Patterning process

1. A process for forming a pattern, comprising the steps of:

(i) exposing a resist film comprising a base resin to high-energy radiation,

(ii) optionally post-exposure baking the resist film at 30 to 70° C., and

(iii) developing the resist film after step (ii),

wherein the base resin consists of

recurring units having the formula (a1) and/or recurring units having the formula (a2), and

recurring units capable of generating a polymer backbone-bound acid upon exposure, and optionally one or more recurring unit(s) selected from the group consisting of

recurring units having a phenolic hydroxyl group as an adhesive group,

recurring units having another adhesive group selected from hydroxyl group other than the phenolic hydroxyl, carboxyl group, lactone ring, carbonate bond, thiocarbonate bond, carbonyl group, cyclic acetal group, ether bond, ester bond, sulfonic acid ester bond, cyano group, amide group, —O—C(═O)—S—, and —O—C(═O)—NH—,

recurring units derived from indene, benzofuran, benzothiophene, acenaphthylene, chromone, coumarin, norbornadiene or derivatives thereof, and

recurring units derived from styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, or methyleneindane,

wherein R A is each independently hydrogen or methyl, R 1 and R 2 are each independently a C 4 -C 6 tertiary alkyl group, R 3 is each independently fluorine or methyl, m is an integer of 0 to 4, X 1 is a single bond, phenylene group, naphthylene group, or a C 1 -C 12 linking group containing at least one moiety selected from an ester bond, lactone ring, phenylene and naphthylene, and X 2 is a single bond, ester bond or amide bond,

wherein the recurring units derived from indene, benzofuran, benzothiophene, acenaphthylene, chromone, coumarin, norbornadiene or derivatives thereof are recurring units derived from monomers selected from the group consisting of the following formulae:

wherein the resist film further comprises a quencher consisting of an onium salt of carboxylic acid having the formula (1)

R 21 —CO 2 − M A +   (1)

wherein R 21 is a C 1 -C 40 monovalent hydrocarbon group which may contain a heteroatom, and M A + is an onium cation.

2. The pattern forming process of claim 1 wherein the C 4 -C 6 tertiary alkyl group is tert-butyl, tert-pentyl, 1-methylcyclobutyl, 3-methyl-3-pentyl, or 1-methylcyclopentyl.

3. The pattern forming process of claim 1 wherein the recurring units capable of generating a polymer backbone-bound acid upon exposure have the formula (b1) or (b2):

wherein R A is as defined above,

R is hydrogen or trifluoromethyl,

Y 1 is a single bond, —C(═O)—O—Z 1 — or —C(═O)—NH—Z 1 —,

Y 2 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, —O—Z 1 —, —C(═O)—O—Z 1 —, or —C(═O)—NH—Z 1 —,

Z 1 is a C 1 -C 10 alkanediyl, phenylene, or C 1 -C 10 alkenediyl group, in which at least one hydrogen may be substituted by hydroxyl, and at least one carbon may be substituted by carbonyl, ester bond or ether bond,

R 11 to R 16 are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, any two of R 11 to R 13 may bond together directly or via a methylene group or ether bond to form a ring with the sulfur atom to which they are attached, and any two of R 14 to R 16 may bond together directly or via a methylene group or ether bond to form a ring with the sulfur atom to which they are attached.

4. The pattern forming process of claim 1 wherein in step (ii), the resist film is not baked.

5. The pattern forming process of claim 1 wherein in step (ii), the resist film is post-exposure baked at a temperature of 30 to 70° C.

6. The pattern forming process of claim 5 wherein the post-exposure bake is carried out in an atmosphere at a temperature of 30 to 70° C.

7. The pattern forming process of claim 5 wherein the baking temperature is in a range of 35 to 65° C.

8. The pattern forming process of claim 7 wherein the baking temperature is in a range of 40 to 60° C.

9. The pattern forming process of claim 1 , further comprising, between steps (ii) and (iii), the step of exposing the resist film to an atmosphere containing a basic substance to neutralize the acid in the resist film.

10. The pattern forming process of claim 1 wherein step (iii) includes developing the resist film in an alkaline aqueous solution as a developer to form a positive pattern.

11. The pattern forming process of claim 1 wherein the high-energy radiation is EUV of wavelength 3 to 15 nm.

12. The pattern forming process of claim 1 wherein the high-energy radiation is EB at an accelerating voltage of 1 to 150 kV.

13. The pattern forming process of claim 1 wherein X 2 is a single bond.

14. The pattern forming process of claim 1 wherein in step (ii), the resist film is post-exposure baked at a temperature of 30 to 55° C.