of the application parameters associated with each of the
first and second cleaning chemistries may include type,
concentration, exposure time, temperature, pressure, and flow rate.
In addition, the application parameters may include speed of the
substrate under a first and a second set of proximity heads and the
width of the meniscus at each proximity head. The exposure time may
be calculated as a function of the speed of the substrate and the
width of the meniscus at each proximity head. The application
parameters are defined based on the target removal rate of the
polymer residue from around the metal gate structure.
[0053] The process concludes with the application of the first and
second cleaning chemistries sequentially in a controlled manner
using the application parameters, as illustrated in operation 940.
The application of the first and second cleaning chemistries
enables substantial removal of the polymer residue from around the
metal gate structure while substantially preserving the structural
integrity of the metal gate structure. The application of the first
and second cleaning chemistries may be accomplished through a
computing system that is communicatively connected to the first and
second proximity heads. One or more precision controls, available
at a chemistry application mechanism communicatively connected to
the proximity heads, may be manipulated using a software in the
computing system to enable controlled application of the first and
second cleaning chemistries so as to optimally remove the polymer
residue from around the metal gate structure on the surface of the
substrate while substantially preserving the structural integrity
of the one or more fabrication layers that make up the gate
structure. The applied cleaning chemistries may be reclaimed so
that they can be re-used in subsequent cleaning operations thereby
enabling optimal use of the simple but expensive cleaning
chemistries. Thus, the various embodiments of the invention provide
ways to remove polymer residues from around metal gate structures
while preserving the structural integrity of the metal gate
structure using aggressive chemistries that are known to easily
dissolve the metal used in the metal gate structures.
[0054] For more information on a substrate supporting device, such
as a wafer carrier, reference can be made to U.S. patent
application Ser. No. 11/743,516, entitled "HYBRID COMPOSITE WAFER
CARRIER FOR WET CLEAN EQUIPMENT", filed on May 2, 2007, and
assigned to the Assignee of the subject application and is
incorporated herein by reference.
[0055] For additional information with respect to the proximity
head, reference can be made to an exemplary proximity head, as
described in the U.S. Pat. No. 6,616,772, issued on Sep. 9, 2003
and entitled "METHODS FOR WAFER PROXIMITY CLEANING AND DRYING."
This U.S. patent, which is assigned to Lam Research Corporation,
the assignee of the subject application, is incorporated herein by
reference.
[0056] For additional information about menisci, reference can be
made to U.S. Pat. No. 6,998,327, issued on Jan. 24, 2005 and
entitled "METHODS AND SYSTEMS FOR PROCESSING A SUBSTRATE USING A
DYNAMIC LIQUID MENISCUS," and U.S. Pat. No. 6,998,326, issued on
Jan. 24, 2005 and entitled "PHOBIC BARRIER MENISCUS SEPARATION AND
CONTAINMENT." These U.S. patents, which are assigned to the
assignee of the subject application, are incorporated herein by
reference in their entirety for all purposes.
[0057] For additional information about top and bottom menisci,
reference can be made to the exemplary meniscus, as disclosed in
U.S. patent application Ser. No. 10/330,843, filed on Dec. 24, 2002
and entitled "MENISCUS, VACUUM, IPA VAPOR, DRYING MANIFOLD." This
U.S. patent, which is assigned to Lam Research Corporation, the
assignee of the subject application, is incorporated herein by
reference.
[0058] Although the foregoing invention has been described in some
detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications can be practiced
within the scope of the appended claims. Accordingly, the present
embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
given herein, but may be modified within the scope and equivalents
of the appended claims.
* * * * *