Sidewall Angle Research Articles

Cryogenic mid-wave infrared hyperspectral Fabry-Perot filter based on a tensile-strained single-layer subwavelength grating mirror.

We report here the first demonstration of a cryogenic mid-wave infrared (MWIR) hyperspectral fixed-cavity Fabry-Perot filter based on a suspended tensile-strained single-layer 2-D subwavelength grating (SWG) mirror. Optical design optimization of the 2-D SWG mirror and parameter tolerance study are performed. For the first time, process control of grating air-hole sidewall angle and the grating air-hole fill-factor fabrication error caused by e-beam lithography electron-scattering effect is reported. At 80 K, namely the operating temperature of MWIR photodetectors, the as-fabricated suspended 2-D SWG mirror has achieved excellent surface flatness with a slight center-to-edge bowing of 15 nm over a 1-mm2 large mirror area and a high average reflectivity of 0.97 across a wavelength range of 3.72-5 µm, which represents an unprecedentedly wide fractional bandwidth Δλ/λc of 30%. The cryogenically cooled Fabry-Perot filter exhibits an unrivaled high spectral resolution of 10 nm that far exceeds the optical requirement for MWIR hyperspectral imaging applications.

A review of hydraulic performance and design methods of labyrinth weirs

Abstract Labyrinth weirs are complex hydraulic structures. They have been widely used as a water regulator and to increase discharge in channels and spillway dams. Labyrinth weirs are an economical and effective method to pass large floods. In addition, they are used to reduce the requirements of the structural footprint. These features make them an interesting and appropriate choice to increase the capacity of discharge. Several factors affect the discharge capacity and the hydraulic performance of labyrinth weirs, including water level to crest height ratio, angle of sidewalls, apex width, conveyance channel conditions, and vertical aspect ratio. The present paper aims to summarise the most relevant knowledge of the hydraulic characteristics of the labyrinth weirs reported in previous articles. The importance of the present study is to provide a better understanding of how these weirs operate, in addition to which future studies deserve further investigation. The results demonstrated that some parameters still need further investigation. Also, energy dissipation over the labyrinth weir needs further investigation with different weir geometry. Furthermore, the results showed that common design equations did not take into account all parameters affecting labyrinth weir performance, including geometries, flow conditions, site conditions, and scale effect. In addition, machine learning techniques need further study.

Simulation and Analysis of the Optical Characteristics of Cylindrical Micropillars with InAs/GaAs Quantum Dots

The optical characteristics of vertical cylindrical micropillars with AlGaAs distributed Bragg reflectors and InAs/GaAs quantum dots, which are designed for the fabrication of single-photon sources, have been studied. The effect of parameters such as the inclination angle of sidewalls, partial oxidation of AlGaAs layers, and deviation of quantum dots from the central axis of a micropillar on the Purcell factor and the radiation extraction efficiency has been numerically simulated by the finite-difference time-domain method. The allowable ranges of the listed parameters have been determined for cylindrical vertical 920-nm micropillars. The comparison of the calculations performed with the refined refractive indices of the used materials at cryogenic temperatures with the measured characteristics of the fabricated micropillar structures has confirmed the adequacy of the used models.

Effect of sidewall roughness on the diffraction efficiency of EUV high aspect ratio freestanding transmission gratings.

Manufacturing-induced sidewall roughness has a significant impact on the diffraction efficiency of extreme ultraviolet (EUV) gratings and masks, which could be evaluated by a Debye-Waller damping factor. The rough profile models of line structures are always parallel to the surface for the reflective elements. In this manuscript, a model of rough lines along the thickness direction is established, which cannot be ignored for high aspect ratio transmission gratings. Numerical calculations are carried out using both a rigorous model and a Fraunhofer approximation model. The two models agree with each other on the low-order transmission efficiencies, and the fitted Debye-Waller factor indicates a larger roughness value than that of the model due to the absorption of EUV irradiation for 90° sidewall angle. When the sidewall angle is smaller than 88°, an extra degree of freedom is introduced to the traditional Debye-Waller factor-based formula. The +1-order transmission efficiency and absorptivity with smooth and rough sidewalls are also analyzed, as well as the effect of incidence angle, wavelength and grating thickness.

