JP2001253709A - Manufacturing method of crystalline cerium (iv) oxide particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a cerium (IV) oxide particle capable of preparing a high stable abrasive slurry and realizing high polishing speed and small surface roughness and also suitable for an abrasive, and to provide an abrasive slurry containing the particle. SOLUTION: In this method, the crystalline cerium (IV) oxide particle is manufactured by reacting an aqueous cerium (III) salt solution with an alkaline material in an inert gas atmosphere at pH 7-11 to prepare the suspension of cerium (III) hydroxide and hydrothermally treating the suspension in the state that the suspension contaion an oxidizing agent. In the crystalline cerium (IV) oxide particle for abrasive, primary particle diameter is >50 nm to <100 nm and the concentration change of the crystalline cerium (IV) oxide particle in the slurry is <=20%/day. The abrasive slurry is obtained from the oxide particle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to crystalline ceric oxide particles suitable for an abrasive, a method for producing the same, and a polishing slurry containing the same.

[0002]

2. Description of the Related Art Among abrasives, cerium oxide is useful and widely used as an abrasive used for finish polishing of glass. Various types of cerium oxide for abrasives, from inexpensive general-purpose products to high-purity products, are industrially produced.

[0003] Since cerium oxide, which is a general-purpose product, is generally obtained by calcining and pulverizing natural bastnaesite ore, it usually has a large primary particle diameter of 1 to 3 µm and contains a large amount of ore-derived impurities. Therefore, it is insufficient as an abrasive used in a semiconductor device manufacturing process.

As a method for producing high-purity cerium oxide, there is a method in which purified cerium carbonate, cerium oxalate, cerium acetate or the like is calcined to obtain cerium oxide. In these production methods, the particles are bonded to each other by firing, and thus a pulverizing step is essential. The powder after pulverization may contain crushed particles having sharp corners on the crushed surface or coarse particles remaining without being pulverized. There are problems such as scratches (polishing scratches) caused by the particles and the surface roughness of the object to be polished may be large, and this is insufficient for the use of precision abrasives. In addition, when coarse particles are contained, coarse particles settle when used as a polishing liquid, which may cause a problem in supply stability and storage stability to a polishing apparatus,
All particles are 100 nm with no settling problems
It was difficult to grind to a primary particle diameter of less than (0.1 μm).

On the other hand, when the primary particle diameter is 10
As a method for producing fine particles of less than 0 nm, a method by hydrothermal treatment (hydrothermal synthesis method) is known. For example, Japanese Patent Application Laid-Open No. 1-148710 discloses that a cerium salt compound is reacted with an alkali metal hydroxide or ammonia to form a gel, which is then subjected to hydrothermal treatment. Average particle size of 90 Å (9 nm) and 170 Å (1
(7 nm) of crystalline ceric oxide.

[0006] Japanese Patent Application Laid-Open No. 8-81218 discloses that "An aqueous medium containing ceric hydroxide and nitrate is adjusted to a pH of 8 to 11 using an alkaline substance,
By heating under pressure at a temperature of ~ 200 ° C ",
"As a result of a transmission electron microscope observation, 20 to 60 n
It is disclosed that "ceric oxide fine particles having an average diameter of m" were obtained.

Japanese Patent Application Laid-Open No. 8-501768 discloses "forming an aqueous solution composed of a water-soluble trivalent cerium salt and an oxidizing agent, and oxidizing the trivalent cerium salt in a liquid phase. It consists of aging for 4 hours or more to change the solid CeO ₂ particles with a chemically active Te, solid CeO with useful chemically active polishing operations
How to prepare _two particles. Having an average crystal size of about 7n as measured by transmission electron microscopy.
m, about 12 nm, about 30 nm, about 40 nm, about 50 n
m, particles of about 100 nm and larger than 100 nm are disclosed.

