US 20080086950A1

(19) United States

(12) Patent Application Publication (10) Pub. No.: US 2008/0086950 A1
KON et al. (43) Pub. Date: Apr. 17, 2008
(54) SEMICONDUCTOR POLISHING (30) Foreign Application Priority Data
COMPOUND
Jun. 6, 2005 (JP)...................................... 2005-165768
Publication Classification
(75) Inventors: Yoshinori KON, Tokyo (JP): Iori
Yoshida, Tokyo (JP); Norihito (51) Int. Cl.
Nakazawa, Tokyo (JP) B24D 3/02 (2006.01)
Correspondence Address: B24B I/00 (2006.01)
OBLON, SPIVAK, MCCLELLAND MAIER & (52) U.S. Cl. ................................................. 51/306; 51/298
NEUSTADT, P.C. (57) ABSTRACT
194O DUKE STREET To provide a semiconductor polishing compound which is
ALEXANDRIA, VA 22314 (US) excellent in dispersion stability and removal rate and which
has a stabilized polishing property, as it is less Susceptible to
(73) Assignees: ASAHI GLASS COMPANY, LIM an influence even when contacted with an alkaline polishing
ITED, Tokyo (JP): AGC Seimi Chemi compound during its application to CMP comprising a
cal Co., Ltd., Chigasaki-shi (JP) multistage process. A polishing compound for chemical
mechanical polishing to polish a surface to be polished in the
(21) Appl. No.: 11/951,540 production of a semiconductor circuit device, said polishing
compound comprising cerium oxide abrasive particles,
(22) Filed: Dec. 6, 2007 water and a dicarboxylic acid represented by the formula 1:
HOOC(CH2)COOH Formula 1
Related U.S. Application Data
wherein n is an integer of from 1 to 4, and the pH of said
(63) Continuation of application No. PCT/JP2006/ polishing compound at 25°C. being within a range of from
309578, filed on May 12, 2006. 3.5 to 6.
Patent Application Publication Apr. 17, 2008 Sheet 1 of 3 US 2008/0086950 A1

Fig. 1

(c)
Patent Application Publication Apr. 17, 2008 Sheet 2 of 3 US 2008/0086950 A1
Fig. 2
Patent Application Publication Apr. 17, 2008 Sheet 3 of 3 US 2008/0086950 A1

Fig. 3

Fig. 4
400. O

350. O

EXAMPLE 3
300. O EXAMPLE 1.

r EXAMPLE 2

: 250. OC
EXAMPLE 5

89, 200.0
A.

150. O
O 5 1) 15 20 25
AMOUNT OF AMMONIA ADDED (ppm)
US 2008/0O8695.0 A1 Apr. 17, 2008

SEMCONDUCTOR POLISHING COMPOUND employ cerium oxide abrasive particles having excellent
polishing selectivity between them. The cerium oxide pol
TECHNICAL FIELD ishing compound exhibits a high removal rate against a
0001. The present invention relates to a semiconductor silicon dioxide film by a chemical reaction with the layer
polishing compound for chemical mechanical polishing in a Surface, and it is expected to improve the throughput in the
process for producing a semiconductor integrated circuit process for producing a semiconductor device. Further, a
device. Particularly, it relates to a semiconductor polishing technique is being developed to improve the dispersibility of
compound comprising cerium oxide, which is suitable for the cerium oxide polishing compound and to improve pla
shallow trench isolation or planarization of an interlayer narization of the Surface to be polished, by adding a surfac
insulation film or a polysilicon. tant, a water-soluble polymer, a water-soluble low molecular
weight Substance, etc. to Such a cerium oxide polishing
BACKGROUND ART
compound.
0002. In recent years, micro-fabrication techniques have 0008 For example, Patent Document 1 discloses a tech
nique whereby rather than a concave portion, a convex
been developed for miniaturization and high densification portion is preferentially polished for planarization by a
along with high integration and high functionality of semi polishing compound comprising cerium oxide abrasive par
conductor integrated circuit devices. Particularly, impor ticles and, as an additive, an organic compound containing
tance of planarization techniques by chemical mechanical hydrophilic groups such as carboxyl groups or carboxylate
polishing (hereinafter referred to as CMP) is increasing. groups. Here, the additive is one to improve the trench width
0003 For example, as miniaturization of semiconductor dependency of dishing, and in order to reduce dishing even
integrated circuit devices and multilayered structures of with a wide trench, it is necessary that the concentration of
wirings progresses, the Surface unevenness (difference in the above additive is high. However, if the concentration of
level) in each layer in the production process tends to the additive is increased, agglomeration of cerium oxide
increase. In order to prevent such a problem that this particles will be accelerated, whereby sedimentation of
difference in level exceeds the depth of focus in photoli abrasive particles will result, and the dispersion stability of
thography so that no adequate resolution can be obtained, the polishing compound tends to deteriorate. Further, if
CMP has become an indispensable technique. agglomeration of particles takes place, Scratches will
0004 Specifically, CMP is used for e.g. planarization of increase, thus leading to a problem that the integrated circuit
device tends to be defective.
inter-level dielectrics (ILD), shallow trench isolation (STI),
formation of a tungsten plug, or in a process for forming 0009 For example, Patent Document 1 discloses
multilayered wirings comprising copper and low dielectric Examples for a polishing compound Solution comprising
films. pure water, and, as abrasive particles, 1% of cerium oxide
and, as an additive, 6.0% of ammonium polycarboxylate,
0005. The STI process will be described with reference to based on the total mass of the polishing solution. However,
FIG. 1. FIG. 1(a) shows such a state that while an element since the additive is at a high concentration, agglomeration
region is masked with a silicon nitride film 3 or the like, a of the abrasive particles is remarkable, and when the pol
trench 10 is formed on a silicon substrate 1, and then an ishing solution is left to stand, cerium oxide abrasive par
insulation film Such as a silicon dioxide film 2 is deposited ticles will be completely sedimented within a few minutes.
so that it is embedded in the trench 10. In this state, any In the polishing process of CMP, there is a waiting time
excess silicon dioxide film 2 on the silicon nitride film 3
being a convex portion is polished and removed by CMP during which no polishing is carried out, and sedimentation
of abrasive particles is likely to result at a portion where the
while the insulation film is permitted to remain in the trench polishing compound is not always stirred or moved, thus
10 being a concave portion, thereby to obtain an element causing clogging of the pipeline.
isolation structure having the insulation film embedded in
the trench. During CMP, it is common to use the silicon 0010. In order to prevent such sedimentation, there is a
nitride film 3 by letting the removal rate of the silicon method of incorporating an additive to the polishing com
dioxide film and the removal rate of the silicon nitride film pound on a polishing pad or in a pipeline immediately before
have a selective ratio, so that polishing is terminated at the the polishing pad, but the mixing tends to be inadequate, the
time when the silicon nitride film 3 is exposed as shown in concentration tends to be non-uniform, or the polishing
FIG. 1(b). characteristics tend to be unstable. Further, the abrasive
particles on the pad tend to be agglomerated or deposited,
0006. Here, if the polishing is excessive, the silicon whereby there has been a problem that scratches will
dioxide film embedded in the trench 10 will be polished and increase.
recessed as shown in FIG. 1(c), whereby a structural defect
Such as a recess 20, so-called dishing, will result, and 0011 Further, cerium oxide particles have a large specific
planarization tends to be inadequate or electrical perfor gravity and thus tend to be readily sedimented, while they
mance tends to deteriorate. The degree of dishing depends are Superior in the polishing property to conventional silica
on the width of the trench and the dishing tends to be large particles. Further, they have a serious problem that if an
with a trench having a wide width. additive to improve the polishing property is incorporated
excessively, agglomeration will be accelerated, whereby
0007 Heretofore, silica abrasive particles have been sedimentation by agglomeration tends to be remarkable.
common as abrasive particles to be used for CMP. However,
the selective ratio between the removal rate of the silicon 0012 Patent Document 2 discloses, as a polishing com
dioxide film and the removal rate of the silicon nitride film pound useful for the STI process, a polishing compound
is Small, and, in the STI process, it has become common to comprising cerium oxide particles, water and an anionic
US 2008/0O8695.0 A1 Apr. 17, 2008

