U.S. patent application number 13/931376 was filed with the patent office on 2013-10-31 for substrate cleaning system using stabilized fluid solutions.
The applicant listed for this patent is Lam Research Corporation. Invention is credited to John M. de Larios, Erik M. Freer, Mikhail Korolik, Katrina Mikhaylichenko, Michael Ravkin, Fred C. Redeker.
Application Number | 20130284217 13/931376 |
Document ID | / |
Family ID | 38228775 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130284217 |
Kind Code |
A1 |
Freer; Erik M. ; et
al. |
October 31, 2013 |
Substrate Cleaning System Using Stabilized Fluid Solutions
Abstract
A substrate cleaning systems are provided. One system includes a
proximity head system for applying a meniscus to a surface of a
substrate during a cleaning operation. Also provided is a container
for holding the solution, the solution being mixed from at least a
continuous medium, a polymer material, and a solid material, the
polymer material in the solution imparting a finite yield stress to
the material, such that the solution is maintained in a stable
elastic gel form. A pump coupled to the container is also provided
for moving the solution from the container to the proximity head
system, where the pump applies at least a minimum shear stress on
the solution. The pump provides agitation that exceeds the finite
yield stress causing the solution to flow. A conduit is provided
between the container and the proximity head system.
Inventors: |
Freer; Erik M.; (Mt. View,
CA) ; de Larios; John M.; (Palo Alto, CA) ;
Ravkin; Michael; (Los Altos, CA) ; Korolik;
Mikhail; (San Jose, CA) ; Mikhaylichenko;
Katrina; (San Jose, CA) ; Redeker; Fred C.;
(Fremont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lam Research Corporation |
Fremont |
CA |
US |
|
|
Family ID: |
38228775 |
Appl. No.: |
13/931376 |
Filed: |
June 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11641362 |
Dec 18, 2006 |
8475599 |
|
|
13931376 |
|
|
|
|
60755377 |
Dec 30, 2005 |
|
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Current U.S.
Class: |
134/184 |
Current CPC
Class: |
H01L 21/67051 20130101;
C11D 11/0047 20130101; H01L 21/02057 20130101; H01L 21/02052
20130101; B05D 3/10 20130101; H01L 21/6715 20130101; C11D 17/0004
20130101; C11D 17/0013 20130101; H01L 21/02096 20130101; C23G 1/00
20130101; C11D 3/14 20130101; G03F 7/42 20130101 |
Class at
Publication: |
134/184 |
International
Class: |
H01L 21/67 20060101
H01L021/67 |
Claims
1. A substrate cleaning system, comprising: a proximity head system
for applying a meniscus to a surface of a substrate during a
cleaning operation, the meniscus being defined by a solution; a
container holding the solution, the solution being mixed from at
least a continuous medium, a polymer material, and a solid
material, the polymer material in the solution imparting a finite
yield stress to the material, such that the solution is maintained
in a stable elastic gel form, the stable elastic gel form being
configured to hold the solid material form in place and prevent the
solid material from fluid flow in the solution if stresses less
than the finite yield stress is imparted on the solid material
after synthesis of the solution and during any storage of the
solution; a pump for moving the solution from the container to the
proximity head system, the pump applies at least a minimum shear
stress on the solution, and the pump provides agitation that
exceeds the finite yield stress causing the solution to flow; a
head of the proximity head system receiving the solution that is
configured to be applied to the surface of the substrate in the
form of the meniscus.
2. A substrate cleaning system as recited in claim 1, wherein the
meniscus is in a fluid form or a foam form.
3. A substrate cleaning system as recited in claim 1, further
comprising, a foam generation system that transforms the solution
into tri-state bodies, the tri-state bodies being defined by a part
fluid, a part gas, and a part solids.
4. A substrate cleaning system, comprising: a proximity head system
for applying a meniscus to a surface of a substrate during a
cleaning operation, the proximity head system having a body and a
surface with a plurality of conduits, the surface being configured
for placement proximate to the substrate when present, the
plurality of conduits of the proximity head system having an input
for receiving a solution and moving the solution internally of the
body within the proximity head and to the plurality of conduits for
delivery of the solution to the substrate when present, the
solution being delivered in a form of the meniscus disposed between
the surface of the proximity head system and the substrate when
present; a container for holding the solution, the solution being
mixed from at least a continuous medium, a polymer material, and a
solid material, the polymer material in the solution imparting a
finite yield stress to the material, such that the solution is
maintained in a stable elastic gel form; a pump coupled to the
container for moving the solution from the container to the
proximity head system, the pump applies at least a minimum shear
stress on the solution, and the pump provides agitation that
exceeds the finite yield stress causing the solution to flow; and a
conduit defined between the container and the proximity head
system, such that the solution is provided to the input of the
proximity head system for application to the surface of the
substrate in the form of the meniscus.
5. A substrate cleaning system as recited in claim 4, wherein the
meniscus is in a fluid form or a foam form.
6. A substrate cleaning system as recited in claim 4, further
comprising, a foam generation system that transforms the solution
into tri-state bodies, the tri-state bodies being defined by a part
fluid, a part gas, and a part solids.
7. A substrate cleaning system as recited in claim 4, further
comprising, a foam generation system disposed between the pump and
the proximity head system, such that the foam generation system
transforms the solution into tri-state bodies.
8. A substrate cleaning system as recited in claim 7, wherein the
tri-state bodies are defined by a part fluid, a part gas, and a
part solids.
9. A substrate cleaning system as recited in claim 4, wherein the
pump includes a shear thinning mechanism.
10. A substrate cleaning system as recited in claim 4, wherein the
stable elastic gel form being configured to hold the solid material
form in place and prevent the solid material from fluid flow in the
solution if stresses less than the finite yield stress is imparted
on the solid material after synthesis of the solution and during
any storage of the solution.
11. A substrate cleaning system, comprising: a jet application
system for applying a solution to a surface of a substrate during a
cleaning operation; a container holding the solution, the solution
being mixed from at least a continuous medium, a polymer material,
and solid material, the polymer material in the solution imparting
a finite yield stress to the material, such that the solution is
maintained in a stable elastic gel form, the stable elastic gel
form being configured to hold the solid material form in place and
prevent the solid material from moving in the solution if stresses
less than the finite yield stress is imparted on the solid material
after synthesis of the solution and during any storage of the
solution; and a pump for moving the solution from the container to
the jet application system, the pump applies at least a minimum
shear stress on the solution, and the pump provides agitation that
exceeds the finite yield stress causing the solution to flow;
wherein the jet sprays the solution to the surface of the substrate
so as to remove unwanted contaminants.
