U.S. patent application number 12/643645 was filed with the patent office on 2011-02-17 for chemical mechanical polishing slurry composition including non-ionized, heat activated nano-catalyst and polishing method using the same.
This patent application is currently assigned to DONGJIN SEMICHEM CO., LTD.. Invention is credited to Jung Min Choi, Jae Hyun Kim, Hyun Goo Kong, Jin Hyuk Lim, Hye Jung Park, Jong Dai Park.
Application Number | 20110039412 12/643645 |
Document ID | / |
Family ID | 41605416 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110039412 |
Kind Code |
A1 |
Park; Jong Dai ; et
al. |
February 17, 2011 |
CHEMICAL MECHANICAL POLISHING SLURRY COMPOSITION INCLUDING
NON-IONIZED, HEAT ACTIVATED NANO-CATALYST AND POLISHING METHOD
USING THE SAME
Abstract
Disclosed herein are a chemical mechanical polishing slurry
composition for chemical mechanical planarization of metal layers,
which comprises a non-ionized, heat-activated nano-catalyst, and a
polishing method using the same. The polishing slurry composition
comprises: a non-ionized, heat-activated nano-catalyst which
releases electrons and holes by energy generated in a chemical
mechanical polishing process; an abrasive; and an oxidizing agent.
The non-ionized, heat-activated nano-catalyst and the abrasive are
different from each other, and the non-ionized, heat-activated
nano-catalyst is preferably a semiconductor material which releases
electrons and holes at a temperature of 10 to 100.degree. C. in an
aqueous solution state, more preferably a transition metal silicide
selected from the group consisting of CrSi, MnSi, CoSi,
ferrosilicon (FeSi), mixtures thereof, and most preferably, a
semiconductor material such as nano ferrosilicon. The content of
the content of the non-ionized, heat-activated nano-catalyst is
0.00001 to 0.1 wt % based on the total weight of the slurry
composition.
Inventors: |
Park; Jong Dai; (Hwaseong,
KR) ; Lim; Jin Hyuk; (Hwaseong, KR) ; Choi;
Jung Min; (Hwaseong, KR) ; Kong; Hyun Goo;
(Hwaseong, KR) ; Kim; Jae Hyun; (Hwaseong, KR)
; Park; Hye Jung; (Hwaseong, KR) |
Correspondence
Address: |
Edwards Angell Palmer & Dodge LLP
P.O. Box 55874
Boston
MA
02205
US
|
Assignee: |
DONGJIN SEMICHEM CO., LTD.
Incheon
KR
|
Family ID: |
41605416 |
Appl. No.: |
12/643645 |
Filed: |
December 21, 2009 |
Current U.S.
Class: |
438/693 ;
252/79.1; 257/E21.23 |
Current CPC
Class: |
H01L 21/3212 20130101;
C09G 1/02 20130101 |
Class at
Publication: |
438/693 ;
252/79.1; 257/E21.23 |
International
Class: |
B24B 1/00 20060101
B24B001/00; C09K 13/00 20060101 C09K013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 12, 2009 |
KR |
10-2009-0074344 |
Claims
1. A chemical mechanical polishing slurry composition for use in a
process for chemical mechanical polishing a substrate by a
polishing pad, the composition comprising: a non-ionized,
heat-activated nano-catalyst which is able to release electrons and
holes by thermal energy generated by friction between the substrae
and the polishing pad; an abrasive; and an oxidizing agent, wherein
the non-ionized, heat-activated nano-catalyst and the abrasive are
different from each other, and the content of the non-ionized,
heat-activated nano-catalyst is 0.00001 to 0.1 wt % based on the
total weight of the chemical mechanical polishing slurry
composition.
2. The chemical mechanical polishing slurry composition of claim 1,
wherein the non-ionized, heat-activated nano-catalyst is a
transition metal silicide represented by MSi (where M is a
transition metal).
3. The chemical mechanical polishing slurry composition of claim 1,
wherein the non-ionized, heat-activated nano-catalyst is selected
from the group consisting of CrSi, MnSi, CoSi, ferrosilicon (FeSi),
and mixtures thereof.
4. The chemical mechanical polishing slurry composition of claim 1,
wherein the non-ionized, heat-activated nano-catalyst is
ferrosilicon (FeSi).
5. The chemical mechanical polishing slurry composition of claims
1, wherein the non-ionized, heat-activated nano-catalyst is a
semiconductor material which releases electrons and holes at a
temperature of 10 to 100.degree. C. in an aqueous solution
state.
6. The chemical mechanical polishing slurry composition of claim 5,
wherein the non-ionized, heat-activated nano-catalyst has a
particle size of 1-20 nm.
7. The chemical mechanical polishing slurry composition of claim 6,
wherein the content of the abrasive is preferably 0.1 to 20.0 wt
%.
8. The chemical mechanical polishing slurry composition of claim 7,
wherein the content of the non-ionized, heat-activated
nano-catalyst in the chemical mechanical polishing slurry
composition is 0.00005-0.07 wt %.
9. The chemical mechanical polishing slurry composition of claims
1, wherein the abrasive is selected from the group consisting of
fumed silica, colloidal silica, .gamma.-alumina or .alpha.-alumina,
ceria, Germania, titania, zirconia, and mixtures thereof.
10. The chemical mechanical polishing slurry composition of claims
1, wherein the oxidizing agent is selected from the group
consisting of monopersulfates, persulfates, peroxides, periodates,
and mixtures thereof, and the content of the oxidizing agent in the
slurry composition of the present invention is 0.1-10.0 wt %.
11. A method for polishing a substrate, comprising the steps of:
applying to a substrate having a metal layer formed thereon a
chemical mechanical polishing slurry composition; bringing the
substrate having the chemical mechanical polishing composition
applied thereto into contact with a polishing pad, and allowing the
polishing pad, the substrate, or both to move; and removing at
least a portion of the metal layer from the substrate, wherein the
chemical mechanical polishing slurry composition comprises a non
ionized, heat-activated nano-catalyst, an abrasive, and an
oxidizing agent; wherein the chemical mechanical polishing slurry
composition comprises a non-ionized, heat-activated nano-catalyst,
an abrasive, and an oxidizing agent; wherein the non-ionized,
heat-activated nano-catalyst is able to release electrons and holes
by thermal energy generated by the movement of the polishing pad,
the substrate, or both, wherein the non-ionized, heat-activated
nano-catalyst and the abrasive are different from each other, and
wherein the content of the non-ionized, heat-activated
nano-catalyst is 0.00001 to 0.1 wt % based on the total weight of
the chemical mechanical polishing slurry composition.