Surfactant, which is preferably a polishing compound falling and abrasive particles and having a pH of from 3 to 11, and
within a regional range defined by four points i.e. point A by using this polishing compound, it is possible to increase
(5.5, 0.9), point B (5.5, 3.0), point C (10.0, 3.0) and point D the selective ratio in the removal rate between a silicon
(9.0, 0.9), as represented by a (x, y) coordinate, whereinx is dioxide film and a silicon nitride film. However, there has
the pH, and y is the viscosity (mPas). And, it is disclosed been a problem that by this method, cerium ions contained
that in order to realize global planarization, it is necessary to in the polishing compound will remain on a Substrate and
adjust the amount of the surfactant and the pH within such will present an adverse effect to the integrated circuit device.
ranges that a polishing characteristic whereby the removal 0017. In order to solve the above problems, we have
rate at a concave portion of a pattern is Sufficiently Small as proposed a polishing compound comprising cerium oxide
compared with the removal rate at a convex portion, can be abrasive particles, water and at least one additive selected
obtained, and the Viscosity of the polishing compound is from the group consisting of a water-soluble organic poly
preferably from 1.0 to 2.5 mPas, particularly preferably
from 1.0 to 1.4 mPa's. mer and an anionic Surfactant and having a pH of from 3.5
to 6, in Patent Document 4. This polishing compound has
0013 Further, it is disclosed that the viscosity will merits such that when it is used for the STI process, it is
increase as the amount of the Surfactant increases, and in possible to obtain excellent polishing planarization charac
order to realize a planarization characteristic with little teristics with little dishing fluctuation, to shorten the pol
pattern dependency by adjusting the viscosity within a range ishing time of a patterned wafer and to reduce Scratches.
of from 1.0 to 1.4 mPas, the pH of the polishing compound However, in a case where CMP is carried out by a multistage
after incorporation of the surfactant is preferably from 5.5 to process wherein the polishing compound of Patent Docu
9, particularly preferably from 6 to 8.5, and within this pH ment 4 is used in combination with another alkaline com
range, the selective ratio between the removal rate of the pound (slurry), it has been likely that the pH changes by the
silicon dioxide film and the removal rate of the silicon influence of the alkaline polishing compound, which may
nitride film, can be made large. Further, it is exemplified to adversely affect the polishing properties. In particular, in
preliminarily incorporate a very Small amount of a dispers Patent Document 4, the pH is adjusted by nitric acid to be
ant to the abrasive particles. within a range of from 3.5 to 6, but, it has been likely that,
for example, ammonia evaporated from the alkaline polish
0014) However, if a polishing compound is prepared in ing compound is absorbed by the polishing compound of
accordance with Examples given in Patent Document 2, Patent Document 4, or the alkaline polishing compound
when a surfactant is added to a dispersion of abrasive used in the first stage process will remain on the wafer
particles, the abrasive particles will be agglomerated to have surface and will be mixed with the polishing compound of
an average particle diameter which is from 2 to 3 times the Patent Document 4, whereby the pH will be changed to
average particle diameter in the dispersion of particles. present an influence over the polishing properties.
Accordingly, the dispersibility of abrasive particles in the
polishing compound was poor, and the abrasive particles 0.018 Patent Document 1: Japanese Patent 3,278.532
were sedimented within a few minutes, whereby it was 0019) Patent Document 2: JP-A-2000-1601.37
difficult to use Such a polishing compound, and the removal
rate was also inadequate. Further, in a case where the 0020 Patent Document 3: JP-A-2001-507739
concentration of the Surfactant is high, dishing fluctuation is 0021) Patent Document 4: WOO4/O10487
Small, and the planarization characteristic is excellent. How
ever, with a polishing compound prepared in accordance DISCLOSURE OF THE INVENTION
with an Example wherein the concentration of the surfactant
is lower, dishing fluctuation was substantial, and the pla Problems which the Invention is to Solve
narization characteristic was poor.
0.015 Further, if the concentration of the surfactant 0022. Under the circumstances, it is an object of the
becomes high, the number of Scratches sharply increases. present invention to solve the above-mentioned problems
This is believed to be attributable to that if the concentration and to provide a semiconductor polishing compound which
of the Surfactant is high, agglomeration and sedimentation of is excellent in dispersion stability and removal rate and
cerium oxide particles are accelerated, and they are accu which has a stabilized polishing property, as it is less
mulated on the polishing pad. Namely, it is considered that Susceptible to an influence even when contacted with an
if coarse particles causing scratches, are present in abrasive alkaline polishing compound during its application to CMP
particles even slightly, the particles will be agglomerated comprising a multistage process.
and accumulated on the polishing pad thereby to cause an
increase of scratches. Further, it is also considered that there Means to Solve the Problems
may be a case where agglomerates of abrasive particles 0023 Namely, The present invention provides the fol
grown by agglomeration themselves will cause Scratches. lowing:
0016. As described in the foregoing, in the prior art, no 0024 (1) A semiconductor polishing compound which is
polishing compound was available which had both disper a polishing compound for chemical mechanical polishing to
sion stability of the polishing compound and excellent polish a surface to be polished in the production of a
scratch characteristics, and excellent polishing planarization semiconductor circuit device, said polishing compound
characteristics, and it was difficult to obtain a semiconductor comprising cerium oxide abrasive particles, water and a
integrated circuit device having adequate properties. On the dicarboxylic acid represented by the formula 1:
other hand, Patent Document 3 proposes a polishing com
pound comprising a soluble cerium, a pH buffering agent HOOC(CH2)COOH Formula 1
US 2008/0O8695.0 A1 Apr. 17, 2008