[0008] However, ceric oxide particles obtained by the hydrothermal synthesis method are easy to obtain fine particles, and secondary particles formed by agglomeration of primary particles have a wide range of particle sizes. The primary particle diameter was often as extremely small as 30 nm or less. The ceric oxide particles having a primary particle diameter of 30 nm or less show good properties in terms of the stability of the polishing liquid, but have a problem that the polishing rate is significantly reduced. Also one
The ceric oxide particles having a diameter of 00 nm or more had problems in that the unevenness (surface roughness) of the polished surface of the object to be polished was large and that the polishing liquid was unstable because the sedimentation was rapid when the slurry was used. .

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly stable polishing slurry and a high polishing rate and a small surface roughness. An object of the present invention is to provide cerium particles, a method for producing the same, and a polishing slurry containing the same.

[0010]

Means for Solving the Problems As a result of continuing research to solve the above problems, the present inventors have been able to produce a highly stable polishing slurry by hydrothermal treatment under specific conditions, and A high polishing rate and a small surface roughness of the polished surface can be realized, and crystalline ceric oxide particles suitable for abrasives can be obtained, and a specific average primary particle diameter and sedimentation by the production method of the present invention. Have found that crystalline ceric oxide particles having a suitable for abrasives,
The present invention has been completed.

That is, according to the present invention, an aqueous solution of a salt of trivalent cerium and an alkaline substance are subjected to pH adjustment in an inert gas atmosphere.
Reacts in the range of 7 to 11 to form a suspension of trivalent cerium hydroxide, and then hydrothermally treats the suspension with the oxidizing agent contained in the suspension. The present invention provides a method for producing crystalline ceric oxide particles. The present invention also provides an abrasive having an average primary particle diameter of more than 50 nm and less than 100 nm, and a change in the concentration of crystalline ceric oxide particles in the slurry when used as an aqueous slurry is not more than 20% / day. The present invention provides crystalline ceric oxide particles. Further, the present invention provides that the average primary particle diameter is more than 50 nm and 100
Provided is an aqueous slurry containing crystalline ceric oxide particles having a diameter of less than 10 nm, wherein a change in the concentration of crystalline ceric oxide particles in the slurry is 20% / day or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The steps in the production method of the present invention can be divided into two steps. The first step is to prepare an aqueous solution of a trivalent cerium salt and an alkaline substance at pH 7 in an inert gas atmosphere. To form a suspension of trivalent cerium hydroxide by reacting in the range of ~ 11. The second step included an oxidizing agent in the suspension generated in the first step. Hydrothermally treating the suspension in this state.

As the inert gas used in the first step, a non-oxidizing gas such as a nitrogen gas or an argon gas can be used. The reason that it is difficult to obtain crystalline cerium oxide particles larger than 30 nm in the conventional hydrothermal treatment is that trivalent cerium is easily oxidized to tetravalent by oxygen in the air, and fine crystalline cerium oxide is finely divided. It is considered that particles are generated before the hydrothermal treatment and affect the reaction of hydrothermal synthesis.In the production method of the present invention, the use of an inert gas prevents the generation of fine crystalline ceric oxide particles. It is considered to be.

For the reaction under an inert gas atmosphere, for example, a gas-replaceable reaction vessel equipped with a stirrer and a thermometer can be used. Materials such as stainless steel and glass lining can be used for the reaction vessel. Water is previously charged in the reaction vessel, and an aqueous solution of a trivalent cerium salt and an alkaline substance can be dropped and reacted. The water previously charged in the reaction vessel may contain a small amount of a water-soluble organic solvent. For gas replacement with an inert gas, for example, one end of a gas introduction pipe is immersed in water charged in advance, an inert gas is blown, and a gas is discharged from a discharge port provided at an upper part of a reaction vessel.
The reaction can be performed by filling the reaction vessel with an inert gas. The reaction is preferably started after the replacement with the inert gas. An inert gas can be flowed throughout the reaction. At this time, the pressure in the reaction vessel is desirably set to the atmospheric pressure. Therefore, it is preferable that the inflow amount and the outflow amount of the gas are substantially the same.

