WO2018100686A1 - Slurry, polishing liquid, method for producing said slurry, method for producing said polishing liquid, and method for polishing substrate - Google Patents

Abstract

One embodiment of the present invention is a method for producing a slurry containing ceria particles and water. This method for producing a slurry comprises a pulverization step wherein ceria particles are obtained by pulverizing colloidal ceria dispersed in water. In the pulverization step, the colloidal ceria is pulverized so that the ratio of the average primary particle diameter of the ceria particles to the average primary particle diameter of the colloidal ceria is less than 0.8.

Description

SLURRY, POLISHING LIQUID, PROCESS FOR PRODUCING THEM, AND METHOD FOR POLISHING SUBSTRATE

The present invention relates to a slurry, a polishing liquid, a manufacturing method thereof, and a polishing method for a substrate.

In the current ULSI (Ultra Large Scale Integration) semiconductor device manufacturing process, processing technologies for high density and miniaturization of semiconductor devices are being researched and developed. CMP (Chemical Mechanical Polishing) technology, which is one of the processing technologies, is used in semiconductor device manufacturing processes, such as planarization of interlayer insulating films, formation of shallow trench isolation (STI), formation of plugs and buried metal wiring, etc. Has become an indispensable technology.

Conventionally, in a semiconductor element manufacturing process, an inorganic insulating film such as a silicon oxide film is formed by a method such as plasma-CVD (chemical vapor deposition) or low-pressure CVD (chemical vapor deposition). As a chemical mechanical polishing liquid for planarizing the inorganic insulating film, it has been generally studied to use a fumed silica-based polishing liquid. The fumed silica-based polishing liquid is produced by adjusting the pH of a slurry containing particles obtained by grain growth by a method such as thermal decomposition of tetrachlorosilicic acid. However, such a fumed silica-based polishing liquid has a technical problem that the polishing rate is low.

In the generations after the design rule 0.25 μm, STI is used for element isolation in the integrated circuit. In the formation of STI, for example, a CMP technique using a colloidal silica-based polishing liquid is used to remove an excess silicon oxide film formed on the substrate. In this case, in order to stop the polishing at an arbitrary depth, a stopper film having a low polishing rate is formed under the silicon oxide film. A silicon nitride film or the like is used for the stopper film. In order to efficiently remove the excess silicon oxide film and sufficiently suppress the subsequent polishing, it is desirable that the ratio of the polishing rate of the silicon oxide film to the polishing rate of the stopper film is large. However, since the ratio of the above-mentioned polishing rates when a conventional colloidal silica-based polishing liquid is used is as small as about 3, the conventional colloidal silica-based polishing liquid does not have a characteristic that can withstand practical use for STI.

On the other hand, a cerium oxide-based polishing liquid containing cerium oxide particles is used as a polishing liquid for glass surfaces such as photomasks and lenses. The hardness of cerium oxide particles is lower than the hardness of silica particles and alumina particles. Therefore, when a cerium oxide-based polishing liquid containing cerium oxide particles is used, the polishing surface is less likely to be damaged when polishing compared to the case where a polishing liquid containing silica particles or alumina particles is used. This polishing liquid is useful for finish mirror polishing. Further, the cerium oxide-based polishing liquid has an advantage that the polishing rate is faster than silica-based polishing liquids such as fumed silica type and colloidal silica type.

By the way, with the progress of miniaturization of wiring and STI design rules, reduction of polishing flaws that occur during polishing is required more than ever. As an abrasive capable of reducing polishing scratches, for example, Patent Document 1 discloses an abrasive having a volume average particle diameter of 1 nm to 95 nm and a number of particles having a diameter of 0.56 μm or more of 1 million or less per ml. A polishing liquid for CMP process characterized by comprising water is disclosed. Patent Document 2 discloses a cerium oxide abrasive containing a slurry in which cerium oxide particles having a particle diameter of more than 10 nm and less than 100 nm of primary particles of 90% or more are dispersed in a medium. Yes.

JP 2003-188122 A JP-A-10-106994

However, when the particle size is reduced, there is a problem that the polishing scratches are reduced, while the polishing rate is lowered and the efficiency of the polishing operation is lowered. The present invention has been made in view of such circumstances, and obtains a polishing liquid that has an excellent polishing rate compared to a polishing liquid containing ceria particles having the same average primary particle diameter, and the polishing liquid. It is an object of the present invention to provide a slurry that can be used, a manufacturing method thereof, and a method of polishing a substrate using the polishing liquid.

In one aspect, the present invention is a method for producing a slurry containing ceria particles and water, comprising a crushing step of crushing colloidal ceria dispersed in water to obtain ceria particles. This is a slurry production method in which grinding is performed so that the ratio of the average primary particle diameter of ceria particles to the average primary particle diameter of ceria is less than 0.8.

