Low abosorbing resists for 157 nm lithography

Details Low abosorbing resists for 157 nm lithography Low abosorbing resists for 157 nm lithography

2001-02-23

2004-09-21

Ashton, Rosemary (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Radiation sensitive composition or product or process of making

C430S907000, C430S914000

Reexamination Certificate

active

06794109

ABSTRACT:

BACKGROUND
The present application relates generally to photoresist materials, and more particularly, to photoresist compositions that can be utilized for lithography at 157 nm.
Photolithography employs photoresists, i.e., radiation sensitive resist materials, for transfer of images onto semiconductor wafers to selectively pattern the wafers for device manufacturing. For example, spin-on organic polymeric photoresists have enabled manufacturing of integrated circuits.
Recent advances in microlithographical techniques lay the foundation for performing lithography at sub-100 nm wavelengths. A wide variety of energy sources, such as X-rays, extreme ultra violet (EUV), low and high keV electrons, ion beams, and extended optical wavelengths, e.g., 157 nm, can potentially be employed for advanced sub-100 nm imaging. For example, lithography with 157 nm F
2
lasers represents the next evolutionary step in optical micro-lithography and has recently emerged as a promising candidate for the 100 run and 70 nm lithographical applications.
The resist materials developed for longer wavelengths, however, are too absorbent to be useful as single layer resists at such low wavelengths, e.g., at 157 nm. For example, polyhydroxystyrene based resists, developed for 248 nm lithography, and polyacrylate and polycyclic copolymer based resists, developed for 193-nm lithography, are too absorbent to provide a single layer resist having a thickness of 150 nm or more for use at 157 nm. A photoresist based on such polymers may be useful for 157 nm lithography only if the thickness of the resist is less than about 100 nm. This constraint on thickness can seriously compromise the resist's ability to perform its intended purpose. For example, such a resist may be too thin to withstand subsequent processing steps such as plasma etching and ion implantation.
Thus, a need exists for providing photoresists for use in microlithography, and in particular, for use at 157 nm wavelength. More particularly, a need exists for providing single layer photoresists for use at 157 nm.
SUMMARY OF THE INVENTION
The present invention provides photoresists for use in lithography at wavelengths less than about 248 nm, and more particularly, at wavelengths about 157 nm. In one aspect, a photoresist composition of the invention includes a polymer having at least one monomeric unit with an aromatic moiety. The monomeric unit further includes at least a group attached to the aromatic moiety. The attached group has at least one CF bond. The polymer further includes an acidic hydroxyl group. A photoresist of the invention has relatively low absorbance at wavelengths less than about 248 nm, e.g., absorbance in a range of 1-5 &mgr;m
−1
, and more preferably in a range of 2-4 &mgr;m
−1
at 157 nm, which allows production of single layer resists at these wavelengths with sufficient thickness to be suitable for photolithography.
In one aspect, a photoresist of the invention includes a homopolymer having a chemical formula:
[-A-A-]
n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene. The polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In another aspect, a photoresist of the invention includes a copolymer having a chemical formula:
[-A-A′-]
n
where A and A′ are two different hexafluoroisopropanol styrene moieties. For example, A can be 2-hexafluoroisopropanol styrene and A′ can be 3-hexafluoroisopropanol styrene. The polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In related aspect, a photoresist of the invention can include a copolymer having a chemical formula:
[-A-B-]
n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene, and
B=2,3, or 4-t-butoxycarbonyl-hexafluoroisopropanol styrene, 2,3, or 4-t-butyl acetate-hexafluoroisopropanol styrene, 2,3, or 4-methoxymethoxy-hexafluoroisopropanol styrene, t-butyl acrylate, t-butyl methacrylate, or t-butyl trifluoromethacrylate.
The molar concentration of the monomeric unit A is in a range of about 40-100%, and more preferably in a range of about 50-80%, and the molar concentration of the monomeric unit B is in a range of about 0-60%, and more preferably in a range of 20-50%. Further, the polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In another aspect, a photoresist of the invention can include a copolymer having a chemical formula:
[-A-C-]
n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene, and
C=styrene, 4-t-butylstyrene, 2,3, or 4-fluorostyrene, 2,3,4,5,6-pentafluorostyrene, 2,3, or 4-trifluoromethylstyrene, 3,5-bis(trifluoromethyl)styrene, 2,3, or 4-hexafluoroisopropylstyrene, 2,3, or 4-trifluoroacetylstyrene, 2,3, or 4-heptafluorobutyrylstyrene, acrylonitrile, or methacrylonitrile.
The molar concentration of the monomeric unit A is in a range of about 40-100%, and more preferably in a range of about 50-80%, and the molar concentration of the monomeric unit C is in a range of about 0-60%, and more preferably in a range of 20-50%. Further, the polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons
In another aspect, a photoresist of the invention can include a terpolymer having a chemical formula:
[-A-A′-A″-]
n
where A is selected to be 2-hexafluoroisopropanol styrene, and A′ is selected to be 3-hexafluoroisopropanol styrene, and A″ is selected to be 4-hexafluoroisopropanol styrene. The polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons
Another photoresist according to the invention can include a terpolymer having a chemical formula:
[-A-B-C-]
n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene, and
B=2,3, or 4-t-butoxycarbonyl-hexafluoroisopropanol styrene, 2,3, or 4-t-butyl acetate-hexafluoroisopropanol styrene, 2,3, or 4-methoxymethoxy-hexafluoroisopropanol styrene, t-butyl acrylate, t-butyl methacrylate, t-butyl trifluoromethacrylate, and
C=styrene, 4-t-butylstyrene, 2,3, or 4-fluorostyrene, 2,3,4,5,6-pentafluorostyrene, 2,3, or 4-trifluoromethylstyrene, 3,5-bis(trifluoromethyl)styrene, 2,3, or 4-hexafluoroisopropylstyrene, 2,3, or 4-trifluoroacetylstyrene, 2,3, or 4-heptafluorobutyrylstyrene, acrylonitrile, or methacrylonitrile.
The molar concentration of A is selected to be in a range of about 40-100%, and more preferably in a range of 50-80%, and the molar concentration of B is selected to be in a range of 0-60%, and more preferably in a range of 20-50%. Further, the molar concentration of C is selected to be in a range of about 0-50%, and more preferably in a range of about 0-30%. The polymer has a molecular weight in a range of about 5000-100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In addition to the polymers described above, a photoresist composition of the invention can also contain a small amount of base which may help to stabilize the polymer system. In general, less than 1% of the polymer composition is a base component, based on the total weight of the polymer composition, e.g., less than 0.5%. Suitable bases typically are organic bases known in the art such as tetrabutylammonium hyroxide, diazabicyclo[5.4.0]undec-7-ene, diphenyl amine, trioctyl amine, or triheptyl amine.
Further, a photoresist composition of the invention can include a photoacid generator. The term “photo-acid generator” is recognized in the art and is intended to include those compounds which generate acid in response to radiant ener

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