U.S. patent application number 16/765586 was filed with the patent office on 2020-10-01 for polishing composition comprising polishing particles having high water affinity.
This patent application is currently assigned to NISSAN CHEMICAL CORPORATION. The applicant listed for this patent is NISSAN CHEMICAL CORPORATION. Invention is credited to Eiichiro ISHIMIZU, Shigeru MITSUI, Tohru NISHIMURA.
Application Number | 20200308448 16/765586 |
Document ID | / |
Family ID | 1000004940101 |
Filed Date | 2020-10-01 |
United States Patent
Application |
20200308448 |
Kind Code |
A1 |
MITSUI; Shigeru ; et
al. |
October 1, 2020 |
POLISHING COMPOSITION COMPRISING POLISHING PARTICLES HAVING HIGH
WATER AFFINITY
Abstract
A polishing composition having silica-based abrasive grains and
a polishing method. A polishing composition having silica
particles, wherein on the basis of a colloidal silica dispersion of
the silica particles, the dispersion has an Rsp of 0.15 to 0.7 as
measured using pulse NMR, and the colloidal silica particles have a
shape coefficient SF1 of 1.20 to 1.80, wherein Rsp is calculated
based on equation (1): Rsp=(Rav-Rb)/(Rb) (1) (wherein Rsp is an
index that indicates water affinity; Rav is an inverse of a
relaxation time of the colloidal silica dispersion; and Rb is an
inverse of a relaxation time of a blank aqueous solution obtained
by removing the silica particles from the colloidal silica
dispersion), and the shape coefficient SF1 is calculated based on
equation (2): SF1=(area of a circle whose diameter is a maximum
diameter of the particle)/(projected area) (2).
Inventors: |
MITSUI; Shigeru;
(Funabashi-shi, JP) ; NISHIMURA; Tohru;
(Funabashi-shi, JP) ; ISHIMIZU; Eiichiro;
(Funabashi-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISSAN CHEMICAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NISSAN CHEMICAL CORPORATION
Tokyo
JP
|
Family ID: |
1000004940101 |
Appl. No.: |
16/765586 |
Filed: |
October 31, 2019 |
PCT Filed: |
October 31, 2019 |
PCT NO: |
PCT/JP2019/042889 |
371 Date: |
May 20, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/30625 20130101;
C09G 1/02 20130101 |
International
Class: |
C09G 1/02 20060101
C09G001/02; H01L 21/306 20060101 H01L021/306 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2018 |
JP |
2018-206414 |
Claims
1. A polishing composition comprising silica particles, wherein on
the basis of a colloidal silica dispersion of the silica particles,
the dispersion has an Rsp of 0.15 to 0.7 as measured using pulse
NMR, and the colloidal silica particles have a shape coefficient
SF1 of 1.20 to 1.80, wherein Rsp is calculated based on equation
(1): Rsp=(Rav-Rb)/(Rb) (1) (wherein Rsp is an index that indicates
water affinity; Ray is an inverse of a relaxation time of the
colloidal silica dispersion; and Rb is an inverse of a relaxation
time of a blank aqueous solution obtained by removing the silica
particles from the colloidal silica dispersion), and the shape
coefficient SF1 is calculated based on equation (2): SF1=(area of a
circle whose diameter is a maximum diameter of the
particle)/(projected area) (2).
2. The polishing composition according to claim 1, wherein the
colloidal silica dispersion has an average particle diameter of 40
to 200 nm as measured by a dynamic light scattering method, and the
silica particles in the dispersion have an average primary particle
diameter of 10 to 80 nm as measured by a nitrogen gas adsorption
method.
3. The polishing composition according to claim 1, wherein the
colloidal silica dispersion is obtained by being subjected to a
thermal history at a temperature of 110.degree. C. or higher and
lower than 150.degree. C., in particle growth of activated silica
under alkaline conditions in the presence of potassium ions.
4. The polishing composition according to claim 1, further
comprising at least one additive selected from the group consisting
of an acid component, an alkali component, a water-soluble
compound, a chelating agent, an oxidizing agent, and a metal
corrosion inhibitor.
5. The polishing composition according to claim 4, wherein the
alkali component is potassium hydroxide or potassium hydrogen
carbonate, or a mixture of potassium hydroxide or potassium
hydrogen carbonate with sodium hydroxide, ammonia, primary ammonium
hydroxide, secondary ammonium hydroxide, tertiary ammonium
hydroxide, quaternary ammonium hydroxide, primary ammonium
carbonate, secondary ammonium carbonate, tertiary ammonium
carbonate, quaternary ammonium carbonate, primary ammonium hydrogen
carbonate, secondary ammonium hydrogen carbonate, tertiary ammonium
hydrogen carbonate, quaternary ammonium hydrogen carbonate, lithium
carbonate, sodium carbonate, potassium carbonate, lithium hydrogen
carbonate, or sodium hydrogen carbonate.
6. The polishing composition according to claim 4, wherein the
chelating agent is an aminocarboxylic acid-based chelating agent or
a phosphonic acid-based chelating agent.
7. The polishing composition according to claim 1, wherein the
polishing composition has a pH of 1 to 12.
8. The polishing composition according to claim 1, wherein the
polishing composition is used to polish a silicon wafer or a device
wafer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing composition
comprising silica-based abrasive grains and a polishing method.
BACKGROUND ART
[0002] Polishing compositions comprising silica-based abrasive
grains have been used to polish silicon wafers.
[0003] As a multilayer interconnection has been recently formed on
the surface of a semiconductor substrate, in the formation of a
device, an integrated circuit is produced by embedding a silicon
oxide film or a metal interconnection in a stepped substrate,
planarizing it, and further applying lithography to the planarized
surface to provide a multilayer interconnection. As a pattern has
become more integrated, the pattern has become even more
miniaturized. The chemical ray used for lithography is now a
near-ultraviolet ray, a far-ultraviolet ray, or an
extreme-ultraviolet ray. The resist exposure wavelength has also
become shorter, i.e., 248 nm, 193 nm, 157 nm, or 13.6 nm. Even
electron beam lithography is now being used. When lithography is
applied many times to form a multilayer interconnection, if a short
wavelength is used as the exposure wavelength used for lithography,
the polishing surface must be planarized to a high level;
otherwise, the exposure light produces a diffuse reflection at the
interface between the resist and the substrate on that surface, and
a rectangular resist pattern cannot be formed. As a result, the
resist pattern cannot be transferred onto the underlayer.
[0004] Thus, it is essential to not only improve the polishing
speed of the silicon oxide film, but also to reduce scratch
formation or defects on the polishing surface.