In one aspect, the present invention is a method for producing a slurry containing ceria particles and water, comprising a crushing step of crushing colloidal ceria dispersed in water to obtain ceria particles. This is a slurry manufacturing method in which crushing is performed so that the ratio of sphericity of ceria particles to sphericity of ceria is 0.97 or less.

In the pulverization step, the colloidal ceria may be pulverized using a bead mill.

In the pulverization step, the colloidal ceria may be pulverized using a jet mill.

In one aspect, the present invention is a method for producing a polishing liquid containing ceria particles, water, and an additive, wherein the slurry obtained by the above production method is mixed with an additive to obtain a polishing liquid. A method for producing a polishing liquid.

In one aspect, the present invention is a slurry obtained by the above-described slurry manufacturing method.

In one aspect, the present invention is a polishing liquid obtained by the above polishing liquid manufacturing method.

In one aspect, the present invention is a method for polishing a substrate, comprising a polishing step of polishing a film to be polished formed on the surface of the substrate using the polishing liquid.

According to the present invention, as compared with a polishing liquid containing ceria particles having the same average primary particle diameter, a polishing liquid having an excellent polishing rate, a slurry constituting the polishing liquid, a manufacturing method thereof, and the polishing A method for polishing a substrate using a liquid can be provided.

(A) An image of colloidal ceria before pulverization. (B) An image of ceria particles after pulverization.

Hereinafter, embodiments of the present invention will be described in detail.

In this specification, “slurry” means a composition containing at least ceria particles (abrasive grains) and water, and “polishing liquid” means a composition containing at least ceria particles (abrasive grains), additives and water. .

[Slurry manufacturing method]
The slurry manufacturing method according to the present embodiment is a slurry manufacturing method containing ceria particles and water. In this manufacturing method, first, colloidal ceria is prepared (preparation process). The colloidal ceria may be, for example, a known one obtained through a process of growing ceria crystals by a liquid phase method. Examples of the liquid phase method include (1) sol-gel method, (2) hydrothermal synthesis method, and (3) precipitation method. Colloidal ceria may be obtained by any method.

The average primary particle diameter of colloidal ceria is, for example, 10 to 200 nm. In addition, the average primary particle diameter of colloidal ceria is calculated | required by the image analysis by SEM observation. That is, first, an image of colloidal ceria obtained by SEM observation is approximated by a circle, and the diameter of the circle is measured as the primary particle diameter. For 50 colloidal ceria randomly selected from an image of colloidal ceria obtained by SEM observation, the primary particle diameter is measured in the same manner, and the average value thereof is taken as the average primary particle diameter.

The average secondary particle diameter of colloidal ceria is, for example, 20 to 600 nm. The average secondary particle size of colloidal ceria is a value of D50 (median diameter of volume distribution, cumulative median value) measured using a laser diffraction particle size distribution analyzer (for example, product name: Master Sizer Microplus manufactured by Malvern). ). In the measurement, a sample obtained by diluting the colloidal ceria dispersion to a concentration at which the measurement transmittance (H) with respect to the He—Ne laser is 60 to 70% is used. Measurement is performed under the conditions of laser and absorption: 0.

The sphericity of colloidal ceria is, for example, 60 to 100%. In addition, the sphericity of colloidal ceria is calculated | required using image analysis by SEM observation and using the sphericity ratio S (%) represented by following formula (1).
S (%) = r / R × 100 (1)
In the formula (1), r indicates the maximum radius (nm) of a circle that can be drawn in one colloidal ceria grain in an image obtained by SEM observation, and R includes one colloidal ceria grain in the image obtained by SEM observation. The minimum radius (nm) of a circle to be played. The sphericity of 50 colloidal ceria randomly selected from the image of colloidal ceria obtained by SEM observation is similarly determined, and the average value thereof is defined as the sphericity of the colloidal ceria.

Following the preparation step, colloidal ceria dispersed in water is pulverized to obtain ceria particles (pulverization step). In the present specification, colloidal ceria pulverized through a pulverization step is referred to as ceria particles.

The method for pulverizing colloidal ceria is not particularly limited. The colloidal ceria may be pulverized using, for example, a bead mill or pulverized using a jet mill. When using a bead mill, first, beads having a hardness equal to or higher than that of a substance to be pulverized (colloidal ceria) are filled in a container (pulverization chamber) for pulverization. After filling, the beads are moved by rotating the rotating shaft in the center of the grinding chamber. Colloidal ceria dispersed in water (colloidal ceria aqueous dispersion, also referred to as “water dispersion”) is sent to the grinding chamber, colliding the beads with the colloidal ceria, and grinding the colloidal ceria to crush the colloidal ceria. .

When using a jet mill, colloidal ceria (water dispersion of colloidal ceria) dispersed in water is injected into the grinding chamber under high pressure and high speed. By injecting at high pressure and high speed, colloidal ceria is pulverized by colliding a colloidal ceria with a substance having hardness equal to or higher than that of colloidal ceria. The shape of the substance to be collided is not particularly limited, and examples thereof include a spherical shape, a cylindrical shape, and a lump shape. The substance to be collided is preferably a dispersion in which colloidal ceria is dispersed.

