JP2007072336A - Protective film forming material and photoresist pattern forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the scan conformability of a liquid for liquid immersion lithography, by imparting a proper contact angle and a proper fall angle to a protective film forming material, and to provide a protective film forming material, having basic characteristics (such as, water repellency) required by a protective film used in a liquid immersion lithographic process, and suitably applicable to a local liquid immersion lithographic process, in particular, and to provide a photoresist pattern forming method that uses the protective film forming material. <P>SOLUTION: The protective film forming material for forming a protective film laminated on a photoresist film on a substrate contains an alkali-soluble polymer containing a cyclic hydrocarbon having a fluorohydroxyalkyl group. The photoresist pattern forming method that uses the protective film forming material is also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a protective film forming material and a photoresist pattern forming method using the same. The present invention is particularly suitably applied to a liquid immersion lithography process.

  Photolithography is frequently used for the production of fine structures in various electronic devices such as semiconductor devices and liquid crystal devices. In recent years, the progress of high integration and miniaturization of semiconductor devices has been remarkable, and further miniaturization is required in forming a photoresist pattern in a photolithography process.

  At present, it is possible to form a fine photoresist pattern with a line width of about 90 nm by the photolithography method, for example, in the most advanced region. Has been done.

In order to achieve such finer pattern formation, generally, countermeasures by improving an exposure apparatus and a photoresist material can be considered. Countermeasures by 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. Measures are listed.

  However, shortening the wavelength of the light source requires an expensive new exposure apparatus. In addition, when the NA is increased, the resolution and the depth of focus are in a trade-off relationship. Therefore, there is a problem that the depth of focus decreases even if the resolution is increased.

  Recently, as a photolithography technique capable of solving such a problem, a liquid immersion lithography method has been reported (for example, see Non-Patent Documents 1 to 3). In this method, during exposure, the photoresist film is exposed by interposing an immersion exposure liquid of a predetermined thickness on at least the photoresist film in the exposure optical path between the exposure apparatus (lens) and the photoresist film on the substrate. Then, a photoresist pattern is formed. In this immersion exposure method, an exposure optical path space, which has conventionally been an inert gas such as air or nitrogen, has a refractive index that is larger than the refractive index of these spaces (gas) and smaller than the refractive index of the photoresist film ( By substituting with an immersion exposure liquid having n) (for example, pure water, fluorine-based inert liquid, etc.), even when a light source having the same exposure wavelength is used, exposure light having a shorter wavelength or high NA Similar to the case of using a lens, high resolution is achieved, and there is an advantage that the depth of focus does not decrease.

  By using such an immersion exposure process, it is possible to form a photoresist pattern that is low in cost, excellent in high resolution, and excellent in depth of focus, using a lens mounted on an existing exposure apparatus. Therefore, it is attracting a lot of attention.

  However, in the immersion exposure process, since the exposure is performed with the immersion exposure liquid interposed in the upper layer of the photoresist film, naturally, the alteration of the photoresist film by the immersion exposure liquid, There is a concern about the refractive index fluctuation accompanying the alteration of the immersion exposure liquid itself due to the eluted components.

  Under such circumstances, by forming a protective film using a fluorine-containing resin on the photoresist film and interposing an immersion exposure liquid on this protective film, the alteration to the photoresist film by the immersion exposure liquid, There has been proposed a technique aimed at simultaneously preventing refractive index fluctuations accompanying alteration of the liquid for immersion exposure (see, for example, Patent Document 1).

  More recently, from the viewpoint of simplification of the photoresist pattern formation process, production efficiency, etc., by using a protective film using an alkali-soluble polymer, it is possible to remove the protective film and eliminate unnecessary photoresist film during alkali development after immersion exposure. Attention has been paid to a technique for obtaining a photoresist pattern by simultaneously performing the removal of (see, for example, Patent Document 2).

"Journal of Vacuum Science & Technology B" (USA), 1999, Vol. 17, No. 6, pages 3306-3309 "Journal of Vacuum Science & Technology B" (USA), 2001, Vol. 19, No. 6, pp. 2353-2356 "Proceedings of SPIE", (USA), 2002, 4691, pp. 459-465. International Publication No. 2004/074937 Pamphlet JP 2005-157259 A

  Recently, however, a local immersion exposure process has been studied in which an immersion exposure liquid is filled only between an exposure lens for scanning at a high speed and a substrate having a protective film formed on a photoresist layer. In the immersion exposure process, the issue of scan followability of the immersion exposure liquid has newly emerged. In the examination of the conventional immersion exposure process, the problem in performing the exposure process while simultaneously scanning the exposure lens and the immersion exposure liquid on the substrate on which the protective film is formed on the photoresist film has not been examined. It was.