12. The method of claim 11, wherein the metal layer is selected
from the group consisting of a titanium layer, a titanium nitride
layer and a tungsten layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 10-2009-74344, filed on Dec. 8, 2009, which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a chemical mechanical
polishing slurry composition which is used in the manufacture of
semiconductor chips, and more particularly to a polishing slurry
composition, which comprises a non-ionized, heat-activated
nano-catalyst and is particularly useful for a process for chemical
mechanical planarization of a metal layer, and to a polishing
method using the same.
[0004] (b) Background of the Related Art
[0005] Semiconductor chips to which integrated circuit technology
has been applied include numerous functional elements (devices),
including transistors, capacitors, resistors and the like. Such
individual functional elements are connected to each other by
interconnects designed in specific shapes to form circuits.
Integrated circuits have become smaller over time, and thus the
function of one chip is also gradually increasing. In
miniaturization of semiconductor chips, simply decreasing the size
of devices has limitations, and thus studies on multilayer
interconnect structures for forming each device in a multilayer
structure have recently been actively conducted. To manufacture
semiconductor devices having such multilayer interconnect
structures, a process of planarizing metal layers by polishing must
be carried out. However, because the metal layers are not easy to
polish due to their high strength, in order to effectively polish
the metal layer, the polishing process must be carried out after
oxidizing the metal layers in the form of metal oxides having
relatively low strength.
[0006] However, conventional chemical mechanical polishing slurry
compositions have a shortcoming in that the efficiency of a
chemical conversion process of oxidizing metal layers in the form
of metal oxides is insufficient. Meanwhile, Korean Patent
Registration No. 745447 discloses a method of promoting the
oxidation of metal layers using a polishing slurry composition
comprising hydrogen peroxide and iron salt (iron ion). However,
because the disclosed method uses a large amount of iron salt, a
metal layer being polished can be contaminated by iron ions,
resulting in defects, or iron ions can remain on plugs (contacts
between interconnects) to cause excessive oxidation, resulting in
excessive etching. Thus, the choice of oxidizing agents and
polishing particles, which can effectively oxidize a metal layer,
to be polished, without causing defects on the metal layer, and the
control of the concentration thereof are very critical to the
development of chemical mechanical polishing (CMP)
compositions.
[0007] Regarding catalysts and oxidizing agents, which are used in
the chemical mechanical polishing processes, Korean Patent
Laid-Open Publication No. 2001-0043798 discloses a metal oxide
(e.g., TiO.sub.2) catalyst such as metal oxide (e.g., TiO.sub.2).
However, the metal oxide (e.g., TiO.sub.2) catalyst is a
photo-activated catalyst which has a problem in that it irradiates
light required for optical activity between a substrate on which a
CMP composition acts and a pad. Moreover, Korean Patent
Registration No. 10-736325 discloses a CMP composition in which an
activating agent selected from the group consisting of metals known
to be activated by Fenton oxidation are bound to the surface of
particles and fluid. However, the CMP composition has a problem in
that a metal layer being polished can be contaminated by the
activating agent Fe ion, because the activating agent has a
plurality of oxidation numbers even when the activating agent is
not separated from the particles. Another problem is that an
organic additive for reducing the contamination level is
required.
[0008] In addition, U.S. Pat. No. 5,861,055 and Korean Patent
Laid-Open Publication No. 2008-0070053 disclose chemical mechanical
slurry compositions which comprise a metal silicide component as an
abrasive, but recognize metal silicide as one of simple abrasives
rather than an activating agent.
SUMMARY OF THE INVENTION
[0009] Accordingly, the present inventors have made many efforts to
the above-mentioned problems occurring in the prior art, and as a
result, have found that, when a chemical mechanical slurry
composition which comprises a non-ionized, heat-activated
nano-catalyst without having metal (Fe) ions, is used,
contamination by metals during a polishing process can be reduced
and excessive oxidation reactions can be prevented to increase
polishing efficiency, thereby completing the present invention.
[0010] It is an object of the present invention to provide a
chemical mechanical polishing slurry composition which utilizes a
non-ionized, heat-activated nano-catalyst adopting a novel
mechanism of releasing electrons and holes by energy generated in a
chemical mechanical polishing process.
[0011] Another of the present invention is to provide a chemical
mechanical polishing slurry composition which can promote the
oxidation of a metal layer using a novel, non-ionized,
heat-activated nano-catalyst instead of using large amounts of iron
ions (iron salts) and hydrogen peroxide and can easily polish a
metal layer.
[0012] Still another object of the present invention is to provide
a chemical mechanical polishing slurry composition which utilizes a
non-ionized, heat-activated nano-catalyst and does not require an
organic additive for reducing the level of contamination by metal
ions, in which the non-ionized, heat-activated nano-catalyst has
excellent stability and does not cause substrate contamination
resulting from the generation of metal ions, and a polishing method
using the same.
[0013] To achieve the above objects, the present invention provides
a chemical mechanical polishing slurry composition comprising: a
non-ionized, heat-activated nano-catalyst which releases electrons
and holes by energy generated in a chemical mechanical polishing
process; an abrasive; and an oxidizing agent, wherein the
non-ionized, heat-activated nano-catalyst and the abrasive are
different from each other, the non-ionized, heat-activated
nano-catalyst is preferably a semiconductor material which releases
electrons and holes at a temperature of 10 to 100.degree. C. in an
aqueous solution state, more preferably a transition metal silicide
selected from the group consisting of CrSi, MnSi, CoSi,
ferrosilicon (FeSi), mixtures thereof, and most preferably, a
semiconductor material such as nano ferrosilicon. Also, the content
of the content of the non-ionized, heat-activated nano-catalyst is
0.00001 to 0.1 wt %. The content of the abrasive is preferably 0.1
to 20.0 wt %.
[0014] The present invention also provides a method for polishing a
substrate, comprising the steps of: applying a chemical mechanical
polishing slurry composition, comprising a non-ionized,
heat-activated nano-catalyst releasing electrons by energy
generated in a chemical mechanical polishing process, an abrasive
and an oxidizing agent, to a substrate having a metal layer formed
thereon; bringing the substrate having the chemical mechanical
polishing composition applied thereto into contact with a polishing
pad, and moving the polishing pad against the substrate; and
removing at least a portion of the metal layer from the substrate,
wherein the non-ionized, heat-activated nano-catalyst and the
abrasive are different from each other, and the content of the
non-ionized, heat-activated nano-catalyst is 0.00001 to 0.1 wt %
based on the total weight of the chemical mechanical polishing
slurry composition.
