JP4275062B2 - Resist protective film forming material and resist pattern forming method using the same - Google Patents

Description

  The present invention relates to a resist protective film forming material suitable for forming a protective film for a resist film, and a resist pattern forming method using the same. In particular, the present invention relates to an immersion exposure (Liquid Immersion Lithography) process, 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. Is used in an immersion exposure process having a structure in which the resolution of the resist pattern is improved 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 suitable resist protective film forming material and a resist pattern forming method using the resist protective film forming material.

  Lithography is often 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 finer resist patterns 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 an expensive new exposure apparatus. Further, 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 is reduced even if the resolution is increased.

  Recently, as a lithography technique capable of solving such a problem, a method called an immersion exposure (liquid immersion lithography) method has been reported (see, for example, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3). . In this method, an immersion exposure liquid is interposed at least on 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 a polymer that is insoluble in water and soluble in alkali as a protective film for the upper layer of the resist has been attracting attention. There is a need for characteristics that can suppress the change in the refractive index caused by the deterioration of the resist film caused by the immersion exposure liquid and the deterioration of the immersion exposure liquid itself as much as possible.

Journal of Vacuum Science & Technology B (Journal of Vacuum Science Technology) (J. Vac. Sci. Technol. B) ((Issuing Country) USA), 1999, Vol. 17, No. 6, pages 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

  The present invention has been made in view of the problems of the prior art, and specifically, by altering the resist film during immersion exposure by forming a specific protective film on the surface of the conventional resist film. It is another object of the present invention to simultaneously prevent alteration of the liquid for immersion exposure and to enable formation of a high-resolution resist pattern using immersion exposure.

（式中、Ｒ₁は炭素数１〜５の直鎖若しくは分岐鎖のアルキレン基であり、Ｒ₂は、炭素数１〜１５の直鎖若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である。）
で表される構成単位を少なくとも有するアクリル系ポリマーと、溶剤と、を少なくとも含有することを特徴とする。 In order to solve the above-mentioned problems, a resist protective film forming material according to the present invention is a resist protective film forming material for forming an upper protective film of a resist film, and has the following general formula (1)

(In the formula, R ₁ is a linear or branched alkylene group having 1 to 5 carbon atoms, and R ₂ is a hydrocarbon having a linear or branched alkyl group having 1 to 15 carbon atoms or an alicyclic structure. Group.)
It contains at least an acrylic polymer having at least a structural unit represented by formula (I) and a solvent.

  The resist pattern forming method according to the present invention is a resist pattern forming method using an immersion exposure process, wherein a photoresist film is formed on a substrate, and the resist protective film is formed on the resist film. Using the material, a resist protective film having characteristics that are substantially incompatible with water and soluble in alkali is formed, and the resist film and the resist protective film are laminated. An immersion exposure liquid is disposed at least on the resist protective film, and the resist film is irradiated with a predetermined pattern light through the immersion exposure liquid and the resist protective film, and heat treatment is performed as necessary. The resist protective film and the resist film are washed with an alkaline developer to remove the resist protective film and develop the resist film at the same time. Characterized in that it comprises obtaining a down.

  In the above-described configuration, the immersion exposure process has a refractive index higher than that of air and lower than that of the resist film on at least the resist film in the path until the lithography exposure light reaches the resist film. A configuration in which the resolution of the resist pattern is improved by performing exposure while the liquid for immersion exposure having a predetermined thickness is interposed is preferable.

  Furthermore, in the present invention, when forming a resist protective film, an acidic component may be added, and the specific fluorine-containing compound described later is more preferable as the component. Furthermore, 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 may be added.

  The material for forming a resist protective film according to the present invention can be directly formed on the resist film, and does not hinder pattern exposure. Since the material for forming a resist protective film of the present invention is insoluble in water, “the most promising liquid for immersion exposure because there is no optical requirement for immersion exposure, ease of handling, and environmental pollution. It is possible to actually use the “water (pure water or deionized water)” that is being viewed as a liquid for immersion exposure. In other words, resist films of various compositions are used in the immersion exposure process even if water that is easy to handle, has good refractive index characteristics, and has no environmental pollution is used as the immersion exposure liquid for immersion exposure. In the meantime, it is possible to obtain a resist pattern with sufficient protection and good characteristics. In addition, when an exposure wavelength of 157 nm is used, a fluorine-based medium is regarded as dominant as the immersion exposure liquid in terms of absorption of exposure light, and even when such a fluorine-based solvent is used. As in the case of the water described above, the resist film is sufficiently protected while being subjected to the immersion exposure process, and a resist pattern having good characteristics can be obtained.

