U.S. patent application number 09/741131 was filed with the patent office on 2002-03-28 for process for forming a metal interconnect.
Invention is credited to Tsuchiya, Yasuaki, Wake, Tomoko.
Application Number | 20020037642 09/741131 |
Document ID | / |
Family ID | 18503926 |
Filed Date | 2002-03-28 |
United States Patent
Application |
20020037642 |
Kind Code |
A1 |
Wake, Tomoko ; et
al. |
March 28, 2002 |
Process for forming a metal interconnect
Abstract
This invention relates to a process for forming a metal
interconnect comprising the steps of forming a concave in an
insulating film formed on a substrate, forming a copper-containing
metal film over the whole surface such that the concave is filled
with the metal and then polishing the copper-containing metal film
by chemical mechanical polishing, characterized in that the
polishing step is conducted using a chemical mechanical polishing
slurry comprising a polishing material, an oxidizing agent and an
adhesion inhibitor preventing adhesion of a polishing product to a
polishing pad, while contacting the polishing pad to a polished
surface with a pressure of at least 27 kPa. This invention allows
us to prevent adhesion of a polishing product to a polishing pad
and to form a uniform interconnect layer with an improved
throughput, even when polishing a large amount of copper-containing
metal during a polishing step.
Inventors: |
Wake, Tomoko; (Tokyo,
JP) ; Tsuchiya, Yasuaki; (Tokyo, JP) |
Correspondence
Address: |
Paul J. Esatto, Jr.
Scully, Scott, Murphy & Presser
400 Garden City Plaza
Garden City
NY
11530
US
|
Family ID: |
18503926 |
Appl. No.: |
09/741131 |
Filed: |
December 19, 2000 |
Current U.S.
Class: |
438/633 ;
257/E21.304; 257/E21.583; 438/638; 438/687 |
Current CPC
Class: |
H01L 21/7684 20130101;
H01L 21/3212 20130101; C09G 1/02 20130101 |
Class at
Publication: |
438/633 ;
438/638; 438/687 |
International
Class: |
H01L 021/4763; H01L
021/44 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 1999 |
JP |
374482/1999 |
Claims
What is claimed is:
1. A process for forming a metal interconnect comprising the steps
of forming a concave in an insulating film formed on a substrate,
forming a copper-containing metal film over the whole surface such
that the concave is filled with the metal and then polishing the
copper-containing metal film by chemical mechanical polishing,
characterized in that the polishing step is conducted using a
chemical mechanical polishing slurry comprising a polishing
material, an oxidizing agent and an adhesion inhibitor preventing
adhesion of a polishing product to a polishing pad, while
contacting the polishing pad to a polished surface with a pressure
of at least 27 kPa.
2. The process for forming a metal interconnect as claimed in claim
1 where the adhesion inhibitor is citric acid.
3. The process for forming a metal interconnect as claimed in claim
1 where the content of the adhesion inhibitor in the chemical
mechanical polishing slurry is 0.01 wt % to 5 wt % both
inclusive.
4. The process for forming a metal interconnect as claimed in claim
1 where the chemical mechanical. polishing slurry comprises
.theta.-alumina mainly containing second particles made of
aggregated primary particles as the polishing material.
5. A process for forming a metal interconnect comprising the steps
of forming a concave in an insulating film formed on a substrate,
forming a copper-containing metal film over the whole surface such
that the concave is filled with the metal and then polishing the
copper-containing metal film by chemical mechanical polishing,
characterized in that the polishing step is conducted using a
chemical mechanical polishing slurry comprising .theta.-alumina
mainly containing secondary particles made of aggregated primary
particles as a polishing material, an oxidizing agent and an
organic acid, while contacting the polishing pad to a polished
surface with a pressure of at least 27 kPa.
6. The process for forming a metal interconnect as claimed in claim
5 where the content of the secondary particles of the
.theta.-alumina is 60 wt % or more to the total amount of the
.theta.-alumina.
7. The process for forming a metal interconnect as claimed in claim
5 where the average particle size of the secondary particles of the
.theta.-alumina is 0.05,.mu.m to 0.5, .mu.m both inclusive.
8. The process for forming a metal interconnect as claimed in claim
5, where the .theta. alumina comprises 50 wt % or more of secondary
particles with a particle size of 0.05 .mu.m to 0.5 .mu.m both
inclusive to the total amount of the secondary particles
9. The process for forming a metal interconnect as claimed in claim
5 where primary and secondary particles with a particle size of
more than 2 .mu.m are substantially absent in the
.theta.-alumina.
10. The process for forming a metal interconnect as claimed in
claim 5 where the average particle size of the primary particles of
the .theta.-alumina is 0.005 .mu.m to 0.1 .mu.m both inclusive.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a process for forming an electric
interconnect made of a copper-containing metal by chemical
mechanical polishing.
[0003] 2. Description of the Prior Art
[0004] With regard to forming a semiconductor integrated circuit
such as ULSI which has been significantly refined and compacted,
copper has been expected to be a useful material for electric
connection because of its good electromigration resistance and
lower electrical resistance.
[0005] To date a copper interconnect is; formed as follows due to
problems such as difficulty in patterning by dry etching.
Specifically, a concave such as a groove and a connection hole is
formed in an insulating film, a barrier metal film is formed on the
surface, a copper film is deposited over the whole surface by
plating such that the concave is filled with the material, and then
the surface is polished to be flat by chemical mechanical polishing
(hereinafter, referred to as "CMP") until the surface of the
insulating film except the concave area is completely exposed, to
form electric connections such as a damascene interconnect in which
the concave is filled with copper, a via plug and a contact
plug.
[0006] There will be described a process for forming a damascene
copper interconnect with reference to FIG. 1.
[0007] As shown in FIG. 1(a), on a first interlayer insulating film
1 in which a lower-layer interconnect 2 is formed are sequentially
formed a silicon nitride film 3 and a second interlayer insulating
film 4. Then in the second interlayer insulating film 4 is formed a
concave having an interconnect pattern, in a part of which is
formed a connecting hole reaching the lower-layer interconnect
2.
[0008] Then, as shown in FIG. 1(b), a barrier metal film 5 is
formed by sputtering. On the whole surface of the film is formed a
copper film 6 by plating such that the concave is filled with the
material. The thickness of the plating is larger than the sum of
the depth of the groove, the depth of the connecting hole and a
manufacturing dispersion in the plating step.
[0009] As shown in FIG. 1(c), the copper film 6 is polished by CMP
using a polishing pad in the presence of a polishing slurry to make
the substrate surface flat. polishing is continued until the metal
over the second insulating film 4 is completely removed, as shown
in FIG. 1(d).
[0010] A slurry for CMP for polishing copper generally comprises an
oxidizing agent and polishing grains. A basic mechanism is that the
copper surface is etched by chemical action of the oxidizing agent
while the oxidized surface layer is mechanically removed by
polishing grains.
[0011] Primary particles of .alpha.-alumina with an average
particle size (diameter) of several hundred nm have been
conventionally used as polishing grains used in a polishing slurry
having a large polishing rate for a copper film, because primary
particles having a desired average particle size can be easily
manufactured and have a higher polishing rate.
