U.S. patent application number 12/232712 was filed with the patent office on 2009-01-29 for free radical-forming activator attached to solid and used to enhance cmp formulations.
This patent application is currently assigned to DuPont Air Products NanoMaterials LLC. Invention is credited to Brandon Shane Scott, Robert J. Small.
Application Number | 20090029553 12/232712 |
Document ID | / |
Family ID | 27732385 |
Filed Date | 2009-01-29 |
United States Patent
Application |
20090029553 |
Kind Code |
A1 |
Scott; Brandon Shane ; et
al. |
January 29, 2009 |
Free radical-forming activator attached to solid and used to
enhance CMP formulations
Abstract
The present invention provides a composition for
chemical-mechanical polishing which comprises at least one abrasive
particle having a surface at least partially coated by a activator.
The activator comprises a metal other than a metal of Group 4(b),
Group 5(b) or Group 6(b). The composition further comprises at
least one oxidizing agent. The composition is believed to be
effective by virtue of the interaction between the activator coated
on the surface of the abrasive particles and the oxidizing agent,
at the activator surface, to form free radicals. The invention
further provides a method that employs the composition in the
polishing of a feature or layer, such as a metal film, on a
substrate surface. The invention additionally provides a substrate
produced this method.
Inventors: |
Scott; Brandon Shane;
(Castro Valley, CA) ; Small; Robert J.; (Hayward,
CA) |
Correspondence
Address: |
MORGAN LEWIS & BOCKIUS LLP
1111 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
20004
US
|
Assignee: |
DuPont Air Products NanoMaterials
LLC
|
Family ID: |
27732385 |
Appl. No.: |
12/232712 |
Filed: |
September 23, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11405485 |
Apr 18, 2006 |
7427305 |
|
|
12232712 |
|
|
|
|
10361822 |
Feb 11, 2003 |
7029508 |
|
|
11405485 |
|
|
|
|
10074757 |
Feb 11, 2002 |
|
|
|
10361822 |
|
|
|
|
Current U.S.
Class: |
438/693 ;
252/79.1; 257/E21.237 |
Current CPC
Class: |
C09K 3/1463 20130101;
C09G 1/02 20130101; C09K 3/1445 20130101; C23F 3/04 20130101; B24B
37/044 20130101; C03C 19/00 20130101; G11B 5/3163 20130101; C09K
3/1436 20130101; Y02P 20/582 20151101; G11B 5/3169 20130101; C23F
3/00 20130101; H01L 21/3212 20130101 |
Class at
Publication: |
438/693 ;
252/79.1; 257/E21.237 |
International
Class: |
H01L 21/304 20060101
H01L021/304; C09K 13/00 20060101 C09K013/00 |
Claims
1.-74. (canceled)
75. A composition for chemical-mechanical polishing comprising: an
aqueous fluid comprising at least one per-compound oxidizer that
produces at least one oxygen-containing free radical when contacted
with at least one activator; and a plurality of metal oxide
abrasive particles, wherein the at least one activator comprises a
photo-activated activator.
76. The composition of claim 1, wherein the photo-activated
activator is selected from TiO.sub.2, Ti.sub.2O.sub.3, and oxides
of Ta, W, V, Nb and combinations thereof.
77. The composition of claim 1, wherein the photo-activated
activator is present in a matrix and the aqueous fluid contacts the
matrix before passing between a pad and a substrate.
78. The composition of claim 1, wherein the amount of the least one
activator is present in an amount from about 0.0001% to about 60%
by weight.
79. The composition of claim 1, further comprising between 0.001 to
about 1 weight percent of a stabilizer selected from vitamin B,
vitamin C, citric acid, and mixtures thereof.
80. The composition of claim 1, wherein the at least one
per-compound oxidizer comprises at least one peroxide.
81. The composition of claim 1, wherein the at least one
per-compound oxidizer comprises hydrogen peroxide.
82. The composition of claim 1, wherein the metal oxide abrasive
particles comprise alumina, silica, ceria and titania.
83. The composition of claim 1, wherein the metal oxide abrasive
particles comprise alumina-coated silica.
84. The composition of claim 1, wherein the metal oxide abrasive
particles have an effective diameter of about 30 to about 170
nanometers.
85. The composition of claim 1, wherein the metal oxide abrasive
particles having an average particle size between 1 and 100
nanometers have a particle size distribution such that one sigma is
10% of the average particle size.
86. The composition of claim 1, further comprising between 0.001%
to about 0.2% by weight of surfactant.
87. The composition of claim 1, further comprising a stabilization
agent comprising ligands that bind with the at least one activator
and reduce activator efficacy and that also reduce undesirable
reactions that degrade the at least one per-compound oxidizer.
88. The composition of claim 1, further comprising between 0.001%
and 2% by weight of a stabilization agent comprising ligands that
bind with the at least one activator and reduce activator efficacy
and that also stabilize the at least one per-compound oxidizer.
89. A method of chemically mechanically polishing comprising: (A)
providing a semiconductor wafer substrate having a surface to be
polished comprising tungsten and a dielectric material; (B)
providing an aqueous composition comprising: 1) at least one
per-compound oxidizer that produces at least one oxygen-containing
free radicals when contacted with at least one activator; and a
plurality of metal oxide abrasive particles, wherein said at the
least one activator comprises a photo-activated activator, and (C)
contacting the substrate surface with an abrasive and with the
aqueous composition thereby polishing tungsten from the surface of
the semiconductor wafer substrate.
90. The method of claim 16, wherein the photo-activated activator
is selected from TiO.sub.2, Ti.sub.2O.sub.3, and oxides of Ta, W,
V, Nb and combinations thereof.
91. The composition of claim 16, wherein the photo-activated
activator is present in a matrix and the aqueous fluid contacts the
matrix before passing between a pad and a substrate.
Description
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 10/074,757 filed Feb. 11, 2002, the entire
contents of which is incorporated herein by express reference
thereto.
FIELD OF THE INVENTION
[0002] The invention relates generally to a system that is useful
in chemical mechanical polishing (hereafter CMP) processes, and an
associated method of polishing a substrate using one or more parts
of the system. More particularly, in one embodiment, the invention
relates to a composition comprising a free radical-producing
oxidizing agent, and a free radical-producing activator which is
affixed to a solid in contact with the composition. In another
embodiment, the invention relates to a non-metallic free
radical-producing activator which is in solution, a free
radical-producing oxidizing agent, and optionally a free
radical-producing activator which is affixed to a solid. The
composition is useful in the polishing of various layers, such as
metal layers, on substrates.
BACKGROUND OF THE INVENTION
[0003] A semiconductor wafer, such as a silicon or a gallium
arsenide wafer, generally has a substrate surface on which one or
more integrated circuits is formed. The substrate surface is
desirably as flat, or planar, as possible before the surface is
processed to form the integrated circuits. A variety of
semiconductor processes are used to form the integrated circuits on
the flat surface, during which the wafer takes on a defined
topography. The topography is subsequently planarized, because an
irregular surface, or a surface having imperfections, seriously
impedes subsequent fabrication processes, such as photolithography.
Thus, it is necessary to polish the wafer surface to render it as
planar or uniform as possible and to remove surface
imperfections.
[0004] Chemical-mechanical polishing or planarization (CMP)
processes are well-known. See, for example, Chemical Mechanical
Polishing in Silicon Processing, Semiconductors and Semimetals,
Vol. 62, Edited by Li, S. et al., which is expressly incorporated
herein by reference. Also directly incorporated by reference for
all purposes are commonly assigned: [0005] U.S. Pat. No. 5,891,205
to Picardi et al., which issued on Apr. 6, 1999, entitled Chemical
Mechanical Polishing Composition; [0006] U.S. Pat. No. 5,981,454 to
Small, which issued on Nov. 9, 1999, entitled Post Clean Treatment
Composition Comprising An Organic Acid And Hydroxylamine; [0007]
U.S. Pat. No. 6,117,783 to Small et al., which issued on Sep. 12,
2000, entitled Chemical Mechanical Polishing Composition And
Process; [0008] U.S. Pat. No. 6,156,661 to Small, which issued on
Dec. 5, 2000, entitled Post Clean Treatment; [0009] U.S. Pat. No.
6,235,693 to Cheng et al., which issued on May 22, 2001, entitled
Lactam Compositions For Cleaning Organic And Plasma Etched Residues
For Semiconductor Devices; [0010] U.S. Pat. No. 6,248,704 to Small
et al., which issued on Jun. 19, 2001, entitled Compositions For
Cleaning Organic And Plasma Etched Residues For Semiconductors
Devices; [0011] U.S. Pat. No. 6,251,150 to Small et al., which
issued on Jun. 26, 2001, entitled Slurry Composition And Method Of
Chemical Mechanical Polishing Using Same; [0012] U.S. Pat. No.
6,313,039 to Small et al., which issued on Nov. 6, 2001, entitled
Chemical Mechanical Polishing Composition And Process; and [0013]
U.S. Pat. No. 6,498,131 to Small et al., which issued on Dec. 24,
2002, entitled Composition For Cleaning Chemical Mechanical
Planarization Apparatus.
[0014] CMP processes are commonly used to polish or "planarize" the
surfaces of wafers at various stages of fabrication to improve
wafer yield, performance and reliability. In CMP, typically the
wafer is held in place on a mount using negative pressure, such as
vacuum, or hydrostatic or pneumatic pressure. The mount is
typically situated over a polishing pad. CMP generally involves
applying a polishing composition or slurry to the polishing pad,
establishing pressure-contact between the composition- or
slurry-coated wafer surface and the polishing pad while providing
relative motion, typically rotational or orbital motion, between
the wafer surface and the polishing pad.
[0015] The polishing composition typically contains an abrasive
material, such as silica, ceria, and/or alumina particles, in an
acidic, neutral, or basic solution. Merely by way of example, a
polishing composition useful in the CMP of tungsten material on a
substrate may contain abrasive alumina, also called aluminum oxide,
an oxidizing agent such as hydrogen peroxide, and either potassium
hydroxide or ammonium hydroxide. A CMP process employing such a
polishing composition may provide a predictable rate of polishing,
while largely preserving desirable features on the wafer
surface.
[0016] For such a semiconductor wafer, a typical CMP process
involves polishing the metal in a controlled manner to
preferentially etch certain conductors, insulators or both over the
oxide beneath the metal, such that the metal is substantially
coplanar with the oxide and remains in the grooves or stud vias of
the oxide. After CMP, the substantially coplanar surface is ready
for further processing. CMP is currently the primary method used to
polish or "planarize" wafers in back end of the line (BEOL)
processes.
[0017] Semiconductor fabrication processes such as photolithography
have evolved significantly, such that advanced devices having very
fine oxide, metal, and other surface features, with sub-0.25 micron
geometries (such as 0.18 micron or less), are now being made.
Process tolerances are necessarily tighter for these advanced
devices, calling for improvements in CMP technology to obtain
desired material removal rates while minimizing wafer defects or
damage. A variety of approaches have been taken in an effort to
improve CMP processes to improve planarity.
[0018] On the other hand, economic forces are requiring the use of
faster processing. One approach has involved increasing the
downward pressure on the wafer carrier in order to increase
material removal rates. This approach is generally disfavored as
the requisite downward pressure is considered too high and too
likely to cause wafer damage, such as scratching, delamination, or
destruction of material layers on the wafer. When the wafer is
fragile, as is generally the case with substrates layered with
films such as porous films having a low dielectric constant, these
damage issues are particularly acute and detrimental in terms of
wafer yield and performance. Generally, faster chemical-mechanical
polishing results in more defects.
[0019] Additional approaches have involved using various protected
combinations of oxidizers, chelators, corrosion inhibitors,
solvents, and other chemicals in the slurry, various abrasives
including for example a zirconium abrasive or mixed abrasives,
and/or using point-of-use mixing techniques. These approaches are
generally undesirable, as they typically complicate CMP in terms of
tooling and process control for example, consume more process time,
and/or increase costs.
[0020] Another approach has involved increasing the amount of
oxidizing agent used in the CMP slurry in an effort to increase
chemical removal of targeted material. This approach is largely
disfavored as the use of increased amounts of oxidizing agents
increase material costs and also detrimentally add to the handling
issues and environmental issues associated with many oxidizing
agents and also increase costs.
[0021] It is generally known that oxidizers admixed in a solution
can provide synergistic etching rates. While ferric salts, cerium
salts, peroxides, persulfates, or hydroxylamines form the oxidizing
capacity of most commercially available CMP slurries, those of
ordinary skill in the art have long known that these oxidizers can
be admixed with others in this group and also with other oxidizers,
and the resulting composition can show synergistic results.
[0022] For example, the compositions claimed in U.S. Pat. No.
6,117,783 to Small et al., which claims priority to a provisional
application filed Jul. 25, 1996, the contents of which is
incorporated herein by reference thereto, claims a CMP slurry
having a hydroxylamine compound and hydrogen peroxide, and teaches
in the specification that the two have a synergistic effect. U.S.
Pat. No. 6,117,783 also claims a CMP slurry having a hydroxylamine
compound and ammonium bifluoride. These are mixtures of
non-metal-containing oxidizers that provide synergistic results.
Similarly, U.S. Pat. No. 5,783,489, the disclosure of which is
incorporated herein by reference thereto, discloses an aqueous CMP
slurry comprising at least two oxidizing agents, an organic acid
and an abrasive having a pH ranging from about 2.0 to about
8.0.
[0023] Without being bound to theory, it is believed that certain
metal salt oxidizers have a greater oxidizing "probability" than
non-metal-containing oxidizers, which may be based at least in part
on affinity of the oxidizer to the substrate. Greater affinity
enhances the possibility of oxidation but also creates a problem in
that the molecule with the greater affinity does not as readily
leave the substrate after oxidizing the substrate as other
oxidizers. Synergy with metal-containing and non-metal-containing
oxidizers may be observed if the other, typically
non-metal-containing, oxidizers can oxidize spent oxidizer that is
near or on the substrate, such that reaction with the substrate
would be fast. Following this line of reasoning, it stands to
reason that it is beneficial to have some minimum amount of the
metal, to have enough metal-containing oxidizer ions near the
surface, but a large excess of the non-metal-containing oxidizer
would be beneficial to more quickly re-oxidize the spent
metal-containing oxidizer.
[0024] Of course, the soluble salt of any metal having multiple
oxidation states may be an oxidizer, provided they have the
oxidative potential to oxidize the substrate. Metal-containing
oxidizers such as permanganate, perchromate, iron salts, aluminum
salts, cerium salts, and the like are commonly used in CMP
slurries, and synergistic combinations of the metal-containing
oxidizers as well as of metal-containing and non-metal-containing
oxidizers is also known. CMP of certain metal substrates, for
example a copper-containing substrate, will doubtless provide
metals, for example cupric and/or cuprous metal ions, in the
solution, but these will not oxidize the remaining copper layer. If
there are two different metals, however, the oxidized and removed
ion of one metal may in turn be an oxidizing metal for another
metal, but the amount will be very small.
[0025] U.S. Pat. No. 4,959,113, reissued, filed on Jul. 31, 1989,
the disclosure of which is incorporated herein by reference
thereto, claims synergistic CMP slurries having two or more salts
where the cations are selected from ionized elements (i.e., metals)
which will not deposit by electroless plating on the metal surface
being polished. This patent states "preferred cationic component of
the salt is an ionized element from Groups IIA, IIIA, IVA and IVB
of the periodic table of elements, as well as zinc, cerium, tin and
iron ions . . . (and) an aqueous polishing composition comprising a
combination of salts with the water and abrasive agent provides
improved polishing of metal surfaces compared to the use of a
single salt. Thus, there appears to be a synergistic effect when a
combination of two or more salts is used in the polishing
composition compared to the use of a single salt."
[0026] One metal-containing oxidizing agent used in CMP is silver
nitrate. Silver nitrate and hydrogen peroxide are present in the
CMP slurry of U.S. Pat. No. 5,354,490, the contents of which is
incorporated herein by reference thereto. Synergy is taught, as the
patent stated the silver nitrate converts, at the copper containing
metal surface, a solid copper film or a solid copper alloy film
into an aqueous phase, while the role of the second oxidizing
agent, i.e., hydrogen peroxide, would be to form a copper oxide.
The copper oxide would be subsequently removed by the mechanical
polishing of the CMP action, such that the addition of the second
oxidizing agent can increase the mechanical polishing component of
the CMP process.
[0027] Another metal-containing oxidizing agent commonly used in
CMP is ferric nitrate. U.S. Pat. No. 5,527,423, the contents of
which is incorporated herein by reference thereto, teaches a CMP
slurry that contains oxidizing components such as mixtures of iron
salts and persulfates. Ferric nitrate has been used extensively
where tungsten metal or alloys present on the substrate require
polishing.
[0028] However, ferric nitrate causes metallic contamination of
many substrates, including tungsten substrates. Raghunath et al
showed in Mechanistic Aspects Of Chemical Mechanical Polishing Of
Tungsten Using Ferric Ion Based Alumina Slurries, in the
Proceedings of the First International Symposium on Chemical
Mechanical Planarization, 1997, that alumina slurries containing
ferric salts is conducive to the formation of an insoluble layer of
ferrous tungstate on tungsten. The addition of hydrogen peroxide to
ferric ion solutions is known. Basak et al., in the same
Proceedings of the First International Symposium on Chemical
Mechanical Planarization: Proceedings of Chemical Mechanical
Planarization in IC Device Manufacturing, 1997, noted that the
electrochemical behaviour of tungsten in solutions containing
ferric nitrate revealed the presence of ferric ions increases the
open circuit potential of W into the regime where oxide films are
stable, but anodic currents increased by at least one order of
magnitude on addition of hydrogen peroxide.
[0029] Some investigators call small quantities of metal-containing
oxidizer salts a catalyst as it causes synergistic etching rates
when admixed with other oxidizers. See for example U.S. Pat. No.
3,293,093, the disclosure of which is incorporated herein by
reference, which teaches a hydrogen peroxide-based etching solution
for copper. The patentees noted that many metals, particularly
copper ions, "form active metal ions which have been found to have
a highly depreciating effect on hydrogen peroxide (so) that it is
rapidly exhausted" These investigators wanted to arrest the
depreciating effect of metal ions and yet to provide compounds
having a catalytic effect on the etch rate of copper. They noted
that a small amount of silver ions, and preferably also a small
amount of phenacetin, gave enhanced etching and stability. This
patent taught a solution having 2-12% hydrogen peroxide and a
"catalytic amount" of silver ions, as silver ions are, highly
effective at improving the etch rate of hydrogen peroxide, and
suggests adding silver nitrate salts. A combination of phenacetin
and silver ions with acidified hydrogen peroxide exhibits
"exceptionally fast etch rates significantly greater than when
either additive is used alone." The patent claims "as little as 10
parts per million" of silver ions is effective, and "about 50-500
parts per million of free silver ion generally represents the
preferred amount." A composition of ammonium persulfate and a
mercuric chloride catalyst was also taught in this patent.
[0030] Other investigators have also tried to mix oxidizers to
achieve synergy. U.S. Pat. No. 5,958,288, the disclosure of which
is incorporated herein by reference, suggests limiting the amount
of "catalyst" to from about 0.001 to about 2.0 weight percent. This
patent describes the catalyst as a compound having multiple
oxidation states, and that the catalyst must be able to shuffle
electrons efficiently and rapidly between the oxidizer and metal
substrate surface. While this broad description of a catalyst
encompasses any oxidizer, including any metal salt, the only
catalysts described therein are metal salt compounds of Ag, Co, Cr,
Cu, Fe, Mo, Mn, Nb, Ni, Os, Pd, Ru, Sn, Ti, and V, most preferably
a compound of iron, copper, and/or silver. This patent defines the
oxidizing agent to have an electrochemical potential greater than
the electrochemical potential necessary to oxidize the catalyst,
including but are not limited to periodic acid, periodate salts,
perbromic acid, perbromate salts, perchloric acid, perchloric
salts, perboric acid, and perborate salts and permanganates, as
well as bromates, chlorates, chromates, iodates, iodic acid, and
cerium (IV) compounds.
[0031] As shown in the above-described art, cerium salts are
another metal-containing oxidizer. U.S. Pat. No. 4,769,073, the
contents of which is incorporated herein by reference thereto,
describes cerium-based polishing compositions for polishing organic
glass surfaces which comprise ceric oxide, a cerous salt, and,
optionally, pyrosilicates or silica. Similarly, U.S. Pat. No.
5,773,364 filed Oct. 21, 1996, the contents of which is
incorporated herein by reference thereto, describes a CMP slurry
where oxidizers include ferric nitrate or cerium nitrate, and note
the problem that metal ions are created as a result of the
oxidizing process. Cerium salts can contaminate an exposed surface
of a semiconductor wafer which could affect the reliability and
functionality of semiconductor devices on the wafer. In addition,
these metallic species will coat/stain the CMP equipment which
creates particulate problems and reduces the life cycle of the CMP
equipment. This in turn causes increased replacement of polishing
equipment and greater cost associated with the manufacturing
process.
[0032] There is another mechanism for synergy that has not been
described in the CMP art, but is known in the unrelated
environmental clean-up art. A reaction used in environmental
remediation systems is Fenton's reaction, where the relatively
benign reactants generate a free radical which can cleave even very
resistant organic contaminants.
[0033] Fenton's reaction is the interaction of hydrogen peroxide
with selected transition metals to produce free radicals. The
interaction of copper or a ferrous salt iron and hydrogen peroxide
to produce a free radical was first observed by Fenton in 1876. The
Fenton reaction is the production of free radicals as a byproduct
of the oxidation of ferrous ions by hydrogen peroxide. Other metals
are known to have special oxygen transfer properties which improve
the utility of hydrogen peroxide.
[0034] The optimal pH for Fenton's reaction occurs between pH 3 and
pH 6, particularly 4 to 5. The drop in efficiency on the basic side
is attributed to the transition of iron from a hydrated ferrous ion
to a colloidal ferric species which catalytically decomposes the
hydrogen peroxide into oxygen and water, without forming hydroxyl
radicals. Fenton's reactions where the iron and the hydrogen
peroxide are in solution are characterized by an optimal dose range
for iron activator. A minimal threshold concentration of 3-15 mg/L
Fe which allows the reaction to proceed within a reasonable period
of time for the digestion of organic material in wastewater, and
generally a ratio of 1 part Fe per 5-25 parts hydrogen peroxide
(wt/wt) is most efficient. For a solution containing organic
material to be degraded, to obtain efficient Fenton's reaction
kinetics, addition of 5% by weight hydrogen peroxide would also
require between about 0.2% to 1% ferrous ions in the solution.
[0035] It is also known that UV light can enhance the efficiency of
Fenton's reaction, and that some activators need actinic radiation
to be operative. For example, U.S. Pat. Nos. 6,117,026 and
6,435,947, the disclosure of which is incorporated herein by
reference, describe a heterogeneous solid metal oxide catalyst that
can be a homogeneous composition of the active catalyst, or the
active heterogeneous solid catalyst can be chemically or physically
associated with the surface of the preferred abrasive as molecular
species, as a small particle or as a monolayer. The solid catalysts
are preferably small particles with high surface areas. The solid
catalysts should have a mean particle diameter less than about 1
micron and a surface area greater that about 10 m.sup.2/g and less
than about 250 m.sup.2/g. It is more preferred that the solid
catalysts have a mean particle diameter that is less than about 0.5
microns and most preferably less than about 0.25 microns.