wherein n is an integer of from 1 to 4, and the pH of said 0035) 31: semiconductor device
polishing compound at 25°C. being within a range of from 0036) 32: polishing head
3.5 to 6.
(2) The semiconductor polishing compound according to the 0037 33: polishing plate
above (1), wherein the pH is within a range of from 4 to 6. 0038 34: polishing pad
(3) The semiconductor polishing compound according to the 0039) 35: polishing compound-supplying pipe
above (1) or (2), wherein the absolute value of the difference 0040) 36: polishing compound
between the pKa value of said dicarboxylic acid and said pH
is at most 1.0.
BEST MODE FOR CARRYING OUT THE
(4) The semiconductor polishing compound according to INVENTION
any one of the above (1) to (3), wherein the dicarboxylic acid
is at least one member selected from the group consisting of 0041. Now, the present invention will be described in
detail.
malonic acid, Succinic acid and adipic acid.
(5) The semiconductor polishing compound according to 0042. In the present invention, cerium oxide is used as
any one of the above (1) to (4), wherein the concentration of abrasive particles. Heretofore, it has been known that cerium
the dicarboxylic acid is from 0.01 to 0.5 mass %. oxide abrasive particles show a specifically high removal
rate in polishing of a glass type material including a silicon
(6) The semiconductor polishing compound according to dioxide film. Namely, when cerium oxide is in contact with
any one of the above (1) to (5), wherein the surface to be a silicon dioxide film in the surface to be polished, a
polished is made of silicon dioxide. chemical bond will be formed between the two, which
(7) The semiconductor polishing compound according to creates a grinding power higher than the mere mechanical
any one of the above (1) to (6), which contain at least one action. Accordingly, in polishing by means of cerium oxide,
additive selected from the group consisting of a water it is important to control the contact of the abrasive particles
soluble organic polymer and an anionic Surfactant. with the surface to be polished. Here, in this invention, “the
Surface to be polished' means an intermediate stage surface
(8) The semiconductor polishing compound according to the which appears in the process for producing a semiconductor
above (7), wherein the water-soluble organic polymer is a device.
polyacrylic acid or an ammonium polyacrylate. 0043. In a STI process or a CMP process for an interlayer
EFFECTS OF THE INVENTION dielectoric film, it is desired to efficiently planarize the
Surface to be polished such as a silicon.dioxide film having
0.025 The semiconductor polishing compound of the surface unevenness. Namely, it is preferred to selectively
present invention is not only excellent in dispersion stability polish convex portions. To realize such selective polishing,
and removal rate but also capable of exhibiting a stabilized it is advisable to incorporate in the polishing compound an
polishing property, as it is less Susceptible to an influence additive which is to be adsorbed on the surface of cerium
even when contacted with an alkaline polishing compound, oxide abrasive particles to prevent direct contact with the
particularly when contacted with ammonia evaporated from surface to be polished such as a silicon dioxide film thereby
an alkaline polishing compound, in a multistage process. to control polishing. By incorporating Such an additive, if a
BRIEF DESCRIPTION OF DRAWINGS
high pressure is exerted, the additive adsorbed on the surface
of cerium oxide abrasive particles, will be peeled off to cause
0026 FIG. 1 is a schematic cross-sectional view illus the contact with the surface to be polished, whereby pol
trating a process for polishing a semiconductor device ishing will proceed.
Substrate by a semiconductor polishing compound. 0044) In a common polishing method wherein a surface
0027 FIG. 2 is a diagrammatic view showing an example to be polished is pressed against e.g. a polishing pad and
of a polishing apparatus to which the polishing compound of relatively moved, the pressure exerted to the surface to be
the present invention is applicable. polished differs locally depending upon the Surface contour.
At a convex portion, the pressure exerted will be high as
0028 FIG. 3 is a schematic sectional side view of a compared with at a concave portion. Accordingly, at the
blanket wafer. convex portion, the additive adsorbed on the surface of
0029 FIG. 4 is a graph showing an interrelation between cerium oxide abrasive particles is likely to be peeled off to
the concentration of ammonia added to the polishing com readily form the contact with the surface to be polished
pounds in Examples 1 to 5 of the present invention and the thereby to facilitate the polishing, and thus, it becomes
removal rate. possible to selectively polish the convex portion against the
concave portion.
MEANINGS OF SYMBOLS
0045. The cerium oxide surface in an aqueous dispersion
0030) 1: silicon substrate is positively charged within a range of from neutral to acidic,
and as the additive, a water-soluble organic polymer or an
0.031) 2: silicon dioxide film anionic Surfactant is preferred. As the water-soluble organic
0032) 3: silicon nitride film polymer, a polymer having carboxylic acid groups or ammo
nium carboxylate groups (—COONH) is preferred.
0033) 10: trench 0046. Further, in the STI process, usually, selectivity is
0034) 20: dishing given between the removal rates of the silicon oxide film and
US 2008/0O8695.0 A1 Apr. 17, 2008

