Sidewall Angle Research Articles

Silicon Micromachined D-Band Diplexer Using Releasable Filling Structure Technique

A D-band waveguide diplexer, implemented by silicon micromachining using releasable filling structure (RFS) technique to obtain high-precision geometries, is presented here for the first time. Prototype devices using this RFS technique are compared with devices using the conventional microfabrication process. The RFS technique allows etching large waveguide structures with nearly 90° sidewall angles for the 400-μm-tall waveguides. The diplexer consists of two direct-coupled cavity six-pole bandpass filters, with the lower and the upper band at 130-134 and 141-148.5 GHz, respectively. The measured insertion loss of the two bands is 1.2 and 0.8 dB, respectively, and the measured return loss is 20 and 18 dB, respectively, across 85% of the passbands. The worst case adjacent channel rejection is better than 59 dB. The unloaded quality factors of a single cavity resonator are estimated from the measurements to reach 1400. Furthermore, for the RFS-based micromachined diplexer, an excellent agreement between measured and simulated data was observed, with a center frequency shift of only 0.8% and a bandwidth deviation of only 8%. In contrast to that, for the conventionally micromachined diplexer of this high complexity, the filter poles are not well controllable, resulting in a large center frequency shift of 3.5%, a huge bandwidth expanding of over 60%, a poor return loss of 6 and 10 dB for the lower and the upper band, respectively, and an adjacent channel rejection of only 22 dB.

High-efficiency edge-coupling based on lithium niobate on an insulator wire waveguide.

Edge-coupling on single-crystal thin-film lithium niobate on insulator (LNOI) was systematically studied in this paper. An inverse taper-shaped spot-size converter (SSC) to convert the mode field from the laser chip to a nanoscale LNOI waveguide was adopted to improve the coupling efficiency. Structure of the edge coupler was fully investigated and optimized by using the eigenmode expansion method. The single-mode conditions of the LNOI waveguide for three common communication bands were taken into consideration. Further, the length and tip width of the inverse taper, the cross-section dimensions of SiON waveguide, and the sidewall angle were investigated with respect to coupling efficiency. As a result, the maximum coupling efficiency from an edge coupler to laser chip can reach 54%, 48%, and 58% at 1550, 1310, and 850 nm in Z-cut LNOI for quasi-TM mode, respectively. This proposed work gives a better understanding of the function of the edge coupler based on LNOI material and provides an appropriate method for the design of an edge coupler with high efficiency, which could benefit the further application of high-density monolithic integrated optical components.

Geometric Effects on Discharge Relationships for Labyrinth Weirs

Published labyrinth weir design methods, along with specific site constraints, are typically used to develop an appropriate labyrinth weir geometry (footprint, weir height, wall thickness, apex dimensions, sidewall length, sidewall angle, number of cycles, crest shape, etc.) for the desired head-discharge relation. When a proposed labyrinth weir geometry deviates from the underlying design data, uncertainty in hydraulic performance increases and may merit additional guidance or numerical or physical modeling. This study quantifies the effects of systematic variations (apex dimensions, sidewall length, channel width, and weir height) on labyrinth weir hydraulic performance. After considering hydraulic performance, constructability, and economics, an optimum apex width was identified. Hydraulic efficiency was found to decrease with increasing cycle number (for a constant-width channel), and upstream apex geometries were more significant than downstream geometries with respect to hydraulic efficiency. The impact of weir height on hydraulic efficiency was variable, with an overly short weir showing a negative impact and taller weirs being beneficial but only up to a certain height.

Energy Dissipation and Hydraulics of Flow over Trapezoidal–Triangular Labyrinth Weirs

In this work experimental and numerical investigations were carried out to study the influence of the geometric parameters of trapezoidal–triangular labyrinth weirs (TTLW) on the discharge coefficient, energy dissipation, and downstream flow regime, considering two different orientations in labyrinth weir position respective to the reservoir discharge channel. To simulate the free flow surface, the volume of fluid (VOF) method, and the Renormalization Group (RNG) k-ε model turbulence were adopted in the FLOW-3D software. The flow over the labyrinth weir (in both orientations) is simulated as a steady-state flow, and the discharge coefficient is validated with experimental data. The results highlighted that the numerical model shows proper coordination with experimental results and also the discharge coefficient decreases by decreasing the sidewall angle due to the collision of the falling jets for the high value of H/P (H: the hydraulic head, P: the weir height). Hydraulics of flow over TTLW has free flow conditions in low discharge and submerged flow conditions in high discharge. TTLW approximately dissipates the maximum amount of energy due to the collision of nappes in the upstream apexes and to the circulating flow in the pool generated behind the nappes; moreover, an increase in sidewall angle and weir height leads to reduced energy. The energy dissipation of TTLW is largest compared to vertical drop and has the least possible value of residual energy as flow increases.

