In this blog post, we’ll explore the concept of nanomanufacturing processes—the foundation of nanotechnology—as well as representative process methods and the characteristics of each technology.
Consider a cube. As the length of one edge decreases, the surface-to-volume ratio increases exponentially, and in the microscopic world, various phenomena emerge that are not observed in the macroscopic world. To study these characteristics, highly precise observation techniques are essential. In the past, due to the limitations of optical microscopes, only structures at the micrometer scale could be analyzed. However, with advancements in science and technology—including electron microscopes—it has become possible to observe structures as small as nanometers, leading to active research in this field. Currently, research is underway in various fields—such as electronics and information and communications technology, biotechnology, environment and energy, defense, and aerospace—to harness the characteristics of the microscopic world.
Nanofabrication (Nanofab) generally refers to all processes involved in the mass production of structures ranging from 1 nm to 100 nm. Fabricating such nanoscale structures requires an approach different from traditional methods used to process structures—such as pipes—that are micrometers or longer in length. For this reason, nanofabrication technology has established itself as a core foundational technology of nanotechnology, covering the approximately 1–100 nm range. The ultimate goal of nanofabrication technology is to mass-produce desired nanostructures easily and economically.
Nanofabrication processes developed to date are broadly categorized into top-down and bottom-up methods. The top-down method involves progressively refining bulk materials to create the desired nanostructures; it represents a more precise evolution of existing microfabrication technologies. Representative examples include photolithography and soft lithography. In contrast, bottom-up methods are technologies that form structures at the atomic or molecular level based on chemical processes. Vapor deposition and self-assembly are representative bottom-up processes.
Photolithography is a representative nanotechnology process that uses a photosensitive polymer (photoresist, PR), which reacts to specific wavelengths such as ultraviolet light, to transfer a mask pattern onto a silicon substrate. The term “lithography” originates from letterpress printing and refers to a method of forming desired structures using a mask. Here, the mask refers to a stencil used to form the desired pattern on the substrate. In this process, resolution—the smallest size that can be realized on the substrate—is a critical factor. Optically based lithography faces fundamental limitations in resolution due to the diffraction of light. Although most semiconductors currently in production are manufactured using this photolithography method, the limitations of the conventional approach are becoming increasingly apparent as semiconductor integration density continues to rise; consequently, various processes to replace or complement it are being actively researched.
Soft lithography is a top-down process that, along with photolithography, is attracting significant attention. Its name derives from the fact that the mold used to form patterns is made of PDMS (polydimethylsiloxane), an elastic material, rather than conventional rigid materials. The PDMS used as a mold has low surface energy and is chemically stable, so it does not readily react with the material onto which the pattern is to be transferred, and it can be easily separated after transfer. Furthermore, it offers excellent gas permeability and thermal stability, providing various process advantages, and is widely used in laboratories researching nanostructures.
Vapor deposition is a process that forms a thin film by growing the desired material onto a substrate. Simply put, it can be likened to the process of snow accumulating in winter. Vapor deposition methods are broadly categorized into chemical vapor deposition (CVD) and physical vapor deposition (PVD). In chemical vapor deposition, the material to be grown on the substrate is supplied in a gaseous state; this material then diffuses to the substrate surface, where it undergoes a chemical reaction to form a thin film. After the thin film is formed, the remaining material detaches from the substrate and is vented back into the gaseous state. Physical vapor deposition involves applying energy to the material used to form the thin film, physically separating the atoms or molecules, and then depositing them onto the substrate. Sputtering, a representative example, is a process in which high-energy particles collide with a target, causing atoms or molecules to be ejected and deposited onto the substrate.
In contrast, self-assembly—unlike the processes introduced earlier—does not involve direct external shaping of the structure; rather, it is a process in which components assemble themselves under their own forces to form a structure. This phenomenon is also commonly observed in biological processes such as protein synthesis. However, at the current level of technology, there are limitations compared to the processes introduced earlier in terms of realizing intended structures with high accuracy and low defect rates. Nevertheless, it is regarded as a crucial technology for fabricating three-dimensional nanostructures and for realizing structures capable of self-healing and self-replication, and it is expected to play a pivotal role in future nanofabrication processes.
