JP2011104680A - Polishing liquid containing cerium oxide particle and polishing method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing liquid containing cerium oxide particles capable of reducing polishing scars. <P>SOLUTION: In the polishing liquid containing cerium oxide particles and water, the number of the particles with a particle diameter of 0.75 μm or larger in 1 ml of the polishing liquid is 3×10<SP>6</SP>or less. The polishing liquid contains the cerium oxide particles prepared by a manufacturing method including: (I) a step of hot-mixing cerium carbonate with an organic acid to obtain hot-mixed powder; (II) a step of baking the hot-mixed powder to obtain cerium oxide powder; and (III) a step of crushing the cerium oxide powder to obtain the cerium oxide particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polishing liquid containing cerium oxide particles suitable for a semiconductor flattening polishing liquid and a polishing method using the same.

  Examples of applications that require precise polishing of the material surface include optical disks, magnetic disks, glass substrates for flat panel displays, watch plates, camera lenses, glass materials used in various lenses for optical components, filters, etc. There are crystal materials, substrates such as semiconductor silicon wafers, insulating films, metal layers, barrier layers and the like formed in each process of semiconductor device manufacturing.

  The surface of these materials is required to be polished with high accuracy. As a polishing process in semiconductor device manufacturing, for example, planarization of an interlayer insulating film such as a silicon oxide film, or a shallow trench excluding an extra silicon oxide film embedded on a substrate to isolate an element in an integrated circuit There are element isolation films and the like.

As a polishing liquid for precision polishing in manufacturing these semiconductor devices, in particular, a silica polishing liquid using silica fine particles as polishing particles is widespread because there are few occurrences of polishing scratches on the surface to be polished. In recent years, a polishing liquid containing cerium oxide, which has a high polishing rate, has attracted attention.
However, there is a problem that such a polishing liquid has more polishing scratches than silica particles.

  Polishing liquids containing cerium oxide have been used for glass polishing for a long time, but it was necessary to avoid contamination with impurities as much as possible in order to apply them to semiconductor planarization. Therefore, high-purity cerium oxide is obtained by once refining the rare earth material and firing it via a cerium salt.

  Examples of cerium salts include cerium carbonate, cerium oxalate, and cerium nitrate. A polishing liquid for semiconductor planarization is produced by dispersing cerium oxide obtained by calcining and grinding these cerium salts.

Polishing flaws that occur during the polishing process tend to be reduced by lowering the content of large-diameter particles in the polishing liquid.
However, in the method of firing and pulverizing cerium compounds such as cerium carbonate conventionally used in the production of cerium oxide, it takes a long time for pulverization, and the parts of the pulverizer are worn and wear powder is mixed into the polishing liquid. The possibility increases. Abrasion powder mixed in the polishing liquid is not preferable because it causes polishing scratches.

  Moreover, since the large particle diameter particles are not pulverized and mixed in the polishing liquid in a short pulverization, it is difficult to reduce the content of the large particle diameter particles (see, for example, Patent Document 1).

  On the other hand, higher integration of semiconductors has progressed, and the processing dimensions of wiring and the like have been reduced to 100 nm. Accordingly, there is an increasing demand for reducing defects such as polishing scratches, and a polishing liquid that satisfies all of the polishing rate, flatness, and polishing scratch reduction is required.

  For the purpose of reducing polishing scratches by the polishing liquid, cerium carbonate and acid such as oxalic acid are mixed and then baked to pulverize the cerium oxide powder and use it as cerium oxide particles as a polishing liquid. A method for manufacturing a reduced semiconductor planarization polishing liquid has been proposed. (For example, see Patent Document 2)

  The cerium oxide powder obtained by firing after mixing cerium carbonate and acid is different in shape from the cerium oxide powder obtained by firing cerium carbonate as it is, and the grindability is improved. Since it is possible to prevent the mixing of equipment wear powder from the machine and at the same time to reduce the content of large particles, polishing flaws can be reduced.

JP 2000-26840 A International Publication No. 07/123203 Pamphlet

  However, in the above production method, the pulverizability of the cerium oxide powder obtained after firing tends to vary depending on the production lot, and it is difficult to stably obtain a cerium oxide powder with good pulverizability.

  In addition, when firing is performed by a continuous operation firing furnace such as a rotary kiln or a tunnel furnace excellent in mass productivity, the crystallinity of the obtained cerium oxide powder tends to increase. When the crystallinity of the cerium oxide powder becomes high, the parts of the pulverizer are easily worn when the cerium oxide powder is pulverized. If it does so, the abrasion powder of a grinder will mix in the cerium oxide particle, and since it mixes also in the polishing liquid containing the obtained cerium oxide particle, it is not preferable.

  Therefore, a method of adjusting the firing temperature and the temperature rising rate so as not to increase the crystallinity is conceivable. On the other hand, if the crystallinity is lowered, there is a problem that the cerium oxide particles to be obtained have poor grindability.

  In view of the above, the present invention is capable of more stably and efficiently obtaining cerium oxide particles having excellent pulverizability while preventing contamination of foreign substances such as pulverizer wear powder that may occur in the cerium oxide particle pulverization step. Thus, an object of the present invention is to provide a polishing liquid containing cerium oxide particles capable of reducing polishing scratches.

In order to solve the above-mentioned problems, the present inventors have intensively studied and found the following.
The reaction of powdered cerium carbonate and organic acid proceeds gradually and gradually in a mixed state using moisture contained in each other as a medium. When the reaction between cerium carbonate and the organic acid is not completed, the reaction proceeds from mixing to firing. For this reason, if the time from mixing to baking is not constant, it was considered that the pulverizability of the cerium oxide powder would vary among production lots.

  Therefore, the present inventors predicted that it is necessary to stop the reaction between cerium carbonate and the organic acid in the middle in order to stably obtain a highly pulverizable cerium oxide powder, and by heating mixing in the reaction system The present inventors have found conditions under which high pulverizable cerium oxide powder can be stably obtained by evaporating water and stopping the reaction.

  More specifically, by evaporating the water in the reaction system by heating and mixing under certain conditions and stopping the reaction, the same degree of pulverization and the same degree can be obtained regardless of the time from mixing to firing. It has been found that cerium oxide powder having crystallinity can be stably produced, and thereby cerium oxide particles capable of reducing polishing scratches can be stably and efficiently obtained even in different production lots.

