Nonionic photoacid generator behavior under high-energy exposure sources

Lawson, Richard A.; Noga, David E.; Tolbert, Laren M.; Henderson, Clifford L.

doi:10.1117/1.3259205

Cited by 13 publications

(11 citation statements)

References 30 publications

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“…In comparing literature results to those of the present work, it is noted that cyclic sulfonium PAGs structurally similar to PAGs (-1,-2,-5) have been characterized as acid generators for ebeam lithography, and their fundamental properties (reduction potential) have been correlated with their acid generation efficiency under ebeam irradiation [35]; however the relationship between EUV and ebeam photospeed has not been clarified and the specific PAG chemistry employed was not disclosed. Similarly, the EA for several disclosed non-ionic PAGs has been correlated with their corresponding acid generation efficiency using ebeam [36], but no correlation with EUV exposures has been made. It is therefore difficult to establish straightforward similarities between results obtained using EUV and ebeam exposures and more work is necessary to clarify this issue.…”

Section: Photospeed Determinationmentioning

confidence: 98%

Acid generation efficiency: EUV photons versus photoelectrons

Goldfarb¹,

Afzali-Ardakani²,

Glodde³

2016

SPIE Proceedings

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EUV photoacid generation efficiency has been described primarily in terms of the EUV photon absorption by the PAG or the resist matrix and the production of low energy photoelectrons, which are reported as being ultimately responsible for the high quantum efficiencies reported in EUV resists (>1). Such observation led to a number of recent studies on PAGs with variable electron affinity (EA) and reduction potential (Ered) presumably conducive to a differential EUV photoelectron harvesting efficiency. However, such studies either did not disclose the PAG chemical structures, replaced the EUV source with an e-beam source, or lacked a fundamental discussion of the underlying physical mechanisms behind EUV PAG decomposition. In this work, we report the EUV photospeed of a methacrylatebased resist formulated with a battery of openly disclosed isostructural sulfonium PAGs covering a wide range of EA's and Ered's, to unveil any preferential photoelectron scavenging effect. In parallel, several iodonium PAGs are also tested in order to compare the direct EUV photon absorption route to the photoelectron-based decomposition path. Contrarily to what has been widely reported, we have found no direct correlation whatsoever between photospeed and the calculated EA's or experimental Ered's for the isostructural sulfonium PAGs studied. Instead, we found that iodonium PAGs make more efficient use of the available EUV power due to their higher photoabsorption cross-section. Additionally, we determined a cation size effect for both PAG groups, which is able to further modulate the acid generation efficiency. Finally, we present a formal explanation for the unselective response towards photoelectron harvesting based on the stabilization of the PAG cation by bulky substituent groups, the spatial and temporal range of the transient photoelectron and the differences in electron transfer processes for the different systems studied.

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Section: Photospeed Determinationmentioning

confidence: 98%

Acid generation efficiency: EUV photons versus photoelectrons

Goldfarb¹,

Afzali-Ardakani²,

Glodde³

2016

SPIE Proceedings

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“…These values are consistent with other studies of the photochemical rate constant for nitrobenzyl groups. For example, a Dill C value of 0.0094 cm 2 / mJ was previously reported for a nitrobenzyl tosylate photoacid generator in a polystyrene matrix 26 and a Dill C value of 0.00243 cm 2 / mJ was recently reported for a nitrobenzyl N,N-diisopropyl carbamate photobase generator in poly͑methyl methacrylate͒. 27 As expected, the Dill C value for this nonionic moiety is lower than triarylsulfonium PAGs, which typically have Dill C values in the range of 0.025-0.05 cm 2 / mJ, 28…”

Section: C6s15mentioning

confidence: 83%

High sensitivity nonchemically amplified molecular resists based on photosensitive dissolution inhibitors

Lawson

Tolbert

Henderson

2010

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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A new class of nonchemically amplified molecular resists has been made based on the use of photosensitive protecting groups. The deprotection during exposure converts a dissolution inhibiting compound into a dissolution promoter. The key benefit of the use of molecular resists in this application is that they can exhibit a sharp solubility transition with relatively low levels of deprotection. Two different inhibiting compounds were made that use a 2-nitrobenzyl protecting group; NBnDCh, an aliphatic molecular resist based on deoxycholic acid, and NBnHPF, based on an aromatic molecular resist containing two phenol groups. Blending these compounds with a calixarene dissolution promoter allowed the contrast and sensitivity of the resist formulations to be tuned. Contrast ratios as high as 27 and deep ultraviolet ͑DUV͒ sensitivities between 150 and 400 mJ/ cm 2 were obtained using NBnDCh. NBnHPF based systems not only showed somewhat lower contrasts but also exhibited much lower clearing doses of only 60 mJ/ cm 2 and smaller. One particular NBnHPF formulation possessed a sensitivity of 10 mJ/ cm 2 and a contrast of 8.3, and it was even possible to formulate one resist with an extremely low dose-to-clear value of only 1 mJ/ cm 2 . Such low dose-to-clear values in nonchemically amplified resists have, to the authors' knowledge, not been reported before. The Dill C parameter for each of the two systems was quantified using Fourier transform infrared spectroscopy. The sensitivity of the NBnHPF systems was found to be very good because they undergo a solubility transition at 75 mol % inhibitor; this means that some formulations only need 0.5% photoconversion to pattern. Despite the excellent DUV sensitivity of these systems, it was found that they do not possess high sensitivity when exposed using extreme ultraviolet or e-beam exposure sources.