[0036] As mentioned in U.S. Pat. No. 5,773,364, U.S. Pat. No.
4,959,113, and others, there are problems with the metal-containing
oxidizers. When a metal-containing oxidizer is admixed with another
metal-containing oxidizer, there is a possibility of plating of one
of the metals due to the differences in electrochemical potential
of the various metals at the various oxidation states, particularly
as the solution is consumed during polishing of a substrate. While
plating was recognized as problematic in the U.S. Pat. No.
4,959,113, there is a further possibility that as the
metal-containing oxidizers change oxidation states, even some
"non-plating" combinations may become plating.
[0037] Another problem with many metal compounds is that they react
with and cause degradation of other oxidizers. When a
metal-containing oxidizer is admixed with a non-metal-containing
oxidizer, for example hydrogen peroxide in a solution, the two
often react in an undesirable fashion, and the oxidizing capacity
of the mixture declines rapidly with time. The nature of the
reaction can take many forms. For example, ferric nitrate reacts
with hydrogen peroxide in CMP formulations at essentially all
usable pHs, making the formulation oxidizing capacity fall with
time, which complicates polishing since there is a non-uniformity
problem, and also causing formation of undesired products. It is
known that if the pH is above about 5, iron precipitates as
Fe(OH).sub.3 which catalytically decomposes the hydrogen peroxide
to oxygen. The mechanism for decomposition at pH below 5 is not
known.
[0038] Another problem with metal-containing oxidizer salts is that
they leave metal contamination on the substrate. This metallic
contamination can result in shorts and unwanted conductive
properties, along with other problems. Metal contamination was
recognized in U.S. Pat. No. 5,445,996, filed May 25, 1993, the
contents of which is incorporated herein by reference thereto,
describes use of a polishing slurry for polishing and planarizing
the semiconductor device that contains less than 100 ppm impurities
such as sodium, potassium, and other alkali metals.
[0039] Certain metals, such as those with a tendency to plate on or
be absorbed on to at least one part of the substrate, are more
damaging than other metals. The industry has developed methods to
remove a portion of the metallic contamination, for example by:
physical desorption by solvents; changing the surface charge with
either acids or bases so that Si--OH or M--OH group can be
protonated (made positive) in acid or made negative with bases by
removing the proton; ion competition, for example removing adsorbed
metal ions by adding acid (i.e. ion exchange); subsequent oxidation
of metals to change the chemical bonds between the impurities and
substrate surface; and subsequent etching the surface, wherein the
impurity and a certain thickness of the substrate surface is
removed, as described in U.S. Pat. No. 6,313,039, the contents of
which has been incorporated herein by reference. There have been
various "post-polishing cleaners" developed to remove metallic
contamination, but removal of all undesired metal ions is
substantially beyond the range of cleaners, and as the size of the
structures continues to decrease, even a very small number of
metallic atoms deposited on a surface will result in undesired
shorts or current leakage.
[0040] Additionally, metal ion-containing fluids are often
environmentally undesirable and expensive treatment may be needed
prior to waste disposal of used product.
[0041] Therefore, despite the known (and heretofore unknown)
advantages of having multiple oxidizers, for example a
metal-containing oxidizer admixed with either another
metal-containing oxidizer or with a non-metal-containing oxidizer,
there has been a tendency in the industry to reduce the amount of
metal ions in CMP slurries. For example, Rodel, a large commercial
manufacturer of CMP slurries that at point of use are designed to
be used with non-metal-containing oxidizers such as peroxides and
persulfates, had about 30 ppm of metals, primarily iron, in the
liquid portion of an MSW1000.TM. slurry produced in 1995. While
this iron would have functioned as a promoter, it is likely the
iron was in the solution as a result of impurities. Later
generations of Rodel slurries, for example the Rodel MSW1500.TM.
slurry that was sold in 2002, has only 4.2 ppm iron.
[0042] Another method of reducing metallic contamination is to use
sequential CMP polishing steps using sequential formulations that
have decreasing amounts of metal, so that metal deposited from
earlier formulations in a CMP process are removed by CMP with
subsequent formulations that are metal-free. For example, the
newest generation of Rodel CMP slurries, the MSW2000 .TM., has a
first formulation (A) having 12 ppm Fe, and a second formulation
(B) that has less than 0.3 ppm Fe. However, use of sequential
formulations adds additional costs to processing, as well as adding
complexity to the required equipment. Cabot Corporation, another
large commercial manufacturer of CMP slurries, now sells several
high-purity, nonmetal-based CMP slurries for tungsten, such as the
Semi-Sperse.RTM. W2000 and the Semi-Sperse.RTM. W2585 slurries,
claiming that the slurries eliminate the secondary-polishing steps
associated with existing tungsten slurries.
[0043] EKC Technology/Dupont Electronic Technologies, another large
commercial manufacturer of CMP slurries, sells several high-purity,
non-metal-based CMP slurries for tungsten, for example the
MicroPlanar.RTM. CMP3550.TM./MicroPlanar.RTM. CMP3510.TM. slurry,
as well as the traditional but effective ferric nitrate as the
oxidizer with a post-CMP cleaner to remove metal contaminants.
[0044] It is clear that the industry is moving away from metals,
for example iron, in the fluids. Also, when iron or other
metal-containing formulation is admixed with non-metal-containing
oxidizers, the "pot-life" of the formulation is very short, so
mixing is generally point-of-use mixing, which complicates CMP
processes and equipment and can create start-up problems even after
a temporary interruption on the processing.
[0045] Further developments in the field of CMP technology are
desired.
SUMMARY OF THE INVENTION
[0046] This invention relates to a method of making selected
oxidizers or other free radical-producing compounds become more
effective chemical etchants and/or oxidizers for CMP activities by
promoting the formation of the free radicals in a CMP composition
with one or more activators. The composition of the present
invention is effective in the CMP of a variety of metal or metal
alloy materials on substrates such as silicon or semiconductor
substrates. Without being bound by theory, it is believed that the
activator coated abrasive and the oxidizing agent react at the
surface interface to generate free radicals that are effective
intermediates in the reaction between the oxidizing agent and the
material targeted for removal from the substrate surface. Further,
it is believed that the activator coated abrasive is particularly
effective as it brings the activator in close proximity to the
targeted material on the substrate surface, and thus facilitates or
accelerates the removal reaction substantially at the site of the
targeted material. Two necessary components of the invention are at
least one compound that can form free radicals and at least one
activator.
[0047] Selected objects of this invention are to provide a system
wherein 1) higher polishing rates of conductors, insulators,
barriers, and/or other surfaces are achieved from a combination of
chemicals and abrasives than were otherwise achievable, 2)
acceptable polishing rates of conductors, insulators, barriers,
and/or other surfaces are achieved from a combination of chemicals
and abrasives at lower concentrations than were achieved in the
prior art; 3) provide a system where CMP can be performed at
commercially acceptable removal rates with commercially acceptable
uniformity in the polished product; 4) provide a system where CMP
can be performed at commercially acceptable removal rates with
commercially acceptable uniformity in the polished product and with
substantially no metallic ion contamination of the substrate; 5)
provide a system where CMP can be performed at commercially
acceptable removal rates with commercially acceptable uniformity in
the polished product, wherein the chemicals used are
environmentally friendly, easily recoverable, or both; 6) provide a
system of increasing the effectiveness of oxidizers and/or
cleaners; 7) provide a method of recovering and re-using selected
components of the system which are otherwise considered consumable
components; and/or 8) provide a one-component system that exhibits
usable shelf life for a period of at least 24 hours; and/or 9)
provide an additive which increases the effectiveness of various
commercial CMP slurries, beneficially without introducing
additional compounds to the slurry fluid. These objects of the
invention are not exhaustive, and it is realized that not all
objects of the invention will be reached by any one system.
[0048] One embodiment of the CMP system of the invention comprises
a fluid having at least one free radical-forming compound, and a
pad which comprises at least one activator associated
therewith.
[0049] Another embodiment of the CMP system of the invention
comprises a fluid having at least one free radical-forming
compound, and a plurality of particles which comprise at least one
activator associated therewith.
[0050] Yet another embodiment of this invention comprises a
material having at least one activator associated therewith and a
fluid having at least one free radical-forming compound, where the
material may not be incorporated in the pad or in particles which
contact the substrate. Such a material may be for example an
activator-containing material having the fluid flow therethrough
immediately prior to for example polishing, and the activator in
this instance may include an actinic component.
[0051] Yet another embodiment of this invention comprises a CMP
fluid comprising a soluble activator, beneficially a
non-metal-containing activator such as iodine, and a fluid having
at least one free radical-forming compound.
[0052] In each of the above embodiments, the free radical-forming
compound is beneficially an oxidizer. Preferred free
radical-forming compounds include monopersulfate, di-persulfate,
peracetic acid, urea hydrogen peroxide, hydrogen peroxide, acids
thereof, salts thereof, adducts thereof, or mixtures thereof.
[0053] Yet another embodiment of this invention comprises a CMP
fluid comprising a compound which produces free radicals that is
not an oxidizer.
[0054] Yet another embodiment of this invention comprises a CMP
fluid comprising a soluble activator, and a compound which produces
free radicals that is not an oxidizer.
[0055] Yet another embodiment of this invention comprises a CMP
fluid comprising a photoactivated solid activator, and a compound
which produces free radicals that is not an oxidizer.
[0056] Yet another embodiment of this invention comprises a CMP
fluid comprising free radicals produced by contacting the fluid
with an activator.
[0057] Of course any or all of the above systems may be combined as
efficiency and utility indicate. The system, i.e., pad, particles,
and/or fluid as appropriate, may contain other components,
including but not limited to: oxidizers other than the free
radical-producing compound(s); other particulates and/or abrasives;
free radical quenchers; stabilizers; promotors; soluble activators
(preferably non-metal-containing activators); chelators;
anticorrosion agents such as film formers; dispersability agents
such as surfactants; pH adjustors such as acid or bases; viscosity
control agents; and biocides. In some embodiments, free radicals
formed in the CMP system of the current invention may be
incompatible with certain compounds listed above. In this case, at
least one of the Free Radical-Producing Compound, the activator, or
the incompatible compounds should be admixed with the others at or
near point-of-use.
[0058] The invention also encompasses the method of CMP of a
substrate, for example a semiconductor substrate, a memory disk
substrate, or any other surface wherein oxidative CMP is desired.
The method includes the step of polishing or abrading the substrate
while contacting the substrate with the fluid, wherein the fluid
comprises free radicals, particularly oxygen-containing free
radicals such as the superoxygen radical and/or the hydroxyl
radical, generated as a result of the interaction of an activator
with the at least one free radical-forming compound. In preferred
embodiments, the fluid is a slurry containing particulates having
activator(s) associated therewith. In preferred embodiments, the
activator is not photoactive.
[0059] Yet another embodiment of the invention is recycling,
recovering, and/or reusing the particulates or abrasives of this
invention that have activator associated therewith from a post use
slurry. Yet another aspect of this invention is
particulate-containing CMP slurry systems described in the various
embodiments thereof wherein the particulate-containing CMP slurry
comprises recycled or recovered particulates having activator
associated therewith.
[0060] A first principal embodiment of the invention is a
composition for chemical-mechanical polishing a semiconductor or
memory device substrate, comprising: a fluid comprising at least
one compound that produces free radicals, wherein the at least one
compound when contacted with at least one activator produces free
radicals, and wherein and the fluid pH is between about 1 to about
11; and a plurality of particles having a surface and having at
least one activator associated with the surface, wherein the at
least one activator comprises a metal other than a metal of Group
IV(B), Group V(B), or Group VI(B), and wherein the metal has
multiple oxidation states, wherein the composition when used in a
chemical mechanical polishing process will remove desired metal but
will not create defects or nonuniformity such that the substrate
can not undergo further fabrication to become a finished operable
semiconductor or memory device.
[0061] A second principal embodiment of the invention is a
composition for chemical-mechanical polishing a semiconductor or
memory device substrate, comprising: a fluid comprising at least
one compound that produces free radicals, wherein the fluid
comprises less than about 500 ppm of dissolved metal ions having
multiple oxidation states and the fluid pH is between about 1 to
about 11, and wherein the at least one compound when contacted with
at least one activator produces free radicals; and a plurality of
particles having a surface in contact with the fluid and having at
least one activator associated with the surface, wherein the
activator associated with the surface is a dissociable salt of a
metal and is present in an amount between 5 to 10000 ppm by weight
of the composition, wherein the composition when used in a chemical
mechanical polishing process will remove desired material but will
not create defects or nonuniformity such that the substrate can not
undergo further fabrication to become a finished operable
semiconductor or memory device.
[0062] A third principal embodiment of the invention is a
composition for chemical-mechanical polishing a semiconductor or
memory device substrate, comprising: a fluid comprising at least
one compound that produces free radicals, wherein the compound is
an oxidizer that produces reactive oxygen-containing free radicals
when contacted by an activator; and a plurality of particles having
a surface and having at least one activator comprising an ion of at
least one of iron, copper, manganese, cobalt, cerium, and nickel
associated with the surface, wherein the activator(s) associated
with the surface is/are present in a total amount ranging from
about 5 ppm to about 30,000 ppm by weight in the composition,
wherein the composition when used in a chemical mechanical
polishing process will remove the desired material but will not
create defects or nonuniformity such that the substrate can not
undergo further fabrication to become a finished operable
semiconductor or memory device.
[0063] The at least one compound in each of the first three
principal embodiments can be a per compound present in the
composition in an amount from about 0.01% to about 30% by weight.
The per compound in one embodiment comprises a peroxide, a
hydrohydrogen peroxide, or derivative thereof. The per compound in
another embodiment comprises hydrogen peroxide and is present in
the composition in an amount from about 0.01% to about 10% by
weight. The per compound in yet another embodiment comprises at
least one perfsulfate. The per compound in yet another embodiment
comprises peracetic acid and is present in the composition in an
amount from about 0.01% to about 10% by weight. The per compound in
yet another embodiment comprises a peroxydisulfate, a
peroxydiphosphate, or mixture thereof.
[0064] The at least one compound in each of the first three
principal embodiments can comprises at least two of peracetic acid,
a peroxide, a persulfate, a hydroxylamine, or mixture thereof, and
the total amount present in the composition is from about 0.01% to
about 30% by weight, and wherein the activator comprises cerium,
iron, copper, or mixture thereof, and wherein the fluid contains
less than about 100 ppm of dissolved metals having multiple
oxidation states.
[0065] The at least one compound in each of the first three
principal embodiments can be ozone. The at least one compound in
each of the first three principal embodiments can comprise
hydroxylamine, a hydroxylamine derivative, a salt thereof, or a
combination thereof present in the composition in an amount from
about 0.01% to about 30% by weight.
[0066] The composition of each of the first three principal
embodiments can comprise an oxidizing agent selected from the group
consisting of a metal salt, a metal complex, and a combination
thereof.
[0067] The plurality of particles having a surface and having at
least one activator associated with the surface in each of the
first three principal embodiments can comprise a metal oxide
abrasive. The metal oxide can in another embodiment comprise
alumina, silica, ceria, or mixtures thereof, and the activator(s)
associated with the surface is/are present in a total amount
ranging from about 10 ppm to about 1,000 ppm by weight in the
composition.
[0068] The plurality of particles having a surface and having at
least one activator associated with the surface in each of the
first three principal embodiments can comprise a substantially
spherical ceramic particle having an average particle size from
about 0.001 to about 1 micron and having a particle size
distribution such that: at least about 95% by weight of the ceramic
particles have a particle size within about 30% of the weight
average particle size, wherein the ceramic particle comprises at
least one metallic oxide selected from the group consisting of zinc
oxide, bismuth oxide, cerium oxide, germanium oxide, silica,
aluminum oxide; and a metallic sulfide, a metallic titanate, a
metallic tantalate, a metallic zirconate, a metallic silicate, a
metallic germanium oxide, a metallic niobate, a metallic borides, a
metallic nitride, a metallic carbide, a metallic telluride, a
metallic arsenide, a metallic silicide, metallic selenide, and
mixtures or combinations thereof.
[0069] The plurality of particles having a surface and having at
least one activator associated with the surface in each of the
first three principal embodiments can comprise a alumina,
optionally wherein the particles have a BET surface area between
about 5 and 430 m.sup.2/g and the weight average particle size is
less than about 0.4 microns, and additionally or alternatively,
wherein the particles have an average particle size from about
0.001 to about 0.2 microns.
[0070] The plurality of particles having a surface and having at
least one activator associated with the surface in each of the
first three principal embodiments can comprise a silica, optionally
wherein the particles have a BET surface area between about 5 and
1000 m.sup.2/g, an average particle size less than about 1 micron,
and a particle size distribution such that at least about 95% by
weight of the silica particles have a particle size within about
30% of the weight average particle size, and additionally or
alternatively, wherein the particles have an average particle size
from about 0.002 to about 0.6 microns. The plurality of particles
having a surface and having at least one activator associated with
the surface in each of the first three principal embodiments can
comprise fumed silica aggregates.
[0071] The plurality of particles having a surface and having at
least one activator associated with the surface in each of the
first three principal embodiments can comprise a ceria, or can
comprise germania, spinel, titania, an oxide of tungsten, a nitride
of tungsten, zirconia, an oxide of vanadium, or a combination
thereof.
[0072] Finally, the plurality of particles having a surface and
having at least one activator associated with the surface in each
of the first three principal embodiments can comprise polymeric
particles, which in one are a composite particle further comprising
a metal oxide.
[0073] The composition of the first three principal embodiments can
further comprise at least one second particle different from the
plurality of particles having a surface and having at least one
activator associated with the surface. This second particle may be
the same or different than the first particle, and if the same,
then the second particle has no activator associated with its
surface. Additionally or alternatively, at least one compound of
the first three principal embodiments can comprise a first
oxidizer, and the compositions can optionally further comprise a
second oxidizer.
[0074] The composition of the first three principal embodiments can
further comprise at least one stabilizer in an amount sufficient to
stabilize the composition. Additionally or alternatively, the
composition of the first three principal embodiments can further
comprise at least one promoter in an amount between 10 ppm and 5000
ppm. Additionally or alternatively, the composition of the first
three principal embodiments can further comprise at least one
chelator. Additionally or alternatively, the composition of the
first three principal embodiments can further comprise at least one
soluble activator, for example iodine. Additionally or
alternatively, the composition of the first three principal
embodiments can further comprise at least one anti-corrosion agent,
at least one dispersability agent, or both. Additionally or
alternatively, the composition of the first three principal
embodiments can further comprise one pH adjustor, and wherein the
fluid pH is between about 2 to about 8, for example between about 3
to about 7, and typically between about 3.5 to about 4.5.
Additionally or alternatively, the composition of the first three
principal embodiments can further comprise at least one polishing
enhancement agent different from the at least one compound, for
example glycol, glycine, a derivative of glycine, or mixture
thereof.
[0075] The plurality of particles having a surface and having at
least one activator associated with the surface of the first three
principal embodiments can comprise a metal oxide particle
comprising silica, alumina, ceria, or mixtures or combinations
thereof, wherein the metal oxide particles a particle size
distribution such that the one-sigma deviation is no more than
about 20% of the average particle size, and wherein the activator
comprises copper oxide, iron oxide, or mixture thereof.
[0076] The plurality of particles having a surface and having at
least one activator associated with the surface of the first three
principal embodiments can comprise a metal oxide, a polymer, or
both, and wherein the activator associated with the surface
comprises a dissociable cerium salt, dissociable copper salt, a
dissociable iron salt, a dissociable manganese salt, a dissociable
cobalt salt, a dissociable nickel salt, or mixture thereof.
[0077] The plurality of particles having a surface and having at
least one activator associated with the surface of the first three
principal embodiments can comprise a metal oxide that has been
doped with a metal selected from iron, copper, manganese, cobalt,
cerium, and nickel.
[0078] The plurality of particles having a surface and having at
least one activator associated with the surface of the first three
principal embodiments can comprise activator associated on from
about 5 to about 80 percent of the connected outer surface, or
alternatively or additionally about 25 to about 50 percent of the
outer surface of the plurality of particles having a surface and
having at least one activator associated with the surface.
[0079] The plurality of particles having a surface and having at
least one activator associated with the surface of the first three
principal embodiments can comprise activator associated on the
surface of the plurality of particles at from about 0.01% to about
3% by weight of the plurality of particles.
[0080] Advantageously, in most every embodiment and especially in
the composition of the first three principal embodiments, the
composition will comprise less than about 10 ppm, for example less
than about 2 ppm, of dissolved metal ions having multiple oxidation
states.
[0081] The plurality of particles having a surface and having at
least one activator associated with the surface of the first three
principal embodiments can comprise silica, alumina, ceria, or
mixtures thereof, and the activator associated on the surface of
the particles comprises iron, wherein the amount of activator iron
is from about 0.01% to about 3% by weight of the plurality of
particles. Even in this embodiment, advantageously the fluid
comprises less than about 10 ppm of dissolved iron.
[0082] The plurality of particles having a surface and having at
least one activator associated with the surface of the first three
principal embodiments can comprise silica, alumina, ceria, or
mixtures thereof, and the activator associated on the surface of
the particles comprises cerium, wherein the amount of activator
cerium is from about 0.01% to about 3% by weight of the plurality
of particles.
[0083] In a fourth principal embodiment, the invention includes a
composition for chemical-mechanical polishing a semiconductor or
memory disk substrate, comprising: a fluid comprising at least one
compound that produces free radicals; and an activator in the fluid
in an amount sufficient to for the desired free radical activity,
wherein the activator when contacted with the at least one compound
produces free radicals, and wherein the activator is not a
promoter, such that the semiconductor or memory disk substrate is
undamaged so the substrate can undergo further fabrication steps.
The activator may comprise iodine when the compound that produces
free radicals is a per compound, such as hydrogen peroxide. The
activator may comprises cerium in an amount between about 10 ppm
and about 1000 ppm. The activator may comprise a metal-glycine
complex, wherein the metal consists essentially of cerium, iron,
manganese, cobalt, or mixture thereof. Finally, the activator may
comprise actinic radiation wherein at least one compound that
produces free radicals comprises an alcohol and/or a ketone
susceptible to forming free radicals when exposed to particular
actinic radiation wavelengths.
[0084] In a fifth principal embodiment, the invention includes
method of polishing a substrate surface having at least one feature
thereon comprising a metal, which method comprises: providing the
composition of any one of the first three principal embodiments of
this invention; and chemically-mechanically polishing the feature
by contacting the feature with the composition, wherein the
polishing process will polish the metal feature but will not create
defects or nonuniformity such that the substrate can not undergo
further fabrication to become a finished operable product.
Optionally, the plurality of abrasive particles having a surface in
contact with the fluid and having at least one activator associated
with the surface may comprise an abrasive present in the
composition in an amount from about 0.01% to about 20% by weight,
and the at least one compound that produces free radicals may
comprise at least one oxidizer-that-produces-free-radicals which is
present in the composition in an amount between about 0.01% to
about 30%. In one embodiment, the substrate is a semiconductor, and
the metal feature comprises aluminum, copper, titanium, tungsten,
tantalum, any alloy thereof, any metal nitride thereof, any metal
silicon alloy thereof, and any combination thereof. In
semiconductors, it is not unusual for the feature to be adjacent to
a material selected from the group consisting of tantalum, tantalum
nitride, titanium, titanium nitride, titanium tungsten, tungsten,
and any combination thereof, and wherein the metal feature material
is different from the material adjacent to it. Advantageously, the
method is sufficient to provide a chemically-mechanically polished
substrate surface having a within-wafer nonuniformity from about
zero to about 12 percent, and additionally or alternatively any
microscratch thereon produced during the chemical-mechanical
polishing is less than about 20 Angstroms in depth.