[0012] As a semiconductor device has been more refined and more
integrated, leading to a more complicated device structure, and as
there has been increased the layer number of a multilayer aiming at
reduction in an interconnect length for dealing with increase in an
interconnect resistance associated with refinement of an
interconnect or a multilayer in a logic system, a substrate surface
has been more bumpy and its level difference has been larger. An
upper interconnect in a multilayer interconnect is used for a
source interconnect, a signal interconnect or a clock interconnect,
and therefore, an interconnect groove must be deeper for improving
some properties by reducing resistances in these interconnects. As
a result, an interlayer insulating film formed on such a substrate
surface has become thicker and thus it has been necessary to form a
thick copper film by which a deep concave can be filled, for
forming a damascene conductive part such as a damascene copper
interconnect or via plug in a thick interlayer insulating film. For
reducing a resistance of a refined interconnect or reducing a
resistance of a signal or clock interconnect to improve a
conduction speed, it is necessary to form an interconnect which is
thick in a depth direction, so that a thick copper film is formed
for providing a deep concave. When a source interconnect is formed
with a damascene copper interconnect, a thick copper film is formed
for reducing a resistance of the source interconnect for minimizing
a potential change. While conventionally a copper film with a
thickness of about several hundred nm has been adequately useful,
several thousand nm may be sometimes required for a copper
film.
[0013] When forming a damascene conductive part by forming such a
thick copper film, the amount of copper to be removed by polishing
during one CMP step increases, so that a large amount of polishing
scrape such as copper or copper oxide adheres to and is accumulated
on the surface of a polishing pad. As a result, a polishing rate
may become too low to continue polishing or a polished surface
cannot be uniform. It is now needed to make a wafer larger for
improving a productivity. However, as a wafer becomes larger, an
area of a copper film increases, and therefore the amount of copper
to be removed by polishing has been increasing. A polishing scrapes
such as copper or copper oxide generated during polishing a copper
metal film is herein designated a "polishing product".
[0014] A surface plate in a CMP apparatus cannot be so large in the
light of factors such as ensuring in-plane uniformity of the
surface plate, even diffusivity of a dropped polishing slurry,
limitation in an area where the CMP apparatus is placed,
workability in replacing a polishing pad and ensuring cleanliness
in a clean room.
[0015] Increase of the amount of polished copper reduces a
throughput at the same polishing rate as that for a thinner film.
It is, therefore, necessary to increase a polishing rate for
copper. Increase of a polishing rate for copper, however, leads to
a large amount of polishing product in a short time, so that
adhesion of copper to the surface of the polishing pad becomes more
significant.
[0016] When a large amount of polishing product adheres to the
surface of the polishing pad as described above, the polishing pad
must be washed or replaced after every polishing, and furthermore,
polishing must be repeated after washing or replacing the polishing
pad, resulting in significant reduction in a throughput.
[0017] When a contact pressure (polishing pressure) of the
polishing pad to the polished surface for increasing a polishing
rate and improving uniformity in the polished surface, adhesion of
the polishing product to the surface of the polishing pad may cause
inadequate in-plane uniformity in the polished surface as well as
may enhance adhesion of the polishing product to the surface of the
polishing pad.
[0018] JP-A 10-116804 has demonstrated the problem that copper ions
generated during CMP are accumulated on a polishing pad and again
adhere to a wafer surface to deteriorate uniformity of the wafer
surface and cause electric short-circuit, and has described that
the problem can be solved by using a polishing composition
comprising a re-adhesion inhibitor such as benzotriazole in CMP.
The publication has mentioned the problem due to re-adhesion of
copper ions on the wafer surface, but there are no descriptions for
the above due to adhesion of a polishing product to a pad surface.
Benzotriazole used as a re-adhesion inhibitor may act as an
antioxidant (J. B. Cotton, Proc. 2nd Intern. Congr. Metallic
Corrosion, (1963) p.590; D. Chadwick et al., Corrosion Sci., 18,
(1978) p.39; T. Notodani, Bousei Kanri, 26(3) (1982), p.74; H.
Okabe ed., "Sekiyu Seihin Tenkazai no Kaihatsu to Saishin Gijutsu"
(1998), CMC, p.77-82), there is a limitation to the amount of the
agent for reducing a polishing rate for copper. Furthermore,
benzotriazole is originally added for preventing dishing (JP-As
8-83780 and 11-238709). When prevention of dishing is given
priority, the amount of the agent is limited.
[0019] JP-A 10-46140 has described a polishing composition
comprising a particular carboxylic acid, an oxidizing agent and
water whose pH is adjusted by an alkali to 5 to 9. Examples in the
publication have disclosed a polishing composition containing
citric acid as a carboxylic acid and aluminum oxide as a polishing
material (Example 7). However, this publication has described only
improvement in a polishing rate and prevention of occurring dishing
associated with a corrosion mark as an effect of addition of a
carboxylic acid such as citric acid.
[0020] JP-A 11-21546 has disclosed a polishing process using a
slurry for chemical mechanical polishing comprising urea, a
polishing material, an oxidizing agent, a film-forming agent and a
complex-forming agent. Examples in this publication have described
alumina as a polishing material, hydrogen peroxide as an oxidizing
agent, benzotriazole as a film-forming agent and citric acid as a
complex-forming agent. The publication, however, has described only
that addition of the complex-forming agent is effective for
disturbing a passive layer formed by a film-forming agent such as
benzotriazole and for limiting a depth of an oxidizing layer.
[0021] JP-A 10-44047 has described that polishing grains may be
aggregates of a metal oxide with a size distribution of less than
about 1.0 .mu.m and an average aggregate diameter of less than
about 0.4 .mu.m, or separate spherical particles of a metal oxide
comprising primary particles of less than 0.4, .mu.m. Objectives of
the invention described in the publication are, however, to prevent
surface defects or contamination due to CMP, to form a uniform
metal layer and a uniform film, and to control selectivity between
a barrier film and an insulating film. There are no descriptions
about problems caused by adhesion of a polishing product to a
polishing pad surface in the publication. In addition, the
publication has listed common precipitated alumina or fumed alumina
as an alumina polishing material, but has not mentioned
.theta.-alumina at all. Furthermore, copper is listed only as a
connection material and in its examples, only Al is used.
[0022] JP-A 10-163141 has described .theta.-alumina as polishing
grains. This publication, however, has described .theta.-alumina as
an example of an aluminum oxide together with other aluminas such
as .alpha.-alumina, but has not mentioned secondary particles of
.theta.-alumina at all. The invention described in the publication
is for preventing scratches or dishing and for providing a
polishing composition with a proper selectivity and exhibiting good
storage stability, and there are no descriptions about preventing
adhesion of a polishing product to a, polishing pad surface.
SUMMARY OF THE INVENTION
[0023] An objective of this invention is to provide a process for
forming a metal interconnect, which can prevent adhesion of a
polishing product to a polishing pad and form a uniform
interconnect layer with an improved throughput, even when polishing
a large amount of copper-containing metal during a polishing
step.