[0015] The prior chemical mechanical polishing slurry composition
for polishing tungsten (W) contains a large amount of metal (iron)
ions. For this reason, after a process of polishing a wafer, the
wafer surface can be contaminated by a large amount of metal (iron)
ions, and slurry remaining on the wafer can additionally corrode
the tungsten plug, thus causing a short circuit in the plug. Also,
the substrate can be contaminated by a large amount of metal ions,
and an organic additive must be added to the composition in order
to reduce the level of contamination by metal ions. On the
contrary, in the chemical mechanical polishing slurry composition
according to the present invention, metal (ion) ions are not
present in the slurry, and thus the metal contamination of a wafer
after polishing of the wafer is low. Also, the CMP composition of
the present invention does not cause any additional oxidation
reaction except for an oxidation reaction in the CMP process, and
thus before and after the CMP process or during the interruption of
the CMP process, it does not cause tungsten plug corrosion
resulting from an unintended additional reaction. Furthermore, the
slurry composition according to the present invention has
advantages in that it does not require an organic additive for
reducing metal (Fe) contamination levels, has a low content of
silica particles compared to the prior tungsten (W) polishing
slurry, and shows a high tungsten (W) polishing rate and excellent
post-polish roughness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The above and other objects, features and advantages of the
present invention will be apparent from the following detailed
description of the preferred embodiments of the invention in
conjunction with the accompanying drawings, in which:
[0017] FIG. 1 is a graph showing a change in the temperature of the
surface of a pad in the case of polishing a tungsten (W) film using
a chemical mechanical polishing slurry composition according to the
present invention;
[0018] FIG. 2 is a graph showing the removal rate of a tungsten (W)
film as a function of polishing time in the case of polishing a
tungsten (W) film using a chemical mechanical polishing slurry
composition according to the present invention;
[0019] FIG. 3 is a graph showing whether or not Fe ions are
detected in a chemical mechanical polishing slurry composition
according to the present invention and a slurry composition
containing ferric nitrate ((Fe(NO.sub.3).sub.3); and
[0020] FIG. 4 is a graph showing the binding state of
nano-ferrosilicon (FeSi) which is used as a nano-catalyst in a
chemical mechanical polishing slurry composition according to the
present invention wherein FIG. 4(a) shows results of XPS
qualitative analysis in a wide scan region; and FIG. 4(b) shows XPS
results of binding states in a narrow scan region.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The present invention relates to a chemical mechanical
polishing slurry composition comprising: a non-ionized,
heat-activated nano-catalyst which releases electrons and holes by
energy generated in a chemical mechanical polishing process; an
abrasive; and an oxidizing agent, wherein the non-ionized,
heat-activated nano-catalyst and the abrasive are different from
each other, and the content of the content of the non-ionized,
heat-activated nano-catalyst is 0.00001 to 0.1 wt %.
[0022] Hereinafter, the present invention will be described in
detail.
[0023] A chemical mechanical polishing (CMP) slurry composition
according to the present invention comprises a non-ionized,
heat-activated nano-catalyst, an abrasive and an oxidizing agent,
wherein the non-ionized, heat-activated nano-catalyst and the
abrasive are different from each other. The non-ionized,
heat-activated nano-catalyst which is used in the chemical
mechanical polishing slurry composition according to the present
invention is a material which releases electrons and/or holes by
energy generated in a chemical mechanical polishing process, in
which the released electrons react with an oxidizing agent such as
hydrogen peroxide to produce hydroxyl radicals. As the non-ionized,
heat-activated nano-catalyst, any semiconductor material having a
low energy band gap may be used. The mechanism by which the
non-ionized, heat-activated nano-catalyst releases electron and
holes by energy generated in a chemical mechanical polishing
process is as follows:
nano FeSi.fwdarw.e.sup.-(release)+h.sup.+(surface)
e.sup.-+H.sub.2O.sub.2.fwdarw..OH+OH.sup.-
e.sup.-+O.sub.2.fwdarw.O.sub.2. (super oxide radical)
2O.sub.2.+2H.sub.2O.fwdarw.2.OH+2OH.sup.-+O.sub.2
2h.sup.++2OH.sup.-.fwdarw.2.OH
.quadrature.6.OH+W.fwdarw.WO.sub.3+3H.sub.2O
[0024] A semiconductor material which can be used as the
non-ionized, heat-activated nano-catalyst releases electron is a
material releasing electrons and holes in an aqueous solution state
at a temperature of 10 to 100 r, preferably 20 to 80 r, and more
preferably 30 to 70, and preferably has an energy band gap of
0.001-3.0 eV, and preferably 0.005-2.0 eV. Herein, if the
temperature is too low, electrons and holes cannot occur, and if
the temperature is too high, non-uniform polishing can be performed
due to an abrupt reaction. If the energy band gap is too low, the
material can become conductive to lose its catalytic function, and
if it is too high, excitation of the catalyst by energy generated
in the polishing process cannot be achieved. The non-ionized,
heat-activated nano-catalyst consists of nano-sized particles.
Specifically, the nano-catalyst has a particle size of 1-1,000 nm,
preferably 1-20 nm, and more preferably 2-10 nm. If the particle
size of the non-ionized, heat-activated nano-catalyst is too small,
the nano-catalyst cannot be formed of particles, and if the
particle size is too large, the catalyst activity can be decreased
or the catalyst can cause defects such as scratches in the
polishing process.
[0025] As the non-ionized, heat-activated nano-catalyst, a
transition metal silicide represented by MSi (M: transition meal)
may be used. It is generally known that transition metal silicides
are inactive in aqueous solution and non-reactive, but react with
molten KOH, KF, KCl and the like at high temperatures. Examples of
the transition metal silicide include CrSi, MnSi, CoSi,
ferrosilicon (FeSi) and the like, and a particularly preferred
example of the non-ionized, heat-activated nano-catalyst is
ferrosilicon (FeSi) having a particle size of about 4-5 nm.
Ferrosilicon synthesized to have a nanometer size is very highly
active, and thus has a characteristic in that it is sufficiently
activated by thermal energy generated in the CMP process.
[0026] As described in the specification of Korean Patent
Registration No. 10-850877 registered in the name of the applicant,
the above ferrosilicon (FeSi) can be prepared by allowing a silica
salt such as SiCl.sub.4 in an aqueous solution in the presence of
an iron salt such as FeCl.sub.3.