[0085] The substrate may alternatively be a memory device, where
the metal feature comprises aluminum, copper, titanium, tungsten,
tantalum, nickel, nickel-iron, or any alloy thereof, Sendust, and
CZT and any combination thereof. Again, advantageously the method
is sufficient to provide a chemically-mechanically polished memory
device substrate surface wherein any microscratch thereon produced
during the chemical-mechanical polishing is less than about 20
Angstroms in depth.
[0086] The substrate may alternatively be a silicon substrate, a
gallium arsenide (GaAs) substrate, a thin film transistor-liquid
crystal display glass substrate, or a Micro Electro Mechanical
Systems structure, wherein said method is sufficient to provide a
chemically-mechanically polished substrate surface wherein any
microscratch thereon produced during the chemical-mechanical
polishing is less than about 20 Angstroms in depth.
[0087] The key to the compositions and to the method is the
particles having activator associated thereon. Advantageously, as
the particles are not destroyed during polishing, advantageously at
least one portion of the particles in any of the compositions of
this invention are recovered from used compositions after polishing
and are re-used to polish another substrate surface. The plurality
of particles may be recovered by filtration, centrifugation, or a
combination thereof.
[0088] Finally, advantageously, wherein the polishing involves
movably contacting the feature or the composition with a polishing
pad, the polishing pad has a surface and may optionally comprise an
activator associated with said polishing pad surface, wherein the
activator is any of the activators in the first three principal
embodiments of this invention.
[0089] These various components and embodiments will be discussed
in greater detail below.
DETAILED DESCRIPTION OF THE INVENTION
[0090] This invention relates to a method of making selected
oxidizers or other compounds become more effective. The system is
adapted to polish substrates, and the invention includes methods of
polishing the substrates. The system comprises a fluid containing a
free radical-producing compound, usually an oxidizer. The system
comprises an activator, which if metal containing is beneficially
associated with a solid, and if none-metal-containing, may be
included in the fluid. The system, i.e., pad, particles, and/or
fluid as appropriate, may contain other components, including but
not limited to: oxidizers other than the free radical-producing
compound(s); other particulates and/or abrasives; free radical
quenchers; stabilizers or passivators; promoters; soluble
activators (preferably non-metal-containing activators); chelators;
anticorrosion agents such as film formers; dispersability agents
such as surfactants; pH adjustors such as acid or bases; viscosity
control agents; and biocides, most of which will be discussed in
detail below.
[0091] Substrate
[0092] The invention is useful for CMP of a substrate. The
substrate can be a metal, a crystal, a semiconductor, an insulator,
a ceramic, a glass, or other materials which may be improved by
oxidative CMP. The invention can be used where very strong
oxidizers or reactors are useful, and can be used in CMP of dual
damascene substrates, silicides, and the like.
[0093] While the invention will be described in terms of
semiconductor substrates, the system herein is also useful for
chemical-mechanical polishing of other substrates. The substrates
may be for example memory storage devices such as hard disks,
floppy disks, magnetic heads, and/or formatted memory devices in a
non-disk shape. The requirements of polishing these memory storage
devices, including high removal rates, low-defect surface finish,
selectivity, and cleanability are the same as for semiconductor
processing, although there are some substrates that are encountered
in memory device planarization that are not normally encountered in
semiconductor processing, including for example nickel, nickel-iron
alloys, Sendust, and CZT. The polishing on the device must remove
the desired material but not create defects or nonuniformity such
that the substrate can not undergo further fabrication to become a
finished operable semiconductor or memory device.
[0094] The systems described herein are useful for CMP of these as
well as for other substrates, which include both polishing on a
small scale such as for semiconductors and also on a much larger
scale including substantially any metallic device. The system
herein is particularly useful for chemical-mechanical polishing of
substrates where close tolerances are needed, for example
telescopes, lenses, finely machined components including
microscopic components, and the like. The invention is also useful
for cleaning various macroscopic structures, especially where
strong oxidizers and abrasives are desired to remove material or
residue but where environmental contamination is a concern, for
example cleaning of structural metal and the like.
[0095] CMP is used in a variety of semiconductor processes to
polish wafers having a variety of surface features, such as oxide
and/or metal layers. By way of example, often the surface of a
semiconductor wafer has exposed insulative structures, exposed
conductor structures, exposed barrier structures which may reside
between conductor and insulative structures, and often "stop`
structures which are designed to stop material removal at a
preselected level. The composition or slurry of this invention may
be used to polish at least one feature or layer on a substrate such
as a silicon substrate, a gallium arsenide (GaAs) substrate, a thin
film transistor-liquid crystal display ("TFT-LCD") glass substrate,
or any other substrate associated with integrated circuits, thin
films, semiconductors, Micro Electro Mechanical Systems (MEMS)
structures, memory storage devices, and the like. By way of
example, the composition of the present invention may be used in
the CMP of a substrate having one or more layers of aluminum,
copper, copper-aluminum alloy, tantalum, titanium, tungsten, or
tantalum-, titanium-, or tungsten-containing alloys, such as
tantalum nitride, titanium nitride, titanium tungsten, or other
combinations thereof.
[0096] The conductor structures are typically one or more layers of
metals, and/or metal alloys such as tungsten-titanium and
aluminum-copper, and/or metallic compounds such as AlSi or metal
nitrides such as TiN. As used herein, unless otherwise stated, when
referring to the substrate the term "metals" includes metals,
alloys of metals, and also metallic compounds, alone or in
combination. Typical metals used include aluminum, copper,
titanium, tantalum, tungsten, gold, silver, platinum, ruthenium, as
well as alloys thereof and/or of metallic compounds such as
nitrides thereof.
[0097] The barrier structures may be metals of a different
composition from the conductor structures, though one of ordinary
skill in the art is aware of certain combinations that are more
useful than others.
[0098] Typical insulative structures include dielectrics such as
silica, alumina, organic silicas, polysilicon, gallium arsenide,
and others known in the art. Spun glass, polysilicon, organic
glass, and other embodiments are also included.
[0099] Stop structures are generally any of the above, though one
of ordinary skill in the art is aware, certain combinations are
more useful for certain chemistries than others.
[0100] Because one object of this invention is to promote formation
of one of the stronger oxidizers known to be compatible with
fluids, the invention is useful on substantially all metals,
including some "noble" metals.
[0101] Fluid Comprising an Oxidizer
[0102] The CMP system of the current invention requires a fluid
comprising an oxidizer for chemical etching of material. The
oxidizing agent of the CMP composition is in a fluid composition
which contacts the substrate, and assists in the chemical removal
of targeted material on the substrate surface. The oxidizing agent
component is thus believed to enhance or increase the material
removal rate of the composition. Preferably, the amount of
oxidizing agent in the composition is sufficient to assist the
chemical removal process, while being as low as possible to
minimize handling, environmental, or similar or related issues,
such as cost. The various amounts of oxidizing agent provided in
Table 1 are all effective and suitable, while the more preferred
amount of oxidizing agents is from about 0.01 to about 6 weight
percent relative to the composition, for example between about 0.1%
and about 3% of oxidizer.
[0103] Advantageously, in one embodiment of this invention, the
oxidizer is a component which will, upon exposure to at least one
activator, produce free radicals giving an increased etching rate
on at least selected structures. The free radicals described infra
will oxidize most metals, and will make the surface more
susceptible to oxidation from other oxidizers. However, oxidizers
are listed separately from the "Compound Producing Free Radicals",
to be discussed infra, because some oxidizers do not readily form
free radicals when exposed to the activators, and in some
embodiments it is advantageous to have one or more oxidizers which
provide matched etching or preferential etching rates on a variety
of combinations of metals which may be found on a substrate.
[0104] As is known in the art, some oxidizers are better suited for
certain components than for other components. In some embodiments
of this invention, the selectivity of the CMP system to one metal
as opposed to another metal is maximized, as is known in the art.
However, in certain embodiments of this invention, the combination
of oxidizers is selected to provide substantially similar CMP rates
(as opposed to simple etching rates) for a conductor and a barrier
combination, so that in many cases acceptable planarization is
achieved by a single CMP formulation.
[0105] The oxidizing agent is in one embodiment an inorganic or
organic per-compound. A per-compound is generally defined as a
compound containing an element in its highest state of oxidation,
such as perchloric acid; or a compound containing at least one
peroxy group (--O--O--), such as peracetic acid and perchromic
acid.
[0106] Suitable per-compounds containing at least one peroxy group
include, but are not limited to, peracetic acid or salt thereof, a
percarbonate, and an organic peroxide, such as benzoyl peroxide,
urea hydrogen peroxide, and/or di-t-butyl peroxide.
[0107] Suitable per-compounds containing at least one peroxy group
include peroxides. As used herein, the term "peroxides" encompasses
R--O--O--R', where R and R' are each independently H, a C.sub.1 to
C.sub.6 straight or branched alkyl, alkanol, carboxylyic acid,
ketone (for example), or amine, and each of the above can
independently be substituted with one or more benzyl group (for
example benzoyl peroxide) which may themselves be substituted with
OH or C1-C5 alkyls, and salts and adducts thereof. This term
therefore includes common examples such as hydrogen peroxide,
hydrohydrogen peroxide, peroxyformic acid, peracetic acid,
propaneperoxoic acid, substituted or unsubstituted butaneperoxoic
acid, hydroperoxy-acetaldehyde, Also encompassed in this term are
common complexes of peroxides, for example urea peroxide.
[0108] Suitable per-compounds containing at least one peroxy group
include persulfates. As used herein, the term "persulfates"
encompasses monopersulfates, di-persulfates, and acids and salts
and adducts thereof. Included for example is peroxydisulfates,
peroxymonosulfuric acid and/or peroxymonosulfates, Caro's acid,
including for example a salt such as potassium peroxymonosulfate,
but preferably a non-metallic salt such as ammonium
peroxymonosulfate.
[0109] Suitable per-compounds containing at least one peroxy group
include perphosphates, defined as above and including
peroxydiphosphates.
[0110] Also, ozone is a suitable oxidizing agent either alone or in
combination with one or more other suitable oxidizing agents.
[0111] Suitable per-compounds that do not contain a peroxy group
include, but are not limited to, periodic acid and/or any
periodiate salt (hereafter "periodates"), perchloric acid and/or
any perchlorate salt (hereafter "perchlorates") perbromic acid
and/or any perbromate salt (hereafter "perbromates"), and perboric
acid and/or any perborate salt (hereafter "perbromates").
[0112] Other oxidizing agents are also suitable components of the
composition of the present invention. Iodates are useful oxidizers
and can be present in an amount ranging from about 0.01% to about
30%.
[0113] An organic and/or inorganic hydroxylamine compound or salt
are also useful oxidizers and can be present in an amount ranging
from about 0.01% to about 30%, but is preferably present in an
amount ranging from about 0.5% to about 15%. Hydroxylamine
compounds, including salts and adducts thereof, can be used as a
polishing enhancer at low concentrations. As used herein, the term
"hydroxlyamine compound" satisfies the general formula
X,Y>N--O-Z, that is, an X and Y are each bonded to the nitrogen
and the Z is bonded to the oxygen, wherein the moieties X, Y, and Z
are independently hydrogen, hydroxyl group, a substituted C1-C6
straight, branched or cyclo alkyl, alkenyl, or alkynyl group, a
substituted acyl group, straight or branched alkoxy group, amidyl
group, carboxyl group, alkoxyalkyl group, alkylamino group,
alkylsulfonyl group, or sulfonic acid group, or salts or
derivatives thereof, or wherein X and Y are linked together form a
nitrogen-containing heterocyclic C.sub.4-C.sub.7 ring. Examples of
hydroxylamine compounds according to the invention include, but are
in no way limited to, hydroxylamine, N-methyl-hydroxylamine,
N,N-dimethyl-hydroxylamine, N-ethyl-hydroxylamine,
N,N-diethyl-hydroxylamine, methoxylamine, ethoxylamine,
N-methyl-methoxylamine, and the like. It should be understood that
hydroxylamine compounds, as defined above, are available (and may
be included in a composition according to the invention) as salts,
e.g., sulfate salts, nitrate salts, formate salts, or the like, or
a combination thereof, and the term includes these forms of
hydroxylamine compounds and their derivatives. Therefore the term
encompasses hydroxylamine, a sulfate or nitrate salt of
hydroxylamine, or a combination thereof.
[0114] Any of these oxidizers can be present in an amount ranging
from about 0.01% to about 30%, for example 0.01% to 10%, but is
preferably present in an amount ranging from about 0.5% to about
15%. As used herein, weight percent is given as weight percent of
the fluid or slurry. These oxidizers are preferably present in an
amount ranging from about 0.5% to about 15%.
[0115] The oxidizing agent may be a salt of a metal having multiple
oxidation states, a complex or coordination compound of a metal
having multiple oxidation states, or any combination thereof,
provided the compound has a sufficient oxidative potential to
oxidize the substrate. Metal-containing oxidizer salts that are
useful oxidizers for the selected substrates can be present in an
amount ranging from about 0.001% to about 12%, for example in an
amount ranging from about 0.1% to about 4%. One embodiment has, in
addition to a per-containing oxidizer that produces free radicals,
between about 0.001% to about 0.5%, for example from about 0.005%
to about 0.05%, of soluble cerium salts. Another embodiment has, in
addition to a per-containing oxidizer that produces free radicals,
between about 0.001% to about 0.5%, for example from about 0.005%
to about 0.05%, of soluble iron or other promoter salts, discussed
below.
[0116] In general, the metal-containing oxidizers are less
preferred. Examples include permanganate, perchromate, iron salts,
aluminum salts, cerium salts, and the like. When admixed with
another common oxidizer such as hydrogen peroxide in a solution,
many of the metal-containing oxidizers, for example ferric nitrate,
react with the hydrogen peroxide, producing safety issues and also
repeatability issues as the oxidizing capacity of the mixture
declines rapidly with time. The nature of the reaction is not
known, although it is known that if the pH is above about 5, iron
precipitates as Fe(OH).sub.3 which catalytically decomposes
hydrogen peroxide to oxygen and water. Such an event is highly
undesirable, as oxygen buildup in confined systems and in pumps can
result in dangerous situations.
[0117] Metal-containing oxidizers in excess in solution can also
quench free radical. For example, the reaction of hydroxyl radical
and ferrous iron is: .OH+Fe.sup.2+=>FeOH.sup.2+.
[0118] Another problem with metal-containing oxidizer salts is that
they can leave metal contamination on the substrate. This metallic
contamination can result in shorts and unwanted conductive
properties, along with other problems. Certain metals, such as
those with a tendency to plate on or be absorbed on to at least one
part of the substrate, are more damaging than other metals. Another
problem with many metal compounds is they react with and cause
degradation of the oxidizer.
[0119] Generally, a mixture of two or more oxidizers provides at
selected concentrations a synergistic effect. In general, the
various oxidizing agents described herein, as well as salts and
adducts thereof, may be used either alone or in combination with
one another, although any combination that might undesirably
complicate the CMP process is preferably avoided.
[0120] Most preferably, the oxidizing agent is a percompound or a
compound possessing a reactive peroxy functional group, such as
persulfates, peracetic acid, peroxides, particularly urea hydrogen
peroxide and/or hydrogen peroxide, peroxydiphosphates, as well as
any acid, salt, or adduct of the preceding, and any combination of
the preceding.
[0121] In one embodiment, the most preferred oxidizing agents for
use in the slurry according to the invention are hydrogen peroxide,
ammonium persulfate, and/or potassium persulfate.
[0122] In another embodiment, particularly preferred oxidizers are
hydrogen peroxide, urea hydrogen peroxide, persulfates such as
ammonium persulfate, or mixture thereof. Because urea hydrogen
peroxide is 34.5 wt % hydrogen peroxide and 65.5 wt % urea, a
greater amount by weight of "urea hydrogen peroxide" must be
included in the CMP slurry to achieve the desired oxidizer loading,
as the loading is expressed as the peroxide component.
[0123] Oxidizer-Based Free Radical-Producing Compound
[0124] The invention requires a free radical-producing compound
which will, upon exposure to at least one activator, produce free
radicals capable of giving an increased etching rate on at least
selected structures of the substrate. A free radical is a chemical
component that contains a free electron which covalently bonds with
a free electron on another molecule or atom. Free radicals are also
generally described as molecular fragments having one or more
unpaired electrons. Free radicals are usually both shortlived and
also are highly reactive. In spite of their transitory existence,
free radicals can initiate many chemical reactions.
[0125] The free radical-producing compound and the formed free
radicals are in a fluid, usually a solution, that contacts the
substrate during CMP. While some free radical-producing compounds
may naturally create free radicals in a small amount, the amount of
naturally-formed free radicals is small, and the amount can be
increased significantly in the presence of an activator. As used
herein, the term free radical-producing compound means a compound
which will, upon exposure to at least one activator, be capable of
producing a free radical. Free radicals can not be readily
measured. The presence of the free radical can be inferred if the
system is capable of giving a significantly increased etching rate
on metal, for example tungsten, structures of the substrate. By a
significant amount, it is meant that the etching rate during the
CMP increases at least 10%, preferably by at least 20%, more
preferably at least 30%, when the activator is present and
contacting the fluid containing the substrate as compared to when
the activator is absent, wherein the other conditions are
identical.
[0126] All transition metals, with the exception of copper, contain
one electron in their outermost shell and can be considered "free
radicals." As used herein, the term "free radical" does not
encompass ions of transition metals.
[0127] In a preferred embodiment the free radical is a reactive
oxygen radical. Any free radical involving oxygen can be referred
to as reactive oxygen radical. Oxygen-containing free radicals
generally are depicted as containing two unpaired electrons in the
outer shell. When free radicals steal an electron from a
surrounding compound or molecule to pair up the unpaired electrons,
a new free radical is often formed in its place. In turn the newly
formed radical then looks to return to its ground state by stealing
electrons. Thus the chain reaction continues and can be thousand of
events long, provided the solution in which the free radical
propagates does not have free radical quenchers or reactants upon
which the free radicals can expend themselves on.
[0128] The oxygen-containing hydroxyl radical is one of the most
reactive chemical species known, second only to elemental fluorine
in its reactivity. This is a preferred free radical. The oxygen
singlet is another preferred free radical. Both are much stronger
reactants than, for example, hydrogen peroxide, but both can be
formed from hydrogen peroxide. Compared to chlorine, the relative
oxidation potential of various oxidants are:
TABLE-US-00001 Fluorine 2.23 Hydroxyl radical 2.06 (Free Radical)
Atomic oxygen (singlet) 1.78 (Free Radical) Hydrogen peroxide 1.31
Permanganate 1.24 Chlorine 1.00 Iodine 0.54
[0129] In a preferred embodiment the system has a fluid that
contacts the substrate during the CMP process, and this fluid
comprises a free radical-producing compound and the free radicals.
More preferably, the free radical-producing compound is an oxidizer
and the free radical is a reactive oxygen radical, for example a
hydroxyl radical. Alternately or additionally, a preferred
embodiment of the system of the invention has a fluid that contacts
the substrate during the CMP process, and this fluid comprises a
free radical-producing compound, the free radicals, and an
oxidizer. In such an embodiment, the free radical-producing
compound is beneficially a first oxidizer, the free radical is a
reactive oxygen radical, for example a hydroxyl radical, and fluid
further comprises a second oxidizer.
[0130] The free radicals, particularly the hydroxyl radical formed
by for example the Fenton-type conversion of hydrogen peroxide, are
believed to greatly accelerate the etching rate of metal
substrates. Without being bound by theory, the hydroxyl radicals
are believed to be very powerful due to the high oxidation
potential. Further, the initiation of oxidation onto the substrate
structure is believed to make the structure more susceptible to
further oxidation, for example from the oxidizer(s) in the
fluid.
[0131] The high oxidation potential of the hydroxyl radical
relative is shown below, along with the oxidation potential of
other compounds. The conversion of Fe.sup.+3 and an electron to
give Fe.sup.+2 has a standard reduction potential of 0.77 volts.
Typical standard reduction potentials for compounds found in CMP
slurries are as follows:
TABLE-US-00002 Hydroxyl radical about 2.8 volts
S.sub.2O.sub.8.sup.-2 to 2SO.sub.4.sup.-2 2.0 volts (persulfate)
H.sub.2O.sub.2 + 2H.sup.+ to 2H.sub.2O 1.78 volts (hydrogen
peroxide) Ce.sup.+4 to Ce.sup.+3 1.44 volts (cerium salt)
O.sub.3.sup.-3 + water to O.sub.2 + 2OH.sup.- 1.24 volts (ozone)
Ag.sup.+ to Ag.sup.+0 0.80 volts Fe.sup.+3 to Fe.sup.+2 0.77 volts
Fe(CN).sub.6.sup.-3 to Fe(CN).sub.6.sup.-4 0.46-0.69 volts I.sub.2
to 2I.sup.- 0.54 volts Ni.sup.+2 to Ni.sup.+0 -0.23 volts Cu.sup.+2
to Cu.sup.+ 0.16 volts Zn.sup.+2 to Zn.sup.+0 -0.76 volts
[0132] The hydroxyl free radical is therefore a much stronger
oxidizing agent than an oxidizer such as hydrogen peroxide or
ferric nitrate. The free radical is formed when needed and does not
pose a safety issue. Fluorine, the only component with a similar
oxidation potential, is not used in CMP slurries due to safety
concerns.
[0133] Generally, free radicals such as the hydroxyl radical will
react with any component. If numerous additives are in a fluid, the
hydroxyl radical will be reacting with these additives to form
other products and/or other radicals which may not be able to
function effectively on the substrate. In some embodiments, the
amount of additives is less than 2% total, for example less than 1%
total, and in some embodiments less than 0.2% total, based on the
weight of the fluid.
[0134] Selected oxidizers, for example peroxides,
peroxydiphosphates, persulfates, and combinations of the foregoing,
are known to produce a small amount of free radicals naturally
(wherein the term "naturally" may be the result of small amounts of
activator that are found in almost every solution), but the amount
of free radical production increases substantially when contacted
by an initiator. Ozone also produces free radicals but the amount
of free radical production can increase substantially when
contacted by an appropriate activator. Each of these compounds
will, upon exposure to at least one activator, produce
significantly increased concentrations of free radicals capable of
giving an increased etching rate on at least selected structures of
the substrate. Not all activators will act with all compounds
[0135] In one embodiment the preferred free radical-producing
compounds in the fluid comprise peroxide compounds, persulfates
compounds, peroxydiphosphate compounds, or a mixture thereof. In
another embodiment the preferred free radical-producing compounds
in the fluid comprise peroxide compounds, persulfates compounds,
peroxydiphosphate compounds, ozone, or a mixture thereof. These
preferred free radical-producing compounds also are excellent
oxidizers, and for these cases the single component can act as an
oxidizer and as a free radical producer.
[0136] In one embodiment the preferred free radical-producing
compounds are persulfates, for example ammonium persulfate. These
compounds also are excellent oxidizers. In one embodiment one or
more are present in a total amount ranging from about 0.1% to about
25%, preferably from about 0.5% to about 12%.
