Fabrication Of Templates Research Articles

Thermal Imprinting of Nano-Patterns Using Thiol-Based Self-Assembled Monolayer-Treated Nickel Template

A highly durable imprint template is essential for the industrialization of nanoimprint lithography (NIL). Conventionally, Si-based materials were used for the fabrication of imprint templates. However, their fabrication is very expensive and they can be easily damaged during repeated imprint processes due to their brittleness and poor mechanical properties. The Ni template has excellent mechanical strength and can be easily and cheaply duplicated by the electroforming process. It has the potential for application to the NIL process if its poor antistiction property, which causes serious detaching issues, is improved. In this study, thin Au and Ti layers were deposited on a Ni template and a thiol-based, hydrophobic, self-assembled monolayer (SAM) layer was stably formed on the Au coated Ni template. Thus, the antistiction property of the Ni template was drastically elevated. Using the prepolymer-based, thermal imprint process and the thiol-based, SAM-coated Ni template, sub-micron sized patterns were successfully formed on the Si substrate.

Continuous-Stage-Movement Blankingless Electron-Beam Lithography for Patterned Media Template Fabrication

A slider and spindle (r–θ) stage electron beam (e-beam) mastering system with continuous-stage-movement blankingless beam shift lithography (BLSL) and flyback e-beam lithography (CSFL) brings together the features of high resolution, high accuracy, and high throughput to meet the various requirements for fabricating master templates for discrete track media and bit patterned media (BPM) for the next generation of hard disk drives. With the CSFL capability, we achieve multiple-overlay bit writing with one, two, four, and eight overlays for a BPM bit array to markedly improve track-to-track phase alignment accuracy from 5.6 nm sigma in a single write to 1.04 nm sigma in an eight overlay write. CSFL, in conjunction with the high-frequency response of the e-beam deflector, achieves 25 MHz high-throughput BPM bit array write with track pitches and bit pitches of 120 nm in the entire write range from 20 to 140 mm in diameter. This write takes only 11.6 h under the conditions of a line velocity of 3,000 mm/s, a beam current of 150 nA, a maximum rotation speed of 2,865 rpm, and a constant line velocity (CLV) write mode.

A Soft-Polymer Piezoelectric Bimorph Cantilever-Actuated Peristaltic Micropump

For this work, a peristaltic micropump was fabricated. Actuation of the micropump was accomplished with piezoelectric cantilevers. To date, a minimal number of soft polymer-based micropump designs, have explored the use of piezoelectric materials as actuators. The fluidic channel for the micropump was fabricated using PDMS and soft lithography. A novel and very simple template fabrication process was employed, where the use of a mask and clean room facilities was not required. Replica molding to the template produces both, a channel measuring ∼95μm in height, and a rounded cross-sectional geometry, the latter of which is known to be favorable for complete valve shutoff. Clamps were adhered to the tips of the cantilevers, and used to secure in place aluminum valves. The valves had finely machined tips [3mm×200μm(L×W)] on one surface. These tips served as contact points for the valve making contact with the PDMS membrane surface, and were used for the purpose of opening and closing the channels. The cantilevers were secured in place with in-house manufactured micropositioners, which were used to position the valves directly over the PDMS channel. The micropump was thoroughly tested where the variables characterized were maximum attainable backpressure, flow rate, valve open/close characteristics, and valve leakage. The effect of the phase difference (60°, 90°, and 120°) between the square wave signals delivered to each of the three cantilevers was investigated for flow rate and maximum attainable backpressure. Of the three signal phases, the 120° signal demonstrated the largest flow rate range of 52–575 nL/min (0.1–25 Hz), as well as the highest attainable backpressure value of 36,800 Pa (5.34 psi). The valve shutoff characteristics for this micropump was also examined. Fluorescein was trapped inside the microchannel, where the fluorescent signal was monitored throughout the valves open/close cycle with the aid of an epifluorescent microscope. It was found that the fluorescent signal went to zero with the valve fully closed, supporting the conclusion that the valve completely closes off the channel. Further evidence of this claim was demonstrated by observing the valve leakage characteristics. An electronic pressure sensor was used to collect data for this experiment, where it was found the valve was able to hold off 36,800 Pa (5.34 psi), only loosing 2% of this pressure over 10 minutes. In conclusion, it has been shown this micropump outperforms many existing micropump designs, and is suitable for integration into a variety of both macro, and microdevice platforms. Experiments are currently underway to examine how the flow and valving characteristics change for valves with different tip dimensions. A discussion will also be given for improved fabrication techniques, where injection molding is currently being used as the fabrication method to examine the performance changes associated with different cross-sectional PDMS channel geometries. The end goal for use of this micropump is twofold; 1) integration into a micro-free flow separation device, and 2) integration into a capillary electrophoresis instrument for use in direct-sampling neuroscience experiments.

