Extreme Ultraviolet Lithography Research Articles

Elastic scattering cross sections and transport of tin ions in extreme ultraviolet lithography sources

Energetic tin ions are created by laser produced plasmas in extreme-ultraviolet lithography sources where hydrogen must be used as a buffer gas to protect critical optical components. In this study, the quantum chemistry code NWChem is used to calculate the interatomic potential between singly ionized tin and molecular hydrogen. The interatomic potential was fit by an inverse-power potential, a modified universal ZBL potential, and a two-piece-Lennard-Jones potential which were in turn used to calculate the classical distance of closest approach, scattering angle, total elastic scattering cross sections. Furthermore, the universal Ziegler-Biersack-Littmark (ZBL) potential was used in the open-source binary collision approximation codes RustBCA as well as Stopping Range in Matter and Transport of Ion in Matter (SRIM/TRIM) to calculate ion ranges, straggling, and stopping cross sections in a hydrogen gas target.

Mask structure optimization for beyond EUV lithography

Mask structure optimization for beyond EUV lithography

Aqueous Developable and CO2‐Sourced Chemical Amplification Photoresist with High Performance

Seeking high‐performance photoresist is an important item for semiconductor industry due to the continuous miniaturization and intelligentization of integrated circuits. Polymer resin containing carbonate group has many desirable properties, such as high transmittance, acid sensitivity and chemical formulation, thus serving as potential photoresist material. In this work, a series of aqueous developable CO2‐sourced polycarbonate (CO2‐PC) were produced via alternating copolymerization of CO2 and epoxides bearing acid‐cleavable cyclic acetal groups in the presence of tetranuclear organoborane catalyst. The produced CO2‐PCs were investigated as chemical amplification resists in deep ultraviolet (DUV) lithography. Under the catalysis of photoacid, the acetal (ketal) groups in CO2‐PC were hydrolysed into two equivalents of hydroxyl groups, which changes the exposed areas from hydrophobicity to hydrophilicity, thus enabling the exposed regions to be developed in water. Through normalized remaining thickness analysis, the optimal CO2‐derived resist achieved a remarkable sensitivity of 1.9 mJ/cm2, a contrast of 7.9, a favorable resolution (750 nm, half pitch), and etching resistance (38% higher than poly(tert‐butyl acrylate)). Such performances outperforming commercial KrF and ArF chemical amplification resists (i.e., polyhydroxystyrene‐derived and polymethacrylate‐based resists), which endows broad application prospects in the field of DUV (248 nm and 193 nm) and extreme ultraviolet (EUV) lithography and nanomanufacturing.

Aqueous Developable and CO2-Sourced Chemical Amplification Photoresist with High Performance.

Seeking high-performance photoresist is an important item for semiconductor industry due to the continuous miniaturization and intelligentization of integrated circuits. Polymer resin containing carbonate group has many desirable properties, such as high transmittance, acid sensitivity and chemical formulation, thus serving as potential photoresist material. In this work, a series of aqueous developable CO2-sourced polycarbonate (CO2-PC) were produced via alternating copolymerization of CO2 and epoxides bearing acid-cleavable cyclic acetal groups in the presence of tetranuclear organoborane catalyst. The produced CO2-PCs were investigated as chemical amplification resists in deep ultraviolet (DUV) lithography. Under the catalysis of photoacid, the acetal (ketal) groups in CO2-PC were hydrolysed into two equivalents of hydroxyl groups, which changes the exposed areas from hydrophobicity to hydrophilicity, thus enabling the exposed regions to be developed in water. Through normalized remaining thickness analysis, the optimal CO2-derived resist achieved a remarkable sensitivity of 1.9 mJ/cm2, a contrast of 7.9, a favorable resolution (750 nm, half pitch), and etching resistance (38% higher than poly(tert-butyl acrylate)). Such performances outperforming commercial KrF and ArF chemical amplification resists (i.e., polyhydroxystyrene-derived and polymethacrylate-based resists), which endows broad application prospects in the field of DUV (248 nm and 193 nm) and extreme ultraviolet (EUV) lithography and nanomanufacturing.