In one embodiment, in the pulverization step, the ratio of the average primary particle diameter of the ceria particles to the average primary particle diameter of the colloidal ceria (average ceria particle primary particle diameter / colloidal ceria average primary particle diameter) is less than 0.8. So that colloidal ceria is crushed. The ratio of the average primary particle diameter of the ceria particles to the average primary particle diameter of the colloidal ceria may be 0.79 or less, 0.78 or less, or 0.70 or less, for example, 0.10 or more. .

The average primary particle diameter of the ceria particles is preferably 5 to 250 nm, more preferably 10 to 200 nm, and still more preferably 10 to 150 nm. If the average primary particle diameter of the ceria particles is 5 nm or more, a better polishing rate tends to be obtained. If the average primary particle size of the ceria particles is 250 nm or less, the film to be polished tends not to be damaged. In addition, the measuring method of the average primary particle diameter of ceria particles is the same as the measuring method of the average primary particle diameter of colloidal ceria.

The average secondary particle size of the ceria particles is preferably 10 to 500 nm, more preferably 20 to 400 nm, and still more preferably 50 to 300 nm. If the average secondary particle diameter of the ceria particles is 10 nm or more, a better polishing rate tends to be obtained. If the average secondary particle diameter of the ceria particles is 500 nm or less, the film to be polished tends to be hardly damaged. In addition, the measuring method of the average secondary particle diameter of ceria particles is the same as the measuring method of the average secondary particle diameter of colloidal ceria.

In another embodiment, the ratio of the sphericity of the ceria particles to the sphericity of the colloidal ceria (the sphericity of the ceria particles / the sphericity of the colloidal ceria) is 0.97 or less in the grinding step. , Crush colloidal ceria. The ratio of the sphericity of the ceria particles to the sphericity of the colloidal ceria may be 0.965 or less, 0.96 or less, or 0.955 or less, for example, 0.30 or more.

The sphericity of the ceria particles is, for example, 30 to 90%, 35 to 85%, or 40 to 80%. The method for measuring the sphericity of ceria particles is the same as the method for measuring the sphericity of colloidal ceria.

Note that whether or not the colloidal ceria has been crushed can be confirmed by observation using, for example, a scanning electron microscope (SEM, for example, S-4800, manufactured by Hitachi High-Technologies Corporation). The shape of colloidal ceria before pulverization is a regular crystal shape, for example, a shape close to a tetrahedron, a hexahedron, a true sphere, etc., whereas the shape of the crushed colloidal ceria is particularly undefined. Shape. The ceria particles after pulverization may contain colloidal ceria remaining without being pulverized. Moreover, you may mix a ceria particle and the colloidal ceria before a grinding | pulverization in arbitrary ratios after a grinding | pulverization process.

Before the pulverization step, an additive may be added to the aqueous dispersion containing colloidal ceria to mix them. Further, after the pulverization step, an additive may be added to the aqueous dispersion containing ceria particles to mix them. The additive used here may be the same as the additive used for the polishing liquid described later. Examples of the mixing method of the colloidal ceria and the additive and the mixing method of the ceria particles and the additive include a mixing method using stirring, a homogenizer, an ultrasonic disperser, or the like.

According to the slurry production method of the present embodiment, the ratio of the average primary particle diameter of the ceria particles to the average primary particle diameter of the colloidal ceria is less than 0.8, or the sphericity of the ceria particles relative to the sphericity of the colloidal ceria. By obtaining a ceria particle by pulverizing colloidal ceria dispersed in water so that the ratio is 0.97 or less, a polishing liquid having an excellent polishing rate can be obtained from the slurry containing the ceria particle and water. Is possible. That is, by producing a slurry by the above production method, it is possible to produce a slurry capable of obtaining a polishing liquid having an excellent polishing rate compared to a polishing liquid containing ceria particles having the same average primary particle diameter. is there.

[Production method of polishing liquid]
The method for producing a polishing liquid according to this embodiment is a method for producing a polishing liquid containing ceria particles, water, and an additive, and the slurry obtained by the above production method is mixed with the additive and polished. A step of obtaining a liquid (additive mixing step) is provided. Examples of the method for mixing the slurry and the additive include the same method as the method for mixing the colloidal ceria and the additive and the method for mixing the ceria particles and the additive.

The content of the ceria particles is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, based on the total amount of the polishing liquid, from the viewpoint of obtaining a good polishing rate. The content of the ceria particles is preferably 20% by mass or less, more preferably 5% by mass or less, and still more preferably 1.5% by mass from the viewpoint that aggregation of the ceria particles is suppressed and the film to be polished is hardly damaged. It is as follows.

