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improvement in reaction contrast. It is thus possible to improve a contrast while suppressing acid diffusion. 

[0078] In the resist composition, the cyclic ammonium salt is preferably present in an amount of 0.001 to 50 parts by weight, more preferably 0.01 to 40 parts by weight per 100 parts by weight of the base polymer, as viewed from sensitivity and acid diffusion suppressing effect. The cyclic ammonium salt may be used alone or in admixture. 

[0079] In the unexposed region or prior to acid decompo› sition, the cyclic ammonium salt is highly lipophilic and least dissolvable in alkaline developer. After acid decompo› sition, it releases a cyclic ammonium salt having a low molecular weight and a carboxylic acid. Thus alkaline solubility is increased, which is particularly effective in the case of alkaline development. That is, any pattern film thickness loss is restrained in the unexposed region whereas scum formation at the pattern bottom is prevented in the exposed region. Particularly when the resist film has a thickness of at least 100 nm, the heterocyclic amine com› pound is effective for preventing scum formation at the pattern bottom in the exposed region. 

[0080] Base Polymer 

[0081] Where the resist composition is of positive tone, the base polymer comprises recurring units containing an acid labile group, preferably recurring units having the formula (al) or recurring units having the formula (a2). These units are simply referred to as recurring units (al) and (a2). 

[0082] In formulae (al) and (a2), RA is each independently hydrogen or methyl. R 11 and R 12 each are an acid labile group. Y$^{1 }$is a single bond, phenylene or naphthylene group, or C$_{5}$-C$_{12 }$ linking group containing at least one moiety selected from ester bond and lactone ring. Y $^{2 }$is a single bond or ester bond. When the base polymer contains both recur› ring units (al) and (a2). R 11 and R$^{12 }$may be the same or different. 

[0083] Examples of the monomer from which the recur› ring units (al) are derived are shown below, but not limited thereto. RA and R$^{11 }$are as defined above. 

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<img src='content_image/915625.jpg'>

<img src='content_image/915626.jpg'>

