JP2015008212A - Polishing liquid and substrate polishing method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing liquid capable of improving flatness after polishing, and a substrate polishing method using the polishing liquid.SOLUTION: The polishing liquid for CMP contains cerium oxide particles, an organic acid A, a polymer compound B, and water. The organic acid A has at least one group selected from the group consisting of a -COOM group, a -Ph-OM group, an -SOM group, and a -POMgroup. The pKa of the organic acid A is less than 9. The polymer compound B has at least one selected from the group consisting of a carboxylic acid group and a carboxylate group, and at least one selected from the group consisting of a sulfurous acid group and a sulfite group.

Description

  The present invention relates to a polishing liquid and a method for polishing a substrate using the polishing liquid. More specifically, the present invention is a semiconductor device manufacturing technique, a planarization process of a substrate surface, in particular, a planarization process of an insulating material, a BPSG material (boron, silicon dioxide doped with phosphorus), shallow trench isolation (STI). ) Forming process and the like, and a method for polishing a substrate using the polishing liquid.

  In the current ULSI semiconductor device manufacturing process, processing technology for high density and miniaturization of semiconductor devices has been researched and developed. One of the processing techniques, planarization technology by CMP (Chemical Mechanical Polishing), is the planarization of insulating material, STI (Shallow Trench Isolation) formation process, and plug formation process in the semiconductor device manufacturing process. It has become an indispensable technique when performing a buried metal wiring forming process (damascene process) and the like. In the CMP process (planarization process using the CMP technique), the polishing material is generally polished while supplying a polishing slurry for CMP between the polishing pad (polishing cloth) and the polishing material on the substrate. Is done by.

  Various polishing liquids for CMP used in the CMP are known. When classified according to abrasive grains (polishing particles) contained in CMP polishing liquid, ceria-based polishing liquid containing cerium oxide (ceria) particles as abrasive grains, silica-based polishing liquid containing silicon oxide (silica) particles as abrasive grains, and abrasives Known are alumina-based polishing liquids containing aluminum oxide (alumina) particles as grains, resin particle-based polishing liquids containing organic resin particles as abrasive grains, and the like.

  As a polishing liquid for polishing an insulating material such as silicon oxide in a semiconductor element manufacturing process, a ceria-based polishing liquid has attracted attention because it has a higher polishing rate for an inorganic insulating material than a silica-based polishing liquid. .

  As a ceria-based polishing liquid, the following Patent Document 1 describes a CMP polishing liquid for semiconductors using high-purity cerium oxide abrasive grains. Patent Documents 2 and 3 listed below describe techniques for adding additives to control the polishing rate of the ceria-based polishing liquid and improve global flatness.

Japanese Patent Laid-Open No. 10-106994 Japanese Patent No. 3278532 International Publication WO2012 / 086781

  A typical example of the process of polishing the insulating material by CMP is the above-described STI formation process. In the STI formation process, CMP is used to remove excess portions of the insulating material deposited on the substrate having the recesses. The polishing liquid for CMP is required to be able to polish the insulating material at a certain high speed, but various other characteristics are also required. For example, it is required to reduce the amount of dishing and to polish with excellent flatness. . Note that dishing is a phenomenon in which an insulating material deposited in the concave portion is removed excessively and a part of the surface to be polished is recessed like a dish. When dishing occurs, it is not preferable because the surface flatness after polishing is poor.

  For such a problem, Patent Document 3 discloses a technique that can be reduced to a dishing amount of about 220 to 390 mm (22 to 39 nm) by adding an organic acid having a predetermined structure to the polishing liquid. .

  However, with the progress of miniaturization of design rules for wiring and STI, further improvement in flatness (for example, reduction of the amount of dishing of an insulating material) is required. In addition, further improvement in the accuracy of semiconductor device production is also required. For example, it is required that the difference in the remaining film thickness of the insulating material in portions with different trench densities is small.

  The present invention has been made in view of the above circumstances, and in a CMP technique for polishing a material to be polished on the surface of a substrate, a polishing liquid capable of improving flatness after polishing and the polishing liquid are used. It is an object of the present invention to provide a method for polishing a substrate.

The present invention is a polishing slurry for CMP containing cerium oxide particles, an organic acid A, a polymer compound B, and water, and the organic acid A includes a —COOM group, a —Ph—OM group, a —SO ₃ M group, and From the group consisting of —PO ₃ M ₂ groups (wherein M is any one selected from H, NH ₄ , Na and K, and Ph represents a phenyl group which may have a substituent). Having at least one selected group, the pKa of the organic acid A is less than 9, and the polymer compound B includes at least one selected from the group consisting of a carboxylic acid group and a carboxylic acid group, and a sulfite group And at least one selected from the group consisting of sulfite groups.

  In the polishing liquid of the present invention, in a CMP technique for polishing a material to be polished (for example, an insulating material, a BPSG material, or an STI material) on the surface of the substrate, a sufficient polishing rate of the material to be polished is maintained, and after polishing. Flatness can be improved.

  The content of the organic acid A is preferably 0.001 to 1% by mass with respect to the total mass of the polishing liquid. This makes it easier to maintain a sufficient polishing rate of the material to be polished and improve flatness after polishing.

  The content of the polymer compound B is preferably 0.01 to 0.50 mass% with respect to the total mass of the polishing liquid. This makes it easier to maintain a sufficient polishing rate of the material to be polished and improve flatness after polishing.

  It is preferable that pH of polishing liquid is 4.0 or more and 6.0 or less. This makes it easier to achieve improved flatness after polishing. In addition, the storage stability of the polishing liquid tends to be improved.

