JP2006323002A - Material for forming photoresist protective film for liquid immersion exposure process, and photoresist pattern forming method using the material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material for forming a protective film which is suitably used in a liquid immersion exposure process, especially in a local liquid immersion exposure process, in which only a space between an exposure lens and a substrate with the protective film formed on a photoresist layer is filled with an immersion exposure liquid, and is formed on a photoresist film, which can be widely used for a commercially available photoresist and has general-purpose applicability, and which is provided with the basic characteristics required for the protective film used in the liquid immersion exposure process, and to provide a photoresist pattern forming method that uses the material. <P>SOLUTION: The material, for forming the photoresist protective film for the liquid immersion exposure process, is a material used in the liquid immersion exposure process and in forming the protective film to be laminated on the photoresist film on the substrate, and contains a cyclic perfluoroalkyl polyether and a fluorine-based organic solvent. The photoresist pattern forming method uses the material for forming the photoresist protective film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoresist protective film forming material applied to a liquid immersion lithography process and a photoresist pattern forming method using the same. In particular, the present invention is suitably applied to a local exposure liquid immersion process in which only a space between a lens of an exposure apparatus and a substrate having a protective film formed on a photoresist layer is filled with an immersion exposure liquid.

  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, but further research and development of finer pattern formation with a line width of 65 nm has been made. Has been done.

In order to achieve such a finer pattern formation, generally, countermeasures using an exposure apparatus or a photoresist material can be considered. Measures 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. As a countermeasure using a photoresist material, there is a strategy of developing a new material corresponding to a shorter wavelength of exposure light.

  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, so that there is a problem that the depth of focus decreases even if the resolution is increased. In addition, the development of a new photoresist material corresponding to the shortening of the wavelength requires a lot of costs.

  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. In addition, currently used photoresist materials can be used.

  By using such an immersion exposure process, a photoresist pattern of a lens that is mounted on an existing exposure apparatus, an exposure light wavelength, a low-cost, higher resolution, and excellent depth of focus. Because it can be formed, it has attracted much attention.

  However, in the immersion exposure process, since exposure is performed with an immersion exposure liquid interposed between the exposure lens and the photoresist film, it is natural that the photoresist film is altered by the immersion exposure liquid. Further, there is a concern that the refractive index changes due to the alteration of the immersion exposure liquid itself due to the components eluted from the photoresist film.

  Therefore, in order to cope with this, a protective film is formed on the photoresist film, and an immersion exposure liquid is interposed on the protective film, whereby the immersion exposure liquid is transformed into a photoresist film, and the immersion exposure liquid is used. There has been proposed a technique aimed at simultaneously preventing refractive index fluctuations accompanying alteration of itself (see, for example, Patent Document 1).

  The above-mentioned patent document 1 is a technique proposed by the present applicant and protects a protective film using a fluorine-containing resin, specifically, a mixed resin of a cyclic perfluoroalkyl polyether and a chain perfluoroalkyl polyether. A film was formed, and it was confirmed that this protective film produced a photoresist profile with a good profile having a rectangular cross-sectional shape in immersion exposure.

"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

  The protective film described in Patent Document 1 is based on immersion exposure in a state where a substrate on which a protective film is formed on a photoresist film is completely immersed in a liquid for immersion exposure, or by a simple method using a prism. The evaluation was performed by immersion exposure, and in the evaluation of such an immersion exposure process, the effect could be sufficiently exhibited. However, in an actual mass production process, a local immersion exposure method in which only the space between the exposure lens that scans at a predetermined speed or more and the substrate is filled with the immersion exposure liquid has been adopted.

  In the local immersion exposure method, 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 at a predetermined interval, and the wafer stage is scanned at high speed. While moving, the liquid for immersion exposure is continuously dropped onto the protective film from one nozzle, and at the same time, the liquid is exposed while being sucked from the other nozzle.

  In such a local liquid immersion exposure method, unlike the conventional evaluation methods, water that continues to be dripped becomes minute water droplets and remains on the surface of the protective film. This water droplet has a very small diameter of the order of several μm or less. As the water droplet diameter decreases, the water droplet internal pressure increases exponentially, and the water pressure applied to the protective film becomes larger than the order that has been regarded as a problem in the conventional evaluation methods.

