Surface contamination on both the tip and the sample complicates tip-sample interaction when operating an AFM in air. In the traditional non-contact mode using small vibration amplitudes, tip-sample spacing is maintained at a few nanometers, and the tip can be captured by the surface due to the capillary force. A popular method that prevents this tip- capture problem is to vibrate the tip at large amplitude, with the tip contacting the surface periodically. With a combined AFM/SEM system, the tips and samples were found to sustain damage by this periodic-contact. To minimize tip-sample damage and achieve maximal lateral resolution, we studied the surface contamination and the tip-sample interaction in air, and discovered a novel working mode producing one nanometer lateral resolution in air. This method uses a cantilever of large enough force constant to avoid the tip being captured, and small vibration amplitudes of only a few nanometers to avoid tip-sample damage. By combining stiff cantilever and small vibration amplitude, the tip can be maintained in the newly discovered 'near contact' region above the sample surface, so tip-sample spacing is minimized and tip sharpness preserved, achieving ultra-high lateral resolution in air. To explain the working mechanisms, we developed a microscopic model of the tip-sample interaction via the surface contamination layers.

Scanning electrostatic force microscopy, along with a subset of this technique, scanning Kelvin probe microscopy, have been used to explore the materials composition and doping of semiconductor surfaces. Moreover, micromachined semiconductor probes are frequently used in SEFM, SKPM and scanning capacitance microscopy instruments in order to probe the nature of generic surfaces. Some work has been done to explore the electromechanical, and electrostatic nature of the probe- surface interaction for SEFM and SKPM. For instance, it has been demonstrated that band pinning at the semiconductor surface, caused by excessively large values of the ac voltage applied between the probe and substrate, creates a false null in an SKPM signal, masking the true nature of the surface. Recently, results of SEFM probes of semiconductor surfaces have been reported, which used large values of the ac voltage applied between the probe and the substrate. In this work, we demonstrate theoretically the effects of both large-signal behavior on the SEFM technique. We also demonstrate the effect of electric field penetration into a semiconductor surface or probe tip on the mechanical response of the probe. The results are compared to measurements, and set in the context of recent work wherein large-signal SEFM techniques are employed.

A new method for tensile testing of thin films is being developed. An electrostatic grip apparatus was designed and implemented to measure the elastic and ultimate tensile properties (Young's modulus, Poisson's ratio and tensile strength) of surface micromachined polysilicon specimens. The tensile specimens are 'dog-bone' shaped ending in a large 'paddle' for electrostatic gripping. The test section of the specimens is 400 micrometers long and with 2 micrometer X 50 micrometer cross section. The method employs Atomic Force Microscope (AFM) or Scanning Tunneling Microscope (STM) acquired surface topologies of deforming specimens to determine (fields of) strains. By way of the method of Digital Image Correlation (DIC), the natural surface roughness features are used as distributed markers. The effect of markers artificially deposited on the surface is examined computationally. Also the significance of other parameters on property measurements, such as surface roughness, has been examined computationally. Initial results obtained using the tensile test apparatus are presented.

A novel concept for the realization of a multifunctional scanning probe designed for simultaneous atomic force microscopy and near-field scanning optical microscopy measurements is described. It is based on micromachining and thin film technology and includes the fabrication of a cantilever, an integrated optical waveguide, an aperture probe tip, and the integration of all components into the complete sensor. Key processes are the fabrication of the probe providing a sharp tip together with a small optical aperture and the coupling of light from the integrated optical waveguide into the probe tip. The aperture probe consists of a transparent silicon nitride cone covered with aluminum except for the sharp cone tip thus forming a circular aperture around the protruding tip apex. In order to couple light from the waveguide into the tip a simple structure has been developed and optimized using numerical simulation procedures for the electromagnetic field distribution in the coupling structure. The complete sensor is fabricated in a reliable batch process and experimental evidence for the validity of the coupling concept is given.

In recent years with the development of MEMS, various microactuators have been developed. In general, the smaller the actuator, the smaller its force becomes, but measurement of such small force is difficult and dependable instruments are not currently available. We developed a probe type sensor to measure very small forces using a semiconductor shear strain gauge of a cantilever type sensor. A highly sensitive, stable probe was created by using a good raw material, single crystal silicon, and by forming both the stress concentration part and the strain sensor on the same silicon crystal. We designed the probe using the finite element method, and invented a structure in which a very small force effectively generates strain on the sensor. We also developed a semiconductor micromachining process including an inducted coupled plasma deep trench etching method to manufacture the probe, and built a calibrator for the probe based on an electronic balance. In preliminary experiments, we successfully measured the force with as small as 1 mN resolution, precisely as designed by FEM. In future, we shall develop a probe with 1 (mu) N resolution.

Different techniques based on the atomic force microscope (AFM) have been developed in the last few years for the electrical characterization of semiconductor devices. The quality of these measurements strongly depends on the tip which should not only have a small radius of curvature but also a high electrical conductivity. Therefore, the choice of metal as tip material is obvious. We have developed a process scheme for the fabrication of pyramidal metal tips which are integrated into a silicon cantilever. This paper discusses this process in detail and shows how the transition was made from prototyping to batch friction using standard 150 mm silicon wafer technology. Results are presented concerning the application of such probes for two-dimensional carrier profiling of InP and silicon structures using scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM). A novel tip configuration called tip-on-tip has also been developed. This concept looks promising for future applications. We demonstrate how such a tip-on-tip configuration can be realized.

