Photoresist Mold Research Articles

Non-PR Sn-3.5Ag Bumping on a Fast Filled Cu-Plug by PPR Current

The electroplating of Sn-3.5 wt% Ag bumps without a photoresist (PR) mould on a Si chip was performed to reduce the production steps and cost for 3-D chip stacking. The electroplating characteristics of Sn-Ag and Sn-Ag bump growth were examined. The Sn-Ag bumps were electroplated on the Cu-plugged TSVs (through-silicon vias) of a Si chip. The Cu plug in the via was produced using a high-speed Cu filling process by a periodic pulse reverse current waveform. The electroplating current was supplied to the exposed Cu surface in the TSVs to produce the Sn-3.5Ag bumps. As the experimental results show, the Sn-3.5Ag bumps were fabricated successfully without a PR mould, with no serious defects by electroplating. The Ag contents in the Sn-Ag bump decreased with increasing current density. Besides, the bump height and width increased with increasing plating time. The bump width grew isotropically because of the absence of a PR mould. The Sn-3.55 wt% Ag bumps were obtained at a current density of -55 mA/cm2 for 20 min on the Cu plugs.

Resin-bonded NdFeB micromagnets for integration into electromagnetic vibration energy harvesters

A micromachining technique is presented for the fabrication of resin-bonded permanent magnets in the microscale. Magnetic paste is prepared from NdFeB powder and an epoxy resin, filled into lithographically defined photoresist molds or metal molds, and formed into resin-bonded magnets after curing at room temperature. A coercivity of 772.4 kA/m, a remanence of 0.27 T, and a maximum energy product of 22.6 kJ/m3 have been achieved in an NdFeB disk micromagnet with dimensions of Φ200 μm×70 μm. Based on the developed micro-patterning of resin-bonded magnets, a fully integrated electromagnetic vibration energy harvester has been designed and fabricated. The dimensions of the energy harvester are only 4.5 mm×4.5 mm×1.0 mm, and those of the micromagnet are 1.5 mm×1.5 mm×0.2 mm. This microfabrication technique can be used for producing permanent magnets tens or hundreds of micrometers in size for use in various magnetic devices.

Nanocrystalline electroplated NiFe‐based alloys for integrated magnetic microsensors

AbstractThe effect of pulse plating (PF) and direct current (DC) plating on the magnetic properties and grain size of electroplated NiFe films for the application in magnetic microsensors, i.e., as integrated magnetic concentrator, has been studied. In order to further improve magnetic properties additional subsequent thermal annealing experiments were carried out with chosen films. A sulphate‐based NiFe electrolyte containing various additives operated at a pH of 3.5 and a temperature of 50 °C was used. The softmagnetic NiFe films were deposited at a thickness of >10 µm on silicon substrates with a sputtered 200 nm thick Cu seed layer and a 50 µm high photoresist mould. The composition and magnetic properties were measured by energy dispersive X‐ray spectroscopy (EDX) and vibrating sample magnetometer (VSM), respectively. The morphology was investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The composition of the fabricated fcc NiFe films ranged from 3 to 42 wt% Fe with a good adhesion. The as‐plated NiFe exhibited nanocrystalline grain sizes ranging from 12 to 18 nm with a coercivity as low as 16 A m−1. It was found that the grain size is generally higher at a lower iron content. However, pulse forward (PF) plating favours a refined grain size over DC plating which can be attributed to an increased nucleation rate caused by the high pulse current densities (high overpotential). By applying a thermal annealing for 2 h at 300 °C in a vacuum oven the coercivity of NiFe samples with ∼18.5 wt% Fe could be further reduced to 6 A m−1.

J112012 移動マスクUV露光による2.5次元形状の生成([J112-01]マイクロナノ理工学:nmからmmまでの表面制御とその応用(1))

A novel moving mask exposure apparatus for 2.5 dimensional patterning of thick photo resist has been developed. In general mask aligner, the UV light intensity that passes through photo mask shows exactly same shape of mask pattern. By in plane moving PZT-stage which carrying photoresist coated substrate, the UV intensity distribution via photo mask has been modified from simple binary pattern to Gaussian like pattern. The stage movement can be controlled by applying signal to stage that enables to generate arbitrary UV intensity distribution. Using the exposure apparatus and backside exposure technique we created photoresist molds for micro well array that have smoothly tilted sidewall. These photo resist molds were replicated by Poly-(dimethylpolysiloxane) to make final product with good shape transferability.

