Extreme ultraviolet (EUV) lithography is a cornerstone of next-generation computer chip patterning technologies, yet continued improvements in photoresist sensitivity and pattern fidelity are required to enable high-numerical-aperture EUV exposure tools. Numerous studies have shown that underlayers can significantly enhance EUV photoresist performance, including reduced dose-to-size and improved pattern quality. The physical and chemical mechanisms underlying these improvements remain incompletely understood. We investigate one such mechanism: the transport of the photo-acid generator (PAG) in an EUV photoresist–underlayer system. Using time-of-flight secondary ion mass spectrometry depth profiling, we demonstrate that PAG molecules from an EUV chemically amplified resist penetrate significantly into a cross-linked siloxane underlayer. Through a series of experiments, we show that this penetration does not arise from secondary ion mass spectrometry knock-on artifacts, the underlayer already containing PAG-like additives in it or thermally enhanced diffusion. Instead, we find that PAG transport occurs during the spin-coating step at room temperature by the casting solvent. Complementary experiments further show that PAG initially loaded into the underlayer can be leached out by solvent during spin-coating. These results establish solvent-assisted small-molecule transport as a dominant mechanism governing photoresist–underlayer interactions and provide a mechanistic explanation for previously reported dose-to-size reductions for EUV photoresists.

This study introduces an innovative extreme ultraviolet (EUV) resist featuring a vertically oriented molecular wire architecture, designed to achieve exceptionally low line edge roughness (LER). The resist is synthesized via molecular layer deposition, a gas-phase technique that allows precise monolayer-level control over thickness, ensuring excellent reproducibility, conformality, and uniformity. The hybrid multilayer resist is constructed through controlled ligand-exchange reactions between diethylzinc and 3-mercaptopropanol (3MP), which create vertically oriented molecular wires with widths below 1 nm. This innovative structure achieves an unprecedentedly low LER of 1.37 nm at a dose of 60 mJ/cm2. EUV exposure induces unique cross-linking coordination bonds between the zinc atoms and the oxygen and sulfur atoms in 3MP without degassing, thereby enhancing EUV sensitivity. The combination of vertically oriented high-aspect-ratio molecular wires and effective lateral cross-linking significantly improves EUV sensitivity and robustness during etching. This pioneering hybrid multilayer EUV resist may satisfy the stringent requirements of advanced semiconductor manufacturing.

Ligands play roles in determining the properties of metal-containing EUV resists. In this study, a new series of complexes of the type R3Sb(O2CR')(2) have been developed, showcasing positive-tone imaging. Ten R3Sb(O2CR')(2) complexes were synthesized with variations in the R and R' groups. Studies focusing on development solution, polymerizable olefin content, and molecular weight of these complexes indicated that styrene carboxylate ligands and low molecular weight R groups demonstrated positive-tone performance with fast photospeeds.

We conducted a series of mechanistic studies involving the exposure of antimony carboxylate complexes (R3Sb(O2CR')(2)) which exhibit positive-tone patterning upon to EUV light or e-beams. The volatile photoproducts were evaluated using in situ mass spectrometry, revealing carbon dioxide and fragments of the R ligands (isopropenyl, isopropyl). Additionally, fragments corresponding to the breaking of the metal-carbon bond and metal-oxygen bond were observed. These results provide evidence that polymerization occurs for photoresists containing terminal olefins, resulting in a nonvolatile R'-group after decarboxylation. Ultimately, we propose a network of plausible mechanistic steps that are consistent with the structure-function and mass-spectral outgassing experiments.

Extreme ultraviolet (EUV) lithography, utilizing a 13.5 nm wavelength, has significantly advanced the semiconductor industry. Key to this progress are developments in chemically amplified photoresists (CAR), though challenges like stochastic effects in photoresists complicate achieving required resolution and line edge roughness. To address these issues, the study explores polymethyl methacrylate (PMMA) as a model system, focusing on the impact of polymer molecular weight on roughness and defectivity. The paper investigates how variations in molecular weight influence the dissolution rate of PMMA in a developer, using commercial PMMA samples mixed with varying molecular weights to assess their dissolution behavior under EUV exposure.

The ability of chemically amplified resists to transfer an aerial image at increasingly smaller dimensions is critical to EUV lithography success at increasingly smaller process nodes [Bisschop and Hendrickx, Extreme Ultraviolet (EUV) Lithography X (SPIE) 10957 37 (2019)]. Stochastic inhomogeneities in resist exposure and patterning have been studied, which include photon shot noise and resist surface roughness. However, previous work has indicated that inhomogeneities and defectivity are present in multicomponent resists beyond those predicted by random statistics [Jablonski et al. (Santa Clara, CA) p. 302 (2004); Woodward et al. Advances in Resist Materials and Processing Technology XXIV (SPIE) 6519 416 (2007); Fedynyshyn et al. Advances in Resist Technology and Processing XXIII (SPIE) 6153 387 (2006); Fedynyshyn et al. J. Vac. Sci. Technol. B, 24, 3031 (2006); Kohyama et al. Advances in Patterning Materials and Processes XXXVI (SPIE) 10960 218 (2019)]. This is thought to be due to self-segregation of components in the multi-component chemically amplified resist. The results in this paper show that the most critical part of the resist chemical segregation occurs during the spin coating process after a significant amount of the solvent has evaporated, but while there is still enough solvent to enable molecular mobility within the resist.

