JP2016089050A - Coating composition and production method of photoresist laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition excellent in storage stability, from which a film having a low refractive index in a short wavelength range and excellent solubility in an alkali aqueous solution can be formed.SOLUTION: A coating composition comprises a fluorine-containing polymer (A) having a unit represented by -[CXX-CY(Rf-COOM)]-, in which a content of -COOM group is 1.5×10to 1.9×10mol/g. In the formula, Xand Xeach independently represent a hydrogen atom, a fluorine atom, or a chlorine atom; Y represents a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, or a trifluoromethyl group, Rfrepresents a linear perfluoroalkylene group which may include an ethereal oxygen atom between carbon atoms or a linear oxyperfluoroalkylene group which may include an ethereal oxygen atom between carbon atoms; and -COOM represents -COOH or -COOZ, where Zrepresents an optionally substituted ammonium ion.SELECTED DRAWING: None

Description

  The present invention relates to a coating composition. In particular, the present invention relates to a coating composition useful as a composition for forming an antireflection film in photolithography, and a method for producing a photoresist laminate using the same.

A photolithography technique is used in a manufacturing process of a semiconductor or the like. For example, a manufacturing process of a semiconductor circuit includes a process of forming a photoresist pattern (resist pattern).
In recent years, along with higher integration and higher speed of LSIs, miniaturization of semiconductor circuits is required. In order to cope with this, the wavelength of an exposure light source used for forming a resist pattern has been shortened.
For example, in a mass production process of 64 Mbit DRAM (Dynamic Random Access Memory), a KrF excimer laser (wavelength 248 nm) was used as an exposure light source. However, it is shorter for manufacturing a DRAM of 256 Mbit or 1 Gbit or more. A wavelength ArF excimer laser (wavelength 193 nm) or F ₂ laser (wavelength 157 nm) is used.
When the exposure light is irradiated to the resist layer formed on the substrate, in addition to the light incident on the resist layer, reflected light from the substrate surface, light reflected from the surface of the resist layer, and the like are generated. These reflected lights interfere to generate a standing wave. Such a standing wave causes a dimensional variation and a shape collapse of the resist pattern.
In addition, a fine resist pattern may be formed on a surface where a step exists. In such a case, the dimensional variation and the shape collapse due to the standing wave are particularly large (standing wave effect).

Conventionally, as a method for suppressing the standing wave effect, a method of putting a light absorber in a resist material, a method of providing an antireflection film on the upper surface of the resist layer (TARC method), a method of providing an antireflection film on the lower surface of the resist layer (BARC method) ) Etc. were proposed.
The TARC method or BARC method is a method in which an antireflection film layer having a refractive index lower than that of the resist layer is provided adjacent to the resist layer, and a higher antireflection effect is obtained as the refractive index of the antireflection film is lower.

Patent Document 1 describes a composition containing a fluorine-containing surfactant, a water-soluble polymer containing a fluorine-containing polymer, and an aqueous medium as an antireflection coating composition used in the TARC method. . The fluorine-containing polymer includes a unit having, as a side chain, an oxyperfluoroalkylene group having an acidic OH group such as —COOH bonded to the terminal. The fluorine-containing polymer described in the Examples of Patent Document 1 is a precursor polymer obtained by polymerizing CF ₂ = CFOCF ₂ CF ₂ CF ₂ COOCH ₃ and having a linear oxyperfluoroalkylene group as a side chain. It is a polymer obtained by converting the methyl ester group at the end of the side chain to -COOH after being obtained. The mass average molecular weight of the precursor polymer is 4,500, and when the number average molecular weight is determined, it is 2,700.
The polymer after conversion of the methyl ester group at the end of the side chain of the precursor polymer to -COOH has a mass average molecular weight of 4,300, and the content of -COOH is 4.13 x ^10-3 mol / g. It becomes.

Patent Document 2 describes a composition containing a fluorine-containing polymer having a hydrophilic group as an antireflection coating composition used in the TARC method. The fluoropolymer has a unit derived from a monomer represented by CH ₂ ═CFCF ₂ —ORf—Y ¹ . Rf is a fluorine-containing alkylene group which may have an ether bond between carbon-carbon atoms, and Y ¹ is a hydrophilic group.
In the fluorine-containing polymer described in Examples of Patent Document 2, Y ¹ is —COOH or —OH. In the case where Y ¹ is —COOH, all of —ORf— are branched oxyperfluoroalkylene groups (which may have an ether bond between carbon-carbon atoms).

International Publication No. 2008/102820 International Publication No. 2005/050320

As shown in Table 1 of Patent Document 1, the antireflection film described in the example of Patent Document 1 can achieve a low refractive index of 1.43 or less in the wavelength band of KrF excimer laser (248 nm). The refractive index in the wavelength band of the ArF excimer laser (193 nm) is as high as around 1.48. For this reason, in order to cope with the ArF excimer laser (193 nm) or the F ₂ laser (157 nm), it is desired to further lower the refractive index of the antireflection film.

  Further, it is desirable that the antireflection film has excellent solubility in an alkaline aqueous solution used for removing the resist layer. It is preferable that the antireflective film is excellent in solubility in an alkaline aqueous solution because development and removal of the antireflective film can be performed simultaneously in the development step.