In the conventional manufacturing method in which cerium oxide particles are obtained by mixing cerium carbonate and an organic acid, followed by firing and pulverization processes, the crystallinity of the cerium oxide powder is affected by the rate of temperature rise. For example, when using a continuous kiln, such as a rotary kiln or a tunnel furnace, rapidly heating and raising the temperature to the firing temperature, when heating it gently in a batch furnace and raising the temperature to the firing temperature and firing In comparison, the crystallinity of the obtained cerium oxide powder tends to increase.
However, in the present invention, cerium oxide powder with good grindability can be obtained without increasing crystallinity even by rapid heating in a continuous operation type firing furnace by heating and mixing, thereby reducing polishing scratches. The present inventors have found that the cerium oxide particles obtained can be obtained stably and efficiently, and have completed the present invention.

That is, the present invention is as follows.
(1) A polishing liquid comprising a cerium oxide particle and water, wherein the number of particles having a particle diameter of 0.75 μm or more in 1 ml of the polishing liquid is 3 × 10 ⁶ or less.
(2) The cerium oxide particles are (I) a step of heating and mixing cerium carbonate and an organic acid to obtain a heated mixed powder, and (II) a step of firing the heated mixed powder to obtain a cerium oxide powder. III) The above polishing liquid, which is a cerium oxide particle produced by a production method comprising the step of pulverizing the cerium oxide powder to obtain cerium oxide particles.
(3) When the mass of the heated mixed powder immediately after the step (I) and the mass of the heated mixed powder after leaving the heated mixed powder at a temperature of 25 ° C. for 24 hours are compared, The said polishing liquid which is 0-0.1 mass%.
(4) The said polishing liquid in which the heating of (I) process is performed in the range of 40-200 degreeC.
(5) The said polishing liquid whose time of the heat mixing of a process (I) is 1.5 to 4 hours.
(6) The cerium oxide powder obtained by firing the heated mixed powder has a half-value width of the diffraction peak due to the (111) plane of the cerium oxide crystal obtained from a powder X-ray diffraction pattern using CuKα rays as a radiation source. The said polishing liquid which is 0.27-0.50 degree and 99 volume% or more of the cerium oxide ground material after grind | pulverizing is a particle diameter of 0.1-1 micrometer.
(7) The said polishing liquid with which baking of a process (II) is performed in 400-900 degreeC.
(8) The said polishing liquid whose median value of the particle diameter of the cerium oxide particle in polishing liquid is 0.1-1 micrometer.
(9) The above polishing liquid, wherein the content of cerium oxide particles having a particle diameter of 3 μm or more in the polishing liquid is 500 ppm or less in the solid.
(10) The polishing liquid further containing a dispersant.
(11) The said polishing liquid whose 99 volume% or more of the whole cerium oxide particle | grains in polishing liquid are 1 micrometer or less in particle diameter.
(12) A method for polishing a substrate, comprising polishing a predetermined substrate with the polishing liquid.
(13) The method for polishing a substrate, wherein the predetermined substrate is a semiconductor chip on which at least a SiO ₂ film is formed.

  According to the present invention, it is possible to efficiently and stably obtain cerium oxide particles capable of polishing a semiconductor surface in a wiring formation process at high speed and having good flatness and capable of reducing polishing scratches. A polishing liquid containing cerium oxide particles and a polishing method using the same can be provided.

One embodiment of the heating and mixing apparatus used in the method for producing cerium oxide particles of the present invention is shown. The measurement example which calculates | requires the half value width of the diffraction peak by the (111) plane of the cerium oxide crystal which is the main peak of the cerium oxide particle in the polishing liquid of this invention is shown.

Hereinafter, the best mode for carrying out the invention will be described in detail.
The polishing liquid of the present invention is characterized in that, in a polishing liquid containing cerium oxide particles and water, the number of particles having a particle diameter of 0.75 μm or more in 1 ml of the polishing liquid is 3 × 10 ⁶ or less.

<Method for producing cerium oxide particles and cerium oxide particles obtained therefrom>
The method for producing cerium oxide particles used in the present invention preferably has the following steps.
(I) a step of heating and mixing cerium carbonate and an organic acid to obtain a heated mixed powder;
(II) firing the heated mixed powder to obtain a cerium oxide powder;
(III) A step of pulverizing the cerium oxide powder to obtain cerium oxide particles.
In the present invention, heat mixing means a method of mixing and heating and a method of mixing while heating, but it is preferable to mix while heating in terms of heating uniformly.

  In the present invention, “heat mixed powder” refers to a powder obtained by heating and mixing cerium carbonate and an organic acid, and is a powder before the firing step. The “cerium oxide powder” is a powder obtained by firing the heated mixed powder, and is a powder before the pulverization step. The “cerium oxide particles” are those obtained by pulverizing the cerium oxide powder, and it is preferable that the cerium oxide particles be treated by sedimentation classification, filtration or the like after pulverization, and the treated particles also correspond to “cerium oxide particles”. Furthermore, “cerium oxide pulverized product” described later refers to a pulverized product obtained by pulverizing cerium oxide powder under specific conditions (details will be described later, pulverization conditions (a)).

In the conventional method of firing cerium salts such as cerium carbonate and cerium oxalate, which has been used in the production of cerium oxide, the cerium salt is thermally decomposed to obtain cerium oxide powder. In that case, there is often no significant difference between the shapes of the cerium salt and the cerium oxide powder.
However, when cerium carbonate and organic acid are mixed and baked, a chemical reaction between cerium carbonate and organic acid takes place, carbonate ions are replaced, and thermal decomposition occurs through the formation of an organic acid salt of cerium. The body is obtained. This cerium oxide powder is greatly different in shape from cerium carbonate, and also different in shape from cerium oxide powder obtained by firing a commercially available cerium salt as it is, and becomes an aggregate of fine particles. Since this cerium oxide powder is an aggregate of fine particles, it is easily pulverized in a short time to become cerium oxide fine particles.

