concentration is, in terms of the solid content concentration of all resist components, preferably from 2 to 30 mass %, more preferably from 3 to 25 mass %. 

Preferred examples of the dissolution medium used here include ethylene dichloride, cyclohexanone, cyclopentanone, 2-heptanone, y-butyrolactone, methyl ethyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 2-methoxyethyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether, propylene gly› col monomethyl ether acetate, toluene, ethyl acetate, methyl lactate, ethyl lactate, methyl methoxypropionate, ethyl ethox› ypropionate, methyl pyruvate, ethyl pyruvate, propyl pyru› vate, N,N-dimethylformamide, dimethylsulfoxide, N-meth› ylpyrrolidone and tetrahydrofuran. These dissolution mediums are used individually or in combination of two or more thereof. As for the solvent, those containing a propylene glycol monomethyl ether acetate are preferred, and those containing a propylene glycol monomethyl ether are more preferred. 

4. Amphoteric Ion Compound 

The photosensitive resin composition of the present inven› tion preferably further contains an amphoteric ion compound. The amphoteric ion compound as used herein indicates a compound containing both a cation moiety and an anion moiety within one molecule. Specific examples thereof include, but are not limited to, amphoteric ions of amino acid, such as alanine, phenylalanine, asparagine, glycine and valine. 

The amount of the amphoteric ion compound added is preferably from 3 to 70 mo! %, more preferably from 5 to 50 mo!%, still more preferably from 7 to 40 mo!%, based on the component (Bl). By adding the component (Y), the sensitiv› ity and contrast are more enhanced. 

In the resist composition of the present invention, the gen- eration of particle (particulate aggregate) ascribable to fluc› tuation of sensitivity is preferably reduced as much as pos› sible. Generally, as the metal content is larger, the number of particles increases because the resin aggregates in the solu› tion by using the metal as the core. Accordingly, in the com› position of the present invention, the content of metal com› ponent such as Na, K, Ca, Fe and Mg contained in the resin as the component (A) is preferably small. More specifically, the content of each metal species contained in the resin is pref› erably 300 ppb or less, more preferably 200 ppb or less, still more preferably 100 ppb or less. 

In the case where the metal impurity content in the resin is large, the number of particles readily increases, because the resin aggregates in the solvent by using the metal, impurity as the core along the change in aging. The aggregation of resin also brings about substantial change in the components con› stituting the resist composition and this is presumed to cause change in the sensitivity. 

Examples of the metal impurity contained in the resist composition include Na, K. Ca, Fe, Mg, Mn, Pd, Ni, Zn, Pt, Ag and Cu. 

As for the method of decreasing the content of metal impu› rities contained in the resist composition, that is, decreasing the number of particles, for example, a method of dissolving the resin in a solvent to prepare a solution and filtering the solution through an ion exchange filter, and also cleaning by liquid separation and treatment with acidic ion exchange resin or chelate resin are known. 

The method for decreasing the metal impurity content in the chemical amplification-type resist composition of the present invention is preferably a method comprising a step of filtering a solution containing the resin of the present inven- 

tion through an ion exchange filter, a step of adding a photo› acid generator and, if desired, an organic basic compound, a surfactant and the like to the solution to prepare a mixed solution, and a step of filtering the mixed solution through an insoluble colloid removing filter. 

The ion exchange filter which can be used is preferably a cation exchange filter with the ion exchange group being fixed to a polyethylene-made porous membrane or a polypro› pylene-made porous membrane, and examples thereof include Ion Clean (produced by Nihon Pall Ltd.) and Ion Clean AQ (produced by Nihon Pall Ltd.). The filtration rate through the ion exchange filter is preferably from 500 to 10,000 ml/min/m 2 . The insoluble colloid removing filter is preferably a synthetic resin-made filter and examples thereof include Mykrolis Optimizer DEV-16/40 (polyethylene filter, produced by Mykrolis Corp.), Microguard Minichem (poly› ethylene filter, produced by Mykrolis Corp.), Enflon (poly› tetrafluoroethylene filter, produced by Nihon Pall Ltd.), Ulti› pore N66 (nylon 66 filter, produced by Nihon Pall Ltd.), Zeta Plus ( cellulose filter, produced by Cuna) and Electropor II (nylon 66 filter, produced by Cuna). Also, in the case of performing the filtration step after adding an ionic compound such as photoacid generator, the insoluble colloid removing filter is preferably a filter not having ion exchanging ability. The ion exchange-type filter and the insoluble colloid remov› ing filter each preferably has a pore size of 0.01 to 0.5 µm, more preferably from 0.01 to 0.1 µm. 

The resist composition of the present invention is coated on a substrate to form a thin film. The thickness ofthis resist film is preferably from 0.05 to 4.0 µm. 

In the present invention, a commercially available inor› ganic or organic antireflection film may be used, if desired. Furthermore, an antireflection film may be used by coating it as a lower layer of the resist. 

The antireflection film used as the lower layer of the resist may be either an inorganic film such as titanium, titanium dioxide, titanium nitride, chromium oxide, carbon and amor› phous silicon, or an organic film comprising a light absorbent and a polymer material. The former requires equipment for the film formation, such as vacuum deposition apparatus, CVD apparatus and sputtering apparatus. Examples of the organic antireflection film include a film comprising a diphe› nylamine derivative and formaldehyde-modified melamine resin condensate, an alkali-soluble resin and a light absorbent described in JP-B-7-69611 (the term "JP-B" as used herein means an "examined Japanese patent publication"), a reac› tion product of a maleic anhydride copolymer and a diamine› type light absorbent described in U.S. Pat. No. 5,294,680, a film comprising a resin binder and a methylolmelamine- based heat crosslinking agent described in JP-A-6-118631, an acrylic resin-type antireflection film containing a carboxy› lic acid group, an epoxy group and a light absorbing group within the same molecule described in JP-A-6-118656, a film comprising methylolmelamine and a benzophenone-based light absorbent described in JP-A-8-87115, and a film obtained by adding a low molecular light absorbent to a polyvinyl alcohol resin described in JP-A-8-179509. 

Also, the organic antireflection film may be a commer› cially available organic antireflection film such as DUV-30 Series, DUV-40 Series (produced by Brewer Science, Inc.), AR-2, AR-3 andAR-5 (produced by Shipley Co., Ltd.). 

In the production or the like of a precision integrated circuit device, the step of forming a pattern on a resist film is per› formed by coating the positive resist composition of the present invention on a substrate (for example, silicon/silicon dioxide-coated substrate, glass substrate, ITO substrate or quartz/chromium oxide-coated substrate), drying it to form a 