Examples of the additive include a dispersant that increases the dispersibility of abrasive grains, a polishing rate improver that improves the polishing rate, a flattening agent (a flattening agent that reduces unevenness of the polished surface after polishing, a substrate after polishing, For example, a global planarizing agent for improving the global planarity), and a selectivity improving agent for improving the polishing selectivity of the inorganic insulating film with respect to the stopper film such as a silicon nitride film and a polysilicon film.

Examples of the dispersant for enhancing the dispersibility of the abrasive grains include a water-soluble anionic dispersant, a water-soluble nonionic dispersant, a water-soluble cationic dispersant, and a water-soluble amphoteric dispersant. The dispersant for enhancing the dispersibility of the abrasive grains is preferably a water-soluble anionic dispersant. The dispersant may be one kind of these, or a mixture of two or more kinds.

The water-soluble anionic dispersant is preferably a polymer compound containing acrylic acid as a copolymerization component and a salt thereof, more preferably a salt of the polymer compound. Examples of the polymer compound containing acrylic acid as a copolymerization component and a salt thereof include, for example, polyacrylic acid and an ammonium salt thereof, a copolymer of acrylic acid and methacrylic acid and an ammonium salt thereof, and acrylic acid amide and acrylic acid. And copolymers thereof and ammonium salts thereof.

Other water-soluble anionic dispersants include, for example, lauryl sulfate triethanolamine, ammonium lauryl sulfate, polyoxyethylene alkyl ether sulfate triethanolamine, and special polycarboxylic acid type polymer dispersants.

Examples of the water-soluble nonionic dispersant include polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, polyoxyethylene alkylamine, polyoxyethylene hydrogenated castor oil, 2 -Hydroxyethyl methacrylate and alkyl alkanolamides.

Examples of the water-soluble cationic dispersant include polyvinyl pyrrolidone, coconut amine acetate, and stearyl amine acetate.

Examples of the water-soluble amphoteric dispersant include lauryl betaine, stearyl betaine, lauryl dimethylamine oxide and 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine.

Examples of the dispersant other than the above include a polymer compound having at least one selected from the group consisting of a carboxylic acid group and a carboxylic acid group. The polymer compound is preferably a polymer obtained by polymerizing a monomer containing at least one selected from the group consisting of acrylic acid and methacrylic acid, or a salt thereof. Examples of the polymer or a salt thereof include acrylic acid homopolymer (polyacrylic acid), methacrylic acid homopolymer (polymethacrylic acid), a copolymer of acrylic acid and methacrylic acid, acrylic acid or methacrylic acid and Examples include at least one selected from the group consisting of copolymers with other monomers, copolymers of acrylic acid and methacrylic acid with other monomers, and salts thereof. An ammonium acid is mentioned.

The content of the dispersant is preferably 0.001 to 10% by mass on the basis of the total amount of the polishing liquid from the viewpoint of improving the dispersibility of the ceria particles to suppress sedimentation and further reducing polishing scratches on the film to be polished. .

When the dispersant contains a polymer, the weight average molecular weight of the polymer is not particularly limited, but is preferably 100 to 150,000, more preferably 1000 to 20000. When the weight average molecular weight of the polymer is 100 or more, a better polishing rate tends to be easily obtained when a film to be polished such as a silicon oxide film or a silicon nitride film is polished. If the weight average molecular weight of the polymer is 150,000 or less, the storage stability of the polishing liquid tends to be difficult to decrease. The weight average molecular weight is a value measured by GPC and converted based on standard polyoxyethylene.

The method for producing a polishing liquid may further include a step (mixing step) of mixing ceria particles and water. Examples of the mixing method of the ceria particles and water include the same method as the mixing method of the colloidal ceria and the additive and the mixing method of the ceria particles and the additive.

Water is not particularly limited, but preferably includes deionized water, ion-exchanged water, ultrapure water, and the like. It suffices if water is contained in the polishing liquid, and the content of water may be the remainder of the polishing liquid excluding the content of other components, and is not particularly limited. The polishing liquid may further contain a solvent other than water as necessary. Examples of the solvent other than water include polar solvents such as ethanol and acetone.

[Characteristics of polishing liquid]
The pH of the polishing liquid at room temperature (25 ° C.) is, for example, 4.0 or more and 8.0 or less. When the pH of the polishing liquid is 4.0 or more, the storage stability of the polishing liquid is improved, and the number of scratches on the film to be polished tends to decrease. From the same viewpoint, the pH of the polishing liquid is preferably 4.5 or more, more preferably 4.8 or more. When the pH of the polishing liquid is 8.0 or less, the flatness improving effect tends to be sufficiently exhibited. From the same viewpoint, the pH of the polishing liquid is preferably 7.5 or less, more preferably 7.0 or less. The pH of the polishing liquid is determined by measuring with a pH meter (for example, Model PH81 (trade name) manufactured by Yokogawa Electric Corporation). The pH of the polishing solution is 2 using, for example, a standard buffer solution (phthalate pH buffer solution, pH: 4.21 (25 ° C.), neutral phosphate pH buffer solution, pH 6.86 (25 ° C.)). After the point calibration, the electrode is put into a polishing liquid and measured as a value after being stabilized at 25 ° C. for 2 minutes or more.