  The reaction between cerium carbonate and the organic acid proceeds sequentially in a mixed state using moisture contained in each other as a medium. Since it is a reaction between solids, it takes a long time to complete the reaction. If the reaction is not completed, the cerium oxide powder having the same degree of grindability can be produced in different production lots unless the time until firing is constant, that is, the reaction progress is constant. Have difficulty. Therefore, in the present invention, even when the reaction is not completed, by evaporating the moisture as a medium from the reaction system by heating and mixing under the same conditions, the reaction does not proceed at the end of heating and mixing. The degree of progress of the reaction can be made constant, which makes it possible to stably produce a cerium oxide powder having the same degree of grindability regardless of the time until firing. Thereby, cerium oxide particles having good flatness and capable of reducing polishing scratches can be obtained efficiently and stably.

The grindability of the cerium oxide powder will be specifically described below.
Conventionally, in a production method in which cerium carbonate and an organic acid are mixed and then fired and pulverized to obtain cerium oxide particles, the pulverizability is determined by the shape and crystallinity of the cerium oxide powder.
The shape of the cerium oxide powder is determined by the shape when cerium carbonate and an organic acid are mixed to produce an organic acid salt of cerium, and the organic acid salt of cerium is thermally decomposed by firing. The shape of the organic acid salt of cerium is determined by the time until it reaches the thermal decomposition temperature after mixing, and the state of the atmosphere such as temperature and moisture. It is also affected by the degree of progress of the reaction produced by the cerium organic acid salt.

  On the other hand, the crystallinity of the cerium oxide powder is determined by the shape during pyrolysis and the firing temperature. Therefore, conventionally, affected by the rate of temperature rise until reaching the thermal decomposition temperature, when heated rapidly using a rotary kiln, tunnel furnace, etc., raised to the firing temperature and fired, the batch furnace is heated gently and fired There is a problem that the crystallinity of the obtained cerium oxide powder is increased as compared with the case where the temperature is raised to a temperature and firing.

  However, in the present invention, by the heating and mixing of cerium carbonate and organic acid before firing, the progress and shape of the reaction that the organic acid salt of cerium is generated can be controlled without increasing the crystallinity even by rapid heating. It became possible to produce cerium oxide powder with good grindability.

The organic acid in the present invention is preferably a solid at 25 ° C. If the organic acid is a gas, handling of the acid and mixing with cerium carbonate is difficult, which is not preferable. Further, when the organic acid is in a liquid or solution state, the mixture with cerium carbonate becomes liquid, and the heating and mixing step takes a long time.
Furthermore, the organic acid in the present invention is preferably in the form of a powder because it is easy to mix with cerium carbonate. The size of the powder is not particularly limited.

  The organic acid in the present invention is preferably composed of a carbon atom, an oxygen atom and a hydrogen atom. In addition to this, it may contain nitrogen atoms or sulfur atoms, but it becomes nitrate ions or sulfate ions at the time of firing, and if the firing temperature is low, it may not be detached and remain in the cerium oxide powder.

The organic acid in the present invention has an acid dissociation constant pKa smaller than the acid dissociation constant pKa ₁ of the first stage of carbonic acid, that is, an organic acid that is a stronger acid than carbonic acid. More preferably, the pKa of the organic acid is 6 or less. In the case where the organic acid is multistage dissociation compares the pKa ₁ of the first stage of the acid dissociation constant pKa ₁ and carbonate. It is preferable to mix an organic acid having an acid dissociation constant pKa smaller than the acid dissociation constant pKa ₁ of carbonic acid with cerium carbonate because a reaction of forming an organic salt of cerium easily occurs. In the present invention, the acid dissociation constant is represented by a common logarithmic value pKa that is the reciprocal of the actual acid dissociation constant Ka. Further, if the organic acid is multistage dissociation, it shall indicate the value of the acid dissociation constant pKa ₁ of the first stage.

  The organic acid in the present invention is succinic acid, malonic acid, citric acid, tartaric acid, malic acid, oxalic acid, maleic acid, adipic acid, salicylic acid, benzoic acid, phthalic acid, glycolic acid, ascorbic acid, isomers thereof, heavy acid It is preferably at least one selected from a coalescence or copolymer, polyacrylic acid, and polymethacrylic acid. These organic acids are solid at room temperature (25 ° C.) and powders are readily available.

  In the present invention, it is important to remove water from the reaction system. The removal of moisture is preferably completely removed from the system, but the reaction must be stopped in the heating and mixing, and the reaction should not proceed between the heating and mixing of cerium carbonate and organic acid until the firing. Even if moisture remains, the effect of the present invention can be obtained. That is, when the powder after heating and mixing (heated mixed powder) is immediately fired, there is no problem if the water is removed to such an extent that the reaction stops. Moreover, it is also possible to store without heating immediately after mixing. In that case, when moisture is completely removed from the reaction system, the reaction does not proceed if moisture is not mixed during storage. When moisture remains in the reaction system, the heating temperature in the heating and mixing, the amount of moisture remaining, and the storage conditions (temperature) are important parameters for whether or not the reaction is stopped during storage. Details will be described later. Also, even when moisture remains, it is important to keep the moisture from entering during storage.

In order to stop the reaction, it is important to remove water from the reaction system, but in order to obtain cerium oxide powder having the same degree of grindability in different lots, heating with cerium carbonate and an organic acid is required. It is important that the mixing conditions are the same. Hereinafter, preferable conditions for heating and mixing in the present invention will be shown.
In the method for producing cerium oxide particles, the heating in the step (I) is preferably performed in the range of 40 to 200 ° C.

  In the present invention, “heating temperature” represents a set temperature of a heating and mixing apparatus used for the reaction. However, if the internal temperature differs by more than ± 20% of the set temperature because the heating and mixing device is large or the preparation amount is large, the internal temperature is measured and used as the heating temperature. The heating temperature in heating can be determined in consideration of external factors such as the size and heat transfer area of the heating and mixing device, the heat transfer efficiency of the equipment material, the mixing method, and the sealing property of the device. The range of 40-200 degreeC is preferable. The heating temperature is preferably 50 ° C. or higher and more preferably 80 ° C. or higher from the viewpoint of easily evaporating moisture. On the other hand, since the organic acid may be decomposed when the heating temperature is high, the upper limit of the heating temperature is preferably 180 ° C. or less, and more preferably 150 ° C. or less.

  In the present invention, the reaction system is preferably decompressed during heating. Specifically, for example, in the case of heating at less than 50 ° C., it is preferable to reduce the pressure to −90 kPa or less because moisture hardly evaporates. Moreover, even when heating at 50 ° C. or higher, moisture removal may proceed more efficiently by appropriately combining reduced pressure.

