This is the first in a planned series of editorials covering all aspects of good science writing.

Abstract unavailable.

Although progress has been reported, the extreme-ultraviolet (EUV) source remains one of the largest challenges for EUV lithography production to be economically viable. This article gives an update on the high-level source requirements, including the origin of these specifications. All requirements are driven by litho system cost-of-ownership considerations and the imaging capabilities. Attention will be paid to conflicting requirements and the consequent tradeoffs that have to be made in making conceptual source decisions and in designing an EUV system. Finally, we will look into the future of the top-level source requirements with the conclusions that not only EUV power requirements will keep on increasing, but that this increase has to be accompanied with a high availability and reliability of the source. Furthermore, an operation mode has to be found that is chemically, particulately, and spectrally clean so that the cost-of-ownership and imaging capabilities of the total system remain intact over its lifetime.

A new approach for discharge-produced plasma (DPP) extreme ultraviolet (EUV) sources based on the usage of two liquid metallic alloy jets as discharge electrodes has been proposed and tested. Discharge was ignited using laser ablation of one of the cathode jets. A system with two jet electrodes was tested at a repetition rate of 1 to 5 kHz with dissipated electrical power up to 20 kW. Radiating spectra, time characteristics, and conversion efficiency are similar to conventional DPP schemes with rotating wheels. In the first experiments, the Ga:Sn eutectic alloy, which is liquid at room temperature, was circulating in a closed loop. The high velocity of the jets (30  m/s) ensures a renewed electrode surface for every shot, for a repetition rate frequency of up to 30 to 50 kHz, and provides effective heat transportation from the discharge zone. Modeling and experiments demonstrate that the proposed scheme is able to dissipate up to 200 kW of electrical power without overheating the nozzles and tin surface. It was found that the flexible electrode configuration allows the channeling of essential parts of debris plasma in directions opposite to the EUV collector.

Powerful extreme ultraviolet (EUV) sources at 13.5 nm are a prerequisite for the economical operation of lithography scanners for semi-conductor manufacturing. These sources have been under development for more than 10 years. At the beginning, many source concepts were considered. Compact technologies like dense plasma focus or capillary Z-pinch discharges reached very rapidly fundamental limits as far as power scalability and lifetime were concerned. Other complex technologies-like synchrotrons-eventually dropped out of the race as well, exceeding by far the footprint and cost targets. Over time, the technology solidified toward the two source concepts: on one hand, the discharge produced plasmas (DPP), which eventually led to the development of the current laser-assisted discharge plasma (LDP); on the other hand, the laser-produced plasmas (LPP). All these technologies generate hot and dense plasmas of similar properties, which emit EUV radiations efficiently as a black body radiator or Planck emitter, in a pulsed manner. The plasma generation method, however, is quite different. DPP uses a pulsed high-voltage current discharge to generate plasma heating a gaseous or vaporized material up to temperatures close to 200,000°C. As for LPP, microscopic droplets of molten tin are fired through a vacuum chamber, individually tracked, vaporized by a pre-pulse laser, and eventually irradiated by a pulsed high-power infrared CO2 laser at 50 to 100 kHz, creating a high-temperature tin plasma, which radiates EUV light. In the case of LDP the plasma is generated between two rotating discs. Partially immersed in baths filled with liquid tin, the discs are wetted and covered with a thin layer of liquid tin. A pulsed laser beam focused on one of the discs evaporates a small amount of tin and generates a tin cloud between the two discs. Next a capacitor bank, which is connected to the discs via the liquid tin, discharges and converts the tin cloud into a plasma heated up to 200,000°C as well.

As extreme-ultraviolet (EUV) lithography moves into pre-production, the requirement for commercially available mask metrology tools becomes more urgent. A key to developing a successful tool is a reliable, high-brightness EUV light source. The Energetiq EQ-10 is a commercially available EUV light source, with an installed base of over 15 sources in the field. The source relies on an electrodeless Z-pinch™ to produce greater than 10 Watts/2Π of 13.5 nm 2% bandwidth light. In order to meet brightness and stability requirements of mask metrology tools, we have investigated modifications to the original design of the EQ-10. The result of these modifications has roughly doubled the source output power, and has achieved brightness greater than 8 Watts/mm²/sr, without sacrificing the spatial and pulse-to-pulse stability of the original design. This level of performance is sufficient for initial mask blank and imaging inspection tools.

Discharge based extreme-ultraviolet (EUV) sources have experienced significant progress in the last decade at different places. They are commercially available and are presently being used in scanners for EUV lithography and related development projects in the semiconductor industry. The technology has been proven to be scalable from a wavelength of 13.5 nm down to the water window spectral range (2.4 to 4.4 nm), which envisions a new generation of compact systems using soft x-rays and extreme ultraviolet (XUV) light for metrology, patterning, or microscopy. Especially for microscopy applications such as aerial imaging microscopy of EUV masks, a high brilliance is required. First results on the achievable brilliance of a gas discharge source in the XUV and soft x-ray range are presented. Currently, a brilliance of 12.9  W/(mm² sr 2% b.w.) at a central wavelength of 13.5 nm and 100  W/(mm² sr 4% b.w.) at 10.9 nm are achieved. For the 2.88-nm single emission line of nitrogen, the source produces 0.28  W/(mm² sr) or 4*109  photons/(μm2 sr s) at a spectral bandwidth of λ/Δλ = 840. Based on existing data, the potential of brilliance scaling is discussed.

