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We propose novel additive manufacturing processes to cost-effectively generate prototypes and small batches of hybrid micro-optical components. We combine UV-molding with inkjet printing techniques using the polymer inks InkOrmo and InkEpo designated for permanent optical applications. This enables the integration of diffractive and refractive optical elements into one monolithic micro-component and thus the implementation of tailor-made optical designs. Finally, the proposed processes allow a high versatile fabrication making individual micro-optics easily accessible.

The challenging fabrication of sub-100-nm structures with high aspect ratio by UV-nanoimprint lithography (NIL) is addressed in this work. Thermal shrinkage is induced by cooling the structures below room temperature to avoid the issues commonly arising during the release of the polymeric nanostructures from the master. The UV-NIL has been performed to obtain OrmoComp(A (R)) nanostructures using OrmoStamp(A (R)) working stamps copied from Si masters. Nanoridges and nanopillars with 45 nm width and 380 nm thickness have been fabricated with a corresponding aspect ratio of 8.5. This is, to the best of our knowledge, the highest aspect ratio achieved using organic-inorganic hybrid materials at the sub-100-nm scale.

A novel manufacturing chain to cost-effectively generate prototypes of hybrid micro-optical components is proposed. UV-molding and inkjet printing techniques are combined with the optical polymer inks InkOrmo and InkEpo for easily implementing tailor-made optical designs.

The fabrication of optical interconnects has been widely investigated for the generation of optical circuit boards. Twophoton absorption (TPA) lithography (or high-precision 3D printing) as an innovative production method for direct manufacture of individual 3D photonic structures gains more and more attention when optical polymers are employed. In this regard, we have evaluated novel ORMOCER-based hybrid polymers tailored for the manufacture of optical waveguides by means of high-precision 3D printing. In order to facilitate future industrial implementation, the processability was evaluated and the optical performance of embedded waveguides was assessed. The results illustrate that hybrid polymers are not only viable consumables for industrial manufacture of polymeric micro-optics using generic processes such as UV molding. They also are potential candidates to fabricate optical waveguide systems down to the chip level where TPA-based emerging manufacturing techniques are engaged. Hence, it is shown that hybrid polymers continue to meet the increasing expectations of dynamically growing markets of micro-optics and optical interconnects due to the flexibility of the employed polymer material concept.

The aim of the work presented here was to develop curing polymers for nanoimprint lithography (NIL) enabling short cycle time, low imprint temperature, and an isothermal imprint process. The result is mr-NIL 6000LT: A photochemically curing polymer system for isothermal imprinting by combined thermal and UV nanoimprint lithography. It allows a lower imprint temperature than materials presented previously [C. Schuster, M. Kubenz, F. Reuther, M. Fink, G. Grutzner, mr-NIL 6000 - New epoxy-based curing resist for efficient processing in combined thermal and UV nanoimprint lithography, in: Proceedings of SPIE 6517 2007, 65172B.; D.W. Johnson, H. Miller, M. Kubenz, F. Reuther, G. Grutzner, Nanoimprinting with SU-8 Epoxy Resists, in: Proceedings of SPIE 6517 2007, 65172A.]. The material system chosen is based on a blend of epoxy resins and a photo acid generator. Such epoxy resists cure during the imprint step in combined thermal and UV nanoimprint lithography. Initiated by UV exposure the cationic polymerisation occurs at elevated temperature forming a polymer pattern with significantly increased thermal stability compared to the uncured system. Apart from the material development leading to mr-NIL 6000LT the correlations between the parameters imprint temperature, exposure time and post exposure hold time are investigated in this work. With the applied resin combination a T"g of -15^oC is obtained. This enables the formation of solid films at room temperature after spin-coating and prebake and nevertheless imprint temperatures in the range of 45-50^oC, which is a distinct decrease compared to the 100-110^oC needed for the previously introduced mr-NIL 6000 [C. Schuster, M. Kubenz, F. Reuther, M. Fink, G. Grutzner, mr-NIL 6000 - New epoxy-based curing resist for efficient processing in combined thermal and UV nanoimprint lithography, in: Proceedings of SPIE 6517 2007, 65172B.] or the 65-70^oC necessary for defect-free imprinting of the epoxy-based polymer described in [D.W. Johnson, H. Miller, M. Kubenz, F. Reuther, G. Grutzner, Nanoimprinting with SU-8 Epoxy Resists, in: Proceedings of SPIE 6517 2007, 65172A.]. mr-NIL 6000LT exhibits good dimensional stability at 120^oC after curing during the imprint process. This is sufficient for an isothermal imprint process as well as subsequent processes, e.g. metallization or etching.