  The polishing liquid of the present invention is stored as a two-part polishing liquid composed of a first liquid containing cerium oxide particles and water, and a second liquid containing organic acid A, polymer compound B and water. You may keep it. Thereby, since dispersion stability of cerium oxide particles can be kept better until just before using the polishing liquid, it is possible to obtain a more effective polishing rate and flatness.

  In the polishing liquid of the present invention, it is preferable that the first liquid further contains a dispersant. Thereby, the dispersion stability of the cerium oxide particles can be kept better.

  The present invention also provides a method for polishing a substrate, wherein a material to be polished on the surface of the substrate is polished using the polishing liquid of the present invention. According to such a polishing method using the polishing liquid of the present invention, it is possible to further improve the flatness after polishing while maintaining a sufficient polishing rate of the material to be polished.

  According to the present invention, in a CMP technique for polishing a material to be polished (for example, an STI material) on a surface of a substrate, a polishing liquid capable of improving surface flatness after polishing and a substrate using the polishing liquid A polishing method can be provided. Thereby, for example, it is possible to reduce dishing and to reduce the difference in the remaining film thickness of the insulating material in portions having different trench densities.

It is a schematic cross section showing an evaluation substrate for polishing characteristics.

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

[Polishing liquid]
The polishing liquid according to this embodiment is a polishing liquid for CMP containing cerium oxide particles, a dispersant, an organic acid A, a polymer compound B, and water. Hereinafter, each component contained in the polishing liquid according to the present embodiment will be described in detail.

(Cerium oxide particles)
There is no restriction | limiting in particular as a cerium oxide particle, A well-known thing can be used. In general, cerium oxide is obtained by oxidizing a cerium compound such as carbonate, nitrate, sulfate, or oxalate. Examples of the method for producing the cerium oxide particles include firing, an oxidation method using hydrogen peroxide, and the like.

  When cerium oxide particles are used for polishing silicon oxide formed by TEOS-CVD or the like, the crystallite diameter (crystallite diameter) of the cerium oxide particles is larger and the crystal distortion is smaller, that is, the crystallinity is better. The higher the polishing speed is, the more easily the polishing material tends to have polishing scratches. From such a point of view, the cerium oxide particles are preferably composed of two or more crystallites, particles having a crystal grain boundary, and more preferably particles having a crystallite diameter in the range of 1 to 300 nm.

  The crystallite diameter can be measured by observation with a scanning electron microscope (SEM). Specifically, the major axis and minor axis of the particle are measured from an image obtained by observation with a scanning electron microscope (SEM), and the square root of the product of the major axis and the minor axis is defined as the particle diameter.

  The content of alkali metal and halogens in the cerium oxide particles is preferably 10 ppm or less because it is suitably used for polishing in the manufacture of semiconductor elements.

  The average particle diameter of the cerium oxide particles is preferably 10 to 500 nm, more preferably 20 to 400 nm, and still more preferably 50 to 300 nm. If the average particle size of the cerium oxide particles is 10 nm or more, a good polishing rate tends to be obtained, and if it is 500 nm or less, the material to be polished tends to be hardly damaged.

  Here, the average particle diameter of the cerium oxide particles is measured by a laser diffraction particle size distribution analyzer (for example, product name: Master Sizer Microplus, refractive index: 1.93, light source: He—Ne laser, absorption 0 manufactured by Malvern). Means the value of D50 (median diameter of volume distribution, cumulative median value). For the measurement of the average particle diameter, a sample in which the polishing liquid is diluted to an appropriate concentration (for example, a concentration at which the measurement transmittance (H) for a He—Ne laser is 60 to 70%) is used. When the cerium oxide polishing liquid is stored separately in a cerium oxide slurry in which cerium oxide particles are dispersed in water and an additive solution in which an additive is dissolved in water as described later, the cerium oxide slurry is stored. Can be diluted to an appropriate concentration.

  The content of the cerium oxide particles is preferably 0.1% by mass or more and more preferably 0.5% by mass or more based on the total mass of the polishing liquid from the viewpoint that a good polishing rate tends to be obtained. The content of the cerium oxide particles is preferably 20% by mass or less, more preferably 5% by mass or less, and more preferably 3% by mass from the viewpoint that the aggregation of the particles is suppressed and the material to be polished is less likely to be damaged. The following is more preferable, and 1.5% by mass or less is particularly preferable.

(Organic acid A)
The polishing liquid according to this embodiment contains an organic acid and / or a salt thereof as the organic acid A. Thereby, the polishing rate can be improved and the flatness of the material to be polished (for example, silicon oxide) after the polishing can be improved. More specifically, when polishing the surface to be polished, the polishing time can be shortened, and the phenomenon that a part of the surface is excessively polished and recessed like a dish, so-called dishing, is suppressed. it can. Further, the difference in the remaining film thickness of the material to be polished in the portions having different trench densities can be reduced. This effect can be obtained more efficiently by using an organic acid and / or a salt thereof and cerium oxide particles in combination.

Organic acids and / or salts thereof, -COOM group, -Ph-OM group (phenolic -OM group), - SO ₃ M group and _-PO 3 _{M 2} group (wherein, M is _H, NH _4, Na And Ph represents at least one group selected from the group consisting of a phenyl group which may have a substituent, and is water-soluble. It is preferable that it is an organic compound.

The organic acid A has an acid dissociation constant pKa at room temperature (25 ° C.) (the lowest first stage pKa ₁ when there are two or more pKa) is less than 9, but the pKa is less than 8. Is preferably less than 7, more preferably less than 6, particularly preferably less than 5, and most preferably less than 3. If the pKa of the organic acid A is less than 9, at least a part of the organic acid A becomes an organic acid ion in the polishing liquid to release hydrogen ions, and the pH can be maintained in a desired pH range. In addition, it is preferable that the lower limit of pKa is -10, for example.