12. A substrate cleaning system 11, wherein the jet applies a
stream of the solution on the surface of the substrate.
Description
CLAIM OF PRIORITY
[0001] This application is a Divisional application claiming
priority from co-pending U.S. application Ser. No. 11/641,362,
filed on Dec. 18, 2006, which claims the benefit of U.S.
Provisional Application No. 60/755,377, filed Dec. 30, 2005. The
disclosure of the above-identified application is incorporated
herein by reference.
CROSS REFERENCE TO RELATED APPLICATIONS
[0002] This application is related to U.S. Pat. No. 7,441,299,
issued on Oct. 28, 2008, and entitled "Apparatuses and Methods for
Cleaning a Substrate," U.S. Pat. No. 8,043,441, issued on Oct. 25,
2011, and entitled "Method and Apparatus for Cleaning a Substrate
Using Non-Newtonian Fluids," U.S. Pat. No. 7,416,370, issued on
Aug. 26, 2008, and entitled "Method and Apparatus for Transporting
a Substrate Using Non-Newtonian Fluid," U.S. Pat. No. 8,323,420,
issued on Dec. 4, 2012, and entitled "Method for Removing Material
from Semiconductor Wafer and Apparatus for Performing the Same,"
U.S. Pat. No. 7,568,490, issued on Aug. 4, 2009, and entitled
"Method and Apparatus for Cleaning Semiconductor Wafers using
Compressed and/or Pressurized Foams, Bubbles, and/or Liquids," U.S.
Pat. No. 7,648,584, issued on Jan. 19, 2010, entitled "Method and
Apparatus for removing contamination from a substrate," U.S. Pat.
No. 7,737,097, issued on Jun. 15, 2010, entitled "Method for
removing contamination from a substrate and for making a cleaning
solution," and U.S. Pat. No. 7,696,141, issued on Apr. 13, 2010,
entitled "Cleaning compound and method and system for using the
cleaning compound." The disclosure of each of the above-identified
related applications is incorporated herein by reference.
BACKGROUND
[0003] In the fabrication of semiconductor devices such as
integrated circuits, memory cells, and the like, a series of
manufacturing operations are performed to define features on
semiconductor wafers ("wafers"). The wafers include integrated
circuit devices in the form of multi-level structures defined on a
silicon substrate. At a substrate level, transistor devices with
diffusion regions are formed. In subsequent levels, interconnect
metallization lines are patterned and electrically connected to the
transistor devices to define a desired integrated circuit device.
Also, patterned conductive layers are insulated from other
conductive layers by dielectric materials.
[0004] During the series of manufacturing operations, the wafer
surface is exposed to various types of contaminants Essentially any
material present in a manufacturing operation is a potential source
of contamination. For example, sources of contamination may include
process gases, chemicals, deposition materials, and liquids, among
others. The various contaminants may deposit on the wafer surface
in particulate form. If the particulate contamination is not
removed, the devices within the vicinity of the contamination will
likely be inoperable. Thus, it is necessary to clean contamination
from the wafer surface in a substantially complete manner without
damaging the features defined on the wafer. However, the size of
particulate contamination is often on the order of the critical
dimension size of features fabricated on the wafer. Removal of such
small particulate contamination without adversely affecting the
features on the wafer can be quite difficult.
[0005] Conventional wafer cleaning methods have relied heavily on
mechanical force to remove particulate contamination from the wafer
surface. As feature sizes continue to decrease and become more
fragile, the probability of feature damage due to application of
mechanical force to the wafer surface increases. For example,
features having high aspect ratios are vulnerable to toppling or
breaking when impacted by a sufficient mechanical force. To further
complicate the cleaning problem, the move toward reduced feature
sizes also causes a reduction in the size of particulate
contamination. Particulate contamination of sufficiently small size
can find its way into difficult to reach areas on the wafer
surface, such as in a trench surrounded by high aspect ratio
features. Thus, efficient and non-damaging removal of contaminants
during modem semiconductor fabrication represents a continuing
challenge to be met by continuing advances in wafer cleaning
technology. It should be appreciated that the manufacturing
operations for flat panel displays suffer from the same
shortcomings of the integrated circuit manufacturing discussed
above.
[0006] Many times, solutions that are engineered for cleaning
surfaces are not sufficiently stable, and over time, their
consistencies may change. An example of changes in consistencies is
when materials in the solutions either float to the top or sink to
the bottom. If this happens, there is a need for re-mixing, or
reconfirming the solution so that it can still be applied to the
surface of the substrate and the anticipated action/result of the
solution will still be valid. For this reason, some solutions
cannot be made and stored for later use, as the solution many not
properly function without extra testing or reconditioning.
[0007] In view of the forgoing, there is a need for solutions that
can be made, stored, and used at later times, without the need for
extra testing, sampling, re-agitation, re-conditioning, re-mixing,
or the like.
SUMMARY
[0008] Broadly speaking, the present invention fills these needs by
providing a stable solution that can elastically hold solid
materials in suspension, so that solid materials are not allowed to
separate from the remainder of the cleaning solution. The solution
preferably includes polymeric macromolecules that stabilize the
solid particles in the fluid, so that the solid particles are
prevented from either floating to the top of the solution or
sinking to the bottom of the solution, due to the relative
buoyancies of the solid particles to the continuous medium of the
solution. In one embodiment, the polymeric macromolecules form a
physical network with junctions that give the solution a finite
yield stress. Thus, the physical network behaves as an elastic
solid when deformed with stresses below the yield value. When
stress above the yield stress is applied to the material, the
network will yield resulting in a fluid like behavior of the
solution. If the stress provided by the buoyancy force of the solid
is below the yield stress of the continuous medium, then the solid
particles will be trapped in the network unable to migrate. This
physical network stabilizes the cleaning solution by keeping the
particles suspended, but does not inhibit utility since the
solution behaves as a fluid above the yield stress. In addition,
the polymeric additives can give the solution elasticity which can
provide a normal force to the wafer surface upon application, which
promotes solid-wafer contact and better contamination removal.