[0137] The free radical producing compound can be hydroxylamine.
These compounds also are excellent oxidizers. In one embodiment one
or more are present in a total amount ranging from about 0.1% to
about 25%, preferably from about 0.5% to about 12%.
[0138] In one embodiment the preferred free radical-producing
compounds are peroxydiphosphates, for example ammonium
peroxydiphosphate. In one embodiment one or more are present in a
total amount ranging from about 0.1% to about 25%, preferably from
about 0.5% to about 12%.
[0139] The most preferred free radical-producing compounds are
peroxide compounds. In one embodiment the most preferred free
radical-producing compounds are peroxide compounds, for example
hydrogen peroxide, urea peroxide, hydrohydrogen peroxide, or
substituted peroxides such as t-butyl peroxide (CAS # 110-05-9) or
t-butyl hydroperoxide (CAS # 75-91-2), or mixtures thereof, most
preferably hydrogen peroxide. In another embodiment one or more are
present in a total amount ranging from about 0.1% to about 20%,
preferably from about 0.5% to about 10%. In one embodiment,
hydrogen peroxide is the sole free radical-producing compound and
is also the sole oxidizer in the fluid, and the hydrogen peroxide
is present in an amount ranging from about 1% to about 10%, for
example from about 3% to about 7%, typically about 5%.
[0140] In one embodiment the preferred free radical-producing
compound is ozone, which is also an excellent oxidizer. Ozone can
be produced in the fluid or can be produced away from the fluid and
then dissolved into the fluid.
[0141] In one embodiment the preferred free radical-producing
compounds include peroxydisulfates, for example ammonium
peroxydisulfate. In one embodiment one or more are present in a
total amount ranging from about 0.015 to about 30%, for example
from about 0.1% to about 25%, preferably from about 0.5% to about
12%.
[0142] Of course, not all oxidizers form a sufficient amount of
free radicals when exposed to one particular activator. Also, not
all oxidizers form a sufficient amount of free radicals when
exposed to any activator.
[0143] In some embodiments of the invention, the fluid composition
contacting the substrate will contain one or more oxidizers which
when contacted by the activator are free radical-producing
compounds, and one or more oxidizers which when contacted by the
activator do not create a significant amount of free radicals. This
allows one method to have the oxidizing capacity of the solution be
at least partially independent of the amount of the one or more
free radical-producing compounds. The process can therefore be
optimized for the requirements of the user through the choice of
formulas for rapid bulk metal removal with moderate to high
selectivity to the common barrier materials; and/or a CMP polish
which may extend through the barrier which may be similarly
optimized through the choice of material and process conditions to
yield the desired selectivity, either 1:1:1 or with a harder stop
on for example TEOS. In these embodiments, depending on the users'
preferences, the entire CMP process might also be accomplished with
a single slurry and simple programming of the polishing tool.
[0144] In general, the amount of oxidizer-based free
radical-producing compounds in the fluid ranges from about 0.01% to
about 25%, more typically from 0.1% to 15%. The amount of free
radical-producing compounds in the fluid can be near the lower
range when there are other oxidizers present, or where oxidation is
a minor part of the polishing. When the amount of activator is
high, for example the activator is present in an amount ranging
from 50 ppm to about 3000 ppm in the slurry, or is present in an
amount covering at least about 2% of the pad, the amount of free
radical-producing compounds is often limited to below about 10% to
control the reaction rate.
[0145] Non-Oxidizer Based Compounds that Produce Free Radicals
[0146] Other compounds other than oxidizers may form free radicals
when contacted by the activator, and the compound may not
necessarily be a reactive oxygen radical. Sulfur-containing free
radicals are also known. Descriptions of redox systems involving
activators that generate free radicals in the presence of oxidizing
agents are provided in Walling, C., Free Radicals in Solution
(1957), pp. 564-579, and Bacon, R, The Initiation of Polymerisation
Processes by Redox Catalysts, Quart. Revs., Vol. IX (1955), pp.
287-3 10, the entire contents of which are incorporated herein by
this reference.
[0147] Organic-based compounds that produce free radicals are
known. Free radicals can be produced by for example irradiating an
R--OH, for example an alcohol, alkanolamine, aminoalcohol, and the
like, where the only activator is actinic radiation, generally with
a wavelength below about 220 nanometers, for example about 185
nanometers. Methanol in water can be irradiated to give OH*,
CH.sub.3*, and other radicals.
[0148] Free radicals can also be produced in alcohols through an
activator, for example a ketone. Actinic radiation is again
required, but the energy of the light can be lower. For example, a
ketone, say benzophenone or acetophenone, can be irradiated with
actinic radiation, generally with a wavelength below about 370
nanometers, for example between about 300 and 350 nanometers. This
forms a long-lived intermediate radical activator, wherein the half
life can be on the order of a tenth of a second. The intermediate
then reacts to form a radical with an R--OH to form free radicals.
One advantage of this system is the activator can be for example on
the moving pad and be activated immediately before, i.e., upstream,
of the substrate. Free radicals would then be formed as the pad
encountered the substrate.
[0149] In general, the amount of non-oxidizer free
radical-producing compounds in the fluid ranges from about 0.01% to
about 30%, more typically from 0.1% to 15%. The amount of free
radical-producing compounds in the fluid can be near the lower
range when there are other oxidizers present, or where oxidation is
a minor part of the polishing. When the amount of activator is
high, for example the activator is present in an amount ranging
from 50 ppm to about 3000 ppm in the slurry, or is present in an
amount covering at least about 2% of the pad, the amount of free
radical-producing compounds is often limited to below about 10% to
control the reaction rate.
[0150] Activator
[0151] The activator is a material that facilitates the formation
of free radicals by at least one free radical-producing compounds
present in the fluid. If the activator is a metal ion, or
metal-containing compound, it is in a thin layer associated with a
surface of a solid which contacts the fluid. If the activator is a
non-metal-containing substance, it can be dissolved in the fluid.
It is preferred that the activator is present in amount that is
sufficient to promote the desired reaction.
[0152] Generally, light-activated activators such as titanium
oxides (and light used as an activator) are not preferred. There is
no method to get light at the desired concentration between a pad
and a substrate. The activator must therefore be pre-activated,
and/or the free radicals must be formed, before the fluid passes
between a pad and a substrate.
[0153] In some configurations use of photo-activated activator is
acceptable. For example, for long-lived free radicals, i.e., with
an average life in solution of a tenth of a second or more, the
photoactivator can be a matrix containing activator that the fluid
must contact just before passing between a pad and a substrate. A
bed of activator can for example be placed immediately upstream of
the fluid outlet, so that free radicals formed have not totally
degraded before passing between the pad and the substrate. The
photoactivated materials of U.S. Pat. No. 6,362,104, the disclosure
of which is incorporated by reference, can be used in this
capacity. These include TiO.sub.2 and Ti.sub.2O.sub.3, as well as
to the less preferred oxides of Ta, W, V, and Nb.
[0154] The activator may be a non-metal-containing compound. Iodine
is a useful with for example hydrogen peroxide to form free
radicals. The iodine may be present in an amount sufficient to
create the desired free radical activity. In some embodiments, the
iodine may be present in an amount ranging from about 1 ppm to
about 5000 ppm, preferably between about 10 ppm and about 1000 ppm.
Non-metallic activators are often synergistically combined with
metal-containing activators.
[0155] The activator can also be a metal-containing compound, in
particular a metal selected from the group consisting of the metals
known to activate a Fenton's Reaction process in hydrogen peroxide.
Advantageously, most metal-containing activators are associated
with a solid as discussed below. Of course, the system of this
invention may optionally comprises both metal-containing activators
and non-metal-containing activators, where the non-metal-containing
activators are in solution in the fluid and where at least a
portion of the metal-containing activators are associated with a
solid.
[0156] In another embodiment, the activator is any metal-containing
compound known to be useful in Fenton's reactions as an activator,
wherein the oxidizer is a peroxide, particularly hydrogen peroxide.
Transition metals like copper, manganese, cobalt, and cerium, as
well as the more traditional iron and copper, are able to catalyze
this reaction. However, these metals having multiple oxidation
states, particularly iron and copper, are known to be particularly
problematic if in solution with for example hydrogen peroxide or
persulfates. Further, cobalt, manganese, and cerium in solution
have environmental concerns. All are a contaminant to the
substrate. Finally, all, if in solution, are believed to act as
promotors rather than activators. We have found, however, that if
these elements or molecules are associated with a solid contacting
the fluid, they can function as activators.
[0157] In one important embodiment, the activator comprises a
metal-containing compound having the metal other than a metal of
Group 4(b), Group 5(b) or Group 6(b) of the Periodic Table of
Elements. In one embodiment, compounds of metals of Group 1(b) or
Group 8 are preferred metal-containing activators. However, the
activity of, the cost of, and the potential of substrate
contamination from these metals varies greatly. See, for example,
Handbook of Chemistry and Physics, 64th Edition Periodic Table of
the Elements, Inside Front Cover, which is fully incorporated
herein by reference.
[0158] In another important embodiment, the activator comprises a
dissociable salt of a metal. As used herein, the phrase
"dissociable salt of a metal" should be understood to mean that
metal portion of the compound can form a metal ion and remain
associated with a surface while counterions can be released into
solution.
[0159] In another important embodiment, the activator comprises any
transition metal-containing compound that can react with a compound
that produces free radicals, is associated with a solid. That is,
the activators of the current invention are not soluble in the
fluid. Activators can be associated with a particle. The particle
may be an abrasive, or it may be a carrier for the activator.
Activators can be associated with a pad. Activators can be held in
a matrix such that the fluid containing the compounds that form
free radicals contacts the activator immediately before contacting
the substrate.
[0160] Preferably, the activator can function effectively without
actinic radiation, and the oxidizer itself can rejuvenate the
activator. This step in some very preferred embodiments will also
result in the formation of a second free radical, though often a
weaker free radical than was produced in the first step. For
example, without being bound to theory, as opposed to the classical
Fenton's reaction which is the oxidation of Fe(II) by hydrogen
peroxide, the reaction of the surface bound Fe activator of this
system by hydrogen peroxide forms both superoxide anion and
hydroxyl radicals. Therefore, hydrogen peroxide is both an oxidant
and reductant in these systems.
[0161] If an activator is itself made effective with light, the
"effectiveness" of the activator will decay when it is not exposed
to light. It is very difficult to get light between a pad and a
substrate, and therefore concentration gradients will occur.
[0162] Generally, the preferred activators are iron, copper,
cerium, nickel, manganese, and/or cobalt. They can be used in any
combination. The more preferred activators are iron or cerium
salts.
[0163] It is advantageous that the activator be associated with a
surface, as opposed to being for example a solid crystal. The
activator can be a homogeneous composition of the active activator.
The homogenous activator are preferably small particles with high
surface areas. This form of activator should have a mean particle
diameter less than about 1 micron, preferably less than 0.4
microns, more preferably less than 0.1 microns, and a surface area
greater that about 10 m.sup.2/g. The same preferred particle
characteristics will also optimize the colloidal stability of the
activator in the polishing compositions.
[0164] Solid crystals of activator-type material often do not have
sufficient binding capacity/flexibility in the binding of the atoms
to allow the activator components to change oxidation states to
react with the compound that produces free radicals. Interaction of
crystals may result in crystal dissolution, as the metal leaves the
crystal and enters the solution. For this reason solid activator
material is generally discouraged, though if metal loss is
insignificant solid activator particles can be contemplated.
[0165] The metal-containing activator compounds associated with a
particle or a pad may be in a variety of forms, such as an oxide, a
nitrate, a halide, a perchlorate, or an acetate of the metal. The
counter-ions are generally of lesser significance, unless they
stabilize the activator by hindering access to the compounds that
form free radicals. In one embodiment, the activator associated
with a particle and/or polishing pad is a metal-containing acetate,
such as copper acetate ("CuAc") or iron acetate ("FeAc") or cerium
acetate ("CeAc"). The metal-containing activator compounds may be a
source of ions associated with a solid and not dissolved in the
fluid containing the oxidizer.
[0166] Activator oxides can often be used but are not preferred. By
way of example, suitable metal oxides include some iron oxides,
copper oxide, and cobalt oxide. Some, for example cerium oxide and
aluminum oxide may not be able to function as an activator, even if
coated on an abrasive. Further, the activators of the current
invention are not for example titanium oxides which require actinic
energy to be effective.
[0167] The activators of the current invention can include iron and
copper oxides at very low amounts. Many forms of iron oxide are not
activators but rather catalyze decomposition of preferred oxidizers
such as hydrogen peroxide without forming the beneficial free
radicals. While iron is a greatly preferred activator, there are
conditions under which it will form an oxide/hydroxide that can
catalytically cause decomposition of hydrogen peroxide and ammonium
persulfate without forming free radicals, and resulting in
dangerous conditions as oxygen levels increase. Certain crystals,
for example certain forms of iron oxide and hydroxide, do not
activate compounds that form free radicals, for example hydrogen
peroxide.
[0168] However, several iron and copper oxides form superoxide
anions and hydroxyl radicals, but may be rate limited by the
oxidation of surface bound iron by hydrogen peroxide. Three iron
oxides: ferrihydrite, goethite, and semi-crystalline iron oxide,
are somewhat active in activating hydrogen peroxide, but activator
disposed as a layer on a surface of a metal oxide particle has much
superior kinetics.
[0169] The activator is preferably chemically or physically
associated with the surface of a particle as molecular species, as
a small particle or as a monolayer. For example, a doped
Ceria-gamma Alumina Supported Nickel is a useful activator for some
compounds that form free radicals. The activator activity of an
alumina supported copper oxide, compared to that of goethite, has
shown that the supported copper oxide was approximately ten times
more active than goethite. For traditional Fenton's reactions, Fe
containing zeolite when compared with the behavior of homogeneous
Fe activators at the same experimental conditions found the
heterogeneous activators have a higher reactivity and a reduced
dependence on the pH of the solution. However, under some
conditions they can also have a higher rate of the side reaction of
hydrogen peroxide decomposition to water and oxygen.
[0170] The abrasive can be a co-formed abrasive in which the
activator is homogeneously mixed with another oxide to form solid
particles containing an intimate mixture of the activator supported
on metal oxide. In addition the activator can be chemically or
physically adsorbed on the surface of the abrasive as molecular
species, small particles or as a monolayer.
[0171] We have found that transition metal-activators that are
associated with solids, for example an abrasive, a particle, or a
pad, can initiate the creation of free radicals without the
undesirable side effects such transition metals may have if they
are in solution in the fluid contacting the substrate. In
particular, we have surprisingly found that transition
metal-containing activators associated with the surface of a solid
are effective as activators, promoting the formation of free
radicals, but these transition metal-containing activators are not
"in solution" and therefore do not significantly oxidize or
contaminate the substrate. Further, we have surprisingly found that
the metal-containing activators so associated with the surface of
the solid do not cause significant degradation of the hydrogen
peroxide or of the oxide when admixed for a period of at least
several hours, often a day or more, which is a typical storage time
in semiconductor fabrication plants.
[0172] The activator can be associated with a polymeric particle or
polishing pad. In a preferred embodiment of the invention, the
polishing pad has at least one of Fe, Cu, or Ce salts associated
with the surface thereof, and/or at least one of Fe and Cu oxides
associated with the surface thereof. As pads are worn during use,
having activators within the pad matrix that will eventually be
contacting a fluid containing the compound that produces free
radicals is advantageous. Generally, a monolayer of activator atoms
associated with the surface of the pad that contacts the fluid and
promotes free radical formation where the free radicals can contact
the substrate will provide maximum activity. However, as polymeric
pad may wear, having between 0.1 and 20% activator within a polymer
pad is acceptable.
[0173] In most embodiments of the invention, however, the
transition-metal-containing-activator is associated with an
abrasive particle.
[0174] The amount of activator in a slurry can be low. Of course,
activator associated with particles in a slurry can be present in
any activating amount, say from about 0.0005% to about 10% by
weight activator. High concentrations are usually wasteful,
however. In a system with transition metal containing activator,
i.e., a slurry having a transition metal activator coated on solid
particles contained within the slurry, excellent free radical
activity is observed if the amount of activator in the slurry is
about 5 to 10000 ppm total activator. If the activator is located
on particles such that access to fluid is not impaired, a slurry
can have between 5 and about 4000 ppm, for example between about 10
and 1000 ppm. In preferred low-activator-content slurries tested,
activator concentrations of between about 5 and about 200 ppm, for
example between about 20 and about 100 ppm, say about 30 ppm, of
activator expressed as a weight percent of the slurry, provided
accelerated etch rates compared to formulations without
activator.
[0175] Compounds or salts that might otherwise be considered an
activator are not included if they do not function as an activator.
As used herein, therefore, a transition metal is an activator only
if it is associated with a solid. For example, activator within a
particle matrix where it can not generate free radicals that can
escape the particle structure is not included in the term
activator. Activator elements or compounds that can not activate
the formation of free radicals, for example because it is
incorporated within a matrix where changes between oxidation states
is discouraged, is not included as activator. Compounds that can
plate out or contaminate the substrate are viewed as contaminants.
Finally, activator that is chelated or otherwise not available for
reaction with the compound that produces free radicals is not
included as activator.
[0176] In one important embodiment of the invention, at least a
portion of the activator is associated with at least a portion of
the abrasive particles. In its most general meaning, the term
"associated" means that activator compounds are affixed to the
surface of an abrasive particle, such that the activator contacts
the fluid containing the Free Radical-Producing Compound, wherein
the contacting results in significant increase in free radical
formation (as determined by significant increase in CMP removal
rates discussed previously). Generally, having the activator be
associated with the abrasive means the activator is coated on the
abrasive, absorbed onto the abrasive, or is adsorbed on to the
abrasive, or is otherwise attached or bound to the abrasive. The
activator coating can be in a pure form, or the activator can be
admixed with other compounds, minerals, metals, and the like, to
form an activator composition that is coated onto at least a
portion of an abrasive.
[0177] In preferred embodiments very little, preferably none, of
the activator breaks the association with the abrasive and enters
the solution as an ion or soluble compound, or plates onto the
substrate. Therefore, the abrasive with the associated activator
may be stabilized. For example, the abrasive with the associated
activator may be calcined. The abrasive with the associated
activator may be subsequently covered with or treated with other
compounds including stabilizers, surfactants, silanes, or other
components. Or, the abrasive with the associated activator may be
covered with or treated with other compounds and calcined.
[0178] A system with iron activator, i.e., a slurry having iron
coated on solid particles contained within the slurry, shows
excellent free radical activity if the amount of activator iron is
about 2 to 500 ppm total activator iron, preferably 3 to 100 ppm
total activator iron, and for low iron embodiments about 4 to 20
ppm total activator iron. Iron that is not contacting the fluid,
including iron for example within a particle matrix where it can
not generate free radicals that can escape the particle structure,
is not included in the term activator iron. Iron that can not
activate the formation of free radicals, for example because it is
incorporated within a matrix where changes between oxidation states
is discouraged, is not included in activator iron. Finally, iron
that is chelated or otherwise not available for reaction with the
compound that produces free radicals is not included as activator
iron. An exemplary slurry has about 50 ppm to about 300 ppm total
activator iron, most of it absorbed, adsorbed, or coated onto the
abrasive.
[0179] In low-metal-containing-activator embodiments, less than 80
ppm total metal-containing activator in a slurry can be used. This
activator may act alone, or be supplemented with for example
activator on the pad and/or non-metal-containing activator in the
fluid. In preferred low-metal-containing-activator embodiments,
less than 40 ppm total metal-containing activator in a slurry can
be used, for example between about 5 ppm and about 30 ppm, or about
5 ppm to 20 ppm. Of course, the limits on the metal content of the
fluid contacting the substrate and having the compound producing
the free radical and optionally other oxidizers is still important.
It is highly beneficial, even when the slurry contains up to 500
ppm of activator associated with particles, to have for example
less than 20 ppm, preferably less than 8 ppm, for example less than
4 ppm, of these metals in solution in the fluid contacting the
substrate.
[0180] An activator associated with an abrasive means the activator
is not in solution in the slurry. Metals in solution act as
promoters and will therefore contaminate a substrate. Further, if
chemical reactions occur to cause the activator to tend to plate
out (i.e., be reduced to a metallic state), the activator will
still not move from the surface of the abrasive, and therefore will
not plate out on the substrate. Additionally, we have surprisingly
found that activator associated with an abrasive has a much lower
tendency to spontaneously decompose certain oxidants, for example
hydrogen peroxide, even at higher pH values where hydrogen
decomposition by metal ions in solution is known. While not being
bound by theory, generally, an activator associated with an
abrasive is believed to only incidentally contact the
substrate.
[0181] Copper is a known Fenton's agent, and therefore copper
associated with solids makes an excellent activator. As copper can
shift from a cuprous and cupric oxidation states, there will always
be two bonding sites whereby the copper may be associated with the
active sites on the abrasive material. The copper can be associated
with the abrasive in the form of a salt, for example a cupric salt,
a cuprous salt, in some forms a copper oxide, and in some forms
metallic metal. Generally, metallic metal will be transformed to
the cupric or cuprous form in the presence of oxidizers.
[0182] Silver is a useful activator for many systems, and can be
coated onto for example silica, ceria, alumina, and other known
abrasives, but if silver changes oxidation states, it may under
some conditions become un-associated from the solid material.
Additionally, the cost of silver is prohibitive unless
recovery/recycle systems are in place. Finally, silver ions can
complicate disposal of used slurry.
[0183] While gold coated onto one or more abrasives may be a useful
activator for many systems, unless there is rigorous recovery and
recycling of the activator-coated particles, the material cost will
be too great foremost commercial operations. On the other hand,
gold may facilitate the production of free radicals without itself
changing oxidation states. The same can be said for platinum and
palladium coated onto a solid.
[0184] Coated or doped noble metals (Au, Ag, Re, Ru, Rh, Pd, Os,
Ir, Pt) are as a rule present in elemental form or also have oxidic
surface regions.
[0185] Iron associated with an abrasive is particularly useful and
is the most preferred activator. Iron associated with silica is the
most preferred system. The silica, with its numerous OH groups, can
multiply bind with the iron, holding the iron firmly associated
with the silica by a number of covalent and/or ionic type bonds.
Yet, the plurality of bonds of iron onto the silica, be it
absorbed, adsorbed, or coated, allows easy transformation between
oxidation states without the iron having a tendency to
dis-associate from the silica surface. Surprisingly, iron
associated with silica can be used at high pH values, for example
from pH 5 to pH 7 and in some cases up to pH 8. It is known that
soluble iron at these pH values forms undesirable precipitates
which contaminate substrate and which catalyze degradation of
hydrogen peroxide into oxygen and water, resulting in unsafe
explosive accumulations of gases.
[0186] The iron can be associated with the abrasive in the form of
a salt, for example a ferric salt, a ferrous salt, in some forms a
ferric oxide, and in some forms metallic metal. Generally, metallic
metal will be transformed to the ferric or ferrous form in the
presence of oxidizers. An additional advantage of iron is that it
is environmentally benign and does not pose significant disposal
problems.
[0187] Iron associated with alumina is also a useful
abrasive/activator, as is iron associated with ceria. Iron
associated with polymeric particles, or particles that have a
polymeric component, are also useful.