Actinic mask defect inspection and metrology requires high-brightness extreme-ultraviolet (EUV) sources. The self-absorption of radiation limits the in-band EUV radiance of the source plasma and makes it difficult to attain the necessary brightness and power from a conventional single unit EUV source. One possible solution is through multiplexing of multiple low etendue sources. NANO-UV is delivering a new generation of EUV light source, the CYCLOPS, in which a micro-plasma-pulsed discharge source is integrated to a photon collector based on an in situ active plasma structure. The source module is characterized by high brightness, low etendue, and high irradiance at moderate output power without the use of external physical optics. Such a source could form the basic building block of EUV source through spatial-temporal multiplexing of several units to deliver the brightness and power required for actinic mask metrology. We report on the EUV source development including the extensive numerical modeling, which provided the basic parameters required for high irradiance operating regimes. A new Sn-alloy cathode material enhances the output. Based upon the multiplexing concept, a family of specially configured multiplexed source structures, the HYDRA design, is being introduced to address the mask metrology needs.

The current status of laser-produced plasma source development for extreme ultraviolet lithography is reviewed. The advantages of using Sn as a fuel for 13.5 nm are discussed as is the rationale for using Nd:YAG prepulses followed by CO₂ irradiation of mass-limited Sn droplet targets. To date CEs of around 6% have been obtained in the laboratory while much lower values closer to 2% have been achieved in high repetition rate industrial sources suitable for use in high-volume manufacturing (HVM). The discrepancy appears largely to arise from the mismatch between the effective target lifetime and pulse duration as well as incomplete vaporization or fragmentation of the droplets. Improvements in laser technology and droplet delivery systems should see a marked improvement in the near future, so that CEs of 5% to 6% should eventually be realized in industrial sources. To keep pace with Moore's law, development work has begun on sources operating at 6.x nm, the wavelength selected for lithography beyond 13.5 nm. It is shown that Gd plasmas with an electron temperature close to 110 eV will provide the solution at this wavelength and the strongest lines ocurring in a Gd plasma are identified.

Today intermediate-focus equivalent extreme ultraviolet (EUV) power of several watts is now available, and EUV lithography scanners are being considered as potential scanners for high-volume manufacturing (HVM) tools. However, for high-volume manufacturing with throughput of over 100 wafers per hour, EUV power of 350 W may be required. We review the history of EUV sources for lithography with tin as fuel. We discuss the ideal plasma for tin sources for extreme ultraviolet lithography (EUVL), conditions for a high conversion efficiency of 4% to 5% in 2Πsr, and the existence of a repetition rate limit at around 40 kHz. We review the present status reported by EUV source suppliers and the prospects of tin laser-produced plasma as an EUV source for HVM EUVL.

Laser-produced plasma sources offer the best option for scalability to support high-throughput lithography. Challenges associated with the complexity of such a source are being addressed in a pilot program where sources have been built and integrated with extreme-ultraviolet (EUV) scanners. Up to now, five pilot sources have been installed at R&D facilities of chip manufacturers. Two pilot sources are dedicated to product development at our facility, where good dose stability has been demonstrated up to levels of 32 W of average EUV power. Experimental tests on a separate experimental system using a laser prepulse to optimize the plasma conditions or EUV conversion show power levels equivalent to approximately 160 W within a low duty-cycle burst, before dose control is applied. The overall stability of the source relies on the generation of Sn droplet targets and large EUV collector mirrors. Stability of the Sn droplet stream is well below 1 μm root mean square during 100+  h of testing. The lifetime of the collector is significantly enhanced with improved coatings, supporting uninterrupted operation for several weeks.

Since 2002, we have been developing a CO₂-Sn-laser plasma produced (LPP) extreme-ultraviolet (EUV) light source, the most promising solution as the 13.5-nm high-power (>200 W) light source for high-volume manufacturing (HVM) EUV lithography. Because of its high efficiency, power scalability, and spatial freedom around plasma, we believe that the CO₂-Sn-LPP scheme is the most feasible candidate as the light source for EUVL. By now, our group has proposed several unique original technologies, such as CO₂ laser-driven Sn plasma generation, double-laser pulse shooting for higher Sn ionization rate and higher CE, Sn debris mitigation with a magnetic field, and a hybrid CO₂ laser system that is a combination of a short-pulse oscillator and commercial cw-CO₂ amplifiers. The theoretical and experimental data have clearly demonstrated the advantage of combining a laser beam at a wavelength of the CO₂ laser system with Sn plasma to achieve high CE from driver laser pulse energy to EUV in-band energy. We have the engineering data from our test tools, which include 20-W average clean power, CE = 2.5%, and 7 h of operating time; the maximum of 3.8% CE with a 20-μm droplet, 93% Sn ionization rate, and 98% Sn debris mitigation by a magnetic field. Based on these data, we are developing our first light source for HVM: "GL200E." The latest data and the overview of EUV light source for the HVM EUVL are reviewed in this paper.