[0009] It should be appreciated that the present invention can be
implemented in numerous ways, including as an apparatus, a method
and a system. Several inventive embodiments of the present
invention are described below.
[0010] In one embodiment, a substrate cleaning system is provided.
The system includes a proximity head system for applying a meniscus
to a surface of a substrate during a cleaning operation. Also
provided is a container for holding the solution, the solution
being mixed from at least a continuous medium, a polymer material,
and a solid material, the polymer material in the solution
imparting a finite yield stress to the material, such that the
solution is maintained in a stable elastic gel form. A pump coupled
to the container is also provided for moving the solution from the
container to the proximity head system, where the pump applies at
least a minimum shear stress on the solution. The pump provides
agitation that exceeds the finite yield stress causing the solution
to flow. A conduit is provided between the container and the
proximity head system.
[0011] In one embodiment, a method for making a solution for use in
preparing a surface of a substrate is provided. The method includes
providing a continuous medium that adds a polymer material to the
continuous medium. A fatty acid is added to the continuous medium
having the polymer material, and the polymer material defines a
physical network that exerts forces in the solution that overcome
buoyancy forces experienced by the fatty acid, thus preventing the
fatty acids from moving within the solution until a yield stress of
the polymer material is exceeded by an applied agitation. The
applied agitation is from transporting the solution from a
container to a preparation station that applies the solution to the
surface of the substrate.
[0012] In another embodiment, a method for using a solution for
cleaning a substrate is provided. The method includes providing a
solution in a container, where the solution is mixed from at least
a continuous medium, a polymer material, and a solid material. The
polymer material in the solution imparting a finite yield stress to
the material, such that the solution is maintained in a stable
elastic gel form. The stable elastic gel form is configured to hold
the solid material from in place and prevent the solid material
from moving in the solution if stresses less than the finite yield
stress is imparted on the solution after synthesis of the solution
and during any storage of the solution. The method further includes
applying at least a minimum shear stress on the solution, and the
minimum shear stress is at least greater than the finite yield
stress so that the stable elastic gel form transforms from solid
like to liquid like behavior. Then, flowing the solution from the
container after imparting the minimum shear stress, where the
solution that is flown from the container has a mixed consistency
of the solid material in the solution. The method then includes
applying the solution to a preparation system for application to a
surface of the substrate.
[0013] In yet another embodiment, a substrate cleaning system is
disclosed. The system includes a proximity head system for applying
a meniscus to a surface of a substrate during a cleaning operation,
where the meniscus is defined by a solution. The system includes a
container for holding the solution, and the solution is mixed from
at least a continuous medium, a polymer material, and a solid
material, where the polymer material in the solution imparts a
finite yield stress to the material that enables a stable elastic
gel form. The stable elastic gel form is configured to hold the
solid material form in place and prevent the solid material from
moving in the solution if stresses less than the finite yield
stress are imparted on the solution, after synthesis of the
solution and during any storage of the solution. The system further
includes a pump for moving the solution from the container to the
proximity head system, where the pump applies at least a minimum
shear stress on the solution. The pump provides agitation that
exceeds the finite yield stress that transforms the stable elastic
gel to liquid. A head of the proximity head system receives the
solution that is configured to be applied to the surface of the
substrate in the form of the meniscus. The meniscus can either be
in a two-state form or a tri-state form, depending on the
application.
[0014] In still another embodiment, a substrate cleaning system is
disclosed. The system includes a jet application system for
applying a solution to a surface of a substrate during a cleaning
operation. A container holding the solution is provided. The
solution is mixed from at least a continuous medium, a polymer
material, and solid material, and the polymer material in the
solution imparts a finite yield stress to the material, such that
the solution is maintained in a stable elastic gel form. The stable
elastic gel form is configured to hold the solid material form in
place and prevent the solid material from moving in the solution if
stresses less than the finite yield stress is imparted on the
solution after synthesis of the solution and during any storage of
the solution. A pump is provided for moving the solution from the
container to the jet application system, and the pump applies at
least a minimum shear stress on the solution. The pump provides
agitation that exceeds the finite yield stress that transforms the
stable elastic gel to liquid. And, the jet sprays the solution to
the surface of the substrate so as to remove unwanted
contaminants.
[0015] Other aspects of the invention will become apparent from the
following detailed description, taken in conjunction with the
accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention will be readily understood by the
following detailed description in conjunction with the accompanying
drawings, and like reference numerals designate like structural
elements.
[0017] FIGS. 1 and 2 illustrate mechanics of the solution, in
accordance with one embodiment of the present invention.
[0018] FIG. 3 illustrates an example of the mixing of the main
constituents of the solution, in accordance with one embodiment of
the present invention.
[0019] FIG. 4 illustrates an example of several containers, which
may be stably stored in an elastic gel-like form, in accordance
with one embodiment of the present invention.
[0020] FIG. 5 illustrates an example use of the solution, which
transforms the solution from the stable gel-like form to a low
viscosity fluid through shear thinning, in accordance with one
embodiment of the present invention.
[0021] FIG. 6 illustrates one example method of making the
solution, in accordance with one embodiment of the present
invention.
[0022] FIG. 7 illustrates one example method of using the solution,
in accordance with one embodiment of the present invention.
DETAILED DESCRIPTION
[0023] An invention is described for methods, systems for use, and
methods for making materials for use in preparation of substrates,
which may be used in the semiconductor industry. In one embodiment,
the material is defined as a solution that can be used in the
preparation of substrates. "Preparation", broadly defined, includes
the cleaning, etching, depositing, removing, or altering of
surfaces of substrates, and in particular, the cleaning of
particulates, contaminants or unwanted materials, layers, or
surfaces form a substrate. A "substrate," as an example used
herein, denotes without limitation, semiconductor wafers, hard
drive disks, optical discs, glass substrates, and flat panel
display surfaces, liquid crystal display surfaces, etc., which may
become contaminated during manufacturing or handling operations.
Depending on the actual substrate, a surface may become
contaminated in different ways, and the acceptable level of
contamination is defined in the particular industry in which the
substrate is handled.
[0024] The solution, defined herein, is a suspended solution, that
is engineered to suspend solids within a polymer network material.
The polymer network defines a physical network that behaves as an
elastic solid when deformed with stresses below its yield value.