  In the local immersion exposure process, for example, a substrate provided with a protective film / photoresist layer is placed on a wafer stage, an exposure lens is arranged above the protective film with a predetermined interval, and the exposure lens is moved at a high speed. The liquid for immersion exposure is continuously dropped onto the protective film from one nozzle while being moved by scanning, and at the same time, the liquid is exposed while being moved together with the exposure lens while being sucked from the other nozzle. In such a local liquid immersion exposure process, the liquid for immersion exposure that continues to drip remains as fine water droplets on the surface of the protective film. It is necessary for the minute water droplets to follow the protective film at the same speed as the scanning lens. In addition, the basic characteristics required as a protective film, high resistance to immersion exposure liquid, low compatibility with the photoresist film provided in the lower layer, components from immersion exposure liquid to photoresist film It is necessary to have properties such as prevention of elution, prevention of elution of components from the photoresist film to the liquid for immersion exposure, and suppression of gas permeation of the protective film.

  Therefore, it is necessary to provide an appropriate contact angle and falling angle as a protective film forming material applied particularly to the local immersion exposure process.

  The present invention solves the above-described conventional problems, improves the scan follow-up performance of the liquid for immersion exposure by providing an appropriate contact angle and drop angle, and is required for a protective film used in the immersion exposure process. An object of the present invention is to provide a protective film forming material having basic characteristics (for example, water repellency) and a photoresist pattern forming method using the same.

  In order to solve the above problems, the present invention is a material for forming a protective film laminated on a photoresist film on a substrate, and contains an alkali-soluble polymer containing a cyclic hydrocarbon having a fluorohydroxyalkyl group. A protective film forming material is provided.

  Further, the present invention is a photoresist pattern forming method using an immersion exposure process, wherein a photoresist film is provided on a substrate, and a protective film is formed on the photoresist film using the photoresist protective film forming material, 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, and heat treatment is performed as necessary. And a photoresist pattern forming method of obtaining a photoresist pattern at the same time as removing the protective film by developing the protective film and the photoresist film using an alkaline developer.

  According to the present invention, by providing an appropriate contact angle and falling angle, the scanning follow-up performance of the immersion exposure liquid is improved, and resistance to the immersion exposure liquid, which is a basic characteristic required as a protective film, is achieved. High, low compatibility with the underlying photoresist film, prevention of elution of components from immersion exposure liquid to photoresist film, prevention of elution of components from photoresist film to immersion exposure liquid, protection film Provided is a material for forming a protective film having characteristics such as suppression of gas permeation. By applying the protective film forming material of the present invention to the immersion exposure process, it becomes possible to form a very fine photoresist pattern exceeding the resolution when lithography is performed using a conventional photoresist material and an exposure apparatus. .

  Hereinafter, the present invention will be described in detail.

  The material for forming a protective film according to the present invention contains an alkali-soluble polymer containing a cyclic hydrocarbon having a fluorohydroxyalkyl group.

  As such an alkali-soluble polymer, a polymer containing at least a monomer unit represented by the following formula (I) as a constituent unit is preferably used.

  In the above formula (I), each substituent has the following meaning.

C _f represents —CH ₂ — (however, part or all of the hydrogen atoms may be substituted with fluorine atoms).

R _f1 represents a linear, branched or cyclic fluoroalkyl group having 1 to 5 carbon atoms in which part or all of the hydrogen atoms are substituted with fluorine atoms.

  s, t, u, and v each represent a number from 0 to 3.

  m means a repeating unit.

  As the monomer unit represented by the above formula (I), specifically, a monomer unit represented by the following formula (II) (m is as defined above) is particularly preferably used.

  By using a polymer containing such a monomer unit as a constituent unit, an appropriate contact angle and falling angle can be provided with a good balance with respect to the protective film material.

  Here, the contact angle refers to an angle formed by the immersion exposure droplet, the upper surface / horizontal line of the material (protective film) in contact with the liquid, and the tangent at the end of the droplet. The appropriate contact angle is preferably 60 ° or more, more preferably 70 ° or more. By providing such an appropriate contact angle, the scan followability of the immersion exposure liquid can be improved.