As the organic acid A, for example,
Formic acid, acetic acid, propionic acid, butyric acid, valeric acid, cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, o-methoxybenzoic acid, m-methoxybenzoic acid, p -Methoxybenzoic acid, acrylic acid, methacrylic acid, crotonic acid, pentenoic acid, hexenoic acid, heptenoic acid, octenoic acid, nonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoic acid, Heptadecenoic acid, isobutyric acid, isovaleric acid, cinnamic acid, quinaldic acid, nicotinic acid, 1-naphthoic acid, 2-naphthoic acid, picolinic acid, vinylacetic acid, phenylacetic acid, phenoxyacetic acid, 2-furancarboxylic acid, mercaptoacetic acid , Levulinic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pime Acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecane Dicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,15-pentadecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, quinolinic acid, quinic acid, naphthalic acid , Phthalic acid, isophthalic acid, terephthalic acid, glycolic acid, lactic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 5-hydroxyvaleric acid, quinic acid , Kynurenic acid, salicylic acid, tartaric acid, aconitic acid, ascorbic acid, Cetylsalicylic acid, acetylmalic acid, acetylenedicarboxylic acid, acetoxysuccinic acid, acetoacetic acid, 3-oxoglutaric acid, atropaic acid, atrolactic acid, anthraquinone carboxylic acid, anthracene carboxylic acid, isocaproic acid, isocamphoric acid, isocrotonic acid, 2-ethyl 2-hydroxybutyric acid, ethylmalonic acid, ethoxyacetic acid, oxaloacetic acid, oxydiacetic acid, 2-oxobutyric acid, camphoric acid, citric acid, glyoxylic acid, glycidic acid, glyceric acid, glucaric acid, gluconic acid, croconic acid, cyclobutane Carboxylic acid, cyclohexanedicarboxylic acid, diphenylacetic acid, di-O-benzoyltartaric acid, dimethylsuccinic acid, dimethoxyphthalic acid, tartronic acid, tannic acid, thiophenecarboxylic acid, tiglic acid, desoxosaric acid, tetrahys Droxysuccinic acid, tetramethyl succinic acid, tetronic acid, dehydroacetic acid, terephthalic acid, tropic acid, vanillic acid, paraconic acid, hydroxyisophthalic acid, hydroxycinnamic acid, hydroxynaphthoic acid, o-hydroxyphenylacetic acid, m-hydroxyphenyl Acetic acid, p-hydroxyphenylacetic acid, 3-hydroxy-3-phenylpropionic acid, pivalic acid, pyridinedicarboxylic acid, pyridinetricarboxylic acid, pyruvic acid, α-phenylcinnamic acid, phenylglycidic acid, phenylsuccinic acid, phenylacetic acid , Phenyllactic acid, propiolic acid, sorbic acid, 2,4-hexadienedioic acid, 2-benzylidenepropionic acid, 3-benzylidenepropionic acid, benzylidenemalonic acid, benzylic acid, benzenetricarboxylic acid, 1,2-benzenediacetic acid, benzoic acid Oxyacetic acid, benzoyloxypropionic acid, benzoylformic acid, benzoylacetic acid, O-benzoyllactic acid, 3-benzoylpropionic acid, gallic acid, mesooxalic acid, 5-methylisophthalic acid, 2-methylcrotonic acid, α-methylcinnamic acid, methylsuccinic acid Acid, methylmalonic acid, 2-methylbutyric acid, o-methoxycinnamic acid, p-methoxycinnamic acid, mercaptosuccinic acid, mercaptoacetic acid, O-lactoyl lactic acid, malic acid, leuconic acid, leucine acid, rosinic acid, rosole Acid, α-ketoglutaric acid, L-alcorbic acid, iduronic acid, galacturonic acid, glucuronic acid, pyroglutamic acid, ethylenediaminetetraacetic acid, triacetic acid acetic acid, aspartic acid, glutamic acid, N′-hydroxyethyl-N, N, N ′ -Carboxylic acids such as triacetic acid and nitrilotriacetic acid;
Methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, heptanesulfonic acid, octanesulfonic acid, nonanesulfonic acid, decanesulfonic acid, undecanesulfonic acid, dodecanesulfonic acid, tridecane Sulfonic acid, tetradecanesulfonic acid, pentadecanesulfonic acid, hexadecanesulfonic acid, heptadecanesulfonic acid, octadecanesulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid, p-toluenesulfonic acid, hydroxyethanesulfonic acid, hydroxyphenolsulfonic acid and anthracenesulfone Sulfonic acids such as acids;
And phosphonic acids such as decylphosphonic acid and phenylphosphonic acid. Furthermore, with regard to the carboxylic acid, sulfonic acid and phosphonic acid, one or more protons of these main chains are represented by atoms or atomic groups such as F, Cl, Br, I, OH, CN and NO _2. It may be a substituted derivative. These can be used alone or in combination of two or more.

  The content of the organic acid A (organic acid and / or salt thereof) is preferably 0.001 to 1% by mass based on the total mass of the polishing liquid. If the content of the organic acid and / or salt thereof is 0.001% by mass or more, the flatness of the material to be polished (for example, silicon oxide) after polishing tends to be improved. The content of the organic acid and / or salt thereof is more preferably 0.005% by mass or more, still more preferably 0.01% by mass or more, particularly preferably 0.05% by mass or more, and extremely preferably 0.1% by mass or more. Is preferred. On the other hand, if the content is 1% by mass or less, the polishing rate of the material to be polished tends to be sufficiently improved, and aggregation of the cerium oxide particles tends to be suppressed. Alternatively, the content of the salt is more preferably 0.7% by mass or less, and further preferably 0.5% by mass or less.

