Dry Etching Techniques Research Articles

Large-scale fabrication of highly ordered sub-20\u2009nm noble metal nanoparticles on silica substrates without metallic adhesion layers

Periodic noble metal nanoparticles offer a wide spectrum of applications including chemical and biological sensors, optical devices, and model catalysts due to their extraordinary properties. For sensing purposes and catalytic studies, substrates made of glass or fused-silica are normally required as supports, without the use of metallic adhesion layers. However, precise patterning of such uniform arrays of silica-supported noble metal nanoparticles, especially at sub-100 nm in diameter, is challenging without adhesion layers. In this paper, we report a robust method to large-scale fabricate highly ordered sub-20 nm noble metal nanoparticles, i.e., gold and platinum, supported on silica substrates without adhesion layers, combining displacement Talbot lithography (DTL) with dry-etching techniques. Periodic photoresist nanocolumns at diameters of ~110 nm are patterned on metal-coated oxidized silicon wafers using DTL, and subsequently transferred at a 1:1 ratio into anti-reflection layer coating (BARC) nanocolumns with the formation of nano-sharp tips, using nitrogen plasma etching. These BARC nanocolumns are then used as a mask for etching the deposited metal layer using inclined argon ion-beam etching. We find that increasing the etching time results in cone-shaped silica features with metal nanoparticles on the tips at diameters ranging from 100 nm to sub-30 nm, over large areas of 3×3 cm2. Moreover, subsequent annealing these sub-30 nm metal nanoparticle arrays at high-temperature results in sub-20 nm metal nanoparticle arrays with ~1010 uniform particles.

Defect-selective dry etching for quick and easy probing of hexagonal boron nitride domains

In this study, we demonstrate a new method to selectively etch the point defects or the boundaries of as-grown hexagonal boron nitride (hBN) films and flakes in situ on copper substrates using hydrogen and argon gases. The initial quality of the chemical vapor deposition-grown hBN films and flakes was confirmed by UV–vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy. Different gas flow ratios of Ar/H2 were then employed to etch the same quality of samples and it was found that etching with hydrogen starts from the point defects and grows epitaxially, which helps in confirming crystalline orientations. However, etching with argon is sensitive to line defects (boundaries) and helps in visualizing the domain size. Finally, based on this defect-selective dry etching technique, it could be visualized that the domains of a polycrystalline hBN monolayer merged together with many parts, even with those that grew from a single nucleation seed.

Assessing the manufacturing tolerances and uniformity of CMOS compatible metamaterial fabrication

The manufacturing tolerances of a stencil-lithography variant, membrane projection lithography, were investigated. In the first part of this work, electron beam lithography was used to create stencils with a range of linewidths. These patterns were transferred into the stencil membrane and used to pattern metallic lines on vertical silicon faces. Only the largest lines, with a nominal width of 84 nm, were resolved, resulting in 45 ± 10 nm (average ± standard deviation) as deposited with 135-nm spacing. Although written in the e-beam write software file as 84-nm in width, the lines exhibited linewidth bias. This can largely be attributed to nonvertical sidewalls inherent to dry etching techniques that cause proportionally larger impact with decreasing feature size. The line edge roughness can be significantly attributed to the grain structure of the aluminum nitride stencil membrane. In the second part of this work, the spatial uniformity of optically defined (as opposed to e-beam written) metamaterial structures over large areas was assessed. A Fourier transform infrared spectrometer microscope was used to collect the reflection spectra of samples with optically defined vertical split ring from 25 spatially resolved 300 × 300 μm regions in a 1-cm2 area. The technique is shown to provide a qualitative measure of the uniformity of the inclusions.