[0024] This invention provides a process for forming a metal
interconnect comprising the steps of forming a concave in an
insulating film formed on a substrate, forming a copper-containing
metal film over the whole surface such that the concave is filled
with the metal and then polishing the copper-containing metal film
by chemical mechanical polishing, characterized in that the
polishing step is conducted using a chemical mechanical polishing
slurry comprising a polishing material, an oxidizing agent and an
adhesion inhibitor preventing adhesion of a polishing product to a
polishing pad, while contacting the polishing pad to a polished
surface with a pressure of at least 27 kPa.
[0025] This invention also provides a process for forming a metal
interconnect comprising the steps of forming a concave in an
insulating film formed on a substrate, forming a copper-containing
metal film over the whole surface such that the concave is filled
with the metal and then polishing the copper-containing metal film
by chemical mechanical polishing, characterized in that the
polishing step is conducted using a chemical mechanical polishing
slurry comprising .theta.-alumina mainly containing secondary
particles made of aggregated primary particles as a polishing
material, an oxidizing agent and an organic acid, while contacting
the polishing pad to a polished surface with a pressure of at least
27 kPa.
[0026] As used herein, the term "a copper-containing metal" means
copper or an alloy mainly containing copper, and the term "a
concave" means a groove for forming a damascene interconnect or a
connection hole such as a contact hole and a through hole. The term
"an insulating film formed on a substrate" includes an interlayer
insulating film formed on a lower interconnect layer.
[0027] This invention allows us to prevent adhesion of a polishing
product to a polishing pad and to form a uniform interconnect layer
with an improved throughput, even when polishing a large amount of
copper-containing metal during a polishing step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a process cross section illustrating a process for
forming a damascene copper interconnect.
[0029] FIG. 2 is a schematic configuration of a chemical mechanical
polishing apparatus.
[0030] FIG. 3 shows variation in a particle size of .theta.-alumina
plotted to a dispersion time.
[0031] FIG. 4 is a graph showing variation in an in-plane
uniformity (k value) plotted to a polishing pressure.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0032] Preferred embodiments of this invention will be
described.
[0033] The polishing step in the process for forming a metal
interconnect is conducted using a chemical mechanical polishing
slurry (hereinafter, referred to as a "polishing slurry")
comprising citric acid as an adhesion inhibitor preventing adhesion
of a polishing product to a polishing pad or .theta.-alumina mainly
containing secondary particles made of primary particles as a
polishing material (hereinafter, referred to as "secondary-particle
containing .theta.-alumina"). CMP using such a polishing slurry
allows us to prevent adhesion of a polishing product to a polishing
pad and to continue satisfactory polishing without discontinuing
polishing operation, even when polishing a thick or large
copper-containing metal film, i.e., when polishing a large amount
of copper-containing metal during one polishing operation.
Furthermore, adhesion of a polishing product to a polishing pad may
be inhibited. Therefore, a contact pressure of the polishing pad to
a polished surface may be increased to increase a polishing rate as
well as to adequately improve in-plane uniformity of the polished
surface. As a result, there may be provided a uniform interconnect
with a small dispersion of its resistance.
[0034] In a chemical mechanical polishing slurry, a carboxylic
acid, an organic acid, has been used as a proton donor for
improving a polishing rate, and citric acid has been known only as
a kind of such a carboxylic acid. We have conducted intense
investigation for solving the above problems and have found that
adhesion of a polishing product to a polishing pad may be prevented
by adding citric acid in a polishing slurry, to achieve this
invention.
[0035] In a chemical mechanical polishing slurry for polishing a
copper-containing metal film, .alpha.-alumina consisting of primary
particles is generally used as alumina as a polishing material. We
have investigated, among various aluminas, .theta.-alumina and have
found that particular .theta.-alumina mainly comprising secondary
particles may be used as a polishing material to prevent adhesion
of a polishing product to a polishing pad, and finally to achieve
this invention.
[0036] CMP in this invention using the above polishing slurry may
satisfactorily polish a substrate on which a copper-containing
metal film is formed without pad contamination, even when polishing
the copper-containing metal with a polishing amount of
2.times.10.sup.-4 g/cm.sup.2 or more, further 1.times.10.sup.-3
g/cm.sup.2 or more, further 1.times.10.sup.-2 g/cm.sup.2 or more
per a unit area of the polishing pad in one polishing operation.
For example, when forming a damascene conductive part in which the
sum of an interconnection thickness and a depth of a connection
hole is about 1.5 .mu.m, in forming an upper interconnect in a
multilayer interconnect structure, it is necessary to form a copper
film with a thickness of about 2.0 .mu.m or more, resulting in a
large amount of copper film per a unit area of the polishing
pad.
[0037] A polishing pad used in polishing such a large amount of
copper metal may be one made of a common porous urethane resin.
[0038] A polishing slurry used in this invention comprises, as a
basic composition, a polishing material, an oxidizing agent, an
organic acid and water. In this basic composition, the slurry
comprises citric acid to be an adhesion inhibitor as an organic
acid or .theta.-alumina mainly containing secondary particles made
of aggregated primary particles (secondary-particle containing
.theta.-alumina) as a polishing material. In this basic
composition, the slurry may comprise both citric acid and
secondary-particle containing .theta.-alumina as a polishing
material. An antioxidant may be further contained for preventing
dishing or controlling a polishing rate.
[0039] The content of citric acid in the polishing slurry used in
this invention is preferably at least 0.01 wt%, more preferably at
least 0.05 wt % to the total amount of the slurry composition for
achieving adequate adhesion-inhibiting effect, and is preferably 5
wt % or less, more preferably 3 wt % or less in the light of, e.g.,
thixotropic nature of the polishing slurry.
[0040] In CMP using a polishing slurry containing citric acid, a
polishing waste was bluish green. It may indicate that there would
be formed a complex of copper ion eluted due to ionization by the
action of the oxidizing agent with citric acid in the polishing
slurry to prevent a copper compound from adhering to a polishing
pad or polished surface as a polishing product, resulting in
discharge of the copper component removed by polishing.
[0041] The content of secondary particles in the secondary-particle
containing .theta.-alumina is preferably at least 60 wt %, more
preferably at least 65 wt %,, further preferably at least 70 wt %
to the total amount of the secondary-particle containing
.theta.-alumina for more completely preventing adhesion of a
polishing product to a polishing pad.
[0042] An average particle size (diameter) of the secondary
particles is preferably at least 0.05 .mu.m, more preferably at
least 0.07 .mu.m. further preferably at least 0.08 .mu.m. As its
upper limit it is preferably 0.5 .mu.m or less, more preferably 0.4
.mu.m or less;, further preferably 0.3 .mu.m or less.
[0043] A proportion of secondary particles with a particle size of
0.05 .mu.m to 0.5 .mu.m both inclusive in the total amount of
secondary-particle .theta.-alumina is preferably at least 50 wt %,
more preferably at least 55 wt %, further preferably at least 60 wt
%.
[0044] In addition, it is desirable that secondary-particle
containing .theta.-alumina substantially contains neither primary
nor secondary particles having a particle size of more than 2
.mu.m, more preferably more than 1.5 .mu.m, further preferably more
than 1 .mu.m.