(Polymer Compound B)
The polishing liquid according to the present embodiment has at least one selected from the group consisting of a carboxylic acid group and a carboxylic acid group, and has a polymer compound having at least one selected from the group consisting of a sulfite group and a sulfite group B is included. Thereby, the flatness of the material to be polished (for example, silicon oxide) after completion of polishing can be improved. More specifically, the occurrence of dishing can be suppressed. Further, the difference in the remaining film thickness of the material to be polished in the portions having different trench densities can be reduced. This effect can be obtained more efficiently by using the organic acid A and cerium oxide particles in combination. In addition, it is preferable that the high molecular compound B has at least 1 type selected from the group which consists of a carboxylic acid group and a carboxylic acid group in a principal chain. Moreover, it is preferable that the high molecular compound B has at least 1 type selected from the group which consists of a sulfite group and a sulfite group at the principal chain terminal.

  The polymer compound B is preferably derived from a polymer of a monomer component containing an unsaturated carboxylic acid. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, fumaric acid, and maleic acid.

  The polymer compound B may be derived from a homopolymer (homopolymer) of the unsaturated carboxylic acid, or may be derived from a plurality of copolymers (copolymers) of the unsaturated carboxylic acid. . Examples of the homopolymer include polyacrylic acid, polymethacrylic acid, polycrotonic acid, polyfumaric acid, polymaleic acid and the like. Among them, polyacrylic acid which is a homopolymer of acrylic acid is preferable. Examples of the copolymer include acrylic acid-methacrylic acid copolymer.

  The copolymer may be a copolymer of another polymerizable compound and a monomer component containing the unsaturated carboxylic acid. Examples of such another polymerizable compound include alkyl acrylate, alkyl methacrylate, and alkyl crotonic acid. Examples of the alkyl include methyl, ethyl, propyl, butyl, pentyl, octyl and the like. Examples of such a copolymer include acrylic acid-methyl acrylate copolymer, acrylic acid-methyl methacrylate copolymer, and the like.

  In the CMP polishing liquid, part or all of the carboxylic acid groups may be carboxylic acid groups. The carboxylate group refers to a group in which the carboxylic acid group moiety is a salt. Specific examples include ammonium base, sodium base, potassium base and the like. In order to do this, a polishing slurry for CMP may be prepared after previously converting a part or all of the carboxylic acid groups of the polymer compound B to a carboxylate group, or the polymer compound B is added to the CMP polishing solution. After the addition, a base may be further added so that a part or all of the carboxylic acid groups of the polymer compound B may be converted to a carboxylic acid base.

  In the polishing slurry for CMP of the present invention, the polymer compound B preferably has a sulfite group as a terminal group. Here, the sulfite group may be a sulfite group in the polishing slurry for CMP. Examples of the sulfite group include a sodium sulfite group, a potassium sulfite group, and an ammonium sulfite group, and an ammonium sulfite group is preferable.

  As a method for obtaining the polymer compound B having a sulfite group as a terminal group, a method of polymerizing a monomer component using sulfite is preferable, and a monomer containing the unsaturated carboxylic acid using sulfite is used. A method of polymerizing the components is more preferable. Examples of the sulfite include sodium sulfite, potassium sulfite, and ammonium sulfite. Among them, ammonium sulfite is preferable because it does not contain alkali metal ions. Moreover, the high molecular compound B can be used individually by 1 type or in combination of 2 or more types.

  The content of the polymer compound B is 0.01% by mass or more based on the total mass of the polishing liquid from the viewpoint that the flatness of the material to be polished (for example, silicon oxide) after the polishing is finished can be improved. Preferably there is. From the same viewpoint, 0.02% by mass or more is more preferable, 0.05% by mass or more is further preferable, and 0.10% by mass or more is particularly preferable. In addition, it is preferable that the polishing rate of the material to be polished is 0.50% by mass or less based on the total mass of the polishing liquid from the viewpoint that the polishing rate tends to be sufficiently improved and aggregation of cerium oxide particles tends to be suppressed. 0.45 mass% or less is more preferable, and 0.40 mass% or less is still more preferable.

  Although there is no restriction | limiting in particular in the weight average molecular weight of the high molecular compound B, From the viewpoint which there exists a tendency which can fully obtain the grinding | polishing speed | rate of to-be-polished material, and there exists a tendency which is easy to suppress aggregation of a cerium oxide particle, it is 100,000 or less. Is preferable, and 10,000 or less is more preferable. Moreover, the weight average molecular weight of the high molecular compound B is preferably 1000 or more from the viewpoint that the flatness improving effect tends to be easily obtained. The weight average molecular weight is measured by GPC (Gel Permeation Chromatography) and can be calculated using a calibration curve prepared with a sodium polyacrylate standard substance.

(water)
Although it does not restrict | limit especially as water, Deionized water, ion-exchange water, ultrapure water, etc. are preferable. The content of water is not particularly limited as long as it is the remainder of the content of each of the above-described components and is contained in the polishing liquid. The polishing liquid may further contain a solvent other than water, for example, a polar solvent such as ethanol or acetone, if necessary.

(Dispersant)
The polishing liquid according to the present embodiment can contain a dispersant for dispersing the cerium oxide particles. Examples of the dispersant include water-soluble anionic dispersants, water-soluble nonionic dispersants, water-soluble cationic dispersants and water-soluble amphoteric dispersants, and among them, water-soluble anionic dispersants are preferable. . These can be used alone or in combination of two or more. In addition, the said compound (for example, ammonium polyacrylate) illustrated as the high molecular compound B can also be used as a dispersing agent.

