JP2006030603A - Protective film forming composition for liquid immersion exposure, and pattern forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new protective film forming composition for forming a protective film which can be stripped with a developing solution in liquid immersion exposure, which shows excellent coating uniformity on a resist film, which reduces the number of particles produced after storage with time and which can improve the sensitivity of an underlayer resist composition. <P>SOLUTION: This protective film forming composition contains (A) a resin insoluble in water and soluble in alkali, and (B) a solvent, and also contains metal impuriies of ≤100 ppb. This pattern forming method is carried out by using the composition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a protective film forming composition used in a semiconductor manufacturing process such as an IC, a circuit board such as a liquid crystal or a thermal head, and a lithography process for other photo applications, and a pattern forming method using the same. It is. In particular, the present invention relates to a protective film forming composition suitable for exposure with an immersion projection exposure apparatus using far ultraviolet light having a wavelength of 300 nm or less as a light source, and a pattern forming method using the same.

With the miniaturization of semiconductor elements, the exposure light source has become shorter in wavelength and the projection lens has a higher numerical aperture (high NA). Currently, an exposure machine with NA 0.84 using an ArF excimer laser having a 193 nm wavelength as a light source has been developed. ing. These can be expressed by the following equations as is generally well known.
(Resolving power) = k ₁ · (λ / NA)
(Depth of focus) = ± k ₂ · λ / NA ²
Where λ is the wavelength of the exposure light source, NA is the numerical aperture of the projection lens, and k ₁ and k ₂ are coefficients related to the process.

An exposure machine using a F ₂ excimer laser having a wavelength of 157 nm as a light source has been studied for higher resolution by further shortening the wavelength. Lens materials and resists used in the exposure apparatus for shorter wavelength have been studied. Because the materials used in the process are very limited, it is very difficult to stabilize the manufacturing cost and quality of the apparatus and materials, and the exposure apparatus and resist that have sufficient performance and stability within the required period are not in time. The possibility is coming out.

As a technique for increasing the resolving power in an optical microscope, a so-called immersion method in which a high refractive index liquid (hereinafter also referred to as “immersion liquid”) is filled between a projection lens and a sample is known.
This “immersion effect” means that when λ ₀ is the wavelength of the exposure light in the air, n is the refractive index of the immersion liquid with respect to air, θ is the convergence angle of the light beam, and NA ₀ = sin θ. The above-described resolving power and depth of focus can be expressed by the following equations.
(Resolving power) = k ₁ · (λ ₀ / n) / NA ₀
(Depth of focus) = ± k ₂ · (λ ₀ / n) / NA ₀ ²
That is, the immersion effect is equivalent to using an exposure wavelength having a wavelength of 1 / n. In other words, in the case of a projection optical system with the same NA, the depth of focus can be increased n times by immersion.
This is effective for all pattern shapes, and can be combined with a super-resolution technique such as a phase shift method and a modified illumination method which are currently being studied.

Examples of apparatuses in which this effect is applied to transfer of a fine pattern of a semiconductor element include Patent Document 1 (Japanese Patent Publication No. 57-153433) and Patent Document 2 (Japanese Patent Laid-Open No. 7-220990). There is no discussion of resists suitable for exposure techniques.
Patent Document 3 (Japanese Patent Laid-Open No. 10-303114) points out that the refractive index control of the immersion liquid is important because the change in the refractive index of the immersion liquid causes deterioration of the projected image due to the wavefront aberration of the exposure machine. Disclosed is a water to which the temperature coefficient of the refractive index of the immersion liquid is controlled within a certain range and, as a suitable immersion liquid, an additive that lowers the surface tension or increases the surface activity is added. Has been. However, the disclosure of additives and the resist suitable for the immersion exposure technique are not discussed.

Recent progress of immersion exposure technology is reported in Non-Patent Document 1 (SPIE Proc 4688, 11 (2002)), Non-Patent Document 2 (J. Vac. Sci. Tecnol. B, 17 (1999)), and the like. In the case of using an ArF excimer laser as a light source, pure water (refractive index at 193 nm: 1.44) is considered to be most promising as an immersion liquid in terms of handling safety, transmittance at 193 nm, and refractive index. .
When an F ₂ excimer laser is used as a light source, a solution containing fluorine has been studied from the balance between transmittance and refractive index at 157 nm. However, a sufficient product has not yet been seen in terms of environmental safety and refractive index. It has not been issued. From the degree of immersion effect and the degree of completeness of the resist, the immersion exposure technique is considered to be installed in the ArF exposure machine earliest.

Since the resist for KrF excimer laser (248 nm), an image forming method called chemical amplification has been used as an image forming method for a resist in order to compensate for sensitivity reduction due to light absorption. Explaining by taking a positive chemical amplification image forming method as an example, the acid generator in the exposed area is decomposed by exposure to generate an acid upon exposure, and the generated acid is reacted as a reaction catalyst by post exposure baking (PEB). Is used to change an alkali-insoluble group to an alkali-soluble group, and an exposed portion is removed by alkali development.
In the immersion exposure, the resist film and the optical lens are filled with an immersion liquid (also referred to as an immersion liquid), and then exposed through a photomask to transfer the photomask pattern to the resist film. At this time, there is a case where the immersion liquid penetrates into the resist film to cause no image formation (Non-patent Document 3). Further, it is expected that the exposure of the resist is expected because organic substances and the like are eluted from the resist film into the immersion liquid, and impurities are mixed in the immersion liquid and contaminate the lens and the exposure apparatus.

As a solution to avoid such problems, a protective film (hereinafter also referred to as “topcoat” or “overcoat”) is provided between the resist film and the lens so that the resist and water do not come into direct contact with each other. A method is known (for example, Non-Patent Document 3).
Although it has not yet been clarified what kind of material is suitable for the top coat, the present inventors have examined, depending on the top coat material, the coating uniformity on the resist film is poor, Further, generation of particles may occur after storage over time, and improvement was necessary. In addition, there is room for improvement in the sensitivity of the lower resist film.

