A degree of dispersion (Mw/Mn) of the component (A2) is not particularly limited, and is preferably 1.0 to 5.0, more preferably I.Oto 4.0, and most preferably I.Oto 3.0. It is to be noted that Mn represents a number average molecular weight. 

The component (A2) may be used alone, or in combination of two or more kinds thereof. 

A proportion of the component (A2) in the component (A) is preferably 25 mass % or more, more preferably 50 mass % or more, and still more preferably 7 5 mass% or more relative to a total mass of the component (A), and it may even be 100 mass %. When the proportion is 25 mass % or more, a resist pattern which is excellent in various lithography properties such as an increase of sensitivity and an improvement of roughness is easily formed. 

In the resist composition (2), regarding the component (A), a base material component ( component ( A3)) which does not fall under the definition of the component (A2) and exhibits changed solubility in a developing solution by the action of an acid may be used in combination. The component (A3) is the same as the above-described component (A3), and may be used alone, or in combination of two or more kinds thereof. 

In the resist composition (2), the base material component may be used alone, or in combination of two or more kinds thereof. 

In the resist composition (2), the content of the base mate› rial component may be adjusted in conformity with the thick› ness of the resist film to be formed, or the like. 

Acid Generator Component (B): Component (B) 

The acid generator component (B) used in the resist com› position (2) is the same as the component (B) used in the resist composition (1). 

Other Components 

The resist composition (2) may further contain other com› ponents in addition to the base material component and the component (B). 

Examples of other components include an acid diffusion control agent component; at least one kind of compound (E) selected from the group consisting of an organic carboxylic acid and a phosphorus oxo acid or a derivative thereof; and a fluorine additive. 

Examples of the acid diffusion control agent component include the same component (D2) and component (D3) as those which may be used in the resist composition (1 ). 

The compound (E) is the same as the component (E) which may be used in the resist composition (1 ). 

Examples of the fluorine additive include the same com› ponent (F) as that which may be used in the resist composition (1 ). 

In addition, in the resist composition (2), if desired, mis› cible additives, for example, an additional resin for improving the performance of the resist film, a dissolution inhibitor, a plasticizer, a stabilizer, a coloring agent, a halation inhibitor, a dye, and the like can be properly added and contained. 

The resist composition (2) can be manufactured by dissolv› ing the resist materials in an organic solvent. As the organic 55 solvent, the same component (S) as that described above can be used in the same manner. 

According to the resist composition of the invention, it is possible to form a resist pattern whose roughness is decreased, while maintaining good sensitivity. 

In the invention, the resist composition has a partial struc› ture represented by the general formula (a0-r-1) therein. In the partial structure represented by the general formula ( a0- r-1 ), the anion moiety thereof becomes an appropriate weakly acidic anion upon exposure to exhibit a quenching (acid dif- fusion control) effect to thus trap the acid generated upon exposure. Accordingly, in the formation of a resist pattern, the 

diffusion of the acid generated upon exposure is suppressed and the roughness of the resist pattern is thus decreased. In addition, even when a component having the partial structure is different from the base material component, the partial structure has a polar group (carbonyloxy group----C(=O)› O-), and thus an interaction acts between the component having the partial structure and the base material component and uniform distribution easily occurs in the resist film. How› ever, when the blending amount of the component having the partial structure is large, sensitivity tends to decrease. 

In the invention, the resist composition contains a high› molecular weight compound which has a partial structure represented by the general formula (a0-r-1) and has a con- stituent unit (a0) having an imide group in a side chain. Due to the combination of the partial structure with the constituent unit ( a0), a significant roughness decreasing effect is obtained in the formation of a resist pattern and a decrease of sensitivity is suppressed. Thus, good sensitivity is maintained. 

Furthermore, in the formation of a resist pattern using the resist composition of the invention, an exposure margin (EL margin) as an index of a variation in pattern size associated with a fluctuation of the exposure amount, which is difficult to balance with a decrease of roughness, is good. 

Resist Pattern Forming Method 

A resist pattern forming method of a second aspect of the invention includes a step of forming a resist film on a support using a resist composition of the first aspect of the invention, a step of exposing the resist film, and a step of developing the resist film after the exposure to form a resist pattern. 

For example, the resist pattern forming method of this aspect can be performed as follows. 

First, the resist composition according to the first aspect is applied to a support using a spinner or the like, and a baking (post applied bake (PAB)) treatment is conducted under a temperature condition of, for example, 80° C. to 150° C. for 40 to 120 seconds, and preferably 60 to 90 seconds, thereby forming a resist film. 

Subsequently, using an exposure apparatus, for example, anArF exposure apparatus, an electron beam drawing appa› ratus, or an EUV exposure apparatus, the resist film is exposed through a mask having a predetermined pattern formed thereon (mask pattern) or selectively exposed without using a mask pattern by drawing by means of direct irradia- tion with electron beams, or the like. Then, a baking (post exposure bake (PEB)) treatment is conducted under a tem› perature condition of, for example, 80° C. to 150° C. for 40 to 120 seconds, and preferably 60 to 90 seconds. 

Subsequently, the resist film is subjected to a development treatment. In the case of an alkali development process, an alkali developing solution is used to perform the development treatment, and in the case of a solvent development process, a developing solution containing an organic solvent ( organic developing solution) is used to perform the development treatment. 

After the development treatment, a rinse treatment is pref› erably performed. In the rinse treatment, in the case of an alkali development process, water rinsing using pure water is preferable, and in the case of a solvent development process, a rinse solution containing an organic solvent is preferably used. 

In the case of the solvent development process, after the development treatment or the rinse treatment, a treatment of removing the developing solution or rinse solution deposited on the pattern with a supercritical fluid may be conducted. 

After the development treatment or the rinse treatment, drying is performed. In some cases, a baking treatment (post- 