Conventional chemically amplified resists (CARs) rely on the usage of photoacid generators to serve as the source of chemical amplification. However, acid diffusion inevitably accompanies CARs and has led to the resolution, line edge roughness, and sensitivity (RLS) trade-off, which is the most challenging technical problem for modern photoresists. Herein, we take advantage of the self-immolative property of polyphthalaldehyde (PPA) derivatives to create end-cap enabled chain scissionable resists for extreme ultraviolet (EUV) lithography. The feasibility of this strategy was demonstrated under UV photodegradation experiments. The dose-to-clear (DTC) under EUV radiation was 90 mJ/cm2 for the most promising resist, representing more than a 100-fold improvement over previous PPA resists. Density functional theory (DFT) calculations were conducted to understand the structural origin of end-cap EUV sensitivity.

We present a new class of EUV antimony carboxylate photoresists with enhanced reactivity and contrast, through the substitution of heteroatoms into the carboxylate. The lithographic performance of (C6H5)(3)Sb(O2CCH2X)(2) photoresists in which X = methoxy, bromine or iodine is presented. The addition of iodine to the photoresist greatly improves dissolution contrast. Utilizing in-situ mass spectrometry, we show how the identity and degree of volatile photoproducts created during EUV exposure change with the composition of the heteroatom.

Extreme ultraviolet (EUV) lithography is required for advanced node semiconductor device fabrication. The stochastic effects in EUV lithography are problematic, especially with regards to pattern roughness and defect formation. In this study, we performed atomic force microscopy (AFM) on an EUV photoresist surface to determine the surface roughness, height histogram, line scan, area ratio, and power spectral density (PSD). Polymethyl methacrylate (PMMA) for nonchemically amplified resist (non-CAR), and poly(4-hydroxystyrene)(t-butyl acrylate) copolymer (PHS:tBA) and poly(4-hydroxystyrene)(polystyrene)( t-butyl acrylate) copolymer (PHSPS:tBA) with/ di-(t-butylphenyl)iodonium perfluorobutane sulfonate (TBPI-PFBS)/tetrabutylammonium lactate (TBAL) for chemically amplified resist (CAR) were examined. In this CAR system, the exposure and dark loss contributed to the surface variation of root mean square (RMS) of 1.5 nm and 0.95 nm under a nominal exposure dosage of 8 mu C/cm2. The contribution of dark loss was further evaluated from the effects of backbone polymer composition and photoacid generator (PAG) loading. The dark loss induced surface roughness can be attributed to the competition of etch selectivity in the resist components. A skewness of the height histogram and change of correlation in PSD are related to the dark loss induced surface variation.

Abstract. Extreme ultraviolet lithography (EUVL) has been adopted into high volume production for advanced logic device manufacturing. Due to the continuous size scaling requirement for interconnect fabrication, EUVL with self-aligned double patterning (SADP) formation has attracted substantial research attention. The current challenge in EUV SADP is the pattern transfer process from lithography to mandrel formation. In this step, the target critical dimension (CD) of the feature needs to shrink by half from the lithography CD during the etch process. The increasing aspect ratio during this etch potentially deteriorates the pattern validity and the line edge roughness (LER). In addition to these challenges, EUVL has a fundamental bottleneck due to stochastic effects, which can lead to device degradation by defect formation and edge placement error (EPE). LER of the line and space pattern is one of the main contributors to EPE. Effective methods of LER reduction in both process and integration are needed in order to reduce pattern variation and boost device performance. In our study, we examine a technique to reduce LER on the EUV SADP line pattern. This technique involves the surface modification on the spin-on carbon (SOC) layer in the patterning stack and tone inversion process. We had found a trend between surface hydrophobicity of the SOC and the EUV SADP LER performance. The condition that increased the hydrophobicity of the SOC resulted in a lower LER performance after tone inversion. The tested conditions include direct current superposition (DCS) function with H2 plasma, fluorocarbon plasma, and the combination of DCS with H2 plasma and trimethylsilane dimethylamine deposition. On 20-nm pitch EUV SADP, this technique shows 26% of LER improvement from lithography to SADP formation. PSD analysis recorded about 6% and 30% of the LER improvement at the correlation length of >200  nm and 200 to 30 nm, respectively. A demonstration of this technique for a further scaling to 15-nm pitch also shows an LER reduction of 30% from lithography to SADP formation.

Equipment failure can cause problems within the semiconductor industry, including product loss or contamination and unscheduled maintenance. In this paper, we apply Weibull analysis on electrochemical sensor failure and suspension data from the last eight years. Further analysis is achieved through breaking down the sensor data by model and chemistry. Using the Weibull parameters calculated and applying them to a simple financial model, we determine which sensor would give the best return on investment (ROI). The results shown in this paper will demonstrate a method for analyzing equipment or component reliability to better determine preventative maintenance practices and equipment selection based on facility operation and costs. It can be applied to a variety of equipment in a fabrication or manufacturing facility to provide a way to better plan for reliability and cost savings.

