This PDF file contains the editorial “Editorial: Impact factor of JM3” for JM3 Vol. 9 Issue 04

This PDF file contains the editorial “Special Section Guest Editorial: Reliability, Packaging, Testing, and Characterization of MEMS and MOEMS II” for JM3 Vol. 9 Issue 04

Comparisons between several pairs of contact materials are done with a new methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate microscale contact physics. Experimental measurements are obtained to characterize the response of a 5-µm²-square contact bump under electromechanical stress with increased applied current. The data provide a better understanding of microcontact behavior related to the impact of current at low- to medium-power levels. Contact temperature rise is observed, leading to shifts of the mechanical properties of contact materials and modifications of the contact surface. The stability of the contact resistance, when the contact force increases, is studied for contact pairs of soft (Au/Au contact), harder (Ru/Ru contact), and mixed material configuration (Au/Ru contact). An enhanced stability of the bimetallic contact Au/Ru is demonstrated, considering sensitivity to power increase related to creep effects and topological modifications of the contact surfaces. These results are compared to previous ones and discussed in a theoretical way by considering the temperature distribution around the hottest area at the contact interface.

We present an overview of our research on nanoelectronics and nanomechanics based on low-dimensional materials, including carbon nanotubes and graphene. Our primary research focus is on carbon nanotube and graphene architectures for electronics, energy harvesting, and sensing applications. We are also investigating an atomically precise graphene nanomachining method as well as a high-throughput desktop nanolithography process. In addition, we are exploiting nanomechanical actuators and nanoscale measurement techniques for reconfigurable arrayed nanostructures with applications in THz antennas, remote detectors, and biomedical nanorobots. Last, we are studying the effect of antibody functionalized nickel nanowires to improve cell separation techniques. These design, nanofabrication, manipulation, and characterization processes will enable next-generation nanoelectronics that have a wide range of applications including sensors, detectors, system-on-a-chip, system-in-a-package, programmable logic controls, energy storage systems, and all-electronic systems.

Time-dependent dielectric breakdown is quickly becoming a very important topic as low-k materials are integrated into back-end-of-the-line processes and as interconnect dielectric thicknesses approach the sub-100-nm range. There still exists a considerable amount of debate on the dominant failure mechanism with or without the presence of a diffusion barrier. We have developed a series of models for copper-accelerated time-to-failure that we are using to guide an experimental program to understand failure mechanisms. The models are based on the injection and drift of copper ions and focus on an increase in the local electric field that allows electrons to enter the dielectric's conduction band. The models are successful at correlating the time-to-failure for SiO₂ dielectrics with and without barriers. The most important aspects of the model that we are trying to verify experimentally include the role of moisture in the dielectric oxidizing Cu to form injectable ions, the initiation of failure at the pore-matrix interface in porous dielectrics, a decrease in the time-to-failure in porous dielectrics due to an increase in Cu solubility, and the need for near-perfect barriers to realize the advantage of using a barrier. The key unknown parameters in all these models are the diffusivities and solubilities of copper ions in the materials. Models of this type are not restricted to just interlayer dielectrics. Several failure mechanisms associated with semiconducting and organic light emitting diodes may also be described by similar models.

Uncooled microbolometer detectors are well suited for space applications due to their low power consumption while still exhibiting adequate performance. Furthermore, the spectral range of their response could be tuned from the mid- to the far-infrared to meet different mission requirements. If radiometric measurements are required, the radiometric error induced by variation of the temperature of the detector environment must be minimized. In a radiometric package, the detector environment is thermally stabilized by means of a temperature-controlled radiation shield. The radiation shield must be designed to prevent stray radiation from reaching the detector. A radiometric packaging technology for uncooled microbolometer FPAs is presented. The selection of materials is discussed and the final choices presented based on thermal simulations and experimental data. The radiometric stability with respect to stray light and variation of the temperature of the environment as well as the different noise components studied by means of the Allan variance are presented. It is also shown that the device successfully passed the prescribed environmental tests without degradation of performance.

