Positive resist composition and pattern forming method using the same

1. A positive resist composition comprising:

(A1) at least one compound selected from a compound capable of generating an acid represented by the following formula (I) upon irradiation with actinic rays or radiation and a compound capable of generating an acid represented by the following formula (II) upon irradiation with actinic rays or radiation;

(A2) a compound capable of generating an acid represented by the following formula (III) upon irradiation with actinic rays or radiation; and

(B) a resin capable of decomposing under the action of an acid to increase its solubility in an alkali developer:

wherein Rc 1 , Rc 2 and Rc 3 each independently represents an alkyl group substituted by at least one fluorine atom, or an aryl group substituted by at least one fluorine atom, and Rc 1 and Rc 2 may combine with each other to form a ring;

wherein Ra 1 , Ra 2 , Ra 3 and Ra 4 each independently represents a hydrogen atom, a fluorine atom or a trifluoromethyl group,

A represents a divalent or trivalent linking group selected from an oxygen atom, a sulfur atom, a nitrogen atom, a carbonyl group, a sulfonyl group, an ester group, an amide group, a sulfonamide group, an imino group, a urethane group, a urea group and a group formed by combining two or more thereof,

Rc 4 represents an organic group, and when n1 is 2, two Rc 4 's may be the same or different or may combine with each other to form a ring,

n1 represents 1 or 2,

n2 represents an integer of from 1 to 3,

n3 represents 0 or 1, and

n4 represents an integer of from 1 to 3.

2. The positive resist composition as claimed in claim 1 , wherein the amount of the compound (A2) is from 10 to 90 mol % based on a total amount of the compound (A1) and the compound (A2).

3. The positive resist composition as claimed in claim 1 , wherein the amount of the compound (A2) is from 20 to 80 mol % based on a total amount of the compound ((A1)) and the compound (A2).

4. The positive resist composition as claimed in claim 1 , further comprising a compound capable of generating an acid upon irradiation with actinic rays or radiation which is other than the compounds (A1) and (A2).

5. The positive resist composition as claimed in claim 4 , wherein the compound other than the compounds (A1) and (A2) is represented by the following formula (ZI), (ZII) or (ZII):

wherein R 201 , R 202 and R 203 each independently represents an organic group, X′ represents a non-nucleophilic anion, and R 204 to R 207 each independently represents an aryl group, an alkyl group or a cycloalkyl group.

6. The positive resist composition as claimed in claim 1 , further comprising a dissolution inhibiting compound capable of decomposing under an action of an acid to increase its solubility in an alkali developer and having a molecular weight of 3,000 or less.

7. The positive resist composition as claimed in claim 1 , further comprising a basic compound.

8. The positive resist composition as claimed in claim 1 , further comprising at least one of a fluorine-containing surfactant and a silicon-containing surfactant.

9. A pattern forming method comprising forming a resist film from the positive resist composition claimed in claim 1 , and exposing and developing the resist film.

10. The pattern forming method as claimed in claim 9 , wherein the resist film is exposed through an immersion liquid.