Extreme Ultraviolet Lithography Research Articles

Aberration budget analysis of EUV lithography from the imaging performance of a contact layer in a 5 nm technology node.

By analyzing the impact of aberration in an extreme ultraviolet lithography projector on the imaging indicators of the test patterns for a contact layer in a 5nm technology node, this paper establishes a mathematical aberration model based on the back propagating neutral network. On the basis of an aberration model, a method for estimating the aberration budget is proposed, which can help reduce the difficulty of achieving imaging performance thresholds in actual production. The performance of the results given by this method is verified by using a rigorous simulation. The results show that the model is highly accurate in predicting an aberration distribution that meets the requirements through an inverse sensitivity analysis and can calculate the wavefront aberration margin based on imaging indicators.

Protective Freely Hanging Films for Projection Lithography Installations in the Extreme UV Range

Variants of the structures of freely hanging films with a high transmittance coefficient at a wave-length of 13.5 nm, which were developed for use in the projection of extreme ultraviolet (EUV) lithography as protective and filtering elements, are considered. Our attention is focused on the most problematic—in terms of manufacturing and the requirements on their characteristics—ultrathin freely hanging films (pelli-cles), which are installed in front of the mask (photomask) in modern EUV scanners and serve to protect the sur-face of the mask from contamination. The main approaches used to manufacture ultrathin freely hanging large-aperture films are compared. A brief review of the research on the development of high transmittance pellicles at a wavelength of 11.2 nm, which may become an operating wavelength for future EUV lithography, is given.

The Moore's Law Machine: The Next Trick to Tinier Transistors is High-Numerical-Aperture EUV Lithography

The Moore's Law Machine: The Next Trick to Tinier Transistors is High-Numerical-Aperture EUV Lithography

Development of EUV interference lithography for 25 nm line/space patterns

In this study, we present the performance of an extreme ultraviolet interference lithography (EUV-IL) setup that was reconstructed at Taiwan Light Source 21B2 EUV beamline in the National Synchrotron Radiation Research Center (NSRRC), Taiwan. An easy-to-perform fabrication method to produce a high-quality transmission grating mask and a simple design of experimental setup for EUV-IL were developed. The current EUV-IL setup is capable of fabricating line/space patterns down to 25 nm half-pitch in hydrogen silsesquioxane (HSQ) resist. Preliminary exposure results revealed that optimized slit width and exposure time significantly improved line/space pattern quality. The current EUV-IL tool at NSRRC can be used for nano-patterning and resist screening to advance the next generation of semiconductor devices.

Particle charging during pulsed EUV exposures with afterglow effect

Nanoparticle charging processes along with background spatial–temporal plasma profile have been investigated using 3D particle-in-cell simulations in a pulsed extreme ultraviolet (EUV) exposure environment. The particle charge polarity (positive or negative) strongly depends on its size, location, and background transient plasma conditions. The particle (100 nm diameter in size and conducting material) charge reaches a steady state in a single pulse (20 µs) within the EUV beams compared to particles outside the beam requiring multiple pulses. The larger the particle size, the lower the number of pulses required to reach a steady state. The charge of a particle decreases with pressure at a faster rate outside the beam compared to inside. These results are crucial for particle contamination (defectivity) control strategies for EUV lithography machines.

Extreme Ultraviolet Radiation Sources from Dense Plasmas

The concept of dense and hot plasmas can be used to build up powerful and brilliant radiation sources in the soft X-ray and extreme ultraviolet spectral range. Such sources are used for nanoscale imaging and structuring applications, such as EUV lithography in the semiconductor industry. An understanding of light-generating atomic processes and radiation transport within the plasma is mandatory for optimization. The basic principles and technical concepts using either a pulsed laser or a gas discharge for plasma generation are presented, and critical aspects in the ionization dynamics are outlined within the framework of a simplified atomic physics model.

Fast diffraction model of an EUV mask based on asymmetric patch data fitting.

Calculating the diffraction near field (DNF) of a three-dimensional (3D) mask is a key problem in the extreme ultraviolet (EUV) lithography imaging modeling. This paper proposes a fast DNF model of an EUV mask based on the asymmetric patch data fitting method. Due to the asymmetric imaging characteristics of the EUV lithography system, a DNF library is built up including the training mask patches posed in different orientations and their rigorous DNF results. These training patches include some representative local mask features such as the convex corners, concave corners, and edge segments in four directions. Then, a convolution-based compact model is developed to rapidly simulate the DNFs of 3D masks, where the convolution kernels are inversely calculated to fit all of the training data. Finally, the proposed model is verified by simulation experiments. Compared to a state-of-the-art EUV mask model based on machine learning, the proposed method can further reduce the computation time by 60%-70% and roughly obtain the same simulation accuracy.

