Philip J. Coane

Polymer-based variable focal length microlens system

A novel polymer-based fluid-actuated variable focal length microlens system with a wide field-of-view (FOV) and large numerical aperture is designed and fabricated using standard photolithographic and silicon micromachining techniques. A flexible polydimethylsiloxane (PDMS) membrane is used to form the lens surface and is actuated by fluidic pressure applied by an external syringe pump. This lens system is capable of working in dual mode, forming either a double convex (DCX) or a double concave (DCV) lens. The relationship between the focal length (f) and FOV of the fabricated dynamic lens system as a function of the volume of the fluid pumped into or out of the lens chamber is investigated. The focal length of the dynamic lens system demonstrated in this paper could be tuned in the range of 75.9 to 3.1 mm and −75.9 to −3.3 mm for the DCX and DCV lens configurations, respectively. The FOV for this lens system was found to be in the range of 0.12 to 61° for DCX lens and 7 to 69° for DCV lens. The smallest F-number (f/#) that could be achieved using this dynamic lens is 0.61, which corresponds to the numerical aperture value of 0.64.

Micromilling development and applications for microfabrication

Abstract In conventional machining, milling is the most versatile of the cutting processes. Micromechanical milling has also been shown to be a very versatile and repid method for the removal of material and the creation of microstructures. These microstructures range form direct fabrication of molds in polymethyl methacrylate (PMMA) to direct fabrication of x-ray lithography masks using a machinable carrier and one of several metallic absorbers, or various combinations of absorbers to better suit the machining environment. The micromilling tools are commercially available in diameters larger than 50 micrometers and custom-fabricated tools 22 micrometers in diameter are made at the Institute for Micromanufacturing (IfM). The custom-fabricated tools are made using the focused ion beam process and the resulting microstructures are machined on a very high precision, custom-built milling machine. The focused ion beam process has also been used to fabricate very small probe tips for biomedical use and microscalpels with extremely sharp cutting edges. These devices are currently under study and development for research applications.

Direct fabrication of deep x-ray lithography masks by micromechanical milling

Micromechanical milling has been shown to be a rapid and direct method for fabricating masks for deep x-ray lithography with lateral absorber features down to 10 micrometers. Conventional x-ray mask fabrication requires complex processes and equipment, and a faster and simpler method using micromechanical milling was investigated for larger microstructures for mesoscale applications. Micromilled x-ray masks consisting of a layered architecture of gold and titanium films on graphite yielded exposures in PMMA with accuracy and repeatability suitable for prototype purposes. A method for compensating milling tool radial runout was adapted, and the average accuracy of mask absorber features was 0.65 micrometers, with an average standard deviation of 0.55 micrometers. The milling process leaves some absorber burrs, and the absorber wall is tapered, which introduces an additional process bias. Mask fabrication by micromilling is fast and, therefore, less costly than conventional mask fabrication processes.

Scum-free patterning of SU-8 resist for electroforming applications

A simple approach is developed to obtain scum-free pattern transfer in SU-8 resist by UV-lithography for electroforming applications. SU-8 is an epoxy-based negative resist used in the fabrication of high-aspect ratio microstructures. SU-8 resist poses considerable processing difficulties and tends to leave organic residues of undeveloped resist on the surface of the exposed metallic seed layer. Scum-free pattern transfer in SU-8 resist is important for the subsequent electroplating process used to fabricate the high-aspect ratio metallic microstructures. Dry plasma etching processes are commonly used to remove the SU-8 residue prior to electroplating. However, these processes are complex and not cost-effective. In this work, it is shown that scum-free SU-8 patterns could be achieved by proper selection of process parameters such as soft-bake temperature, exposure time, post-exposure-bake temperature, developing time and rinsing in solvents. The success of this particular process is due to controlled rinsing of the patterned sample in acetone to remove the resist scum. The results of our method for patterning the SU-8 resist to fabricate nickel microstructures using this mold are reported.

Fabrication of graphite masks for deep and ultradeep x-ray lithography

Masks made from graphite stock material have been demonstrated as a cost-effective and reliable method of fabricating X-ray masks for deep and ultra-deep x-ray lithography (DXRL and UDXRL, respectively). The focus on this research effort was to fabricate masks that were compatible with the requirements for deep and ultra deep X-ray lithography by using UV optical lithography and gold electroforming. The major focus was on the uniform application of a thick resist on a porous graphite substrate. After patterning the resist, gold deposition was performed to build up the absorber structures using pulsed- electroplating. In this paper we will report on the current status of the mask fabrication process and present some preliminary exposure results.

Graphite-based x-ray masks for deep and ultradeep x-ray lithography

The cost-effective fabrication of high-aspect-ratio microstructures using x rays largely depends on the availability and quality of x-ray masks. The architecture of a mask is mainly determined by the photon energy of the synchrotron source, the x-ray flux, and the thickness of the resist. Typically, the mask membrane is made from a low-atomic-number material and can either be a frame-supported, several microns thin membrane (carbon, silicon carbide, silicon nitride, or silicon) or a bulk material (beryllium) with a thickness of up to 1 mm. The absorber pattern is formed from high atomic number materials such as gold, tungsten, or tantalum, and the final pattern geometry can be defined either with additive (electroplating) or subtractive (etching, milling) processes. One approach that is designed to reduce cost and turn-around time is the fabrication of x-ray masks using graphite sheet stock for the mask membrane. Rigid graphite offers unique properties, such as moderate x-ray transmission, relatively low ...

