Sulfonium salt, resist composition, and patterning process
A sulfonium salt having a triphenylsulfonium cation and a sulfite anion within the molecule is best suited as a photoacid generator in chemically amplified resist compositions. Upon exposure to high-energy radiation, the sulfonium salt generates a sulfonic acid, which facilitates efficient scission of acid labile groups in chemically amplified positive resist compositions. Because of substantial non-volatility under high vacuum conditions in the EB or EUV lithography, the risk of the exposure tool being contaminated is minimized.
1. A sulfonium salt having the general formula (1):
wherein R 1 is a C 1 -C 10 alkylene or C 6 -C 10 arylene group which may be substituted with fluorine or another heteroatom, R 2 is each independently methyl, tert-butyl, methoxy or tert-butoxy, or a linking group in the form of oxygen, methylene or sulfone or a direct bond between different benzene rings, m is an integer of 0 to 5, and n is an integer of 0 to 4.
2. A sulfonium salt having the general formula (2):
wherein X is hydrogen or trifluoromethyl.
3. A chemically amplified resist composition comprising the sulfonium salt of claim 1 .
4. A chemically amplified positive resist composition comprising the sulfonium salt of claim 1 .
5. A pattern forming process comprising the steps of:
applying the resist composition of claim 3 onto a substrate to form a coating,
heat treating the coating and exposing it to high-energy radiation through a photomask,
optionally heat treating the exposed coating and developing it with a developer.
6. A pattern forming process comprising the steps of:
applying the resist composition of claim 3 onto a substrate to form a resist coating,
heat treating the resist coating,
applying onto the resist coating a protective film which is insoluble in water and soluble in an alkaline developer,
exposing the coated substrate to high-energy radiation from a projection lens through a photomask while holding water between the substrate and the projection lens,
optionally heat treating the exposed coating and developing it with a developer.
7. A pattern forming process comprising the steps of applying the positive resist composition of claim 3 onto a substrate to form a coating, heat treating the coating, imagewise writing with an electron beam, optionally heat treating the coating, and developing it with a developer.
8. A pattern forming process comprising the steps of applying the positive resist composition of claim 3 onto a substrate to form a coating, heat treating the coating, exposing the coating to soft x-ray having a wavelength of 3 to 15 nm, optionally heat treating the coating, and developing it with a developer.