  If there is a portion where the surface of the protective film in which microdroplets with extremely high internal pressure remain in this way is uneven, there may be problems such as causing the droplets to penetrate into the protective film through this portion.

  According to the studies by the present inventors, it has been found that a liquid may permeate into the protective film to cause a pattern defect (“water mark defect”) when forming a photoresist pattern. In Patent Document 1, an ordinary evaluation method such as liquid immersion is used, and such a liquid immersion exposure method can provide a photoresist pattern with a good profile and has an excellent effect. However, in actual mass production, The above-mentioned point in local immersion exposure using a lens that scans at a predetermined speed or higher has not been studied.

  The present invention solves the above-mentioned new problems, particularly suppresses the occurrence of photoresist pattern defects ("water mark defects") due to local immersion, and is widely applicable to commercially available photoresists. An object of the present invention is to provide a protective film forming material having excellent properties and having basic characteristics required for a protective film used in an immersion exposure process, and a photoresist pattern forming method using the same.

  In order to solve the above-described problems, the present invention solves the above-mentioned problem by further uniformizing the surface of the protective film and reducing the contact angle between the water droplet and the protective film in the local immersion exposure. The knowledge that it can be solved was obtained, thereby completing the present invention.

  That is, the present invention is a material for forming a protective film that is used in an immersion exposure process and is laminated on a photoresist film on a substrate, and includes a cyclic perfluoroalkyl polyether and a fluorine-based organic solvent. A material for forming a photoresist protective film for an immersion exposure process 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 the photoresist film is selectively exposed by an exposure apparatus through the immersion exposure liquid and the protective film, and heated as necessary. Provided is a method for forming a photoresist pattern in which a protective film is removed from a photoresist film after the treatment, and then the photoresist film is developed to obtain a photoresist pattern.

  The material for forming the protective film and the method for forming the photoresist pattern include a method in which the immersion exposure process fills only a space between the lens of the exposure apparatus and the substrate on which the protective film is formed on the photoresist layer with the liquid for immersion exposure. An immersion exposure process is preferred.

  According to the present invention, the surface of the protective film can be made more uniform, and the contact angle between the minute water droplets and the protective film can be reduced, which is particularly generated in the local liquid immersion exposure process. It is possible to suppress the occurrence of easy photoresist pattern defects (“water mark defects”).

  In addition, the present invention is widely applicable to photoresists currently on the market and is versatile. In addition to this, it is a basic characteristic required as a protective film, which is highly resistant to liquid for immersion exposure, and is a lower layer. Low compatibility with the photoresist film provided on the substrate, prevention of elution of components from the liquid for immersion exposure to the photoresist film, prevention of elution of components from the photoresist film to the liquid for immersion exposure, gas permeation of the protective film A material for forming a protective film having characteristics such as deterrence is provided. 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 a cyclic perfluoroalkyl polyether and a fluorinated organic solvent. In the present invention, no chain perfluoroalkyl polyether is contained.

  As the cyclic perfluoroalkyl polyether, a polymer represented by the following formula (I) is preferably used.

In the above formula (I), Rf ₁ is a fluorine atom, a C 1-5 perfluoroalkyl group or a perfluoroalkyl ether group, and Rf ₂ may or may not be present. The case (which may be present in plural) is a C 1-5 perfluoroalkyl group or a perfluoroalkyl ether group, and X is —O— or — (CF ₂ ) _q — (where q is 0 or 1). Y represents —O— or — (CF ₂ ) _v — (where v represents a number of 1 or more), and Z represents — (O) _s — (where s is 0 or 1). P, t, and u each represent a number from 0 to 3, and m represents a repeating unit.

  Among these, polymers having structural units represented by the following formulas (II) and (III) are preferable.

  In formula (II), p, t, and u each represent a number of 0 to 3, r represents a number of 1 to 3, and m represents a repeating unit.

  A polymer having a structural unit represented by the formula (II) is commercially available as the “Cytop” series (manufactured by Asahi Glass Co., Ltd.) and can be suitably used.