[0027] Also, as described in the specification of Korean Patent
Application No. 10-2009-42594 filed in the name of the applicant,
the above ferrosilicon (FeSi) can be prepared by a method of
preparing transition metal silicide using supercritical fluid, the
method comprising the steps of: introducing a transition metal
compound and an organic solvent into a reaction tank, and heating
and pressurizing the introduced materials, such that the organic
solvent reaches a supercritical state; introducing a silicon
compound into the reaction tank; and transferring the mixture
solution of the reaction tank to an impurity removal tank, and
removing the organic solvent and unreacted material.
[0028] In the ferrosilicon (FeSi) described in the specifications
of the registered invention and filed invention of the applicant,
unreacted ions can exist as impurities after the preparation
process, the removal of ions from the reaction solution in a
process of preparing a heat-activated, solid polishing composition
can be carried out using an ion exchange resin method in which
impurities in the composition are treated with, for example, ion
exchange resin, such that the composition can be exchanged with
OH.sup.- and H.sup.+ ions.
[0029] Moreover, the ferrosilicon (FeSi), an alloy of iron and
silicon, is conventionally prepared as a melt in a melting furnace,
an electric furnace or the like and has a silicon content of about
15-90 wt % for commercially available products. The content of iron
(Fe) in the ferrosilicon (FeSi) is preferably 0.01-99 wt %, and
more preferably 0.1-50 wt %. If the content of the iron (Fe)
component is too low, the ferrosilicon cannot be activated by the
energy of the polishing process, and if the content is too high,
the ferrosilicon can become conduct to lose its catalytic
function.
[0030] The transition metal silicide including the ferrosilicon
(FeSi) can be prepared by a liquid-phase method, a solid-phase
method or a vapor-phase method, which are used to prepare
nanoparticles. Moreover, it can also be prepared while controlling
physical properties using a supercritical method. The content of
each component in the transition metal silicide which is used in
the preset invention can be selected within a range which does not
impair the object of the present invention, depending on the
configurations of structures and elements of semiconductor devices
having a multilayer interconnect structure. Specifically, the
content of each component in the transition metal silicide can be
selected in a wide range of 0.0001-99.9999 wt %, preferably
0.1-99.9 wt %, more preferably 1-99 wt %, and most preferably 10-90
wt %.
[0031] The non-ionized, heat-activated nano-catalyst according to
the present invention releases electrons and holes in a chemical
mechanical polishing process, which react with an oxidizing agent
such as hydrogen peroxide to produce very strongly hydroxyl
radicals, thus oxidizing a metal layer. The content of the
non-ionized, heat-activated nano-catalyst in the chemical
mechanical polishing slurry composition according to the present
invention is 0.00001-0.1 wt %, 0.00005-0.07 wt %, more preferably
0.0001-0.05 wt %, and most preferably 0.001-0.03 wt %, based on the
total weight of the composition. If the content of the non-ionized,
heat-activated nano-catalyst is too low, the catalytic action can
be insufficient, and if the content is too high, the reactivity of
the nano-catalyst can be excessively increased, thus causing
non-uniform polishing.
[0032] The chemical mechanical polishing slurry composition
according to the present invention comprises an oxidizing agent
which forms an oxide layer on the surface of a metal layer during
polishing, in which the formed layer helps to polish the metal
layer. Examples of the oxidizing agent which can be used in the
present invention include monopersulfates, persulfates, peroxides,
periodates, and mixtures thereof. Preferably, hydrogen peroxide may
be used. Examples of the monoperoxides include KHSO.sub.5,
KHSO.sub.4, K.sub.2SO.sub.4 and the like, and examples of the
peroxide compounds include hydrogen peroxide, benzoyl peroxide,
peracetic acid, di-t-butyl peroxide, sodium peroxide, etc. The
content of the oxidizing agent which is included in the slurry
composition of the present invention is preferably 0.1-10.0 wt %,
and 0.2-5.0 wt %, based on the total weight of the composition. If
the content of the oxidizing agent is less than 0.1, the formation
of an oxide layer can be insufficient, and if the content of the
oxidizing agent is more than 10.0 wt %, polishing efficiency can be
decreased. The oxidizing agent highly reactive hydroxyl radicals
(--OH) by reaction with the electrons and holes released from the
heat-activated nano-catalyst activated by thermal energy.
[0033] The slurry composition of the present invention comprises a
conventional abrasive which performs the mechanical polishing of a
metal layer. Example of the abrasive which can be used in the
present invention include fumed silica such as silica or colloidal
silica, alumina such as .gamma.-alumina or .alpha.-alumina, ceria,
Germania, titania, zirconia, etc. These abrasives may be used alone
or in combination, and fumed silica is preferred. The size of the
abrasive is generally less than 1.0 .mu.m, and preferably less than
400 nm, and the content of the abrasive is 0.1-20.0 wt %, and
preferably 0.5-10.0 wt %, based on the total weight of the
composition. If the content of the abrasive is less than 0.1 wt %,
the polishing of a metal layer can be insufficient, and if the
content of the abrasive exceeds 20.0%, the stability of the slurry
can be reduced.
[0034] The remaining component of the slurry composition according
to the present invention is water, preferably deionized water or
distilled water. If necessary, the slurry composition of the
present invention may contain a dispersing agent for inhibiting the
gelling and particle precipitation caused by storage temperature
and aging and maintaining dispersion stability, and a reaction
regulating agent for regulating the non-uniform reaction of the
oxidizing agent resulting from the difference in the roughness of a
substrate. As the reaction regulating agent, malonic acid may be
used in a suitable amount, and organic additives for reducing the
level of metal ion contamination, such as dihydroxy enol compounds
and ascorbic acid, are not required in the present invention. The
slurry composition of the present invention may further comprise
conventional additives such as a buffer solution for inhibiting the
effect of a change in pH. The pH of the slurry composition
according to the present invention is 1-10, preferably 1-9, and
more preferably 1-7. If The pH of the slurry composition is less
than 1, the particles of the composition can be agglomerated to
form gel, and if the pH of the composition exceeds 10, an oxidation
reaction can be insufficient. In order to adjust the pH of the
slurry composition to the above range, a pH adjusting agent may be
added, if necessary. Examples of the pH adjusting agent which can
be used in the present invention include inorganic acids such as
nitric acid, sulfuric acid, hydrochloric acid or phosphoric acid,
and organic acids such as tartaric acid, citric acid, oxalic acid
or benzoic acid.