Adaptive optics (AO) applications in astronomy and vision science require deformable mirrors (DMs) with high-stroke, high-order packing density at a lower cost than the currently available technology. The required AO specifications are achievable with microelectromechanical systems (MEMS) devices fabricated with LIGA (lithographie galvanofomung abformung) high-aspect-ratio processing techniques. Different actuator designs and a bonded faceplate fabricated in a LIGA process, enabling multilayer fabrication of MEMS devices, are investigated. Various types of high-stroke gold actuators for AO consisting of folded springs with rectangular and circular membranes as well as x-beam actuators supported diagonally by fixed-guided springs are designed, simulated, and fabricated individually and as part of a continuous-face-sheet DM system. The actuators and DM displacement versus voltage are measured with an interferometer and the corresponding results are compared to finite element analysis simulations. Simulations and interferometer scans show the ability of the actuators to achieve displacements of greater than 1/3 of the initial gap. A stroke of ~9.4 µm is achieved, thus showing that this fabrication process holds promise in the manufacture of future MEMS DMs for the next generation of extremely large telescopes.

The fundamentals of room temperature bonding methods-surface activated bonding (SAB) and sequentially plasma-activated bonding (SPAB)-are reviewed with applications for packaging of microelectromechanical systems (MEMS) and microfluidic devices. The room temperature bonding strength of the silicon/silicon interface in the SAB and SPAB is as high as that of the hydrophilic bonding method, which requires annealing as high as 1000°C to achieve covalent bonding. After heating, voids are not observed and bonding strengths are not changed in the SAB. In the SPAB, interfacial voids are increased and decreased the bonding strength. Water rearrangement such as absorption and desorption across the bonded interface is found below 225°C. While voids are not significant up to 400°C, a considerable amount of thermal voids above 600°C is found due to viscous flow of oxides. Before heating, interfacial amorphous layers are observed both in the SAB (8.3 nm) and SPAB (4.8 nm), but after heating these disappear and enlarge in the SAB and SPAB, respectively. This enlarged amorphous layer is SiO₂, which is due to the oxidation of silicon/silicon interface after sequential heating. The bonding strength, sealing, and chemical performances of the interfaces meet the requirements for MEMS and microfluidics applications.

A novel conductive adhesive is used to interconnect MEMS test structures with different pad sizes directly to a printed circuit board (PCB) in a medium caliber ammunition fuze. The fuze environment is very demanding, with a setback acceleration exceeding 60,000 g and a centripetal acceleration increasing radially with 9000 g/mm. The adhesive shows excellent mechanical and thermal properties. The mounted MEMS test structures perform well when subjected to rapid temperature cycling according to military-standard 883G method 1010.8 test condition B. The test structures pass 100 temperature cycles, followed by a firing test where the test structures are exposed to an acceleration of more than 60,000 g.

Packaging constitutes one of the most costly steps of MEMS/MOEMS manufacturing. Uncooled IR bolometers require a vacuum atmosphere of <10 mTorr to operate at their highest sensitivity. The bolometer response is also dependent on the package temperature. In order to minimize cost, real estate, and power consumption, temperature stabilization is typically not provided to the package. Hence, long-term high-sensitivity operation of IR bolometric radiometers requires a calibration as function of in-package pressure and temperature. A low-cost and accurate means of measuring the pressure in the package without being affected by the operating temperature is therefore needed. The Institut National d'Optique (INO) has developed a low-cost, low-temperature hybrid vacuum micropackaging technology. An equivalent flow rate of 4 × 10⁻¹⁴ Torr L /s for storage at 80°C has been obtained without getter. Even with such low flow, the long-term stabilization of residual pressure variations affects the sensitivity and calibration of the IR bolometers. INO has developed microelectromechanical systems pressure sensors that allow for real-time measurement of package pressure of >1 mTorr and can be integrated with the IR bolometers in a die-level packaging process or microfabricated simultaneously on the same die. We present the typical performance and measurement uncertainty of these pressure sensors along with a reading method that provides a pressure measurement with a dependence on the package temperature as low as 0.7%/°C. A complex reading circuit or temperature control of the packages are not required, making the pressure sensor well adapted for low-cost high-volume production and integration with IR bolometer arrays.

We present the characterization of a dry-etching process for high-contrast TiO₂/SiO₂ distributed Bragg reflectors, by inductively coupled plasma reactive ion etching, focusing on the etch rate and the etch selectivity. Photoresists and metals as etch masks were investigated. An excellent etch profile using an indium tin oxide mask was obtained, with an etch rate of >80 nm/min at a pressure of 6 mTorr. The experiments were developed for structuring Fabry-Pérot filters for tunable optical sensor arrays.