According to the method for producing a polishing liquid according to the present embodiment, the ratio of the average primary particle diameter of the ceria particles to the average primary particle diameter of the colloidal ceria is less than 0.8, or the spheres of the ceria particles with respect to the sphericity of the colloidal ceria By crushing colloidal ceria dispersed in water so that the degree ratio is 0.97 or less to obtain ceria particles, it is possible to obtain a polishing liquid having an excellent polishing rate. That is, by producing a polishing liquid by the above production method, it is possible to obtain a polishing liquid having an excellent polishing rate as compared with a polishing liquid containing ceria particles having the same average primary particle diameter.

The polishing liquid according to this embodiment is preferably used for polishing a film to be polished, which will be described later, and is also preferably used for shallow trench isolation.

[Method of storing slurry and polishing liquid]
The polishing liquid according to the present embodiment may be stored as a one-part polishing liquid containing ceria particles, an additive, and water, and a ceria particle dispersion (first liquid) containing ceria particles, a dispersant, and water; And an additive liquid (second liquid) containing an additive other than the dispersant and water, and may be stored as a two-component polishing liquid. From the standpoint that additives other than the dispersant do not affect the dispersion stability of the ceria particles, the polishing liquid is preferably stored as a two-part polishing liquid. In the case of a two-component polishing liquid, additives other than the dispersant may be contained in the ceria particle dispersion.

When storing as a two-part polishing liquid divided into a ceria particle dispersion and an additive liquid, the planarization characteristics and polishing rate can be adjusted by arbitrarily changing the blend of these two liquids.

In another embodiment, the polishing liquid may be stored as a two-part polishing liquid composed of a first liquid containing ceria particles and water and a second liquid containing an additive and water. By storing ceria particles and additives separately, the dispersion stability of the ceria particles can be kept better until just before using the polishing liquid, so that more effective polishing speed and flatness can be obtained. Is possible.

The slurry and polishing liquid according to the present embodiment is a slurry storage liquid that is used after being diluted with a liquid medium such as water at the time of use, for example, by a factor of 2 or more, from the viewpoint of suppressing costs related to storage, transportation, storage, and the like. Or it can be stored as a stock solution for polishing liquid.

The dilution rate of the stock solution is preferably 2 times or more, more preferably 3 times or more, from the viewpoint that the higher the magnification, the higher the cost-saving effect related to storage, transportation, storage and the like. The upper limit of the dilution ratio of the stock solution is not particularly limited, but from the viewpoint of increasing the amount of components contained in the stock solution (higher concentration) and lowering the stability during storage as the magnification increases. In general, it is preferably 10 times or less, more preferably 7 times or less, and still more preferably 5 times or less. In addition, you may divide a structural component into 3 or more liquids, and also in that case, the dilution rate is the same as the above.

[Substrate polishing method]
Next, a method for polishing a substrate according to the present embodiment will be described. First, a substrate on which a film to be polished is formed is prepared (substrate preparing step). The substrate on which the film to be polished is formed is obtained, for example, by forming a film to be polished on the substrate by a low-pressure CVD method, a plasma CVD method, or the like, which will be described later.

Examples of the substrate include a substrate (semiconductor substrate) for manufacturing a semiconductor element. Examples of the substrate related to the manufacture of the semiconductor element include a semiconductor substrate in which an inorganic insulating film is formed on the semiconductor substrate. For example, the semiconductor substrate in the stage where the circuit element and the wiring pattern are formed, the stage in which the circuit element is formed And the like.

Examples of the film to be polished include interlayer insulating films, BPSG films (silicon dioxide films doped with boron and phosphorus), STI formation films, and the like. Examples of the interlayer insulating film include inorganic insulating films. Examples of the inorganic insulating film include a silicon oxide film, a silicon nitride film, a composite film of a silicon oxide film, and the like.

Subsequent to the substrate preparation step, the polishing film formed on the substrate surface is polished using the polishing liquid (polishing step). More specifically, for example, while the polishing film formed on the substrate surface is pressed against the polishing pad of the polishing surface plate, the polishing liquid is supplied between the polishing film and the polishing pad while the polishing liquid is being supplied between the polishing film and the polishing pad. The film to be polished is polished by moving the disk relatively.

When polishing with a two-part polishing liquid, the ceria particle dispersion and additive liquid are sent through separate pipes, and these pipes are merged just before the outlet of the supply pipe to mix the two liquids, thereby polishing the pad. The ceria particle dispersion liquid and the additive liquid may be mixed immediately before polishing.