Dynamic response and vibration isolation of pipes inside a utility tunnel passing through nonhomogeneous soil under seismic action

An unreasonable design of the pipe support between a utility tunnel and the pipe can result in a large deformation of internal pipes under seismic action. In this study, aiming at the seismic response problem of pipes inside a utility tunnel passing through nonhomogeneous soil, a shaking table test and a finite element simulation were conducted. First, the boundary effect caused by the laminated shear box was studied, and the influences of the pipe acceleration, longitudinal and transverse relative slippages, the form of the pipe support, and the pipe material on the pipe deformation were analyzed. Finally, the attenuation effect of the acceleration peak response of the internal pipes and the attenuation law of the energy transmitted to the pipes were obtained. The results showed that the attenuation degree of the energy transmitted to the pipes was more than 80%; the longitudinal relative slippage of the pipes caused by the high-amplitude segment of the input acceleration was generally significant; the vibration isolation effect of the side-wall angle steel support on the pipeline was stronger than those of other supports. This paper provides a basis for the seismic design of pipelines inside a utility tunnel.

Investigation and process control of the grating fill-factor and sidewall angle impacts on 2-D metamaterial infrared mirrors

We report the first study of the effects of grating fill-factor variation and sidewall angle on 2-D subwavelength grating shortwave infrared mirrors, and the first development of a geometry compensation approach to correct for the grating fill-factor patterning error caused by EBL proximity effect and a plasma etching process based on CHF3 passivation to control grating sidewall angle. Mirrors with a large grating air-hole diameter-to-pitch ratio of 0.954 and vertical sidewall angle of 89.8° are demonstrated with an average reflectivity of 99% over an ultrabroad wavelength range of 560 nm (1.92-2.48 µm), which represents an unprecedented fractional bandwidth of 26%.

Inductively coupled plasma etching of bulk tungsten for MEMS applications

As a promising material for bulk micromachining for MEMS applications, tungsten can be used as microneedles for medicine injection and tools for micro-inject molding, ultrasonic machining, and electrical discharge machining. However, it is difficult to fabricate microstructures with high aspect ratios and small feature sizes due to the excellent material of tungsten properties, such as chemical stability, high hardness, and high melting point. Here, an inductively coupled plasma (ICP) deep etching process is developed for bulk tungsten, and its process parameters are studied. After optimizing the process parameters, three recipes were developed for different MEMS applications. A patterned tungsten structure with a depth of more than 300 µm was etched by tungsten (W) ICP deep etching (WIDE) at an etch rate of 2.73 µm/min and etch selectivity of 35. The WIDE process produced a tungsten microstructure with a high aspect ratio (> 20), a small feature size (< 3 µm), and a surface roughness of Ra 30 nm. To demonstrate the potential application prospect of deep etching bulk of tungsten, tungsten microneedles with a positive sidewall angle and several non-silicon substrates for MEMS applications were achieved based on the WIDE process. • Bulk tungsten ICP deep etching process development based SF 6 +O 2 +C 4 F 8 . • Effect of process parameters on ER, ES, DUR, roughness, sidewall angle. • μ-structures with > 300 µm deep, > 20 AR, and Ra 30 nm roughness. • Die steel, glass, and polymer μ-structures machined by etched tungsten. • Metal-based and non-silicon-based MEMS application prospect.

Fabrication of grooved LGS resonators based high temperature SAW sensors and analysis with FEM simulation

Langasite (LGS) based surface acoustic wave (SAW) sensors are widely used in high temperature circumstances due to their advantages of being passive and wireless. In this research, the platinum electrodes are deposited into the grooves of the LGS instead of on the surface to further improve the acoustic properties and prolong the lifetime of the resonators at high temperature. Proper MEMS fabrication techniques are proposed to fabricate such structures. The result of every step is evaluated, and the corresponding process parameters are optimized. With the optimal processes, two types of resonators with different Euler angles of (0∘, 22∘, 30∘) and (0∘, 22∘, 90∘) are fabricated on the LGS substrate. Furthermore, the process-influenced structure parameters such as metal ratio and sidewall angle are well investigated via a weak form nonlinear finite element method simulation model. The temperature dependence of the resonance frequency is measured, and the recorded thermal behaviors match well with the prediction of the simulation. In addition, the further endurance test shows that the devices could work at 1000 ∘C for 12 h. This research proves the validity of the grooved resonator structure and the prominent role of the simulation model in further optimizing the LGS-based SAW devices design.

Optical singularity assisted method for accurate parameter detection of step-shaped nanostructure in coherent Fourier scatterometry.

Accurate determination of the physical parameters of nanostructures from optical far-field scattering is an important and challenging topic in the semiconductor industry. Here, we propose a novel metrology method to determine simultaneously the height and side-wall angle of a step-shaped silicon nanostructure. By employing an optical singular beam into a typical coherent Fourier scatterometry system, both parameters can be retrieved through analyzing the intensity profile of the far-field scattering pattern. The use of singular beam is shown to be sensitive to slight changes of the parameters of the step. By changing the relative direction between the singularity and structure, the height and side-wall angle can both be retrieved with high precision. This new method is robust, simple, and can provide valuable means for micro-and-nano- metrologies.