Chemical Identification of Sub-20 nm Defects and Sub-Monolayer Residues with Nano IR PiFM

With the advent of EUV lithography and other emerging processes such as area selective deposition, and SOIC hybrid bonding, the need to identify the chemical composition of defects is of paramount importance. The defects of concern range from 10nm to 500nm in lateral size and as thin as ~ 1 nm in thickness, which the current batch of molecular analytical tools cannot address adequately since the indications are that many of the defects and residues detected are organic in nature. In this paper, a relatively new nanoscale technique called infrared photo-induced force microscopy (IR PiFM), which combines non-contact atomic force microscopy (AFM) and infrared (IR) spectroscopy with ~ 5 nm spatial resolution, is introduced. The paper will show how the nanoscale hyperspectral IR PiFM data can provide unambiguous and speedy feedback to process engineers engaged in EUV lithography and other advanced semiconductor processes.

On Gas-Phase Selective Dry Etching in 3D Inflections

Semiconductor industry periodically goes through major transitions in the architectures and materials. The previous such transition was the Logic transition to FinFET and NAND transition to 3DNAND that revolutionized the two devices and accelerated PPAC (power, performance, area, cost) progress. Over the last decade, introduction of EUV lithography has driven the device miniaturization and furthered the cause of PPAC, but with the same architecture. The accelerating technological needs at lower cost point with better power efficiency are driving the current push in fundamental architectural changes and new materials introductions, especially in Logic and DRAM with a transition to 3D structures. This moves the critical etches from traditional RIE to selective isotropic etching. Furthermore, newer materials and requirements of better interfaces in these 3D structures are driving the need for dry selective treatments with good isotropicity and free of damage. This paper will give an overview of the current state of selective dry etch and progress in treatments.

Pinpoint Particle Removal for EUV Pellicle Productivity Enhancement

The EUV lithography process is increasingly employed in the advanced semiconductor process, and high-NA EUV equipment is being developed for high-volume manufacturing. Therefore, particle contamination control for EUV masks is a key success factor for the yield increase of the EUV lithography process in the future and for this, the needs of EUV pellicle will increase. Although materials for the EUV pellicle membrane are still under development, unlike ArF pellicles, its fabrication is complicated and difficult, resulting in low production yield and high production costs. To reduce EUV pellicle operating costs, it is possible to consider ways to reduce production costs by enhancing the yield of EUV pellicle or reusing particle contaminated EUV pellicle by particle removal. Both methods require damage-free particle removal technology of EUV pellicle. Pinpoint particle removal technology, a cleaning technology that satisfies these requirements, was developed, and particles bigger than 5 μm could be removed in a cleanroom environment without damaging fragile EUV pellicle. The possibility of the damage-free EUV pellicle cleaning process was verified through the process window evaluation of Pinpoint cleaning technology.

Extreme ultraviolet pellicle wrinkles influence on mask 3D effects: experimental demonstration.

Extreme ultraviolet (EUV) lithography uses reflective optics and a thick mask absorber, leading to mask 3D (M3D) effects. These M3D effects cause disparities in the amplitudes and phases of EUV mask diffractions, impacting mask imaging performance and reducing process yields. Our findings demonstrate that wrinkles in the EUV pellicle can exacerbate M3D effects. This imbalance results in critical dimension variation, image contrast loss, and pattern shift in mask images. Therefore, the use of a pellicle material with thermodynamic characteristics that minimize wrinkles when exposed to EUV rays is imperative.

Optimizing extreme ultraviolet lithography imaging metrics as a function of absorber thickness and illumination source: a simulation case study of Ta-Co alloy

Optimizing extreme ultraviolet lithography imaging metrics as a function of absorber thickness and illumination source: a simulation case study of Ta-Co alloy

Vapor‐Phase Infiltrated Organic–Inorganic Positive‐Tone Hybrid Photoresist for Extreme UV Lithography