In a close collaboration the team of Micromotion, micro resist technology, BESSY, and LSU-CAMD have successfully mastered the challenges of LIGA production of ultra-precision microparts for Micro Harmonic Drive® gears. The complementary expertise ranging from design and application know-how to process research and technical support resulted in high quality LIGA microparts and superior Micro Harmonic Drive® gears taking advantages of the free 2D design capability and material choice. It is also an excellent example that through contributions from partners with different background and expertise LIGA precision parts can be produced with high quality and yield and for a market competitive price.

LIGA is a well-established process to fabricate metallic micro parts with high resolution, high precision and very low sidewall roughness by means of X-ray lithography and electroplating. The availability of a precise X-ray mask is a precondition for the final precision of the manufactured micro parts. Typical mask substrate materials, e.g. beryllium, carbon based foils, Si3N4 or SiC show different disadvantages such as low X-ray transparency or high toxicity or high prices or low conductivity or high thermal expansion or surface porosity causing X-ray scattering. For the fabrication of X-ray masks, PMMA with its unique features such as high aspect ratio patterns with high precision, exhibits low sensitivity and the layers preparation is not easy. SU-8, an epoxy-based UV and X-ray sensitive, chemically amplified, negative tone photoresist exhibits high aspect ratio patterns with vertical sidewalls. The difficult remove of the resist after the electroplating process significantly hinders the inspection of the fabricated X-ray mask. We present the use and suitability of an UV sensitive, chemically amplified, viscous, aqueous-alkaline developable, and easy removable positive tone photoresist, XP mr-P 15 AV, exhibiting high aspect ratio patterns with vertical sidewalls for the fabrication of X-ray masks by means of UV lithography on vitreous carbon substrates.

First promising investigations of SU-8 removal experiments with a novel plasma etching technique are presented. The basic idea of this technique is to separate the highly effective generation of chemical radicals (e.g. oxygen radicals) using a traveling wave reactor (TWR) microwave source with water cooled plasma zone from the chemical reaction with the resist polymer. The etching tool operates in a remote and downstream mode with very high radical density allowing precise thermal management of the substrates on the chuck giving controlled process conditions without deviation in temperature, and generally preventing ion bombardment, at least resulting in gentle processing without jeopardizing the integrity of the metal structures. Very good removal of SU-8 with very few residues and very high etching rates up to 10 μm per minute are observed in first experiments which are offering chances to get even more than 20 μm per minute. The etching process is isotropic, and the rate stays stable during the whole removing process even for very thick films of 1 mm and more. First application examples of SU-8 removal are demonstrating the great potential of the presented microwave plasma based technique not only for the cleaning of metallic microparts but also for other more sensitive materials which is demonstrated by SU-8 removal from graphite X-ray mask substrates.

The behaviour of a new epoxy based resist (mr-EBL 6000.1 XP) as a negative resist for e-beam lithography is presented. We demonstrate that it is possible to define sub-100nm patterns when irradiating thin (120nm) layers of resist with a 10keV electron beam. The dependence of resolution and remaining thickness on electron dose, electron energy and photo acid generator (PAG) content is determined. After the electron beam lithography process, the resist is used as a mask for reactive ion etching. It presents a good etch resistance, that allows transfer of patterns to the substrate with resolution below 100nm.

Hybrid polymers have been already widely applied in photonic applications to manufacture microlenses or 2D and 3D waveguides. Thus, they are promising candidates to manufacture optical systems down to the chip level. A brief review on hybrid polymers consisting of both inorganic and organic functional units and thus combine superior material properties in just one material class will be given in this report. The material properties, which can be adjusted to the application in wide ranges enable to fabricate micro-optical elements (e.g. microlenses) using replication techniques such as UV-assisted replication or nano-imprint lithography. Aside of their applicability in 2D, emphasis will be in particular on the evaluation of hybrid polymer materials for two-photon absorption lithography, which is employed to directly manufacture sophisticated 3D photonic structures impossible to be generated with conventional 2D techniques.

A case study of use of negative type SU-8 X-ray sensitive resist for fabrication of advanced, highly precise, ultra tall direct LIGA mechanical microparts is presented in this paper. Using direct LIGA technique, ∼1 mm tall highly precise metallic gear wheels are being fabricated, previously using PMMA based process. Starting from a non-optimized non-satisfying SU-8 process, significant process parameters for process optimization were identified using statistical design of experiment. By varying the significant process parameters, SU-8 process was further optimized with respect to critical aspect of sidewall bow and tilt of metallic structures. After the optimization, metallic parts fabricated using SU-8 process showed comparable quality as those fabricated using PMMA based process.

