EUV lithography has been realized to use the mass production. Therefore, the greatest interest of the EUV lithography is sub 10nm resolution patterning capability using high NA optics system. Currently, some of the new resist platform have been investigated and metal oxide resist and dry film resist were particularly achieved good patterning performance and etching durability as negative type resist by using metal component in the systems. Previously, we proposed a novel positive tone organometal chemically amplified resist by making dissolution contrast though chain scission and polarity change to develop for nonpolar solvent. After some modification of the resist material, we demonstrate positive and negative tone pattering by using 125keV EB drawing system with alkyl acetates as developers. We will share some of the progress to improve sensitivity and resolution of positive and negative tone organometallic resist in the conference.
While metal oxide resists showing good patterning performance and etching durability have been developed for a next generation resist as negative type resist, high performance positive tone resists are still needed for logic device manufacturing. We recently developed an organometal resist based on polarity change and chain scission, which resolved 22nm HP L/S pattern in EB drawing. However, it has some problems including film thickness loss and scum formation after development in the unexposed and exposed area, respectively. In this work, to resolve these problems, we attempted modification of our polymer-type resists in terms of chemical reactions that occurs in the exposed area. The results were discussed from their dissolution behavior by QCM method and printability by EB patterning. We found that newly designed anion D improved dissolution rate of exposed area and suppressed scum formation in exposed area. Our resist in this work resolved less than 20nm line and space patterns by such alkyl acetates as butyl acetate and PGMEA as developers.
EUV lithography has been realize to use the mass production for 5nm logic device manufacture and beyond and semiconductor manufacturing plants that introduce EUV exposure system are being built or planned around the world. Therefore, the greatest interest of the EUV lithography is sub 10nm resolution patterning capability using high NA optics system. However, EUV chemically amplified resists (CARs) have had big problems about pattern defects due to stochastic effects from photon shot noise and acid diffusion blur less than 13nm HP. There is a trade-off relationship between resolution, line width roughness (LWR), and sensitivity (RLS trade-off). The RLS trade-off problems have come to a head with the progress of pattern miniaturization. The improvement of LWR and sensitivity without degrading the resolution is technically difficult because of acid diffusion and stochastic effect. Moreover, etching durability of CARs are also gradually surfaced as an issue due to reducing film thickness to prevent pattern collapse. The development of a novel platform for high resolution patterning becomes important. Currently, some of the new resist platform have been investigated and metal oxide resist and dry film resist were particularly achieved good patterning performance and etching durability as negative type resist by using metal component in the systems. On the contrary, performances of metal containing positive type resist by treating metal infiltration have not been sufficient to compare with the negative type resists. Sensitivity of non-CAR resists have a limitation by lack of the reaction probability because of only one reaction per photon at maximum. Therefore, including high concentration of EUV absorbing metal component, using chemically amplified reaction or other sensitivity enhancement techniques are necessary to meet the sensitivity requirement for high NA EUV resist. Previously, we proposed a positive tone organometal chemically amplified resist by making dissolution contrast though chain scission and polarity change to develop for butyl acetate. However, sensitivity and resolution were not sufficient as a photoresist for high NA EUV lithography. Although performance can be improved by modification of some structures, at first, we explored a way to significantly improve sensitivity by using PS-CAR process and new acid generator which can change the structure to UV sensitive one by EUV exposure only exposed area because of an aiming to reduce massive power consumption of EUV lithography.
KEYWORDS: Polymers, Extreme ultraviolet lithography, Extreme ultraviolet, Electron beam lithography, Design and modelling, Tin, Scanning electron microscopy, Internet of things, Electron beams
Since 2019, the extreme ultraviolet lithography (EUVL) has been applied to the high-volume production of devices. For further scaling, high-numerical aperture (NA) tool and resist materials applicable to high-NA EUVL are required. However, there are no resists applicable to high-NA EUVL. These days, resist materials containing Sn whose EUV absorption cross section is particularly high are attracting much attention. In this research, radiation-induced reaction mechanisms of Sncomplex- side-chain polymers were investigated to obtain the guidelines of material design.
EUV chemically amplified resists (CARs) have had big problems about pattern defects due to stochastic effects from photon shot noise and acid diffusion blur less than 13 nm HP. There is a trade-off relationship between resolution, line width roughness (LWR), and sensitivity (RLS trade-off). Moreover, etching durability of CARs have also been gradually surfaced as an issue due to reducing film thickness to prevent pattern collapse. In the circumstances, some of the new resist platform have been investigated. Above all, metal oxide resist and dry resist were particularly achieved good patterning performance and etching durability as negative type resist by using metal component in the systems. However, EUV lithography mainly need positive tone resist for logic device patterning. From these viewpoints, we aimed to make an organometal positive tone EUV chemically amplified resist concept based on our negative type metal resist. Previously, we proposed a novel chemically amplified resist platform that consists of polarity changer, organotin compound and others. Polymers having triarylsulfonium cations, organotin compound and diarylmethanol as side chains were designed to realize a negative imaging property. Upon exposure to EUV or electron beam (EB), the ionic component is transferred to nonionic component through the decomposition of polymer-bounded onium cation (PBC). The polymer molecules are also crosslinked through the acid catalytic etherification. We demonstrated a high sensitivity and low LER property by using acetonitrile aqueous solution developer. This resist obtains a dissolution contrast to polar solvent by changing to hydrophobic structure though the decomposition of the onium cation and crosslinking. Presumably, this resist can convert from negative to positive tone by changing the part of reaction for making dissolution contrast from cross-link to chain scission and developer from polar solvent to nonpolar solvent for exposed material dissolution. After some modification of the resist material, we demonstrate positive tone imaging by using alkyl acetate as a developer.