Ultra-broadband fabrication-tolerant mode division (de)multiplexer on thin film Lithium niobate

Mode division (de) multiplexers based on asymmetric directional coupler are designed and analysed on the emerging thin film lithium niobate platform in rib, buried and strip waveguide configurations. Rib configuration offers a large bandwidth of ∼215 nm with a crosstalk level lower than −10 dB, and provides a large fabrication tolerance of ±50 nm. Strip configuration exhibits a better crosstalk of −19.7 dB at the design wavelength of 1550 nm, and has a reasonable fabrication tolerance of ±30 nm. Performance of (de) multiplexers on all three waveguide configurations are analysed in terms of modal crosstalk, mode conversion efficiency, bandwidth, along with fabrication tolerance to width and sidewall angle. The influence of electro-optic effect on the coupling length of lithium niobate mode multiplexers is also investigated.

Patterning nickel for extreme ultraviolet lithography mask application I. Atomic layer etch processing

The stringent requirement for patterning highly absorbing metal thin films as a mask for the next-generation extreme ultra-violet lithography system dictates the development of an atomic layer etching process to tailor the etch rate and the etch profile. A “plasma-thermal” atomic layer etching process is developed where an oxygen plasma is used to convert the metallic Ni layer into NiO, followed by formic acid vapor reacting with NiO to form nickel formate [Ni(COOH)2], thereby removing nickel. The directionality of the oxygen ions is used to create a directional chemical conversion of Ni into NiO, resulting in an anisotropic etch profile. Using the SiO2 patterned Ni thin film, a high etching selectivity to the mask (virtually no etching of SiO2) and a high etching anisotropy (a sidewall angle up to 87°) are achieved.

Characterization of nanoscale gratings by spectroscopic reflectometry in the extreme ultraviolet with a stand-alone setup.

The authors present a study on the dimensional characterization of nanoscale line gratings by spectroscopic reflectometry in the extreme ultraviolet spectral range (5 nm to 20 nm wavelength). The investigated grating parameters include the line height, the line width, the sidewall angle and corner radii. The study demonstrates that the utilization of shorter wavelengths in state-of-the-art optical scatterometry provides a high sensitivity with respect to the geometrical dimensions of nanoscale gratings. Measurable contrasts are demonstrated for dimensional variations in the sub-percent regime, down to one tenth of a nanometer and one tenth of a degree in absolute terms. In an experimental validation of the method, it is shown that reflectance curves can be obtained in a stand-alone setup using the broadband emission of a discharge produced plasma as the source of EUV radiation, demonstrating the potential scalability of the method for industrial uses. Simulated reflectance curves are fit to the experimental curves by variation of the grating parameters using rigorous electromagnetic modeling. The obtained grating parameters are cross-checked by a scanning electron microscopy analysis.

Enhancement of Er luminescence in microdisk resonators made of Er,O-codoped GaAs

We report on the fabrication and optical characteristics of microdisk (MD) resonators with Er,O-codoped GaAs (GaAs:Er,O) as an active component. MD resonators based on GaAs:Er,O with different sidewall angles are fabricated by electron beam lithography followed by two different processes: dry and wet etching. Numerical simulations using a finite-difference time-domain method demonstrate an increase in the cavity quality (Q) factor of the MDs when sharpening the taper angle of the MDs. Micro-photoluminescence characterization of the MD resonators with excitation by a He–Ne laser reveals an 11.4-fold enhancement of Er-related luminescence and a cavity Q factor of 4.2 × 103. For the MD resonators with tapered sidewalls, further enhancement of Er luminescence and increased Q factor (>9.0 × 103) are observed.

Dispersion tailoring in wedge microcavities for Kerr comb generation.