In this paper, we present the suitability of easy to handle negative tone photoresists providing examples of lift-off applications. The lithographic process of this single layer resist system requires standard broadband or i-line process conditions. At first, the capability to obtain an undercut pattern and the thermal stability of the resist ma-N 1400 is demonstrated in the lift-off patterning of magnetron sputtered thin three layer contact system Ti/Pt/Au. Temperature of the substrate during sputtering was measured time-resolved using a thermal couple. Secondly, an example to achieve AuSn solder bumps of [email protected] diameter by a combination of sputtering and metal evaporation using the lift-off resist ma-N 400 is given. Regarding the further miniaturization of electronic devices, this process is a cost-effective method to achieve solder depots for flip chip bonding of ultra thin chips.

UV curing of resists after imprint is of interest for mix and match applications or when the thermo-mechanical stability of the resist has to be increased. In those cases the imprint into a curable resist like the mr-L 6000XP is followed by a UV exposure. This exposure is different from an exposure during UV lithography, as the pre-patterned resist results in a lateral intensity modulation, depending on the pattern geometries (width, distance, height, residual thickness) and depending on potential polarisation directions as well, which may be induced by reflecting elements within the optical path. We have simulated the exposure of line patterns of different geometries under polarisation of the incident light under directions parallel and perpendicular to the imprinted lines. Corresponding UV curing experiments after imprint suggest that the stabilisation should be feasible at adequate increase of the exposure dose independent from the polarisation direction.

The benefits of allyl prepolymers for nanoimprint lithography (NIL) are investigated. Allyl prepolymers cure during the imprint process as a result of heating. They have the potential to enable NIL at lower temperatures, while the imprinted patterns show high thermal stability in contrast to thermoplastic polymers, where the thermal behaviour of the imprinted patterns is strictly determined by the glass transition temperature (T"g) of the polymer. Allyl prepolymers reported here are modified with the aim of obtaining high quality imprints at decreased imprint temperature and reduced cycle time of the imprint process. Free-radical initiators are applied to increase the polymerization rate and to let the polymerization start at lower temperatures. Adding plasticizers results in a decrease in T"g. Most favourable systems are selected out of a variety of various mixtures for imprint tests.

IR baking as an approach to effective baking of thick and ultra-thick photoresist layers is reported. An experimental set-up is presented. The resist temperature is pyrometrically determined and is used to control the system. The performance and benefits of IR baking are proved by patterning results. Examples of two positive tone resists, ma-P 100 and ma-P 1275 (Micro Resist Technology GmbH), with layer thicknesses up to 60 µm and the chemically amplified negative tone photoresist SU-8 (MCC) (500 µm) are presented. IR baking enables reduction of process time and temperature. Because of the gentle baking, high aspect ratios can be attained and stress reduction is achieved in SU-8.

The characteristics and benefits of two types of cross-linking prepolymers with low glass transition temperature (Tg) for nanoimprinting are reported. They are soluble in organic solvents and their solutions can be processed like those of common thermoplastics. The imprinted patterns receive high thermal and mechanical stability through cross-linking polymerization. The course of the polymerization was investigated to determine the appropriate conditions for the imprint process. In thermally cross-linked polymers mr-I 9000, the cross-linking occurs during imprinting. Process time and temperature depend on the polymerization rate. Volume shrinkage during the polymerization does not adversely affect imprinting. Photochemically crosslinked polymers mr-L 6000 make possible imprint temperatures below 100 °C and short imprint times. The Tg of the prepolymer determines the imprint temperature. The cross-linking reaction and structural stabilization is performed after imprinting. 50-nm trenches and sub-50-nm dots confirm the successful application of the polymers.

A status report of nanoimprint lithography is given in the context of alternative nanofabrication methods. Since the ultimate resolution of nanoimprint appears to be determined by the stamp, this is discussed in detail, particularly the recent developments on polymer stamps. The scope of the technique is illustrated with applications in passive optical structures and organic devices. Throughout the report, critical dimensions are discussed, as well as other challenges facing nanoimprint lithography.

A novel crosslinkable, conductive, highly transparent composite material based on a photoresist and an ionic liquid (the names of the composites are not announced here due to the current procedure of patenting) is presented. The composite possesses a good and stable ionic conductivity (up to 10 mS cm−1 at room temperature) over a wide frequency bandwidth (1 kHz – 1 MHz) and is optically transparent (transmission value of 90 % for a 170 µm thick film). In addition, an approach for the patterning of the composite material by conventional photolithography with a good spatial resolution (line width of 20 – 30 µm) is introduced. The unique properties of the material are utilized for time- and cost-saving direct manufacturing of electrically conductive, highly transparent microcomponents.