[0045] An average particle size of primary particles constituting
secondary-particle .theta.-alumina described above is preferably at
least 0.005 .mu.m, more preferably at least 0.007 .mu.m, further
preferably at least 0.008 .mu.m. As an upper limit it is preferably
0.1 9 .mu.m or less, more preferably 0.09 .mu.m or less, further
preferably 0.08 .mu.m or less.
[0046] An average particle size of primary particles constituting
secondary-particle containing .theta.-alumina in this invention is
considerably smaller than that of primary particles of
.alpha.-alumina commonly used as a conventional polishing grains.
An average particle size of secondary particles consisting of such
primary particles may be, therefore, adjusted to about that of
primary particles of the conventional .alpha.-alumina. When
conducting CMP using a polishing slurry comprising such
.theta.-alumina mainly containing the secondary particles
(secondary-particle containing .theta.-alumina) as a main component
in polishing grains, a polishing product generated after mechanical
removal is small because a contact area is small between a polished
surface of copper and a primary particle constituting a secondary
particle. Furthermore, a polishing product generated is further
pulverized to provide a finer polishing product by spaces between
primary particles constituting secondary particles or an irregular
surface.
[0047] Secondary-particle containing .theta.-alumina has a larger
surface area than a primary particle of a conventional
.alpha.-alumina. It, therefore, exhibits good dispersibility, which
may prevent forming a giant particle due to association of
secondary particles. Thus, it may prevent generation of a large
size polishing product from a polished surface due to scratching by
a giant particle.
[0048] As described above, in CMP using a polishing slurry
comprising secondary-particle containing .theta.-alumina, a
polishing product generated is so small that clogging with the
polishing product can be minimized in the polishing pad surface
while a fine polishing product can be readily washed out by the
polishing slurry which is continuously fed. Thus, polishing pad
contamination can be prevented even when a large amount of copper
is removed by polishing.
[0049] In CMP using the above polishing slurry, scratches in a
polished surface may be also prevented in addition to effect of
inhibiting polishing pad contamination. Since secondary-particle
containing .theta.-alumina can be deformed by a polishing load from
a polishing pad, stress concentration can be avoided in a contact
area between the polished surface and a primary particle
constituting a secondary particle. Consequently, the polished
surface may not be significantly removed and thus may prevent
scratches.
[0050] .theta.-alumina has a Mohs'hardness of 7 while
.alpha.-alumina has 9. In other words, .theta.-alumina has a lower
hardness than .alpha.-alumina, and has a proper hardness for
polishing a soft metal such as copper, leading to prevention of
scratches.
[0051] Furthermore, a secondary particle in secondary-particle
containing .theta.-alumina has a large surface area and thus
exhibits good dispersibility, and a primary particle is extremely
small. The polishing slurry used in this invention, therefore, has
a property of good long term stability.
[0052] An average particle size of polishing grains, a proportion
of grains having a particular range of particle size and a maximum
particle size may be estimated by determining a particle size
distribution of polishing grains by a light scattering method and
statistically processing the particle size distribution obtained.
Furthermore, a particle size distribution of polishing grains may
be determined by measuring a particle size for an adequately large
number of polishing grains using an electron microscope.
[0053] .theta.-alumina may be prepared by removing crystal water
from a colloid made of an Al-containing salt hydrate or hydroxide
by heating under controlling a programming rate. A secondary
particle is an aggregate formed by fusion of contact parts in
primary particles during heating. Since it is possible to prepare
fine colloid particles whose particle size is controlled in
preparation of .theta.-alumina, fine primary particles having an
average particle size and a particle size distribution suitable to
this invention may be prepared. It may, therefore, allow us to form
secondary particles of .theta.-alumina having a similar particle
size to primary particles of conventional .alpha.-alumina.
Furthermore, since a binding strength of fusion between primary
particles formed during heating is within a proper range,
dispersion under appropriate conditions may break a bond between
several primary particles to form secondary particles with a
particle size suitable to this invention.
[0054] Secondary-particle containing .theta.-alumina used in this
invention may be prepared by dispersing .theta.-alumina prepared as
described above into a dispersive medium under appropriate
conditions. .theta.-alumina prepared by heating a colloid consists
of giant aggregates with an average particle size of about 10 L m,
consisting of a number of fused primary particles. It is added to
an aqueous medium within a range of 10 wt % to 70 wt % both
inclusive. A dispersing agent may be, if necessary, added within a
range of 0.01 wt % to 10 wt %. The amounts of .theta.-alumina and
the dispersing agent affect a particle size of secondary particles
obtained.
[0055] Dispersion may be conducted using, for example, an
ultrasonic disperser, a bead mill disperser, a ball mill disperser
or a kneader disperser. Among these, a bead mill or ball mill
disperser may be preferably used because it may stably form
secondary particles with a desirable particle size. Furthermore, a
filter mechanism may be provided to the disperser for removing
particles with a particle size of more than 2, .mu.m.
[0056] A dispersion time, which affects a secondary particle size
distribution, is preferably at least 140 min, more preferably at
least 150 min, further preferably at least 180 min for providing
secondary particles with a highly monodisperse particle size
distribution. In the light of preventing contamination with foreign
matters, as its upper limit it is preferably 400 min or less, more
preferably 350 min or less, further preferably 300 min or less.
[0057] A dispersing agent may consist of at least one of surfactant
and aqueous polymer types of dispersing agents.
[0058] Examples of surfactant dispersing agents include anionic,
cationic, ampholytic and nonionic surfactants. Anionic surfactants
which may be used include soluble salts of sulfonic acids,
sulfates, carboxylic acids, phosphates and phosphonic acids; for
example, sodium alkylbenzenesulfonate (ABS), sodium dodecylsulfate
(SDS), sodium stearate and sodium hexamethaphosphate. Cationic
surfactants include amine salts containing a salt-forming primary,
secondary or tertiary amine and their modified salts; onium
compounds such as quaternary ammonium, phosphonium and sulfonium
salts; circular nitrogen-containing compounds such as pyridinium,
quinolinium and imidazolinium salts; and heterocyclic compounds;
for example, cetyl-trimethyl-ammonium chloride (CTAC),
cetyl-trimethyl-ammonium bromide (CTAB), cetylpyridinium chloride,
dodecylpyridinium chloride, alkyl-dimethylchlorobenzyl-ammonium
chloride and alkyl-naphthalene-pyridinium chloride.
[0059] Nonionic surfactants include products of addition
polymerization of a fatty acid with ethylene oxide such as
polyethyleneglycol fatty acid esters, polyoxyethylene alkyl ethers,
polyoxyethylene alkylphenyl ethers; ether types of nonionic
surfactants; and polyethyleneglycol condensation types of
surfactants; for example, POE (10) monolaurate, POE (10)
monostearate, POE (25) monostearate, POE (40) monostearate, POE
(45) monostearate, POE (55) monostearate, POE(21) lauryl ether,
POE(25) lauryl ether, POE(15) cetyl ether, POE(20) cetyl ether,
POE(23) cetyl ether, POE(25) cetyl ether, POE(30) cetyl ether,
POE(40) cetyl ether, POE(20) stearyl ether, POE(2) nonyl phenyl
ether, POE(3) nonyl phenyl ether, POE(2) nonyl phenyl ether, POE(7)
nonyl phenyl ether, POE(10) nonyl phenyl ether, POE(15) nonyl
phenyl ether, POE(18) nonyl phenyl ether, POE(20) nonyl phenyl
ether, POE(10) octyl phenyl ether, POE(30) octyl phenyl ether,
POE(6) sorbitan monooleate, POE(20) sorbitan monooleate, POE(6)
sorbitan 20 monolaurate, POE(20) sorbitan monolaurate, POE(20)
sorbitan monopalmitate, POE(6) sorbitan monostearate, POE( 20)
sorbitan monostearate, POE(20) sorbitan tristearate, POE(20)
sorbitan trioleate, POE(6) sorbitan monooleate and POE(20) sorbitan
monooleate, wherein POE represents polyoxyethylene and a number in
parentheses is the number of the repeating unit
--CH.sub.2CH.sub.2O--.