Microelectromechanical systems (MEMS) is a relatively new field dealing with the design and manufacturing of miniaturized devices (micromachines) using techniques adapted mainly from the integrated-circuit industry. Micromachine fabrication comprises the growth, deposition, and selective removal of thin films. Early indications suggest that although significant opportunities exist for MEMS, there are several obstacles preventing the evolution of micromachines from the research environment to the application world. Among challenging problems is the identification and analysis of microscopic processes encountered at MEMS interfaces during fabrication and operation that often render the devices dysfunctional. The development of high adhesion forces at micromachine interfaces during release-etch drying and/or operation often leads to permanent adhesion of contacting surfaces, a phenomenon referred to as stiction, hence affecting the micromachine yield and operation life. In this publication, an appraisal of the important issues involved in micromachine stiction is presented, accompanied by an assessment of the contribution of various surface forces (e.g., van der Waals, capillary, electrostatic, and asperity deformation forces) to the total stiction force arising at MEMS interfaces. The critical micromachine stiffness required to overcome stiction is interpreted in terms of the composite surface roughness and material properties. In addition, various surface modification techniques compatible with standard surface micromachining, such as surface roughening (texturing) and deposition of low surface energy films (e.g., diamond-like carbon coatings and self-assembled monolayer films) are presented, and their efficacy to reduce etch- release and in-use micromachine stiction is discussed in light of experimental and analytical results.

Raman spectroscopy is used as a non-contact method in measuring stresses at the surface of a crystalline structure or the crystalline-coated surface of an amorphous structure. The stress measurement capability is based on the relative frequency shift of Raman spectra when the crystal lattice is strained. The Raman spectroscopy has a resolution on the order of a few micrometer (micrometers ) which may be used to probe the local non-uniform stress distribution and thus address the material nonhomogeneity. This paper presents the Raman secular equation for general and cubic crystal systems and discusses the stress field effects to Raman frequency shifts and polarization. Experimental testing will include the calibration of the Raman signal versus mechanically applied stresses using single crystal strips, poly-silicon coatings deposited on different specimen configurations, and the stress measurements on a frequently used MEMS structure, cantilever beam, subject to electrostatic forces. Correlation of the experimental results with the analytical prediction will be addressed.

This paper presents the results and conclusions from tensile tests performed on four lots of microtensile specimens produced by the LIGA method. The specimens tested are 3 millimeters long, 0.2 millimeters wide and 0.2 millimeters thick. The specimen is held in specially designed grips, and friction is eliminated by the use of a linear air bearing in the load train. Strain is measured by laser interferometry between two Vickers microhardness indentations placed 0.2 millimeters apart in the center of the specimen. Two sets of pure nickel specimens from two different Microelectronics Center of North Carolina (MCNC) LIGA Multi-User MEMS Process (LIGAMUMPs) runs were tested along with one set of pure nickel specimens from the HI-MEMS Alliance. In addition, four tests were conducted on a 0.03 millimeter thick nickel-iron alloy with a target composition of 78% Ni, 22% Fe. One set of LIGAMUMPs specimens had an average Young's modulus of 181 GPa, which was almost exactly the same as measured on the HI-MEMS material. However, the other set showed a much lower modulus of 158 GPa. Modulus measurements of the nickel-iron alloy were inconclusive. The two LIGAMUMPs materials had yield and ultimate strengths on the order of 330 and 530 MPa respectively, while the HI-MEMS material was stronger at 420 MPa and 600 MPa. The nickel-iron alloy was considerably stronger, with a yield strength of 1.8 GPa and an ultimate strength of 2.4 GPa.

A separate-target sputtering process has been applied to fabrication of TiNi shape memory alloy (SMA) for microelectromechanical systems (MEMS). This process employs separate Ti and Ni sputtering targets and independently controllable RF power source for each target. Since RF power ratio can change the composition of the films as required, the shape memory properties can be better controlled. This process would enable efficient batch production of MEMS devices and components similarly to the LSI batch process. This process is expected to be a more appropriate method for mass production than other techniques such as machining from bulk SMA sheets or wires and deposition of SMA films from a single TiNi alloy target. The TiNi SMA films in the present study were fabricated by co-sputtering from two separate targets and vacuum-annealing for crystallization. The phase transformation behavior of the crystallized films was observed by differential scanning calorimetry (DSC) and x-ray diffractometry (XRD). DSC showed exothermic/endothermic peaks corresponding to phase transformations: martensitic transformation around at 345 K and reverse martensitic transformation around at 365 K. The transformations of crystal structure were also examined by temperature-controlled XRD analysis. The formed films were confirmed to show shape memory effect (SME) by these results.

An investigation of the influence of the process parameters pressure and flow on the room-temperature deposition of electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) of silicon nitride has been performed. The suitability of these films for micromachining applications has been studied, in particular for the use with KOH:isopropyl:H₂O etching solutions. The deposition rate and the effect of process parameters on the physical properties of the films, as-deposited and after KOH etching, were investigated. Buffered HF etch rate, refractive index, and the infrared absorption spectra, especially the Si-N peak absorption wavenumber, were studied. We have found that films that withstand KOH etching with little modification of their physical properties can be obtained at room-temperature for depositions with low flows and low process pressures.

