Fabrication of a seamless roll mold using inorganic electron beam resist with postexposure bake

Abstract

The fabrication of next-generation devices via roll-to-roll (RTR) nanoimprinting has received considerable attention due to the high throughput and resolution associated with the process. In particular, RTR nanoimprinting with ultraviolet (UV)-curable resin is expected to be useful for the fabrication of large-area devices such as nonreflective films, transparent conductive sheets, and organic solar cells. In order to improve the resolution of such devices, the roll mold must be able to produce seamless fine patterns. Generally, a roll mold for nanoimprinting is made by attaching a planar mold replicated from the master mold via a nickel electroforming technique. However, this method produces seams, which reduces the product yield. In order to resolve these issues, the authors have developed a direct writing method using electron beam (EB) lithography on a rotating cylindrical substrate. In this study, the authors examined the potential for fabricating a seamless roll mold using high-resolution inorganic EB resist and the pattern shrink effect from postexposure bake (PEB). The authors used the dip-and-pull method to form the EB resist layer on the roll mold substrate (32 mm diameter, made of brass). The cleaned roll mold was dipped in the inorganic EB resist and then pulled out at a constant speed. The resulting sample was cured at 300 °C for 1 h. Next, the sample was mounted on rotating equipment and placed in a scanning electron microscope (SEM) equipped with an EB writing system, and the roll substrate was exposed to 10 kV EB while rotating at a constant speed. The revolution speed was set to ten turns per line pattern. Subsequently, PEB was carried out at 200 °C for 10 min in air. After the sample was cooled to room temperature, the EB-exposed area of the EB resist layer was developed using buffered HF. The obtained pattern on the roll mold was examined with the same SEM used for writing. Finally, RTR nanoimprinting using the obtained roll mold was carried out using UV-photocurable resin. At that time, the sample was coated with an antisticking layer of fluorinated silane coupling agent. As a result, a seamless line pattern 190 nm wide was obtained on a polyethylene terephthalate film over a length of 10 cm.

Fabrication System for Large-Area Seamless Nanopatterned Cylinder Mold Using the Spiral Laser Interference Exposure Method

“…However, it is practically impossible to expose two beams at 180°; hence, we aim to create a pattern whose period is slightly greater than half the wavelength. LIL can quickly fabricate both micro and nanopatterns over a relatively large area [18,19,[22][23][24][25][26][27][28][29][30]. In addition, the construction costs for LIL are lower than those for e-beam lithography systems.…”

“…Thus, micropatterns and nanopatterns can be quickly produced using the laser interference pattern. Various methods, such as Lloyd's mirror [22,23], beam splitter [18,19,[24][25][26], phase mask [27], and prism-based laser interference [28][29][30] have been investigated. The Lloyd's mirror method performs interference exposure in a basic manner; however, both the interference angle and structure period are fixed in this method.…”

Laser direct write system for fabricating seamless roll-to-roll lithography tools

“…Different approaches have used ultraviolet (UV), 4,5 x-ray, 6 or electron beam [7][8][9] sources to pattern a photoresist layer. The patterned photoresist can then be used directly for imprinting or act as a mask for etching or deposition of more durable metal patterns.…”