  As the water-soluble anionic dispersant, a polymer containing acrylic acid as a copolymerization component and a salt thereof are preferable, and a salt of the polymer is more preferable. Polymers containing acrylic acid as a copolymerization component and salts thereof include, for example, polyacrylic acid and ammonium salts thereof, copolymers of acrylic acid and methacrylic acid and ammonium salts thereof, and acrylic amides and acrylic acids. And copolymers thereof and ammonium salts thereof.

  Examples of other water-soluble anionic dispersants include 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, and polyoxyethylene hydrogenated castor oil. 2-hydroxyethyl methacrylate and alkylalkanolamides.

  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.

  The content of the dispersant is in the range of 0.001 to 10% by mass based on the total mass of the polishing liquid from the viewpoint of improving the dispersibility of the cerium oxide particles to suppress sedimentation and further reducing polishing scratches on the material to be polished. preferable.

  Although the weight average molecular weight of a dispersing agent does not have a restriction | limiting in particular, 100-150,000 are preferable and 1000-20000 are more preferable. When the molecular weight of the dispersant is 100 or more, a good polishing rate tends to be easily obtained when polishing a material to be polished such as silicon oxide or silicon nitride. If the molecular weight of the dispersant is 150,000 or less, the storage stability of the polishing liquid tends to be difficult to decrease. The weight average molecular weight is measured by GPC and can be calculated using a calibration curve prepared with a sodium polyacrylate standard substance.

(Other additives)
The polishing liquid according to the present embodiment includes a water-soluble polymer as an additive different from the organic acid and / or salt thereof, and the water-soluble organic polymer having a carboxylic acid group or a carboxylate group and a sulfite group or a sulfite group. Can be used. Examples of such water-soluble polymers include polysaccharides such as alginic acid, pectic acid, carboxymethyl cellulose, agar, curdlan and pullulan; vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone and polyacrolein. These water-soluble polymers preferably have a weight average molecular weight of 500 or more. Further, the content of these water-soluble polymers is preferably 0.01 to 5% by mass based on the total mass of the polishing liquid.

[Preparation and storage method of polishing liquid]
The polishing liquid according to the present embodiment can be obtained, for example, by adding cerium oxide particles, water, and a dispersing agent to disperse the cerium oxide particles, and further adding an organic acid A and a polymer compound B. . The polishing liquid according to this embodiment may be stored as a one-part polishing liquid containing cerium oxide particles, a dispersant, an organic acid A, a polymer compound B, water, and optionally a water-soluble polymer. A cerium oxide slurry (first liquid) containing cerium particles, a dispersant and water, and an additive liquid (second liquid) containing an organic acid A, a polymer compound B, water and optionally a water-soluble polymer. You may preserve | save as a two-component polishing liquid comprised.

  In the case of a two-part polishing liquid, additives other than the organic acid A and the polymer compound B may be included in either the cerium oxide slurry or the additive liquid, but this affects the dispersion stability of the cerium oxide particles. It is preferable that it is contained in an additive liquid at the point which does not have.

  When storing as a two-component polishing liquid in which the cerium oxide slurry and the additive liquid are separated, the planarization characteristics and the polishing rate can be adjusted by arbitrarily changing the combination of these two liquids. When polishing with a two-part polishing liquid, the cerium oxide slurry and additive liquid are sent through separate pipes, and these pipes are combined just before the supply pipe outlet to mix the two liquids onto the polishing pad. Or a method of mixing the cerium oxide slurry and the additive solution immediately before polishing.

  The polishing liquid and slurry according to the present embodiment are used for polishing liquid storage, which is used after being diluted with a liquid medium such as water, for example, twice or more at the time of use, from the viewpoint of suppressing costs related to storage, transportation, storage and the like. Can be stored as a liquid or slurry stock. Each of the storage liquids may be diluted with a liquid medium immediately before polishing, or may be diluted on the polishing pad by supplying the storage liquid and the liquid medium onto the polishing pad.

  The dilution ratio of the stock solution is preferably 2 times or more and more preferably 3 times or more because the higher the magnification is, the higher the cost suppressing effect related to storage, transportation, storage, and the like. The upper limit is not particularly limited. However, the higher the magnification, the greater the amount of components contained in the stock solution (the higher the concentration), and the lower the stability during storage. Is preferably 7 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 three liquids or more, and it is the same also in that case. Note that the dilution factor is X times that the stock solution is mixed with a liquid medium having a mass (X-1) times the mass of the stock solution, and the total mass is finally X times that of the stock solution. means.

  The polishing liquid according to this embodiment can be adjusted to a desired pH and used for polishing. The pH adjuster is not particularly limited, and examples thereof include acids such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, boric acid and acetic acid, and bases such as sodium hydroxide, aqueous ammonia, potassium hydroxide and calcium hydroxide. It is done. When the polishing liquid is used for semiconductor polishing, ammonia water and an acid component are preferably used. As the pH adjuster, an ammonium salt of a water-soluble polymer that has been partially neutralized with ammonia in advance can be used.

  The pH of the polishing liquid at room temperature (25 ° C.) is preferably 4.0 or more and 6.0 or less. When the pH is 4.0 or more, the storage stability of the polishing liquid tends to be improved, and the number of scratches on the material to be polished tends to decrease. From the same viewpoint, the pH is 4.3. The above is more preferable, and 4.5 or more is more preferable. Further, when the pH is 6.0 or less, there is a tendency that the effect of improving the flatness can be sufficiently exhibited. From the same viewpoint, the pH is more preferably 5.7 or less, and further preferably 5.5 or less. . The pH of the polishing liquid can be measured with a pH meter (for example, Model PH81 (trade name) manufactured by Yokogawa Electric Corporation). For example, after calibrating two points 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 electrode is polished. The pH of the polishing liquid can be measured by putting it in the liquid and measuring the value after 2 minutes have passed and stabilized at 25 ° C.