[0060] Amphoteric surfactants include which may be used include
compounds intramolecularly having at least one anion-forming atomic
group selected from --COOH, --SO.sub.3H, --OSO.sub.3H and
--OPO.sub.3H.sub.2 groups and cation-forming atomic group selected
from primary, secondary and tertiary amine groups and quaternary
ammonium groups; for example, betaines, sulfobetaines and
sulfatebetaines; more specifically, lauryl dimethylaminoacetate
betaine and sodium N-acyl-palm oil fatty
acid-N-carboxymethyl-N-hydroxyethylenediamine.
[0061] Aqueous polymer dispersing agents include ionic and nonionic
polymers. Ionic polymers include alginic acid and its salts,
polyacrylic acid and its salts, a polycarboxylic acid and its
salts, cellulose, carboxymethylcellulose and
hydroxylethylcellulose. Nonionic polymers include polyvinyl
alcohol, polyvinylpyrrolidone, polyethylene glycol and
polyacrylamide.
[0062] A weight-average molecular weight of an aqueous polymer
dispersing agent is preferably at least 100, more preferably at
least 500, further preferably at least 1000. As its upper limit it
is preferably 100000 or less, more preferably 80000 or less,
further preferably 50000 or less. A weight-average molecular weight
within the range may inhibit increase in a viscosity of a slurry
obtained to provide secondary-particles with a good particle size
distribution.
[0063] As long as it does not adversely affect the effects of
secondary-particle containing .theta.-alumina, additional polishing
grains may be used, which includes aluminas such as .alpha.-alumina
and .delta.-alumina other than .theta.-alumina; silicas such as
fumed silica and colloidal silica; titania; zirconia; germania;
ceria; and a mixture of two or more selected from these metal oxide
polishing grains.
[0064] The content of secondary-particle containing .theta.-alumina
is preferably at least 1 wt%, more preferably at least 3 wt % to
the total amount of the chemical mechanical polishing slurry. As
its upper limit it is 30 wt % or less, more preferably 10 wt % or
less. When the polishing slurry contains two or more types of
polishing grains, the sum of the contents of individual polishing
grains is preferably at least 1 wt %, more preferably at least 3 wt
%, and as its upper limit it is preferably 30 wt % or less, more
preferably 10 wt % or less.
[0065] When using a polishing slurry comprising citric acid in this
invention, a polishing material may be, instead of the above
secondary-particle containing .theta.-alumina, aluminas such as
commonly used .alpha.-alumina, .theta.-alumina and .delta.-alumina;
silicas such as fumed silica and colloidal silica; titania;
zirconia; germania; ceria; and a combination of two or more
selected from these metal oxide polishing grains. An average
particle size of such a polishing material is preferably at least 5
nm, more preferably at least 50 nm, and also preferably 500 nm or
less, more preferably 300 nm or less as determined by a light
scattering diffraction technique, in the light of a polishing rate,
dispersion stability and surface roughness of a polished surface. A
particle size distribution is preferably 3 .mu.m or less, more
preferably 1 .mu.m or less for the maximum particle size
(d100).
[0066] The content of a polishing material in a polishing slurry
may be appropriately selected within the range of 0.1 to 50 wt % to
the total amount of the slurry composition in the light of factors
such as a polishing efficiency and polishing accuracy. It is
preferably at least 1 wt %, more preferably at least 2 wt %,
further preferably at least 3 wt %, and as its upper limit it is
preferably 30 wt % or less, more preferably 10 wt % or less,
further preferably 8 wt % or less.
[0067] In the light of a polishing rate and corrosion, a slurry
viscosity and dispersion stability of a polishing material, a
polishing slurry used in this invention has a pH of preferably at
least 4, more preferably at least 5 and preferably 8 or less, more
preferably 7 or less. Too high pH may cause dissociation of citric
acid which leads to reduction in its complex-forming capacity with
a polishing product and its adhesion-inhibiting effect, so that the
polishing product tends to adhere to a polishing pad. On the other
hand, too low pH may excessively increase a polishing rate for
copper, leading to deterioration in a surface shape of a copper
interconnect, i.e., a recession, which may often cause a step.
[0068] For the polishing slurry, pH may be adjusted by a known
technique. For example, an alkali may be directly added to a slurry
in which polishing grains are dispersed and a carboxylic acid is
dissolved. Alternatively, a part or all of an alkali to be added
may be added as a carboxylic acid alkali salt. Examples of an
alkali which may be used include alkali metal hydroxides such as
sodium hydroxide and potassium hydroxide; alkali metal carbonates
such as sodium carbonate and potassium carbonate; ammonia; and
amines.
[0069] The oxidizing agent may be appropriately selected from known
water-soluble oxidizing agents in the light of a type of a
conductive metal film, polishing accuracy and a polishing
efficiency. For example,, those which may not cause heavy-metal ion
contamination include peroxides such as H.sub.2O.sub.2,
Na.sub.2O.sub.2, Ba.sub.2O.sub.2 and
(C.sub.6H.sub.5C).sub.2O.sub.2; hypochlorous acid (HC10);
perchloric acid; nitric acid; ozone water; and organic acid
peroxides such as peracetic acid and nitrobenzene. Among these,
hydrogen peroxide (H.sub.2O.sub.2) is preferable because it does
not contain a metal component and does not generate a harmful
byproduct. The content of the oxidizing agent in the polishing
slurry used in this invention is preferably at least 0.01 wt %,
more preferably at least 0.05 wt %, further preferably at least 0.1
wt % for achieving adequate effects of its addition while it is
preferably 15 wt % or less, more preferably 10 wt % or less for
preventing dishing and adjusting a polishing rate to a proper
value. When using an oxidizing agent which is relatively
susceptible to deterioration with age such as hydrogen peroxide, it
may be possible to separately prepare a solution containing an
oxidizing agent at a given concentration and a composition which
provides a given polishing slurry after addition of the solution
containing an oxidizing agent, which are then combined just before
use.
[0070] A known carboxylic acid or amino acid may be added as a
proton donor for enhancing oxidization by the oxidizing agent and
achieving stable polishing. Although citric acid which is a
carboxylic acid may act as such a proton donor, a different organic
acid such as a carboxylic acid and an amino acid may be added.
