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Arrays of SU-8 photoresist pillars (10 μm ×10 μm × 50 μm) on copper substrates were fabricated by X-ray lithography. The photoresist-coated substrates were irradiated by X-ray from a synchrotron source through patterned silver dots on a graphite mask. After the resist development, the chemically stable and mechanically hardened SU-8 pillars exhibited smooth vertical sidewalls and cross section with up to 10 % dimensional errors from the designated pattern. Cobalt of thickness ranging from 50 to 80 nm was then deposited on these patterned substrates by RF sputtering. These cobalt films on SU-8 pillars showed a lower in-plane magnetization than that of continuous cobalt films because of their smaller grain size. The measurement with out-of-plane magnetic field gave rise to a higher magnetization and this anisotropic behavior was observed only in cobalt-coated pillars.

In this work, low-cost and high resolution X-ray lithography is developed by employing low-cost sputtered lift-off lead film on mylar sheet substrate and applied for fabrication of electrostatic actuators. X-ray mask was fabricated by conventional photolithography, Pb sputtering and lift-off process. The Pb mask is used for X-ray lithography of electrostatic actuator structures with 5 µm interdigitate electrodes. For 140 µm-thick SU-8 photoresist on Cr-coated glass substrates, Pb film thickness of around 10 µm was used to block X-ray with 95% x-ray image contrast at a critical dose of 4,200mJ/cm3. A high aspect ratio of 26.5 of SU8 microstructure with 5 µm lateral resolution has been achieved by the developed low cost Pb based X-ray mask. In addition, a steep sidewall angle of nearly 90o for SU-8 structure is confirmed. The results demonstrate that the Pb based X-ray mask offers high resolution X-ray lithography at a very low cost and is promising for microactuator applications.

A 2-D simulation system based on a 2-D dynamic cellular automata method, integrating aerial image simulation, exposure simulation, post-exposure bake simulation, and development simulation modules is presented for inclined ultraviolet (UV) lithography processes of thick photoresists such as SU-8 photoresists. To verify the simulation system, a series of experiments have been performed for SU-8 2000 series photoresists under UV source with 365 nm (2.6 mW/cm2) radiation. The simulation results demonstrate to be in agreement with the experimental results. This is useful to optimize the inclined UV lithography processes of SU-8 photoresists, and to accurately design and control the dimensions of some SU-8 microstructures.

A highly transparent barrier rib was investigated for use in a transparent ac plasma display panel. SU-8 photoresist is an appropriate material for a highly transparent barrier rib because it absorbs only a small amount of light and provides a simple fabrication method for a rectangular barrier rib. SU-8 photoresist barrier rib had a problem with reliability because it can be damaged by the plasma. Therefore, a silicon dioxide layer covered the SU-8 photoresist barrier rib for protection. Using this method, we obtained a highly transparent barrier rib with a long lifetime and a transmittance level of approximately 90%.

The purpose of this work is to reduce the internal stress in cured SU-8 photoresist layer by ultrasonic stress relief technology. The stress relief mechanism of SU-8 photoresist layer was presented. Based on improved Stoney's formula, a theoretical calculation model for SU-8 internal stress was proposed. Profile method was used to measure the curvature radius of substrate. The effect of ultrasonic stress relief on SU-8 layers was studied by experiments. Meanwhile, some important factors, such as amplitude of vibration, power input and relief time, have been discussed. The values of internal stress before and after the ultrasonic stress relief process were compared. The experimental results show that the internal stress in cured SU-8 layers can be effectively reduced if the proper experimental parameters are chosen.

At present, high internal stress in SU-8 photoresist layer has become one of the most primary problems and restricted structure stability and higher aspect ratio of SU-8 photoresist. However, the existing studies all focused on optimizing the process parameters or mask design, and could not be popularized. The purpose of this paper is to reduce the internal stress in cured SU-8 photoresist layer by ultrasonic stress relief technology. The ultrasonic stress relief mechanism in SU-8 photoresist layer was presented. Based on improved Stoney’s formula, the profile mothod calculation model for SU-8 internal stress was proposed. The effect of ultrasonic stress relief on SU-8 layers was studied by experiments. Some important factors, such as amplitude of vibration, power input and relief time, were discussed. The values of internal stress before and after the ultrasonic stress relief process were compared. The research results show that the internal stress in cured SU-8 layer can be reduced effectively if the proper experimental parameters are chosen, and ultrasonic stress relief technology in nonmetal field has some practical value.