In the formula (III), Rf ₁ is a fluorine atom, a C 1-5 perfluoroalkyl group or a perfluoroalkyl ether group, and Rf ₂ may or may not be present. (Plural may exist) is a C1-C5 perfluoroalkyl group or a perfluoroalkyl ether group, t shows the number of 0-3, and m means a repeating unit.

  Polymers having a structural unit represented by the formula (III) are commercially available as “Teflon AF1600”, “Teflon AF2400” (all of which are manufactured by DuPont) and can be suitably used.

  Any fluorine-based organic solvent may be used as long as it can dissolve the cyclic perfluoroalkyl polyether used in the present invention. Specifically, perfluoroalkanes or perfluorocycloalkanes such as perfluorohexane and perfluoroheptane, perfluoroalkenes in which some of the double bonds remain, perfluorotetrahydrofuran, perfluoro (2-butyl) And fluorinated organic solvents such as perfluoro cyclic ethers such as tetrahydrofuran), perfluorotributylamine, perfluorotetrapentylamine, and perfluorotetrahexylamine. These may be used singly or in combination of two or more. Further, other organic solvents having compatibility and surfactants may be added as additives to improve the solubility.

  When the above polymer is dissolved in the fluorine-based organic solvent, it is preferable to dissolve the polymer so that its concentration is about 0.1 to 30% by mass, particularly 0.5 to 10% by mass, from the viewpoint of applicability and the like. .

  Furthermore, in the present invention, it is preferable to use only one kind of polymer as the cyclic perfluoroalkyl polyether. Thus, if the protective film using a single kind of cyclic perfluoroalkyl polyether, the surface of the protective film becomes more uniform, and the penetration of droplets into the protective film can be more effectively suppressed, As a result, water mark defects occurring in the photoresist pattern can be more effectively suppressed.

  In the protective film-forming material in which the cyclic perfluoroalkyl polyether is dissolved in a fluorine-based organic solvent, various additives such as preservatives, stabilizers, surfactants and the like are added as long as the effects of the present invention are not impaired. An agent may be blended.

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

  The material for forming a protective film of the present invention is used for an immersion exposure process, and is particularly preferably used for local immersion exposure. 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. In addition, it is insoluble in water, so that water can be used as a liquid for immersion exposure, and photoresist films of various compositions can be sufficiently protected and subjected to an 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 leading 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 is formed. Obtainable.

  The immersion exposure method using the photoresist protective film forming material of the present invention, particularly the photoresist pattern formation method by the local immersion exposure method, 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 naphthoquinone diazide compound and a novolak resin, (ii) a compound that generates an acid upon exposure, a compound that decomposes with an 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 thereof include, but are not limited to, a negative photoresist containing a compound that generates an acid or a 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.

  The substrate on which the photoresist film and the protective film are laminated is placed on the local immersion exposure wafer stage.

  An exposure apparatus (lens) is arranged above the protective film with a predetermined distance from the protective film.

  Next, the photoresist layer is selectively exposed through the protective film while the wafer stage is moved at high speed while the immersion exposure liquid is continuously dropped from the nozzle onto the protective film.

  In this local immersion exposure, the immersion exposure liquid is dropped on the protective film and moves at a predetermined speed or higher, so that very fine water droplets are scattered on the surface of the protective film.

  In the present invention, since the cyclic perfluoroalkyl polyether is used alone as the protective film, the surface of the protective film is more uniform (such as the uniformity of water repellency) than in the case of a mixed resin with a chain perfluoroalkyl polyether. In addition, the contact angle between the protective film and the droplets could be reduced.

  This will be described below.

  As shown in the following formula 1, it is known that the stress (difference between the internal pressure and the external pressure) applied to the fine droplet is proportional to the surface tension of the droplet and inversely proportional to the sphere radius.

(P _i −P _o ) = 2γ / r (Formula 1)

[In Equation 1, P _i represents the internal pressure (unit: Pa) of the droplet, P _o represents the external pressure (unit: Pa) of the droplet, and γ represents the surface tension of the droplet (unit: N / m ² ). R represents the sphere radius (unit: m) of the droplet. ]

Since the surface tension of water is constant at room temperature, it can be seen that the internal pressure (P _i ) of the droplet increases in inverse proportion to the sphere radius (r).

