Photo-induced Fragmentation of a Tin-oxo Cage Compound

J. Photopol. Sci. Technol.

et al. 2020

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Inorganic molecular materials such as tin oxo cages are a promising generation of photoresists compatible with the demands of the recently developed Extreme UltraViolet (EUV) lithography technology. Therefore, a detailed understanding of the photon-induced reactions which occur in photoresists after exposure is important. We used XUV broadband laser pulses in the range of 25 -40 eV from a table-top high-harmonic source to expose thin films of the tin oxo cage resist to shed light on some of the photo-induced chemistry via XUV absorption spectroscopy. During the exposure, the transmitted spectra were recorded and a noticeable absorbance decrease was observed in the resist. Dill parameters were extracted to quantify the XUV induced conversion and compared to EUV exposure results at 92 eV. Based on the absorption changes, we estimate that approximately 60% of tin-carbon bonds are cleaved at the end of the exposure.

Section: Introductionmentioning

confidence: 70%

XUV Induced Bleaching of a Tin Oxo Cage Photoresist Studied by High Harmonic Absorption Spectroscopy

Sadegh

Geest

J. Photopol. Sci. Technol.

et al. 2020

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“…30,31 The tin-oxo cage dication can be isolated in the gas phase using a linear or quadrupole ion trap without any modification. 32,33 While irradiation of the doubly charged tin-oxo cage (dication) gives inside into its fundamental reactivity, studies on mono-cation complexes are also of interest. In a tin-oxo cage film, the +2 charge of each cage is balanced by two counterions.…”

Section: Introductionmentioning

confidence: 99%

UV and VUV-induced fragmentation of tin-oxo cage ions

Phys. Chem. Chem. Phys.

Giuliani

et al. 2021

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“…8,10,29,30 The mechanism responsible for the solubility change of TinOH promoted by EUV photons was proposed in previous works. [8][9][10]31 Here, we investigate how LEEs directly induce changes in the solubility properties of this material as a function of electron energy and dose within a relevant energy window for EUVL (0−40 eV). 15,32−34 The design of our LEEM experimental setup allows us to evaluate the effect of LEEs on the photoresist using in situ and ex situ approaches.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Electrons that can transfer >5 eV can bring the tin cage molecules to their electronically excited states, and, at energies >7 eV, they can cause their ionization. 9 Both electronically excited and ionized tin cages undergo facile Sn− C bond cleavage. 8 This is because the lowest unoccupied molecular orbital in the neutral molecule (singly occupied in the ground state of the radical anion) has Sn−C σ* antibonding character.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Key Role of Very Low Energy Electrons in Tin-Based Molecular Resists for Extreme Ultraviolet Nanolithography

Bespalov

Zhang

ACS Appl. Mater. Interfaces

et al. 2020

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Extreme ultraviolet (EUV) lithography (13.5 nm) is the newest technology that allows high-throughput fabrication of electronic circuitry in the sub-20 nm scale. It is commonly assumed that low-energy electrons (LEEs) generated in the resist materials by EUV photons are mostly responsible for the solubility switch that leads to nanopattern formation. Yet, reliable quantitative information on this electron-induced process is scarce. In this work, we combine LEE microscopy (LEEM), electron energy loss spectroscopy (EELS), and atomic force microscopy (AFM) to study changes induced by electrons in the 0−40 eV range in thin films of a state-of-the-art molecular organometallic EUV resist known as tin-oxo cage. LEEM−EELS uniquely allows to correct for surface charging and thus to accurately determine the electron landing energy. AFM postexposure analyses revealed that irradiation of the resist with LEEs leads to the densification of the resist layer because of carbon loss. Remarkably, electrons with energies as low as 1.2 eV can induce chemical reactions in the Sn-based resist. Electrons with higher energies are expected to cause electronic excitation or ionization, opening up more pathways to enhanced conversion. However, we do not observe a substantial increase of chemical conversion (densification) with the electron energy increase in the 2−40 eV range. Based on the dose-dependent thickness profiles, a simplified reaction model is proposed where the resist undergoes sequential chemical reactions, first yielding a sparsely cross-linked network and then a more densely cross-linked network. This model allows us to estimate a maximum reaction volume on the initial material of 0.15 nm 3 per incident electron in the energy range studied, which means that about 10 LEEs per molecule on average are needed to turn the material insoluble and thus render a pattern. Our observations are consistent with the observed EUV sensitivity of tin-oxo cages.