[0188] Cerium salts, be they absorbed, adsorbed, or coated onto a
solid, are also very useful abrasive/activators. Like iron, these
ions can be strongly held by the active sites on the abrasive
and/or particle, and once absorbed, adsorbed or coated, do not tend
to become un-associated with the particle. Cerium salts can be used
beneficially with for example iodine.
[0189] In another embodiment, metal-containing activator compounds
comprising cobalt, copper, iron, cerium, or mixtures thereof are
suitable activators.
[0190] Nickel, silver, or any combination thereof are suitable
activators for some compounds which produce free radicals.
[0191] In another embodiment, metal-containing compounds having
standard oxidization potential of from about -0.52 to about -0.25
eV are suitable activators. Examples of metal activators with
oxidation potentials in this range include copper (-0.52 eV), iron
(-0.44 eV), cobalt (-0.28 eV), and nickel (-0.25 eV). In another
embodiment, formation of free radicals is promoted by an electric
potential externally imposed across an activator/fluid system so
the activator has an oxidation potential within this range.
[0192] Descriptions of redox systems involving activators that
generate free radicals in the presence of oxidizing agents are
provided in Walling, C., Free Radicals in Solution (1957), pp.
564-579, and Bacon, R, The Initiation of Polymerisation Processes
by Redox Catalysts, Quart. Revs., Vol. IX (1955), pp. 287-3 10, the
entire contents of which are incorporated herein by this reference.
Such catalysts are candidate activators, and may be for example
associated with the abrasive used in the composition.
[0193] Compounds that do not need actinic radiation, for example UV
radiation, to be effective as an activator are preferred
activators. It is known that titanium oxides, when activated with
actinic radiation, may form free radicals under certain conditions.
This is not useful under CMP polishing conditions.
[0194] However, where the production of free radicals might be
promoted where the production is acceptable without actinic
radiation can be included. For example, formation of free radicals
may promoted by actinic radiation for certain iron-based or a
copper-based activators.
[0195] A preferred Group 8 metal is iron. A preferred Group 1(b)
metal is copper. Another preferred metal activator is cerium, a
Group 3(b) activator. However, it is known that iron, copper, and
cerium ions can cause metallic contamination of the substrate
surface. Further, iron ions added as ferric nitrate to a hydrogen
peroxide mixture was found to create undesirable degradation of the
hydrogen peroxide and of the ferric ions. Other metallic ions have
similar problems.
[0196] Surprisingly, the metal compounds, particularly the iron
compounds, associated with an abrasive were found to have a large
effect on the etching rate of a CMP slurry despite the fact that
the iron ions largely did not contact the substrate, and did not
cause direct oxidation of the substrate by taking electrons from
the substrate, did not cause oxidation of the substrate by
shuttling electrons from the oxidizer to the substrate. Rather, the
iron compounds cause formation of free radicals, most preferably
reactive oxygen radicals.
[0197] It is believed that the composition of one important
embodiment of the present invention is particularly advantageous by
virtue of the interaction between at least one activator that is
associated with a surface of a solid and at least free
radical-forming compound, i.e., oxidizing agent, that is in the
fluid. That is, it is believed that a reaction takes place between
the activator that is for example coated on an abrasive, and the
oxidizing agent that is in the fluid, such as a peroxide or
hydroperoxide, at the solid activator/liquid interface. It is
believed that this reaction generates free radicals or active
reaction intermediates, such as hydroxyl free radicals, at the
activator surface, which favorably interact with the targeted
material on the substrate when the free radicals contact the
targeted substrate, which may be facilitated when the activator
coating on the abrasive contacts the substrate surface.
[0198] The activator may include a metal-glycine complex, wherein
the metal consists essentially of cerium, iron, manganese, cobalt,
or mixture thereof.
[0199] Mixtures of activators can give increased activity. Cerium
salts are particularly useful when admixed with iron or copper.
Manganese salts are particularly useful when admixed with iron or
copper. Rare earth metals may be useful when admixed with iron or
copper. U.S. Pat. No. 5,097,071, the disclosure of which is
incorporated herein by reference, teaches preparation process for
an alumina supported copper useful for initiating Fenton's
reaction, where the copper is impregnated with compounds of
manganese and of one or more rare earth metals, having a Cu content
of 0.1-5% by weight, a total content of compounds of manganese and
of the rare earth metal or metals of 0.05 to 8% by weight,
calculated as metals. The following may be mentioned as rare earth
metals (subgroup III of the periodic table of elements): scandium,
yttrium, lanthanum and the lanthanies. Yttrium, lanthanum, cerium,
praseodymium, neodymium and dysprosium are preferred, cerium and
lanthanum are particularly preferred and cerium is very
particularly preferred.
[0200] In some embodiments, compounds of Ag, Cr, Mo, Mn, Nb, Nd,
Os, Pd, Pt, Rh, Ru, Sc, Sm, Ta, Ti, V, or W which are associated
with the surface of a particle which contains activator are useful.
They may facilitate the action of the activators or with some
compounds that form free radicals they may themselves become
activators.
[0201] Fluid Additives
[0202] The fluid composition contains one or more compounds that
produce free radicals, and contains or contacts one or more
activators. The composition may contain a variety of other
additives, such as a typical abrasive (i.e., an abrasive lacking a
activator coating); other abrasives or particles, which may or may
not be of the same characteristics (material, size, and the like)
as activator-containing particles; one or more typical oxidizing
agents (i.e., an oxidizer that is not a free radical producer);
promoters; surfactant; stabilizing and passivating agents;
dispersion agents; chelators; film-forming anticorrosion agents; a
polish enhancement agent; and/or pH adjusting agents.
[0203] In some embodiments, for example when the abrasives or other
particles having the activator associated with the surface are to
be stored or handled, or when the activator makes a portion of the
slurry unstable, the surface of the activator can be passivated.
passivating agents are beneficially relatively insoluble with
respect to the bound activator (will not cause the activator to
leave the particle) and also to have an affinity for the
activator-coated particle. At selected pH values, selected
carboxylic acid salts, for example oxalate, gallate, citrate, and
the like can be made to coat the activator-containing particles.
These passivators often can eliminate free radicals, which further
enhances stability. Other passivators include succinates,
benzoates, formates, cupferons, and 8-hydroxyquinoline. However, it
is generally advisable to have the pH and or ionic conditions
change prior to polishing so that the activator can be exposed and
function.
[0204] Particles having the activator can be treated with various
agents to enhance colloidal stability, including carboxylic acids
and polycarboxylic acids.
[0205] Promoters
[0206] As stated above, although metals having multiple oxidation
states that are dissolved in the fluid contacting the substrate can
act as oxidizers, the most preferred embodiments of this invention
have substantially no metals having multiple oxidation states.
[0207] In some embodiments, compounds of Al, Ag, Ce, Co, Cr, Cu,
Fe, Mo, Mn, Nb, Nd, Ni, Os, Pd, Pt, Rh, Ru, Sc, Sm, Ta, Ti, V, or W
in minor amounts dissolved in the solution are useful. These are
believed to facilitate the action of the oxidizers, as discussed in
U.S. Pat. No. 5,958,288, the disclosure of which is incorporated
herein by reference. Metal ions in solution are believed to act as
oxidizers with a degree of affinity to the substrate, particularly
to metal substrates. If they are able to be oxidized by other
oxidizers in the fluid, there will be some synergistic action
between the two. In most cases the promoters are believed not to
facilitate the action of the free radicals, however. Compounds that
form promoters on exposure to a catalyst or substrate, such as
those compounds described in U.S. Pat. No. 5,863,838, the
disclosure of which is incorporated by reference, are also
useful.
[0208] In some embodiments of the present invention, the fluid
composition contacting the substrate has a small amount of metal
ion oxidizers, herein called promoters. Soluble compounds or salts
of copper, aluminum, cerium, and iron are used as oxidizers or
promoters in CMP solutions. If used, a preferred metal-containing
oxidizer promoter is soluble cerium salts or aluminum salts.
[0209] A promoter has some effect at low concentrations, about as
low as 4 ppm. As this affinity between promoters and substrates in
turn results in the probability of metallic ion contamination of
the substrate, the fluid beneficially contains less than 5000 ppm,
preferably less than 2000 ppm, more preferably less than 500 ppm
(0.05%) of dissolved metal-containing promoters, particularly
copper, cerium, and iron. In preferred embodiments of this
invention, the fluid composition contacting the substrate has less
than 50 ppm, preferably less than 20 ppm, and more preferably less
than 10 ppm total of dissolved metal-containing promoters,
particularly copper and iron;.
[0210] In preferred low-(dissolved)-metal-containing embodiments of
this invention, the fluid composition contacting the substrate has
less than 50-ppm, preferably less than 20 ppm, and more preferably
less than 10 ppm of dissolved metals having multiple oxidation
states.
[0211] In preferred no-(dissolved)-metal-containing embodiments of
this invention, the fluid composition contacting the substrate has
less than 5 ppm of dissolved metals having multiple oxidation
states, for example less than 2 ppm of dissolved metals having
multiple oxidation states. One example that performed well had less
than 1 ppm of dissolved metals having multiple oxidation states,
though it had been in contact with an abrasive having an activator
associated on the surface thereof. In the most preferred
embodiments of this invention, the fluid composition contacting the
substrate has less than. 5 ppm, for example less than 2 ppm, of
total dissolved copper, aluminum, cerium, and iron.
[0212] If copper or iron are present in dissolved form, it is
preferred that they be in chelated form, which essentially isolates
these metals from the fluid and from the substrate and makes them
not useful as an oxidizer or as a promoter. For iron in particular,
in preferred embodiments the fluid contacting the substrate has
less than 8 ppm, preferably less than 4 ppm, more preferably less
than 2 ppm, most preferably less than 1 ppm of iron salts or
compounds dissolved in the fluid, i.e., the liquid portion of the
slurry.
[0213] Additionally, for the same reasons as above for metal
oxidants, metal salts of other components are generally
discouraged. These include sodium salts (such as sodium periodate),
potassium salts (such as potassium persulfate), lithium salts, and
the like. Generally, potassium salts are much less prone to
creating contamination than are sodium salts. It is also or
alternatively preferred to have less than 2000 ppm of total metals
dissolved in the fluid portion of the CMP slurry, and it is more
preferred to have less than 500 ppm, for example less than 50 ppm,
and in a metal-free embodiment less than 10 ppm, of total metals
dissolved in the fluid portion of the CMP slurry. By total metals,
it is meant metals in groups 1(a), 2(a), 3(b), 4(b), 5(b), 6(b),
7(b), 8, 1 (b), and 2(b).
[0214] Chelators
[0215] If no-(dissolved)-metal-containing embodiments are desired,
the fluid may have chelators. Chelators can essentially trap and
isolate metals having multiple oxidation states that are present in
dissolved form in the fluid. If dissolved metals are in chelated
form, this essentially isolates them from the substrate, which
impairs their efficiency as a promoter but prevents metal ion
contamination. This can extend the potlife of a slurry of oxidizer,
however, and at low concentrations the chelators will not
effectively impair the efficiency of the free radicals.
[0216] Therefore, only small amounts of chelator should be used.
Chelators generally contain organic acid moieties, which can act as
free radical quenchers. This could adversely effect the system
performance.
[0217] Generally, less than 3%, preferably less than 1%, for
example less than 0.5% by weight of chelators are preferred.
[0218] Stabilizers
[0219] The composition may also include one or more of various
optional additives. Suitable optional additives include
stabilization agents. These optional additives are generally
employed to facilitate or promote stabilization of the composition
against settling, flocculation (including precipitation,
aggregation or agglomeration of particles, and the like), and
decomposition. Stabilizers can be used to extend the pot-life of
the oxidizing agent(s), including compounds that produce free
radicals, by isolating the activator material, by quenching free
radicals, or by otherwise stabilizing the compounds that form free
radicals.
[0220] Some materials are useful to stabilize hydrogen peroxide.
One exception to the metal contamination is the presence of
selected stabilizing metals such as tin. In some embodiments of
this invention, tin can be present in small quantities, typically
less than about 25 ppm, for example between about 3 and about 20
ppm. Similarly, zinc is often used as a stabilizer. In some
embodiments of this invention, zinc can be present in small
quantities, typically less than about 20 ppm, for example between
about 1 and about 20 ppm. In another preferred embodiment the fluid
composition contacting the substrate has less than 500 ppm, for
example less than 100 ppm, of dissolved metals, except for tin and
zinc, having multiple oxidation states. In the most preferred
commercial embodiments of this invention, the fluid composition
contacting the substrate has less than 9 ppm of dissolved metals
having multiple oxidation states, for example less than 2 ppm of
dissolved metals having multiple oxidation states, except for tin
and zinc. In some preferred embodiments of this invention, the
fluid composition contacting the substrate has less than 50 ppm,
preferably less than 20 ppm, and more preferably less than 10 ppm
of dissolved total metals, except for tin and zinc.
[0221] As metals in solution are generally discouraged, it is
preferred that those non-metal-containing oxidizers that are
typically present in salt forms, for example persulfates, are in
the acid form and/or in the ammonium salt form, such as ammonium
persulfate.
[0222] Other stabilizers include free radical quenchers. As
discussed, these will impair the utility of the free radicals
produced. Therefore, it is preferred that if present they are
present in small quantities. Most antioxidants, i.e., vitamin B,
vitamin C, citric acid, and the like, are free radical quenchers.
Most organic acids are free radical quenchers, but three that are
effective and have other beneficial stabilizing properties are
phosphonic acid, the binding agent oxalic acid, and the
non-radical-scavenging sequestering agent gallic acid.
[0223] In addition, it is believed that carbonate and phosphate
will bind onto the activator and hinder access of the fluid.
Carbonate is particularly useful as it can be used to stabilize a
slurry, but a small amount of acid can quickly remove the
stabilizing ions. Stabilization agents useful for absorbed
activator can be film forming agents forming films on the silica
particle.
[0224] Suitable stabilizing agents include organic acids, such as
adipic acid, phthalic acid, citric acid, malonic acid,
orthophthalic acid; and, phosphoric acid; substituted or
unsubstituted phosphoric acids, i.e., phosphonate compounds;
nitrites; and other ligands, such as those that bind the activator
material and thus reduce reactions that degrade the oxidizing
agent, and any combination of the foregoing agents. As used herein,
an acid stabilizing agent refers to both the acid stabilizer and
its conjugate base. That is, the various acid stabilizing agents
may also be used in their conjugate form. By way of example,
herein, an adipic acid stabilizing agent encompasses adipic acid
and/or its conjugate base, a carboxylic acid stabilizing agent
encompasses carboxylic acid and/or its conjugate base, carboxylate,
and so on for the above mentioned acid stabilizing agents. A
suitable stabilizer, used alone or in combination with one or more
other stabilizers, decreases the rate at which an oxidizing agent
such as hydrogen peroxide decomposes when admixed into the CMP
slurry.
[0225] On the other hand, the presence of a stabilization agent in
the composition may compromise the efficacy of the activator. The
amount should be adjusted to match the required stability with the
lowest adverse effect on the effectiveness of the CMP system. In
general, any of these optional additives should be present in an
amount sufficient to substantially stabilize the composition. The
necessary amount varies depending on the particular additive
selected and the particular make up of the CMP composition, such as
the nature of the surface of the abrasive component. If too little
of the additive is used, the additive will have little or no effect
on the stability of the composition. On the other hand, if too much
of the additive is used, the additive may contribute to the
formation of undesirable foam and/or flocculant in the composition.
Generally, suitable amounts of these optional additives range from
about 0.001 to about 2 weight percent relative to the composition,
and preferably from about 0.001 to about 1 weight percent. These
optional additives may be added directly to the composition or
applied to the surface of the abrasive component of the
composition.
[0226] pH Adjustors
[0227] The pH of the composition is desirably on the order of from
about pH 1 to about pH 11, and preferably, from about pH 2 to about
pH 8. These pH levels, and particularly the preferred levels, are
believed to facilitate control of the CMP process. A composition
having a pH that is too low, such as below pH 2, may present
problems in terms of the handling of the composition and the
quality of the polishing itself. A composition having a pH that is
too high, such as above pH 11, may detrimentally contribute to
corrosion or other attack on the metal layer, such as copper or
tungsten, on the substrate surface, depending on the nature of the
metal layer. This may not be an issue in the polishing of metal
layers such as aluminum or exotic metals, which may tolerate a CMP
composition of relatively high pH without ill effect.
[0228] The pH of the composition may be adjusted using an
appropriate pH adjusting agent, such as a suitable acid, base,
amine, or any combination thereof. Preferably, a pH adjusting agent
used in the composition does not contain metal ions, such that
undesirable metal components are not introduced into the
composition. Suitable pH adjusting agents include amines, ammonium
hydroxide, nitric acid, phosphoric acid, sulfuric acid, organic
acids, and/or salts thereof, and any combination thereof. The pH
level of the composition should could be as low as about pH 1.5,
but the formulation becomes difficult to work with at that low pH.
Generally, the fluid pH is kept in a range of from about pH 2 to
about pH 11, with a preferred upper level of about pH 8. The more
preferred range is about pH 3 to about pH 7.5, for example pH
between pH 3.5 and pH 4.5.
[0229] Surfactants
[0230] While there are many suitable surfactant additives for the
composition, preferred surfactant additives include dodecyl sulfate
sodium salt, sodium lauryl sulfate, dodecyl sulfate ammonium salt,
and any combination thereof. Suitable commercially available
surfactants include TRITON DF 16 .TM. manufactured by Union Carbide
and SUIRFYNOL.TM. manufactured by Air Products and Chemicals.
[0231] Various anionic and cationic surfactants having molecular
weight in the range from less than 1000 to greater than 30,000 are
contemplated as dispersants. Included are sodium, potassium, or
preferably ammonia salts of stearate, lauryl sulfate, alkyl
polyphosphate, dodecyl benzene sulfonate, disopropylnaphthalene
sulfonate, dioctylsulfosuccinate, ethoxylated and sulfated lauryl
alcohol, and ethoxylated and sulfated alkyl phenol.
[0232] Various cationic surfactants include polyethyleneimine,
ethoxylated fatty amine and stearylbenzyldimethylammonium chloride
or nitrate. Alternate dispersants contemplated in the present
invention include: polyethylene glycols, lecithin, polyvinyl
pyrrolidone, polyoxyethylene, isoctylphenyl ether, polyoxyethylene
nonylphenyl ether, amine salts of alkylaryl sulfonates,
polyacrylate and related salts, polymethacrylate.
[0233] If a surfactant is added to the first CMP slurry, then it
may be an anionic, cationic, nonionic, or amphoteric surfactant or
a combination of two or more surfactants can be employed.
Furthermore, it has been found that the addition of a surfactant
may be useful to reduce the within-wafer-non-uniformity (WIWNU of
the wafers, thereby improving the surface of the wafer and reducing
wafer defects.
[0234] In general, the amount of additive such as a surfactant that
may be used in the first CMP slurry should be sufficient to achieve
effective stabilization of the slurry and will typically vary
depending on the particular surfactant selected and the nature of
the surface of the metal oxide abrasive. For example, if not enough
of a selected surfactant is used, it will have little or no effect
on first CMP slurry stabilization. On the other hand, too much
surfactant in the CMP slurry may result in undesirable foaming
and/or flocculation in the slurry. As a result, stabilizers such as
surfactants should generally be present in the slurry of this
invention in an amount ranging from about 0.001% to about 0.2% by
weight, and preferably from about 0.001 to about 0.1 weight
percent. Furthermore, the additive may be added directly to the
slurry or treated onto the surface of the metal oxide abrasive
utilizing known techniques. In either case, the amount of additive
is adjusted to achieve the desired concentration in the first
polishing slurry.
[0235] Polishing-Enhancement Additives
[0236] Optionally, certain additives or polish enhancement agents
may be added to the composition to enhance or improve the polishing
rate of targeted material on the substrate surface, such as
tantalum and titanium material often present in the form of barrier
layers on the substrate surface. An example of a polish enhancement
agent is hydroxylamine, which is particularly effective when the
targeted material is tantalum. Polishing enhancement agents other
than hydroxylamine, such as fluoride based agents, are generally
preferred for use with peroxide-containing compositions. The
optional polishing enhancement agent, if any, is generally present
in an amount of from about 0.001 to about 2 weight percent, or
preferably, from about 0.001 to about 1 weight percent, relative to
the composition.
[0237] Other polishing enhancers can include glycols, including
mono, di, and tri ethylene glycols and the like, glycine or
derivatives thereof such as glycine having between one and three C1
to C4 alkyl groups substituted on the nitrogen, the OH moiety, or
both, or mixture thereof, in an amount between about 0.05% to about
5%, preferably between about 0.1% to about 1% by weight of
slurry.
[0238] Other polishing enhancers include nucleophilic amines and
alkanolamines, which can be present in amounts from about 0.01% to
about 30%, for example between about 0.01% and 3%.
[0239] Film-Forming Anticorrosion Compounds
[0240] Its known that some oxidation reactions can occur too fast,
especially on susceptible metals such as copper. For this reason it
is sometimes beneficial to have one or more film forming agents in
the slurry. Film forming agents have a tendency to adhere to one or
more metals, partially protecting the metals from the actions of
the oxidizer and/or free radicals.
[0241] The CMP composition may include an optional film forming
agent. The film forming agent may be any compound or mixtures of
compounds that are capable of facilitating the formation of a
passivation layer of metal oxides and dissolution inhibiting layers
on the surface of the metal layer. Passivation of the substrate
surface layer is important to prevent wet etching of the substrate
surface. Useful film forming agents are nitrogen containing cyclic
compounds such as imidazole, benzotriazole, benzimidazole and
benzothiazole and their derivatives with hydroxy, amino, imino,
carboxy, mercapto, nitro and alkyl substituted groups, as well as
urea, thiourea and others. Preferred film forming agents include
benzotriazole ("BTA"), thiazole, and thiocarbamamide.
[0242] The optional film forming agent may be present in the first
CMP slurry of this invention in an amount ranging from about 0.01
weight percent to about 1.0 weight percent. It is preferred that
film forming agent is present in the first CMP slurry in an amount
ranging from about 0.01 to about 0.2 weight percent.
[0243] Abrasive Particles
[0244] The CMP slurry of the present invention may comprise one or
more particulates, herein termed abrasives. The abrasive particle
may be a metal oxide particle, a resinous particle, or a plastic
particle, and is preferably a metal oxide particle.
[0245] Advantageously, the abrasives are engineered to provide the
desired combination of particle size, hardness, surface area,
inertness, selectivity, and ability to remain suspended in a
formulation. While for some applications grit or sand can be useful
as an abrasive, for semiconductors, memory devices, and the like
much smaller particles are required. For semiconductors, particles
with an average size of between about 1 and about 4000 nanometers
are useful. The BET surface area of the metal oxide or metalloid
oxide can be between about 5 and about 1000 m.sup.2/g. Generally,
it is preferred that the particles have a similar surface area,
such that for example at least 90% by weight of the particles have
a surface area within about 20%, preferably within about 10%, of
the mean average surface area of the particles.
[0246] It is within the ability of one of ordinary skill in the
art, with the benefit of this disclosure, to maximize the content
of the useful activator on abrasive, or to alter the abrasive
properties including mineral content, particulate size, the surface
area, and the surfactants, stabilizers, and other compounds to keep
the particles comprising the activator suspended in for example a
colloid form.
[0247] Particle size distribution is important. Generally, superior
polishing is achieved with a solution of equally sized particles of
a given type. Also, large particles, i.e., particles that are more
than about two or three times the average particle size, are
generally responsible for most scratching and damage of substrates.
