This PDF file contains the editorial “Editorial: On overcoming the worse than worst earthquake” for JM3 Vol. 10 Issue 1

This work demonstrated the ability to transfer a nanoscale 3-D polynomial structure of arbitrary shape into Si with a single step electron-beam lithography process. The technique involved employing a proximity correction algorithm, PYRAMID, to derive the dose distribution for a given 3-D structure by accounting for the electron scattering effects of the surrounding pixels. The pattern was written into a polymethyl methacrylate (PMMA) resist and then successively transferred into Si via reactive ion etching, where a 1:1 etching ratio between PMMA and Si was achieved. The pattern transferred into Si possessed nanoscale features and matched the desired pattern with high fidelity.

This PDF file contains the editorial “Special Section Guest Editorial: Theory and Practice of MEMS, NEMS, and MOEMS” for JM3 Vol. 10 Issue 1

In this paper, a high resolution Vernier-type displacement sensing mechanism is proposed by utilizing Vernier-type suspended gate field-effect transistors (SGFETs), The field-effect transistor benefits from its linear output signal and simple structure, and the concept of Vernier gate is used to enhance the resolution. The displacement of the comb-drive actuator is sensed via the output drain current of SGFET. Design and analysis for Vernier-type suspended gate were presented and some characteristics of the Vernier-type SGFETs were also discussed in simulation results.

We demonstrate the fabrication of polymer microneedle arrays using soft lithography. A photomask was designed to use Fresnel diffraction of UV light to create sharp, tapered hollows in SU-8, a negative photoresist, after development. Polymer microneedles were formed using these SU-8 structures as a mold. These polymer needles may be applicable as flexible electrodes in brain-machine interfaces because they are more likely to survive movement of the skin than conventional brittle silicon needles. Similar needles, made from medicinal substances, could be used for transdermal drug administration. For these applications, the needles must be long, sharp, and stiff enough to penetrate the stratum corneum (∼20 μm in thickness) and reach the viable epidermis (200-300 μm in thickness), but must not reach the dermis, which contains sensitive nerve endings. We successfully manufactured 20×20 microneedle arrays of polydimethylsiloxane with a needle length of 200 μm. We experimentally verified that these manufactured electrodes successfully penetrated the stratum corneum of a cultured skin.

A microdeformable mirror was designed. One important design issue was whether or not the gap between substrates would be airtight. Another design issue was whether residual stress and annealing would affect the deformation. A theoretical description of the deformation of the mirror was obtained by means of the ideal gas law and the theory of plates and shells. It was found that an airtight gap would require application of greater voltages to deform the mirror, but would help the device avoid pull-in phenomena. The results showed that an annealed mirror would have a larger deformation and would be reliably useful even with a large voltage. To test the theory, an electrostatically actuated microdeformable focusing mirror was fabricated by bulk micromachining. To avoid high-temperature bonding, SU-8 photoresist was used as a wafer bonding layer. The results show that electrostatic force can be used to deform the mirror into a parabolic shape and that the parabolic mirror focuses light well. The theoretical predictions were confirmed by the experimental results.

We report a novel multicontact radio frequency (RF) microelectromechanical system (MEMS) switch with mechanical independent switch elements and microspring contacts. The consistent contact arrangement and the robust contact design can effectively increase the contact area, reduce the current density, and therefore improve the power-/current-handling capability. The working mechanism of the switch with microspring contact is investigated by CoventorWare® simulation tools. The switch, fabricated by the Cu-Ni dual-metallic-sacrificial-layer surface micromachining, is actuated at 55 V for characterization. The closing time is 11 μs, and the opening time is 13.5 μs. The isolation is -30.9 dB at 2 GHz and -11.5 dB at 20 GHz; the insertion loss is -0.12 dB at 2 GHz and -0.22 dB at 20 GHz. The contact metal is Pt-Au, and the measured switch resistance drops from 48 to 1.2 Ω when the actuation voltage increases from 40 to 65 V. The switch element handles a current of 300 mA at 0.1 Hz. The switch is an excellent candidate for microwave applications requiring high-power handling.

We present the new mold fabrications for nanoimprint lithography for the application of ordered array of rod or pore patterning. The concave and convex types of the mold are achieved. For this technology, the master is required preparation before the mold fabrication. The master is utilized by step and repeated to achieve the structures over a large area on the mold. The master, mold, and imprint results demonstrate that the new approaches of mold fabrication could be a feasible scheme with low cost and high throughput.