The transmission properties of SU-8 photoresist in the ultraviolet (UV) range are reported for resist thicknesses between 1 and 150 μm in the soft-baked state prior to lithographic exposure. Multiple transmission wavelengths in the UV region between 200 and 400 nm are found to be suitable candidates for self-limiting exposure and thus polymerization depth. This enables a novel method to realize microarchitectures via standard photolithographic techniques. Examples of three dimensional hollow polymer microarchitectures are presented to demonstrate the advantages of this method. The coefficient of attenuation is calculated using Beer–Lambert’s principle for different resist thicknesses.

In this study, we try to produce SU-8 photoresist microstructure devices using nano-imprint technology, and try to conduct nano-indention tests on SU-8 photoresist with nano-indention detector, in order to describe the behaviors and characteristics of nano-indentions on SU-8 microstructure devices and establish the deformation mode for the indention under nano-meter level. The tests tell us that, after nano-indention tests, the result indention hardness increases with the loading rate, indention repeats, and reduction of load or depth. Similarly, the indention hardness decreases because of reduction of loading rate, extension of loading time, and increase of load, and depth. Finally, we propose a deformation mode for nano-indention. This mode can also be used to explain the deformation behavior of SU-8 under nano-indention.

We report a Secondary Electron (SE) contrast modulation observed in scanning electron microscope photographs of the cross-section of SU-8 photoresist films exposed holographically. The modulation occurs along the whole depth of the sample and its contrast disappears when the samples are submitted to the post exposure bake (PEB). Diffraction and atomic force microscopy measurements of the samples were performed before and after PEB to investigate this modulation. The results indicate that this SE emission contrast modulation comes from the spatial chemical modulation generated by the photolysis during the exposure of the SU-8 films.

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.

In Back-End-of-Line processing, the remaining photoresist layer after plasma etch is traditionally removed using a plasma process. Plasma process was reported to induce damage to porous dielectric [1-3]. To minimize damage to low-k material, wet alternative methods of removal of photoresist layer on porous low-k dielectrics are gaining a renewed interest [4]. However, the presence of a “crust” generated by etch plasma at the photoresist surface makes it impossible to completely remove by a pure organic solvent. Indeed, the crust, most likely composed of crosslinked polymer, is not soluble in organic solvents [5]. For this reason, a UV pre-treatment is investigated to break cross-links in the crust or to modify the crust to enhance removal efficiency with solvent stripping in more advanced generations.

Based on the refraction theory of the lens, the SU-8 photoresist hard X-ray hourglass lenses with three different structure parameters are fabricated. The mask-back exposure technique is introduced to fabricate the lenses. The focusing performance of this device is tested at Beijing Synchrotron Radiation Facility (BSRF). At the distance of 1.65m from the lenses, an obviously focusing performance in one dimension is observed. The relative intensity of the lenses with the largest gain is about 217.7, the gain of the lens is about 1.15, and the dimension of the focus is about 33µm. The focusing performance of this device can be improved through the developing of the mask-back exposure technique.

Photoresist stripping in IC manufacturing has become more challenging as the number of photoresist levels has increased while at the same time allowable material loss and surface damage has decreased. Heavily implanted photoresist is especially challenging due to the dehydrogenated, amorphous carbon layer that forms on the surface [1]. To facilitate implanted photoresist removal, this layer can be attacked by physical processes such as ion bombardment as part of the common dry ashing approach. However, these physical approaches can lead to surface damage and increased material loss. Another approach is to increase the reactivity of the sulfuric acid – hydrogen peroxide mixture (SPM), so that it can penetrate and dissolve the amorphous carbon layer and achieve complete photoresist removal.