This PDF file contains the editorial “Special Section Guest Editorial: Line-Edge Roughness” for JM3 Vol. 9 Issue 04

The concepts of dynamical scaling in the study of kinetic roughness are applied to the problem of photoresist development. Uniform, open-frame exposure and development of photoresist corresponds to the problem of quenched noise and the etching of random disordered media and is expected to fall in the Kadar-Parisi-Zhang (KPZ) universality class for the case of fast development. To verify this expectation, simulations of photoresist development in 1+1 and 2+1 dimensions were carried out with various amounts of random, uncorrelated noise added to an otherwise uniform development rate. The resulting roughness exponent and the growth exponent were found to match the KPZ values nearly exactly. The impact of the magnitude of the underlying development randomness on the values of these exponents was also determined, and an empirical expression for predicting the kinetic roughness over a wide range of conditions is presented.

A previously developed linewidth roughness analysis technique is used to characterize post-lithography process roughness reduction in the frequency domain. Post-lithography processes are likely to be required to reach the International Technology Roadmap for Semiconductors roughness specifications for the 32-nm and 22-nm technological nodes. The aim of these processes is to reduce 3 linewidth roughness after etch without dramatic changes in critical dimensions. Various techniques are discussed: in-track chemical processes, ion-beam sputtering, and thermal and plasma treatments-each technique manifests a characteristic smoothing, reducing roughness up to 34%. Exploiting roughness mitigation at different frequencies, our target is to determine whether 50% 3 linewidth roughness reduction after etch is feasible.

The impact of an EUV mask absorber defect with pattern roughness on lithographic images was studied. In order to reduce systematic line width roughness (LWR) of wafer printed patterns, the mask making process was improved; and in order to reduce random LWR, low line-edge roughness resist material and a critical dimension averaging method of multiple-exposure shots were introduced. Then, by using a small field exposure tool, a mask-induced systematic printed LWR was quantified and estimated at 32-nm half-pitch and 28-nm half-pitch. The measurement results of the critical mask absorber defect size were compared with the simulation, and the results were then discussed.

Extreme UV (EUV)-wavelength actinic microscopy yields detailed information about EUV mask patterns, architectures, defects, and the performance of defect repair strategies without the complications of photoresist imaging.To understand the pattern measurement limits of EUV mask microscopy, we investigate the effects of shot noise on aerial image linewidth measurements in the 22- and 16-nm lithography generations. Using a simple model we probe the influence of photon shot noise on measured, apparent line roughness, and find general flux density requirements independent of the specific EUV microscope configurations. Analysis reveals the trade-offs between photon energy density, effective pixel dimension on the CCD, and image log slope (ILS). We find that shot-noise-induced linewidth roughness (LWR) varies inversely with the square root of the photon energy density and is proportional to the magnification ratio. While high magnification is necessary for adequate spatial resolution, for a given flux density, higher magnification ratios have diminishing benefits. We find that to achieve an LWR (3) value of 5% of linewidth for dense, 88-nm mask features with a 2.52 normalized ILS value (image log-slope, ILS, equal to 28.6/µm) and 13.5-nm effective pixel width (1000 × magnification ratio), a peak photon flux of approximately 1400 photons/pixel per exposure is required.

Since line-end roughness (LER) has been reported to be of the order of several nanometers and to not decrease as the device shrinks, it has evolved as a critical problem in sub-45-nm devices and may lead to serious device parameter fluctuations and performance limitations for future very large scale integration (VLSI) circuit applications. We present a new cell characterization methodology that uses the nonrectangular gate print images generated by lithography and etch simulations with the random LER variation. We systematically analyze the random LER by taking the impact on circuit performance due to LER variation into consideration. We observed that the saturation current, delay, and leakage current are highly affected by LER as the gate length becomes thinner. Results show that when the root mean square value of LER is 6 nm from its nominal line edge, the worst case saturation current, delay, and leakage current degradation are as much as 10.3% decrease, 12.4% increase, and 7× increase at a 45-nm-node standard cell. Meanwhile the current, delay, and leakage current degradation at a 32-nm-node cell are up to 19.0% decrease, 21.8% increase, and 4600× increase, respectively.