  Furthermore, when the present inventors formed a coating film by a spin coating method after storing a commercially available coating composition for an antireflection film at room temperature for 2 weeks, for example, a coating failure in which a uniform coating film cannot be obtained occurs. I found that there was a case. That is, it was found that the coating composition has a problem of storage stability.

  The present invention has been made in view of the above circumstances, and can form a film having a low refractive index in a short wavelength band and excellent in solubility in an alkaline aqueous solution, and is excellent in storage stability, It is another object of the present invention to provide a method for producing a photoresist laminate using the same.

The present invention is a coating composition having the following configurations [1] to [6] and a method for producing a photoresist laminate.
[1] Fluorine-containing compound having a unit represented by the following formula (I) and having a group content represented by -COOM of 1.5 × 10 ^{−3 to} 1.9 × 10 ⁻³ mol / g A coating composition comprising a polymer (A).
^{- [CX 1 X 2 -CY (} Rf 1 -COOM)] - ··· (I)
(Wherein, X ¹ and X ² each independently represent a hydrogen atom, a fluorine atom or a chlorine atom, Y represents a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group or a trifluoromethyl group, and Rf ¹ represents A linear perfluoroalkylene group which may contain an etheric oxygen atom between carbon-carbon atoms, or a linear oxyperfluoroalkylene group which may contain an etheric oxygen atom between carbon-carbon atoms, -COOM Represents —COOH or —COOZ ¹ (Z ¹ is an optionally substituted ammonium ion).

[2] The coating composition according to [1], wherein the fluoropolymer (A) has a number average molecular weight of 1,000 to 30,000.
[3] The coating composition according to [1] or [2], wherein the film made of the fluoropolymer (A) has a refractive index of 1.42 or less at a wavelength of 193 nm.
[4] The coating composition according to any one of [1] to [3], wherein the content of the fluoropolymer (A) is 1 to 10% by mass.
[5] Further containing a solvent, the solvent contains a fluorinated alcohol, and the content of the fluorinated alcohol in the coating composition is 9 to 49.5% by mass. [1] to [4] Any of the coating compositions.

  [6] A method for producing a photoresist laminate in which an antireflection film is provided on the surface of the photoresist layer, the coating being any one of [1] to [5] on the surface of the photoresist layer The manufacturing method of a photoresist laminated body characterized by including the process of apply | coating a composition.

ADVANTAGE OF THE INVENTION According to this invention, while being able to form the film | membrane which is low in the refractive index in a short wavelength band and excellent in the solubility to alkaline aqueous solution, the coating composition excellent in storage stability is obtained.
If the coating composition is excellent in storage stability, it can be stored for a longer period of time, so that the amount of the coating composition that is unused and discarded is reduced. Therefore, it can contribute to the reduction of the manufacturing cost in the semiconductor manufacturing etc. using this coating composition.
According to the method for producing a photoresist laminate of the present invention, an antireflection film having a low refractive index in the short wavelength band and excellent solubility in an alkaline aqueous solution is satisfactorily formed on the surface of the photoresist layer. Can do.

The value of the weight average molecular weight and the number average molecular weight of the polymer in this specification is a polystyrene (PS) equivalent molecular weight by a gel permeation chromatography (GPC) method.
The fluorine atom content of the fluorine-containing copolymer in the present specification is obtained by fluorine atom content analysis, and indicates the ratio of the mass of fluorine atoms to the total mass of all atoms constituting the fluorine-containing copolymer.
The molecular weight of the monomer in this specification is a formula weight obtained based on the chemical formula.

The coating composition of the present invention contains a fluoropolymer (A).
[Fluoropolymer (A)]
The fluoropolymer (A) has a unit represented by the above formula (I) (hereinafter also referred to as unit (I)).
The fluoropolymer (A) may contain other units (hereinafter also referred to as units (II)) that do not have -COOM (M has the same meaning as M in formula (I)).
The unit (I) in the fluoropolymer (A) may be one type or two or more types. The unit (II) in the fluoropolymer (A) may be one type or two or more types.
As will be described later, the unit (I) is formed by introducing a side chain (—COOM) after polymerizing a precursor monomer (for example, the precursor monomer (a)). Unit (II) is formed by polymerizing other monomer (b).

(Unit (I))
In the formula (I), X ¹ and X ² each independently represent a hydrogen atom, a fluorine atom or a chlorine atom. From the viewpoint of availability of the precursor monomer for forming the unit (I), a hydrogen atom or a fluorine atom is preferable. From the viewpoint of easily obtaining a film having a high fluorine atom content and a sufficiently low refractive index in the fluoropolymer (A), a fluorine atom is preferred.
Y represents a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group or a trifluoromethyl group. From the viewpoint of availability of the precursor monomer for forming the unit (I), a fluorine atom is preferable.

