Nanoelectrode lithography using a flat mold with a pattern defined by different conductivities

Nanoelectrode lithography is a pattern duplication method that combines nanoimprint with an electrochemical reaction. The method can form an oxide pattern directly on a semiconductor or metal. This method can use flat molds with patterns defined by substances with different conductivities, while the conventional nanoimprint technique must use a mold with a relief pattern. In this paper, the mold pattern for the technique is defined with an oxide material on the surface of a conductive substrate. Nanoelectrode lithography itself can be used to form a flat mold by using a conductive mold with a relief pattern, which leaves an oxide pattern via the anodic oxidation of Si. AFM lithography also can utilize an electrochemical reaction in the air to generate an oxide pattern on a conductive substrate, which gives us a flat mold. This paper shows that both types of flat mold can transfer a pattern to a target substrate. These strategies will allow us to realize on-demand mold fabrication, mold modification, and an easy way of obtaining a mold with a finer pattern.     

UV-nanoimprinting using non-transparent molds and non-transparent substrates

A new ultraviolet assisted nanoimprint lithography technique with an exposure through non-transparent molds and a nm-resolution capability is reported. The UV imprint material was not cured by direct irradiation, but substantially exposed to indirect and diffuse irradiation. The nanoimprint molds consisted of a transparent support and a non-transparent, patterned element. Successful imprints were conducted on transparent glass and polymer foils placed on non-transparent substrate holders as well as on SiO₂ on Si. The reported technique enables the application of non-transparent mold materials like Si, new mold materials and alternative antisticking layers like metals in UV-NIL.     

Filling behavior of UV nanoimprint resin observed by using a midair structure mold

The filling behavior of resin during UV nanoimprint lithography (UV-NIL) was observed by using a “midair structure mold” and by changing the imprint pressure. The midair structure molds were fabricated by electron beam lithography (EBL) using hydrogen silsesquioxane (HSQ) as a negative tone resist. After the fabrication of midair structure mold, two types of surface treatment molds, which were with or without release coating, were prepared. Using these molds, the filling behavior of a UV curable resin was investigated at various pressures. The results indicate that a pressure of approximately 1.2 MPa is necessary for complete filling in the case of molds treated with a release agent. This method demonstrates effect of a release coating for UV-NIL.     

A versatile pattern inversion process based on thermal and soft UV nanoimprint lithography techniques

Si master molds are generally patterned by electron-beam lithography (EBL) that is known to be a time-consuming nanopatterning technique. Thus, developing mold duplication process based on high throughput technique such as nanoimprint lithography can be helpful in reducing its fabrication time and cost. Moreover, it could be of interest to get inverted patterns (holes instead of pillars) without changing the master EBL process. In this paper, we propose a two step process based on thermal nanoimprint lithography (T-NIL) (step 1) and soft UV assisted nanoimprint lithography (UV-NIL) (step 2) to invert a master EBL mold. After the two inversion steps, the grand-daughter Si mold exhibits the same pattern polarity as the EBL mold. For step 1, pattern transfer using ion beam etching (IBE) of a thin metallic underlayer is the critical step for dimension control due to the low NXR1020 resistance. For step 2, the optimized reactive ion etching (RIE) step allows transfer with good anisotropy even for nanostructures at the 50 nm-scale. For structures larger than 100 nm, this inversion process has been successfully applied to large field replication (up to 1.5 cm²) on whole wafer.     

UV nanoimprint lithography with rigid polymer molds

Transparent polymers are considered as alternative low-cost mold materials in UV nanoimprint lithography (UV-NIL). Here, we demonstrate a nanoimprint process with molds made of rigid polymers novel for this application. These polymer molds are found to show high performance in the patterning with UV-NIL. Sub-50 nm structures were fabricated with this process.     

Anodized Aluminum Oxide/Polydimethylsiloxane Hybrid Mold for Roll‐to‐Roll Nanoimprinting

Two types (hard and soft) of the molds are widely used in nanoimprint lithography for a high throughput over a large area, and high‐resolution parallel patterning. Although hard molds have proven excellent resolutions and can be used at high temperatures, cracks often occur in the mold in addition to the requirement of high imprinting pressure. On the other hand, though soft molds can operate at lower pressures, they give poor pattern resolution. Here, a novel hybrid mold of anodized aluminum oxide (AAO) template attached to a flexible polydimethylsiloxane (PDMS) plate is introduced. Due to the flexible nature of PDMS, various polymer nanostructures are obtained on flat and curved substrates without crack formation on the AAO mold surface. Furthermore, the hybrid mold is successfully used for roll‐to‐roll imprinting for the fabrication of high density array of various shaped polymeric nanostructures over a large area.     