The study of surface-roughness evolution of resist films during development may elucidate the material origins of line-edge roughness. We use a stochastic simulator of resist development and analyze the resulting surface roughness evolution with dynamic scaling theory in polymers with homogeneous and inhomogeneous local dissolution behavior. In all cases, a power-law increase of root mean square (rms) roughness and correlation length is found. In homogenous polymers, a slow rms roughness increase is reported and the scaling exponents are shown to obey the dynamic scaling hypothesis of Family-Viscek. Dissolution inhomogeneity is inserted on a monomer scale (using copolymers), on a chain scale (using mixture of copolymers), or on a film scale by the activation of photo acid generator (PAG) molecules and the concomitant acid diffusion. Our simulator predicts that any kind of inhomogeneity may cause much larger rms roughness than homogeneous solubility. Furthermore, PAG-induced inhomogeneity results in a faster increase and larger values of roughness compared to chain-level inhomogeneity and this, in turn, leads to larger values compared to polymers with monomer-scale inhomogeneity. The differences in roughness are abruptly magnified when one reduces the resist solubility to levels in the range of the "clearing dose." A comparison with experimental results shows good agreement with the simulation predictions.

Much work has already been done on how both the resist and line-edge roughness (LER) on a mask affect the final printed LER. What is poorly understood, however, is the extent to which system-level effects such as mask surface roughness, illumination conditions, and defocus couple to speckle at the image plane and factor into current LER limits. We propose a "rule-of-thumb" simplified solution that provides a fast and powerful method to determine mask-roughness-induced LER. Using a one-time aerial image modeling of the mask surface roughness to obtain clear-field speckle statistics, the LER for any feature can quickly be calculated from a simple analytic extension using feature-specific image log slope. We investigate how the clear-field speckle is scaled by the intensity at the line edge, and mathematically couples to LER in the simplified case of a knife edge. We apply this relation to nested lines and spaces and compare this analytic LER to fully simulated values. We present modeling data on an older generation mask with a roughness of 230 pm as well as the ultimate target roughness of 50 pm. Moreover, we consider feature sizes of 50 and 22 nm and show that as a function of correlation length, the LER peaks at the condition that the correlation length is approximately equal to the resolution of the imaging optic.

Measurements of the sidewall morphology of commercial resist lines (3-D line-edge roughness) after lithography and before etching by critical dimension atomic force microscopy (CD-AFM) and scanning electron microscopy show that they exhibit anisotropy in the form of striations perpendicular to line direction. When this anisotropy of postlithography resist sidewalls is included in the models for trimming and pattern transfer proposed in an earlier paper [Constantoudis et al., J. Micro/Nanolith. MEMS MOEMS 8(4), 043004 (2009)], the models predict the beneficial role of trimming process in line-edge roughness reduction during pattern transfer, in agreement with experimental results. Furthermore, experimental and simulation studies show that the CD-AFM measurements of the 3-D line width roughness may overestimate the correlation length. Taking into account this finding in the model for trimming, we find that model predictions further approach the experimental results.

The accuracy of estimated line-edge-roughness and line-width-roughness (LER and LWR) statistics is mostly determined by the noise inherent in experimental power spectral densities (PSDs). One type of noise is statistical noise, a kind of jagged structure, that is caused by the finiteness of a number NL of line segments used in analyses. To keep the estimation error below 5%, the ratio of sampling interval to correlation length should be 0.3 or smaller, and NL needs to be larger than 100 under the condition that the length of line segments is 2000 nm or larger, in compliance with the Semiconductor Equipment and Materials International standard. Another noise type is scanning-electron-microscope image noise. It causes edge-detection errors and induces an additional variation in LER/LWR. This variation raises the minima of PSDs and accordingly enhances the errors. The factor of the error enhancement is suppressed below 1.5 by controlling the ratio of image-noise-induced LER/LWR variance to the true variance below 0.6. This is achieved by averaging image pixels perpendicularly to fine lines, and is free from any appreciable drawbacks. The experimental results agree well with analytical approximations to Monte-Carlo results that are separately obtained. This leads us to obtain more general guidelines for accurate analyses by using the analytical formulas.