A high-diffraction-efficiency subwavelength silica Dammann grating

In this paper, a large scale and highly efficient 1×9 Dammann beam splitter operating in 1.064μm wavelength for TE polarization is designed and fabricated under normal incidence. This element consisting of a triple-groove fused silica grating layer is designed using the inverse mathematical method and rigorous vector diffraction theory. The beam splitter is fabricated by using the self-developed blue light laser writing system and dry etching technique. The fabricated beam splitter presents excellent beam splitter ability for TE polarization light with the average diffraction efficiencies is more than 85% at 1.064μm wavelength (96.4% in theory), which is over 20% higher than the traditional one.

Mid-infrared guided photoluminescence from integrated Pr3+-doped selenide ridge waveguides

Praseodymium-doped selenide thin films are deposited by radio frequency magnetron sputtering on thermally oxidized silicon wafers and undoped selenide layers. Ridge waveguides are then processed using photolithography and dry etching techniques. Under optical pumping at 1.55 μm, broadband guided mid-infrared photoluminescence is recorded for the first time for wavelengths above 4 μm from rare earth-doped integrated chalcogenides waveguides. Optical design confirmed that these active waveguides allow single-mode optical propagation at a wavelength of 4.70 μm.

Mode and Lasing Characteristics for Hybrid Square-Rectangular Lasers

Whispering-gallery mode (WGM) microlasers are potential light sources for monolithic photonic integration circuits and optical interconnects. In this study, stable single-mode hybrid square-rectangular lasers (HSRLs) are reported, based on mode coupling between WGM and Fabry–Perot (FP) modes. Mode selection mechanisms are explained based on numerical results of the resonant reflection of the square microcavity and energy distributions of coupled mode in the two cavities, and the reduction of effective linewidth enhancement factor is expected as two cavities are modulated individually. HSRLs with different sizes are fabricated by contact photolithography and dry-etching techniques. For a hybrid laser with a square-side length a = 15 μm and the FP cavity length and width of L = 300 μm and d = 2 μm, stable single-mode operation with a side-mode suppression ratio up to 47 dB is obtained, and a small-signal modulation bandwidth of 13.3 GHz is realized by modulating the current of the FP cavity. The dynamic characteristics are further investigated for the hybrid laser. Furthermore, threshold currents and tunable behaviors are compared for HSRLs with a = 10, 15, and 20 μm and d = 1.5 and 2 μm.

Demonstration of GaN Static Induction Transistor (SIT) Using Self-Aligned Process

The rapid development of RF power electronics requires amplifier operating at high frequency with high output power. GaN-based HEMTs as RF devices have made continuous progress in the last two decades showing great potential for working up to G band range. However, vertical structure is preferred to obtain higher output power. In this paper, we have designed and fabricated GaN static induction transistor using the self-aligned technology, which was accomplished mainly by using a SiO2 lift-off step in buffered oxide etch (BOE). By optimizing the time in ultrasonic bath and in BOE, the SiO2 and the metal on top were removed completely which resulted in the gate metal only on the sidewalls. Both dry and wet etch techniques were investigated to reduce the gate leakage on the etched surface. The low power dry etch combined with the tetramethylammonium hydroxide wet etch can effectively reduce the etch damages, decrease the gate leakage and enhance the gate control over the channel.

Angstrom-scale flatness using selective nanoscale etching.

The realization of flat surfaces on the angstrom scale is required in advanced devices to avoid loss due to carrier (electron and/or photon) scattering. In this work, we have developed a new surface flattening method that involves near-field etching, where optical near-fields (ONFs) act to dissociate the molecules. ONFs selectively generated at the apex of protrusions on the surface selectively etch the protrusions. To confirm the selective etching of the nanoscale structure, we compared near-field etching using both gas molecules and ions in liquid phase. Using two-dimensional Fourier analysis, we found that near-field etching is an effective way to etch on the scale of less than 10 nm for both wet and dry etching techniques. In addition, near-field dry etching may be effective for the selective etching of nanoscale structures with large mean free path values.