AbstractContinuing extreme downscaling of semiconductor devices, essential for high performance and energy efficiency of future microelectronics, hinges on extreme ultraviolet lithography (EUVL) and addressing associated challenges. One of such challenges is a need for improved EUV photoresists featuring simultaneously high sensitivity, resolution, and etch selectivity. Here, a new, positive‐tone, organic–inorganic hybrid EUV photoresist is demonstrated that delivers a high‐resolution EUVL and electron‐beam lithography (EBL) patterning capability combined with high sensitivity and etch resistance. The new resist, poly(methyl methacrylate) infiltrated with indium oxide (PMMA‐InOx), is synthesized via vapor‐phase infiltration (VPI), a material hybridization technique derived from atomic layer deposition. The weak binding of the gaseous indium precursor, trimethylindium, to the carbonyl group in PMMA allows the synthesis of hybrids with inorganic content distributed uniformly in the resist, enabling high EUVL and EBL sensitivities (18 mJ cm−2 and 300 µC cm−2, respectively) and high‐resolution positive‐tone EUVL patterning (e.g., 40 nm half‐pitch line‐space and 50 nm diameter contact hole patterns) with high Si etch selectivity (>30–40). The low exposure doses required to pattern the PMMA‐InOx hybrid resist, high etch resistance, and processing strategies, which are developed, can pave the way for using infiltration‐synthesized hybrid thin films as reliable positive‐tone EUV photoresists for future semiconductor patterning.

Photoemission spectroscopy on photoresist materials: A protocol for analysis of radiation sensitive materials

The continued downscaling, following the so-called Moore's law, has motivated the development and use of extreme ultraviolet (EUV) lithography scanners with specialized photoresists. Since the quality and precision of the transferred circuit pattern are determined by the EUV-induced chemical changes in the photoresist, having a deep understanding of these chemical changes is of pivotal importance. For this purpose, several spectroscopic and material characterization techniques have already been employed. Among them, photoemission can be essential as it not only allows direct probing of chemical bonds in a quantitative way but also provides useful information regarding the generation and distribution of primary and secondary electrons. However, since high energy photons are being employed for characterization of a photosensitive material, modification of the sample during the measurement is possible, and this must be considered when investigating the chemical changes in the photoresist before and after exposure to EUV light. In this paper, we investigate the chemical changes occurring during the photoemission measurements of an unexposed, model chemically amplified resist based on the well-known environmentally stable chemically amplified photoresist as a function of a number of measurement parameters, using both an x ray (AlKα, 1486.6 eV) and a UV source (HeII, 40.8 eV). We will show that these chemical changes can be simulated through theoretical modeling of the photoemission spectra. Based on these results, we propose a measurement protocol allowing to minimize or eliminate this modification which will help to guide (or enable) photoemission measurements on radiation-sensitive materials (e.g., photoresists).

Chemically Amplified Molecular Glass Photoresist Regulated by 2-Aminoanthracene Additive for Electron Beam Lithography and Extreme Ultraviolet Lithography.

2-Aminoanthracene was used as a nucleophilic additive in a molecular glass photoresist, bisphenol A derivative (BPA-6-epoxy), to improve advanced lithography performance. The effect of 2-aminoanthracene on BPA-6-epoxy was studied by electron beam lithography (EBL) and extreme ultraviolet lithography (EUVL). The result indicates that the additive can optimize the pattern outline by regulating epoxy cross-linking reaction, avoiding photoresist footing effectively in EBL. The EUVL result demonstrates that 2-aminoanthracene can significantly reduce line width roughness (LWR) for HP (Half-Pitch) 25 nm (from 4.9 to 3.8 nm) and HP 22 nm (from 6.9 to 3.0 nm). The power spectrum density (PSD) curve further confirms the reduction of roughness at medium and high frequency for HP 25 nm and the whole range of frequency for HP 22 nm, respectively. The study offers useful guidelines to improve the roughness of a chemically amplified molecular glass photoresist with epoxy groups for electron beam lithography and extreme ultraviolet lithography.

Mean Free Path of Electrons in Organic Photoresists for Extreme Ultraviolet Lithography in the Kinetic Energy Range 20-450 eV.

The blur caused by the nonzero mean free path of electrons in photoresists exposed by extreme ultraviolet lithography has detrimental consequences on patterning resolution, but its effect is difficult to quantify experimentally. So far, most mean free path calculations use the dielectric formalism, which is an approximation valid in the optical limit and fails at low kinetic energy. In this work, we used a modified substrate-overlayer technique that exploited the attenuation of the Si 2p core level originating specifically from the native silicon dioxide to evaluate the attenuation of electrons traveling through 2 and 4 nm of photoresist overlayers to provide a close estimation of the inelastic mean free path relevant for photoresist lithography patterning and for electron microscopy. The photoemission spectra were collected in the proximity of the Si 2p edge (binding energy ∼101 eV) using synchrotron light of energy ℏω ranging between 120 and 550 eV. The photoresist films were prototypical chemically amplified resists based on organic copolymer of poly hydroxystyrene and tertbutyl methacrylate with and without triphenyl sulfonium perfluoro-1-butanesufonate photoacid generator and trioctylamine quencher. The inelastic mean free path of electrons, in the range that is relevant for photoresist exposure in extreme ultraviolet lithography (20-92 eV), was found to be between 1 and 2 nm. At higher kinetic energy, the mean free path increased, consistently with the well-known behavior. The presence of the photoacid generator and quencher did not change the mean free path, within experimental error. Our results are discussed and compared with the existing literature on organic molecules measured via dielectric formalism and electron transmission experiments.

