JP2007078743A - Protective film forming material and photoresist pattern forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protective film forming material which simultaneously prevents deterioration of a resist film during liquid immersion lithography and deterioration of a liquid used for the liquid immersion lithography, and which forms a resist pattern of a good shape without increasing the number of processing steps. <P>SOLUTION: The protective film forming material comprises an alkali-soluble polymer having a constitutional unit represented by formula (I) and a constitutional unit of an α-hydroxyalkyl substituted alkyl acrylate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a resist protective film forming material suitable for forming a protective film for a resist film and a photoresist pattern forming method using the same. In particular, the present invention relates to a liquid immersion lithography process, and in particular, a refractive index higher than air on at least the resist film in a path through which lithography exposure light reaches the resist film, and a refractive index higher than that of the resist film. In an immersion exposure process that improves the resolution of the resist pattern by exposing the resist film in a state where a liquid having a low predetermined thickness (hereinafter referred to as “liquid for immersion exposure”) is interposed. The present invention relates to a resist protective film forming material suitable for use and a photoresist pattern forming method using the protective film forming material.

  Lithography is frequently used to manufacture fine structures in various electronic devices such as semiconductor devices and liquid crystal devices. However, with the miniaturization of device structures, it is required to make resist patterns finer in the lithography process.

  At present, it is possible to form a fine resist pattern having a line width of about 90 nm by the lithography method, for example, in the most advanced region. However, further fine pattern formation is required in the future.

In order to achieve such fine pattern formation of less than 90 nm, the development of an exposure apparatus and a corresponding resist is the first point. Development points for exposure equipment include shortening the wavelength of light sources such as F ₂ excimer laser, EUV (extreme ultraviolet light), electron beam, X-ray, soft X-ray, and increasing the numerical aperture (NA) of the lens. It is common.

  However, shortening the wavelength of the light source requires a new expensive exposure apparatus, and in increasing the NA, there is a trade-off between the resolution and the depth of focus. There is a problem that decreases.

  Recently, as a lithography technique capable of solving such a problem, a method called an immersion exposure (liquid immersion lithography) method has been reported (for example, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3). In this method, an immersion exposure liquid such as pure water or a fluorine-based inert liquid having a predetermined thickness is interposed between at least the resist film between the lens and the resist film on the substrate during exposure. . In this method, a light source having the same exposure wavelength can be used by replacing the exposure optical path space, which has conventionally been an inert gas such as air or nitrogen, with a liquid having a higher refractive index (n), such as pure water. Similar to the case of using a light source having a shorter wavelength or the case of using a high NA lens, high resolution is achieved and at the same time, there is no reduction in the depth of focus.

  By using such immersion exposure, it is possible to realize the formation of a resist pattern that is low in cost, excellent in high resolution, and excellent in depth of focus, using a lens mounted on an existing apparatus. It is attracting a lot of attention.

  However, in a process using such an immersion exposure process, an immersion exposure liquid such as pure water or a fluorine-based inert liquid is interposed in the upper layer of the resist film. There is a concern about the change in the resist film during immersion exposure by the liquid and the refractive index fluctuation accompanying the change in the immersion exposure liquid itself due to the elution component from the resist film.

  Even in such an immersion exposure process, the material system used in the conventional lithography method may be diverted as it is, but the immersion exposure liquid is interposed between the lens and the resist film. Because of the difference in exposure environment, it has been proposed to use a material system different from the conventional lithography method.

  Under such circumstances, the above-mentioned means for simultaneously preventing the deterioration of the resist film caused by the immersion exposure liquid during the immersion exposure and the refractive index fluctuation accompanying the alteration of the immersion exposure liquid itself. A material for forming a protective film using a fluorine-containing resin has been proposed (for example, see Patent Document 1). However, when such a protective film forming material is used, the above-mentioned object can be achieved, but a special cleaning solvent and a coating apparatus are necessary, and the number of steps for removing the protective film is increased. Yield problems occur.

  Furthermore, recently, a process of using an alkali-soluble polymer as a protective film for an upper layer of a resist has attracted attention (for example, see Patent Document 2). For this type of protective film forming material, There is a need for further characteristics that can suppress as much as possible the change in the resist film caused by the immersion exposure liquid during immersion exposure and the change in the refractive index associated with the alteration of the immersion exposure liquid itself.

