Sidewall Angle Research Articles

Fabrication of locally micro-structured fiber Bragg gratings by fs-laser machining

Here, we describe a method for producing locally micro-structured fiber Bragg gratings (LMFGB) by fs-laser machining. This technique enables the precise and reproducible ablation of cladding material to create circumferential grooves inside the claddings of optical fibers. From initial ablation experiments we acquired optimized process parameters. The fabricated grooves were located in the middle of uniform type I fiber Bragg gratings. LMFBGs with four different groove widths of 48, 85, 135 and 205 $$\upmu {\text {m}}$$ were produced. The grooves exhibited constant depths of about 30 $$\upmu {\text{m}}$$ and steep sidewall angles. With the combination of micro-structures and fiber Bragg gratings, fiber optic sensor elements with enhanced functionalities can be achieved.

Analytical calculation on the determination of steep side wall angles from far field measurements

In the semiconductor industry, the performance and capabilities of the lithographic process are evaluated by measuring specific structures. These structures are often gratings of which the shape is described by a few parameters such as period, middle critical dimension, height, and side wall angle (SWA). Upon direct measurement or retrieval of these parameters, the determination of the SWA suffers from considerable inaccuracies. Although the scattering effects that steep SWAs have on the illumination can be obtained with rigorous numerical simulations, analytical models constitute a very useful tool to get insights into the problem we are treating. In this paper, we develop an approach based on analytical calculations to describe the scattering of a cliff and a ridge with steep SWAs. We also propose a detection system to determine the SWAs of the structures.

Design of neural network arc sensor for gap width detection in automated narrow gap GMAW

An approach to develop an arc sensor for gap width estimation during automated NG-GMAW with a weaving electrode motion is introduced by combining arc sensor readings with optical measurements of the groove shape to allow precise analyses of the process. The two test specimen welded for this study were designed to feature a variable groove geometry in order to maximize efficiency of the conducted experimental efforts, resulting in 1696 individual weaving cycle records with associated arc sensor measurements, process parameters and groove shape information. Gap width was varied from 18 mm to 25 mm and wire feed rates in the range of 9 m/min to 13 m/min were used in the course of this study. Artificial neural networks were applied as a modelling tool to derive an arc sensor for estimation of gap width suitable for online process control that can adapt to changes in process parameters as well as changes in the weaving motion of the electrode. Wire feed rate, weaving current, sidewall dwell currents and angles were defined as inputs to calculate the gap width. The evaluation of the proposed arc sensor model shows very good estimation capabilities for parameters sufficiently covered during the experiments.

Use of model-based library in critical dimension measurement by CD-SEM

Model-based library (MBL) method, based on the fundamental physics of electron-solid interaction and Monte Carlo simulation of electron transport and secondary electron (SE) cascades, is an ideal algorithm in critical dimension (CD) metrology by CD-SEM, which exceeds the experiential structure characterization with SE profile curve. Particularly, comparing to the threshold method, the MBL method can extends to 3D metrology of CD by including many more geometrical structural parameters, such as, top CD, bottom CD, height and sidewall angles. In this work, we study the SE signal profile shape in CD metrology for the MBL method. The gate lines in trapezoidal cross section shape with arc corners are modeled for the simulation of SE linescans. The sensitivity of the SE intensity profiles to the different topographic parameters are investigated. In addition, the practical aspects of CD evaluation including pre-processing of experimental SE image and profile matching procedure are discussed. The work will be beneficial to the related standardization of CD measurement.

Natural Convection Heat Transfer in 2D and 3D Trapezoidal Enclosures Filled with Nanofluid

The purpose of the present study is to investigate the heat transfer performance due to free convection of nanofluids with variable properties inside 2D and 3D channels with trapezoidal cross sections. The governing equations are solved numerically using the finite volume method and the SIMPLER algorithm. In this study, the effect of the nanoparticle volume fraction, Rayleigh number, side wall angles of the trapezoidal section, and axial slope of the 3D channel are examined. The presented results include the average Nusselt number, flow circulation streamlines, and isothermal contours. The heat transfer rate (i.e., Nusselt number) is seen to increase in both 2D and 3D channels with an increase in the Rayleigh number. In 2D trapezoidal enclosures, the Nusselt number decreases with an increase in the nanoparticle volume fraction from zero to 2% and increases if the nanoparticle volume fraction is greater than 2%. In 3D channels, an increase in the axial slope of the channel leads to an increase in the Nusselt number.