In this research, electroplated magnetically isotropic and anisotropic soft alloys and screen-printed soft ferrites applicable to micromachined micromagnetic devices are fabricated and characterized using in-situ measurement techniques. Appropriate magnetic materials and deposition methods, such as electroplating and screen-printing techniques, are examined and material test structures are fabricated. Following material characterization, micromachined inductors with three-dimensional structure are fabricated to determine the usefulness of the magnetic materials and deposition methods. The micromachined inductor is a key component and geometry for realizing micromagnetic devices such as amplifiers, filters, sensors, and actuators. Three different material types are studied in this work. Electroplated magnetically isotropic soft alloys, permalloy (Ni80Fe20), orthonol (Ni50Fe50), and amorphous cobalt-iron- copper (CoFeCu) alloys, are studied, followed by electroplated magnetically anisotropic soft alloys of permalloy (Ni80Fe20) and supermalloy (NiFeMo), which have magnetically easy and hard axes. Finally, screen-printed polymers filled with soft ferrite (NiZn and MnZn) powders, are fabricated and characterized.

Photopolymerization initiated by the simultaneous absorption of two photons is unique in its ability to produce complex three-dimensional (3D) structures from a single, thick photopolymer film. Strong 3D confinement of the polymerization process is not possible in other polymer microfabrication techniques such as LIGA, rapid prototyping, and conventional photoresist technology. Two-photon polymerization also permits the fabrication of 3D structures and the definition of lithographic features on non-planar surfaces. We have developed a wide array of chromophores which hold great promise for 3D microfabrication, as well as other applications, such as two-photon fluorescence imaging and 3D optical data storage. These materials are based on a donor- (pi) -donor, donor-acceptor-donor, or acceptor-donor-acceptor structural motif. The magnitude of the two-photon absorption cross-section, (delta) , and the position of the two-photon absorption maximum, (lambda) ⁽²)_max, can be controlled by varying the length of the conjugated bridge and by varying the strength of the donor/acceptor groups. In this way, chromophores have been developed which exhibit strong two- photon absorption in the range of 500 - 975 nm, in some cases as high as 4400 X 10^-50 cm⁴ s/photon-molecule. In the case of donor-(pi) -donor structures, quantum-chemical calculations show that the large absorption cross-sections arise from the symmetric re-distribution of charge from the donor end-groups to the conjugated bridge, resulting in an electronic excited-state which is more delocalized than the ground state. For many of these molecules, two-photon excitation populates a state which is sufficiently reducing that a charge transfer reaction can occur with acrylate monomers. The efficiency of these processes can be described using Marcus theory. Under suitable conditions, such reactions can induce radical polymerization of acrylate resins. Polymerization rates have been measured, and we show that these two-photon chromophores display increased sensitivity and recording speed over conventional photoinitiators. Complex 3D structures can be fabricated in acrylate films doped with these chromophores using tightly focused near-infrared femtosecond laser pulses. A 3D periodic array of polymeric columns has been produced for use in photonic bandgap applications. Tapered waveguide structures for interconnecting disparate-sized optical components have been constructed. More traditional MEMS structures, such as cantilevers, have also been produced. Such structures may be useful for organic vapor sensors. The two-photon photopolymerization process can be extended to other material systems, such as metallic, ceramic, and composite materials, by templating the photopolymer structures.

The development of the future-generation magnetic recording heads is based on availability of high resolution and high- aspect ratio lithography. A key step in the magnetic head fabrication process is the formation of high-aspect ratio trenches in photoresist that are subsequently used as a plating mask for the magnetic read-write heads. Currently, 1.2 to 1.5 micrometer wide and 10 micrometer tall trenches in the resist are formed using optical lithography. In the near future, more than 6 micrometer tall resist patterns with trenches of 0.5 micrometer or smaller will be required. A study of using X-ray lithography to generate patterns suitable for future-generation magnetic recording heads was undertaken at the Center for X-ray Lithography at UW-Madison. It was successfully demonstrated that 0.8 micrometer trenches in 15 micrometer thick resist and 0.4 micrometer trenches in 6 micrometer thick resist can be formed. The main steps in the fabrication of the high-aspect ratio resist patterns included (1) production of an initial (master) mask using e-beam lithography, (2) high-contrast replicated (final) X-ray mask manufacturing using X-ray replication process, and (3) actual patterning of thick PMMA resist using the final masks. Both X- ray masks were formed on a 2 micrometer thick silicon-nitride membranes as mask carrier. APEX-E resist 0.5 micrometer thick was used for e-beam writing, and 2 micrometer thick PMMA was utilized for the replicated mask. The absorber was electroplated gold: 0.4 micrometer thick for the master and 1.5 micrometer thick for the final mask. Details are given for 6 micrometer and 15 micrometer thick crack-free PMMA resist formation and characterization, exposure and development conditions.

1.5 micrometer thick polycrystalline diamond film was deposited using microwave plasma chemical vapor deposition (MPCVD) as x-ray mask membrane with 0.1 approximately 0.25 micrometer seeding. The temperature is controlled between 820 to 830 degree Celsius and the ratios of CH₄/H₂ gas mixtures are varied for the quality and stress of the diamond film. The optical properties and radiation damage of the membrane will be demonstrated. Low tensile stress diamond membrane has been formed with backside KOH etching. Surface morphology was monitored by the AFM and the quality of the diamond film was measured by the Raman spectroscopy.

