JP6405776B2 - Abrasive for tungsten, stock solution for abrasive, and polishing method - Google Patents

Description

  The present invention relates to an abrasive for tungsten, a storage liquid for abrasive, and a polishing method. In particular, the present invention relates to a tungsten abrasive, an abrasive storage solution, and a polishing method used in chemical mechanical polishing (hereinafter referred to as “CMP”).

  In recent years, new microfabrication techniques have been developed along with higher integration and higher performance of semiconductor integrated circuits (hereinafter referred to as “LSI”). CMP is one of them, and is a technique that is frequently used in planarization of an interlayer insulating material, formation of a metal plug, formation of a buried wiring, etc. in an LSI manufacturing process, particularly in a multilayer wiring forming process.

  A damascene method is known as a buried wiring formation using CMP. For example, after a groove is formed in advance on the surface of an insulating material such as silicon oxide, a barrier material (for example, a barrier film) having a shape following the surface of the insulating material is formed, and further, the entire barrier material is embedded so as to fill the groove. The wiring metal is deposited on. Next, after removing unnecessary wiring metal other than the wiring metal buried in the trench, a part of the barrier material under the wiring metal is removed by CMP to form a buried wiring.

  In LSI, a wide variety of substances are used. An LSI has a plurality of layer structures, and CMP is performed at each stage in order to obtain each layer structure. Therefore, there are a wide variety of abrasives used in CMP because the constituents are adjusted depending on which material is removed or which material is not removed.

  In recent years, a tungsten material is used as a wiring metal or a barrier material in LSI, and an abrasive for removing the tungsten material is required. As an abrasive | polishing agent for tungsten, the abrasive | polishing agent described in the following patent documents 1-4 is mentioned, for example.

Japanese Patent No. 3822339 Japanese Patent No. 4083528 JP 2004-363228 A JP 2002-80827 A

  Patent Document 1 describes an abrasive containing abrasive grains, hydrogen peroxide, and an iron compound. However, such an abrasive has a problem that the polishing rate for tungsten is improved, while the etching rate for tungsten is also increased.

  Patent Document 2 describes an abrasive containing abrasive grains and periodic acid. When such an abrasive contains periodic acid as an oxidizing agent, a brittle oxide film is formed on the surface of tungsten, and the oxide film is polished by the mechanical action of abrasive grains. It is said that the polishing rate for tungsten is improved by the action of such periodic acid. However, periodic acid has a strong corrosive action on tungsten and it is difficult to suppress etching. Moreover, since iodine tends to precipitate on the polishing cloth (polishing pad) after polishing by using the abrasive, the polishing rate may decrease.

  Patent Document 3 describes an abrasive containing abrasive grains, an oxidizing agent, and a compound having a hetero atom. In such an abrasive, a hetero atom forms a hetero compound with a metal film, so that a film more fragile than an oxide film is formed on the surface of tungsten, and the fragile film is polished. However, a higher polishing rate is required as a polishing rate for tungsten.

  Patent Document 4 describes an abrasive containing abrasive grains and a heteropolyacid. According to such a polishing agent, the polishing rate for tungsten, aluminum, and copper is improved by the action of the heteropolyacid, the etching rate at room temperature is small, dishing can be suppressed, and excellent in-plane uniformity. However, since heteropolyacid has a strong corrosive action on tungsten, it has a problem from the viewpoint of further suppressing the etching rate.

  An object of the present invention is to provide an abrasive capable of polishing a tungsten material at a high polishing rate and suppressing an etching rate with respect to the tungsten material. Another object of the present invention is to provide an abrasive storage solution for obtaining the abrasive and a polishing method using the abrasive.

  As a result of extensive research, the present inventors have been able to polish tungsten materials at a high polishing rate and to etch tungsten materials by using hydrogen peroxide, silicomolybdate compounds, and water-soluble polymers in combination. It has been found that the speed can be suppressed.

  A first aspect of the present invention relates to an abrasive for tungsten containing abrasive grains, hydrogen peroxide, a silicomolybdate compound, and a water-soluble polymer.

  According to the abrasive | polishing agent which concerns on a 1st aspect, while being able to grind | polish tungsten material with a high grinding | polishing rate, the etching rate with respect to tungsten material can be suppressed.

  By the way, when the polishing agent of Patent Document 1 is used, there is a problem that polishing scratches (referred to as scratches appearing on the polished surface after polishing; the same applies hereinafter) occur on the polished surface due to impurities such as iron ions. Alternatively, there may occur a problem that impurities such as iron ions adhere to the polished surface after polishing and affect the characteristics of the LSI. On the other hand, the polishing agent according to the first aspect can maintain a high polishing rate while suppressing generation and contamination of polishing flaws due to impurities (iron ions, etc.) when a buried wiring of tungsten material is formed by CMP. At the same time, the etching rate can be suppressed.

  The abrasive preferably contains colloidal silica. Thereby, polishing scratches can be reduced while maintaining a high polishing rate.

  The water-soluble polymer preferably includes a polymer having a structure obtained by polymerizing at least one selected from the group consisting of acrylic acid and methacrylic acid. Thereby, the etching rate with respect to the tungsten material can be further suppressed.

  The pH of the abrasive according to the first aspect is preferably 1.0 to 6.0. As a result, the tungsten material can be polished at a higher polishing rate, and it can be suppressed that the abrasive grains are dissolved and the liquid stability of the abrasive is lowered.

  The second aspect of the present invention relates to an abrasive storage liquid for obtaining the abrasive according to the first aspect, wherein the abrasive is obtained by diluting with a liquid medium. According to such a storage solution for abrasives, the cost, space, etc. required for transporting and storing the abrasives can be reduced.

  A third aspect of the present invention relates to a polishing method for polishing a surface to be polished using the abrasive according to the first aspect. According to such a polishing method, the tungsten material can be polished at a high polishing rate, and the etching rate for the tungsten material can be suppressed. In addition, according to the polishing method according to the third aspect, when forming an embedded wiring of a tungsten material by CMP, it is possible to maintain a high polishing rate while suppressing generation and contamination of polishing flaws due to impurities (iron ions and the like). At the same time, the etching rate can be suppressed.