Further, the sphere radius (r) of the droplet is determined by the liquid volume of the droplet and the contact angle with the material (protective film) in contact with the liquid. As a result, the internal pressure (P _i ) of the droplet increases. Therefore, in order to reduce the internal pressure, it is required to reduce the contact angle.

  In addition to the above, if there is a non-uniform surface (non-uniform water repellency, etc.) on the surface of the protective film where the liquid droplets drop and come into contact, it is possible that the liquid droplets penetrate into the protective film through this region. Further, the uniformity of the film quality of the protective film is required.

  By forming the protective film using the protective film-forming material of the present invention, the above-mentioned problems could be solved, as confirmed in the examples described later.

  Next, the protective film / photoresist film on the substrate in the continuous dropping state is selectively exposed through a mask pattern. Therefore, at this time, 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. Further, since the protective film maintains the uniformity as described above and has a low contact angle, the dropped microdroplet does not infiltrate inward from the upper surface of the protective film or the interface with the photoresist on the peripheral edge.

  The exposure light is not particularly limited, and can be performed using radiation that is widely used in the current photolithographic field, such as ArF excimer laser, KrF excimer laser, and 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 immersion exposure process by dripping is completed, the substrate is taken out of the exposure stage, the liquid is removed from the substrate, and then the protective film is peeled off. For removing the protective film, a fluorine-based solvent that dissolves the cyclic perfluoroalkyl polyether can be used as it is. However, from the viewpoint of drying properties after washing, it is preferable to use a solvent having a boiling point of about 150 ° C. or less, and from this viewpoint, perfluoro (2-butyltetrahydrofuran) (boiling point: 102 ° C.) is preferable.

  Next, PEB (post-exposure heating) is performed on the exposed photoresist film, followed by development using an alkali developer. As the alkali developer, a conventional one can be arbitrarily used. For example, an aqueous solution of tetramethylammonium hydroxide (TMAH) is preferably used, but is not limited thereto. Post-baking may be performed following the 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 photoresist composition dissolved by the developer. Then, by 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, since the protective film is uniform and the contact angle can be reduced, the liquid for immersion exposure does not penetrate into the protective film even in the local exposure liquid immersion, and the water mark defect Occurrence and pattern defects derived therefrom can be prevented in advance. The protective film formed from the protective film forming material of the present invention is excellent in water repellency, so that the liquid for immersion exposure after the completion of the exposure is well separated and the amount of adhesion of the liquid for liquid immersion exposure 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, it can be widely applied to photoresists currently on the market (especially photoresists for ArF), has excellent versatility, has excellent solubility in alcohol solvents, etc., and has basic characteristics required as a protective film. High resistance to immersion exposure liquid, low compatibility with the underlying photoresist film, prevention of elution of components from immersion exposure liquid to photoresist film, immersion photoresist to immersion exposure liquid Thus, a protective film forming material having characteristics such as prevention of elution of components into the protective layer and suppression of permeation of gas through the protective film was obtained.

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

Example 1
A positive photoresist composition “TARF-P6111” (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied on a silicon wafer by a spinner method, and dried on a hot plate at 130 ° C. for 90 seconds to give a film thickness of 200 nm. A photoresist layer was formed.

  On the photoresist layer, “Cytop CTX-809SP2” (manufactured by Asahi Glass Co., Ltd.) was dissolved in perfluorotributylamine, and a protective film material having a concentration of 1% by mass was applied by a spinner method, and then at 90 ° C. Soft baking was performed for 60 seconds to form a protective film having a thickness of 33 nm.

  Next, droplets (pure water, droplet size 1.9 μL) were dropped on the protective film and air-dried. At this time, the contact angle between the protective film and the droplet (that is, the angle formed between the upper surface / horizontal line of the protective film and the tangent line at the edge of the droplet) was measured over time and graphed. The results are shown in FIG. Further, FIG. 2 shows a photomicrograph (photo taken from above) showing the time-dependent change of the air-dried droplets. In the figure, the descriptions of 0 s, 500 s, and 1000 s indicate elapsed time 0 seconds (= immediately after dropping), 500 seconds, and 1000 seconds after dropping the droplets, respectively. A white broken line in the figure indicates a dropping center line.