[0005] These polishing compositions each contain silica-based
abrasive grains, an alkali component, a water-soluble compound, a
chelating agent, an oxidizing agent, a metal corrosion inhibitor,
and the like in an aqueous medium.
[0006] A polishing composition is disclosed in which silica
particles used as abrasive grains are defined using a function that
indicates the affinity with water, which is determined from the
relationship between the inverse of a relaxation time in pulse NMR
and the total surface area of the silica particles (see Patent
Document 1).
[0007] A polishing composition is disclosed which is defined in
terms of the relationship between the BET specific surface area and
the specific surface area measured by the pulse NMR method of
silica particles contained in abrasive grains (see Patent Document
2).
[0008] Polishing compositions are disclosed for which the solvent
affinity of abrasive grains is evaluated using an NMR relaxation
time (see Patent Documents 3 and 4).
PRIOR ART DOCUMENTS
Patent Documents
[0009] Patent Document 1: WO 2018/116890
[0010] Patent Document 2: WO 2015/152151
[0011] Patent Document 3: Japanese Unexamined Patent Application
Publication No. 2017-117894 (JP 2017-117894 A)
[0012] Patent Document 4: WO 2018/012174
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0013] In the present invention, attention was given to the
affinity with an aqueous medium of silica particles used as
abrasive grains, in the aqueous medium of a polishing composition,
and the value of a parameter used as an index of the affinity was
defined. Then, it was found that a combination of an optimal value
of the affinity with a shape of the silica particles can improve
the polishing speed, and achieve a good polishing surface.
Accordingly, it is an object of the present invention to achieve a
high polishing speed when the polishing composition is used for CMP
polishing of a device wafer, and reduce the formation of
defects.
Means for Solving the Problems
[0014] A first aspect of the present invention is a polishing
composition comprising silica particles, wherein on the basis of a
colloidal silica dispersion of the silica particles, the dispersion
has an Rsp of 0.15 to 0.7 as measured using pulse NMR, and the
colloidal silica particles have a shape coefficient SF1 of 1.20 to
1.80, wherein Rsp is calculated based on equation (1):
Rsp=(Rav-Rb)/(Rb) (1)
[0015] (wherein Rsp is an index that indicates water affinity; Rav
is an inverse of a relaxation time of the colloidal silica
dispersion; and Rb is an inverse of a relaxation time of a blank
aqueous solution obtained by removing the silica particles from the
colloidal silica dispersion), and
[0016] the shape coefficient SF1 is calculated based on equation
(2):
SF1=(area of a circle whose diameter is a maximum diameter of the
particle)/(projected area) (2);
[0017] a second aspect of the present invention is the polishing
composition according to the first aspect, wherein the colloidal
silica dispersion has an average particle diameter of 40 to 200 nm
as measured by a dynamic light scattering method, and the silica
particles in the dispersion have an average primary particle
diameter of 10 to 80 nm as measured by a nitrogen gas adsorption
method;
[0018] a third aspect of the present invention is the polishing
composition according to the first or second aspect, wherein the
colloidal silica dispersion is obtained by being subjected to a
thermal history at a temperature of 110.degree. C. or higher and
lower than 150.degree. C., in particle growth of activated silica
under alkaline conditions in the presence of potassium ions;
[0019] a fourth aspect of the present invention is the polishing
composition according to any one of the first to third aspects,
further comprising at least one additive selected from the group
consisting of an acid component, an alkali component, a
water-soluble compound, a chelating agent, an oxidizing agent, and
a metal corrosion inhibitor;
[0020] a fifth aspect of the present invention is the polishing
composition according to the fourth aspect, wherein the alkali
component is potassium hydroxide or potassium hydrogen carbonate,
or a mixture of potassium hydroxide or potassium hydrogen carbonate
with sodium hydroxide, ammonia, primary ammonium hydroxide,
secondary ammonium hydroxide, tertiary ammonium hydroxide,
quaternary ammonium hydroxide, primary ammonium carbonate,
secondary ammonium carbonate, tertiary ammonium carbonate,
quaternary ammonium carbonate, primary ammonium hydrogen carbonate,
secondary ammonium hydrogen carbonate, tertiary ammonium hydrogen
carbonate, quaternary ammonium hydrogen carbonate, lithium
carbonate, sodium carbonate, potassium carbonate, lithium hydrogen
carbonate, or sodium hydrogen carbonate; a sixth aspect of the
present invention is the polishing composition according to the
fourth aspect, wherein the chelating agent is an aminocarboxylic
acid-based chelating agent or a phosphonic acid-based chelating
agent;
[0021] a seventh aspect of the present invention is the polishing
composition according to any one of the first to sixth aspects,
wherein the polishing composition has a pH of 1 to 12; and
[0022] an eighth aspect of the present invention is the polishing
composition according to any one of the first to seventh aspects,
wherein the polishing composition is used to polish a silicon wafer
or a device wafer.
Effects of the Invention
[0023] In the present invention, attention was given to the
affinity with an aqueous medium (water affinity) of silica
particles used as abrasive grains, in the aqueous medium of a
polishing composition, and the value of a parameter used as an
index of the affinity was defined. Then, it could be found that a
combination of an optimal value of the affinity with a shape of the
silica particles can improve the polishing speed, and reduce
defects formed on the polishing surface. Defect formation is caused
by scratch formation or adhesion of foreign matter on a stepped
substrate. While the cause of scratch formation has not been
elucidated, some scratches are considered to result from the
abrasive grains, and others from the object to be polished, and
these scratches can exist together.
[0024] When lithography is applied to an upper layer after
planarization of the polishing surface, the formation of defects
(minute foreign matter having a size of several tens of nanometers
or more that remains on the substrate after polishing) may cause
the resist exposure light to produce a diffuse reflection, or cause
a defocus failure, which prevents the formation of a rectangular
pattern. Moreover, when a substrate is processed, such defects may
form a mask to produce etching resistance, which causes a substrate
processing failure, resulting in a defect in the production of a
semiconductor element. It is therefore necessary to reduce
defects.
[0025] Improvement in polishing speed and planarization of the
polishing surface have been effects that trade off with each other,
and difficult to achieve both; however, both these effects that
trade off with each other can be achieved by providing the silica
particles with water affinity in a specific range and a shape in a
specific range.
[0026] A polishing composition contains silica particles as
polishing abrasive grains. The silica particles have effect on the
polishing speed and the planarization property for the polishing
surface, through an interaction with an aqueous medium in the
polishing composition, depending on the surface condition.
