Quartz Stamp Research Articles

Removal of UV-cured resin using a hybrid cleaning process for nanoimprint lithography

Removal of resin residues from quartz surfaces is one of the most critical issues in ultraviolet (UV) nanoimprint lithography (NIL) processes. Traces of resin residues on a quartz stamp cause pattern defects in the subsequent UV NIL process. This study investigates the effect of UV/O3 pretreatment and ozone dissolved water (DIO3) cleaning with megasonic (MS) on UV-cured resin removal. The bulk resin was oxidized and removed partly by UV/O3 pretreatment. The resin residues which remained on the surface in the form of a thin layer were removed by cleaning with 40ppm DIO3 along with megasonic. Subsequently, cleaning was performed using a 10% KOH solution to remove the adhesion promoter. Contact angle measurements showed that the surface was hydrophilic in nature, which confirms the complete removal of the UV-cured resin and adhesion promoter from the SiO2 substrate.

Rapid fabrication of nano-structured quartz stamps

Replication of surface nano-structures from a master stamp allows large-area volume production that is otherwise cost prohibitive through conventional direct-write methods, such as electron beam lithography and focused ion beam milling. However, the creation of a master stamp containing sophisticated patterns still requires significant time on such direct-write tools. We demonstrate a method for reducing this tool time by patterning smaller nano-structures, and then enlarging them to the desired size through isotropic etching. We can create circular structures of any arrangement and size, down to the patterning limits of the direct-write tools. Subsequent metal mask deposition, lift-off, and anisotropic etching transforms the circular patterns to out-of-plane pillar structures for the final stamp. A 1 cm2 area filled with a pattern of 200 nm diameter nano-holes spaced 520 nm apart, requires only 21 h to complete using our process, compared to 75 h using conventional fabrication. We demonstrate the utility and practicality of the quartz stamps through polymer embossing and replication. Embossed polymer nano-hole arrays are coated with a Cr/Au (5/100 nm) film to create surface plasmon resonance structures. Extraordinary optical transmission spectra from the metallized arrays show the expected spectral features when compared to focused ion beam milled structures.

Nanopatterned UV curable hydrogels for biomedical applications

With an increasing use of emerging patterning technologies such as UV-NIL in biotechnological applications there is at the same time a raising demand for new material for such applications. Here we present a PEG based precursor mixed with a photoinitiator to make it UV sensitive as a new material aimed at biotechnological applications. Using HSQ patterned quartz stamps we observed excellent pattern replication indicating good flow properties of the resist. We were able to obtain imprints with <20 nm residual layer. The PEG based resist has hydrogel properties and it swelling in water was observed by AFM.

Novel transparent hybrid polymer working stamp for UV-imprinting

Transparent stamps are an integral and crucial part of the UV-imprinting. Time consuming fabrication of quartz stamps increases the price of the technology. In the presented work a thermally stable transparent imprint stamp made of a novel hybrid polymer system is demonstrated. As a low-cost and highly efficient alternative the hybrid polymer stamp contributes to the acceptance and application of the nanoimprint technology. By using the UV-patternable inorganic–organic hybrid polymer quartz stamps might become superfluous in the UV-imprint process entirely, because transparent working stamps can be manufactured also with use of opaque silicon master stamps.

Development of a very large-area ultraviolet imprint lithography process

We propose a very large-area ultraviolet imprint lithography process as a promising alternative to expensive conventional optical lithography for the production of display panels. This process uses a large-area hard stamp in a low vacuum environment. The hard quartz stamp is used to achieve high overlay accuracy, and the vacuum environment is required to ensure that air bubble defects do not occur during imprinting. We demonstrate that the quartz stamp with microscale patterns can be used for imprinting 18-in. diagonal substrates via single-step UV imprint in a low vacuum environment to obtain a practical residual layer thickness (RLT) for micro pattern transfer to the substrate. Numerical analysis is performed to clarify the physical phenomena underlying imprint process.