(Comparative Example 1)
A positive photoresist composition “TARF-P6111” (manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied onto a silicon wafer by a spinner method, prebaked on a hot plate at 130 ° C. for 90 seconds, and dried to obtain a film thickness. A 200 nm photoresist layer was formed.

  On the photoresist layer, a mixed resin composed of “DEMNUM S-20” (manufactured by Daikin Co., Ltd.) and “CYTOP CTX-809SP2” (mixing mass ratio = 1: 5) was dissolved in perfluorotributylamine to obtain a concentration. After applying a protective film material of 1.2 mass% by spinner method, soft baking was performed at 90 ° C. for 60 seconds to form a protective film having a thickness of 33 nm.

  Next, droplets (pure water, droplet size 1.9 μL) were dropped on the protective film and air-dried. At this time, the contact angle between the protective film and the droplet (that is, the angle formed between the upper surface / horizontal line of the protective film and the tangent line at the edge of the droplet) was measured over time and graphed. The results are shown in FIG. FIG. 4 shows a photomicrograph (taken from above) showing the time-dependent change of the air-dried droplets. In the figure, the descriptions of 0 s, 500 s, and 1000 s indicate elapsed time 0 seconds (= immediately after dropping), 500 seconds, and 1000 seconds after dropping the droplets, respectively. A white broken line in the figure indicates a dropping center line.

<Evaluation>
As apparent from the comparison between FIG. 1 and FIG. 3, the protective film of FIG. 1 (Example 1) has an initial contact angle of 114.7 °, whereas the protective film of FIG. 3 (Comparative Example 1) The initial contact angle was 118.0 °. That is, by using the protective film-forming material of the present invention, the initial contact angle can be reduced by 3.3 °, the assumed radius of the same volume droplet can be increased, and the internal pressure of the droplet can be reduced. As a result, it seems that the droplets are less likely to penetrate into the protective film.

  In FIG. 3, the measurement after 1000 seconds could not be performed. This is considered to be impossible to measure because the center of the droplet is shifted as shown in FIG. 4 (described later).

  In addition, when the time required for drying and disappearing from the time when the initial droplet size became 1.8 μL was measured, it took 1482 seconds under the conditions using the protective film of Example 1, When the protective film of Comparative Example 1 is used, the time is 1252 seconds, and the time required for drying the droplets is longer when the protective film of Example 1 is used, that is, the speed of the liquid soaking into the protective film is higher. Lately, the water mark risk appears to have decreased.

  Further, as is clear from the comparison between FIG. 2 and FIG. 4, in FIG. 2 (Example 1), the dropped liquid droplet hardly shows a deviation from the center line with time, whereas FIG. In Example 1), the dripped droplet already had a considerable deviation from the center line (shift to the left in the figure) after 500 seconds, and after 1000 seconds, the contact angle as described above. The shift to the left was so great that no measurement was possible. This is considered because the surface of the protective film of Comparative Example 1 lacks uniformity. That is, it was proved that the protective film used in Example 1 had higher surface uniformity than the protective film used in Comparative Example 1.

(Example 2)
An organic antireflection film composition “ARC-29A” (manufactured by Nissan Chemical Industries, Ltd.) is applied onto a silicon wafer by a spinner method, and baked on a hot plate at 210 ° C. for 60 seconds to dry. An organic liquid antireflection film having a thickness of 77 nm was formed. On this antireflection film, a positive photoresist composition “TARF-P6111” (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied by a spinner method, prebaked on a hot plate at 130 ° C. for 90 seconds, and dried. Thus, a 200 nm thick photoresist layer was formed on the antireflection film.

  On the photoresist layer, “Cytop CTX-809SP2” (manufactured by Asahi Glass Co., Ltd.) was dissolved in perfluorotributylamine, and a protective film material having a concentration of 1% by mass was applied by a spinner method, and then at 90 ° C. Soft baking was performed for 60 seconds to form a protective film having a thickness of 33 nm.

  The substrate on which the protective film was formed was subjected to immersion exposure using an experimental apparatus manufactured by Nikon Corporation using a prism, a liquid, and a two-beam interference exposure with a wavelength of 193 nm. It was in contact with the protective film).

