Chemically amplified resists (CAR) have successfully facilitated the development of deep ultra-violet (DUV) and 193 nm lithography techniques for more than two decades due to their acid-catalyzed deprotection scheme that enhances their photospeed. This acid-catalyzed mechanism provides a method for amplifying the initial chemical reactions caused by interaction of radiation with the resist film, thus making each interaction event between radiation and resist more productive. However, when switching from low energy photolysis to high energy radiolysis, changes in the manner in which the radiation interacts with the resist material can alter the acid generation efficiency and mechanism of PAG excitation. In high energy radiation cases where the radiation energy exceeds the ionization potential of the PAG and the polymer resin, the radiation absorption in the resist film becomes non-selective. The ratio of PAG excited by direct excitation as compared to polymer or matrix sensitization pathways can shift heavily in favor of matrix sensitization in such high energy exposure cases. Such sensitization pathways may become a potential method for enhancing resist sensitivity under high energy radiation through careful selection of matrix and PAG materials. A better understanding and study the efficiency of acid generation through direct and indirect PAG excitation pathways and the effect of PAG and matrix structure on these pathways would be extremely valuable for the design of future high sensitivity resist materials. In this work, the acid generation of typical ionic (onium salt) and non-ionic PAGs under DUV (248 nm) and electron-beam exposure in polymer film have been studied. The effect of PAG type and structure on its acid generation under photolysis and radiolysis has been determined. The effect of polymer resin structure on PAG photoacid generation under photolysis and radiolysis has also been investigated. Concepts for PAG and polymer design for producing enhanced sensitivity resists for excitational and ionizational exposure is discussed.
The objective of to develop high refractive index (HRI) chemical amplified resists (CAR), which are composed of HRI
photoacid generator (PAG) bound polymer resists, and incorporate HRI nanoparticles into the polymer matrix.
Therefore, this new series of nanocomposite resists should be effective for 193 nm immersion lithography with high RI,
to obtain feature sizes down to 32 nm or lower.
A new series of methacrylate substituted benzene sulfonic photoacid generators (PAGs) and a perfluoro alkanesulfonic
PAG, bound polymeric resists based on hydroxystyrene (HS) and 2-ethyl-2-adamantyl methacrylate (EA) were prepared
and characterized. The acid yield of these PAG bound polymer resists was among the range of 54-81% under deep
ultraviolet exposure (254 nm) that agrees well with the electron withdrawing effect of the substituents on the PAG anion
for enhancing acid generation efficiency. The intrinsic lithography performance of these polymer-bound PAG resists
showed sub-50 nm half-pitch resolution and < 5 nm LER (3σ).
Substantially improved photoresist material designs, which can provide higher photosensitivity and precise critical
dimension and edge roughness control, will be required to enable the application of next generation lithography
technology to the production of future sub-65 nm node IC device generations. The development and characterization of
novel material platforms that solve the aforementioned basic problems with chemically amplified resists (CARs) is
essential and is already one of the major subjects of modern lithography research. In that regard, we have pursued
development of a variety of 193 nm and EUV CARs that contain photoacid generator (PAG) units covalently bonded
directly to the resin polymer backbone. However, the detailed structure-property relationships that result from this
direct attachment of the PAG functional group to the polymer have previously not yet been rigorously characterized. In
this work, the lithographic properties of a polymer-bound PAG CAR (GBLMA-co-EAMA-co-F4-MBS.TPS) and its
blended-PAG analog resist (GBLMA-co-EAMA blend F4-IBBS.TPS) were studied and compared. The direct
incorporation of PAG functionality into the resist polymer, where the resulting photoacid remains bound to the polymer,
showed improved photosensitivity, resolution, and lower LER as compared with the analogous blended-PAG resist.
The improved resolution and LER were expected due to the restricted photoacid diffusion and uniform PAG distribution
provided by direct incorporation of the PAG into the polymer backbone to make a single-component resist material.
The ability to load higher levels of PAG into the resist provided by this PAG incorporation into the polymer, as compared
to the low PAG concentrations attainable by traditional blending approaches, overcomes the sensitivity loss that should
result from reduction in photoacid diffusivity and concomitant smaller acid-catalytic chain lengths. In fact, the
polymer-bound PAG resist achieves a faster photospeed than the blended-PAG analog material under DUV radiation in
the case of the materials reported here while still providing all of the aforementioned improvements such as the improved
line edge roughness.