  The polished surface preferably contains a tungsten material. Thereby, the said effect of the grinding | polishing method which concerns on a 3rd aspect can fully be acquired.

  According to the present invention, the tungsten material can be polished at a high polishing rate, and the etching rate for the tungsten material can be suppressed. In addition, according to the present invention, when a buried wiring of tungsten material is formed by CMP, a high polishing rate can be maintained and an etching rate can be suppressed while suppressing generation and contamination of polishing flaws due to impurities (iron ions, etc.). it can.

It is a schematic cross section showing wiring formation by a damascene process.

  Hereinafter, embodiments of the present invention will be described.

<Definition>
In this specification, the term “process” is not limited to an independent process, and is included in the term if the intended action of the process is achieved even when it cannot be clearly distinguished from other processes. It is.

  In this specification, the numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  In the present specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. means.

  In this specification, “polishing rate” means a rate at which material is removed per unit time (Removal Rate).

  In the present specification, “tungsten abrasive” means an abrasive for polishing a tungsten material. “Tungsten material” means a material containing 50 mol% or more of tungsten, and includes tungsten, a tungsten alloy, a tungsten compound (for example, tungsten silicide and tungsten nitride), and the like.

<Abrasive>
The abrasive | polishing agent which concerns on this embodiment is a composition which touches a to-be-polished surface at the time of grinding | polishing, for example, is an abrasive | polishing agent for CMP. The abrasive | polishing agent which concerns on this embodiment is an abrasive | polishing agent for tungsten containing an abrasive grain, hydrogen peroxide, a silicomolybdate compound, and a water-soluble polymer.

  In the polishing agent according to this embodiment, by using hydrogen peroxide, a silicomolybdic acid compound, and a water-soluble polymer in combination, the tungsten material can be polished at a high polishing rate and the etching rate can be suppressed. Although the mechanism of action for obtaining such an effect has not been clarified, the present inventor thinks as follows.

Silicomolybdate compounds oxidize the surface of the tungsten material. Then, the oxidized tungsten material (for example, H ₂ WO ₄ ) and the water-soluble polymer react to form a new reaction layer. This reaction layer has sufficient resistance to the chemical action of the silicomolybdate compound, but can be easily removed by the mechanical action of the abrasive grains. Therefore, it is considered that the formation of such a reaction layer is effective in achieving a high polishing rate for the tungsten material while suppressing the etching rate.

  On the other hand, when a silicomolybdic acid compound is used without using a water-soluble polymer, the polishing rate for the tungsten material is high, but the etching rate is also high.

  Moreover, in order to express the said action mechanism, it is necessary to use hydrogen peroxide together with the silicomolybdate compound and the water-soluble polymer. By using hydrogen peroxide together, the polishing rate can be improved while suppressing the etching rate for the tungsten material. Although this reason is not clear, it is considered that the chemical reaction between the silicomolybdate compound and the tungsten material is promoted by using the silicomolybdate compound and hydrogen peroxide together. Even if a large amount of hydrogen peroxide is used, the polishing rate does not improve as the content increases. From this, it is considered that hydrogen peroxide acts as a catalyst for the chemical reaction between the silicomolybdate compound and the tungsten material.

  Hereinafter, the components contained in the abrasive will be described in detail.

(Abrasive grains)
The abrasive | polishing agent which concerns on this embodiment contains an abrasive grain. Examples of the constituent material of the abrasive grains include oxides such as silica, alumina, ceria and zirconia, hydroxides such as cerium, and resins. These can be used alone or in combination of two or more. Among them, as a constituent material of the abrasive grains, the affinity with the tungsten material is higher than other types of abrasive grains, the contact frequency with the tungsten material is increased, and a good polishing rate for the tungsten material is easily obtained. From the viewpoint, an oxide is preferable, at least one selected from the group consisting of silica and alumina is more preferable, and silica is more preferable.

  Examples of silica include colloidal silica and fumed silica. Among these, colloidal silica is preferable because it has a higher polishing rate with respect to the tungsten material, has fewer scratches, and can easily select the particle size.

  The lower limit of the silica content is preferably more than 50% by mass, more preferably 60% by mass or more, still more preferably 70% by mass or more, and particularly preferably 80% by mass or more, based on the total mass of the abrasive grains. Mass% or more is very preferable, and 95 mass% or more is very preferable.

  The lower limit of the content of the abrasive grains is 0.10% by mass or more based on the total mass of the abrasive from the viewpoint that sufficient mechanical polishing force is easily obtained and the polishing rate for the tungsten material tends to be higher. Preferably, 0.20 mass% or more is more preferable, and 0.30 mass% or more is still more preferable. The upper limit of the content of the abrasive is polishing from the point that it is easy to avoid an increase in the viscosity of the abrasive, the point that it is easy to avoid agglomeration of the abrasive, the point that the polishing scratches are easy to reduce, and the point that the abrasive is easy to handle. 15.00% by mass or less, preferably 10.00% by mass or less, more preferably 7.00% by mass or less, particularly preferably 4.00% by mass or less, and 3.00% by mass based on the total mass of the agent. % Or less is very preferable, and 2.50% by mass or less is very preferable.

  The lower limit of the average particle diameter of the abrasive grains is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more, from the viewpoint that sufficient mechanical polishing power is easily obtained and the polishing rate for the tungsten material tends to be further increased. Preferably, 50 nm or more is particularly preferable. The upper limit of the average particle diameter of the abrasive grains is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 130 nm or less, from the viewpoint of good dispersion stability of the abrasive grains.