Examples of the trivalent cerium salt include cerous nitrate, cerous chloride, cerous sulfate, cerium ammonium nitrate (trivalent) and the like. The above trivalent cerium salts can be used alone or as a mixture. In particular, cerous nitrate,
When cerium ammonium nitrate (trivalent) is used, nitrate acting as an oxidizing agent at the end of the first step becomes 3%.
Since it is already contained in the suspension of monovalent cerium hydroxide, it is not necessary to add an oxidizing agent before the hydrothermal treatment in the second step.

Examples of the alkaline substance include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, aqueous ammonia, amines, and quaternary ammonium hydroxide. A sodium compound or an organic substance may need to be avoided as an impurity when used as an abrasive. Therefore, ammonia water and potassium hydroxide are particularly preferable, and these can be used alone or as a mixture.

The aqueous solution of the trivalent cerium salt and the alkaline substance can be added dropwise while adjusting the flow rate so that the pH of the mixture is in the range of 7 to 11. It is desirable to stir during the reaction. When the pH is less than 7, the neutralization reaction is not completed, and the trivalent cerium salt remains in the suspension without being completely converted into hydroxide. When the pH is higher than 11, the viscosity of the suspension of trivalent cerium hydroxide becomes high, and it becomes difficult to promote the reaction uniformly.
Therefore, in the production method of the present invention, the pH range is from 7 to
11, preferably 8 to 10.

The reaction time varies depending on the charged amount.
A range from minutes to 24 hours is preferred. If the reaction time is 1 minute or less, it becomes difficult to adjust the pH to a range of 7 to 11. If the reaction time exceeds 24 hours, the formed precipitate may aggregate, which is not preferable.

The present invention comprises, as a second step, a step of subjecting the suspension prepared in the first step to a hydrothermal treatment with the oxidizing agent contained therein. By performing the second step, it becomes possible to produce crystalline ceric oxide particles having an average primary particle diameter in the range of more than 50 nm and less than 100 nm. In the present invention, the oxidizing agent is
It may be added to the portion where the suspension is generated in the first step, may be added to the generated suspension, or may be added during the hydrothermal treatment of the second step.

Examples of the oxidizing agent include nitrate, hydrogen peroxide, perchloric acid and the like, and nitrate is particularly preferable because it is inexpensive and easy to handle. Examples of the nitrate include ammonium nitrate, lithium nitrate, sodium nitrate, potassium nitrate, and the like. Particularly, ammonium nitrate and potassium nitrate are preferable, and these can be used alone or as a mixture. If hydrogen peroxide is added to the suspension generated in the first step, cerium will be oxidized to tetravalent, but the device must be devised so that hydrogen peroxide can be added during the hydrothermal treatment in the second step. Thus, it is possible to use hydrogen peroxide or the like.

When cerous nitrate or cerium ammonium nitrate (trivalent) is used as the trivalent cerium salt, the hydrothermal treatment in the second step can be performed without separately adding an oxidizing agent. When a trivalent cerium salt other than a nitrate is used, an oxidizing agent is added to the suspension of the trivalent cerium hydroxide. The added amount of the oxidizing agent is preferably 3
3 to 5 times the molar amount of monovalent cerium.

In the hydrothermal treatment of the second step of the present invention,
The temperature is preferably in the range of 100 to 200C.
Pressure is 1-30kg / cm^TwoPreferably in the range
No. This pressure can also be obtained by applying external pressure.
But usually obtained by the vapor pressure of water. Temperature is 100 ° C
If it is less than 10, the growth of crystalline cerium oxide crystals is insufficient
If the temperature exceeds 200 ° C, the water vapor pressure
Pressure is 30kg / cm ^TwoSpecial pressure vessel required
And industrial implementation becomes difficult. Pressure is 1kg / cm
^TwoIf it is less than 10, the crystal growth of crystalline cerium oxide is insufficient.
Can be minutes. The reaction time depends on the reaction temperature
Although it is not necessarily limited, preferably 1 to 12 hours
Range. If the reaction time is less than 1 hour, crystal growth is insufficient.
May be confusing. If the reaction time exceeds 12 hours, crystals
Since re-melting occurs and the crystal shape is rounded,
The polishing rate may be reduced when used in this manner.