Pulsed laser photoablation of polymers is a rapid prototyping technique that has applications for the manufacturing of high aspect ratio microparts. To enhance the manufacturing capability of the process, it is necessary to develop mathematical models to predict the scanning pattern of the pulsed laser on the material surface in order to etch a microstructure with a pre-specified geometry. In this study, we consider a model that predicts the number of pulses at each pixel of the surface to be scanned in order to produce a microstructure of a given geometry. In predicting the number of pulses at a pixel, the model takes into account the etch depth per pulse, the laser intensity distribution, and the geometry of the microstructure.

Microelectronic failure analysis (FA) has been an integral part of the development of state-of-the-art integrated circuits. FA of MicroElectroMechanical Systems (MEMS) is moving from its infancy to assume an important role in the successful design, fabrication, performance and reliability analysis for this new technology. In previous work, we focused on the application of several techniques developed for integrated circuit analysis to an earlier version of a surface micromachined microengine fabricated at Sandia. Recently, we have identified important new failure modes in binary counters that incorporate a newer design of the microengine, using a subset of integrated circuit failure analysis techniques including optical microscopy, focused ion beam (FIB) techniques, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The primary failure mode we have identified is directly related to visible wear on bearing surfaces. In this paper, we describe in detail the characteristics of the failure modes in binary counters. We also compare the failure characteristics with those of an earlier version of the microengine.

An important performance criterion for practicable microactuators is the value of output torque. For the torque to be measured is very small, the influence of frictional force and other factors on testing are difficult avoided. So a new noncontact and direct experimental method was proposed, the basic theory and a simple and low-cost design of the measuring instrument is described in this paper. The testing range of shaft torque is from 10^-4Nm to 10^-7.

This paper describes the new diaphragm structure using SiNx/SOG for a micro flow sensor. Its purpose is the measurement of a correct flow rate of various gases or liquids. The proposed sensor consists of sputtered SiNx/Pt/SiNx thin film diaphragm structure, which reduces thermal capacitance. The platinum film resistors detect a change of the temperature distribution on the membrane caused by forced convection. In sensors having these film structures, sputtering methods make it much easier than other film fabrication methods, such as CVD (Chemical Vapor Deposition) to control the internal stress of SiNx film in order to stretch the diaphragm tight. However, the reliability is often spoiled by the column structue of the sputtered SiNx protective film which grows on the platinum film resistors. In order to prevent the growth of the column structure, Spin-On Glass (SOG) film is introduced between platinum film resistors and sputtered SiNx protective film. Because the SOG film is an amorphous structure. SiNx films on SOG films are dense. Additionally, SOG films reduce the step height of platinum film resistors, so the step-coverage of sputtered SiNx protective film is improved.

The reliability of microengines is a function of the design of the mechanical linkage used to connect the electrostatic actuator to the drive. We have completed a series of reliability stress tests on surface micromachined microengines driving an inertial load. In these experiments, we used microengines that had pin mechanisms with guides connecting the drive arms to the electrostatic actuators. Comparing this data to previous results using flexure linkages revealed that the pin linkage design was less reliable. The devices were stressed to failure at eight frequencies, both above and below the measured resonance frequency of the microengine. Significant amounts of wear debris were observed both around the hub and pin joint of the drive gear. Additionally, wear tracks were observed in the area where the moving shuttle rubbed against the guides of the pin linkage. At each frequency, we analyzed the statistical data yielding a lifetime (t₅₀) for median cycles to failure and (sigma) , the shape parameter of the distribution. A model was developed to describe the failure data based on fundamental wear mechanisms and forces exhibited in mechanical resonant systems. The comparison to the model will be discussed.

Low-cost, micromachined inertial measurement sensors have been steadily emerging into the commercial marketplace. Some of these sensors were evaluated through ground and flight tests for their insertion potential into military applications. High-g shock test results suggest that some of these sensors are rugged enough for both low-g and high-g launch survivability. A description of dynamic loading on the sensors and techniques used to mitigate failures is presented. Artillery projectiles and rockets, instrumented with 'automobile grade: microelectromechanical (MEMS) accelerometers and telemetry units, have recently been flight tested with good success. Analyses of the accelerometer data show good comparison to radar-based acceleration measurements and 6-degree-of-freedom trajectory simulations. This paper presents the flight and ground test results and describe the challenges for using these strapdown devices on rolling projectiles.

The microtribology phenomena on the micro contact (or slide) surface, where the effects of surface forces are more significant than those of gravity, is very different with the conventional machine. The friction force that works on a friction face of a microsystems is significantly high relative to the size of the machine, the fluid lubrication in the conventional size mechanical parts cannot reduce the friction force on the microsystems, the solid lubrication (self- lubrication) should be applied to reduce the friction force. In this paper, the solid lubrication MoS₂ was studied. MoS₂ is embedded into the Ni structure in electroforming process. The results show that MoS₂ can be used as the solid lubrication in the microsystems to reduce the friction force and enhance the hardness of microsystem.

We describe the design, modeling, fabrication and initial testing of a new test structure for friction measurement in MEMS. The device consists of a cantilevered forked beam and a friction pad attached via a hinge. Compared to previous test structures, the proposed structure can measure friction over much larger pressure ranges, yet occupies one hundred times less area. The placement of the hinge is crucial to obtaining a well-known and constant pressure distribution in the device. Static deflections on the device were measured and modeled numerically. Preliminary results indicate that friction pad slip is sensitive to friction pad normal force.

