JP2008090081A - Detergent for lithography and method for forming resist pattern using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detergent for lithography that can be used without causing environmental problems, is easily controlled about the quality, efficiently removes a coating film comprising a fluorine-substituted polymer formed on a resist film and requiring a special detergent, and moreover, that can be recycled and achieves formation of a resist pattern at an extremely low cost. <P>SOLUTION: The detergent for lithography contains a fluoroalkylamine in which hydrogen atoms are partially or wholly substituted by fluorine atoms. A method for forming a resist pattern using the detergent is also disclosed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithographic cleaning agent suitable for cleaning a film made of a fluorine-substituted polymer used in a lithography process, and a resist pattern forming method using the same. In particular, a lithographic cleaning agent suitable for removing a coating made of a fluorine-substituted polymer formed on a resist film in a liquid immersion lithography process, and a resist pattern forming method using the lithographic cleaning agent About.

  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, and soft X-ray, and increasing the numerical aperture (NA) of the lens. It is common.

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

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

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

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

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

Under such circumstances, as a means for simultaneously preventing the deterioration of the resist film due to the immersion exposure liquid during the immersion exposure described above and the refractive index fluctuation accompanying the deterioration of the immersion exposure liquid itself. A process for forming a film (protective film) made of a fluorine-substituted polymer on a resist film has been proposed. However, when such a film made of a fluorine-substituted polymer is used, the above-mentioned purpose can be achieved, but a special special cleaning agent is required. The use of fluoro (2-butyl) tetrahydrofuran is described.
International Publication No. 2004/074937 Pamphlet

  However, these special cleaning agents are difficult to control quality because they are other component systems that contain many impurities, which increases production costs and makes it difficult to recover and reuse them. There were some problems. In addition, perfluoro (2-butyl) tetrahydrofuran described in Patent Document 1 has a large global warming potential (GWP) and high volatility. Therefore, when such a cleaning agent is used, a large amount of volatile matter is released into the atmosphere, which has a problem of having a great influence on the environment.

  The present invention has been made in view of the problems as described above, has a smaller GWP than the conventional lithography cleaning agent, is easy in quality control, and further allows the lithography cleaning agent itself to be recycled. An object of the present invention is to provide a lithography cleaning agent capable of forming a resist pattern for immersion exposure at low cost, and a resist pattern forming method using the lithography cleaning agent.

  In order to solve the above-mentioned problems, the present inventors have conducted extensive research and found that the above-mentioned problems can be solved by using a fluoroalkylamine as a component of a lithographic cleaning agent. It came. More specifically, the present invention provides the following.

  Provided is a lithographic cleaning agent containing a fluoroalkylamine in which part or all of hydrogen atoms are substituted with fluorine atoms.

  Furthermore, after providing a photoresist film on the substrate and forming a protective film on the photoresist film, after selectively exposing the photoresist film, the protective film is removed using the lithography cleaning agent, Subsequently, a photoresist pattern forming method for obtaining a photoresist pattern by developing a photoresist film is provided.

  The lithographic cleaning agent of the present invention can be used without environmental problems, is easy in quality control, and efficiently removes a coating made of a fluorine-substituted polymer that requires a special cleaning agent formed on a resist film. Furthermore, by making the cleaning agent itself recyclable, a resist pattern can be formed at a very low cost.

  The lithography cleaning agent of the present invention needs to contain a fluoroalkylamine in which some or all of the hydrogen atoms are substituted with fluorine atoms.

≪Lithography cleaning agent≫
[Fluoroalkylamine]
The fluoroalkylamine is an alkylamine in which some or all of the hydrogen atoms are substituted with fluorine atoms. Specific examples of such fluoroalkylamines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, trimethylamine, wherein some or all of the hydrogen atoms are replaced by fluorine atoms. Examples include propylamine, butylamine, isobutylamine, dibutylamine, tributylamine, pentylamine, isopentylamine, dipentylamine, tripentylamine, tetrapentylamine, and tetrahexylamine.

  Among the fluoroalkylamines, perfluoroalkylamines in which all of the hydrogen atoms are substituted with fluorine atoms are preferred, and tertiary fluoroalkylamines having a fluoroalkyl group having 2 to 4 carbon atoms are particularly preferred.

  These fluoroalkylamines may be used in combination of two or more. Even when two or more kinds are mixed and used, it is only necessary to add insufficient fluoroalkylamine so that a desired composition ratio is obtained in the recycling, and therefore, it can be easily used for recycling the cleaning agent.

  The lithography cleaning agent of the present invention can efficiently remove a film made of a fluorine-substituted polymer that requires a special cleaning agent formed on a resist film. Such a film made of a fluorine-substituted polymer is a film for forming a protective film as a resist upper layer in the immersion exposure process. Therefore, the lithography cleaning agent of the present invention can be suitably used for removing the resist protective film in the immersion exposure process.