An integrated strategy for improving contrast, durability, and portability of a Pocket Colposcope for cervical cancer screening and diagnosis.

IntroductionWe have previously developed a portable Pocket Colposcope for cervical cancer screening in resource-limited settings. In this manuscript we report two different strategies (cross-polarization and an integrated reflector) to improve image contrast levels achieved with the Pocket Colposcope and evaluate the merits of each strategy compared to a standard-of-care digital colposcope. The desired outcomes included reduced specular reflection (glare), increased illumination beam pattern uniformity, and reduced electrical power budget. In addition, anti-fogging and waterproofing features were incorporated to prevent the Pocket Colposcope from fogging in the vaginal canal and to enable rapid disinfection by submersion in chemical agents.MethodsCross-polarization (Generation 3 Pocket Colposcope) and a new reflector design (Generation 4 Pocket Colposcope) were used to reduce glare and improve contrast. The reflector design (including the angle and height of the reflector sidewalls) was optimized through ray-tracing simulations. Both systems were characterized with a series of bench tests to assess specular reflection, beam pattern uniformity, and image contrast. A pilot clinical study was conducted to compare the Generation 3 and 4 Pocket Colposcopes to a standard-of-care colposcope (Leisegang Optik 2). Specifically, paired images of cervices were collected from the standard-of-care colposcope and either the Generation 3 (n = 24 patients) or the Generation 4 (n = 32 patients) Pocket Colposcopes. The paired images were blinded by device, randomized, and sent to an expert physician who provided a diagnosis for each image. Corresponding pathology was obtained for all image pairs. The primary outcome measures were the level of agreement (%) and κ (kappa) statistic between the standard-of-care colposcope and each Pocket Colposcope (Generation 3 and Generation 4).ResultsBoth generations of Pocket Colposcope had significantly higher image contrast when compared to the standard-of-care colposcope. The addition of anti-fog and waterproofing features to the Generation 3 and 4 Pocket Colposcope did not impact image quality based on qualitative and quantitative metrics. The level of agreement between the Generation 3 Pocket Colposcope and the standard-of-care colposcope was 75.0% (kappa = 0.4000, p = 0.0028, n = 24). This closely matched the level of agreement between the Generation 4 Pocket Colposcope and the standard-of-care colposcope which was also 75.0% (kappa = 0.4941, p = 0.0024, n = 32).ConclusionOur results indicate that the Generation 3 and 4 Pocket Colposcopes perform comparably to the standard-of-care colposcope, with the added benefit of being low-cost and waterproof, which is ideal for use in resource-limited settings. Additionally, the reflector significantly reduces the electrical requirements of the Generation 4 Pocket Colposcope enhancing portability without altering performance compared to the Generation 3 system.

Ultra-low loss photonic circuits in lithium niobate on insulator.

Lithium niobate on insulator (LNOI) photonics promises to combine the excellent nonlinear properties of lithium niobate with the high complexity achievable by high contrast waveguides. However, to date, fabrication challenges have resulted in high-loss and sidewall-angled waveguides, limiting its applicability. We report LNOI single mode waveguides with ultra low propagation loss of 0.4 dB/cm and sidewall angle of 75°. Our results open the route to a highly efficient photonic platform with applications ranging from high-speed telecommunication to quantum technology.

Atomic Force Microscopy Sidewall Imaging with a Quartz Tuning Fork Force Sensor.

Sidewall roughness measurement is becoming increasingly important in the micro-electromechanical systems and nanoelectronics devices. Atomic force microscopy (AFM) is an emerging technique for sidewall scanning and roughness measurement due to its high resolution, three-dimensional imaging capability and high accuracy. We report an AFM sidewall imaging method with a quartz tuning fork (QTF) force sensor. A self sensing and actuating force sensor is fabricated by microassembling a commercial AFM cantilever (tip apex radius ≤10 nm) to a QTF. The attached lightweight cantilever allows high-sensitivity force detection (7.4% Q factor reduction) and sidewall imaging with high lateral resolution. Owing to its unique configuration, the tip of the sensor can detect sidewall surface orthogonally during imaging, which reduces lateral friction. In experiments, sidewalls of a micro-electro-mechanical system (MEMS) structure fabricated by deep reactive ion etching process and a standard step grating are scanned and the sidewall roughness, line edge roughness and sidewall angles are measured.