The negative epoxy-based photoresist SU-8 has a variety of applications within microelectromechanical systems (MEMS) and lab-on-a-chip systems. Here, several methods to functionalize SU-8 surfaces with IgG proteins were investigated. Fluorescent labeled proteins and fluorescent sandwich immunoassays were employed to characterize the binding efficiency of model proteins to bare SU-8 surface, SU-8 treated with cerium ammonium nitrate (CAN) etchant and CAN treated surfaces modified by aminosilanization. The highest binding capacity of antibodies was observed on bare SU-8. This explains why bare SU-8 in a functional fluorescent sandwich immunoassay detecting C-reactive protein (CRP) gave twice as high signal as compared with the other two surfaces. Immunoassays performed on bare SU-8 and CAN treated SU-8 resulted in detection limits of CRP of 30 and 80 ng/ml respectively which is sufficient for detecting CRP in clinical samples, where concentrations of 3–10 μg/ml are normal for healthy individuals. In conclusion, bare SU-8 and etched SU-8 can be modified with antibodies by a simple adsorption procedure which simplifies building lab-on-a-chip systems in SU-8. Additionally, we report the fabrication process and use of microwells created in a SU-8 layer with the same dimensions as a standard microscope glass slide that could fit into fluorescent scanners. The SU-8 microwells minimize the reagent consumption and are straightforward to handle compared to SU-8 coated microscope slides.

A series of silica modified photoresists had been successfully developed through incorporation of a particular nanoparticles suspension. Free radical polymerization was employed to synthesize the binder, an acrylate copolymer resin of benzyl methacrylate, methacrylic acid and 2-hydroxyethyl methacrylate, of the photoresist. The acid value, viscosity, molecular weight and thermal properties of the formed binders were measured. Then, surface-modified silica particles prepared by the sol–gel method were introduced to the photoresist. Because the modified silica particles contained considerable amount of reactive double bonds (C C) on their surfaces, they would react with the polyfunctional monomers in the photoresist to form an organic–inorganic nanohybrid. Fourier transform infrared spectrometer was used to analyze the evolution of chemical bonds at various stages of the preparation process. Thermal analyses including thermal gravimetric analyzer, differential scanning calorimeter and thermo-mechanical analyzer were used to evaluate the level of enhancement on thermal and dimensional stabilities of the photoresist due to silica incorporation.

In this study, we explored a rapid and low-cost process for patterning in a SU-8 photoresist by thermal imprinting with a non-transparent mold such as Ni mold. One of major obstacles in the process is that the extremely good formability of uncured SU-8 even near room temperature causes the collapse of imprinted patterns during and after de-molding because a sample cannot be exposed to UV light during imprinting owing to the non-transparency of a mold. To overcome this problem, un-cured SU-8 resists were pre-treated with UV light, heat, and O"2 plasma for controlling their formability, and applied to thermal imprint tests to be compared each other in terms of the replication fidelity. As a result, a SU-8 sample pre-treated with UV light for 8s resulted in the best replication quality for given imprint conditions and mold dimensions, and we could successfully replicate micro patterns in SU-8 resist without a quartz mold. As compared with conventional UV-imprint processes, this process has potential merits such as a lower mold cost, an easier mold release and a less air-entrapment.

Wet processes are gaining renewed interest for the removal of post-etch photoresist on porous dielectrics in semiconductor manufacturing. However, specifications on material loss and k-value integrity considerably reduce formulation space for a purely wet-chemical clean. Hence characterization of photoresist degradation by etch is needed to support the selection of wet cleaning chemistries. In this work, the degradation of a DUV (deep ultra-violet) photoresist by a dielectric etch plasma is characterized by spectroscopic as well as by polymer science characterization techniques. Results show that degradation of the DUV photoresist under study does not follow the mechanisms previously proposed for etched DUV photoresist films, but is rather comparable to the degradation of PMMA under low energy radiation. Degradation is more intense in the photoresist top layer, forming a cross-linked crust that is insoluble in organic solvents. Based on FTIR and H-1 NMR analysis of isolated crust samples, a cross-linking mechanism is proposed that is based on the reaction between intra-chain radicals and/or between intra-chain radicals and end-chain propagating radicals. Implications for the wet removal of photoresist layers are discussed. (C) 2008 Elsevier B.V. All rights reserved.

Digital image correlation (DIC) is a whole-field and non-contact strain measuring method. It could provide deformation information of a specimen by processing two digital images that are captured before and after the deformation. To search the deformed images, a hybrid genetic algorithm, in which a simulated annealing mutation process and adaptive mechanisms are added to the real-parameter genetic algorithm, is proposed in this work. To increase the accuracy and reliability of this method, some key parameters of this method are suggested. Then, this method is used to measure the strain during the micro tensile testing of SU-8 photoresist. In addition to the conventional single region, a double region is proposed to calculate the strain by DIC. The results indicate that while the strains obtained by single region are reasonable, those obtained by double region are accurate. Also the mechanical properties of SU-8 could be accurately obtained.