Rf ¹ is a linear perfluoroalkylene group or a linear oxyperfluoroalkylene group. The perfluoroalkylene group or oxyperfluoroalkylene group may contain an etheric oxygen atom between carbon-carbon atoms.
A “perfluoro” alkylene group means a group in which all of the hydrogen atoms bonded to carbon atoms of the alkylene group are substituted with fluorine atoms.
The “oxy” perfluoroalkylene group means that the perfluoroalkylene group is bonded to the carbon atom to which Y is bonded in formula (I) through an ether bond (—O—).
“Contains an etheric oxygen atom between carbon-carbon atoms” means that an etheric oxygen atom is inserted in the middle of the carbon chain constituting the perfluoroalkylene group or oxyperfluoroalkylene group (between the carbon-carbon atoms). Means that
The number of carbon atoms of the linear perfluoroalkylene group or linear oxyperfluoroalkylene group as Rf ¹ is preferably 3 to 11, and more preferably 3 to 9. When the number of carbon atoms is not less than the lower limit of the above range, a film having a sufficiently low refractive index is easily obtained. When the amount is not more than the upper limit of the above range, a film excellent in solubility in an alkaline aqueous solution is easily obtained, and excellent storage stability of the coating composition is easily obtained.
-Rf ¹ - as a preferred _{example, -O (CF 2) 3 -} , - O (CF 2) 3 O (CF 2) 3 -, - O (CF 2) 3 O (CF 2) 3 O (CF 2 ₃ ) etc. are mentioned.

In the formula (I), —COOM is —COOH or —COOZ ¹ (Z ¹ is an optionally substituted ammonium ion).
The Z ^1, substituted by NH 4 ^_+, or NH ₄ ⁺ of 1 or more alkyl groups of a hydrogen atom, a plurality of part of which is substituted with an acid group and a hydroxyl group of a hydrogen atom of an alkyl group, acid group or a hydroxyl group The thing which was done is mentioned. Z ¹ is preferably —NR ¹ R ² R ³ R ⁴⁺ (where R ^{1 to} R ⁴ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms), and can be used for various applications. In view of low cost, NH ₄ ⁺ is particularly preferable.

(Unit (II))
The unit (II) may be any unit that does not have -COOM and can form a copolymer with the unit (I).
The unit (II) is preferably a unit containing fluorine in that the fluorine atom content of the fluoropolymer (A) is high and the refractive index of the film tends to be low.
Unit Specific examples of other monomers forming the (II) (b) _{is, CF 2 = CF 2, CH} 2 = CF 2, CF 2 = fluoroethylene such as CFCl; perfluorovinyl ethers; 3 carbon atoms Polymerizable perfluoro compounds such as the above perfluoroolefins;
When an etheric oxygen atom is present in the fluoropolymer (A), the solubility of the fluoropolymer (A) in water is likely to be improved. In this respect, the other monomer (b) forming the unit (II) is preferably a perfluorovinyl ether, and specifically, a monomer represented by the following formula (II-1) is preferable.
CF ₂ = CF—O—Rf ² (II-1)
(In the formula, Rf ² represents a linear or branched perfluoroalkyl group which may contain an etheric oxygen atom between carbon-carbon atoms.)
In the formula (II-1), the number of carbon atoms of Rf ² is 1 or more, preferably 3 or more, and particularly preferably 3-6. When the number of carbon atoms is not less than the lower limit of the above range, the boiling point becomes not less than room temperature, so that it is easy to control the copolymerization reaction with the precursor monomer forming the unit (I). When the amount is not more than the upper limit of the above range, the difference in boiling point between the other monomer (b) forming the unit (II) and the precursor monomer forming the unit (I) becomes moderate, and after completion of the copolymerization reaction The unreacted monomer can be easily recovered by fractional distillation.

Preferred examples of -Rf ² include the following perfluoroalkyl groups.
-CF ₂ CF ₂ CF _{3,
-CF 2 CF (CF 3) -O} -CF 2 CF 2 CF 3,
_{-CF 2 CF (CF 3) -O} -CF 2 CF (CF 3) -O-CF 2 CF 2 CF 3.
Of these, —CF ₂ CF ₂ CF ₃ is particularly preferable in terms of easy production.

The content of the group represented by -COOM per 1 g of the fluoropolymer (A) (hereinafter, also simply referred to as -COOM content) was 1.5 × 10 ^{−3 to} 1.9 × 10. ^-3 mol / g. 1.5 × 10 ^{−3 to} 1.8 × 10 ⁻³ mol / g is more preferable, and 1.5 × 10 ^{−3 to} 1.6 × 10 ⁻³ mol / g is particularly preferable.
When the content of —COOM is at least the lower limit of the above range, the film made of the fluoropolymer (A) is excellent in solubility in an alkaline aqueous solution, and the storage stability of the coating composition is also excellent. When the content of —COOM is not more than the upper limit of the above range, the refractive index of the film made of the fluoropolymer (A) tends to be sufficiently low.

The content of -COOM per gram of the fluoropolymer (A) increases as the molecular weight of the unit (I) decreases. The molecular weight of the unit (I) is a formula weight obtained based on the chemical formula.
When all the units constituting the fluoropolymer (A) are the unit (I), the molecular weight of the unit (I) is preferably 540 to 660, particularly preferably 600 to 660. When the molecular weight of the unit (I) is at least the lower limit of the above range, the refractive index of the film tends to be sufficiently low. When the amount is less than or equal to the upper limit, the effect of improving the solubility of the film in an alkaline aqueous solution and the storage stability of the coating composition can be sufficiently obtained by -COOM.
When the fluorine-containing polymer (A) contains two or more types of units (I), the molecular weight of each may be within the above range.

