This PDF file contains the editorial “Implementing JM3 Acronyms” for JM3 Vol. 7 Issue 03

This letter reports the development of a novel microshunt by combining biocompatible materials with well-established, robust microelectromechanical systems (MEMS) fabrication processes. The key features of our microshunt fabrication process are summarized as follows: (1) Control over the thickness of channels' enclosure, (2) channels' height scalable by multiple thick resist patterning, (3) structural material deposition by electroplating, and (4) an easy fabrication process suitable for mass production. These features were realized using electroplating for the gold structural material, photoresist sacrificial material, and e-beam evaporation of adhesion layers. The combination of these techniques allows precise control on the microchannels width, depth, and length. A novel channel sealing technique that is extendable to more complex geometries is also presented. The developed method involves using a thin gold seed layer deposited via evaporation prior to electroplating the last structural layer, the cover of the channels. This method enhanced the electroplating process, yielding more control of the final thickness of the cover layer compared to methods consisting of overgrowing the channels until they seal.

We investigate the effect of finite laser bandwidth on line-space (L/S) imaging, both through simulations and experiment. We will show that the primary effect of laser bandwidth is a change of the optical-proximity behavior of the scanner, i.e., a modification of the critical dimensional pitch [CD(Pitch)] characteristic, and that depth of focus typically remains unaffected. The simulation part of this study resulted in a simple estimator, expressing bandwidth-induced CD changes in terms of the “quadratic focus-sensitivity” (≡1/2 d²CD/dF²) of the L/S structure, a parameter which we call the “second moment” of the laser spectrum, M₂, and the longitudinal chromatic-aberration of the scanner (dF/d λ) only. The experimental part of this study, in which we measured CD (pitch) curves at different laser-bandwidth settings of the ASML XT:1700i NA=1.20 immersion scanner at Interuniversitary Micro-Electronic Centre (IMEC), confirms the results of the theoretical part, while relating the bandwidth dependency of the CD effects also to the experimentally available E95 metric. We conclude that even though the laser bandwidth of modern scanners is quite low, bandwidth effects do contribute to their proximity behavior and impact proximity stability as well as scanner-to-scanner proximity differences. We present a critical evaluation of current laser-bandwidth metrics and comment on the trade-off between the average laser bandwidth and laser bandwidth stability in order to achieve a required level of proximity control (e.g., between scanners).

To achieve the numerical aperture required for the next generation of immersion lithography, water may be replaced with a high index liquid as the immersion fluid. Because of their low surface tension to viscosity ratios, candidate high index fluids have an increased tendency to lose liquid from the under-lens region during scanning. Because any residual liquid left on the wafer is a potential defect mechanism, the conversion to high index fluids may drastically reduce scanning speeds and wafer throughput. The mechanism for liquid loss strongly depends on the behavior of the three-phase contact line; thus, this work focuses on the experimental study of the static and dynamic contact line behavior of five high index fluids. Contact angle and critical liquid loss velocity data is compared to the current model, which has been updated to better fit this new range of fluids. Liquid loss behaviors and their implications to the immersion lithography industry are discussed.

We analyzed the electron-irradiation damage induced by electron-beam inspection of metal nitride oxide semiconductor (MNOS) capacitors with various gate-dielectric thicknesses. Damage induced in an MNOS capacitor with a SiON dielectric for high-performance CMOS devices was compared to that induced on a metal oxide semiconductor (MOS) capacitor. We found that there is no remarkable difference between the damage to MOS capacitors and that to metal nitride oxide semiconductor MNOS capacitors. Damage was induced when a high-energy electron beam, whose electron range was larger than the thickness of the gate electrode, was irradiated. The induced damage strongly depends on the thickness of the gate dielectric. When the beam was irradiated onto a capacitor with a gate-dielectric thickness of 10.0 nm the flatband voltage shifted. When the beam was scanned onto a capacitor with a gate-dielectric thickness of 4.0 nm, the flatband voltage shifted minimally. However, the leakage-current density increased to 10^-7 A/cm² at a gate voltage of 3.0 V. On the other hand, when the beam was scanned onto an MNOS capacitor with 2.5-nm-thick dielectric, not even the leakage current was increased. Accordingly, for damage-free inspection when a gate-dielectric thickness is 4.0 nm or more, the beam energy needs to be lower so that the electron range is shorter than the thickness of the gate electrode.