  The average particle diameter of the abrasive grains can be measured by a photon correlation method. Specifically, for example, the average particle diameter can be measured by a device name: Zetasizer 3000HS manufactured by Malvern Instruments, a device name: N5 manufactured by Beckman Coulter, and the like. The measurement method using N5 is, for example, as follows. First, an abrasive is diluted with pure water to prepare an aqueous dispersion in which the content of abrasive grains is adjusted to 0.2% by mass. This aqueous dispersion is about 4 mL (L is “liter” in a 1 cm square cell. The same shall apply hereinafter) and place the cell in the measuring device. A value obtained by setting the refractive index of the dispersion medium to 1.33, the viscosity to 0.887 mPa · s, and measuring at 25 ° C. can be adopted as the average particle diameter of the abrasive grains.

(Oxidant)
The abrasive according to this embodiment contains hydrogen peroxide as an oxidizing agent for the tungsten material. Since hydrogen peroxide has a higher standard electrode potential for tungsten materials than other oxidants, it is considered that the chemical reaction to tungsten materials is likely to be promoted compared to other types of oxidants.

  The abrasive | polishing agent which concerns on this embodiment can contain oxidizing agents (except a silicomolybdate compound) other than hydrogen peroxide. Examples of such an oxidizing agent include peracetic acid; perbenzoic acid; permanganic acid compound; ammonium persulfate; heteropolyacid compound (heteropolyacid (excluding silicomolybdic acid) and heteropolyacid salt (excluding silicomolybdate) ). Examples of the permanganate compound include potassium permanganate. Examples of the heteropolyacid include phosphomolybdic acid, silicotungstic acid, phosphotungstic acid, phosphotungstomolybdic acid, and phosphovanadomolybdic acid. Examples of the heteropolyacid salt include sodium salt, potassium salt, ammonium salt and the like. Examples of sodium salts include sodium phosphomolybdate and sodium phosphotungstate. Examples of potassium salts include potassium phosphomolybdate and potassium phosphotungstate. Examples of ammonium salts include ammonium phosphomolybdate and ammonium phosphotungstate. Oxidizing agents other than hydrogen peroxide can be used alone or in combination of two or more.

  The lower limit of the content of the oxidizing agent (including hydrogen peroxide, excluding the silicomolybdic acid compound) is 0.10% by mass or more based on the total mass of the abrasive from the viewpoint of easily obtaining an effect of improving the polishing rate. Is preferable, and 0.50 mass% or more is more preferable. The upper limit of the content of the oxidizing agent (including hydrogen peroxide, excluding silicomolybdic acid compounds) is easy to suppress the etching rate for the tungsten material and from the viewpoint of easily controlling the polishing rate for the tungsten material. 10.00 mass% or less is preferable on a mass basis, 7.00 mass% or less is more preferable, and 4.00 mass% or less is still more preferable.

  From the viewpoint of further suppressing the etching rate, the lower limit of the hydrogen peroxide content is preferably more than 50% by mass, more preferably 60% by mass or more, based on the total mass of the oxidizing agent (excluding silicomolybdic acid compounds). Preferably, 70% by mass or more is more preferable, 80% by mass or more is particularly preferable, 90% by mass or more is extremely preferable, and 95% by mass or more is very preferable.

  The lower limit of the hydrogen peroxide content is preferably 0.10% by mass or more, more preferably 0.50% by mass or more, based on the total mass of the polishing agent, from the viewpoint of easily obtaining an effect of improving the polishing rate. More preferably 0.000% by mass or more. Since hydrogen peroxide is considered to act as a catalyst for the chemical reaction between the silicomolybdate compound and the tungsten material, it is not necessary to add a large amount. The upper limit of the hydrogen peroxide content is preferably 10.00% by mass or less based on the total mass of the abrasive from the viewpoint of easily suppressing the etching rate for the tungsten material and easily controlling the polishing rate for the tungsten material. 0.000 mass% or less is more preferable, and 4.00 mass% or less is still more preferable.

(Silicomolybdate compound)
The abrasive | polishing agent which concerns on this embodiment contains a silicomolybdic acid compound. The “silicomolybdic acid compound” is a compound having a silicomolybdic acid structure, and specific examples thereof include silicomolybdic acid and silicomolybdate. Examples of silicomolybdate include sodium salt, potassium salt, ammonium salt and the like. The silicomolybdic acid compounds can be used alone or in combination of two or more.

  When the abrasive contains the silicomolybdic acid compound, the polishing rate for the tungsten material is increased. Even if a heteropoly acid compound other than the silicomolybdate compound is used without using the silicomolybdate compound, the effect of increasing the polishing rate for the tungsten material is small.

  The reason for this is not clear, but the following reasons are possible. Since the silicomolybdic acid compound contains silicon as a hetero atom, an interaction acts between the abrasive grains and the silicomolybdic acid compound, and it is more easily adsorbed to the abrasive grains than other heteropoly acid compounds. In this case, when the abrasive grains come into contact with the tungsten material and the silicomolybdate compound adsorbed on the abrasive grains comes into contact with the tungsten material, the tungsten material is oxidized and the polishing rate is increased. In addition, since heterotungstic acid contains the same tungsten as tungsten material, the oxidizing power with respect to tungsten material is scarce compared with heteromolybdic acid.

  In addition, a polymer having a carboxyl group (for example, a (meth) acrylic acid polymer described later) is used as a water-soluble polymer, and abrasive grains (such as silica) that can have a hydroxyl group (hydroxy group) on the surface thereof are used. In some cases, a higher polishing rate can be obtained. The reason for this is not clear, but the following reasons are possible. That is, the carboxyl group of the water-soluble polymer and the abrasive grains are easily adsorbed by hydrogen bonding. Further, since the water-soluble polymer and the silicomolybdic acid compound are hydrophilic, they are likely to exist in the vicinity of the tungsten material. Thereby, when the silicomolybdate compound adsorbed on the abrasive grains comes into contact with the tungsten material, it is considered that the water-soluble polymer also easily comes into contact with the tungsten material. In this case, the tungsten material is oxidized by the silicomolybdic acid compound, and the oxidized tungsten material reacts with the water-soluble polymer to easily form a new tungsten reaction layer. Thereby, it is considered that a higher polishing rate can be obtained.

