Studying secondary electron behavior in EUV resists using experimentation and modeling

Narasimhan, Amrit; Grzeskowiak, Steven; Srivats, Bharath; Herbol, Henry C.; Wisehart, Liam; Kelly, C. F.; Earley, William; Ocola, Leonidas E.; Neisser, Mark; Denbeaux, Greg; Brainard, Robert L.

doi:10.1117/12.2086596

Cited by 19 publications

(18 citation statements)

References 11 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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“…It is a significant demonstration that EUV photons can achieve such a resolution and there is no fundamental limiting factor in terms of materials and photochemistry. The secondary electron blur for EUV is estimated to be 1 to 3 nm [24]. If, in reality, this is about 3 nm, we have probably reached the ultimate limit in photolithography.…”

Section: Discussionmentioning

confidence: 99%

Photolithography reaches 6 nm half-pitch using EUV light

Fan

Ekinci

2016

Extreme Ultraviolet (EUV) Lithography VII

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EUV interference lithography records the interference pattern of two diffracted, coherent light beams, where the pattern resolution is half the diffraction grating resolution. The fabrication of diffraction grating masks by ebeam lithography is restricted by the electron proximity effect and pattern transfer limitations into diffraction efficient materials. By patterning HSQ lines at a relaxed pitch to avoid the electron proximity effect, depositing conformal iridium via atomic layer deposition, followed by ion milling the top and bottom iridium and HSQ removal, we fabricated iridium diffraction gratings at double the line spacing of the original HSQ lines. 6 nm half-pitch patterns were achieved using these masks marking a new record resolution in photolithography.

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“…A group at CNSE Polytechnic is measuring electron interactions with resist films and developing Monte Carlo modeling software that can simulate the trajectories in the energy range expected for EUV secondary electrons. 8 Most importantly, many novel resist systems are now under development. Table 2 shows a list of novel resist systems on which work has been reported.…”

Section: Presentmentioning

confidence: 99%

Novel resist approaches to enable EUV lithography in high volume manufacturing and extensions to future nodes

Neisser¹,

Cummings²,

Valente³

et al. 2015

SPIE Proceedings

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EUV lithography is needed by the semiconductor industry for both its resolution and for the process simplification it provides compared to multiple patterning. However it needs innovations to make it a success. One area where innovation is needed is resist performance. Resists that are commercially available for EUV use are typically based on conventional chemically amplified resist chemistry. So far, this has not provided the required performance at fast enough photo speed. Many innovative resist systems have been introduced in the last few years that have novel mechanisms and/or incorporate novel chemical elements with high EUV absorbance. These new systems are promising enough for EUV use that work on many of them now needs to shift to characterizing their functional parameters and optimizing their performance. For the future, new systems beyond these will have to focus on reducing the inherent noise in resist imaging. The concept of pixelated resists is introduced and it is suggested pixelated resists are one possible avenue for imaging sub 10nm features with sufficient feature size and profile control.

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Studying secondary electron behavior in EUV resists using experimentation and modeling

Cited by 19 publications

References 11 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

Photolithography reaches 6 nm half-pitch using EUV light

Novel resist approaches to enable EUV lithography in high volume manufacturing and extensions to future nodes

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