Journal of Vacuum Science & Technology B (Journal of Vacuum Science Technology) (J.Vac.Sci.Technol.B) ((Issuing Country) USA), 1999, Vol. 17, No. 6, 3306-3309 Journal of Vacuum Science & Technology B (Journal of Vacuum Science Technology) (J.Vac.Sci.Technol.B) ((Publishing Country) USA), 2001, Vol. 19, No. 6, pp. 2353-2356 Proceedings of SPIE Vol.4691 (Proceedings of SPAI ((Issuing country) USA) 2002, 4691, 459-465 International Publication No. 2004/074937 Pamphlet JP 2005-157259 A

  The present invention has been made in view of the above-mentioned problems of the prior art. Specifically, by forming a specific protective film on the surface of the resist film, the resist film can be altered and liquid can be obtained during immersion exposure. It is an object of the present invention to simultaneously prevent deterioration of the immersion exposure liquid itself and to form a high-resolution resist pattern using immersion exposure.

In order to solve the above problems, a resist protective film forming material according to the present invention is a material for forming a protective film laminated on a photoresist film on a substrate,
The following general formula (I)

〔式（Ｉ）中、Ｃ_fは−ＣＨ₂−（ただし、水素原子の一部もしくは全部がフッ素原子に置換されていてもよい）を示し；Ｒ_f1は水素原子、または、直鎖、分岐鎖もしくは環状の炭素原子数１〜５のアルキル基（ただし、アルキル基の水素原子の一部もしくは全部がフッ素原子に置換されていてもよい）を示し；Ｒ_f2は直鎖、分岐鎖もしくは環状の炭素原子数１〜５のアルキル基（ただし、アルキル基の水素原子の一部もしくは全部がフッ素原子に置換されていてもよい）を示し；ｐ、ｔ、ｕはそれぞれ０〜３の数を示し；ｍは繰り返し単位の数を意味する。なお、Ｃ_f、Ｒ_f1、Ｒ_f2の少なくともいずれかにおいてフッ素置換基を有するものとする。〕で表される構成単位と、
下記一般式（II）

[In the formula (I), C _f represents —CH ₂ — (wherein a part or all of the hydrogen atoms may be substituted with fluorine atoms); R _f1 represents a hydrogen atom or a straight chain or branched chain Represents a chain or cyclic alkyl group having 1 to 5 carbon atoms (however, part or all of the hydrogen atoms of the alkyl group may be substituted with a fluorine atom); R _f2 represents linear, branched or cyclic And an alkyl group having 1 to 5 carbon atoms (however, part or all of the hydrogen atoms of the alkyl group may be substituted with fluorine atoms); p, t and u each represent a number of 0 to 3; Shown; m means the number of repeating units. Note that at least one of C _f , R _f1 , and R _f2 has a fluorine substituent. A structural unit represented by
The following general formula (II)

〔式（II）中、Ｒ₁は炭素数１〜５の直鎖もしくは分岐鎖のアルキレン鎖であり、Ｒ₂は炭素数１〜１５の直鎖もしくは分岐鎖のアルキル基または脂環構造を有する炭化水素基を示す。〕で表される構成単位との少なくとも２種の構成単位を有するアルカリ可溶性ポリマーを含有してなることを特徴とする。

[In Formula (II), R ₁ is a linear or branched alkylene chain having 1 to 5 carbon atoms, and R ₂ has a linear or branched alkyl group having 1 to 15 carbon atoms or an alicyclic structure. A hydrocarbon group is shown. It is characterized by containing an alkali-soluble polymer having at least two types of structural units with the structural unit represented by

  Furthermore, a resist pattern forming method according to the present invention is a photoresist pattern forming method using an immersion exposure process, wherein a photoresist film is provided on a substrate, and the above-described protective film forming material is used on the photoresist film. After forming the protective film, an immersion exposure liquid is disposed on at least the protective film of the substrate, and then the photoresist film is selectively exposed through the immersion exposure liquid and the protective film. Then, after performing heat treatment as necessary, the protective film and the photoresist film are developed with an alkali developer to remove the protective film and obtain a photoresist pattern at the same time.