Despite intensive attention on line-edge roughness (LER), contact-edge roughness (CER) has been relatively less studied. Contact patterning is one of the critical steps in a state of the art lithography process; meanwhile, design rule shrinking leads to larger CER in contact holes. Since source/drain (S/D) contact resistance depends on contact area and shape, larger CER results in significant change in a device current. We first propose a CER model based on the power spectral density function, which is a function of rms edge roughness, correlation length, and fractal dimension. Then, we present a comprehensive contact extraction methodology for analyzing process-induced CER effects on circuit performance. In our new contact extraction model, we first dissect the contact with a same distance, and then calculate the effective resistance considering both the shape weighting factor and the distance weighting factor for stress-induced complementary metal-oxide semiconductor (CMOS) cells. Using the results of CER, we analyze the impact of both random CER and systematic variation on the S/D contact resistance, and the device saturation current. Results show that the S/D contact resistance and the device saturation current can vary by as much as 135.7 and 4.9%, respectively.

The physical processes that underpin a recently developed commercial stochastic resist model are introduced and the model details discussed. The model is calibrated to experimental data for a commercially available immersion chemically amplified photoresist using basic physical information about the resist and an iterative fitting procedure. This data comprises CD (critical dimension) and LWR (linewidth roughness) measurements through focus and exposure for three separate line-type features on varying pitches: dense, semidense, and isolated. A root mean square error (RMSE) of 2.0 nm is observed between the calibrated model and the experimental CD data. The ability of the calibrated model to predict experimentally observed CD uniformity distributions is tested for a variety of 1-D and 2-D patterns under fixed focus and exposure conditions. The subnanometer RMSE obtained between experiment and simulation suggests that the calibrated stochastic model has excellent predictive power for a variety of applications.

To study line-edge roughness (LER), we develop a simulation method for the formation process of line edges based on the mesoscale simulation of the dissipative particle dynamics (DPD) method. We model the development and rinse processes based on the coarse-grained resist polymer model. It is important that the block copolymer in which the soluble and insoluble blocks are bonded exists at the line edge. Though the soluble part of this block copolymer is stretched out in the development process, it shrinks in the rinse process. The shrunken polymers contribute to the formation of line edges, and LER is very influenced by these polymers. Our simulations help to analyze the formation process of line edges based on resist polymer chain dynamics.

This PDF file contains the editorial “Special Section Guest Editorial: Metrology” for JM3 Vol. 9 Issue 04

When measured scanning electron microscope (SEM) image contours are used to generate or verify optical proximity correction (OPC) models, it is important that the contours are correctly aligned. If this is not the case, alignment errors will negatively impact the OPC model quality or its verification result. We present the approach we have developed to accurately align SEM contours for a variety of structure types. We discuss what one should align them to and how to do this, making the distinction between the case where the contours are to be used for verification of an already existing OPC model, or for generation of an OPC model. We show that our approach to contour alignment also offers the possibility to do contour averaging. We demonstrate the validity and limitations of our approach for a large number of SEM contours, taken from a 22-nm random-logic poly-type application.

Electrical validation of through process optical proximity correction verification limits in 32-nm process technology is presented. Correlation plots comparing electrical and optical simulations are generated by weighting the probability of occurrence of each process conditions. The design of electrical layouts is extended to subdesign rules to force failure and derive better correlation between electrical and simulated outputs. Some of these subdesign rule designs amplify the failures induced by an exposure tool, such as optical aberrations. Observations in this regard are reported. Sensitivity with respect to dimensions, orientations, and wafer distribution are discussed in detail.

We develope an in-line inspection method for partial-electrical measurement of defect resistance, which is quantitatively estimated from the voltage contrast formed in a scanning electron microscopy (SEM) image of an incomplete-contact defect. We first manufacture standard calibration wafers for the voltage-contrast calibration. The contact resistance of systematically formed defects varied from 10⁸ to 10¹⁷ . Then, we quantitatively analyze the gray scales of these defect images captured using a review SEM. As a result, calibration curves for estimating the contact resistance of the incomplete-contact defect are obtained at a probe current of 60 pA and a charging voltage of 4 V. The estimated contact resistance is between 10⁷ and 10¹² . Finally, this inspection method is applied to wafers manufactured for a static random access memory device. Accordingly, the gray scales of defective plugs formed for shared contact patterns are classified into two levels. The resistances of these defects are estimated from the calibration curve. The estimated resistances of the lower contrast defects (with an accuracy of about one order of magnitude) agree well with the resistances measured using a nanoprober. The resistances of the higher contrast defects are estimated as well, although they are too high to be measured using a nanoprober.