In a preferred embodiment, the particle size distribution can be
expressed as in U.S. Pat. No. 5,626,715, the contents of which is
incorporated herein by reference. Abrasive particles, for example
alpha aluminum oxide particles or silica particles or ceria
particles, used for polishing have a particle size of 1 to 100 mm,
and the distribution (one sigma deviation) is controlled to within
20%, preferably 10%, of the particle size.
[0248] In one embodiment, for most types of abrasive particles in a
slurry where the aggregate size distribution is less than about 4
microns and the mean aggregate diameter is between about 0.2
microns to about 1 micron, it is advantageous to have a restricted
particle size distribution such that greater than 70%, preferably
greater than 80%, by weight of the particles have a size that is
within 20% of the average size, and less than 10%, preferably less
than 5%, by weight of the particles have a size more than 100% over
the average size. Further, essentially none, i.e., less than 0.5%,
preferably less than 0.1%, by weight of the particles have a size
more than 200% over the average size.
[0249] In another embodiment, for most types of abrasive particles
in a slurry where the aggregate size distribution is less than
about 0.5 microns and the mean aggregate diameter is between about
0.005 microns to about 0.2 micron, it is advantageous to have a
restricted particle size distribution such that greater than 50%,
preferably greater than 80%, by weight of the particles have a size
that is within 20% of the average size, and less than 20%,
preferably less than 10%, by weight of the particles have a size
more than 100% over the average size. Further, essentially none,
i.e., less than 5%, preferably less than 1%, by weight of the
particles have a size more than 200% over the average size.
[0250] In another embodiment, the particles can comprises a metal
oxide produced by a process selected from the group consisting of a
sol-gel process, a hydrothermal process, a plasma process, a fuming
process, a precipitation process, and any combination thereof.
[0251] While sharp edges on abrasives give faster polishing, in
many instances speed can be sacrificed if there is less scratching
of the kind which results in degradation of performance of the
substrate product. Even particles as small as 0.1 micron give
unacceptable scratches for some applications. In some embodiments,
therefore, the abrasive is a substantially spherical particle. By
substantially spherical it is meant that the radius in any
direction is within about 30%, preferably within about 20%, even
more preferably within about 10%, of the average radius for that
particle.
[0252] Ceramic particles are also useful particles and abrasive
materials for this invention. Suitable ceramic particles are
available commercially. The ceramic particle size ranges from
greater than one micron to about 0.01 microns, and preferred sizes
are between about 0.01 microns to about 0.2 microns. Smaller sizes
than 0.01 microns are expected to provide excellent results when
they can be produced at reasonable cost. The term ceramic powders
defined to include metallic oxides such as zinc oxide, bismuth
oxide, cerium oxide, germanium oxide, silica, or aluminum oxide, or
mixtures thereof; metallic sulfides, metallic titanates, metallic
borides, metallic nitrides, metallic carbides, metallic tellurides,
metallic arsenides, metallic silicides, metallic selenides, and
metallic halides; and including mixed materials such as metallic
titanates, metallic tantalates, metallic zirconates, metallic
silicates, metallic germinates, and metallic niobates. The metal
component of the metallic oxides may include those metals of the
periodic table of elements found in groups IIA through IIB, and
also including the Lanthanum and Actinium series. In one
embodiment, ceramic powders are defined to include metal oxides
containing one or more dopants. As the quantity of dopants to be
added is normally a small weight percent of the total solids, the
addition of a dopant generally does not affect the physical
characteristics of the slip or suspension. Those skilled in the art
will therefore recognize that a variety of "dopants" may be used.
The term "dopants" shall be defined to include an additive which is
used to tailor the electrical properties and/or the binding
properties of the ceramic powder. In the present invention, dopants
may be defined to include one or more metal compounds, typically
metal oxides, selected from the group consisting of aluminum,
antimony, bismuth, boron, calcium, cadmium, chromium, copper,
cobalt, hafnium, iron, lanthanum, lead, manganese, molybdenum,
neodymium, nickel, niobium, praseodymium, samarium, scandium,
silicon, silver, tantalum, titanium, tin, tungsten, vanadium,
yttrium, zinc, and zirconium. The dopants can change the zeta
potential of the particles, altering the stability of a colloid
thereof, and/or be treated to become an active activator, and/or be
useful for securing the activator to selected sites on the
particle. One ceramic particle that can be useful is barium
titanate, commercially available in spherical form as BT-10 (TM,
Cabot Corporation) having an average particle size of about 0.1
micron. Often, lighter materials are desired. Another useful
ceramic sphere is a spherical aluminum oxide particle. These
particles have the added feature that substantially all the surface
area is outside surface area, and there is little porosity. The
ceramic particles of U.S. Pat. Nos. 6,214,756 and 6,514,894, the
disclosures of which are incorporated here by reference, form
suitable abrasive powders for the CMP system of the current
invention. Preferred ceramic powder particles are substantially
spherical with a very controlled particle size, for example,
greater than about 80% of the particles are within 15% of the
average particle size, and greater than 99% of the particles are
within about 30% of the average particle size. Further, these
patents teach a coating to form a stable suspension of ceramic
particles by forming a coating on the particles which weakens the
zeta potential-related inherent inter-particle attraction.
[0253] Generally, the activator is associated with the surface area
of the particle. In most preferred embodiments, the activator is
associated with the outer surface area and with the area just
inside pores, which is called here the "outside surface area". One
method of quantifying this is the pore volume in the outer surface
and in the 10% of the surface area within the particle that is
closest to the outer surface. In addition to being easier to place
selected activators on this surface, the free radicals generated by
the interaction of the activator and the compounds that produce
free radicals can easily move from the abrasive and contact the
substrate. In some embodiments, therefore, the activator covers
some or all of this outside surface area. The activator may be
associated with and cover between about 0.01% to about 100% of the
outside surface area of the abrasive. In some embodiments, the
activator covers between about 0.01% and about 5% of the outside
area.
[0254] The very high surface area alumina particles also have
surface area that is less accessible to fluids, compounds producing
free radicals, and the like. Additionally, free radicals produced
in some inside pores may cease to exist before the free radicals
escape the particle pore structure. While activator may also
beneficially be associated with this "inside" surface area, this
activator will be less effective on a weight basis than activator
associated with the outside surface. The activator may be
associated with and cover between about 0.01% to about 100% of the
surface area of the abrasive.
[0255] In some embodiments, the abrasive comprises particles
ranging from about 1 to about 100 nanometers, say for example about
10 nanometers. U.S. Pat. No. 5,128,081, the contents of which is
incorporated here by reference, describes a method of manufacturing
particles of metal oxide particles suitable for use with the
current invention with a particle size range of from 1 to 100
nanometers and with a very narrow particle size distribution,
including nanocrystalline alpha alumina. The patent discloses an
apparatus for preparation of nanocrystalline or nanophase materials
which include crystalline, quasicrystalline and amorphous phases.
The patent discusses the preparation of nanocrystalline aluminum
oxide, with a treatment that results in transformation of
nanocrystalline aluminum powders (likely with a very thin oxide
coating) to the thermodynamically stable alpha phase of aluminum
oxide having an average particle size of about 18 nm. Abrasives
mentioned in U.S. Pat. No. 4,910,155, the disclosure of which is
incorporated herein, are suitable, including 0.06 micron alumina
particles, silica particulates with an average diameter of 0.02
microns, and particulates of sizes as small as 0.006 microns
average size.
[0256] One advantage of the systems of this invention is that very
small, for example 1 to 10 nanometer particles, can be used and
still very high material removal rates, for example about 1000
angstroms to about 6000 angstroms per minute can be obtained.
Further, with the small particles scratches are substantially
reduced. Of course, even higher removal rates can be achieved with
more aggressive chemistries. For example, some tests showed removal
rates in excess of 15000 angstroms per minute with sub-micron sized
particles. But, this removal rate is generally considered too high
to control with current semiconductor processing tools.
[0257] The abrasive is generally in the form of an abrasive
particle, and typically many abrasive particles, of one material or
a combination of different materials. Generally, a suitable
abrasive particle is more or less spherical and has an effective
diameter of about 30 to about 170 nanometers (nm), although
individual particle size may vary. Abrasive in the form of
aggregated or agglomerated particles are preferably processed
further to form individual abrasive particles. A slurry may have
more than one type of abrasive, and it may be advantageous to have
different sizes for different types of abrasives.
[0258] A suitable metal oxide abrasive can be a metal oxide or
metalloid oxide or a chemical mixture of metal oxides or metalloid
oxides. Suitable metal oxide abrasive includes, but is not limited
to, alumina, ceria, germania, silica, spinel, titania, an oxide or
nitride of tungsten, zirconia, or any of the above doped with one
or more other minerals or elements, and any combination thereof.
The metal oxide abrasive may be produced by any of a variety of
techniques, including sol-gel, hydrothermal, hydrolytic, plasma,
pyrogenic, aerogel, fuming and precipitation techniques, and any
combination thereof.
[0259] Precipitated metal oxides and metalloid oxides can be
obtained by known processes by reaction of metal salts and acids or
other precipitating agents. Pyrogenic metal oxide and/or metalloid
oxide particles are obtained by hydrolysis of a suitable,
vaporizable starting material in a oxygen/hydrogen flame. An
example is pyrogenic silicon dioxide from silicon tetrachloride.
The pyrogenic oxides of aluminum oxide, titanium oxide, zirconium
oxide, silicon dioxide, cerium oxide, germanium oxide and vanadium
oxide and chemical and physical mixtures thereof are suitable.
[0260] The abrasive may be a mixed oxide. We have found that
certain activators are more closely held by silica than by alumina
under certain conditions. A process for the preparation of mixed
oxides is described, for example, in EP-A-1048617. In a pyrogenic
process, an SiCl.sub.4/AlCl.sub.3 mixture is brought together in an
oxygen/hydrogen flame and a mixed oxide of silicon dioxide and
aluminum oxide material is obtained in a hydrolysis step, forming a
mixed oxide particle consists of the two molecular species
SiO.sub.2 and Al.sub.2O.sub.3. Such a mixed-oxide particle will
under some conditions have a greater affinity to (or tenacity with)
the associated activator than single metal oxide particles.
[0261] Abrasives comprising alumina coated silica can also be
useful.
[0262] In one preferred embodiment, the metal oxide abrasive is a
precipitated or fumed abrasive, and preferably a fumed abrasive. By
way of example, a fumed metal oxide abrasive may be a fumed silica
or fumed alumina or a fumed silica/alumina.
[0263] In one embodiment, the activator may be incorporated into
the matrix of the abrasive particle. If a abrasive particle is
precipitated, for example from a sol, one or more activators may be
added to the sol such that the activator compounds (or elements)
are incorporated into the abrasive particle, provided a sufficient
amount of the activator is at the surface of the abrasive and is or
can be put into an active state. If the abrasive is made by a
pyrogenic or fumed process, compounds can be added to the material
being fumed, thereby incorporating the material into the formed
particle. The doped, pyrogenic oxides described in DE-A-196 50 500
may incorporate activators into the abrasive matrix. The doping
component, which is distributed in the entire particle, changes the
structure and the properties of the particular particle and
therefore the polishing properties, such as rate of removal of
material and selectivity. Or, forming particles can be admixed with
salts of activators, where the salts may be fused to the surface of
forming particles.
[0264] Abrasives can generally be used for many metals and
combinations of metals, though it is known in the art that ceria,
silica, and alumina are each preferentially used in certain
conditions with certain combinations of metals.
[0265] One abrasive can be alumina The alumina can be present here
in various forms, including amorphous or crystalline forms. The
crystalline forms including the alpha, gamma, delta, theta and
kappa types, as well as pyrogenic aluminum oxide, named for its
preparation process, and mixtures of the abovementioned aluminum
oxides. The alumina can be a mixture of phases, and/or can be doped
with one or more adjuvants.
[0266] The alumina may or may not be pure. For example, metal oxide
particles which may or may not themselves be alumina can be coated
with an alumina containing one or more activators, where the
alumina-activator coating is adhered (for example, adsorbed or
absorbed) to the outside of the abrasive, or the alumina-activator
coating is fused to the outside of the abrasive, or the
alumina-activator alumina-activator coating is in particulate form
trapped within the porosity of an abrasive, or an alumina-activator
coating is in particulate form and is fused to the abrasive, or a
combination thereof.
[0267] In some embodiments, the activator is doped into the
abrasive. For example, it is possible to formulate abrasive wherein
a desired amount of activator is included within the abrasive
matrix, provided that the abrasive so manufactured has the required
amount of activator in contact with the fluid containing the Free
Radical-Producing Compound, and providing the activator so exposed
to the fluid can cause the desired increase in free radical
formation. Generally, in another embodiment, it may be advantageous
to have sites comprising elements or compounds in the alumina
matrix which allow the alumina to more closely hold the selected
activators coated, absorbed, or adsorbed onto the surface. An
abrasive, for example alumina, having doped therein at least 0.01%,
preferably at least 1%, of compounds that if exposed at the surface
act as activators or facilitate adherence of activators to the
surface of the abrasive are preferred.
[0268] While any alumina is useful, surface area between about 3
and about 800, for example between about 100 and 600, square meters
per gram may be particularly useful for semiconductor substrates.
The alumina and silica abrasives of U.S. Pat. No. 5,527,423, the
disclosure of which is incorporated herein by reference. Of course,
the aluminum particles that contain activator affixed thereto will
not be "high purity as defined in that patent, but the described
alumina and silica particles make a good abrasive substrate for
having activator associated thereon.
[0269] For titanium and tungsten, alumina particles having a
primary particle diameter less than 0.400 micron and a surface area
ranging from 5 to 430 square meters per gram, for example between
about 10 and 250 square meters per gram, or between about 30 and
170 square meters per gram, may be preferred. Generally, it is
preferred that the particles have a similar surface area, such that
for example at least 90% by weight of the particles have a surface
area within about 20% of the mean average surface area of the
particles.
[0270] Silica is the preferred abrasive. Silica, treated to expose
a number of --OH groups, can bind to or hold the activator, say
iron, by a number of bonds. Therefore, the activator is robust when
deposited on silica, but is also so tightly bound that iron does
not leave the surface of the silica in the course of repeated
interactions with the compound that produces free radicals. The BET
surface area of the silica is typically between about 5 and about
1000 m.sup.2/g, though the upper limit can be extended as nanometer
sized particles are used. The silica can be any of precipitated
silica, fumed silica, silica fumed, pyrogenic silica, silica doped
with one or more adjutants, or any other silica-based compound. In
an alternate embodiment the silica can be produced, for example, by
a process selected from the group consisting of a sol-gel process,
a hydrothermal process, a plasma process, a fuming process, a
precipitation process, and any combination thereof. The silica in
one embodiment is advantageously at a particle size between about 2
and about 200 nanometers, for example between about 8 and about 40
nanometers. Of course, these are average particle size diameters,
and a tight particle size distribution, i.e., greater than 99% of
the particles by weight are within about 30%, preferably within
about 15%, of the average particle size is desired.
[0271] In general, the above-mentioned abrasives may be used either
alone or in combination with one another, although any combination
that might undesirably complicate the CMP process is preferably
avoided. U.S. Pat. No. 5,264,010, the disclosure of which is
incorporated by reference, describes for example abrasive
combinations of ceria, fumed silica, and precipitated silica. In
this invention, such combinations can be used, and the activator
may be associated with one or more of the abrasive types in the
slurry. Certain forms of iron oxide, iron hydroxide, and iron
nitride abrasives are preferentially avoided, as are others that
may contaminate the substrate or cause catalytic degradation of the
oxidizers and/or compounds that produce free radicals (without
production of the desired radicals). Copper can have the same
effect as iron.
[0272] Polymeric Particles
[0273] The particle can also be partially or fully made of a
polymer, resin, ionomer, or combination thereof. The particles can
be solid polymeric type particles. The polymeric particle may be
deformable or relatively stiff, and each has a desired
characteristic known to those of skill in the art. As mentioned
above, plastic or resinous abrasives are suitable components of the
composition of the present invention. For example, a suitable
plastic abrasive particle may be composed of a polyacrylic acid, a
polymethylacrylic acid, a polyvinyl alcohol, or any combination
thereof. Further by way of example, a suitable resinous abrasive
particle may be composed of a polyacrylic acid, a polymethylacrylic
acid, a polymelamine, or any combination thereof, or any particle
of a ion exchange resin, such as a plastic ion exchange resin.
[0274] Polymeric or resinous abrasives are suitable components of
the composition of the present invention. For example, a suitable
plastic abrasive particle may be composed of a polyacrylic acid, a
polymethylacrylic acid, a polyvinyl alcohol, or any combination
thereof. Further by way of example, a suitable resinous abrasive
particle may be composed of a polyacrylic acid, a polymethylacrylic
acid, a polymelamine, or any combination thereof, or any particle
of a ion exchange resin, such as a plastic ion exchange resin. One
embodiment includes a coated particle comprising resin or plastic
impregnated with abrasive metal oxide particles. Resin or polymeric
particles of between 200 to 400 nanometers with smaller metal oxide
particles, between about 2 to about 50 nanometers, can be embedded
thereon or on the surface. Said embedded particles may carry the
activator. Alternatively, a resin or polymeric particle can
substantially encapsulate a metal oxide particle.
[0275] Published U.S. Application US 2002/1093451, incorporated
herein by reference, describes polymer particles having functional
groups thereon which react with metal. While in some embodiments an
activator can interact with a substrate, by far the dominant effect
of activators is not to interact with the substrate but rather to
interact with the compound that produces free radicals to form free
radicals. In some embodiments, the particles can have a crosslinked
structure. The polymer can be a compound having two or more
copolymerizable double bonds in the molecule, for example, a
divinyl compound of which divinylbenzene is representative, or a
polyvalent acrylate compound of which ethyleneglycol diacrylate,
ethyleneglycol dimethacrylate, trimethylolpropane triacrylate and
trimethylolpropane trimethacrylate are representative. These
crosslinkable monomers may be used alone or in combinations of two
or more.
[0276] Selected resin or plastic particles may not be considered
abrasives in certain systems, but these particles can nevertheless
be effective carriers of the activator. It is imperative, however,
that if the polymeric particles have transition-metal-containing
activators associated thereon, that these activator be accessible
to the fluid and that these activators be in a form that can cause
the compound that produces free radicals to be activated and to
form the desired free radicals. As polymeric particles may be worn
during use, having activators within the particle matrix that will
eventually be contacting a fluid containing the compound that
produces free radicals is also advantageous. Generally, a monolayer
of activator atoms associated with the surface of the particles
that contacts the fluid and promotes free radical formation where
the free radicals can contact the substrate will provide maximum
activity. However, as polymeric particles may wear, having between
0.1 and 20% activator within a polymer particle matrix can be
advantageous.
[0277] In one embodiment of the invention, a metal oxide particle
has polymer, resin, ionomer, or combination thereof within at least
some of the pore space. For example, the polymer, resin, ionomer,
or combination thereof may substantially, i.e., greater than about
70%, fill up the pore volume of for example a metal oxide, say
alumina, silica, combinations thereof, and the like. In another
embodiment, the polymer, resin, ionomer, or combination thereof may
only fill the outer 10 to 40% of the pore volume of for example a
metal oxide, say alumina, silica, combinations thereof, and the
like. Alternatively, the polymer, resin, ionomer, or combination
thereof may substantially, i.e., greater than about 70%, cover the
surface of a particle. The polymeric material may be such that the
matrix metal oxide materials are substantially totally encapsulated
or surrounded, i.e., a coated substrate, or a portion of the
substrate may be coated by the polymeric material. In another
embodiment of the invention, a particle made from a polymer, resin,
ionomer, or combination thereof may have incorporated at least on
the surface thereof metal oxide particles that are less than about
25%, preferably less than about 10%, of the polymeric particle
size. In any of these cases, the activator may be on the exposed
(to the fluid) surface of the polymer, on the exposed (to the
fluid) surface of one or more associated metal oxide particles, or
a combination thereof.
[0278] A method of coating for example iron onto a polymer, resin,
ionomer, combination thereof, or the like are discussed in for
example U.S. Pat. No. 5,352,517, the disclosure of which is
incorporated by reference. The polymer, resin, ionomer, combination
thereof, or the like may be a thermoplastic material or a thermoset
material. Among the thermoplastics useful in the present invention
are the polyolefins; poly vinyl polymers; polystyrene, epoxies,
phenol-formaldehyde polymers, polyesters, polyvinyl esters,
polyurethanes, melamine-formaldehyde polymers, urea-formaldehyde
polymers, polyacrylates, ionomeric polymers, and mixtures thereof.
Similarly, U.S. Pat. No. 4,642,161, the disclosure of which is
incorporated herein by reference, teaches a method of bonding for
example copper and a resin together forming a copper layer on the
surface of copper bonded to a resin. These same methods can be
used, with minor modifications, to incorporate activator onto
polishing pads.
[0279] Particles with Associated Activator
[0280] A wide variety of abrasives and particles have been
discussed. As used herein, unless specifically noted the term
abrasive is meant to include all particles, and the term particles
is meant to include all abrasives. This list is not exhaustive,
however, as we have not found abrasive substrates yet where
activator associated on the surface thereof can not be active with
at least some oxidative compounds that form free radicals, i.e.,
superoxygen radicals, hydroxyl radicals, and the like.
[0281] The activators, particularly the metal-containing
activators, are advantageously associated with a surface of a
particle. The particle onto which the activator(s) is/are
associated can be a metal oxide particle, a metal nitride particle,
a ceramic particle, a polymeric particle, any of the various
combinations discussed herein, and any other particle where the
particle is in contact with the fluid and the fluid contains a free
oxygen generator. Of course, oxygen-containing free radicals are
the most advantageous, as these free radicals have a very large
although non-specific oxidizing potential.
[0282] Generally, in most preferred embodiments the activator is
associated with the surface area of the particle. According to one
embodiment of the present invention, an abrasive is at least
partially coated by an activator. The activator enhances, or
increases, the rate of the chemical reaction between the oxidizing
agent of the composition and the targeted material, particularly
metal material, on the substrate surface during a CMP process.
Without being bound by theory, the activator is believed to assist
in the formation of activated oxidizing species, such as activated
peroxy radicals, at reaction sites on the abrasive.
[0283] Preferably, the activator is substantially insoluble in the
composition such that it remains for the most part associated with
the surface of the abrasive particle during the CMP process. Of
course, with the advent of nanotechnology and with polymeric
particles, it is recognized that the distinction between "soluble"
activator and activator associated with the surface of a particle
will become blurred. Particles with a size below one nanometer are
envisioned in this process, but some may call a sub-nanometer
particle "solubilized". One distinction is that applicator
associated with a particle can usually be physically separated from
the fluid. Another distinction is that the activator is associated
with a group of molecules that at least partially hinder the
activator or a portion thereof from the surface such that metal
contamination is not an issue. A third distinction is that the
activator is not simply part of a single molecule. Of course, not
all, but rather any one of these conditions is sufficient to meet
the criteria for being associated with a particle.