In microsystem technology, the lithographical processing of substrates with a topography is very important. Interconnecting lines, which are routed over sloped topography sidewalls from the top of the protecting wafer to the contact pads of the device wafer, are one example of patterning over a topography. For structuring such circuit paths, a photolithography process, and therefore a process for homogeneous photoresist coating, is required. The most flexible and advantageous way of depositing a homogeneous photoresist film over structures with high topography steps is spray-coating. As a pattern transfer process for circuit paths in cavities, the lift-off process is widely used. A negative resist, like ma-N (MRT) or AZnLOF (AZ) is favoured for lift-off processes due to the existing negative angle of the sidewalls. Only a few sprayable negative photoresists are commercially available. In this paper, the development of a novel negative resist spray-coating based on a commercially available single-layer lift-off resist for spin-coating, especially for the patterning of structures inside the cavity and on the cavity wall, is presented. A variety of parameters influences the spray-coating process, and therefore the patterning results. Besides the spray-coating tool and the parameters, the composition of the resist solution itself also influences the coating results. For homogeneous resist coverage over the topography of the substrate, different solvent combinations for diluting the resist solution, different chuck temperatures during the coating process, and also the softbake conditions, are all investigated. The solvent formulations and the process conditions are optimized with respect to the homogeneity of the resist coverage on the top edge of the cavities. Finally, the developed spray-coating process, the resist material and the process stability are demonstrated by the following applications: (i) lift-off, (ii) electroplating, (iii) the wet and (iv) the dry chemical etching of metals on substrates with topographies.

Driven by the steadily increasing scale of integration in microelectronics much effort has been made in recent years to establish the technique of nanoimprint lithography (NIL) as a promising approach to time and cost-effective fabrication of nanometer scale patterns. NIL enables high throughput for mass fabrication in a simple way. Experiments have revealed that nanoimprint of small and periodic patterns in the nm range is much easier obtained than for μm scale patterns due to polymer transport phenomena. Thus a combination of NIL with optical lithography is considered to be advantageous for the definition of small patterns adjacent to large patterns. The multifunctionality of the material within one layer offers new routes in device design, in particular as multistep profiles are obtainable. In this contribution a combination of NIL and UV lithography is reported using polymers which are both imprintable and photosensitive. Based on an epoxy type negative tone chemically amplified resist system patterns were easily obtained using both techniques. In the first step a pattern relief was produced through imprinting. In the second step this relief was UV exposed in a contact printer and then developed. In this way three-step profiles could be generated within one single polymer layer.

Aromatic polymers based on methacrylates (linear polymers) and multifunctional allylesters (crosslinked polymers) have been prepared. They feature high dry etch resistance and good imprintability in a hot embossing process. The crosslinked polymers and their prepolymers were investigated in detail. Their characteristic molecular weight distribution and thermo-mechanical behaviour were studied with respect to the crosslinking process and compared with those of linear polymers. The thermal stability of imprinted patterns has been investigated for both, linear and crosslinked aromatic polymers. The latter ones show excellent stability up to test temperatures of 200 ^oC directly after the imprint process.

Interest in thick photoresist applications is steadily growing. Specialised equipment has been developed to cope with the new challenges to process and pattern extremely thick photoresist layers. A decisive step in the preparation of resist layers is the prebaking. The impact of three different prebaking technologies on the resist performance has been investigated. Resist patterns obtained after oven, hotplate or IR prebaking exhibit equal high quality. Compared to oven and hotplate baking the process length and energy consumption is markedly reduced using IR radiation favouring this variant to be the optimum prebaking process for very thick photoresist layers.

This paper presents the design, fabrication and characterization of all-optical polymer-based Micro-optoelectromechanical system (MOEMS) Variable Optical Attenuator (VOA). It consists of an SU-8 quad-beam structure and a suspended waveguide aligned to input/output fiber optics. Actuation is achieved by defining dye-doped SU-8 structures on the mechanical beams. Specific wavelengths focused on such structures have a strong absorption resulting in a heating and, straightforwardly, an expansion of the dye-doped SU-8. This entails a displacement of the seismic mass causing a misalignment (i.e. an increase of the coupling losses) between the waveguides and the input/output fiber optics. Experimental results have validated this approach, by showing the effect of the pumping power on the optical losses, with a slope of 0.17 dB/mW.