A wafer-level vacuum packaging based on anodic bonded glass-silicon-glass triple stack with both lateral interconnections and vertical feedthroughs is presented. A z-axis gyroscope is packaged and tested to verify the packaging process. The packaged gyroscope achieved a Q factor of 26000, increased by a factor of 30 when compared to the same gyroscope without vacuum packaging. The pressure in the packaged cavity is ∼100 Pa, and the stability of the Q factor in three months is ∼3%. Experiment results indicate that the proposed wafer-level vacuum packaging is feasible and suitable for high-performance wafer-level packaged gyroscopes.

The characteristics of biochemical sensors based on photonic crystal (PC) resonators are investigated in this work. The PC structure consists of holes arranged in a hexagonal lattice on a silicon slab. The nanoring resonator is formed by removing certain holes along a hexagonal trace. The hexagonal nanoring resonator is sandwiched by two PC waveguides that are formed by removing two lines of holes. The trapping of biomolecules, e.g., DNAs or proteins, in a functionalized sensing hole introduces a shift in resonant wavelength peak in the output terminal. We demonstrate two resonator designs: single and dual nanorings. The quality factor of the single nanoring resonator is 2400. The dual nanoring resonator reveals two different resonant modes. The propagated directions of dropped light for these two modes are antiparallel. The quality factors for these two resonant modes are 2100 and 1855, respectively. This dual nanoring resonator has a novel sensing mechanism, making it capable of simultaneously sensing two different biomolecules.

One of the critical issues for extreme ultraviolet lithography masks is particle-free mask handling. We report that the number of particle adders on the front side of a mask in a dual pod can be reduced to less than 0.01 particles/cycle (>46-nm polystyrene latex) during the process of starting from the load port to placing an electrostatic chuck (ESC) in vacuum. In addition, we find that chucking the mask on the ESC causes serious issues. One of these issues is whether the masks will be electrically charged by chucking the ESC and whether some particles will be added on the front side. We measure the electric potential of the back and front sides of the mask and examine the particle adders. We find that when the mask is electrically floated, potential on the front side of the mask increases during ESC chucking; when the mask is released from the ESC, it is electrically charged. This electrification causes adhesion of the particles. Our experiments show that to protect the mask from particles, the mask must be grounded throughout the entire process. For electrification, we confirm that a dual-pod system is effective in protecting the mask from particles.

We evaluate the sensor sensibility by immersing the sensor in phosphate buffer solution of pH 7.0 and measuring the background noise using a glass substrate for long-term monitoring. We propose a design of asymmetric planar electrodes for long-term monitoring in the phosphate buffer solution at 37°C. The background signals have been observed in cyclic voltammetric measurements, and the surface morphologies of platinum sensors were investigated by the scanning electron microscopy for the long-term experiment. With the same conditions, background oxidize current graphs were obtained over the range from 1.28 to 2.14 μA for the first 18 days. The sensor is intended for use in controlling of blood sugar and tissue sugar in diabetics and is suitable to be employed in a portable diagnostic and therapeutic apparatus.

Extreme ultraviolet (EUV) lithography is a promising candidate for high-volume manufacturing at the 22-nm half-pitch node and beyond. EUV projection lithography systems need to rely on reflective optical elements and masks with oblique illumination for image formation. It leads to undesired effects such as pattern shift and horizontal-to-vertical critical dimension bias, which are generally reported as shadowing. Rule-based approaches proposed to compensate for shadowing include changing mask topography, introducing mask defocus, and biasing patterns differently at different slit positions. However, the electromagnetic interaction between the incident light and the mask topography with complicated geometric patterns, such as optical diffraction, not only causes shadowing but also induces proximity effects. This phenomenon cannot be easily taken into account by rule-based corrections and thus imposes a challenge on a partially model-based correction flow, the so-called combination of rule- and model-based corrections. A fully model-based correction flow, which integrates an in-house optical proximity correction algorithm with rigorous three-dimensional mask simulation, is proposed to simultaneously compensate for shadowing and proximity effects. Simulation results for practical circuit layouts indicate that the fully model-based correction flow significantly outperforms the partially model-based one in terms of correction accuracy, while the total run time is slightly increased.