  Next, the application (Use) of the polishing liquid according to the present embodiment to the polishing of the material to be polished on the substrate surface will be described.

[Polishing method]
In the substrate polishing method according to this embodiment, the material to be polished on the substrate surface is polished using the polishing liquid. More specifically, for example, while pressing the polishing material on the substrate surface against the polishing pad of the polishing surface plate, while supplying the polishing liquid between the polishing material and the polishing pad, the substrate and the polishing surface plate are The material to be polished is polished by relatively moving.

  As a substrate, semiconductor element manufacturing such as a substrate in which an insulating material is formed on a semiconductor substrate, such as a semiconductor substrate in a stage where a circuit element and a wiring pattern are formed, or a semiconductor substrate in a stage where a circuit element is formed And the like.

  Examples of the material to be polished include inorganic insulating materials such as silicon oxide, silicon nitride, and silicon oxide composite materials. By polishing such an inorganic insulating material on the substrate with the polishing liquid according to the present embodiment, unevenness on the surface of the insulating material can be eliminated, and the entire surface of the substrate can be made smooth. Further, the polishing liquid according to the present embodiment can also be used for shallow trench isolation.

  Hereinafter, the method for polishing a substrate will be described in more detail, taking as an example the case of a semiconductor substrate on which a film of an inorganic insulating material is formed as an insulating material.

  As a polishing apparatus, a holder for holding a substrate such as a semiconductor substrate having a material to be polished, a motor capable of changing the number of rotations, etc. are attached, and a polishing surface plate on which a polishing pad (polishing cloth) can be attached, A general polishing apparatus having the following can be used. As a polishing apparatus, for example, a polishing apparatus manufactured by Ebara Manufacturing Co., Ltd .: model number EPO-111, MIRRA, Reflexion manufactured by AMAT, etc. can be used.

  As the polishing pad, a general nonwoven fabric, foamed polyurethane, porous fluororesin, or the like can be used without particular limitation. Moreover, it is preferable that the polishing pad is grooved so that the polishing liquid is accumulated.

  The polishing conditions are not limited, but the rotation speed of the surface plate is preferably low rotation of 200 rotations / minute or less so that the semiconductor substrate does not pop out, and the pressure (working load) applied to the semiconductor substrate is scratched after polishing. 100 kPa or less is preferable. During polishing, the polishing liquid is continuously supplied to the polishing pad with a pump or the like. Although there is no restriction | limiting in this supply amount, it is preferable that the surface of a polishing pad is always covered with polishing liquid.

  The semiconductor substrate after polishing is preferably washed in running water, and then dried by removing water droplets adhering to the semiconductor substrate using a spin dryer or the like.

  By polishing the inorganic insulating film, which is the material to be polished, with the polishing liquid in this manner, surface irregularities can be eliminated and a smooth surface can be obtained over the entire surface of the semiconductor substrate. After the planarized shallow trench is formed, an aluminum wiring is formed on the inorganic insulating film, an inorganic insulating film is formed again between the wirings and on the wiring, and then the inorganic insulating film is polished with a polishing liquid. To obtain a smooth surface. By repeating this step a predetermined number of times, a semiconductor substrate having a desired number of layers can be manufactured.

  Examples of the inorganic insulating material polished with the polishing liquid according to the present embodiment include silicon oxide and silicon nitride. Silicon oxide may be doped with elements such as phosphorus and boron. As a method for manufacturing the inorganic insulating material, a low pressure CVD method, a plasma CVD method, or the like can be given.

The silicon oxide film formation by the low pressure CVD method uses monosilane: SiH ₄ as the Si source and oxygen: O ₂ as the oxygen source. A silicon oxide film can be obtained by performing this SiH ₄ —O ₂ -based oxidation reaction at a low temperature of 400 ° C. or lower. In some cases, the silicon oxide film obtained by CVD is heat-treated at a temperature of 1000 ° C. or lower. In order to planarize the surface by high-temperature reflow, when doping silicon: P with phosphorus: P, it is preferable to use a SiH ₄ —O ₂ —PH ₃ -based reactive gas.

The plasma CVD method has an advantage that a chemical reaction requiring a high temperature can be performed at a low temperature under normal thermal equilibrium. There are two plasma generation methods, capacitive coupling type and inductive coupling type. The reaction gases, SiH ₄ as an Si source, an oxygen source as _{N 2} O was used was _SiH 4 -N ₂ O-based gas 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.

Silicon nitride film formation by the low pressure CVD method uses dichlorosilane: SiH ₂ Cl ₂ as a Si source and ammonia: NH ₃ as a nitrogen source. A silicon nitride film is obtained by performing this SiH ₂ Cl ₂ —NH ₃ -based oxidation reaction at a high temperature of 900 ° C. In the formation of a silicon nitride film by the plasma CVD method, examples of the reactive gas 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.

