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[0219] The resist composition is shown in Table 1 together with the sensitivity and CDU of EUV lithography. 

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[0220] It is demonstrated in Table 1 that positive resist compositions comprising a base polymer comprising recur› ring units having a nitrogen-containing tertiary ester struc› ture offer a high sensitivity and improved CDU. 

[0221] Japanese Patent Application No. 2018-234513 1s incorporated herein by reference. 

[0222] 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 having a carboxyl group in which the hydrogen is substituted by a nitrogen-containing tertiary hydrocarbon group. 

2. The positive resist composition of claim 1 wherein the nitrogen-containing tertiary hydrocarbon group is a nitro› gen-containing tertiary cyclic hydrocarbon group. 

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

wherein RA is hydrogen or methyl, X 1 is each indepen› dently a single bond, phenylene, naphthylene, or a C$_{1 }$-C$_{12 }$ linking group containing an ester bond, ether bond or lactone ring, and R is a nitrogen-containing tertiary hydrocarbon group having the formula (al) or (a2): 

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