Photoresist Materials Research Articles

Convolutional Neural Network-Assisted Photoresist Formulation Discriminator Design of a Contact Layer for Electron Beam Lithography.

The photoresist formulation is closely related to the material properties, and its composition content determines the lithography imaging quality. To satisfy the process requirements, imaging verification of extensive formulations is required through lithography experiments. Identifying photoresist formulations with a high imaging performance has become a challenge. Herein, we develop a formulation discriminator of a metal oxide nanoparticle photoresist for a contact layer applied to electron beam lithography. This discriminator consists of convolutional neural network photoresist imaging and formulation classification models. A photoresist imaging model is adopted to predict the contact width of variable formulations, while a formulation classification model is used to classify formulations according to relative local critical dimension uniformity (RLCDU). The verification results indicate that the discriminator can accurately recognize photoresist formulations that simultaneously meet the conditions of contact width and RLCDU, and its feasibility has been demonstrated, providing a valuable reference for the preparation of photoresist materials.

Layer-Ordered Organooxotin Clusters for Extreme-Ultraviolet Photolithography.

Extreme-ultraviolet (EUV) photolithography, which enables the high-throughput production of well-defined patterns with critical dimensions on the scale of several nanometers, is essential for the fabrication of a highly integrated semiconductor. The full exploitation of EUV lithographic techniques necessitates the development of photoresist (PR) materials with both high EUV sensitivity and a long shelf-life. However, despite notable advances, the available library of EUV PR materials remains limited. Here we report EUV PRs capable of forming preorganized layers consisting of ladder-structured tetranuclear stannoxanes. Single-crystal X-ray structure analyses reveal a close interlayer distance of 8.5 Å through interdigitation of the pseudoaxial butyl chains. The developed EUV PR materials exhibit high solubility in organic solvents commonly used in semiconductor processing, enabling the preparation of PR solutions with superior wettability and uniform film-forming ability on Si wafer substrates. These PR solutions also demonstrate notable resistance to hydrolytic decomposition for as long as 1 month, indicating a long shelf-life. Our PR materials enabled negative-tone patterning processes that involved a solubility decrease upon irradiation. The presence of chromophoric ligands makes our PR materials compatible with conventional UV photolithography, through photochemical reactions involving carbonyl units. In addition, e-beam and EUV lithography could produce fine line patterns of our PRs, with critical dimensions of 20 and 15 nm, respectively. Our research showcases the potential of layer-ordered organooxotin clusters for EUV PR applications.

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

AbstractSeeking high‐performance photoresists 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 promising photoresist material. In this work, a series of aqueous developable CO2‐sourced polycarbonates (CO2‐PCs) 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 photogenerated acid, the acetal (ketal) groups in CO2‐PC were hydrolysed into two equivalents of hydroxyl groups, which change the exposed area from hydrophobicity to hydrophilicity, thus enabling the exposed area to be developed with 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 a good etch resistance (38 % higher than poly(tert‐butyl acrylate)). Such performances outperform 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 (KrF and ArF) and extreme ultraviolet (EUV) lithography for nanomanufacturing.

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

Seeking high-performance photoresists 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 promising photoresist material. In this work, a series of aqueous developable CO2-sourced polycarbonates (CO2-PCs) 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 photogenerated acid, the acetal (ketal) groups in CO2-PC were hydrolysed into two equivalents of hydroxyl groups, which change the exposed area from hydrophobicity to hydrophilicity, thus enabling the exposed area to be developed with 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 a good etch resistance (38 % higher than poly(tert-butyl acrylate)). Such performances outperform 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 (KrF and ArF) and extreme ultraviolet (EUV) lithography for nanomanufacturing.

Recent Advances in Positive Photoresists: Mechanisms and Fabrication.

Photoresists are fundamental materials in photolithography and are crucial for precise patterning in microelectronic devices, MEMS, and nanostructures. This paper provides an in-depth review of recent advancements in positive photoresist research and development, focusing on discussion regarding the underlying mechanisms governing their behavior, exploring innovative fabrication techniques, and highlighting the advantages of the photoresist classes discussed. The paper begins by discussing the need for the development of new photoresist technologies, highlighting issues associated with adopting extreme ultraviolet photolithography and addressing these challenges through the development of advanced positive-tone resist materials with improved patterning features, resolution, and sensitivity. Subsequently, it discusses the working mechanisms and synthesis methods of different types and subtypes of photoresists, starting from non-chemically amplified, organic, and inorganic-organic hybrid photoresists and progressing to dry film resists, with an emphasis on the upsides of each. The paper concludes by discussing how future research in the field of lithography-prioritizing concerns related to environmental impacts, improved photoresist material and properties, and utilization of advanced quantum technology-can assist with revolutionizing lithography techniques.