Scatterometry has been used extensively for the characterization of critical dimensions (CDs) and detailed sidewall profiles of periodic structures in microelectronics fabrication processes. In most cases devices are designed to be symmetric, although errors could occur during the fabrication process and result in undesired asymmetry. Conventional optical scatterometry techniques have difficulties distinguishing between left and right asymmetries. We investigate the possibility of measuring grating asymmetry with Mueller matrix spectroscopic ellipsometry (MM-SE) for a patterned hard disk sample prepared by a nanoimprint technique. The relief image on the disk sometimes has an asymmetrical sidewall profile, presumably due to the uneven separation of the template from the disk. Cross section SEM reveals that asymmetrical resist lines are typically tilted toward the outer diameter direction. Simulation and experimental data show that certain Mueller matrix elements are proportional to the direction and amplitude of profile asymmetry, providing a direct indication to the sidewall tilting. The tilting parameter can be extracted using rigorous optical critical dimension (OCD) modeling or calibration methods. We demonstrate that this technique has good sensitivity for measuring and distinguishing left and right asymmetry caused by sidewall tilting, and can therefore be used for monitoring processes for which symmetric structures are desired.

Optical properties (n and k) of the material films under measurement are commonly assumed invariant and fixed in scatterometry modeling. This assumption keeps the modeling simple by limiting the number of floating parameters in the model. Such scatterometry measurement has the potential to measure with high precision some of the profile parameters (critical dimension, sidewall angle). The question is: if the optical properties modeled as "fixed" are actually changing, would this modeling assumption impact the accuracy of reported geometrical parameters? Using the example of a resist profile measurement, we quantify the "bias" effect of unmodeled variation of optical properties on the accuracy of the reported geometry by utilizing a traditional fixed n and k model. With a second model, we float an additional optical parameter and lower the bias of the reported values, at the expense of slightly increased "noise" of the measurement (more floating parameters, less precision). Finally, we extend our multistack approach (previously introduced as an enabler to the product-driven material characterization methodology) to augment the spectral information and increase both precision and accuracy through the simultaneous modeling of multiple targets.

Roughness of lithographic patterns is typically expressed as the absolute 3σ variation of resist lines by means of edge variation. However, full characterization of the roughness requires both its amplitude and frequency distribution. This necessity arises from the requirement to reduce different roughness frequencies for different lithographic levels. The International Technology Roadmap of Semiconductors (ITRS) has established a dedicated specification for low frequency roughness. To obtain full knowledge of the roughness behavior in the frequency domain, a power spectral density analysis technique is used. It is found that power spectral density has a unique profile for each process. Moreover, the major contribution to the roughness came from the low frequencies range. Besides this, an on-line metrological study on scanning electron microscopy resist roughness repeatability is executed to optimize the capturing image parameters and estimate eventual short- (daily) and long-term (yearly) contributions. In the end, 0.2-nm 3σ line width roughness stability value is found. To verify the validity of analysis and metrology, 32-nm extreme ultraviolet lithography exposures at different flare levels, 45-nm ArF immersion lithography through dose, and a rinse postlithography smoothing process are characterized with the aim to highlight the importance of low frequency roughness detection.

Double patterning technology overlay errors result in critical dimension (CD) distortions, and CD nonuniformity leads to overlay errors, demanding increased critical dimension uniformity (CDU) and improved overlay control. Scatterometry techniques are used to characterize the CD uniformity, focus, and dose control. We present CDU and profile characterization for spacer double patterning structures by advanced scatterometry methods. Our results include normal incidence spectroscopic reflectometry (NISR) and spectroscopic ellipsometry (SE) characterization of CDU sensitivity in spacer double patterning stacks. We further show the results of spacer DP structures by NISR and SE measurements. Metrology comparisons at various process steps including litho, etch, and spacer, and validation of CDU and profile, are all benchmarked against traditional critical dimension scanning electron microscope measurements.

The ever-shrinking lithography process window dictates that we maximize our process window, minimize process variation, and quantify the disturbances to an imaging process caused upstream of the imaging step. Relevant factors include across-wafer and wafer-to-wafer film thickness variation, wafer flatness, wafer edge effects, and design-induced topography. We present our effort to predict design-induced focus error hot spots based on prior knowledge of the wafer surface topography. This knowledge of wafer areas challenging the edge of our process window enables a constructive discussion with our design and integration team to prevent or mitigate focus error hot spots upstream of the imaging process.

