Ken-ichiro Nakamatsu

Fluorinated diamond-like carbon coating as antisticking layer on nanoimprint mold

Fluorinated diamond-like carbon (F-DLC) has recently been applied as an antisticking layer on nanoimprint molds for semipermanent use, replacing the self-assembled monolayer currently used. An SiO2/Si mold was successfully coated with an F-DLC thin layer by chemical vapor deposition (CVD). The measured water contact angle of the F-DLC surface was 103°, which is 30° higher than that of the DLC surface. This value indicates the adequacy of F-DLC as an antisticking layer. Moreover, an F-DLC film had a high hardness of 24 GPa, similar to that of a DLC film (26 GPa). AZ resist patterns of 150 nm linewidth and 350 nm pitch were successfully obtained by thermal nanoimprinting using an F-DLC-coated mold. Finally, after repeating the imprinting for more than 100 times, the initial water contact angle of 103° for the surface of the F-DLC-coated mold was maintained.

Effect of Oxygen Plasma Irradiation on Hydrogen Silsesquioxane Nanopatterns Replicated by Room-Temperature Nanoimprinting

We investigated the effect of oxygen (O2) plasma irradiation on hydrogen silsesquioxane (HSQ) patterns replicated by room-temperature nanoimprinting. The HSQ-imprinted patterns with rectangular shapes changed when heated to 200 °C. Furthermore, they disappeared immediately when they were placed on a hot plate at a temperature of 300 °C. In contrast, O2 plasma preirradiation of HSQ-imprinted nanostructures prevented the pattern deformation during postbaking. Even at the high annealing temperature of 1000 °C, HSQ-replicated patterns with 200 nm linewidth, retained its initial pattern profiles. The measured water contact angle of O2-plasma-irradiated HSQ surface decreased from 104 to 25°. The relative intensity of O 1s/Si 2p of the O2-irradiated HSQ surface, measured by X-ray photoemission spectroscopy increased from 3.13 to 4.23. These values were very close to those of thermally grown SiO2 (26.2° and 4.87).

Nanostructure Analysis of Nanosprings Fabricated by Focused-Ion-Beam Chemical Vapor Deposition

We performed a nanostructure analysis of diamond-like carbon (DLC) nanowires used to compose nanosprings fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD). The DLC nanowires of the as-grown nanosprings had elastic double structures, in which a 50-nm-diameter core containing 3-at. % gallium (Ga) in addition to carbon (C) was enclosed in an outer 25-nm-wide DLC shell. The Youngs modulus of the core was 322 GPa, approximately 12 times that (26 GPa) of the DLC shell. Energy dispersion X-ray spectroscopy (EDX) revealed that the C densities of the core and the shell were similar, indicating that the density of the core was higher than that of the shell owing to the incorporation of Ga into the core. However, the core density was approximately halved by 800 °C annealing. This is attributed to the vaporization of Ga and the movement of C from the core to the shell.

Fabrication of High-Aspect Si Structures by Deep Reactive Ion Etching Using Hydrogen Silsesquioxane Masks Replicated by Room Temperature Nanoimprinting

The authors developed a method of fabricating high-aspect Si structures by deep reactive-ion etching (D-RIE) using hydrogen silsesquioxane (HSQ) masks replicated by room-temperature nanoimprinting. The measured dry-etching rates of HSQ without annealing, 1000 °C-annealed HSQ, and Si when subjected to D-RIE gas sources alternately switching from SF6 to C4H8 were 20, 11.4, and 460 nm/min, respectively. This indicates that annealing generated HSQ patterns with approximately twice as much durability against dry etching; however, nonannealed HSQ patterns were shown to be sufficient dry-etching masks. We demonstrated high-aspect-ratio Si gratings 6500 nm in height with an aspect ratio of 43 by using 280-nm-high and 300-nm-pitch HSQ line-and-spacing (L/S) gratings without annealing. The results proved the suitability of HSQ-imprinted patterns as the dry-etching masks for fabricating high-aspect nanostructures.