The solution includes at least a continuous medium (e.g., water), a
polymer, and solids (e.g., fatty acids). The solids, although may
have some buoyancy relative to the continuous medium of the
solution, will be held in place, and thus will not be allowed to
either sink or float. If the solids were to sink or float, the
solution would have to be re-mixed before use, with may introduce
downtime or uncertainty in the degree of mixing needed to produce a
ready to use solution.
[0025] As will be described below, the polymer of the solution is
configured to make the solution behave like a viscoplastic fluid
(e.g., gel-like), which will suspend and hold the solids in place
within the mixed solution. The solution, which in one embodiment
acts like a physical gel, has a finite yield stress that is greater
than the stress from the buoyancy force of the suspended solids,
thus preventing sedimentation or creaming, which stabilizes the
solution. In addition, the stabilizing macromolecules of the
polymer give the solution elasticity, which enhances contamination
removal.
[0026] 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.
[0027] FIG. 1 illustrates a graph 100 which plots shear stress in
the Y-axis versus shear rate in the X-axis. Graph 100 is provided
to illustrate a plot 102a and a plot 102b, each of which define a
different plastic viscosity. Plot 102a will have a plastic
viscosity A and plot 102b will have a plastic viscosity B, which is
distinguished by the graphed slope. As shown, each of plots 102a
and 102b begin at X-axes, at zero. A viscoplastic fluid will
therefore possess a yield stress, .tau..sub.y, that must be
exceeded before the viscoplastic fluid will deform continuously.
Below the yield stress, only elastic deformation occurs on the
viscoplastic fluid. Once the yield stress is exceeded, the
viscoplastic fluid will begin to deform continuously, and as
additional shear stress is applied, the shear rate will increase
proportionally; the proportionality constant is the viscosity of
the viscoplastic fluid.
[0028] Examples of viscoplastic fluids may include materials, but
not limited to, materials commonly referred to as "Bingham
plastics." Bingham plastics exhibit a linear behavior of shear
stress versus the shear rate, as defined in FIG. 1. The higher the
shear rate that is applied to the viscoplastic fluid, the more the
viscosity drops, which allows the viscoplastic fluid to exhibit
Newtonian characteristics. As used herein, Newtonian fluids are
those that will adhere to the rheological definition of Newton's
Law of viscosity.
[0029] A non-Newtonian fluid, as used herein, is a fluid in which
the viscosity changes with an applied shear stress. A non-Newtonian
fluid does not obey Newton's Law of viscosity. The shear stress is
a non-linear function of the shear rate. Depending on how the
apparent viscosity changes with shear rate, the flow behavior will
also change. An example of a non-Newtonian fluid is a soft
condensed matter which occupies a middle ground between the
extremes of a solid and a liquid. The soft condensed matter is
easily deformable by external stresses and examples of the soft
condensed matter include emulsions, gels, colloids, foam, etc. It
should be appreciated that an emulsion is a mixture of immiscible
liquids such as, for example, toothpaste, mayonnaise, oil in water,
etc.
[0030] For additional information regarding the functionality and
constituents of Newtonian and non-Newtonian fluids, reference can
be made to: (1) U.S. application Ser. No. 11/174,080, filed on Jun.
30, 2005 and entitled "METHOD FOR REMOVING MATERIAL FROM
SEMICONDUCTOR WAFER AND APPARATUS FOR PERFORMING THE SAME"; (2)
U.S. patent application Ser. No. 11/153,957, filed on Jun. 15,
2005, and entitled "METHOD AND APPARATUS FOR CLEANING A SUBSTRATE
USING NON-NEWTONIAN FLUIDS"; and (3) U.S. patent application Ser.
No. 11/154,129, filed on Jun. 15, 2005, and entitled "METHOD AND
APPARATUS FOR TRANSPORTING A SUBSTRATE USING NON-NEWTONIAN FLUID,"
each of which is incorporated herein by reference.
[0031] FIG. 2 illustrates a graph 120 that plots shear rate in the
X-axes versus viscosity in the Y-axes. A curve 122 is shown to
illustrate the mechanics of shear thinning when a viscoplastic
fluid experiences an increase in shear rate. In essence, the
viscosity of the viscoplastic fluid will drop along the curve 122
as the shear rate increases. As the shear thinning direction
illustrates, the more shear rate that is applied to the
viscoplastic fluid, the characteristic of a non-Newtonian behavior
will change into a more Newtonian behavior, as the shear rate
increases. Accordingly, the viscoplastic fluid will be in a
substantially stable and substantially elastic solid form (i.e.,
substantially non-deformed state) when the shear rate is zero, as
illustrated in both FIGS. 1 and 2. However, as the shear rate
increases, the viscosity will drop, having crossed the critical
yield stress point, to cause the transformation of the viscoplastic
fluid from a substantially solid elastic form to a substantially
fluid form. The shear thinning process is therefore one in which
the apparent viscosity of the fluid decreases with increasing shear
rate. This type of behavior may also be referred to as
"pseudoplastic", and no initial stress (yield stress) is required
to initiate shearing.
[0032] With the mechanics of viscoplastic fluids in mind, one
embodiment of the present invention will define a solution that is
constructed so as to place the solution into a substantially stable
suspended form. The substantially stable suspended form will be one
that is substantially elastically solid and non-flowing. Some
elastic movement may occur, similar to the movement of jelly.
Further, the stable suspended form will hold in place (i.e.,
suspend) any constituents that define the solution. The solution
will therefore exhibit a viscoplastic behavior, such that a minimum
yield stress will be required to be applied to the solution before
the solution can be used and applied in the form of a Newtonian
fluid.
[0033] FIG. 3 illustrates a system diagram 300 identifying
constituents that may be mixed together to define a suspended
solution having a viscoplastic fluid characteristic, in accordance
with one embodiment of the present invention. The basic components
of the solution, in accordance with one embodiment of the present
invention, will be three components. Other parts, fluids,
chemicals, or additives may also be added, but the basic elements
are defined by the three shown in FIG. 3. Thus, a first component
will be a polymer network producing material 302, a second
component will be a continuous media 304, and the third component
will be a solid material 306. The polymer network producing
material 302 is preferably a polymer, such as a poly (acrylic acid)
that is capable of defining a polymer network when combined with
the other components of the solution.