[0027] The state of water involved in the surface of the silica
particles used as polishing abrasive grains in the polishing
composition is divided into bound water and free water. Free water
refers to the water that is present around the silica particles,
but is not bound therewith and present in a free state, and not the
water as a solvent. Bound water refers to the water bound with the
silica particles by hydrogen bonding with silanol groups on the
silica particle surface. Bound water plays an important role in
ensuring good contact of the silica particles with water.
[0028] The state of the water can be grasped by measuring the
relaxation time of the protons of water molecules.
[0029] Relaxation involves the process in which absorbed energy is
emitted; and the process in which the phases of precession of
nuclear spins are disordered from the aligned state. The former is
denoted as spin-lattice relaxation (longitudinal relaxation), and
the relaxation time is denoted as T1; and the latter is denoted as
spin-spin relaxation (transverse relaxation), and the relaxation
time is denoted as T2. In T1 relaxation, relaxation is most likely
to occur when the speed of molecular motion is approximately the
same as the resonant frequency. The response time to a change in
magnetic field, that is, the relaxation time, differs between free
water molecules not in contact with the silica particles and water
molecules in contact with the silica particles. A shorter
relaxation time is considered to indicate greater particle surface
in contact with water, and higher dispersibility of the
particles.
[0030] In T2 relaxation, relaxation occurs through a magnetic
interaction. The measurement of relaxation time using pulse NMR can
be regarded as the measurement method that utilizes the difference
in T2 relaxation.
[0031] During polishing, the presence of the bound water in a
specific range of amounts functions effectively to improve the
polishing speed, and reduce scratches and defects on the polishing
surface. Moreover, the shape of the silica particles also has
effect on the presence of the bound water in a specific range of
amounts, and the shape factor (shape coefficient SF1) needs to fall
in a specific range of values.
[0032] The shape factor (shape coefficient SF1) of the silica
particles is also greatly related to the polishing speed. When the
shape of the silica particles changes from a spherical to a
different shape, the number of contacts with the surface to be
polished is considered to increase, which improves the polishing
speed. In contrast, the possibility of scratch formation also
increases. Thus, the shape factor (shape coefficient SF1) also
preferably falls in a specific range.
[0033] In the present invention, by controlling the shape factor
(shape coefficient SF1) and the affinity with an aqueous medium of
the silica particles used as polishing abrasive grains to a high
level, it is possible to achieve an improvement in polishing speed
and a scratch reduction (defect reduction), particularly in CMP
polishing.
MODES FOR CARRYING OUT THE INVENTION
[0034] The present invention is a polishing composition comprising
silica particles, wherein on the basis of a colloidal silica
dispersion of the silica particles, the dispersion has a
measurement value of pulse NMR, namely, Rsp=(Rav-Rb)/(Rb), of 0.15
to 0.7, 0.35 to 0.7, or 0.35 to 0.65, and
[0035] the silica particles have a shape coefficient, namely,
SF1=(area of a circle whose diameter is a maximum diameter of the
particle)/(projected area), of 1.20 to 1.80, 1.23 to 1.80, or 1.24
to 1.60,
[0036] wherein Rsp is an index that indicates water affinity; Rav
is an inverse of a relaxation time of the colloidal silica
dispersion; and Rb is an inverse of a relaxation time of a blank
aqueous solution obtained by removing the silica particles from the
colloidal silica dispersion.
[0037] The colloidal silica dispersion has an average particle
diameter of 40 to 200 nm or 30 to 150 nm as measured by a dynamic
light scattering method, and the silica particles in the dispersion
have an average primary particle diameter of 10 to 80 nm or 20 to
70 nm as measured by a nitrogen gas adsorption method.
[0038] The measurement principle of the technique used herein
(pulse NMR) is based on the fact that solvent molecules that are in
contact with or adsorbed on the particle surface and solvent
molecules in the solvent bulk (solvent molecules in a free state
that are not in contact with the particle surface) respond
differently to a change in magnetic field. In general, the motion
of liquid molecules adsorbed on the particle surface is restricted,
while liquid molecules in the bulk liquid can move freely. As a
result, the NMR relaxation time of the liquid molecules adsorbed on
the particle surface is shorter than the relaxation time of the
molecules in the bulk liquid.
[0039] The relaxation time measured in the dispersion of the
particles is the average value of two relaxation times that reflect
the volume concentration of the liquid on the particle surface and
the volume concentration of the liquid in a free state (liquid that
is in the bulk liquid, but is not adsorbed on the particle
surface).
[0040] It is noted here that a relaxation time constant R is the
inverse of a relaxation time T, and is determined based on the
equation:
Rac=PsRs+PbRb
[0041] Rav: average relaxation time constant, that is, the inverse
of the relaxation time of the colloidal silica dispersion;
[0042] Ps: volume concentration of the liquid on the particle
surface, that is, the volume concentration of the colloidal silica
dispersion;
[0043] Rs: relaxation time constant of adsorbed-phase liquid
molecules onto the particle surface, that is, the inverse of the
relaxation time of the colloidal silica dispersion;
[0044] Pb: volume concentration of the bulk liquid, that is, the
volume concentration of a blank aqueous solution obtained by
removing the silica particles from the colloidal silica dispersion;
and
[0045] Rb: relaxation time constant of bulk liquid molecules, that
is, the inverse of the relaxation time of the blank aqueous
solution obtained by removing the silica particles from the
colloidal silica dispersion.
[0046] The measurement value of pulse NMR of the dispersion can be
determined based on the equation: Rsp=(Rav-Rb)/(Rb).
[0047] Ray and Rb are each the inverse of a relaxation time
(transverse relaxation time T2; specifically, an NMR relaxation
time obtained after the silica abrasive grains are dispersed and an
NMR relaxation time obtained before the silica abrasive grains are
dispersed (only the dispersion medium)) measured using a pulse NMR
system, Acorn area, manufactured by Xigo nanotools Inc. (USA). The
measurement conditions may be as follows: magnetic field: 0.3 T,
measurement frequency: 13 MHz, measurement nucleus: .sup.1H NMR,
measurement method: CPMG pulse sequence method, sample volume: 0.4
mL, temperature: 30.degree. C.
[0048] Rsp serves as an index of the water affinity of the particle
surface. When the specific surface area is the same, a higher value
(Rsp) indicates higher water affinity. The shape coefficient SF1
can be determined based on the equation: (area of a circle whose
diameter is a maximum diameter of the particle)/(projected
area).