An integrated model is developed to describe the hydrodynamics, atomic, and radiation processes that take place in extreme ultraviolet (EUV) radiation sources based on a laser-produced plasma with a distributed tin target. The modeling was performed using the return-to-zero line code-a numerical code for the simulation of EUV emission by hot dense plasmas. The purpose of the simulation is to evaluate the spectral characteristics of the radiation source, conversion efficiency, source size, evaporation rate of the target, energetic, and space distribution of debris (nanoparticles, neutrals, and ions). The advantages of a distributed target in comparison with a single droplet target are also discussed.

The scaling rule of high average power, short-pulse CO2 lasers is described based on the physical fundamentals. Specifications are required for lasers applied to high-volume manufacturing extreme-ultraviolet light sources, simultaneously on the average power over 10 kW, the beam quality less than 2 for M², and the pulse width in the 10 ns range. The amplifier is operated by a cascade amplifier arrangement, and the ruling principle is approximately described by the Frantz-Nodvik equation, with effective small-signal gain g₀ and saturation fluence E_s depending on the amplifier medium and amplified pulse width. Thermal distortion is caused in the optical components, leading to beam propagation instability. The general rule of g₀L<3, where L is the optical gain length, is the requirement to isolate each amplifier by optical shutters. Multiline amplification is efficient to increase the extraction efficiency in the case of less-efficient rotational relaxation. It is concluded that a well-designed single-beam, short-pulse CO₂ laser is operable at 20 kW average output power based on available components, by satisfying all requirements.

High-brightness extreme-ultraviolet light sources are required for mask inspections and metrology, including mask blank inspection, actinic pattern inspection, and aerial image measurement system to improve yield and lower cost of ownership. Laser-produced plasma (LPP) light sources have the highest potential to achieve the brightness requirements for all the range of mask inspection tools currently foreseen. High brightness of LPP sources (100 to 1000  W/mm² sr) is the result of a smaller source size ( ∼ 0.1  mm) than that of competing technologies. Since brightness is inversely proportional to the area of the source, smaller source size corresponds with greater brightness and hence greater inspection throughput.At the Laboratory for Energy Conversion of ETH Zurich, a fully operational continuous-running multi-kHz LPP light source has been developed over the last five years and is now undergoing system optimization. Adlyte, a spin-off of ETH Zurich, is working with industry leaders to commercialize this LPP source. Individual subsystem configuration and the physical boundary conditions and limitations that affect power, brightness, stability, and lifetime management are discussed. This integrated system produces a measured brightness of 259  W/mm² sr. Outlook for the future growth and integration of the source in high-volume manufacturing tools is then discussed.

Free-standing multilayer films consisting of Si, Zr, Mo and silicides of both metals have been fabricated and studied as spectral purity filters (SPF) for extreme ultraviolet (EUV) (13.5 nm) lithography tools. Comparative tests of multilayer SPF structures of various compositions have been performed at high power loads. It was found that a Mo/ZrSi₂ structure with MoSi₂ capping layers is featured with capability to withstand prolonged heating in vacuum (10−7  mbar) at 900-950°C. A technique of fabrication of large aperture free-standing multilayers was developed, and a pilot sample of the above film structure of 160 mm in diameter, 50 nm thick, with transparency at 13.5 nm above 70% was fabricated as a conceptual prototype of SPFs with large dimensions.

Out-of-band radiation in extreme ultraviolet (EUV) exposure tools remains one of the critical issues that must be addressed before the implementation of this lithography technique for high-volume manufacturing. The out-of-band spectrum at the intermediate focus of EUV sources that use a CO₂ laser-produced plasma is dominated by scattered radiation from the drive laser, which operates near 10.6-μm wavelength. To reduce the unwanted heating of optical components in the exposure tool caused by the infrared wavelength, a 10.6-μm wavelength-absorbing gas can be used to reduce the number of photons at this wavelength reaching the intermediate focus. Gaseous sulfur hexafluoride (SF₆), whose _U3 infrared active mode is vibrationally excited by radiation around 10.6-μm wavelength, can be used to function as a molecular absorber and thus, mitigate part of the infrared radiation. In this work, the optical absorption of gaseous SF₆ is experimentally investigated at the CO₂ laser wavelengths close to 10.6 μm as well as the EUV wavelength. Various considerations affecting the use of a gas-based spectral filter are also discussed in this paper.