Fabrication of diamond microlens arrays for monolithic imaging homogenizer

Compact microlens arrays (MLAs) have been fabricated on diamond substrates using thermal reflow and dry etching techniques for laser beam homogenization. Firstly, close-packed hexagonal photoresist pillars developed by photolithography were reflowed upon heat plate to form MLAs mask on one side of diamond substrate. Secondly, the mask pattern was transferred into substrate with inductively coupled plasma etching to form closely arranged diamond MLAs. Then, the same processes were utilized to fabricate MLAs on the other side of diamond substrate. The MLAs on both sides of substrate are aligned. Thirdly, the obtained diamond MLAs demonstrate compact arrangement, well-uniformity, and good imaging performance with projection experiment. Eventually, the double-sides MLAs-patterned diamond substrate was utilized as monolithic imaging homogenizer, exhibiting a good homogenizing performance.

Study on the wettability and condensation heat transfer of sine-shaped micro-grooved surfaces

In this study, sine-shaped micro-grooved surfaces with depth of 12–24μm and width of 30–60μm were precisely and smoothly fabricated using dry etching technique on aluminium surfaces. After hydrophobic modification, the wettability and the heat transfer characteristics of dropwise condensation on the micro-grooved surfaces were investigated experimentally, and the coalescence and sweeping processes of droplets on micro-grooved surfaces were dynamically analyzed. As the results show, the wetting behavior and heat transfer characteristics on the micro-grooved surfaces presented anisotropic characteristics, the static contact angle in perpendicular direction θ⊥ was significantly larger than that in parallel direction θ∥, and same trends can also be observed for contact angle hysteresis. In heat transfer experiments, the plates were set vertically and the grooves were arranged in two positions, vertical and horizontal. For the vertically grooved surface, the sweeping effects of falling droplets were enhanced by the vertical grooves and the heat transfer during dropwise condensation was increased to 30–50%. Better heat transfer performance can be achieved when the ratio of height to pitch, A/P, increased. Different from vertical grooved surfaces, the experimental results obtained from horizontal grooved surfaces were similar to the results of smooth surface. Both net force and sliding velocity increased as droplets grew, and larger geometrical size was favorable to droplets falling for same ratio of A/P. The velocities of sliding down on horizontal grooved surface were only 60–70% of that on smooth surface, while the velocities of sliding down on vertical grooved surfaces can reach 1.2 times or higher than that on smooth surface.

Fabrication of AlGaN nanorods with different Al compositions for emission enhancement in UV range

Highly ordered AlxGa1−xN nanorods with varied aluminum alloy compositions (0.18 ≤ x ≤ 0.8) are fabricated with nanoimprint lithography and top-down dry etching techniques. And the structural properties and morphology are obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compared with as-grown AlGaN samples, nanorod samples reveal outstanding optical performance on account of strain releasing and light extraction enhancement. Through Raman scattering and cathodeluminescence measurements, it has been observed clear red-shifts of E2h modes and near band edge emission (NBE) peaks of AlGaN nanorods compared to the planar ones, indicating the residual strain releasing after nano-fabrication. The integrated intensities of NBE peaks of AlGaN nanorods manifest light emission enhancement up to 2.7 at deep-UV range. Finite-difference time-domain (FDTD) simulations have been adopted to investigate the light extraction and far-field distribution of such structures, it turned out that ordered nanorod array can enhance the TM polarized emission extraction 2–7 folds compared to the planar structure. The optical regulation in nanorod arrays should take the responsibility for the observed optical enhancements, which is proved by the far-field distribution of light, thus it can improve the performance of ultraviolet LEDs.

