Mold Fabrication Process Research Articles

Fabrication Process for Large Size Mold and Alignment Method for Nanoimprint System

Nanoimprint technology is considered one of the mass production methods of the display for cellular phone or notebook computer, with Anti-Reflection Structures (ARS) pattern and so on. In this case, the large size mold with nanometer order pattern is very important. Then, we describe the fabrication process for large size mold, and the alignment method for UV nanoimprint system. We developed the original mold fabrication process using nanoimprint method and etching techniques. In 66 × 45 mm2 area, 200nm period seamless patterns were formed using this process. And, we constructed original alignment system that consists of the CCD-camera system, X-Y-θ table, method of moire fringe, and image processing system, because the accuracy of pattern connection depends on the alignment method. This alignment system accuracy was within 20nm.

Fabrication of high-aspect-ratio polymer nanochannels using a novel Si nanoimprint mold and solvent-assisted sealing

We present a low cost nanofabrication method to fabricate high-aspect-ratio (HAR) polymer nanochannels using a novel silicon nanoimprint mold fabrication technique and a solvent-assisted sealing method. These nanofluidic channels are being developed for single biomolecule detection. The silicon nanoimprint mold fabrication process is based on the combination of anisotropic etching of silicon by potassium hydroxide (KOH) solution and the local oxidation of silicon (LOCOS) process. The resulting high-aspect-ratio silicon mold has smooth sidewalls owing to the anisotropic KOH etching process along the silicon crystalline geometry as well as the LOCOS process. The nanostructures in the nanoimprint molds that form the nanochannels can be easily controlled by the initial micropattern sizes defined using conventional UV lithography and the oxidation time, making this technique a practical solution for low cost and high-throughput HAR silicon nanoimprint mold fabrication. Nanoimprint molds having aspect ratios of more than 1:5.5 (width: 200 nm, height: 1.1 μm, length: 1 cm) were successfully fabricated. Nanoimprinting technique was used to create poly(methyl methacrylate) (PMMA) nanotrenches out of this nanoimprint mold. A novel solvent-assisted sealing technique was developed in order to seal the HAR PMMA nanotrenches. This technique enables the generation of nanochannels with various nanoscale dimensions without the need for complicated and expensive nanolithography tools.

Fabrication of Capacity-Equalized Mold for Homogenizing Residual Layer Thickness in Imprint Lithography

Residual layer control is the key issue in imprint lithography. A thin and uniform residual layer is easily realized for uniform pattern density but it is hardly realizable for nonuniform pattern densities where the moldable materials are supplied by spin coating. The author proposes a new type of mold called capacity-equalized mold that homogenizes the residual layer for a variety of pattern densities and is even suitable for spin-coated films. The capacity-equalized mold was fabricated by introducing an additional lithography step to the conventional mold fabrication process by employing a supplementary mask for modulating the cavity depths in molds. The uniform residual layer for a variety of pattern densities was confirmed by UV nanoimprint using a capacity-equalized mold.

Micro/nanoimprinting of glass under high temperature using a CVD diamond mold

For micro/nanoimprinting of glass, the appropriate combination of glass and mold material was clarified by an adhesion test using chemical vapor deposition (CVD) diamond, silicon, glassy carbon and sintered nitride ceramics as the mold material, and Pyrex, TEMPAX and BK7 as the glass material. The result of the adhesion test shows that CVD diamond is suitable for imprinting with a wide variety of glass materials under various temperature conditions. The method of fabricating the CVD diamond mold using focused ion beam (FIB) was examined, and it was clarified that the grain boundary of CVD diamond has little effect on the surface condition. Glass micro/nanoimprinting was performed using the CVD diamond mold. The effect of the molding conditions, such as the molding temperature and mold-release temperature, on the height of glass transcription was clarified. The effects of pattern size and shape were also investigated. On the basis of the results, a method of selecting the molding conditions to obtain the desired transcript height was developed. In this research, the entire flow of glass micro/nanoimprinting, including mold material selection, the mold fabrication process and molding process, was proposed experimentally, and the selection method of the molding conditions was shown.

The fabrication of a flexible mold for high resolution soft ultraviolet nanoimprintlithography

One key issue for all nanoimprint techniques is an appropriate method for thefabrication of desirable molds. We report on a novel flexible mold fabricationprocess—pressure-assisted molding (PAM)—for high resolution soft ultravioletnanoimprint lithography (soft UV-NIL). In PAM, enhanced master filling is achievedby applying an external pressure during the mold fabrication process. Flexiblemolds, fabricated with PAM using different pressures in the range of 10–90 kPa, arecompared to determine the role of pressures applied in the imprint performance.

Improved mold fabrication for the definition of high quality nanopatterns by Soft UV-Nanoimprint lithography using diluted PDMS material

An improved mold fabrication process that utilizes toluene diluted polydimethylsiloxane (PDMS) as flexible mold material was developed. Various toluene concentrations and their implication on the pattern definition using the Soft UV-Nanoimprint process were analyzed and discussed. Dots with a resolution of 50 nm are well replicated and an excellent imprint homogeneity across a 4 in. wafer with one imprint step only is demonstrated.