Stamping-Based Planarization of Flexible Substrate for Low-Pressure UV Nanoimprint Lithography

Patterning flexible substrates in nano scale is an important and challenging issue in the fabrication of next-generation devices based on a non-silicon substrate. Step and Flash imprint lithography (S-FIL) which is a room temperature and low pressure process offers several important advantages, such as the use of a smaller and therefore cheaper stamp or the possibility of the overlay imprinting, as a transparent stamp is utilized. However, it is very difficult to perform S-FIL on a flexible substrate successfully due to the high waviness. The waviness of a flexible substrate is not a constant value in contrast to a rigid substrate. It depends on the imprint pressure applied onto the substrate. In this paper, in section two, the effect of the imprint pressure on the waviness of the surface of the flexible substrate is examined. It is proved that the waviness of the surface of the flexible substrate could not be reduced sufficiently to assure a successful imprint at low imprint pressures. In the third section, a method of patterning polymer substrates using ultra-violet nanoimprint lithography (UV-NIL) is presented. The method consists of two stages, stamping-based planarization and S-FIL. In stamping-based planarization, a planarization layer of transparent polymer is formed onto the flexible substrate. Waviness of the blank stamp (in this study, glass wafer) is transferred to the planarization layer. S-FIL is performed with the nanoimprint tool IMPRIO100 directly onto the planarization layer employing a 1 x 1 in. quartz stamp. Optical microscope and SEM images of the successfully imprinted patterns were also presented.

Fabrication of carbon nanotube arrays for field emission and sensor devices by nanoimprint lithography

This work brings forth the idea of incorporating insulation in the resist used for ultraviolet (UV) curing nanoimprint lithography (NIL). Carbon nanotubes (CNTs) are grown in the space between two insulated resist patterns on the conductive substrate to make CNTs arrays. Two imprinting processes, soft UV curing NIL with DRPPR process and novel NIL without cured residual resist, are presented to achieve the insulation patterns. First the fabricating process is performed using a polydimethylsiloxane (PDMS) stamp. Subsequently, inductively coupled plasma (ICP) is essential to wipe off the residual resist film. To avoid the ICP process, a novel UV curing NIL is presented. Its special hard quartz stamp with chrome shelter can protect the residual resist film out of curing during the UV exposure process, and the uncured resist can be easily removed by ultrasonic vibration in organic solutions. The CNT arrays are prepared on the patterned substrates by the pyrolysis of iron phthalocyanine (FePc). Field emission experiments reveal that the turn-on field of those CNTs arrays is low to 1.3V/um.

Imprinted 50 nm Features Fabricated by Step and Stamp UV Imprinting

We fabricated features down to 50 nm by UV step and stamp imprint lithography (UV-SSIL). This method enables fast sequential imprinting for large areas operating at room temperature with a low-viscosity material. This allows the patterning of both large micron-scale and submicron-scale structures simultaneously. A low-viscosity polymer allows pattern transfer at moderate pressures, thereby reducing mechanical stress on the stamp and substrate. Processing at room temperature helps to maintain the alignment and to prevent the distortion of the features caused by the thermal expansion of the mold and substrate. A UV-SSIL experiment with a novel photosensitive polymer was performed using a prototype of currently commercially available machines used for both thermal and UV step and stamp imprintings. As a master, we used a transparent quartz stamp (with features down to 50 nm) patterned by electron-beam lithography. The polymer was dispensed on a 100 mm silicon substrate using a syringe-type dispensing system. The results were analyzed by atomic force microscopy and a scanning electron microscopy. The fabricated structures exhibited good lateral and vertical feature replication fidelities.

Effects of a compliant layer in solid parallel-plate UV-based nanoimprint lithography

We deal with solid parallel-plate UV-based nanoimprint lithography (UV-NIL) using rigid quartz stamps and spin coated substrates. Achieving homogeneous imprints with a thin residual layer are important for a succeeding reactive ion etching (RIE) step. Since the solid stamp and the substrate are not perfectly flat and mounted on solid parallel plates giving them little chance to adapt and compensate for the unevenness and causing additional distortions, this is difficult to achieve. We investigated the bending of a rigid quartz stamp during imprinting and the effect of a thin compliant layer located below the substrate with finite element simulations and compared them with experimental results. We show that a close contact of stamp and substrate can be achieved with a correctly designed compliant layer and using a commercially available EVG®620 mask aligner.

UV-curable nanoimprint resin with enhanced anti-sticking property

This paper reports on a newly developed anti-sticking resin obtained by mixing a fluorine-containing monomer (F-monomer) for UV nanoimprinting lithography (UV-NIL) to reduce the contact adhesion force during the demolding process. The new resin system shows an enhanced reliability and resolution of pattern transfer with no treatment on the surface of the quartz stamp. We fabricated various nanopatterns with F-monomer resins of various concentrations in the low pressure UV-NIL. The number of process steps of a release layer treatment for UV-NIL was reduced by using F-monomer with anti-sticking property.