Extreme ultraviolet (EUV) lithography is a promising candidate for 2x-nm-node device manufacturing. Management of effective dose is important to meet the stringent requirements for critical dimension control. As a test pattern for a lithography tool evaluation, the effective dose monitor (EDM) demonstrates sound performance in dose monitoring for optical lithography, such as KrF lithography. The EDM can measure an exposure dose with no influence on defocus, because the image of an EDM pattern is produced by the zeroth-order ray in diffraction only. When this technique is applied to EUV lithography, the mask shadowing effect should be taken into consideration. We calculated the shadowing effect as a function of field position and applied it to correction of the experimental dose variation. We estimated the dose variation in EUV exposure field to be 2.55% when corrected by the shadowing effect. We showed that the EDM is useful for EUV lithography.

A key requirement for nanomanufacturing is maintaining acceptable traceability of measurements performed to determine size. Given that properties and functionality at the nanoscale are governed by absolute size, maintaining the traceability of dimensional measurements of nanoscale devices is crucial to the success of nanomanufacturing. There are various strategies for introducing traceability into the nanomanufacturing environment. Some involve first principles, but most entail the use of calibrated artifacts. In an environment where different types of products are manufactured, it is challenging to maintain traceability across different products mix. In this paper, we present some of the work we have done in developing methods to track the traceability of dimensional measurements performed in a wafer fabrication facility. We combine the concepts of reference measurement system, measurement assurance, and metrological timelines to ensure that traceability is maintained through a series of measurements that involve different instruments and product mixes, spanning a four-year period. We show how to use knowledge of process-induced and instrument systematic errors, among others, to ensure that the traceability of the measurements is maintained.

We have calibrated a physical resist model for extreme ultra-violet (EUV) lithography, and discuss model calibration and validation over a larger set of structures. The study is conducted on an extensive data set, collected at imec, for ShinEtsu resist SEVR-59 exposed on the ASML EUV alpha demo tool (ADT). The data set included more than a thousand measured feature widths (critical dimensions or CD) on wafer and mask. We address practical aspects of the calibration, such as the speed of calibration and selection of calibration input. The model is calibrated by simultaneously fitting 12 process windows of features with different mask CD (32, 36, 40 nm), orientation (horizontal, vertical), and pitch (dense, isolated). The smallest feature size at nominal process condition is a 32 nm CD at a dense pitch of 64 nm. Mask CD metrology was used to fit the model versus actually measured mask CD's. Cross-sectional scanning electron microscopy information was included in the calibration, to tune the simulated resist loss and sidewall angle. The achieved calibration root-mean-squared (RMS) error is ∼1.0 nm. We discuss the elements that were essential to obtain a well calibrated model. We discuss the impact of 3-D mask effects on the Bossung tilt. We demonstrate that a correct representation of the flare level during the calibration is key in order to achieve a high CD predictability at various flare levels. Although the model calibration is performed on a limited subset of the measurement data collected on 12 different patterns (one dimensional structure process windows), its accuracy is validated on a large number of patterns used to calibrate models for optical proximity correction―several hundred different feature types, at nominal dose and focus conditions. These were not included in the calibration; validation RMS results as small as 1 nm can be reached. Furthermore, we study the model's extendibility to two-dimensional end of line structures.

The use of customized illumination modes is part of the pursuit to stretch the applicability of immersion ArF lithography. Indeed, a specific illumination source shape that is optimized for a particular design leads to enhanced imaging results. Recently, freeform illumination has become available through pixelated diffractive optical elements or through ASML's programmable illuminator system (FlexRay^TM) allowing for virtually unconstrained intensity distribution within the source pupil. In this paper, the benefit of freeform over traditional illumination is evaluated, by applying source mask co-optimization (SMO) for an aggressive use case and wafer-based verification. For a 22-nm node SRAM of 0.099 and 0.078 μm² bit cell area, the patterning of the full contact and metal layer into a hard mask is demonstrated with the application of SMO and freeform illumination. In this work, both pixelated diffractive optical elements and FlexRay are applied. Additionally, the match between the latter two is confirmed on wafer, in terms of critical dimension and process window.