Japanese Patent Publication No.57-153433 JP-A-7-220990 JP-A-10-303114 Proc. SPIE, 2002, Vol. 4688, p. 11 J.Vac.Sci.Tecnol.B, 17 (1999) Nikkei Microdevices, April 2004 issue

  The object of the present invention is to allow peeling in the development step in the fine pattern formation process by immersion exposure, and to be excellent in uniform coating on the resist film, to reduce the number of particles generated after storage over time, and to further lower layer It is an object of the present invention to provide a novel protective film forming composition that can improve the sensitivity of a resist composition.

  The present invention is a protective film forming composition having the following constitution and a pattern forming method using the same, thereby solving the above-mentioned problems of the present invention.

(1) Formation of a protective film for immersion exposure, comprising (A) a water-insoluble and alkali-soluble resin, and (B) a solvent, and a metal impurity content of 100 ppb or less. Composition.
(2) The protective film forming composition for immersion exposure as described in (1) above, wherein the iron content is 20 ppb or less.
(3) The protective film-forming composition for immersion exposure as described in (1) or (2) above, further comprising (C) a surfactant.
(4) The protection for immersion exposure according to any one of (1) to (3) above, wherein the solvent (B) is a mixed solvent comprising at least two different compounds. Film-forming composition.
(5) The composition for forming a protective film for immersion exposure according to any one of (1) to (4) above, wherein the residual monomer contained in the resin (A) is 5% by weight or less. object.
(6) The method for producing a protective film-forming composition for immersion exposure according to the above (1) to (5), comprising the step of (A) filtering a solution containing a resin with an ion exchange filter. The manufacturing method of the protective film formation composition for immersion exposure.
(7) A resist film is formed on the substrate, a protective film is formed on the resist film by the protective film forming composition according to any one of (1) to (6), and the resist film is subjected to immersion exposure. And developing the pattern.

  According to the present invention, immersion of the immersion liquid into the resist film (particularly, penetration of water in ArF immersion lithography) and dissolution of the resist film components into the immersion liquid without complicating the process steps during immersion exposure. Provided is a protective film forming composition for immersion exposure that not only prevents coating but also has excellent coating uniformity on a resist film, reduces the amount of particles generated after storage over time, and further improves the sensitivity of the underlying resist. It becomes possible.

  Hereinafter, the present invention will be described in detail.

[1] Water-insoluble and alkali-soluble resin (A)
The protective film-forming composition for immersion exposure of the present invention contains a water-insoluble and alkali-soluble resin (hereinafter also referred to as resin (A)).

The protective film containing the water-insoluble resin (A) is interposed between the resist film and the immersion liquid, so that the immersion liquid is prevented from penetrating into the resist film, and the resist component is in the immersion liquid. In order to prevent elution, an appropriate pattern can be obtained in pattern formation by immersion exposure.
Further, since the resin (A) is alkali-soluble, it is possible to easily dissolve and remove the protective film by alkali development without providing a separate step of removing the protective film.

  Here, “water-insoluble” means a film in which a solution obtained by dissolving a resin in a solvent is applied on a silicon wafer, dried, dipped in pure water at 23 ° C. for 10 minutes and dried, and then the film thickness is measured. The property that thickness does not decrease.

  “Alkali-soluble” means that it is soluble in an alkaline developer used for development in pattern formation with a resist, and a film obtained by applying a solution obtained by dissolving a resin in a solvent onto a silicon wafer and drying it. Is dissolved at a dissolution rate of 1 nm / second or more and the film thickness becomes zero when processed with a developer using a 2.38 mass% tetramethylammonium hydroxide aqueous solution at 23 ° C.

Although the monomer unit which comprises resin (A) is not specifically limited, From the point of alkali solubility improvement, pKa of the monomer which comprises resin (A) is less than 14, Preferably it is 0-13, Most preferably, it is 4-11. It is preferable that at least one monomer having an acid group (hereinafter also referred to as an acidic monomer) is contained.
The acid dissociation constant pKa is described in Chemical Handbook (II) (4th revised edition, 1993, edited by The Chemical Society of Japan, Maruzen Co., Ltd.), and the pKa value of the monomer is 25 ° C. using an infinite dilution solvent. The value measured in.

  Although the acid group contained in the acidic monomer is not particularly limited, for example, a carboxylic acid group, an ammonium salt, a phenolic hydroxyl group, a sulfonamide group, an active methylene group, a fluoroalcohol group, and the like are preferable.

Among these acid groups, monomers containing a fluoroalcohol group, in particular, exhibit water repellency with respect to pure water when pure water is used as the immersion liquid, and liquid when the wafer is scanned at high speed during immersion exposure. It is preferable because the followability of the immersion liquid is easily improved. The fluoroalcohol group is a fluoroalkyl group substituted with at least one hydroxyl group, preferably having 1 to 10 carbon atoms, more preferably having 1 to 5 carbon atoms. Specific examples of the fluoroalcohol group include, for example, —CF ₂ OH, —CH ₂ CF ₂ OH, —CH ₂ CF ₂ CF ₂ OH, —C (CF ₃ ) ₂ OH, —CF ₂ CF (CF ₃ ) OH. , —CH ₂ C (CF ₃ ) ₂ OH, and the like. Particularly preferred as the fluoroalcohol group is a hexafluoroisopropanol group.

  The acidic monomer may contain only one acid group or two or more acid groups. The repeating unit derived from the monomer preferably has two or more acid groups per repeating unit, more preferably 2 to 5 acid groups, and 2 to 3 acid groups. It is particularly preferred.

  Although the preferable specific example of the repeating unit derived from the acidic monomer which resin (A) contains is shown below, it is not limited to these.

  Preferred specific examples of the resin (A) are shown below. Note that the present invention is not limited to this.