Electrospray deposition has been investigated as a substitute for photoresist spin coating. The morphology of Microposit S1813 photoresist films has been studied as a function of several spray conditions including resist concentration, substrate surface, and flow rate. Film morphology is controlled by three process parameters: the surface energy determines the equilibrium conditions of resist on the substrate; the viscosity and volume flux determine the relaxation time for the depositing resist solution after impact on the substrate. Electrosprayed photoresist films have been used for photolithographic patterning and it has been demonstrated that electrospray deposition is an effective method for deposition of photoresist on top of fragile, thin films, which can be used for multilayered thin film fabrication.

[Claes, M.; Le, Q. T.; Kesters, E.; Lux, M.; Franquet, A.; Vereecke, G.; Mertens, P. W.] IMEC VZW, B-3001 Louvain, Belgium.

Chemical and morphological changes of phenol formaldehyde-based photoresist after radiofrequency(RF) plasma treatment depending on exposure time and source power were investigated. It was found that etch rate of photoresist sharply increased after discharge turn on and reached a limit with increase in plasma exposure time. Contact angle measurements and X-ray photoelectron spectroscopy(XPS) analysis showed that the surface chemical structure become nearly constant after 15 sec of the treatment. Atomic force microprobe(AFM) measurements were shown that surface roughness was increased with plasma exposure time.

A new, environmentally friendly, inexpensive and non-destructive method for removing SU-8 after being an electroplating mold in microfluidic fabrication is demonstrated in this paper. A controllable thermal delaminating method assisted by an efficient high-speed aerosol jet consisting of two major steps, delamination followed by removal by lifting, is presented. Experiments with the thermal process, operated at a rising temperature ΔT of 340 °C for 30 min, were carried out. Four delaminations were observed and the critical buckling stresses were calculated to be 38.98, 35.24, 42.04 and 41.26 MPa, respectively. The results show that these delaminations occurred at a rising temperature ΔT of 290, 260.5, 314.7 and 308.5 °C, respectively. The morphology of the thermal buckling-driven delamination was edge initiated and straight sided. The effects of the carbon dioxide (CO2) snow jet at a distance of 10 mm from the nozzle exit as well as the lift force Fdp, drag force Fd and impact force Fi were determined to be 79 × 10−3 N, 0.625 × 10−3 N and (1.65–4.95) × 10−3 N, respectively. Based on the analysis of the lift, drag and impact forces, the lifting force dominates the effects of the CO2 snow jet and is tens of times larger than the others. The experiments and analyses showed that the best distance for the CO2 snow jet to the nozzle exit was 6–10 mm.

【For the application to optic devices, wafer level package including spacer with particular thickness according to optical design could be required. In these cases, the uniformity of spacer thickness is important for bonding strength and optical performance. Packaging process has to be performed at low temperature in order to prevent damage to devices fabricated before packaging. And if photosensitive material is used as spacer layer, size and shape of pattern and thickness of spacer can be easily controlled. This paper presents polymer bonding using thick, uniform and patterned spacing layer of SU-8 2100 photoresist for wafer level package. SU-8, negative photoresist, can be coated uniformly by spin coater and it is cured at $95^{\circ}C$ and bonded well near the temperature. It can be bonded to silicon well, patterned with high aspect ratio and easy to form thick layer due to its high viscosity. It is also mechanically strong, chemically resistive and thermally stable. But adhesion of SU-8 to glass is poor, and in the case of forming thick layer, SU-8 layer leans from the perpendicular due to imbalance to gravity. To solve leaning problem, the wafer rotating system was introduced. Imbalance to gravity of thick layer was cancelled out through rotating wafer during curing time. And depositing additional layer of gold onto glass could improve adhesion strength of SU-8 to glass. Conclusively, we established the coating condition for forming patterned SU-8 layer with $400{\mu}m$ of thickness and 3.25 % of uniformity through single coating. Also we improved tensile strength from hundreds kPa to maximum 9.43 MPa through depositing gold layer onto glass substrate.】

The faster coating speed is required to the photoresist for slit coating process. When the photoresist is coated at high coating speed, the film thickness uniformity becomes worse. The carboxylic acids and the ester compounds with long alkyl chain were added into photoresist for the slit coating process. Such photoresist showed really good film thickness uniformity of photoresist film on the glass substrate at high coating speed condition.