Deep X-ray lithography with synchrotron radiation (DXRL) represents the technological core of the LIGA technique, which is a modem microfabrication technology facilitating the high volume production of micro products from a huge variety of materials. Since several applications make use of the high structure accuracy obtained in the primary lithography process, the demands of a detailed investigation of structure accuracy limiting aspects came to rise. Therefore, thorough theoretical and experimental research has been undertaken in order to understand the different radiation effects influencing the shape of the side walls and the lateral resolution to be obtained. Physical effects like diffraction, divergence of the synchrotron radiation beam, photo and Auger electrons, fluorescence and scattering have been calculated and are condensed in a computer code. The calculation results are discussed in detail with respect to LIGA mask production by x-ray lithography as well as for deep x-ray lithography applications. The model can be partially extended to new irradiation techniques like tilted and rotated exposures. Different absorber gradients due to various tilt angles have to be taken into account and the resulting dose contour lines resulting from inclined irradiations are compared with experimental data. In order to enhance the normal shadow printing process and to realize shaping in the third dimension, previous studies used the aligned multiple exposure technique realizing step like structures. We will discuss a novel approach using 500 m thick Beryllium mask blanks with free standing absorber structures (gold) on open windows for alignment purposes. First results show an overlay accuracy of about 0.4 tm using an internal alignment system installed in a DEX 2 JENOPTIK exposure apparatus.

PMMA has been the primary resist used in synchrotron exposures for micro-machined parts fabricated by the LIGA process. Because development of this resist directly influences both tolerances and surface finish of completed LIGA structures, it is important to have a good quantitative understanding of PMMA development as a function of the absorbed dose, as well as both the exposure and development conditions. The various synchrotron sources used for LIGA fabrication vary widely in beam energy and flux, and these variations would be expected to influence development rates. Here we present a simple method to measure PMMA development rate over a moderate range of doses using only a single exposure at the synchrotron source. By employing several exposures, this method allows ready determination of development rates over a wide range of exposure and development conditions. Results are presented for the kinetics of PMMA development over a range of development temperatures, absorbed doses, dose rates and sample ages for exposures performed at three major x-ray sources in the United States.

Deep x-ray lithography/LIGA has proven to be a well established framework of x-ray based technologies for the fabrication of microstructures and pseudo three-dimensional objects. Inherently, x-ray lithography/LIGA is not fully three-dimensional because of the principle of simple shadow printing onto resists of constant thickness. Thus, it would be impossible to obtain 3D spheres, but series of stacked monolithic 2D cylinders. Hence, until recently, LIGA was mainly concerned with simple uni-level (1D) monolithic structures, using optically opaque mask-membranes like Be, Si or Ti with grown-on Au absorbers. In the course for mastering pseudo three-dimensional microstructures like micro-coils or electromagnetic applications, an alignment in between the lithographic steps becomes necessary which requires optically transparent membrane materials, if optical alignment is chosen. Diamond or SiC membranes are the actual suitable materials for such purposes, but their pricing and/or process robustness inhibit their frequent use in simple projects. We would like to report on a new promising material: a glued-on thin glass membrane. The advantages are incomparably lower costs compared to Diamond or SiC technologies, a considerable ease of fabrication, handling, quite favorable mechanical/optical properties, sufficient for lithographic purposes and multi-level deep x-ray lithography/LIGA activities.

The use of hard X-ray energies for ultra-deep X-ray lithography requires a thorough re-investigation of all issues associated with the LIGA technology materials issues and processes, in particular for the manufacture of high-energy-X- ray masks. Calculations were performed to compare various mask blanks in particular thick Kapton^R and thinned silicon blanks. Absorber pattern formation schemes have been investigated using UV contact printing or X-ray lithography with SU8 photoresist. SU8 photoresist also offers an improved X-ray sensitivity over PMMA resist. Resist patterns over 500 micron deep with aspect ratio over 10 and vertical sidewalls were achieved in SU-8, allowing the use of medium energy range X-rays to obtain high quality patterns of much greater resist thickness.

The (mu) SET research group at LSU is developing the three-step LIGA process to inexpensively manufacture high aspect ratio microstructure (HARMs). The first two steps of the process (lithography and electroplating) produce a metallic mold insert that is used as a template for molding microstructure. This paper focuses on injection molding of thermoplastics to produce surfaces covered with HARMs hundreds of micrometers in height, tens of micrometers in width, and separated by gaps on the order of tens of micrometers. Injecting plastic into the narrow, high aspect ratio gaps existing in the HARMs mold inserts (micromolding) offers a set of challenges different from classical injection molding of larger scale parts. This paper provides results of a series of injection molding experiments using a commercially available injection molding machine. Replication of the HARMs was achieved by increasing the injection speed, elevating the tool temperature, and venting the mold cavity. Electron microscopy was used to investigate and assess the molding results.

