Asymmetric Sidewall Research Articles

Designing Highly Precise Overlay Targets for Asymmetric Sidewall Structures Using Quasi-Periodic Line Widths and Finite-Difference Time-Domain Simulation.

The present study introduces an optimized overlay target design to minimize the overlay error caused by asymmetric sidewall structures in semiconductor manufacturing. To achieve this goal, the overlay error formula was derived by separating the asymmetric bottom grating structure into symmetric and asymmetric parts. Based on this formula, it was found that the overlay target design with the linewidth of the bottom grating closed to the grating period could effectively reduce the overlay error caused by the sidewall asymmetry structure. Simulation results demonstrate that the proposed design can effectively control the measurement error of different wavelengths within ±0.3 nm, even under varying sidewall angles and film thicknesses. Overall, the proposed overlay target design can significantly improve the overlay accuracy in semiconductor manufacturing processes.

Robust nanotransfer printing by imidization-induced interlocking

The importance of the nanotransfer technique has been increased owing to its possibility in nanoscale mass-production, enabled by cost-effective and simply fabricable features. In this study, we developed a novel method for robust nanotransfer printing based on imidization-induced mechanical interlocking. The proposed imidization-induced nanotransfer printing (InTP) method enables various metal nanostructures to be easily transferred onto a polyimide substrate based on the mechanical interlocking force by using a controlled imidization process. The designed functional nanopatterns are transferred with high robustness. In addition, using a partial imidization process, we apply an additional adhesion force at the pattern-substrate interface to transfer materials with poor intrinsic adhesion, such as nickel, successfully. Owing to the exceptional robustness of the method, various 3D nanostructures, such as asymmetric sidewalls, suspended nanowires, and dual-layer line patterns, can be successfully transferred. Moreover, the InTP method was used to fabricate a uniform and high-temperature film heater and an asymmetric blind film.

Numerical investigation of a small footprint plasmonic Bragg grating structure with a high extinction ratio