[0034] Examples of the polymer material used to define the polymer
network producing material 302 is now provided. In one embodiment,
without limitation, polymers capable of absorbing a yield stress
without substantial deformation may include, without limitation,
Carbapol, Stabileze, Rheovis ATA and Rheovis ATN, Poly(acrylic
acid), Carageenan, Methylcellulose, Hydroxypropylmethylcellulose,
Hydroxyethylcellulose, Gum Arabic (Acacia), Gum Tragacanth,
Polyacrylates, Carbomer, etc. However, it should be understood that
although different types of polymer material may be used, the
selected polymer should be one that will allow the resulting
solution to produce a network that will assist in stabilizing the
solution into an elastic solid state.
[0035] Broadly, the continuous media 304 may be de-ionized water, a
hydrocarbon, selected base fluids, hydrofluoric acid (HF), ammonia,
and other chemicals and/or mixtures of chemicals in DI water, that
may be useful in cleaning surfaces of semiconductor substrates. In
specific examples, the continuous media 304 is an aqueous liquid
defined by water (de-ionized or otherwise) alone. In another
embodiment, an aqueous liquid is defined by water in combination
with other constituents that are in solution with the water. In
still another embodiment, a non-aqueous liquid is defined by a
hydrocarbon, a fluorocarbon, a mineral oil, or an alcohol, among
others. Irrespective of whether the liquid is aqueous or
non-aqueous, it should be understood that the liquid can be
modified to include ionic or non-ionic solvents and other chemical
additives. For example, the chemical additives to the liquid can
include any combination of co-solvents, pH modifiers (e.g., acids
and bases), chelating agents, polar solvents, surfactants, ammonia
hydroxide, hydrogen peroxide, hydrofluoric acid, potassium
hydroxide, sodium hydroxide, tetramethylammonium hydroxide, and
rheology modifiers such as polymers, particulates, and
polypeptides.
[0036] The solids material 306, in one embodiment, may be defined
by aliphatic acids, carboxylic acids, paraffin, wax, polymers,
polystyrene, resins, polypeptides, and other visco-elastic
materials. In one embodiment, the solid portion 306 material should
be present at a concentration that exceeds its solubility limit
within the continuous media 304. Also, it should be understood that
the cleaning effectiveness associated with a particular solid
material may vary as a function of temperature, pH, and other
environmental conditions.
[0037] The aliphatic acids represent essentially any acid defined
by organic compounds in which carbon atoms form open chains. A
fatty acid is an example of an aliphatic acid that can be used as
the solid material. Examples of fatty acids that may be used as the
solid include lauric acid, palmitic acid, stearic acid, oleic acid,
linoleic acid, linolenic acid, arachidonic acid, gadoleic acid,
eurcic acid, butyric acid, caproic acid, caprylic acid, myristic
acid, margaric acid, behenic acid, lignoseric acid, myristoleic
acid, palmitoleic acid, nervanic acid, parinaric acid, timnodonic
acid, brassic acid, clupanodonic acid, lignoceric acid, cerotic
acid, and mixtures thereof, among others. In one embodiment, the
solids material 306 can represent a mixture of fatty acids defined
by various carbon chain lengths extending from C-1 to about C-26
(fatty acids only have an even number of carbons). Carboxylic acids
are defined by essentially any organic acid that includes one or
more carboxyl groups (COOH). The carboxylic acids can include
mixtures of various carbon chain lengths extending from C-1 through
about C-100. Also, the carboxylic acids can include long-chain
alcohols, ethers, and/or ketones, above the solubility limit in the
continuous medium 304. In one embodiment, the fatty acid used as
the solid acts as a surfactant when coming into contact with a
contaminant particle on a surface of a substrate.
[0038] The polymer network producing material 302, the continuous
media 304, and the solids material 306 are then passed through
lines 308, by way of valves 310a, 310b, and 310c, which provide the
material to a synthesis container 320. Control may be by way of
computer control or manual control. The lines 308 and the valves
310 are illustrated to show structure that can be used for
transporting fluids and controlling access to fluids that may be
delivered to a receiving source. However, it should be understood
that any number for structures are possible, so long as the fluids
can be communicated to their desired location for processing,
storing, or use. In this example, synthesis container 320 may be a
beaker, a tank, a mixing manifold, a staging pipe, a holding
cylinder, a container capable of being pressurized, a temperature
controlled tank, or any type of structural container that will hold
at least the received materials from the polymer network producing
material 302, the continuous media 304, and the solids material
306. The materials from 302, 304, and 306 may be provided directly
through facilities, and may not necessarily be pre-stored in a
container, but for ease of illustration, containers are shown
providing their contents in a controlled manner, as dictated by a
human or computer, to the synthesis container 320. The synthesis
container 320 may be provider with a mixer 324, that will enable
the synthesis container to mix the constituents, at given times,
when introduced into the synthesis container 320.
[0039] The result of mixing and synthesizing the different
constituents in the synthesis container 320 will be to produce a
suspended solution 322. The suspended solution, when mixed and
synthesized, is provided with a heat source 326, that is controlled
so as to enable temperature specific mixing, blending, and/or
dissolving of the various constituents at specific times. The
resulting suspended solution 322 is then moved to a container 330,
by way of an output flow line 328. The output flow line may be any
type of conduit or conduits, that can transfer the suspended
solution 322 from the synthesis container 320 to the container 330.
Initially, when the suspended solution 322 is moved from the
synthesis container 322, a minimum shear stress may be applied so
as to cause the viscoplastic nature of the suspense solution 322 to
flow along the output flow line 328 and into container 330.
[0040] Once the suspended solution 322 is transferred to the
container 330, the suspended solution may continue to ripen over
time, such that nucleation of the solids will occur, and the solids
will either join or grow together so as to produce larger sized
solids within the suspended solution 322. During the ripening
process, however, the solids within the suspended solution 322 will
be suspended by the polymer network material so that the solids do
not either rise to the top of the container 330 or fall to the
bottom of the container 330.
[0041] That is, although the buoyancy of each of the individual
suspended solids (relative to the continuous medium) within the
suspended solution 322 will impact the solids tendency to either
float or sink, any tendency to move will be counter-acted by the
polymer network of the suspended solution 322. The solids will
therefore remain in a substantially elastic suspension until the
solution needs to be used. When the suspended solution 322 is
needed for use or needs to be transported, the yield stress of the
suspended solution 322 will need to be overcome, so that the
solution can experience shear thinning as the shear rate
increases.
