US 2020/0133122 Al  110  Apr. 30, 2020  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.  [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  (F) Surfactant  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.  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.  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  (surf-!) 