Energy deposition and charging in EUV lithography: Monte Carlo studies

Wiseheart, Liam; Narasimhan, Amrit; Grzeskowiak, Steven; Neisser, Mark; Ocola, Leonidas E.; Denbeaux, Greg; Brainard, Robert L.

doi:10.1117/12.2219849

Cited by 3 publications

(2 citation statements)

References 10 publications

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“…As the same basic mechanisms apply, the experimental and theoretical methodology developed here will make it possible to study such EUV resists more fully, and to contribute directly to their characterization and optimization. Surface charging, resist conductance, secondary electron emission, charging instabilities, and dielectric breakdown are not routinely considered in simulations of resist exposure, nor is the role of low electron energy processes such as dissociative electron attachment [28,29]. We suggest that these effects can no longer be ignored.…”

Section: H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 99%

Charge Catastrophe and Dielectric Breakdown During Exposure of Organic Thin Films to Low-Energy Electron Radiation

et al. 2017

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The effects of exposure to ionizing radiation are central in many areas of science and technology, including medicine and biology. Absorption of UV and soft-x-ray photons releases photoelectrons, followed by a cascade of lower energy secondary electrons with energies down to 0 eV. While these low energy electrons give rise to most chemical and physical changes, their interactions with soft materials are not well studied or understood. Here, we use a low energy electron microscope to expose thin organic resist films to electrons in the range 0-50 eV, and to analyze the energy distribution of electrons returned to the vacuum. We observe surface charging that depends strongly and nonlinearly on electron energy and electron beam current, abruptly switching sign during exposure. Charging can even be sufficiently severe to induce dielectric breakdown across the film. We provide a simple but comprehensive theoretical description of these phenomena, identifying the presence of a cusp catastrophe to explain the sudden switching phenomena seen in the experiments. Surprisingly, the films undergo changes at all incident electron energies, starting at ∼0 eV. DOI: 10.1103/PhysRevLett.119.266803 The interaction of ionizing radiation with matter is of vast scientific and technological (including biological and medical) importance. The interaction of UV and x-ray photons with matter is mediated by photoelectrons, as well as secondary electrons with a broad energy distribution that induce chemical changes in the material, be it a polymer, organic or inorganic hybrid, biological tissue, or even DNA. But these complex processes are hard to disentangle, as photon illumination sets the entire electron cascade in motion at once, without the possibility of discerning the role of electrons with different energies. As a result, the interaction of low energy electrons (LEEs) with soft matter is not well understood. Here, we focus primarily on the interaction of low energy electrons with polymethylmethacrylate (PMMA) and related resist materials as used in extreme ultraviolet (EUV) lithography [1] to obtain a new understanding of key processes at low electron energies.In a low energy electron microscope [2] (LEEM) a sample is illuminated with electrons with adjustable 0-100 eV energy [3]. We use LEEM to expose thin PMMA films, monitoring changes both after and during exposure [4]. The radiation chemistry of PMMA and related materials has been well studied, and there is consensus that irradiation causes scission of the main chains and removal of side groups [5][6][7][8][9][10]. Here, we identify key physical processes largely ignored in the literature: resist charging, exposure-induced changes in conductivity and secondary electron emission, and dielectric breakdown. We present a simple quantitative theory describing our data, identifying a cusp catastrophe [11] causing the instabilities seen during exposure. Even electrons with near-zero energy change the resist, suggestive of dissociative electron attachment processes [12] commonly neg...

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Section: H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 99%

Charge Catastrophe and Dielectric Breakdown During Exposure of Organic Thin Films to Low-Energy Electron Radiation

et al. 2017

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“…Various groups have developed methods for simulating the pattern formation process. [8][9][10][11][12][13][14][15][16] The stochastic nature of the patterning process is included at various levels of approximation, and includes in general the randomness of the locations of photon absorption. The stochasticity of the subsequent processes, leading via electron-hole pair formation to a cascade of secondary electrons that lead to damage in a certain region around the point of absorption, is included at various level of approximation.…”

Section: Introductionmentioning

confidence: 99%

Towards molecular-scale kinetic Monte Carlo simulation of pattern formation in photoresist materials for EUV nanolithography

Miguez

Bobbert

Coehoorn

2023

Advances in Patterning Materials and Processes XL

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Modelling the pattern formation process in photoresist materials for extreme ultraviolet (EUV) lithography in a stochastic and mechanistic manner, with molecular-scale resolution, should enable predicting the effect of variations of material parameters and process conditions, leading to insights into the ultimate resolution limits. In this work, we present the results of the first steps toward that goal. We describe the physics of the development with time of cascades of electrons and holes, created by the stochastic absorption of 92 eV photons, using a kinetic Monte Carlo model with molecular resolution. The thin film material is modelled assuming a cubic array of lattice sites, at a distance that is consistent with the molecular density of the photoresist material that is considered. The simulation of the cascading process is based on the experimental optical energy loss function, extended to include also excitations with momentum transfer. The method allows for including the Coulomb interactions between charges. In contrast to earlier work, within which the high-energy electrons move ballistically until scattering takes place, the trajectories are in our model formed by stochastically determined interconnected molecular sites. In future extensions of the model, this approach will facilitate including in a natural way a transition from delocalized electron transport at high energies to hopping transport of localized electrons at low energies. The simulations are used to study the sensitivity of the average number of degradations per absorbed photon and the average electron blur length on the rates of elastic scattering and of molecular degradation, and on the energy that is lost upon a molecular degradation process.

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Novel Sn-based photoresist for high aspect ratio patterning

Manichev

et al. 2018

Advances in Patterning Materials and Processes XXXV

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Energy deposition and charging in EUV lithography: Monte Carlo studies

Cited by 3 publications

References 10 publications

Charge Catastrophe and Dielectric Breakdown During Exposure of Organic Thin Films to Low-Energy Electron Radiation

Charge Catastrophe and Dielectric Breakdown During Exposure of Organic Thin Films to Low-Energy Electron Radiation

Towards molecular-scale kinetic Monte Carlo simulation of pattern formation in photoresist materials for EUV nanolithography

Novel Sn-based photoresist for high aspect ratio patterning

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