Foldable paper-based photoelectrochemical biosensor based on etching reaction of CoOOH nanosheets-coated laser-induced PbS/CdS/graphene for sensitive detection of ampicillin

Timely and rapid detection of antibiotic residues in the environment is conducive to safeguarding human health and promoting an ecological virtuous cycle. A foldable paper-based photoelectrochemical (PEC) sensor was successfully developed for the detection of ampicillin (AMP) based on glutathione/zirconium dioxide hollow nanorods/aptamer (GSH@ZrO2 HS@apt) modified cellulose paper as a reactive zone with laser direct-writing lead sulfide/cadmium sulfide/graphene (PbS/CdS/LIG) as photoelectrode and cobalt hydroxide (CoOOH) as a photoresist material. Initially, AMP was introduced into the paper-based reaction zone as a biogate aptamer, which specifically recognized the target and then left the ZrO2 HS surface, releasing glutathione (GSH) encapsulated inside. Subsequently, the introduction of GSH into the reaction region and etching of CoOOH nanosheets to expose the PbS/CdS/LIG photosensitive material increased photocurrent. Under optimal conditions, the paper-based PEC biosensor showed a linear response to AMP in the range of 5.0 - 2 × 104 pM with a detection limit of 1.36 pM (S/N = 3). In addition, the constructed PEC sensing platform has excellent selectivity, high stability and favorable reproducibility, and can be used to assess AMP residue levels in various real water samples (milk, tap water, river water), indicating its promising application in environmental antibiotic detection.

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.

Inkjet-Printed Dielectric Layer for the Enhancement of Electrowetting Display Devices.

Electrowetting with a dielectric layer is commonly preferred in practical applications. However, its potential is often limited by factors like the properties of the dielectric layer and its breakdown, along with the complexity of the deposition method. Fortunately, advancements in 3D inkjet printing offer a more adaptable solution for making patterned functional layers. In this study, we used a negative photoresist (HN-1901) to create a new dielectric layer for an electrowetting display on a 3-inch ITO glass using a Dimatix DMP-2580 inkjet printer. The resulting devices performed better due to their enhanced resistance to dielectric breakdown. We meticulously investigated the physical properties of the photoresist material and printer settings to achieve optimal printing. We also controlled the uniformity of the dielectric layer by adjusting ink drop spacing. Compared to traditional electrowetting display devices, those with inkjet-printed dielectric layers showed significantly fewer defects like bubbles and electrode corrosion. They maintained an outstanding response time and breakdown resistance, operating at an open voltage of 20 V. Remarkably, these devices achieved faster response times of ton 22.3 ms and toff 14.2 ms, surpassing the performance of the standard device.

Physical model-based ArF photoresist formulation development

Since the logic 28 nm technology and beyond, ArF immersion lithography has been widely used in manufacturing. To fully utilize the potential of the lithographic resolution, process simulation has been used since the lithography process setup step. The accuracy of the model prediction can be a key factor in the process stability, defectivity, and yield of the final product. To get better model prediction, it is very important to develop a process model with as many parameters as possible with physical meanings. Since the analysis of exposure data with a physical model can provide insights into the process and the photoresist material, it may greatly accelerate the photoresist formulation development or improvement process. From another aspect, as the function of the photoresist is to record the aerial image information on wafer, theoretically, the photoresist image should not deviate much from the aerial image or it will inevitably reduce the information content of the aerial image, i.e., through various kinds of averaging, mixing, etc. Since the emergence of Optical Proximity Correction (OPC), the time that takes to finalize a photolithography process has been significantly lengthened and made more complicated. To make the OPC model more reliable and less dependent on patches, a more physical OPC model is necessary. Therefore, it is clear that if we can develop a photoresist formulation to realize a more physical photoresist image, or a photoresist image closer to the aerial image, we can greatly improve the photolithography process performance and the time consumed for the process setup including OPC. In this paper, we focus on several physical model parameters for photoresist, especially the effective photoacid diffusion length and photo decomposable base parameters. We will show that these two parameters can provide a good description of photoresist imaging behavior, and the resist formulation can be improved to match the physical model prediction with more accuracy.

Synthesis and properties of a series of sulfonate ester photoacid generators

A total of six sulfonate polymeric nonionic photoacid generators (PAGs) have been synthesised and subjected to comprehensive characterization for their application in photoresist materials.