The ratio of the acidic monomer contained in the resin (A) is appropriately set so that both insolubility in water and solubility in an alkali developer can be achieved.
When the acidic monomer contained in the resin (A) is less than pKa 8 and has a relatively strong acidity, the resin (A) is preferably contained so that the acid value is 1.0 to 5.0. It is more preferable to make it contain so that it may become 2.0-4.5.
In addition, when the acidic monomer contained in the resin (A) is pKa 8 or more and has a relatively weak acidity, the resin (A) is contained so that the acid value is 3.0 to 7.0. Is preferable, and it is more preferable to make it contain so that it may become 3.5-5.5.
Moreover, as an acidic monomer unit which comprises resin (A), you may contain both the monomer with comparatively strong acidity below pKa8, and the monomer with comparatively weak acidity more than pKa8. In this case, it is preferable to adjust suitably so that the acid value of resin (A) may be set to 2.0-5.0, and it is more preferable to set it as 2.5-4.5.

  Resin (A) can contain other repeating structural units in addition to the repeating structural unit derived from the acidic monomer. Examples of monomers that form other repeating structural units include addition polymerizable unsaturated bonds selected from, for example, acrylic esters, methacrylic esters, acrylamides, methacrylamides, allyl compounds, vinyl ethers, vinyl esters, and the like. And the like. In addition, any addition-polymerizable unsaturated compound that can be copolymerized with monomers corresponding to the above various repeating structural units may be copolymerized.

  The resin (A) is preferably transparent in the exposure light source to be used because light reaches the resist film through the protective film during exposure. When used for ArF immersion exposure, the resin (A) preferably has no aromatic group from the viewpoint of transparency to ArF light.

The resin (A) can be synthesized according to a conventional method (for example, radical polymerization).
For example, as a general synthesis method, monomer species are charged into a reaction vessel in a batch or in the course of reaction, and if necessary, a reaction solvent such as ethers such as tetrahydrofuran, 1,4-dioxane, diisopropyl ether, methyl ethyl ketone, A ketone such as methyl isobutyl ketone, an ester solvent such as ethyl acetate, and further dissolved in a solvent for dissolving the composition of the present invention such as propylene glycol monomethyl ether acetate described later, and then nitrogen, argon, etc. Polymerization is started using a commercially available radical initiator (such as an azo-based initiator or peroxide) under an inert gas atmosphere as necessary. If desired, an initiator is added or added in portions, and after completion of the reaction, it is put into a solvent and a desired polymer is recovered by a method such as powder or solid recovery. The concentration of the reaction is usually 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more. The reaction temperature is usually from 10 ° C to 150 ° C, preferably from 30 ° C to 120 ° C, more preferably from 50 to 100 ° C.

The resin (A) can be synthesized by various methods without being limited to the radical polymerization. In addition to radical polymerization, it can also be synthesized by, for example, cationic polymerization, anionic polymerization, addition polymerization, cyclopolymerization, polyaddition, polycondensation, addition condensation and the like.
In addition, various commercially available resins can also be used.

  Each of the above repeating structural units may be used alone or in combination. In the present invention, the resins may be used alone or in combination.

The weight average molecular weight of the resin (A) is preferably 1,000 or more, more preferably 1,000 to 200,000, and still more preferably as a polystyrene conversion value by a gas permeation chromatography (GPC) method. Is 3000-20000.
In the resin (A), the residual monomer is preferably 5% by mass or less from the viewpoint of preventing the eluate. More preferably, the residual monomer is 3% by mass or less. The residual monomer contained in the resin (A) can be reduced by an analytical means such as gel filtration chromatography (GPC), high performance liquid chromatography (HPLC), gas chromatography (GC).
Setting the amount of the residual monomer in the resin (A) within the above range can be achieved, for example, by recrystallizing the synthetic resin (A) in a solvent in which the residual monomer is well dissolved, This can be done by passing through an alumina column.

  The molecular weight distribution (Mw / Mn, also referred to as dispersity) is usually 1 to 5, preferably 1 to 4, more preferably 1 to 3.

  In the protective film-forming composition of the present invention, the blending amount of the resin (A) is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, based on the total solid content of the protective film-forming composition. .

  Further, it usually contains a solvent, and may further contain a surfactant and other components as required. These components will be described below.

[2] Solvent (B)
The protective film forming composition for immersion exposure of the present invention is usually prepared by dissolving the above components in a predetermined organic solvent. In order to avoid mixing with the resist, the solvent is preferably different from the organic solvent used in the resist. Further, from the viewpoint of preventing elution into the immersion liquid, it is preferably water-insoluble. A solvent having a boiling point of 100 ° C. to 200 ° C. is preferable.

Examples of the solvent that can be used include the following.
Benzene, toluene, ethylbenzene, amylbenzene, isopropylbenzene, hexane, heptane, octane, nonane, decane, cyclohexane, methylcyclohexane, p-menthane, decalin, xylene, cyclohexylbenzene, cyclohexene, cyclopentane, dipentene, naphthalene, Hydrocarbon solvents such as dimethylnaphthalene, cymene, tetralin, biphenyl, mesitylene;
-Halogenated hydrocarbon solvents such as methylene chloride, hexyl chloride, chlorobenzene, bromobenzene;
Alcohols such as amyl alcohol, isoamyl alcohol, butanol, hexanol, 3-heptanol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol, octanol, nonanol, neopentyl alcohol, cyclohexanol, tetrahydrofurfuryl alcohol;
Nitrogen-containing solvents such as acetonitrile, isopropanolamine, ethylhexylamine, N-ethylmorpholine, diisopropylamine, cyclohexylamine, di-n-butylamine, tetramethylethylenediamine, tripropylamine;
-Carboxylic acid solvents such as formic acid, acetic acid, butyric acid, isobutyric acid, itaconic acid, propionic acid;
-Acid anhydride solvents such as acetic anhydride, propionic anhydride, itaconic anhydride;

1,4-difluorobenzene, 1,1,2,2-tetrachlorodifluoroethane, tetrafluoropropanol, ethyl trifluoroacetoacetate, perfluoroheptane, hexafluoroisopropanol, perfluorobutylethanol, pentafluoropropanol, hexafluorobenzene Fluorine-based solvents such as perfluorobutyltetrahydrofuran, perfluoropolyethers, and fluorophenols;
Others, anisole, dioxane, dioxolane, dibutyl ether, ethyl n-butyl ketone, diacetone alcohol, diisobutyl ketone, methyl isobutyl ketone, methyl n-butyl ketone, ethylene glycol, diglycidyl ether, ethylene dichloride, cyclohexanone, cyclopentanone 2-heptanone, γ-butyrolactone, methyl ethyl ketone, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 2-methoxyethyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol, propylene glycol monomethyl ether, propylene glycol monomethyl ether Acetate, toluene, ethyl acetate, methyl lactate, lactate ester , Methyl methoxypropionate, ethyl ethoxypropionate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, N, N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, methoxybutanol, tetrahydrofuran, ethyl ethoxypropionate, Butyl acetate, N, N-dimethylacetamide.