Fabrication of three-dimensional photonic crystals by interference lithography with low light absorption

We report on the fabrication of polymer templates of photonic crystals by means of holographic (or interference) lithography. The grating is written in a SU-8 photoresist using a He-Cd laser of wavelength 442 nm. The use of the wavelength found within the photoresist low absorption band enables fabricating structures that are uniform in depth. Parameters of the photoresist exposure and development for obtaining a porous structure corresponding to an orthorhombic lattice are determined.

Fabrication of macroporous platinum using monodisperse silica nanoparticle template and its application in methanol catalytic oxidation

This is to report a practical and convenient method for 3D macroporous Pt synthesis based on the monodispersion silica template. The silica nanospheres were fabricated using an improved Stöber method. The alternative method of tetraethoxysilane (TEOS) addition to the reaction system was found to be helpful in gaining silica spheres with high monodispersion. The diameter of the final silica spheres increased proportionally with adding TEOS. The silica template was built with the self-assembling method by dispersing a dilute suspension of SiO 2 nanosphere onto the smooth Au support surface. After evaporating the solvent naturally, a three-dimensional template with some void spaces around the arranged nanospheres, on the Au slide, was obtained. The macroporous Pt was synthesized by electrodeposition of Pt into the void spaces of the template, which was confirmed by SEM images. The surface activities of the resultant macroporous Pt were investigated by comparing the hydrogen adsorption/desorption peaks in H 2SO 4 and the methanol oxidation activity. The resultant macroporous Pt displayed high activity level during Pt loading of 0.532 mg cm −2. The current work presents a useful method for nanoparticle synthesis, 3D template and macroporous material fabrication.

Photodefinable PDMS thin films for microfabrication applications

In this work, direct patterning of polydimethylsiloxane (PDMS) is demonstrated by the addition of a UV-sensitive photoinitiator benzophenone. As an improvement to our previous work, patterns with both positive and negative features have been fabricated on the same substrate. Infrared spectroscopy was used to investigate photocrosslinking behavior and reaction chemistry of this new photodefinable PDMS (photoPDMS) material. Several applications of the photoPDMS process have been successfully demonstrated. Multi-layer structures and multi-level microfluidic chips can be easily fabricated using this photopatterning process. Patterned PDMS thin films can also be removed from the underlying substrates and used as shadow masks for defining patterns on both planar and non-planar surfaces. The photopatternable PDMS was also found to be biocompatible once un-reacted benzophenone is extracted from the cured film. Overall, photoPDMS offers a number of critical advantages over conventional PDMS processing, including elimination of master template fabrication, ability to process under ambient light processing conditions, positive-acting tone, low cost, and rapid and easy fabrication.

Step and flash imprint lithography for manufacturing patterned media

The ever-growing demand for hard drives with greater storage density has motivated a technology shift from continuous magnetic media to patterned media hard disks, which are expected to be implemented in future generations of hard disk drives to provide data storage at densities exceeding 1012 bits/in.2. Step and flash imprint lithography (S-FIL) technology has been employed to pattern the hard disk substrates. This article discusses the infrastructure required to enable S-FIL in high-volume manufacturing, namely, fabrication of master templates, template replication, high-volume imprinting with precisely controlled residual layers, and dual-sided imprinting. Imprinting of disks is demonstrated with substrate throughput currently as high as 180 disks/h (dual sided). These processes are applied to patterning hard disk substrates with both discrete tracks and bit-patterned designs.

