Ultraviolet Photoresist Research Articles

Study of molecular layer deposition of zinc-based hybrid film as photoresist

Molecular layer deposition (MLD) of metal oxide and organic hybrid thin films has great potential to be utilized in extreme ultraviolet photoresist, thanks to its excellent uniformity on the nanometer scale thickness control. Zn has large photoelectron effect cross-section, resulting in lots of secondary electrons, which can break the organic bonds, causing changes in solubility upon the ultraviolet (UV) light exposure. In this work, Zn-based MLD thin films have been demonstrated for their potential to be used as photoresist for extreme ultraviolet(EUV) application. UV light exposure mechanisms have been proposed based on X-ray photoelectron spectroscopy(XPS) analysis.

POSS and PAG Dual-Containing Chemically Amplified Photoresists by RAFT Polymerization for Enhanced Thermal Performance and Acid Diffusion Inhibition

A random copolymer (PTBM), utilized as deep ultra-violet (DUV) photoresist, was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization with tert-butyl methacrylate (tBMA), methyl methacrylate (MMA), triphenylsulfonium p-styrenesulfonate (TPS-SS), and functional poly (sesquicarbonylsiloxanes) (POSS-MA) as the monomer components, and 4-cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl]pentanoic acid (CDSPA) as the RAFT reagent. Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) proved successful synthesis. Ultraviolet absorption spectroscopy (UV) analysis verified the transparency of the polymer in the DUV band. RAFT polymerization kinetics showed that the polymerization rate conformed to the first-order kinetic relationship, and the polymerization process exhibited a typical controlled free radical polymerization behavior. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and static thermo-mechanical analysis (TMA) showed that the incorporation of POSS groups improved the thermal properties of the copolymer. According to scanning electron microscopy (SEM) images, the copolymerization of photoacid monomers (TPS-SS) resulted in photoresist copolymers exhibiting good resistance to acid diffusion and low roughness.

Accurate and efficient evaluation of the ionization potentials of extreme ultraviolet photoresists using density functionals and semi-empirical methods

Extreme ultraviolet (EUV) photoresists have become the core materials in lithography with nanometer-sized patterns and are actively explored on the path to realizing smaller critical dimensions. These photoresists can be small molecule-, polymer-, or organic–inorganic hybrid-based, with the full molecular working mechanism under investigation. For the rational design of EUV photoresists, theoretical guidance using tools like first-principle calculations and multi-scale simulations can be of great help. Considering the extremely high standard of accuracy in EUV lithography, it is critical to ensure the adoption of the appropriate methodologies in the theoretical evaluation of EUV photoresists. However, it is known that density functionals and semi-empirical methods differ in accuracy and efficiency, without a universal rule across materials. This poses a challenge in developing a reliable theoretical framework for calculating EUV photoresists. Here, we present a benchmark investigation of density functionals and semi-empirical methods on the three main types of EUV photoresists, focusing on the ionization potential, a key parameter in their microscopic molecular reactions. The vertical detachment energies (VDE) and adiabatic detachment energies (ADE) were calculated using 12 functionals, including pure functionals, hybrid functionals, Minnesota functionals, and the recently developed optimally tuned range-separated (OTRS) functionals. Several efficient semi-empirical methods were also chosen, including AM1, PM6, PM7, and GFN1-xTB in the extended tight-binding theoretical framework. These results guide the accurate and efficient calculation of EUV photoresists and are valuable for the development of multi-scale lithography protocols.Graphical

Tin-oxo nanoclusters for extreme ultraviolet photoresists: Effects of ligands, counterions, and doping

Tin-oxo nanoclusters for extreme ultraviolet photoresists: Effects of ligands, counterions, and doping

Research Progress and Prospects of Extreme Ultraviolet Photoresists

Research Progress and Prospects of Extreme Ultraviolet Photoresists

An overview of photopolymerization and its diverse applications

AbstractPhotopolymerization is an energy‐saving and environmentally friendly technology and has been widely applied and continuously developed in various fields since the mid‐20th century. Today, photopolymerization technology has become ubiquitous in every aspect of our lives. This review initially explains the principle of photopolymerization reactions, introducing the process of photopolymerization and the initiation mechanisms of photoinitiators. Then, this review focuses on the applications of photopolymerization technology in thiol‐based click reactions, photoinduced controlled/living polymerizations, three‐dimensional printing, ultraviolet nanoimprint lithography photoresist and hydrogels to demonstrate its irreplaceable role at present.