Characteristics of electroplated Sn bumps fabricated without a PR mould on a Si chip for 3D packaging

The characteristics of electroplated Sn bumps, fabricated without a PR (photoresist) mould on copper-plugged TSVs (through-silicon vias), in a Si chip were investigated. A new process of non-PR bumping developed in this research was considered to enhance the productivity and reduce the cost for three-dimensional (3D) chip stacking. To produce Sn bumps, Pt was adopted as an anode, and thinned Si die with Cu-plugged TSVs as a cathode. The polarization curve of the Sn electrolyte was analysed to determine the reduction potential of the Sn ion. The heights, widths, and uniformities of the Sn bumps produced through the proposed non-PR process were evaluated to assess the feasibility of reliable Sn bumping using this process. The experimental results showed that the Sn electrolyte had a reduction potential of -0.463V. The Sn bumps with rivet-head shapes were produced successfully without a PR mould on Cu-plugged TSV. The Sn bumps grew in both vertical (thickness) and lateral (width) directions due to the absence of a PR mould. The plating time was varied from 2 to 60min at a constant current density of -30mA/cm^2, and the bump height and width became 39 and [email protected] at 60min, respectively. The morphologies of the Sn bumps without a PR mould showed the preferred facet growth by increasing the plating time, which resulted in increase of Sn facet size but decrease of number of facets. The uniformity of the bump widths on a chip was within the range of 86.9-95.4%.

Design, Fabrication and Levitation Experiments of a Micromachined Electrostatically Suspended Six-Axis Accelerometer

A micromachined electrostatically suspended six-axis accelerometer, with a square plate as proof mass housed by a top stator and bottom stator, is presented. The device structure and related techniques concerning its operating principles, such as calculation of capacitances and electrostatic forces/moments, detection and levitation control of the proof mass, acceleration measurement, and structural parameters design, are described. Hybrid MEMS manufacturing techniques, including surface micromachining fabrication of thin film electrodes and interconnections, integration fabrication of thick nickel structures about 500 μm using UV-LIGA by successful removal of SU-8 photoresist mold, DRIE of silicon proof mass in thickness of 450 μm, microassembly and solder bonding, were employed to fabricate this prototype microdevice. A levitation experiment system for the fabricated microaccelerometer chip is introduced, and levitation results show that fast initial levitation within 10 ms and stable full suspension of the proof mass have been successfully demonstrated.

New process of electroplate Sn bumping on TSV without a PR mould for 3D-chip stacking

A new method of fabricating Sn bumps by electroplating without a PR (photoresist) mould on a Si die was investigated in terms of the bump growth and morphology for application to 3D-chip stacking. The omission of the PR mould was expected to result in a reduction of the process time and of the cost of electroplate bumping on the Si chip. For the electroplating of Sn bumps, a cathode consisting of a Si die with a Cuplugged TSV (through-silicon via) was used, with Sn or Pt adopted as an anode. The current densities and plating times were varied to assess the change in the Sn bump size and morphology. As a result, Sn bumps with rivet-head shapes were successfully fabricated via electroplating on Cu-plugged TSV without a PR mould. The height and width of the Sn bump were increased at a longer plating time and a larger current density. The Sn or Pt anode had a minimal effect on the electroplating results: The deposition rates and morphologies of the Sn bumps with different anodes were nearly identical in the range from 15 to 60 min at −30 mA/cm2. The Sn deposit without a PR mould developed a facet with various directions less than 5 min of plating time. After 15 min, however, the selective growth of some facets became dominant, which enlarged the preferred facets and caused a decrease in the number of facets.

Fabrication of a large-scale Ni stamp using a multi-level SU-8 photoresist mold for advanced printed circuit board manufacturing

Recently, as integration density of electrical devices has increased, multi-layered, fine-patterned printed circuit board (PCB) technology has been advancing. As a high-volume, low-cost manufacturing method, PCB fabrication by imprinting has gained much attention. A large-sized Ni stamp plays a critical role in this method. We thus developed a novel fabrication method for a large-sized multi-level Ni stamp, which imprints patterns directly onto PCB resin, using multi-level patterning of an SU-8 photoresist. In this study, we focused on two aspects: (i) the property of SU-8 adhering to a large-sized glass substrate and (ii) neat and complete removal of SU-8 from the Ni stamp using a self-assembled monolayer. Using the processes we developed which will be described in detail in this paper, we successfully demonstrated a multi-level Ni stamp as large as 190 mm × 190 mm in size. The actual imprinting test exhibited successful results showing suitability of the developed method for large-scale, low-cost and high-volume manufacturing of the advanced PCBs.