[0042] FIG. 4 illustrates a plurality of containers 330 having
solids dispersed in a suspended solution, which will sit, hold and
store in a substantially elastic state (e.g., a solid). As noted
above, the solid state of the solution is therefore designed to
function as a viscoplastic fluid that is elastic, and any buoyancy
associated with solids within the continuous medium of the
suspended solution 332 will remain substantially in place. As such,
the suspended solution 332 will be ready for use in a well
dispersed manner, and any storage associated with the solution will
not require pre-use mixing, as the suspended solution and its
constituents are already in a dispersed and mixed form.
[0043] Advantages of having the solution in a viscoplastic fluid
state is that the solution may be pre-mixed in larger batches, and
then stored and transported to their point of use. If use of the
solution is not needed until a later point in time, the solution
will continue to hold its dispersed and stable suspended form until
its use is dictated.
[0044] FIG. 5 illustrates a system diagram for using the suspended
solution from a container 330, when its use is required on
substrate preparation systems 400. As illustrated, the container
330 will be holding the suspended solution 332. When use of the
suspended solution 332 is needed, the solution may be pumped out of
the container 330 using a pump 352. The pump 352 is shown connected
to a conduit 350 that is placed within the suspended solution 332.
The agitation provided by the pump 352 will therefore work to apply
a shear stress to the suspended solution 332, which therefore
causes a shear stress application zone 344 (somewhere in the
container) to cause the solution (or at least part of the solution)
to flow continuously. The lower viscosity fluid will thus freely
move along the conduit 350, as shown by indicator 332a. The flowing
solution will then be transported by the pump 352, that directs the
fluid to some destination.
[0045] Thus, the pump 352 acts to transport the suspended solution
332, and the shear thinning behavior of the suspended solids allows
for easy transport through conduits 360a and 362. In one
embodiment, the pump 352 may be connected to flow the low viscosity
solution through conduit 360a into a foam generation system 370.
The foam generation system 370 may include a gas pressure chamber
372 that is configured to allow a foaming process to occur to the
solution before it is communicated through a conduit 360b. Conduit
360b will therefore carry the solution in a tri-state body form to
one or more systems of the substrate preparation systems 400. A
tri-state body is one where a "gas" component is added to the
"fluid" component and the "solids" component of the solution. A
tri-state body will be defined in greater detail below.
[0046] In another embodiment, the pump 352 may simply communicate
the solution along conduit 362, in a two-state body to the
substrate preparation system 400. A two-state body is one that has
a "fluid" component and a "solids" component, but substantially no
"gas" component. It is said that substantially no gas is part of a
two state body solution, but some gas may be inherently in the
solution.
[0047] The substrate preparation system 400 may include any number
of systems, and a few are provided as an example. One example
system may be a proximity head system 402, that uses a proximity
head to apply a meniscus to the surface of a substrate between a
head surface and the substrate surface. One proximity head on the
top of the substrate may be used, or two proximity heads may be
used, such that both the top and bottom of the substrate is
processed at about the same time.
[0048] In one embodiment, the substrate is caused to move along a
horizontal direction, such that the meniscus is caused to traverse
the surface of the substrate. In another embodiment, the heads of
the proximity head system may be moved across the surface of the
substrate.
[0049] A "meniscus", as used herein, may be a controlled fluid
meniscus that forms between the surface of a proximity head and a
substrate surface, and surface tension of the fluid holds the
meniscus in place and in a controlled form. Controlling the
meniscus is also ensured by the controlled delivery and removal of
fluid, which enables the controlled definition of the meniscus, as
defined by the fluid. The meniscus may be used to either clean,
process, etch, or process the surface of the substrate. The
processing on the surface may be such that particulates or unwanted
materials are removed by the meniscus. In a related embodiment, the
meniscus may be formed out of a tristate body (e.g., a foamed
solution), and the solution may simply sit on the surface at the
substrate, but mechanically function different than fluid solutions
that are affected by surface tension. A foamed solution behaves
more like a non-Newtonian fluid.
[0050] A Newtonian meniscus fluid, however, is controlled by
supplying a fluid to the proximity heads while removing the fluid
with a vacuum in a controlled manner. Optionally, a gas tension
reducer may be provided to the proximity heads, so as to reduce the
surface tension between the meniscus and the substrate. The gas
tension reducer supplied to the proximity heads allow the meniscus
to move over the surface of the substrate at an increased speed
(thus increasing throughput). An example of a gas tension reducer
may be isopropyl alcohol mixed with nitrogen (IPA/N.sub.2). Another
example of a gas tension reducer may be carbon dioxide (CO2). Other
types of gasses may also be used so long as the gasses do not
interfere with the processing desired for the particular surface of
the substrate.
[0051] For more information on the formation of a meniscus and the
application to the surface of a substrate, reference may be made
to: (1) U.S. Pat. No. 6,616,772, issued on Sep. 9, 2003 and
entitled "METHODS FOR WAFER PROXIMITY CLEANING AND DRYING,"; (2)
U.S. patent application Ser. No. 10/330,843, filed on Dec. 24, 2002
and entitled "MENISCUS, VACUUM, IPA VAPOR, DRYING MANIFOLD," (3)
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," (4) U.S. Pat. No. 6,998,326, issued on Jan. 24,
2005 and entitled "PHOBIC BARRIER MENISCUS SEPARATION AND
CONTAINMENT," and (5) U.S. Pat. No. 6,488,040, issued on Dec. 3,
2002 and entitled "CAPILLARY PROXIMITY HEADS FOR SINGLE WAFER
CLEANING AND DRYING," each is assigned to Lam Research Corporation,
the assignee of the subject application, and each is incorporated
herein by reference.
[0052] A next example is a proximity head-brush system 404. This
example is provided to illustrate that the proximity head system
may be combined with other types of cleaning systems, such brush
rollers that are configured to scrub the surface of a wafer. The
surface may be scrubbed either on top or bottom with a brush, and a
proximity head system may be used either on the top or the
bottom.
[0053] The brushes may be polyvinyl alcohol (PVA) brushes, that may
provide fluids to the surface of the substrate while rotating. The
fluids provided by the brushes may be provided through the brush
(TTB) core and the fluids may be for cleaning, and/or etching,
and/or configuring the surface of the substrate to be either
hydrophobic or hydrophilic, depending on the application.