[0035] The composition of the present invention can be prepared by
any known method depending on the configurations of the structures
and elements of semiconductor devices having a multilayer
structure. For example, the composition of the present invention
can be prepared by adding an abrasive and a non-ionized,
heat-activated nano-catalyst to an aqueous medium such as deinized
water or distilled water at required concentrations, and then
adding an oxidizing agent or an oxidizing agent aqueous solution to
the aqueous medium. In addition, conventional additives such as a
dispersing agent may be added to the composition of the present
invention by any conventional method. It is to be understood that
organic additives for reducing the level of metal ion
contamination, such as dihydroxy enol compounds and ascorbic acid,
are not required in the present invention.
[0036] The components of the inventive composition may be mixed
with each other immediately before they are used in a polishing
process. Alternatively, the components may also be used in a
polishing process after a given time after mixing. Alternatively,
the components may be provided as more than two package units
containing one or more components, and then the components
contained in the package units may be mixed with each other
immediately before carrying out the polishing process. In order to
use the slurry composition of the present invention to polish a
substrate such as a wafer, a silicon substrate or a glass
substrate, particularly a metal layer formed on the substrate, the
slurry composition is applied to the substrate, a polishing pad is
brought into contact with the substrate, and the polishing pad is
moved against the substrate to remove at least a portion of the
metal layer. Substrates which can be polished by the polishing
composition of the present invention can be exemplified by
substrates including at least one metal layer, for example, a
titanium layer, a titanium nitride layer or a tungsten layer, and
preferably substrates including a tungsten layer.
[0037] Hereinafter, the present invention will be described in
further detail with reference to examples. It is to be understood,
however, that these examples are illustrative purposes only and are
not to be construed to limit the scope of the present
invention.
Examples 1 to 5 and Comparative Example 1
Tests of Tungsten Layers for Polishing Rate at Various Silica
Contents
[0038] As shown in Table 1 below, chemical mechanical polishing
slurry compositions comprising silica (SiO.sub.2), hydrogen
peroxide, nano-ferrosilicon (FeSi) as a non-ionized, heat-activated
nano-catalyst according to the present invention and deionized
waster were prepared (Examples 1 to 5). Also, a chemical mechanical
polishing slurry composition was prepared using ferric nitrate
(Fe(NO.sub.3).sub.3) as a conventional catalyst instead of the
non-ionized, heat-activated nano-catalyst (Comparative Example 1).
The prepared slurry compositions were used to polish tungsten
wafers having a 0.8 .mu.m-thick tungsten layer formed thereon, and
the polishing results are shown in Table 1. The polishing process
was carried out using Frex-200 CMP Polisher (Ebara, Japan) as a
polishing machine and IC1000 (Rohm & Haas, USA) as a polishing
pad. The polishing conditions were as follows: a pad pressure of
200 hPa, a pad rotation speed of 90 rpm, and a slurry flow rate of
150 ml/min.
TABLE-US-00001 TABLE 1 Hydrogen Nano- Silica Peroxide Ferric
Nitrate Ferrosilicon Removal Contents Contents (Fe(NO.sub.3).sub.3)
(FeSi) Rate Roughness (wt %) (wt %) Contents (ppm) Contents (ppm)
(.ANG./min) (%) Example 1 1.0 3.0 None 17 867 2.86 Example 2 1.5
3.0 None 17 976 2.37 Example 3 2.0 3.0 None 17 1,005 1.42 Example 4
2.5 3.0 None 17 1,063 3.13 Example 5 3.0 3.0 None 17 1,152 3.29
Comp. Ex. 1 3.0 3.0 434 None 1,000 5.00
[0039] The content of iron ions in the composition of Comparative
Example 1 was 60 ppm (see Experimental Example 4 below). The
content of iron in the nano-ferrosilicon (FeSi) used in Examples 1
to 5 was 8 ppm (based on the total weight of the composition), and
the iron was not present in the form of ions. Also, in Table 1
above, the removal rate and roughness are values relative to the
case in which the removal rate and roughness of Comparative Example
1 were normalized to 1000 .ANG./min and 5%, respectively. As can be
seen from the results from Table 1 above, as the content of the
abrasive particle silica increased, the removal rate linearly
increased. In comparison with the prior slurry composition of
Comparative Example 1, in the cases in which the abrasive particles
(silica) were used in the same amount (Example 5 and Comparative
Example 1), the inventive slurry showed a removal rate which was
higher than that for the prior slurry by about 15%.
Examples 6 to 9 and Comparative Example 1
Tests for Removal Rate of Tungsten Layer at Various Contents of
Oxidizing Agent
[0040] As shown in Table 2 below, chemical mechanical polishing
slurry compositions comprising silica (SiO.sub.2), hydrogen
peroxide, nano-ferrosilicon (FeSi) as a non-ionized, heat-activated
nano-catalyst according to the present invention and deionized
waster were prepared (Examples 6 to 9). Also, a chemical mechanical
polishing slurry composition was prepared using ferric nitrate
(Fe(NO.sub.3).sub.3) as a conventional catalyst instead of the
non-ionized, heat-activated nano-catalyst (Comparative Example 2).
Polishing was carried out using the prepared slurry compositions in
the same conditions as in Examples 1 to 5, and the polishing
results are shown in Table 2 below.
TABLE-US-00002 TABLE 2 Hydrogen Nano- Silica Peroxide Ferric
Nitrate Ferrosilicon Removal Contents Contents (Fe(NO.sub.3).sub.3)
(FeSi) Rate Roughness (wt %) (wt %) Contents (ppm) Contents (ppm)
(.ANG./min) (%) Example 6 2.0 1.5 None 17 740 2.67 Example 7 2.0
2.0 None 17 839 2.60 Example 8 2.0 2.5 None 17 954 2.67 Example 9
2.0 3.0 None 17 1,005 1.42 Example 5 3.0 3.0 None 17 1,152 3.29
Comp. Ex. 2 3.0 2.0 434 None 787 5.38 Comp. Ex. 1 3.0 3.0 434 None
1,000 5.00
[0041] The content of iron ions in the compositions of Comparative
Examples 1 and 2 was 60 ppm. The content of iron in the
nano-ferrosilicon (FeSi) used in Examples 6 to 9 was 8 ppm, and the
iron was not present in the form of ions. Also, in Table 2 above,
the removal rate and roughness are values relative to the case in
which the removal rate and roughness of Comparative Example 1 were
normalized to 1000 .ANG./min and 5%, respectively. As can be seen
from the results from Table 2 above, as the content of hydrogen
peroxide used as the oxidizing agent increased, the removal rate
increased. The slurry compositions of Examples 6 to 9 showed
removal rate and roughness which were equal or superior to those of
the prior slurry compositions of Comparative Examples 1 and 2.