Negative SU-8 photoresist processed at several levels of lower temperature than conventional approach was investigated, and its low-temperature processing has been characterized in terms of delamination. According to two phases of statistical design of experiment (DOE), initially statistically significant variables of SU-8 photoresist processing were selected, and the selected variables were further investigated to find their effects on delamination of SU-8 microstructure. A three leveled factorial designed experiments were performed followed by a 2(6-1) fractional factorial designed as a screening experiment. Characterizing low-temperature SU-8 photoresist process, 27 samples were fabricated and the degree of delamination was measured. In addition, nine additional samples were fabricated for the purpose of verification. Employing a neural network modeling technique, a process model is established, and response surfaces are generated to investigate the degree of delamination associated with three process parameters: post exposure bake (PEB) temperature, PEB time, and exposure energy. From the response surfaces generated, two significant parameters associated with delamination are identified, and their effects on delamination were analyzed. The higher the post exposure bake (PEB) temperature at a fixed PEB time and the more delamination occurred. In addition, the higher the dose of exposure energy, the lower the temperature at which the delamination begins and the larger the degree of delamination. The results identified acceptable ranges of the three process variables to avoid the delamination of SU-8 film, which in turn might lead to potential defects in MEMS device fabrication.

Micro hot embossing mold of microfluidic chip used in flow cytometry is designed and microfabricated. After some kinds of microfabrication processes are tried, this paper presents a novel microfabrication technology of micro hot embossing metal mold. Micro metal mold is fabricated by low-cost UV-LIGA surface micro fabrication process using negative thick photoresist, SU-8. Different from other micro hot embossing molds, the micro mold with vertical sidewalls is fabricated by micro nickel electroforming directly on Nickel base. Based on the micro Nickel mold and automation fabrication system, high precision and mass-producing microfluidic chips have been fabricated and they have been used in flow cytometry

Suppression of 193-nm photoresist deformation by H2 addition to fluorocarbon plasmas in via-hole etching is investigated for sub-65-nm-node dual-damascene patterning. Photoresist deformation causes profile distortion and results in degradation of reliability, such as the line-to-line time dependent dielectric breakdown. To prevent profile distortion, H2 addition to fluorocarbon plasma is investigated in terms of fluorocarbon polymer and photoresist modification. XPS, FT-IR, and highlight etching investigations reveal that the H2 plasma treatment extracts oxygen from the photoresist and modifies it. This modification suppresses the photoresist deformation and H2 addition to fluorocarbon plasmas can have the same effects as the H2 plasma treatment. Finally, a highly reliable damascene interconnection is successfully achieved.

We report a new type of negative-tone photoresist in this paper. The resist is based on a composite of EPON resins 154 and 165 (both from Hexion Specialty Chemicals, Inc., Columbus, OH 43215). These two epoxy-based resins were mixed in an optimal ratio and dissolved in gamma-butyrolactone (GBL) solvent. The mixture was then photosensitized by adding a given amount of triaryl sulfonium salt to obtain a new negative-tone photoresist that can be used in for ultra-high-aspect-ratio microstructure fabrication with UV lithography. Preliminary studies have found that microstructures with heights of more than 1000 μm and feature sizes down to 10 μm (aspect-ratios of more than 100) can be obtained using the new resist film with ultraviolet lithography. The microstructures have excellent sidewall quality. In this paper, both the material properties and lithography properties of this new type of UV resist will be presented. The potential applications of the new resist in microfabrication and MEMS systems are also discussed.

The permanent photoresist is a versatile material to fabricate three-dimensional structures for the Micro Electro Mechanical Systems (MEMS) field. The replacement to non-antimonite initiators is ongoing toward the mass manufacturing. We investigate on the reaction mechanism of cross-linking formulating chemically amplified negative-tone photoresists by adopting an infrared spectra measurement system. The consumption of epoxy group is monitored during post exposure bake (PEB). The patterning profile of 40 μm lines with 30 μm thickness indicates no significant difference on the photoresist formulation. However, the FT-IR measurement results and the simulation models describe the difference in cross-linking behavior in tested photoresists. The activation energy of cross-linking reaction is also calculated. The impact on cross-linking reaction from the residual solvent in photoresist film is also discussed utilizing a Thermal Desorption Spectrometer (TDS).