Vertical and Lateral Etch Survey of Ferroelectric AlN/Al1-xScxN in Aqueous KOH Solutions.

Due to their favorable electromechanical properties, such as high sound velocity, low dielectric permittivity and high electromechanical coupling, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al1−xScxN) thin films have achieved widespread application in radio frequency (RF) acoustic devices. The resistance to etching at high scandium alloying, however, has inhibited the realization of devices able to exploit the highest electromechanical coupling coefficients. In this work, we investigated the vertical and lateral etch rates of sputtered AlN and Al1−xScxN with Sc concentration x ranging from 0 to 0.42 in aqueous potassium hydroxide (KOH). Etch rates and the sidewall angles were reported at different temperatures and KOH concentrations. We found that the trends of the etch rate were unanimous: while the vertical etch rate decreases with increasing Sc alloying, the lateral etch rate exhibits a V-shaped transition with a minimum etch rate at x = 0.125. By performing an etch on an 800 nm thick Al0.875Sc0.125N film with 10 wt% KOH at 65 °C for 20 min, a vertical sidewall was formed by exploiting the ratio of the planes and planes etch rates. This method does not require preliminary processing and is potentially beneficial for the fabrication of lamb wave resonators (LWRs) or other microelectromechanical systems (MEMS) structures, laser mirrors and Ultraviolet Light-Emitting Diodes (UV-LEDs). It was demonstrated that the sidewall angle tracks the trajectory that follows the of the hexagonal crystal structure when different c/a ratios were considered for elevated Sc alloying levels, which may be used as a convenient tool for structure/composition analysis.

Depth estimation from a single SEM image using pixel-wise fine-tuning with multimodal data

To support the ongoing size reduction in integrated circuits, the need for accurate depth measurements of on-chip structures becomes increasingly important. Unfortunately, present metrology tools do not offer a practical solution. In the semiconductor industry, critical dimension scanning electron microscopes (CD-SEMs) are predominantly used for 2D imaging at a local scale. The main objective of this work is to investigate whether sufficient 3D information is present in a single SEM image for accurate surface reconstruction of the device topology. In this work, we present a method that is able to produce depth maps from synthetic and experimental SEM images. We demonstrate that the proposed neural network architecture, together with a tailored training procedure, leads to accurate depth predictions. The training procedure includes a weakly supervised domain adaptation step, which is further referred to as pixel-wise fine-tuning. This step employs scatterometry data to address the ground-truth scarcity problem. We have tested this method first on a synthetic contact hole dataset, where a mean relative error smaller than 6.2% is achieved at realistic noise levels. Additionally, it is shown that this method is well suited for other important semiconductor metrics, such as top critical dimension (CD), bottom CD and sidewall angle. To the extent of our knowledge, we are the first to achieve accurate depth estimation results on real experimental data, by combining data from SEM and scatterometry measurements. An experiment on a dense line space dataset yields a mean relative error smaller than 1%.

Accurate Inner Profile Measurement of a High Aspect Ratio Aspheric Workpiece Using a Two-Probe Measuring System

This paper presents a novel method for inner profile measurement and geometric parameter evaluation, such as the radius of the bottom, steepness and straightness of the steep sidewall of a high aspect ratio aspheric workpiece, by utilizing a two-probe measuring system, which includes a lateral displacement gauge for the inner steep sidewall profile measurement and an axial displacement gauge for the inner deep underside profile measurement. To qualify the measurement accuracy, the systematic errors associated with the measurement procedure, including the miscalibration, misalignment and the roundness error of the gauge probes, as well as the slide motion error of the four-axis motion platform, are all evaluated and separated from the measurement results. A point cloud registration algorithm is employed to stitch the evaluated inner sidewall profile and the inner underside profile to form an entire inner profile of the workpiece. To verify the performance of the newly proposed method, the inner profile of a high aspect ratio aspheric workpiece, which has a tapered cone shape with a maximum inner radius of 40 mm, a maximum inner depth of 140 mm and a steep sidewall angle approaching 85°, is measured in experiments. The measurement result is compared with that of a coordinate measuring machine (CMM), and the comparison verifies the feasibility of the proposed measurement system.

