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substrate to form a resist coating, heat treating the resist coating, applying on the resist coating a protective coating which is insoluble in water and soluble in an alkaline devel› oper, exposing the coated substrate to high-energy radiation through a photomask and a projection lens, while holding water between the coated substrate and the projection lens, and optionally heat treating, and developing the exposed coat› ing with a developer. 

[ 15] A pattern forming process comprising the steps ofapply› ing the resist composition of any one of [9] to [12] onto a substrate to form a coating, heat treating the coating, image› wise writing with an electron beam, optionally heat treating the coating, and developing it with a developer. 

[ 16] A pattern forming process comprising the steps ofapply› ing the resist composition of any one of [9] to [12] onto a substrate to form a coating, heat treating the coating and exposing it to high-energy radiation through a photomask, and heat treating and developing the exposed coating with a developer, wherein the process further comprises the step of applying a protective coating on the resist coating, and the exposure step is performed by immersion lithography with a liquid having a refractive index of at least 1.0 held between the protective coating and a projection lens. 

Since the photoacid generators have a carboxyl group, carboxylate structure or lactone structure in addition to the acyloxy group at ~-position relative to the sulfonate, they enable to adequately control acid diffusion and are fully com› patible with resins and other components in resist composi› tions. The photoacid generators that generate these sulfonic acids perform well without raising problems during the device fabrication process including coating, pre-baking, exposure, post-exposure baking, and developing steps. The leach-out of sulfonic acids in water during theArF immersion lithography is minimized. The influence of water left on the wafer is minimized, restraining defects from forming. In the disposal of resist-containing waste liquid after the device fabrication, acyloxy groups at ~-position are hydrolyzable under basic conditions so that the sulfonic acids are trans› formed into less accumulative compounds oflower molecular weight. In the disposal by combustion, the sulfonic acids are more combustible because of a low degree of fluorine substi› tution. 

FIG.1 is a diagram showing the $^{1}$H-NMR/DMSO-d$_{6 }$ spec› trum of PAG-A in Synthesis Example 14. 

FIG. 2 is a diagram showing the $^{19}$F-NMR/DMSO-d$_{6 }$spec› trum of PAG-A in Synthesis Example 14. 

FIG. 3 is a diagram showing the $^{19}$F-NMR/CDC1$_{3 }$ spec› trum of PAG-B in Synthesis Example 15. 

FIG. 4 is a diagram showing the $^{1 }$H-NMR/CDC1$_{3 }$ spectrum 55 of PAG-B in Synthesis Example 15. 

The singular forms "a," "an" and "the" include plural ref› erents unless the context clearly dictates otherwise. 

The notation (Cn-Cm) means a group containing from n to m carbon atoms per group. Photoacid Generator 

The photoacid generators of the invention are compounds, typically sulfonium salts, iodonium salts, oxime sulfonates 

## ADVANTAGEOUS EFFECT OF INVENTION 

## BRIEF DESCRIPTION OF DRAWINGS 

## DESCRIPTION OF THE PREFERRED EMBODIMENTS 

and sulfonyloxyimides. These compounds are sensitive to high-energy radiation such as UV, deep-UV, EUV, electron beam, x-ray, excimer laser, gamma-ray and synchrotron radiation and generate sulfonic acids having the general for› mula (la) in response to high-energy radiation, so that they are useful as photoacid generators in chemically amplified resist compositions. 

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Herein RO is hydroxyl or a substituted or unsubstituted, straight, branched or cyclic C$_{1 }$-C$_{20 }$organoxy group, R $^{1 }$is a divalent C$_{1 }$-C$_{20 }$aliphatic group which may contain a substitu› ent group having a heteroatom such as oxygen, nitrogen or sulfur, or R $^{1 }$may form a mono- or polycyclic structure with RO. 

In formula (la), RO is hydroxyl or a substituted or unsub- stituted, straight, branched or cyclic C$_{1 }$-C$_{20 }$organoxy group, typically alkoxy group. R 1 is a divalent C$_{1 }$-C$_{20 }$ aliphatic group, typically alkylene or alkenylene group, which may contain a substituent group having a heteroatom such as oxy- gen, nitrogen or sulfur. Alternatively, R $^{1 }$forms a monocyclic or polycyclic structure with RO. Suitable substituent groups on RO include hydroxy, alkoxyl, aryloxy, fluoro, chloro, bromo, iodo, carboxyl, alkoxycarbonyl, amido, carbonyl, and ether-bonding oxygen. When RO is an alkoxy group, one or more hydrogen atoms on the alkoxy may be substituted by aryl groups. 

Illustrative examples of RO include hydroxy, methoxy, ethoxy, n-propoxy, isopropoxy, cyclopropyloxy, n-butoxy, sec-butoxy, isobutoxy, tert-butoxy, n-pentyloxy, cyclopenty› loxy, n-hexyloxy, cyclohexyloxy, n-octyloxy, n-decyloxy, n-dodecyloxy, 1-adamantyloxy, 2-adamantyloxy, bicyclo [2.2.1 ]hepten-2-yloxy, 1-adamantanemethoxy, 2-adaman- tanemethoxy, phenoxy, 4-methoxyphenyloxy, 4-tert-bu› tylphenyloxy, 4-biphenyloxy, 1-naphthyloxy, 2-naphthyloxy, 10-anthranyloxy, 2-furanyloxy, 2,2,2-trifluoroethoxy, 1, 1, 1, 3,3,3-hexafluoro-2-propyloxy, and 2,2,3,3-tetrafluoropro› poxy. Inter alia, hydroxy, methoxy, cyclohexyloxy, and 1-adamantanemethoxy are preferred. 

R $^{1 }$is a divalent C$_{1 }$-C$_{20 }$aliphatic group which may contain a substituent group having a heteroatom such as oxygen, nitrogen or sulfur, or may form a cyclic structure with RO. Suitable substituent groups on R 1 include hydroxy, alkoxy, aryloxy, fluoro, chloro, bromo, iodo, carboxyl, alkoxycarbo› nyl, amido, carbonyl, acyloxy, benzoyloxy, and ether-bond› ing oxygen. Illustrative examples of R 1 include methylene, ethylene, 1,3-propylene, 1,2-propylene, isopropylidene, 1,4- butylene, 1,6-hexylene, and those of the following structural formulae wherein the broken line denotes a bonding site. 

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