[0284] Advantages of having the activator be associated with the
particles include 1) that metal ion contamination of the substrate
is prevented; 2) that the activator ions do not simply act as
promoters shuffling electrons from the other oxidizer to the
substrate; 3) that the free radicals are formed in-situ and very
close to the point of use; 4) the activator-containing particles
can be readily recovered and re-used; 5) that the fluids do not
have troublesome metal ion contaminants; 6) that the pot life of a
slurry is long, and can be as long as several days without
significant (10%) loss of oxidizers; 7) that the activators can
change the zeta potential of the particles, altering the colloidal
properties; 8) that the amount of activator contacting the slurry
can be highly controlled. Any of the activator/"particle
combinations that meets a plurality of these conditions, and is
still active, can be called "associated with the surface of a
particle" rather than "dissolved".
[0285] The activator in these embodiments is associated with a
surface of a particle. The term "associated" means the activator is
absorbed, adsorbed, coated to, or in any way bound to the surface
of the surface if the particle. In a less preferred embodiment, the
activator may be partially or fully doped into the particle or
abrasive or into a portion of the particle or abrasive. The doped
portions may be treated to expose the activator and make it active.
Generally, however, metal oxides that are a part of a crystalline
or semi-crystalline matrix structure, as opposed to being disposed
on the surface of such a (semi)crystalline structure, are not as
able to readily change oxidation states and are not as able to be
contacted as readily by the compounds that produce free radicals,
both of which are required to have the activators activate the
compound that produces free radicals.
[0286] In most preferred embodiments, the activator is associates
with the outer surface area and with the area just inside pores
opening directly to the outside of the particle, which surface area
is called here the outer or outside surface area. In addition to
being easier to place selected activators on this surface, the free
radicals generated by the interaction of the activator and the
compounds that produce free radicals can easily move from the outer
surface area of the abrasive and immediately contact the substrate.
In most embodiments of this invention, therefore, the activator is
associated with some or all of this outside surface area.
[0287] There are many meanings for the term "surface area". There
is the "outside surface area", which is about equal to pi times the
particle size D. This is the only surface area of many ceramic
particles, as the porosity of those particles can be
insignificant.
[0288] However, the very high surface area alumina and silica
particles may also have surface area that is less accessible to
fluids, compounds producing free radicals, and the like.
Additionally, free radicals produced in some inside pores may cease
to exist before the free radicals escape the particle pore
structure. Generally, when describing a particle, the surface area
is that measured by any of a number of techniques, such as BET or
gas absorption. This provides a "total surface area" of for example
200 square meters per gram with a particle size of for example 0.1
microns. The activator can cover substantially all or only a very
small fraction of this total surface area.
[0289] While activator may beneficially be associated with this
total surface area, the activator near the center of the particle
will be less effective on a weight basis than activator associated
with the outside surface. We therefore define a surface area which
is about pi times D plus about 10% to about 30%, say about 15%, of
the remaining surface area as "connected surface area". For larger
particles, i.e., greater than 0.8 microns, this percentage is
smaller, and for very small particles, i.e., particles smaller than
0.2 microns, this percentage gets larger. This is an arbitrary
value and is intended to be the surface area of the pore structure
"near" the outside surface, where the term near is arbitrarily
chosen. For large particles with large surface areas, i.e., 1
micron particles with a surface area of about 100 square meters per
gram, the outside surface area can be very small compared to the
"connected surface area. One advantage of this
interior-surface-located activator is that if the activator
particles are re-used, the abrasive will still have activity even
if the outer surface of the abrasive particle is to some extent
worn away.
[0290] The amount of activator on a particle can be very small,
covering for example between less than 0.01% to greater than 90% of
any of the total surface area, the connected surface area, or the
outer surface area. Generally, less than 100% coverage can be
beneficial, because the reaction that produces free radicals, which
is usually exothermic, can go so fast that the required control
necessary for flat planarization can be lost. The activator in one
embodiment is associated with and covers between about 0.0001% to
about 100% of the available surface area of the abrasive or
particle or polishing pad.
[0291] Yet the amount of activator, on a weight basis, on a
particle can be very small. A layer that is between one and a few
hundred atoms thick can be effective, and a thinner layer has a
lower tendency to lose activator to the solution. The amount of
activator on a particle can range from about 0.0001% by weight of
the particle to about 60% by weight of the particle. In larger
particles, the amount of activator is beneficially toward the lower
end of the range, while in very small particles the activator may
form a significant portion of the activator. Generally, for silica
with a size of about 0.4 microns, the amount of activator on a
particle will range from about 0.01% to about 2%, for example
between about 0.1% and about 1%.
[0292] For those instances where crystals of activator are used,
the amount of activator in the crystal can of course approach
100%.
[0293] The tenacity of the activator to the particle is important,
because metallic activator that leaves the particle and becomes
dissolved can plate onto the substrate, or can become associated
with the substrate so that it merely acts as a promoter shuttling
electrons from the oxidizer to the substrate. Therefore, dissolved
metal-containing activator is usually a contaminant. Further, it
often degrades oxidizers. A slurry should have most, i.e., more
than 50%, preferably more than 90%, more preferably more than 99%,
of the activator associated with a solid (pad, material, or
particle) compared to the total "activator species including that
associated with a solid and that dissolved. For example, a prepared
slurry had about 200 ppm total iron when calculated based on the
weight of the slurry, where less than 1 ppm was in solution and the
rest was absorbed on the abrasive.
[0294] Various methods can be used to reduce the amount of
activator dissolved in a slurry. Pretreating the metal oxides,
primarily silica, with agents to obtain OH groups can be
beneficial. Post treating the activator-containing particles with
various dispersants, passivating agents, and the like can reduce
activator leaching.
[0295] The activator layer can be made very thin, approaching a
monolayer, so that each activator atom is bound by a plurality of
OH groups from the silica. Additionally or alternatively, particles
containing activator associated therewith can be soaked or washed
in a variety of acids, oxidizers, optionally bases, and chelators
to remove from the particle that portion of the activator that is
less firmly bound, insofar as a sufficient amount of activator
remains for the desired activity.
[0296] The activator activity is a function of the particle
characteristics (which increases if the activator is available to
the compounds that form free radicals and is able to readily change
oxidation states), the amount of activator on a particle, and the
activity of the activator(s) selected relative to the compound that
produces free radicals, the concentration of the compound that
produces free radicals, and the amount of activator-containing
particles in a slurry.
[0297] It should be noted that merely adding a transition metal
salt and a surface, for example a abrasive, together in a slurry
will not give activator that is associated with surface. Ion
repulsion and other forces keep the slurry from absorbing or
adsorbing onto the surface well.
[0298] Any or all of the particles in a slurry can have activator
associated therewith. The same abrasive can be used, wherein a
portion of the abrasive has activator associated thereon and a
portion of the abrasive is activator-free. Alternatively, a mixture
of one or more abrasives can be used, where one type of abrasive
has activator and another type is activator-free. In some
embodiments the activator can be on smaller particles than the
abrasive. For example, silica is a preferred abrasive for being a
carrier of activator associated with the surface thereof, because
silica holds the activator atoms tenaciously while at the same time
allowing free radical formation to proceed, especially by a
Fenton-type process where the activator changes oxidation states.
However, some metals may exhibit better polishing with a different
abrasive, for example alumina or ceria. A slurry may be made where
activator-containing silica is admixed in a slurry with
non-activator alumina or ceria. There is an unlimited number of
combinations that one skilled in the art, with the benefit of this
disclosure, will be able to devise.
[0299] In one embodiment abrasive metal oxide particles having at
least about 25% of the outside area with activator associated
therewith, is used in an amount of between 0.1 and 1% by weight of
the activator-containing abrasive of the slurry. Abrasive that does
not contain activator makes up the remainder, say up to about 5% as
an example by weight of this pure abrasive by weight in the slurry.
One problem with this is that the different zeta potentials of pure
abrasive versus abrasive that has activator associated therewith
can result in for example uneven settling of the particles in a
stagnant slurry, and therefore gradients in compositions after even
relatively short term interruptions. The particles can of course be
treated as is known in the art to remain in solution.
[0300] However, if all 5.1% to 6% of the abrasive particles in the
above-mentioned case have activator thereon, but the amount of
activator is much smaller than the 25% coating on the particles in
the above case, say maybe only covering 5% of the surface of every
particle, then all particles will behave similarly in solution and
there will be less a tendency to have problems associated with
short term interruptions in polishing. At the same time, the
activator activity level in the slurry can be preserved.
[0301] All or a portion of particles may be polymeric.
[0302] Additives Associated with Particles
[0303] A polymer, for example ionomer, a polycarboxylic acid, a
fatty amine, and the like can be treated onto a metal oxide
abrasive, for example onto the aluminum and/or silica.
[0304] In some embodiments abrasives containing activator
associated on the surface thereof can be encapsulated by a
polymeric material, or can be substantially encapsulated by
compounds bound to the surface. Such materials should be removable
or should be made ineffective on polishing, so that activator can
contact the fluid. The amount of plastic/polymer/ionomer can be as
little as to fill about between about 5 to about 20% of the
porosity of the particles.
[0305] Abrasive with activators at greater than 1% coating may be
advantageous.
[0306] Alternatively, other metals and compounds added to the
abrasive particles may be useful. A coating that is only partially
activator, where the remainder is an inert or substantially inert
metal (i.e., a promoter that is not an activator, for example a tin
compound) may be useful to coating but "space" the activator active
sites.
[0307] Silanes bound to the surface of abrasives may be useful,
altering the surface of the abrasive, i.e., silica.
[0308] Slurry
[0309] In one embodiment of this invention the CMP system comprises
a slurry having a compound that forms free radicals and an
activator associated with particles suspended within the slurry,
i.e., an abrasive with a available activator attached on a surface
of the abrasive where the attached activator is contactable by the
fluid.
[0310] Generally, throughout this description, any mention of a
component of the slurry, also called composition, refers to at
least one such component, for example, one such component or
multiple such components. Further, any amount of a component of the
composition is given as a weight percent (wt. %) relative to the
composition. Additionally, any amount of a component is given as an
approximate amount, for example, more or less than, or equal to,
the precise numerical amount stated. This convention concerning
approximate amounts applies to any numerical measure stated herein
in connection with the composition, such as a numerical pH level
stated for the composition or a numerical process parameter stated
for a CMP process employing the composition. The foregoing
conventions apply throughout this specification unless specified or
clearly intended or implied otherwise.
[0311] The composition generally comprises at least one oxidizing
agent and at least one abrasive that is at least partially coated
by a activator, as further described herein. Typically, the
abrasive component comprises a portion of abrasive that coated with
activator (sometimes referred to herein as "coated activator") and
a portion of abrasive that is not coated with activator (sometimes
referred to herein as "normal abrasive"), although only the former
need be present. For example, the abrasive may comprise a ratio of
coated abrasive to normal abrasive of about 1 to about 9. Each of
the components of the composition and typical, preferred, and more
preferred amounts thereof, in approximate weight percent (wt. %)
relative to the composition, are provided below in Table 1.
TABLE-US-00003 TABLE 1 Chemical Mechanical Polishing Composition
More Preferred Component Typical Amount Preferred Amount Amount
Oxidizing 0.01 to 30 wt. % 0.01 to 10 wt. % 0.01 to 6 wt. % Agent
Normal 0.01 to 30 wt. % 0.01 to 20 wt. % 0.01 to 10 wt. % Abrasive
Coated 0.01 to 50 wt. % 0.01 to 20 wt. % 0.01 to 10 wt. %
Abrasive
[0312] In addition to the oxidizing agent component, the
composition also comprises an abrasive that is at least partially
coated by a activator. The abrasive is effective in the mechanical
removal of targeted material on the substrate surface. Suitable
amounts of activator coated abrasive, such as the preferred range
of from about 0.01 to about 20 weight percent relative to the
composition, are listed in Table 1 above. Suitable amounts of
normal abrasive, if any, are also listed in Table 1.
[0313] It is generally preferred to use the activators at a pH
between about 1.5 and about 9, more preferably between pH of 2 and
8. Fenton's reaction type formation of free radicals has
historically been limited to between pH of about 3 and 6, and this
is a preferred pH range for most activator/compound that produces
free radicals combinations of this invention. However, the
association of the activator to a surface, particularly to a metal
oxide (hydroxide) surface, has allowed the pH range for Fenton's
reaction to be surprisingly extended into the basic pH range (7 and
above). Too high a pH, depending on the materials used, will
degrade the effectiveness of most activator/compound that produces
free radical combinations. For this reason a mild buffer can
advantageously be incorporated into the slurry. Any buffer will
work, including organic acids and salts thereof, inorganic acids
and salts, or mixtures or combinations thereof. Several organic
acids are free radical quenchers, and this should be accounted for
in determining activator activity.
[0314] The user must take care of the conditions under which the
polishing takes place. Free radical formation is often temperature
dependent, and optimum results are often found at between about 40
and about 60 degrees Centigrade.
[0315] Not all of the abrasive particles or other particles need be
coated with activator.
[0316] Less activator is better. The amount of activator in a
slurry, wherein the activator is expressed as weight of the metal
ion in the slurry, can be between about 5 to 5000 ppm total
activator, preferably about 10 to about 1000 ppm total activator,
more preferably about 20 to about 200 ppm total activator. Low
amounts of activator, between about 5 ppm and about 40 ppm, for
example between about 10 and about 30 ppm, have been found to be
effective.
[0317] For iron activator with hydrogen peroxide, the amount of
activator iron is preferably less than 0.008% by weight in a
slurry. For iron activator with ammonium persulfate, the amount of
activator iron is preferably less than 0.08% in a slurry.
[0318] Polishing Pad
[0319] Activators can be associated with for example a polishing
pad. Polishing pads are described for example in U.S. Pat. Nos.
6,435,947 and 6,383,065, the disclosures of which are incorporated
herein by reference. The polishing pad are generally of a polymeric
material. The polishing pads of the current invention can be any
polishing pad, circular or belt or vibrational, wherein the pad
comprises an activator that is substantially bound and insoluble in
the fluid. In one embodiment the activator is associated with the
polymeric surface. Alternatively or additionally, the activator may
be associated with particles, for example abrasives, on the surface
of the polymeric material. Of course, like polymeric particles, the
pads may wear. Therefore, it is advantageous to incorporate the
activator in the matrix of the pad such that a substantially
constant activator "activity", that is, generation of free
radicals, can be maintained as the pad wears.
[0320] Polishing pads are generally a porous polyurethane. The
incorporation of abrasive particles into polishing pads is
disclosed in several U.S. Pat. Nos. 5,849,051 and 5,849,052, the
disclosures of which are incorporated herein by reference. In
addition, solid metal materials have been incorporated into
polishing pads as described in U.S. Pat. No. 5,948,697, and the
materials increase semiconductor polishing upon application of an
electrical bias to the semiconductor. Polishing pads including a
polishing pad substrate and a metal-containing soluble catalyst
having multiple oxidation states (an oxidizer) for use in
conjunction with an oxidizing agent to chemically mechanically
polish metal features associated with integrated circuits is
described in U.S. Pat. No. 6,383,065, the disclosure of which is
incorporated herein by reference.
[0321] U.S. Pat. No. 6,435,947, the disclosure of which is
incorporated herein by reference, describes a pad having a solid
heterogenous catalyst which may be an activator, the polishing pad
being useful to remove metal layers from a substrate. The patent
teaches that the activator-like material can be an oxide of Ti, Ta,
W, V, Nb, Zr, and mixtures thereof. The only catalyst taught,
however, was TiO.sub.2 and/or TiO.sub.3. The term "heterogeneous
solid catalyst" is defined as solid catalyst which is distinct from
the liquid phase and not significantly soluble in the chemical
mechanical composition liquid phase. The patent taught that this
catalyst needed actinic radiation, and that the polishing pad is
exposed to light in the UV range.
[0322] The activator containing polishing pads of this invention
include a polishing pad substrate and at least one activator,
wherein the activator is associated with the surface of the pad.
The activator is substantially insoluble, and is coated on,
absorbed, and/or absorbed onto the surface of the pad. The
preferred pad-based activators are absorbed, adsorbed, coated, or
otherwise bound transition metals that can act as activators
without the addition of actinic energy (such as is required by for
example titanium oxides)
[0323] Activator may be incorporated into a polishing pad substrate
by any method known in the art for incorporating a material into or
onto a polymeric substrate. Examples of methods for incorporating
the activator into a polishing pad substrate include encapsulation,
impregnation, creating a polymer/activator complex, incorporating
the activator as a small molecule into the polishing pad substrate
polymer matrix, or any combinations of these methods.
[0324] The polishing pad substrate may be any type of polishing pad
substrate that are useful for CMP, for example the hard pad IC 1000
on SUBA IV (TM, Rodel). Typical polishing pad substrates available
for polishing applications, such as CMP, are manufactured using
both soft and/or rigid materials and may be divided into at least
four groups: (1) polymer-impregnated fabrics; (2) microporous
films; (3) cellular polymer foams and (4) porous
sintered-substrates. For example, a pad substrate containing a
polyurethane resin impregnated into a polyester non-woven fabric is
illustrative of the first group. Polishing pad substrates of the
second group consist of microporous urethane films coated onto a
base material which is often an impregnated fabric of the first
group. These porous films are composed of a series of vertically
oriented closed end cylindrical pores. Polishing pad substrates of
the third group are closed cell polymer foams having a bulk
porosity which is randomly and uniformly distributed in all three
dimensions. Polishing pad substrates of the fourth group are
opened-celled, porous substrates having sintered particles of
synthetic resin. Representative examples of polishing pad
substrates useful in the present invention, are described in U.S.
Pat. Nos. 4,728,552, 4,841,680, 4,927,432, 4,954,141, 5,020,283,
5,197,999, 5,212,910, 5,297,364, 5,394,655, 5,489,233 and
6,062,968, each of the disclosures of which are incorporated herein
by reference.
[0325] The preferred embodiment is the incorporation of molecules
and/or layers of activator chemically or physically bound to the
pad material. The layer of activator, rather than dissolving,
contacts the fluid containing the compound that produces free
radicals to produce free radicals.
[0326] In another embodiment the activator is associated with
abrasive particles contained within the pad. For example, very
small, for example 1 to 10 nanometer sized particles, can be
embedded into the structure of a polishing pad. With the advent of
nanotechnology, subnanometer particles of fairly similar size can
even be manufactured. These abrasive can function as abrasives in
the slurry function, and can have activator associated thereon.
[0327] The polishing pad substrates used in the present invention
may be any one of the substrates described above. In addition, the
polishing pad substrate may be made from a material other than a
polymer such as cellulose fabric or any other materials that are
known in the art to be useful for chemical mechanical polishing.
What is important is that the polishing substrate chosen must be
capable of being combined with at least one activator to form a
activator containing polishing pad.
[0328] Additional features, aspects and advantages of the present
invention will become apparent from the description of preferred
embodiments and the various methods and examples set forth
below.
[0329] Method
[0330] The compositions and systems of the present invention are
usefully employed in the chemical-mechanical polishing (CMP) of a
substrate.
[0331] In a typical chemical mechanical polishing process, the
substrate is placed in direct contact with a rotating polishing
pad. A carrier applies pressure against the backside of the
substrate. During the polishing process, the pad and table are
rotated while a downward force is maintained against the substrate
back. An abrasive and chemically reactive solution, commonly
referred to as a "slurry" is deposited onto the pad during
polishing. Polishing without an abrasive is also possible using
selected compositions of this invention. The slurry initiates the
polishing process by chemically reacting with the film being
polished. The polishing process is facilitated by the rotational
movement of the pad relative to the substrate as slurry is provided
to the wafer/pad interface. Polishing is continued in this manner
until the desired film on the insulator is removed.
[0332] In its basic components, a method for polishing a substrate
including at least one metal layer comprising the steps of:
[0333] (a) admixing the CMP fluid of this invention, the fluid
containing a compound that produces free radicals;
[0334] (b) contacting the fluid with an activator to form free
radicals in the fluid;
[0335] (c) contacting the free radical-containing fluid to the
substrate; and
[0336] (d) mechanically abrading the substrate contacting the free
radical-containing fluid to the substrate, thereby removing at
least a portion of the metal layer from the substrate.
[0337] The slurry composition is an important factor in the CMP
step. Depending on the choice of the oxidizing agent, the abrasive,
and other useful additives, the polishing slurry can be tailored to
provide effective polishing to metal layers at desired polishing
rates while minimizing surface imperfections, defects, corrosion,
and erosion. Furthermore, the polishing slurry may be used to
provide controlled polishing selectivities to other thin-film
materials used in current integrated circuit technology such as
titanium, titanium nitride and the like.
[0338] The compositions of this invention provides very desirable
material rates, for example, up to 15,000 Angstroms (A) per minute
using concentrations normally found in CMP slurries, in a CMP
process. Generally, a rate of between about 4000 and about 8000 A/m
is preferred for better control. It may be desirable to adjust the
composition or the CMP process to bring the rate down to a level
suitable for certain applications, such as the CMP of very thin
films, for example, a copper film of about 3000 A in thickness. For
copper, a preferred slurry has between 1% and 7%, say between 3%
and 5%, of hydroxylamine at a pH of between 6 and 7, say about pH
6.7.
[0339] The composition is effective when used in conventional CMP
processes, as well as CMP processes having relatively low carrier
pressures. Substrates polished using the composition show good
uniformity values, as reflected by relatively low within wafer
nonuniformity percentages. For example, in one example provided
herein, the within wafer nonuniformity of the polished substrate
was about 4.57 percent.
[0340] Care should be taken as to the amount of activator-coated
abrasive used, as using too much activator may compromise control
of the CMP process. The amount of activator-coated abrasive should
generally not exceed 50 weight percent of the composition. Where
activator concentration is a concern, an increased amount of normal
abrasive, absent a activator coating, may be used to dilute the
activator in the composition and facilitate control of the CMP
process.
[0341] In one embodiment of this invention particles having
associated activator are recovered from used CMP slurries after
polishing and are re-used. The activator is not used up in the
process. A simple expedient of separating particles having
activator thereon, which may or may not also contain a small amount
of the used fluid, can be recovered from the slurry by for example
filtration, centrifugation, or the like. Various additives such as
salts can be added to destabilize the slurry to enhance separation,
but such material should subsequently be washed, for example with a
dilute mineral acid, prior to reuse.
[0342] Such a system would have an additional amount of
activator-coated particles added thereto to replace that lost to
for example grinding. A small fraction of the recycled
activator-coated particles may be disposed of to keep the amount of
activator-coated particles in the CMP slurry constant.
[0343] If activator coated particles have different zeta potentials
in the slurry than non-activator coated abrasive, separation may be
done by partially destabilizing the slurry and recovering the
particles having activator associated thereon.
[0344] In another embodiment, if actinic energy is needed for an
activator to perform, or if actinic energy is itself the activator,
it is beneficial to expose the free radical-containing fluid to the
activator immediately prior to placing the fluid between the pad
and the substrate. If an activator is used, it may be in the form
of a mesh where actinic radiation can be easily applied in the
desired amounts. If the activator is actinic radiation, then this
radiation is also beneficially applied to the incoming fluid
immediately before the fluid enters the system and passes between
the substrate and the pad. Chambers to photoactively promote a
reaction, and actinic radiation sources such as mercury lamps, are
well known.
[0345] In another embodiment, the temperature of the slurry is
controlled to an average temperature of between about 30 degrees
and 60 degrees Centigrade, but where the temperature variation is
less than about 3 degrees centigrade. Free radical formation is
very temperature dependent, and the etch rate can be varied by for
example changing the temperature.