Fabrication of low-cost mold and nanoimprint lithography using polystyrene nanosphere

The periodic arrays of nanostructure were successfully patterned on Si wafers by ultraviolet nanoimprint lithography (UV-NIL) using nanosphere lithography (NSL). Two-dimensional (2D) well ordered self-assembled arrays were obtained on Si wafer by using nanosphere and the tilted-drain method. We tried to combine two techniques and hard mold of Si mold for NIL and polymer mold of acrylate-based polymer were fabricated by NSL. The Si master mold and polymer mold were formed by Cr lift-off and ICP-RIE process. The surface has a low surface energy at the interface with 1H, 1H, 2H, 2H-perfluorooctyl-trichlorosilane (FOTS) vapor-coating, which can eliminate the problem of the adherence to the surface of the mold during demolding. Finally, nanopatterns were formed by UV-NIL, where the residual layer was not observed.     

UV nanoimprint lithography of sub-100 nm nanostructures using a novel UV curable epoxy siloxane polymer

We reported the replication of sub-100 nm nanostructures by an ultraviolet (UV) nanoimprint lithography (NIL) technique. We used a novel UV curable epoxy siloxane polymer as the NIL resist to achieve features as small as 50 nm. The polymeric soft molds for the NIL were fabricated by casting toluene diluted poly(dimethyl-siloxane) (PDMS) on the hydrogensilsesquioxane (HSQ) hard mold. The NIL results were characterized by using a scanning electron microscope and an atomic force microscope. Our results illustrate that, with the epoxy siloxane resist, the 50 nm HSQ features on the hard mold can be successfully replicated using PDMS soft molds.     

Metallic and dielectric photonic crystals with chiral elements by combined nanoimprint and reversal lithography in SU-8

We report a novel nanoprocess combining nanoimprint lithography and conventional lithography to fabricate metallic and dielectric nanophotonic crystals with chiral elements in SU-8. The previously developed nanoimprint process was modified for much smaller feature size. Four different types of nanophotonic crystals with different materials in both large and small dimensions are fabricated. The new proposed reversal lithography is used to fabricate one type among the above mentioned four. The success of reversal lithography provides a solution for near-field lithography to achieve nanosize structures with simple conventional lithography. Optical measurements of the laser polarization state from the fabricated photonic crystals indicate an optical chirality which distinguishes the chiral elements from other normal symmetric structures.     

Reproduction of fine structures by nanocasting lithography

Novel reproduction technique for nanostructures is newly proposed based on nanoimprint and nanocasting lithography. First, a master nanostructure is replicated using fluorinated polymer by conventional thermal nanoimprint. Then, the master structure is reproduced using the replicated fluorinated polymer by nanocasting lithography. Using the fluorinated polymer as a mold, fine pattern is successfully transferred without releasing failure. Also, low cost reproduction is realized by nanocasting lithography without using special tools and materials. Using the proposed method, reproduction of the anti-reflection structure having 250 nm feature size is successfully demonstrated.     

Low cost, rapid fabrication of durable molds of grating arrays for nanoimprint lithography

This study proposes a new fabrication method for the mold of a sub-micron grating array used in the nanoimprint lithography process. In general, the mold of a sub-micron grating array is fabricated by electron beam lithography (EBL) and reactive ion etching (RIE), and then, nanoimprint lithography (NIL) is used to achieve the required amount of replication. Such a method is expensive and has a low throughput, and the pattern is limited by the original mold. In this paper, we constructed a durable mold of a sub-micron grating array with good adaptability, using a commercial epoxy grating (EG) and a hybrid inorganic/organic sol-gel material combined with nanoimprint lithography and photolithography. Due to its low cost and ease of use, this method is suitable for both laboratory research and mass production without the need for expensive equipment like EBL or RIE.     

Mold cleaning and fluorinated anti-sticking treatments in nanoimprint lithography

Fluorinated anti-sticking layers (F-ASLs) are generally used to prevent adhesion between molds and resists in nanoimprint lithography (NIL). Nevertheless, these layers are degraded after a certain number of imprints and the mold needs to be cleaned and re-treated. We have observed that the cleaning procedures before re-treatment impacts on the grafting of the fluorinated molecules and on the longevity of the ASL. We propose an efficient cleaning procedure of the damaged anti-sticking layers on both silicon and fused silica molds allowing a reproducible re-deposition. Surface chemistry analyses were conducted using a specific procedure based on X-ray photoelectron spectroscopy (XPS) experiments. This procedure was proven to be suitable for ultra thin organic layer composition analysis.     