As extreme ultraviolet light lithography matures, critical deficits in the technology are being resolved. Research has largely focused on solving the debris issue caused by using warm (Te ∼ 30  eV) and dense (ne ∼ 1020  cm−3) plasma to create 13.5-nm light. This research has been largely focused on the mitigation of the debris between the plasma and the collector optics. The next step of debris mitigation is investigated, namely the effect of debris mitigation on the transport of undesired contaminants to the intermediate focus (IF). In order to investigate emissions from the IF, the Center for Plasma-Material Interactions at the University of Illinois at Urbana-Champaign has developed the Sn intermediate focus flux emission detector. The effects of a secondary RF-plasma, buffer gas flow rate, chamber pressure, and charged plate deflection are investigated. By increasing the chamber pressure to 10 mTorr, flowing 1000 sccm Ar buffer gas, and utilizing charged particle deflection, it is possible to reduce the measured number of post-IF species by greater than 99%. Furthermore, it is shown that typical debris mitigation techniques lead to the development of a plasma near the IF that can be detrimental to post-IF optics.

We have investigated the use of atomic-hydrogen-based cleaning to remove Sn contamination from extreme ultraviolet (EUV) multilayer mirrors. Mo and Si surfaces were cleaned at a relatively slow rate due to catalyzed dissociation of tin hydride on these surfaces. Mo/Si mirrors with B4C and Si₃N₄ cap layers and DLC-terminated DLC/Si mirrors showed complete removal of 10 nm Sn in 20 sec with full restoration of EUV reflectance. In addition, a prolonged cleaning treatment of 300 sec of a DLC/Si mirror resulted in only a minor EUV peak reflection loss of 1.2% absolute and no significant changes in infrared reflectance.

Extreme ultraviolet (EUV) lasers in the wavelength range of ~ 10 to 20 nm have matured to a point where dedicated applications such as at-wavelength inspection of extreme-ultraviolet lithography (EUVL) masks become possible on the laboratory scale. The authors briefly review the principles of plasma-based EUV lasers, the progress made so far, and the output characteristics of interest to the EUVL community.

We review the factors governing the performance of inverse-Compton light sources in the extreme-ultraviolet (EUV) region. While the use of an optical storage cavity and the minimization of the laser pump focal spot area remain critical to the optimization of power and brightness in the EUV, the appearance of a strong space charge forces at the low electron energies required for operation in the EUV sets an independent lower limit to the focal spot area, and therefore an upper limit to source power and brightness. These limitations are at least partially compensated by the very high average electron currents realizable at these lower electron energies. Based on these considerations, we describe the design and estimated performance of an EUV inverse-Compton scattering light source optimized for average power output and brightness consistent with the limits imposed by the capabilities of existing materials, laser pumps, and radio frequency power sources.

Advances of tabletop electron storage rings for generating a brilliant extreme ultraviolet (EUV) or soft x-ray beam are discussed. An electron storage ring called MIRRORCLE-20SX currently provides a stored beam current with an average of 3 A, a 1-minute lifetime, 15 ms radiation damping time, and a beam size of about 3×3 mm². We generate EUV by a thin-film target placed in the electron orbit. Photons in the wavelength around 13.9 nm is generated by an Si thin film, and 4.3 nm by a diamond-like carbon (DLC) film placed in the circulating electron beam. It is known from previous experimental studies that the mechanism of EUV emission is a synchrotron Cherenkov radiation (SCR). The observed photon power is 14 W/sr by the DLC film. We report that SCR is suitable for EUV lithography (EUVL) because the spectrum is monochromatic, the radiation angular spread is as narrow as 20×5 mrad², and the emitter size can be 0.01×3 mm². An optimized EUV source for lithography based on the tabletop synchrotron is proposed.

The driving engine of the free electron laser in Hamburg (FLASH) is an L-band superconducting accelerator. It is designed to operate in burst mode with an 800-ms pulse duration at a repetition rate of 10 Hz. The maximum accelerated beam current during the macropulse is 9 mA. Our analysis shows that the FLASH technology has great potential since it is possible to construct a FLASH-like free electron laser operating at the wavelength of 13.5 and 6.8 nm with an average power of up to 2.6 kW. Such a source meets the physical requirements for the light source for next-generation lithography.

An extreme-ultraviolet (EUV) source based on a low-pressure discharge sustained in a magnetic trap by the high-power millimeter-wave radiation under electron-cyclotron-resonance (ECR) conditions is discussed. Multiple charged ions are efficiently generated and excited in such a discharge (tin ions injected into the trap from a vacuum-arc discharge were used) and emit line radiation in the desired wavelength range. A radiation power of 50 W into a solid angle of 4Π sr in a wavelength range of 13.5 nm±1% and an efficiency of about 1% for the conversion of the microwave radiation absorbed in the plasma to the extreme ultraviolet radiation were achieved in the preliminary experiments. The article describes in detail the method of measuring EUV light emission power and background radiation. The emissivity of the plasma heated by gyrotron radiation with frequencies of 170 and 300 GHz is calculated. The proposed scheme can reduce the size of the emitting region up to ~ 1 mm. The source can operate in both continuous and in pulsed mode.