  Further, since the resist protective film forming material according to the present invention is soluble in alkali, the formed protective film is removed from the resist film before the development process even when the exposure is completed and the development process is performed. There is no need to do. That is, since the protective film obtained using the resist protective film forming material of the present invention is soluble in alkali, there is no need to provide a protective film removing step before the development step after exposure, and the resist film alkali. The development treatment with the 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 at the same time. 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.

  The greatest feature of the material for forming a resist protective film of the present invention is that it contains the structural unit represented by the general formula (1) as an essential component. In the protective film-forming material of the present invention, intramolecular or intermolecular bonds are formed by the hydroxyl groups in the structural unit represented by the general formula (1). This bonding improves the film density and suppresses the invasion of the resist film by the immersion exposure liquid.

  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 dense and can suppress the invasion of the resist film by the liquid for immersion exposure.

  As the resist film that can be used in the present invention, a general-purpose resist 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 characteristics as a resist protective film are that it is not compatible with water and is soluble in alkali, and is transparent to exposure light. No mixing occurs between them, the adhesiveness to the resist film is good, the solubility in the developer is good, and it is dense and can prevent the permeation of environmental amines. As a resist protective film forming material capable of forming a protective film having such characteristics, a composition obtained by dissolving an acrylic polymer having at least the structural unit represented by the general formula (1) in a solvent It is.

  The acrylic polymer used in the present invention may further have a (meth) acrylic acid structural unit represented by the following general formula (2). By having this structural unit, alkali solubility can be improved.

（式中、Ｒ₃は水素原子、メチル基、あるいは炭素数１〜５のヒドロキシアルキル基である。）

(In the formula, R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms.)

  In addition to the structural unit represented by the general formula (2), the acrylic polymer used in the present invention may further have a structural unit represented by the following general formula (3). By having this structural unit, the contact angle between the resist protective film and the immersion exposure liquid can be improved.

（式中、Ｒ₃は水素原子、メチル基、あるいは炭素数１〜５のヒドロキシアルキル基であり、Ｒ₄は少なくとも１以上の脂環構造を有する炭化水素基である。）

(In the formula, R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R ₄ is a hydrocarbon group having at least one alicyclic structure.)

  The structural unit represented by the general formula (3) is composed of two structural units of a structural unit represented by the following general formula (4) and a structural unit represented by the following general formula (5). preferable.

（式中、Ｒ₃は水素原子、メチル基、あるいは炭素数１〜５のヒドロキシアルキル基であり、Ｒ_4aは多環式炭化水素基である。）

(Wherein R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R _4a is a polycyclic hydrocarbon group.)

（式中、Ｒ₃は水素原子、メチル基、あるいは炭素数１〜５のヒドロキシアルキル基であり、Ｒ_4bは単環式炭化水素基である。）

(Wherein R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R _4b is a monocyclic hydrocarbon group.)

R _4a is at least one hydrocarbon group selected from a hydroxyl group-substituted or unsubstituted dicyclopentanyl group, adamantyl group, norbornyl group, isobornyl group, tricyclodecyl group, and tetracyclododecyl group. It is preferable.

R _4b is preferably at least one hydrocarbon group selected from a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group.

  In addition to the structural unit represented by the general formula (3), the acrylic polymer used in the present invention may further have a structural unit represented by the following general formula (6). By having this structural unit, the coating properties can be improved.

（式中、Ｒ₃は水素原子、メチル基、あるいは炭素数１〜５のヒドロキシアルキル基であり、Ｒ₅は炭素数１〜１０の置換もしくは非置換の分岐もしくは直鎖アルキル基である。）

(In the formula, R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R ₅ is a substituted or unsubstituted branched or straight chain alkyl group having 1 to 10 carbon atoms.)

