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[0215] It is demonstrated in Table 1 that positive resist compositions comprising a polymer comprising recurring units having the structure of an ammonium salt of a car› boxylic acid having an iodized or brominated hydrocarbyl group ( exclusive of iodized or brominated aromatic ring) offer a high sensitivity and improved CDU. 

[0216] Japanese Patent Application No. 2019-142916 is incorporated herein by reference. 

[0217] Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

1. A positive resist composition comprising a base poly› mer comprising recurring units (a) having the structure of an ammonium salt of a carboxylic acid having an iodine or bromine-substituted hydrocarbyl group which does not con› tain an iodine or bromine-substituted aromatic ring and recurring units of at least one type selected from recurring units (bl) having a carboxyl group substituted with an acid labile group and recurring units (b2) having a phenolic hydroxyl group substituted with an acid labile group. 

2. The resist composition of claim 1 wherein the recurring units (a) have the formula (a): 

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wherein RA is hydrogen or methyl, 1 

X A is a single bond, ester bond or amide bond, 1 

X B is a single bond or a C$_{1 }$-C$_{20 }$ di- or trivalent hydro› carbon group which may contain an ether bond, car› bonyl moiety, ester bond, amide bond, sultone ring, lactam ring, carbonate moiety, halogen, hydroxyl moi› ety or carboxyl moiety, 

R 1 , R $^{2 }$and R3 are each independently hydrogen, a C$_{1 }$-C$_{12 }$ alkyl group, C$_{2}$ -C$_{12 }$ alkenyl group, CcC$_{12 }$ aryl group, or C$_{7}$-C$_{12 }$aralkyl group, R$^{1 }$and R 2 , or R $^{1 }$and X1 B may bond together to form a ring with the nitrogen atom to which they are attached, the ring optionally containing oxygen, sulfur, nitrogen, or a double bond, 

XBI is iodine or bromine, 

X 2 is a single bond, ether bond, ester bond, amide bond, carbonyl group or carbonate group, 

X 3 is a single bond or a C$_{1}$-C$_{20 }$ (m$^{1}$+1)-valent hydrocar› bon group which may contain a heteroatom exclusive of iodine and bromine, 

R 4 is a C$_{1 }$-C$_{20 }$ (m$^{2 }$+ 1 )-valent aliphatic hydrocarbon group which may contain at least one moiety selected from fluorine, chlorine, hydroxyl, carboxyl, CcC$_{12 }$ aryl, ether bond, ester bond, carbonyl, amide bond, carbon› ate, urethane bond, and urea bond, 

m 1 and m 2 are each independently an integer of 1 to 3, n is 1 or 2. 

3. The resist composition of claim 1 wherein the recurring units (bl) have the formula (bl) and the recurring units (b2) have the formula (b2): 

wherein RA is each independently hydrogen or methyl, Y$^{1 }$is a single bond, phenylene group, naphthylene group, or C$_{1 }$-C$_{12 }$linking group containing an ester bond, ether bond or lactone ring, Y 2 is a single bond, ester bond or amide bond, Y 3 is a single bond, ether bond or ester bond, R 11 and R 12 each are an acid labile group, R $^{13 }$is fluorine, trifluoromethyl, cyano or a C$_{1}$-C$_{6 }$ saturatedhydrocarbyl group, R$^{14 }$is a single bond or C$_{1 }$-C$_{6 }$ alkanediyl group, a is 1 or 2, and b is an integer of O to 4. 

4. The resist composition of claim 1 wherein the base polymer further comprises recurring units ( c) having an adhesive group selected from the group consisting of hydroxyl, carboxyl, lactone ring, carbonate, thiocarbonate, 

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