Substrate Integrated Waveguide Structural Transmission Line and Filter on Silicon Carbide Substrate

Substrate integrated waveguide (SIW) structural transmission line (TL) and filter are designed and fabricated on semi-insulating silicon carbide (SiC) substrates for operation at the low end of $H$ -band. The via-holes as the sidewall of SIW are achieved by using a fine dry-etching technique, where the radius and the via–via distance of the via-hole row are determined according to the transmission characteristics and the fabrication process. Measurements show that SIW-based TLs have the attenuation constant of as low as 0.45 dB/mm at 220 GHz, a third of that for TLs on grounded coplanar waveguide, and SIW-structural filters have the minimum insertion loss of <1 dB at the center frequency of 183 GHz with a bandwidth of 5.3 %. It illustrates the availability of passive device fabrications on SiC substrate, and paves the way for the forthcoming terahertz monolithic integrated circuits based on wide bandgap semiconductors.

Periodic Micro Hole Texturing with Metal Assisted Chemical Etching for Solar Cell Applications: Dependence of Etch Rate on Orientation

Surface texturing is an indispensable process for solar cell fabrication. The interaction of the surface with the incoming sunlight is controlled by texturing in such a way that the absorption is maximized through multiple interactions. Wet and dry etching techniques have been used to create textured surfaces on solar cells.

Evanescently Coupled Rectangular Microresonators in Silicon-on-Insulator with High Q-Values: Experimental Characterization

We report on evanescently coupled rectangular microresonators with dimensions up to 20 × 10 μm2 in silicon-on-insulator in an add-drop filter configuration. The influence of the geometrical parameters of the device was experimentally characterized and a high Q value of 13,000 was demonstrated as well as the multimode optical resonance characteristics in the drop port. We also show a 95% energy transfer between ports when the device is operated in TM-polarization and determine the full symmetry of the device by using an eight-port configuration, allowing the drop waveguide to be placed on any of its sides, providing a way to filter and route optical signals. We used the FDTD method to analyze the device and e-beam lithography and dry etching techniques for fabrication.

High-aspect ratio nanopatterning via combined thermal scanning probe lithography and dry etching

Thermal scanning probe lithography is an emerging nanofabrication technique for rapid prototyping of arbitrary topographies in thermally sensitive resist. This feature, paired to the recent advances in dry plasma etching techniques, allows the fabrication of high-resolution nanopatterns in hard substrates. Here, we investigate the key process parameters allowing the fabrication of high aspect ratio nanopatterns in silicon. By a combination of resist heat treatment, the use of a hard mask and optimized etch parameters during pattern transfer, we amplified the shallow resist patterns by a factor of 100 into the silicon substrate. Low surface roughness and vertical sidewalls are thereby maintained. We demonstrate the fabrication of 240nm wide lines and 4μm deep single crystal silicon patterns.

Tuning the thickness of exfoliated quasi-two-dimensional β-Ga2O3 flakes by plasma etching

We demonstrated the thinning of exfoliated quasi-two-dimensional β-Ga2O3 flakes by using a reactive ion etching technique. Mechanical exfoliation of the bulk β-Ga2O3 by using an adhesive tape was followed by plasma etching to tune its thickness. Since β-Ga2O3 is not a van der Waals material, it is challenging to obtain ultra-thin flakes below a thickness of 100 nm. In this study, an etch rate of approximately 16 nm/min was achieved at a power of 200 W with a flow of 50 sccm of SF6, and under these conditions, thinning of β-Ga2O3 flakes from 300 nm down to ∼60 nm was achieved with smooth morphology. We believe that the reaction between SF6 and Ga2O3 results in oxygen and volatile oxygen fluoride compounds, and non-volatile compounds such as GaFX that can be removed by ion bombardment. The opto-electrical properties were also characterized by fabricating solar-blind photodetectors using the plasma-thinned β-Ga2O3 flakes; these detectors showed fast response and decay with excellent responsivity and selectivity. Our results pave the way for tuning the thickness of two-dimensional materials by using this scalable, industry-compatible dry etching technique.