When using a stock solution for polishing liquid, a polishing liquid may be obtained by diluting the stock solution for polishing liquid with a liquid medium before the polishing step (stock solution diluting step). The polishing liquid is obtained, for example, by supplying a polishing storage liquid and a liquid medium onto a polishing pad and diluting the polishing liquid on the polishing pad. In the case of using the storage liquid for polishing liquid, in the polishing process, the film to be polished is polished using the polishing liquid obtained in the storage liquid dilution process.

The polishing liquid may be adjusted to a desired pH before the polishing step (pH adjustment step). The pH is adjusted by, for example, a pH adjuster. Although there is no restriction | limiting in particular as a pH adjuster, For example, an acid and a base are mentioned. Examples of the acid include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, boric acid, and acetic acid. Examples of the base include sodium hydroxide, ammonia, potassium hydroxide and calcium hydroxide. When the polishing liquid is used for polishing a film to be polished on a semiconductor substrate, the base is preferably ammonia. Examples of the pH adjuster include ammonium salts of water-soluble polymers that have been partially neutralized with ammonia in advance.

According to the method for polishing a substrate according to the present embodiment, by polishing the film to be polished using the above polishing liquid, unevenness on the surface of the film to be polished (for example, an inorganic insulating film) is eliminated, and the entire surface of the substrate is removed. A smooth surface can be obtained.

Hereinafter, the method for polishing a substrate will be described in more detail by taking a method for polishing a semiconductor substrate on which an inorganic insulating film is formed as an example. First, a substrate on which an inorganic insulating film is formed is prepared (first step). The substrate on which the inorganic insulating film is formed can be obtained, for example, by forming an inorganic insulating film on the substrate by a low pressure CVD method, a plasma CVD method or the like.

Examples of the inorganic insulating film include a silicon oxide film and a silicon nitride film. The silicon oxide film may be doped with elements such as phosphorus and boron.

In the formation of the silicon oxide film by the low pressure CVD method, monosilane: SiH _{4 is} used as the Si source, and oxygen: O ₂ is used as the oxygen source. By performing the SiH ₄ —O ₂ -based oxidation reaction at a low temperature of 400 ° C. or lower, a silicon oxide film can be obtained. In some cases, the silicon oxide film obtained by the low temperature CVD method is heat-treated at a temperature of 1000 ° C. or lower. When the silicon oxide film is doped with phosphorus: P in order to achieve surface planarization by high-temperature reflow, the silicon oxide film is preferably doped with phosphorus using a SiH ₄ —O ₂ —PH ₃ based reaction gas.

Formation of a silicon oxide film by plasma CVD has an advantage that a chemical reaction requiring a high temperature can be performed at a low temperature under normal thermal equilibrium. As the plasma generation method, there are two methods of capacitive coupling type and inductive coupling type. The reaction gases, SiH ₄ as an Si source, _SiH 4 -N ₂ O-containing gas using _{N 2} O as oxygen source, and TEOS-O-based gas using tetraethoxysilane (TEOS) in an Si source (TEOS- Plasma CVD method). The substrate temperature is preferably 250 to 400 ° C., and the reaction pressure is preferably 67 to 400 Pa.

A silicon nitride film formed by low pressure CVD method, dichlorosilane as Si source: _SiH 2 Cl _2, ammonia as a nitrogen source: the NH ₃ is used. By performing the SiH ₂ Cl ₂ —NH ₃ oxidation reaction at a high temperature of 900 ° C., a silicon nitride film can be obtained.

Examples of the reaction gas used for forming the silicon nitride film by the plasma CVD method include SiH ₄ —NH ₃ based gas using SiH ₄ as the Si source and NH ₃ as the nitrogen source. The substrate temperature is preferably 300 to 400 ° C.

Subsequent to the first step, the substrate on which the inorganic insulating film is formed is placed in a polishing apparatus (second step). The substrate is arranged so that the inorganic insulating film on the substrate faces the polishing pad of the polishing apparatus.

As a polishing apparatus, a general polishing apparatus having a holder for holding a substrate such as a semiconductor substrate having a film to be polished, a motor capable of changing the number of rotations, and a polishing surface plate to which a polishing pad (polishing cloth) can be attached Is mentioned. Examples of the polishing apparatus include polishing apparatuses manufactured by Ebara Corporation: F-REX, MIRRA manufactured by AMAT, and Reflexion.

The polishing pad is not particularly limited, and examples thereof include general nonwoven fabrics, foamed polyurethane, and porous fluororesins. The polishing pad is preferably grooved so that the polishing liquid is accumulated.

Subsequent to the second step, the film to be polished is polished using the polishing liquid (third step). The method for polishing the film to be polished is the same as the method for polishing the film to be polished in the polishing step. The polishing liquid is continuously supplied to the polishing pad with a pump or the like during polishing.