Surface hardening of extreme ultraviolet(EUV) photoresist by CS2 plasma for highly selective and low damage patterning

Extreme ultraviolet (EUV) lithography has the advantage of implementing a finer pattern by using a wavelength of 13.5 nm light source with a higher resolution value than the existing ArF light source. However, there are several issues regarding EUV photoresist (PR), such as low etch resistance due to thin thickness and pattern mismatch during subsequent processing/deterioration of electrical characteristics of the device due to increase in line edge roughness (LER). In this study, the effect of CS2 plasma treatment and/or followed annealing at 80 °C on the EUV PR properties was investigated to improve PR characteristics such as LER, etch resistance, etc. during the etching by CF4 plasma. The CS2 plasma treatment and followed annealing improved the PR characteristics such as decreased ΔLER, decreased ΔCritical dimension, and decreased ΔThickness of the PR after the etching compared to the reference and/or annealed PR. Especially, the PR treated by CS2 plasma + annealing showed the improvement of etch resistance of ∼ 70 % compared to the reference PR. The X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that the improvement of EUV PR properties were related to the formation of CS, OS bonds on the surface of PR by the CS2 plasma treatment + annealing.

Surface Hardening of Extreme Ultraviolet(Euv) Photoresist by Cs2 Plasma for Highly Selective and Low Damage Patterning

Surface Hardening of Extreme Ultraviolet(Euv) Photoresist by Cs2 Plasma for Highly Selective and Low Damage Patterning

Influence of Counteranions on the Performance of Tin-based EUV Photoresists

A positive-tone extreme ultraviolet (EUV) photoresist was obtained via the exchange of the hydroxide ions of tin-oxo-hydroxo cages with tetrakis(pentafluorophenyl)-borate. Thin films were obtained after spin coating on silicon substrates and exposed to line patterns in interference lithography at 92 eV (13.5 nm). For low doses and development with ethylbenzene positive tone patterns were obtained. In contrast, the exchange of the hydroxide ions of tin-oxo-hydroxo cages with tetrakis(4-methylphenyl)-borate or tetrakis[3,5-bis(1,1,1,3,3,3-hexafluoro-2-methoxy-2-propyl)phenyl]-borate led to the negative-tone photoresist behaviour that has previously been observed for tin-oxo cages with all other counterions. In situ exposures at 92 eV and subsequent X-ray Photoelectron Spectroscopy were performed on a film of tin-oxo-hydroxo cages with tetrakis(pentafluorophenyl)-borate anions to probe the chemical changes induced by the EUV exposure. This shows that the C-F bonds of the anions are relatively stable.

Chemical Mechanisms of Metal-Based Extreme Ultraviolet Resists

Hybrid organic/inorganic materials are considered as the Extreme Ultraviolet photoresists of the future. Compared to chemically amplified polymer-based photoresists they offer higher EUV absorption cross sections, and higher etch resistance. The chemical reactions that occur in these materials upon excitation with EUV or other high energy radiation have been investigated over the past 8 years. This paper summarizes the findings for two classes of metal-based resists: metal oxo clusters with acrylate ligands, and organotin oxo cages.

Nanometrology for evaluating rare sites for molecular homogeneity

Here, we present a methodology for identifying and characterizing nanoscale sites in extreme ultraviolet (EUV) photoresists that deviate from the mean composition by 3σ. The methodology is based on nano-projectile secondary ion mass spectrometry (SIMS) operating in the event-by-event bombardment detection mode. Nanoscale analysis is achieved by probing the surface stochastically with a suite of individual nanoprojectile impacts in which each nano-projectile samples a volume that is 10 to 15 nm in diameter and up to 10 nm in depth. For each impact, the coemitted secondary ions are collected and mass-analyzed, allowing for the analysis of colocalized moieties. We applied this technique to study the fundamental processes occurring in partially developed positive-tone EUV resists, which simulate a critical problem in EUV resists, incomplete resist removal, and production of line edge features. Such features erode device yield and have been the focus of many previous studies. Using NP-SIMS, we examined the changing molecular composition in the partially developed resist and isolated measurements with a probability below 0.3%. Grouping measurements based on the number and type of detected molecular species allowed for the identification of rare sites on the surface that deviate from the mean composition. The mass spectrometry measurements showed that both the photoacid generator (PAG) cation and anion displayed decreased homogeneity on average with increasing exposure dose. The effect was more pronounced in the sites with probabilities below 0.3%, where the measured intensity of the PAG-related ions in these sites was more than twofold larger than the mean. Thus, we attribute these nanoscale sites to aggregations of PAG within the top 10 nm of the remaining film. These results suggest that identifying and characterizing the molecular composition of rare sites may be important in defect production and film stochastics.