  The solvent used in the protective film-forming composition of the present invention is preferably used by mixing a plurality of solvents as a mixed solvent, thereby further improving the effects of the present invention. The mixed solvent is not particularly limited, but it is not limited to nonpolar solvents such as hydrocarbon solvents, halogenated hydrocarbon solvents, fluorine-containing nonpolar solvents, alcohol solvents, ether solvents, nitrogen-containing solvents, carboxylic acids. A mixed solvent to which a polar solvent such as a solvent, an acid anhydride solvent, an ester solvent or a ketone solvent is added is preferable.

As the nonpolar solvent, for example, the following are preferable.
Hydrocarbon solvents: benzene, toluene, ethylbenzene, amylbenzene, isopropylbenzene, hexane, heptane, octane, nonane, decane, dodecane, cyclohexane, methylcyclohexane, p-menthane, decalin, xylene, cyclohexylbenzene, cyclohexene, cyclopentane , Dipentene, naphthalene, dimethylnaphthalene, cymene, tetralin, biphenyl, mesitylene and the like.
Halogenated hydrocarbon solvent: chloroform, hexyl chloride, ethylene dichloride, chlorobenzene, bromobenzene, iodobenzene, etc.
Fluorine-containing nonpolar solvent: 1,4-difluorobenzene, 1,1,2,2-tetrachlorodifluoroethane, perfluoroheptane, hexafluorobenzene, perfluorobutyltetrahydrofuran and the like.

As the polar solvent, for example, the following are preferable.
Alcohol solvents: amyl alcohol, isoamyl alcohol, butanol, hexanol, 3-heptanol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol, octanol, nonanol, neopentyl alcohol, cyclohexanol, tetrahydrofurfuryl alcohol, Ethylene glycol, propylene glycol, tetrafluoropropanol, hexafluoroisopropanol, perfluorobutyl ethanol, pentafluoropropanol, fluorophenol and the like.
Ether solvents: Anisole, dioxane, dioxolane, dibutyl ether, tetrahydrofuran, etc.
Nitrogen-containing solvent: acetonitrile, isopropanolamine, ethylhexylamine, N-ethylmorpholine, diisopropylamine, cyclohexylamine, di-n-butylamine, tetramethylethylenediamine, tripropylamine and the like.
Carboxylic acid solvents: formic acid, acetic acid, butyric acid, isobutyric acid, itaconic acid, propionic acid, etc.
Acid anhydride solvents: acetic anhydride, propionic anhydride, itaconic anhydride, etc.
Ester solvent: ethyl acetate, methyl lactate, ethyl lactate, methyl methoxypropionate, ethyl ethoxypropionate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, γ-butyrolactone, etc.
Ketone solvents: ethyl n-butyl ketone, diisobutyl ketone, methyl isobutyl ketone, methyl n-butyl ketone, cyclohexanone, cyclopentanone, 2-heptanone, methyl ethyl ketone, and the like.
Other polar solvents: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether 2-methoxyethyl acetate, ethylene glycol monoethyl ether acetate, N, N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, methoxybutanol, ethyl ethoxypro Pionate, N, N-dimethylacetamide and the like.

  The combination of the above-mentioned polar solvent and nonpolar solvent is not particularly limited, but in particular, there is a combination using the above hydrocarbon solvent or fluorine-containing nonpolar solvent as the nonpolar solvent and the above alcohol solvent as the polar solvent. preferable.

  The mixing ratio of the solvent in the mixed solvent is preferably 95: 5 to 40:60 (nonpolar solvent: polar solvent), more preferably 90:10 to 50:50, and still more preferably 85:15 to 60: by mass ratio. 40.

[3] Surfactant The protective film-forming composition of the present invention can further contain a surfactant. As the surfactant, any one of fluorine-based and / or silicon-based surfactant (fluorine-based surfactant, silicon-based surfactant, surfactant having both fluorine atom and silicon atom), or two or more kinds thereof It is more preferable to contain. By containing the above-mentioned surfactant, when using an exposure light source of 250 nm or less, particularly 220 nm or less, it contributes to performance improvement such as sensitivity, resolution, adhesion, and development defect suppression, and particularly to coating uniformity.

  Examples of the fluorine-based and / or silicon-based surfactant include, for example, JP-A No. 62-36663, JP-A No. 61-226746, JP-A No. 61-226745, JP-A No. 62-170950, JP 63-34540 A, JP 7-230165 A, JP 8-62834 A, JP 9-54432 A, JP 9-5988 A, JP 2002-277862 A, US Patent Nos. 5,405,720, 5,360,692, 5,529,881, 5,296,330, 5,436,098, 5,576,143, 5,294,511, 5,824,451 Surfactant can be mentioned, The following commercially available surfactant can also be used as it is.

  Examples of commercially available surfactants that can be used include F-top EF301, EF303 (manufactured by Shin-Akita Kasei Co., Ltd.), Florard FC430, 431 (manufactured by Sumitomo 3M Co., Ltd.), MegaFuck F171, F173, F176, F189, R08 (Dainippon Ink Chemical Co., Ltd.), Surflon S-382, SC101, 102, 103, 104, 105, 106 (Asahi Glass Co., Ltd.), Troisol S-366 (Troy Chemical Co., Ltd.), etc. Fluorine type surfactant or silicon type surfactant can be mentioned. Polysiloxane polymer KP-341 (manufactured by Shin-Etsu Chemical Co., Ltd.) can also be used as a silicon-based surfactant.