  The lower limit of the content of the silicomolybdic acid compound is preferably 0.01% by mass or more, based on the total mass of the abrasive, and 0.05% by mass from the viewpoint that a sufficient improvement effect of the polishing rate with respect to the tungsten material is easily obtained. The above is more preferable, 0.08% by mass or more is further preferable, and 0.10% by mass or more is particularly preferable. The upper limit of the content of the silicomolybdic acid compound is preferably 3.00% by mass or less, more preferably 2.50% by mass or less, based on the total mass of the abrasive, from the viewpoint of easily suppressing the etching rate for the tungsten material. 2.00% by mass or less is more preferable, 1.50% by mass or less is particularly preferable, and 1.00% by mass or less is extremely preferable.

(Water-soluble polymer)
The abrasive according to this embodiment contains a water-soluble polymer. When the abrasive contains the water-soluble polymer, the etching rate for the tungsten material is suppressed. From the viewpoint of easily obtaining such a mechanism of action, the water-soluble polymer preferably contains a polymer having a carboxyl group, and is obtained by polymerizing at least one selected from the group consisting of acrylic acid and methacrylic acid. It is more preferable to include a polymer having a structure. It is considered that a carboxyl group derived from acrylic acid and methacrylic acid interacts with a hydroxyl group of an oxidized tungsten material (for example, H ₂ WO ₄ ) to easily form a new reaction layer.

  As the water-soluble polymer, a copolymer having a structure obtained by polymerizing a composition containing at least one selected from the group consisting of acrylic acid and methacrylic acid as a monomer component (hereinafter referred to as “(meth) acrylic acid”). Copolymer) having a structure obtained by polymerizing a composition containing at least one selected from the group consisting of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as a monomer component (Meth) acrylic acid polymer is preferable. The (meth) acrylic acid polymer may be a homopolymer of acrylic acid (polyacrylic acid) or a homopolymer of methacrylic acid (polymethacrylic acid). The water-soluble polymer can be used alone or in combination of two or more. The composition for obtaining a (meth) acrylic acid polymer contains monomer components other than acrylic acid and methacrylic acid (for example, alkyl (meth) acrylates such as methyl acrylate and methyl methacrylate). Also good. In addition, as a (meth) acrylic-acid type polymer, the copolymer (acrylic acid / methacrylic acid copolymer) which has a structure obtained by polymerizing the monomer component which consists of acrylic acid and methacrylic acid is preferable.

  The (meth) acrylic acid polymer can be prepared by using the monomer components other than acrylic acid and methacrylic acid, such as amide group, hydroxyl group, urea group, carboxyl group, alkyl group (methyl group, etc.), sulfo group, etc. You may have a side chain. The polymerization form of the (meth) acrylic acid polymer is not particularly limited, and examples thereof include block copolymerization and random copolymerization.

  The copolymerization ratio (molar ratio) of acrylic acid and methacrylic acid in the (meth) acrylic acid polymer is not particularly limited, but the copolymerization ratio of acrylic acid to methacrylic acid (acrylic acid / methacrylic acid) is a tungsten material. 1/99 to 95/5 is preferable from the viewpoint of achieving both a high polishing rate with respect to the above and a low etching rate with respect to the tungsten material to a higher degree and excellent solubility.

  The lower limit of the weight average molecular weight of the water-soluble polymer is preferably 1000 or more from the viewpoint of easily suppressing the etching rate for the tungsten material. The lower limit of the weight average molecular weight of the water-soluble polymer is more preferably 3000 or more, still more preferably 4000 or more, and particularly preferably 5000 or more, from the viewpoint that a high polishing rate is easily exhibited. The upper limit of the weight average molecular weight of the water-soluble polymer is not particularly limited, but is preferably 5 million or less, more preferably 1 million or less, from the viewpoint of excellent solubility in the abrasive and storage stability of the abrasive. 10,000 or less is more preferable, 100,000 or less is particularly preferable, 50,000 or less is extremely preferable, 30,000 or less is very preferable, and 10,000 or less is even more preferable. From the above viewpoint, the weight average molecular weight of the water-soluble polymer is preferably 1,000 to 5,000,000.

The weight average molecular weight (Mw) can be measured, for example, by using gel permeation chromatography (GPC: Gel Permeation Chromatography) under the following conditions and reading the value obtained as “Mw”.
Equipment used (detector): Hitachi, Ltd., “L-3300” differential refractometer for liquid chromatograph Pump: Hitachi, Ltd., “L-7100” for liquid chromatograph
Degas equipment: None Data processing: GPC integrator “D-2520” manufactured by Hitachi, Ltd.
Column: “Shodex Asahipak GF-710HQ” manufactured by Showa Denko KK, inner diameter 7.6 mm × 300 mm
Eluent: 50 mM Na ₂ HPO ₄ aqueous solution / acetonitrile = 90/10 (v / v)
Measurement temperature: 25 ° C
Flow rate: 0.6mL / min
Measurement time: 30 min
Sample: A sample prepared by adjusting the resin content with a solution having the same composition as the eluent so that the resin content is adjusted to 2% by mass and filtering through a 0.45 μm polytetrafluoroethylene filter Injection amount: 0 .4 μL
Reference material: Polymer Laboratories, narrow molecular weight sodium polyacrylate

  The lower limit of the content of the water-soluble polymer is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, based on the total mass of the abrasive, from the viewpoint of further suppressing the etching rate with respect to the tungsten material. 0.03 mass% or more is still more preferable. The upper limit of the content of the water-soluble polymer is preferably 2.00% by mass or less, more preferably 1.00% by mass or less, based on the total mass of the abrasive, from the viewpoint of polishing the tungsten material at a higher polishing rate. 0.50% by mass or less is more preferable, 0.30% by mass or less is particularly preferable, and 0.20% by mass or less is extremely preferable.