When the fluoropolymer (A) is a copolymer comprising the units (I) and (II), the content of the unit (I) having -COOM with respect to all units of the fluoropolymer (A) The higher the (unit: mol%), the higher the content of -COOM.
The content of the unit (I) having -COOM with respect to all the units is preferably 35 to 100 mol%, particularly preferably 50 to 100 mol%. When the content of the unit (I) is at least the lower limit of the above range, the film made of the fluoropolymer (A) is excellent in solubility in an alkaline aqueous solution, and when it is below the upper limit of the above range, the fluorine-containing The refractive index of the film made of the polymer (A) tends to be sufficiently low.
When the content of the unit (I) having -COOM with respect to all the units is the same, the content of -COOM increases as the molecular weight of the unit (I) decreases, and the content of -COOM increases as the molecular weight of the unit (II) decreases. The content is high.

When the fluorinated polymer (A) is a copolymer, the molecular weight of the unit (I) is preferably from 200 to 500, particularly preferably from 250 to 450. When the molecular weight of the unit (I) is at least the lower limit of the above range, the refractive index of the film tends to be sufficiently low. When it is at most the upper limit, the effect of improving the solubility of the film in an alkaline aqueous solution by -COOM and the storage stability of the coating composition can be sufficiently obtained.
The molecular weight of the unit (II) is preferably 260 or more, particularly preferably 260 to 430. When the molecular weight of the unit (II) is not less than the lower limit of the above range, the boiling point becomes not less than room temperature, so that the copolymerization reaction control with the precursor monomer forming the unit (I) becomes easy. If it is less than the upper limit, the difference in boiling point between the other monomer (b) forming the unit (II) and the precursor monomer forming the unit (I) becomes moderate, and the unreacted after completion of the copolymerization reaction Fraction collection of monomer is facilitated.

The higher the fluorine atom content of the fluoropolymer (A), the lower the refractive index of the film made of the fluoropolymer (A).
The fluorine atom content of the fluoropolymer (A) is preferably 62.5 to 66.5% by mass, more preferably 62.5 to 64.0% by mass, and particularly preferably 63.0 to 64.0% by mass. . When the fluorine atom content is at least the lower limit of the above range, the refractive index of the film tends to be sufficiently low. When the amount is not more than the upper limit, excellent solubility of the film in an alkaline aqueous solution and excellent storage stability of the coating composition are easily obtained.

The number average molecular weight of the fluoropolymer (A) is preferably 1,000 to 30,000, more preferably 1,500 to 6,000, and particularly preferably 3,000 to 6,000.
When the number average molecular weight is not less than the lower limit, the film forming property is excellent and the film thickness uniformity in the flat portion is excellent. If it is not more than the above upper limit value, the followability to the level difference at the time of coating is excellent, and when the surface of the resist layer has irregularities, the amount of coating necessary to cover the entire surface of the convex and concave portions can be reduced.

  The method for producing the fluoropolymer (A) and the polymer in which —COOM is —COOH is not particularly limited, but the following method (i) or method (ii) is preferable. (I) A method in which a precursor monomer having a precursor functional group that can be converted to “—COOH” is polymerized to polymerize the precursor polymer, and then the precursor functional group is converted to “—COOH”. (Ii) A method of introducing “—COOH” into a part of the polymer after polymerizing a fluorine-containing monomer (precursor monomer) having no precursor functional group.

The method ^{(i), CX 1 X 2} = CY (Rf 1 -COOCH 3) [X 1, X 2, Y, Rf 1 is the same as the formula (I). A precursor monomer (a) (that is, a precursor monomer that forms unit (I)) is obtained by polymerizing the precursor monomer, and then hydrolyzing the —COOCH ₃ moiety. Is mentioned.
When the fluorinated polymer (A) is a copolymer, the precursor monomer (a) is copolymerized with another monomer (b) forming another unit (II) to give a precursor weight. After obtaining the coalescence, the -COOCH ₃ moiety is hydrolyzed.

The polymerization method is not particularly limited, but a polymerization method in which a polymerization initiator is added to the monomer and heated is preferable.
As the polymerization initiator, peroxides, azo compounds and the like are preferable. As the peroxide, hydrogen peroxide, dialkyl peroxides, peroxyketals, diacyl peroxides, peroxycarbonates, peroxyesters, ammonium persulfate, potassium persulfate and the like are preferable.
As the azo compound, azonitriles, azoamides, cyclic azoamides, azoamidines and the like are preferable.
It is preferable that the usage-amount of a polymerization initiator is 0.01-10 mol% with respect to the total number of moles of the monomer used for a polymerization reaction.
In the polymerization reaction, a chain transfer agent may be used. The amount of the chain transfer agent used for the polymerization reaction is preferably 0.01 to 10 mol% based on the total number of moles of monomers. By increasing the amount of chain transfer agent used, the number average molecular weight of the fluoropolymer (A) can be reduced.
In the polymerization reaction, a medium may or may not be used. When used, the polymerization reaction is preferably carried out in a state where the monomer used for the polymerization reaction is dissolved or dispersed in the medium. As the medium, water, a fluorine-containing solvent or the like is preferably used.