Fast diffraction model of lithography mask based on improved pixel-to-pixel generative adversarial network.

Mask three-dimensional (3D) effect is a vital influence factor of imaging performance in the advanced extreme ultraviolet (EUV) lithography system. However, the rigorous 3D mask diffraction model is very time-consuming and brings a great computational burden. This paper develops a fast and accurate method to calculate the mask diffraction near-field (DNF) based on an improved pixel-to-pixel generative adversarial network, where the deformable convolution is introduced for fitting the crosstalk effect between mask feature edges. The long short-term memory model is added to the generator network to fuse and exchange information between the real parts and imaginary parts of DNF matrices. In addition, the simulation accuracy of DNF is enhanced by using the subpixel super-resolution method in the up-sampling step. The calculation accuracy is improved by more than 50% compared to the traditional network, and the calculational efficiency is improved by 128-folds compared to the rigorous electromagnetic field simulation method.

Suppressing of secondary electron diffusion for high-precision nanofabrication

Nanopatterning is a well-established approach to fabricating nanostructures in electronics and optics, and exploiting patterning strategy to achieve smaller feature sizes and higher precision is urgently and constantly pursued. State-of-the-art extreme ultraviolet lithography and electron beam lithography have proven to produce smaller sizes. However, for such energetic radiation-based approaches, the serious diffusion behavior of the radiolytic low-energy secondary electrons will result in unpredictable defects in the unexposed matrix, limiting the ultimate resolution and hindering its potential in sub-10 nm patterning. Herein, we report significant progress in high-resolution patterning via suppressing of residues caused by secondary electron diffusion, and 10 nm line-space nanostructures are achieved by utilizing a free radical quencher in patterning a highly sensitive zirconium-containing photoresist. Lithography evaluation combined with theoretical calculation reveals this novel radical quencher approach can effectively suppress undesired electronic excitation and ionization reactions, thereby significantly improving resolution and edge roughness. By inhibiting secondary electron-induced active species, this quenching mechanism is found to increase the onset dose and effectively narrow the energy deposition; thus improving the patterning contrast and facilitating the acquisition of straight lines with sharp edges. This work provides a new perspective on active species diffusion control for higher precision nanoscale fabrication.

Reaction mechanisms of Sn-complex-side-chain polymer used for extreme ultraviolet lithography, studied by electron pulse radiolysis and γ-radiolysis

The development of highly sensitive resists containing tin, which has a large EUV absorption cross section, has recently attracted considerable attention in EUV lithography. The effective utilization of secondary electrons is required for the development of high-performance resists. It is important to design resist materials on the basis of the mechanism of radiation chemical reactions. In this study, the radiation-induced reactions of tetraphenyltin (TPSn), triphenylsulfonium triflate (TPS-Tf), and the copolymer of triphenyl(4-vinylphenyl) stannane (TPSnSt) and 4-methacryloxyphenyldiphenylsulfonium triflate (MAPDPS-Tf) were investigated by electron pulse radiolysis and γ-radiolysis in controlled reaction systems. The decomposed products were analyzed by high-performance liquid chromatography. The G values of decomposed products were determined. For the copolymer, the holes generated by ionizing radiations moved to Sn units and electrons moved to TPS-Tf units. The tin complex side chain decomposed, producing benzene after hole transfer.

Defect risks at interfaces of chemically amplified resists in extreme ultraviolet lithography process

In EUV lithography, stochastically generated defects (stochastic defects) are a significant issue. In this study, the formation of the latent images of line-and-space resist patterns was simulated to assess the dependence of defect risks on the conditions of resist interfaces. The protected unit distribution was calculated on the basis of the sensitization and reaction mechanisms of chemically amplified EUV resists using a Monte Carlo method. The pinching and bridging risks were calculated to be 7.4 × 10−3–2.0 × 10−2 and 1.5 × 10−3–2.6 × 10−1, respectively, depending on the boundary conditions of low-energy secondary electrons at the interfaces. Using the obtained defect risks, we roughly estimated that the impacts of interfacial effects on pinching and bridging probabilities for low-energy secondary electrons were more than one order of magnitude and more than six orders of magnitude, respectively. Controlling the low-energy electrons at the interfaces is important for the suppression of stochastic defects.