Pellicles are mounted on the masks used in ArF lithography for integrated circuit manufacturing to ensure defect-free printing. The pellicle, a thin transparent polymer film, protects the reticle from dust. But, as the light transmittance through the pellicle has an angular dependency, the pellicle also acts as an apodization filter. In the current work, we present both experimental and simulation results at 1.35 numerical aperture immersion ArF lithography showing the influence of two types of pellicles on proximity and intra-die critical dimension uniformity (CDU). To do so, we mounted and dismounted the different pellicle types on one and the same mask. The considered structures on wafer are compatible with the 32-nm logic node for poly and metal. For the standard ArF pellicle (thickness 830 nm), we experimentally observe a distinct effect of several nm due to the pellicle presence on both the proximity and the intra-die CDU. For the more advanced pellicle (thickness 280 nm), no signature of the pellicle on proximity or CDU could be found. By modeling the pellicle's optical properties as a Jones Pupil, we are able to simulate the pellicle effects with good accuracy. These results indicate that for the 32-nm node, it is recommended to take the pellicle properties into account in the optical proximity correction calculation when using a standard pellicle. In addition, simulations also indicate that a local dose correction can compensate to a large extent for the intra-die pellicle effect. When using the more advanced thin pellicle (280 nm), no such corrections are needed.

Our purpose is to reduce the critical dimension (CD) bias for very small patterns with line widths of <15 nm. The model-based library (MBL) method, which estimates the dimensions and shape of a target pattern by comparing a measured scanning electron microscopy image waveform with a library of simulated waveforms, was modified in two ways. The first modification was the introduction of line-width variation into the library to overcome problems caused by significant changes in waveform due to changes in both sidewall shape and line width. The second modification was the fixation of MBL tool parameters to overcome problems caused by the reduction in pattern shape information due to merging of right and left white bands. We verified the effectiveness of the modified MBL method by applying it to actual silicon patterns with line widths in the range 10-30 nm. The CD bias measured by MBL method for three heights (20, 50, and 80%) was consistent with the atomic force microscopy results. The CD biases at all heights were <0.5 nm, and the slopes of the CD biases with respect to the CD were <3%.

Complex, submicron Cu metallic mesh nanostructures are made by electrochemical deposition using polymer templates made from photoresist. The polymer templates are fabricated with photoresist using two-beam interference holography and phase mask holography with three diffracted beams. Freestanding metallic mesh structures are made in two separate electrodepositions with perpendicular photoresist grating templates. Cu mesh square nanostructures having large (52.6%) open areas are also made by single electrodeposition with a photoresist template made with a phase mask. These structures have potential as electrodes in photonic devices.

Optical proximity correction (OPC) modeling is traditionally based on critical dimension (CD) measurements. As design rules shrink and process windows become smaller, there is an unavoidable increase in the complexity of OPC resolution enhancement technique (RET) schemes required to enable design printability. The number of measurement points for OPC modeling has increased to several hundred points per layer, and metrology requirements are no longer limited to simple 1-D measurements. Contour-based OPC modeling has recently arisen as an alternative to the conventional CD-based method. In this work, the technology of contour alignment and averaging is extended to arbitrary 2-D structures. Furthermore, the quality of scanning electron microscope (SEM) contours is significantly improved in cases where the image has both horizontal and vertical edges (as is the case for most 2-D structures) by a new SEM image method, which we call fine SEM edge (FSE). OPC model calibration is done using SEM contours from 2-D structures. Then, the effectiveness of contour-based calibration is examined by doing model verification. The experimental results of the model quality with innovative SEM contours that was developed by Hitachi High-Technologies Corporation (Ibaraki-ken, Japan) are reported. This combination of advanced alignment and averaging, and FSE technologies, makes the best use of the advantage of contour-based OPC-modeling, and should be of use for next-generation lithography.

Communication between lithography and metrology is becoming increasingly demanding in advanced nodes. This is where the requirements for metrology become extremely tight. This work is dedicated to the search for "clean" metrology that is required to address these requirements. Metrology measurements are obtained via an angle-resolved scatterometry-based platform (called YieldStar). Details of the technology behind YieldStar were thoroughly discussed by Vanoppen et al. in 2010. In this current work, measurement limits are challenged to test resolution and measurement uncertainty for overlay, critical dimension (CD), and sidewall angle (focus). Results indicate an atomic-scale performance of deep subnanometers. Two different sizes of scatterometry-based overlay targets are evaluated and compared using a technique called the similarity index. A CD reconstruction model is tested for cross talk of underlying thin-film layers, specifically the case where one of the underlying layers is anisotropic. A systematic approach is taken to increase the complexity of a CD reconstruction model in steps to evaluate the capability of handling birefringence effects of anisotropic material in the model. CD metrology data (1-D and 2-D/hole layers) are compared to CD scanning electron microscope data. Focus measurements are also extended for product wafers, and focus precision is evaluated. In addition, CD metrology monitor wafer applications, such as hotplate monitoring and overlay metrology monitor wafer application for scanner stability and matched machine overlay, are tested.