Polishing conditions are not limited. The rotation speed of the polishing platen is preferably a low rotation of 200 rotations / minute or less so that the semiconductor substrate does not jump out. The pressure (processing load) applied to the semiconductor substrate is preferably 100 kPa or less so as not to cause scratches after polishing. The supply amount of the polishing liquid is not particularly limited, but is preferably such an amount that the surface of the polishing pad is always covered with the polishing liquid.

Subsequent to the third step, the polished substrate may be washed and dried (cleaning and drying step). The substrate is thoroughly washed in running water, for example, and then dried by removing water droplets adhering to the substrate using a spin dryer or the like.

According to the method for polishing a substrate according to this embodiment, it is possible to obtain a high polishing rate by polishing the film to be polished using the above polishing liquid (the film to be polished can be quickly polished). By polishing an inorganic insulating film, which is a film to be polished, with the above-described polishing liquid, surface irregularities can be eliminated and the entire surface of the substrate can be made smooth.

The substrate polishing method according to the present embodiment can be applied not only to polishing an inorganic insulating film formed on a semiconductor substrate but also to manufacturing processes of various semiconductor devices. The substrate polishing method according to the present embodiment includes, for example, a silicon oxide film formed on a wiring board having predetermined wiring, an inorganic insulating film such as glass and silicon nitride, polysilicon, Al, Cu, Ti, TiN, W , Optical glass such as photomasks, lenses and prisms, inorganic conductive films such as ITO, optical integrated circuits, optical switching elements, optical waveguides, optical fibers Polishing of the end face of the substrate, optical single crystal such as scintillator, solid laser single crystal, sapphire substrate for blue laser LED, semiconductor single crystal such as SiC, GaP and GaAs, glass substrate for magnetic disk, magnetic head, etc. Can be applied.

The semiconductor substrate is manufactured as follows, for example. First, a flattened shallow trench is formed, then a metal wiring such as aluminum is formed on the inorganic insulating film, and an inorganic insulating film is formed again between and on the wiring. Thereafter, the inorganic insulating film is polished using a polishing liquid to obtain a smooth surface. By repeating these steps a predetermined number of times, a semiconductor substrate having a desired number of layers can be obtained.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

<Example 1>
(Production of slurry)
An aqueous dispersion containing colloidal ceria having an average primary particle diameter of 90 nm and an average secondary particle diameter of 213 nm was prepared. The bead mill treatment was performed for 100 minutes, and colloidal ceria was pulverized until the average primary particle size was 50 nm and the average secondary particle size was 145 nm, to obtain a slurry containing ceria particles (ground abrasive grains) and water. That is, the ratio R2 / R1 of the average primary particle diameter (R2) of the ceria particles to the average primary particle diameter (R1) of the colloidal ceria is 0.56, and the sphericity S of the ceria particles relative to the sphericity S _a of the colloidal ceria the ratio _S b / _{S a} and _b were crushed colloidal ceria as 0.95 or less.
Colloidal ceria before the bead mill treatment and ceria particles after the bead mill treatment were observed with an SEM. The obtained image is shown in FIG.

The average primary particle size of colloidal silica before pulverization and ceria particles after pulverization was determined by image analysis by SEM observation. That is, first, an image of ceria particles was obtained by SEM observation, and the obtained image of ceria particles was approximated by a circle, and the diameter of the circle was measured as the primary particle diameter. The primary particle diameters of 50 particles randomly selected from the image of the particles obtained by SEM observation were measured, and the average value was defined as the average primary particle diameter.

The average secondary particle size of the ceria particles contained in the slurry was measured using a laser diffraction particle size distribution meter (trade name: Master Sizer Microplus manufactured by Malvern). That is, first, the slurry for measurement was obtained by diluting the slurry to a concentration at which the measurement transmittance (H) for the He—Ne laser was 60 to 70%. The value of D50 obtained by measurement under the conditions of a refractive index of 1.93, a light source He—Ne laser, and zero absorption was taken as the average secondary particle diameter.

The sphericity of colloidal ceria before pulverization and ceria particles after pulverization was determined as follows. That is, first, image analysis by SEM observation was performed, and the true sphericity was obtained by the following formula (1).
S (%) = r / R × 100 (1)
In the formula (1), S represents the sphericity ratio (%), r represents the maximum radius of a circle that can be drawn in one particle obtained by SEM observation, and R represents one particle obtained by SEM observation. Indicates the minimum radius of the circle that contains. The sphericity of 50 particles randomly selected from the image of the particles obtained by SEM observation was determined by the above method, and the average value thereof was defined as the sphericity.

(Preparation of polishing liquid)
An appropriate amount of the obtained slurry was sampled, and the slurry and polyacrylic acid were adjusted so that the content of crushed abrasive grains was 5% by mass and the concentration of ammonium polyacrylate (weight average molecular weight: 8000) was 0.1% by mass. Ammonium and water were mixed to obtain a mixed solution. This mixed liquid was dispersed using an ultrasonic disperser to obtain a pulverized abrasive dispersion.

