The present invention makes it feasible to provide a resist composition that excels in resolution and etching resistance performance and ensures reduction of development residue defects and to provide a method of forming a pattern with the use of the resist composition. 

## DETAILED DESCRIPTION OF THE INVENTION 

The present invention will be described below. 

With respect to the expression of a group ( atomic group) used in this specification, the expression even when there is no mention of "substituted and unsubstituted" encompasses groups not only having no substituent but also having sub› stituents. For example, the expression "alkyl groups" encom› passes not only alkyls having no substituent (unsubstituted alkyls) but also alkyls having substituents (substituted alkyls). 

In the present invention, the terms "actinic rays" and "radiation" mean, for example, a mercury lamp bright line spectrum, far ultraviolet rays represented by an excimer laser, extreme ultraviolet rays (EUV light), X-rays, electron beams (EB) and the like. In the present invention, the term "light" means actinic rays or radiation. 

The expression "exposure" used herein, unless otherwise noted, means not only light irradiation using a mercury lamp, far ultraviolet, X-rays, EUV light, etc. but also lithography using particle beams, such as an electron beam and an ion beam. 

The method of forming a pattern according to the present invention comprises the operations of forming an actinic-ray› or radiation-sensitive resin composition into a film, the actinic-ray- or radiation-sensitive resin composition compris› ing an acid-decomposable resin that contains a group that when acted on by an acid, is decomposed to thereby produce a polar group and contains an aromatic group and comprising a nonionic acid generator; exposing the film to light; and developing the exposed film with a developer comprising an organic solvent to thereby form a negative pattern. 

It has been found by the inventors that the method of forming a pattern according to the present invention in which use is made of the above actinic-ray- or radiation-sensitive resin composition makes it feasible to form a pattern excel› ling in resolution and etching resistance performance while ensuring reduction of development residue defects in espe› cially the negative pattern formation through exposure by means of a KrF light, electron beams or an EUV light and development with a developer comprising an organic solvent. 

First, the actinic-ray- or radiation-sensitive resin composi› tion for use in the pattern forming method of the present invention (hereinafter also referred to as "the actinic-ray- or radiation-sensitive resin composition of the present inven› tion" or "the composition of the present invention") will be described in detail below. 

In this connection, the actinic-ray- or radiation-sensitive film of the present invention is a film formed from the actinic› ray- or radiation-sensitive resin composition of the present invention. For example, it is a film formed by applying the actinic-ray- or radiation-sensitive resin composition onto a substrate. 

<Actinic-Ray- or Radiation-Sensitive Resin Composi- tion> 

The actinic-ray- or radiation-sensitive resin composition of the present invention finds application in negative develop› ment ( development in which upon exposure, exposed areas come to have a decreased solubility in a developer to thereby remain as a pattern while unexposed areas are removed). Namely, the actinic-ray- or radiation-sensitive resin compo- 

sition of the present invention can be an actinic-ray- or radia› tion-sensitive resin composition for organic solvent develop› ment that is used in the development with a developer comprising an organic solvent. Herein, the expression "for organic solvent development" means usage in at least the operation of developing with a developer comprising an organic solvent. 

The actinic-ray- or radiation-sensitive resin composition of the present invention is typically a resist composition. From the viewpoint that especially high effects can be attained, it is preferred for the same to be a negative resist composition (namely, resist composition for organic solvent develop› ment). Moreover, the composition of the present invention is typically a chemically amplified resist composition. 

[1] Resin (A) that when acted on by an acid, decreases its solubility in an organic solvent 

The resin (A) for use in the actinic-ray- or radiation-sensi› tive resin composition of the present invention is a resin (hereinafter also referred to as "an acid-decomposable resin") comprising a repeating unit containing a group (hereinafter also referred to as "an acid-decomposable group") that when acted on by an acid, is decomposed to thereby produce a polar group. The resin (A) is a resin that when acted on by an acid, increases its polarity to thereby decrease its solubility in a developer comprising an organic solvent. The resin (A) fur› ther contains an aromatic group. This aromatic group may be contained in the repeating unit containing the acid-decom› posable group, or in a repeating unit other than this repeating unit. Hereinafter, both of these repeating units are each referred to as "a repeating unit containing an aromatic group." 

Incidentally, the resin (A) is a resin that when acted on by an acid, increases its polarity to thereby increase its solubility in an alkali developer. 

[Repeating Unit Containing an Acid-Decomposable Group] 

The resin (A) comprises a repeating unit containing an acid-decomposable group. 

It is preferred for the acid-decomposable group to have a structure in which a polar group is protected by a group that when acted on by an acid, is decomposed and cleaved. 

The polar group is not particularly limited as long as it is rendered poorly soluble or insoluble in a developer compris› ing an organic solvent. As preferred polar groups, there can be mentioned an acid group (group dissociated in a 2.38 mass% aqueous tetramethylammonium hydroxide solution conven› tionally used as a resist developer), such as a carboxyl group or a sulfonic acid group, an alcoholic hydroxyl group and the like. 

The alcoholic hydroxyl group refers to a hydroxyl group bonded to a hydrocarbon group, which is other than the hydroxyl group (phenolic hydroxyl group) directly bonded to an aromatic ring. Any aliphatic alcohol substituted at its a-po› sition with an electron withdrawing group, such as a fluorine atom, as an acid group (for example, a fluorinated alcohol group (a hexafluoroisopropanol group, etc.)) is not included in the category of the alcoholic hydroxyl group. It is preferred for the alcoholic hydroxyl group to be a hydroxyl whose pKa value is in the range of 12 to 20. 

It is preferred for the acid-decomposable group to be a group whose hydrogen atom is replaced by a group cleaved by the action of an acid. 

As the group cleaved by the action of an acid, there can be mentioned, for example, -C(R$_{36}$)(R$_{37}$)(R$_{38}$), ----C(R$_{36}$)(R$_{37}$) (OR$_{39}$), ----C(R $_{01}$)(R$_{02}$)(OR$_{39}$ ) or the like. 

In the general formulae, each ofR$_{36 }$to R$_{39 }$independently represents an alkyl group, a cycloalkyl group, an aryl group, 

