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aliphatic hydrocarbon group containing a ring in the structure thereof, and a combination thereof. 

The linear or branched aliphatic hydrocarbon group pref› erably has 10 to 20 carbon atoms, and more preferably 10 to 15 carbon atoms. 

As the linear aliphatic hydrocarbon group, a linear alkyl group is preferable. Specific examples thereofinclude a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group. 

The branched aliphatic hydrocarbon group preferably has 10 to 20 carbon atoms, and more preferably 10 to 15 carbon atoms. 

As the branched aliphatic hydrocarbon group, a branched alkyl group is preferable. Specific examples thereof include an isodecyl group and an isoundecyl group. 

The linear or branched aliphatic hydrocarbon group (chain-like aliphatic hydrocarbon group) may or may not have a substituent. Examples of the substituent include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (=0). 

As examples of the hydrocarbon group containing a ring in the structure thereof, a cyclic aliphatic hydrocarbon group (a group in which one hydrogen atom has been removed from an aliphatic hydrocarbon ring), and a group in which the cyclic aliphatic hydrocarbon group is bonded to the terminal of the aforementioned chain-like aliphatic hydrocarbon group or interposed within the aforementioned chain-like aliphatic hydrocarbon group, can be given. 

The cyclic aliphatic hydrocarbon group preferably has 10 to 20 carbon atoms, and more preferably 10 to 15 carbon atoms. 

The cyclic aliphatic hydrocarbon group may be either a polycyclic group or a monocyclic group. 

Examples of the monocyclic group include cyclodecane and cyclododecane. 

As the polycyclic group, a group in which one hydrogen atom has been removed from a polycycloalkane of 10 to 20 carbon atoms is preferable. Specific examples of the polycy- cloalkane include adamantane, diadamantane, dicyclohex› ane, tricyclodecane and tetracyclododecane. 

The cyclic aliphatic hydrocarbon group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluori- nated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (=0). 

Examples of the aromatic hydrocarbon group include an aryl group in which one hydrogen atom has been removed from an aromatic hydrocarbon ring, such as a bipheny 1 group, a fluorenyl group, a naphthyl group, an anthryl group or a phenanthryl group; 

an aromatic hydrocarbon group in which part of the carbon atoms constituting the ring of the aforementioned monova- lent aromatic hydrocarbon group has been substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom; and 

an arylalkyl group, such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethyl group. 

The alkyl chain within the arylalkyl group preferably has 1 to 4 carbon atom, more preferably 1 or 2, and most preferably 1. 

The aromatic hydrocarbon group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (=0). 

In the present invention, as R 1, an aliphatic hydrocarbon group is preferable, and an aliphatic polycyclic group is more preferable in terms of improvement in etching resistance, suppression of thickness loss of a resist pattern, shape of the resist pattern and suppression of outgas. 

Specific examples of the structural unit (a0-1) are shown below. 

<img src='content_image/922372.jpg'>

[Chemical Formula 5] 

