Patterning Technology: From Supporting Role to Main Player in Materials Chemistry

Published as part of Chemistry of Materials special issue “Precision Patterning”. I recall, when I traveled to Italy, how comfortable I felt browsing items on the shelves of a grocery store (see Figure 1). The neatly and periodically arranged cans and pasta boxes exhibited a satisfying symmetry, adhering to a certain pattern. Like many other scientists, I appreciate symmetry and predictability. Generally, in science and engineering, patterning technology has not received as much attention as other fields, for example those that investigate novel materials’ properties or demonstrate new applications. Instead, patterning technology has often been considered as a type of advance in measurement and device fabrication processes. For instance, the interesting properties and new applications of graphene, which originate from its unique dimensions and atomic structure, attract more interest than the fabrication methods using patterning technology for measurements and demonstrations of graphene’s potential usefulness. Nevertheless, patterning is considered a key technology for commercialization and materials device fabrication. In other words, patterning is akin to arranging pasta sauce cans on shelves in an attractive manner to increase sales rather than changing their taste directly. However, as patterns become smaller, denser, and more complex on a large scale, patterning is evolving into a major player in future research and development. Fundamentally, the purposes of patterning in science and technology can be categorized as follows: 1) to obtain novel properties from interactions within periodic structures and 2) to fabricate repeated structures or devices with a desired level of integration within a given area or space. The first purpose tends to attract interest from scientists, as periodic patterns exhibit fascinating physical properties through their interactions with environmental inputs such as photons and electrons. Plasmonics, for instance, exemplifies the significance of patterning technology (see Fan et al., DOI: 10.1021/acs.chemmater.4c00134). Surface plasmons with periodic quantum dot patterns show great potential for various applications, including sensors, photovoltaics, photocatalysts, and lasers (see Sen et al., DOI: 10.1021/acs.chemmater.4c01090. Additionally, crystalline metal–organic frameworks (MOFs) exhibit novel catalytic properties due to their porosity and periodicity (see Patel et al., DOI: 10.1021/acs.chemmater.4c01137). The second purpose is important from a manufacturing perspective, as many production processes rely on patterning technology to optimize time, resources, and operational efficiency. As integrated electronic device technology advances, patterning has become an indispensable tool for increasing integration levels, thereby enhancing capacity, speed, and resolution. For example, the number of pixels on a display screen is determined by the number of thin-film transistors (TFTs), which serve as essential components of display devices. Consequently, patterning technology plays a crucial role in fabricating as many TFTs as possible within a single display panel to achieve higher resolution. (1) Figure 1. Patterns in a grocery store in Italy, with photos taken by the author. As readers may be aware, the drive to increase integration levels in patterning technology has been largely propelled by the growth of the silicon industry. The performance of large language models (LLMs) like ChatGPT and Gemini is heavily dependent on the operational speed of graphics processing units (GPUs). High-speed memory devices, such as high-bandwidth memory (HBM) based on dynamic random-access memory (DRAM), are key components in ensuring the high-speed operation of GPUs. (2) DRAM consists of one transistor and one capacitor, meaning that increasing memory capacity and speed necessitates the addition of more transistors and capacitors within the same space. Consequently, the density of patterns continues to increase, presenting new fabrication challenges. Modern Si devices now are fabricated at scales ranging from a few nanometers to a few tens of nanometers in the front-end-of-the-line (FEOL) process. As a result, the most advanced patterning technologies are first developed and adopted for Si devices. The key criteria for patterning technology are 1) the uniformity of the pattern over a large-scale area and 2) the minimum feature size achievable within a given space. Since the most advanced patterning technologies originate from Si device fabrication, the size of patterning substrates generally corresponds to that of Si wafers or glass panels. Uniformity control is closely related to optimizing high-volume manufacturing processes in industry, meaning it can be improved once a new fabrication method is adopted. In the modern Si device era, however, the primary challenge lies in achieving ever-smaller patterns. Because modern patterning technology is rooted in photolithography, the minimum achievable pattern size is strongly dependent on the shortest wavelength of the light source used. The most widely used light source for photolithography, deep ultraviolet (DUV), with a wavelength of 193 nm, can produce feature sizes below 20 nm when combined with other advanced techniques. (3) For even smaller features, cutting-edge extreme ultraviolet (EUV) technology, with a wavelength of 13.5 nm, is now being introduced to fabricate Si devices with minimum feature sizes below 5 nm. (3) However, several challenges remain in the transition to EUV technology, including mask/pellicle fabrication, photoresist materials, lens materials/systems, and EUV source intensity (see Gangnaik et al., DOI: 10.1021/acs.chemmater.6b03483). Now, patterning technology is also being evaluated based on a new criterion: not only how small the pattern is but also how complex it is. Photolithography operates similarly to photography─in other words, it is a process that transfers three-dimensional (3D) structures onto a two-dimensional (2D) surface. However, ironically, while Si device structures are evolving from 2D to 3D, we still rely on 2D-compatible patterning technology to fabricate them. To address this technological paradox, both academia and industry have proposed numerous innovative ideas. Although various engineering solutions have been explored, materials and chemistry remain fundamental to the advancement of patterning technology. Techniques such as bottom-up growth and self-limiting etching offer promising solutions for 3D nanoscale patterning. Precisely controlled isotropic reactions on all surfaces of a 3D structure enable the fabrication of smaller patterns at the nanoscale. Achieving this requires a fundamental understanding of surface chemical reactions specific to different materials and a thorough study of interfacial interactions in multimaterial systems. Furthermore, the development of additional materials to complement conventional methods is essential. More EUV-sensitive materials will be crucial in bridging the transition from the DUV era to the EUV era, and materials chemistry is at the forefront of this transition. Patterning technology no longer has just a supporting role in realizing our scientific ideas but has become a key player in the transition to the next high-tech era created by humans. In this Special Issue, we have compiled a selection of innovative approaches and ideas published in the past year that address current challenges in patterning technology. We hope readers enjoy the research featured in this Special Issue and find inspiration for further advancements in the field. This article references 3 other publications. This article has not yet been cited by other publications.