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“…Meanwhile, imino/imido sulfonates and tosylates are gaining interest in photoresist technology [43,44]. Due to properties like high thermal stability and solubility, they are used as alternative photoacid generators (PAGs) in place of sulfonium/iodonium triflate based PAGs.…”

Section: Methodsmentioning

confidence: 99%

“…The resists reported in this study are directly sensitive to the radiations and hence belong to the class of non-chemically amplified (n-CAR) resists. Aryl sulfonates such as imino/imido sulfonates and other related compounds are well explored for their photochemical behaviours [43,44]. In such compounds, the sensitive N-O bond undergoes photo cleavage and releases the radical sulfonate (RSO 3 • ) moiety upon irradiation, which further reacts with the medium and generates strong triflic acid products [43,44].…”

Section: (B)mentioning

confidence: 99%

“…Aryl sulfonates such as imino/imido sulfonates and other related compounds are well explored for their photochemical behaviours [43,44]. In such compounds, the sensitive N-O bond undergoes photo cleavage and releases the radical sulfonate (RSO 3 • ) moiety upon irradiation, which further reacts with the medium and generates strong triflic acid products [43,44]. Therefore, imino/imido sulfonate derivatives are utilized as photo acid generators (PAGs) for CARs structural transformations [44].…”

Section: (B)mentioning

confidence: 99%

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Ferrocene Bearing Non-ionic Poly-aryl Tosylates: Synthesis, Characterization and Electron Beam Lithography Applications

Reddy

Moinuddin

Joseph

et al. 2018

J. Photopol. Sci. Technol.

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The development of new organic-inorganic hybrid photoresists with optimal lithographic performances is an extremely important but challenging task. In this regard, we have synthesized a new family of homo-and hybrid-polymer resists based on 4-(tosyloxy)phenyl methacrylate (TPMA) and ferrocene methacrylate (FEMA) monomers for micro-/nano-lithography applications. The homo polymer resist, poly(TPMA), was synthesized by a free radical polymerization of TPMA monomer in ACN/THF (2:1, v/v) solvent system using azobisisobutyronitrile (AIBN) as the radical initiator. The hybrid copolymer resists, 2.0%-&4.0%-poly(FEMA-co-TPMA), containing 2.0 and 4.0 weight percentages of FEMA respectively, were synthesized by reacting FEMA (10 and 20% initial feed ratios respectively) and TPMA (90 and 80% initial feed ratios respectively) under similar reaction conditions. The ferrocene contents of the hybrid copolymers were calculated by proton NMR analysis. The potential of these polymer resists to pattern microand nano-features were tested under deep ultraviolet (DUV) and electron beam (e-beam) lithography tools respectively. The thin films formed by 4.0%-poly(FEMA-co-TPMA) exhibited high surface roughness in comparison to those of poly(TPMA) and 2.0%-poly(FEMA-co-TPMA) resists, probably due to the high ferrocene content of the former. The scanning electron microscopy (SEM) analysis of the e-beam exposed (dose 950 µC/cm 2 ) thin films of poly(TPMA) revealed patterning of 40 nm (L/10S to L/4S), 30 nm (L/10S & L/5S) and 22 nm (L/10S) line features. Similarly, 2.0%-poly(FEMA-co-TPMA) patterned 40 nm (L/5S to L/S), 30 (L/5S to L/S) and 20 nm (L/5S & L/4S) line features under the e-beam exposure (dose 500 µC/cm 2 ). The sensitivity and contrast values were calculated from the normalized remaining thickness (NRT) curve analysis as 270 µC/cm 2 ; 5.2 and 153 µC/cm 2 ; 1.98 respectively for poly(TPMA) and 2.0%-poly(FEMA-co-TPMA) resists. The present study therefore reveals that the incorporation of small amounts of ferrocene into the poly-aryl tosylate based resist formulations helps to enhance its sensitivity and resolution.

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Nonionic photoacid generator behavior under high-energy exposure sources

Cited by 13 publications

References 30 publications

Acid generation efficiency: EUV photons versus photoelectrons

Acid generation efficiency: EUV photons versus photoelectrons

High sensitivity nonchemically amplified molecular resists based on photosensitive dissolution inhibitors

Ferrocene Bearing Non-ionic Poly-aryl Tosylates: Synthesis, Characterization and Electron Beam Lithography Applications

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