Design of a clean, high-brightness light source is presented for extreme ultraviolet/soft x-ray (EUV/SXR) lithography research and mask inspection. Basic characteristics of classical laser-Compton scattering are reviewed, and the laser and electron beam parameters at relatively low energy (EUV to SXR) photon generation are optimized. Recent achievements in each component technology are evaluated on a continuous wave (CW)-operated electron linac and energy recovery linac system, based on superconducting technologies at a 1.3 GHz operation frequency, 10 kW average power, short pulse CO₂ laser, and optical super cavity with a 600- enhancement- factor at 10.6 μm wavelength. Combining both the CW electron beam and short pulse CO₂ laser with super-cavity enhancement, 1  mW/2%  ?startb.w.end? flux and 30  kW/mm²/sr/2%  ?startb.w.end? brightness laser-Compton source is designed at 6.7-nm wavelength. The technological gap in the present component technologies are discussed, as well as any further required developments.

Abstract unavailable.

A method for die-attach based on sintering of micro- and nano-silver-particles, which is stable in harsh environments, was described. A modified flip-chip bonder providing high placement accuracy was used for precise pick and place die-attach. Components of sensors designed for data logging during deep drilling, i.e., a MEMS vibration sensor and a MOEMS pressure sensor, were assembled and tested at temperatures up to 250°C. Shear tests of bonded devices were performed before and after temperature load. Bonded silicon-on-insulator Wheatstone bridges and GaP-PD were tested by temperature cycling (50 cycles from 100°C up to 250°C).

Microcantilever is the fundamental structure for the realization of a microelectromechanical systems sensor with higher sensitivity and selectivity in a number of fields like biomedical, defense, and environmental. Present research is also focusing on the applications of microcantilever in the field of food industry. Among the two fundamental techniques for microcantilever, deflection and resonant peak shift, it was proven that the latter one is the best suited for added mass detection. In our study, we derive an analytical expression for δm based on the shift in frequency (δf') that accounts for the elasticity of the added mass and the location of the mass on the beam. In particular, we create a finite element methods model of our system in a commercial package, COMSOL (Bangalore, India), and carry out modal analysis for the cantilever beam resonator with and without the added mass, varying the relative stiffness and mass of the two components (the cantilever beam and the added mass), to compare the results of shift in resonant frequency with those obtained from rigid mass models. The results show the effect of elasticity clearly in certain ranges of relative stiffness and mass.

We present an integrated reliability test methodology for electrostatic discharge (ESD) testing of micro-electromechanical systems (MEMS). It is shown that conventional ESD test methods for failure detection, like current and voltage waveforms during ESD stress and direct current leakage are insufficient for MEMS. A functionality-based approach using the mechanical response of the MEMS during ESD is needed to accurately and conclusively detect ESD failure in MEMS. A novel test setup with a probe-mountable human body model (HBM) tester is presented for this purpose. This setup can perform simultaneous measurements of MEMS out-of-plane displacement, HBM current and HBM voltage in the MEMS in situ during ESD stress. Using this setup, a few examples are demonstrated that show that traditional electrical characterization is overestimating the ESD robustness of MEMS devices. ESD testing of MEMS is performed at different pressures on RF MEMS actuators and show that more than one type of failure mechanism can occur due to ESD stress. ESD-induced charging and functionality degradation in RF MEMS actuators are also briefly discussed.

A new extraction approach for MEMS comb-drive equivalent circuit parameters is presented. The proposed method eliminates the need for fitting and optimization by direct extraction from the measured data and, thus, avoids the nonuniqueness problem associated with fitting algorithms. A silicon-on-insulator-based MEMS comb-drive actuator is designed, fabricated, and measured, and its equivalent circuit is obtained by the proposed procedure. Analytical estimation for the uncertainty in the extracted values due to the discrete nature of the measurement frequency resolution is carried out. Uncertainty in the extracted values of the equivalent motional parameters is well below 0.6% when a 0.1-Hz frequency resolution is used. The method has been used to extract the resonator quality factor at both atmospheric and vacuum operations and can be extended to other types of resonators.

Microcantilever beams have been widely used in micro-electromechanical systems (MEMS) devices. Their reliability is an essential factor for a successful MEMS product in an industrial setting. This study discusses the fatigue life of polysilicon microcantilever beams of various dimensions that were subjected to bending by a piezoelectric actuator. Both experimental and analytical results were obtained. A 100-Hz piezoelectric actuator was used to facilitate the test runs with good repeatability of the fatigue load. A finite element-modeling program, ANSYS, was used to investigate the stress distribution on the microcantilever beam. The fatigue life of the specimen was found to lie between 1.23×10⁷ and 1.29×10⁸ cycles for stress level ranges from 4.07 to 2.31 GPa. The experimental data from this study were incorporated with published references into an S-N curve, which showed that the fatigue life was dependent on both stress and frequency levels of the loading cycles. Low frequency loading was associated with increased sensitivity of fatigue life versus stress level. An empirical correlation was established for predicting fatigue to provide the MEMS designer with a reference for various applications.