R ₅ is preferably at least one group selected from an n-butyl group, an isobutyl group, an n-pentyl group, an n-hexyl group, and a 2-ethylhexyl group.

  More specifically, such an acrylic polymer is a polymer having a structural unit represented by the following general formula (7).

（式中、ｊ、ｋ、ｌa、lb、ｍは各構成単位の含有モル％を示すもので、それぞれ２〜６０モル％である。）

(In the formula, j, k, la, lb, and m represent the mol% content of each structural unit, and are 2 to 60 mol%, respectively.)

  Among the structural units represented by the general formula (7), the leftmost (meth) acrylic acid structural unit occupying k mol% is a unit that mainly improves alkali solubility of the acrylic polymer. Moreover, the structural unit which has the 2 types of central alicyclic structure which occupies la mol% and lb mol%, respectively is a unit which mainly improves a contact angle of this acrylic polymer. The rightmost constituent unit occupying m mol% is a unit that mainly improves the coating property of the acrylic polymer. In the present invention, k mol% of the alkali-soluble contributing component, l (la + lb) mol% of the contact angle contributing component, and m mol% of the coating property contributing component are appropriately controlled for use conditions. Thus obtained protective film material can be obtained.

  When the acrylic polymer used in the present invention is used as a copolymer composed of two or more kinds of structural units, if it is a binary system of the structural units represented by the general formulas (1) and (2), The content mol% of the structural units represented by the general formulas (1) and (2) may be 1 to 99 mol%, respectively.

  Further, in the case of a ternary or quaternary acrylic polymer to which the structural unit represented by the general formula (3) is added, the content mol% of the structural unit represented by the general formulas (1), (2) and (3) is Each is 2 to 60 mol%. In this case, even when two types of structural units represented by the general formulas (4) and (5) are used as the configuration of the general formula (3), the general formulas (1) and (2) in all acrylic polymers are used. , (4) and the content mol% of the structural unit shown in (5) is 2 to 60 mol%, respectively.

  Furthermore, in the case of a quaternary acrylic polymer to which the structural unit represented by the general formula (6) is added, the general formulas (1), (2), (3) (or the general formulas (4) and (5) )) And the content mol% of the structural unit represented by the general formula (6) is 2 to 60 mol%, respectively.

  Such an acrylic polymer can be synthesized by a known acrylic polymer polymerization method. Moreover, the polystyrene conversion mass mean molecular weight by GPC of resin of these polymer components is although it does not specifically limit, It shall be 3000-50000.

  As the solvent for dissolving the acrylic polymer, any solvent that can dissolve the acrylic polymer can be used. Examples of such solvents include alcohol solvents, paraffin solvents, and fluorine solvents. As the alcohol solvent, conventional alcohol solvents such as isopropyl alcohol, 1-hexanol, 2-methyl-1-propanol (isobutanol), 4-methyl-2-pentanol can be used, and in particular, 2-methyl -1-propanol and 4-methyl-2-pentanol are preferred. It has been confirmed that n-heptane can be used as a paraffin solvent and perfluoro-2-butyltetrahydrofuran can be used as a fluorine solvent. Of these, alcohol solvents are preferred from the viewpoint of alkali solubility during development.

  It is desirable to add an acidic component, particularly a fluorine-containing compound, to the resist protective film forming material of the present invention. Even if the resist film is left in an atmosphere containing a trace amount of amine after development after immersion exposure, the adverse effect of the amine can be suppressed by the intervention of the protective film. This is because the obtained resist pattern does not cause a large deviation in dimensions.

  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 (8)
_{(C n F 2n + 1 SO} 2) 2 NH ····· (8)
(In the formula, n is an integer of 1 to 5.)
A fluorocarbon compound represented by
The following general formula (9)
C _x F _{2x + 1} COOH (9)
(In the formula, x is an integer of 10 to 15.)
A fluorocarbon compound represented by
The following general formula (10)

（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（１１）

(In the formula, o is an integer of 2 to 3.)
A fluorocarbon compound represented by
The following general formula (11)

（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, and 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. Good.)
And a fluorine-containing compound represented by the formula:

Specifically, as the fluorine-containing compound represented by the general formula (8), the following chemical formula (12)
(C ₄ F ₉ SO ₂ ) ₂ NH (12)
Or a compound represented by the following chemical formula (13):
(C ₃ F ₇ SO ₂ ) ₂ NH (13)
The fluorine-containing compound represented by these is suitable.