Examples 10 to 18 and Comparative Example 1
Tests for Removal Rates at Various Contents of Nano-Catalysts
[0042] As shown in Table 3 below, chemical mechanical polishing
slurry compositions comprising silica (SiO.sub.2), hydrogen
peroxide, nano-ferrosilicon (FeSi) as a non-ionized, heat-activated
nano-catalyst according to the present invention and deionized
waster were prepared (Examples 10 to 18). Also, a chemical
mechanical polishing slurry composition was prepared using ferric
nitrate (Fe(NO.sub.3).sub.3) as a conventional catalyst instead of
the non-ionized, heat-activated nano-catalyst (Comparative Example
2). Polishing was carried out using the prepared slurry
compositions in the same conditions as in Examples 1 to 5, and the
polishing results are shown in Table 3 below.
TABLE-US-00003 TABLE 3 Hydrogen Nano- Silica Peroxide Ferric
Nitrate Ferrosilicon Removal Contents Contents (Fe(NO.sub.3).sub.3)
(FeSi) Rate Roughness (wt %) (wt %) Contents (ppm) Contents (ppm)
(.ANG./min) (%) Example 10 2 3 None 0.1 47 17.4 Example 11 2 3 None
1 133 2.2 Example 12 2 3 None 5 722 4.4 Example 9 2 3 None 17 1,005
1.4 Example 13 2 3 None 34 1,107 2.3 Example 14 2 3 None 64 1,121
3.0 Example 15 2 3 None 128 1,118 3.4 Example 16 2 3 None 255 1,057
2.7 Example 17 2 3 None 510 1,087 3.0 Example 18 2 3 None 1,000
1,127 3.2 Comp. Ex. 1 3 3 434 None 1,000 5.0
[0043] The content of iron ions in the composition of Comparative
Examples 1 was 60 ppm. The content of iron in the nano-ferrosilicon
(FeSi) used in Examples 10 to 18 ranged from 100 ppb to 1,000 ppm,
and the iron was not present in the form of ions. Also, in Table 3
above, the removal rate and roughness are values relative to the
case in which the removal rate and roughness of Comparative Example
1 were normalized to 1000 .ANG./min and 5%, respectively. As can be
seen in Table 3 above, as the content of the nano-ferrosilicon
(catalyst) increased, the removal rate increased. When the content
of the nano-ferrosilicon was more than 17 ppm, the removal rate was
maintained at a substantially constant level. When examining the
post-polish roughness in the cases of applying the
nano-ferrosilicon in comparison with Comparative Example 1, the
roughness in the case of applying the nano-ferrosilicon was more
uniform except for Example 10 in which a very small amount of the
ferrosilicon was used.
Examples 19 to 21
Tests for Polishing Performance of Metal Silicides (MSi) with
Different Transition Metals
[0044] The polishing performance of ferrosilicon and metal
silicides (MSi) with different transition metals was comparatively
tested, and the test results are shown in Table 4 below. As can be
seen from the results in Table 4, the removal rate of the tungsten
substrate in the cases of manganese silicide and cobalt silicide
was reduced compared to the case of nano-ferrosilicide, but the
polishing function thereof could be confirmed. Accordingly, it
could be found that other transition metal silicides such as
manganese silicide and cobalt silicide, in addition to
ferrosilicide as the non-ionized heat-activated nano-catalyst, also
belong to a class of non-ionized, heat-activated nano-catalysts
which release electrons and holes by energy generated in chemical
mechanical polishing processes.
[0045] The polishing performance tests were carried out using the
same polishing machine, method and conditions as in Examples 1 to
5. Specifically, the polishing process was carried out using
Frex-200 CMP Polisher (Ebara, Japan) as a polishing machine and
IC1000 (Rohm & Haas, USA) as a polishing pad, and the polishing
conditions were as follows: a pad pressure of 200 hPa, a pad
rotation speed of 90 rpm, and a slurry flow rate of 150 ml/min.
TABLE-US-00004 TABLE 4 Reaction Silica Nano- Manganese Cobalt
Hydrogen Regulating Removal Contents ferrosilicide Silicide Slicide
Peroxide Agent Rate Roughness Division (w %) (ppm) (ppm) (ppm) (w
%) (w %) (.ANG./min) (%) Example 3.0 0 0 17 3.0 0.01 613 6.33 19
Example 3.0 0 17 0 3.0 0.01 748 5.70 20 Example 3.0 17 0 0 3.0 0.01
1000 4.08 21
Experimental Examples 1 to 3
Experiments of Reactivity by Thermal Energy
[0046] To examine the reactivity between the oxidizing agent
(hydrogen peroxide) and the catalyst, 3.0 wt % of the oxidizing
agent was added to each of an aqueous solution containing pure
deionized water and 0.0017 wt % of nano-ferrosilicon (Fe content: 8
ppm) as the non-ionized, heat-activated nano-catalyst according to
the present invention, and an aqueous solution containing 0.0434 wt
% of ferric nitrate ((Fe(NO.sub.3).sub.3; Fe content: 60 ppm) as
the prior catalyst, and the states (the change in color caused by
reaction with the oxidizing agent, and the generation of bubbles)
of the aqueous solutions were observed. Also, the aqueous solutions
were heated to 60.degree. C., and the oxidizing agent was then
added thereto, after which the states of the aqueous solutions were
observed. The observation results are shown in Table 5 below.
TABLE-US-00005 TABLE 5 Before Addition Immediately of Immediately
After Heating Within 30 mins Oxidizing After Addition of to After
Heating Catalyst Agent Oxidizing Agent 60.degree. C. to 60.degree.
C. Experimental None Clear No Change No Change No Change Example 1
Experimental Heat- Clear No Change Excessive Excessive Example 2
Activated Amount of Amount of Nano Bubbles Bubbles Catalyst
Generated/ Generated/ Light Yellow (90 mins) Experimental Ferric
Light Excessive Excessive Reaction Example 3 Nitrate Brown Amount
of Amount of Terminated/ Bubbles Bubbles Dark Brown Generated/Brown
Generated/ Brown
[0047] As can be seen from the results in Table 5 above, the
aqueous solution containing 0.0017 wt % of nano-ferrosilicon as the
non-ionized, heat-activated nano-catalyst according to the present
invention did not react when the oxidizing agent was added.