An analytical design of radio frequency microelectromechanical (RF MEMS) devices and fabrication and encapsulation results is discussed. The encapsulated MEMS device is an in-plane variable capacitor (varactor), continuously tuned up to 115% at 3.25 V, showing a Q factor of 49 at 1 GHz at zero bias and self-resonance frequency above 5 GHz. The 60-μm-thick device measures 0.6  mm×0.6  mm and is fabricated using high-aspect ratio single-crystal and polysilicon technology, having an air gap of 0.8 μm for tuning and 2 μm for actuation. The effect of gap size, substrate doping, and gold coating on Q is studied. The wafer-level encapsulation is done by the thermal decomposition of a sacrificial polymer through a polymer overcoat at 130°C-150°C, followed by gold evaporation to provide a degree of hermeticity. The overcoat polymer is patterned instead of screen printed, which defines the package boundary, providing a small amount of interconnection. The encapsulated device measures 0.7  mm×0.7  mm, which is only 35% larger than the MEMS device. The insertion loss of the 1 μm/20 μm gold/Avatrel package is measured to be 1.4 dB at 1 GHz and 1.51 dB at 5 GHz, and the calculated nitrogen permeability is less than 1 Barrer. The temperature stability of the rest and the maximum capacitance is better than 7%, in the range of −30-50°C.

This study reports on the investigation of the potential applicability of poly-glycidyl methacrylate (PGMA) films deposited via initiated chemical vapor deposition (i-CVD) as lithographic resists in the microfabrication of non-planar structures. We investigate the appropriate deposition conditions of i-CVD required to form PGMA films with smooth surfaces. As a result, under the optimal conditions determined by us, we fabricate films with nanometer-scale flat surfaces. Subsequently, we demonstrate that i-CVD is effective for conformally coating a high-aspect-ratio Si trench with PGMA film via our deposition experiments. In our deep-ultraviolet lithography experiment, we successfully fabricate a fine 20-μm line-and-space (L/S) pattern with a height of approximately 1  μm. Furthermore, in our electron-beam (EB) lithography experiment, we define a fine 350-nm L/S pattern with a height of 120 nm. In addition, the i-CVD process can be used to form highly-sensitive EB resist films; the lowest dose amount for patterning these films is evaluated to be less than 0.01  μC/cm². Our results demonstrate that i-CVD is a potentially powerful method to conformally coat lithographic resist films on three-dimensional structures.

A homogeneous one-dimensional optical lattice is demonstrated by using a high-precision beam shaper based on a digital micromirror device (DMD) with an imaging system containing a pinhole low-pass filter (LPF). This system is capable of producing a high-quality flattop beam profile to form a standing-wave optical lattice with a 50×50 μm² flattop region. The periodic potential generated by the optical lattice confines ultracold atoms in Bose-Einstein condensate experiments. We conducted beam shaping tests at several wavelengths by implementing various coherent and incoherent light sources in the visible and infrared wavelength ranges. Experiments produced flattop and other well-controlled beam profiles with 0.2% to 0.26% root-mean-square (RMS) error after applying a digital LPF and nearly flat phase. Several concerns for the system design are presented. First, the energy requirement was determined by power conversion analysis and DMD diffraction efficiency simulation. In addition, a LabVIEW program was written to accelerate the speed of the iterative process for beam profile refinement. Finally, various camera calibrations improved the measurement accuracy. We achieved a 1.25% RMS error flattop beam with diameter of 70.4 μm at the atoms' plane. Other beam profile measurements in different diagnostic planes demonstrated a good intensity uniformity of the optical lattice.

New tuneable MOEMS filters have been developed to cover the spectral range from 400 to 750 nm. Compared with previous MEMS based visible light filters, these Fabry-Perot Interferometers (FPIs) have increased transmission (90%), spectral resolution of ∼ 4 to 9 nm, and larger aperture diameter (2 mm), which allows them to be used in spectral imaging devices. We present the fabrication process and characterization of tuneable MOEMS FPIs for central wavelengths of λ = 420  nm and λ = 670  nm. Miniature imaging spectrometers have potential novel applications in diagnostics and health care, bioprocess, and environmental monitoring, process analytical instrumentation, and water-quality analysis.

We study the distributions of line/space (L/S) patterns based on exposure dose variation using point array techniques (a type of digital maskless lithography). The intensity distributions of L/S patterns were simulated using the point array technique, and the pattern profiles were obtained by applying the effect of the photoresist contrast to the intensity distribution. As the dose increased, line width also increased. An experiment was performed to verify the simulation results. The minimum line widths of the L/S patterns were about 3.44 and 3.89 μm at laser power levels of 100% and 60%, respectively. The standard deviations of the line widths were 0.28 and 0.03 μm at the 4 and 13 μm L/S patterns, respectively.