In this paper, miniaturized design of a plasmonic Bragg grating filter is investigated via the finite element method (FEM). The filter is based on a plasmonic metal-insulator-metal waveguide deposited on a quartz substrate. The corrugated Bragg grating designed for near-infrared wavelength range is structured on both sides of the waveguide. The spectral characteristics of the filter are studied by varying the geometric parameters of the filter design. As a result, the maximum ER and bandwidth of 36.2 dB and 173 nm is obtained at λBragg=976 nm with a filter footprint of as small as 1.0 x 8.75 µm2, respectively. The ER and bandwidth can be further improved by increasing the number of grating periods and the strength of the grating, respectively. Moreover, the Bragg grating structure is quite receptive to the refractive index of the medium. These features allow the employment of materials such as polymers in the metal-insulator-metal waveguide which can be externally tuned or it can be used for refractive index sensing applications. The sensitivity of the proposed Bragg grating structure can offer a sensitivity of 950 nm/RIU. We believe that the study presented in this paper provides a guideline for the realization of small footprint plasmonic Bragg grating structures which can be employed in filter and refractive index sensing applications. Full Text: PDF ReferencesJ. W. Field et al., "Miniaturised, Planar, Integrated Bragg Grating Spectrometer", 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference (CLEO/Europe-EQEC), Munich, Germany, 2019, CrossRef L. Cheng, S. Mao, Z. Li, Y. Han, H.Y. Fu, "Grating Couplers on Silicon Photonics: Design Principles, Emerging Trends and Practical Issues", Micromachines, 11, 666 (2020). CrossRef J. Missinne, N. T. Beneitez, M-A. Mattelin, A. Lamberti, G. Luyckx, W. V. Paepegem, G. V. Steenberge, "Bragg-Grating-Based Photonic Strain and Temperature Sensor Foils Realized Using Imprinting and Operating at Very Near Infrared Wavelengths", Sensors, 18, 2717 (2018). CrossRef M. A. Butt, S.N. Khonina, N.L. Kazanskiy, "Numerical analysis of a miniaturized design of a Fabry–Perot resonator based on silicon strip and slot waveguides for bio-sensing applications", Journal of Modern Optics, 66, 1172-1178 (2019). CrossRef H. Qiu, J. Jiang, P. Yu, T. Dai, J. Yang, H. Yu, X. Jiang, "Silicon band-rejection and band-pass filter based on asymmetric Bragg sidewall gratings in a multimode waveguide", Optics Letters, 41, 2450 (2016). CrossRef M. A. Butt, S.N. Khonina, N.L. Kazanskiy, "Optical elements based on silicon photonics", Computer Optics, 43, 1079-1083 (2019). CrossRef N. L. Kazanskiy, S.N. Khonina, M.A. Butt, "Plasmonic sensors based on Metal-insulator-metal waveguides for refractive index sensing applications: A brief review", Physica E, 117, 113798 (2020). CrossRef L. Lu et al, "Mode-Selective Hybrid Plasmonic Bragg Grating Reflector", IEEE Photonics Technology Letters, 22, 1765-1767 (2012). CrossRef R. Negahdari, E. Rafiee, F. Emami, "Design and simulation of a novel nano-plasmonic split-ring resonator filter", Journal of Electromagnetic Waves and Applications, 32, 1925-1938 (2018). CrossRef M. Janfaza, M. A. Mansouri-Birjandi, "Tunable plasmonic band-pass filter based on Fabry–Perot graphene nanoribbons", Applied Physics B, 123, 262 (2017). CrossRef C. Wu, G. Song, L. Yu, J.H. Xiao, "Tunable narrow band filter based on a surface plasmon polaritons Bragg grating with a metal–insulator–metal waveguide", Journal of Modern Optics, 60, 1217-1222 (2013). CrossRef J. Zhu, G. Wang, "Sense high refractive index sensitivity with bragg grating and MIM nanocavity", Results in Physics, 15, 102763 (2019). CrossRef Y. Binfeng, H. Guohua, C. Yiping, "Design of a compact and high sensitive refractive index sensor base on metal-insulator-metal plasmonic Bragg grating", Optics Express, 22, 28662-28670 (2014). CrossRef A.D. Simard, Y. Painchaud, S. Larochelle, "Small-footprint integrated Bragg gratings in SOI spiral waveguides", International Quantum Electronics Conference Lasers and Electro-Optics Europe, IEEE, Munich, Germany (2013). CrossRef C. Klitis, G. Cantarella, M. J. Strain, M. Sorel, "High-extinction-ratio TE/TM selective Bragg grating filters on silicon-on-insulator", Optics Letters, 42, 3040 (2017). CrossRef J. Ctyroky et al., "Design of narrowband Bragg spectral filters in subwavelength grating metamaterial waveguides", Optics Express, 26, 179 (2018). CrossRef M.A. Butt, N.L. Kazanskiy, S.N. Khonina, "Hybrid plasmonic waveguide race-track µ-ring resonator: Analysis of dielectric and hybrid mode for refractive index sensing applications", Laser Phys., 30, 016202 (2020). CrossRef M. A. Butt, N.L. Kazanskiy, S.N. Khonina, "Label-free detection of ambient refractive index based on plasmonic Bragg gratings embedded resonator cavity sensor", Journal of Modern Optics, 66, 1920-1925 (2019). CrossRef N. L. Kazanskiy, M.A. Butt, Photonics Letters of Poland, 12, 1-3 (2020). CrossRef Z. Guo, K. Wen, Q. Hu, W. Lai, J. Lin, Y. Fang, "Plasmonic Multichannel Refractive Index Sensor Based on Subwavelength Tangent-Ring Metal–Insulator–Metal Waveguide", Sensors, 18, 1348 (2018). CrossRef

Enhancement of Diffraction-Based Overlay Model for Overlay Target With Asymmetric Sidewall

Overlay metrology is crucial to process control in manufacturing semiconductor devices. Diffraction-based overlay (DBO) is an effective overlay measurement approach because it exhibits multiple advantages. This study analyzed measurement errors caused by sidewalls in the bottom gratings of DBO targets. Accordingly, improvement was proposed using a neural network. First, rigorous coupled wave analysis was employed to calculate the pupil images generated by an overlay target. These images were then used as a data set. Next, two-directional twodimensional principal component analysis was used to reduce the dimension of features in these images. The features were then used to train a neural network and determine weighting coefficients in each network layer to create a DBO model. This study used virtual metrology to analyze 30 types of overlay targets and generated 18900 pupil images to create a data set. Each overlay target model was measured 10 times, and shot noise, dark noise, and quantization noise in the pupil images were accounted for. The simulation results revealed that when the dose level was 1000 mJ/s·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the overlay mean square error of the testing data was 0.40nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , indicating notable improvement in the measurement results of overlay targets with bottom grating sidewalls. Therefore, the proposed neural network-based DBO model can be applied to overlay targets with sidewalls and effectively improve the overlay accuracy.

Directional coupling of surface plasmon polaritons using single nano-slit with asymmetric sidewall structure and material composition.