RHDLPP: A multigroup radiation hydrodynamics code for laser-produced plasmas

In this paper, we introduce the RHDLPP, a flux-limited multigroup radiation hydrodynamics numerical code designed for simulating laser-produced plasmas in diverse environments. The code bifurcates into two packages: RHDLPP-LTP for low-temperature plasmas generated by moderate-intensity nanosecond lasers, and RHDLPP-HTP for high-temperature, high-density plasmas formed by high-intensity laser pulses. The core radiation hydrodynamic equations are resolved in the Eulerian frame, employing an operator-split method. This method decomposes the solution into two substeps: first, the explicit resolution of the hyperbolic subsystems integrating radiation and fluid dynamics; second, the implicit treatment of the parabolic part comprising stiff radiation diffusion, heat conduction, and energy exchange. Laser propagation and energy deposition are modeled through a hybrid approach, combining geometrical-optics ray-tracing in sub-critical plasma regions with a one-dimensional solution of the Helmholtz wave equation in super-critical areas. The thermodynamic states are ascertained using an equation of state, based on either the real gas approximation or the quotidian equation of state (QEOS). For ionization calculations, the code employs a steady-state collisional-radiation (CR) model using the screened-hydrogenic approximation. Additionally, RHDLPP includes RHDLPP-SpeIma3D, a three-dimensional spectral simulation post-processing module, for generating both temporally-spatially resolved and time-integrated spectra and imaging, facilitating direct comparisons with experimental data. The paper showcases a series of verification tests to establish the code's accuracy and efficiency, followed by application cases, including simulations of laser-produced aluminium (Al) plasmas, pre-pulse-induced target deformation of tin (Sn) microdroplets relevant to extreme ultraviolet lithography light sources, and varied imaging and spectroscopic simulations. These simulations highlight RHDLPP's effectiveness and applicability in fields such as laser-induced breakdown spectroscopy, extreme ultraviolet lithography sources, and high-energy-density physics.

Zn-Ti oxo cluster photoresists for EUV Lithography: Cluster structure and lithographic performance

Low reflectivity of multilayer mirror–induced low efficiency of existing extreme ultraviolet lithography (EUVL) has triggered the search for photoresists with heightened sensitivity. For this purpose, considerable research has focused on elements with high extreme ultraviolet (EUV) absorption, leading to considerable advancements. Solubility alteration, often resulting from ligand variations after exposure, is influenced by the cluster structure, markedly impacting lithography sensitivity. Herein, three Ti-based metal clusters, Ti6O4(OEt)8(OMc)8 (T-2), Zn2Ti4O4(OiPr)2(OMc)10 (TZ-1), and Zn4Ti2O2(OAc)2(OBu)2(OMc)10 (TZ-2), are designed and synthesized to elucidate the effects of the structure on lithography. These mixed metal–oxo clusters derived from Ti6O4(OR)8(OOCR)8 and stabilized by identical ligands exhibit structural diversity. The increase in the number of zinc atoms results in marked alterations in the oxo core, thereby triggering alterations in ligand coordination modes. These variations confer metal clusters with different solubility and lithographic properties. Analysis of the photochemical reaction mechanism and theoretical calculations reveal a reactive tridentate ligand coordination mode that considerably improves lithography sensitivity. Therefore, changing the ligand coordination mode by designing a mixed metal–oxo core holds promise for discovering new photoresists for EUV lithography.

Optimization strategy for epoxy cross-linked molecular glass photoresist in EUV lithography

The development of new resist materials is vital for fabrication techniques for next-generation microelectronics. A class of photosensitizer compositions with reactivity differences has been developed that can be used in epoxy cross-linked photoresist formulations for advanced microlithography techniques like extreme ultraviolet lithography (EUVL). With “PDN first, PAG second” combination strategy containing slow photolysis initiators (photoacid generator, PAG) and fast photolysis terminators (photodegradable nucleophile, PDN), photoresists produce photolithographic patterns with dense structure that are insoluble in the developer by epoxy cationic polymerization. This combination enhances chemical contrast between the exposed and non-exposed areas while eliminating the stochastic impact to get a lithographic structure with high mechanical strength. Lithographic formulations have been developed and tested in line-and-space patterning experiments using EUVL, and 18 nm half-pitch (HP) at a dose of 25.2 mJ·cm−2 with a line edge roughness (LER) of 2.8 nm was achieved by the combination strategy. This strategy offers the possibility of achieving higher resolution for photoresists based on a cationic polymerization mechanism.

