Photoacid generator containing two kinds of sulfonium salt compound, chemically amplified resist containing the same and pattern transfer method

A chemically amplified photo-resist comprising:

• a resin having at least one acid decomposable group and changing solubility in alkaline solution through an acid decomposition of said at least one acid decomposable group;
• and
• a photoacid generator containing at least one first sulfonium salt compound selected from the group consisting of first sulfonium salt compounds expressed by general formula [1]
• where each of R1 and R2 is straight chain, branching, monocyclic or cross-linked cyclic alkyl group, or R1 and R2 from a ring, each of R3, R4, R5 and R6 is hydrogen atom, halogen atom, alkyl group having carbon number from 1 to 4 or alkoxyl group, X is —CH2—, —C2H4— or —OCR2— and Y− is a counter ion, and
• at least one second sulfonium salt compound selected from the group consisting of second sulfonium salt compounds expressed by general formula [2]
• where R7 is alkylene group or 2-oxoalkylene group, R8 is straight chain, branching, monocyclic, polycyclic or cross-linked cyclic alkyl group having oxo group or straight chain, branching, monocyclic, polycyclic or cross-linked cyclic alkyl group without oxo group and Y− is a counter ion,
• at least one of R7 and R8 having said oxo group.

A pattern transfer method comprising the steps of:

• a) forming a chemically amplified photo-resist layer on a target layer, said chemically amplified photo-resist comprising a resin having at least one acid decomposable group and increasing solubility in alkaline solution through an acid decomposition of said at least one acid decomposable group, and a photoacid generator containing at least one first sulfonium salt compound selected from the group consisting of first sulfonium salt compounds expressed by general formula [1]
• where each of R1 and R2 is straight chain, branching, monocyclic or cross-linked cyclic alkyl group, or R1 and R2 form a ring, each of R3, R4, R5 and R6 is hydrogen atom, halogen atom, alkyl group having carbon number from 1 to 4 or alkoxyl group, X is —CH2—, —C2H4— or —OCH2— and Y− is a counter ion, and
• at least one second sulfonium salt compound selected from the group consisting of second sulfonium salt compounds expressed by general formula [2]
• where R7 is alkylene group or 2-oxoalkylene group, R8 is straight chain, branching, monocyclic, polycyclic or cross-linked cyclic alkyl group having oxo group or straight chain, branching, monocyclic, polycyclic or cross-linked cyclic alkyl group without oxo group and Y− is a counter ion,
• at least one of R7 and R8 having said oxo group.