We report on the performance of the asymmetric nano-slit that we design and fabricated with electron beam lithography (EBL) and glancing angle deposition techniques (GLAD) for directional coupling of surface plasmon polariton (SPP) on Ag surfaces. The slit structure includes asymmetric sidewalls in terms of material composition as well as structural morphology. The overall width of the slit was varied for optimization. We illuminated the slit with a focused 532nm laser beam and characterized the SPP signal on the Ag surface near the slit with nearfield scanning optical microscopy (NSOM). We demonstrate that optimal directional coupling of SPP toward either side of the slit can be achieved by selecting proper slit widths, with the best extinction ratio of 79000 ± 18000. We also carried out numerical calculations to simulate the interaction between the incident light and the slit structure. The results reproduced the experiment qualitatively. Detailed analysis of the distribution of the E-field and the time-averaged Poynting vector indicates that SPP excited on the Ag pad substructure in the slit plays an important role in the directional coupling of SPP.

Improved semipolar green InGaN/GaN quantum wells on asymmetrically grown (112̄2) GaN templates and their correlations

Asymmetric island sidewall growth (AISG) is employed to reduce the threading defect density and to modify the surface/interface properties of semipolar GaN templates and InGaN/GaN quantum wells (QWs).

Asymmetric underlap spacer layer enabled nanoscale double gate MOSFETs for design of ultra-wideband cascode amplifiers

Using extensive numerical analysis we investigate effects of asymmetric sidewall spacers on various device parameters of 20-nm double gate MOSFETs associated with analog/RF applications. Our studies show that the device with underlap drain-side spacer length LED of 10 nm and source-side spacer length LES of 5 nm shows improvement in terms of the peak value of transconductance efficiency, voltage gain Av, unity-gain cut-off frequency fT and maximum frequency of oscillations fMAX by 8.6%, 51.7%, 5% and 10.3%, respectively compared to the symmetric 5 nm underlap spacer device with HfO2 spacer of dielectric constant k = 22. Additionally, a higher spacer dielectric constant increases the peak Av while decreasing both peak fT and fMAX. The detailed physical insight is exploited to design a cascode amplifier which yields an ultra-wide gain bandwidth of 2.48 THz at LED = 10 nm with a SiO2 spacer.

Silicon band-rejection and band-pass filter based on asymmetric Bragg sidewall gratings in a multimode waveguide.

A silicon photonic wire filter based on an asymmetric sidewall Bragg grating in a multimode silicon-on-insulator strip waveguide is demonstrated. The operating principle is based on the contra-directional coupling between the transverse electric fundamental (TE0) and first-order (TE1) modes, which is enabled by the asymmetric spatially periodic refractive-index perturbations. An asymmetric Y-junction is cascaded at the input port of the filter so as to drop the Bragg reflection. Compared with conventional Bragg grating-based filters, this device eliminates the back reflection at the input port and the 6dB inherent insertion loss at the drop port; moreover, a narrow 3dB bandwidth can be obtained with a large critical dimension as a result of the weak coupling strength between the TE0 and TE1 modes inside the multimode waveguide. Experimental results show that a bandwidth of ∼2.8 nm is achieved by a large corrugation width of 150nm. The insertion loss at the drop port is -2.1 dB, and the extinction ratio is -33 dB at the through port.

In situ asymmetric island sidewall growth of high-quality semipolar (112̄2) GaN on m-plane sapphire

In situ asymmetric island sidewall growth (AISG) was developed to enhance Ga-face facet growth and improve the crystalline quality of (112) GaN epilayers on m-plane sapphire substrates. In the early growth stage island shaping and sidewall faceting were distinct and controlled by growth design. Using in situ AISG, {0002} instead of {103} sidewall facets were formed on the Ga-rich island surface, which eliminated formation of a {103} phase during subsequent layer growth of semipolar GaN. Enhanced Ga-face sidewall facet growth led to +c regions overlapping −c regions, which reduced defect density. Pure semipolar (112) epilayers with a reduced surface striation density and a basal-plane stacking fault density of 8 × 103 cm−1 were obtained. The observation of a narrow EH2 peak and an intense E1(LO) peak in Raman spectra indicates that almost strain-free high-quality semipolar (112) GaN films were achieved. The photoluminescence emission intensity from the (112) GaN film prepared by in situ AISG was dominated by band-edge emission and enhanced ∼4 times more than that from conventional (112) GaN.

Multichannel Bragg gratings in silicon waveguides with asymmetric sidewall modulation.