In the nanoimprint lithography (NIL) process the mould release is a limiting step. Regardless of the carefully designed special properties a resist may have, it has to come over this challenging process step to be employed in a NIL process. Generally, the moulds are coated with anti-sticking layers. Here, an alternative solution is developed by modification of two well-established NIL polymers through integration of fluorinated additives in their formulation. An effective additive concentration window was successfully defined, in which the substrate adhesion and imprint behaviour is not influenced. Defect-free patterning down to 30 nm is possible. A release force reduction of about 40% was observed with the modified polymer mr-I 7000R compared to the unmodified original.

A method to enhance the photoluminescence of dye chromophores-loaded by coupling the emission to surface plasmons in nanoimprinted photonic crystals is reported. A 9-fold enhancement in the spontaneous emission intensity of a rhodamine-doped polymer film is achieved on a silver layer due to surface plasmon excitation. By changing the surface plasmon frequency, this enhancement can be suppressed. When the polymer film is patterned by nanoimprint lithography with a two-dimensional photonic crystal the photoluminescence intensity increases up to 27 times compared to unpatterned samples on a quartz substrate.

Nanocomposites based on an organic polymer and inorganic nanocrystals (NCs) represent a class of high impact functional materials able to convey the unique size and shape dependent properties of nano-objects to highly processable resists.[1] In this work, a novel magnetic nanocomposite based on a negative tone epoxy photoresist and magnetic colloidal Fe2O3 NCs has been manufactured for fabricating AFM probes. Epoxy-type photoresist grant superior lithographic performances when patterned by standard near- ultraviolet (UV) optical lithography, providing structures with high aspect-ratio and nearly vertical sidewalls. Such resists are at present employed in optical and micromechanical applications for the fabrication of optical waveguides, microfluidic systems and scanning probes.[2] However, these materials lack of any inherent functionality, e.g. electrical conductivity, luminescence, magnetism, piezoresistivity and dielectricity. Hence, the incorporation of NCs can confer them new properties maintaining the patterning resolutions required for the manufacturing of highly miniaturized devices. These added properties can be interesting for the fabrication of novel micro/nanoelectromechanical systems (MEMS/NEMS).

Highly luminescent (CdSe)ZnS nanocrystals, with band edge emission in the red region of the visible spectrum, were successfully synthesized and incorporated in a resist, namely mr-NIL 6000. The nanocomposite material was imprinted by using conventional nanoimprint lithography (NIL) process. We report on the fabrication and characterization of nanoimprinted photonic crystals in this new functional material. Experiments showed good imprint properties of the NC/polymer based material and that the surface nanostructuration improves the light extraction efficiency by over 2 compared to a nanoimprinted unpatterned surface.

The motivation for the presented research was the known issue of very expansive UV transparent stamps and moulds, which are necessary tools for UV-based patterning methods such as UV-based nanoimprint lithography, which has been developing as an attractive alternative lithography approach in recent 10 years. Low priced polymer working stamps could be an alternative to quartz as stamp material. UV transparent nanoimprint stamps were fabricated from sol-gel process-derived hybrid polymer, which has the benefit of high thermal, chemical and UV radiation stability. Tailored surface treatment and release agents were applied to ease the de-moulding process and secure the accuracy and fidelity of the transferred patterns. To increase the life time of the hybrid polymer nanoimprint stamps some adhesives between stamp substrate and the stamp material were used. The hybrid polymer stamps are compatible with NIL polymers and long-term stable even at elevated temperatures of thermal imprint processes.

International audience; The fabrication of two-dimensional photonic crystals by nanoimprint lithography is established to realize lasing oscillations at three band edge frequencies. The optically pumped lasers are based on a dye-chromophore-loaded polymer matrix on a transparent substrate. A two-dimensional plane-wave algorithm was used to design the band-edge lasers showing a good agreement with the experimental lasing frequencies. These results show that nanoimprint lithography is well-suited to the one-step fabrication of two-dimensional active-polymer photonic crystals.

We present two novel methods for the preparation of arbitrary micro-scale patterns of polymers on surfaces with pre-defined topography. While photosensitive polymers are used commonly together with optical lithography, the methods presented can be used for nonphotostructurable polymers and where spin-coating cannot be performed. As demonstrator of the viability of the proposed fabrication process, they have been applied for the definition of hydrophobic barriers on a microfluidics network, which is dedicated to selectively dispense liquid to a spotting device consisting of 12 silicon microcantilevers.