A trans-scaled nanofabrication using 3D diffuser lithography, metal molding and nano-imprinting

This paper describes our proposal and successful demonstration of a trans-scaled nanofabrication using conventional micro-technologies. In order to achieve this, we first performed ‘3D diffuser lithography,’ which is simply conventional contact microlithography with an optical diffuser sheet, to make submicron-sized nanopatterns on a photoresist mold. We then replicated these patterns onto a nickel mold, thereby successfully fabricating nickel nano-tip arrays 300 nm in diameter without the use of any specially-designed nanopatterning equipment or techniques. Then, the conventional thermal nano-imprinting onto a PMMA target was conducted using the fabricated Ni stamp, producing nano-dot arrays in an area of several hundreds of microns per side, where each dot diameter was 700 nm with 5.8% uniformity. The largest size which can accommodate this method depends on the size of the conventional contact lithography tool, which currently extends to several meters, according to contemporary machinery. The proposed method is cost effective for mass production, and can be applied to various fields of nanoscale applications.

Fabrication and Characterization of Bonded NdFeB Microstructures for Microelectromechanical Systems Applications

A micromachining technique has been developed for the fabrication of microscale polymer-bonded magnet. Two types of lithographically defined molds, photoresist mold and electroplated metal mold, were introduced. Photoresist mold is convenient, while electroplated metal mold can be fabricated on the glass or steel substrate which can bear much more compression. NdFeB films of thickness between 50 and 500 µm were prepared by micro-patterning of composites containing 83-95wt% of commercial NdFeB powder after curing at the room temperature. Magnetic properties mainly depend on the types and percentage of volume loading of magnetic powder. Coercivity of 772.4kA/m (9.70kOe), remanence of 275.1mT (2.751kG), and energy product of 22.6kJ/m3 (2.8MGOe) have been achieved. This easily developed magnet could be a promising candidate for applications in magnetic microelectromechanical systems (MEMS).

Sn Bumping Without Photoresist Mould and Si Dice Stacking for 3-D Packaging

Chip stacking with through-silicon-vias (TSV) technology for 3-D packaging of electronic devices was investigated. A new process of direct solder bumping on Si wafers without photoresist (PR) mould was designed and applied in this study. The Cu extrusion process on the via was also omitted for process simplification. This simplified process can be useful for cost reduction and increased productivity. The substrate for the experiments was a p-type 〈100 〉 Si wafer of 100 mm diameter. In order to produce the vias, the Si wafer was etched by a deep reactive ion etcher (DRIE) using SF6 and C4F8 plasmas alternately. The produced vias were 40 μm in diameter and 80 μm in depth. On the via side walls, SiO2, Ti, and Au layers were formed with thicknesses of 1, 0.1, and 0.7μm, respectively. Pulsed direct current (DC) electroplating was used to fill the vias with Cu. Then the Si wafer was back ground to a thickness of 80 μm until the Cu filling in the vias was exposed to the surface without extrusion. Plating current subsequently flowed through the vias to the bumping surface, and Sn was electroplated on the Cu filling directly without a PR mould. To optimize the bumping process, the current density and time for Sn plating were varied from 0.04 to 0.06 A/cm2 and from 10 to 40 min, respectively. Bumps with a height of 20 μm were formed successfully with 0.05 A/cm2 and 30 min without a PR mould. The bump height increased with increasing plating current and time; for example, from 13 μm at 10 min to 33 μm at 40 min in case of 0.06 A/cm2. The Si dice with electroplated Sn bumps had dimensions of 5 × 5 mm and thickness of 80 μm. Three Si dice were stacked successfully by micro-soldering at 260°C. In the interface between the Sn bumps and the Cu filling, a Cu6Sn5 intermetallic compound was produced with a thickness of 3.2 μm. Through this study, a process for non-PR solder bumping by electroplating and wafer stacking with TSV was achieved successfully.