critical challenge for the success of extreme ultraviolet (EUV) lithography is to prevent collector mirror surface damage and reflectivity loss. Plasma debris and radiation damage the mirror and degrade the reflectivity. We study an innovative approach to the design and fabrication of collector mirror surface materials to improve collector lifetime. A Mo-Au Gibbsian segregation (GS) alloy is developed on silicon using a dc dual-magnetron cosputtering system, and the temperature effect on mirror damage is investigated. Result shows that a thin Au segregating layer is maintained during exposure, even though overall erosion is taking place. The reflective material underneath the segregating layer, Mo, is protected by the Au sacrificial layer, which is preferentially sputtered. Both theoretical and experimental studies have been performed to prove the effectiveness of the GS alloys for use as an EUV collector optics material.

The step-and-flash imprint lithography process requires the clean separation of a quartz template from a polymer, and the force required to create this separation must be minimized to prevent the generation of defects. Fluorinated surfactant additives to the imprint fluid address this problem by migrating to the template-polymer interface and forming a local layer with ideal properties for adhesive fracture. Tensile and four-point bend fracture experiments show that surfactants lower the modulus of the imprint polymer and decrease the fracture energy. The fracture energy is further decreased by using a nonreactive, liquid surfactant versus a surfactant that reacts with the polymer matrix. Angle-resolved x-ray photoelectron spectroscopy results indicate that surfactant migration is more effective with a fluorinated surface treatment compared to an untreated quartz surface. This result shows that the use of fluorinated surfactants must be accompanied by a surface treatment that produces a similar energy or polarity to induce migration and lower the adhesive strength.

We report a simple method for fabricating quartz molds with submicrometer- and nanoscaled surface structures. It utilizes an excimer laser as the energy source and a roller-type contact-printing setup for directly transferring a patterned metallic thin film from a silicon mold to a quartz substrate. The transferred metallic patterns are subsequently used as an etching mask for dry etching on the quartz plate. Experiments have been carried out to determine the optimal parameters for successful pattern transformation. Experimental results on fabricating quartz molds are presented, and potential applications of this innovative pattern transformation method are addressed.

The proposed application of holographically formed polymer dispersed liquid-crystal (H-PDLC) thin films is a real-time dynamically reconfigurable mask for the resist exposure step in the photolithographic process. An adaptable photomask has advantages over traditional binary masks that include multiple fabrication patterns using a single mask, reduction in realignment error between different masks, real-time correction and adjustment of fabricated structures, and the ability to alter the mask pattern during exposure. H-PDLC films, or thin periodic nanostructures of alternating layers of polymer and liquid crystal, have unique electro-optic properties, including the ability to modulate a particular wavelength as a function of bias applied to the film. Structures formed using the H-PDLC photomask device have been compared to similar structures formed with a static photomask using an optical profilometer. Features studied were decreasing lines with a maximum width of 121 µm to a minimum width of 84 µm. Edge width between structures formed using the H-PDLC mask and static photomask differ by <5%. Additionally, morphology studies have been performed on developed regions of glass and resist formed using a static and an H-PDLC mask to demonstrate that no structural defects exist due to formation under an H-PDLC grating.

Novolak resins have had a significant impact on modern life, in general, and more specifically, on photolithography and the microelectronic market in particular. Since their commercialization around 1910, they have found a wide variety of uses. With the switch from solvent developable negative photoresists to the base soluble novolak/diazonaphthoquinone systems, the growth of the resist market has skyrocketed. Successive generations of higher quality resists required refinements in the synthesis, fractionation and purification of the novolak resins used in making those resists. The use of stabilization techniques and continuous processing methods for the preparation of novolak resins and the resists made with them are discussed.