  The falling angle means the tilt angle of the substrate when the droplet on the immersion exposure is gradually tilted and the droplet on the substrate starts to move. The appropriate sliding angle is preferably 30 ° or less, and more preferably 25 ° or less. By providing such an appropriate falling angle, it is possible to improve the scan followability of the immersion exposure liquid.

  In the present invention, it may be a homopolymer obtained by polymerizing the monomer unit represented by the above formula (I), and does not impair the characteristics required for the monomer unit and the protective film-forming material described above. In the range, it may be used as a copolymer obtained by copolymerization with an arbitrary monomer unit, or may be used as a copolymer obtained by copolymerization with a polymer having at least the arbitrary monomer unit.

  As the monomer unit for forming the copolymer, or the unit constituting the polymer having at least the monomer unit, the following monomer units are preferable examples.

  1. Structural unit (monomer unit) represented by the following formula (III)

  In the above formula (III), each substituent has the following meaning.

C _f represents —CH ₂ — (however, part or all of the hydrogen atoms may be substituted with fluorine atoms).

R _f2 represents 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 in the alkyl group may be substituted with fluorine atoms). Show.

R _f3 represents 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 fluorine atoms).

  s, t, and u each represent a number from 0 to 3.

  m means a repeating unit.

Note that at least one of C _f , R _f2 , and R _f3 has a fluorine substituent.

  Examples of the monomer unit represented by the above formula (III) include (III-1) an aliphatic cyclic group having both a fluorine atom or a fluorinated alkyl group and (III-2) an alcoholic hydroxyl group or an oxyalkyl group. Water-soluble and alkali-soluble monomer units are preferred.

  That is, in the monomer unit (III), (III-1) a fluorine atom or a fluorinated alkyl group and (III-2) an alcoholic hydroxyl group or an alkyloxy group are bonded to the aliphatic cyclic group, respectively. It constitutes the main chain. Examples of the (III-1) fluorine atom or fluorinated alkyl group include those in which part or all of the hydrogen atoms of the fluorine atom or lower alkyl group are substituted with fluorine atoms. Specific examples include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, and a nonafluorobutyl group, and industrially preferred are a fluorine atom and a trifluoromethyl group. The (III-2) alcoholic hydroxyl group or alkyloxy group is simply a hydroxyl group, and the alkyloxy group is a linear, branched, or cyclic alkyloxyalkyl group having 1 to 15 carbon atoms, or an alkyl group. It is an oxy group.

The polymer having at least such a unit is formed by cyclopolymerization of a diene compound having a hydroxyl group and a fluorine atom. As the diene compound, heptadiene that easily forms a polymer having a 5-membered ring or a 6-membered ring excellent in transparency and dry etching resistance is preferable. Further, 1,1,2,3,3-pentafluoro- polymer formed by cyclic polymerization of 4-trifluoromethyl-4-hydroxy-1,6-heptadiene _{(CF 2 = CFCF 2 C (} CF 3) (OH) CH 2 CH = CH 2) is most preferred.

Specific examples of the polymer having at least the structural unit represented by the above formula (III) include a polymer containing at least one of the structural units represented by the following formulas (IV) and (V), or the following formula (IV ) And (V) are preferably used. In the formulas (IV) and (V), R _f2 and m are as defined above.

  When the formulas (IV) and (V) constitute a copolymer and / or a mixed polymer, it is preferable to constitute the copolymer and / or the mixed polymer at 10 to 90 mol%, respectively.

  2. Structural unit (monomer unit) represented by the following formula (VI)

  In the above formula (IV), each substituent has the following meaning.

R _f4 represents 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 fluorine atoms).

R _f5 represents a hydrogen atom, a fluorine atom, or a linear, branched or cyclic alkyl group having 1 to 5 carbon atoms (provided that a part or all of the hydrogen atoms in the alkyl group are substituted by fluorine atoms) Good).

  m means a repeating unit.

Note that at least one of R _f4 and R _f5 has a fluorine substituent.

  Specific examples of the monomer unit represented by the above formula (VI) include monomer units represented by the following formula (VI-a) (wherein m is as defined above).

  Furthermore, the polymer containing the monomer unit represented by the formula (VI) is a copolymer and / or a mixture of the monomer unit represented by the formula (VI) and the monomer unit represented by the following formula (VII). It may be a polymer.

In formula (VII), R _f6 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 in the alkyl group are substituted with fluorine atoms). M represents a repeating unit. Note that at least one of R _f6 has a fluorine substituent.

  Specific examples of the monomer unit represented by the above formula (VI) and the copolymer represented by the above general formula (VII) include a monomer unit represented by the following formula (VIII) (wherein m is the above). As defined).

