content_image/938656.jpg content_image/938657.jpg
<img src='content_image/938656.jpg'>

<img src='content_image/938657.jpg'>

Exemplary structures for the inventive sulfonium salt include arbitrary combinations of cations with anions, both as exemplified above. 

The resist composition comprising the inventive sulfo› nium salt is improved in lithography properties such as EL, MEF and LWR for the following reason. The nitrogen atom in the triarylamine structure contained in the inventive sulfonium salt has a very low basicity due to the conjugated effect with the three aryl rings and the inductive effect of sulfonium ion and aryl groups. The conjugated acid exhibits an acidity as demonstrated by a pKa value of about -7 to -3. However, since the sulfonium ion is decomposed in the course of acid generation upon exposure, the inductive effect is lost, and the nitrogen atom has a pKa value of about -5 to -2. This acidity is at an equivalent level as compared with an a,a-difluorosulfonic acid generating PAG which is com› mon as the PAG in ArF resist compositions. For example, the PAG having 2-acyloxy-1,1,3,3,3-pentafluoropropane-l- 