A new permanent dry film photoresist, TMMF S2000, is tested and evaluated for microsystem applications. The resist provides high resolution, high aspect ratios, and homogeneous resist thicknesses. Aspect ratios up to 6:1 (height:width) may be achieved for both structures and channels. Buried structures are created by covering channels with a laminated resist layer. In addition, a very fast direct wafer bonding process is developed. In this process, the resist is patterned on a wafer and directly bonded to a second wafer using pressure and heat. Both techniques enable the fabrication of microfluidic chips with high aspect ratio structures.

The optical properties of three grades of Teflon^® AF—AF1300, AF1601, and AF2400—were investigated using a J.A. Woollam VUV-VASE spectroscopic ellipsometry system. The refractive indices for each grade were obtained from multiple measurements with different film thicknesses on Si substrates. The absorbances of Teflon^® AF films were determined by measuring the transmission intensity of Teflon^® AF films on CaF₂ substrates. In addition to the refractive index and absorbance per cm (base 10), the extinction coefficient (k), and absorption coefficient (α) per cm (base e), Urbach parameters of absorption edge position and edge width, and two-pole Sellmeier parameters were determined for the three grades of Teflon^® AF. We found that the optical properties of the three grades of Teflon^® AF varied systematically with the AF TFE/PDD composition. The indices of refraction, extinction coefficient (k), absorption coefficient (α), and absorbance (A) increased, as did the TFE content, while the PDD content decreased. In addition, the Urbach edge position moved to a longer wavelength, and the Urbach edge width became wider.

We report a novel prototype of a two-dimensional micromachined accelerometer based on thermocapillary heat transfer. The only moving element in this accelerometer is a thermal bubble generated by vaporizing the working liquid in the microchamber. The accelerometer consists of two key components, a heating resistor for creating symmetrical temperature profiles and two pairs of temperature detectors placed symmetrically and orthogonally to each other. The prototype devices demonstrate that a sensitivity of 1.5°C/g for an operating power of 60 mW can be realized. The frequency response of the accelerometer containing deionized water is 200 Hz, and the corresponding noise equivalent acceleration is ~1 mg/Hz^1/2.

Photonics modulation techniques can be effectively used for the laser microfabrication of biomedical implants to achieve better flexibility and control of the available optical power. These enable the processing and manufacturing of biomedical implants like cardiovascular stents and micro-metallic components with reduced heat affected zone (HAZ) and extremely precise edge cutting. Our investigation deals with the study of acousto-optic modulation of a pulsed Nd:YAG laser beam and further profile cutting of thin cobalt-chromium tubes for cardiovascular stent manufacturing. The acousto-optic modulator used in the investigations is a Bragg diffraction device. During one piercing process, the focused laser power is gradually varied from a low value and reaches the maximum as the beam goes deeper into the material. The optimum value for dwell time during which the laser piercing is occurring is found as 58 ms. A 14-step staircase modulating voltage with a maximum AC component of 900 mV was used, and the laser power was 4.4 W in TEM₀₀ operation. Pulsed Nd:YAG laser modulated using an acousto-optic device in the Bragg regime is capable of cutting extremely complex geometries of stents on L605 tubing. Laser cutting resulted in a kerf width of 22.5±0.5 µm. Precise strut dimensions of 112±15 µm for the subsidiary strut, 140±15 µm for the main strut, and 140±15 µm for the link were also obtained. Scanning electron microscopy (SEM) images of L605 stents illustrate the higher strength Co-Cr alloy L605 with the same ductility, its ability to be translated into thinner struts, and improved deliverability. L605 also exhibits enhanced radio visibility thanks to its tungsten content and exceptional work hardening rate for a uniform expansion with minimal recoil.