The method for obtaining the fluoropolymer (A) by hydrolyzing the -COOCH ₃ portion after obtaining the precursor polymer is not particularly limited, but the solution obtained by mixing the precursor polymer with water or a solvent containing water is stirred. And the like. It is preferable to stir the solution while heating. The temperature of the solution at that time is preferably 50 to 150 ° C.
Both water and the precursor polymer can be used because the stirring time can be shortened, the filterability of the hydrofluoric polymer (A) solution after hydrolysis is excellent, and the storage stability of the coating composition is excellent. The method of using the mixed solvent of the organic solvent and water which can melt | dissolve is preferable.
As the organic solvent used by mixing with water in the hydrolysis step, alcohols are preferable from the viewpoint of excellent solubility in water, and fluorine-containing alcohols are preferable from the viewpoint of excellent solubility in the precursor polymer. . The fluorine-containing alcohol is preferably a compound having a fluorine content of 50% by weight or more. For example, 2- (perfluorobutyl) ethanol, 2- (perfluorohexyl) ethanol, hexafluoroisopropanol, 2,2,3,3 -Tetrafluoropropanol etc. are mentioned.
The mass ratio of water and organic solvent in the mixed solvent is preferably 3: 7 to 9: 1, and particularly preferably 4: 6 to 6: 4. Within the above range, both water and the precursor polymer are likely to be dissolved.

When using a fluorine-containing alcohol as an organic solvent in the mixed solvent used in the hydrolysis step, the group represented by —COOM in the fluorine-containing polymer (A) is 1.5 × 10 ^{−3 to} 1.9. When it is × 10 ⁻³ mol / g, the amount of the fluorinated alcohol in the mixed solvent is preferably 20 to 50% by mass. When this combination is used, the effect (improvement of filterability and improvement of storage stability) when not only water but also a fluorinated alcohol is mixed as a solvent is excellent.
When water is used as a solvent for dissolving the precursor polymer at the time of hydrolysis, the organic solvent is added after the hydrolysis, and the mixture is stirred while heating to the same degree as at the time of hydrolysis. The same effect can be obtained by the method of obtaining a solution.
The organic solvent is preferably present at the time of hydrolysis in that the number of steps is small and the filterability is improved and the storage stability is improved.

As an example of the method (ii), after polymerizing a fluorine-containing monomer (precursor monomer) represented by CX ¹ X ² = CY (Rf ¹ -CCl ₃ ), sulfuric acid and water are added, A method of converting CCl ₃ to COOH is mentioned.
The method for producing the fluoropolymer (A) and -COOM of -COOZ ¹ is obtained by obtaining a precursor polymer having -COOH by the method (i) or the method (ii), and then an organic amine. It was added, and a method of converting the -COOH into -COOZ ^1. Examples of the organic amine include monoalkylamines such as ethylamine and propylamine; dialkylamines such as diethylamine; trialkylamines such as triethylamine; alkanolamines such as ethanolamine and diethanolamine. These may be used individually by 1 type and may use 2 or more types together.

The refractive index of the film made of the fluoropolymer (A) tends to be low. The refractive index is preferably 1.42 or less and particularly preferably 1.41 or less at a wavelength of 193 nm.
The refractive index is determined by dissolving the fluoropolymer (A) in a solvent so that the concentration is 3% by mass, and applying the obtained solution on a silicon wafer so that the film thickness is about 100 nm. This is a value obtained by measuring the refractive index at a wavelength of 193 nm with an ellipsometer for a film obtained by removing the solvent by drying for 90 seconds on a hot plate whose temperature is adjusted to a low temperature.
The reason why such a low refractive index can be obtained is considered that the fluoropolymer (A) contains a lot of fluorine atoms.
A film having a refractive index of 1.42 or less at a wavelength of 193 nm is suitable as an antireflection film for a photoresist layer for an ArF excimer laser (wavelength 193 nm), and the lower the refractive index, the better the antireflection effect.

[Coating composition]
The coating composition contains a polymer component containing the fluoropolymer (A) and, if necessary, a solvent, a surfactant, and other additives. When the coating composition contains a solvent, the fluoropolymer (A) is preferably dissolved in the solvent.
As a polymer component, you may contain other polymer components other than a fluoropolymer (A) in the range which does not impair the effect of this invention.
The concentration of all polymer components in the coating composition is preferably 1 to 10% by mass.
The ratio of the fluoropolymer (A) to the total polymer component in the coating composition is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 100% by mass.
The concentration of the fluoropolymer (A) in the coating composition is preferably 1 to 10% by mass.

(solvent)
As the solvent contained in the coating composition of the present invention, water, an organic solvent, or a mixed solvent of water and an organic solvent can be used. Examples of the organic solvent include alcohols such as methanol, ethanol, isopropanol, 2-butanol, and fluorine-containing alcohol. Examples of the fluorinated alcohol include the fluorinated alcohols mentioned in the hydrolysis step. When performing the hydrolysis step, the fluorinated alcohol used in the hydrolysis step can be used as a part or all of the solvent in the coating composition.
The coating composition of the present invention is particularly useful as an antireflective coating composition applied on a photoresist layer. The solvent for the antireflection coating composition is preferably selected from those that do not damage the photoresist film when the antireflection coating composition is applied to the photoresist layer.