Effect of UV Irradiation on Microlens Arrays Fabricated by Room Temperature Nanoimprinting Using Organic Spin-on-Glass

Organic spin-on-glass (O-SOG) has been newly proposed as a replication material used in room-temperature (RT)-nanoimprinting. O-SOG is very suitable for optical applications thanks to its good optical properties, including a high refractive index of 1.56 and a transparency that exceeds 98%. O-SOG microlens arrays were successfully replicated by using RT-nanoimprinting. UV pre-irradiation offered O-SOG-nanoimprinted patterns the property of maintaining their initial profiles after 300 °C annealing, while the patterns without any treatment completely disappeared after 300 °C annealing due to the polymer reflow.

Room-Temperature Nanoimprinting Using Ladder Hydrogen Silsesquioxane

Ladder hydrogen silsesquioxane (HSQ) has been proposed as a replication material to be used in nanoimprinting processes at room temperature. We replicated ladder-HSQ patterns by nanoimprinting at room temperature that were as accurate as replicated caged-HSQ patterns. Caged HSQ is the standard replication material currently used in nanoimprinting at room temperature. Caged-HSQ-imprinted patterns completely disappeared when annealed at 300 °C. However, ladder-HSQ-imprinted patterns retained almost the same rectangular profile as they had before annealing, even after being subject to high-temperature annealing at 1000 °C. Fourier transform infrared spectroscopy showed that high-temperature annealing transformed the HSQ into a SiOx structure. This vitrification of HSQ resin improved its dry-etching durability, with the dry-etching rate when subject to CHF3 reactive-ion etching decreasing from 32 to 27 nm/min, which is close to the value of 26 nm/min for thermally grown SiO2 and a quartz substrate.

Characteristics of Antisticking Layer Formed by CHF3 Plasma Irradiation for Nanoimprint Molds

Nanoimprint lithography (NIL) is very useful for mass-producing nanostructure devices at a low cost and a high throughput. To avoid the adhesion of replication materials, NIL molds are usually coated with an antisticking fluorinated self-assembled monolayer. In this study, we used a fluorinated plasma chemical vapor deposition film as the antisticking layer. First, we formed a CHF3 plasma chemical vapor deposition (CVD) film on SiO2/Si and quartz molds and carried out thermal and UV nanoimprint using these molds. However, the film was removed from these molds. We found that the proposed method can solve this problem. We irradiated plasma using a gas mixture of CHF3 and O2 as the source gas onto SiO2/Si and quartz molds. As imprinting results, the patterns were successfully imprinted onto the resins without the removal of the plasma CVD film. In addition, we were able to carry out 100 times of repeated nanoimprinting using the plasma-CVD-film-coated SiO2/Si mold.

Room Temperature Nanoimprinting Using Release-Agent Spray-Coated Hydrogen Silsesquioxane

Room temperature nanoimprint lithography (RT-NIL) is a simpler process than thermal and UV NIL because it can be carried out without a resist thermal cycle and UV exposure. A fluorinated self-assembled monolayer (F-SAM) is mainly used as an antisticking layer. However, the F-SAM deteriorates due to repeated nanoimprinting. To prevent the F-SAM coating on the NIL mold from deteriorating, we propose a new imprinting technique using release-agent spray-coated hydrogen silsesquioxane (RASC-HSQ). We carried out RT-NIL onto it using a mold without F-SAM. The pattern was successfully imprinted on the resin without any signs of adhesion.

Fabrication of Fine Electron Biprism Filament by Free-Space-Nanowiring Technique of Focused-Ion-Beam + Chemical Vapor Deposition for Accurate Off-Axis Electron Holography

We have developed a new method of producing a fine electron biprism filament by chemical vapor deposition (CVD) in a focused-ion-beam (FIB) system. An 80-nm-diameter filament of diamond-like carbon (DLC) was bridged in 90 s between two tungsten rods fixed on a biprism holder. The filament was stable enough for taking electron holography. Moreover, the fine filament offered not only wider interference regions but also higher fringe contrasts than those of the filament with a diameter of 400 nm that is a common diameter of conventional electron biprism.