The reactor used for the hydrothermal treatment in the second step of the present invention only needs to have a structure that can withstand high pressure and be made of a material that does not corrode with nitrate solution. Stainless steel, Hastelloy, Teflon (registered trademark) (Trademark) An autoclave device having resin or glass as an inner wall can be used.

During the hydrothermal treatment in the second step of the present invention, nucleation of crystalline ceric oxide particles and crystal growth thereof proceed. The nucleation rate and the crystal growth rate can be controlled by changing the concentration of the cerium salt, the concentration of the alkaline substance, the reaction temperature, the concentration of the aqueous nitrate solution, and the like.
It is also possible to control the particle size by adding crystalline ceric oxide having a primary particle size of 30 nm or less as seed particles before the hydrothermal treatment. That is, if the amount of the crystalline ceric oxide particles having a primary particle diameter of 30 nm or less is large, the crystalline ceric oxide particles generated after the hydrothermal treatment are small.

Since the crystalline ceric oxide particles of the present invention are fine particles, it is difficult to measure the particle size using a sedimentation type or laser diffraction type particle size distribution measuring device, and thus can be obtained by powder X-ray diffraction measurement. Scherr from the peak
The crystallite diameter determined using the equation of er was taken as the value of the average primary particle diameter. The average primary particle diameter and the primary particle diameter obtained by observation with a transmission electron microscope almost coincide with each other.

Since the crystalline ceric oxide particles obtained according to the present invention are taken out of the reactor as a slurry, they can be obtained by ultrafiltration or filter pressing.
The crystalline ceric oxide particles obtained according to the present invention can be removed from the slurry or washed with water.

The crystalline ceric oxide particles of the present invention include:
The average primary particle diameter is in the range of more than 50 nm and less than 100 nm, preferably more than 60 nm and 90 nm or less, more preferably 65 nm or more and 80 nm or less. The crystalline ceric oxide particles according to the present invention can be made into a slurry by being redispersed in water, a water-soluble organic solvent or a mixed solvent of water and a water-soluble organic solvent, and can be used as an abrasive. The crystalline ceric oxide particles according to the present invention are much less likely to settle in the slurry than conventional particles having an average primary particle diameter of 100 nm or more, and the slurry is more stable in supply to a polishing apparatus. It is excellent. If the change in the concentration of crystalline ceric oxide particles in the slurry is more than 20% / day, the slurry may not be supplied stably to the polishing apparatus. Since the crystalline cerium oxide particles of the present invention are larger than 50 nm,
The change in the concentration of crystalline ceric oxide particles in the slurry occurs at 1% / day or more. Sedimentation Although a part of the particles of the slurry is settled by storage for a long time, the slurry can be easily redispersed by stirring, and thus has excellent storage stability.

The main object of polishing is a Si thermal oxide film in a semiconductor manufacturing process, and the crystalline cerium oxide particles of the present invention have a polishing rate of 0.3 μm for the Si thermal oxide film.
Since it is larger than m / hour, it can be preferably applied to a polishing step in a semiconductor manufacturing process. Crystalline ceric oxide particles having an average primary particle diameter of 50 nm or less
When used for polishing of thermal oxide film, polishing rate is 0.3μ
m / hour or less.

When the slurry of the crystalline cerium oxide particles according to the present invention is used as an abrasive, a polishing slurry having a lower sedimentation and higher stability can be produced as compared with a conventional slurry of ceric oxide particles. At the same time, a high polishing rate can be realized, and the unevenness (surface roughness) of the polished surface of the object to be polished is reduced, thereby exhibiting excellent performance as an abrasive.

[0030]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A 1-liter glass reactor equipped with a pH electrode was charged with 350 g of water, and nitrogen gas was blown at a flow rate of 200 ml / min to replace the inside of the reactor with nitrogen gas. An aqueous solution of 132 g of cerium nitrate dissolved in 150 g of water and 28% by weight
Ammonia water was dropped into the reaction vessel while adjusting the flow rate so that the pH was constant at 9. After dropping the entire amount of the cerium nitrate solution, ammonia water was dropped until the pH reached 10, and the mixture was stirred for 80 minutes to prepare a suspension of trivalent cerium hydroxide. The molar ratio in the suspension was ^NO3- /
Ce ³⁺ = 3 and NH ₃ / Ce ³⁺ = 6. This suspension was charged into a stainless steel pressure vessel having a capacity of 1 liter, the temperature was raised to 180 ° C. in 90 minutes, the temperature was maintained for 5 hours, and then cooled. A pale yellow suspension was obtained.

