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Examples of the solvent used in Scheme A include hydrocarbons such as toluene, xylene, hexane and heptane; chlorinated solvents such as methylene chloride, chloroform and dichloroethane; ethers such as diethyl ether, tetrahydro› furan and dibutyl ether, ketones such as acetone and 2-bu- tanone; esters such as ethyl acetate and butyl acetate; nitriles such as acetonitrile; and aprotic polar solvents such as N,N-dimethylformamide and N,N-dimethylacetamide, which may be used alone or in admixture. The reaction may be performed even in a solventless system. The reaction temperature is preferably from - 70° C. to about the boiling point of the solvent if any. While the reaction temperature may be selected as appropriate depending on other reaction conditions, it is typically from -10° C. to about the boiling point of the solvent. 

By further effecting ion exchange with sulfonium salt (le) using a salt having a predetermined anion (Z-), the desired sulfonium salt (1) may be synthesized. Ion exchange is readily performed by any well-known methods, for example, with reference to Patent Document 4. 

Another exemplary method for synthesizing the inventive sulfonium salt is illustrated by the following Scheme B. 

<img src='content_image/932939.jpg'>

Herein R$^{1 }$to R 5 , p, q, r, Z, and M $_{1 }$+areas defined above, Hal is halogen, X$_{2 }$- is an anion, and M$_{2 }$ is a metal. 

A sulfonium salt (le) is synthesized by acting an orga› nometallic reagent or metal on a triarylamine (ld) to form a nucleophile, and reacting it with a sulfoxide (1 b ). Suitable organometallic reagents include trityl lithium, trityl sodium, trityl potassium, methyl lithium, phenyl lithium, sec-butyl 

lithium, tert-butyl lithium, and ethylmagnesium bromide. Suitable metals include lithium, sodium, potassium and magnesium. The amount of the organometallic reagent or metal used is preferably 0.5 to 5.0 moles, more preferably 0.8 to 2.0 moles per mole oftriarylamine (ld). If the amount is too short, formation of the nucleophile may be retarded, resulting in a lowering of yield. If the amount is excessive, there may occur side-reactions such as reaction of unreacted organometallic reagent with sulfoxide (1 b ), and it may be difficult to reduce the metal content in the final product, sulfonium salt (1 ), which is detrimental from the standpoint of quality control. 

The amount oftriarylamine (ld) used is preferably 0.5 to 10.0 moles, more preferably 0.8 to 5.0 moles per mole of sulfoxide (1 b ). If the amount is too short, the reaction may be retarded, resulting in a lowering of yield. If the amount is excessive, there may arise economic disadvantages due to increase of reactant cost and lowering of pot yield, and there may be formed more impurities originating from triarylam› ine (ld), leading to difficulty of purification. 

Examples of the solvent used in Scheme B include aprotic solvents, for example, hydrocarbons such as toluene, xylene, hexane and heptane; chlorinated solvents such as methylene chloride, chloroform and dichloroethane; and ethers such as diethyl ether, tetrahydrofuran and dibutyl ether, which may be used alone or in admixture. The reaction temperature is preferably from - 70° C. to about the boiling point of the solvent. While the reaction temperature may be selected as appropriate depending on other reaction conditions, it is typically from -10° C. to about the boiling point of the solvent. 

Where little reaction takes place with the nucleophile alone, an activator for sulfoxide (1 b) may be added. The activator used herein may be selected from the aforemen- tioned esterifying agents and chlorosilanes such as trimeth› ylsilyl chloride and triethylsilyl chloride. In case an esteri› fying agent which is able to react with the nucleophile is used as the activator, preferably the sulfoxide (1 b) is first reacted with the activator to form an active intermediate before it is reacted with the nucleophile. 

By further effecting ion exchange with sulfonium salt (1 e) using a salt having a predetermined anion (z-), the desired sulfonium salt (1) may be synthesized. Ion exchange is readily performed by any well-known methods, for example, with reference to Patent Document 4. 

Resist Composition 

Another embodiment of the invention is a chemically amplified resist composition comprising (A) a photoacid generator in the form of a sulfonium salt having formula (1) as an essential component. The resist composition may further comprise: 

(B) a base resin, 

(C) an organic solvent, 

(D) a photoacid generator other than the sulfonium salt 

having formula (1) (also referred to as second photoacid generator), 

(E) a quencher, 

(F) a surfactant which is insoluble or substantially 

insoluble in water and soluble in alkaline developer, and/or a surfactant which is insoluble or substantially insoluble in water and alkaline developer, and 

(G) another component. 

Components (D),(E),(F) and (G) are optional, that is, may be added if necessary. 

In the resist composition, an appropriate amount of the PAG as component (A) is 0.1 to 40 parts by weight, more preferably 0.2 to 20 parts by weight per 100 parts by weight 