  3. Structural unit (monomer unit) represented by the following formula (IX)

  In the above formula (IX), each substituent has the following meaning.

R _f7 represents 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 fluorine atoms).

R _f8 represents a hydrogen atom, a fluorine atom, or a linear, branched or cyclic alkyl group having 1 to 5 carbon atoms (provided that a part or all of the hydrogen atoms in the alkyl group are substituted by fluorine atoms) Good).

  R represents a hydrogen atom or a methyl group; m represents a repeating unit.

Note that at least one of R _f7 and R _f8 has a fluorine substituent.

  Specific examples of the monomer unit represented by (IX) include a monomer unit represented by the following formula (IX-a) (wherein m is as defined above).

  As the alkali-soluble polymer used in the present invention, those having a polystyrene-equivalent weight average molecular weight by GPC of about 3,000 to 50,000 are preferably used, but are not limited thereto.

  The blending amount of the alkali-soluble polymer is preferably about 0.1 to 20% by mass, particularly 0.3 to 5% by mass with respect to the total amount of the protective film forming material (including the organic solvent described later). It is preferable to do.

  The alkali-soluble polymer can be synthesized by a known alkali-soluble polymer polymerization method.

  The protective film-forming material of the present invention contains an organic solvent in addition to the alkali-soluble polymer as an essential component. Any organic solvent can be used as long as it can dissolve the alkali-soluble polymer. For example, in addition to an alcohol solvent, a paraffin solvent, and a fluorine solvent, the organic solvent does not contain an epoxy ring and contains hydrogen atoms. Examples thereof include, but are not limited to, fluoroalkyl ethers and fluoroalkyl esters partially or entirely substituted with fluorine atoms.

  Examples of the alcohol solvent include isopropyl alcohol, 1-hexanol, 2-methyl-1-propanol (= isobutyl alcohol), 4-methyl-2-pentanol and the like, and particularly 2-methyl-1-propanol, 4- Methyl-2-pentanol and the like are preferably used. Examples of the paraffinic solvent include n-heptane. It has been confirmed that perfluoro-2-butyltetrahydrofuran can be used as the fluorine-based solvent.

  As fluoroalkyl ethers and fluoroalkyl esters that do not contain an epoxy ring and in which some or all of the hydrogen atoms are substituted with fluorine atoms, those having 4 to 15 carbon atoms are preferably used. Among these, preferred fluoroalkyl ethers are represented by the formula: ROR ′ (R and R ′ each represents an alkyl group, the total number of carbon atoms of both alkyl groups is 4 to 15, and part or all of the hydrogen atoms are fluorine. Substituted with an atom). Further, when a preferred fluoroalkyl ester is represented by a formula, RCOOR ′ (R and R ′ each represents an alkyl group, the total number of carbon atoms of both alkyl groups is 3 to 14, and part or all of the hydrogen atoms are Substituted with a fluorine atom).

  Preferable examples of the fluoroalkyl ether include compounds represented by the following formula (X).

  Further, preferred examples of the fluoroalkyl ester include compounds represented by the following formulas (XI) and (XII).

  The blending amount of the organic solvent is preferably adjusted so that the protective film forming material is a solution having a concentration of 0.1 to 20% by mass, and particularly adjusted to be 0.3 to 5% by mass. Is preferred.

  The protective film-forming material of the present invention may further contain an acidic substance, particularly a fluorine-containing compound. By blending the acidic substance, the effect of improving the shape of the photoresist pattern can be obtained.

  As such a fluorocarbon compound, for example, the following formula (XIII)

(C _n F _{2n + 1} SO ₂ ) ₂ NH (XIII)

(In the formula, n is an integer of 1 to 5.)
Fluorocarbon compound represented by the following formula (XIV)

C _x F _{2x + 1} COOH (XIV)

(In the formula, x is an integer of 10 to 15.)
Fluorocarbon compound represented by the following formula (XV)

(In the formula, o is an integer of 2 to 3.)
Fluorocarbon compound represented by the following formula (XVI)

(In the formula, p is an integer of 2 to 3, R _f9 represents 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. Good.)
Examples of the fluorine-containing compound represented by the formula (1) include, but are not limited to these examples. Note that none of the above-mentioned fluorocarbon compounds are subject to important new usage rules (SNUR) and can be used.

Specific examples of the fluorine-containing compound represented by the above formula (XIII) include compounds such as (C ₄ F ₉ SO ₂ ) ₂ NH and (C ₃ F ₇ SO ₂ ) ₂ NH.