Impact of vacuum ultraviolet photons on ultrathin polymethylmethacrylate during plasma etching

State-of-the-art extreme ultraviolet lithography requires the use of ultrathin photoresists (or resists) due to pattern stability concerns and reduced depth of focus of the extreme ultraviolet lithography scanners. Current resists for extreme ultraviolet lithography are less than 50 nm thick. These ultrathin resists further complicate pattern transfer as unintended plasma-induced damage during dry etching is more pronounced. A better understanding of the interaction of plasma species with ultrathin resists is critical for enabling pattern transfer of sub-10 nm features. Here, we study the impact of vacuum ultraviolet photons, argon ions, and argon plasma on a 40 nm thick polymethylmethacrylate film. Using a deuterium lamp, an industrial ion beam etch tool, and an industrial inductively coupled plasma etch tool, we exposed the polymer to photons, ions, and plasma, respectively. The exposed samples were then analyzed for chemical and physical changes using different characterization techniques. It was observed that the vacuum ultraviolet photons interact with the entire bulk of polymer film, while the ions only affect the surface and subsurface region. The photon exposed samples formed smaller polymer fragments at low exposure doses and further started to cross-link at high doses. In contrast, the ion modification leads to carbonization of only the top few nanometers of the polymer film, leaving the bottom bulk intact. The plasma exposed sample showed changes characteristic to both vacuum ultraviolet photons and ions and their synergism. It was stratified with a 1.34 ± 0.03 nm thick ion-caused carbonized layer on top of a 13.25 ± 0.12 nm photon-induced cross-linked layer. By studying the impact of plasma photons on ultrathin polymethylmethacrylate, we were able to establish a baseline for a testing methodology that can be extended to novel ultrathin resist platforms.

Absolute density measurement of hydrogen radicals in XUV induced plasma for tin contamination cleaning via laser-induced fluorescence

Effective cleaning of tin contamination on the collecting mirrors in extreme ultraviolet source is one of the key techniques to improve throughput and cost performance of extreme ultraviolet lithography. Hydrogen radicals produced in hydrogen plasma that is induced by wideband extreme ultraviolet radiation are expected to be utilized for in situ tin contamination cleaning in extreme ultraviolet sources. In this Letter, we clarified absolute density and cleaning ability of the hydrogen radicals produced by intense extreme ultraviolet pulse through ground state population density measurement by laser-induced fluorescence technique. The experimentally obtained radical parameters coincided well with simulation results and collisional radiative model. It was found that the extreme ultraviolet induced plasma was in quasi-steady state with abundant amount of hydrogen radicals in ground state. Further, it was found that the in situ tin contamination cleaning in extreme ultraviolet lithography source would become more practical with increase in operational parameters, such as extreme ultraviolet emission intensity, gas pressure, and radical production cross section.

A study on the resist performance of inorganic-organic resist materials for EUV and electron-beam lithography

In the realization of further miniaturization at scales of 10 nm and below in semiconductor devices, it is essential to create new resist designs, such as hybrid inorganic-organic resist materials for ionizing radiation, in order to clarify the effect the structure of metal resist on resist performance. In this study, some hybrid inorganic-organic resist materials known as metal-oxo clusters were synthesized, and their lithographic characteristics were investigated to clarify the relationship between resist performance, such as sensitivity, resolution, and their absorption coefficient or cross section, and the density of their elements by using EUV and electron-beam (EB) exposure. Our results indicated that the sensitivity in Hf-based oxo clusters was higher than that of Ti-based and Zr-based oxo clusters in both EB and EUV exposure. Although the exposure dose was not optimized, the patterns of Ti-based, Zr-based, and Hf-based oxo clusters showed 100, 50, and 32 nm line-and-space patterns at doses of 250, 80, and 25 μC cm−2, respectively. We clarified that it is very important for new resist designs such as hybrid inorganic-organic resists to increase the photo-absorption cross section and density of elements for EUV and EB without degradation of film quality. In addition, the size and homogeneity of the building blocks and film quality are very important for the resist performance of hybrid inorganic-organic resist materials. Furthermore, it is clarified that the etch durability of metal-oxo clusters is higher than conventional resist materials, and this is much increased by annealing them at 800 °C.