Further, as the fluorine-containing compound represented by the general formula (9), specifically, the following chemical formula (14)
C ₁₀ F ₂₁ COOH (14)
The fluorine-containing compound represented by these is suitable.

  Further, as the fluorocarbon compound represented by the general formula (10), specifically, the following chemical formula (15)

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 fluorocarbon compound represented by the general formula (11) include the following chemical formula (16):

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 resist protective film-forming material of the present invention can 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 resist protective film forming material 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). Note that an organic or inorganic antireflection film may be provided between the substrate and the coating layer of the resist composition to form a two-layer laminate.

  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, a polymer having a structural unit represented by the chemical formula (7) (j: k: la: lb: m = 3: 51: 8: 6: 32 (mol%)) diluted with 2-methyl-1-propanol (isobutanol) was uniformly applied and then cured, and then the resist protective film was cured. Form.

  In this way, the substrate having the resist film covered with the resist protective film is formed into an immersion exposure liquid (a liquid having a refractive index larger than the refractive index of air and smaller than the refractive index of the resist film: pure water, desorption). Immersion in ionic water or fluorine-based solvent.

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

  At this time, the resist film is shielded from the immersion exposure liquid such as pure water by the resist protective film, so that the resist film may be affected by the invasion of the immersion exposure liquid and suffer from alteration such as swelling. It effectively suppresses optical properties such as refractive index of the immersion exposure liquid itself from being altered by eluting the components in the liquid for use (pure water, deionized water, fluorine-based solvent, etc.).

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 refraction is larger than the refractive index of air and smaller than the refractive index of the resist film to be used via the resist protective film on the resist film. An immersion exposure liquid having a rate is interposed. Examples of such immersion exposure liquid include water (pure water, deionized water), and 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. Among these, from the viewpoint of cost, safety, environmental problems and versatility, it is preferable to use water (pure water or deionized water). However, when exposure light having a wavelength of 157 nm is used, the 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”. However, in the present invention, it is considered that an immersion exposure liquid having a high refractive index characteristic that is expected to be developed in the near future can be used.

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

  Next, PEB (post-exposure heating) is performed on the resist film with a resist protective film on the exposed resist film, and then 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 resist 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. As described above, in the present invention, the removal of the resist protective film and the development of the resist film are realized simultaneously by the development process. The protective film formed of the resist protective film forming material of the present invention has improved water repellency, so that the immersion exposure liquid is well separated after the exposure is completed, and the immersion exposure liquid adheres. The amount is small, and so-called immersion exposure liquid leakage is reduced.

  By forming a 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 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. In addition, about the reagent etc. which were used except what was described especially, what was marketed generally was used.

(Examples 1-6)
The developer solubility of the protective film obtained from the resist protective film-forming material according to the present invention was measured.
The base polymer of the resist protective film forming material was synthesized by the following procedure.
Into a 2-liter four-necked flask equipped with a reflux condenser and a stirrer, 750 g of isobutyl alcohol was charged and nitrogen blowing was started. After heating up to 80 ° C. with stirring, a mixed liquid of 57 g of acrylic acid, 38 g of dicyclopentanyl methacrylate, 76 g of n-butyl acrylate, 19 g of cyclohexyl methacrylate, 10 g of ethyl (α-hydroxymethyl) acrylate, and isobutyl alcohol as a solvent A mixed solution consisting of 50 g and 1.7 g of benzoyl peroxide as a polymerization initiator was added dropwise from a separate dropping nozzle over 4 hours. The dropping was continuously performed, and the dropping speed of each component was constant throughout the dropping.

  After completion of dropping, the polymerization reaction solution was aged at 80 ° C. for 4 hours. Thereafter, the temperature of the polymerization reaction solution was increased until reflux of the solvent was observed, and the mixture was further aged for 1 hour to complete the polymerization. The polymer represented by the following chemical formula (7) (j: k: la: lb: m = 3) : 51: 8: 6: 32 (mol%)) solution was obtained.

  The resulting polymerization reaction solution had a solid content concentration of 20.3% and a weight average molecular weight (Mw) of 38,000 in terms of polystyrene.