The particles were separated from the pale yellow liquid by an ultrafiltration method, washed, and dried. Transmission electron microscope (TEM)
As a result, particles having a particle diameter of 50 to 100 nm were observed. The yield of the particles is approximately 10
It was 0%. When the powder X-ray diffraction of the particles was measured,
Diffraction angles 2θ = 28.6 °, 47.5 ° and 56.4 °
A large peak was detected, and A
The peak coincided with the peak of cubic crystalline ceric oxide described in STM Card No. 34-394. The crystallite diameter, that is, the average primary particle diameter, determined from the peak at 47.5 ° using the Scherrer equation was 77 nm. The value of the crystallite diameter indicated the average size of the particles as observed by TEM.

SN dispersant 5468 (trade name, manufactured by San Nopco Co., Ltd.) was added as a dispersant to the crystalline ceric oxide particles at 1.5% by weight based on the crystalline ceric oxide particles, and water was added. The concentration was adjusted to 2% by weight as crystalline ceric oxide particles. Using this slurry as a polishing slurry, a polishing test was performed under the following polishing conditions. [Polishing conditions] Polishing object: 6 "φ solid oxide film wafer (thermal oxide film 1 μm /
Si) Pad: Two-layer type polishing pad for semiconductor device (IC1000 / Suba40 manufactured by Rodel Nitta Co., Ltd.)
0) Polishing machine: Polishing machine for polishing semiconductor devices (manufactured by Preshi Corporation, model number: Mecapol-E460, platen diameter: 460 m)
m) Platen rotation speed: 39 rpm Slurry supply speed: 100 ml / min Processing pressure: 300 g / cm ² Polishing time: 1 min The polishing characteristics (polishing speed and surface roughness Rmax values) were evaluated under the above conditions, and are shown in Table 1. did.

Example 2 Hydrothermal treatment was performed under the same conditions as in Example 1 except that only the temperature of the hydrothermal treatment was changed to 120 ° C., to obtain a pale yellow liquid. The particles were separated from the liquid by an ultrafiltration method, washed, dried, and analyzed in the same manner as in Example 1. Crystalline ceric oxide particles having a primary particle diameter of 30 to 100 nm as determined by TEM observation were obtained. The average primary particle size determined from powder X-ray diffraction measurement was 68 nm.

Comparative Example 1 A suspension was prepared and subjected to hydrothermal treatment under the same conditions as in Example 1 except that the reaction was performed in an air atmosphere without replacing with nitrogen gas. As a result, a pale yellow liquid was obtained. .

The particles are separated from the liquid by an ultrafiltration method,
After washing and drying, the same analysis as in Example 1 was performed. As a result, crystalline ceric oxide particles having a primary particle diameter of 10 to 30 nm by TEM observation were obtained. Also, powder X
The average primary particle diameter determined from the line diffraction measurement was 21 nm. With respect to the particles obtained in Comparative Example 1, SN Dispersant 5468 (trade name, manufactured by San Nopco Co., Ltd.) was used as a dispersant with respect to the crystalline ceric oxide particles.
% By weight and water was added to prepare a 2% by weight slurry as crystalline ceric oxide particles. Using this slurry as a polishing liquid, the polishing characteristics (polishing rate and surface roughness Rmax values) were evaluated under the same conditions as in Example 1, and the results are shown in Table 1.

Comparative Example 2 For comparison, a commercially available cerium oxide powder (average primary particle diameter: 0.3 μm) was dispersed in water, and SN was used as a dispersant.
Dispersant 5468 was added in an amount of 1.5% by weight based on ceric oxide, and then water was added to adjust the concentration to 2% by weight as ceric oxide. Using this slurry as a polishing liquid, the polishing characteristics (polishing rate and surface roughness Rmax values) were evaluated under the same conditions as in Example 1, and the results are shown in Table 1.