Adhesion and collapse of extreme ultraviolet photoresists and the role of underlayers

Pattern collapse and photoresist scumming are major limiting factors to achieve a failure-free process window in extreme ultraviolet lithography. Previous works on this topic have empirically proven the importance of matching photoresist and underlayer surface energy, and the role played by developer liquid in wet development. In this work, we extend those concepts and formulate a figure of merit for the free energy at the exposed and unexposed photoresist-underlayer-developer interfaces. This figure of merit provides a tool to optimize the underlayer surface energy components that best match a given photoresist and developer process. The model is tested against experimental patterning of a chemically amplified resist at pitch 32 nm and pitch 80-nm line spaces, successfully predicting the likelihood of pattern collapse and photoresist scumming. Moreover, we write a quantitative expression for the peeling force acting on photoresist lines owing to unbalanced capillary forces and the threshold energy at which film delamination onsets. It is shown that adhesion and scumming are two manifestations of the same phenomenon at these interfaces.

Fluorine-Rich Zinc Oxoclusters as Extreme Ultraviolet Photoresists: Chemical Reactions and Lithography Performance.

The absorption of extreme ultraviolet (EUV) radiation by a photoresist strongly depends on its atomic composition. Consequently, elements with a high EUV absorption cross section can assist in meeting the demand for higher photon absorbance by the photoresist to improve the sensitivity and reduce the photon shot noise induced roughness. In this work, we enhanced the EUV absorption of the methacrylic acid ligands of Zn oxoclusters by introducing fluorine atoms. We evaluated the lithography performance of this fluorine-rich material as a negative tone EUV photoresist along with extensive spectroscopic and microscopic studies, providing deep insights into the underlying mechanism. UV-vis spectroscopy studies demonstrate that the presence of fluorine in the oxocluster enhances its stability in the thin films to the ambient atmosphere. However, the EUV photoresist sensitivity (D 50) of the fluorine-rich oxocluster is decreased compared to its previously studied methacrylic acid analogue. Scanning transmission X-ray microscopy and in situ X-ray photoelectron spectroscopy in combination with FTIR and UV-vis spectroscopy were used to gain insights into the chemical changes in the material responsible for the solubility switch. The results support decarboxylation of the ligands and subsequent radical-induced polymerization reactions in the thin film upon EUV irradiation. The rupture of carbon-fluorine bonds via dissociative electron attachment offers a parallel way of generating radicals. The mechanistic insights obtained here will be applicable to other hybrid materials and potentially pave the way for the development of EUV materials with better performance.

Development of Extreme Ultraviolet Photoresists

Development of Extreme Ultraviolet Photoresists

Electron-beam lithography on M108Y and M35G chemically amplified DUV photoresists

Despite the development of high-end optical lithography systems, electron-beam lithography (EBL) remains the preferred solution for rapid fabrication of deep sub-micrometric features. Although poly-methylmethacrylate (PMMA), HSQ and ZEP remain the most popular resists on the market, a variety of alternatives have emerged, including chemically amplified resists like CSAR. Here, we investigate the use of two resists initially intended for deep ultraviolet (DUV) lithography, namely M108Y and M35G from JSR, as EBL resists. Their chemically amplified nature involves high sensitivity, de facto increasing the throughput. The critical dimensions of each resist are studied, as well as the pattern transfer into the underlying silicon substrate. They yield similar CD performance as ZEP or CSAR; at the same time, they are more resistant than those resists with respect to different dry etching recipes. Overall, the two analyzed DUV photoresists are proven to be valid solutions as alternatives to standard EBL resists. • Electron-beam lithography on M108Y and M35G deep ultraviolet photoresists. • Chemically amplified nature of resists yields high sensitivity. • Critical dimensions performance are similar to ZEP and CSAR. • Resists are more resistant to dry etching than standard solutions. • Pronounced undercut in M35G allows single-layer lift-off.

Research Progress on High Resolution Extreme Ultraviolet Photoresist

Research Progress on High Resolution Extreme Ultraviolet Photoresist

Extreme Ultraviolet Photoresist Inspection Platform in Shanghai Synchrotron Radiation Facility

Extreme Ultraviolet Photoresist Inspection Platform in Shanghai Synchrotron Radiation Facility

Extreme ultraviolet photoemission of a tin-based photoresist

Tin is a suitable element for inclusion in extreme ultraviolet photoresists because of its relatively high-absorption cross section at 92 eV. The electrons emitted after photon absorption are expected to generate secondary electrons in the solid film. In this way, several pathways lead to reactive species that cause a solubility switch. Here, we report the photoelectron spectra of tin oxo cage photoresists over the photon energy range 60–150 eV, and the relative yields of photoelectrons from the valence band of the resist, from the Sn 4d orbitals, and of inelastically scattered electrons. The experimental excitation spectra differ considerably from those predicted by commonly used database cross section values, and from the combined computed subshell spectra: the maximum efficiency of ionization of Sn 4d both in the photoresists and in Sn metal occurs near the industrially relevant EUV wavelength of 13.5 nm.