硅油稀释PDMS法制备紫外纳米压印软模板

软模板的制作是紫外纳米压印中关键的技术,模版的分辨率直接决定了压印图形的最小分辨率。使用具有高度均匀、100nm级孔洞阵列结构的多孔氧化铝作为母版,使用基于液态浇铸的硅油稀释聚二甲基硅氧烷(硅油和聚二甲基硅氧烷的质量比为1:2)法制备出具有规则点阵结构的软模板。通过SEM和AFM表征发现,特征图形得到了有效转移,特征尺度保持在100nm左右。相对于传统的模板制备方法,此方法成本低、流程简单、适合大规模生产,是一种非常有前途的软模板制备方法。     

Fabrication of multi-dimensional colloid crystals on raised surfaces via reversal nanoimprint lithography

Fabrication of multi-dimensional colloidal crystals on raised polymer substrate has been achieved by reversal nanoimprint technique. The combine effects of the feature size of the mold, particle diameter and imprinting steps control ordering of the colloidal particles. It is shown that using ‘Reversal nanoimprint lithography’, 3D colloidal particles can be selectively patterned on soft (polymer) substrates. Reversal nanoimprint lithography offers a relatively easy, fast and versatile method for patterning of colloidal particles.     

Preparation methods and characteristics of fluorinated polymers for mold replication

Mold replication process using fluorinated materials by thermal nanoimprint and UV nanoimprint was investigated by three different experiments. Firstly, the influence of particulate contamination was examined. It was estimated that the damage to the master mold by particles can be suppressed by applying a thicker polymer layer for mold replication. Secondly, it was shown that the surface properties of UV curable resin containing fluorinated components can be controlled by the curing conditions. Thirdly, the stability of the surface properties of the fluorinated materials was compared. The surface of the perfluorinated polymer showed high stability against UV imprint. UV cured molds have lower stability but they are suitable for disposable molds which can be used for several times to several tens of times.     

Replication of high ordered nano-sphere array by nanoimprint lithography

High ordered nano-sphere array patterns on Si substrate were fabricated using nanoimprint lithography. First, using hot embossing method, poly vinyl chloride (PVC) based polymer replica template was duplicated from original high ordered nano-sphere array patterns, which was fabricated by evaporation method. The monolayer transferring condition can be achieved by varying hot embossing pressure. Then, through UV nanoimprint lithography with the replicated polymer template, imprinted patterns, which has high ordered nano-sphere array patterns, was successfully fabricated on Si and flexible PET substrate.     

纳米印刷光刻技术

介绍了纳米结构制作的一种新方法———纳米印刷光刻的基本原理、总体方案。该技术与其它微刻印技术相比,具有成本低、生产效率高、可批量生产、工艺过程简单等优点。介绍了SiC模板的制作方法、用纳米印刷光刻技术制作纳米结构的加工步骤及刻印结果。结果表明该技术可制作特征尺寸小于100nm的图形。本文还展望了其应用于微电子学等领域的前景。     

Evaluation of filling behavior on UV nanoimprint lithography using release coating

Ultra violet nanoimprint lithography (UV-NIL), which is able to obtain the nano-scale pattern effectively and quickly, is strongly desired for the next-generation lithography technology. However, it is well known that the higher viscosity UV-curable resin with UV-NIL tends to be the shorter obtained pattern without the sufficient transfer pressure. This phenomenon is caused by the filling behavior of UV-curable resin into the UV-NIL mold, thus, the investigation of the filling behavior is very important. In this study, the filling behavior in UV-NIL was observed by using a “midair structure mold”, which is able to eliminate the bubble defect. As a result, it is clear that the filling behavior with low transfer pressure was depended on the capillary force in the mold pattern, which is described by the mold aperture size, the mold surface condition and the resin property.     

Large area pattern replication by nanoimprint lithography for LCD–TFT application

Nanoimprint lithography is a high-throughput, low-cost, non-conventional lithographic method for fabricating micro/nanoscale patterns. In this study, we will present recent achievement in developing nanoimprint lithography for LCD–TFT fabrication. We fabricated metal gate for LCD–TFT with imprinting process. First, mold is pressed into a thin resist cast on a Cr layer which is deposited on a glass substrate. And the pressed resin is exposed to UV for curing, followed by demolding process. To acquire metal gate for LCD–TFT, subsequent process such as RIE with O₂ Plasmas, wet etching of Cr and striping of remained resin is followed. Finally, the fabricated metal gate has 3.5 μm level width, 97% uniformity overall on 1G size in a single imprint. Herewith nanoimprint lithography can substitute conventional photolithography steps in LCD–TFT process. Also it is expected that large area fine pattering such as functional optical films and PCBs could be effectively produced by nanoimprint process.     

Fabrication of nano-scaled patterns on ceramic thin films and silicon substrates by soft ultraviolet nanoimprint lithography

Soft ultraviolet nanoimprint lithography is a cost-effective and versatile technique for the transfer of nano-scaled patterns to various surfaces. Here, we report on the fabrication of sub-micron square pillar arrays in epitaxial Ba_0.7Sr_0.3TiO₃ ceramic films, using a combination of nanoimprint lithography and inductively coupled plasma etching techniques. Based on a similar approach we have also succeeded in preparing positive (direct) and negative (inverse) replicas of silicon master molds. Such a generic process could find application in various materials.