[0054] Another system may be a spray/jet system 406, which is
configured to apply either the tri-state bodies or the two-state
bodies to the surface of the substrate. Sprays and jets may be
applied such that the solids in the tri-state bodies or two-state
bodies can be efficiently dispensed so as to allow the appropriate
preparation operation. For more information on jet application,
reference may be made to U.S. application Ser. No. 11/543,365,
filed on Oct. 4, 2006, entitled "Method and Apparatus for Particle
Removal", and is herein incorporated by reference. In still another
embodiment, a module can be configured as a tank. The tank can be
filled with the solution, and a substrate (or batches of
substrates) can be lowered into the tank and then removed from the
tank. This type of substrate processing may be referred to as
dipping. When the dipping occurs, the solution can either be in an
elastic state or in a fluid state. The movement of the substrate
into the solution may provide the needed shear stresses that will
overcome the yield stress of the suspended solution 332.
[0055] The preparation operation may be for cleaning, drying,
etching, transformation of surface states (e.g.,
hydrophobic/hydrophilic), and/or general cleaning to remove
particles with the assistance of the solids, that are applied using
the systems of the substrate preparation system 400.
[0056] It should be understood, however, that the container 330 and
the suspended solution 332 may be stored for a period of time and
when used, can be transformed from a substantial solid state to a
fluid flowing Newtonian state, by the application of shear stresses
that will overcome the yield stress of the suspended solution 332
so that it can flow and be applied to the surface of a substrate
for its application. An example amount of minimum sheer stress may
be between about le-6 Pa and about 100 Pa. However, the exact
amount will change depending on the combined elements of the
particular solution.
[0057] By maintaining the suspended solution 332 in its suspended
form, the problems associated with having solids either float to
the surface, or sink to the bottom of a container, are avoided, and
its dispersed and well mixed state will remain until the suspended
solution is needed for application and use. Any downtime that would
have been spent for re-adjusting the fluid to allow for a
consistent distribution can now be avoided, and more throughput and
efficient processing with the suspended solution can now be
performed, and applied to substrates when needed.
[0058] FIG. 6 illustrates an example recipe 600 for generating a
solution that will exhibit a substantial solid elastic state when
stored, and then transformed to a substantial Newtonian fluid upon
the application of shear stresses when the solution is needed. The
recipe includes operation 602 where a continuous medium is
supplied. As noted above, the continuous medium can be defined by a
number of fluids and/or materials, but for this specific example,
the continuous medium is de-ionized (DI) water.
[0059] The continuous medium is then supplied with a polymer, where
it is mixed until it is substantially dissolved in the de-ionized
water in operation 604. The mixed solution of 604 is them heated in
operation 606. The heating of the solution should take place such
that the temperature is between about 30.degree. C. and about
100.degree. C., and in one embodiment, between about 65.degree. C.,
and about 85.degree. C.
[0060] While the solution is heated, in operation 608, a surfactant
is added to the mixture. The surfactant material is preferably one
of ammonium lauryl sulfate, linear alkyl benzene sulfonic acic,
triethanol amine lauryl sulfate, or a ionic surfactant. Once the
surfactant has been added to the heated mixture in operation 608,
the solution is continued to be mixed at a high RPM. An example of
a high revolution per minute (RPM) may be between about 50 RPMs and
about 1,500 RPMs. High RPM mixing should continue as long as
possible, but without generating a noticeable froth layer. If some
bubbles are created during this mixing operation, a minimum amount
of bubbles would be allowable. In operation 612, a neutralizing
base component will be added to the solution once the solution is
again heated to a temperature range of between about 70.degree. C.
and about 80.degree. C. In one embodiment, the neutralizing basic
component is ammonia (i.e. NH4OH). Other neutralizing basic
components may also work, for instance, tetramethyl ammonium
hydroxide, triethanol amine, sodium hydroxide, potassium hydroxide
can work.
[0061] In operation 614, immediately after the neutralizing basic
component is added in operation 612, the solid component is added
and mixed until the solid is substantially melted in the heated
mixture. Mixing of the solid component in the solution in operation
614 will continue until the solid component is substantially
dissolved in the solution. In operation 616, a chelating agent is
added and then mixed. Other chelating agents may also work, for
instance, EDTA, lactic acid, glycine, gluconic acid, citric acid
may work. At this point, the solution is still preferably held at
about a temperature range between 65.degree. C. and about
85.degree. C.
[0062] The solution will mix in operation 616, for between about 5
minutes and about 120 minutes. In operation 618, the solution is
cool to about room temperature and then moved into a container,
such as container 330 of FIG. 3. Alternatively, the solution will
cool once moved to the container 330. During cooling, the solution
will undergo nucleation until its end solid elastic state is
reached and held. The final solution will appear to have a milky
white color, and the viscosity of the solution. Further, during
cooling, the solution will change in time, to a consistency having
slightly more viscosity than water. At this point, the solution
will behave like a viscoplastic, or equivalently like a Bingham
plastic. In operation 620, the solution can be stored, having the
solids (e.g., fatty acids) in a stable and substantial
suspension.
[0063] In one embodiment, another example recipe for formulating a
basic solution is defined in Table A. A beaker of having a size of
about 1 liter, is used to illustrate an example formulation of the
solution.
TABLE-US-00001 TABLE A (a) Add DI water to a beaker and begin to
stir; (b) Add a rheology modifier (e.g., polymer) to the solution
and mix at high RPM until the component is dissolved; (c) Begin to
heat the solution to about 75.degree. C. (d) Add a surfactant
component once the solution is around 50.degree. C. (e) Mix at a
relatively high RPM (e.g., as high as possible without generating a
noticeable froth layer), although it is fine if some bubbles are
mixed into the solution. (f) After the solution reaches 75.degree.
C., add a neutralizing basic component (e.g., NH4OH). (g)
Immediately after the base is added, add stearic acid (e.g., fatty
acid). (h) Mix for about 10 minutes, so that the stearic acid has
substantially melted (adjust stirring rate maximize mixing -
decrease mixing rate if too many bubbles). (i) With the solution
still at approximately 75.degree. C., add a chelating agent. (j)
Mix for an additional 10 minutes. (k) At this point the solution
may be removed from the mixing source and cooled in a container (or
stored for later use).