(Liquid medium)
The abrasive according to this embodiment preferably contains a liquid medium that acts as a dispersion medium or solvent for other components. Examples of the liquid medium include water such as pure water, ultrapure water, and distilled water; organic solvents such as alcohols, ethers, and esters (for example, organic solvents that are soluble in water). A liquid medium can be used individually by 1 type or in combination of 2 or more types.

(Additive)
The abrasive according to the present embodiment further contains additives other than the above components for the purpose of improving the dispersibility of abrasive grains in the abrasive, improving the chemical stability of the abrasive, and improving the polishing rate. be able to. Examples of such additives include acid components (excluding compounds corresponding to the oxidizing agent), corrosion inhibitors, antifoaming agents, and the like. These additives can be used alone or in combination of two or more. The content of the additive in the abrasive can be arbitrarily determined as long as the characteristics of the abrasive are not impaired.

  By controlling the pH of the abrasive using the acid component, the dispersibility, stability and polishing rate of the abrasive (eg, aqueous dispersion) can be further improved. Examples of the acid component include organic acids and inorganic acids. The organic acid is not particularly limited, but formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid , N-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid , Pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid and the like. The inorganic acid is not particularly limited, and examples thereof include hydrochloric acid, sulfuric acid, nitric acid, and chromic acid. An acid component can be used individually by 1 type or in combination of 2 or more types.

  When the abrasive | polishing agent which concerns on this embodiment contains a corrosion inhibitor, the etching rate with respect to tungsten material can further be suppressed. The corrosion inhibitor is not particularly limited, and examples thereof include compounds having a triazole skeleton, compounds having a pyrimidine skeleton, compounds having an imidazole skeleton, compounds having a guanidine skeleton, compounds having a thiazole skeleton, compounds having a pyrazole skeleton, and the like. It is done. Corrosion inhibitors can be used alone or in combination of two or more.

  The corrosion inhibitor is at least selected from the group consisting of a compound having a triazole skeleton and a compound having an imidazole skeleton from the viewpoint of further suppressing the etching rate for the tungsten material while maintaining a high polishing rate for the tungsten material. One type is preferred.

  The lower limit of the content of the corrosion inhibitor is preferably 0.005% by mass or more and more preferably 0.01% by mass or more, based on the total mass of the abrasive, from the viewpoint of easily obtaining an etching rate suppressing effect on the tungsten material. preferable. The upper limit of the content of the corrosion inhibitor is preferably 5.00% by mass or less, and more preferably 3.00% by mass or less, based on the total mass of the abrasive, from the viewpoint of easily maintaining a high polishing rate for the tungsten material.

(Abrasive pH)
The lower limit of the pH of the abrasive according to this embodiment is preferably 1.0 or more, more preferably 1.5 or more, still more preferably 2.0 or more, particularly preferably 2.2 or more, and extremely preferably 2.3 or more. preferable. When the pH of the abrasive is in such a range, the surface of the tungsten material has a negative zeta potential, and the absolute value of the zeta potential is sufficiently large. As a result, it is easy to ensure a sufficient amount of abrasive grains adsorbed on the tungsten material, so that a sufficient mechanical polishing force is easily obtained. The upper limit of the pH of the abrasive according to this embodiment is preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.5 or less, from the viewpoint of good dispersion stability of the abrasive grains. 0 or less is particularly preferable. From the viewpoint of achieving both of these effects, the pH of the abrasive is preferably 1.0 to 6.0. You may adjust pH of an abrasive | polishing agent with base components, such as ammonia, sodium hydroxide, potassium hydroxide, TMAH (tetramethylammonium hydride), the said acid component, etc. The pH of the abrasive is defined as the pH at a liquid temperature of 25 ° C.

  The pH of the abrasive can be measured by a general pH meter using a glass electrode. For example, the product name Model (F-51) of HORIBA, Ltd. can be used. The pH meter was adjusted using a phthalate pH standard solution (4.01), a neutral phosphate pH standard solution (pH 6.86), and a borate pH standard solution (pH 9.18) as pH standard solutions. After calibrating three points, the pH is obtained by putting the electrode of the pH meter into the abrasive and measuring the value after 2 minutes or more has passed and stabilized. At this time, the liquid temperature of the standard buffer solution and the abrasive can be set to 25 ° C., for example.

  The blending method and dilution method of the abrasive are not particularly limited, but can be adjusted by dispersing or dissolving each component by, for example, stirring with a blade-type stirrer or ultrasonic dispersion. Moreover, the mixing order of the other components with respect to a liquid medium (for example, water) is not limited.

<Abrasive stock solution>
The abrasive according to the present embodiment can be stored by reducing the amount of liquid medium (for example, water) from the amount expected at the time of use from the viewpoint of reducing the cost, space, and the like necessary for transportation and storage. Yes, it can be stored as a stock solution for abrasives that is diluted with a liquid medium (for example, water) at the time of use. The abrasive stock solution according to this embodiment is an abrasive stock solution for obtaining an abrasive, and is diluted with a liquid medium (for example, diluted 1.5 times or more on a mass basis). Is obtained. In the present embodiment, the abrasive may be prepared by diluting the storage liquid with a liquid medium immediately before polishing. Further, the storage liquid and the liquid medium may be supplied on a surface plate (polishing surface plate) to prepare the abrasive on the surface plate.

  Note that “diluting to X times” is defined as the mass of the abrasive becomes X times the mass of the original abrasive liquid by adding a liquid medium to the abrasive liquid. For example, adding a liquid medium of the same mass to the mass of the stock solution for abrasives to obtain an abrasive is defined as diluting twice.

<Polishing method>
The polishing method according to the present embodiment includes a polishing step of polishing the surface to be polished using the tungsten abrasive according to the present embodiment. The surface to be polished preferably contains at least a tungsten material. In the polishing step, for example, the tungsten material is polished and removed. The tungsten material may be in the form of a film (a tungsten material film including a tungsten material), for example.