The shaping of group velocity dispersion in microresonators is an important component in the generation of wideband optical frequency combs. Small resonators-with tight bending radii-offer the large free-spectral range desirable for wide comb formation. However, the tighter bending usually limits comb formation as it enhances normal group velocity dispersion. We experimentally demonstrate that engineering the sidewall angle of a small-radius (∼100µm), 3-µm-thick silica wedge microdisk enables dispersion tuning in both normal and anomalous regimes, without significantly affecting the free spectral range. A microdisk with a wedge angle of 55° (anomalous dispersion) is used to demonstrate a 300 nm bandwidth Kerr optical frequency comb.

Comprehensive characterization of TSV etching performance with phase-contrast X-ray microtomography

Comprehensive evaluation of through-silicon via (TSV) reliability often requires deterministic and 3D descriptions of local morphological and statistical features of via formation with the Bosch process. Here, a highly sensitive phase-contrast X-ray microtomography approach is presented based on recorrection of abnormal projections, which provides comprehensive and quantitative characterization of TSV etching performance. The key idea is to replace the abnormal projections at specific angles in principles of linear interpolation of neighboring projections, and to distinguish the interface between silicon and air by using phase-retrieval algorithms. It is demonstrated that such a scheme achieves high accuracy in obtaining the etch profile based on the 3D microstructure of the vias, including diameter, bottom curvature radius, depth and sidewall angle. More importantly, the 3D profile error of the via sidewall and the consistency of parameters among all the vias are achieved and analyzed statistically. The datasets in the results and the 3D microstructure can be applied directly to a reference and model for further finite element analysis. This method is general and has potentially broad applications in 3D integrated circuits.

High-voltage CD-SEM-based application to monitor 3D profile of high-aspect-ratio features

Background: In-line metrology for three-dimensional (3D) profiling high-aspect-ratio (HAR) features is highly important for manufacturing semiconductor devices, particularly for memory devices, such as 3D NAND and DRAM. Aim: Our purpose was to obtain the cross-sectional profiles of the HAR features from top-view critical dimension scanning electron microscopy (CD-SEM) images. Approach: Based on Monte Carlo simulation results, we proposed a method for 3D profiling of HAR features using backscattered electron (BSE) signal intensities. Several kinds of HAR holes with different taper angles and bowing geometries were fabricated. High-voltage CD-SEM was used for experiments to determine the feasibility of our approach. Results: Using the BSE line-profile, we constructed cross sections of the taper holes and estimated sidewall angles (SWAs), which were approximately the same as those observed using field-emission scanning electron microscopy (FE-SEM). The constructed cross sections of the bowing holes and the trends of the geometric variance, which were estimated by the middle CD and its depth, were consistent with the cross sections observed by FE-SEM. Conclusions: The results demonstrate that the variation in the HAR holes, such as SWA and bowing geometry, can be measured and monitored using the BSE images.

Multimode silicon photonic waveguide corner-bend.

An ultra-sharp multimode waveguide bend (MWB) based on a multimode waveguide corner-bend (MWCB) is proposed and realized. With the present MWCB, total internal reflection (TIR) happens and the light propagation direction of all the mode-channels can be modified with low excess losses (ELs) and low inter-mode crosstalk (CT) in the optical communication bands from 1260 nm to 1680 nm. For the MWCB designed for the TE0 and TE1 modes, the ELs are less than 0.18 dB and the inter-mode CTs are less than -36 dB in the wavelength range of 1260-1680 nm. The measurement results show the fabricated MWCB works very well as predicted by the theory. It is very flexible to extend the present MWCB for more mode-channels by simply adjusting the core width. For example, the MWCB designed with a 35 µm-wide core has an EL less than 0.54 dB and inter-mode CT less than -24 dB for the ten TE-polarization modes (i.e., TE0∼TE9) in the wavelength-band of 1260-1680 nm. For the present MWCB, the fabrication is also very convenient because no tiny nano-structure and no additional fabrication steps are needed. It also shows that the present MWCB is not sensitive to the sidewall angles even when the angle is up to 8°. The proposed MWCB is promising for multimode silicon photonics because of the simple structure, easy design, easy fabrication as well as excellent performances in an ultra-broad wavelength-band.