  The time for heating and mixing is also related to the heating temperature, but is preferably 1.5 to 4 hours, more preferably 2 to 3 hours. In the present invention, the heating and mixing time refers to the time from when cerium carbonate and an organic acid are charged into a heating and mixing apparatus and the mixing and heating of the apparatus are started until the mixing and heating of the apparatus are stopped. .

  Although there is no restriction | limiting in particular about a heating mixing system, Since a carbon dioxide and water vapor | steam generate | occur | produce by heating mixing, the heating mixing apparatus which is not sealed or the heating mixing apparatus which is sealed and has an exhaust function is preferable. Specifically, as shown in FIG. 1, for example, a non-sealed heated mixing and stirring apparatus 1 having a stirring blade 2 inside the reaction vessel 3 and a heating means 4 on the outer periphery of the vessel can be used. The shapes of the reaction vessel 3 and the stirring blade 2 are not particularly limited.

  Further, in the heating and mixing apparatus 1, the portion where the apparatus and the organic acid of the raw material are in contact is caused by metal corrosion due to the organic acid, and the corroded metal may be mixed into the mixed powder and become a metal foreign matter. In consideration of metal corrosivity, it is preferable that the contact portion such as the stirring blade 2 or the inner wall of the reaction vessel 3 has a corrosion-resistant resin or metal specification.

  Cerium carbonate contains moisture, has poor powder flowability, and has strong adhesion to a heating and mixing apparatus. Therefore, it is preferable to apply a polyfluorinated ethylene resin coating treatment with improved surface slip and good flatness to the powder contact portion of the heating and mixing apparatus because it also has corrosion resistance against organic acids.

  In the case of heating and mixing with a non-sealed heating and mixing apparatus, a vessel having a sufficient vapor outlet is preferable in order to evaporate and remove moisture contained in the cerium carbonate and organic acid as raw materials. If there is not enough steam outlets, steam will stay in the heating and mixing device and moisture removal cannot be performed quickly, or if the staying steam comes into contact with the raw material, the raw material will become a clay-like state. May end up.

  When using a heating and mixing apparatus that is hermetically sealed and has an exhaust function, an apparatus having sufficient exhaust capability is preferable. If the exhaust capacity is not sufficient, steam will remain in the heating and mixing device, moisture removal cannot be performed quickly, or the staying steam comes into contact with the raw material, and the raw material becomes a clay-like state. May end up.

  When using a heating and mixing apparatus that is sealed and has an exhaust function, it is possible to make it easier to remove moisture by reducing the pressure simultaneously with exhaust. Although there is no restriction | limiting regarding the vacuum degree at the time of pressure reduction, Parameters, such as heating temperature, heating mixing time, a mixing system, the raw material preparation amount to a heating mixing apparatus, and the heat transfer area with respect to the powder of a heating mixing apparatus, are related. Taking these parameters into consideration, it is preferable to remove moisture by sufficiently discharging steam.

  As a method for confirming that the reaction between cerium carbonate and the organic acid has been stopped by removing moisture by heat mixing, there is a method for confirming the presence or absence of mass reduction of the heat mixed powder over time. Since carbon dioxide is generated as the reaction proceeds, the corresponding mass decreases. Therefore, if the mass does not decrease, it can be determined that the reaction does not proceed.

  As a method of determining the presence or absence of mass reduction, the mass of the powder immediately after the end of heating and mixing (heated mixed powder) and the mass of the powder immediately before firing are measured, and the amount of mass reduction between them is measured. it can. In the present invention, it can be determined that the reaction has stopped when the mass loss after the heated mixed powder is left at a temperature of 25 ° C. for 24 hours is 0 to 0.1 mass%. In the present invention, “the mass of the powder immediately after completion of heating and mixing” is specifically the mass measured in the range of 5 to 40 ° C. within 30 minutes after the completion of heating and mixing.

  Specific measurement methods include the following. That is, cerium carbonate and an organic acid are heated and mixed, and the heating and mixing apparatus is stopped to obtain a heated mixed powder (within 30 minutes), and then about 1 to 100 g of the heated mixed powder is weighed. Next, the heated mixed powder sample is left at a temperature of 25 ° C. for 24 hours, and the mass is measured again. Then, a mass reduction amount is obtained by calculation from the mass of the heat-mixed powder immediately after completion of the heat-mixing and the mass of the powder after being left for 24 hours. The mass reduction amount of the heated mixed powder after standing for 24 hours determined in this manner is preferably 0 to 0.1% by mass, and 0 to 0.05% by mass with respect to the mass of the heated mixed powder. Is more preferably 0 to 0.02% by mass. If the amount of mass reduction is at least 0.1% by mass, it can be determined that there is no mass reduction and the reaction is stopped.

  When moisture is not completely removed from the reaction system, the reaction between cerium carbonate and organic acid may or may not stop depending on the environment in which the heated mixed powder is stored. The reaction is more difficult to stop if the storage environment is hot. For example, when storage is performed at room temperature, it is necessary to set the heating temperature in consideration of summer temperature conditions in an environment where there is a difference of about 30 ° C. in the atmospheric temperature, such as in summer and winter. In the heating and mixing step, when moisture is completely removed from the reaction system, the storage temperature and heating temperature need not be taken into consideration. In any case, in the present invention, it can be determined that the reaction is stopped when the mass loss after the heated mixed powder is left at a temperature of 25 ° C. for 24 hours is 0 to 0.1 mass%.

Further, as another determination method for determining whether there is a decrease in mass, it is also possible to determine by sampling a small amount of the heated mixed powder, heating it to a temperature higher than the storage environment, and performing an accelerated test for mass change. Specifically, for example, when the storage environment is 10 to 25 ° C., the mass of the heated sample after evaporating moisture is measured, and the sample is placed in a high-temperature bath or oven in an environment of 40 ° C. for 2 hours. Examples of the method include leaving it alone and measuring the mass again. Thereby, the presence or absence of mass reduction can be judged easily.
That is, if the “mass loss after standing at 40 ° C. for 2 hours” is 0 to 0.1% by mass, the “mass loss after 24 hours at 25 ° C.” is also determined to be 0 to 0.1% by mass. That is, it can be judged that the reaction has stopped. However, when the “mass loss after standing at 40 ° C. for 2 hours” exceeds 0.1% by mass, it is necessary to confirm the mass reduction after leaving at 25 ° C. for 24 hours.