In the present study, we have been trying to improve adhesion, heat resistant and chemistry resistant of positive photoresists through introducing rubber nanoparticles into positive photoresist (Novolac-diazonaphthoquinone) system. Thereinto, the photoresist sample with 8 wt% of rubber nanoparticles possess higher thermal stability (322.8 °C@ 5wt% loss), higher adhesion strength (402.50 Kg/cm2). Furthermore, the photoresist film after curing can sustain various chemicals, such as acid, base and organic solvent. At last, the novel positive photoresist was also exposed at 365 nm (I line) and developed in base solution to yield ultrafine pattern. Therefore, we developed novel photoresist including rubber nanoparticles which possess excellent complex performance and can be used as structural material in device.

This paper shows the study of the effect of etch by product towards photoresist residue defect found in Polysilicon-Insulator-Polysilicon (PIP) processes. Initial finding show the correlation with the big size poly PIP capacitor structure. Therefore, the challenge was to focus on big size PIP structure. But during partition check, we found the weakness of the photoresist stripping during O2 plasma ashing. The weakness show not only big size pattern but also small size area. Through EDX analysis, we found Si byproduct block oxygen reaction with photoresist. As a consequence, following sulfuric clean has no margin to remove all photoresist which cause photoresist residue on big size of pattern. Several approaches were carried out to identify the optimal solution for defect removal. And, it was found that the additional sulfuric clean without HF is best solution. The photoresist residue defect was then eliminated completely with the new cleaning condition.

In this paper, a novel method to fabricate ultralong focal length microlens arrays has been proposed. The microlens arrays were fabricated based on surface tension when heating temperature is over a glass transition temperature of SU-8 photoresist. An ultralong focal length was achieved by the large radius of curvature of a photoresist surface. Microlenses of widths from 30 to 210 μm were successfully fabricated. The longest focal length was up to 4.4 mm from the microlens of 210 μm width. The formation mechanism was also studied and validated by simulation based on the finite element method.

A new nanocomposite photoresist based on SU-8 epoxy resin has been developed. It consists in a homogeneous dispersion of nano-silica particles in the negative tone photosensitive SU-8. The nanocomposite photoresist is more sensitive than the SU-8 photoresist and the photopatterned composite structures show low stress and less cracks than pure SU-8 structures. No significant resolution difference has been observed for both materials.

This paper presents the results of an investigation of the influence of soft baking temperature on the lithographic performance of the negative photoresist SU-8. The work was initiated in order to obtain a lithographic resolution suitable for integration of diffractive optical components for near-infrared wavelengths. The study was carried out on 40 µm SU-8 layers on thermally oxidized silicon wafers, a widespread platform for integration of microfluidic systems and waveguides. A series of experiments covering soft bake temperatures in the range 65–115 °C were performed under otherwise identical processing conditions. The influence of the soft bake temperature on polymerization temperature as well as cracking, lithographic resolution and hardness of the resist was investigated. The kinetics of the polymerization process were observed to change with soft bake temperature, leading to changes in sensitivity and contrast of the resist, as well as changes in the material strength of the developed structures. Soft baking at 65 °C proved superior with respect to all the inspected properties, providing a sample showing full resolution of 3.8 µm wide trenches and no stress-related cracking.

SU-8 has gained widespread acceptance as a negative photoresist. It is also finding increasing use as a structural material in microanalytical devices. Consequently, methods to tailor the surface properties of SU-8 as well as to micropattern coatings on the surface of SU-8 are needed. The SU-8 photoresist consists of EPON SU-8 resin mixed with the photoacid generator triarylsulfonium hexafluoroantimonate. This photoacid generator can also serve as a photoinitiator generating free radicals when illuminated with UV light. Under the appropriate conditions, sufficient triarylsulfonium hexafluoroantimonate remains within cured SU-8 to act as a source of free radicals and initiate UV-mediated grafting of polymers onto the surface of the SU-8. UV-mediated grafting was used to coat SU-8 surfaces with poly(acrylic acid) and other water-soluble monomers. The SU-8 surface was chemically micropatterned by placing a mask between the UV light and SU-8. The X-Y spatial resolution of micropatterned poly(acrylic acid) on the SU-8 surface was 2 mum. Three applications of these chemically modified SU-8 surfaces were demonstrated. In the first, poly(ethylene glycol) was used to protect the SU-8 from interactions with proteins, yielding a surface resistant to biofouling. In the second demonstration, the SU-8 surface was micropatterned with a cell-resistant layer to guide cellular attachment and growth. In the final application, SU-8 micropallets were encoded with polymer lines. The bar codes were read by either absorbance or fluorescence measurements. Thus, UV-mediated graft polymerization is an efficient and effective method to micropattern coatings onto the surface of SU-8.