the silicon nitride film, so that the silicon nitride film is used oxide surface, and they tend to be adsorbed in multilayers.
as a stopper. In an aqueous dispersion medium, the Surface Therefore, in the pH range in the present invention, even if
of the silicon dioxide film is negatively charged, and the the additive concentration is low, the additive will
surface of the silicon nitride film is positively charged, adequately be adsorbed on the surface of cerium oxide
within a range of from neutral to acidic (about pH 3), abrasive particles, whereby polishing planarization charac
whereby the above-mentioned anionic additive will selec teristics can be provided.
tively be adsorbed on the surface of the silicon nitride film. 0050. The pH of the polishing compound of the present
Therefore, contact of the silicon nitride film with the cerium invention is from 3.5 to 6, particularly preferably from 4 to
oxide abrasive particles will be prevented thereby to provide 6. If the pH is lower than 3.5, the amount of the additive to
selectivity between the removal rates of the silicon dioxide be adsorbed on the surface of the silicon nitride film tends
film and the silicon nitride film.
to be extremely small, whereby the surface protection of the
0047. With a conventional semiconductor polishing com silicon nitride film tends to be inadequate. Further, the
pound, as mentioned above, in order to selectively polish electric charge of the additive will be small, whereby the
convex portions and to provide selectivity between the adsorbability of the additive to the cerium oxide abrasive
removal rates of the silicon dioxide film and the silicon particles will be weakened. Further, the electric charge of the
nitride film, it has been believed desirable that the concen additive adsorbed on the cerium oxide surface will also be
tration of the above-mentioned additive is within a range of small, whereby the electrical repulsion will decrease, and the
from 2 to 3%, and the pH of the polishing compound is at dispersion stability of the polishing compound tends to
a level of from 7 to 8 i.e. in the vicinity of neutral. However, deteriorate. Inversely, if the pH exceeds 6, a large amount of
under these conditions, agglomeration of abrasive particles the additive will be required to provide the planarization
by the additive has been remarkable, and the dispersion characteristics, whereby the dispersibility of the cerium
stability of abrasive particles has been inadequate although oxide abrasive particles tends to be poor, whereby agglom
the planarization characteristics by polishing may be excel eration and sedimentation of the polishing compound tend to
lent. proceed.
0.048. As a result of an extensive study, the present 0051. In the present invention, the cerium oxide abrasive
inventors have found that by selecting the pH range of the particles are not particularly limited, but, for example,
polishing compound, it is possible to improve the planariza cerium oxide abrasive particles disclosed in JP-A-11-12561
tion characteristics by polishing even when the amount of or JP-A-2001-35818 may preferably be used. Namely, a
the additive in the polishing compound is reduced, and cerium oxide powder obtained by adding an alkali to an
further it is possible to increase the dispersion stability of ammonium aqueous solution of cerium (IV) nitrate to pre
abrasive particles in the polishing compound, and thus have pare a cerium hydroxide gel, followed by filtration, washing
arrived at the present invention. In the semiconductor pol and firing, may preferably be used. Further, cerium oxide
ishing compound of the present invention, the concentration abrasive particles obtained by milling and firing cerium
of the additive is preferably from 0.01 to 0.5% (mass ratio) carbonate of high purity, followed by further milling and
based on the total mass of the polishing compound. How classification, may also preferably be used.
ever, with Such a concentration range, it has heretofore been 0052 The average particle diameter of the cerium oxide
considered that the concentration of the additive is too low
and inadequate to provide the necessary polishing charac abrasive particles is preferably from 0.05 to 0.5 um, par
teristics. However, if the pH of the polishing compound is ticularly preferably from 0.1 to 0.3 um, further preferably
within a range of from 3 to 7, it is possible to provide from 0.1 to 0.2 Lum. If the average particle diameter is too
adequate polishing characteristics at a concentration of the large, abrasion flaws such as scratches are likely to be
formed on the surface of the semiconductor substrate. On the
additive lower than before. Further, if the concentration of other hand, if the average particle diameter is too small, the
the additive is reduced, agglomeration of abrasive particles removal rate tends to below. Further, as the proportion of the
by the additive tends to scarcely occur, whereby the disper Surface area per unit volume is large, the polishing com
sion stability will be improved, and it will be possible to pound is susceptible to the influence of the surface condi
simultaneously satisfy the planarization characteristics by tion, and depending upon the conditions such as the pH and
polishing and the dispersion stability of abrasive particles. the concentration of the additive, the polishing compound
0049. Within the pH range in the present invention, as may tend to be agglomerated.
compared with in the vicinity of neutral, the positive poten 0053 For the measurement of the average particle diam
tial on the cerium oxide surface will increase, whereby the eter, a particle size distribution meter of e.g. laser diffrac
additive tends to be readily adsorbed on the cerium oxide tion-scattering type, dynamic light scattering type or photon
Surface. Further, in a case where the negative charge of the correlation type, may be used. In a case where the particle
additive is substantial, due to the electrical repulsion of the diameter is large to Some extent and the particles are likely
additive particles among themselves, the additive tends to be to be sedimented, it is preferred to use a laser diffraction
hardly adsorbed in multilayers on the cerium oxide surface. scattering type particle size distribution meter, and the
However, in this pH range, the degree of dissociation of the above-mentioned range is a preferred range in a case where
additive itself will be small, and the negative charge will be the average particle diameter is measured by using a laser
small, whereby multiple adsorption will be possible. Further, diffraction-scattering type particle size distribution meter.
in a case where a water-soluble organic polymer having
carboxylic acid groups, is, for example, used as the additive, 0054 The additive in the present invention is at least one
if the water-soluble organic polymer is not dissociated, the member selected from the group consisting of a water
water-soluble organic polymer particles among themselves soluble organic polymer and an anionic Surfactant. The
tend to be entangled by the hydrogen bonds on the cerium water-soluble organic polymer is preferably one having
US 2008/0O8695.0 A1 Apr. 17, 2008