  The material for forming a protective film according to the present invention can be directly formed on a resist film and does not hinder pattern exposure. Since the material for forming a protective film of the present invention is insoluble in water, it is “the most suitable liquid for immersion exposure because it satisfies the optical requirements of immersion exposure, is easy to handle and has no environmental pollution. It is possible to actually use “water (pure water or deionized water)” regarded as promising as a liquid for immersion exposure. In other words, it is easy to handle, optical properties such as refractive index are good, and water with no environmental pollution is used as a liquid for immersion exposure. It is possible to obtain a resist pattern with sufficient protection and good characteristics during In addition, when an exposure wavelength of 157 nm is used as the liquid for immersion exposure, a fluorine-based medium is regarded as dominant from the viewpoint of absorption of exposure light, and such a fluorine-based solvent is used. However, like the above-described water, the resist film is sufficiently protected during the immersion exposure process, and a resist pattern with good characteristics can be obtained.

  Furthermore, since the protective film-forming material according to the present invention is soluble in alkali (developer), the formed protective film is subjected to the resist film before the development process even after the exposure is completed and the development process is performed. There is no need to remove it. That is, since the protective film obtained using the protective film-forming material of the present invention is soluble in alkali (developer), there is no need to provide a protective film removal step before the development step after exposure, and the resist film The development with an alkali developer can be performed while leaving the protective film, whereby the removal of the protective film and the development of the resist film can be realized simultaneously. Therefore, the pattern forming method performed using the protective film forming material of the present invention can efficiently form a resist film with good pattern characteristics with extremely low environmental pollution and a reduced number of steps. it can.

  In particular, since the alkali-soluble polymer used in the protective film-forming material of the present invention is soluble in various alcohols, it can provide a protective film-forming material with good coating properties. Further, the protective film formed using the protective film-forming material of the present invention is insoluble in water and soluble in an alkaline developer, and hardly changes the shape of the resist pattern even when used in an immersion exposure process. .

  In the present invention having the above-described configuration, the immersion exposure can be performed by using water or a fluorine-based inert liquid which is substantially pure water or deionized water as the immersion exposure liquid. As described above, in consideration of cost, ease of post-processing, low environmental pollution, etc., water is a more suitable immersion exposure liquid, but when 157 nm exposure light is used. For this, it is preferable to use a fluorine-based solvent that absorbs less exposure light. Furthermore, the protective film formed from the material for forming a resist protective film of the present invention is denser than conventional protective films using an alkali-soluble polymer, and suppresses invasion of the resist film by liquid for immersion exposure. be able to.

  As the resist film that can be used in the present invention, any resist film obtained using a conventionally used resist composition can be used, and there is no need to use it in a particularly limited manner. This is also the greatest feature of the present invention.

  In addition, as described above, the essential property as the protective film of the present invention is that it has no substantial compatibility with water and is soluble in alkali, and further transparent to exposure light. The protective film material that does not cause mixing with the resist film, has good adhesion to the resist film, and has good solubility in a developer, and can form a protective film having such characteristics. As a composition obtained by dissolving an alkali-soluble polymer having at least one of the structural unit represented by the general formula (I) and the structural unit represented by the general formula (II) in a solvent described later. Use things.

  Examples of the structural unit represented by the general formula (I) include the following general formulas (III) and (IV).

〔式（III）、（IV）中、Ｒ_f1は水素原子、または、直鎖、分岐鎖、もしくは環状の炭素原子数１〜５のアルキル基（ただし、アルキル基の水素原子の一部もしくは全部がフッ素原子に置換されていてもよい）を示し；ｍは繰り返し単位を意味する。〕で、それぞれ表される２種の構成単位から選ばれる少なくとも１種を好ましくは用いることができる。

[In the formulas (III) and (IV), R _f1 is a hydrogen atom or a linear, branched, or cyclic alkyl group having 1 to 5 carbon atoms (however, part or all of the hydrogen atoms of the alkyl group) May be substituted with a fluorine atom); m means a repeating unit. ] At least one selected from the two types of structural units represented respectively can be preferably used.

  In this case, in other words, the structural unit represented by the general formula (I) is at least one polymer selected from two structural units respectively represented by the chemical formulas (III) and (IV), or These two kinds of copolymers or these two kinds of mixed polymers. With this configuration, alkali solubility can be improved.

