Positive resist material and patterning process

1. A positive resist material comprising a base polymer comprising:

a repeating unit comprising two carboxyl groups whose hydrogen atoms are substituted with two tertiary carbon atoms each bonded to a double bond or triple bond, shown by the following formula (a):

and

a repeating unit having an acid generator, shown by any of the following formulae (b1) to (b3):

wherein:

R A 's are identical to or different from one another and each represent a hydrogen atom or a methyl group;

X 1 represents a single bond, or a linking group having 1 to 12 carbon atoms containing at least one selected from the group consisting of an ester bond, an ether bond, and a lactone ring;

X 2 represents a vinylene group or an ethynylene group;

X 3 represents a single bond, a phenylene group, or a linking group having 1 to 12 carbon atoms containing at least one selected from the group consisting of an ester bond, an ether bond, and a lactone ring;

R 1 to R 4 each represent a linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms;

Z 1 represents a single bond, a phenylene group, —Z 11 —, —O—Z 11 —, —C(═O)—O—Z 11 —, or —C(═O)—NH—Z 11 —;

each Z 11 represents an aliphatic hydrocarbylene group having 1 to 6 carbon atoms, a phenylene group, a naphthylene group, or a group having 7 to 18 carbon atoms obtained from a combination thereof, and optionally contains a carbonyl group, an ester bond, an ether bond, or a hydroxy group in a carbon chain of Z 11 ;

Z 2 represents a single bond, a phenylene group, or an ester bond;

Z 3 represents a single bond, —Z 31 —C(═O)—O—, —Z 31 —O—, or —Z 31 —O—C(═O)—;

each Z 31 represents a divalent hydrocarbon group having 1 to 12 carbon atoms, and optionally contains a carbonyl group, an ester bond, an ether bond, a bromine atom, or an iodine atom;

Z 4 represents a methylene group, a 2,2,2-trifluoro-1,1-ethanediyl group, or a carbonyl group;

Z 5 represents a single bond, a methylene group, an ethylene group, a phenylene group, a fluorinated phenylene group, —O—Z 51 —, —C(═O)—O—Z 51 — or —C(═O)—NH—Z 51 —;

each Z 51 represents an alkanediyl group having 1 to 12 carbon atoms, an alkenediyl group having 2 to 12 carbon atoms, a phenylene group, a fluorinated phenylene group, or a trifluoromethyl group-substituted phenylene group, and optionally contains a carbonyl group, an ester bond, an ether bond, or a hydroxy group;

R 21 to R 28 each independently represent a hydrocarbyl group having 1 to 20 carbon atoms optionally containing a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, or a heteroatom;

R 23 and R 24 , or R 26 and R 27 , are optionally bonded to each other to form a ring together with a sulfur atom bonded thereto; and

M − represents a non-nucleophilic counter ion.

2. The positive resist material according to claim 1 , wherein the base polymer further comprises at least one selected from the group consisting of:

a repeating unit containing a carboxyl group whose hydrogen atom is substituted with a first acid labile group different from the two tertiary carbon atoms each bonded to a double bond or triple bond, and

a repeating unit containing a phenolic hydroxy group whose hydrogen atom is substituted with a second acid labile group.

3. The positive resist material according to claim 2 , wherein:

the repeating unit having the substituted first acid labile group is a repeating unit shown by the following formula (c1):

and

the repeating unit having the substituted second acid labile group is a repeating unit shown by the following formula (c2):

wherein:

each R A independently represents a hydrogen atom or a methyl group;

Y 1 represents a single bond, a phenylene group, a naphthylene group, or a linking group having 1 to 14 carbon atoms containing at least one selected from the group consisting of an ester bond, an ether bond, and a lactone ring;

Y 2 represents a single bond, an ester bond, or an amide bond;

Y 3 represents a single bond, an ether bond, or an ester bond;

R 11 represents the first acid labile group that is different from the two tertiary carbon atoms each bonded to a double bond or triple bond;

R 12 represents the second acid labile group;

R 13 represents a fluorine atom, a trifluoromethyl group, a cyano group, or a saturated hydrocarbyl group having 1 to 6 carbon atoms;

R 14 represents a single bond or an alkanediyl group having 1 to 6 carbon atoms, and some of the carbon atoms are optionally substituted with an ether bond or an ester bond; and

“a” represents 1 or 2, and “b” represents an integer of 0 to 4, with 1≤a+b≤5.

4. The positive resist material according to claim 3 , wherein the base polymer further comprises a repeating unit comprising an adhesive group selected from the group consisting of a hydroxy group, a carboxyl group, a lactone ring, a carbonate group, a thiocarbonate group, a carbonyl group, a cyclic acetal group, an ether bond, an ester bond, a sulfonic acid ester group, a cyano group, an amide bond, —O—C(═O)—S—, and —O—C(═O)—NH—.

5. The positive resist material according to claim 2 , wherein the base polymer further comprises a repeating unit comprising an adhesive group selected from the group consisting of a hydroxy group, a carboxyl group, a lactone ring, a carbonate group, a thiocarbonate group, a carbonyl group, a cyclic acetal group, an ether bond, an ester bond, a sulfonic acid ester group, a cyano group, an amide bond, —O—C(═O)—S—, and —O—C(═O)—NH—.

6. The positive resist material according to claim 2 , further comprising one or more selected from the group consisting of an additive-type acid generator, an organic solvent, a quencher, and a surfactant.

7. The positive resist material according to claim 1 , wherein the base polymer further comprises a repeating unit comprising an adhesive group selected from the group consisting of a hydroxy group, a carboxyl group, a lactone ring, a carbonate group, a thiocarbonate group, a carbonyl group, a cyclic acetal group, an ether bond, an ester bond, a sulfonic acid ester group, a cyano group, an amide bond, —O—C(═O)—S—, and —O—C(═O)—NH—.

8. The positive resist material according to claim 1 , further comprising one or more selected from the group consisting of an additive-type acid generator, an organic solvent, a quencher, and a surfactant.

9. A patterning process comprising steps of:

forming a resist film on a substrate by using the positive resist material according to claim 1 ;

exposing the resist film to a high-energy beam; and

developing the exposed resist film by using a developer.

10. The patterning process according to claim 9 , wherein the high-energy beam is an i-line beam, a KrF excimer laser beam, an ArF excimer laser beam, an electron beam, or an extreme ultraviolet ray having a wavelength of 3 to 15 nm.