Specific examples of the fluorocarbon compound represented by the above formula (XIV) include compounds such as C ₁₀ F ₂₁ COOH.

  Specific examples of the fluorine-containing compound represented by the above formula (XV) include compounds represented by the following formula (XV-a).

  Specific examples of the fluorine-containing compound represented by the above formula (XVI) include compounds represented by the following formula (XVI-a).

  When the acidic substance is blended, the blending amount is preferably about 0.1 to 10% by mass with respect to the blending amount of the alkali-soluble polymer.

  The material for forming a photoresist protective film of the present invention may further contain a crosslinking agent.

  As the crosslinking agent, a nitrogen-containing compound having an amino group and / or an imino group in which at least two hydrogen atoms are substituted with a hydroxyalkyl group and / or an alkoxyalkyl group is preferably used. Examples of these nitrogen-containing compounds include melamine derivatives, urea derivatives, guanamine derivatives, acetoguanamine derivatives, benzoguanamine derivatives, wherein a hydrogen atom of an amino group is substituted with a methylol group or an alkoxymethyl group or both, Examples include succinylamide derivatives, glycoluril derivatives in which a hydrogen atom of an imino group is substituted, and ethylene urea derivatives.

  These nitrogen-containing compounds include, for example, melamine derivatives, urea derivatives, guanamine derivatives, acetoguanamine derivatives, benzoguanamine derivatives, succinylamide derivatives, glycoluril derivatives, ethylene urea derivatives, etc. in boiling water. It can be obtained by reacting with formalin to methylol, or further by reacting with lower alcohol, specifically methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, etc. be able to.

  More preferably, tetrabutoxymethylated glycoluril is used as the cross-linking agent.

  Furthermore, 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 crosslinking agent. As the monohydroxy monocarboxylic 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.

  When the crosslinking agent is blended, the blending amount is preferably about 0.5 to 10% by mass with respect to the blending amount of the alkali-soluble polymer.

  The protective film-forming material of the present invention may further contain an optional surfactant as desired. Examples of the surfactant include “XR-104” (trade name, manufactured by Dainippon Ink & Chemicals, Inc.), but are not limited thereto. By blending such a surfactant, the coating properties and the ability to suppress the eluate can be further improved.

  When the surfactant is blended, the blending amount is preferably about 0.001 to 10% by mass with respect to the blending amount of the alkali-soluble polymer.

  Production of the material for forming a protective film of the present invention can be carried out by a conventional method.

  The protective film-forming material of the present invention is particularly suitable for use in an immersion exposure process. In the immersion exposure process, the refractive index of the photoresist film provided on the substrate is larger than the refractive index of air and smaller than the refractive index of the photoresist film on at least the photoresist film in the path through which the exposure light reaches the photoresist film. A method of improving the resolution of a photoresist pattern by exposing a photoresist film in a state where a liquid having a predetermined thickness (liquid for immersion exposure) is interposed.

  As the liquid for immersion exposure, water (pure water, deionized water, etc.), a fluorinated solvent, or the like is preferably used. Among these, water is regarded as the most preferable material from the viewpoints of optical requirements for immersion exposure (eg, good refractive index characteristics), ease of handling, and lack of environmental pollution.

The material for forming a protective film according to the present invention can be directly formed on a photoresist film and does not hinder pattern exposure. Since it is insoluble in water, water is used as a liquid for immersion exposure, and photoresist films of various compositions are sufficiently protected during the immersion exposure process to obtain a photoresist pattern with good characteristics. Can do. On the other hand, when exposure light having a wavelength of 157 nm (F ₂ excimer laser or the like) is used, a fluorine-based medium is regarded as a promising liquid for immersion exposure because it reduces absorption of exposure light into the liquid for immersion exposure. However, even when such a fluorinated solvent is used, as in the case of the above-described water, the photoresist film is sufficiently protected while being subjected to the immersion exposure process, and a photoresist pattern with good characteristics can be formed. Obtainable.

  Furthermore, since the protective film-forming material of the present invention is alkali-soluble, it is not necessary to provide a step of removing the protective film from the photoresist film before the development process even when the exposure is completed and the alkali development process is performed. That is, since the development treatment of the photoresist film with an alkaline developer can be performed while leaving the protective film, the removal of the protective film and the development of the photoresist film (removal of unnecessary photoresist film) can be realized simultaneously. Therefore, according to the present invention, it is possible to efficiently form a photoresist pattern having good pattern characteristics with extremely low environmental pollution and a reduced number of steps.