[0064] FIG. 7 illustrates a flowchart 700 defining example
operations for using the suspended solution, in accordance with one
embodiment of the present invention. The method begins at operation
720, where a container of the solution characterized as a stable
suspended solution is obtained. The solution may have been stored
for some time, or may have just been created, and allowed to
cool.
[0065] In either case, the container will hold a viscoplastic fluid
that holds the solids in a suspended form, thus not allowing the
buoyancy of the solids relative to the continuous medium to be
overcome. In operation 720, a shear stress is applied to the
solution to transform its non-Newtonian character to a Newtonian
character. The non-Newtonian character is that of the viscoplastic
material with a yield stress (e.g., exhibits a substantially solid
form).
[0066] Once the shear stress is applied, as noted with reference to
FIGS. 1 and 2, the viscoplastic material will shear thin until
Newtonian behavior dominates in operation 704. In operation 706,
the solution is allowed to flow from the container to a next stage,
before application to a substrate, through one or more application
systems. In operation 708, the solution is optionally foamed so as
to create a tri-state body. If a tri-state body is not desired, the
method moves to operation 710 where the solution in two-state form
is flowed to an application system.
[0067] The application system may be any system such as those
described with reference to FIG. 5, or any other system that may be
involved in the cleaning of parts, surfaces, or semiconductor
substrates. In operation 712, the solution is applied to a surface
of a substrate. The solution will then act to assist in the
cleaning operation of a substrate, where the solids assist in
removing of particles that may be present on the surface.
[0068] As used herein, a tri-state body cleaning material contains
a plurality of tri-state bodies that include a gas phase, a liquid
phase and a solid phase. In one embodiment, the gas phase and
liquid phase provides an intermediary to bring the solid phase into
close proximity with contaminant particles on a substrate
surface
[0069] In one embodiment, the gas portion is defined to occupy 5%
to 99.9% of the tri-state body cleaning material by volume. In
another embodiment, the gas portion can occupy between about 15%
and about 40% of the tri-state body, and still another embodiment,
the gas portion can occupy between about 20% and about 30% of the
tri-state body. The gas or gases defining a gas portion can be
either inert, e.g., nitrogen (N.sub.2), argon (Ar), etc., or
reactive, e.g., oxygen (O.sub.2), ozone (O.sub.3), hydrogen
peroxide (H.sub.2O.sub.2), air, hydrogen (H.sub.2), ammonia
(NH.sub.3), hydrogen fluoride (HF), hydrochloric acid (HCl), etc.
In one embodiment, the gas portion includes only a single type of
gas, for example, nitrogen (N.sub.2). In another embodiment, the
gas portion is a gas mixture that includes mixtures of various
types of gases, such as: ozone (O.sub.3), oxygen (O.sub.2), carbon
dioxide (CO.sub.2), hydrochloric acid (HCl), hydrofluoric acid
(HF), nitrogen (N.sub.2), and argon (Ar); ozone (O.sub.3) and
nitrogen (N.sub.2); ozone (O.sub.3) and argon (Ar); ozone
(O.sub.3), oxygen (O.sub.2) and nitrogen (N.sub.2); ozone
(O.sub.3), oxygen (O.sub.2) and argon (Ar); ozone (O.sub.3), oxygen
(O.sub.2), nitrogen (N.sub.2), and argon (Ar); and oxygen
(O.sub.2), argon (Ar), and nitrogen (N.sub.2). It should be
appreciated that the gas portion can include essentially any
combination of gas types as long as the resulting gas mixture can
be combined with a liquid portion and a solid portion to form a
tri-state body that can be utilized in substrate cleaning or
preparation operations.
[0070] It should be understood that depending on the particular
embodiment, the solid portion of the tri-state body may possess
physical properties representing essentially any sub-state, wherein
the solid portion is defined as a portion other than the liquid or
gas portions. For example, physical properties such as elasticity
and plasticity can vary among different types of solid portions
within the tri-state body. Additionally, it should be understood
that in various embodiments the solid portion can be defined as
crystalline solids or non-crystalline solids. Regardless of their
particular physical properties, the solid portion of the tri-state
body should be capable of avoiding adherence to the substrate
surface when positioned in either close proximity to or in contact
with the substrate surface or capable of being easily removed
(e.g., hydrodynamic removal with rinse). Additionally, the physical
properties of the solid portion should not cause damage to the
substrate surface during the cleaning process. Furthermore, the
solid portion should be capable of establishing an interaction with
the contaminant particle present on the substrate surface when
positioned in either close proximity to or contact with the
particle. In one embodiment, the solid portion has foam inhibiting
properties. In another embodiment, the solid portion has foam
enhancing properties. Depending on the application and the
apparatus used to handle the tristate body, the foam enhancing or
inhibiting properties can be adjusted, either in a stepped manner
or in accordance with a recipe.
[0071] In one embodiment, the solid portion avoids dissolution into
the liquid portion and gas portions and has a surface functionality
that enables dispersion throughout the liquid portion. In another
embodiment, the solid portions does not have surface functionality
that enables dispersion throughout the liquid portion, therefore
requiring chemical dispersants to be added to the liquid portion to
before the solid portions can be dispersed through the liquid
portion. In one embodiment, the solid portions form through a
precipitation reaction where a dissolved component in the liquid
phase reacts by the addition of one or more components to form an
insoluble compound. In one embodiment, the solid portion goes into
suspension in the liquid portion when a base is added to the liquid
portion (i.e., by altering the zeta potential). Depending on their
specific chemical characteristics and their interaction with the
surrounding liquid portion, the solid portion may take one or more
of several different forms.
[0072] For example, in various embodiments the solid portion may
form aggregates, colloids, gels, coalesced spheres, or essentially
any other type of agglutination, coagulation, flocculation,
agglomeration, or coalescence. It should be appreciated that the
exemplary list of solid portion forms identified above is not
intended to represent an inclusive list, and alternates or
extensions falling within the spirit of the disclosed embodiments
are possible. It should further be understood that the solid
portion can be defined as essentially any solid material capable of
functioning in the manner previously described with respect to
their interaction with the substrate and the contaminant
particle.
[0073] Although a few embodiments of the present invention have
been described in detail herein, it should be understood, by those
of ordinary skill, that the present invention may be embodied in
many other specific forms without departing from the spirit or
scope of the invention. Therefore, the present examples and
embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
provided therein, but may be modified and practiced within the
scope of the appended claims.
* * * * *