[0346] In some embodiments the temperature can be changed during a
CMP process, following a profile to give increased free radicals in
the initial polishing and less free radicals in the later stage of
polishing. Similarly, the amount of formation of free radicals can
be changed by altering the pH of the solution. Other combinations
will be devised by one of ordinary skill in the art with the
benefit of this disclosure.
[0347] Additionally, magnetism and electric field potentials, as
described for example in U.S. Pat. No. 6,030,425 may be useful, but
are not preferred as they unduly complicate the CMP equipment.
[0348] As mentioned above, the abrasive material of the composition
is at least partially coated with the activator. As used herein,
"coating" and its various linguistic or grammatical forms or
counterparts generally refer to forming a physical connection
between the abrasive and the activator, such as by forming at least
a partial layer of activator material on at least a portion of the
abrasive, absorbing or adsorbing the activator material on at least
a portion of the abrasive, forming adhesion between the activator
material and at least a portion of the abrasive, and the like, by
any suitable means or method.
[0349] By way of example, a method of producing a silica sol coated
with iron acetate is provided in U.S. Pat. No. 4,478,742 of Payne,
the entire contents of which are incorporated herein by this
reference. Similarly, U.S. Pat. Nos. 3,007,878, 3,139,406 and
3,252,917, which describe ways of putting metals on a core of
silica, are incorporated herein by this reference. The activator
may coat from about 0.001% to about 100%, for example about 5 to
about 100 percent of the surface of the abrasive particle, such as
from about 5 to about 80 percent of the particle surface, or
preferably, from about 25 to about 50 percent of the particle
surface.
[0350] In one embodiment, activator is put on to substantially all
the outer surface or all the connected surface, and then activator
is removed by for example washing in heated acids, oxidizers,
and/or chelators to obtain a desired coating, for example between
about 1% and about 25% of surface area coated. The remaining
activator will be very tenaciously bound to the surface, reducing
activator loss due to leaching to the solution.
[0351] The CMP composition or slurry of the present invention may
be prepared using conventional techniques. Typically, the water,
additives, and abrasive components are combined, activator-coated
abrasive is then added, oxidizer is then added, and the pH is
adjusted.
[0352] Alternatively, according to one aspect of the present
invention, the activator-coated abrasive may be added to an
existing CMP composition, such as a commercially available CMP
composition that contains an oxidizing agent. For example, the
activator-coated abrasive may be added to a previously formulated
peroxide composition to provide a CMP composition of this
invention.
[0353] In some CMP processes, particularly some of the advanced
polishing processes, the composition is prepared by adjusting the
amount of each composition component in real time, just prior to a
re-mixing of the composition at the point of use. For most CMP
processes, the prepared composition is re-mixed at the point of
use, whereupon it is poured onto the polishing pad. Typically, the
composition is poured onto the pad as it is moved or rotated. As
the CMP process proceeds, additional slurry may be added or excess
slurry may be removed, as desired or necessary.
EXAMPLES
[0354] Examples of the composition according to the present
invention are provided below The abrasive used was Mirasol 3070
.TM., hereafter Mirasol, a commercially available aqueous solution
of abrasive silica particles. Mirasol, commercially available from
Precision Colloids, LLC of Cartersville, Ga., contains
approximately 30 weight percent silica (SiO.sub.2) particles, which
generally have an effective diameter of approximately 70
nanometers. Mirasol 3070 coated with activator contains the
above-described Mirasol with for example iron acetate activator
coated/absorbed onto at least a portion of the surface of the
silica particles, i.e., on about 70 percent of the surface area of
each silica particle. Mirasol having as an activator, i.e.,
cationic iron is hereafter Mirasol/Fe-Ac, or copper which is
hereafter Mirasol/Cu-Ac, provided the activator. Generally, the
compounds that form free radicals include hydrogen peroxide
(H.sub.2O.sub.2), persulfate, and/or peracetic acid. Unless
otherwise specified, water formed the balance of the slurries.
[0355] A first example concerns two CMP compositions, Example A and
Example B, both at pH 2, which are particularly suited to CMP of a
wafer, such as a silicon wafer, having a tungsten layer or feature
on its surface. The components of the two compositions and the
approximate amounts thereof, as well as the approximate pH of the
compositions, are set forth in Table 2.
TABLE-US-00004 TABLE 2 CMP Example A and Example B H.sub.2O.sub.2
Peracetic Acid Mirasol Mirasol w/Fe--Ac Example A 3 wt. % 0 wt. % 5
wt. % 0.5 wt. % Example B 0 wt. % 5 wt. % 5 wt. % 0.5 wt. %
[0356] In Example A, hydrogen peroxide served as an oxidizing
agent, Mirasol 3070 and Mirasol 3070 with a cationic iron activator
absorbed onto at least a portion of the surface of the silica
particles served as an abrasive and abrasive coated with a
activator, respectively, and deionized water made up the remainder
of the composition. Example B differed from Composition A in that
peracetic acid (CH.sub.3COOOH), rather than hydrogen peroxide,
served as an oxidizing agent. For both Example A and Example B, the
Mirasol 3070 component was believed to be predominantly responsible
for determining the pH of the composition.
[0357] Each of the Example A and B were used in a conventional CMP
process performed on a silicon substrate at least partially layered
with a tungsten film of about 8000 Angstroms (A) in thickness. The
process parameters for both included a carrier pressure of about 6
pounds per square inch (psi), a carrier speed of about 90
revolutions per minute (rpm), a platen speed of about 90 rpm, and a
flow rate for the CMP composition used of about 175 milliliters per
minute (ml/min). The processes differed only in terms of which CMP
composition was used. The results of each CMP process in terms of
the approximate material (tungsten) removal rate in Angstroms per
minute (A/mm) and the approximate within-wafer nonuniformity
percentage (% WIWNU) are set forth in Table 3.
TABLE-US-00005 TABLE 3 CMP Results on Tungsten Using Example A or
Example B Removal Rate (A/mm) Nonuniformity (% WIWNU) Example A
5040 10.9 Example B 5077 7.42
[0358] As mentioned previously, in CMP processes, and particularly
modern or advanced CMP processes, it is desirable to obtain
acceptable or optimal, such as increased, material removal rates
while using acceptable or optimal, such as not unduly high, carrier
pressures. In the CMP of tungsten-layered wafers, a good carrier
pressure is about 9 psi or less, such as about 6 psi, and a good
outcome at a pressure of about 6 psi is a removal rate of greater
than about 5000 A/mm. Further, obtaining polished wafers with
uniformity values of from about 3 to about 12% WLWNIJ percent is
considered a good result. While the foregoing examples of process
parameters, outcomes and results are often desirable, other
suitable outcomes and results are contemplated herein.
[0359] In the CMP processes performed with Example A and Example B,
desirable tungsten removal rates of about 5040 and 5077 A/mm,
respectively, were obtained. Additionally, the surfaces of the
polished wafers were substantially uniform, having 10.9 and 7.42%
WIWNU, respectively. Example B is generally preferred over Example
A, given its higher removal rate and better uniformity value (lower
% WIWNU). It should be noted that while there is a general
preference for compositions that provide high removal rates, other
factors, such as good uniformity values (for example, low % WIWNU),
efficient use of oxidizer, and good storage and handling
characteristics, are also important considerations in the
evaluation of a composition of the present invention.
[0360] A second example of the composition of the present invention
concerns two CMP compositions, Example C and Example D, which were
used in the CMP of a silicon wafer that had a copper layer or
feature on its surface. In this example, the copper layer had a
thickness of about 15,000 A. One oxidizer was hydroxylamine
(HDA.RTM., EKC Technology, Inc.). The components of the two
compositions and the approximate amounts thereof, as well as the
approximate pH of the compositions, are set forth in Table 4.
TABLE-US-00006 TABLE 4 CMP Example C and Example D Peracetic HDA
.RTM. Acid Mirasol Mirasol w/Fe--Ac pH Example C 0 wt. % 1.5 wt. %
5 wt. % 0.5 wt. % 2 Example D 4 wt. % 0 wt. % 5 wt. % 0.5 wt. %
6.7
[0361] The two compositions also differed in terms of pH,
Composition C having a pH of about 2 and Composition D having a pH
of about 6.7.
[0362] Each of the Examples C and D were used in a conventional CMP
process performed on a silicon wafer at least partially layered
with copper. When Example C was used, the process parameters
included a carrier pressure of about 4 psi, a carrier speed of
about 40 rpm, a platen speed of about 40 rpm, and a flow rate for
the Example C of about 100 ml/min. When Example D was used, the
process parameters included a carrier pressure of about 4 psi, a
carrier speed of about 75 rpm, a platen speed of about 75 rpm, and
a flow rate for the Example D of about 175 ml/mm. The parameters of
each CMP process are set forth in Table 5 and the results thereof
in terms of the approximate material (copper) removal rate and the
approximate within-wafer nonuniformity percentage are set forth in
Table 6.
TABLE-US-00007 TABLE 5 CMP Process Using Example C or Example D
Carrier Pressure Carrier Speed Platen Speed Flow Rate (psi) (rpm)
(rpm) (ml/min) Example C 4 40 40 100 Example D 4 75 75 175
TABLE-US-00008 TABLE 6 CMP Results on Copper Using Example C or
Example D Removal Rate (A/mm) Nonuniformity (% WIWNU) Example C
~15,000 Not measurable Example D 7800 8.87
[0363] As mentioned previously, in CMP processes, and particularly
modern or advanced CMI processes, it is desirable to obtain
acceptable or optimal, such as increased, material removal rates
while using acceptable or optimal, such as not unduly high, carrier
pressures. In the CMP of copper-layered wafers, a good carrier
pressure is about 9 psi or less, such as about 4 psi, and a good
outcome at a pressure of about 4 psi is a removal rate of greater
than about 7500 A/mm. While the foregoing examples of process
parameters, outcomes and results are often desirable, other
suitable outcomes and results are contemplated herein.
[0364] In the CMP process performed with Example C, an unusually
high copper removal rate was obtained, such that all of the copper
was removed. This result prevented measurement of a uniformity
value. In the CMP process performed with Example D, a desirable
copper removal rate was obtained. Additionally, the surface of the
wafer polished using Example D was substantially uniform. Example D
is thus a desirable composition of the present invention.
[0365] Example C, with only 1.5% peracetic acid, is also a useful
composition of the present invention, although it may be a bit too
aggressive in terms of removal rate for some applications such as
the polishing of very thin layers of copper on a substrate.
Accordingly, for some applications, a CMP process using Example C
may be altered by diluting the composition, diluting the
activator-coated abrasive and/or oxidizing agent components of the
composition, changing the composition flow rate, or the like. this
suggests that oxidizer concentrations well below 1% may be useful.
Too low a concentration, on the other hand, can create problems of
non-uniformity due to minor interruptions, especially if the slurry
is not stable. It is generally preferred to keep the compound that
forms free radicals, here the peracetic acid, at a concentration
above 0.5%.
[0366] A third example concerns two CMP compositions of the present
invention, Example B, from the first example above, and Example E,
each of which were used in the CMP of a silicon wafer that had a
tungsten layer on its surface, the layer being of about 8000 A in
thickness. Example B was compared to a similar comparative example,
Example 1, and Example E was compared to a similar comparative
example, Example 2. Neither of comparative examples 1 and 2
contained activator-coated abrasive. The pH of all four
compositions was about 2. The components of the four compositions
and the approximate amounts thereof are set forth in Table 7
below.
[0367] Example E and comparative example 2 contained ethylene
glycol, the purpose of which was to boost the removal rate.
TABLE-US-00009 TABLE 7 CMP Examples B and E and Comparative
Examples 1 and 2 Peracetic Mirasol/ Ethylene H.sub.2O.sub.2 Acid
Mirasol Fe--Ac Glycol Example B 0 wt. % 5 wt. % 5 wt. % 0.5 wt. % 0
wt. % Comp. Ex. 1 0 wt. % 5 wt. % 5 wt. % 0 wt. % 0 wt. % Example E
3 wt. % 0 wt. % 5 wt. % 0.5 wt. % 0.25 wt. % Comp. Ex. 2 3 wt. % 0
wt. % 5 wt. % 0 wt. % 0.25 wt. %
[0368] Each of the four compositions were used in a conventional
CMP process having the same process parameters as previously
described in the first example and set forth in Table 3 above. Each
of Comparative Examples 1 and 2 were tested twice, in a Trail A and
a Trial B, respectively. The results of each CMP process in terms
of the approximate material (tungsten) removal rate in A/mm and the
approximate % WIWNU are set forth in Table 8.
TABLE-US-00010 TABLE 8 CMP Results Using Examples B or E or
Comparative Examples 1 or 2 Nonuniformity Removal Rate (A/mm) (%
WIWNU) Example B 5077 7.42 Comp. Ex. 1, Trial A 2215 6.96 Comp. Ex.
1, Trial B 2466 6.94 Example E 4476 4.57 Comp. Ex. 2, TrialA 1556
3.42 Comp. Ex. 2, Trial B 1582 3.34
[0369] In terms of the tungsten removal rate, Example B
outperformed Comparative Example 1 by over 200 percent (up to about
229%) and Example E outperformed Comparative Example 2 by over 280
percent (up to about 288%). The CMP performances of Example B and
Example E are impressive, even when the moderate decreases in
surface uniformity are considered. These results demonstrate that
the activator-coated abrasive is an effective, if not potent,
component in the compositions of this invention.
[0370] The minor increases in the Nonuniformity with the activator
coated abrasives may in part be due to using a mixture of highly
coated abrasive (about 70% of outer surface coated with activator)
and a greater amount of abrasive without activator. It is believed
that uniform abrasive with activator, where the activator is both
present in a small percentage of the surface area and is
preferentially substantially evenly spaced, for example in spaces
clumps, about the surface will reduce non-uniformity.
[0371] Example F used a composition having 0.1% Mirasol with copper
activator, 5% peracetic acid, and 5% Mirasol. This composition
exhibited superior CMP etch rate over a similar composition without
the activator.
[0372] Example G used a composition having 0.2% Mirasol with
Mn-acetate activator, 5% peracetic acid, and 5% Mirasol. This
composition exhibited superior CMP etch rate over a similar
composition without the activator.
[0373] Example H used a composition having 0.5% Mirasol with
Mn-acetate activator, 3% hydrogen peroxide, and 5% Mirasol. This
composition exhibited superior CMP etch rate over a similar
composition without the activator for tungsten (246 angstroms per
minute), TEOS (778 angstroms per minute), and titanium (>2200
angstroms per minute). Manganese is a less effective activator than
either iron or copper, but can be useful.
[0374] Example I used a composition having 0.1% Mirasol with
Fe-acetate activator, 3% 0.1% peracetic acid, and 5% Mirasol. This
composition exhibited superior CMP etch rate over a similar
composition without the activator for copper, ranging from 2200 to
4700 angstroms per minute at different processing conditions, but
the best nonuniformity observed in these tests was 13.7%. Manganese
is a less effective activator than either iron or copper, but can
be useful.
[0375] Example J used a composition having 0.5% Mirasol with
Mn-acetate activator, 5% hydrogen peroxide, and 5% Mirasol. This
composition exhibited superior CMP etch rate, about 2380 angstroms
per minute, over a similar composition without the activator which
had etch rates of 270 to 380 angstroms per minute, for copper.
Further, those wafers polished without activator had about three
times the nonuniformity as those wafers polished with the slurry of
this invention, which exhibited nonuniformity between 8.8 and
11.9%.
[0376] Example J used mixed oxidizers in a slurry having 5%
peracetic acid, 2.5% Mirasol, and 0.5% Mirasol with Fe-Acetate at
pH 2. The etch rate through tungsten was 4300 angstroms per minute,
and the percent nonuniformity was very low, between 2.7% and
5.6%.
[0377] Slurry Stability
[0378] The next example shows slurry stability. This effective
activator-coated abrasive component functions optimally in
commercial settings when it is relatively, if not substantially,
stable. Slurry stability is a desirable characteristic in the
composition, as it facilitates control of the CMP process. Thus,
tests were conducted to determine the relative stability of the
activator-coated abrasive used in the composition of the present
invention, as compared with that of a soluble promoter of similar
chemical composition, in the presence of an oxidizing agent, in two
other compositions.
[0379] The activator which is attached to a surface, for example to
an abrasive, functions differently than a similar component which
is a soluble promoter. Further, just adding metal salts to a
solution containing abrasives does not attach activator to the
abrasive.
[0380] In these slurry stability tests, the activator-coated
abrasive was Mirasol/Fe-Ac, and an oxidizing agent in the form of
hydroxylamine ("HDA"), and had a pH of about 7. The first "free
promoter" composition was composed of normal abrasive in the form
of silica particles, soluble promoter in the form of iron nitrate,
and oxidizing agent in the form of HDA, and had a pH of about 7.
The second "free promoter" composition was composed of all of the
components of the first "free promoter" composition except for the
abrasive component.
[0381] The three test compositions were prepared as set forth
below. A activator-coated abrasive preparation was obtained by
adding an appropriate amount of the activator-coated abrasive to 50
milliliters of water, while a first "free promoter" preparation was
obtained by adding the silica particles to 50 ml of water, and then
adding an appropriate amount of the iron nitrate to the
water-abrasive mixture to give the same iron content in the slurry.
The amount of abrasive in the first "free promoter" preparation was
similar to the amount of activator-coated abrasive used in the
"coated activator" preparation. A second "free promoter"
preparation containing only iron nitrate dissolved in 50 ml of
water (i.e., no abrasive) was also prepared.
[0382] The same designated amount of 50% HDA was added to each of
these preparations to obtain the three test compositions. At a pH
of over 6, HDA is a good reducing agent, the stability of which is
extremely sensitive to trace metals in solution. HDA reacts easily
with many soluble transition metal ion promoters, such as cobalt,
copper and iron ions, resulting in the reduction of the metal ions
by at least one oxidation level and the formation of by-products
including nitrogen gas, ammonia (NH.sub.3), water, and possibly
heat, depending on the concentration of the HDA. A high level of
reactivity, or a very fast reaction rate, is a sign of relative
instability.
[0383] When the HDA component was added to obtain the
"activator-coated abrasive" composition, little color change,
little or no outgassing, and little or no precipitation were
observed. When the first "free promoter" composition containing
silica abrasive was formed, an immediate color change (light orange
to brown), substantial outgassing, and precipitation were observed.
When the second "free promoter" composition containing no abrasive
was formed, an even more immediate color change (light orange to
very dark brown) and similar outgassing, as compared to the first
"free promoter" composition, were observed.
[0384] The "activator-coated abrasive" composition was clearly more
stable than the two relatively unstable "free promoter"
compositions tested. The slurry remained useable, that is, had a
CMP rate on tungsten and TEOS of at least about one half of the CMP
rate for a freshly prepared formulation, after 24 hours.
[0385] The compositions of the present invention are all of the
"coated activator" variety, comprising a activator-coated abrasive
rather than solely a free, soluble promoter such as iron nitrate.
As demonstrated above, this relatively stable, activator-coated
abrasive is an extremely effective component of the composition of
this invention.
[0386] The composition of the present invention is advantageously
used in conventional CMP processes, and more particularly, in CMP
processes that call for reduced carrier pressures. Generally,
carrier pressures of from about 0.5 to about 2 psi are considered
low carrier pressures, although this pressure range depends on the
particular CMP process under consideration. Low carrier pressures
are often desirable because they reduce the risk of wafer damage,
such as scratching, delaminating, or destroying of material layers,
particularly metal layers, on the wafer surface. When the
composition of the present invention is used in a
low-carrier-pressure process, desirable material removal rates are
obtainable even though the carrier pressure is low. Appropriate use
of the composition in CMP processes may reduce the risk of wafer
damage and improve wafer yield and performance.
[0387] Additionally, the composition of the present invention may
be advantageously used in the CMP of wafers layered with relatively
fragile films, such as porous films, that have low dielectric
constants. At the pressures used in typical CMP processes, these
films are particularly vulnerable to delamination, crushing, or
other damage. In advanced CMP processes used for these wafers,
carrier pressures of about 2 psi are desirable and carrier and
platen speeds are about the same as, or often greater than, those
used in typical CMP processes. For a wafer layered with a porous
material of relatively low dielectric constant, such as from about
1.5 or about 1.7 to about 2.3, and of about 0.1 micron in
thickness, a removal rate of greater than about 5000 A/mm is
desirable. As demonstrated herein, these removable rates are
obtainable when the composition of the present invention is used in
CMP, even when the carrier pressure is relatively low. The
compositions of the present invention are believed suitable for use
in CMP processes having even lower carrier pressures, such as the
low carrier pressures described above.
[0388] As demonstrated herein, the composition of the present
invention may be used in CMP processes to obtain desirable material
removal rates and within-wafer nonuniformity values. Merely by way
of example, the composition may be used in the CMP of a substrate
surface having a feature, layer or film thereon, such as a film of
aluminum, copper, titanium, tungsten, an alloy thereof, or any
combination thereof. Further by way of example, the composition may
be used in the CMP of such a substrate surface, where the film has
an adjacent or an underlying feature, layer or film, such as a film
of tantalum, tantalum nitride, titanium, titanium nitride, titanium
tungsten, tungsten, and any combination thereof.
[0389] Accordingly, the present invention includes a method of
polishing a substrate surface having at least one feature thereon
that comprises a metal, such as metal or metal alloy feature. The
substrate undergoing polishing may be any suitable substrate, such
as any of the substrates described herein. According to the method
of the invention, a composition of the invention is provided and
the feature on the substrate surface is polished. The polishing is
chemical mechanical polishing, such as that associated with any
conventional or known CMP process, any suitable later-developed CMP
process, or any CMP process described herein. The polishing process
parameters may be any suitable parameters, such as any of the
parameters described herein. For example, the carrier pressure
applied to the substrate surface, or the feature thereon, may be
from about 1 to about 6 psi.
[0390] Generally, the polishing of the substrate surface continues
until the targeted feature or layer is substantially coplanar with
surrounding material, such as an oxide material, on the substrate.
For example, the polishing of a metal-featured substrate may
continue until any metal excess is sufficiently removed to provide
a substantially uniform profile across the substrate surface. By
way of example, suitable surface uniformity (typically measured
using known wafer profiling techniques) is reflected by
within-wafer nonuniformity (WI WNU) values of less than about 12%,
and preferably, from about 4% to about 6%, the lower values
typically reflecting better process control. Appropriate WIWNU
values may vary depending on the characteristics of the CMP process
and the substrates undergoing polishing.
[0391] The inventive method may be used to remove targeted
material, such as metal or metal alloy, from the substrate surface
at a rate of from about 100 to about 10,000 or to about 15,000
A/mm. The present method may be used to provide a polished
substrate surface of good uniformity, such as a substrate surface
having from about zero to about 40 percent, preferably, from about
zero to about 12 percent, or more preferably, from about zero to
about 10 percent, within-wafer nonuniformity. Further, the present
method may be used to provide a polished substrate surface wherein
any microscratch on the surface that is associated with the
polishing is less than about 20 A. The present invention further
encompasses a substrate produced by the inventive method, including
any of the substrates described herein, and any of the substrates
having any of the qualities, such as desirable uniformity values
and surface characteristics, described herein.
[0392] Various aspects and features of the present invention have
been explained or described in relation to beliefs or theories,
although it will be understood that the invention is not bound to
any particular belief or theory. Further, although the various
aspects and features of the present invention have been described
with respect to preferred embodiments and specific examples herein,
it will be understood that the invention is entitled to protection
within the full scope of the appended claims.
* * * * *