Next, the heated mixed powder obtained as described above is fired by using a conventionally known apparatus such as a batch furnace, a rotary kiln, a tunnel furnace, etc., to obtain a cerium oxide powder. The firing temperature in the present invention is preferably 350 ° C. or higher, more preferably 400 ° C. or higher and 900 ° C. or lower, and still more preferably 600 ° C. or higher and 800 ° C. or lower because the oxidation temperature of the cerium compound is 300 ° C.
In the present invention, there is no particular limitation on the heating rate of firing.

  The cerium oxide powder produced by the above method has a half-value width of the diffraction peak due to the (111) plane of the cerium oxide crystal, which is the main peak obtained from a powder X-ray diffraction pattern using a CuKα ray as a radiation source. It is preferably 0.50 °. When the full width at half maximum is 0.27 ° or more, the parts of the pulverizer are not worn, and the possibility that the abrasion powder is mixed into the polishing liquid is increased, which is preferable without causing a polishing flaw. When the full width at half maximum is 0.50 ° or less, the pulverizability is not lowered, and the large particle size remains without being pulverized and is preferably mixed into the polishing liquid without causing polishing scratches.

A powder X-ray diffraction pattern (hereinafter also referred to as “CuKα powder X-ray diffraction pattern”) using CuKα rays as a radiation source can be measured with an X-ray diffractometer (product name: RINT2100, manufactured by Rigaku Corporation).
The measurement conditions are a diverging slit 1 °, a scattering slit 1 °, a light receiving slit 0.30 mm, a step width 0.02 °, a counting time 5.0 sec, a tube voltage 40 kV, and a tube current 20 mA. The diffraction angle (2θ) is taken on the horizontal axis and the diffraction X-ray intensity (cps) is taken on the vertical axis, and the obtained data is plotted, and the (111) plane of the cerium oxide crystal that is the main peak of the cerium oxide particles in the polishing liquid. Find the half-width of the diffraction peak. The full width at half maximum is the peak width at half the peak height. FIG. 2 shows an example of measuring the half width.

The cerium oxide powder produced by the above method has a particle size of 0.1 to 1 μm with 99 volume% (hereinafter referred to as “D99”) of the pulverized cerium oxide after pulverization under the following pulverization conditions (a). Is more preferable, and 0.1 to 0.8 μm is more preferable. D99 of the cerium oxide pulverized product after the following pulverization condition (a) can be used as an index of pulverization in the pulverization step of the method for producing cerium oxide particles used in the present invention.
When D99 of the cerium oxide pulverized product after the pulverization condition (a) exceeds 1 μm, there is no problem in use, but the pulverization property is poor, and the large particle size particles remain without being pulverized in the pulverization step described below, It is not preferable because it tends to be mixed into the polishing liquid and cause polishing scratches. When D99 of the cerium oxide pulverized product after pulverization under the pulverization condition (a) is less than 0.1 μm, there is no problem in use, but it tends to be difficult to polish the SiO ₂ film or the silicon nitride film at high speed. This is not preferable.

Pulverization condition (a): Dispersion chamber having a pressure of 100 MPa and an orifice diameter of 0.1 mm using a wet pulverizer of a type in which cerium oxide powder is pulverized by accelerating at a high pressure with an orifice in a micro dispersion chamber of a wet pulverizer. Is passed 15 times to perform wet grinding.
More specifically, 27 g of cerium oxide powder, 6.8 g of an ammonium polyacrylate aqueous solution (40% by mass) and 152 g of deionized water were mixed, and then a wet pulverizer (manufactured by Microfluidics, product name: Microfluidic). Dicer M-110EH, crushing chamber type: H10Z-1, orifice diameter: 0.1 mm) is passed 15 times at a crushing pressure of 100 MPa and a liquid temperature of 5 to 20 ° C., and wet crushing is performed to obtain a cerium oxide pulverized product. . The particle diameter of the cerium oxide pulverized product in the slurry after the wet pulverization treatment was measured using a laser diffraction particle size distribution meter (manufactured by Horiba, Ltd., trade name: LA-920), with a refractive index of 1.93 and a transmittance of 85%. D99 is obtained by measuring under the following conditions.

  Moreover, since it uses for semiconductor element grinding | polishing, it is preferable to suppress the content rate of an alkali metal and halogens to 10 ppm or less in a cerium oxide particle.

  The cerium oxide particles used in the present invention can be obtained by pulverizing the cerium oxide powder produced by the above method. The pulverization method in the present invention is not particularly limited, and examples thereof include dry pulverization using a jet mill or the like, and wet pulverization using a planetary bead mill or the like. In particular, when the pulverization is performed by wet pulverization, it is preferable in that the adhesion of the fine particles in the cerium oxide particles to the pulverization equipment is small. In the case of pulverization by dry pulverization, it is preferable in that the temperature rise in the pulverization equipment is less likely to occur. The jet mill is described, for example, in Chemical Industrial Papers, Vol. 6, No. 5, (1980), pages 527-532.

<Polishing liquid and polishing method using the same>
The polishing liquid of the present invention refers to a polishing liquid containing at least cerium oxide particles and water.
The cerium oxide particles of the present invention produced as described above are suitably used as a polishing liquid, particularly as a polishing liquid for semiconductor planarization.

  The polishing liquid of the present invention contains cerium oxide particles and water obtained by the above production method, and is obtained, for example, by dispersing cerium oxide particles in water.

The polishing liquid of the present invention preferably further contains a dispersant. For example, the polishing liquid of the present invention is obtained by dispersing a composition containing cerium oxide particles and a dispersant prepared by the above-described production method in water. It is done.
Although there is no restriction | limiting in the density | concentration of a cerium oxide particle, From the ease of handling of a dispersion | distribution liquid polishing liquid, the range of 0.1 mass% or more and 20 mass% or less is preferable.

  As the dispersant, for example, a polymer obtained by polymerizing an acrylic acid monomer or a salt thereof is preferable. Examples of the acrylic acid monomer include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and these homopolymers or copolymers may be used. Since it is used for semiconductor element polishing, it is preferable to suppress the content of alkali metals such as sodium ions and potassium ions and halogens to 10 ppm or less. More specifically, for example, a salt of polyacrylic acid, a salt of a copolymer of acrylic acid and methacrylic acid, and the like are preferable, and the salt is preferably an ammonium salt.