M. Lucia Curri and co-workers report on p. 2009 an epoxy-based negative tone photoresist that can be functionalized with red emitting CdSe@ZnS core/shell type nanocrystals and patterned by UV lithography. The 3D high aspect ratio of the microfabricated structures proves that lithographic properties of the functional nanocomposite are retained and the nanocrystals properties conveyed into the resist. The emitting nanocomposite represents a convenient model for material functionalization expandable to nanocrystals with different properties. An epoxy-based negative-tone photoresist, which is known as a suitable material for high-aspect-ratio surface micromachining, is functionalized with red-light-emitting CdSe@ZnS nanocrystals (NCs). The proper selection of a common solvent for the NCs and the resist is found to be critical for the efficient incorporation of the NCs in the epoxy matrix. The NC-modified resist can be patterned by standard UV lithography down to micrometer-scale resolution, and high-aspect-ratio structures have been successfully fabricated on a 100 mm scaled wafer. The “as-fabricated”, 3D, epoxy-based surface microstructures show the characteristic luminescent properties of the embedded NCs, as verified by fluorescence microscopy. This issue demonstrates that the NC emission properties can be conveniently conveyed into the polymer matrix without deteriorating the lithographic performance of the latter. The dimensions, the resolution, and the surface morphology of the NC-modified-epoxy microstructures exhibit only minor deviations with respect to that of the unmodified reference material, as examined by means of microscopic and metrologic investigations. The proposed approach of the incorporation of emitting and non-bleachable NCs into a photoresist opens novel routes for surface patterning of integrated microsystems with inherent photonic functionality at the micro- and nanometer-scale for light sensing and emitting applications.

We report the new epoxy-based curing resist mr-NIL 6000 designed for thermal NIL, where the curing reaction is initiated by UV exposure and concurrently occurs at elevated temperature, both preferably in the imprint machine. Especially for the application in NIL the requirements to a resist differ much from those in radiation-based lithography where epoxy-based resists have been used for many years. High sensitivity is vital for a short cycle time. The imprint temperature is determined by the glass transition temperature (T g ) of the resist system before curing and roughly controls T g of the cured polymer, which on its part, affects the mold release temperature and the thermal stability of the imprints. An epoxy resin with low T g was chosen allowing imprinting at 100 °C or lower temperature. UV-coupled differential scanning calorimetry (Photo DSC) was applied to assist establishing the conditions of the resist processing. Optimum processing conditions were finally elaborated in imprinting tests. Flow tests were performed with the imprinted and cured resist patterns. The optimum imprint temperature was determined to be 100 °C. The imprinted patterns exhibited good dimensional stability up to at least 120 °C. This allows releasing the mold at the imprint temperature and running an isothermal process. The thermal stability is sufficient for subsequent processes, such as etching or metallization. The curing reaction during imprinting enables excellent pattern transfer fidelity and a high aspect ratio of the imprinted features. A short cycle time of ~ 1 min could be achieved so that the resist is promising for industrial applications.

This paper reports on the evaluation of XP SU-8 4000NPG for potential use in nanoimprint applications using hot UV imprint lithography. The use of this material is advantageous in that it can be imprinted, exposed and sufficiently cured all at the same temperature without any temperature cycling providing an isothermal process leading to short cycle times. Uncured XP SU-8 4000NPG has a Tg below 10oC, yet its films are sufficiently robust to be handled at temperatures from 40 to 70oC. This resist exhibits excellent flow properties in this temperature range, which is also a range where the post exposure bake of the exposed areas is sufficient to lock in the imprinted patterns and allow easy stamp removal. Wafers can be spin coated with the 4000NPG to provide films of less than 100nm thickness to more than 500 nm and subsequently baked to remove the residual coating solvent. Precoated wafers are introduced into the imprint tool and placed on a pre-heated chuck for a few seconds to reach the set temperature, and then the imprint stamp is applied under pressure for 30-60 sec to allow adequate time to properly fill the mold. While still in the mold, the resist is exposed through the transparent stamp and simultaneously cured for as little as 10 sec in order to remove the stamp without tearing or pattern deformation. The wafer can then be immediately removed from the imprint tool. The optimal temperature is a balance between resist flow, cure rate and the thermal stresses imparted into the cured film at the higher operating temperatures.