  The polishing liquid and the substrate polishing method according to the present embodiment can be applied not only to the inorganic insulating film formed on the semiconductor substrate but also to the manufacturing processes of various semiconductor devices. The polishing liquid and substrate polishing method according to this embodiment include, for example, a silicon oxide material on a wiring board having predetermined wiring, an inorganic insulating material such as glass and silicon nitride, polysilicon, Al, Cu, Ti, TiN, Optically integrated circuit / optical switching element / optical waveguide composed of materials mainly containing W, Ta and TaN, optical glass such as photomask / lens / prism, inorganic conductive material such as ITO, glass and crystalline material, Polishing optical fiber end faces, optical single crystals such as scintillators, solid state laser single crystals, sapphire substrates for blue laser LEDs, semiconductor single crystals such as SiC, GaP and GaAs, glass substrates for magnetic disks, magnetic heads, etc. Is also applicable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not restrict | limited to these Examples.

(1. Preparation of cerium oxide particles)
40 kg of commercially available cerium carbonate hydrate was placed in an alumina container and baked in air at 830 ° C. for 2 hours to obtain 20 kg of yellowish white powder. When the phase of this powder was identified by X-ray diffraction, it was confirmed that the powder was cerium oxide. 20 kg of the obtained cerium oxide powder was dry pulverized using a jet mill to obtain powdered (particulate) cerium oxide. When the obtained powdered cerium oxide was observed with a scanning electron microscope (SEM), it contained crystallite-sized particles and particles composed of two or more crystallites and having a crystal grain boundary. Arbitrary 50 crystallites were selected from the obtained SEM images, and when the particle diameter was determined from the square root of the product of the major axis and the minor axis for each, the crystallite diameter was included in the range of 1 to 300 nm. It was.

(2. Synthesis of polymer compounds)
(2.1 Polymer compound 1)
214 g of deionized water was put into a 1 L synthesis flask equipped with a stirrer, a thermometer, and an air inlet (L is liter, the same applies hereinafter), and the liquid temperature was adjusted to 25 ° C. After that, air made into fine bubbles through the sintered filter is introduced into deionized water, and 250 g of acrylic acid and an aqueous solution in which 100 g of diammonium sulfite is dissolved in 200 g of deionized water are set in separate inlets. Both were dropped simultaneously at a dropping speed at which dropping was completed over 4 hours. During the dropwise addition, the liquid temperature was maintained at 25 ° C. to 30 ° C. while cooling the exotherm due to the polymerization reaction with cold water. After the completion of the dropwise addition, air was further blown for 1 hour, and then adjusted so that the nonvolatile content was 40% by mass, whereby an aqueous solution of polymer compound 1 was obtained. As shown in the following general formula (I), the polymer compound 1 was polyacrylic acid having an ammonium sulfite base at the end, and the weight average molecular weight was 4000.

(2.2 Polymer compound 2)
160 g of deionized water and 140 g of 2-propanol were put into a 1 L synthesis flask equipped with a stirrer, a thermometer and an air inlet, and the liquid temperature was raised to 80 ° C. while stirring in a nitrogen gas atmosphere. . Then 234.6 g of acrylic acid and 64.8 g of 2,2′-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate were dissolved in 169.8 g of deionized water. The two were simultaneously dropped at a dropping speed at which dropping was completed over 2 hours. Thereafter, the liquid temperature was kept at 80 ° C. to 85 ° C. for 3 hours, and after cooling to 25 ° C. to 30 ° C., the aqueous solution of the polymer compound 2 was obtained by adjusting the nonvolatile content to 40% by mass. As shown in the following general formula (II), the polymer compound 2 was polyacrylic acid having 2- (2-imidazolin-2-yl) propane at the terminal, and the weight average molecular weight was 3000.

(Example 1-1)
200.0 g of the cerium oxide particles prepared above and 795.0 g of deionized water are mixed, and 5 g of an aqueous solution of ammonium polyacrylate (weight average molecular weight: 8000, 40% by mass) is added as a dispersant and stirred. Then, ultrasonic dispersion was performed to obtain a cerium oxide dispersion. Ultrasonic dispersion was performed at an ultrasonic frequency of 400 kHz and a dispersion time of 20 minutes.

  Thereafter, 1 kg of cerium oxide dispersion was placed in a 1 L container (height: 17 cm) and allowed to stand, and sedimentation classification was performed. After 15 hours of classification time, the supernatant above a depth of 13 cm from the water surface was pumped up. The obtained supernatant cerium oxide dispersion was diluted with deionized water so that the content of cerium oxide particles was 5% by mass to obtain a cerium oxide slurry.

  In order to measure the average particle diameter (D50) of the cerium oxide particles in the cerium oxide slurry, the slurry is diluted so that the measurement transmittance (H) with respect to the He—Ne laser is 60 to 70%, and a measurement sample is obtained. It was. When this measurement sample was measured using a laser diffraction particle size distribution meter Master Sizer Microplus (trade name, manufactured by Malvern) as a refractive index of 1.93 and an absorption of 0, the value of D50 was 150 nm.

  2 g of p-toluenesulfonic acid monohydrate (pKa (25 ° C.) = − 2.8) as an organic acid A and 700 g of deionized water are mixed, and the polymer compound 1 (40 mass) as a polymer compound B is mixed. % Aqueous solution) was added, and aqueous ammonia (25% by mass) was added to adjust the pH to 4.5 (25 ° C.). Further, deionized water was added to obtain an organic acid addition liquid with a total amount of 750 g.

  Here, 200 g of the cerium oxide slurry is added, aqueous ammonia (25% by mass aqueous solution) is added to adjust the pH to 5.0 (25 ° C.), deionized water is further added to make the total amount 1000 g, A cerium oxide polishing liquid (cerium oxide particle content: 1.0 mass%) was prepared.

  Further, a measurement sample was prepared in the same manner as described above, and the average particle size of the particles in the polishing liquid was measured with a laser diffraction particle size distribution meter. As a result, the value of D50 was 150 nm.