Extreme ultraviolet (EUV) lithography is currently the most promising technology for advanced manufacturing nodes. This study aims to assess in detail the quality of a full chip optical correction for a EUV design, as well to discuss the available approaches to compensate for EUV-specific effects. Extensive data sets have been collected on the ASML EUV Alpha-Demo Tool using the latest Interuniversity Microelectronics Center baseline resist Shin-Etsu SEVR59. In total ~1300 critical dimension (CD) measurements at wafer level and 700 at mask level were used as input for model calibration and validation. The smallest feature size in the data set was 32 nm. Both one-dimensional and two-dimensional structures through CD and pitch were measured. The reticle used in this calibration exercise allowed one to modulate flare by varying tiling densities. The shadowing effect was modeled by means of a single bias correction throughout the design. Horizontal and vertical features of different types through pitch and CD were used to calibrate the shadowing correction. The model calibration yielded an root-mean square of ~1 nm, which was observed to improve by including reticle CD data. An EUV mask fully corrected for optical proximity correction, flare and shadowing was fabricated and qualified, demonstrating the effectiveness of the implemented corrections.

We propose a new approach to fabricating micro-optical elements, in particular, microlenses and microlens arrays using an adjustable gray-scale mask and a microfluidic conveyor module. A liquid with acrylate oligomer is photopolymerized while it flows through this module, thus forming the micro-optical components. The adjustable gray-scale mask contains a layer filled with a UV-absorbing liquid and transparent elastomer structures in the shape of microlenses. By applying a high voltage, the shape of these microlenses can be altered, enabling one to change the intensity transmission distribution of the gray-scale mask and, as a consequence, the surface profile of the corresponding microlens structures in the microfluidic conveyor module below. The produced microlens structures are washed out of the conveyor module without adhesion on the walls of the PDMS microchannel surfaces due to the existence of an oxygen-aided inhibition layer. The dependence of the produced microlens morphology on the index-matching oil, the concentration of UV-absorbing liquids, and the electrostatic force modulation of the adjustable gray-scale mask are characterized. The adjustable gray-scale mask combined with a suitable flow/stop sequence enables one to fabricate microlenses and microlens arrays in a continuous and high-throughput mode.

The modified transmission line theory is used to calculate equivalent refractive indices of the extreme ultraviolet (EUV) mask multilayer (ML) over wavelengths from 13.35 to 13.65 nm for finite-difference time-domain (FDTD) simulation. Generally speaking, a fine mesh requiring huge memory and computation time are necessary to get accurate results in an FDTD simulation. However, it is hard to get accurate results for ML simulation due to the thin thickness of each layer. By means of an equivalent refractive index, the ML can be treated as one layer with the bulk effective material. Using FDTD simulations, we study the reflectivities of 40 Mo/Si ML and bulk material cases. The ML structure and bulk material with periodic excessive surface roughness as well as patterned with periodic contact holes are also studied by using two- and three-dimensional FDTD simulations. The simulation cases for a single wavelength and for a full-bandwidth EUV light source with a 6 ML system are studied. The results from each simulation show that the root mean square error between ML simulations and the bulk material simulations are confined within 3.3%, and all cases indicate that the FDTD computation time of bulk material is about half as compared with a 40-ML simulation.

A molybdenum (Mo)-doped zinc oxide thin film is deposited on a glass substrate by a rf magnetron sputtering technique. The structural and optical characteristics of ZnO:Mo (ZMO) thin films prepared with various deposition parameters are investigated. A series of SEM images obtained reveal that the average grain size of ZMO thin films is small and uniform. Energy dispersive spectroscopy analysis also verifies that traces of Mo are present in the as-grown thin films. The thicknesses of these ZMO films ranging from 150 to 390 nm are obtained by varying pertinent sputtering parameters. The average transmittance of ZMO thin films measured is more than 80% in the visible spectrum.