Fabrication and Characterization of the Capillary Performance of Superhydrophilic Cu Micropost Arrays

We report the fabrication of dense arrays of super-hydrophilic Cu microposts at solid fractions as high as 58% and aspect ratios as high as four using electrochemical deposition and chemical oxidation techniques. Oxygen surface plasma treatments of photoresist molds and a precise control of the initial electrodeposition current are found to be critical in creating arrays of nearly defect-free Cu posts. The capillary performance of the micropost arrays is characterized using capillary rate of rise experiments and numerical simulations that account for the finite curvatures of liquid menisci. For the given wick morphology, the capillary performance generally decreases with increasing solid fraction and is enhanced by almost an order of magnitude when thin nanostructured copper oxide layers are formed on the post surface. The present work provides a useful starting point to achieve optimal balance between the capillary performance and the effective thermal conductivity of advanced wicks for micro heat pipes.

Demonstration of Cancer Cell Migration Using a Novel Microfluidic Device

Migration of cancer cells from the primary organ site via the bloodstream to distant sites is critical to the development of malignant metastasis and is in part determined by soluble host factors in the serum. Conventional Boyden chamber assays to evaluate cell motility require high volumes of reagents and are impractical for high-throughput analysis. We have designed and evaluated a poly-dimethylsiloxane (PDMS) microfluidic device in order to systematically study cancer cell migration. Photolithography and soft lithography processes were used to fabricate the PDMS devices from a negative photoresist (SU-8) mold. The device provides two separate identical chambers that are interconnected by an array of identical narrow channels, 10 μm high, 25 μm wide, and 1000 μm long. One chamber is seeded with cancer cells whose migration characteristics are to be evaluated, while the other chamber contains media with chemoattractants toward which the cancer cells migrate. In this microfluidic chamber model, the migration of cancer cells within and across the microfluidic channels over a prescribed time was quantified using time-lapse photographs. The microfluidic chamber is a cost-effective platform that uses small volumes of reagents, can maintain stable chemokine gradients, allow real-time quantitative study of cancer cell migration, and provide information about cellular dynamics and biomechanical analysis. This work demonstrated the utility of the microfluidic device as a platform to study cancer cell migration as well as the potential applications in the identification of specific chemokine agents and development of drugs targeting cell migration.

A New Non-PRM Bumping Process by Electroplating on Si Die for Three Dimensional Packaging

A new bumping process on a Si die by electroplating without a photo-resist-mold (PRM) was assessed for the three dimensional (3D) stacking of Si dice. In this process, solder bumps were deposited selectively onto the surface of a Cu plugged-through silicon-via (TSV) in a Si die. Since lithography related processes to make a PRM for solder bumping were omitted, it can reduce the production time and cost for bumping. The substrate was a Si wafer, and TSVs were produced by deep-ion-reactive-etching (DRIE). As an insulation layer, SiO2 was formed by high-density-plasma-chemical-vapor-deposition (HDPCVD) or wet oxidation method. A Ti adhesion and an Au seed layers were deposited by sputtering. Cu was plugged into the vias by pulsed direct-current (DC) electroplating. The backside of the Si wafer was ground by chemicalmechanical-polishing (CMP). Sn bumps were electroplated on the Cu plugged vias by a current supplied through a Cu-overplated layer (COL) on the vias surface. As experimental results, wet oxidation provided a uniform SiO2 thickness through the via depth, whereas the SiO2 thickness by HDPCVD decreased with the via depth. The Ti and Au thicknesses also decreased along the via depth. In electroplating for Cu plugging,

Direct molding of dry adhesives with anisotropic peel strength using an offset lift-off photoresist mold

We demonstrate for the first time a wafer scale, directly molded anisotropic dry adhesive made of silicone that can be produced in a two-mask process. We demonstrate that the peel strength of this adhesive is dependent on the amount of overhang of a thin flexible cap on the top of each fiber. By precisely placing the center of this cap offset to the center of the supporting post, the peel strength of the adhesive can be altered when pulled off in different directions.

Fabrication of three-dimensional microstructure by nickel plating and photolithography

A combination of plating technology and photolithography has long been applied for the preparation of minute metallic structures, for example the metal stamper for replication of master discs. This replication technique exhibits a highly precise traceability even with shapes in submicrometre order. Microelectro mechanical systems (MEMS) are expected to progress and the field requires minute metal components. In particular, three-dimensional metal components are greatly in demand. In the conventional process, however, a two-dimensional developed image of thick photoresist is formed to increase the height of the structure. In other words, it allows industry to merely form so called '2·5-dimensional (pseudo 3D) structure'. Consequently, it is difficult and/or impossible to fabricate a metal structure with variation in the horizontal direction such as overhangs. Recently, the formation method of multilayered photoresist moulds has been reported. This technique enables the formation of the stacked photoresist mould having a structure formed with different images for the 1st and 2nd layers. In this study, formation of a micrometallic structure by combination of the double layered photoresist mould and plating method is reported.