Enhancing reliability of InGaN/GaN light-emitting diodes by controlling the etching profile of the current blocking layer

SiO2 was used as the current blocking layer (CBL) during fabricating the InGaN/GaN-based light-emitting diodes (LEDs). The SiO2 film was prepared by plasma enhanced chemical vapor deposition (PECVD) at a lower temperature (LT) of 180 °C and a higher temperature (HT) of 280 °C for characterizing the reliability of LEDs. The degradation of output power in LT-CBL LED is as high as 6.8% during 1000 h in the high-temperature and humidity (85 °C/85 RH) condition. Experimental results demonstrate the low temperature grown CBL forms a larger side-wall angle via wet etching. The thinner side-wall ITO film cracks and the current spreading effect is suppressed, causing drastic power degradation. On the contrary, the HT-CBL SiO2 demonstrates optimal step coverage of ITO film for current spreading and then the HT-CBL LEDs slightly degrade as low as 5% in the accelerated reliability test. A dense quality of HT-CBL SiO2 as well as a good CBL decreased parasitic optical absorption in the p-pad electrode and p-finger. Besides, the HT-CBL SiO2 showed a small side-wall angle of 40˚ which increased the step coverage and current spreading of ITO. An approach is conducted to confirm the side-wall profile of CBL for each process.

Mesa-Sidewall Effect on Coherent Terahertz Radiation via Spontaneous Synchronization of Intrinsic Josephson Junctions in Bi2Sr2CaCu2O8+δ

We investigate the effect of the ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ mesa sidewall on the spontaneous synchronization of intrinsic Josephson junctions and concomitant terahertz radiation. We develop a lithography technique to control the sidewall angles. Using a Fourier interferometer, we characterize the radiation emitted from a series of mesas with different sidewall angles. We determine that a uniform distribution of the oscillation frequencies is essential to produce coherent radiation outside the mesa. It is also noted that in the resonant state, the input excess energy is transferred to the excitation of the coherent state.

Discharge characteristics and structure of flow in labyrinth weirs with a downstream pool

A new design of a labyrinth weir is introduced in this study by adding a square pool to the vertex of a one-cycle triangular labyrinth weir with a sidewall angle of 45°. The addition of the square pool increased weir length without causing an excessive nappe interaction, and as a result, reduced the head water over the weir with the same discharge. Laboratory experiments were carried out to investigate the hydraulic performance of the new design with a potential application in pool-weir fishways. Mean and turbulence characteristics of flow for different weir geometries and in both free and submerged flow regimes were measured to be used for prediction of fish behaviour in the upstream of the proposed weir models. Discharge coefficients based on channel width and weir length were calculated. It was found that the new design can significantly increase the capacity of triangular labyrinth weirs and provide financial advantages in construction over triangular labyrinth weirs without pools in low discharges. In submerged flow conditions, the proposed model performed better than sharp-crested linear weirs in low discharges. Contour plots of the three-dimensional velocity components showed a region of strong mean flow around the neck of the new weir model. Turbulent characteristics such as turbulent kinetic energy, power spectra, exuberance ratio, and joint probability distribution functions of velocity fluctuations were extracted from instantaneous three dimensional velocities for different weir depths and flow regimes. Two vertical planes were identified based on the highest turbulent mixing in free and submerged flow regimes. The depths contributing the most to turbulent mixing were identified; active depths decreased as the flow regime changed from free to submerge flow regime.

Influence of operation parameters on BOSCH-process technological characteristics

Authors investigated direct plasmachemical etching of silicon with Bosch-process using installation for inductively coupled plasma (PLATRAN-100) in gas area consist of SF6 and CHF3 gases in etching and deposition steps respectively. Defined correlations of etching rate, selectivity Si/photoresist, anisotropy, etch uniformity and sidewall angle on flow rate of polymerizing gas and electrical bias on deposition step. It is shown that increasing of CHF3 flow rate leads to higher etch selectivity Si/photoresist, anisotropy and uniformity of silicon but increase etching rate and sidewall angle. Also there was demonstrated that increasing of electrical bias on deposition step leads to higher silicon etching rate, uniformity and sidewall angle but at the same time decrease anisotropy and selectivity Si/photoresist. Authors reached etch selectivity Si/photoresist about 38 with etch uniformity 99.3% and depth about 18 mkm. The highest speed of silicon etch was 3.12 μm/min with uniformaty 99.7% and sidewall angle 89.6 °.