≪Resist film≫
As the resist film that can be used in the present invention, any resist film obtained using a conventionally used resist composition can be used, and there is no need to use it in a particularly limited manner. Conventionally used resist compositions are not particularly limited, and resist compositions that can be developed with an aqueous alkali solution, including negative and positive resists, can be arbitrarily used. Examples of such a resist composition include (i) a positive resist composition containing a naphthoquinonediazide compound and a novolac resin, (ii) a compound that generates an acid upon exposure, and an acid that decomposes with an acid to increase solubility in an alkaline aqueous solution. A positive resist composition containing a compound and an alkali-soluble resin, (iii) a compound that generates an acid upon exposure, a positive resist containing an alkali-soluble resin having a group that decomposes with an acid and increases the solubility in an aqueous alkali solution Examples include, but are not limited to, compositions and (iv) negative resist compositions containing a compound that generates acid upon exposure, a crosslinking agent, and an alkali-soluble resin.

≪Protective film≫
The film made of the fluorine-substituted polymer (hereinafter also referred to as “protective film”) to be removed using the lithographic cleaning agent of the present invention is a film containing at least a fluorine-substituted polymer that is insoluble in water and alkali. Examples of such fluorine-substituted polymers include chain fluoroalkyl ether polymers, cyclic fluoroalkyl ether polymers, polychlorotrifluoroethylene, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxyethylene copolymers, tetra Examples thereof include a fluoroethylene-hexafluoropropylene copolymer.

  Among the fluorine-substituted polymers, it is preferable to use a chain fluoroalkyl ether polymer and a cyclic fluoroalkyl ether polymer. Specifically, among the commercially available products, demnum S-20, demnum are used as the chain fluoroalkyl ether polymer. S-65, demnum S-100, demnam S-200 (above, Daikin Industries, Ltd.), cyclic perfluoroalkyl polyether, Cytop series (Asahi Glass Co., Ltd.), Teflon (registered trademark) (R) -AF1600 , Teflon (registered trademark) (R) -AF2400 (manufactured by DuPont) or the like can be used.

  Among the fluoroalkyl ether polymers, it is most preferable to use a mixed resin of a cyclic fluoroalkyl ether polymer and a chain fluoroalkyl ether polymer, or a cyclic fluoroalkyl ether polymer alone.

  Furthermore, it is desirable to use a film made of such a fluorine-substituted polymer by dissolving the fluorine-substituted polymer in a specific fluorine-based solvent. As such a specific fluorine-based solvent, the above-mentioned fluorine-substituted polymer is dissolved. The solvent is not particularly limited as long as it is a solvent to be obtained, and examples thereof include fluorine-based solvents such as perfluorotributylamine, perfluorotetrapentylamine, and perfluorotetrahexylamine.

  In addition, other organic solvents having compatibility with a specific fluorine-based solvent that dissolves the fluorine-substituted polymer, a surfactant, and the like can be appropriately mixed and used.

  In the fluorine-substituted polymer-containing chemical solution, the concentration of the fluorine-substituted polymer is not particularly limited as long as it can form a film, but is preferably about 0.1 to 30 wt% in consideration of applicability and the like.

<< Liquid for immersion exposure >>
As the immersion exposure liquid, immersion exposure is possible by using water or a fluorine-based inert liquid which is substantially pure water or deionized water. In view of cost, ease of post-processing, low environmental pollution, and the like, water is a more suitable immersion exposure liquid.

<< Photoresist pattern formation method >>
Next, a resist pattern forming method using an immersion exposure method using the lithography cleaning agent 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 a two-layer laminate in which an organic or inorganic antireflection film is provided between the substrate and the coating layer of the resist composition may be used. 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, the above-described fluorine-substituted polymer-containing chemical solution is uniformly applied to the surface of the resist film (single layer, multiple layers) cured as described above, and then cured to form a film made of the fluorine-substituted polymer. .

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

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

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

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

  As described above, in the resist pattern forming method of the present invention, the refractive index is larger than the refractive index of air and smaller than the refractive index of the resist film to be used on the resist film through the protective film during exposure. A liquid for immersion exposure having Examples of such immersion exposure liquid include water (pure water, deionized water), and a fluorine-based inert liquid. Among these, it is preferable to use water (pure water or deionized water) from the viewpoints of cost, safety, environmental problems, and versatility.

  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”.

  Next, PEB (post-exposure heating) is performed on the resist film, and then the protective film is removed by bringing the cleaning agent for lithography of the present invention into contact with the exposed substrate. The contact method may be any of paddle method, dipping method, shower method and the like.

  After removing the protective film, development processing is performed using an alkaline developer composed of an alkaline aqueous solution. 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 and the resist composition dissolved by the developer. And by drying, the resist pattern by which the resist film was patterned in the shape according to the mask pattern is obtained.

  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.