As a preferred solvent, water alone or a mixed solvent of water and the above-mentioned alcohols can be mentioned. If the ratio of alcohols in the mixed solvent is large, for example, the photoresist layer may be damaged. Therefore, the ratio of alcohols in the mixed solvent is preferably 50% by mass or less, and particularly preferably 20% by mass or less.
The coating composition preferably contains 9 to 49.5% by mass of fluorine-containing alcohol, particularly preferably 9 to 18% by mass.
When the content of the fluorinated alcohol is not less than the lower limit of the above range, it is preferable in terms of suppressing the generation of aggregates of the fluorinated polymer contained in the coating composition, and when it is not more than the upper limit, the photoresist layer It is preferable in that it does not cause damage.

(Surfactant)
In the coating composition of the present invention, a surfactant may be contained as an additive for improving wettability at the time of application and uniformity of the formed film. Examples of the surfactant include amine salts of fluorine-based organic acids. Specifically, a compound having a polyfluoroalkyl group and a polyoxyethylene group (manufactured by 3M, product names: Florard “FC-430”, “FC-4430”, etc.), acetylene glycol and polyoxyethylene were added thereto. Compound (manufactured by Air Products, product name: “Surfinol 104”, “Surfinol 420”), alkyl sulfonic acid and alkyl benzene sulfonic acid (for example, product name: Nikkor “SBL-2N-27” manufactured by Nikko Chemicals) ), And a compound containing a hydroxyl group and not containing a polyoxyethylene group (polyglycerin fatty acid ester or the like).
If the content of the surfactant in the composition is too large, it may lead to whitening of the film or may diffuse into the photoresist film under the antireflection film to cause exposure failure. 10 mass% or less is preferable, and 5 mass% or less is especially preferable.

(Other additives)
Other additives that may be included in the coating composition of the present invention include known additives in the coating composition for forming an antireflection film.
Specific examples include photoacid generators such as onium salts, haloalkyl group-containing compounds, o-quinonediazide compounds, nitrobenzyl compounds, sulfonic acid ester compounds, and sulfone compounds.
The total content of other additives in the coating composition is preferably 10% by mass or less, particularly preferably 5% by mass or less, based on all polymer components.

[Method for producing photoresist laminate]
The method for producing a photoresist laminate of the present invention is a method for producing a photoresist laminate in which an antireflection film is provided on the surface of a photoresist layer, the coating of the present invention on the surface of the photoresist layer. A step of applying the composition.

As a method for applying the coating composition of the present invention on the surface of the photoresist layer, a known method can be used. The spin coating method is preferable from the viewpoint of the uniformity and simplicity of the antireflection film.
An antireflection film is obtained by removing the solvent after coating. As a method for removing the solvent, it is preferable to perform heat drying using, for example, a hot plate or an oven. As drying conditions, for example, in the case of a hot plate, conditions of 80 to 150 ° C. and 30 to 200 seconds are preferable.
The film thickness of the antireflection film may be set in accordance with a known antireflection theory. The film thickness is set to an odd multiple of “(exposure wavelength) / (4 × (refractive index of antireflection film))”. Since prevention performance becomes high, it is preferable.

In the present invention, a photoresist layer is formed on a substrate, an antireflection film is formed on the surface to form a photoresist laminate, the photoresist laminate is exposed, and then developed using an alkaline aqueous solution. It can be suitably used for a method of forming a resist pattern.
That is, by forming the antireflection film using the coating composition of the present invention, the standing wave effect can be suppressed, and the dimensional variation and shape collapse of the resist pattern can be suppressed. The antireflection film is excellent in solubility in an alkaline aqueous solution, and development and removal of the antireflection film can be performed simultaneously in the development process.
In particular, a high antireflection effect is exhibited particularly in a method of performing exposure using an ArF excimer laser (wavelength 193 nm) or an F ₂ laser (wavelength 157 nm).

  Further, when the resist layer is a layer made of a so-called chemically amplified resist that utilizes the catalytic action of protons generated by exposure, the resist surface is likely to be altered if the resist layer is left in the atmosphere after exposure. When a film is formed on the surface of such a resist layer using the coating composition of the present invention, it functions as a protective film, and alteration of the resist layer surface can be prevented.

According to the present invention, the storage stability of the coating composition can be improved by making the Rf ¹ of the unit (I) having —COOM linear, as shown in the examples below. it can.
The reason for this is that the volume per unit mass of the fluoropolymer is smaller than that in the case where Rf ¹ has a branched structure, and as a result, when fluoropolymer aggregates are generated during storage, Since the volume of the agglomerates is small, it is considered that application failure is unlikely to occur.
The unit (I) having -COOM at the end of the side chain is hydrophilic. Therefore, in a coating composition containing water, an organic solvent or a mixed solvent of water and an organic solvent as a medium, the polymer chain is likely to spread, and it is considered that a volume difference due to the presence or absence of a branched structure in Rf ¹ is greatly developed.
In addition, as shown in Examples described later, the presence or absence of a branched structure in the other unit (II) does not affect the storage stability. The reason is considered that the hydrophobic unit (II) having no -COOM is contracted in the coating composition, and the volume difference due to the presence or absence of the branched structure is small.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. Of Examples 1 to 9, Examples 1 to 4 are Examples, and Examples 5 to 9 are Comparative Examples.
The measurement method and evaluation method used the following methods.
[Mass average molecular weight / Number average molecular weight]
The value of the weight average molecular weight and the number average molecular weight of a polymer is a polystyrene (PS) conversion molecular weight by a gel permeation chromatography (GPC) method.