In addition to the known surfactants described above, surfactants are derived from fluoroaliphatic compounds produced by the telomerization method (also referred to as the telomer method) or the oligomerization method (also referred to as the oligomer method). A surfactant using a polymer having a fluoroaliphatic group can be used. The fluoroaliphatic compound can be synthesized by the method described in JP-A-2002-90991.
As the polymer having a fluoroaliphatic group, a copolymer of a monomer having a fluoroaliphatic group and (poly (oxyalkylene)) acrylate and / or (poly (oxyalkylene)) methacrylate is preferable and distributed irregularly. Or may be block copolymerized. Examples of the poly (oxyalkylene) group include a poly (oxyethylene) group, a poly (oxypropylene) group, a poly (oxybutylene) group, and the like, and a poly (oxyethylene, oxypropylene, and oxyethylene group). A unit having different chain lengths in the same chain length, such as a block link) or poly (block link of oxyethylene and oxypropylene) may be used. Furthermore, a copolymer of a monomer having a fluoroaliphatic group and (poly (oxyalkylene)) acrylate (or methacrylate) is not only a binary copolymer but also a monomer having two or more different fluoroaliphatic groups, Further, it may be a ternary or higher copolymer obtained by simultaneously copolymerizing two or more different (poly (oxyalkylene)) acrylates (or methacrylates).

Examples of commercially available surfactants include Megafac F178, F-470, F-473, F-475, F-476, and F-472 (Dainippon Ink Chemical Co., Ltd.). Further, a copolymer of an acrylate (or methacrylate) having a C ₆ F ₁₃ group and (poly (oxyalkylene)) acrylate (or methacrylate), an acrylate (or methacrylate) having a C ₆ F ₁₃ group and (poly (oxy) (Ethylene)) acrylate (or methacrylate) and (poly (oxypropylene)) acrylate (or methacrylate) copolymer, acrylate (or methacrylate) and (poly (oxyalkylene)) acrylate having C ₈ F ₁₇ groups (or Copolymer of acrylate (or methacrylate), (poly (oxyethylene)) acrylate (or methacrylate), and (poly (oxypropylene)) acrylate (or methacrylate) having a C ₈ F ₁₇ group List union It can be.

  In the present invention, other surfactants other than fluorine-based and / or silicon-based surfactants can also be used. Specifically, polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether, polyoxyethylene alkyl ethers such as polyoxyethylene oleyl ether, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, etc. Sorbitans such as polyoxyethylene alkyl allyl ethers, polyoxyethylene / polyoxypropylene block copolymers, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan trioleate, sorbitan tristearate Fatty acid esters, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopal Te - DOO, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate, may be mentioned polyoxyethylene sorbitan tristearate nonionic surfactants of polyoxyethylene sorbitan fatty acid esters such as such.

  These surfactants may be used alone or in several combinations.

  The amount of the surfactant used is preferably 0.0001 to 2% by mass, more preferably 0.001 to 1% by mass, based on the total amount (excluding the solvent) of the protective film forming composition for immersion exposure. .

[4] Protective film The protective film-forming composition for immersion exposure according to the present invention forms a protective film by, for example, being applied onto a resist film, and the immersion liquid penetrates into the resist film. It prevents elution of components into the immersion liquid.

  The composition for forming a protective film for immersion exposure (hereinafter also referred to as a top coat composition) of the present invention is characterized in that the content of metal impurities contained in the composition is 100 ppb or less. Examples of metal impurities that can be contained in the protective film-forming composition include Na, K, Ca, Fe, Mg, Mn, Pd, Ni, Zn, Pt, Ag, and Cu. Among these, iron, in particular, It is more preferable to suppress the content of (Fe) to 20 ppb or less.

  When the content of metal impurities in the protective film-forming composition is reduced, the coating uniformity is improved because the metal impurities in the protective film-forming composition serve as nuclei during spin coating. This is presumed to prevent the occurrence of uneven coating. When the content of metal impurities in the protective film-forming composition is reduced, the number of particles generated can be reduced because the resin is less aggregated in the solvent with the metal impurities as nuclei with time. ,It is estimated to be.

  In addition, the cause of improving the resist sensitivity of the lower layer when the content of metal impurities in the protective film forming composition is reduced is not clear, but iron and iron in the topcoat composition under high energy photon irradiation In the presence of a metal impurity, there may be an effect of preventing a negative reaction of the resist from being promoted by some chemical interaction with the resist surface of the lower layer.

  As a method of setting the content of metal impurities contained in the protective film forming composition to 100 ppb or less, for example, a resin (A) that is insoluble in water and soluble in an alkaline developer is dissolved in a solvent to form a solution. And a method of filtering with an ion exchange filter. In addition, the purity improvement of the material to be used, a liquid separation washing | cleaning, the process by acidic ion exchange resin or a chelate resin are known. Therefore, as a method for producing a protective film forming composition for immersion exposure according to the present invention, for example, a step of filtering a solution containing the resin (A) with an ion exchange filter, and then adding a surfactant or the like to the solution as necessary. And a method for producing a protective film-forming composition comprising a step of preparing a mixed solution and then a step of filtering the mixed solution through an insoluble colloid removal filter.

As an ion exchange filter that can be used in the present invention, a cation exchange type filter in which an ion exchange group is fixed to a polyethylene porous membrane or a polypropylene porous membrane is preferable, for example, Ion Clean (manufactured by Nippon Pole Co., Ltd.), Examples thereof include Ion Clean AQ (manufactured by Nippon Pole Co., Ltd.), but the present invention is not limited thereto.
The filtration rate by the ion exchange filter is preferably 500 to 10,000 cc / min / m ² .