We demonstrate a new type of on-chip Bragg grating designed to possess multiple stopbands at predetermined wavelengths. By employing sidewall modulation to control the full width half-maximum and extinction ratio, and through the incorporation of multiple spatial frequencies into the gratings' periodicities, we show that Bragg reflection can be achieved at particular wavelengths of interest without compromising spectrally distinct characteristics. Multiple device geometries are theoretically studied using the finite-difference time-domain method, and the results these analyses yield are shown to be in good agreement with experimental data. We additionally demonstrate how such devices may be employed to fabricate so-called dual-mode Bragg gratings, which are capable of reflecting both TE- and TM-like modes at a single wavelength of operation.

Effect of inter-bit material on the performance of directly deposited bit patterned media

We evaluated the effects of inter-bit material on the switching performance of bit patterned media (BPM) fabricated by direct deposition of magnetic material onto pre-patterned substrates. We performed a controlled experiment to vary the sidewall thickness and symmetry in bits with nominally identical size and pitch. Thick, asymmetric sidewalls resulted in significant broadening of the switching field distribution to 14%–20% compared to 10%–11% for bits with thin, symmetric sidewalls. These differences were attributed to changes in the intrinsic properties and dipolar interactions as supported by micromagnetic simulations. Our results highlight the importance of controlling inter-bit material to achieve high-density BPM.

Characterization of Thick GaN Films Directly Grown on Wet-Etching Patterned Sapphire by HVPE

Thick GaN films of high quality are directly grown on wet-etching patterned sapphire in a vertical hydride vapour phase epitaxy reactor. The optical and structural properties of GaN films are studied using scanning electronic microscopy and cathodoluminescence. Test results show that initial growth of hydride vapour phase epitaxy GaN occurs not only on the mesas but also on the two asymmetric sidewalls of the V-shaped grooves without selectivity. After the two-step coalescence near the interface, the GaN films near the surface keep on growing along the direction perpendicular to the long sidewall. Based on Raman results, GaN of the coalescence region in the grooves has the maximum residual stress and poor crystalline quality over the whole GaN film, and the coalescence process can release the stress. Therefore, stress-free thick GaN films are prepared with smooth and crack-free surfaces by this particular growth mode on wet-etching patterned sapphire substrates.

Silicon Photonic Wire Filter Using Asymmetric Sidewall Long-Period Waveguide Grating in a Two-Mode Waveguide

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We demonstrate a silicon photonic wire filter using asymmetric sidewall long-period waveguide gratings for the first time. The proposed device consists of single-mode waveguide sections, a two-mode section with corrugated gratings, and taper sections to connect them. The operation of this device is based on the codirectional coupling between two core modes. By adopting a high refractive index contrast waveguide, the period and depth of grating are given as 4.44 <emphasis><formula formulatype="inline"><tex>$\mu$</tex></formula></emphasis>m and 5 nm, respectively. Thus, the total length of long-period grating is significantly reduced to 260 <emphasis><formula formulatype="inline"><tex>$\mu$</tex> </formula></emphasis>m. The measured maximum attenuation at the center wavelength is about 13 dB. The bandwidth of the transmission dip is 15 nm. Finally, issues on the design and the performance of our device are discussed. </para>

Shape/Size-Controlled Syntheses of Metal Nanoparticles for Site-Selective Modification of Carbon Nanotubes

Shape- and size-controlled syntheses of metal nanoparticles have been achieved by galvanic displacement reaction between an aqueous solution of metal salt and Cu foil substrate. In particular, cubic and spheric nanoparticles of Pt (Au) with a fairly narrow size distribution were produced by reacting K(2)PtCl(4) (HAuCl(4)) with a Cu foil in an aqueous medium with and without CuCl(2) under different reaction conditions (e.g., different concentrations and reaction times). In conjunction with the substrate-enhanced electroless deposition (SEED) technique (Qu, L.; Dai, L. J. Am. Chem. Soc. 2005, 127, 10806), the shape/size-controlled syntheses have been successfully exploited to site-selectively deposit these metal nanoparticles onto the outerwall, innerwall, or end-tip of carbon nanotubes (CNTs). Asymmetric sidewall modification by attaching the innerwall and outerwall of CNTs with metal nanoparticles of different shapes was also achieved. Furthermore, it was demonstrated that the nanotube-supported Pt nanoparticles could be converted into hollow Au nanoboxes by galvanic displacement of Pt with Au. These CNT-supported metal nanoparticles were shown to possess interesting optical and electrocatalytic properties.