That is, SF1=(D.sub.L.sup.2.times.7.pi./4)/S
[0049] D.sub.L is the maximum diameter nm of the particle, the
maximum length (nm) of the silica particle determined based on a
transmission electron micrograph, and is the greatest length
between given two points on the circumference in the micrograph;
and
[0050] S is the projected area (nm.sup.2) of the silica
particle.
[0051] D.sub.L is the maximum length of the silica particle
determined based on image analysis of a transmission electron
micrograph (TEM), and S is the projected area of the silica
particle determined based on image analysis of the transmission
electron micrograph. Specifically, a transmission electron
micrograph taken at a magnification of 10,000 or 30,000 times is
captured as electronic data into an image analysis apparatus (trade
name LUZEX manufactured by Nireco Corporation) at a resolution of
146 dpi, and the projected area is determined by converting the
number of pixels occupied by the silica particle to area. For
example, in a micrograph with a magnification of 10,000 times, the
length of one side of a pixel is 17.8 nm; therefore, the area per
pixel can be converted as 319 nm.sup.2. In a micrograph with a
magnification of 30,000 times, the length of one side of a pixel is
6.0 nm; therefore, the area per pixel can be converted as 36
nm.sup.2.
[0052] SF1 is determined by determining the maximum length D.sub.L
and the projected area S for each of 300 particles recognized by
the image analysis apparatus, calculating, for each particle, a
calculation value based on the equation shown above, and obtaining
an average value of the calculation values.
[0053] The method for producing the colloidal silica dispersion
(silica sol) to be used in the present invention can be broadly
divided into a step (I) of obtaining activated silica; a step (II)
of heating and regulating the size of the activated silica; and a
step (III) of adjusting the concentration of the resulting silica
sol.
[0054] The step (I) of obtaining activated silica is divided into a
step (a) of obtaining activated silica; a step (a1) of increasing
the purity of the activated silica; and a step (a2) of collecting
the activated silica with an increased purity. The step (a) is
essential, and the steps (a1) and (a2) are optional.
[0055] For example, the step (a) is the step of contacting a
hydrogen-type strongly acidic cation exchange resin with an aqueous
solution of an alkali metal silicate in which an aqueous alkali
metal silicate containing 300 to 10,000 ppm of a metal oxide other
than silica, based on the silica content, is dissolved at a
concentration of 1 to 6% by weight, as the SiO.sub.2 content
derived from the silicate, to thereby produce an aqueous solution
of activated silica having a SiO.sub.2 concentration of 1 to 6% by
mass, and collecting the resulting solution.
[0056] The step (II) of heating and regulating the size of the
activated silica includes the following steps (b) and (c):
[0057] step (b): adding an aqueous solution of potassium hydroxide
to the aqueous solution of the activated silica collected in the
step (a) to produce a stabilized aqueous solution of the activated
silica having a SiO.sub.2 concentration of 1 to 6% by mass, and
having a pH of 7 to 9; and
[0058] step (c): supplying, with sufficient stirring, an aqueous
solution of an alkali metal silicate obtained by adding an aqueous
solution of potassium hydroxide to the aqueous solution of the
activated silica collected in the step (b) or an aqueous solution
of an alkali metal silicate having a pH of 10 to 12.5 and a
SiO.sub.2 concentration of 0.1 to 8% by weight obtained by
concentrating or diluting the aqueous solution obtained above, and
an aqueous solution of activated silica obtained as in the step
(b), while maintaining the temperature of the resulting mixture at
110.degree. C. to lower than 150.degree. C., 110 to 145.degree. C.,
110 to 140.degree. C., 110 to 135.degree. C., or 110 to 130.degree.
C., in a period of 1 to 30 hours, until the pH of the mixture
reaches 9 to 12.
[0059] The step (III) of adjusting the concentration of the
resulting silica sol is the step of concentrating the silica sol to
a concentration of 10 to 50% by mass, wherein impurities may be
removed from the silica sol before or after being concentrated. The
step (III) is not essential, but may be performed as required.
[0060] For example, the step (III) includes:
[0061] a step (d): contacting the stable aqueous silica sol
obtained in the step (c) with a hydrogen-type strongly acidic
cation exchange resin, and then contacting an aqueous silica sol
produced by this contact with a hydroxyl group-type strongly basic
anion exchange resin to thereby produce an acidic aqueous silica
sol substantially free of a polyvalent metal oxide other than
silica; and
[0062] a step (e): adding ammonia or potassium hydroxide to the
acidic aqueous sol produced in the step (d) such that the pH of the
sol becomes 8 to 11 to thereby produce a stable aqueous silica sol
having a SiO.sub.2 concentration of 10 to 50% by mass or 30 to 50%
by mass, substantially free of a polyvalent metal oxide other than
silica, and having an average particle diameter of the colloidal
silica of 10 to 30 nm.
[0063] In the step (a), it is preferred to use sodium water glass
having a SiO.sub.2/Na.sub.2O molar ratio of about 2 to 4, which is
available as an inexpensive industrial product. Polyvalent metals
typically contained at relatively high concentrations as impurities
include aluminum, iron, calcium, and magnesium. The aqueous
solution of the alkali metal silicate is contacted with the
hydrogen-type strongly acidic cation exchange resin. This contact
may be preferably performed by passing the aqueous solution of the
alkali metal silicate through a column packed with the ion exchange
resin, and the solution that has passed through the column is
collected as an aqueous solution of activated silica having a
SiO.sub.2 concentration of 1 to 6% by mass, preferably 2 to 6% by
mass. The hydrogen-type cation exchange resin may be used in an
amount sufficient to exchange the total amount of alkali metal ions
in the aqueous solution of the alkali metal silicate with hydrogen
ions. The aqueous solution of the alkali metal silicate is
preferably passed through the column at a space velocity of about 1
to 10 per hour.
[0064] Examples of the strong acid used in the step (a1) include
inorganic acids, such as hydrochloric acid, nitric acid, and
sulfuric acid. Nitric acid is the most preferred to improve the
removal ratio of the aluminum content and the iron content.
[0065] In the step (a2), initially, the aqueous solution obtained
in the step (a1) is contacted with the hydrogen-type strongly
acidic cation exchange resin. This contact may be preferably
performed by passing the aqueous solution through a column packed
with the hydrogen-type strongly acidic cation exchange resin at a
space velocity of 2 to 20 per hour, at 0 to 60.degree. C.,
preferably 5 to 50.degree. C. Subsequently, the aqueous solution
obtained by passage through the column is contacted, preferably
immediately after being obtained, with the hydroxyl group-type
strongly basic anion exchange resin, at 0 to 60.degree. C.,
preferably 5 to 50.degree. C.