[0071] Carboxylic acids other than citric acid include formic acid,
acetic acid, propionic acid, butyric acid, valeric acid, acrylic
acid, lactic acid, succinic acid, nicotinic acid, oxalic acid,
malonic acid, tartaric acid, malic acid, glutaric acid, citric
acid, maleic acid and their salts.
[0072] An amino acid may be added as such, as a salt or as a
hydrate. Examples of those which may be added include arginine,
arginine hydrochloride, arginine picrate, arginine flavianate,
lysine, lysine hydrochloride, lysine dihydrochloride, lysine
picrate, histidine, histidine hydrochloride, histidine
dihydrochloride, glutamic acid, glutamic acid hydrochloride, sodium
glutaminate monohydrate, glutamine, glutathione, glycylglycine,
alanine, .beta.-alanine, .gamma.-aminobutyric acid,
.epsilon.-aminocarproic acid, aspartic acid, aspartic acid
monohydrate, potassium aspartate, potassium aspartate trihydrate,
tryptophan, threonine, glycine, cystine, cysteine, cysteine
hydrochloride monohydrate, oxyproline, isoleucine, leucine,
methionine, ornithine hydrochloride, phenylalanine, phenylglycine,
proline, serine, tyrosine, valine, and a mixture of these amino
acids.
[0073] The content of the organic acid is preferably at least 0.01
wt %, more preferably at least 0.05 wt % to the total amount of the
polishing slurry for achieving adequate effects of its addition,
while it is preferably 5 wt % or less, more preferably 3 wt % or
less as a content including citric acid for preventing dishing and
adjusting a polishing rate to a proper value.
[0074] An antioxidant may be further added to a polishing slurry in
this invention. Addition of an antioxidant may allow a polishing
rate for a copper-containing metal film to be easily adjusted and
may result in forming a coating film over the surface of the
copper-containing metal film to prevent deterioration in the
surface shape of the copper-containing interconnect due to chemical
polishing, i.e., dishing and recession.
[0075] Examples of an antioxidant include benzotriazole,
1,2,4-triazole, benzofuroxan, 2,1,3-benzothiazole,
o-phenylenediamine, m-phenylenediamine, cathechol, o-aminophenol,
2-mercaptobenzothiazole, 2-mercaptobenzimidazole,
2-mercaptobenzoxazole, melamine, and their derivatives. Among
these, benzotriazole and its derivatives are preferable. Examples
of a benzotriazole derivative include substituted benzotriazoles
having a benzene ring substituted with hydroxy; alkoxy such as
methoxy and ethoxy; amino; nitro; alkyl such as methyl, ethyl and
butyl; halogen such as fluorine, chlorine, bromine and iodine.
Furthermore, naphthalenetriazole and naphthalenebistriazole as well
as substituted naphthalenetriazoles and substituted
naphthalenebistriazoles substituted as described above may be
used.
[0076] The content of the antioxidant is preferably at least 0.0001
wt %, more preferably at least 0.001 wt % to the total amount of
the polishing slurry for achieving adequate effects of its
addition, while it is preferably 5.0 wt % or less, more preferably
2.5 wt % or less for adjusting a polishing rate to a proper value.
An excessive amount of antioxidant may be excessively
anti-corrosive and thus a polishing rate for copper-containing
metal may be excessively reduced, leading to a longer CMP time.
[0077] A polishing slurry used in this invention may contain a
variety of additives such as dispersing agents, buffers and
viscosity modifiers commonly added to a polishing slurry as long as
it does not deteriorate the properties of the slurry.
[0078] A composition of the polishing slurry used in this invention
is preferably adjusted such that a polishing rate for a
copper-containing metal film becomes preferably at least 300
nm/min, more preferably at least 400 nm/min. Furthermore, a
composition of the polishing slurry used in this invention is
preferably adjusted such that a polishing rate for a copper metal
film becomes preferably 1500 nm/min or less, more preferably 1000
nm/min or less.
[0079] A polishing slurry used in this invention may be prepared by
a common process for preparing a free grain polishing slurry.
Specifically, polishing grain particles are added to a dispersion
medium to an appropriate amount. A protective agent may be, if
necessary, added to an appropriate amount. In such a state, air is
strongly adsorbed in the surface of the grain particles, so that
the grains are aggregated due to poor wettability. Thus, the
aggregated polishing material particles are dispersed into primary
particles. In a dispersion process, a dispersion technique and a
dispersion apparatus commonly used may be employed. Specifically,
dispersion may be conducted using an apparatus such as an
ultrasonic disperser, a variety of bead mill dispersers, a kneader
and a ball mill by a known process. Citric acid may cause
flocculation of polishing grains while enhancing thixotropy. It is,
therefore, preferable to add and mix the component after dispersion
for achieving good dispersion.
[0080] Polishing in this invention may be conducted using, for
example, a common chemical mechanical polishing apparatus (CMP
apparatus) as shown in FIG. 2.
[0081] A wafer 21 in which, for example, an insulating film and a
copper-containing metal film are deposited on a substrate is placed
on a spindle wafer carrier 22. The surface of the wafer 21 is
contacted with a polishing pad 24 adhered on a rotary plate
(surface plate) 23. While supplying a polishing slurry to the
surface of the polishing pad 24 from a polishing slurry inlet 25,
both the wafer 21 and the polishing pad 24 are rotated to polish
the wafer. If necessary, a pad conditioner 26 is contacted with the
surface of the polishing pad 24 to condition the surface of the
polishing pad. The polishing slurry may be fed to the surface of
the polishing pad 24 from the side of the rotary plate 23.
[0082] In this invention, a contact pressure of the polishing pad
to the polishing surface during CMP is 27 kPa or more, preferably
34 kPa or more. Increase in the contact pressure of the polishing
pad may prevent bending of the polishing pad to improve in-plane
uniformity of the polished surface, leading to reduction in a
dispersion in the height of the interconnect and thus reduction in
a dispersion in an interconnect resistance. Furthermore, in-plane
uniformity may be improved and a polishing rate may be increased,
so that a throughput may be improved. Even in high-speed polishing,
the content of an oxidizing agent such as hydrogen peroxide in the
polishing slurry may be adjusted within a range where stable
polishing can be conducted with improved handling properties. There
are no restrictions to an upper limit of the contact pressure
(polishing pressure) of the polishing pad to the polished surface,
but it may be preferably 48.3 kPa (7 psi) or less for ensuring
adequate contact between a wafer and the polishing pad and feeding
a polishing slurry between the wafer and the polishing pad in the
light of a polishing rate and in-plane uniformity of the polished
surface.
[0083] For other CMP conditions, for example, the followings may be
selected when using a polishing pad slightly larger than a wafer (a
polishing pad having a radius smaller than a wafer diameter): a
retainer pressure: 25.2 kPa (3.65 psi) to 27.9 kPa (4.05 psi); a
rotating speed of the surface plate: 260 to 280 rpm; and a feeding
rate of the polishing slurry: 80 to 150 mL/min. When using a
polishing pad having a radius larger than a wafer diameter, the
followings may be selected: a rotating speed of the surface plate:
30 to 100 rpm; and a feeding rate of the polishing slurry: 100 to
300 mL/min.