Silicon template fabrication for imprint lithography with a very smooth side wall profile

A new fabrication process of silicon template for nanoimprint lithography is developed. A very fine and high aspect Si lines are fabricated by the combination of plasma process for Si deep etching and anisotropic wet etching by potassium hydroxide solution (KOH treatment). Improved switching process, which consists of sequentially alternating etching and deposition steps, is used as the Si deep etching. The side wall profile of the Si lines can be controlled by the deposition step time. Line pattern with vertical side wall is fabricated. The line width and height are 0.2 µm and 2.9 µm, respectively. By the KOH treatment the side wall corrugation can be reduced and the line width also decreases. Very fine line of 45 nm width at the line top with the pattern height of 3.0 µm can be fabricated by use of the line width shrink by the KOH treatment.

Structural features of self-organized nanopore arrays formed by anodization of aluminum in oxalic acid at relatively high temperatures

Anodic aluminum oxide (AAO) membranes with a highly ordered nanopore arrangement typically serve as ideal templates for the formation of various nanostructured materials. A typical procedure of the template preparation is based on a two-step self-organized anodization of aluminum carried out at the temperature of about 1–3 °C. In the current study, AAO templates were fabricated in 0.3 M oxalic acid under the anodizing potential range of 30–65 V at a relatively high electrolyte temperature ranging from 20 to 30 °C. Due to a high rate of porous oxide growth, about 5–10-fold higher than in low-temperature anodizing, the process of the template fabrication can be shorten significantly. Similarly to the low-temperature anodization, the best hexagonal pore arrangement is observed for samples anodized at 40 V. With a prolonged duration of the first anodizing step the order degree of triangular nanoporous lattice, observed after the second anodization, improves considerably. The effects of the anodizing potential and the process duration on the structural features of porous anodic alumina such as: pore diameter ( D p), interpore distance ( D c), porosity ( P), pore density ( n) and anodizing ratio ( B U) were investigated in details at various temperatures. The obtained results were compared with theoretical predictions and data reported in the literature.

Review of Template Fabrication for Nanoimprint Lithography

Nanoimprint lithography (NIL) is attracting attention as a low-cost and high-throughput method for printing nanometer-scale geometries, and has been included on the ITRS lithography roadmap at the 32 and 22 nm nodes. The template making is one of the most critical issues for the realization of NIL. The ultimate resolution of the patterns fabricated by NIL is primarily determined by the resolution of the features on the surface of the mold. Because of the 1X nature of NIL compared with 4X for photolithography, the 1X template fabrication is considered as the greatest challenge for NIL. Advances in NIL template fabrication processes are reviewed. The fabrication methods of 3D, large area and high resolution templates are currently critical requirements and challenges. As a result, new mold making methods should be further developed to meet the requirements from emerging market applications such as patterned media, photonic crystals and wire grid polarizers.

Highly Ordered Pd Nanowire Array by Template Fabrication for Propanol Electrooxidation

Highly ordered Pd nanowire arrays (NWAs) prepared by electrodeposition method using the fresh prepared anodic aluminum oxide (AAO) as the template have been characterized by X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscopy (SEM), and electrochemical measurements. SEM results revealed that the brush-shaped Pd NWAs are dispersed uniformly. The diameter and length of the obtained Pd NWAs are about 50 nm and 850 nm, respectively. Furthermore, the electrocatalytic activity of Pd NWAs electrode for propanol oxidation in alkaline media has also been studied. It is found that the obtained nanostructurs exhibit excellent electrocatalytic activity toward the oxidation of propanol, demonstrating the potential application in portable direct alcohol fuel cells (DAFCs).