[0066] The aqueous solution of potassium hydroxide used in the step
(b) is obtained by dissolving potassium hydroxide as a commercially
available industrial product preferably having a purity of 95% or
more in ion exchange water or industrial water from which cations
have been removed, to give a concentration of preferably 2 to 20%
by mass.
[0067] As the apparatus used in the step (c), a usual container
that is acid-resistant, alkali-resistant, and pressure-resistant,
equipped with a stirrer, a temperature controller, a liquid level
sensor, a pressure-reducing device, a liquid supply device, the
cooling device, and the like, may be used.
[0068] In the step (c), the liquid temperature inside the container
is maintained at 110.degree. C. to lower than 150.degree. C.
[0069] The contact between the stable aqueous sol and the ion
exchange resin in the step (d) may be performed as in the contact
in the step (a).
[0070] Ammonia or potassium hydroxide used in the step (e) may be a
commercially available industrial product, which preferably has a
high purity. In the case of ammonia, it is preferably used as
aqueous ammonia having a concentration of about 5 to 28% by mass.
Instead of ammonia, quaternary ammonium hydroxide, guanidine
hydroxide, a water-soluble amine, or the like may be used. In the
present invention, potassium hydroxide can be suitably used.
[0071] In the present invention, the polishing composition may
further comprise, in addition to the silica particles as abrasive
grains and the aqueous medium, at least one additive selected from
the group consisting of an alkali component, a water-soluble
compound, a chelating agent, an oxidizing agent, and a metal
corrosion inhibitor.
[0072] The solids content excluding the aqueous medium from the
polishing composition is 0.01 to 20% by mass or 0.1 to 10% by mass,
and the content of the silica particles in the solids content is 90
to 100% by mass or 90 to 99.9% by mass.
[0073] Examples of the alkali component include potassium hydroxide
or potassium hydrogen carbonate, or a mixture of potassium
hydroxide or potassium hydrogen carbonate with sodium hydroxide,
ammonia, primary ammonium hydroxide, secondary ammonium hydroxide,
tertiary ammonium hydroxide, quaternary ammonium hydroxide, lithium
carbonate, sodium carbonate, potassium carbonate, lithium hydrogen
carbonate, or sodium hydrogen carbonate.
[0074] It is preferred to use potassium hydroxide or potassium
hydrogen carbonate. An alkali component other than those mentioned
above may be used in combination at a mass ratio in the range of
10% or less, relative to potassium hydroxide or potassium hydrogen
carbonate.
[0075] By adding these alkali components, the pH can be adjusted in
the range of 7 to 12 or 8 to 11.
[0076] Any water-soluble compound may be used as the water-soluble
compound. Examples of the water-soluble compound include monomers
having carboxylic acid groups, such as acrylic acid, methacrylic
acid, and maleic acid, polymers thereof, such as polyacrylic acid
and polymethacrylic acid, and salts thereof, such as ammonium
polyacrylate, potassium polyacrylate, ammonium polymethacrylate,
and potassium polymethacrylate. Moreover, alginic acid, pectic
acid, carboxymethyl cellulose, polyaspartic acid, polyglutamic
acid, polyamide acid, polyamide acid ammonium salt, polyvinyl
pyrrolidone, hydroxyethyl cellulose, glycerin, polyglycerin,
polyvinyl alcohol, or carboxyl group- or sulfonic acid
group-modified polyvinyl alcohol can be used.
[0077] The content of the water-soluble compound may be 0.01 to 10%
by mass based on the silica particles.
[0078] As the chelating agent, an aminocarboxylic acid-based
chelating agent or a phosphonic acid-based chelating agent may be
used. The content of the chelating resin may be 0.01 to 10% by mass
based on the silica particles.
[0079] Examples of the oxidizing agent include hydrogen peroxide,
nitric acid, potassium periodate, hypochlorous acid, and ozone
water. The content of the oxidizing agent may be 0.01 to 10% by
mass based on the silica particles.
[0080] Examples of the metal corrosion inhibitor include triazole
compounds, pyridine compounds, pyrazole compounds, pyrimidine
compounds, imidazole compounds, guanidine compounds, thiazole
compounds, tetrazole compounds, triazine compounds, and
hexamethylenetetramine.
[0081] Examples of triazole compounds include 1,2,3-triazole,
1,2,4-triazole, 3-amino-1H-1,2,4-triazole, benzotriazole (BTA),
1-hydroxybenzotriazole, 1-hydroxypropylbenzotriazole,
2,3-dicarboxypropylbenzotriazole, 4-hydroxybenzotriazole,
4-carboxy-1H-benzotriazole, 4-carboxy-1H-benzotriazole methyl ester
(methyl 1H-benzotriazole-4-carboxylate), 4-carboxy-1H-benzotriazole
butyl ester (butyl 1H-benzotriazole-4-carboxylate),
4-carboxy-1H-benzotriazole octyl ester (octyl
1H-benzotriazole-4-carboxylate), 5-hexylbenzotriazole,
(1,2,3-benzotriazolyl-1-methyl) (1,2,4-triazolyl-1-methyl)
(2-ethylhexyl)amine, tolyltriazole, naphthotriazole,
bis[(1-benzotriazolyl)methyl]phosphonic acid,
3H-1,2,3-triazolo[4,5-b]pyridin-3-ol,
1H-1,2,3-triazolo[4,5-b]pyridine,
1-acetyl-1H-1,2,3-triazolo[4,5-b]pyridine, 3-hydroxypyridine,
1,2,4-triazolo[1,5-a]pyrimidine,
1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine,
2-methyl-5,7-diphenyl-[1,2,4]triazolo[1,5-a]pyrimidine,
2-methylsulfanyl-5,7-diphenyl-[1,2,4]triazolo[1,5-a]pyrimidine, and
2-methylsulfanyl-5,7-diphenyl-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidin-
e.
[0082] Examples of pyridine compounds include pyridine,
8-hydroxyquinoline, protionamide, 2-nitropyridin-3-ol,
pyridoxamine, nicotinamide, iproniazid, isonicotinic acid,
benzo[f]quinoline, 2,5-pyridinedicarboxylic acid, 4-styrylpyridine,
anabasine, 4-nitropyridine-1-oxide, ethyl 3-pyridylacetate,
quinoline, 2-ethylpyridine, quinolinic acid, arecoline, citrazinic
acid, pyridine-3-methanol, 2-methyl-5-ethylpyridine,
2-fluoropyridine, pentafluoropyridine, 6-methylpyridin-3-ol, and
ethyl 2-pyridylacetate.