Fabrication of microneedle array using LIGA and hot embossing process

We demonstrate a novel fabrication technology of the microneedle array applied to painless drug delivery and minimal invasive blood extraction. The fabrication technology consists of a vertical deep X-ray exposure and a successive inclined deep X-ray exposure with a deep X-ray mask whose pattern has a hollow triangular array. The vertical exposure makes triangular column array with a needle conduit. With the successive inclined exposure, the column array shapes into the microneedle array without deep X-ray mask alignment. Changing the inclined angle and the gap between the mask and PMMA (PolyMethylMetaAcrylic) substrate, different types of microneedle array are fabricated in 750–1000 μm shafts length, 15o–20o tapered tips angle, and 190–300 μm bases area. The masks are designed to 400–600 μm triangles length, 70–100 μm conduits diameter, 25–60EA/5 mm2 arrays density, and various tip shapes such as triangular, rounded, or arrow-like features. In the medical application, the fabricated PMMA microneedle array fulfills the structural requirements such as three-dimensional sharp tapered tip, HAR (High-Aspect-Ratio) shafts, small invasive surface area, and out-of-plane structure. In the skin test, the microneedle array penetrates back of the hand skin with minimum pain and without tip break and blood is drawn after puncturing the skin. Hot embossing process and mold fabrication process are also investigated with silicon and PDMS mold. The processed tetrahedral PMMA structures are fabricated into the microneedle array by the additional deep X-ray exposure. With these processes, the microneedle array can be utilized as the mold base for electroplating process.

Edge-shaped diamond field emission arrays

This article presents the fabrication, characterization, and field emission behavior of edge-shaped diamond field emission arrays. Edge-shaped field emitter geometry is advantageous in the pursuit of high emission current since each edge can have a continuous multiple emission site along the edge as determined by the microstructure of the edge surface. Thus in totality an edge emitter provides significantly larger emission area and hence has the potential for larger current or transconductance for field emission devices. The edge arrays were fabricated via a mold transfer technique on a silicon substrate utilizing silicon micropatterning and etching, followed by chemical-vapor deposited diamond deposition. Arrays of micropatterned edge-shaped diamond emitters were developed and tested for field emission. Moreover, field emission characteristics were improved by further sharpening the edge apex achieving a lower turn-on field and higher emission current. Edge sharpening was achieved by introducing a silicon oxidation step in the mold fabrication process before the diamond deposition step. This oxidation process not only sharpened the edge but also served as a gate dielectric for the development of a self-aligned gated triode device.

UV-LIGA process for high aspect ratio structure using stress barrier and C-shaped etch hole

SU-8 is a well-known thick photoresist used in fabrication of high aspect ratio Micro EectroMechanical System (MEMS) structure. However, it is hard to get fine patterns in the high aspect ratio structures because of high internal stress and difficulty of removing SU-8. The purpose of this paper is to set up the process condition for both low film stress and high aspect ratio and to find design rules that make the pattern be less dependent on stress problem. Firstly, the mold fabrication process is optimized by adjustment of exposure and heat treatment. These two conditions control the amount of cross-linkage in polymer structure, which is the most important parameter of both pattern generation and remaining stress. Heat treatment is dealt with soft bake and post-exposure bake (PEB). Temperature and time duration of each step are varied with heat treatment condition. Exposure time is varied with exposure condition. Secondly, stress barrier and C-shaped etch hole are proposed for layout design scheme. The stress barrier is introduced to minimize stress from the large area polymerized SU-8 film. The etch hole designed to be the shape of character “C” instead of conventional square or wall type etch hole. Some test patterns are fabricated to evaluate the proposed process. Ultra Violet (UV)-LIGA process was performed by nickel electroplating with the mold fabricated through the proposed process to confirm the SU-8 as a good electroplating mold.

Fracture Behavior of Kaolin-Reinforced High Density Polyethylene

The addition of the low-cost mineral filler kaolin to high-density polyethylene (HDPE) creates a composite with both improved stiffness and toughness properties. This study focuses on two aspects of the toughness of these composites: the fracture toughness increment produced by work at the fracture surface and the directionality induced by the injection molding fabrication process. The Essential Work of Fracture (EWF) method gives results which show that a higher volume fraction of kaolin produces more surface work, consistent with earlier work using Compact Tension (CT) tests. The EWF method also demonstrates that a lower volume fraction can produce a higher overall plastic work and apparent toughness. A heat treatment that removes the orientation of the matrix but not that of the particles was applied to study the effect of matrix crystallinity. The results indicate that the matrix supramolecular structure (crystallinity and skin-core effect) is responsible for the directionality of toughness, and that a heat treatment can be used to produce high toughness behavior in both major directions.