A new series of anionic photoacid generators (PAGs), and corresponding polymers were prepared. The thermostability
of PAG bound polymers was superior to PAG blend polymers. PAG incorporated into the polymer main chain showed
improved resolution when compared with the PAG blend polymers. This was demonstrated by Extreme Ultraviolet
lithography (EUVL) results: the fluorine PAG bound polymer resist gave 45 nm (1:1), 35 nm (1:2), 30 nm (1:3) and 20
nm (1:4) Line/Space as well as the 50 nm (1:1),30 nm (1:2) elbow patterns.
A series of new anionic PAGs, as well as PAG bound polymers designed for use in 193 nm photoresist materials have
been synthesized and characterized. These novel materials provide optical transparency at 193 nm and also etch
resistance. The fluorine substituted PAG bound polymer and PAG blend resist provided 110 nm (220 nm pitch)
line/space at 11.5, 13.0 mJ/cm2, and 80 nm isolated features at 3, 1 mJ/cm2, respectively. The LER (3&sgr;) results showed
the fluorinated PAG bound polymer have LER values 6.7 nm and 6.8 nm for isolated 80 nm and dense 110 nm lines
respectively, which were lower than the PAG Blend polymers
Conventional chemically amplified photoresist formulations are complex mixtures that include a protected polymer resin and a small molecule photoacid generator (PAG). The limited compatibility of the PAG with resist resin and the mobility of the small molecule additive can lead to problems including PAG phase separation, non-uniform initial PAG and photoacid distribution, and acid migration during the post-exposure baking (PEB) processes. The incorporation of PAG units into the main chain of the polymer resin is one possible method to alleviate these problems. Recently, we have investigated methacrylate based resists which incorporate novel PAG functional groups into the polymer main chain. These materials have demonstrated good resolution performance for both 193 nm and EUV exposure for sub-100 nm patterning. However, limited information is available on the effect of binding the PAG to the polymer on PAG photoreactivity and photoacid diffusivity. In this work, the photoacid generation rate constant (commonly referred to as the Dill C parameter for the PAG) of both triflate polymer-bound PAG and blended PAG photoresists based on poly(γ-butyrolactone methacrylate -co-2-ethyl-2-adamantyl methacrylate ) resists were determined by a new technique utilizing both quantitative FTIR spectroscopy and kinetic model fitting. The results indicate that the polymer-bound PAG resist has a lower photoacid generation rate constant (C=0.0122) than the blend PAG one (C=0.2647). This large difference in Dill C parameters would indicate that the sensitivity of the polymer-bound PAG resist is substantially lower than that of the analogous blended sample which is consistent with contrast curve data for these two samples.
Current resist materials suffer from a number of problems which must be addressed to allow continued scaling of memory and logic devices. The incompatibility of the photoacid generator (PAG) and the polymer matrix is addressed in this study. This incompatibility leads to lowered acid generation efficiency, non-uniform acid distribution and migration, and phase separation. These issues ultimately lead to undesirable, premature and non-uniform deprotection reactions in the chemically amplified resist. To alleviate these problems, it is proposed that PAG units be incorporated in the resist chain to make a one-component resist, rather than blending monomeric PAG with the resist polymer. Also, polymer bound PAG resists exhibit higher stability, lower outgassing, and lower line edge roughness (LER) than corresponding resists. The polymer bound PAG resists, poly (γ-butyrolactone methacrylate-co-2-ethyl-2-adamantyl methacrylate-co-PAG), were synthesized using free radical polymerization. PAG incorporated resists, as well as PAG blended resists were exposed using the 193 nm ASML 5500/9xx optical lithography system, with 0.63 NA. Exposed wafers were evaluated using SEM. The triflate PAG incorporated resists provided 110 nm (220 nm pitch) line space features, and 80 nm isolated features. The PAG blended resists provided 130 nm (260 nm pitch) line space features. The associated photospeed for the 110 nm line space features was 8.2 mJ/cm2, which is within road map standards.
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