As the structural unit represented by the general formula (II), it is possible to use a structural unit in which R ₁ is a methylene chain and R ₂ is an ethyl group in the structural formula of the general formula (II). This is preferable from the viewpoint of improving the properties and improving the barrier property between the immersion exposure liquid and the resist.

  Such a polymer can be synthesized by a known polymerization method. Moreover, although the polystyrene conversion mass mean molecular weight by GPC of resin of these polymer components is not specifically limited, It is 5000-80000, More preferably, it is 8000-50000.

  As the solvent for dissolving the alkali-soluble polymer, any solvent can be used as long as it is not compatible with the resist film and can dissolve the fluoropolymer. Examples of such solvents include alcohol solvents having 1 to 10 carbon atoms, partially or fully partially fluorinated alcohol solvents having 1 to 10 carbon atoms, partially or completely partially fluorinated alkyl ether solvents having 4 to 15 carbon atoms, Alternatively, a partially or fully partially fluorinated alkyl ester solvent having 4 to 15 carbon atoms can be used. The solvent used in the present invention contains at least one solvent selected from the solvent group.

  The alcohol solvent is an alcohol solvent having 1 to 10 carbon atoms, specifically, n-butyl alcohol, isobutyl alcohol, n-pentanol, 4-methyl-2-pentanol, and 2-octanol. Alcohol solvents such as are preferred.

  As the solvent for dissolving the alkali-soluble polymer, a fluorinated alcohol solvent can also be used as described above. Such a fluorinated alcohol solvent is not compatible with the resist film and can dissolve the alkali-soluble polymer. The fluorinated alcohol solvent is preferably a solvent having a larger number of fluorine atoms than the number of hydrogen atoms contained in the fluorinated alcohol molecule.

As described above, the fluorinated alcohol preferably has 1 to 10 carbon atoms. As such a fluorine atom-containing alcohol, specifically, C ₄ F ₉ CH ₂ CH ₂ OH and / or C ₃ F ₇ CH ₂ OH can be preferably used.

  A partially or fully partially fluorinated alkyl ether solvent having 4 to 15 carbon atoms is represented by ROR ′ (R and R ′ each represents an alkyl group, and the total number of carbon atoms of both alkyl groups is 4 to 15; Some or all of the atoms are replaced by fluorine atoms).

As a suitable example of such a fluoroalkyl ether, a compound represented by the following formula (V) is exemplified.

  A partially or fully partially fluorinated alkyl ester solvent having 4 to 15 carbon atoms is represented by RCOOR ′ (R and R ′ each represents an alkyl group, and the total number of carbon atoms of both alkyl groups is 4 to 15; Some or all of the atoms are replaced by fluorine atoms).

  Preferable examples of such fluoroalkyl esters include compounds represented by the following formulas (VI) and (VII).

  The protective film-forming material of the present invention may further contain an acidic substance, and it is preferable to use a fluorocarbon compound as the acidic substance. The effect of improving the shape of the resist pattern can be obtained by adding a fluorocarbon compound to the protective film-forming material of the present invention.

  Such fluorocarbon compounds are shown below, but these fluorocarbon compounds are not subject to important new usage rules (SNUR) and can be used.

As such a fluorocarbon compound, the following general formula (201)
(C _n F _{2n + 1} SO ₂ ) ₂ NH (201)
(Wherein n is an integer of 1 to 5),
The following general formula (202)
C _m F _{2m + 1} COOH (202)
(Wherein, m is an integer of 10 to 15),
The following general formula (203)

（式中、ｏは２〜３の整数である。）で示される炭化フッ素化合物と、
下記一般式（２０４）

(Wherein, o is an integer of 2 to 3),
The following general formula (204)

（式中、ｐは２〜３の整数であり、Ｒｆは１部もしくは全部がフッ素原子により置換されているアルキル基であり、水酸基、アルコキシ基、カルボキシル基、アミノ基により置換されていてもよい。）で示される炭化フッ素化合物とが好適である。

(In the formula, p is an integer of 2 to 3, Rf is an alkyl group partially or entirely substituted with a fluorine atom, and may be substituted with a hydroxyl group, an alkoxy group, a carboxyl group, or an amino group. )) Is preferred.