  The obtained polymer was diluted with 2-methyl-1-propanol (isobutanol) to prepare a 2.5 wt% polymer solution, which was used as a resist protective film forming material. Note that the composition unit represented by the chemical formula (7) is the composition ratio described above as the resist protective film forming material of Example 1, and the composition ratio is (j: k: la: lb: m = 6: 45). : 9: 6: 34) was used as the resist protective film forming material of Example 2, and the composition ratio was (j: k: la: lb: m = 11: 43: 8: 5: 33) Was used as the resist protective film forming material of Example 3. Further, in the chemical formula (7), the ethyl group in the structural unit represented by the molar ratio j is a methyl group, and the composition ratio of Example 1 is used as the resist protective film forming material of Example 4, The composition ratio of Example 2 was used as the resist protective film forming material of Example 5, and the composition ratio of Example 3 was used as the resist protective film forming material of Example 6.

  Each of the resist protective film forming materials was applied on a semiconductor substrate using a spin coater under a coating condition of 1500 rpm. After application, the film was cured by heating at 90 ° C. for 60 seconds to obtain a protective film for evaluation. The film thickness was 170 nm.

  Next, the dissolution rate (film thickness conversion: nm / second) of the protective film was measured when immersed in an alkaline developer (2.38% concentration TMAH) at 23.5 ° C.

  As a result, as shown in Table 1 below, it was confirmed that all of the protective films obtained from the resist protective film forming materials of Examples 1 to 6 were in a range that was practically dissolved without problems.

  Next, the protective film obtained in the same manner as described above was rinsed with water for 120 seconds, and the film thickness before and after rinsing was measured to examine the resistance to water. As a result, as shown in Table 2 below, the film thickness hardly changed before and after rinsing, and resistance to water was confirmed.

(Examples 7 to 12)
The following resin component, acid generator, and nitrogen-containing organic compound were uniformly dissolved in an organic solvent to prepare a resist composition.
As the resin component, 100 parts by mass of a copolymer composed of structural units represented by the following chemical formula (8) was used. The ratio of each structural unit a, b, c used for the preparation of the resin component was a = 20 mol%, b = 40 mol%, and c = 40 mol%.

  As the acid generator, 2.0 parts by mass of triphenylsulfonium nonafluorobutanesulfonate and 0.8 parts by mass of tri (tertbutylphenyl) sulfonium trifluoromethanesulfonate were used.

  As the organic solvent, a 7.0% aqueous solution of a mixed solvent of propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate (mixing ratio 6: 4) was used. Further, 0.25 parts by mass of triethanolamine was used as the nitrogen-containing organic compound. Furthermore, 25 parts by mass of γ-butyrolactone was added as an additive.

  A resist pattern was formed using the resist composition produced as described above. First, an organic antireflection film composition “ARC29” (trade name, manufactured by Brewer) was applied onto a silicon wafer using a spinner, and baked on a hot plate at 205 ° C. for 60 seconds to dry. An organic antireflection film having a thickness of 77 nm was formed. Then, the resist composition is applied onto the antireflection film by using a spinner, prebaked on a hot plate at 130 ° C. for 90 seconds, and dried to thereby form a resist film having a thickness of 225 nm on the antireflection film. Formed.

  On the resist film, the acrylic polymer used in Example 1 was dissolved in 2-methyl-1-propanol to prepare a 2.5 wt% solution to prepare a resist protective film forming material. The protective film-forming material was spin-coated and heated at 90 ° C. for 60 seconds to form a protective film (Example 7) having a thickness of 70.0 nm. In Example 7, the acrylic polymer used in Example 2 was changed to Example 8, the acrylic polymer used in Example 3 was set as Example 9, and the Example was used. The acrylic polymer used in 4 was designated as Example 10. Also, the acrylic polymer used in Example 5 was designated as Example 11, and the acrylic polymer used in Example 6 was designated as Example 12.