(Insulating film polishing)
As a polishing test wafer, a pattern wafer (trade name: 864 wafer, diameter: 200 mm) manufactured by SEMATECH was used. The polishing test wafer and a method for evaluating polishing characteristics using the wafer will be described with reference to FIG.

  FIG. 1A is a schematic cross-sectional view in which a part of a polishing test wafer is enlarged. A plurality of grooves are formed on the surface of the wafer 1, and a silicon nitride film 2 having a thickness of 150 nm (1500 mm) is formed on the surface of the convex portion of the wafer 1. The depth of the groove (step from the surface of the convex portion to the bottom surface of the concave portion) is 500 nm (5000 mm). Hereinafter, the convex portion is referred to as an active portion, and the concave portion is referred to as a trench portion. Although not clearly shown in FIG. 1, the wafer 1 is formed with three regions having trench / active section cross-sectional widths of 100 μm / 100 μm, 20 μm / 80 μm, and 80 μm / 20 μm.

  FIG. 1B is an enlarged schematic cross-sectional view of a part of the polishing test wafer. In the polishing test wafer, the silicon oxide film 3 is formed in the active part and the trench part by the plasma TEOS method so that the thickness of the silicon oxide film 3 from the surface of the active part becomes 600 nm (6000 mm). In the polishing test, the silicon oxide film 3 of the polishing test wafer is polished and planarized.

  FIG. 1C is a schematic cross-sectional view showing an enlarged part of a polishing test wafer after polishing the silicon oxide film 3. Polishing is completed on the surface of the silicon nitride film 2 in the active portion, and the time required for polishing at this time is defined as the polishing time, and the thickness of the silicon oxide film 3 in the trench portion from the depth 4 of the trench portion (the remaining silicon oxide film remaining) The value obtained by subtracting (film thickness) 5 is the dishing amount 6. It should be noted that the polishing time should be shorter and the dishing amount 6 should be smaller.

A polishing apparatus (manufactured by Applied Materials, product name: Reflexion) was used for polishing the polishing test wafer. A polishing test wafer was set in a holder on which a suction pad for mounting the substrate was attached. A polishing pad made of porous urethane resin (groove shape = perforate type: manufactured by Rohm and Haas, model number IC1010) was attached to a polishing surface plate having a diameter of 600 mm of a polishing apparatus. Furthermore, the holder was placed on the polishing surface plate with the surface of the insulating material (silicon oxide film) as the film to be polished facing down, and the processing load was set to 352 gf / cm ² (34.5 kPa).

  While the cerium oxide polishing liquid was dropped on the polishing pad at a rate of 150 mL / min, the polishing platen and the polishing test wafer were each operated at 90 rpm to polish the polishing test wafer. The polishing time when the silicon nitride film of the active part in the 100 μm / 100 μm region was exposed on the surface was defined as the polishing end time. The polished test wafer after polishing was thoroughly washed with pure water and then dried.

The following two items were evaluated as evaluation items for flatness.
Item 1: Dishing amount of trench in 100 μm / 100 μm region: Measured using a stylus type step meter (model number P16, manufactured by KLA-tencor).
Item 2: SiO ₂ residual film thickness difference (SiO ₂ density difference) in the trench portions of the 20 μm / 80 μm region and the 80 μm / 20 μm region: using an interference type film thickness measuring device Nanospec / AFT5100 (trade name) manufactured by Nanometrics The residual film thickness of the silicon oxide film (SiO ₂ film) in each region was measured, and the difference was obtained.

(Examples 2 to 4 and Comparative Examples 1 to 3)
A cerium oxide polishing liquid was prepared in the same manner as in Example 1 except that the pH of the polishing liquid, the amount of organic acid used, the type and amount of polymer compound used were changed to those shown in Table 1, and the insulating film Polishing was performed. The results are shown in the same table. From Table 1, it became clear that the flatness was improved by the polishing liquid provided by the present invention, and the reduction in dishing and the difference in the residual film thickness of the SiO ₂ film were achieved.

  DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 ... Silicon nitride film, 3 ... Silicon oxide film formed by plasma TEOS method, 4 ... Depth of trench part, 5 ... Silicon oxide film thickness of trench part after grinding | polishing, 6 ... Dishing amount.

Claims (7)

A polishing liquid for CMP containing cerium oxide particles, organic acid A, polymer compound B and water,
The organic acid A is a —COOM group, —Ph—OM group, —SO ₃ M group and —PO ₃ M ₂ group (wherein M is any selected from the group consisting of H, NH ₄ , Na and K) And Ph has at least one group selected from the group consisting of a phenyl group which may have a substituent),
PKa of the organic acid A is less than 9,
The polymer compound B is a polishing liquid having at least one selected from the group consisting of a carboxylic acid group and a carboxylic acid group and at least one selected from the group consisting of a sulfite group and a sulfite group.   The polishing liquid according to claim 1, wherein the content of the organic acid A is 0.001 to 1 mass% with respect to the total mass of the polishing liquid.   The polishing liquid according to claim 1 or 2, wherein the content of the polymer compound B is 0.01 to 0.50 mass% with respect to the total mass of the polishing liquid.   The polishing liquid according to any one of claims 1 to 3, wherein the pH is 4.0 or more and 6.0 or less.   It is preserve | saved as a two-component polishing liquid comprised from the 1st liquid containing the said cerium oxide particle and water, and the 2nd liquid containing the said organic acid A, the said high molecular compound B, and water. The polishing liquid as described in any one of 1-4.   The polishing liquid according to claim 5, wherein the first liquid further contains a dispersant. A method for polishing a substrate, comprising polishing a material to be polished on the surface of the substrate using the polishing liquid according to claim 1.

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