Specific examples of the fluorocarbon compound represented by the general formula (201) include the following chemical formula (205)
(C ₄ F ₉ SO ₂ ) ₂ NH (205)
Or a compound represented by the following chemical formula (206)
(C ₃ F ₇ SO ₂ ) ₂ NH (206)
The fluorine-containing compound represented by these is suitable.

Further, as the fluorocarbon compound represented by the general formula (202), specifically, the following chemical formula (207)
C ₁₀ F ₂₁ COOH (207)
The fluorine-containing compound represented by these is suitable.

  Further, as the fluorocarbon compound represented by the general formula (203), specifically, the following chemical formula (208)

で表される炭化フッ素化合物が好適である。

The fluorine-containing compound represented by these is suitable.

  Specific examples of the fluorine-containing compound represented by the general formula (204) include the following chemical formula (209).

で表される炭化フッ素化合物が好適である。

The fluorine-containing compound represented by these is suitable.

  The material for forming a resist protective film of the present invention may further contain a crosslinking agent comprising a nitrogen-containing compound having an amino group and / or an imino group substituted with a hydroxyalkyl group and / or an alkoxyalkyl group.

  The nitrogen-containing compound is preferably at least one selected from melamine derivatives, guanamine derivatives, glycoluril derivatives, succinylamide derivatives, and urea derivatives.

  Specifically, these nitrogen-containing compounds include, for example, the melamine compounds, urea compounds, guanamine compounds, acetoguanamine compounds, benzoguanamine compounds, glycoluril compounds, succinylamide compounds, and ethylene urea compounds. Are reacted with formalin in boiling water to form methylol, or these are further reacted with lower alcohols, specifically methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and the like. It can be obtained by alkoxylation.

  As such a cross-linking agent, tetrabutoxymethylated glycoluril is more preferably used.

  Furthermore, as the cross-linking agent, a condensation reaction product of a hydrocarbon compound substituted with at least one hydroxyl group and / or alkyloxy group and a monohydroxymonocarboxylic acid compound can also be suitably used.

  As the monohydroxymonocarboxylic acid, those in which a hydroxyl group and a carboxyl group are bonded to the same carbon atom or two adjacent carbon atoms are preferable.

  Next, a resist pattern forming method by an immersion exposure method using the protective film of the present invention will be described.

  First, a conventional resist composition is applied onto a substrate such as a silicon wafer with a spinner or the like, and then pre-baked (PAB treatment). In addition, it can also be set as the 2 layer laminated body which provided the organic type or the inorganic type antireflection film between the board | substrate and the application layer of the resist composition.

  The steps so far can be performed using a known method. The operating conditions and the like are preferably set as appropriate according to the composition and characteristics of the resist composition to be used.

  Next, on the surface of the resist film (single layer, multiple layers) cured as described above, for example, “an alkali-soluble polymer having each structural unit represented by the above chemical formulas (I) and (II) is converted to isobutyl alcohol”. After the protective film-forming material composition according to the present invention such as “the composition dissolved in” is uniformly applied, the resist protective film is formed by curing.

  On the substrate on which the resist film thus covered with the protective film is formed, the liquid for immersion exposure (liquid having a refractive index larger than the refractive index of air and smaller than the refractive index of the resist film: the present invention In the case specialized in the above, pure water, deionized water, or a fluorinated solvent) is disposed.

  The resist film on the substrate in this state is selectively exposed through a desired mask pattern. Accordingly, at this time, the exposure light passes through the immersion exposure liquid and the protective film and reaches the resist film.

  At this time, the resist film is completely shielded from the immersion exposure liquid such as pure water by the protective film, and is subject to alteration such as swelling due to the invasion of the immersion exposure liquid. Effectively suppressing optical properties such as refractive index of the immersion exposure liquid by eluting the components in the exposure liquid (pure water, deionized water, fluorine-based solvent, etc.) is effectively suppressed.

The wavelength used for exposure in this case is not particularly limited, and ArF excimer laser, KrF excimer laser, F ₂ excimer laser, EUV (extreme ultraviolet), VUV (vacuum ultraviolet), electron beam, X-ray, soft X-ray, etc. Can be done using radiation. This is mainly determined by the characteristics of the resist film.