  The insoluble colloid removal filter that can be used in the present invention is preferably a filter made of a synthetic resin, such as Microlith Optimizer DEV-16 / 40 (polyethylene filter manufactured by Microlith), Microguard Minichem (Microlith). Polyethylene filter), Enflon (Nippon Pole polytetrafluoroethylene filter), Ultipor N66 (Nippon Pole nylon 66 filter), Zetaplus (Cuno Cellulose filter), Electropore II (Cuno nylon 66) Filter) and the like, but the present invention is not limited to this. Moreover, when performing a filtration process after adding ionic compounds, such as a photo-acid generator, it is preferable that an insoluble colloid removal filter does not have an ion exchange ability.

  The pore sizes of the ion exchange filter and the insoluble colloid removal filter are both preferably 0.01 to 0.5 μm, and more preferably 0.01 to 0.1 μm.

The means for applying the protective film-forming composition of the present invention on the resist is appropriately set according to the process to be applied, and is not particularly limited, and means such as spin coating can be used.
The protective film is preferably a thin film from the viewpoint that it is preferably transparent to the exposure light source, and is usually formed with a thickness of 1 nm to 300 nm, preferably 10 nm to 150 nm. Specifically, the film thickness is such that the exposure light transmittance of the film is preferably 50% to 80%, more preferably 60% to 70%. The exposure light transmittance can be adjusted by adjusting the polymerization component of the resin. For example, the transmittance of ArF light can be increased by reducing the amount of aromatic rings contained in the resin.
In order to prevent the immersion liquid and the lens from being contaminated by the eluate from the protective film, it is preferable that there is no eluate from the protective film. The protective film preferably has a low content of low molecular weight compounds (for example, compounds having a molecular weight of 1000 or less) from the viewpoint of preventing eluate.

From the viewpoint of affinity with the immersion liquid, the protective film preferably has a contact angle (23 ° C.) of the immersion liquid to the protective film of 50 to 80 degrees, more preferably 60 to 80 degrees. preferable. The contact angle can be adjusted to the above range by adjusting the amount of acid groups or controlling the hydrophilicity / hydrophobicity of the copolymer component.
The refractive index of the protective film is preferably close to the refractive index of the resist film from the viewpoint of resolution. The refractive index can be adjusted by controlling the components of the protective film forming composition, particularly the resin composition and the ratio of repeating units.
The protective film-forming composition is preferably one that can be applied uniformly when forming the protective film. The applicability (coating uniformity) can be improved by appropriately selecting the type of solvent, surfactant, etc. and other additives and adjusting the amount of addition.

  The protective film forming composition for immersion exposure is preferably not mixed with the resist film because it is formed on the resist film by coating.

[5] Pattern Forming Method The protective film forming composition for immersion exposure of the present invention is usually used by dissolving the above components in a solvent and applying the solution on a resist film on a substrate.
That is, the resist composition for immersion exposure is applied to an arbitrary thickness (usually 50 to 500 nm) by a suitable application method such as a spinner or a coater on a substrate used for manufacturing a precision integrated circuit element. At this time, it is also preferable to form a resist film after appropriately providing an antireflection film on the substrate. After application, the resist film is formed by drying by spinning or baking.
Further, similarly to the resist composition, a protective film forming composition for immersion exposure is applied onto the resist film using a spinner, a coater or the like, and dried by spinning or baking to form a protective film.

Next, exposure (immersion exposure) is performed through an immersion liquid through a mask for pattern formation. The exposure amount can be set as appropriate, but is usually 1 to 100 mJ / cm ² . After exposure, preferably, spinning or / and baking is performed, development and rinsing are performed to obtain a pattern. In the present invention, the protective film dissolves and peels in the developing solution in the developing step, so that it is not necessary to provide a separate peeling step.
Baking is preferably performed after exposure, and the baking temperature is usually 30 to 300 ° C. From the viewpoint of the change in the line width of the resist pattern due to fluctuations in the holding time (PED) from exposure to development processing, the time from exposure to baking is better.
Here, the exposure light is preferably far ultraviolet rays having a wavelength of 250 nm or less, more preferably 220 nm or less. Specific examples include KrF excimer laser (248 nm), ArF excimer laser (193 nm), F ₂ excimer laser (157 nm), X-rays, and the like.

  Examples of the substrate that can be used include a normal BareSi substrate, an SOG substrate, and a substrate having an antireflection film.

As the antireflection film, an inorganic film type such as titanium, titanium dioxide, titanium nitride, chromium oxide, carbon, α-silicon, and an organic film type made of a light absorber and a polymer material can be used. The former requires equipment such as a vacuum deposition apparatus, a CVD apparatus, and a sputtering apparatus for film formation. Examples of the organic antireflection film include a condensate of a diphenylamine derivative and a formaldehyde-modified melamine resin described in JP-B-7-69611, an alkali-soluble resin, a light absorber, and maleic anhydride copolymer described in US Pat. No. 5,294,680. A reaction product of a coalescence and a diamine type light absorbing agent, a resin binder described in JP-A-6-186863 and a methylolmelamine thermal crosslinking agent, a carboxylic acid group, an epoxy group and a light-absorbing group described in JP-A-6-118656. An acrylic resin-type antireflection film in the same molecule, a composition comprising methylol melamine and a benzophenone-based light absorber described in JP-A-8-7115, and a low-molecular light absorber added to a polyvinyl alcohol resin described in JP-A-8-179509 And the like.
Further, as the organic antireflection film, DUV30 series, DUV-40 series, ARC25, AC-2, AC-3, AR19, AR20, etc., manufactured by Brewer Science can be used.

The immersion liquid used for the immersion exposure will be described below.
The immersion liquid is preferably a liquid that is transparent to the exposure wavelength and has a refractive index temperature coefficient as small as possible so as to minimize distortion of the optical image projected onto the resist. In the case of an ArF excimer laser (wavelength: 193 nm), it is preferable to use water from the viewpoints of availability and ease of handling in addition to the above-described viewpoints.