CAD/CAM fabrication and clinical application of surgical template and bone model in oral implant surgery

A novel implant surgery support system with computer simulation for implant insertion and fabrication of a surgical template that helps in drilling bone was developed. A virtual reality haptic device that gives the sense of touch was used for simulation and a surgical template was fabricated by CAD/CAM method. Surgical guides were applied for two clinical cases. Three-dimensional (3D) jaw bone images transferred from DICOM data filmed by CT scanner were fed to the software and manipulated using the haptic device. The site for implant insertion was determined after evaluating the quality of bone and position of the mandibular canal. The surgical template was designed with ease using the free design CAD function of haptic device. The surgical template and bone model were fabricated by a fused deposit modeling machine. Two clinical cases were applied using the present system. Simulation to determine the site of implant insertion and fabrication of the surgical bone templates were successfully done in two clinical cases, one for three implant insertion in lower right jaw and the other is for seven implant insertion in lower edentulous jaw, respectively. During surgery, the templates could be firmly adapted on the bone and drilling was successfully performed in both cases. The present simulation and drilling support using the surgical template may help to perform safe and accurate implant surgery.

Process control for 32 nm imprint masks using variable shape beam pattern generators

Step and Flash Imprint Lithography (S-FIL ®) is a unique method that has been designed from the beginning to enable precise overlay for creating multi-level devices. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates (imprint masks). For device manufacturing, one of the major technical challenges remains the fabrication of full-field 1X templates with commercially viable write times. Recent progress in the writing of sub-40 nm patterns using commercial variable shape e-beam tools and non-chemically amplified resists has demonstrated a very promising route to realizing these objectives, and in doing so, has considerably strengthened imprint lithography as a competitive manufacturing technology for the sub-32 nm node. Here we report the critical dimension (CD) uniformity and process latitude of dense 32 nm patterns from templates written with variable shape beam pattern generators. Uniformity on the template and in the imprinted field was 3.22 and 3.45 nm, 3 σ. Process latitude during the writing of the template was improved by increasing both feature bias and exposure dose. As an example, the slopes for the 36 and 32 nm features are approximately 0.30 and 0.25 nm/μC/cm 2, respectively, indicating a substantial process window for exposure dose.

Silicon template fabrication for imprint process with good demolding characteristics

Demolding force for thermal imprint process to polymethylmethacrylate (PMMA) film is examined by use of Si templates with various side wall profiles. Patterns with tapered side wall profile can be fabricated by control of etching conditions. Side wall profile can be smoothened by anisotropic etching by use of mixed solution of potassium hydroxide (KOH) solution and isopropyl-alcohol. It is confirmed that demolding force can be reduced when mold with tapered side wall pattern is used. Demolding force can be greatly reduced by KOH treatment. Especially, when the template with taper and smooth side wall patterns is used, demolding force is below our measurement system limit of 0.1 kgf. It is confirmed that the KOH treatment is very effective in order to reduce demolding force.

Holographic fabrication of photonic crystals using multidimensional phase masks

This paper reports the experimental approaches to the fabrication of two-layer integrated phase masks and the fabrication of photonic crystal templates using the phase mask based on holographic lithography technique. The photonic crystal template is formed by exposing photoresist mixtures to five-beam interference patterns generated through the phase mask. The fabricated phase mask consists of two layers of orthogonally oriented gratings produced in a liquid crystal and photoresist mixture. A polymerization-induced phase separation preserves the grating structure during the exposure. The vertical spatial separation between two layers of gratings produces a phase difference among diffracted laser beams, which enables the holographic fabrication of diamondlike photonic crystal structures. The fabricated photonic crystal structure is consistent with simulations based on the five-beam interference. The two-layer phase mask opens up an opportunity of direct printing photonic structures.

Full field imprint masks using variable shape beam pattern generators

Imprint lithography has been included on the ITRS lithography roadmap at the 32, 22, and 16nm nodes. Step and flash imprint lithography (S-FIL®) is a unique method that has been designed from the beginning to enable precise overlay for creating multilevel devices. A photocurable low viscosity monomer is dispensed dropwise to meet the pattern density requirements of the device, thus enabling imprint patterning with a uniform residual layer across a field and across entire wafers. Further, S-FIL provides sub-100-nm feature resolution without the significant expense of multielement, high quality projection optics, or advanced illumination sources. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates. For device manufacturing, one of the major technical challenges remains the fabrication of full field 1X templates with commercially viable write times. Recent progress in the writing of sub-40-nm patterns using commercial variable shape e-beam tools and nonchemically amplified resists has demonstrated a very promising route to realizing these objectives, and in doing so, has considerably strengthened imprint lithography as a competitive manufacturing technology for the sub-32-nm node. Here the authors report the first imprinting results from sub-40-nm full field patterns, using Samsung’s current flash memory production device design. The fabrication of the template is discussed and the resulting critical dimension control and uniformity are reported. A second experiment has also demonstrated feasibility for resolving several types of features at half pitches of 32nm.