carboxylic acid groups or carboxylate groups. It may spe reliability of various polishing characteristics, it is preferred
cifically be a homopolymer of a monomer having a car to prepare a semiconductor polishing compound by prepar
boxylic acid group Such as acrylic acid, methacrylic acid or ing liquid 1 comprising cerium oxide abrasive particles and
maleic acid, or a homopolymer corresponding to such a water, and liquid 2 comprising the additive and water, and
homopolymer wherein the carboxylic acid group portions mixing liquids 1 and 2 prior to the polishing. The method for
are in the form of salts such as ammonium salts. Further, a mixing liquids 1 and 2 may be a method of mixing them on
copolymer of a monomer having a carboxylic acid group a polishing pad or in a pipeline immediately before the
with a monomer having a carboxylate group, or a copolymer polishing pad. However, the semiconductor polishing com
of a monomer having a carboxylate group with a derivative pound of the present invention undergoes substantially no
of a carboxylic acid such as an alkyl ester thereof, is also agglomeration even after Such mixing and is stable for a
preferred. Further, a water-soluble organic polymer Such as practically sufficient period of time, and therefore they may
a polyvinyl alcohol, or an anionic Surfactant Such as ammo be preliminarily be mixed. Namely, a commonly employed
nium oleate, ammonium lauryl Sulfate or triethanolamine semiconductor polishing compound-supplying system may
lauryl Sulfate, may also suitably be used. be utilized whereby liquids 1 and 2 are put into a polishing
0.055 Particularly preferred is a polymer having carboxy compound storage tank and stirred and mixed by a propeller
lic acid groups or carboxylate groups. Specifically, it may, stirring machine, or the polishing compound may be con
for example, be a polyacrylic acid or a polymer having at tinuously moved by a circulation line. Further, it is also
possible to employ a polishing compound prepared by
least some of carboxylic acid groups in a polyacrylic acid preliminarily mixing liquids 1 and 2 at a plant for producing
Substituted by ammonium carboxylate groups (hereinafter the semiconductor polishing compound of the present inven
referred to as an ammonium polyacrylate). tion. In Such a case, depending upon the period for storage
0056. Here, in a case where a water-soluble organic without stirring, abrasive particles may settle by gravity, and
polymer Such as an ammonium polyacrylate is used as the therefore, it is advisable to thoroughly stir it to redisperse the
additive, its molecular weight is preferably from 1,000 to settled abrasive particles before use.
50,000, particularly preferably from 2,000 to 30,000. 0060. In the present invention, in order to sufficiently mix
0057 The present inventors have conducted an extensive the cerium oxide abrasive particles and the additive and to
study and as a result, have found that by using a dicarboxylic stabilize the adsorbed state of the additive on the particle
acid represented by the formula 1 as a pH-controlling agent surface, it is preferred to preliminarily mix and stir liquid 1
for the polishing compound, it is possible to obtain a comprising the cerium oxide particles and water with liquid
polishing compound capable of providing a stabilized pol 2 comprising the additive and water and then use the
ishing characteristics, as it is less Susceptible to an influence obtained polishing compound. The polishing compound
by contact with ammonia evaporated from an alkaline may be used immediately after mixing liquids 1 and 2, but
polishing compound or by contact with an alkaline polishing it is preferred to use it at least a few minutes after the mixing.
compound for the first stage process remaining on a wafer It is particularly preferred to use the polishing compound
Surface, as compared with a conventional polishing com upon expiration of at least 15 minutes after the mixing. By
pound containing an inorganic acid or an inorganic acid salt Supplying the semiconductor polishing compound prepared
commonly used as a pH-controlling agent, and thus arrived by mixing, via a pump, to a polishing apparatus, it is possible
at the present invention. This is considered attributable to the to carry out CMP polishing constantly. To the supply line, a
fact that pKa of the carboxylic acid is in the vicinity of 5, circulation line may be provided for uniformity of the
whereby an adequate pH-buffering performance is provided. semiconductor polishing compound.
Among dicarboxylic acids represented by the formula 1, it 0061 For the preparation of liquid 1, it is preferred to
is particularly preferred to employ at least one member employ a method of dispersing cerium oxide abrasive par
selected from the group consisting of malonic acid (n=1), ticles in pure water or deionized water, and at the time of
Succinic acid (n=2) and adipic acid (n=4), whereby the effect dispersion, it is preferred to employ an ultrasonic disperser
for stabilizing the polishing characteristics can be made whereby agglomerates are disintegrated by the energy of
high. ultrasonic waves to disperse abrasive particles in water, or a
HOOC(CH2)COOH Formula 1 homogenizer, or Ultimizer (tradename, manufactured by
Sugino Machine) or Nanomizer (tradename, manufactured
0058. Here, when the absolute value of the difference by Yoshida Kikai Co., Ltd.) whereby agglomerates are
between the pKa value of the dicarboxylic acid represented disintegrated by the collision kinetic energy by collision of
by the formula 1 and the pH of the polishing compound is abrasive particles one another to disperse abrasive particles
preferably at most 1.0, it is possible to obtain a polishing in water. Further, it is also preferred to simultaneously add
compound having high pH-buffering effects and stabilized a dispersant at that time. Here, the dispersant is one to be
polishing characteristics. In order to further increase the added to stably disperse abrasive particles in a dispersing
pH-buffering effects, it is preferred to adjust the absolute medium Such as pure water, and as Such a dispersant, the
value of the above difference to be at most 0.5. Here, pKa same one as the above-described additive may be used.
of malonic acid is 5.28, pKa of succinic acid is 5.24, pKa Namely, the additive in the present invention may be added
of glutaric acid (n=3) is 5.01, and pKa of adipic acid is 5.03, not only to liquid 2 but also to liquid 1 as one having a
and by suitably selecting the dicarboxylic acid of the for function as a dispersant.
mula 1, it is possible to obtain desired polishing character
istics. 0062) When a dispersant is to be added to liquid 1, its
concentration is preferably within a range of from 0.1 to
0059. As the polishing compound of the present inven 1.0%, more preferably from 0.3 to 0.7%, by a mass ratio to
tion, in view of the long term storage stability or the the mass of the cerium oxide abrasive particles. If the
US 2008/0O8695.0 A1 Apr. 17, 2008