A robust technique is presented for auto-aligning nanostructures to slow-etching planes during crystallographic etching of silicon. Lithographic mask patterns are modified from the intended dimensions of the nanostructures to compensate for uncertainty in crystal axis orientation. The technique was employed in fabricating silicon nanolines having lengths of 600 nm and widths less than 5 nm, subjected to intentional misalignment of up to ±1 deg. After anisotropic etching, the auto-aligned structures exhibited as little as 1 nm of width variation, as measured by a critical dimension atomic force microscope, across 2 deg of variation in orientation. By contrast, the widths of control structures fabricated without auto-alignment showed 8 nm of variation. Use of the auto-alignment technique can eliminate the need for fiducial-based alignment methods in a variety of applications.

This work presents the mechanical characterization of SU-8 photoresists studied in the form of microscaled free-standing thin films with various effective length/width (aspect) ratios, achieved by a tensile testing method. Specimens were designed with gauge segments measuring 240 to 540 μm long and 40 to 80 μm wide with thickness fixed at 20 μm, all fabricated in the same processing conditions. The experiments were carried out on a microtensile testing system which had a load and displacement resolution of 0.25 mN and 10 nm, respectively. With a tensile loading speed of 0.02  μm/s, the average fracture strength of SU-8 photoresist was measured to be 66.34 MPa, and the calculated Young's modulus ranged from 0.86 to 2.33 GPa and the maximum strain from 1.02% to 9.70%, with variation dependent on the effective aspect ratio of the tested films. As a result, effective aspect ratio is concluded to be a significant factor mechanically charactering the size effect of SU-8 photoresist in microscale.

We explore how photoresist shrinkage behavior due to e-beam measurement by critical dimension-scanning electron microscope (CD-SEM) depends on various time-related factors. This will include an investigation of how the photoresist critical dimension (CD) and CD shrinkage varies with photoresist age and the differences in shrinkage trends between load/unload and static and dynamic repeatability cases, where time between measurements is a key variable. The results for this typical immersion argon flouride photoresist process will show that resist CD and shrinkage variation due to resist age and vacuum-cycling is insignificant, yet the shrinkage is strongly linked to time between consecutive measurements, with a well-defined, high-certainty logarithmic decay with time. These experiments identify a key difference between the shrinkage seen in static versus dynamic measurements, which will be shown to have far-reaching implications for the shrinkage phenomenon in general and for the best-known methods for executing CD-SEM metrology with photoresist samples.

An in-line inspection method for estimating defect resistances from the grayscale of voltage contrast in scanning electron microscope (SEM) images of manufactured patterns was developed. This method applies a circuit simulator to calculate the intensity of the secondary electrons according to an equivalent-circuit model considering the charge-up voltage on the patterns. To accurately estimate the resistance of defects formed in a device, first, the simulator was improved by considering the variation in defect resistance, which strongly depends on the differential voltage between the plug surfaces and the backside wafer. The defect resistances were obtained from the measured current-voltage (I-V) characteristics of the intentional defect on the standard calibration wafers, in which some incomplete-contact defects were systematically formed. Next, to consider the effect of the electronic characteristics of the pattern under the normal plugs on the grayscale, the I-V characteristics of the normal plugs were measured. The equivalent circuit of the simulator was improved by taking into account the measured I-V characteristics. The calibration curve for the manufactured patterns was calculated from the improved circuit simulator. Finally, the inspection method was applied to estimate the resistance of defects formed on an static random access memory (SRAM) pattern. The calculated calibration curve was used to estimate the defect resistance from the voltage contrast formed on the defects in the manufactured SRAM patterns. The accuracy of the estimation was about an order of magnitude.

In this paper, we propose a new method that can extract aberrations using aerial image measurements and present its experimental results on lithographic tools. Based on physical simulation and statistical analysis, a linear regression matrix is obtained establishing a connection between principal component coefficients of specific aerial images and Zernike coefficients. In the application phase, the aberrations of the projection lens are solved via the use of this regression matrix. An engineering model is established based on an extension of theoretical model that incorporates all the significant systematic errors. The performance of the engineering model as applied on a 0.75 NA ArF scanner is reported. In the experiment, measurement marks oriented in orthogonal directions are used and aerial images at 9 field points are measured. To verify the repeatability of this technique, every point is measured 20 times. By inputting the aerial images into the engineering model, Zernike coefficients are solved and the results are analyzed. The wafer exposures were performed to evaluate the results of aberration correction.