  The photoresist pattern forming method by the immersion exposure method using the photoresist protective film forming material of the present invention is performed as follows, for example.

  First, a conventional photoresist composition is applied onto a substrate such as a silicon wafer with a spinner or the like and then pre-baked (PAB treatment) to form a photoresist film. Note that a photoresist film may be formed after an organic or inorganic antireflection film (lower antireflection film) is provided on the substrate.

  The photoresist composition is not particularly limited, and any photoresist that can be developed with an alkaline aqueous solution, including negative and positive photoresists, can be used. Such photoresists include (i) a positive photoresist containing a naphthoquinonediazide compound and a novolak resin, (ii) a compound that generates an acid upon exposure, a compound that decomposes by acid and increases its solubility in an aqueous alkali solution, and an alkali-soluble compound. A positive photoresist containing a resin, (iii) a compound that generates an acid upon exposure, a positive photoresist containing an alkali-soluble resin having a group that decomposes with acid and increases solubility in an alkaline aqueous solution, and (iv) by light Examples include, but are not limited to, a negative photoresist containing a compound that generates an acid or radical, a crosslinking agent, and an alkali-soluble resin.

  Next, the protective film-forming material according to the present invention is uniformly applied to the surface of the photoresist film, and then cured by heating or the like, thereby forming a protective film.

  Next, an immersion exposure liquid is disposed on the substrate on which the photoresist film and the protective film are laminated. The photoresist film on the substrate in this state is selectively exposed through a mask pattern.

  Here, in the local immersion exposure method, the substrate on which the photoresist film and the protective film are laminated is placed on a wafer stage. Next, the photoresist layer is selectively exposed through the protective film while the exposure lens is moved at high speed while the immersion exposure liquid is continuously dropped from the nozzle onto the protective film. The protective film / photoresist film on the substrate in the continuous dropping state is selectively exposed through a mask pattern.

  Therefore, the exposure light passes through the immersion exposure liquid and the protective film and reaches the photoresist film.

  At this time, the photoresist film is shielded from the immersion exposure liquid by the protective film, and is subject to alteration such as swelling due to the invasion of the immersion exposure liquid, or conversely, the components in the immersion exposure liquid It is possible to prevent optical properties such as the refractive index of the immersion exposure liquid itself from being altered by elution.

The exposure light is not particularly limited and can be performed using radiation such as ArF excimer laser, KrF excimer laser, F ₂ excimer laser, EB, EUV, VUV (vacuum ultraviolet).

The immersion exposure liquid is not particularly limited as long as it is a liquid having a refractive index larger than that of air and smaller than that of the photoresist film to be used. Examples of such immersion exposure liquids include water (pure water, deionized water), fluorine-based inert liquids, etc., but immersion exposure liquids having high refractive index characteristics that are expected to be developed in the near future. Can also be used. 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. Among these, from the viewpoint of cost, safety, environmental problems and versatility, it is preferable to use water (pure water, deionized water), but exposure light having a wavelength of 157 nm (for example, F ₂ excimer laser) is used. When used, it is preferable to use a fluorinated solvent from the viewpoint of low exposure light absorption.

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

  Next, PEB (post-exposure heating) is performed on the photoresist film while the protective film is laminated on the exposed photoresist film, and then development processing is performed using an alkaline developer composed of an alkaline aqueous solution. Any conventional alkali developer can be used. By this alkali development, the protective film is dissolved and removed simultaneously with the soluble portion of the photoresist film. In addition, you may post-bake following a development process. Subsequently, rinsing is performed using pure water or the like. In this water rinse, 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 and the protective film component and the photoresist composition dissolved by the developer. Then, by performing drying, a photoresist pattern in which the photoresist film is patterned into a shape corresponding to the mask pattern is obtained. As described above, in the present invention, the removal of the protective film and the development of the photoresist film are realized simultaneously by the development process. In addition, since the protective film formed of the material for forming a protective film of the present invention has a good balance between the contact angle and the falling angle, the scan follow-up performance can be improved, and an excellent pattern profile can be formed. In addition to being excellent in water repellency, the immersion exposure liquid is well separated after the exposure is completed, the amount of the immersion exposure liquid is small, and so-called immersion exposure liquid leakage is reduced.