concentration of the dispersant is lower than this concen 0067. The silicon dioxide film 2 may, for example, be a
tration range, the dispersibility of abrasive particles tends to so-called PE-TEOS film formed by a plasma CVD method
be inadequate, and if the concentration of the dispersant is using tetraethoxysilane as starting material. Further, a so
higher than this range, agglomeration of abrasive particles called HDP film formed by a high density plasma CVD
tends to gradually proceed. method may also be mentioned. The silicon nitride film 3
0063 For the preparation of liquid 2, a method of dis may, for example, be one formed by a low pressure CVD
solving the above-described additive to pure water or deion method or a plasma CVD method using silane or dichlo
ized water, may, for example, be mentioned. Further, by rosilane and ammonia as starting materials. Further, instead
incorporating a dicarboxylic acid of the formula 1 to liquid of the silicon dioxide film, a SiOF film, a BPSG (Boro
2 to preliminarily carry out the pH adjustment, it is possible Phospho-Silicate Glass) film or a PSG (Phospho-Silicate
to bring the pH of the semiconductor polishing compound to Glass) film may, for example, be also used. Further, instead
be prepared by mixing liquids 1 and 2, to a predetermined of the silicon nitride film, a SiON film or a SiCN film may,
level. Further, as a method of bringing the pH of the for example, be used.
semiconductor polishing compound after the mixing to the 0068. When a semiconductor substrate is polished by
predetermined level, a method of controlling the pH of the means of the polishing compound of the present invention,
above additive, may also be employed. For example, in a the polishing compound is Supplied to a polishing pad, the
case where a copolymer made of a carboxylic acid with a surface to be polished, of the semiconductor device, is
carboxylate, is used as the additive, it is possible to employ brought in contact with the polishing pad, and the Surface to
a method of adjusting the pH by controlling the polymer be polished, of the silicon dioxide material layer is polished
ization ratio of the carboxylic acid with the carboxylate. by relative motion between them. Here, the conditions with
HOOC(CH2)COOH Formula 1
respect to the silicon dioxide material, are the same as
described in connection with the polishing compound of the
0064. The concentrations of liquids 1 and 2 may, for present invention.
example, be made to be twice the concentration at the time 0069. As the polishing apparatus, a common polishing
of use for polishing, so that the prescribed concentration apparatus may be used. For example, FIG. 2 is a view
may be obtained by mixing liquids 1 and 2 in a mass ratio showing an example of a polishing apparatus which can be
of 1:1. Further, for the sake of convenience for storage or used for the polishing method of the present invention. This
transportation, the concentrations of liquids 1 and 2 may, for is a system wherein while the semiconductor polishing
example, be made so that the concentrations of the compo compound 36 is supplied from a polishing compound
nents such as the abrasive particles, the additive, etc. would supply pipe 35, a semiconductor device 31 is held by a
be about ten times the concentration at the time of use for
polishing, and they are diluted to a concentration of twice at polishing head 32 and is brought in contact with a polishing
the time of use, and liquids 1 and 2 are further mixed in a pad 34 bonded to the surface of a polishing table 33, and the
mass ratio of 1:1 to obtain the prescribed concentration. polishing head 32 and the polishing table 33 are rotated for
Further, liquids 1 and 2 having concentrations often times relative movement. However, the polishing apparatus of the
and deionized water may be mixed in a mass ratio of 1:1:8 present invention is not limited thereto.
to obtain the prescribed concentration. However, the method 0070 The polishing head 32 may perform not only
for adjusting the concentration is not limited to Such specific rotational but also a linear movement. The polishing table 33
methods. and the polishing pad 34 may be of the same size as or
Smaller than the semiconductor device 31. In Such a case, it
0065. The method for preparing the polishing compound is preferred to relatively move the polishing head 32 and the
of the present invention is not limited to the above-described polishing table 33, so that the entire surface of the semi
method of dividing into liquids 1 and 2, followed by mixing. conductor device can be polished. Otherwise, the polishing
For example, cerium oxide abrasive particles, the dicarboxy table 33 and the polishing pad 34 may not be of a rotational
lic acid of the formula 1 and, if necessary, an additive, may type, but may for example be of a type moving in one
be added to water, followed by mixing to prepare the direction by a belt system.
polishing compound. 0071. The polishing conditions of the polishing apparatus
HOOC(CH2)COOH Formula 1 are not particularly limited, but the removal rate can be
0.066 As the semiconductor substrate to be polished by improved by exerting a load to the polishing head 32 to press
the semiconductor polishing compound of the present inven it against the polishing pad 34. The polishing pressure at that
tion, the above-mentioned STI substrate for shallow trench time is preferably at a level of from 0.5 to 50 kPa, and from
isolation may be mentioned as a preferred example. As the viewpoint of the uniformity of the removal rate within
described above, the semiconductor polishing compound of the semiconductor device, flatness and prevention of pol
the present invention has high selectivity for the removal ishing defects such as scratches, it is particularly preferably
rate against a silicon dioxide film and a silicon nitride film at a level of from 3 to 40 kPa. Further, the rotational speeds
and is capable of polishing a silicon dioxide film at a high of the polishing table and the polishing head are preferably
removal rate with no Substantial dishing. Thus, the polishing from about 50 to 500 rpm, but not limited thereto.
compound of the present invention is effective for polishing 0072 The polishing pad may be one made of e.g. a
a semiconductor Substrate having a silicon dioxide film 2 common non-woven fabric, a foamed polyurethane, a
and a silicon nitride film 3 formed on a silicon substrate 1. porous resin or a non-porous resin. Further, lattice, concen
Further, as an application, the polishing compound of the tric or helical grooves may be formed on the surface of the
present invention is effective also for polishing for pla polishing pad in order to promote the Supply of the semi
narization of an interlayer insulation film between multilayer conductor polishing compound or to let a certain amount of
wirings or for planarization of a polysilicon. the semiconductor polishing compound stay there.
US 2008/0O8695.0 A1 Apr. 17, 2008

