94  US 9,221,742 B2  93  Notably, the compound having the anion of formula (8)  does not have fluorine at the a-position relative to the sulfa  group, but two trifluoromethyl groups at the ~-position. For  this reason, it has a sufficient acidity to sever the acid labile  groups in the resist polymer. Thus the compound is an effec› tive PAG.  The organic solvent (E) used herein may be any organic  solvent in which the polymer (base resin), PAG, quencher,  and other components are soluble. Examples of the organic  solvent include ketones such as cyclohexanone and methyl  2-n-amyl ketone; alcohols such as 3-methoxybutanol, 3-me› thyl-3-methoxybutanol,  l-methoxy-2-propanol,  and  l-ethoxy-2-propanol; ethers such as  propylene glycol  monomethyl ether, ethylene glycol monomethyl ether, pro› pylene glycol monoethyl ether, ethylene glycol monoethyl  ether, propylene glycol dimethyl ether, and diethylene glycol  dimethyl ether; esters such as propylene glycol monomethyl  ether acetate (PGMEA), propylene glycol monoethyl ether  acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl  3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl  acetate, tert-butyl propionate, and propylene glycol mono› tert-butyl ether acetate; and lactones such as y-butyrolactone,  and mixtures thereof, as described in JP-A 2008-111103,  paragraphs [0144] to [0145]. Where an acid labile group of  acetal type is used, a high-boiling alcohol solvent may be  added for accelerating deprotection reaction of acetal, for  example, diethylene glycol, propylene glycol, glycerol, 1,4- butanediol, or 1,3-butanediol. Of the above organic solvents,  (E) Organic Solvent  Also, a PAG having a nitrogen-containing substituent may  be used in combination. This compound functions as  quencher in the unexposed region and as so-called photo› degradable base, which loses quencher ability through neu› tralization with the acid generated by itself, in the exposed  region. The use of photo-degradable base is effective for  enhancing the contrast between exposed and unexposed  regions. With respect to the photo-degradable base, reference  may be made to JP-A 2009-109595 and JP-A 2012-046501,  for example.  The quenchers may be used alone or in admixture of two or  more. The quencher is preferably used in an amount of0.001  to 12 parts, more preferably 0.01 to 8 parts by weight per 100  parts by weight of the base resin. The inclusion of quencher  facilitates adjustment of resist sensitivity and holds down the  rate of acid diffusion within the resist film, resulting in better  resolution. In addition, it suppresses changes in sensitivity  following exposure and reduces substrate and environment  dependence, as well as improving the exposure latitude and  the pattern profile. The inclusion of quencher is also effective  for improving adhesion to the substrate.  To the resist composition, a nitrogen-containing com› pound may be added as the quencher. The inclusion of the  nitrogen-containing compound holds down the diffusion rate  at which the acid generated by PAG diffuses within the resist  film. Suitable nitrogen-containing compounds include pri› mary, secondary and tertiary amine compounds, 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, paragraphs [0146] to [0164]  (U.S. Pat. No. 7,537,880). Also useful are compounds whose  primary or secondary amine is protected in carbamate form as  described in JP 3790649.  (D) Nitrogen-Containing Compound  The amount of the PAG (C) added is preferably  O  to 40  parts, specifically 0.1 to 40 parts ifused, more preferably 0.1  to 20 parts by weight per 100 parts by weight of the base resin.  Too large an amount of the PAG may give rise to problems  such as degraded resolution and foreign particles during  development and resist film stripping.  Of the foregoing PAG’s, those compounds having the  structure of formula (5’) or formula (8) are preferred because  of suppressed acid diffusion and high solubility in the resist  solvent. 