Probe measurements of plasma potential nonuniformity due to edge asymmetry in large-area radio-frequency reactors: The telegraph effect

In large-area radio-frequency (rf) capacitive reactors, the redistribution of rf current to maintain current continuity near asymmetric sidewalls causes a perturbation in rf plasma potential to propagate along the resistive plasma between capacitive sheaths. The damping length of the perturbation can be determined by a telegraph equation. Experiments are described using a surface array of unbiased electrostatic probes in the ground electrode to verify the theoretical model of the telegraph effect in Howling et al. [J. Appl. Phys. 96, 5429 (2004)]. The measured spatial dependence of the plasma potential rf amplitude and circulating nonambipolar current agree well with two-dimensional numerical solutions of the telegraph equation. The rf plasma potential can be made uniform by using symmetric reactor sidewalls.

Geometry and kinematics of adhesive wear in brittle strike-slip fault zones

Detailed outcrop surface mapping in Late Paleozoic cataclastic strike-slip faults of coastal Maine shows that asymmetric sidewall ripouts, 0.1–200 m in length, are a significant component of many mapped faults and an important wall rock deformation mechanism during faulting. The geometry of these structures ranges from simple lenses to elongate slabs cut out of the sidewalls of strike-slip faults by a lateral jump of the active zone of slip during adhesion along a section of the main fault. The new irregular trace of the active fault after this jump creates an indenting asperity that is forced to plow through the adjoining wall rock during continued adhesion or be cut off by renewed motion along the main section of the fault. Ripout translation during adhesion sets up the structural asymmetry with trailing extensional and leading contractional ends to the ripout block. The inactive section of the main fault trace at the trailing end can develop a ‘sag’ or ‘half-graben’ type geometry due to block movement along the scallop-shaped connecting ramp to the flanking ripout fault. Leading contractional ramps can develop ‘thrust’ type imbrication and forces the ‘humpback’ geometry to the ripout slab due to distortion of the inactive main fault surface by ripout translation. Similar asymmetric ripout geometries are recognized in many other major crustal scale strike-slip fault zones worldwide. Ripout structures in the 5–500 km length range can be found on the Atacama fault system of northern Chile, the Qujiang and Xiaojiang fault zones in western China, the Yalakom–Hozameen fault zone in British Columbia and the San Andreas fault system in southern California. For active crustal-scale faults the surface expression of ripout translation includes a coupled system of extensional trailing ramps as normal oblique-slip faults with pull-apart basin sedimentation and contractional leading ramps as oblique thrust or high angle reverse faults with associated uplift and erosion. The sidewall ripout model, as a mechanism for adhesive wear during fault zone deformation, can be useful in studies of fault zone geometry, kinematics and evolution from outcrop- to crustal-scales.

Mixed Convection Heat Transfer in a Vertical Duct with Different Side-Wall Temperatures.

In this paper, numerical and experimental investigation on natural and mixed convection heat transfer in a vertical duct with asymmetric side-wall heating has been carried out. The present study is triggered by a possible thermal insulation created on the cold wall in a vertical duct via an upward forced flow. We discuss how the velocity and temperature of forced flow influences the cold-wall average Nusselt number. It was found that two critical values of Reynolds number exist. One is associated with flow structure (ReFScr), and causes the disapperance of natural convection cell. The other gives the critical value on heat transfer (ReHTcr), which makes cold-wall effectively insulated. The latter is found independent of Ra and only dependent of aspect ratio scaled as ReHTcr &vprop; A2.

An asymmetric sidewall process for high performance LDD MOSFET's

An asymmetric LDD sidewall spacer technology is presented which gives a high drivability of LDD MOSFET without sacrificing hot carrier immunity. The asymmetric spacer is fabricated by using a selective oxide deposition technique. The process implemented in a CMOS fabrication sequence requires no additional masking step. The fact that no reliability problems are introduced in the transistor characteristics by the selective oxide deposition process is also examined. >

Experimental investigation of normal-shock/turbulent-boundary-layer interactions with and without mass removal

Interactions of a normal shock with a turbulent boundary layer over a flat surface were investigated with and without imposing mass removal. The approach flow was very nearly two-dimensional, with a uniform freestream Mach number of 1.48, strong enough to cause separation at the shock foot. Suction was imposed immediately upstream of the shock over a finely perforated surface, removing much of the boundary-layer flow. The time-mean wall pressure distributions and two components of the time-mean velocity vector field were determined for both cases. Mass removal distorted the original shock pattern and eliminated the separation at the shock foot while reducing the boundary-layer thicknesses and growth rates to less than half. Mass removal also introduced some undesirable effects: asymmetric sidewall boundary-layer growth in the subsonic flow and increased shock oscillation amplitudes. The removed mass flow varied strongly in the streamwise direction in a manner that indicated wide variations of the flow coefficients for the individual perforations.