  The added amount of the dispersant is 0.01 parts by mass or more and 5.0 parts by mass with respect to 100 parts by mass of the cerium oxide particles from the relationship between the dispersibility of the particles in the polishing liquid and settling prevention, and the relationship between the polishing scratches and the added amount of the dispersant. A range of parts or less is preferred.

The weight average molecular weight of the dispersant is preferably from 100 to 50,000, and more preferably from 1,000 to 10,000. When the molecular weight of the dispersant is 100 or more, it is easy to obtain a sufficient polishing rate when polishing the SiO ₂ film or the silicon nitride film, and when the molecular weight of the dispersant is 50,000 or less, the viscosity becomes high. In addition, the storage stability of the polishing liquid is not lowered.
In the present invention, the weight average molecular weight is a value measured by gel permeation chromatography and converted to standard polystyrene.

  As a method for dispersing these cerium oxide particles in water, a homogenizer, an ultrasonic disperser, a wet ball mill or the like can be used in addition to a dispersion treatment using a normal stirrer.

The number of particles having a particle diameter of 0.75 μm or more contained in the polishing liquid of the present invention is 3 × 10 ⁶ or less in 1 ml. This improves the effect of reducing polishing scratches. If the number of particles in 1 ml exceeds 3 × 10 ^6, there is a possibility that polishing scratches due to the polishing liquid increase.
As a specific measurement method, the number of particles having a particle size of 0.75 μm or more in 1 ml of polishing liquid is 90 ml of ISOTON II (manufactured by Beckman Coulter, Inc .: electrolyte for measurement) using Multisizer 3 made by Beckman Coulter. An example is a method in which 600 μl of a polishing liquid having a cerium oxide concentration of 4% by mass is introduced and an analysis volume of 50 μl is measured using an aperture having a diameter of 30 μm.

  The coarse particle content of cerium oxide particles having a particle diameter of 3 μm or more in the entire solid in the polishing liquid of the present invention is preferably small. In the present invention, the coarse particles of 3 μm or more mean particles captured by filtering with a filter having a pore diameter of 3 μm. In the present invention, the content of particles having a particle diameter of 3 μm or more in the entire solid in the polishing liquid is preferably 500 ppm or less in terms of mass ratio. When the content of particles of 3 μm or more occupying the whole solid is 200 ppm or less, the effect of reducing polishing scratches is large, which is more preferable. When the content of particles of 3 μm or more occupying the whole solid is 100 ppm or less, the effect of reducing polishing scratches is the largest and more preferable.

The coarse particle content of 3 μm or more can be obtained by mass measurement of particles captured by filtering with a filter having a pore diameter of 3 μm. The content of the entire solid in the polishing liquid is measured by separately drying the polishing liquid. For example, 10 g of the polishing liquid is dried at 150 ° C. for 1 hour, and the mass of the remainder is measured to obtain the solid concentration. And the content of the whole solid can be obtained by multiplying the mass of the polishing liquid used for filtration with a filter having a pore diameter of 3 μm by the solid concentration.
Filtration and classification are possible as means for reducing the coarse particle content, but are not limited thereto.

The median particle diameter of the cerium oxide particles in the polishing liquid of the present invention (hereinafter also referred to as “D50”) is preferably 0.1 to 1 μm, more preferably 0.1 to 0.5 μm, and still more preferably 0. .1 to 0.3 μm. This is because if the median particle diameter is 0.1 μm or more, the polishing rate of the SiO ₂ film or silicon nitride film does not decrease, and if it is 1 μm or less, polishing scratches do not occur on the surface of the film to be polished. .

The D99 of the cerium oxide particles in the polishing liquid of the present invention is preferably 1 μm or less. When D99 exceeds 1 μm, the generation of polishing scratches increases. When D99 is 0.7 μm or less, polishing scratches can be reduced, which is more preferable.
The median value (D50) and D99 of the cerium oxide particles in the polishing liquid are determined using a laser diffraction particle size distribution analyzer (for example, LA-920, manufactured by HORIBA, Ltd.) under the conditions of a refractive index of 1.93 and a transmittance of 74%. taking measurement.
Moreover, in order to make the median value (D50) and D99 of the cerium oxide particles in the polishing liquid fall within the above range, it is preferable to prepare the particles by pulverization, sedimentation, filtration, or the like.

In addition, a polymer additive that further improves the flatness and dispersibility can be added to the polishing liquid. Although not necessarily limited to the following, for example, a polymer such as an acrylate derivative, acrylic acid, acrylate, or the like can be added. The addition amount of the polymer additive is not particularly limited, but is preferably 5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the cerium oxide particles.
Acrylic acid is also used as the dispersant, but when acrylic acid is used as the polymer additive, the amount of acrylic acid added may be based on the amount of polymer additive added.

The weight average molecular weight of the polymer additive is preferably 100 to 50,000, more preferably 1,000 to 10,000. When the weight average molecular weight is 100 or more, a sufficient polishing rate can be obtained when polishing the SiO ₂ film or the silicon nitride film, and when the weight average molecular weight is 50,000 or less, the viscosity becomes high, This is because the storage stability of the polishing liquid is not lowered.

The polishing liquid of the present invention preferably has a pH of 3 or more and 9 or less, and more preferably 5 or more and 8 or less. If the pH is 3 or more, the chemical action force is not too small, and the polishing rate is not reduced. If the pH is 9 or less, the chemical action is too strong and the surface to be polished is not dished (dishing).
The pH can be measured with a pH meter (for example, Model pH81 manufactured by Yokogawa Electric Corporation). Specifically, after two-point calibration using a standard buffer solution (phthalate pH buffer solution pH: 4.21 (25 ° C.), neutral phosphate pH buffer solution pH 6.86 (25 ° C.)) The value after the electrode is put into the polishing liquid and stabilized for 2 minutes or more is measured.

  The polishing liquid of the present invention can be prepared as a one-part polishing liquid composed of, for example, cerium oxide particles, a dispersant, a polymer additive, and water, and is also composed of cerium oxide particles, a dispersant, and water. It can also be prepared as a two-part polishing liquid in which the cerium oxide slurry is separated from an additive composed of a polymer additive and water. In either case, stable characteristics can be obtained.