A process window is a collection of values of process parameters that allow a circuit to be printed and to operate under desired specifications. A conventional process window, which is determined through geometrical fidelity, geometric process window (GPW), does not account for lithography effects on electrical metrics such as delay, static noise margin (SNM), and power. In contrast to GPW, this paper introduces an electrical process window (EPW) which accounts for electrical specifications. Process parameters are considered within EPW if the performance (delay, SNM, and leakage power) of printed circuit is within desired specifications. Our experiment results show that the area of EPW is 1.5 to 8× larger than that of GPW. This implies that even if a layout falls outside geometric tolerance, the electrical performance of the circuit may satisfy desired specifications. In addition to process window evaluation, we show that EPW can be enlarged by 10% on average using gate length biasing and V_th push. We also propose approximate methods to evaluate EPW, which can be used with little or no design information. Our results show that the proposed approximation method can estimate more than 70% of the area of reference EPW. We also propose a method to extract representative layouts for large designs which can then be used to evaluate a process window, thereby improving the runtime by 49%.

The National Institute of Standards and Technology (NIST), Advanced Surface Microscopy (ASM), and the National Metrology Centre (NMC) of the Agency for Science, Technology, and Research (A*STAR) in Singapore have completed a three-way interlaboratory comparison of traceable pitch measurements using atomic force microscopy (AFM). The specimen being used for this comparison is provided by ASM and consists of SiO2 lines having a 70-nm pitch patterned on a silicon substrate. For this comparison, NIST used its calibrated atomic force microscope (C-AFM), an AFM with incorporated displacement interferometry, to participate in this comparison. ASM used a commercially available AFM with an open-loop scanner, calibrated with a 144-nm pitch transfer standard. NMC/A*STAR used a large scanning range metrological atomic force microscope with He-Ne laser displacement interferometry incorporated. The three participants have independently established traceability to the SI (International System of Units) meter. The results obtained by the three organizations are in agreement within their expanded uncertainties and at the level of a few parts in 10⁴.

This paper proposes an integrated model of a scratch drive actuator (SDA) based on a fourth-order governing equation of the Euler-Bernoulli theory. By solving this equation with proper boundary conditions, typical SDA output characteristics, such as noncontact length, priming voltage, deflection curve, output force, and bending stress, can be determined. The results of the output force in a static model are then used as the input of single degree-of-freedom dynamic SDA model to investigate the friction effect. Electroplated nickel SDA arrays, 80 μm in main beam length and 65 μm in width with a suspended spring, are fabricated and tested. The average travel distances after 1500 input pulses of 80-120 V are measured and found to be from 4.7 to 12.9 μm. The average measured output forces are from 10.2 to 28.3 μN. The simulation from the dynamic model is closer to the measured total travel distance and the output force than the static model, in general. The difference between simulations and experimental data due to energy dissipation can be reduced by including the friction effect in the dynamic model. Deviations between simulations and measured results are less than 10% in full range showing the superior capability of the proposed SDA model.

The goal of this work is to use a combination of experiment and calibrated resist models to understand the impact of photo-acid generator (PAG) and sensitizer loading on the performance of a polymer bound PAG resist based processes for extreme ultraviolet (EUV) lithography. This paper describes construction of a chemically amplified resist model across 248 nm, 193 nm, and EUV imaging wavelengths. Using resist absorbance input as obtained from experiment and modeling, only the acid formation kinetics are allowed to vary across imaging wavelengths. This constraining system affords very good fitting results, which provides high confidence that the extracted parameters from the model have actual physical significance. The quantum efficiency for acid formation in EUV is found to be ∼8× higher than at 248 or 193 nm, due to the excitation mechanism by secondary electrons. Most notably for the polymer bound PAG system under study the model provides an extremely low acid diffusion length (∼8 nm), suggesting an excellent inherent resolution for this material. Next, resist models are created for a series of sensitizer containing polymer bound PAG formulations, where the sensitizer loading is systematically varied. Compared to the reference polymer bound PAG resist without sensitizer the efficiency of acid formation is significantly increased, without a negative impact on either resolution or linewidth roughness. For these materials the quantum efficiency of acid formation in EUV is found to be ∼12× higher than at 248 nm. In these formulations the impact of sensitizer loading on the sizing dose is found to be rather moderate. This may suggest that even at the lowest sensitizer loading studied the energy of the secondary electrons is already efficiently transferred to the PAGs.