Toward 1Tdot∕in.2 nanoimprint lithography for magnetic bit-patterned media: Opportunities and challenges

Nanoimprint lithography presents unique opportunities for patterned media applications due to its advantages of sub-10nm resolution capability, patterning of a whole disk in a single imprint step with reasonably high throughput, and the relatively low capital cost in comparison to other next generation lithography technologies. However, there are several critical issues that still remain very challenging. This article will briefly discuss these challenges in general and then focus on imprint lithography work including the fabrication of templates and demonstrate the imprinted results. In this work two types of polarities of high-density templates (pillar tone and hole tone) have been fabricated on fused silica substrates for the UV imprint process. The difficulties and limitations in each of the template fabrication processes will be discussed. The authors have successfully demonstrated template fabrication followed by imprinted results with a pitch of 24nm (1.1Tdots∕in.2) for both tones of templates. Initial imprinted results of dense dot patterns with a pitch as small as 18nm (2.0Tdots∕in.2) have been achieved. High-resolution scanning electron microscopy images are used as the primary metrology for both the dot size uniformity and the placement accuracy analysis. The difficulties and the limitations in template fabrication, the imprint process, and associated metrology will be discussed.

Laser-induced local dehydroxylation on surface-oxidized silicon substrates: mechanistic aspects and prospects in nanofabrication

Processing of silicon oxide surfaces with a focused laser beam at a wavelength of 514 nm has been investigated. Laser processing of native silicon samples (dox=1–2 nm) allows the fabrication of reactive templates with laterally varying hydroxyl group density. Very similar results were also obtained on thermally oxidized silicon samples (dox≈100 nm), whereas respective experiments on quartz plates have failed. These results support a photothermal mechanism where laser irradiation causes a local temperature rise and initiates dehydroxylation. In agreement with a photothermally induced dehydroxylation reaction, a thermokinetic analysis of the experimental data points to a highly activated process. In conjunction with site-selective functionalization routines this opens up an avenue towards functional surface structures with lateral dimensions significantly below the optical diffraction limit.

Sub-30-nm patterning on quartz for imprint lithography templates

A parallel and economical method for obtaining nanoscale features on large-area quartz substrates has been developed for use in nanoimprint lithography template fabrication. Self-assembled multilayer films (molecular rulers) are used in conjunction with photolithographically defined metallic features to generate precise nanogaps with sub-30-nm resolution on quartz substrates. These nanopatterns are then transferred to the quartz substrates using the metallic thin films as etch masks.

Template synthesis of NiFe nanowires using diblock copolymers

Abstract Fabrication of self-assembled diblock copolymer nanoporous templates, electrodeposition of NiFe nanowires into the templates, and their magnetic behaviour were studied. Standard spin coated polymer films on gold coated substrates were subjected to usual field annealing and etching procedures for successful removal of one of the polymer blocks and to obtain hexagonally ordered nanoporous templates. Electrodeposition of NiFe nanowires into these template pores was carried out in potentiostatic three-electrode configuration for different deposition times while keeping the deposition parameters such as electrolyte pH value and the reduction potential constant at 3.82 and −1.0 V, respectively. Current–time profiles obtained during the deposition process were analyzed to understand the mechanism of growth. Using the SEM image of the nanoporous template, the pore-diameter, inter-pore distance and pore-length were estimated as 35, 100 and 700 nm, respectively. Hysteresis loops of the nanowires exhibit easy axis of magnetization along the wire axis. The magnetic behaviour was analyzed taking into account the wire dimensions and the respective contributions from dipolar interactions and demagnetizing energy.