content_image/911744.jpg content_image/911745.jpg content_image/911746.jpg content_image/911749.jpg content_image/911748.jpg content_image/911747.jpg
wherein R$^{1 }$and R 2 are each independently a C$_{1}$-C$_{6 }$ alkyl group, C$_{2}$-C$_{6 }$ alkenyl group orC$_{2}$ -C$_{6 }$ alkynyl group, R 1 and R 2 may bond together to form a ring with the carbon atom to which they are attached, R 3 and R 5 are each independently hydrogen, a C$_{1 }$-C$_{9 }$ straight, branched or cyclic alkyl group, C$_{2}$ -C$_{10 }$ straight or branched alkoxycarbonyl group, C$_{3}$-C$_{10 }$ straight or branched alkenyloxycarbonyl group, or C$_{8}$-C$_{14 }$aralky› loxycarbonyl group, the group optionally containing an ether bond, R 4 is a C$_{1 }$-C$_{6 }$ alkyl group, C$_{2}$ -C$_{6 }$ alkenyl group or C$_{2}$ -C$_{6 }$ alkynyl group, the circle Ra is a C$_{2}$ -C$_{10 }$ alicyclic group including the nitrogen atom, and the broken line designates a valence bond to the oxygen atom in formula (a). 

4. The positive resist composition of claim 1 wherein the base polymer further comprises recurring units having a carboxyl group in which the hydrogen is substituted by an acid labile group and/or recurring units having a phenolic hydroxyl group in which the hydrogen is substituted by an acid labile group. 

5. The positive resist composition of claim 4 wherein the recurring units having a carboxyl group in which the hydro› gen is substituted by an acid labile group and the recurring units having a phenolic hydroxyl group in which the hydro› gen is substituted by an acid labile group are recurring units having the formula (b 1) and recurring units having the formula (b2), respectively, 

wherein RA is each independently hydrogen or methyl, Y 1 is a single bond, phenylene, naphthylene, or a 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, R$^{11 }$and R 12 each are an acid labile group, R 13 is fluorine, trifluoromethyl, cyano or C$_{1 }$-C$_{6 }$ alkyl, R $^{14 }$is a 

<img src='content_image/911744.jpg'>

<img src='content_image/911745.jpg'>

<img src='content_image/911746.jpg'>

single bond or a C$_{1 }$-C$_{6 }$ straight or branched alkanediyl group in which some carbon may be replaced by an ether bond or ester bond, a is 1 or 2, and b is an integer of Oto 4. 

(a2) 

6. The positive resist composition of claim 1 wherein the base polymer further comprises recurring units containing an adhesive group selected from the group consisting of hydroxyl, carboxyl, lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether bond, ester bond, sulfonic ester bond, cyano, amide, ---0----C(=O)-S-, and -0----C (=0)-NH-. 

7. The positive resist composition of claim 1 wherein the base polymer further comprises recurring units of at least one type selected from recuring units having the formulae (dl) to (d3): 

(bl) 

wherein RA is each independently hydrogen or methyl, 1 11 

Z is a single bond, phenylene, ---O-Z -, -C(=0)---0-Z 11 - or ----C(=0)-NH-Z 11 -, Z 1 is a C$_{1}$-C$_{6 }$ alkanediyl group, C$_{2}$ -C$_{6 }$ alkenediyl group, or phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety, 2 

(b2) 

Z is a single bond or a C$_{5}$-C$_{12 }$ divalent group which may contain an ester bond, ether bond or lactone ring, 3 

Z is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, ---O-Z 31 -, ----C(=0)- 0-Z31- or -C(=0)-NH-Z 31 -, Z 31 is a C$_{1 }$-C$_{6 }$ alkanediyl group, C$_{2}$-C$_{6 }$ alkenediyl group, or phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxyl moiety, 

Rf$^{1 }$to R:t4 are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf 1 to R:t4 being fluorine, 

<img src='content_image/911749.jpg'>

<img src='content_image/911748.jpg'>

<img src='content_image/911747.jpg'>

(dl) 

(d2) 

(d3) 