Sculpturing patterns of plasmonic silver nanoprisms by means of photocatalytic lithography

The controlled shaping of nanoparticles’ morphology is one of the pillars of nanotechnology. Here, we demonstrate that photocatalytic lithography, a technique already proved to be useful in materials science, can act as a dry etching technique for noble metal nanoparticles. Triangular silver nanoprisms are self-assembled on titanium dioxide films and photocatalytically shaped into discoidal particles upon irradiation with near-UV light. The obtained patterned surfaces show a dramatically different surface-enhanced Raman scattering response, suggesting the utility of our approach for the development of sensors. The photocatalytic nature of the particle shaping is demonstrated and a plausible mechanism drawn by performing photocatalysis in different configurations (direct and remote) and by irradiating in different solvents.

Laguerre-Gauss beam generation in IR and UV by subwavelength surface-relief gratings.

The angular momentum of light can be described by the states of spin angular momentum, associated with polarization, and orbital angular momentum, related to the helical structure of the wave front. Laguerre-Gaussian beams carry orbital angular momentum and their generation can be done by using an optical device known as q-plate. However, due to the usage of liquid crystals, these components may be restricted to operate in specific wavelengths and low power sources. Here we present the fabrication and characterization of q-plates made without liquid crystals, using processes of electron beam lithography, atomic layer deposition and dry etch techniques. We exploit the phenomenon of form birefringence to give rise to the spin-to-orbital angular momentum conversion. We demonstrate that these plates can generate beams with high quality for the UV and IR range, allowing them to interact with high power laser sources or inside laser cavities.

Vertical few-layer graphene/metalized Si-nanocone arrays as 3D electrodes for solid-state supercapacitors with large areal capacitance and superior rate capability

A strategy to promote the energy density of graphene-based supercapacitors by a combination of dry etching and chemical vapor deposition (CVD) techniques is demonstrated. A three dimensional (3D) electrode is composed of vertically oriented graphene that is deposited on metalized silicon nanocones. The design of the 3D electrodes improves specific surface area, electrolyte ion migration and electrical contact, resulting in an enhancement of areal capacitance and rate capability. Furthermore, a solid-state supercapacitor was prepared based on the 3D graphene electrodes and gel polymer electrolyte. The 3D electrode with 10min of CVD growth of graphene endows the electrical double layer capacitor with the highest areal capacitance of 667.2μFcm−2, which is larger than that of supercapacitors with flat electrodes.

In brief

PAGE 40 A methane-hydrogen dry etching technique has been used to fabricate GaSb-based cascade diode lasers emitting near 3 µm. The process, developed by researchers in the USA, produces a diffraction-limited laser with minimal increase in threshold current density and no voltage penalty when compared with wide ridge multimode lasers. PAGE 36 A performance trade-off was found when examining different methods for inserting microstrip lines into aerospace composite structures. Research from Australia showed that embroidered microstrip lines exhibited better electromagnetic performance, whilst stencil transfer was more resistant to mechanical deformation. Cascade diode lasers fabricated using methane-hydrogen dry etching technique. PAGE 34 Researchers from the UK have designed an easy to control microstrip coupler that enhances power coupling between two microstrips. Two small slot lines are inserted in the ground plane underneath the microstrips, forcing an increased number of shared field lines between strips, thus eliminating the need to narrow the distance between microstrip lines. Microstrip lines stitched into HexPly 914 S-Glass. PAGE 7 A high-performing 3D terahertz (THz) filtering antenna was designed by researchers in China, using a low-temperature co-fired ceramic (LTCC) process. This 3D structure is more compact, has enhanced radiation performance and allows for more design flexibility compared with traditional planar designs. Slot lines underneath microstrips enhance coupling. PAGE 16 Researchers from Korea have developed a dual correlated double sampling scheme (CDS) for low-noise CMOS imagers, without the need for a power-consuming programmable gain amplifier (PGA). This scheme reduces noise by removing sampling error, and reduces power consumption by amplifying the readout channel's output. Photograph of 3D THz filtering antenna. The correlated double sampling scheme can be applied to SAR-based ADCs for CMOS imagers without the use of a PGA.