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acid) and an onium salt capable of generating a weak acid (e.g., a-position non-fluorinated sulfonic acid or carboxylic acid), if the strong acid generated from the PAG upon exposure to high-energy radiation collides with the unre› acted onium salt having a weak acid anion, then a salt exchange occurs whereby the weak acid is released and an onium salt having a strong acid anion is formed. In this course, the strong acid is exchanged into the weak acid having a low catalysis, incurring apparent deactivation of the acid for enabling to control acid diffusion. 

[0192] If a PAG capable of generating a strong acid is an onium salt, an exchange from the strong acid generated upon exposure to high-energy radiation to a weak acid as above can take place, but it never happens that the weak acid generated upon exposure to high-energy radiation collides with the unreacted onium salt capable of generating a strong acid to induce a salt exchange. This is because of a likeli› hood of an onium cation forming an ion pair with a stronger acid anion. 

[0193] When the onium salt having formula (5) or (6) is used as the quencher (E), the amount of the onium salt used is preferably 0.1 to 10 parts by weight, more preferably 0.1 to 5 parts by weight per 80 parts by weight of the base resin (B). As long as the amount of component (E) is in the range, a satisfactory resolution is available without a substantial lowering of sensitivity. The onium salt having formula ( 5) or (6) may be used alone or in admixture. 

[0194] Also nitrogen-containing compounds may be used as the quencher (E). Suitable nitrogen-containing com› pounds include primary, secondary and tertiary amine com› pounds, specifically amine compounds having a hydroxyl group, ether bond, ester bond, lactone ring, cyano group or sulfonate bond, as described in JP-A 2008-111103, para› graphs [0146]-[0164] (U.S. Pat. No. 7,537,880), and pri› mary or secondary amine compounds protected with a carbamate group, as described in JP 3790649. 

[0195] A sulfonic acid sulfonium salt having a nitrogen› containing substituent may also be used as the nitrogen› containing compound. This compound functions as a quencher in the unexposed region, but as a so-called photo› degradable base in the exposed region because it loses the quencher function in the exposed region due to neutraliza› tion thereof with the acid generated by itself. Using a photo-degradable base, the contrast between exposed and unexposed regions can be further enhanced. With respect to the photo-degradable base, reference may be made to JP-A 2009-109595 and JP-A 2012-046501, for example. 

[0196] When the nitrogen-containing compound is used as the quencher (E), the amount of the nitrogen-containing compound used is preferably 0.001 to 12 parts by weight, more preferably 0.01 to 8 parts by weight per 80 parts by weight of the base resin (B). The nitrogen-containing com› pound may be used alone or in admixture. 

## (F) Surfactant 

[0197] The resist composition may further include (F) a surfactant which is insoluble or substantially insoluble in water and soluble in alkaline developer, and/or a surfactant (hydrophobic resin) which is insoluble or substantially insoluble in water and alkaline developer. For the surfactant, reference should be made to those compounds described in JP-A 2010-215608 and JP-A 2011-016746. 

[0198] While many examples of the surfactant which is insoluble or substantially insoluble in water and alkaline 

developer are described in the patent documents cited herein, preferred examples are fluorochemical surfactants FC-4430 (3M), Olfinefi E1004 (Nissin Chemical Co., Ltd.), Surflonfi S-381, KH-20 and KH-30 (AGC Seimi Chemical Co., Ltd.). Partially fluorinated oxetane ring-opened poly› mers having the formula (surf-I) are also useful. 

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It is provided herein that R, Rf, A, B, C, m, and n are applied to only formula (surf-1), independent of their descriptions other than for the surfactant. R is a di- to tetra-valent C$_{2}$-C$_{5 }$ aliphatic group. Exemplary divalent aliphatic groups include ethylene, 1,4-butylene, 1,2-propylene, 2,2-dimethyl-1,3- propylene and 1,5-pentylene. Exemplary tri- and tetra-valent groups are shown below. 

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Herein the broken line denotes a valence bond. These formulae are partial structures derived from glycerol, trim› ethylol ethane, trimethylol propane, and pentaerythritol, respectively. Of these, 1,4-butylene and 2,2-dimethyl-1,3- propylene are preferably used. 

[0199] Rf is trifluoromethyl or pentafluoroethyl, and pref› erably trifluoromethyl. The letter m is an integer of O to 3, n is an integer of 1 to 4, and the sum of m and n, which represents the valence of R, is an integer of 2 to 4. "A" is equal to 1, B is an integer of 2 to 25, and C is an integer of 0 to 10. Preferably, Bis an integer of 4 to 20, and C is O or 1. Note that the formula (surf-I) does not prescribe the arrangement of respective constituent units while they may be arranged either blockwise or randomly. For the prepara› tion of surfactants in the form of partially fluorinated oxet› ane ring-opened polymers, reference should be made to U.S. Pat. No. 5,650,483, for example. 

[0200] The surfactant which is insoluble or substantially insoluble in water and soluble in alkaline developer is useful when ArF immersion lithography is applied to the resist composition in the absence of a resist protective film. In this embodiment, the surfactant has a propensity to segregate on the resist surface after spin coating for achieving a function of minimizing water penetration or leaching. The surfactant is also effective for preventing water-soluble components 