Extreme-ultraviolet (~13.5 nm) lithography is much different than the previous lithographic wavelength such that chemical reactions within the resist are caused by electrons generated from ionization. As the lithographic community moves towards printing more advanced nodes, the secondary electron blur from extreme-ultraviolet photons becomes more critical. Understanding the range of the secondary electrons from the photoionization site would provide insight into patterning capabilities for different photoresists and aid in the development of improved models. Here, we aim to determine the range of electrons by measuring the thickness loss due to top-down electron beam exposure. More importantly, this work focuses on measuring the thickness loss due to incident electrons with energies less than 80 eV for two different resist systems: (1) a chemically amplified photoresist where acid diffusion affects the depth of solubility changing reactions, and (2) a non-chemically amplified photoresist, PMMA, where no acid diffusion occurs. Photoresists are exposed to electrons, baked, and developed; subsequent ellipsometry is used to quantify the depth at which solubility changing reactions occur based on the incident energy and dose. Quencher concentration and post-exposure bake parameters are varied to mitigate acid diffusion to extrapolate the electron range. The results are then compared to the thickness loss of the non-chemically amplified photoresist.

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is used to evaluate the composition of nonvolatile photoproducts created by EUV photolysis of antimony carboxylate photoresists [R3Sb(O2CR′)2]. Dozens of potential photoproduct ions were identified using exact mass and 121Sb/123Sb isotopic ratios. Several oxygen-rich antimony ions were found to increase in abundance with exposure. Two methods were employed to identify photoproducts which create solubility contrast. First, samples were analyzed pre- and post-development to examine the effects of EUV exposure and developer solvent on secondary ion intensity. Secondly, changes in intensity of select ions were compared to dissolution contrast over a range of doses. Through these studies, ion intensities were found to correlate with dissolution contrast for several fragments, indicating their active role in creating negative-tone response.

The EUV photoproducts of antimony carboxylate photoresists [R3Sb(O2CR')(2)] are used to evaluate a possible free radical exposure mechanism by studying the change in molecular weight distribution with dose. We demonstrate the redistribution of carboxylate ligands across the metal centers in solution and use this property to create a statistical mono-olefin resist system with blended solutions of olefinic and non-olefinic antimony compounds that limit crosslinking and improve solubility of the photoproducts. Through gel permeation chromatography (GPC) analysis, we demonstrate the formation of high molecular weight oligomers with exposure dose and provide further support for the free-radical polymerization mechanism.

During the photolithographic process, a photoresist is exposed to EUV photons; it is believed that the secondary low energy electrons generated during this exposure decompose the PAG molecule, producing acid. Regardless of how these secondary electrons are produced, whether by incident electrons or photons, the number of acids produced will lead to a solubility change within the photoresist. The goal of this study is to observe the solubility changing reactions due to low energy electron exposures (approximately 5- 80 eV). The reactions occurring in the photoresist are monitored through outgassing measurements during EUV photon exposures, and low energy electron exposures. Outgassing results indicate that PAG decomposition occurs with electrons as low as 4.5 eV, and subsequent deprotection reactions are observed due to the acid generated from the PAG. Without being in the presence of PAG decomposition, deprotection reactions are caused by electron exposures with energies down to at least 15 eV. These deprotections that occur in the absence of PAG decomposition are referred to as direct deprotection reactions. Sentaurus Lithography simulations show that these direct deprotection reactions can affect the resist modeling.

The photo-mechanism of EUV exposures in chemically amplified photoresists are much different than that of previous lithographic wavelengths. Electrons generated during EUV exposure are demonstrated to be a source of acid production through a process referred to as electron trapping. Density functional theory modeling indicates that it is energetically favorable for the PAG molecule to decompose if an electron is trapped. Low-energy electrons unlikely to produce holes and secondary electrons generate acid indicating electron-PAG interactions are capable to induce decomposition. Additionally, a more easily reduced PAG (i.e. higher likelihood of trapping an electron) produces a higher acid yield supporting electron trapping as a process of acid production. An acid indicator, Coumarin 6, was used to determine the number of acids generated per absorbed EUV photon. The results of these measurements indicate that electron-PAG interactions are a source of acid production through electron trapping; thus, increasing the number of electron-hole pairs available to induce chemical reactions would improve sensitivity. It is expected that lower band gap materials produce more electron-hole pairs after an absorption event. Subsequently, these measurements show that lower band gap polymers generate higher acid yields.

This paper describes the photoreactivity of six organometallic complexes of the type PhnMX2 containing bismuth, antimony and tellurium, where n = 3 for bismuth and antimony and n = 2 for tellurium, and where X = acetate (O2CCH3) or pivalate (O2CC(CH3)(3)). These compounds were exposed to EUV light to monitor photodecomposition via in situ mass spectral analysis of the primary outgassing products of CO2, benzene and phenol. This paper explores the effect of metal center and carboxylate ligand on the EUV reactivity of these EUV photoresists.