Fabrication of a poly(dimethylsiloxane) membrane with well-defined through-holes for three-dimensional microfluidic networks

We report a simple method for the fabrication of a poly(dimethylsiloxane) (PDMS) membrane with through-holes by blowing a residual prepolymer away from a photoresist (PR)-patterned Si wafer. The fabrication method for the perforated polymer membrane is crucial to achieve both complicated three-dimensional microfluidic devices and polymer sieve sheets. This method has several advantages over the previous methods in that we can repeatedly make the well-defined holes on the PDMS membranes even if the excess prepolymer remains on the PR mold after spincoating at a relatively low rpm. In addition, the desired pattern can be selectively perforated from the whole wafer even if the mold is fabricated by single-step lithography.

Lost Mold Rapid Infiltration Forming of Mesoscale Ceramics: Part 1, Fabrication

Free-standing mesoscale (340 mum x 30 mum x 20 mum) bend bars with an aspect ratio over 15:1 and an edge resolution as fine as a single grain diameter ( approximately 400 nm) have been fabricated in large numbers on refractory ceramic substrates by combining a novel powder processing approach with photoresist molds and an innovative lost-mold thermal process. The colloid and interfacial chemistry of the nanoscale zirconia particulates has been modeled and used to prepare highly concentrated suspensions. Engineering solutions to challenges in mold fabrication and casting have yielded free-standing, crack-free parts. Molds are fabricated using high-aspect-ratio photoresist on ceramic substrates. Green parts are formed using a rapid infiltration method that exploits the shear thinning behavior of the highly concentrated ceramic suspension in combination with gelcasting. The mold is thermally decomposed and the parts are sintered in place on the ceramic substrate. Chemically aided attrition milling disperses and concentrates the as-received 3Y-TZP powder to produce a dense, fine-grained sintered microstructure. Initial three-point bend strength data are comparable to that of conventional zirconia; however, geometric irregularities (e.g., trapezoidal cross sections) are present in this first generation and are discussed with respect to the distribution of bend strength.

Densely-Packed Microbowl Array with Balanced Dielectrophoretic Forces for Single-Cell Microarray

AbstractIn this paper, we demonstrate a perfectly-ordered microbowl array with balanced dielectrophoresis (DEP) for a high-throughput single-cell analysis. In order to fabricate well-ordered microbowl array in a large area, we utilized three-dimensional diffuser lithography for photoresist mold and nickel electroplating technique for final microbowl structures on a silicon substrate. Single microbowl has six sharp apexes surrounding the microbowl perimeter. Each microbowl has a diameter of 10 μm, and a height of 9 μm, which can be controllable by patterns on mask and lithography conditions. To investigate feasibility for application to the microbowl array as a single-cell microarray, we used latex beads of 6.4 μm in an average diameter to be captured by dielectrophoretic force. The nickel microbowl array densely packed with a hexagonal geometry played as a bottom electrode, and an ITO-coated glass covered the nickel microbowl array as a top electrode while keeping a uniform gap between two electrodes. After injecting solution containing latex beads through the gap, we applied an AC signal (2 VPP, 1 MHz) between two electrodes to induce high electric field near the sharp apexes of the single microbowl. A negative DEP trap is formed at the center of the single microbowl with balanced DEP force from the six apexes. The experimental result shows that injected latex beads had been successfully and uniformly aligned and trapped at the microbowl array sustained by negative DEP.

Grinding characteristics of micro-abrasive pellet tools fabricated by a LIGA-like process

The purpose of this paper was to investigate the wearing and grinding characteristics of the micro-abrasive pellet tools with 4–6 μm diamond particles fabricated by a LIGA-like process that has micro-lithography with photoresist mold and nickel/diamond composite electroforming. The results showed that when the micro-pellet tool containing partial resist joint with a root on the substrate was designed and fabricated, the tool against alumina sandpaper in wear test showed lesser amount of micro-pulled-out pellets than the tools with flat joint type, which displayed the tool to have better adhesion strength. In addition, when the micro-diamond tools were used to grind silicon wafers, the surface appearance of wafers showed ductile behavior. The surface roughness of wafers ground with increased pellet tool rotation speed became better and R a=0.05 μm was achieved.