Equalising stamp and substrate deformations in solid parallel-plate UV-based nanoimprint lithography

We deal with solid parallel-plate UV-based nanoimprint lithography (UV-NIL) using rigid quartz stamps and spin coated substrates. Achieving a conformal contact of stamp and substrate in a parallel-plate setup is challenging, since the solid stamp and the substrate usually are not perfectly flat. Finite element simulations and experimental results show that a correctly designed compliant layer underneath the substrate guarantees a conformal contact of stamp and substrate and therefore imprints of a high quality with a homogeneous and thin residual layer down to 10nm can be achieved.

Nano Sized Patterning on the Thermoset Materials Using Thermal Curing Nano-Imprinting Technology

Nano-imprinting technology, currently developing as an alternative technology for photolithography, is mostly dealing with photo resist materials for etching barrier. In other words, the materials imprinted are used as the barriers for wet etching or RIE (reactive ion etching), and then are removed after all. Thus, most materials developed for nano-imprinting technology have relatively low Tg(&lt;100oC), in case of solids or have a low viscosity before curing in order to fill the gap of the stamp. Such materials could not be suitable for the structures that require relatively high temperature process ability, high modulus or high durability. Epoxy is one of candidates that meet such requirements for the structures. However, it has not been reported about imprinting on epoxy materials. In this paper, nano-imprinting technology was developed to fabricate the microstructures. Instead of thermoplastic imprint resin, solid phase epoxy films, which is thermoset polymer, were imprinted with SAM (self assembly monolayer) coated quartz and silicon stamps. Feature size of stamp varies from 150nm to 1 μm and height was 300nm for quartz stamp and 3μm for Si stamp.

Nanoimprinting of Thin Polymer Films Using Elementwise Patterned Stamp and Subsequent Application of Pressurized Air

To improve the throughput of ultraviolet nanoimprint lithography (UV-NIL), a cost-effective method of fabricating sub-100-nm-wide line patterns, research studies have been focused on employing a large-area nanostamp. In this paper, we present a new single-step UV-NIL process in which an elementwise patterned stamp (EPS), a 5''×5'' quartz stamp, is first used to imprint resin droplets against a 4'' Si wafer. The EPS consists of 16 elements, each of which is 10×10 mm2, i.e., the effective pattern area is 1,600 mm3. Pressurized air is subsequently applied to the bottom of wafer to improve directly the contact between the wafer and the elements, and resultantly, the uniformity of residual layer thickness. To examine the effects of the pressurized air on the uniformity, we have carried out experiments. Resin droplets with a viscosity of 7 mPa s were dispensed on each element. Results show that the air pressure range of 0.05–0.2 MPa does not significantly affect the average thickness distribution but the uniformity. Line patterns of 70 nm width were successfully imprinted at an air pressure of 0.1 MPa.

Fabrication of three-dimensional stamps for embossing techniques by lithographically controlled isotropic wet etching

The excellent characteristics that nanoimprint lithography (NIL) shows as a two-dimensional patterning technique, such as resolution and throughput, are shared with its three-dimensional (3D) structuring version. Nevertheless, the potentialities of NIL for 3D structuring remain largely unexplored and unexploited, hindered by the difficulties in the fabrication of high quality masters with throughput suitable for practical purposes. We present a technique that allows production of stamps with tightly controlled three-dimensional profiles in the 10nm–100μm scale range. This technique consists of a sequence of lithographic steps alternated with isotropic wet etching processes performed on a quartz substrate. Scanning electron microscopy and atomic force microscopy characterization shows that 3D structures with very accurate shape control and nanometer scale surface roughness can be formed with this method. Quartz stamps have been employed in nanoimprint, hot embossing, or casting processes to shape complex plastic elements. This technique is expected to have many applications in different nanotechnology-related fields such as optics, nanomechanics, microfluidics, and plasmon nano-optics.

Full wafer scale near zero residual nano-imprinting lithography using UV curable monomer solution

The nano-imprinting lithography is regarded as one of the most promising technologies for nano-sized pattern fabrication and is being focused as a key technology for the mass production. However, significant progress must be made to improve uniform imprinting over large area, low temperature and low pressure operation and imprinting with minimized residual layer. A unique pressure vessel type imprinting system was used to imprint the patterns as small as 150 nm over whole 4-in. diameter wafer with near zero residual layer. To cover the whole surface of 100 mm diameter Si wafer, an array of 18 mm by 18 mm quartz stamps was used as an imprint stamp. UV curable benzylmethacrylate (C 11H 12O 2) based monomer solution is used as an imprinting resin in this study. Near zero residual nano-imprinting over 100 mm diameter Si wafers was successfully demonstrated with 25 atm of imprinting pressure by using liquid state monomer based UV curable resin.