Multi-objective optimisation of profile accuracy in two point incremental forming using Taguchi-based grey relation analysis

This study investigates the effect of four key process parameters in two point incremental forming (TPIF) on the profile accuracy of the manufactured parts. The experiment was applied to A1050-H14 commercial aluminium sheets under different values for tool diameter, feed rate, vertical step size, and sheet thickness. The experiments were designed using the Taguchi L8 orthogonal array. Profile accuracy was estimated by measuring four quality parameters, namely, circularity error, waviness error, depth error, and side wall angle error. Analysis of variance (ANOVA) was used for studying the significance of each process parameter. Grey relational analysis (GRA) was then used to perform a multi-objective optimisation of the four quality parameters simultaneously. The results showed that while each quality parameter may be optimised separately, it is considerably difficult to optimise all of them together. In practice, a compromise must be made based on the profile feature necessary in a given situation.

Experimental study on flow over in-reservoir arced labyrinth weirs

For a given width, labyrinth weirs provide an increase in the weir crest length, which increases the weir flow capacity. Labyrinth weirs are generally designed in linear configurations. However, arced configurations have been employed in reservoir applications to improve the orientation of the weir cycles to the approach flow and to further increase the weir crest length. This paper experimentally studies the flow characteristics of arced labyrinth weirs. Experimental observations are presented and the parameters affecting the flow capacity are discussed. The effects of the headwater ratio (Ho/P), the sidewall angle (α), and the weir arc angle (Θ) on the discharge coefficient and the efficiency are also investigated. The results indicate that the efficiency of an arced labyrinth weir can be increased up to almost 4.5 times of that of a linear weir. However, the benefits of increasing Θ and decreasing α diminish by increasing Ho/P. Finally, a design method is presented for in-reservoir arced labyrinth weirs.

MEMS Industry-Worth Etching to Fabricate Tapered Structures in SiO2

This paper presents the results for developing SiO2 plasma etching with tapered sidewalls for microelectromechanical systems (MEMS). The experiment was designed in an industrial inductively-coupled plasma reactive ion etching tool, wherein a two-step etching process was developed for opening vias in the SiO2 with a sidewall angle of 68°–70°. The first step modified the photoresist profile from a vertical to a tapered profile using Ar/O2/CF4 plasma with a high wafer platen power. The second step of SiO2 etching was performed in C4F8/H2-based plasma with added inert gases and used a dual mechanism of photoresist pattern transfer and etch by-product redeposition on the sidewalls. The introduction of the photoresist profile tapering as the first step of the etching process not only facilitated fabrication of tapered sidewalls, but also helped to avoid etch-stop in structures with a critical dimension (CD) down to 1.5 $\mu \text{m}$ and minimize the etch CD shrink. [2017-0089]

Implementation of light extraction improvements of GaN-based light-emitting diodes with specific textured sidewalls

Textured-sidewall GaN-based light-emitting diodes (LEDs) with various sidewall angles (15–90°) and convex or concave sidewalls prepared using an inductively-coupled-plasma approach are comprehensively fabricated and studied. The device with 45° sidewalls (Device F) and that with convex sidewalls (Device B) show significant improvements in optical properties. Experiments show that, at an injection current of 350 mA, the light output power, external quantum efficiency, wall-plug efficiency, and luminous flux of Device F (Device B) are greatly improved by 18.3% (18.2%), 18.2% (18.2%), 17.3% (19.8%), and 16.6% (18.4%), respectively, compared to those of a conventional LED with flat sidewalls. In addition, negligible degradation in electrical properties is found. The enhanced optical performance is mainly attributed to increased light extraction in the horizontal direction due to a significant reduction in total internal reflection at the textured sidewalls. Therefore, the reported specific textured-sidewall structures (Devices B and F) are promising for high-power GaN-based LED applications.