[-COOM content, content of units having -COOM with respect to all units]
80 ° C. for 4 hours in a vacuum-dried fluoropolymer and the standard substance was a mass of (p- hexafluoroxylene), were weighed using an electronic balance, etc., was dissolved in pel et fluorobenzene (PFB) ¹ 1 H-NMR measurement was performed. From the peak area ratio obtained by measurement and the previously weighed mass, the content (unit: mol / g) of -COOM of the fluoropolymer was calculated. In the case of a copolymer, the content (unit: mol%) of units having —COOM with respect to all units constituting the fluoropolymer was calculated at the same time.
[Fluorine atom content of fluorine-containing copolymer]
The fluorine atom content (unit: mass%) of the fluorine-containing copolymer is obtained by fluorine atom content analysis, and indicates the ratio of the mass of fluorine atoms to the total mass of all atoms constituting the fluorine-containing copolymer. .

[Refractive index of film]
The solution of the fluoropolymer obtained in each example (polymer concentration 10%) was applied on a silicon wafer by spin coating so that the film thickness was about 100 nm, and the temperature was adjusted to 150 ° C. Was dried for 90 seconds to form a film (antireflection film) made of a fluoropolymer. The refractive index of the film at a wavelength of 193 nm was measured with an ellipsometer.

[Solubility of membrane in alkaline aqueous solution (also called alkali solubility)]
In the method for measuring the refractive index of the film, an aqueous solution of tetramethylammonium hydroxide (TMAH) having a concentration of 2.38% by mass (room temperature (20 to 25 ° C.)) is applied to the film on the silicon wafer whose refractive index has been measured. Was added dropwise and left for 10 seconds. Thereafter, the dropped solution was blown off with a blower, and the portion in contact with the solution was visually observed. If the film was dissolved and the silicon wafer could be visually recognized, the alkali solubility was judged as ◯ (good), and if not visible, it was judged as x (bad).

[Storage stability of coating composition]
The fluoropolymer solution (polymer concentration 10%) obtained in each example was allowed to stand (store) at room temperature for 2 weeks after production, and then the film thickness was about 100 nm on a silicon wafer by spin coating. It was applied to. The surface state of the formed coating film was visually observed.
When aggregates of fluoropolymer are generated during storage, even if the aggregates are so small that they cannot be visually recognized, the surface of the coating film does not become uniform when formed into a thin film by spin coating. Occur. For example, film thickness unevenness called repelling occurs.
The case where the surface of the coating film was uniform and completely free of abnormalities was judged as being ◯ (good), and when even one abnormality occurred, it was judged as x (bad).

In the following examples, the following monomers and polymerization initiators were used.
[Linear precursor monomer (a)]
(A1): CF ₂ = CFOCF ₂ CF ₂ CF ₂ OCF ₂ CF ₂ CF ₂ OCF ₂ CF ₂ CF ₂ COOCH ₃ (molecular weight 623)
(A2): CF ₂ = CFOCF ₂ CF ₂ CF ₂ COOCH ₃ (molecular weight 307)
[Branched precursor monomer (c) (comparative example)]
(C1): CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ CF ₂ COOCH ₃ (molecular weight 623)
_{(C2): CF 2 = CFOCF} 2 CF (CF 3) OCF 2 CF 2 COOCH 3 ( molecular weight 422)
[Other monomer (b)]
(B1): CF ₂ = CF—O—CF ₂ CF ₂ CF ₃ (molecular weight 266)
_{(B2): CF 2 = CF} -O-CF 2 CF (CF 3) -O-CF 2 CF 2 CF 3 ( molecular weight 451)
[Polymerization initiator]
Initiator solution (1): Diisopropyl peroxydicarbonate solution (concentration: 50% by mass, solvent: CF ₃ CH ₂ OCF ₂ CF ₂ H)

(Example 1)
First, a monomer and a polymerization initiator were charged in a 50 mL pressure-resistant glass container, and then the system was replaced with nitrogen. 50 g of the linear precursor monomer (a1) was used as the monomer, and 0.29 g of the initiator solution (1) was used as the polymerization initiator.
Next, the polymerization reaction was carried out by stirring while heating so that the internal temperature was 40 ° C., which is the polymerization reaction temperature. The polymerization reaction time was 72 hours. After completion of the polymerization reaction, the unreacted raw material was distilled off by vacuum drying at 80 ° C. to obtain a precursor polymer. The yield of the precursor polymer was 24.0 g.

Next, the precursor polymer was hydrolyzed. As the solvent, a mixed solvent of water and fluorine-containing alcohol (mass ratio 5: 5) was used. Hexafluoroisopropanol was used as the fluorinated alcohol.
That is, a 1 L separable flask was charged with a mixed solvent of water and a fluorinated alcohol and the precursor polymer so that the concentration of the precursor polymer was 10% by mass. This was heated to 80 ° C. and stirred for 24 hours while maintaining the temperature to obtain a solution (coating composition) of the fluoropolymer (A) in which the precursor polymer was hydrolyzed. The content (concentration) of the fluoropolymer (A) in the solution is 10% by mass, and the content of the fluoroalcohol is 45% by mass.
When the precursor polymer is hydrolyzed, the unit —COOCH ₃ based on the linear precursor monomer (a) is hydrolyzed to the unit (I) represented by the formula (I).
The weight average molecular weight, number average molecular weight, fluorine atom content, -COOM content of the fluoropolymer (A), and the content of the unit (I) relative to all units are the mass average molecular weight, number average of the precursor polymer. The molecular weight, the fluorine atom content, the content of —COOCH ₃ , and the content of units based on the precursor monomer with respect to all units can be regarded as the same. These are shown in Table 1 (hereinafter the same).
The storage stability of the obtained fluoropolymer (A) solution (coating composition) was evaluated by the above method. The refractive index of the film made of the obtained fluoropolymer (A) and the solubility in an aqueous alkali solution were evaluated by the above methods. These results are shown in Table 1 (hereinafter the same).
Table 1 also describes the main manufacturing conditions. Moreover, the value which converted the usage-amount of the polymerization initiator into the ratio (unit: mol%) with respect to the sum total of the number-of-moles of the monomer used for a polymerization reaction is described (hereinafter, the same).