  In the case of storing as a two-component polishing liquid in which the cerium oxide slurry and the additive are separated, the flattening characteristics and the polishing rate can be adjusted by arbitrarily changing the composition of these two liquids. In the case of the two-pack type, the additive and the cerium oxide slurry are sent at different flow rates through separate pipes, and these pipes are merged, that is, both are mixed just before the supply pipe outlet, and the polishing surface plate Either a method of supplying the above or a method of supplying them after mixing them in a container in an arbitrary ratio in advance (pre-mixing method) is used.

  The polishing liquid of the present invention is to press and press the substrate against the polishing cloth so that the polishing film is in contact with the polishing cloth while supplying the polishing liquid between the polishing film formed on the substrate and the polishing cloth. The film to be polished and the polishing cloth are relatively moved to be used for planarization polishing of the film to be polished.

  As the substrate on which the film to be polished is formed, for example, a substrate relating to a semiconductor device formation process, specifically, a substrate in which an inorganic insulating layer is formed on a semiconductor substrate at a stage where a circuit element is formed, or a shallow trench Examples include a substrate in which an inorganic insulating layer is embedded on a substrate in the element isolation formation step. And as the said inorganic insulating layer which is a to-be-polished film | membrane, the insulating layer which consists of a silicon oxide film at least is mentioned.

Hereinafter, the present invention will be described more specifically with reference to examples of the present invention and comparative examples thereof, but the present invention is not limited to these examples.
Example 1
<Manufacture of polishing liquid>
Cylindrical rotary blade type mixing device (product name: PMT-18, option: Indirect heating is installed by winding a heater around the outside of the cylinder, and the powder contact part inside the device is coated with a polyfluorinated ethylene fiber. In this apparatus, 2.8 kg of commercially available cerium carbonate and 2.3 kg of oxalic acid were put into the apparatus.

Thereafter, rotation of the mixing blade and heating of the apparatus were started simultaneously, and heating and mixing were performed at a heater set temperature of 110 ° C. for 2.5 hours. Thereafter, the rotation and heating of the mixing blade were stopped, and the heated mixed powder was recovered. When the mass of the heated mixed powder was measured immediately after collection and 1 hour after collection, the mass reduction during the measurement was 0% by mass. Moreover, when the mass of the heat-mixed powder 24 hours after 25 degreeC was measured, the mass reduction | decrease was 0 mass%.
After measuring the mass one hour after the recovery, the heated mixed powder was put into a rotary kiln (furnace diameter 250 mm, furnace length 4000 mm) at a rate of 8 kg / hour and fired at 730 ° C. for 1 hour while blowing air (heated and mixed heat-in). The heating rate at which the powder was heated to a calcination temperature of 730 ° C. was 53 ° C. per minute), and 1.4 kg of yellowish white powder was obtained. When this powder was phase-identified by X-ray diffraction, it was confirmed to be a cerium oxide powder. Further, the half width of the diffraction peak due to the (111) plane of the cerium oxide crystal in the CuKα powder X-ray diffraction pattern was 0.273 °.

  In order to confirm the grindability, D99 of the ground cerium oxide was measured as follows. 27 g of the prepared cerium oxide powder, 6.8 g of an ammonium polyacrylate aqueous solution (40% by mass) and 152 g of deionized water were mixed, and then a wet pulverizer (manufactured by Microfluidics, product name: Microfluidizer M- 110EH, crushing chamber type: H10Z-1, orifice diameter: 0.1 mm) was passed 15 times at a crushing pressure of 100 MPa and a liquid temperature of 5 to 20 ° C. to perform wet crushing treatment. The particle diameter of the cerium oxide pulverized product in the slurry after the wet pulverization treatment was measured using a laser diffraction particle size distribution meter (manufactured by Horiba, Ltd., trade name: LA-920), with a refractive index of 1.93 and a transmittance of 85%. As a result, the D99 of the cerium oxide ground product was 0.80 μm.

  Further, 1000 g of the prepared cerium oxide powder, 25 g of an aqueous solution of ammonium polyacrylate (40% by mass) and 5600 g of deionized water were mixed and stirred for 10 minutes, and then a wet pulverizer (manufactured by Microfluidics, product name: Microfluidizer M-110EH) was passed 6 times at a pulverization pressure of 100 MPa and a liquid temperature of 5 to 20 ° C. to perform wet pulverization. The obtained dispersion was allowed to settle at room temperature (25 ° C.) for 100 hours, and the supernatant was collected. This supernatant liquid is filtered through a filter having a pore size of 0.7 μm, then filtered again through a 0.7 μm filter, deionized water is added to adjust the solid content concentration to 5% by mass, and a polishing liquid for semiconductor planarization is prepared. Produced.

The particle diameter of the cerium oxide particles in the obtained polishing liquid for semiconductor flattening was measured using a laser diffraction particle size distribution meter (manufactured by Horiba, Ltd., trade name: LA-920) with a refractive index of 1.93 and transmission. As a result of measurement under the condition of a degree of 74%, the median particle diameter (D50) was 0.16 μm and D99 was 0.5 μm.
Moreover, the impurity (Fe) in the slurry containing cerium oxide particles measured using an atomic absorption photometer (manufactured by Shimadzu Corporation, model number: AA-6650) was 0.2 ppm or less in mass ratio. Impurities (Fe) are considered to be mixed due to wear of the pulverizer during wet pulverization.

The number of particles having a particle diameter of 0.75 μm or more in the polishing liquid was measured as follows. The polishing liquid for semiconductor planarization was diluted 5 times with deionized water to adjust the cerium oxide concentration to 4% by mass. Using a multisizer 3 manufactured by Beckman Coulter, 600 μl of the diluted polishing solution was put into 90 ml of ISOTON II (manufactured by Beckman Coulter, Inc .: measurement electrolyte), and an aperture with a diameter of 30 μm was used and the analysis volume was 50 μl. It was measured. As a result, the number of particles having a particle size of 0.75 μm or more in 50 μl of the measurement sample was 700. When this was converted into a value in 1 ml of polishing liquid, it was 700 ÷ 50 μl × (90 ml ÷ 600 μl) = 2.1 × 10 ⁶ pieces / ml.