Dissolution dynamics of zirconia nanocluster resist

The metal oxide resists are promising materials for the high numerical aperture EUV lithography. In the metal oxide resists, the bridging ligands are generated upon exposure to radiations, which results in the formation of a pattern insoluble in developers. In this study, the dissolution dynamics of zirconia nanocluster resist was investigated using a quartz crystal microbalance method. The ligand was methacrylate. The developers used were ethyl, butyl, amyl, hexyl, 2-methylbutyl, and 3-methylbutyl acetates. The zirconia nanocluster resist showed characteristic dissolution dynamics. After the immersion into developers, the frequency slowly decreased with approximately constant impedance (no viscosity change of the film) for a while and then rapidly dissolved with the softening of resist film. The dependences of dissolution dynamics on the molecular structures of acetates and post exposure baking were clarified. The effect of branched structure at the third position of butyl was, in particular, remarkable.

Progress in Polyhedral Oligomeric Silsesquioxane (POSS) Photoresists: A Comprehensive Review across Lithographic Systems.

This paper offers a comprehensive overview of the polyhedral oligomeric silsesquioxane (POSS) and POSS-based composites within the realm of photoresist resin. The study involves a systematic exploration and discussion of the contributions made by POSS across various lithographic systems, with specific emphasis on critical parameters such as film formation, sensitivity, resolution, solubility, and edge roughness. These lithographic systems encompass X-ray lithography (XRL), deep ultraviolet nanoimprint lithography (DUV-NIL), extreme ultraviolet lithography (EUV), and guided self-assembled lithography (DSA). The principal objective of this paper is to furnish valuable insights into the development and utilization of POSS-based photoresist materials in diverse lithographic contexts.

SCAPSM: attenuated phase-shift mask structure for EUV lithography.

The attenuated phase-shift mask (Att. PSM) is proven to be a promising resolution enhancement technology (RET) to improve the imaging performance in extreme ultraviolet (EUV) lithography. However, due to the reflective nature of the mask structure, the serious shadowing effect can affect the diffraction near field of the mask intensely and further impact the lithography imaging. With the purpose of improving the contrast of lithography imaging, a novel structure of the Att. PSM, to the best of our knowledge, is proposed in this paper. By introducing an absorbent sidewall along the edge of the mask absorber, the diffraction and shadowing effects can be mitigated. By applying the Kirchhoff approximation of mask diffraction, the ability of the novel structure to improve imaging performance is theoretically analyzed. Additionally, these analyses are confirmed by rigorous lithography simulations. The simulation results demonstrate that the proposed mask structure can improve the imaging contrast of EUV lithography, which has potential usage in advanced integrated circuit (IC) manufacturing.

Pattern deformation mitigation for EUV photoresists using wafer backside cleaning techniques

This study delves into the effects of wafer backside particles on pattern defocus in EUV lithography (EUVL). Additionally, the potential mitigation of this pattern defocus was examined through wafer backside cleaning. Comparative analyses were conducted between EUVL patterning tests performed using wafers with contaminated and cleaned wafer backside. Defocus points and abnormal critical dimensions (CDs) on the photoresist patterns at the wafer frontside were detected using scanning electron microscopy and optical CD measurement, respectively. The specific locations of these defocus or abnormal CD points were compared and confirmed to be correlated with particles that were present on the same locations on the backside of the wafer. Furthermore, it was found that an effective backside cleaning process can mitigate pattern defocus caused by these wafer backside particles.

Patterning Infrastructure Development for Advanced EUV Lithography: Continuing Dimensional Scaling Through EUV Lithography to Support Moore’s Law

Patterning Infrastructure Development for Advanced EUV Lithography: Continuing Dimensional Scaling Through EUV Lithography to Support Moore’s Law

The Evolvement of Lithography Optics Towards Advanced EUV Lithography: Enabling the Continuation of Moore’s Law for Six Decades

The Evolvement of Lithography Optics Towards Advanced EUV Lithography: Enabling the Continuation of Moore’s Law for Six Decades

XUV Absorption Spectroscopy and Photoconversion of a Tin-Oxo Cage Photoresist.