EXAMPLES water with stirring, and Subjected to ultrasonic dispersion

and filtering to obtain a mixture having a concentration of
0073. Now, Examples of the present invention will be abrasive particles of 10% by mass ratio and a concentration
described. Examples 1 to 3 are Examples of the present of the additive of 0.07%. This mixture was diluted five times
invention, and Examples 4 and 5 are Comparative with deionized water to prepare an abrasive particle mixed
Examples. In Examples, "9/6" means “mass %' unless oth liquid Ahaving an abrasive particle concentration of 2% and
erwise specified. The property values were evaluated by the an additive concentration of 0.014%. The abrasive particle
following methods. mixed liquid A had a pH of 7.6 and an average particle
ph diameter of 0.18 um.
0074) Measured by pH81-11, manufactured by 0088. Then, an ammonium polyacrylate having a
Yokogawa Electric Corporation. molecular weight of 5,000 was dissolved in deionized water,
and the pH adjustment was carried out by adding malonic
Average Particle Diameter of Abrasive Particles acid (pKa=5.28) to bring the pH to from 4.7 to 5.0, to
0075 Measured by using a laser scattering-diffraction prepare an additive liquid B having an ammonium poly
apparatus (tradename: LA-920, manufactured by HORIBA, acrylate concentration of 0.289% and a malonic acid con
LTD.). centration of 0.166%.
Dispersion Stability of Polishing Compound 0089. The abrasive particle mixed liquid A and the addi
tive liquid B were mixed in a mass ratio of 1:1 with stirring
0.076 With respect to “Time for agglomeration and sedi to prepare a polishing compound having an abrasive particle
mentation' in Examples, 20 mL of a polishing compound concentration of 1%, a concentration of an ammonium
was put in a glass test tube having a diameter of 18 mm and polyacrylate added as an additive to the abrasive particle
left to stand still for 10 days, whereby it was obtained as a mixed liquid A of 0.007%, a concentration of an ammonium
time until the polishing compound was separated into two polyacrylate added from the additive liquid B of 0.145%, a
layers to form a Supernatant. total concentration of an ammonium polyacrylate added as
Polishing Characteristics additives of 0.152%, a malonic acid concentration of
0.083% and a pH of 5.06.
(1) Polishing Conditions
0077 Polishing was carried out by the following appa Example 2
ratus under the following conditions. 0090 An additive liquid C was prepared in the same
0078 Polishing machine: Fully automatic CMP appara manner as the preparation of the additive liquid B in
tus MIRRA (manufactured by APPLIED MATERIALS) Example 1 except that instead of malonic acid, adipic acid
(pKa=5.03) was used, and the concentration of adipic acid
0079 Polishing compound-supplying rate: 200 mL/min was adjusted to be 0.272%. This additive liquid C and the
0080 Polishing pad: K-groove of double layer pad abrasive particle mixed liquid A prepared in the same
IC-1400, or K-groove of single layer pd IC-1000 (manufac manner as in Example 1 were mixed in a mass ratio of 1:1
tured by Rodel) with stirring to prepare a polishing compound having an
abrasive particle concentration of 1%, an adipic acid con
0081 Conditioning of polishing pad: MEC100-PH3.5L centration of 0.136% and a pH of 4.90.
(manufactured by Mitsubishi Material)
0082 Rotational speed of polishing plate: 77 rpm Example 3
0.083 Rotational speed of polishing head: 73 rpm 0091 An additive liquid D was prepared in the same
manner as the preparation of the additive liquid B in
0084 Polishing pressure: 27.5 kPa Example 1 except that instead of malonic acid, Succinic acid
(2) Object to be Polished (pKa=5.24) was used, and the concentration of succinic
acid was adjusted to be 0.198%. This additive liquid D and
0085 HDP silicon dioxide film-coated blanket wafer the abrasive particle mixed liquid A prepared in the is same
manufactured by Advance Materials Technology, was used manner as in Example 1 were mixed in a mass ratio of 1:1
as an object to be polished. A schematic sectional side view with stirring to obtain a polishing compound having an
of the blanket wafer is shown in FIG. 3. abrasive particle concentration of 1%, a Succinic acid con
(3) Method for Evaluation of Properties centration of 0.099% and a pH of 5.06.
0086) The above blanket wafer was polished for 60 Example 4
seconds, whereby the difference in the film thickness
between before and after the polishing was taken as the Comparative Example
removal rate. For measurement of the film thickness, an
optical interfere type fully automatic measuring apparatus 0092 An additive liquid E was prepared in the same
UV-1280SE (manufactured by KLA-Tencor) was used. manner as the preparation of the additive liquid B in
Example 1 except that instead of malonic acid, tartaric acid
Example 1 (pKa=4.37) was used, the concentration of tartaric acid was
adjusted to be 0.100%, and the concentration of an ammo
0087 Cerium oxide abrasive particles and, as an additive, nium polyacrylate was changed to 0.17%. This additive
an ammonium polyacrylate having a molecular weight of liquid E and the abrasive particle mixed liquid A prepared in
5,000 were mixed in a mass ratio of 100:0.7 in deionized the same manner as in Example 1 were mixed in a mass ratio
US 2008/0O8695.0 A1 Apr. 17, 2008