Influence of incident illumination on optical scattering measurement of typical photoresist nanostructure

<sec>Optical scatterometry, as a fast, low-cost, and non-contact measurement instrument, is widely used in the profile characterization of nanostructure in the semiconductor manufacturing industry. In general, it involves two procedures, i.e. the forward optical modeling of sub-wavelength nanostructures and the reconstruction of structural profiles from the measured signatures. Here, the general term signature means the scattered light information from the diffractive grating structure, which can be in the form of reflectance, ellipsometric angles, Stokes vector elements, or Mueller matrix elements. The profile reconstruction process is an inverse problem with the objective of optimizing a set of floating profile parameters (e.g., critical dimension, sidewall angle, and height) whose theoretical signatures can best match the measured ones through regression analysis or library search. </sec><sec>During solving the inverse problem, the refractive index and distinction coefficient of the material of nanostructure are assumed to be constants and they are generally fixed. This assumption is valid for most of the materials in semiconductor industry, but not for certain materials that are very photosensitive. That is, the optical constants of photosensitive materials may vary with the illumination time of the incident light beam in spectroscopic ellipsometer, and the error caused by the variation of optical constants propagates to the final extracted results of structural profiles, which should not be neglected, especially for high precision and accuracy metrology.</sec><sec>Experiments performed on SiO<sub>2</sub> and polymethyl methacrylate (PMMA) thin films are conducted and demonstrate that the extracted geometric parameters and optical constants of SiO<sub>2</sub> film do not change with illumination time increasing, while the twenty groups of values of extracted refractive index <i>n</i> and distinction coefficient <i>k</i> of PMMA resist film vary obviously, and the difference between the extracted maximum and minimum film thickness has reached 40.5 nm, which to some extent illustrates that the above assumption is not valid for PMMA resist, so that the incident light beam of spectroscopic ellipsometer has a great influence on the extracted film thickness. Further, simulations based on a three-dimensional PMMA grating also indicate that the error of optical constant has considerably transferred to the extracted profile parameters. This finding is of significance for improving the accuracy of nanostructure characterization in optical scatterometry.</sec>

Micro-Faraday cup array structures fabrication in silicon using deep reactive ion etching

Micro-Faraday cup array (MFCA) detectors are used for the detection and analysis of incident ion particles with greater stability and precision. New and simple micro FCA structures have been designed and fabricated considering the application in mass spectrometry and laser plasma techniques. MFCA structures were fabricated using UV lithography followed by deep reactive ion etching (DRIE). The UV lithography process was utilised for fabrication of micro-Faraday cup array structure in photoresist (AZ4903) deposited on n-type silicon substrate. After that DRIE process was used for creating array pattern in silicon. Ultimately 1 × 16 arrays having 25 μm widths with 125 μm spacing were fabricated. Maximum depth achieved with DRIE process was 16 μm. Exposure time of lithography was found to be reduced by 110% using UV-LED source for these structures. Effects of etch cycle time on cup depth and sidewall angle have also been discussed.

Modulation Asymmetry Suppression of Multifunction Integrated Optic Circuit by Sinking Electrode

The modulation asymmetry of a multifunction integrated optic circuit (MIOC) indicates the difference in the phase response to modulation electric fields with the same magnitude but different directions, and is partly caused by the vertical component of the modulation signal. This introduces a nonlinear phase error that is difficult to compensate in fiber optic gyroscopes (FOGs), which needs to be suppressed. In this paper, a sinking-electrode MIOC design to suppress the modulation asymmetry is proposed and verified through numerical simulations. Optimal parameters of the gap, height, side-wall angle, and center position error of the sinking electrodes are obtained on the basis of the simulation results. With the proposed method, the modulation asymmetry of MIOC can be reduced from 5 × 10 -4 rad to 1 × 10 -6 rad, thus facilitating the development of high-performance FOGs. Furthermore, compared with the traditional electrode design, the sinking-electrode design can increase the tolerance for the manufacturing process, and the design configuration can be obtained through the general process method.

Characteristic and Robustness of Trench Floating Limiting Rings for 4H-SiC Junction Barrier Schottky Rectifiers

In this letter, planar floating limiting rings (FLRs) and trench FLRs with different trench depths for the 4H-SiC junction barrier Schottky (JBS) rectifiers are analyzed and compared with simulations and experiments. Compared with the planar FLRs, the experimental results present that the first ring spacing window that termination efficiency exceeds 80% of the parallel plane breakdown voltage (BV) can be widened and termination area can be reduced at the same BV by adopting the trench FLRs. The simulations also indicate that there is an optimal trench depth for the trench FLRs and a smaller sidewall angle can achieve better device performance. Additionally, the repetitive avalanche current stress measurements imply that the trench FLRs has better robustness regarding the BV shift, achieving better device reliability.