[0084] Now, a wafer size (diameter) is predominantly 6 or 8 inch,
but according to this invention, adhesion of a polishing product to
a polishing pad may be prevented for a wafer having a diameter of
12 inch or more, leading to satisfactory CMP.
[0085] This invention described above may be suitably applied to a
process for forming an electric connection part such as a damascene
interconnect, a via plug and a contact plug by CMP of a substrate
where a barrier metal film is formed on an insulating film having a
concave such as a groove and a connection hole and a copper metal
film is formed over the whole surface such that the concave is
filled with the metal, until the surface of the insulating film is
substantially completely exposed. Examples of a barrier metal
include Ta, TaN, Ti, TiN, W, WN and WSiN. Examples of an insulating
film include a silicon oxide film, a BPSG film and an SOG film.
Examples of a copper-containing metal film include a copper film as
well as a copper alloy film comprising a metal selected from a
variety of conductive metals such as silver, gold, platinum,
titanium, tungsten, aluminum.
[0086] This invention described above can prevent adhesion of a
polishing product to a polishing pad and thus can eliminate
necessity of washing a pad surface, even when a large amount of
copper-containing metal must be removed by polishing because of a
thick or large copper-containing metal film. A large amount of
copper-containing metal may be, therefore, satisfactorily subject
to CMP in one polishing step without discontinuing polishing
operation.
[0087] In addition to elimination of necessity of washing the
surface of the polishing pad, a conditioning time may be reduced,
leading to a longer life of the polishing pad.
[0088] Furthermore, according to this invention, adhesion of a
polishing product to a polishing pad can be inhibited. Therefore, a
contact pressure of the polishing pad to a polished surface may be
increased to increase a polishing rate as well as to adequately
improve in-plane uniformity of the polished surface. Consequently a
dispersion of a interconnect height may be reduced and thus there
may be provided a uniform interconnect with a small dispersion of
its resistance.
[0089] According to this invention, since adhesion of a polishing
product may be prevented not only on a polishing pad surface but
also on a polished surface during polishing, an excellent polished
surface may be formed without problems of device properties such as
electric short-circuit between interconnects, and also an excellent
polished surface having good in-plane uniformity may be formed to
prevent dishing and erosion.
EXAMPLES
[0090] This invention will be more specifically described with
reference to examples.
[0091] CMP Conditions
[0092] CMP was conducted using a Speedfam-Ipec Type SH-24
apparatus. The polisher was used, on whose surface plate a
polishing pad (Rodel-Nitta IC 1400) with a diameter of 61 cm (24
inch) was attached. Polishing conditions were as follows: a contact
pressure of the polishing pad: 27.6 kPa (4 psi); a polishing area
of the polishing pad: 1820 cm; a rotating speed of the surface
plate: 55 rpm; a carrier rotating speed: 55 rpm; and a polishing
slurry feeding rate: 100 mL/min.
[0093] Determination of a Polishing Rate
[0094] A polishing rate was calculated from surface resistivities
before and after processing. Specifically, four needle electrodes
were aligned on a wafer with a given interval. A given current was
applied between the outer two probes to detect a potential
difference between two inner probes for determining a resistance
(R') and further the value is multiplied by a correction factor RCF
(Resistivity Correction Factor) to a surface resistivity (.rho.s').
A surface resistivity (.rho.s) is determined for a wafer film whose
thickness (T) (nm) is known. The surface resistivity is inversely
proportional to the thickness. Thus, when a thickness for a surface
resistivity of .rho.'s is d, an equation
d(nm)=(.rho.s.times.T)/.rho.s' holds true. Using the equation, the
thickness d can be determined. Furthermore, a variation between
before and after polishing was divided by a polishing time to
estimate a polishing rate. A surface resistivity was determined
using Mitsubishi Chemical Industries Four Probe Resistance Detector
(Lorest-GP).
[0095] Evaluation of In-Plane Uniformity of a Polished Surface
[0096] Surface resistivities (specific resistances) before and
after polishing were measured at 40 points in the wafer surface to
determine a k value for distribution in an absolute polishing
amount, which was then used as an indication for in-plane
uniformity.
[0097] A measured surface resistance at each point in the wafer
surface was used to determine a thickness of the copper film at
each point, and a film thickness after polishing was subtracted
from that before polishing to determine a polishing amount for each
point. Then, the maximum P.sub.max, the minimum P.sub.min and an
average P.sub.av in 40 points were determined, and these values
were used to calculate an in-plane uniformity rate k
(%)=(P.sub.max-P.sub.min) .times.100 / (2.times.P.sub.av).
Example 1
[0098] A copper damascene interconnect comprising a Ta film as a
barrier metal film was prepared.
[0099] As shown in FIG. 1(a), on a 6 inch wafer (silicon substrate,
not shown) in which a semiconductor device such as a transistor was
formed was deposited a first silicon oxide film 1 comprising a
lower interconnect 2 (not shown). On the film 1 were formed a
silicon nitride film 3 and a second silicon oxide film 4 with a
thickness of about 1.5, .mu.m. The second silicon oxide film 4 was
then patterned as usual by, for example, photolithography and
reactive ion etching to form a groove for interconnection and in a
given area of the groove a connection hole reaching the lower
interconnect 2. Then, Ta film with a thickness of 50 nm was formed
by sputtering, a copper film with a thickness of about 50 nm was
formed by sputtering, and then a copper film 6 with a thickness of
about 2.0 .mu.m was formed by plating.
[0100] The substrate thus prepared was subject to CMP using various
polishing slurries shown in Table 1, and contamination in a
polishing pad after polishing the copper film to about 2 .mu.m was
evaluated visually or on the basis of a polishing rate.
[0101] Citric acid, glutaric acid, glycine and benzotriazole (BTA)
were obtained from Kanto Chemical Co. Silica was fumed silica Qs-9
from Tokuyama Sha and alumina was .theta.-alumina (AKP-G008) from
Sumitomo Chemical Co., Ltd.
[0102] Table 1 shows the CMP results together with the compositions
of the polishing slurries. In CMP using a polishing slurry
comprising citric acid, adhesion of a polishing product to the
polishing pad was little observed and a polishing rate was stable
and constant until termination of polishing. On the other hand, in
CMP using a polishing slurry comprising not citric acid but a
carboxylic acid (glutaric acid) or an amino acid (glycine), a large
amount of polishing product was adhered to the polishing pad at the
end of polishing.
[0103] In CMP using a polishing slurry comprising citric acid, an
in-plane uniformity of the polished surface was 5%. Then, CMP was
conducted as described above, increasing a contact pressure of the
polishing pad from 27.6 kPa (4 psi) to 34.5 kPa (5 psi). An
in-plane uniformity was 3.5%. Adhesion of a polishing product to
the polished surface was not observed.
[0104] FIG. 4 shows variation of an in-plane uniformity (k value)
plotted to a polishing pressure when CMP was conducted using a
polishing slurry with or without citric acid. It can bee seen from
the figure that CMP using a polishing slurry with citric acid ()
gave a smaller k value, i.e., polishing with better in-plane
uniformity at the same polishing pressure, compared with CMP using
a polishing slurry without citric acid (.quadrature.). It may be
because a polishing product adheres to the polishing pad in CMP
using a polishing slurry without citric acid while not in CMP using
a polishing slurry comprising citric acid.