Electroless Deposition of Soft Magnetic CoNiP Thin Films

The ternary CoNiP soft magnetic films were deposited on silicon substrates by the autocatalytic electroless process. The deposition of these magnetic thin films was carried out by using different concentrations of cobalt (Co 2+ ), nickel (Ni 2+ ) and hypophosphite (H 2 PO - 2) ions in the bath, and by maintaining the bath at different pH levels. The composition and the magnetic characteristics of the deposited films were studied. The effects of varying the concentration of both metal ions and nonmetal ion (reducing agent) on the magnetic properties of the films were explored by increasing the concentration of precursor salts of Co 2+ ions from 0.002 to 0.008 M, Ni 2+ ions from 0.004 to 0.02 M, and H 2 PO - 2 ions from 0.02 to 0.25 M. The pH of the bath was varied in the range 7.0-9.0 in steps of 0.5. The magnetic moment and coercivity of the CoNiP films decreased when the concentrations of the metal ion was increased. However, when the pH was increased, the magnetic moment increased with a corresponding reduction in the coercivity values. Maintaining the bath pH within a narrow range of 8.5 to 9.0 was found to be critical for the formation of high quality soft-magnetic films which exhibit large magnetic moments and low coercivity.

Magnetic properties of Ni1−x−yCoxFey films deposited by polyol electroless process

Abstract Electroless deposition using a nonaqueous, polyol process is carried out to produce nickel-rich Ni0.5Co0.5−xFex and cobalt-rich Co0.5Ni0.5−xFex (x=0, 0.1, 0.3, 0.5) ternary alloy films, and investigate the effect of incorporating iron on the morphology and magnetic properties of these two series of films. The plating solution used to deposit these films is prepared by mixing proportional volumes of equimolar metal salts suspended in ethylene glycol. Plating was performed by refluxing the nonaqueous solution at a temperature of 194 °C. The deposited films were characterized by electron microscopy, optical interferometry and X-ray diffraction. In the case of cobalt-rich films (Co0.5Ni0.5−xFex, x=0.0–0.5), a transition in the crystal structure from lower symmetric orthogonal to higher symmetric tetragonal or cubic structures was observed with increasing iron content. There was no such change for the nickel-rich films (Ni0.5Co0.5−xFex, x=0–0.5). The addition of iron was found to increase the surface roughness of both series of films. The magnetic measurements showed excellent soft-magnetic characteristics for as synthesized Co0.5Fe0.1Ni0.4 film with Ms, Hc, Ms⊥ and Hc⊥ values of 725.2 emu/cm3, 28 Oe, 205 emu/g and 176.5 Oe, respectively. The incorporation of iron was found to enhance the soft-magnetic characteristics of the otherwise weak magnetic Ni0.5Co0.5 film.

Fabrication of composite x-ray masks by micromilling

An important aspect for the development of micromanufactured components and systems is to reduce the time and cost required to reach the prototype stage. At present, this development typically spans several years. Any fabrication approach which would reduce the cost and time-to-prototype would allow for the more rapid development of design concepts and the more rapid evolution of the design cycle. Direct fabrication of masks for X-ray lithography, by mechanical micromilling, is one potential avenue for rapid, lower cost development. The key process requirements for the fabrication of a typical X-ray mask involves the selection of both substrate and absorber materials. The substrate must provide a mechanically stable support for the patterned absorber without introducing excessive attenuation of the X- ray flux that ultimately reaches the resist surface. Frame supported, thin membranes (such as SiC, C, Si3N4, Si) are most often used as well as low atomic number bulk materials (Be). The choice of elemental composition and thickness for the absorber will be largely determined by the resist sensitivity and the X-ray wavelength used. Many process steps are required in order to define the final absorber pattern geometry and will generally involve either additive or subtractive processes. Mechanical micromilling techniques may be used with either a single bulk material which serves the dual role of both substrate and absorber or with a composite structure consisting of a thin gold layer deposited on a thick, low atomic number bulk substrate. Single material masks of aluminum and graphite have been investigated. A composite mask of graphite with a thin layer of sputtered gold has also been investigated. The paper will report on the developmental work for both types of masks and will give results for synchrotron X-ray exposure using these masks. Problems associated with using micromilling as an X- ray mask fabrication method will also be presented.

Preliminary results at the ultradeep x-ray lithography beamline at CAMD

The Center for Advanced Micro structures and Devices (CAMD) at Louisiana State University supports one of the strongest programs in synchrotron radiation micro fabrication in the USA and, in particular, in deep x-ray lithography. Synchrotron radiation emitted form CAMDs bending magnets has photon energies in the range extending from the IR to approximately 20 keV. CAMD operates at 1.3 and 1.5 GeV, providing characteristic energies of 1.66 and 2.55 keV, respectively. CAMD bending magnets provide a relatively soft x-ray spectrum that limits the maximal structure height achievable within a reasonable exposure time to approximately 500 micrometers . In order to extend the x-ray spectrum to higher photon energies, a 5 pole 7T superconducting wiggler was inserted in one of the straight sections. A beam line and exposure station designed for ultra deep x-ray lithography was constructed and connected to the wiggler. First exposures into 1 mm and 2 mm thick PMMA resist using a graphite mask with 40 micrometers thick gold absorber has been completed.