The handling of a continuously increasing amount of data leads to a strong need for high-speed short-range connections. Conventional Cu technology between chips on a board is limited. Optical interconnects will dominate the market, since they can overcome the limitations. One of the issues for materials used, e.g., for waveguides embedded in printed circuit boards (PCBs) is the compatibility with standard epoxies used for PCBs during the entire board fabrication process. Materials applied for optical interconnects should be mechanically and optically reliable, and also allow low-cost production. From the material production side, the process should be easy to up-scale. Therefore, anticipatory research strategy and suitable tailoring is asked for. The handling of light in the UV and visible range often requires the use of specially designed materials. Most polymer materials show an increased yellowing effect upon being exposed to shorter wavelength light. The major influence on the absorption in the UV and visible range of a UV curable material is related to the UV initiator, beside any other chromophores formed mainly during the exposure. Different material approaches will be presented which fulfil the requirements for highly sophisticated applications in optics / optical packaging technology. Firstly, an epoxy-based material system for optical chip-to-chip interconnection will be introduced. Secondly, the adaptation of a UV patternable inorganic-organic hybrid material (ORMOCER®) originally developed for waveguide applications in the data and telecom regime, will be discussed with respect to applications in the visible regime. Spectroscopy and UV-DSC measurements were carried out to investigate the influence of standard photoinitiators on the optical properties for an ORMOCER® system suitable for microoptic applications. The results show that the resulting material properties were significantly improved by exchange of the initiators compared to the originally incorporated one.

We report on the fabrication and characterization of two-dimensional polymer photonic crystal band-edge lasers operating in the visible range. The components have been fabricated in a dye chromophore-loaded polymer matrix by nanoimprint lithography. High-symmetry band-edge modes are used to generate laser emission. The experimental lasing frequencies are in good agreement with those calculated using a two-dimensional plane wave algorithm. These results demonstrate the potential of nanoimprint lithography for the fabrication of two-dimensional planar photonic crystal structures in an active medium in a one-step process.(C) 2007 American Institute of Physics. (DOI:10.1063/1.2798250)

In this work, a novel nanofabrication technique is presented, namely ''Reverse contact Ultraviolet Nanoimprint Lithography'' (RUVNIL). It is based on reverse nanoimprint lithography and ultraviolet contact lithography. It provides flexibility in building complex three-dimensional structures allowing selective imprint over pre-patterned surfaces with or without residual layer in opposition to what is often encountered in the normal NIL process. We have investigated and optimized the imprinting parameters that are required for three-dimensional nanofabrication and applied it to the fabrication of nano-fluidic channels. This lithography technique is a very promising process for three-dimensional nanofabrication.

We fabricated polymer photonic crystal band edge lasers using nanoimprint lithography. The laser emission wavelength can be tuned by controlling the lattice constant of the PhCs, covering a wavelength range of 30 nm around 550 nm. Unlike the electron-beam lithography commonly used for patterning nanophotonic structures, NIL offers a cost-efficient, rapid and large area processing capability. The direct transfer of the PhC pattern in an active layer reduces the number of process steps for the fabrication of this type of lasers.

In this paper, we report results on a newly developed nanofabrication technique, namely reverse-contact UV nanoimprint lithography. This technique is a combination of nanoimprint lithography and contact printing lithography. In this process, a lift-off resist and a UV cross-linkable polymer are spin-coated successively onto a patterned UV mask-mould. These thin polymer films are then transferred from the mould to the substrate by contact at a suitable temperature and pressure. The whole assembly is then exposed to UV light. After separation of the mould and the substrate, the unexposed polymer areas are dissolved in a developer solution leaving behind the negative features of the original stamp. This method delivers resist pattern transfer without a residual layer, thereby rending unnecessary the etching steps typically needed in the imprint lithography techniques for three-dimensional patterning. Three-dimensional woodpile-like structures were successfully fabricated with this new technique.

The authors report on the fabrication and optical characterizations of two-dimensional photonic crystals fabricated by nanoimprint lithography in a nanocomposite polymer incorporating highly luminescent and red emitting (CdSe)ZnS core-shell colloidal nanocrystals. Photonic crystal structures enhance the light emitted from the quantum sized nanoparticles in the composite layer by slowing the propagation speed of the photons, thus increasing the coupling to the out-of-plane radiative modes. A 200% enhancement of the light collection is achieved compared to an unpatterned sample. (c) 2007 American Institute of Physics. (DOI:10.1063/1.2430625)

A 1.7-fold enhancement in the spontaneous emission intensity of dye chromophore loaded in a printable polymer is achieved by coupling the dye emission to surface plasmons of metallic nanoparticles. The nanocomposite material, embossed into arrays of wires by nanoimprint lithography process, shows good imprint properties. The results prove the potential of the prepared luminescent functional materials for micro- and nanofabrication and suggest the use of nanocomposite materials in prospective nanoplasmonic applications.