(Examples 2-9)
The content (concentration) of the fluoropolymer (A) is 10% by mass and the content of the fluoroalcohol is 45% by mass, as in Example 1, except that the polymerization process conditions are changed as shown in Table 1. A solution (coating composition) of the fluoropolymer (A) was obtained and evaluated in the same manner as in Example 1.
In Examples 6 to 9, when the precursor polymer is hydrolyzed, the unit —COOCH ₃ based on the branched precursor monomer (c) is hydrolyzed, and Rf ¹ in the formula (I) is branched. It becomes a unit (comparative example) which is an oxyperfluoroalkylene group.

As shown in the results of Table 1, it has the unit (I) represented by the formula (I), and the content of -COOM is 1.5 x ^{10-3 to} 1.9 x ^10-3 mol / The solution (coating composition) of the fluoropolymer (A) of Examples 1 to 4 containing the fluoropolymer (A) that is g is excellent in storage stability, and the fluorine-containing polymer formed using the solution The film made of the union (A) had a sufficiently low refractive index and excellent solubility in an aqueous alkali solution.
On the other hand, Example 5 has the unit (I), but the content of -COOM is 1.5 × 10 5 because the content of the unit (I) is low with respect to all the units of the fluoropolymer (A). ^This is an example of less than ^-3 mol / g. Although the refractive index of the film was sufficiently low, the storage stability of the fluoropolymer solution (coating composition) was insufficient, and the solubility of the film in an alkaline aqueous solution was also insufficient.

Examples 6 to 9 are examples having units in which Rf ¹ in the formula (I) is a branched oxyperfluoroalkylene group instead of the unit (I) represented by the formula (I). In either case, the refractive index of the film was sufficiently low, but the storage stability was insufficient.
In particular, in Example 9 in which the content of -COOM was lower than 1.5 × 10 ^-3 mol / g, the solubility of the membrane in an alkaline aqueous solution was also insufficient.

In particular, when Examples 1 and 6 are compared, Example 6 in which Rf ¹ in the formula (I) is branched is inferior in storage stability even when the content of -COOM is the same.
On the other hand, when Examples 2 and 4 are compared, Example 2 in which the content of -COOM is the same and the other monomer (b) has a branched structure and the other monomer (b) have a branched structure. All of the examples 4 that did not have excellent storage stability. That is, it can be seen that the presence or absence of a branched structure in the other monomer (b) does not affect the storage stability.

Further, from the results of Examples 5 and 9, when the content of —COOM is as low as 1.1 × 10 ⁻³ mol / g, regardless of the presence or absence of the branched structure in Rf ¹ , the alkali solubility of the film is insufficient. It turns out that it is unsuitable for an antireflection film. A fluorine-containing polymer having excellent alkali solubility can be used for an antireflection film.

Claims (6)

A fluorine-containing polymer having a unit represented by the following formula (I) and having a content of a group represented by —COOM of 1.5 × 10 ^{−3 to} 1.9 × 10 ⁻³ mol / g ( A composition for coating comprising A).
^{- [CX 1 X 2 -CY (} Rf 1 -COOM)] - ··· (I)
(Wherein, X ¹ and X ² each independently represent a hydrogen atom, a fluorine atom or a chlorine atom, Y represents a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group or a trifluoromethyl group, and Rf ¹ represents A linear perfluoroalkylene group which may contain an etheric oxygen atom between carbon-carbon atoms, or a linear oxyperfluoroalkylene group which may contain an etheric oxygen atom between carbon-carbon atoms, -COOM Represents —COOH or —COOZ ¹ (Z ¹ is an optionally substituted ammonium ion).   The coating composition according to claim 1, wherein the fluoropolymer (A) has a number average molecular weight of 1,000 to 30,000.   The coating composition according to claim 1 or 2, wherein the film made of the fluoropolymer (A) has a refractive index of 1.42 or less at a wavelength of 193 nm.   The coating composition as described in any one of Claims 1-3 whose content of the said fluoropolymer (A) is 1-10 mass%.   Furthermore, a solvent is contained, this solvent contains a fluorine-containing alcohol, and content of this fluorine-containing alcohol in the said composition for coating is 9-49.5 mass%, Any one of Claims 1-4. The coating composition as described in 1. A method for producing a photoresist laminate in which an antireflection film is provided on the surface of a photoresist layer,
A method for producing a photoresist laminate, comprising a step of applying the coating composition according to any one of claims 1 to 5 on the surface of a photoresist layer.