  In order to examine the content of coarse particles having a particle diameter of 3 μm or more in the polishing liquid, the obtained polishing liquid for planarizing the semiconductor was diluted 15 times, and 30 g was filtered with a 3 μm filter (a cyclopore track etch membrane filter manufactured by Whatman). did. After filtration, the filter was dried at room temperature (25 ° C.), the mass of the filter was measured, and the amount of coarse particles of 3 μm or more was determined from the mass increase before and after filtration. Separately, 10 g of this polishing liquid was dried at 150 ° C. for 1 hour, and the solid concentration in the polishing liquid was calculated. As a result, the amount of coarse particles (mass ratio) of 3 μm or more was 20 ppm in the solid of the polishing liquid.

<Evaluation of polishing liquid>
Further, the polishing liquid for semiconductor flattening was diluted 5 times with deionized water and polished by the following method. When the polishing speed was 350 nm / min and the wafer surface was observed with an optical microscope, five polishing scratches were observed on the entire surface of the 200 mm wafer.

[Polishing test method]
Polishing load: 30 kPa
Polishing pad: Rodel foam polyurethane resin (IC-1000)
Rotation speed: surface plate 75rpm, pad 75rpm
Polishing liquid supply rate: 200 mL / min
Polishing object: Si wafer with P-TEOS film (200mm)

(Comparative Example 1)
2.8 kg of commercially available cerium carbonate is put in an alumina container, heated in a batch furnace to 800 ° C. at a heating rate of 6.5 ° C./min in an air atmosphere, and then held at 800 ° C. for 1 hour for firing. As a result, 1.4 kg of a yellowish white powder was obtained. When this powder was phase-identified by X-ray diffraction, it was confirmed to be a cerium oxide powder. Moreover, the half width of the diffraction peak due to the (111) plane of the cerium oxide crystal in the CuKα powder X-ray diffraction pattern was 0.274 °.

  In order to confirm the pulverizability of the prepared cerium oxide powder, wet pulverization treatment was performed in the same manner as in Example 1, and the particle diameter of the cerium oxide pulverized product was measured. It was 55 μm.

  Also, a semiconductor planarization polishing liquid was prepared in the same manner as in Example 1 using the cerium oxide powder prepared above.

As a result of measuring the particle diameter of the cerium oxide particles in the obtained polishing liquid for semiconductor flattening in the same manner as in Example 1, the median particle diameter of the cerium oxide particles was 0.16 μm, and D99 was 0.50 μm. there were. Moreover, the impurity (Fe) in the cerium oxide slurry measured in the same manner as in Example 1 was 0.2 ppm or less by mass ratio.
When the number of particles having a particle diameter of 0.75 μm or more in 1 ml of the polishing liquid was measured in the same manner as in Example 1, it was 6.0 × 10 ⁷ particles / ml.
In order to examine the content of coarse particles having a particle diameter of 3 μm or more in the polishing liquid, the amount of coarse particles of 3 μm or more was determined from the increase in mass before and after filtration of the obtained semiconductor flattening polishing liquid in the same manner as in Example 1. . As a result, the amount of coarse particles having a particle diameter of 3 μm or more was 60 ppm in the solid.

  Further, the polishing liquid for semiconductor flattening was diluted 5 times with deionized water, and polishing was performed by the same polishing test method as in Example 1. When the polishing speed was 350 nm / min and the wafer surface was observed with an optical microscope, 30 polishing scratches were observed on the entire surface of the 200 mm wafer.

As described above, Example 1 in which the number of particles having a particle diameter of 0.75 μm or more is 2.1 × 10 ⁶ particles / ml (3 × 10 ⁶ particles / ml or less) is larger than that of Comparative Example 1 on the wafer surface. The polishing liquid and the polishing method of the present invention can polish the semiconductor surface at a high speed in the wiring formation process, and have a good flatness and can reduce the polishing scratches. It was found that this was the polishing method used.

1 Heating and mixing equipment
2 Stirring blade 3 Reaction vessel 4 Heating means

Claims (13)

A polishing liquid comprising cerium oxide particles and water, wherein the number of particles having a particle diameter of 0.75 μm or more in 1 ml of the polishing liquid is 3 × 10 ⁶ or less.   The cerium oxide particles are (I) a step of heating and mixing cerium carbonate and an organic acid to obtain a heated mixed powder, (II) a step of firing the heated mixed powder to obtain a cerium oxide powder, (III) the step The polishing liquid according to claim 1, wherein the polishing liquid is cerium oxide particles produced by a production method comprising pulverizing cerium oxide powder to obtain cerium oxide particles.   (I) When the mass of the heated mixed powder immediately after the step and the mass of the heated mixed powder after leaving the heated mixed powder at a temperature of 25 ° C. for 24 hours are compared, the mass reduction amount is 0 to 0. The polishing liquid according to claim 2, wherein the polishing liquid is 1% by mass.   The polishing liquid according to claim 2 or 3, wherein the heating in the step (I) is performed in a range of 40 to 200 ° C.   The polishing liquid according to any one of claims 2 to 4, wherein the heating and mixing time in the step (I) is 1.5 to 4 hours.   The cerium oxide powder obtained by firing the heat-mixed powder has a FWHM of the diffraction peak due to the (111) plane of the cerium oxide crystal determined from the powder X-ray diffraction pattern using CuKα rays as the radiation source. The polishing liquid according to any one of claims 2 to 5, which has a particle diameter of 0.1 to 1 µm, and is 99% by volume or more of the pulverized cerium oxide after pulverization.   (II) Polishing liquid as described in any one of Claims 2-6 by which baking of a process is performed in 400-900 degreeC.   The polishing liquid according to claim 1, wherein the median particle diameter of the cerium oxide particles in the polishing liquid is 0.1 to 1 μm.   The polishing liquid according to claim 1, wherein the content of cerium oxide particles having a particle diameter of 3 μm or more in the polishing liquid is 500 ppm or less in the solid.   Furthermore, the polishing liquid as described in any one of Claims 1-9 containing a dispersing agent.   The polishing liquid according to claim 1, wherein 99% by volume or more of the entire cerium oxide particles in the polishing liquid has a particle diameter of 1 μm or less.   A method for polishing a substrate, comprising polishing a predetermined substrate with the polishing liquid according to claim 1. The method for polishing a substrate according to claim 12, wherein the predetermined substrate is a semiconductor chip on which at least a SiO ₂ film is formed.

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