There is a growing interest in using optical steppers for Micromachining and Microfabrication (MEMS) applications due to the tighter overlay and improved critical dimension (CD) control possible with these lithography tools versus a contact printer or full wafer scanner. MEMS applications frequently require the use of ultra-thick photoresists which can easily exceed fifty microns. Extremely large structure heights and high aspect ratios are often required for micro- electrodeposition of mechanical components such as coils, cantilevers and valves. A stepper has an additional advantage with these structures since the focus can be adjusted at various levels into a thick photoresist, which will result in improved wall angles and enhanced aspect ratios. The patterning of high aspect ratio structures in these ultra- thick photoresist films is extremely challenging. The aspect ratios easily exceed those encountered in submicron lithography for standard integrated circuit (IC) manufacturing. In addition, the specific photoresist optical properties and develop characteristics degrade the CD control for these ultra-thick films. The bulk absorption effect of the photoresist reduces the effective dose at the bottom of the film. This effect is exacerbated by the isotropic wet development process, which produces sloped profiles. Unlike thin photoresist for IC manufacturing, lithography modeling and characterization tools are not available for ultra-thick photoresist films. For this study the performance of several commercially available positive and negative ultra-thick photoresists is examined at a thickness of fifty microns using both high throughput i-line and gh-line lithography systems optimized for thick photoresist processing. The photoresists used in this study are selected to represent the full range of available chemistries available from different suppliers. Basic photoresist characterization techniques created for thin films are applied to the ultra-thick photoresist films. Cross sectional SEM analysis, process linearity and Bossung plots are used to establish relative lithographic capabilities of each photoresist. The trade-offs between the various photoresist chemistries are reviewed and compared with the process requirements for high aspect ratio applications.

We have developed a novel two-step baking process to achieve high-aspect-ratios in UV photolithography with a conventional positive thick photoresist. We newly report high-aspect-ratio (greater than 10:1) results in a single coated 91 micrometer- thick photoresist AZ9262, which was introduced Hoechst at SPIE in 1996. From extensive experiments, we improved the aspect ratio by minimum exposure, diluted development, reabsorption of sufficient water before exposure, and especially by extended and effective soft bake in two steps. In the optimum two-step baking, first the baking is performed at an intermediate temperature in a forced convection oven for hours to evaporate large amounts of solvent. Second, the photoresist is heat-treated at an elevated temperature on an air-gapped hotplate with cover for minutes to enhance aspect ratios. The reason for this improvement has been studied based on the photochemical process of the DNQ/novolac-type positive photoresist. Using this two-step baking, we have obtained lines of 4.4 micrometer-wide bottom in a single coated 91 micrometer-thick photoresist (aspect ratio: 20). The line width in the mask was 8.9 micrometer, and hence 2.2 micrometer undercut was observed.

For the inspection and measurement of microstructures small accurate three-dimensional coordinate measuring machines are needed. Typical measurement volumes are 10 mm by 10 mm by 3 mm and the desired 3D-measurement uncertainty is 0.1 micrometer. Up to now only optical coordinate measuring machines (CMM) offer the necessary lateral measurement ranges. But optical CMMs are restricted to two-dimensional measurements and moreover the aimed uncertainty has not been achieved yet. Since a few years new optical techniques are available which are able to measure nearly three-dimensionally (scanning white light, fringe projection, confocal microscopy, photogrammetry). In order to use these instruments and to specify their measurement uncertainty, calibration of these instruments is necessary. The calibration of the three measurement axes is divided into calibration of the lateral axes and calibration of the vertical axis. The contribution focuses on the development of new depth setting standards (1 micrometer - 1 milimeter) and their traceability.

High aspect-ratio microposts of bismuth-telluride alloy with a height of up to 750 micrometer and a diameter of 150 micrometer have been fabricated with the LIGA technique. This work is the part of an on-going research effort to develop a microprobe based on Peltier effect for highly localized temperature manipulation on the microscale. Bismuth-telluride alloys were electrodeposited galvanostatically on a titanium substrate using an acidic solution containing Bi³⁺ and HTeO₂^- ions in 1 mol dm^-3 nitric acid (pH equals 0). The Bi-Te alloy microposts were found to be monophasic, exhibit a polycrystalline structure, demonstrate excellent adhesion on the substrate and with good mechanical strength. The chemical composition of the microposts was dependent on the electrolyte composition of deposition bath and the current density used in the electroplating; by controlling these two factors either p- or n-type Bi-Te alloy microposts may be produced. This research demonstrates that the microfabrication of Peltier effect probes is feasible.

High-aspect-ratio microstructures (HARMs) have a variety of potential applications in heat transfer, fluid mechanics, catalysts and other microelectromechanical systems (MEMS). The aim of this work is to demonstrate the feasibility to fabricate high performance particulate metal-matrix composite and intermetallic micromechanical structures using the LIGA process. Well-defined functionally graded Ni-Al₂O₃ and Ni-Al high-aspect-ratio microposts were electroformed into lithographically patterned PMMA holes from a nickel sulfamate bath containing submicron alumina and a diluted Watts bath containing microsized aluminum particles, respectively. SEM image analysis showed that the volume fraction of the alumina reached up to around 30% in the Ni-Al₂O₃ deposit. The Vickers microhardness of these composites is in the range of 418 through 545, which is higher than those of nickel microstructures from a similar particle-free bath and other Ni-based electrodeposits. In the work on Ni-Al electroplating, a newly developed diluted Watts bath was used to codeposit micron-sized aluminum particles. The intermetallic compound Ni₃Al was formed by the reaction of nickel matrices and aluminum particles through subsequent annealing at 630 degrees Celsius. WDS and XRD analyses confirmed that the annealed coating is a two-phase (Ni-Ni₃Al) composite. The maximum aluminum volume fraction reached 19% at a cathode current density of 12 mA cm^-2, and the Vickers microhardness of the as-deposited coatings is in the range 392 - 515 depending on the amount of aluminum incorporated.