A conductive composite photoresist has been developed for the direct photopatterning of electrodes. It is based on a dispersion of silver nanoparticles in SU8, a non-conductive, negative-tone photoresist. Manufactured structures have an electrical conductivity at a low silver content of around 6 vol.-%

Studies on two-photon lithography in negative SU-8 photoresist demonstrate the possibility of obtaining mechanically stable, stress-free, extended nanorods having lateral sizes of about 30 nm (corresponding to λ/25 resolution). The high resolution achievable with the given combination of materials and fabrication techniques demonstrates its potential for the fabrication of large-scale nanostructures, such as photonic crystals with photonic stop gaps at visible wavelengths.

A novel fabrication process was developed to create high aspect ratio (>10:1) carbon posts, all-carbon suspended bridges and wires, self-organized bunches of carbon posts, and carbon plates supported by carbon beams. The structures are all made from a two-step pyrolysis process with SU-8 photoresist as the starting material. In this paper we describe the fabrication of these various new C-MEMS structures and detail an important application of the high aspect ratio carbon posts arrays. The carbon post arrays can be reversible charged/discharged with Li ions, an application that may greatly impact the application of C-MEMS in three-dimensional microbatteries. Complex suspended C-MEMS structures, such as wires, plates, ribbons, and self-organized bunches of posts, were built. Methods to accurately and repeatedly fabricate all the above 3-D C-MEMS structures are given.

Technologies for flexible electronics have been developed to make electronic or microelectromechanical (MEMS) devices on inexpensive and flexible organic substrates. In order to fabricate the interconnect lines between device elements or layers in flexible electronic devices, metallization on the flexible substrate is essential. In this case, the width and conductivity of metallization line are very important for minimizing the size of device. Therefore, the realization of metallization process with the scale of a few micrometers on the flexible substrate is required. In this work, micro-scale metallization lines of Cu were fabricated on the flexible substrate by electroplating using the patterned mask of a negative-tone SU-8 photoresist. Polyimide surface was treated by O 2 /Ar atmospheric plasma for the improvement in adhesion between Cr layer and polyimide and in situ sputter deposition of 100-nm-thick Cu seed layers on the sputter-deposited 50-nm-thick Cr adhesion layer was followed. SU-8 photoresist was spin-coated and patterned by photolithography. Electroplating of Cu line, removal of SU-8, and selective wet etch of Cr adhesion and Cu seed layers were carried out. Gap between the Cu lines was successfully filled by spin-coating of polyimide. Micro-scale Cu metal lines with gap filling on the polyimide substrate with a thickness of 6–12 μm and an aspect ratio of 1–3 were successfully fabricated.

In order to fabricate flexible microelectronic devices, fabrication of metallization lines and metal electrodes on the flexible substrate is essential. Cu lines are often used as interconnect lines in electronic devices and Au as microelectrodes in organic transistors and bioelectronics devices due to its good electrochemical stability and biocompatibility. For minimizing the size of device, the realization of metallization lines and microelectrodes with the scale of a few micrometers on the flexible substrate is very important. In this work, micro-scale metallization lines of Cu and Au were fabricated on the flexible polyimide (PI) substrate by electroplating using the patterned mask of a negative-tone SU-8 photoresist. Surface of PI substrate was treated by O"2 inductively coupled plasma for improvement of the adhesion strength between Cr layer and PI and in situ sputter-deposition of 100-nm thick Cu seed layers on the sputter-deposited 50-nm thick Cr adhesion layer was followed. Electroplating of high aspect-ratio Cu and Au lines using a sulfuric acid and a noncyanide solution with the patterned SU-8 mask, respectively, removal of SU-8, and selective wet etch of Cr adhesion and Cu seed layers were carried out. Micro-scale Au electrode lines were successfully fabricated on the PI substrate. Micro-scale gap-filled Cu lines with spin-coated polyimide on the PI substrate with the thickness of 6-12 @mm and the aspect ratio of 1-3 were successfully fabricated.