1TABLE 1 Polishing pH Adhesion of a grains Organic Acid
H.sub.2O.sub.2 content BTA content regulator Cu polishing polishing
product No. (content/wt %) (content/wt %) (wt %) (wt %) (pH) rate
(nm/min) to a polishing pad 1 Alumina (8) Glycine (0.125) 1.7 0.005
None (8.0) 211.3 Yes 2 Silica (5) Glutaric acid (0.16) 0.51 0.005
KOH (4.3) 181.6 Yes 3 Silica (5) Citric acid (0.254) 0.51 0.005 KOH
(4.3) 300.8 No 4 Alumina (5) Citric acid (1.50) 2.38 0.005 KOH
(5.5) 911.1 No Glutaric acid (0.16) Glycine (0.30) 5 Alumina (5)
Citric acid (1.50) 2.38 0.005 KOH (5.5) 808.8 No Glutaric acid
(0.16) Glycine (0.30) 6 Alumina (8) Citric acid (0.75) 2.38 0.010
KOH (5.5) 616.2 No Glutaric acid (0.16) Glycine (0.30) 7 Alumina
(8) Citric acid (0.75) 2.38 0.010 NH.sub.3 (5.5) 623.2 No Glutaric
acid (0.16) Glycine (0.30) 8 Alumina (8) Citric acid (0.75) 2.38
0.005 KOH (5.5) 768.9 No Glutaric acid (0.16) Glycine (0.30) 9
Alumina (8) Citric acid (0.50) 2.38 0.005 KOH (5.5) 619.9 No
Glutaric acid (0.16) Glycine (0.30) 10 Alumina (8) Citric acid
(0.50) 2.38 0.005 NH.sub.3 (5.5) 610.5 No Glutaric acid (0.16)
Glycine (0.30)
[0105] Preparation of a Secondary-Particle Containing
.theta.-Alumina Dispersion
[0106] Secondary-particle containing .theta.-alumina was prepared
using .theta.-alumina (Sumitomo Chemical Co., Ltd.; AKP-G008).
Observation of the .theta.-alumina before preparation by SEM
indicated that it consisted of aggregates made of a number of fused
primary particles with the minimum and the maximum particle sizes
of 0.03 .mu.m and 0.08, .mu.m (an average particle size: 0.05
.mu.m), respectively. The average particle size of the aggregates
were 10 .mu.m. Although there were sometimes observed primary
particles with a particle size considerably smaller or larger in
relation to the minimum or the maximum size, respectively, they did
not affect properties of a polishing slurry finally obtained or
contribute an average particle size at all.
[0107] Then, Aqualic HL415, a dispersing agent from Nippon Shokubai
Co., Ltd., was added to ion-exchanged water to 4 wt %, and then
.theta.-alumina before preparation was added to 40 wt %. The
resultant mixture was subject to dispersion at a rotating speed of
1000 rpm using a bead mill (Inoue Seisakusho; Super mill). A
plurality of dispersions were prepared, varying a dispersion time
from 20 to 400 min.
[0108] A particle size distribution for the overall particles was
determined for the .theta.-alumina contained in each dispersion
using a particle size analyzer (Beckmann-Kolter; LS-230). The
maximum particle size was determined from the particle size
distribution for the overall particles. A particle size
distribution for secondary particles was calculated by subtracting
the particle size distribution for primary particles from that for
the overall particles. An average particle size of secondary
particles was determined by statistically processing the particle
distribution of secondary particles. Furthermore, for a dispersion
in which a dispersion time was 200 min, were determined the content
of secondary particles to the overall secondary-particle containing
.theta.-alumina and the proportion of secondary particles with a
particle size of 0.05 .mu.m to 0.5 .mu.m both inclusive to the
overall secondary particles.
[0109] Table 3 shows the maximum particle size (.circle-solid.) and
an average particle size of secondary particles (.largecircle.) for
.theta.-alumina in a dispersion at several dispersion times. Large
secondary particles with a particle size of more than 3 .mu.m were
present for a dispersion time of 120 min or less, while the maximum
particle size was less than 1 .mu.m for a dispersion time of 140
min or longer.
[0110] When a dispersion time was 200 min, an average particle size
of secondary particles was 0.15 .mu.m, the maximum particle size
was 0.6 .mu.m, the content of secondary particles to the overall
secondary-particle containing .theta.-alumina was 74 wt %, and the
proportion of secondary particles with a particle size of 0.05
.mu.m to 0.5 .mu.m both inclusive to the overall secondary
particles was 62 wt %. In addition, there were observed no
significant foreign matters.
Example 2
[0111] Among the dispersions prepared as described above, the
dispersion in which a dispersion time was 200 min was used to
prepare polishing slurry 1 with pH 7 comprising 5.03 wt % of
secondary-particle containing .theta.-alumina, 0.47 wt % of citric
acid and 1.9 wt % of H.sub.2O.sub.2, in which pH was adjusted with
ammonia and H.sub.2O.sub.2 was added just before CMP.
[0112] On a 6 inch silicon substrate were formed a silicon oxide
film, a groove for interconnection, an opening for an interconnect,
a barrier metal film and a copper film as described in Example
1.
[0113] The substrate thus obtained was subject to CMP using
polishing slurry 1 and the copper film was polished by about 2
.mu.m. A polishing rate was constant and polishing was stable until
termination of polishing. Then, contamination of the polishing pad
was evaluated visually or on the basis of the polishing rate, and
it was found that there was little adhesion of a polishing product
to the polishing pad. SEM observation of the polished surface
indicated that scratches were prevented and an in-plane uniformity
of the polished surface was 5%. Furthermore, CMP was conducted as
described above, increasing a contact pressure of the polishing pad
from 27.6 kPa (4 psi) to 34.5 kPa (5 psi). An in-plane uniformity
was 3.5%. Adhesion of a polishing product to the polished surface
was not observed and scratches were prevented.
Example 3
[0114] Polishing slurry 2 was prepared as described for polishing
slurry 1, replacing citric acid with malic acid. Using polishing
slurry 2, CMP was conducted as described above. A polishing rate
was constant and polishing was stable until termination of
polishing. Then, contamination of the polishing pad was evaluated
visually or on the basis of the polishing rate, and it was found
that there was little adhesion of a polishing product to the
polishing pad. SEM observation of the polished surface indicated
that scratches were prevented and an in-plane uniformity of the
polished surface was 5% or less. Furthermore, CMP was conducted as
described above, increasing a contact pressure of the polishing pad
from 27.6 kPa (4 psi) to 34.5 kPa (5 psi). An in-plane uniformity
was 3.5%. Adhesion of a copper polishing product to the polished
surface was riot observed and scratches were prevented.
Comparative Example 1
[0115] Polishing slurry 3 was prepared as described for polishing
slurry 2, replacing .theta.-alumina with commercially available
.alpha.-alumina. Using polishing slurry 3, CMP was conducted as
described above, and a large amount of a polishing product adhered
to the polishing pad. An in-plane uniformity was 8% at a contact
pressure of the polishing pad of 27.6 kPa (4 psi) while 6. 5% at
34.5 kPa (5 psi).
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