Design Space of GaN Vertical Trench Junction Barrier Schottky Diodes: Comprehensive Study and Analytical Modeling

We report gallium nitride (GaN) vertical trench junction barrier Schottky (TJBS) diodes and systematically analyzed the effects of the key design parameters on the reverse and forward characteristics of the devices. By taking advantage of the shielding effects from both the trenches and pn junctions in the TJBS structure, the high electric field at the Schottky contact region can be effectively suppressed. We found that the doping concentration, thickness, and spacing of p-GaN, as well as the depth and angle of the trench sidewalls are closely associated with the electric field distribution and the reverse characteristics of the TJBS diodes. With an optimal set of design parameters, the local electric field crowding at either the corner of the trench or the edge of the p-GaN can also be alleviated, resulting in a boosted breakdown voltage of up to 1250 V in the TJBS diodes. In addition, an analytical model was developed to explore the physical mechanism behind the forward conduction behaviors. We believe that the results can provide a systematical design strategy for the development of low-loss, high-voltage, and high-power GaN power diodes towards an efficient power system.

Numerical modeling of thermo‐flows in a trapezoidal cavity containing different solid objects

AbstractHeat transfer in chambers is essential in the industry as heating/cooling systems, as well as electronic equipment. This study investigates the mixed heat transfer of fluid inside a trapezoidal chamber with a hot obstacle. The variable parameters include trapezoidal side angles, Rayleigh number, surface emissivity coefficient of obstacle, heat conduction ratio, and aspect ratio of obstacle. In addition, the geometry of solid obstacles is considered rectangular and circular. The governing equations are solved numerically by a fourth‐order characteristics‐based scheme. The bottom wall of the obstacle has persistent heat flux, another wall is adiabatic and the sidelong walls of the cavity are cold, and the upper and lower walls are adiabatic. Moreover, the other walls are insulated. The results demonstrate that the mean Nusselt number of cold walls declines as the angle of side walls increases in different Rayleigh numbers. Nusselt number rises with an increment of Rayleigh number at sustained angles. Higher aspect ratios and emissivity coefficients lead to higher Nusselt numbers for various Rayleigh numbers. The results show that by increasing the angle, the Nusselt number decreases up to 50%. Also, the Nusselt number for rectangle obstacles is up to 30% more than that for a circular obstacle. The working fluid here is water, with Prandtl number 6.9.

Experimental study of cavitation index in an ogee spillway by considering convergence angle of sidewalls

Abstract Cavitation is among the most complex and common damage occurring in spillway structures, which is one of the most expensive parts of a dam. The cavitation index, as the one of the most efficient approaches, can be used to analyze this important hydraulic phenomenon. The present study examines the changes in the cavitation index caused by changes in the convergence angle of an ogee spillway's sidewalls with an arc in the plan. To this end, a spillway was constructed on the 1:50 scale. Then, it was tested with four different convergence angles, including 0°, 60°, 90°, and 120°, relative to the spillway's sidewalls and six different flow rates per unit width ranging from 6.74 to 48.42 (l/s)/m. The results indicated that as the flow rate increased, the cavitation index relatively declined at both crest and chute of the spillway while growing at its toe. It was observed that the lowest cavitation index was found to be 1.54 in.X/Hd = 2.42 at an angle of 0° and a flow rate per unit width of 40.52 (L/s)/m.

A Study of 4H-SiC Semi-Superjunction Rectifiers for Practical Realisation

This paper discusses the design and simulation of 4H-SiC semi-SJ structures producing results that are below the unipolar limit, whilst also ensuring practical and cost-effective realisation. The results demonstrate that a semi-SJ structure with a 10° sidewall angle increases the implantation window of the device by 45%, relative to the full-SJ, whilst maintaining a high VBD of ~2 kV and a low RON,SP. This design facilitates a wide implantation window with a reduced trench aspect ratio, significantly improving the practical realisation of the device. It also offers softer reverse recovery characteristics as a result of both the angled trench sidewall and the n-bottom assist layer (n‑BAL) which allows for the structure to be depleted gradually.

Etch the borosilicate glass to form a straight through-glass-via based on the FLACE technology

Interposers will become in demand for advanced electronic systems and through the substrate, vias are essential for 3D integration. A straight via is necessary because a tapered hole is accompanied by large signal loss. This article reports a straight through-glass-via (TGV) fabricated by femtosecond laser-assisted chemical etching (FLACE). The femtosecond laser was used to modify the glass substrates, and the modified glass samples were etched with hydrofluoric acid (HF) solution to form TGV. The effects of key processing parameters, including laser pulse energy, the number of burst pulses, and the HF solution concentration, on the TGV taper profile, were systematically investigated. It was found that The TGV taper sidewall angle decreases with increasing laser pulse energy and increases with increasing HF solution concentration. The number of bursts should be optimized because more than 10 bursts would prevent TGV formation. The study shows via etched in 3 wt% HF after irradiation with 3 bursts of 60 μJ can become approximately vertical. Among the three processing parameters, HF concentration was found to be the most crucial parameter. This work can serve as a critical reference for applications of TGV in high-performance 3D integrated circuits.