[0083] Examples of pyrazole compounds include pyrazole,
1-allyl-3,5-dimethylpyrazole, 3,5-di(2-pyridyl)pyrazole,
3,5-diisopropylpyrazole, 3,5-dimethyl-1-hydroxymethylpyrazole,
3,5-dimethyl-1-phenylpyrazole, 3,5-dimethylpyrazole,
3-amino-5-hydroxypyrazole, 4-methylpyrazole, N-methylpyrazole, and
3-aminopyrazole.
[0084] Examples of pyrimidine compounds include pyrimidine,
1,3-diphenyl-pyrimidine-2,4,6-trione, 1,4,5,6-tetrahydropyrimidine,
2,4,5,6-tetraaminopyrimidine sulfate, 2,4,5-trihydroxypyrimidine,
2,4,6-triaminopyrimidine, 2,4,6-trichloropyrimidine,
2,4,6-trimethoxypyrimidine, 2,4,6-triphenylpyrimidine,
2,4-diamino-6-hydroxylpyrimidine, 2,4-diaminopyrimidine,
2-acetamidopyrimidine, 2-aminopyrimidine, and
4-aminopyrazolo[3,4-d]pyrimidine.
[0085] Examples of imidazole compounds include imidazole,
1,1'-carbonylbis-1H-imidazole, 1,1'-oxalyldiimidazole,
1,2,4,5-tetramethylimidazole, 1,2-dimethyl-5-nitroimidazole,
1,2-dimethylimidazole, 1-(3-aminopropyl)imidazole,
1-butylimidazole, 1-ethylimidazole, 1-methylimidazole, and
benzimidazole.
[0086] Examples of guanidine compounds include guanidine,
1,1,3,3-tetramethylguanidine, 1,2,3-triphenylguanidine,
1,3-di-o-tolylguanidine, and 1,3-diphenylguanidine.
[0087] Examples of thiazole compounds include thiazole,
2-mercaptobenzothiazole, and 2,4-dimethylthiazole.
[0088] Examples of tetrazole compounds include tetrazole,
5-methyltetrazole, 5-amino-1H-tetrazole, and
1-(2-dimethylaminoethyl)-5-mercaptotetrazole.
[0089] Examples of triazine compounds include triazine and
3,4-dihydro-3-hydroxy-4-oxo-1,2,4-triazine.
[0090] The metal corrosion inhibitor may be added to give a content
of 0.0001 to 10% by mass based on the silica particles.
[0091] The polishing composition of the present invention can be
used to polish a semiconductor wafer or a semiconductor device.
[0092] CMP (Chemical Mechanical Polishing) is used to polish the
semiconductor device. CMP can be adopted to form an interconnection
on a semiconductor substrate. Examples of the object to be polished
include a conductive material layer (interconnection layer), a
barrier layer (layer composed of a barrier metal, for example,
titanium nitride, tantalum nitride, or the like for preventing
copper from diffusing into an insulating layer), and an insulating
layer (layer composed of an interlayer insulating material, for
example, a low-k material, such as SiO.sub.2, SiOC, or porous
silica).
[0093] More specifically, examples of the material constituting the
conductive material layer include copper-based metals, such as
copper, copper alloys, copper oxides, and copper alloy oxides;
tungsten-based metals, such as tungsten, tungsten nitride, and
tungsten alloys; cobalt-based metals, such as cobalt, cobalt
alloys, cobalt oxides, and cobalt alloy oxides; silver; and gold.
Among the above, at least one copper-based metal selected from the
group consisting of copper, copper alloys, copper oxides, and
copper alloy oxides is preferred, and copper is more preferred. The
conductive material can be formed using a known method such as a
sputtering method, a plating method, or the like.
[0094] The barrier metal constituting the barrier layer is formed
to prevent the conductive material from diffusing into the
insulating material, and improve the adhesion between the
insulating material and the conductive material. The barrier metal
material constituting the barrier metal is preferably at least one
selected from the group consisting of tantalum-based metals,
titanium-based metals, tungsten-based metals, ruthenium-based
metals, cobalt-based metals, and manganese-based metals.
Specifically, examples include tantalum-based metals, such as
tantalum, tantalum nitride, and tantalum alloys; titanium-based
metals, such as titanium, titanium nitride, and titanium alloys;
tungsten-based metals, such as tungsten and tungsten alloys;
ruthenium-based metals, such as ruthenium and ruthenium alloys;
cobalt-based metals, such as cobalt and cobalt alloys; and
manganese-based metals, such as manganese and manganese alloys.
[0095] Examples of the material constituting the insulating
material include silicon-based materials and organic polymers. The
insulating material may be in the form of a film (an insulating
film; for example, an interlayer insulating film). Examples of the
insulating film include a silicon-based coating and an organic
polymer film. The insulating film can be formed using a CVD method,
a spin coating method, a dip coating method, a spraying method, or
the like.
[0096] Examples of the silicon-based materials include silica-based
materials and low-k materials (low dielectric constant materials).
Examples of the silica-based materials include silicon dioxide;
fluorosilicate glass; organosilicate glass obtained using
trimethylsilane or dimethoxydimethylsilane as a starting material;
porous organosilicate glass; silicon oxynitride; and hydrogenated
silsesquioxane.
[0097] Examples of the low-k materials include silicon carbide and
silicon nitride.
[0098] A polishing method according to the present invention is
performed, for example, as follows: A conductive thin film composed
of a conductive material is formed on a silicon substrate. A resist
film is formed on the conductive film, and the resist layer is
exposed and developed with a circuit pattern as a mask by means of
lithography to transfer the pattern onto the resist layer. With the
transferred pattern as a mask, the conductive film is dry etched
with a highly anisotropic ionic gas. Examples of the gas that can
be used include tetrafluoromethane (CF.sub.4), perfluorocyclobutane
(C.sub.4F.sub.8), perfluoropropane (C.sub.3F.sub.8),
trifluoromethane, carbon monoxide, argon, oxygen, nitrogen, sulfur
hexafluoride, difluoromethane, nitrogen trifluoride and chlorine
trifluoride, chlorine, and trichloroborane and dichloroborane.
[0099] Then, the resist film is ashed with oxygen gas to remove the
resist layer. Alternatively, the resist layer may be removed with a
chemical (for example, a mixture of sulfuric acid and hydrogen
peroxide or a mixture of ammonia and hydrogen peroxide) to protect
the substrate.