As described above, in the resist pattern forming method of the present invention, during exposure, the refractive index is larger than the refractive index of air and smaller than the refractive index of the resist film to be used via the protective film on the resist film. A liquid for immersion exposure having Examples of such immersion exposure liquid include water (pure water, deionized water), or a fluorine-based inert liquid. Specific examples of the fluorinated inert liquid include fluorinated compounds such as C ₃ HCl ₂ F ₅ , C ₄ F ₉ OCH ₃ , C ₄ F ₉ OC ₂ H ₅ , and C ₅ H ₃ F ₇ as main components. Liquid to be used. Of these, water (pure water or deionized water) is preferably used from the viewpoint of cost, safety, environmental problems, and versatility, but when exposure light having a wavelength of 157 nm is used, exposure light From the viewpoint of low absorption, it is preferable to use a fluorinated solvent.

  Further, the refractive index of the immersion exposure liquid to be used is not particularly limited as long as it is within the range of “greater than the refractive index of air and smaller than the refractive index of the resist composition to be used”.

  When the exposure process in the immersion state is completed, the immersion exposure liquid is removed from the substrate.

  Next, PEB (post-exposure heating) is performed on the resist film, and subsequently development processing is performed using an alkaline developer composed of an alkaline aqueous solution. Since the developer used in this development process is alkaline, the protective film is dissolved and removed simultaneously with the soluble portion of the resist film. In addition, you may post-bake following a development process. Subsequently, rinsing is performed using pure water or the like. In this water rinsing, for example, water is dropped or sprayed on the surface of the substrate while rotating the substrate to wash away the developer on the substrate, the protective film component dissolved by the developer, and the resist composition. And by drying, the resist pattern by which the resist film was patterned in the shape according to the mask pattern is obtained. Thus, in the present invention, the removal of the protective film and the development of the resist film are realized simultaneously by the development process. Since the protective film formed of the resist protective film forming material of the present invention has improved water repellency, the liquid for immersion exposure after the completion of the exposure is well separated. The amount of adhering liquid is small, and so-called liquid leakage for immersion exposure is reduced.

  By forming the resist pattern in this manner, a resist pattern with a fine line width, particularly a line-and-space pattern with a small pitch can be manufactured with a good resolution. Here, the pitch in the line and space pattern refers to the total distance of the resist pattern width and the space width in the line width direction of the pattern.

  Examples of the present invention will be described below. However, these examples are merely examples for suitably explaining the present invention, and do not limit the present invention.

Example 1
In this example, the material for forming a protective film according to the present invention is, as a basic property evaluation, (1) soluble in an alcohol solvent or (2) a protective film forming material solution dissolved in an alkaline solvent. Four types of evaluations are possible: whether the substrate can be coated uniformly, (3) the obtained protective film is resistant to pure water, and (4) the obtained protective film is soluble in the developer. went.

  For the evaluation (1), the following two types of protective film forming materials were put in isobutanol and observed whether or not they were soluble.

  As a protective film forming material, a copolymer represented by the following chemical formula (VIII) was used. In the formula, m and n indicate the number of repeating units of each monomer unit. As sample 1, a copolymer of m: n = 92: 8 (mol%) is used, and as sample 2, m: n = 86: 14 (mol%) copolymer was used.

  For the evaluation (2), a 2.8 mass% isobutanol solution of each of the protective film forming materials was spin-coated on a substrate at 1200 rpm, and the obtained coating film was cured by heating at 90 ° C. for 60 seconds. The surface state of the cured film (protective film) was observed visually.

  For the evaluation (3), pure water was poured into the cured film (protective film) for 120 seconds, and the film slip (change in film thickness) before and after the comparison was compared.

  For the evaluation (4), the cured film (protective film) was washed with an alkaline developer (2.38% concentration tetramethylammonium hydroxide aqueous solution), and the dissolution rate at that time (film thickness conversion: nm / second) ) Was calculated. The dissolution rate with the alkali developer was measured with a resist dissolution analyzer (RDA: manufactured by Risotech Japan).

  The evaluation results are shown in Table 1 below. From Table 1, the basic characteristics of the protective film material according to the present invention are as follows: (1) soluble in alcohol solvent, and (2) protective film forming material solution dissolved in alkaline solvent uniformly coated on the substrate It can be confirmed that (3) the obtained protective film is resistant to pure water, and (4) the obtained protective film is sufficiently soluble in the developer.