[Test Example 1: Volatility test]
In Test Example 1, the volatility of the lithography cleaning agent was evaluated. The cleaning agents A and B are the lithography cleaning agents of the present invention, and the cleaning agents C to F are conventional cleaning agents.

In the test, 1 L of the following cleaning agent was placed in a 1 L container and left at room temperature, and the residual ratio of the solvent after 24 hours and 48 hours was measured. The results are shown in Table 1.
Cleaning agent A: perfluorotripropylamine (boiling point 130 ° C.)
Cleaning agent B: perfluorotributylamine (boiling point 174 ° C.)
Cleaning agent C: perfluoro (2-butyl) tetrahydrofuran (boiling point 102 ° C.)
Cleaning agent D: perfluorobutyl methyl ether (boiling point: 61 ° C.)
Detergent E: Propylene glycol monoethyl ether and propylene glycol monomethyl ether mixed solvent (mass mixing ratio 7: 3)

  From the results in Table 1, the cleaning agents A and B, which are fluoroalkylamines contained in the lithography cleaning agent of the present invention, have a small amount of volatilization. It was confirmed that the solvent was a small load.

[Test Example 2: Lithography evaluation test]
In Test Example 2, a resist pattern was formed using the lithography cleaning agent of the present invention, and the pattern shape was confirmed.

  On a substrate on which an organic antireflection film having a film thickness of 77 nm is formed using “ARC-29A” (manufactured by Brewer Science), which is an organic antireflection film composition, “TArF-P6111ME” (Tokyo) Oka Kogyo Co., Ltd.) was applied and pre-baked on a hot plate at 130 ° C. for 90 seconds to form a resist film having a thickness of 200 nm on the antireflection film.

  Next, a resin (weight average molecular weight: 35000) made of Cytop CTX-809SP2 (Asahi Glass Co., Ltd.) was dissolved in perfluorotributylamine to produce a fluorine-substituted polymer solution with a resin concentration of 1 wt%. A fluorine-substituted polymer solution was spin-coated on the resist film and heated at 90 ° C. for 60 seconds to form a protective film having a thickness of 28 nm.

  Next, a two-beam interference experiment was performed using an immersion exposure experimental machine LEIES 193-1 (manufactured by Nikon Corporation). Thereafter, PEB treatment was performed at 130 ° C. for 90 seconds, and the protective film was removed by contacting the cleaning agent A at 23 ° C. for 60 seconds, followed by using a 23.8 mass% tetramethylammonium hydroxide aqueous solution. Development was performed at 23 ° C. for 60 seconds to form a resist pattern.

When the 90 nm line and space resist pattern obtained in this way was observed with a scanning electron microscope (SEM), this pattern profile was a good rectangular shape, and no adverse effects on patterning were observed. Was not.
In other words, it was confirmed that even when the protective film was treated with the cleaning agent A, the patterning of the resist film was not adversely affected.

  A resist pattern was formed by the same method as in Example 1 except that the cleaning agent in Example 1 was changed to Cleaning Agent B. When the obtained pattern was observed with a scanning electron microscope, this pattern profile was a good rectangular shape.

  A resist pattern was formed in the same manner as in Example 1 except that the cleaning agent in Example 1 was changed to Cleaning Agent C. When the obtained pattern was observed with a scanning electron microscope, this pattern profile was a good rectangular shape.

  From the above, it was confirmed that even when the cleaning agent of the present invention was used, a resist pattern equivalent to the case where a conventional cleaning agent was used could be formed.

Claims (7)

  A cleaning agent for lithography, comprising a fluoroalkylamine in which part or all of hydrogen atoms are substituted with fluorine atoms.   The lithographic cleaning agent according to claim 1, wherein the fluoroalkylamine is a perfluoroalkylamine in which all of the hydrogen atoms are substituted with fluorine atoms.   The lithographic cleaning agent according to claim 1 or 2, wherein the fluoroalkylamine is a tertiary fluoroalkylamine having a fluoroalkyl group having 2 to 4 carbon atoms.   The lithographic cleaning agent according to any one of claims 1 to 3, wherein the lithographic cleaning agent is a cleaning agent for cleaning a film made of a fluorine-substituted polymer used in a photolithography process. Agent.   The lithography cleaning agent according to claim 4, wherein the fluorine-substituted polymer contains at least a cyclic fluoroalkyl ether.   6. The lithographic cleaning agent according to claim 4, wherein the coating film made of the fluorine-substituted polymer is a coating film for forming a protective film on the upper layer of the resist in an immersion exposure process.   The lithography cleaning according to claim 1, wherein a photoresist film is provided on the substrate, a protective film is formed on the photoresist film, and the photoresist film is selectively exposed, and then the lithography cleaning according to claim 1. A method for forming a photoresist pattern, comprising: removing the protective film using an agent, and subsequently developing the photoresist film to obtain a photoresist pattern.