  In the polishing step, for example, the surface to be polished of the substrate (for example, the substrate) is pressed against the polishing cloth of the surface plate, and a predetermined pressure is applied to the substrate from the back surface of the substrate (the surface opposite to the surface to be polished). An abrasive is supplied between the surface to be polished of the substrate and the polishing cloth, and the surface to be polished is polished by moving the substrate relative to the surface plate.

As a polishing apparatus, for example, a general polishing apparatus having a motor or the like that can change the number of rotations and having a surface plate to which a polishing cloth (pad) can be attached and a holder that holds a substrate can be used. . Although there is no restriction | limiting in particular as abrasive cloth, A general nonwoven fabric, a polyurethane foam, a porous fluororesin, etc. can be used. The polishing conditions are not particularly limited, but it is preferable to adjust the rotation speed of the surface plate to a low rotation of 200 min ⁻¹ (rpm) or less so that the substrate does not pop out. During polishing, for example, an abrasive is continuously supplied to the polishing cloth with a pump or the like. Although there is no restriction | limiting in this supply amount, It is preferable that the surface of polishing cloth is always covered with an abrasive | polishing agent, and the formation by progress of grinding | polishing is discharged | emitted continuously.

  The polishing method according to the present embodiment preferably includes a polishing cloth conditioning step before the polishing step in order to perform CMP with the same surface state of the polishing cloth. For example, a polishing cloth may be conditioned with a liquid containing at least water using a dresser with diamond particles. Subsequently, it is preferable to perform the substrate cleaning step after performing the polishing method according to the present embodiment in the polishing step.

  The substrate after polishing is preferably washed in running water and then dried after removing water droplets adhering to the substrate using spin drying or the like. Also, a known cleaning method (for example, a method of removing deposits on the substrate by flowing a commercially available cleaning solution over the surface of the substrate and rotating the brush made of polyurethane while pressing the brush against the substrate with a certain pressure) It is more preferable to dry after performing.

  As an example of the polishing method according to the present embodiment, wiring formation by a general damascene process will be described with reference to FIG. First, as shown in FIG. 1A, a substrate 100 before polishing is prepared. The substrate 100 has an insulating material 1 having a groove formed on the surface, a barrier material 2 formed so as to follow the unevenness of the surface of the insulating material 1, and a wiring metal 3 deposited so as to fill the recess. doing. Here, examples of the barrier material 2 include tantalum, tantalum nitride, titanium, and titanium nitride. The wiring metal 3 is a tungsten material.

  Next, as shown in FIG. 1B, CMP is performed using the abrasive according to the present embodiment, and the wiring metal 3 is removed until the barrier material 2 is exposed to obtain a substrate 200 (first polishing). Process). Subsequently, as shown in FIG. 1C, CMP is performed using an abrasive for the barrier material, and the barrier material 2 is removed until the convex portion of the insulating material 1 is exposed to obtain the substrate 300 (second). Polishing step). In the second polishing step, over-polishing that polishes the insulating material 1 excessively may be performed. By such overpolishing, the flatness of the polished surface after polishing can be improved.

  The lower limit of the polishing rate for the tungsten material is preferably 40.0 nm / min or more, more preferably 42.5 nm / min or more, and still more preferably 45.0 nm / min or more. When the polishing rate is 40.0 nm / min or more, the polishing time can be shortened.

  The upper limit of the etching rate for the tungsten material is preferably 15.0 nm / min or less, more preferably 13.0 nm / min or less, and still more preferably 10.0 nm / min or less. When the etching rate is 15.0 nm / min or less, the occurrence of corrosion marks such as keyholes on the surface of the tungsten material is suppressed, and a good finished surface can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the following Example. In Examples and Comparative Examples, ammonia or malic acid was used for pH adjustment as necessary.

<Preparation of abrasive>
Example 1
0.40 part by mass of silicomolybdic acid and water-soluble polymer (acrylic acid / methacrylic acid copolymer 1 (AA / MA copolymer), block copolymer, copolymerization ratio: 1/99, Mw: 7000) 0.05 part by mass was placed in a container. And after pouring ultrapure water X mass part into a container, it stirred and dissolved each component. Next, colloidal silica (silica-containing liquid) in an amount corresponding to 2.00 parts by mass was added as the content of silica particles. Finally, an amount of hydrogen peroxide solution corresponding to 3.00 parts by mass of hydrogen peroxide was added to obtain an abrasive. As said content X of ultrapure water, content adjusted so that an abrasive | polishing agent might be 100 mass parts was used.

(Example 2)
An abrasive was obtained in the same manner as in Example 1 except that the content of silicomolybdic acid was changed from 0.40 parts by mass to 0.10 parts by mass.

(Example 3)
An abrasive was obtained in the same manner as in Example 1 except that the abrasive content was changed from 2.00 parts by mass to 0.50 parts by mass, and the pH was changed from 2.6 to 2.5. It was.

Example 4
An abrasive was obtained in the same manner as in Example 1 except that the content of hydrogen peroxide was changed from 3.00 parts by mass to 0.50 parts by mass.

(Example 5)
The abrasive was changed in the same manner as in Example 1 except that the content of silicomolybdic acid was changed from 0.40 parts by mass to 2.50 parts by mass and the pH was changed from 2.6 to 2.4. Obtained.

(Example 6)
An abrasive was obtained in the same manner as in Example 1 except that the pH of the abrasive was changed from 2.6 to 3.5.

(Example 7)
Acrylic acid / methacrylic acid copolymer 1 was changed to acrylic acid / methacrylic acid copolymer 2 (block copolymer, copolymerization ratio: 60/40, Mw: 8000), and pH was changed from 2.6. An abrasive was obtained in the same manner as in Example 1 except that it was changed to 2.4.