[0100] Subsequently, an insulating film is formed to prevent a
short circuit with an upper-layer interconnection. The pattern of
an underlayer interconnection is reflected on the wafer surface on
which the interlayer insulating film is formed, and irregularities
of various sizes are formed on the insulating film. When an
interconnection is processed by further coating the upper layer
with a resist film by means of lithography, the presence of these
irregularities causes a diffuse reflection at the interface between
the resist and the insulating film during resist exposure, which
prevents the formation of a rectangular resist pattern, which makes
the processing of the surface of the underlayer difficult. Thus,
the wafer surface is planarized. The interlayer insulating film is
planarized by CMP.
[0101] Moreover, although aluminum has been heretofore used as the
interconnection material, it has a low melting point and has
problems with reliability, such as a disconnection when a large
current flows. Thus, aluminum interconnections are being replaced
with copper interconnections. However, there is a problem in that
copper may diffuse into an insulating layer. In a damascene
process, therefore, trenches called "damascene" are formed, and
then copper is embedded in the trenches. To prevent diffusion of
copper into the insulating layer, a barrier layer may be formed
between copper and the insulating film. Because of irregularities
of copper produced by embedding copper to form a copper
interconnection layer, the planarization of the surface of the
copper interconnection layer is required to further apply
lithography to an upper layer. In the planarization of copper, dry
etching with a gas is difficult because of the hardness of copper,
and therefore, polishing by CMP is performed here again.
EXAMPLES
[0102] (Production of Activated Silica)
[0103] Step (a)
[0104] JIS No. 3 sodium water glass was prepared as a raw-material
aqueous alkali metal silicate. The water glass contained 28.8% by
weight of SiO.sub.2 and 9.47% by mass of Na.sub.2O as main
components other than water. 478 g of the water glass was dissolved
in 2,992 g of pure water to prepare 3,500 g of an aqueous solution
of sodium silicate (a). Subsequently, the aqueous solution of
sodium silicate (a) was passed through a column packed with a
hydrogen-type strongly acidic cation exchange resin, Amberlite
IR-120B, at a space velocity of 4.5 per hour, and then 3,000 g of
the resulting aqueous solution of activated silica was collected in
a container.
Synthesis Example 1
[0105] A SUS pressure-resistant container having an internal volume
of 3 L, equipped with a stirrer, a heating device, and the like,
was used as a reactor. The aqueous solution of the activated silica
(SiO.sub.2 content: 3.2% by mass), a 10% by mass aqueous solution
of potassium hydroxide, and pure water were used, and the mixture
was adjusted to pH=11.1; thereafter, the liquid temperature inside
the container was controlled to 110 to 130.degree. C. by heating.
After the temperature inside the container reached 100 to
130.degree. C., while the temperature inside the container was
being maintained at 110 to 130.degree. C., the aqueous solution of
the activated silica was further continuously supplied as a supply
solution, until the pH of the reaction solution reached 11.2.
[0106] Heating was subsequently continued for 2 hours, while the
resulting reaction solution was being maintained at 110 to
130.degree. C., to obtain a silica sol.
[0107] The resulting silica sol was concentrated to give a
SiO.sub.2 concentration of 40% by mass at room temperature, using a
commercially available ultrafiltration apparatus equipped with a
tubular polysulfone ultrafiltration membrane with a pore diameter
of about 5 nm. During concentration, the solution was stable, and
concentration was extremely smoothly performed.
Synthesis Example 2
[0108] A SUS pressure-resistant container having an internal volume
of 3 L, equipped with a stirrer, a heating device, and the like,
was used as a reactor. The aqueous solution of the activated silica
(SiO.sub.2 content: 3.2% by mass), a 10% by mass aqueous solution
of potassium hydroxide, and pure water were used, and the mixture
was adjusted to pH=11.2; thereafter, the liquid temperature inside
the container was controlled to 110 to 130.degree. C. by heating.
After the temperature inside the container reached 120 to
140.degree. C., while the temperature inside the container was
being maintained at 120 to 140.degree. C., the aqueous solution of
the activated silica was continuously supplied as a supply
solution, until the pH of the reaction solution reached 11.3. After
the supply of the aqueous solution of the activated silica, the
reaction was performed for 1 hour, while the temperature inside the
container was being maintained at 120 to 140.degree. C., and the
aqueous solution of the activated silica was further continuously
supplied as a supply solution, until the pH of the reaction
solution reached 10.9.
[0109] Heating was subsequently continued for 2 hours, while the
resulting reaction solution was being maintained at 120 to
140.degree. C., to obtain a silica sol.
[0110] The resulting silica sol was concentrated to give a
SiO.sub.2 concentration of 40% by mass at room temperature, using a
commercially available ultrafiltration apparatus equipped with a
tubular polysulfone ultrafiltration membrane with a pore diameter
of about 5 nm. During concentration, the solution was stable, and
concentration was extremely smoothly performed.
Synthesis Example 3
[0111] A SUS pressure-resistant container having an internal volume
of 3 L, equipped with a stirrer, a heating device, and the like,
was used as a reactor. The aqueous solution of the activated silica
(SiO.sub.2 content: 3.2% by mass), a 10% by mass aqueous solution
of potassium hydroxide, and pure water were used, and the mixture
was adjusted to pH=11.1; thereafter, the liquid temperature inside
the container was controlled to 110 to 130.degree. C. by heating.
After the temperature inside the container reached 110 to
130.degree. C., while the temperature inside the container was
being maintained at 110 to 130.degree. C., the aqueous solution of
the activated silica was continuously supplied for 6.0 hours as a
supply solution, until the pH of the reaction solution reached
9.6.
[0112] The resulting silica sol was concentrated to give a
SiO.sub.2 concentration of 40% by mass at room temperature, using a
commercially available ultrafiltration apparatus equipped with a
tubular polysulfone ultrafiltration membrane with a pore diameter
of about 5 nm. During concentration, the solution was stable, and
concentration was extremely smoothly performed.
Synthesis Example 4
[0113] A SUS pressure-resistant container having an internal volume
of 3 L, equipped with a stirrer, a heating device, and the like,
was used as a reactor. The aqueous solution of the activated silica
(SiO.sub.2 content: 3.2% by mass), a 10% by mass aqueous solution
of potassium hydroxide, and pure water were used, and the mixture
was adjusted to pH=12.0; thereafter, the liquid temperature inside
the container was controlled to 110 to 130.degree. C. by heating.
After the temperature inside the container reached 110 to
130.degree. C., while the temperature inside the container was
being maintained at 110 to 130.degree. C., the aqueous solution of
the activated silica obtained in the steps (a) to (c) described
above was continuously supplied as a supply solution, until the pH
of the reaction solution reached 11.4. After the supply of the
aqueous solution of the activated silica, the reaction was
performed for 1 hour, while the temperature inside the container
was being maintained at 110.degree. C., and the aqueous solution of
the activated silica was further continuously supplied as a supply
solution, until the pH of the reaction solution reached 11.1.