Applications of graphene transistor optimized fabrication process in monolithic integrated driving gallium nitride micro-light-emitting diode

In the information display field, micro-light-emitting diodes (micro-LEDs) possess high potentials and they are expected to lead the direction of developing the next-generation new display technologies. Their display performances are superior to those produced by the currently prevailing liquid crystal and organic light-emitting diode based technologies. However, the micro-LED pixels and their driving circuits are often fabricated on different wafers, which implies that the so-called mass transfer seems to be inevitable, thus facing an obvious bottleneck. In this paper, the emerging graphene field effect transistors are used as the driving elements and integrated onto the GaN micro-LEDs, which is because the pixels and drivers are prepared directly on the same wafer, the technical problem of mass transfer is fundamentally bypassed. Furthermore, in traditional lithographic process, the ultraviolet photoresist directly contacts the graphene, which introduces severe carrier doping, thereby leading to deteriorated graphene transistor properties. This, not surprisingly, further translates into lower performances of the integrated devices. In the present work, proposed is a technique in which the polymethyl methacrylate (PMMA) thin films act as both the protection layers and the interlayers when optimizing the graphene field effect transistor processing. The PMMA layers are sandwiched between the graphene and the ultraviolet photoresist, which is a brand new device fabrication process. First, the new process is tested in discrete graphene field effect transistors. Compared with those devices that are processed without the PMMA protection thin films, the graphene devices fabricated with the new technology typically show their Dirac point at a gate voltage (<i>V</i><sub>g</sub>) deviation from <i>V</i><sub>g</sub> = 0, that is, 22 V lower than their counterparts. In addition, an increase in the carrier mobility of 32% is also observed. Finally, after applying the newly developed fabrication process to the pixel-and-driver integrated devices, it is found that their performances are improved significantly. With this new technique, the ultraviolet photoresist no longer directly contacts the sensitive graphene channel because of the PMMA protection. The doping effect and the performance dropping are dramatically reduced. The technique is facile and cheap, and it is also applicable to two-dimensional materials besides graphene, such as MoS<sub>2</sub> and h-BN. It is hoped that it is of some value for device engineers working in this field.

Significance of plasma-photoresist interactions for atomic layer etching processes with extreme ultraviolet photoresist

Extreme ultraviolet (EUV) lithography has emerged as the next generational step in advancing the manufacturing of increasingly complex semiconductor devices. The commercial viability of this new lithographic technique requires compatible photoresist (PR) materials that satisfy both the lithographic and etch requirements of good feature resolution, chemical sensitivity, a low line edge roughness, and good critical dimension uniformity. Achieving the decreased feature pitches of modern processing nodes via EUV lithography places a limit on the available photoresist thickness for a pattern transfer process. Therefore, etch processes are required to maximize the etching selectivity of a hard mask material, such as SiO2, to an EUV photoresist. In this work, the authors evaluated the ability of an atomic layer etching (ALE) process to maximize the SiO2/EUV PR etching selectivity. Through the flexible parameter space available in an ALE process, the authors evaluated the etching behaviors as a function of the ALE parameters of ion energy, etch step length, fluorocarbon (FC) deposition thickness, and precursor gas type. The authors found that the interaction between the energetic argon ion bombardment and a deposited FC layer produces a modified surface layer on the PR material that can strongly control the PR etch rate and even produce an etch stop under some conditions. Under the same processing conditions, the etching behavior of SiO2 continues unimpeded, thus resulting in a high overall SiO2/PR etching selectivity. Secondary characterization using x-ray photoelectron spectroscopy and atomic force microscopy was used to support the conclusions derived from the ellipsometric modeling based on the surface chemistry evolution and determine the impact of the ALE process on the surface roughness of the EUV PR, respectively. Additionally, attenuated total reflection Fourier-transform infrared spectroscopy was used to track the impact on specific functional groups within the PR composition from both the argon ion bombardment and FC deposition components of the ALE process. The ALE-based PR etching concept established in this work serves as a foundation for both the understanding of the impacts of an ALE process on an EUV PR material and for future works, employing an ALE process for PR-based pattern transfer.