of 1:1 with stirring to prepare a polishing compound having

an abrasive particle concentration of 1%, a tartaric acid TABLE 2
concentration of 0.050% and a pH of 5.03. Ammonia
concentration Removal rate
Example 5 Example No. (ppm) pH (nmmin)
1 O S.O6 3O2
Comparative Example O S.13 295
2O 5.20 301
2 O 4.90 259
0093. An additive liquid F was prepared in the same O 4.94 258
manner as the preparation of the additive liquid B in 2O 4.99 266
Example 1 except that instead of malonic acid, nitric acid 3 O S.O6 319
O S.12 3.18
was used, the concentration of nitric acid was adjusted to be 2O 5.17 324
0.082%, and the concentration of an ammonium polyacry 4 O S.O.3 274
late was changed to 0.17%. This additive liquid F and the O
2O
S.22
5.43
309
353
abrasive particle mixed liquid A prepared in the same 5 O S.O.3 249
manner as in Example 1 were mixed in a mass ratio of 1:1 O 5.30 295
with stirring to prepare a polishing compound having an 2O 5.55 358

abrasive particle concentration of 1%, a nitric acid concen

tration of 0.04.1% and a pH of 5.03.
0096. Further, the interrelation between the ammonia
0094. With respect to each of the above Examples, the concentration (ppm) in each of the polishing compounds of
composition, pH, average particle diameter (Lm) of abrasive Examples 1 to 5 and the removal rate is shown in FIG. 4.
particles, of the polishing compound, and the time for 0097. From the results in Table 2 and FIG.4, it is evident
agglomeration and sedimentation of the polishing com that the polishing compounds of Examples 1 to 3 as working
pound are shown in Table 1. In each of Examples 1 to 5, the examples of the present invention have the same levels of
average particle diameter of the final polishing compound dispersion stability and removal rate as the polishing com
was 0.19 um like the abrasive particle mixed liquid A. positions of Examples 4 and 5 and exhibit stabilized pol
Namely, no progress in agglomeration of particles was ishing characteristics even in the presence of ammonia.
observed by the mixing with the additive liquids B to F. INDUSTRIAL APPLICABILITY
These polishing compounds were left to stand to evaluate
the dispersion stability, whereby even upon expiration of 10 0098. The semiconductor polishing compound of the
days, no agglomeration or sedimentation was observed, and present invention is not only excellent in dispersion stability
the dispersion was maintained. Such a dispersed state was at and removal rate but also capable of providing stabilized
an equal level as the abrasive particle mixed liquid Ahaving polishing characteristics even in the presence of ammonia,
no additive incorporated. Even when the polishing com and thus, it is particularly effective for a STI process
pound was left to stand for 10 days by the above dispersion comprising a multistage process.
stability evaluation method, no Supernatant layer appeared, 0099. The entire disclosure of Japanese Patent Applica
and the dispersibility was excellent. tion No. 2005-165768 filed on Jun. 6, 2005 including
specification, claims, drawings and Summary is incorporated
TABLE 1. herein by reference in its entirety.
Time for
Cerium oxide Average agglomeration
Example concentration particle and What is claimed is:
No. (%) pH diameter sedimentation
1. A semiconductor polishing compound which is a pol
1 1.OOO S.O6 O.19 >10 days ishing compound for chemical mechanical polishing to
2 1.OOO 4.90 O.19 >10 days polish a surface to be polished in the production of a
3 1.OOO S.O6 O.19 >10 days semiconductor circuit device, said polishing compound
4 1.OOO S.O.3 O.19 >10 days comprising cerium oxide abrasive particles, water and a
5 1.OOO S.O.3 O.19 >10 days dicarboxylic acid represented by the formula 1:
HOOC(CH2)COOH Formula 1
wherein n is an integer of from 1 to 4, and the pH of said
0.095 Now, the results of evaluation of the polishing polishing compound at 25° C. being within a range of
characteristics when the respective polishing compounds of from 3.5 to 6.
Examples 1 to 5 were used, are shown in Table 2. Here, the 2. The semiconductor polishing compound according to
results having the polishing characteristics evaluated when claim 1, wherein the pH is within a range of from 4 to 6.
the ammonia concentration became 10 (ppm) or 20 (ppm) by 3. The semiconductor polishing compound according to is
gradually adding 1.0% aqueous ammonia to each of the claim 1, wherein the absolute value of the difference
polishing compounds of Examples 1 to 5, are also shown in between the pKa value of said dicarboxylic acid and said pH
Table 2. is at most 1.0.
US 2008/0O8695.0 A1 Apr. 17, 2008

4. The semiconductor polishing compound according to 7. The semiconductor polishing compound according to
claim 1, wherein the dicarboxylic acid is at least one claim 1, which contain at least one additive selected from the
member selected from the group consisting of malonic acid, group consisting of a water-soluble organic polymer and an
Succinic acid and adipic acid. anionic Surfactant.
5. The semiconductor polishing compound according to 8. The semiconductor polishing compound according to
claim 1, wherein the concentration of the dicarboxylic acid
is from 0.01 to 0.5 mass %. claim 7, wherein the water-soluble organic polymer is a
6. The semiconductor polishing compound according to polyacrylic acid or an ammonium polyacrylate.
claim 1, wherein the surface to be polished is made of silicon
dioxide.