We describe the fabrication of wafer-scale alkali vapor cells based on silicon micromachining and anodic bonding. The principle of the proposed micromachined alkali cell is based on an extremely compact sealed vacuum cavity of a few cubic millimeters containing caesium vapors, illuminated by a high-frequency modulated laser beam. The alkali cells are formed by sealing an etched silicon wafer between two glass wafers. The technique of cell filling involves the use of an alkali dispenser. The activation of cesium vapors is made by local heating of the dispenser below temperature range causing degradations of cesium vapor purity. Thus, the procedure avoids negative effects of cesium chemistry on the quality of cell surfaces and sealing procedure. To demonstrate the clock operation, cesium absorption as well as coherent population trapping resonance was measured in the cells.

As demonstrated earlier, gas-phase etching of sacrificial oxide with a vapor mixture of anhydrous HF (AHF) and methanol (CH₃OH) offers a clean, stiction-free, effective etching technique for microelectromechanical systems (MEMS) release. The use of AHF/methanol process in MEMS release operations is explored in the deep lateral etching of patterned silicon-on-insulator (SOI) substrates using a 200 mm multiwafer commercial module, which assures adequate process throughput. It was determined that highly selective, with respect to both Si and Si₃N₄, etching of SiO₂ can be accomplished by controlling pressure and wafer temperature. It was also observed that the vertical etch rates for both the AHF/methanol and the HF: H₂O solution was higher than the rates of lateral etches in confined geometries. Furthermore, the AHF/methanol and 1:10 HF: H₂O etch chemistries were directly compared in releasing silicon cantilevers up to 500 µm in length and a significantly faster, stiction-free process was observed in the former case. Adequate process reproducibility from wafer to wafer as well uniformity across the wafer was demonstrated.

A detailed theoretical modeling of the electrochemical micromachining (EMM) process has been conducted here. The model takes into account a very small interelectrode gap thickness (order of a few micrometers) under which the electric field between the electrodes becomes a predominant factor in governing the machining process. The effect of electric double layer (EDL) also becomes significant under such conditions. The governing equations of the material removal rate are derived by considering a one-dimensional electric field, which is perpendicular to the cross section of the electrode. The model also incorporates the applied pulsed voltage used in EMM. A comparison between the theoretical and the experimental results indicate that, under high voltage and small interelectrode gap, the electric field and the formation of EDL have a significant effect on the material removal rate.

We present a method for the design and fabrication of InP-based free-standing microelectromechanical systems structures, which include microcantilever beams and Fabry–Perot membranes. The membrane is designed to satisfy both mechanical and optical requirements for a wavelength division multiplexing device and micro-Raman spectroscopy technique is used to evaluate surface stresses. The membrane profile is measured using a white-light interferometry technique, and the effect of the structure geometry on residual stress formation is discussed. From the results obtained, we propose a novel filter design that shows minimum surface profile deviation and stresses.

This paper introduces a visual-servoing system used in the automation of microelectromechanical system microassembly. In the proposed system, small microparts, 20 µm wide and 2 µm thick, are automatically grasped using a passive compliant microgripper in a first step toward achieving complete automation of the microassembly process. A fuzzy logic controller uses vision-based position and force feedback to correct the microgripper and micropart alignment and to guide the system toward achievement of a successful grasp. A depth-from-defocus depth estimation technique is used to properly align the micropart in the same horizontal plane as the microgripper. The performance of the system is investigated experimentally, and experimental results are presented.

We report on spontaneous formation of nanoscale surface domains obtained in lithium niobate substrates by electric field discharge poling. A constant high voltage was applied at room temperature to virgin and unpatterned crystals in air, by using metal tip-shaped electrodes. An enhancement of the electric field in correspondence of the electrode tips was expected due to the fringing field effect, and electric discharge was observed during the process. The standard wet etching in hydrofluoric acid solution revealed the formation of nanoscale domain structures that exhibit filamentous self-organized geometries. Topographic measurements of the fabricated structures were performed by an atomic force microscope, and the corresponding results are presented and discussed. The investigation provides remarkable information about the shortest domain size possibly obtainable by electric field poling.