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

  According to the present invention, the scan followability of the immersion exposure liquid is excellent, the solubility in an alcohol solvent is excellent, and the basic characteristics required as a protective film are high resistance to the immersion exposure liquid. Low compatibility with the photoresist film provided in the lower layer, prevention of elution of components from the immersion exposure liquid to the photoresist film, prevention of elution of components from the photoresist film to the immersion exposure liquid, protection film gas A protective film forming material having properties such as permeation suppression was obtained.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

  In the following examples, the alkali-soluble polymer, the organic solvent, and the photoresist blended in the protective film-forming material mean the following compositions unless otherwise specified.

<Alkali-soluble polymer>
Polymer 1: Homopolymer (Mw = 5000) containing the monomer unit represented by the above formula (II) as a constituent unit [alkali-soluble polymer used in the present invention]
Polymer 2: Homopolymer (Mw = 5000) containing a monomer unit represented by the above formula (IV) as a constituent unit

<Organic solvent>
Solvent 1: 2-methyl-1-propanol (= isobutyl alcohol)

<Photoresist>
Photoresist 1: ArF positive photoresist (“TARF-P6111ME”; manufactured by Tokyo Ohka Kogyo Co., Ltd.)

1. Evaluation of physical properties of development-soluble protective film <Material for protective film formation>
The following samples were used. Sample 2 is a control sample.
Sample 1: Solution obtained by dissolving polymer 1 in solvent 1 (solid content concentration 2.8% by mass)
Sample 2: Solution in which polymer 2 is dissolved in solvent 1 (solid content concentration: 2.8% by mass)

Example 1
The following evaluation method evaluated the solubility with respect to the organic solvent of the alkali-soluble polymer used for this invention.
That is, when the solubility of the polymer 1 in the sample 1 was visually observed, the solubility of the polymer 1 in the solvent 1 was good.

(Example 2)
The water repellency and scan followability of Sample 1 and Sample 2 were evaluated by measuring the falling angle and contact angle.

<Falling angle>
After 50 μL of each solution was dropped on the substrate, the substrate was ramped up at a rate of 1 ′ tilt rate per second, and the tilt angle of the substrate at the point when the droplet on the substrate began to move (rolling down). Corner). The drop angle was measured using a drop angle meter “Drop Master 700” (manufactured by Kyowa Interface Science Co., Ltd.). As a result, the falling angle of Sample 1 was 18 °, and the falling angle of Sample 2 was 30 °.

<Contact angle>
2 μL of each solution was dropped on the substrate, and the contact angle between the droplet and the substrate was measured. As a result, the contact angle was 73 ° for both Sample 1 and Sample 2.

  From the above results, the solution 1 containing the polymer 1 is excellent in water repellency and scan followability compared to the polymer 2 (control polymer), and is suitable for the local immersion exposure process.

(Example 3)
The coatability of Sample 1 was evaluated as follows.
That is, after the sample 1 was spin-coated (1200 rpm) on the substrate, it was baked at 90 ° C. for 60 seconds to form a protective film, and the coating state on the protective film surface was visually observed. It was applied to.

Example 4
The presence or absence of water resistance of the protective film formed in Example 3 was evaluated by the following evaluation method.
That is, it was carried out by bringing pure water into contact with the protective film formed in Example 3 for 120 seconds and measuring the film thickness fluctuation before and after that. As a result, the protective film thickness before contact with pure water was 72.2 nm, the protective film thickness after contact with pure water was 72.7 nm, and there was almost no change.

(Example 5)
The presence or absence of solubility (development solubility) of the protective film formed in Example 3 in the developer was evaluated by the following evaluation method.
That is, the substrate having the protective film formed in Example 3 was brought into contact with an aqueous 2.38 mass% tetramethylammonium hydroxide (TMAH) solution for 60 seconds, and the solubility in an alkali developer was evaluated. The evaluation was performed by measuring the dissolution rate of the protective film by contact with an alkali developer. As a result, the protective film dissolution rate was 950 nm / sec.

  On the other hand, a protective film formed by the same method as that described in Example 3 was evaluated in the same manner as described above except that Sample 2 was used instead of Sample 1 in Example 3. As a result, the dissolution rate of the protective film was 500 nm / sec.

  From the above results, it was confirmed that the alkali-soluble polymer used in the present invention is excellent in solubility.