  More specifically, the copolymer represented by the chemical formula (VIII) is easily dissolved in isobutanol, for example, at a concentration of 2.8% by mass. Moreover, each 2.8 mass% resin solution of the samples 1 and 2 can be apply | coated to the uniform film thickness without a spot by spin coating. Moreover, the cured film (protective film) obtained from this uniform coating film was also uniform, and the film thicknesses of the cured films of Samples 1 and 2 were 75.2 nm and 79.5 nm. The thickness of each cured film (protective film) after pouring pure water for 120 seconds is 75.6 nm for sample 1 and 79.8 nm for sample 2, and it is determined that there is no film slippage. It is. Further, the dissolution rate of each of the protective films with an alkaline developer is 180 nm / sec for sample 1 and 150 nm / sec for sample 2, which has sufficient developer solubility for development.

(Example 2)
An organic antireflection film composition “ARC-29A” (trade name, manufactured by Brewer Science) was applied onto a silicon wafer using a spinner, and baked on a hot plate at 225 ° C. for 60 seconds to dry. An organic antireflection film having a thickness of 77 nm was formed. Then, apply “TArF-P6111ME (manufactured by Tokyo Ohka Kogyo Co., Ltd.)” which is a positive resist on this antireflection film using a spinner, pre-bake on a hot plate at 130 ° C. for 90 seconds, and dry. Thus, a resist film having a film thickness of 225 nm was formed on the antireflection film.

  On the resist film, a copolymer (sample 1 and sample 2) represented by the chemical formula (VIII) was dissolved in isobutanol, and a protective film material having a resin concentration of 2.0% by mass was applied by spin coating. Heating was carried out at 60 ° C. for 60 seconds to form two types of protective films (protective films A and B) having a film thickness of 70.0 nm.

  Next, using an ArF excimer laser (wavelength 193 nm) with an exposure apparatus NSR-S302A (Nikon Corporation, NA (numerical aperture) = 0.60, σ = 2/3 ring) through the mask pattern, Pattern light was irradiated (exposure processing). After rotating the substrate, pure water was continuously dropped on the protective film at 23 ° C. for 2 minutes while rotating the substrate, and the substrate was placed in a simulated liquid immersion environment.

  After the pure water dropping step, PEB treatment was performed under conditions of 130 ° C. and 90 seconds, and then developed with an alkaline developer at 23 ° C. for 60 seconds while leaving each protective film. As the alkaline developer, a 2.38 mass% tetramethylammonium hydroxide aqueous solution (TMAH) was used. By this development process, each protective film was completely removed, and the development of the resist film could be realized well.

  When the resist pattern with a 130 nm line-and-space ratio of 1: 1 obtained in this way was observed with a scanning electron microscope (SEM), all of these pattern profiles were good, and fluctuations and the like were completely absent. Not observed.

(Example 3)
In the same manner as in Example 2, an organic antireflection film composition “ARC-29A” (trade name, manufactured by Brewer Science) was applied onto a silicon wafer using a spinner, and then heated on a hot plate at 225 ° C. for 60 seconds. By baking and drying, an organic antireflection film having a thickness of 77 nm was formed. Then, apply “TArF-P6111ME (manufactured by Tokyo Ohka Kogyo Co., Ltd.)” which is a positive resist on this antireflection film using a spinner, pre-bake on a hot plate at 130 ° C. for 90 seconds, and dry. Thus, a resist film having a thickness of 150 nm was formed on the antireflection film.

  On the resist film, two types of protective film materials each having a resin concentration of 2.0% by mass were prepared by dissolving the copolymer (sample 1 and sample 2) represented by the chemical formula (VIII) in isobutanol. The film was spin-coated and heated at 90 ° C. for 60 seconds to form two types of protective films (protective films A and B) having a film thickness of 70.0 nm.

  Next, a two-beam interference experiment was performed using immersion exposure using an immersion exposure experimental machine LEIES 193-1 (manufactured by Nikon Corporation). Thereafter, PEB treatment was performed at 115 ° C. for 90 seconds, followed by development treatment at 23 ° C. for 60 seconds using a 2.38 mass% TMAH aqueous solution. Each protective film was completely removed by this development process, and the development of the photoresist film was also good.