However, when the oxidizing agent was added to the aqueous solution
after heating the aqueous solution to 60.degree. C. on a hot plate,
a reaction (bubble generation) occurred for 90 minutes, and after
completion of the reaction, the aqueous solution showed a clear
color (Experimental Example 2). On the contrary, the aqueous
solution containing 0.0434 wt % of ferric nitrate
((Fe(NO.sub.3).sub.3) as the prior catalyst showed a light brown
color when the oxidizing agent was added. Also, it generated
bubbles (Fenton oxidation; a chemical reaction frequently used in
wastewater treatment plants) at room temperature immediately after
addition of the oxidizing agent), and the reaction was terminated
within 30 minutes after heating to 60.degree. C. Finally, the
aqueous solution showed a dark brown color. Meanwhile, in the case
in which only the oxidizing agent (hydrogen peroxide) was added
without adding the catalyst (Experimental Example 3), there was no
reaction at room temperature and a heated state, suggesting that
the aqueous solution was not decomposed by the oxidizing agent
alone and did not generate bubbles, even when heat was applied
thereto. In the case in which the non-ionized, heat-activated
nano-catalyst according to the present invention was used, very
fine bubbles were generated compared to the case in which ferric
nitrate was used. As can be seen from the above experimental
results, unlike the prior reaction mechanism utilizing ferric
nitrate, the heat-activated nano-catalyst according to the present
invention generates electrons in a thermally excited state, which
react with hydrogen peroxide.
Experimental Example 4
Relationship Between Polishing Temperature and Removal Rate
[0048] In order to examine the relationship between polishing
temperature and removal rate, a wafer having a 8,000 .ANG.-thick
tungsten (W) CVD (chemical vapor deposition) film coated thereon
was polished using a CMP system (FREX-200, Ebara, Japan) and the
chemical mechanical polishing slurry composition of Example 7. The
change in the temperature of the surface of the pad (IC 1000, Rohm
& Haas, USA) during the polishing process was measured by using
an IR sensor (SK-8700; SATO, Japan) to detect the temperature of
the pad surface closest to the CMP head, and the measurement
results are shown in FIG. 1. As can be seen in FIG. 1, after about
30-40 seconds after the start of polishing, the polishing
temperature increased to and was maintained at about 50.degree.
C.
[0049] In addition, the removal rate (.ANG./sec) of the W film
according to polishing time (sec) was measured, and the measurement
results are shown in FIG. 2. In FIG. 2, ".quadrature." is removal
rate (RR) obtained in the case of the slurry composition of Example
7 having a silica abrasive content of 2 wt % and an oxidizing agent
content of 2 wt %, and "s" is removal rate (RR) obtained in the
case of using the slurry composition of Example 5 having a silica
abrasive content of 3 wt % and an oxidizing agent content of 3 wt
%. As can be seen in FIG. 2, during the chemical mechanical
polishing process, thermal energy was maintained constant at a
specific level rather than continuing to increase, and thus the
removal rate of the metal (W) film was also maintained constant at
a specific level. Namely, it can be seen that, when the polishing
process is carried out using the slurry composition according to
the present invention, the removal rate is maintained within a
specific range, and when the content of the abrasive particles or
the oxidizing agent increases, the polishing rate also
increases.
Experimental Example 5
Experiment for Detection of Fe Ions in Slurry Composition Using
Electrophoresis
[0050] In order to examine whether or not Fe ions are present in
slurries, a slurry containing 17 ppm of nano-ferrosilicon (FeSi) as
the non-ionized, heat-activated nano-catalyst according to the
present invention, and a slurry containing 434 ppm of ferric
nitrate (Fe(NO.sub.3).sub.3) as the prior catalyst were prepared.
Then, each of the slurries was separated into the abrasive
particles and the liquid phase using an ultra-high-speed
centrifuge. The separated liquid phase samples were collected and
injected into a column for 60 seconds and electrophoresed to detect
the presence of Fe ions in the samples. The experimental results
are shown in Table 6 below. In the above experiment, a CAPI-3200
system (Otsuka Electronics, Japan) was used as an electrophoresis
system, a column having a diameter of 75 .mu.m and a length of 50
cm was used, and an Fe.sup.3+ buffer solution was used as an
eluent. The detection limit of the system used was 1 ppm.
Meanwhile, the slurry containing 17 ppm of nano-ferrosilicon (FeSi)
was dissolved completely with an acid and analyzed by ICP-MS
(inductively coupled plasma mass spectrometry), and the analysis
results showed that the content of Fe in the slurry was 8 ppm.
TABLE-US-00006 TABLE 6 Analysis Result of Fe Samples Ions Slurry
containing 17 ppm of ND (Not-Detected) Nano-Ferrosilicon (FeSi)
Slurry containing 434 ppm of 60 ppm Ferric Nitrate (Fe(NO3)3)
[0051] As can be seen from the results in Table 6 above, Fe ions
were not present in the slurry containing the nano-ferrosilicon
(FeSi) as the non-ionized, heat-activated nano-catalyst as the
present invention, whereas a large amount of Fe ions were present
in the slurry containing ferric nitrate (Fe(NO.sub.3).sub.3).
Experimental Example 6
Experiment for Detection of Fe Ions in Slurry Solution Remaining
after CMP
[0052] After the chemical mechanical (CMP) process, in order to
examine whether or not the non-ionized, heat-activated
nano-catalyst was dissociated into ions due to the influence of
chemical and mechanical environments, an experiment for the
detection of Fe ions was carried out.
[0053] After the CMP process, in order to examine whether or not Fe
ions were generated, polishing was carried out using each of a
slurry composition containing the non-ionized, heat-activated
nano-catalyst and a slurry composition containing ferric nitrate,
the detection of Fe ions in the remaining slurry solutions was
performed. Specifically, the polishing was carried out using each
of the slurry composition of Example 5 having a silica abrasive
content of 3 wt %, an oxidizing agent content of 3 wt % and a
nano-ferrosilicon content of 17 ppm and the slurry composition of
Comparative Example 1 having a silica abrasive content of 3 wt %,
an oxidizing agent content of 3 wt % and a ferric nitrate
(Fe(NO.sub.3).sub.3) content of 434 ppm in the same conditions as
in Examples 1 to 5. Fe ions in the slurries remaining after the
polishing were analyzed and the analysis results are shown in Table
7 below. In the above experiment, CAPI-3200 was used as an analysis
system, and the Fe ions were measured at 235 nm at room temperature
by a fused silica capillary column (I.D.: 75 .mu.m, and length: 50
cm) using an Fe.sup.3+ buffer solution as a standard. The detection
limit of the system used was 1 ppm.