We fabricated patterned polymer photonic crystals by holographic lithography in conjunction with soft lithography. A patterned SU-8 photoresist film was created by preformed pattern of a hard-baked SU-8 photoresist, transferred by a PDMS mold. Then, four-beam holographic exposure carved 3D photonic crystal structures onto the patterned photoresist. Because of refractive index matching of the photoresist and the hard-baked photoresist, scattering, which might have caused a distortion of interference pattern, did not occur. Eventually, an f.c.c. polymer structure with a line pattern was successfully created after development.

Supercritical CO"2 emulsion (SCE) was found to be effective in removal of epoxy-type SU-8 photoresist. The ability to remove SU-8 was compared between a commercially available Remover PG (RPG) solution and SCE. Both RPG and SCE were effective in removing not-hard-baked SU-8 dots, with height of [email protected] and diameter ranged from 50 to [email protected] When the SU-8 dots were hard-baked at 150^oC for 10min, RPG could not remove any of the SU-8 dots. On the other hand, SCE could still remove 42.11% of the [email protected] SU-8 dots. When the SU-8 dots were hard baked at 200^oC for 10min, 5.75% of the [email protected] SU-8 dots could be removed by SCE.

This paper describes a simple method for the microfabrication of mechanically compliant, magnetically-responsive microstructures. These microstructures were fabricated in one step by using a ferromagnetic photoresist, which, in turn, was prepared by suspending nickel nanospheres in a negative photosensitive epoxy (SU8). The nominal diameter of the nickel nanospheres was 80–150 nm, that is, much smaller than the wavelength of the UV light (365 and 405 nm) used to expose the photoresist. Diffraction and scattering of light from the nanospheres allowed for full exposure of the photoresist, even after the incorporation of nanospheres at levels at which it became opaque. The ferromagnetic photoresist was cross-linked after exposure and development, and yielded a stable, compliant, ferromagnetic pattern. The paper characterizes the effect of the weight density of the nickel nanospheres on the transmittance of films made by this technique at wavelengths from 330 nm to 610 nm. It also describes a number of microstructures made with the photoresist: examples include lines, posts and meshes. As a demonstration, the procedure was applied to the microfabrication of a set of magnetically-actuated micromirrors. These micromirrors achieved large deflections: deflection at the tip of a 12 mm long, 250 µ mw ide and 70 µm thick cantilever of the ferromagnetic photoresist exceeded 1.4 mm, when actuated by a NbFeB permanent magnet with field strength ∼120 mT. The cantilever maintained its mechanical properties after cycling ∼10 6 times. S This article has online supplementary material

The thick-film photoresists are essential to fabricate high-aspect-ratio microstructures by the UV-LIGA process. However, current thick-film photoresists have some weaknesses including a thickness of only up to 100 µm, a poor line-width resolution and difficulty in being stripped. Consequently, a new type of thick-film photoresist is required. This work presents a novel positive-tone MMA/TBMA photoresist, formed by combining copolymerization and chemically amplification (CA) for use in the ultra-thick UV-LIGA process. An MMA/TBMA photoresist film with a thickness of 500 µm is easily achieved. For MMA/TBMA photoresist layers with thicknesses from 100 µm to 500 µm, an exposure dose from 80 to 100 mJ cm−2 per micron is required to remove all of the exposed photoresist, revealing that the selectivity between radiated and non-radiated zones during a long development process is sufficiently high; the sidewall verticality and aspect ratio of the microstructure are excellent; stress-induced cracks are not observed in the non-radiated zones after development. MMA/TBMA photoresist is demonstrated to fabricate open microstructures with aspect ratios of at least 10 and close microstructures with aspect ratios of not more than 10, such values of aspect ratio are still sufficient for most ultra-thick mold applications. Moreover, MMA/TBMA photoresist can undergo erosion by acidic electrolyte and easily be stripped using usual organic solvents. These findings demonstrate that MMA/TBMA photoresist has the potential to replace SU-8 resist in the ultra-thick UV-LIGA process.

An adhesive bonding method for fabrication of structures for microelectromechanical systems (MEMS) has been investigated. Negative photoresist SU-8 is used both as the structural material and as the adhesive material. Ultraviolet initiated crosslinking of SU-8 was investigated for bonding of small pillars as well as large uniform areas. Fabrication of thermally- and electrically insulated structures was also done and is reported here. Insulated structures are fabricated with SU-8 as roof, floor and sidewalls of the structure to ensure uniform wetting and surface electrochemistry for microfluidic applications.