When water is used as the immersion liquid, the surface tension of the water is decreased and the surface activity is increased, so that the resist layer on the wafer is not dissolved and the influence on the optical coating on the lower surface of the lens element can be ignored. An additive (liquid) may be added in a small proportion. The additive is preferably an aliphatic alcohol having a refractive index substantially equal to that of water, and specifically includes methyl alcohol, ethyl alcohol, isopropyl alcohol and the like. By adding an alcohol having a refractive index substantially equal to that of water, even if the alcohol component in water evaporates and the content concentration changes, an advantage that the change in the refractive index of the entire liquid can be extremely small can be obtained. On the other hand, when an opaque substance or impurities whose refractive index is significantly different from that of water are mixed with respect to 193 nm light, the optical image projected on the resist is distorted. Therefore, distilled water is preferable as the water to be used. Further, pure water filtered through an ion exchange filter or the like may be used.
The electrical resistance of water is desirably 18.3 M ohm · cm or more, and the TOC (organic concentration) is desirably 20 ppb or less. Moreover, it is desirable to have deaerated.

Examples of the alkaline developer used in the development step include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, aqueous ammonia and other primary amines, ethylamine, n-propylamine and other primary amines, Secondary amines such as diethylamine and di-n-butylamine, tertiary amines such as triethylamine and methyldiethylamine, alcohol amines such as dimethylethanolamine and triethanolamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide and the like Alkaline aqueous solutions such as quaternary ammonium salts, cyclic amines such as pyrrole and pihelidine can be used.
Furthermore, alcohols and surfactants can be added in appropriate amounts to the alkaline aqueous solution.

The alkali concentration of the alkali developer is usually from 0.1 to 20% by mass.
The pH of the alkali developer is usually from 10.0 to 15.0.
As the rinsing liquid, pure water or an appropriate amount of a surfactant added to pure water can be used.

  Further, after the development process or the rinsing process, a process of removing the developer or the rinsing liquid adhering to the pattern with a supercritical fluid can be performed.

  In immersion exposure using the protective film of the present invention, the resist is not particularly limited, and can be arbitrarily selected from those usually used, and may be either positive type or negative type.

  As the resist, positive type and negative type resists having sufficient characteristics that can be applied to recent ultra-fine processing can be suitably used. In the present invention, a chemically amplified resist, and further a positive type resist is preferably used. Can do.

  Typical examples of the chemically amplified resist include those using a so-called acid generator that generates an acid by active energy rays such as light. For example, as the negative chemically amplified resist, a three-component system of a base polymer, a photoacid generator, and a crosslinking agent is usually used. At the time of resist exposure, the acid generated by light irradiation causes a crosslinking reaction in the exposed portion, and acts to reduce the solubility in the developer. On the other hand, a positive chemically amplified resist is usually a two-component system including a base polymer having a site blocked with a protective group having a dissolution inhibiting function and a photoacid generator, a base polymer, an acid generator, There are some three-component dissolution inhibitors. Then, at the time of resist exposure, in the exposed portion, the acid generated by light irradiation acts to remove the protective group of the polymer and increase the solubility in the developer.

  When the exposure light source is an ArF excimer laser (wavelength: 193 nm), a two-component system containing a resin that is solubilized in an alkaline developer by the action of an acid and a photoacid generator is preferred. In particular, the resin that is solubilized in the alkaline developer by the action of an acid is preferably an acrylic or methacrylic resin having a monocyclic or polycyclic alicyclic hydrocarbon structure, and has a lactone residue or an adamantane residue. Is more preferable.

  In addition, since it is preferable that the formed resist pattern does not have electroconductivity, it is preferable that a resist does not contain a metal. The amount of metal contained is preferably 100 ppb or less, more preferably 50 ppb or less. The amount of metal can be suppressed by usual purification such as improvement of the purity of the material used or filtration.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, the content of this invention is not limited by this.

<Synthesis of Resin (1)>
4- [Bis (trifluoromethyl) hydroxymethyl] styrene 8.11 g (0.03 mol) and tetrahydro-5-oxofuran-3-yl acrylate 10.93 g (0.07 mol) were dissolved in 250 ml of propylene glycol monomethyl ether. Then, 0.25 g of 2,2′-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd .; trade name V-65) was added as a polymerization initiator. This solution was stirred at 70 ° C. for 4 hours under a nitrogen stream. Thereafter, the reaction solution was charged into 1 L of hexane with vigorous stirring. The precipitated resin was washed with ion-exchanged water, filtered and dried under vacuum to obtain 15 g of a white resin. It was confirmed by GPC measurement that the weight average molecular weight (polystyrene standard) was 4,800, and the content ratio of the residual monomer in the resin was 1%.
Thereafter, resins (2) to (9) were obtained in the same manner.
The structures and weight average molecular weights, dispersities, and residual monomer contents of the resins (1) to (9) are summarized below.

<Preparation of protective film composition for immersion exposure>
As shown in Table 1 below, the resin is dissolved in a solvent, and TC-2, 3, 4 and 6-15 are filtered twice with an ion exchange filter (Nippon Pole Co., Ltd., Ion Clean, pore size 0.1 μm). , TC-1, 5 were filtered only once. Further, TC-16 and 17 were not filtered with an ion exchange filter. Subsequently, a surfactant was added, and a protective film forming composition TC-1 to TC-17 having a solid content concentration of 4.5% by mass was filtered through a polytetrafluoroethylene filter (ENFLON manufactured by Nippon Pole Co., Ltd., pore size: 0.1 μm). Prepared.
Using a polarized Zeeman atomic absorption spectrophotometer (manufactured by Hitachi, Z-9000), the content (unit ppb) of metal impurities contained in the protective film-forming composition obtained by the above-described procedure was changed to Na, K, Ca, Measurements were performed on seven elements of Fe, Cu, Mg, and Mn. The results are also shown in Table 1 below.