  Next, pattern light was irradiated (exposed) using an ArF excimer laser (wavelength: 193 nm) with an exposure apparatus Nikon-S302A (manufactured by Nikon) through the mask pattern. Then, as immersion exposure processing, pure water was continuously dropped on the resist protective film for 2 minutes at 23 ° C. while rotating the silicon wafer provided with the resist film and the resist protective film after the exposure. This part of the process is an exposure process in a completely immersed state in the actual manufacturing process, but the resist film is exposed first, and only the influence of the liquid for immersion exposure on the resist film and the resist protective film is affected. Therefore, the resist film and the resist protective film are loaded with pure water which is a liquid for immersion exposure after exposure.

  After the pure water dropping step, PEB treatment was performed at 115 ° C. for 90 seconds. Next, the resist protective film was left and developed with an alkaline developer at 23 ° C. for 60 seconds. As the alkaline developer, an aqueous 2.38 mass% tetramethylammonium hydroxide solution was used. By this development step, the resist protective films of Examples 7 to 12 were completely removed, and the development of the resist film could be realized well.

  When the thus obtained resist pattern with a 130 nm line and space of 1: 1 was observed with a scanning electron microscope (SEM), this pattern profile was a good rectangular shape.

(Example 13)
A resist film was formed in the same manner as in Examples 7-12. 2.5 parts by mass of the acrylic polymer used in Example 1, 5 parts by mass of a crosslinking agent (tetrabutoxymethylated glycoluril), and 0.6 parts by mass of (CF ₂ ) ₃ (SO ₂ ) ₂ NH, A protective film material dissolved in 2-methyl-1-propyl alcohol and having a solid content mass concentration of 2.8% by mass is spin-coated and heated at 90 ° C. for 60 seconds to form a protective film having a thickness of 70.0 nm. Formed.

  Next, pattern light was irradiated (exposed) using an ArF excimer laser (wavelength: 193 nm) with an exposure apparatus Nikon-S302A (manufactured by Nikon) through the mask pattern. Then, as immersion exposure processing, pure water was continuously dropped on the resist film at 23 ° C. for 2 minutes while rotating the silicon wafer provided with the resist film and the resist protective film after the exposure.

  After the pure water dropping step, PEB treatment was performed at 115 ° C. for 90 seconds. After this PEB, development was performed with an alkaline developer at 23 ° C. for 60 seconds with the resist protective film remaining. As the alkaline developer, an aqueous 2.38 mass% tetramethylammonium hydroxide solution was used. By this development process, the protective film was completely removed, and the development of the resist film could be realized well. Further, when the thus obtained resist pattern with a 130 nm line and space of 1: 1 was observed with a scanning electron microscope (SEM), the pattern profile was a good rectangular shape.

(Example 14)
A resist film was formed in the same manner as in Examples 7-12. A 2.5% by mass isobutanol solution of the homopolymer consisting of the general formula (1) was prepared, and this was spin-coated on the substrate by the same method as described above, and heated at 90 ° C. for 60 seconds. A 70.0 nm resist protective film was formed.

  Next, pattern light was irradiated (exposed) using an ArF excimer laser (wavelength: 193 nm) with an exposure apparatus Nikon-S302A (manufactured by Nikon) through the mask pattern. Then, as immersion exposure processing, pure water was continuously dropped on the resist film at 23 ° C. for 2 minutes while rotating the silicon wafer provided with the exposed resist film and protective film.

  After the pure water dropping step, PEB treatment was performed at 115 ° C. for 90 seconds. After this PEB, development was performed with an alkaline developer at 23 ° C. for 60 seconds with the resist protective film remaining. As the alkaline developer, an aqueous 2.38 mass% tetramethylammonium hydroxide solution was used. The resist protective film was completely removed by this development process, and the development of the resist film could be realized well. Further, when the thus obtained resist pattern with a 130 nm line and space of 1: 1 was observed with a scanning electron microscope (SEM), the pattern profile was a good rectangular shape.

  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, the resist pattern has a T-top shape and the surface of the resist pattern is not rough, the sensitivity is high, the resist pattern profile shape is excellent, and the depth of focus and exposure margin are high. It is possible to obtain a highly accurate resist pattern having good stability over time. In addition, the film quality is dense, and it is possible to simultaneously prevent alteration of the resist film and immersion exposure liquid during immersion exposure using various immersion exposure liquids such as water, and the number of processing steps. Resisting resistance of the resist film can be improved without causing an increase. Therefore, when the resist protective film forming material of the present invention is used, a resist pattern can be efficiently formed using an immersion exposure process.