EUV chemically amplified resists (CARs) have had big problems about a trade-off relationship between resolution, line width roughness (LWR), and sensitivity (RLS trade-off). The RLS trade-off problems have come to a head with the progress of pattern miniaturization. Moreover, etching durability of CARs are also gradually surfaced as an issue due to reducing film thickness to prevent pattern collapse. Previously, we proposed a novel chemically amplified resist platform that consists of polarity changer, cross linker and organotin compound. Polymers having triarylsulfonium cations, diarylmethanol and organotin compound as side chains were designed to realize a negative imaging property by using crosslinking through the acid catalytic etherification. It demonstrated RLS trade -off mitigation and low LER property by using two concentration of acetonitrile aqueous solution developer. Moreover, it could be observed two or threefold sensitization by using a UV flood exposure after EB lithography process applying new sulfonium cation structure which can be converted to UV absorbing structure by acid catalytic reaction.
The acid diffusion in chemically amplified resists (CARs) which are a current standard resist for semiconductor device manufacturing is a significant concern in the development of highly resolving resists. Thus, high resolution CARs are reduced the number of the acid catalytic reaction per acid by high amount of acid quencher to suppressed acid diffusion blur for remaining low line width roughness (LWR) number. Non-chemically amplified resists (non-CARs) are generally lower LWR than CARs. However, non-CARs are generally less sensitive to radiation than CARs due to lack of amplification mechanism. Recently, we proposed a negative-type resist utilizing non-CAR and CAR reactions on the same platform. This resist use radiation induced non-catalitic reactions which are polarity change of onium decomposition and radical crosslinking of radiation decomposed monomers. And also, the resist uses an acid catalytic etherification utilizing diphenyl methanol derivative and aliphatic alcohol. These combination reaction by non-CARs and CAR are expected to contribute the sensitivity improvement for high resolution resist. The synthesized resists were composed of triarylsulfonium cations as a polarity changer and radical generator, 2,2,2-trisubstituted acetophenone as a radical generator, triphenyl(4-vinylphenyl)stannane (TPSnSt) as an EUV absorption enhancer and a quencher, and 4- [(2,4-Dimethoxyphenyl)hydroxymethyl]phenylmethacrylate (ARMA) as a polymer-bound acid-reactive unit. As the result, a 25 nm HP pattern could be obtained with 2.1 nm LWR and at 160 μC/cm2.
The acid diffusion in chemically amplified resists (a current standard resist for semiconductor device manufacturing) is a significant concern in the development of highly resolving resists. However, non-chemically amplified resists (non- CARs) are generally less sensitive to radiation than CARs due to lack of amplification mechanism. Recently, a negativetype non-CAR resist utilizing polarity change and radical crosslinking (a dual insolubilization resist) was proposed. In this study, an acid reactive compound was introduced into the organotin-containing dual insolubilization resists to improve their sensitivity. The synthesized resists were composed of triarylsulfonium cations as a polarity changer and radical generator, 2,2,2-trisubstituted acetophenone as a radical generator, triphenyl(4-vinylphenyl)stannane (TPSnSt) as an EUV absorption enhancer and a quencher, and 4-[(2,4-Dimethoxyphenyl)hydroxymethyl]phenylmethacrylate (ARMA) as a polymer-bound acid-reactive unit. By the incorporation of ARMA, the sensitivity to extreme ultraviolet (EUV) radiation was increased by 2.4 times (the exposure dose for insolubilization was decreased by approximately 60%). The sensitivity enhancement is considered to have been caused by the acid catalytic etherification of ARMA through dimerization and/or with 2,2,2-trisubstituted acetophenone units.
Chemically amplified resists have been used for the fabrication of semiconductor devices. With the miniaturization of circuits, the performance of chemically amplified resists approaches their limit due to the acid diffusion. The development of a novel platform without acid diffusion becomes important. In this study, we proposed a negative-type polymer resist used for extreme ultraviolet (EUV) and electron beam (EB) lithography. The proposed resist utilizes polarity change and radical crosslinking triggered by EUV/EB exposure. Polymers having triarylsulfonium cations and 2,2,2-trisubstitued acetophenone as side chains were designed for realizing the dual insolubilization property. 2,2,2- trisubstitued acetophenone was incorporated for the efficient radical generation on the polymer structure for the crosslinking. An onium salt was incorporated for the efficient use of thermalized electrons for the polarity change and the radical generation of the side chain. In addition, triphenyl-(4-vinyl-phenyl)-stannane (StTPSn) was incorporated into the resist polymer as the EUV/EB absorber to enhance sensitivity. The highly sensitive property of the designed polymers was demonstrated.