An effective electrochemical approach for the preparation of tips suitable for in-situ scanning tunneling microscopy (STM) studies in aqueous solutions is presented. An insulting polymer film has been applied to all except the very end of electrochemically etched platinum-iridium (Pt-Ir) STM tips using anodic electrophoretic deposition of paint (EDP). EDP- insulated Pt-Ir STM tips allowed consistently to image the atomic structure of highly oriented pyrographite (HOPG) in electrolytic solutions, and to observe the electrodeposition of copper crystallites along monatomic steps in the surface of single-crystalline Au (111) electrodes. The insulation of STM tips by anodic EDP has the significant advantages of great simplicity and short processing time, important considerations for those who work with in-situ STM on a daily basis.

We developed a useful method to obtain multilevel microstructures simply by single-step 3D photolithography followed by single-step electroplating. By varying UV exposure depth with multiple photomasks in a single-coated conventional thick photoresist, we form multilevel photoresist molds in a single lithography step. After the 3D mold patterning, metal electroplating is performed on it until 3D metallic microstructures are obtained. The critical issue in this process, the exposure depth control, was carefully examined by observing the exposure time versus development characteristic of the resist, in the film thickness range of 40 to 90 micrometer. We proposed a simple method to reproducibly obtain the resist thickness of each level as designed. Using the unique overplating feature in electroplating process, we demonstrated two utmost practical examples: a unified Orifice Plate Assembly (OPA), which has orifice, channel, and reservoirs in a single body, for high-resolution inkjet printhead, and an electroplated Solenoid-type Integrated Inductor (SI²). Both were fabricated using a single-coated 80 micrometer-thick photoresist with only two photomasks, and have many advantages in productivity and performance. This method does not stack planar layer vertically to make 3D microstructures as in the conventional ways, therefore, is a simple, low-cost, and high-yield process. And also, it is IC compatible due to its low process temperature and monolithic process.

In this paper we present a novel technique to measure the thermal conductivity of thin film membranes. A very simple structure consisting of a polysilicon resistor as a heater and a polysilicon-aluminum thermocouple as a temperature sensor, both placed on a SiN membrane, is needed. Next to characterize the thermal conductivity of the SiN thin film, we have also been able to measure the thermal conductivity of SiO and polysilicon thin layers deposited onto the SiN membrane. The results obtained are in good agreement with previously published data obtained with different techniques.

To demonstrate proof of concept and obtain faster turnaround times on prototype development, an integrated excimer laser microfabrication system can be used for direct drawing-to- production of photoablated microstructures. A system currently in use consists of excimer lasers (248 nm and 351 nm), high- resolution stages, CAD system, and a visual observation and real-time metrology system. The material for the process is selected depending on the required edge wall definition, aspect ratio, surface roughness, and debris formation and ablation threshold. If the material is already defined, then the best process is found by selecting the following parameters: (1) machining feedrate, (2) laser pulse characteristics, (3) beam defocus, (4) number of passes, (5) laser aided cleaning, (6) high velocity gas cleaning, (7) vacuum machining. Some of the structures fabricated include microtube holders incorporating snap-fasteners for click-on microassembly. Where necessary, laser ablation is complemented by other micromachining processes like micromilling.

In this work, a new micromachining technology, namely reshaping, which combines advantages of two-dimensional IC fabrication with the third dimension of the mechanical world, is investigated in detail. With the new technology, surface micromachined and released polysilicon structures are deformed with external forces and then they are annealed to any desired 3D shape by Joule heating generated by the current through the devices. A similar technique was proposed before, however a detailed investigation is given in this work. Other available 3D fabrication techniques (e.g. LIGA) are expensive and there are still many challenges to overcome. In order to understand the reshaping process, polysilicon layers, whose crystallographical structure was modified by doping and annealing, were utilized. U-shaped cantilever beam microactuators were fabricated, reshaped and tested. Reshaping process was carried out at varying power levels with varying current pulse durations. Experimental results showed that microstructures in the desired shape with the optimized elastic properties can be obtained by controlling recrystallization, grain growth and plastic deformation parameters, which play a major role in reshaping.

Deep x-ray lithography, together with high quality electrogrowth (LIGA) is known for its capacity in fabricating extreme high aspect ratio structures of very good sidewall roughness and perpendicularity. Since LIGA-resists are plastics, and elastically deformable, we describe the physics and fabrication of Orthogonal Reflection Optics (ORO), LIGA- based multimirror lenses. Such optics operate by reflections from precisely inclined sidewalls. Diffraction calculations show excellent behavior in comparison even to Fresnel zone plates. OROs produce piecewise linear approximations of ideal lenses and can perform accordingly. Unlike classical lenses, OROs may work well in the VUV and soft x-ray region, and even for hard x-rays or function as particle-optics. OROs can be designed intrinsically achromatic. OROs are lightweight, quite planar and a large number of material choice exists for adjusting lens behavior to desired functions, e.g. high melting point metals (Pt, Os) for very heat resistant lenses operating above 2000 K. A classification of an entire ORO family, together with other modern concepts concerning x-ray micro transmission lenses by micromachining is included. First fabrications of 2D and 1D planar ORO-Fresnel lenses by LIGA are described.