Optical coherence tomography (OCT) is a contactless and non-invasive technique nearly exclusively applied for bio-medical imaging of tissues. Besides the internal structure, additionally strains within the sample can be mapped when OCT is performed in a polarization sensitive (PS) way. In this work, we demonstrate the benefits of PS-OCT imaging for non-biological applications. We have developed the OCT technique beyond the state-of-the-art: based on transversal ultra-high resolution (UHR-)OCT, where an axial resolution below 2 μm within materials is obtained using a femtosecond laser as light source, we have modified the setup for polarization sensitive measurements (transversal UHR-PS-OCT). We perform structural analysis and strain mapping for different types of samples: for a highly strained elastomer specimen we demonstrate the necessity of UHR-imaging. Furthermore, we investigate epoxy waveguide structures, photoresist moulds for the fabrication of micro-electromechanical parts (MEMS), and the glass-fibre composite outer shell of helicopter rotor blades where cracks are present. For these examples, transversal scanning UHR-PS-OCT is shown to provide important information about the structural properties and the strain distribution within the samples.

Prepolymers formed from multifunctional allyl monomers can beneficially used in nanoimprint lithography (NIL), since they cure as a consequence of heating during the imprint process. Thus they have the potential to enable NIL at comparatively low temperatures while the imprinted patterns concurrently show high thermal stability, in contrast to thermoplastic polymers, where the thermal behaviour of the imprinted patterns is closely related to the glass transition temperature (Tg) of the polymers. The use of allyl prepolymers for NIL was previously described, but only very few experimental data are known. In recent investigations on the application of allyl prepolymers for NIL a displacement of the patterns on the wafer has been observed after cooling down the imprinted polymer in the press. This could be avoided by detaching the stamp at the imprint temperature, i.e. without cooling down the press, which requires the polymer to be crosslinked to a great extent in this stage. Since high temperatures are necessary (150 °C - 190 °C), and the imprint time is still long, allyl prepolymers to be reported here have been modified aiming at a reduction of imprint temperature and time. The admixture of free-radical initiators increases the polymerization rate and allows the polymerization to start at lower temperatures. A reduced imprint temperature (100 °C) and shorter imprint time (10 min) are achieved. Additional polymer modification by plasticizers improves the material flow during the imprint due to a lower Tg. Recipes for polymer modifications have been found out, which result in thermally stable imprints under the specified processing conditions.

Optical coherence tomography (OCT), so far mainly used in the biomedical field, has a high potential as non-destructive and contactless technique for material characterization and analysis. For these applications, OCT systems with ultra-high resolution in the micrometer range and capable of high imaging speeds are required. In this work, we combine ultra-high resolution imaging using a femtosecond Ti:sapphire laser as light source with the concepts of transversal OCT. Based on acquisition by heterodyne detection via acousto-optic modulators (AOMs), and by using an xy-galvano scanner unit we are able to obtain en-face scans with sizes as large as 3 x 3 mm2 within a few seconds. The ultra-high resolution of our OCT system of 2.95 mm axially and 4 mm laterally, both in air, is shown to be essential for imaging of different compounds and fibre materials. We demonstrate the benefits of en-face scanning OCT for various applications in material investigation where in-plane information is of interest which can hardly be obtained by cross-sectional OCT.

There is an increasing need for highly viscous and easy to process thick and ultra thick photoresists for the production of Micro-Electro-Mechanical-Systems (MEMS) and advanced packaging. Here we present results with some novel positive tone photoresists formulated for this purpose. For that we transfered the concept of chemically amplified resists (CARs), originally designed to meet the IC-industry demands for miniaturization and higher resolution, to highly viscous resists. Various polymeric materials have been tested regarding their use in thick CARs. Appropriate resist formulations were developed and their lithographic performance was investigated in a thickness range of 50-150 microns. The CARs are sensitive to UV400.

In this work we address key fabrication issues, specific to fabricating an embedded single mode waveguide system for the telecommunication window. These are the control of adhesion between polymer layers and filling in cavities on pre-patterned polymer substrates. We report the fabrication of two embedded polymer single-mode waveguides, namely, polystyrene/Teflon® AF and mr-L 6000/Teflon® AF, fabricated by means of electron beam lithography and/or nanoimprint lithography. For both waveguides, it is possible to realize a low confinement of the guided mode in the core due to the low refractive index contrast between the core material and the cladding layer (around 0.05–0.2). This gives the flexibility to reduce waveguides optical losses if the losses of the core polymer are too high, which is usually the case in near infrared for most polymers.