In the field of microfabrication such as production of integrated circuit devices, a fine resist pattern may be formed by forming a resist film on a substrate using a resin composition, exposing the resist film via a mask pattern, and removing the exposed area or the unexposed area using an alkaline developer.  A chemically-amplified resist is generally utilized as the resist.  The chemically-amplified resist includes a polymer (base resin) that includes a functional group (acid-labile group) that dissociates (is deprotected) due to an acid.  The acid-labile group dissociates due to an acid generated upon exposure, so that the base resin changes in solubility in a developer.  A pattern is formed by utilizing the above phenomenon. 
Various chemically-amplified resist resin compositions have been proposed (see Japanese Patent Application Publication (KOKAI) No.  9-73173 and Japanese Patent Application Publication (KOKAI) No.  2010-122579, for example).  Japanese Patent Application Publication (KOKAI) No.  9-73173 discloses a resin composition that includes a polymer (base resin) that includes an alicyclic hydrocarbon group as the acid-labile group, and Japanese Patent Application Publication (KOKAI) No.  2010-122579 discloses a resin composition that includes a polymer (base resin) that includes an aromatic ring-containing group as the acid-labile group. 
In recent years, liquid immersion lithography that exposes a resist film in a state in which an immersion liquid (e.g., purified water or fluorine-containing inert liquid) is provided between the lens and the resist film has become widespread as a method that can form a fine resist pattern having a line width of about 60 nm or less.  The numerical aperture (NA) of the lens can be increased when using liquid immersion lithography.  Moreover, the depth of focus decreases to only a small extent, and high resolution can be obtained even when increasing the NA of the lens. 
It is preferable that the resist film used for liquid immersion lithography exhibit high surface hydrophobicity during liquid immersion lithography from the viewpoint of improving the scan speed resistance while suppressing elution of the resist film composition into the immersion liquid, occurrence of defects due to droplets that remain on the surface of the film, and the like.  On the other hand, it is necessary to improve the solubility of the exposed area (when using a positive-tone resist) in a developer during development. 
In view of the above situation, various resin compositions used for liquid immersion lithography have been proposed (see Japanese Patent Application Publication (KOKAI) No.  2006-309245, WO2007/116664, and Japanese Patent Application Publication (KOKAI) No.  2010-2870).  Japanese Patent Application Publication (KOKAI) No.  2006-309245, WO2007/116664, and Japanese Patent Application Publication (KOKAI) No.  2010-2870 disclose a resin composition that includes a fluorine-containing polymer that includes a group that exhibits high water repellency and includes a fluorine atom, and an acid-labile group that includes an alicyclic or chain-like hydrocarbon group.  Specifically, the fluorine-containing polymer is localized in the surface layer of the resist film, so that the surface of the resist film exhibits hydrophobicity due to the fluorine atom.  The fluorine-containing polymer disclosed in Patent Document 5 is designed so that the group that exhibits high water repellency dissociates via a reaction with a developer to produce a polar group, and the acid-labile group dissociates upon exposure to produce a polar group, so that the fluorine-containing polymer present in the exposed area exhibits improved solubility in a developer. 
According to the invention, a radiation-sensitive resin composition includes (A) a polymer that includes a repeating unit (a1) and a fluorine atom, the repeating unit (a1) including a group shown by a formula (1) or (2), the radiation-sensitive resin composition including the polymer (A) in an amount of 0.1 mass % or more and less than 20 mass % based on a total amount of polymers included in the radiation-sensitive resin composition,
wherein the following formula represents a substituted or unsubstituted aromatic hydrocarbon group,
R2 represents a hydrogen atom, a linear, branched, or cyclic alkyl group having 1 to 12 carbon atoms, or an aromatic hydrocarbon group, R3 represents a linear, branched, or cyclic alkyl group having 1 to 12 carbon atoms, provided that R2 and R3 may form a divalent alicyclic hydrocarbon group having 5 to 12 carbon atoms together with a carbon atom bonded to R2 and R3, and a is 1 or 2. 
The surface of the resist film formed using the radiation-sensitive resin composition that includes the polymer (A) exhibits hydrophobicity during liquid immersion lithography, and the exposed area rarely remains undeveloped during development after liquid immersion lithography.  As a result, defects such as bridge defects can be advantageously suppressed. 
According to the invention, a resist film is formed using the radiation-sensitive resin composition.  Since the resist film is formed using the radiation-sensitive resin composition described above, occurrence of defects can be suppressed as much as possible when forming a resist pattern using the resist film.  Moreover, the resist film exhibits excellent lithographic performance. 
The term “chain-like hydrocarbon group” used herein refers to a hydrocarbon group that does not include a cyclic structure in the main chain, and includes only a chain-like structure.  The term “chain-like hydrocarbon group” used herein includes a linear hydrocarbon group and a branched hydrocarbon group.  The term “alicyclic hydrocarbon group” used herein refers to a hydrocarbon group that includes only an alicyclic hydrocarbon structure as a cyclic structure, and does not include an aromatic ring structure.  Note that the alicyclic hydrocarbon group need not necessarily include only an alicyclic hydrocarbon structure, but may also include a chain-like structure.  The term “aromatic hydrocarbon group” used herein refers to a hydrocarbon group that includes an aromatic ring structure.  Note that the aromatic hydrocarbon group need not necessarily be formed only of an aromatic ring structure, but may also include a chain structure or an alicyclic hydrocarbon structure. 
The term “(meth)acryl” used herein refers to “acryl” or “methacryl”.