Thy monolithic integration of MicroElectroMechanical Systems (MEMS) with the driving, controlling, and signal processing electronics promises to improve the performance of micromechanical devices as well as lower their manufacturing, packaging, and instrumentation costs. Key to this integration is the proper interleaving, combining, and customizing of the manufacturing processes to produce functional integrated micromechanical devices with electronics. We have developed a MEMS-first monolithic integrated process that first seals the micromechanical devices in a planarized trench and then builds the electronics in a conventional CMOS process. To date, most of the research published on this technology has focused on the performance characteristics of the mechanical portion of the devices, with little information on the attributes of the accompanying electronics. This work attempts to reduce this information void by presenting the results of SPICE Level 3 and BSIM3v3.1 model parameters extracted for the CMOS portion of the MEMS-first process. Transistor-level simulations of MOSFET current, capacitance, output resistance, and transconductance versus voltage using the extracted model parameters closely match the measured data. Moreover, in model validation efforts, circuit-level simulation values for the average gate propagation delay in a 101-stage ring oscillator are within 13 - 18% of the measured data. These results establish the following: (1) the MEMS-first approach produces functional CMOS devices integrated on a single chip with MEMS devices and (2) the devices manufactured in the approach have excellent transistor characteristics. Thus, the MEMS-first approach renders a solid technology foundation for customers designing in the technology.

The adhesion of PMMA layers on silicon wafer has been studied in order to protect the front side of the silicon wafer while etching the backside in KOH aqueous solution. Pre and post-bake treatment have been performed, different primers have been used to optimise the superficial and interfacial tension of both mask layer and substrate. An adherent layer has been obtained and its behaviour has been explained based on the polar and nonpolar interactions across the interface.

Keywords: PMMA, silicon, KOH, work of adhesion, surface energy, interfacial tension, superficial tension, contact angle.

The aim of this work was to determine the constant of elasticity for a static silicon micromechanical structure with a given shape, having its width and length in the hundredths of micrometers range and its thickness in the micrometer domain, subject to torsion. This is done by experimentally studying the torsion vibration of the structure. On this purpose, test structures have been manufactured, with thickness varying in a certain domain. Special alignment marks have been used in order to align the structures with respect to the crystallographic directions of the silicon. The structures have been activated with acoustic waves. The resonance frequency in the torsion mode has been measured by means of an optical set-up. Successive measurements and etch-thinnings of the structures provided the dependency of the resonant frequency on the structure thickness. A theoretical formula expressing the resonance frequency fr in terms of the shear modulus G, thickness e, and damping coefficient γ has been fitted with the experimental points in order to obtain the values of G and g. The proportionality factor k between the activation force and the angular or linear displacement has been caluclated in terms of mechanical engineering. Considerations regarding the bending phenomenon complete the strategy to determine the constant of elasticity for arbitrary structures.

Microassembly promises to extend MEMS beyond the confines of silicon micromachining. This paper surveys research in both serial and parallel microassembly. The former extends conventional 'pick and place' assembly into the micro-domain, where surface forces play a dominant role. Parallel assembly involves the simultaneous precise organization of an ensemble of micro components. This can be achieved by microstructure transfer between aligned wafers or arrays of binding sites that trap an initially random collection of parts. Binding sites can be micromachined cavities or electrostatic traps; short-range attractive forces and random agitation of the parts serve to fill the sites. Microassembly strategies should furnish reliable mechanical bonds and electrical interconnection between the micropart and the target substrate or subassembly.

Silicon became well known as the base material for high performance microstructures on the basis of cost, performance, durability, and excellent mechanical as well as electrical properties. Numerous market surveys and projections have identified a myriad of high volume opportunities over the past two decades. Yet true commercial success has remained in isolated pockets. The appeal of mechanical and electrical on the same miniature device combined with the photogenic resulting structures has resulted in a general hype of the technology. In concept, microstructures in silicon can fill just about any role as a small scale physical to electrical interface. However, the danger lies in assuming that these applications justify the cost. These costs of ownership include infrastructure cost, cost of compensating for performance limits, time to market, and hidden manufacturing costs. Many technically elegant microstructure solutions become solutions looking for problems. This presentation looks first at the opportunity and characteristics of silicon microstructures that make it an enabling technology, followed by examples where the technology has found markets. A summary of the industry characteristics and a comparison and contrast with the traditional electronics industry follows. A profile of successful microstructure applications and future trends leads to insight on how to structure a commercially viable approach. Finally, a summary of the market drivers and requirements and the true cost of ownership provides guidance on markets where a microstructure solution makes sense.

An overview of the key micromachining technologies that enable communications applications for MEMS is presented with a focus on frequency-selective devices. In particular, micromechanical filters are briefly reviewed and key technologies needed to extend their frequencies into the high VHF and UHF ranges are anticipated. Series resistance in interconnect or structural materials is shown to be a common concern for virtually all RF MEMS components, from mechanical vibrating beams, to high-Q inductors and tunable capacitors, to switches and antennas. Environmental parasites --such as feedthrough capacitance, eddy currents, and molecular contaminants -- are identified as major performance limiters for RF MEMS. Strategies for eliminating them via combinations of monolithic integration and encapsulation packaging are described.