  When the resist pattern in which the 65 nm line and space pattern thus obtained was 1: 1 was observed with a scanning electron microscope (SEM), a good line and space pattern was found in each case. I was able to form.

(Comparative Example 1)
Although using the same positive photoresist as in Example 2 above, except that the protective film was not formed, a resist pattern with a 130 nm line and space of 1: 1 was formed in exactly the same way, When observed with a scanning electron microscope (SEM), pattern fluctuation, swelling, etc. occurred, and the pattern could not be observed.

  As described above, according to the present invention, any conventional resist composition can be used to form a resist film, and any immersion exposure liquid can be used in the immersion exposure process. Even when a fluorine-based medium is used, a highly accurate resist pattern with high sensitivity, excellent resist pattern profile shape, and good depth of focus, exposure margin, and stability over time is obtained. Can do. In addition, the film quality is dense, preventing resist film alteration and immersion exposure liquid alteration during immersion exposure using various immersion exposure liquids such as water, and increasing the number of processing steps. It is possible to improve the resistance of the resist film to be placed without causing any damage. Therefore, when the resist protective film forming material of the present invention is used, a resist pattern can be efficiently formed by an immersion exposure process.

Claims (8)

A material for forming a protective film laminated on a photoresist film on a substrate, which has the following general formula (I)

[In the formula (I), C _f represents —CH ₂ — (wherein a part or all of the hydrogen atoms may be substituted with fluorine atoms); R _f1 represents a hydrogen atom or a straight chain or branched chain Represents a chain or cyclic alkyl group having 1 to 5 carbon atoms (however, part or all of the hydrogen atoms of the alkyl group may be substituted with a fluorine atom); R _f2 represents linear, branched or cyclic And an alkyl group having 1 to 5 carbon atoms (however, part or all of the hydrogen atoms of the alkyl group may be substituted with fluorine atoms); p, t and u each represent a number of 0 to 3; Shown; m means the number of repeating units. Note that at least one of C _f , R _f1 , and R _f2 has a fluorine substituent. And the following general formula (II)

[In Formula (II), R ₁ is a linear or branched alkylene chain having 1 to 5 carbon atoms, and R ₂ has a linear or branched alkyl group having 1 to 15 carbon atoms or an alicyclic structure. A hydrocarbon group is shown. A protective film-forming material comprising an alkali-soluble polymer having at least two types of structural units represented by   2. The protective film forming material according to claim 1, which is a protective film forming material used in an immersion exposure process. The structural unit represented by the general formula (I) is represented by the following general formulas (III) and (IV):

[In the formulas (III) and (IV), R _f1 is a hydrogen atom or a linear, branched, or cyclic alkyl group having 1 to 5 carbon atoms (however, part or all of the hydrogen atoms of the alkyl group) May be substituted with a fluorine atom); m means a repeating unit. Or at least one polymer selected from two types of structural units represented by the above, or a copolymer thereof, or a mixed polymer of these two types. 2. The material for forming a protective film according to 2.   Further, an alcohol solvent having 1 to 10 carbon atoms, a partially or fully partially fluorinated alcohol solvent having 1 to 10 carbon atoms, a partially or completely partially fluorinated alkyl ether solvent having 4 to 15 carbon atoms, and 4 carbon atoms. The material for forming a protective film according to any one of claims 1 to 3, further comprising at least one solvent selected from the group consisting of a part or a partly fluorinated alkyl ester solvent.   Furthermore, an acidic substance is contained, The material for protective film formation of any one of Claims 1-4 characterized by the above-mentioned.   6. The protective film forming material according to claim 5, wherein the acidic substance is a fluorocarbon compound.   Furthermore, a crosslinking agent is included, The material for protective film formation of any one of Claims 1-6 characterized by the above-mentioned.   A photoresist pattern forming method using an immersion exposure process, wherein a photoresist film is provided on a substrate, and the photoresist film is protected using the protective film forming material according to any one of claims 1 to 7. After forming the film, an immersion exposure liquid is disposed on at least the protective film of the substrate, and then the photoresist film is selectively exposed through the immersion exposure liquid and the protective film, A photoresist pattern characterized by obtaining a photoresist pattern at the same time as removing the protective film by developing the protective film and the photoresist film using an alkali developer after heat treatment as necessary Forming method.