In EUV lithography (EUVL), the most critical issue has been low intensity of the EUV light source. Light-source intensity and resist sensitivity have a complementary relationship. Therefore, the sensitization of EUV resist is very important to compensate the low intensity of the EUV light source. However, dramatically improving the resist sensitivity of chemically amplified resist (CAR) is very difficult because of the resolution/line-width roughness/sensitivity (RLS) trade-off. Therefore, we propose a very new process: high resist sensitization by the combination lithography of EUV or EB pattern exposure with UV flood exposure (PF combination lithography) of photosensitized chemically amplified resist (PS-CAR). The combination lithography of EB pattern exposure with UV flood exposure achieved a sensitivity enhancement of more than a factor of 10 with respect to conventional EB single-exposure lithography, without loss in space resolution of line/space of 75 nm1. The breakthrough of RLS trade-off by PF combination lithography of PS-CAR is explained based on RLS trade-off simulation method2 and acid generation mechanism of PF combination lithography of PS-CAR. One of the problems of the PF combination lithography of PS-CAR is postexposure delay (PED) effects suffered from airborne contamination. The present paper describes forming of 75 nm contact hole and PED effects in the PF combination lithography of PS-CAR. The sensitization of EUV resists by new method accelerates EUVL implementation.
Recently, polymer-bound PAGs (anion bound) are actively investigated as Extreme ultra violet (EUV) resist. Some
experimental results showed, in case of shot diffusion length acid generator bounded polymer showed lower sensitivity comparing with long diffusion length acid generator. In our previous investigation, short diffusion length PAG reactivity is changed due to binding to polymer by pulse radiolysis method. However, shot diffusion PAG bound to polymer showed lower LWR than long diffusion length PAG. Therefore, acid diffusion length difference originate in
PAG is important to resist performance. The diffusion length difference influence deprotection reaction in PEB process.
In this paper, we evaluated polymer-bound PAGs and polymer blend PAGs by electron beam (EB) exposure tool employing various PEB temperature and PEB time to conform the influence of acid diffusion regulation about polymer-bound PAGs for resist performances. As the result, even if acid generator bound polymer applied as a resist, acid diffusion regulation isn’t so strict that acid can migrate in the polymer matrix during PEB.
We synthesized three type polymers 1) Poly hydroxyl-styrene (PHS resist). 2) hydroxyl-styrene methacrylate copolymer (Hybrid resist). 3) methacrylic acid tertiary aliphatic esters copolymer (Methacrylate resist). These polymers have been used in ArF, KrF lithography. Recently, these resists have been investigated to employ for Extreme ultra violet (EUV) lithography because absorption of EUV doesn’t depend on the molecular structure. But EUV has very higher energy
than ArF, KrF and it is exceed ionization potential of resist materials. Thus, polymer behavior under the EUV exposure is different from ArF, KrF exposure. For analyzing difference between ArF, KrF and EUV, we conducted to exposed resist materials (PHS, Hybrid, Methacrylate resist) using electron beam (EB) radiation source. As the results, we observed PHS resist showed crosslinking behavior less than 5μ C/cm2 , Hybrid resist showed cross-linking behavior more than 20μ C/cm2, Methacrylate resist showed moderate main chain scission behavior less than 20μ C/cm2 respectively.
Extreme ultraviolet lithography (EUVL) at 13.5 nm will soon be applied in high-volume manufacturing of
semiconductors, as a replacement to the ArF excimer laser immersion lithography. Recently, the potential application of
exposure wavelengths of 6.x nm (particularly 6.6-6.8 nm) has been discussed as EUVL extension. The 6.x nm exposure
source is currently under development, therefore screening of resists with conventional exposure tools will accelerate the
selection or novel development of high sensitivity resists for 6.x nm EUVL. In the present study, the sensitivities of a
chemically amplified (CA) resist (OEBR-CAP112) and non-CA resists (ZEP520A and poly(methyl methacrylate)) were
evaluated with 30 keV and 75 keV electron beam lithography (EBL) tools. In terms of radiation chemistry, the obtained
dose/sensitivities (μC cm-2) were converted into the absorbed doses (Gray; Gy = J kg-1). If EB- and EUV-induced
chemical reactions are the same, the required absorbed doses for EB and EUV would be similar values. The sensitivities
for EUV/soft X-rays including 6.x nm were predicted assuming the required absorbed doses in a resist would show
similar values for both EB and EUV. We investigated precise sensitivities of the resists for EUV/soft X-rays including
6.7 nm using highly-monochromated synchrotron radiation. For both CA and non-CA resists, the predicted and
experimentally obtained sensitivities agreed well with each other. These results suggested that almost the same chemical
reactions are induced in resists for both EUVL and EBL. Hence, it was found that we can predict the resist sensitivities
for EUV/soft X-rays at any exposure wavelength from the exposure results for EBL.
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