Claims (17)

A material for forming an upper protective film of a resist film,
The following general formula (1)

(Wherein R ₁ is a linear or branched alkylene group having 1 to 5 carbon atoms, and R ₂ is a hydrocarbon group having a linear or branched alkyl group having 1 to 15 carbon atoms or an alicyclic structure. .)
An acrylic polymer having at least a structural unit represented by:
Solvent,
A resist protective film-forming material comprising at least   The material for forming a resist protective film according to claim 1, wherein the resist film is a resist film subjected to an immersion exposure process. The acrylic polymer is further represented by the following general formula (2)

(In the formula, R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms.)
The material for forming a resist protective film according to claim 1, comprising a (meth) acrylic acid structural unit represented by: The acrylic polymer is further represented by the following general formula (3)

(In the formula, R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R ₄ is a hydrocarbon group having at least one alicyclic structure.)
The material for forming a resist protective film according to claim 3, comprising: a structural unit represented by: The structural unit represented by the general formula (3) is represented by the following general formula (4).

(Wherein R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R _4a is a polycyclic hydrocarbon group.)
And the following general formula (5)

(Wherein R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R _4b is a monocyclic hydrocarbon group.)
The resist protective film forming material according to claim 4, wherein the resist protective film forming material is composed of two types of structural units represented by: R _4a is at least one hydrocarbon group selected from a hydroxyl group-substituted or unsubstituted dicyclopentanyl group, adamantyl group, norbornyl group, isobornyl group, tricyclodecyl group, and tetracyclododecyl group. The material for forming a resist protective film according to claim 5. 6. The resist protective film forming material according to claim 5, wherein R _4b is at least one hydrocarbon group selected from a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. The acrylic polymer is further represented by the following general formula (6)

(In the formula, R ₃ is a hydrogen atom, a methyl group, or a hydroxyalkyl group having 1 to 5 carbon atoms, and R ₅ is a substituted or unsubstituted branched or straight chain alkyl group having 1 to 10 carbon atoms.)
The material for forming a resist protective film according to claim 4, comprising a structural unit represented by: 9. The R ₅ is at least one group selected from n-butyl group, isobutyl group, n-pentyl group, n-hexyl group, and 2-ethylhexyl group. Resist protective film forming material.   The resist protective film forming material according to claim 1, wherein the solvent is an alcohol solvent.   Furthermore, the acidic protective component is contained, The resist protective film forming material of any one of Claims 1-10 characterized by the above-mentioned.   The material for forming a resist protective film according to claim 11, wherein the acidic component is a fluorocarbon compound.   Furthermore, the crosslinking agent which consists of a nitrogen-containing compound which has an amino group and / or imino group substituted by the hydroxyalkyl group and / or the alkoxyalkyl group is contained in any one of Claims 1-12 characterized by the above-mentioned. The material for forming a resist protective film as described.   14. The resist protective film forming material according to claim 13, wherein the cross-linking agent is at least one selected from melamine derivatives, guanamine derivatives, glycoluril derivatives, succinylamide derivatives, and urea derivatives. .   The immersion exposure process includes immersion exposure with a predetermined thickness that has a refractive index greater than air and a refractive index smaller than that of the resist film on at least the resist film in a path until the lithography exposure light reaches the resist film. The resist protective film forming material according to claim 2, wherein the resist film resolution is improved by exposing the resist film in a state in which a working liquid is interposed.   16. The resist protective film forming material according to claim 2, wherein the immersion exposure liquid is water substantially composed of pure water or deionized water, or a fluorine-based solvent. A resist pattern forming method using an immersion exposure process,
A resist film is formed on the substrate,
On the resist film, using the resist protective film forming material according to any one of claims 1 to 16, a protective film is formed,
The immersion exposure liquid having a predetermined thickness is directly disposed on at least the protective film of the substrate on which the resist film and the protective film are laminated,
The resist film is selectively irradiated with light through the immersion exposure liquid and the protective film, and heat treatment is performed as necessary.
A method for forming a resist pattern, comprising: removing the protective film by developing the protective film and the resist film using an alkali developer, and simultaneously obtaining a resist pattern.