Cr/C lamellar multilayer grating in conical diffraction mounting for beam splitter used in X-ray free-electron lasers.

A lamellar multilayer grating in a conical diffraction mounting was proposed as a beam splitter for X-ray free-electron lasers. Theoretical calculations demonstrated that the distribution of diffraction efficiency can be adjusted by optimizing the groove depth or d-spacing. A Cr/C multilayer lamellar grating with a line density of approximately 2500 L/mm was fabricated. The performance of the element was measured in the Optics Beamline PM-1 (BESSY-II) at an energy of 1500 eV. A five-order diffraction pattern was recognized, and the diffraction efficiencies of the -/+first-order were approximately 12.6 and 4.4%, respectively. The asymmetric distribution of diffraction efficiency can be caused by the different sidewall angles of the grating groove.

Thermo-fluidic transport process in a novel M-shaped cavity packed with non-Darcian porous medium and hybrid nanofluid: Application of artificial neural network (ANN)

In this work, an attempt has been made to explore numerically the thermo-fluidic transport process in a novel M-shaped enclosure filled with permeable material along with Al2O3-Cu hybrid nanoparticles suspended in water under the influence of a horizontal magnetizing field. To exercise the influence of geometric parameters, a classical trapezoidal cavity is modified with an inverted triangle at the top to construct an M-shaped cavity. The cavity is heated isothermally from the bottom and cooled from the top, whereas the inclined sidewalls are insulated. The role of geometric parameters on the thermal performance is scrutinized thoroughly by changing the sidewall inclination, number, and height of the top inverted triangular undulation under similar boundary conditions. The governing equations transformed into dimensionless form are solved by using a computing code written in the finite volume approach. The analysis is conducted by considering a wide range of parametric influences like sidewall angles (γ), number (n), and height (δ) of the top triangular undulations, modified Rayleigh number (Ram), Darcy number (Da), Hartmann number (Ha), and hybrid nanoparticle concentrations (φ). Furthermore, the artificial neural network (ANN) technique is implemented and tested to predict the overall thermal behavior of the novel cavity to predict new cases. The results revealed that the design of sidewall inclination (γ) is an important parameter for modulating the thermo-flow physics. The M-shaped cavity (compared to trapezoidal) reveals either a rise or drop in the fluid circulation strength depending upon the magnitude of δ, but the heat transfer rate always increases due to an increase in the cooling length. The heat transfer increment is ∼61.01% as δ increases. Single undulation with higher depth is the optimum choice for achieving improved heat transfer (which may go up to ∼355.75% for δ = 0.5 and γ = 45°). A decrease in Da or Ha causes a drop in the flow strength, which consequently leads to a drop in the heat transfer rate. Furthermore, the concepts of ANN will help researchers predict the behavior for such complicated cavity shapes with a multiphysics approach. This will save efforts as well as computing time for exploring the thermal behavior of any range of a dataset.

Analysis of diffraction-based wafer alignment rejection for thick aluminum process

A diffraction-based alignment method has been widely used during lithography processes. The alignment position is obtained by analyzing the light intensity changes of the moiré fringes. In order to ensure the reliability of the alignment, the alignment system sets a preset threshold value during measurement and then rejects the measurement data that do not meet the requirements directly. In the diffraction-based alignment system, the photolithographic technology encounters the situation of alignment rejection frequently when processing the thick aluminum film alignment process and most of the reasons for rejection are wafer quality and delta shift. In this paper, we proposed a fast and adaptable analysis method for asymmetric structures and have carried out a systematic study. The calculation results of our model are verified with a rigorous physical model with high accuracy. The influences of the thickness fluctuation of the deposited aluminum and the sidewall angle of the alignment mark on wafer quality are studied. The reasons and degrees of delta shift induced by the process are also explored and studied. The results show that for the same alignment mark, the thickness fluctuation has a greater impact on wafer quality than the sidewall angle. For different alignment strategies, such as to align to a metal layer or to a contact layer, different alignment rejection is experimentally obtained and analyzed. Our model gave a conclusion as to why aligning to a contact layer mark is more process-robust than to a metal layer. The delta shift is mostly generated by the grating inconsistent of the moiré alignment grating. Process induced wafer distortion of the alignment mark will increase inconsistency and then make the delta shift out of threshold.