2. Resolution evaluation

2-1. Immersion exposure evaluation by two-bundle optical interference experiment <Photoresist>
The photoresist 1 (positive photoresist for ArF) was used.
<Material for protective film formation>
The following samples were used.
Sample 3: Solution in which polymer 1 is dissolved in solvent 1 (solid content concentration 2 mass%)

(Example 6)
An organic antireflective coating composition “ARC29” (manufactured by Brewer) is applied onto a silicon wafer using a spinner, baked on a hot plate at 225 ° C. for 60 seconds, and dried to prevent reflection of 77 nm in thickness. A film was formed. Then, the photoresist 1 was applied onto the antireflection film, prebaked on a hot plate at 130 ° C. for 90 seconds, and dried to form a photoresist film having a thickness of 150 nm on the antireflection film.

  The sample 3 was coated on the photoresist film and heated at 90 ° C. for 60 seconds to form a protective film having a thickness of 70 nm.

  Next, a two-beam interference experiment was performed using an immersion exposure experimental machine (“LEIES 193-1”; manufactured by Nikon Corporation). Pure water was used as the immersion exposure liquid. Thereafter, PEB treatment was performed at 130 ° C. for 90 seconds, followed by development treatment at 23 ° C. for 60 seconds using a 2.38 mass% TMAH aqueous solution. The protective film was completely removed by this development process, and the development of the photoresist film was also good.

  The 90 nm line and space pattern (1: 1) thus obtained was observed with a scanning electron microscope (SEM), and a line and space pattern with a good shape could be formed.

2-2. Pseudo immersion exposure evaluation using ArF dry exposure machine (= non-immersion exposure machine) <Photoresist>
The photoresist 1 (positive photoresist for ArF) was used.
<Material for protective film formation>
Sample 3 above was used.

(Example 7)
An organic antireflective coating composition “ARC29” (manufactured by Brewer) is applied onto a silicon wafer using a spinner, baked on a hot plate at 225 ° C. for 60 seconds, and dried to prevent reflection of 77 nm in thickness. A film was formed. Then, the photoresist 1 was applied on the antireflection film, prebaked on a hot plate at 130 ° C. for 90 seconds, and dried to form a photoresist film having a thickness of 225 nm on the antireflection film.

  The sample 3 was coated on the photoresist film and heated at 90 ° C. for 60 seconds to form a protective film having a thickness of 70 nm.

Next, exposure was performed at an exposure intensity of 24.5 mJ / cm ² using an ArF exposure machine (“NSR-S302A”; manufactured by Nikon Corporation). After the exposure, pure water was dropped for 1 minute and placed in a simulated immersion environment. Thereafter, PEB treatment was performed at 100 ° C. for 90 seconds, followed by development treatment at 23 ° C. for 60 seconds using a 2.38 mass% TMAH aqueous solution. The protective film was completely removed by this development step, and the development of the photoresist film was also good.

  The 130 nm line and space pattern (1: 1) thus obtained was observed with a scanning electron microscope (SEM), and a good shape line and space pattern could be formed.

Claims (9)

  A material for forming a protective film, which is laminated on a photoresist film on a substrate, comprising an alkali-soluble polymer containing a cyclic hydrocarbon having a fluorohydroxyalkyl group.   The protective film forming material according to claim 1, which is a protective film forming material used in an immersion exposure process. The protective film-forming material according to claim 1 or 2, wherein the alkali-soluble polymer contains at least a monomer unit represented by the following formula (I) as a constituent unit.

[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 part or all of the hydrogen atoms represented by fluorine atoms; Represents a linear, branched or cyclic fluoroalkyl group having 1 to 5 carbon atoms substituted with s, t, u and v each represent a number of 0 to 3; m represents a repeating unit . ] The material for forming a protective film according to claim 3, wherein the monomer unit represented by the formula (I) is a monomer unit represented by the following formula (II).

[In formula (II), m means a repeating unit. ]   Furthermore, the protective film formation material of any one of Claims 1-4 containing an acidic substance.   The material for forming a protective film according to claim 5, wherein the acidic substance is a fluorocarbon compound.   Furthermore, the protective film formation material of any one of Claims 1-6 containing a crosslinking agent.   The material for forming a protective film according to claim 7, wherein the crosslinking agent is a nitrogen-containing compound having an amino group and / or an imino group in which at least two hydrogen atoms are substituted with a hydroxyalkyl group and / or an alkoxyalkyl group. .   A photoresist pattern forming method using an immersion exposure process, wherein a photoresist film is provided on a substrate, and the protective film is formed on the photoresist film using the photoresist protective film forming material according to claim 1. After that, 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, and necessary. A method for forming a photoresist pattern, in which after the heat treatment is performed, the protective film and the photoresist film are developed using an alkali developer to remove the protective film and simultaneously obtain a photoresist pattern.