Photoresist Fabrication for High-NA EUV Lithography: Material and Mechanism

Extreme ultraviolet (EUV) lithography is critical for the semiconductor industry nowadays. However, high-numerical aperture (NA) EUV systems face challenges in many areas, especially in photoresists. This paper reviews requirements and recent progress in EUV photoresists for high-NA EUV lithography. The key needs for photoresists include high resolution, low stochastic defects, minimal pattern collapse, and high sensitivity. Proposed solutions involve new photoresist materials and mechanisms, such as metal-containing photoresists, non-chemically amplified photoresists and tin-oxo cages photoresists. Basic fabrication and processing procedures are also discussed. Other than photoresists, the weak EUV light source also heavily restrains the development of photoresists. In the future, improvements in EUV light sources and patterning techniques will further help high-NA EUV photoresist development. In summary, the realization of high-NA EUV lithography system depends critically on the breakthrough of photoresists, while solutions are emerging to meet demanding requirements from various directions. Overall, these results shed light on guiding further exploration of next generation lithography.

Investigation of Quantum Dot Color Filter Micro-LED Display

In this work, we present the investigation of the quantum dot color filter (QDCF) micro-light emitting diode (micro-LED) display. Green and red quantum dot photoresist (QDPR) materials are patterned into a pixelated array and precisely bonded with an all-blue micro-light emitting diode (micro-LED) substrate, forming a red, green, and blue (RGB) full color display through color conversion. A few factors that influence the achievable color gamut are further investigated. The resulting 1.1-inch 228-pixels per inch (ppi) display demo shows the good performance. The findings in this paper pave a way to the future industrialization of the micro-LED display.

Polymeric electronic materials for microelectronics manufacturing: A review

This review paper is part of a series of papers dedicated to the centenary celebration of the American Chemical Society Division of Polymeric Materials: Science and Engineering which has been the scientific home of many polymer scientists and engineers in the semiconductor industry. It is a review of parts of the research and development of advanced polymeric electronic materials for the fabrication and manufacturing of modern integrated circuits at the International Business Machines Corporation. This paper covers three types of advanced polymeric electronic materials: (1) photoresist materials used to “print” integrated circuits on silicon wafers, (2) on-chip low dielectric constant (low-κ) materials to insulate electrically conducting copper wires and (3) photo-patternable on-chip low-κ materials which function both as a photoresist and as an on-chip low-κ material. The photoresist materials are thin film imaging material systems of bilayer photoresist materials for 248 nm lithography and trilayer photoresist materials for 193 nm lithography. The low-κ dielectric material part focuses on fundamental understanding of plasma-induced damage to nanoporous organosilicate low-κ dielectric materials and the design of damage-resistant low-κ dielectric materials. Finally, the photo-patternable low-κ dielectric materials part describes the design and the development of dual-functional photo-patternable low-κ dielectric materials for both 193 nm and 248 nm lithography patterning of semiconductor Back-End-Of-the-Line. Several of these materials have been adopted for high-volume manufacturing of semiconductor chips for some of the most popular electronic devices in the world today.

Two-photon polymerization for fabrication of metalenses for diffraction-limited focusing and high-resolution imaging

Metalenses consisting of nanoscale unit cells provide new opportunities for miniaturization, light-weight, and diversification of conventional optical lenses. Fabrication of metalenses is conventionally by photolithography technique, which is complex involving multi-steps. In this study, two-photon polymerization (TPP) was used to directly write single-layer metalenses. The metalenses was designed according to Pancharatnam Berry (P-B) phase distribution model at the wavelengths of 515, 628, and 1030 nm, respectively. The focusing performance of the designed metalenses was simulated using a Finite Difference Time Domain (FDTD) software. Near optical diffraction limit focusing of the incident light was achieved on a low refractive index photoresist. The geometrical dimensions of the fabricated unit cells were compared with the designed parameters. The influence of laser power density on dimensions of the unit and the resultant the focusing effect were investigated. The metalenses prepared by TPP with optimum parameters show a minimum full width at half maximum (FWHM) of 978 nm and a focusing efficiency of 1.02% with 628 nm light source. A line width of 980 nm was obtained under a white light source. The research results demonstrate that TPP can be a feasible and simplified approach for fabrication of metalenses, but for higher focusing efficiency and imaging resolution metalenses, some high refractive index photoresist materials being suitable for the TPP should be developed.

