A compact nanoimprint lithography (NIL) apparatus using the driving power of a servomotor has been newly developed. A bilayer resist method using hydrogen silsequioxane (HSQ) as a top layer and AZ photoresist as a bottom layer has been proposed to achieve high-aspect resist patterns on a nonflat surface for room-temperature nanoimprint lithography (RT-NIL). The etching rate ratio of HSQ to AZ photoresist was higher than 100 for O2 reactive ion etching (RIE), indicating that the HSQ top layer has sufficient etching tolerance. We have achieved the high-aspect nanostructure patterns of 100-nm-linewidth and 1-µm-height using the NIL apparatus developed here.

Room-temperature nanoimprint lithography (RT-NIL) and nanocontact printing (RT-NCP) processes using hydrogen silsesquioxane (HSQ) are promising techniques for fabricating various nanostructure devices. We have evaluated the linewidth dependence of the HSQ imprinted depth and the baking-temperature dependence of HSQ replicated patterns after RT-NIL. We have also demonstrated an advanced bilayer resist process with HSQ as a top layer and AZ photoresist as a bottom layer; this process can be used to fabricate high-aspect resist patterns on a Si substrate for RT-NIL and RT-NCP. The etching-rate ratio of the AZ photoresist to HSQ exceeds 100 for O2 reactive-ion etching, which means the etching tolerance of the HSQ top layer is sufficient to enable its use as a mask. We have fabricated high-aspect nanostructure patterns with 100 nm linewidth and 1 μm height using RT-NIL and 150 nm linewidth and 1 μm height by using RT-NCP. Furthermore, we have successfully transferred Au electrode patterns from a mold onto HSQ resin by using the adhesion properties of HSQ.

We developed a lift-off process for a nanoimprint lithography (NIL) using poly(vinyl alcohol) (PVA) as the replicated material. PVA could easily be dissolved in water. A conventional lift-off process using poly(metyl methacrylate) (PMMA) uses acetone as a solvent, while the lift-off process using PVA uses water as a solvent, which is an ecologically friendly process. We demonstrated Au patterns with sub-µm dimensions using a lift-off process with a PVA single layer. In addition, an Hydrogen silsesquioxane (HSQ)/PVA bilayer structure was used for the lift-off process. This bilayer structure could be fabricated by room-temperature NIL and dry etching. Au patterns were easily obtained using the bilayer structure having an inverse tapered shape. In the lift-off process without using HSQ/PVA bilayer, Au wiring with sub-µm linewidth could be obtained, however, 100-nm-linewidth patterns did not remained. Line-and-spacing gratings of 100 nm in the Au patterns were demonstrated using the water lift-off process with the HSQ/PVA bilayer structure.

Articles you may be interested inFacile fabrication of functional PDMS surfaces with tunable wettablity and high adhesive force via femtosecond laser textured templating A new approach to fabricating high density nanoarrays by nanocontact printing Direct pattern transfer technology by room-temperature nanocontact printing using hydrogen silsesquioxane ͑HSQ͒ and Ag paste, which takes advantage of adhesion properties of these transfer materials, has been developed. The use of poly͑ethylene͒ laminated on poly͑methylmethacrylate͒ sheet has been proposed as the soft template for the contact printing. The HSQ transferred pattern with 35 nm linewidth was obtained onto Si surface. In addition, 1 m linewidth, and 2 m pitch Ag patterns were successfully transferred from the soft template to the SiO 2 / Si substrate. The transferred Ag wiring with 1 m linewidth showed good conduction characteristic, resistivity to be 1.7ϫ 10 −7 ⍀ m.

In the UV nanoimprinting process an antisticking layer such as fluorinated self-assembled monolayer (F-SAM) is grafted on the mold surface to diminish the demolding impact. These layers are supposed to deteriorate as the imprint steps mount up, resulting in defects in the cured resist layer. In this work, continuous multiple shots of UV nanoimprint were conducted in the air and in pentafluoropropane (PFP) gas environment and demolding forces in every imprint step were determined. The experiments revealed that the demolding forces for the imprint in PFP atmosphere drastically reduced compared with those in the air. Water contact angles of the mold surface were also determined in every 225 imprint steps to observe the degree of degradation of the antisticking layer. It was found that the antisticking layer was less damaged or contaminated in the PFP environment than it was in the air after a certain number of imprint steps.