[0114] Heating was subsequently continued for 2 hours, while the
resulting reaction mixture was being maintained at 110 to
130.degree. C.
[0115] The resulting silica sol was concentrated to give a
SiO.sub.2 concentration of 40% by mass at room temperature, using a
commercially available ultrafiltration apparatus equipped with a
tubular polysulfone ultrafiltration membrane with a pore diameter
of about 5 nm. During concentration, the solution was stable, and
concentration was extremely smoothly performed.
Comparative Synthesis Example 1
[0116] A SUS pressure-resistant container having an internal volume
of 3 L, equipped with a stirrer, a heating device, and the like,
was used as a reactor. The aqueous solution of the activated silica
(SiO.sub.2 content: 3.2% by mass), a 10% by mass aqueous solution
of sodium hydroxide, and pure water were used, and the mixture was
adjusted to pH=7.6; thereafter, the liquid temperature inside the
container was controlled to 150 to 230.degree. C. by heating.
[0117] The resulting silica sol was heated at 150 to 200.degree. C.
for 2 to 5 hours. The resulting silica sol was diluted with pure
water to give a SiO.sub.2 concentration of 30% by mass at room
temperature.
Comparative Synthesis Example 2
[0118] Tetramethoxysilane was subjected to hydrolysis and
condensation using an alkali catalyst (ammonia) at a temperature
from room temperature (20.degree. C.) to 60.degree. C. to obtain a
silica sol.
[0119] Table 1 shows the average particle diameter (DLS particle
diameter in the unit nm) of the silica particles in each polishing
composition based on a dynamic light scattering method; the average
primary particle diameter (BET diameter in the unit nm) of the
silica particles calculated as spherical shapes, which was
converted from the specific surface area based on a nitrogen gas
adsorption method; the shape coefficient SF1 value of the silica
particles; and the Rsp value of the silica particles based on pulse
NMR.
[0120] In the table shown below, the silica sol obtained in
Synthesis Example 1 was used for Synthesis Example 1; the silica
sol obtained in Synthesis Example 2 was used for Synthesis Example
2; the silica sol obtained in Synthesis Example 3 was used for
Synthesis Example 3; the silica sol obtained in Synthesis Example 4
was used for Synthesis Example 4; the silica sol obtained in
Comparative Synthesis Example 1 was used for Comparative Synthesis
Example 1; and the silica sol obtained in Comparative Synthesis
Example 2 was used for Comparative Synthesis Example 2.
TABLE-US-00001 TABLE 1 DLS Diameter BET Diameter (nm) (nm) SF1 Rsp
Synthesis 56 20 1.60 0.61 Example 1 Synthesis 143 51 1.38 0.44
Example 2 Synthesis 30 20 1.24 0.37 Example 3 Synthesis 68 43 1.27
0.43 Example 4 Comparative 100 69 1.15 0.18 Synthesis Example 1
Comparative 19 17 1.36 1.46 Synthesis Example 2
[0121] (Preparation of Polishing Compositions)
[0122] Each of the aqueous silica sols obtained in Synthesis
Examples 1 and 2, and Comparative Synthesis Examples 1 to 4 was
adjusted to a SiO.sub.2 concentration of 5% by mass with pure
water, and adjusted to pH 10.0 with a 10% by mass aqueous solution
of potassium hydroxide, and then filtered through a cartridge
filter with a pore diameter of 0.5 .mu.m to obtain a polishing
composition.
[0123] The polishing conditions and the cleaning method were as
shown below:
[0124] [Polishing Conditions]
[0125] Polishing machine: ChaMP332 (for 12 inches) manufactured by
Tokyo Seimitsu Co., Ltd.
[0126] Processing pressure: 1.7 psi
[0127] Platen rotation speed: 90 rpm
[0128] Head rotation speed: 90 rpm
[0129] Polishing pad: Nitta&Haas IC1400XY+Perforate
[0130] Dresser: 3M A2865 (#80 diamond)
[0131] Amount of supply of the polishing diluent: 300 mL/min
[0132] Polishing time: 60 sec
[0133] Substrate: wafer with a TEOS film
[0134] [Cleaning Conditions]
[0135] Cleaning was performed with a chemical brush. Initially,
cleaning with an acid chemical was performed, rinsing with pure
water was performed next, and then drying was performed.
[0136] Polishing tests were performed in Example 1 using the silica
sol obtained in Synthesis Example 1; Example 2 using the silica sol
obtained in Synthesis Example 2; Example 3 using the silica sol
obtained in Synthesis Example 3; Example 4 using the silica sol
obtained in Synthesis Example 4; Comparative Example 1 using the
silica sol obtained in Comparative Synthesis Example 1; and
Comparative Example 2 using the silica sol obtained in Comparative
Synthesis Example 2.
[0137] [Measurement of Polishing Speed]
[0138] The polishing speed (nm/minute) was measured using the
Nanometrics optical thickness gauge NanoSpec 78300.
[0139] [Measurement of Defects]
[0140] In the measurement of the number of defects, defects with a
size of 180 nm or more were measured using Hitachi LS6700.
TABLE-US-00002 TABLE 2 Polishing Speed Number of Defects (nm/min)
(180 nm or more) Example 1 6.90 3850 Example 2 25.22 227 Example 3
2.46 2339 Example 4 4.15 2329 Comparative Example 1 1.44 10480
Comparative Example 2 0.81 1822
[0141] In each of the examples of the present invention, the silica
sol used in the polishing composition has an Rsp value based on
pulse NMR that falls in a specific range of values, and the silica
particles contained in the silica sol have a shape coefficient SF1
value that falls in a specific range of values; therefore, when the
silica sol is used as a polishing composition for CMP polishing of
a device wafer, a high polishing speed can be achieved, and the
formation of defects can be reduced. The polishing composition of
the present invention can be used not only as a polishing agent for
CMP of a device wafer, but also as a polishing agent for a silicon
wafer, because of its high polishing speed.
INDUSTRIAL APPLICABILITY
[0142] The silica sol used in the polishing composition has an Rsp
value based on pulse NMR that falls in a specific range of values,
and the silica particles contained in the silica sol have a shape
coefficient SF1 value that falls in a specific range of values;
therefore, when the silica sol is used as a polishing composition
for CMP polishing of a device wafer, a high polishing speed can be
achieved, and the formation of defects can be reduced.
* * * * *