We present a bilayer cantilever microelectromechanical systems probe card configuration aiming to achieve an optimization of the mechanical and electrical properties of the probes. This bilayer cantilever structure is analyzed by an analytical method, and then further validated by finite element analysis. A prototype probe card structure is designed for the parallel I/O pads layout with a pitch of 100 µm, and developed via combining Si micromachining and ultraviolet Lithographie, Galvanoformung, Abformung (lithography, electroplating, and molding) (UV-LIGA) technique. The measured spring constant of the cantilever is 0.6362 Nm^-1, close to the theoretical prediction. The resistance from the probe tip to the end of the Cu conductive line is as low as 0.035 , indicating a very small electrical loss on the probe structure. In the radio frequency (rf) range of 0 to 40 MHz, the characteristic impedance is higher than 20 k, while the capacitance between two adjacent probes is around 0.13 pF. These measurement data indicate that the designed cantilever probe card structure has a good rf isolation property that makes it suitable for the testing of high-speed signal ICs.

We propose a recessed pyramid microstructure (PYM) to be used on the base of the light guide as micro-optical components to replace the conventional diffuser dot made by direct etching on the steel stamper. The PYM is made by microelectromechanical systems technology, which uses a silicon wafer for the original PYM mold, which is replicated on a Ni micromold using the electroforming method. An effective optical design tool is used to find the optimal PYM distribution integrating the random microstructure generation scheme based on the molecular dynamics method into optical commercial software. The scanning electron microscopy images show intact PYMs can be produced on the Si micromold and then replicated fully on the Ni micromold by the electroforming process. An intact PYM on the base of the light guide can then be produced by injection molding, completing the transformation of the Ni micromold for use in the light guide. The luminance measurement of a 2.4-in. backlight module with four LEDs shows an average luminance of 4769 nit with 86.3% uniformity for the PYM on the base of light guide, 10% higher than that of the diffuser dot microstructure.

A strong demand exists for techniques that extend application of ArF immersion lithography. Besides techniques such as litho-friendly design, dual exposure/patterning schemes, customized illumination, alternative processing schemes are also viable candidates. One of the most promising alternative flows uses image reversal by means of a negative tone development (NTD) step with a Fujifilm solvent-based developer. Traditionally, contact and trench printing uses a dark-field mask in combination with positive tone resist and positive tone development. With NTD, the same features are printed in positive resist using light-field masks, and consequently with better image contrast. We present an overview of NTD applications, comparing the NTD performance to that of the traditional development. Experimental work is performed at a 1.35 numerical aperture, targeting the contact/metal layers of the 32- and 22-nm nodes. For contact printing, we consider both single- and dual-exposure schemes for regular arrays and 2-D patterns. For trench printing, we study 1-D, line end, and 2-D patterns. We also assess the etch capability and critical dimension uniformity performance of the NTD process. We proves the added value of NTD. It enables us to achieve a broader pitch range and/or smaller litho targets, which makes NTD attractive for the most advanced lithography applications, including double patterning.

This study demonstrates a novel approach to lift the inductor from the lossy substrate by static magnetic field. The lift angle of the inductor, which tuned by a position stage, is employed to control the quality factor of the inductor. The lifted inductor is then welded by localized induction heating using the ac magnetic field. Thus, the heating-induced thermal problem is prevented. In addition, the inductor is also simultaneously packaged inside a Si capping by the alternating magnetic field. To demonstrate the feasibility of the proposed concept, the meander strip inductor was fabricated and tested. The radio frequency performance of the inductor at various tilting angles away from the substrate (0, 45, and 90 deg) was characterized by using a two-port vector network analyzer. The quality factor has been improved from 4.2 (at the central frequency of 0.64 GHz) to 7.9 (at the central frequency of 0.74 GHz), as the lift angle increased from 0 to 90 deg. In other words, the central frequency of the inductor can also be varied from 0.64 to 0.74 GHz. Measurement results also indicate that the bonded Si capping has a good shear strength of 23.5 MPa.

The design and fabrication of a poly(dimethyl-siloxane) (PDMS)-based microfluidic device for microsphere single-pass applications are presented. The fabrication process includes the use of high-throughput hot embossing lithography (HEL) technology for the definition of the microchannels and standard cast molding process. The sealing of the Pyrex cover and the PDMS substrate is achieved using thermal bonding. The chip, including 20-µm microchannels for microsphere single-passing is already realized, and the fact that the size of the microchannels can be altered makes it convenient to be further optimized. Such single-pass separation of microspheres is very useful for the detection and counting of microspheres. As a new method, the design and fabrication of a microcarrier-controlled microfluidic device described here can be applied to flow cytometric systems for automated, integrated, and ultrafast bioassays and screenings.