Design and fabrication of micro-LED array with application-specific integrated circuits (ASICs) light emitting display

An optimized array process of micro light-emitting diode (LED) display is descripted as follows. Silicon nitride (SiNx) is the main component of dielectric protective layer as a mask layer in the fine-grain etching process of LED pixel platform. GaN-based material is etched by the etching mask layer. The size of 12 ? 12 μm micro-die LED array is used as the test pattern, and an approximate thickness of SiNx film is 2.63 μm during LED epitaxial growth. An etch mask of SiNx dielectric protection layer and the inductively coupled plasma etching equipment are utilized for etching the pattern and transferring to GaN LED epitaxial film. The etch depth is about 6.4 μm, and the final pattern size is about 11.06 μm. The ultimate etched sidewall angle of micro-grain GaN LED is close to vertical. During the dip-coating process, the etching shift on top of the fine crystal GaN LED platform becomes narrower because of the larger size of the dielectric protection layer. The metal contact electrodes are fabricated on micro LED die platform. The results of this research are valuable for driving the micro-LED display with application-specific integrated circuits (ASICs) system. The shift register, the counter, and the decoder module are combined in ASIC system as a novel technique. Three-dimensional multi-data processing chip can control the drive of 128 ? 40 matrix and a total of 5120 LED number, and driving the entire panel takes only 20.5 ms.

Deep etching of Zerodur glass ceramics in a fluorine-based plasma

The etching of glass is still much more challenging than the deep etching of silicon. But in contrast to pure silica, most glasses are complex alloys of serval oxides including aluminium oxide. For this reason, it is quite difficult to find suitable high-rate deep dry etching processes and related masking materials. For extremely temperature-insensitive micromechanical systems it is of interest to use zero-expansion glass ceramics such as Zerodur. But the microstructure of Zerodur consists of crystalline and amorphous phases and shows a high percentage of Al2O3-bonds. This makes plasma etching challenging. Here, deep etching of Zerodur only in a fluorine-based plasma for micro-technical applications is investigated. Different process parameters such as the physical power and gas mixtures of the ICP-RIE-process have been varied. Etch rates of about 250nm/min and sidewall angles of approximately 71° were reached with a nickel mask and the etch gas SF6. The achieved total etching depth is as large as 150μm resulting in a release of microelements such as springs and gears from a Zerodur wafer.

Polarization multiplexed all-dielectric metasurfaces for wavefront manipulation in a transmission mode

All-dielectric metasurfaces are planar structures completely consisting of dielectric materials, which enable the control of phase, amplitude and polarization of light. Due to the good process compatibility and high transmittivity, they have drawn considerable attention in diverse applications for polarization conversion and wavefront manipulation in a transmission mode. Although several kinds of all-dielectric metasurfaces have been reported in literature to achieve wavefront manipulation, they either have only one fixed wavefront output or have susceptible efficiency to the side-wall-angle (SWA) error, which is extremely difficult to be minimized with current top-down fabrication processes. In this work, we propose an elliptical silicon nanopillar array, which possesses a polarization multiplexed response and high transmittivity, and more importantly, it is less sensitive to the SWA error. Two metasurfaces, namely a beam deflector and a vortex convertor, are exemplified to examine the performance of the proposed elliptical nanopillar array at a visible wavelength of 600 nm. We achieve high transmittivity of 76.7% and 81.4% for the beam deflector and the vortex convertor, respectively. Moreover, both the deflecting direction of the beam deflector and the chirality of the generated beam from the vortex convertor can be controlled by the incident polarization. The proposed all-dielectric metasurfaces demonstrate great potential for practical and polarization multiplexed optical elements.

Numerical study on fabricating rectangle microchannel in microfluidic chips by glass molding process

This paper studied the glass molding process (GMP) for fabricating a typical microstructure of glass microfluidic chips, i. e., rectangle microchannel, on soda-lime glass by finite element method. More than 100 models were established on the platform of Abaqus/Standard. The influence of parameters, i. e., temperature, aspect ratio, side wall angle and friction coefficient on deformation were studied, and the predicted morphology of the molded microchannel were presented as well. The research could provide fundamental experience for optimizing GMP process in the future.