Extreme ultraviolet lithography has recently been introduced in high-volume production of integrated circuits for manufacturing the smallest features in high-end computer chips. Hybrid organic/inorganic materials are considered as the next generation of photoresists for this technology, but detailed knowledge about the response of such materials to the ionizing radiation used (13.5 nm, 92 eV) is still scarce. In the present work, we use broadband high-harmonic radiation in the energy range 22-70 eV for absorption spectroscopy and photobleaching (that is, the decrease of absorbance) of thin films of an n-butyltin oxo-cage, a representative of the class of metal-based EUV photoresist. The shape of the absorption spectrum in the range 22-92 eV matches well with the spectrum predicted using tabulated atomic cross sections. The photobleaching results are consistent with loss of the butyl side groups due to the breaking of Sn-C bonds following photoionization. Bleaching is strongest in the low-energy range (<40 eV), where the absorption is largely due to the carbon atoms in the organic groups. At higher energies (42-70 eV), absorption is dominated by the tin atoms, and since these remain in the film after photoconversion, the absorption change in this region is smaller. It is estimated that after prolonged irradiation (up to ∼3 J cm-2 in the range 22-40 eV) about 70% of the hydrocarbon groups are removed from the film. The rate of bleaching is high at the beginning of exposure, but it rapidly decreases with increasing conversion. We rationalize this using density functional theory calculations: the first Sn-C bonds are efficiently cleaved (quantum yield Φ ≈ 0.9), because the highest occupied molecular orbitals (HOMOs) (from which an electron is removed after photoionization) are located on Sn-C sigma bonds. In the photoproducts, the HOMO is localized on tin atoms that have lost their hydrocarbon group (formally reduced to the Sn(II) oxidation state), and holes formed on those tin atoms lead to less efficient cleavage reactions. Our results reveal the primary reaction steps following excitation with ionizing radiation of tin-oxo cages. Our methodology represents a systematic approach of studying and quantitatively assessing the performance of new photoresists and as such enables the development of future EUV photoresists.

Wet cleaning of Ta-based extreme ultraviolet photomasks at room temperature

Owing to the wavelength-dependent limits of the deep ultraviolet exposure process, the semiconductor industry introduced extreme ultraviolet (EUV) lithography operating at a 13.5 nm wavelength. Traditional photomasks employ pellicles for protection; however, EUV-specific pellicles are not widely applicable to commercial processes, requiring the development of a EUV photomask cleaning method. In this study, a wet cleaning method for Ta-based EUV photomasks at room temperature was systematically examined in terms of key parameters, including the pattern step height, surface topography, and particulate count, via atomic force microscopy and x-ray reflectivity. Post sulfuric acid-hydrogen peroxide mixture (SPM) treatment, the photomask exhibited a stable step height, indicating minimal pattern degradation. Additionally, discernible alterations in the surface roughness and a decrease in particle count were observed, further indicating to the effectiveness of SPM-mediated cleaning. Conversely, following standard clean-1 (SC-1) treatment, while the pattern step height remained relatively unchanged, a notable increase in surface irregularities and macroscopic particulates was observed, suggesting a suboptimal cleaning efficiency of the SC-1 solution despite its potential for pattern structure preservation. Our room temperature wet cleaning method efficiently reduces wear-out and successfully eliminates contaminants, potentially prolonging the EUV photomask’s productivity and durability.

Dissolution dynamics of poly(4-hydroxystyrene-co-methacrylic acid) in tetraalkylammonium hydroxide aqueous solutions

Resist materials and their lithography processes are essential for achieving further miniaturization in semiconductor microfabrication. In the sub-20 nm half-pitch region, the development process becomes particularly important due to the occurrence of stochastic defects (pinching and bridging). However, the details of dissolution dynamics are still unclear. In this study, we investigated the dissolution dynamics of poly(4-hydroxystyrene-co-methacrylic acid) (PHSMA) films in tetraalkylammonium hydroxide (TAAH) aqueous solutions using a quartz crystal microbalance method. PHSMA is a typical backbone polymer used in extreme UV lithography. For poly(4-hydroxystyrene) films, it has been reported that the dissolution mode changed when the alkyl chain length of TAAH increased. However, the mode change was not observed for PHSMA films. This difference is considered to be caused by the formation of thick transient swelling layers of PHSMA films owing to the fast water intake and the molecular interaction of the hydroxyl groups of hydroxystyrene units.

Multi-beam mask writing opens up new fields of application, including curvilinear mask pattern for high numerical aperture extreme ultraviolet lithography

Multi-beam mask writing opens up new fields of application, including curvilinear mask pattern for high numerical aperture extreme ultraviolet lithography