[0054] As shown in Table 7 indicating the results of the Fe ion
detection experiment, Fe ions were detected in Comparative Example
1 after the CMP process, whereas the presence of Fe ions was not
detected in Example 5 even after the CMP process in the same manner
as before the CMP process.
[0055] The above experimental results suggest that the
heat-activated nano-catalyst is not ionized even by the pressure
and friction occurring during the CMP process.
TABLE-US-00007 TABLE 7 Hydrogen Nano- Silica Peroxide Ferric
Nitrate Ferrosilicon Removal Fe Contents Contents
(Fe(NO.sub.3).sub.3) (FeSi) Rate Ions (wt %) (wt %) Contents (ppm)
Contents (ppm) (.ANG./min) (ppm) Example 5 3.0 3.0 None 17 1,152
N.D. Comp. Ex. 1 3.0 3.0 434 None 1,000 10.6
Experimental Example 7
Experiment for Detection of Impurities on Wafer Surface after
CMP
[0056] In order to examine whether or not Fe ions were detected in
slurries, a wafer was polished using each of a slurry composition
containing the non-ionized, heat-activated nano-catalyst and a
slurry composition containing ferric nitrate, and then the
detection of impurities on the wafer surface was conducted. As the
slurry composition containing the non-ionized, heat-activated
nano-catalyst, the slurry composition of Example 5 having a silica
abrasive content of 3 wt %, an oxidizing agent content of 3 wt %
and a nano-ferrosilicon content of 17 ppm was used, and as the
slurry composition containing ferric nitrate, the slurry
composition of Example 1 having a silica abrasive content of 3 wt
%, an oxidizing agent content of 3 wt % and a ferric nitrate
(Fe(NO.sub.3).sub.3) of 434 ppm was used.
[0057] The above polishing process was carried out using the same
method, machine and conditions as in Examples 1 to 5. Specifically,
the polishing process was carried out using a Frex-200 CMP Polisher
(Ebara, Japan) as a polishing machine and IC 1000 (Rohm & Haas,
USA as a polishing pad, and the polishing conditions were as
follows: a pad pressure of 200 hPa, a pad rotation speed of 90 rpm,
and a slurry flow rate of 150 ml/min. Under the above polishing
conditions, a tungsten wafer having a 0.8 .mu.m-thick tungsten film
formed thereon was polished.
[0058] After the polishing process, the wafer was washed with
deionized water (DIW) and rinsed with dilute ammonia solution, and
then impurities on the wafer surface were measured using TXRF 3750
(Rigaku). The detection limit of the measurement system used was
10.sup.8 atoms/cm.sup.2. After the wafer had been polished by CMP
using each of the slurry composition containing the non-ionized,
heat-activated nano-catalyst and the slurry composition containing
ferric nitrate, impurities on the wafer surface were measured.
TABLE-US-00008 TABLE 8 Unit: .times.10.sup.10 Atoms/cm.sup.2
Samples Na Mg Al Cr Mn Fe Ni Co Cu Zn reference.sup.Note 1) N.D N.D
N.D 2.8 N.D 4.7 2.1 N.D 0.6 1.8 (Blanket Wafer) Slurry containing
Non-Ionized, N.D N.D N.D 2.4 N.D 5.2 2.4 N.D N.D N.D Heat-Activated
Nano-Catalyst Slurry containing Ferric Nitrate 48.7 72.4 10.1 2.7
0.2 197.2 2.3 N.D 6.2 13.4 .sup.Note 1)Reference shows measurement
results for impurities on a clean blanket wafer surface before
CMP.
[0059] As can be seen in Table 8, in the case of the slurry
containing the non-ionized, heat-activated nano-catalyst,
precipitates of Fe ions, etc., which cause substrate contamination
during the CMP process, did not act as impurities on the wafer,
unlike the case of the slurry containing ferric nitrate. In
addition, a very small increase in the amounts of Fe and Ni metals
was presumed to be attributable to mechanical action in the
polishing process, and any substantial increase in impurities
caused by ionization did not was not shown in the materials other
than Fe and Ni.
Experimental Example 8
Experiment for Detection of Fe Ions in Slurry Compositions Using
EPR
[0060] In order to examine whether or not Fe ions are present in
slurries, the slurry composition (Example 5) containing 17 ppm of
nano-ferrosilicon (FeSi) as the non-ionized, heat-activated
nano-catalyst according to the present invention, and the slurry
composition (Comparative Example 1) containing 434 ppm of ferric
nitrate (Fe(NO.sub.3).sub.3) as the prior art catalyst were
freeze-dried to prepare solid samples. The presence of Fe ions in
the samples was analyzed using EPR (electron paramagnetic
resonance) at X-band microwave frequency (9.3 GHz) at a magnetic
field modulation of 100 kHz, and the analysis results are shown in
FIG. 3. In the above experiment, Bruker E500 was used in the EPR
analysis.
[0061] As can be seen from FIG. 3, the analysis results of EPR data
on the slurry containing nano-ferrosilicon as the non-ionized,
heat-activated nano-catalyst according to the present invention and
on the slurry containing ferric nitrate (Fe(NO.sub.3).sub.3)
revealed that the presence of Fe ions (Fe.sup.3+) in the slurry of
the present invention was not detected and the difference between
the inventive slurry and the prior slurry was evident.
Example 9
Analysis of Binding State of Heat-Activated Nano-Catalyst (FeSi)
using XPS (X-Ray Photoelectron Spectroscopy)
[0062] In order to analyze the binding state of the heat-activated
nano-catalyst, nano-ferrosilicon as the non-ionized, heat-activated
nano-catalyst according to the present invention, and commercially
available ferroaluminum (FeAl), cobalt amuminate (CoAl) and cobalt
silicate (CoSi) were prepared as solid samples (size of 7.times.7
mm to 10.times.10 mm). Alka radiation sources having a spot size of
60-800 .mu.m were used as X-ray photons in a ultra-high vacuum
(UHV). In the above experiment, a PHI 5800 ESCA system was used as
the XPS system.
[0063] As can be seen in FIG. 4 showing analysis results for the
binding state of FeSi, the presence of synthesized FeSi could be
found in a wide scan region, and a narrow scan region showed that
FeSi was present in a bound state.
[0064] Although the present invention has been described in detail
with reference to the specific features, it will be apparent to
those skilled in the art that this description is only for a
preferred embodiment and does not limit the scope of the present
invention. Thus, the substantial scope of the present invention
will be defined by the appended claims and equivalents thereof.
* * * * *