Low-Temperature Cu–Cu Direct Bonding Using Pillar–Concave Structure in Advanced 3-D Heterogeneous Integration

Low-temperature Cu–Cu bonding utilizing pillar and concave on silicon substrate with and without polymer layer is successfully implemented at 200 °C under atmospheric pressure. Finite-element method (FEM) simulations on stress and deformation generated during bonding process are also presented in order to discuss their influence on bonding result of several pillar diameters and of concave sidewall angles originating from the manufacturing process. The alteration of parameters in FEM simulations would also be investigated to enhance the bonding outcome. The parameters include the diameter of pillar, the sidewall angle of concave, the shape of the concave opening, the addition of extra polymer layer under Cu concave layer, the bonding temperature, and the pitch of the pillar–concave structure. The implementation of Cu–Cu bonding using pillar–concave structure could have a prospective effect on existing packaging methods in semiconductor industry with benefits of applicability to various sorts of substrates and low bonding temperature.

Influence of a non-ideal sidewall angle of extreme ultra-violet mask absorber for 1 ×-nm patterning in isomorphic and anamorphic lithography

The impact of non-ideal absorber sidewall angle (SWA) has been a serious problem as target pattern sizes have been reduced. During mask fabrication, it is difficult to obtain an absorber sidewall angle of 90° due to the imperfect etching process. Furthermore, it is known that repeated mask cleaning processes can worsen this problem. We investigated various patterning results of non-ideal absorbers with sidewall angles <90°. Moreover, we simulated how this affects anamorphic high-numerical aperture (NA) patterning for targeted patterns of 7nm node and smaller. The resist critical dimension (CD) can be varied by about 20% with a 5° variation in the SWA for a horizontal 16nm 1:1 periodic line and space pattern compared to a target CD. For an anamorphic high-NA system, the CD variation caused by the SWA effect is larger in the vertical direction than it is in the horizontal direction due to the asymmetric reduction ratio on the anamorphic mask (4x/8y), which is different from the isomorphic mask (4x/4y). Thus, we must determine the horizontal-vertical bias (H-V bias) generated by non-ideal absorbers in the anamorphic system. Decreasing the SWA from 90° to 85° increased the HV bias of a 10nm 1:1 line and space pattern by 52%.

Control of Sidewall Profile in Dry Plasma Etching of Polyimide

Spin-on polyimide is an organic thin film often used as a sacrificial layer for surface micromachining due to its high thermal stability, ease of removal, and compatibility with many materials and processes used in the realization of microelectromechanical systems (MEMS). The incorporation of sloped sidewalls in polyimide for fabricating pedestal structures is crucial in order to provide strong anchors in free-standing MEMS devices, especially in cases having a high aspect ratio and/or where structural materials have limited deposition conformality. This paper demonstrates a reliable reactive ion etching (RIE) methodology for tuning the polyimide sidewall angle, ranging from a vertical sidewall up to an angle of about 25° from the vertical. The key modifications to the process parameter space include changes to the process temperature and chamber pressure. This paper also presents a novel lift-off process, which is based on the use of an interfacial polymer layer to facilitate removal of an overlying silicon oxide hard mask. This procedure allows polyimide sacrificial layers employing a silicon oxide hard mask to be used on samples that have exposed silicon oxide layers elsewhere on the chip that are required to remain intact during hard mask removal. Therefore, this lift-off process is applicable in situations where the silicon oxide hard mask removal cannot be accomplished by wet etching in hydrofluoric acid solutions.

Overcoming Etch Challenges on a 6″ Hg1−x Cd x Te MBE on Si Wafer

The effect of increasing photoresist (PR) thickness on the inductively coupled plasma (ICP) dry etched characteristics of a 6″ (c.15 cm) molecular beam epitaxy Hg1−x Cd x Te/Si wafer is investigated. It is determined that the Hg1−x Cd x Te etch rate (ER) does not vary significantly with a change in the PR thickness. Also, the vertical ER of the PR is seen to be independent of the PR thickness, but the lateral ER is seen to reduce significantly with increased PR thickness. Indeed, very little reduction in the pixel mesa area post-dry etch is seen for the thicker PR. Consequently, the trench sidewall angle is also seen to vary as a function of the PR thickness. Since ICP is the more attractive choice for dry etching Hg1−x Cd x Te, this simple, cost-effective way to extend the capabilities of dry etching (larger mesa top area post-dry etch, ability to create tailor-made trench sidewall angles for optimal conformal passivation deposition, and potential for reduced dry etch damage) described here would allow for the fabrication of next generation infrared detectors with increased yield and reduced cost. Although similar results have been presented using the electron cyclotron resonance system to dry etch Hg1−x Cd x Te, to the best of our knowledge, this is the first time that such results have been presented using an ICP system.