A design of barometric pressure sensor is presented in this paper, which is compatible with the standard complementary metal-oxide semiconductor process, and can solve the problem of the electrode feed-through out of the sealed cavity at the same time. Both electrodes of the sensor are led from the top side of the chip. Mechanical characteristics of the sensor are theoretically analyzed based on the plate theory and evaluated by finite element analysis. Square membrane sensors with side lengths of 300, 500, and 700 μm were fabricated, providing a measured sensitivity of 0.9. 1.2, and 1.7 fF/hPa, respectively. The nonlinearity of the sensor is less than 3.1% over a dynamic range 500 to 700 hPa. The experimental results and the theoretical analysis show that the device is suitable to be used in measuring the low pressure, and is more sensitive when the initial gap of the capacitor is smaller.

A technique is developed to enable accurate layer thickness control and planarization in a multilayer SU-8 2000 micromachining process, while maintaining a high quality surface finish. Relying on carefully controlled mechanical lapping and polishing stages, layer thicknesses from 30-400 μm have been routinely achieved to an accuracy of ±3 μm with excellent planarity. High-aspect ratio structures (intended for use in a millimeter-wave engineering application) with up to five layers and of 770-μm thickness have been fabricated using this method. The quality of the resulting surfaces has been investigated and characterized using scanning probe microscopy: a typical rms surface roughness of around 10 nm has been measured. The problem of air-bubble formation and migration encountered during the lapping stage has been documented along with a technique for their elimination. It is also shown that the common problem of the expansion of the lower layers in a multilayer structure due to solvent reabsorption can be effectively eliminated through careful process optimization.

Continuous shrinkage of the design rule in large-scale integrated circuit devices brings about greater difficulty in the manufacturing process. The keys to meeting small process margin are adequate extraction of critical dimension tolerance for each object, considering design intent in terms of electrical behavior, and assigning the tolerance for each process step. However, once the design data are converted to layout data and signed off, most of the design intent is abandoned and unrecognized in the process phase. Thus, uniform and redundant tolerance is used, and therefore, excess tolerance is assigned for some layouts. To solve the problem described above, a tolerance-based manufacturing system utilizing flexible layout-dependent speculation derived from design intent has been discussed. Using a 40-nm node test chip, electrically critical spots, such as timing, cross-talk noise, electromigration, with small margins are extracted, assigned to the physical layout, and utilized in the manufacturing process. The flow is applicable for optical proximity effect correction (OPC) turnaround time reduction, optimization of OPC/lithography compliance check (LCC) specification, and failure-analysis acceleration. Consequently, a design-intent-aware manufacturing system is promising for realizing proper process specifications and computational cost reduction, in addition to yield enhancement.

We present a novel multilayer grating pattern with a sub-50-nm pitch for critical dimension-scanning electron microscope (CD-SEM) magnification calibration as an advanced version of the conventional 100-nm pitch grating reference. A 25-nm pitch grating reference is fabricated by multilayer deposition of alternating materials and then material-selective chemical etching of the polished cross-sectional surface. A line and space pattern with 25-nm pitch is easily resolved, and a high-contrast secondary electron image of the grating pattern is obtained under 1-kV acceleration voltage using the CD-SEM. The uniformity of the 25-nm pitch of the grating is <1 nm in three standard deviations of the mean. The line-edge roughness of the grating pattern is also <0.5 nm. Such a fine and uniform grating pattern will fulfill the requirements of a magnification calibration reference for a next-generation CD-SEM.

This PDF file contains the errata for “JM3 Vol. 10 Issue 1 Paper 3562169” for JM3 Vol. 10 Issue 1