(Example 8)
An abrasive was obtained in the same manner as in Example 1 except that the water-soluble polymer was changed to polyacrylic acid having an Mw of 25,000 and the pH was changed from 2.6 to 2.4.

Example 9
An abrasive was obtained in the same manner as in Example 1 except that the silica was changed to alumina and the pH was changed from 2.6 to 2.5.

(Comparative Example 1)
An abrasive was obtained in the same manner as in Example 1 except that silicomolybdic acid was not used and the pH was changed from 2.6 to 2.7.

(Comparative Example 2)
An abrasive was obtained in the same manner as in Example 1 except that silicomolybdic acid and hydrogen peroxide were not used.

(Comparative Example 3)
An abrasive was obtained in the same manner as in Example 1 except that hydrogen peroxide was not used.

(Comparative Example 4)
An abrasive was obtained in the same manner as in Example 1 except that hydrogen peroxide and water-soluble polymer were not used.

(Comparative Example 5)
An abrasive was obtained in the same manner as in Example 1 except that the water-soluble polymer was not used.

(Comparative Example 6)
An abrasive was obtained in the same manner as in Example 1 except that molybdic acid as a polyacid was used instead of silicomolybdic acid as a heteropolyacid and that the pH was changed from 2.6 to 2.4. It was.

(Comparative Example 7)
An abrasive was obtained in the same manner as in Example 1 except that silicotungstic acid was used instead of silicomolybdic acid and that the pH was changed from 2.6 to 2.4.

(Comparative Example 8)
An abrasive was obtained in the same manner as in Example 1 except that phosphomolybdic acid was used instead of silicomolybdic acid and that the pH was changed from 2.6 to 2.5.

(Comparative Example 9)
An abrasive was obtained in the same manner as in Example 1 except that phosphotungstic acid was used in place of silicomolybdic acid and the pH was changed from 2.6 to 2.5.

(Comparative Example 10)
An abrasive was obtained in the same manner as in Example 1 except that periodic acid was used in place of hydrogen peroxide as the oxidizing agent, and the pH was changed from 2.6 to 2.5.

<Measurement of average particle diameter>
The abrasive was diluted with pure water to prepare an aqueous dispersion in which the content of abrasive grains was adjusted to 0.2% by mass. About 4 mL of this aqueous dispersion was placed in a 1 cm square cell, and the cell was placed in a measuring device (device name: N5 manufactured by Beckman Coulter, Inc.). The value obtained by setting the refractive index of the dispersion medium to 1.33, the viscosity to 0.887 mPa · s, and measuring at 25 ° C. was adopted as the average particle diameter of the abrasive grains. The measurement results are shown in Tables 1 and 2.

<Measurement of pH>
The pH of the abrasive was measured under the following conditions. The measurement results are shown in Tables 1 and 2.
Measurement temperature: 25 ± 5 ° C
Measuring device: Product name of Horiba, Ltd .: Model (F-51)
Measurement method: Phthalate pH standard solution (4.01), neutral phosphate pH standard solution (pH 6.86), and borate pH standard solution (pH 9.18) were used as pH standard solutions. After the pH meter was calibrated at three points, the electrode of the pH meter was put into an abrasive and the value after 2 minutes had passed and stabilized was measured.

<Evaluation of polishing rate>
A laminated body in which a tungsten film having a thickness of 600 nm was formed on a silicon substrate by a CVD method was cut into 2 cm squares to obtain test pieces. Next, the said test piece was fixed to the holder which affixed the adsorption pad for board | substrate attachment of a grinding | polishing apparatus (product made from Nanofactor, FACT-200). Further, after placing a holder with a tungsten film facing down on a surface plate to which a foamed polyurethane polishing cloth was attached, a weight was placed so that the processing load was 300 g / cm ² . While the abrasive was dripped onto the surface plate at 10 mL / min, the surface plate rotation speed was set to 80 min ⁻¹ and the tungsten film was polished for 60 seconds. And the film thickness of the tungsten film before and behind polishing was measured using a sheet resistance measuring device (RT-80 / RG-80, manufactured by Napson Co., Ltd.), and the polishing rate was calculated from the film thickness difference. The results are shown in Tables 1 and 2.

<Evaluation of scratches and contamination caused by impurities>
About each Example, generation | occurrence | production of the damage | wound resulting from an impurity (iron ion etc.) and the presence or absence of contamination were confirmed. The presence or absence of scratches due to impurities was determined using a defect inspection device ComPLUS3 manufactured by Applied Materials technology, and a Review SEM observation device, SEM vision G3 manufactured by Applied Materials technology. The presence or absence of contamination was determined by immersing the polished specimen in 3% by mass hydrogen peroxide solution for 3 minutes, and then removing the metal impurities in the immersion liquid (hydrogen peroxide solution) from Agilent Technologies, Inc., Agilent 7700x Judgment was made by quantitative analysis. The results will be described later.

<Evaluation of etching rate>
First, the abrasive was maintained at 60 ° C. Next, the test piece similar to the evaluation of the polishing rate was attached to a stirring blade. The test piece was immersed in an abrasive for 5 minutes while stirring with the rotation speed of the stirrer set to 100 min- ¹ . The etching rate was calculated from the difference in film thickness obtained by converting the difference in thickness of the tungsten film before and after immersion from the electrical resistance value and the immersion time. The results are shown in Tables 1 and 2.