[0038]

Table 1 Cerium oxide abrasives Polishing characteristics Polishing rate Surface roughness Rmax (μm / hour) (nm) Example 1 0.42 2.1 Comparative Example 1 0.18 2.0 Cerium powder 1.2 2.6

When the crystalline cerium oxide particles of Example 1 according to the production method of the present invention were used, the polishing rate was about 2.3 times higher than when the crystalline ceric oxide particles of Comparative Example 1 were used. Improved. Further, when the crystalline cerium oxide particles of Example 1 according to the production method of the present invention were used, the surface roughness of the polished surface was smaller than when commercially available cerium oxide particles were used.

The sedimentation behavior of Example 1 and commercially available ceric oxide powder was examined as follows. A slurry prepared so that the ceric oxide concentration becomes 5% by weight is 10
100 ml was dispensed into a 0 ml measuring cylinder, shaken sufficiently, and allowed to stand. After that, 15 ml of the uppermost supernatant was dispensed over time, and the concentration of the crystalline ceric oxide particles contained therein was determined. It was measured. The results are shown in Table 2.

[0041]

Table 2 Elapsed time 0 minutes 60 minutes 1 day 5 days Example 1 5.0% by weight 5.0% by weight 4.5% by weight 4.3% by weight Commercial powder 5.0% by weight 4.2% by weight 1 0.3% by weight 0.4% by weight

The slurry of the crystalline ceric oxide particles of Example 1 according to the present invention settled down much slower than the commercially available slurry of ceric oxide powder. The change in the concentration of the crystalline ceric oxide particles in the slurry of the crystalline ceric oxide particles of Example 1 was (5.0-4.5) /
Whereas 5.0 × 100 = 10% / day, the change in the concentration of cerium oxide in the slurry of commercially available cerium oxide powder is (5.0-1.3) /5.0×100.
= 74% / day. Therefore, the slurry of the crystalline ceric oxide particles of the present invention of Example 1 has a low sedimentation of the crystalline ceric oxide particles and is excellent in the supply stability to the polishing apparatus.

[0043]

When the crystalline ceric oxide particles of the present invention are used as an abrasive, the polishing rate is high and the surface roughness of the polished surface is small, and the polishing using the crystalline ceric oxide particles of the present invention is effective. The slurry for use has a high sedimentation stability and is excellent in the supply stability to the polishing apparatus. According to the production method of the present invention, crystalline ceric oxide particles suitable for the above-mentioned abrasive can be produced.

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Claims (7)

[Claims] An aqueous solution of a trivalent cerium salt and an alkaline substance are reacted in an inert gas atmosphere at a pH of 7 to 11 to form a suspension of a trivalent cerium hydroxide. A method for producing crystalline ceric oxide particles, wherein the suspension is subjected to hydrothermal treatment in a state where the suspension contains an oxidizing agent. 2. The method according to claim 1, wherein the oxidizing agent is a nitrate. 3. The method for producing crystalline ceric oxide particles according to claim 1, wherein the alkaline substance is aqueous ammonia, potassium hydroxide or a mixture thereof. 4. The method for producing crystalline ceric oxide particles according to claim 1, wherein the temperature for the hydrothermal treatment is in the range of 100 to 200 ° C. 5. The method for producing crystalline ceric oxide particles according to claim 2, wherein the nitrate is ammonium nitrate, potassium nitrate or a mixture thereof. 6. An average primary particle diameter of more than 50 nm and 100 n
m and the change in the concentration of crystalline ceric oxide particles in the slurry when the slurry is an aqueous slurry is 20%.
% / Day of crystalline ceric oxide particles for abrasives. 7. An average primary particle diameter of more than 50 nm and 100 n
An aqueous slurry containing crystalline ceric oxide particles in a range of less than m, wherein a change in the concentration of crystalline ceric oxide particles in the slurry is 20% / day or less.