Abbreviations in Table 1 are as follows.
W-1; Megafac F176 (Dainippon Ink Chemical Co., Ltd.) (Fluorine)
W-2; Megafuck R08 (Dainippon Ink Chemical Co., Ltd.) (fluorine and silicon)
SL-1; 2-ethylbutanol SL-2; perfluorobutyltetrahydrofuran

Examples 1-60 and Comparative Examples 1-8
<Number of particles increased after storage over time>
For the protective film forming composition shown in Table 1 above, the number of particles in the liquid immediately after preparation (particle initial value) and after storage for 1 week at 40 ° C. (number of particles after aging) was measured by Rion Co., Ltd. Counted at the counter. The number of particles increased calculated by (number of particles after time) − (initial particle value) was evaluated. The number of particles counted was 0.2 μm or more in 1 ml of the resist solution.

<Applicability test of protective film forming composition>
An antireflection film (ARC29A, manufactured by Brewer Science Co., Ltd.) was uniformly applied on a silicon substrate with a spin coater at a film thickness of 720 angstrom, and dried at 205 ° C. for 60 seconds. Next, each positive resist composition shown in the following Table 2 was applied by a spin coater, and the wafer was heated and dried at 115 ° C. for 60 seconds to form a 0.25 μm resist film. Subsequently, the protective film forming composition shown in Table 2 was applied onto the resist film by a spin coater, and the wafer was heated and dried at 115 ° C. for 60 seconds to form a 0.05 μm protective film. Observe the coating unevenness of the protective film formed on the resist film at this time, ○ if it is uniformly applied without coating unevenness, △ if there is some coating unevenness, and if the coating unevenness is severe X.
<Sensitivity evaluation of lower layer resist>
An antireflection film (ARC29A, manufactured by Brewer Science Co., Ltd.) was uniformly applied on a silicon substrate with a spin coater at a film thickness of 720 angstrom, and dried at 205 ° C. for 60 seconds. Next, each positive resist composition shown in the following Table 2 was applied by a spin coater, and the wafer was heated and dried at 115 ° C. for 60 seconds to form a 0.25 μm resist film. Subsequently, the protective film-forming composition shown in Table 2 was applied onto the resist film by a spin coater, and the wafer was heated and dried at 115 ° C. for 60 seconds to form a 0.05 μm topcoat layer. Subsequently, the immersion sensitivity of the resist film by 193 nm exposure was evaluated using an immersion exposure / dissolution behavior analyzer MODEL IMES-5500 (manufactured by RISOTEC Japan).
The sensitivity here means that the wafer after exposure is heated and dried at 120 ° C. for 90 seconds, then developed using a 2.38 mass% tetramethylammonium hydroxide aqueous solution at 23 ° C. for 30 seconds, and pure water for 30 seconds. When the film thickness is measured after rinsing and drying, it indicates the minimum exposure amount at which the film thickness becomes zero.

Abbreviations in Table 2 are as follows.
PR1: Resist composition described in Example 1 of JP-A-2000-275845, that is, 10 parts of the following resin P-1 (weight average molecular weight: about 10,000), acid generator (triphenylsulfonium perfluorobutanesulfonate ( "TPS-109" manufactured by Midori Chemical Co., Ltd.)) 0.2 parts, 0.015 parts of a basic compound (2,6-diisopropylaniline), and a solvent (47.5 parts of propylene glycol monomethyl ether acetate and 2.5 parts of γ-butyrolactone) .

PR2: Resist composition described in Example 1 of JP-A No. 2003-167347, that is, 100 parts by mass of the following resin P-2 (weight average molecular weight 10,000), acid generator component (triphenylsulfonimnonafluorobutanesulfonate) ) A resist composition containing 2 parts by mass, 0.2 parts by mass of a basic compound (triethanolamine), and an organic solvent (750 parts by mass of propylene glycol monomethyl ether acetate / 30 parts by mass of γ-butyrolactone).

PR3: Resist composition described in Example 1 of JP 2002-12622 A, that is, 80 parts by weight of the following resin P-3, 1 part by weight of an acid generator (PAG1), 0.078 of a basic compound (TBA: tributylamine) A resist composition containing 480 parts by weight of a solvent (PGMEA: propylene glycol methyl ether acetate).

PR4: Resist composition described in Example 1 of JP-A-2003-177538, that is, 2 g of the following resin P-4 (weight average molecular weight 10600), 38 mg of acid generator (PAG2), basic compound (1,5 -Diazabicyclo [4.3.0] -5-nonene (DBN)) 4 mg, surfactant (Megafac F176 (Dainippon Ink Co., Ltd.)) 10 g, solvent (propylene glycol methyl ether acetate (PGMEA) / lactic acid A resist composition containing ethyl = 70/30 and a solid content concentration of 14% by weight.

  As shown in Table 2, it can be seen that the protective film-forming composition of the present invention has improved coatability and the number of particles generated after storage over time is suppressed. Furthermore, it can be seen that the sensitivity of the lower layer resist composition is also improved.

Claims (7)

A protective film forming composition for immersion exposure, comprising (A) a water-insoluble and alkali-soluble resin, and (B) a solvent, and a metal impurity content of 100 ppb or less. The protective film forming composition for immersion exposure according to claim 1, wherein the iron content is 20 ppb or less. 3. The protective film forming composition for immersion exposure according to claim 1, further comprising (C) a surfactant. The protective film forming composition for immersion exposure according to any one of claims 1 to 3, wherein (B) the solvent is a mixed solvent comprising at least two different compounds. The protective film forming composition for immersion exposure according to any one of claims 1 to 4, wherein (A) the residual monomer contained in the resin is 5% by weight or less. In the manufacturing method of the protective film formation composition for liquid immersion exposure of Claims 1-5, (A) The process of filtering the solution containing resin with an ion exchange filter is included, The liquid immersion exposure characterized by the above-mentioned. For producing a protective film forming composition. A resist film is formed on a substrate, a protective film is formed on the resist film with the protective film-forming composition according to claim 1, the resist film is subjected to immersion exposure and developed. A characteristic pattern forming method.