Deionized water and propionic acid were added to the pulverized abrasive dispersion to prepare a polishing liquid (content of pulverized abrasive: 0.25% by mass) having a total amount of 1000 g and a pH of 6.0 (25 ° C.). . The ceria particles contained in the polishing liquid had an average primary particle size of 50 nm and an average secondary particle size of 145 nm. The average primary particle size and average secondary particle size of the ceria particles contained in the polishing liquid were determined in the same manner as the average primary particle size and average secondary particle size of the ceria particles contained in the slurry, respectively. The pH of the polishing liquid was measured with a pH meter (Model PH81 (trade name) manufactured by Yokogawa Electric Corporation).

(Polishing the film to be polished)
As a wafer used for the polishing test, a blanket wafer on which no pattern was formed was used. As a blanket wafer, a silicon (Si) substrate having a silicon oxide film formed by a plasma TEOS method and a silicon (Si) substrate having a silicon nitride film formed by a low pressure CVD method were used.

The wafer was polished by a polishing apparatus (F-REX-300 manufactured by Ebara Corporation). The wafer was set in a holder to which a substrate mounting suction pad was attached in a polishing apparatus. A polishing pad made of porous urethane resin (groove shape = groove type: manufactured by Dow Corning, model number VP3100) was attached to a polishing surface plate having a diameter of 600 mm in a polishing apparatus. Further, the holder was placed on a polishing surface plate so that an insulating film (silicon oxide film or silicon nitride film) as a film to be polished was opposed to the polishing pad. The processing load is set to 210 gf / cm ² (20.6 kPa), and the polishing platen and the wafer are rotated at 130 rpm for each time while the polishing liquid is dropped on the polishing pad at a rate of 250 ml / min. The wafer was polished. After polishing, the wafer was thoroughly washed with pure water and dried. The film thickness before and after polishing was measured using an optical interference type film thickness measuring apparatus to examine the polishing rate. The results are shown in Table 1.

(Examples 2 and 4)
Slurry and polishing were carried out in the same manner as in Example 1 except that the processing time of the bead mill was changed as follows to pulverize the colloidal ceria until the average primary particle size and average secondary particle size shown in Table 1 were obtained. A liquid was prepared. Using the prepared polishing liquid, the film to be polished was polished in the same manner as in Example 1, and the polishing rate was examined. The results are shown in Table 1.
Processing time of bead mill Example 2: 50 minutes Example 4: 20 minutes

(Example 3)
A slurry and a polishing liquid were prepared in the same manner as in Example 1 except that a jet mill was used instead of the bead mill. Using the prepared polishing liquid, the film to be polished was polished in the same manner as in Example 1, and the polishing rate was examined. The results are shown in Table 1.

(Comparative Examples 1 to 3)
A polishing liquid was prepared in the same manner as in Example 1 except that a slurry containing colloidal ceria having the average primary particle size and average secondary particle size shown in Table 1 and water was prepared without pulverizing the colloidal ceria. . Using the prepared polishing liquid, the film to be polished was polished in the same manner as in Example 1, and the polishing rate was examined. The results are shown in Table 1.

From Table 1, in the polishing liquid containing ceria particles having the same average primary particle diameter, the polishing liquid obtained by subjecting colloidal ceria to the grinding treatment is the same as the polishing liquid obtained without performing the grinding treatment. It can be seen that the polishing rate is higher than that.

Claims (8)

A method for producing a slurry containing ceria particles and water,
Crushing colloidal ceria dispersed in water to provide the ceria particles,
In the pulverizing step, the slurry is pulverized so that a ratio of an average primary particle diameter of the ceria particles to an average primary particle diameter of the colloidal ceria is less than 0.8. A method for producing a slurry containing ceria particles and water,
Crushing colloidal ceria dispersed in water to provide the ceria particles,
In the pulverizing step, the slurry is pulverized so that a ratio of the sphericity of the ceria particles to the sphericity of the colloidal ceria is 0.97 or less. The method for producing a slurry according to claim 1 or 2, wherein in the pulverizing step, the colloidal ceria is pulverized using a bead mill. The method for producing a slurry according to claim 1 or 2, wherein in the pulverizing step, the colloidal ceria is pulverized using a jet mill. A method for producing a polishing liquid comprising ceria particles, water and an additive,
A method for producing a polishing liquid, comprising the step of mixing the slurry obtained by the production method according to any one of claims 1 to 4 with an additive to obtain a polishing liquid. A slurry obtained by the slurry production method according to any one of claims 1 to 4. A polishing liquid obtained by the method for producing a polishing liquid according to claim 5. A method for polishing a substrate, comprising a polishing step of polishing a film to be polished formed on the surface of the substrate using the polishing liquid according to claim 7.

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