  Subsequently, after PEB treatment was performed at 115 ° C. for 90 seconds, the protective film was removed using perfluoro (2-butyltetrahydrofuran). Thereafter, development was further performed at 23 ° C. with an alkali developer for 60 seconds. As the alkaline developer, an aqueous 2.38 mass% tetramethylammonium hydroxide solution was used.

  When the 65 nm line and space photoresist pattern obtained in this way was observed with a scanning electron microscope (SEM), the photoresist pattern profile was good and no fluctuations were observed. There was no.

  The material for forming a protective film of the present invention is extremely excellent in film surface uniformity and can reduce the contact angle with respect to droplets dropped during local liquid immersion exposure, so that a photoresist pattern can be formed by local liquid immersion exposure. In (1), a photoresist pattern free of pattern defects can be obtained. Therefore, it is particularly preferably used for local liquid immersion exposure.

4 is a graph showing a change with time of a contact angle between a protective film and a droplet used in Example 1; 2 is a photomicrograph (drawing substitute photo) showing a change with time of a droplet dropped on the protective film used in Example 1. FIG. 6 is a graph showing a change with time of a contact angle between a protective film and a droplet used in Comparative Example 1; 6 is a photomicrograph (drawing substitute photo) showing a change with time of a droplet dropped on the protective film used in Comparative Example 1. FIG.

Claims (8)

  Immersion exposure process for forming a protective film used in an immersion exposure process and laminated on a photoresist film on a substrate, comprising a cyclic perfluoroalkyl polyether and a fluorinated organic solvent Photoresist protective film forming material. The material for forming a photoresist protective film for an immersion exposure process according to claim 1, wherein the cyclic perfluoroalkyl polyether is a polymer having a structural unit represented by the following formula (I).

[In Formula (I), Rf ₁ is a fluorine atom, or a C 1-5 perfluoroalkyl group or perfluoroalkyl ether group, and Rf ₂ may or may not be present. The case (which may be present in plural) is a C 1-5 perfluoroalkyl group or a perfluoroalkyl ether group, and X is —O— or — (CF ₂ ) _q — (where q is 0 or 1). Y represents —O— or — (CF ₂ ) _v — (where v represents a number of 1 or more), and Z represents — (O) _s — (where s is 0 or 1). P, t, and u each represent a number from 0 to 3, and m represents a repeating unit. ] The material for forming a photoresist protective film for an immersion exposure process according to claim 1 or 2, wherein the cyclic perfluoroalkyl polyether is a polymer having a structural unit represented by the following formula (II).

[In the formula (II), p, t and u each represent a number of 0 to 3, r represents a number of 1 to 3, and m represents a repeating unit. ] The material for forming a photoresist protective film for an immersion exposure process according to claim 1 or 2, wherein the cyclic perfluoroalkyl polyether is a polymer having a structural unit represented by the following formula (III).

[In Formula (III), Rf ₁ is a fluorine atom, or a C 1-5 perfluoroalkyl group or perfluoroalkyl ether group, and Rf ₂ may or may not be present. The case (which may be present in plural) is a perfluoroalkyl group or perfluoroalkyl ether group having 1 to 5 carbon atoms, t is a number from 0 to 3, and m is a repeating unit. ]   The material for forming a photoresist protective film for an immersion exposure process according to any one of claims 1 to 4, wherein only one type of polymer is used as the cyclic perfluoroalkyl polyether.   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. Is formed, an immersion exposure liquid is disposed on at least the protective film of the substrate, and the photoresist film is selectively exposed by an exposure apparatus through the immersion exposure liquid and the protective film, A method for forming a photoresist pattern, in which a heat treatment is performed as necessary, the protective film is removed from the photoresist film, and then the photoresist film is developed to obtain a photoresist pattern.   The liquid immersion exposure process is a local liquid immersion exposure process in which only a space between a lens of an exposure apparatus and a substrate having a protective film formed between a photoresist layer is filled with a liquid for liquid immersion exposure. The material for forming a photoresist protective film for an immersion exposure process according to any one of the above items.   7. The photoresist pattern according to claim 6, wherein the immersion exposure process is a local immersion exposure process in which only a space between a lens of an exposure apparatus and a substrate having a protective film formed on the photoresist layer is filled with an immersion exposure liquid. Forming method.

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