As shown in Table 1, when an abrasive containing abrasive grains, hydrogen peroxide, a silicomolybdate compound, and a water-soluble polymer was used (Examples 1 to 9), the polishing rate for the tungsten material And the etching rate for tungsten material is low. Moreover, the generation | occurrence | production and contamination of the damage | wound resulting from an impurity (iron ion etc.) were suppressed.
The polishing rate for the tungsten material in Example 1 is higher than that of Comparative Example 3, and the etching rate for the tungsten material is equivalent to that of Comparative Example 3.
When the content of silicomolybdic acid is small (Example 2), the polishing rate and the etching rate are low as compared with Example 1 where the content of silicomolybdic acid is large. This is presumably because, in Example 1 where the content of silicomolybdic acid is large, the chemical action of silicomolybdic acid on the tungsten material is strong.
When the content of abrasive grains is small (Example 3), the polishing rate is lower than that of Example 1, but the polishing rate is higher than those of Comparative Examples 1 to 4 and 6 to 9, and Comparative Examples 3 to 5 are used. And the etching rate is low compared to 10.
When the hydrogen peroxide content is low (Example 4), the polishing rate is lower than that in Example 1, and the etching rate is equivalent to Example 1. This is probably because the chemical action of hydrogen peroxide on the tungsten material is weak.
When the content of silicomolybdic acid is large (Example 5), the polishing rate is higher than that of Example 1. This is probably because the chemical action of silicomolybdic acid on the tungsten material is strong.
When the pH of the abrasive is high (Example 6), the polishing rate is higher than that of Example 1. This is presumably because the higher the pH of the abrasive, the more easily the tungsten material is ionized and the stronger the chemical action.
When the acrylic acid / methacrylic acid copolymer 1 is changed to an acrylic acid / methacrylic acid copolymer 2 having a different copolymerization ratio and weight average molecular weight (Example 7), the polishing rate and the etching rate are equivalent to those of Example 1. It is.
When the acrylic acid / methacrylic acid copolymer 1 is changed to polyacrylic acid (Example 8), the polishing rate is the same as that of Example 1. This is considered because polyacrylic acid is harder to form a reaction layer with oxidized tungsten material than acrylic acid / methacrylic acid copolymer 1.
When the abrasive grains are changed from colloidal silica to alumina (Example 9), the polishing rate is higher than that of Example 1, and the etching rate is equivalent to that of Example 1. This is probably because alumina is harder than colloidal silica.

As Table 2 shows, when an abrasive | polishing agent does not contain silicomolybdic acid (Comparative Examples 1, 2, 6-9), the grinding | polishing rate with respect to a tungsten material is lower than each Example.
The cause of Comparative Example 1 is considered to be because the chemical action of hydrogen peroxide on the tungsten material is weak due to the absence of silicomolybdic acid.
When the polishing agent contains a water-soluble polymer but does not contain silicomolybdic acid and hydrogen peroxide (Comparative Example 2), the polishing rate for the tungsten material is lower than that of Comparative Example 1. This is presumably because the chemical action on the tungsten material is very weak because the abrasive does not contain hydrogen peroxide in addition to silicomolybdic acid. From the comparison between Comparative Examples 1 and 2, the significant reduction in polishing rate in Comparative Example 2 is not due to the loss of chemical action due to hydrogen peroxide alone, but hydrogen peroxide and silicomolybdic acid are used in combination. This is thought to be due to the loss of the chemical action promoted by this.
In Comparative Example 6, since the chemical action of molybdic acid on the tungsten material is much weaker than that of silicomolybdic acid, it is considered that the polishing rate for the tungsten material is low.
In Comparative Example 7, as in Comparative Example 6, the chemical action of silicotungstic acid on the tungsten material is much weaker than that of silicomolybdic acid, and therefore it is considered that the polishing rate on the tungsten material is low.
In Comparative Example 8, as in Comparative Example 6, the chemical action of phosphomolybdic acid on the tungsten material is much weaker than that of silicomolybdic acid, so it is considered that the polishing rate for the tungsten material is low.
In Comparative Example 9, as in Comparative Example 6, since the chemical action of phosphotungstic acid on the tungsten material is much weaker than that of silicomolybdic acid, it is considered that the polishing rate for the tungsten material is low.

When the polishing agent contains silicomolybdic acid and a water-soluble polymer but does not contain hydrogen peroxide (Comparative Example 3), the polishing rate for the tungsten material is lower than in each example.
When the abrasive contains silicomolybdic acid but does not contain hydrogen peroxide and water-soluble polymer (Comparative Example 4), the etching rate for the tungsten material is higher than in each example.
When the abrasive contains silicomolybdic acid and hydrogen peroxide but no water-soluble polymer (Comparative Example 5), the polishing rate for the tungsten material is slightly higher than that of Example 1, but the etching rate is higher than that of each Example. Is also very expensive. This is presumably because the water-soluble polymer has a function of suppressing the etching rate without significantly reducing the polishing rate for the tungsten material.
Although the polishing agent contains silicomolybdic acid and a water-soluble polymer, when periodic acid is used as the oxidizing agent instead of hydrogen peroxide (Comparative Example 10), the polishing rate for the tungsten material is high, but the etching rate is also high. . This is thought to be because the chemical action of periodic acid on the tungsten material is much stronger than hydrogen peroxide, so the polishing rate and etching rate on the tungsten material are high.

  DESCRIPTION OF SYMBOLS 1 ... Insulating material, 2 ... Barrier material, 3 ... Wiring metal, 100, 200, 300 ... Board | substrate.

Claims (7)

Containing abrasive grains, hydrogen peroxide, silicomolybdic acid compound, and water-soluble polymer ,
The tungsten abrasive | polishing agent whose content of the said abrasive grain is 2.50 mass% or less on the basis of the total mass of an abrasive | polishing agent.   The abrasive | polishing agent of Claim 1 in which the said abrasive grain contains colloidal silica. The abrasive | polishing agent of Claim 1 in which the said abrasive grain contains an alumina. The abrasive according to any one of claims 1 to 3, wherein the water-soluble polymer contains a polymer having a structure obtained by polymerizing at least one selected from the group consisting of acrylic acid and methacrylic acid. . The abrasive | polishing agent as described in any one of Claims 1-4 whose pH is 1.0-6.0. An abrasive stock solution for obtaining the abrasive according to any one of claims 1 to 5 ,
A storage solution for an abrasive, wherein the abrasive is obtained by diluting with a liquid medium. A polishing method for polishing a surface to be polished containing a tungsten material using the abrasive according to any one of claims 1 to 5 .