Predicting photoresist sensitivity using machine learning

AbstractWe introduce a scheme for predicting photoresist sensitivity using machine learning (ML) work flow on the basis of previously reported experimental data. Different ML models, specifically Linear Regression, Kernel Ridge Regression, Gaussian Process Regressor, Random Forest Regressor, and Multilayer Perceptron Regressor, were evaluated to rapidly identify the best sensitivity prediction model. The experiment was carried out on the Google Colab platform using the Materials Simulation Toolkit for Machine Learning and Sci‐kit Learn. Different ensemble models were utilized without splitting the dataset to determine the prediction accuracy of the ML models. The hyperparameter optimization was established with a 70/30 ratio, followed by a K‐Fold cross‐validation to improve the model prediction performance. The optimized ML model showed a prediction performance of R2 = 0.83, RMSE = 10.53, and MARE = 0.68. Hence, by optimizing the hyperparameters used in the ML model, the sensitivity of the photoresist materials can be predicted with improved prediction performance.

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).

Multi‐Material 3D Microprinting of Magnetically Deformable Biocompatible Structures

AbstractTwo‐photon polymerization (2PP) allows precise 3D printing at the micrometer scale, and by associating it with magnetic materials, the creation of remotely actuatable micro‐structures. Such structures attract a growing interest for biomedical applications, thanks to their size and to the biocompatibility of some photoresist materials. Gelatin methacryloyl (Gel‐MA) is one such material, and can be used to create physiological scaffolds for cell culture. Here, the physico‐chemical properties of two resins are exploited, the first being a silica‐based hybrid polymer, the OrmoComp, and the second a Gel‐MA‐based hydrogel. A 2PP manufacturing protocol is defined and designed to print both materials in succession as a single structure, which is then linked to a neodymium‐iron‐boron (NdFeB) magnetic bead for actuation. By this combination, a magnetically deformable 3D culture substrate is created to study cells in an environment that mimics soft, curved, and dynamic properties of tissues in vivo. The structure is actuated via an external magnetic field and bends back and forth along its longest axis. Lastly, preliminary cell culture trials are conducted showing the proliferation of cells on the structures.

Amylopectin-based Eco-friendly Photoresist Material in Water-developable Lithography Processes for Surface Micropatterns on Polymer Substrates

Amylopectin-based Eco-friendly Photoresist Material in Water-developable Lithography Processes for Surface Micropatterns on Polymer Substrates

The Study of Highest Thickness Photo Resist for Cu Post of Fan-Out Wafer Level Packaging

The mobile device’s limited thermal budget hardly allows the use of a high-performance application (AP) at its full speed. However, as artificial intelligence technologies has been rapidly applied for mobile devices, the demand like high-speed and large-capacity signal processing is continuously increasing. Therefore, controlling the heat generation of AP chip is becoming a key factor, and it is necessary to develop a Re-Distribution Layer (RDL) based Fan-Out Package (FOPKG) structure that does not increase the thickness of the package while maximizing the die thickness for heat dissipation. The height of Cu post is getting higher for the production of FOPKG that can apply thick die, and in this study, the world’s thickest photoresist material (>350um thickness) was developed for the production of Cu post (>300um thickness). The effect of light transmittance of the photoresist and the effect of solubility depending on the molecular structure of the main polymer were studied for lithography process of thick photoresist. Based on the understanding of this thick photoresist behavior, the optimal liquid type photoresist composition was developed. Through lithography evaluation based on thick photoresist characteristics, deep-hole via implementation and Cu electro-plating were performed to obtain a yield of Cpk 1.27 in the AP product design applied wafer. Depending on this in-depth understanding and experimentation on thick photoresist, it is possible to build an advanced research foundation of increasing the photoresist thickness and finer Cu post pitch to secure heat dissipation characteristics and improve the degree of freedom of architecture.

Resistless EUV lithography: Photon-induced oxide patterning on silicon

In this work, we show the feasibility of extreme ultraviolet (EUV) patterning on an HF-treated silicon (100) surface in the absence of a photoresist. EUV lithography is the leading lithography technique in semiconductor manufacturing due to its high resolution and throughput, but future progress in resolution can be hampered because of the inherent limitations of the resists. We show that EUV photons can induce surface reactions on a partially hydrogen-terminated silicon surface and assist the growth of an oxide layer, which serves as an etch mask. This mechanism is different from the hydrogen desorption in scanning tunneling microscopy-based lithography. We achieve silicon dioxide/silicon gratings with 75-nanometer half-pitch and 31-nanometer height, demonstrating the efficacy of the method and the feasibility of patterning with EUV lithography without the use of a photoresist. Further development of the resistless EUV lithography method can be a viable approach to nanometer-scale lithography by overcoming the inherent resolution and roughness limitations of photoresist materials.