Transparent electrodes using carbon nanotube (CNT) have recently been studied as potential replacements for conventional indium tin oxide (ITO). In this work, CNT and ITO coated polyethylene terephthalate samples were prepared and studied. The degree of cohesion is dependent on the drying conditions. To explore affects of changing surface conditions, three drying temperatures, 20, 80, and 120°C, were used. Electrical resistance measurements were used to evaluate the interfacial durability and electrical properties of prepared transparent electrodes. A field emission scanning electron microscope was used to investigate surface changes and UV-spectroscopy was used to evaluate transparency as functions of the different drying temperatures. The electronic properties for these nanoparticle coated surfaces were evaluated using a cyclic voltametry method. Interfacial durability was evaluated by static contact angle measurement versus elapsed time. The pH values of the coatings were measured in a water solution. The durability of the CNT coated surfaces was found to be better than that of the ITO coated surfaces. The higher drying temperatures were found to produce better coated surfaces because of improved cohesion between the nanoparticles which resulted in improved electrical properties and improved durability.

Existing analytical and numerical methodologies are discussed and then extended in order to calculate critical contamination-particle sizes, which will result in deleterious effects during extreme ultraviolet lithography E-chucking in the face of an error budget on the image-placement-error (IPE). The enhanced analytical models include a gap-dependent clamping pressure formulation, the consideration of a general material law for realistic particle crushing and the influence of frictional contact. We present a discussion of the defects of the classical de-coupled modeling approach where particle crushing and mask/chuck-indentation are separated from the global computation of mask bending. To repair this defect we present a new analytic approach based on an exact Hankel transform method which allows a fully coupled solution. This will capture the contribution of the mask-indentation to the image-placement-error (estimated IPE increase of 20%). A fully coupled finite element model is used to validate the analytical models and to further investigate the impact of a mask back-side CrN-layer. The models are applied to existing experimental data with good agreement. For a standard material combination, a given IPE tolerance of 1 nm and a 15 kPa closing pressure, we derive bounds for single particles of cylindrical shape (radius×height<44  μm2) and spherical shape (diameter<12  μm).

Rotary comb-drive electrostatic actuators with smooth vertical sidewalls were designed and fabricated for photonic applications. Silicon on insulator wafers with device layer thicknesses of up to 100 μm and oxide layers of 1 to 2 μm were used. Structures were fabricated through bulk micromachining of the handle layer, followed by removal of the buried oxide. Deep reactive ion etching (DRIE) of the device layer defined the comb structure with simultaneous release of the movable arm. Thick photoresist and oxide masking layers were used for the high aspect ratio deep etches. Notching effects or depth variations of device layers were not observed. Etch/passivation cycles in DRIE were optimized to obtain smooth sidewalls of less than 5 nm roughness. Traces of etch scallops were confined only to the first few microns of the top and bottom edges of the reflecting sidewall. A movable arm length of 2 mm with a maximum rotation of 2.8 deg was achieved. The edge deflection was over 100 μm at 100 V. The fabricated structure provides a long reflecting sidewall, that is accessible for hybrid integration, in three dimensional space. The fabricated structures can be reliably operated in the kilohertz range.

Nanoimprint lithography was used to fabricate arrays of SiCN nanoscale resonators for biological analysis applications. A bilayer resist consisting of PMMA 495/LOR 3A allowed high fabrication yields for resonators of widths ranging from 120 to 300 nm, thicknesses of 40 and 70 nm, and a length of 14 μm. To our knowledge, these 120 nm resonators are the narrowest suspended structures ever fabricated via nanoimprinting. Device to device uniformity of resonant frequency was dictated by the uniformity of the tensile stress over the device layer. The 40 nm thick and 70 nm thick devices showed average resonant frequencies of 16.6±2  MHz, and 21.7±0.3  MHz, respectively. These devices were successfully employed as elements of arrays for the detection of a biological analyte. The biotin-streptavidin system was used for such purpose. The specific capture of streptavidin induced downward frequency shifts ranging from 100 to 300 kHz, corresponding to capture densities of roughly 1 to 5 molecules per 100  nm². Negative control experiments showed no net downward frequency shifts, demonstrating the specificity of the detection.

Since frictional interactions in microscopically small components are becoming increasingly important for the development of new products for all modern technology, we present a laser-based technique for micro-patterning surfaces of materials using low-cost microlens arrays. By combining a laser direct-write technique on soda-lime glass and a thermal treatment, it was possible to obtain high quality microlens array elements using a low cost infrared laser widely implemented in industry which makes this technique attractive in comparison with other more expensive methods. The main advantage of using microlens arrays for micropatterning surfaces is the possibility of fabricating a large number of identical structures simultaneously, leading to a highly efficient process. In order to study the capabilities of the microlenses fabricated for microstructuring materials, identical structures and arrays of holes were fabricated over a variety of materials, such as stainless steel, polymer, and ceramic. The minimum diameter of the individual microstructure generated at surface was 5 µm. Different nanosecond lasers operating at infrared and green wavelengths were used. The topography and morphology of the elements obtained were determined using confocal microscopy.

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