Reactive Ion Etching Conditions Research Articles

Maximizing visible Raman resolution of nanodiamond grains fabricated by coaxial arc plasma deposition through oxygen plasma etching optimization

Among the nondestructive carbon material characterization tools, the prominence of visible Raman spectroscopy has surged remarkably for many years due to its ability to explore a diverse array of carbon bonding configurations. However, to fully unlock the distinctive features concealed within carbon composite materials, additional specimen treatments or precise spectroscope calibrations are necessary. In the same regard, the tiny diamond grain size (5–10 nm) and the pronounced amount of sp2 carbon in the ultrananocrystalline diamond film represent major challenges in visible light excitation. In this work, we employ calibrated oxygen plasma reactive ion etching conditions to manifest the nanodiamond visible Raman signature from ultrananocrystalline diamond/amorphous carbon composite (UNCD/a‐C) films fabricated by coaxial arc plasma deposition. Upon plasma etching, the broad defect band in the visible Raman spectra converged toward the diamond characteristic Raman peak at 1332 cm−1. A detailed explanation of band components of the Raman spectra is extracted through peak fitting procedures. The results of Raman spectroscopy are further correlated with the electrical characteristics of the nitrogen‐doped UNCD/a‐C films due to the optimized oxygen plasma etching processes.

Optimizing the reactive ion etching conditions with minimal damage for high functional magnetic nano device application in BiFeO3-based thin film by Eu/Co substitution

To reduce energy consumption in magnetic devices, effective magnetization control by electric fields is essential. Ferromagnetic and ferroelectric thin films are promising materials for the magnetization control by electric field. However, the BiFeO3-based thin films having good magnetic properties are developed, but there is no discussion about suitable microfabrication procedures which are important for growth of damage free magnetic devices. To determine the suitable etching conditions with low magnetic damage in BiFeO3-based (Bi,Eu)(Fe,Co)O3 thin film with high saturation magnetization, low coercivity, ferroelectricity, suitable reactive ion etching (RIE) conditions as well as process parameters for microfabrication procedures were investigated. A very poor etching rate, resulting in minimal material removal was obtained, when reactive etching gas of SF6 was used. We could achieve an efficient etching rate by using CHF3 as reactive etching gas, but morphological and magnetic damage were observed. One reason for this damage was the generation of oxygen vacancies in the grain boundaries. Effective etching rates with minimized damage were realized when CHF3/O2 was used as reactive etching gas.

The Influence of Small F2, H2, and HF Additives on the Concentration of Active Particles in Tetrafluoromethane Plasma

A comparative study of the effect of small (up to 20%) substituting additives F2, H2, and HF on the kinetics and stationary concentrations of neutral particles in 50% CF4 + 50% Ar plasma under the typical conditions of reactive ion etching (RIE) of silicon and its compounds is carried out. It is shown that the vari-ation of the CF4/F2 and CF4/H2 ratios leads to opposite, interrelated, and nonadditive changes in the con-centrations of fluorine atoms and fluorocarbon radicals. This provides wide ranges of regulation of the etch-ing rate and polymerization capacity with the minimal disturbance of the parameters of the electronic and ionic components of the plasma. In contrast, the CF4/HF relation has the minimal effect on the rate of sur-face polymerization, but noticeably changes the concentration of fluorine atoms. Thus, there is a selective effect on the rate of the heterogeneous chemical reaction.

PLASMA PARAMETERS AND COMPOSITION IN CF4 + O2 + Ar AND CHF3 + O2 +Ar IN REACTIVE ION ETCHING PROCESSES

The comparative analysis of both CF4+O2+Ar and CHF3+O2+Ar plasma systems under the typical conditions of reactive ion etching of silicon and silicon-based compounds was carried out. The data on internal plasma parameters, plasma chemistry as well as the steady-state plasma composition were obtained using a description of Langmuir probe diagnostics and 0-dimensional (global) plasma modeling. As a presented in the literature, both experimental and modeling procedures were carried out at constant total gas pressure, input power, bias power. The obtained results allowed one 1) to figure out the influence of oxygen on steady-state densities of plasma active species through the kinetics of both electron-impact and atom-molecular reactions; 2) to understand the features of fluorine atoms and fluorocarbon radicals kinetics which determine chemical activity and polymerization ability of plasmas in respect to treated surfaces; 3) to perform the model-bases analysis of heterogeneous process kinetics (etching, polymerization, polymer destruction) which determine the overall etching regime and output parameters. It was found that the substitution of argon for oxygen in both gas mixtures 1) results in monotonic increase in fluorine atom density; 2) is accompanied by decreasing polymerization ability of a gas phase and 3) causes the rapid (by about two orders of magnitude at ~ 20% О2) decrease in fluorocarbon polymer film thickness with the higher values for CHF3+O2+Ar system.

Silicon‐Based Photonic Architectures from Hierarchically Porous Carbon Opals

AbstractSilicon‐based materials are needed in cutting‐edge technological fields, for which hierarchical porosity and photonic properties help improve performance. In this work, the versatility of several fabrication routes that combine silicon infiltration by chemical vapor deposition (CVD), reactive ion etching (RIE), and carbon calcination, which produce a palette of novel silicon‐based material architectures, is demonstrated. Design strategies are discussed and the main features of the processing steps are addressed to provide a variety of new silicon‐based materials with high morphological versatility and photonic quality. Three‐dimensional hollow carbon opals (HCO) permit control of the porosity of subsequent architectures through the initial silicon infiltration, while open or closed surfaces are achieved primarily as a function of RIE conditions. The composition of derived structures depends on the sequence in which the processes are applied. As a result, pure Si and hybrid C–Si inverse structures can be produced with open or closed spheres in the top layer and with an optional passivation layer. Remarkably, by properly choosing the Si infiltration parameters and the calcination/RIE procedure, final structures are achieved with double‐shell spheres.

Direct observation for atomically flat and ordered vertical {111} side-surfaces on three-dimensionally figured Si(110) substrate using scanning tunneling microscopy

A three-dimensional Si{111} vertical side-surface structure on a Si(110) wafer was fabricated by reactive ion etching (RIE) followed by wet-etching and flash-annealing treatments. The side-surface was studied with scanning tunneling microscopy (STM) in atomic scale for the first time, in addition to atomic force microscopy (AFM), scanning electron microscopy (SEM), and low-energy electron diffraction (LEED). AFM and SEM showed flat and smooth vertical side-surfaces without scallops, and STM proved the realization of an atomically-flat 7 × 7-reconstructed structure, under optimized RIE and wet-etching conditions. STM also showed that a step-bunching occurred on the produced {111} side-surface corresponding to a reversely taped side-surface with a tilt angle of a few degrees, but did not show disordered structures. Characteristic LEED patterns from both side- and top-reconstructed surfaces were also demonstrated.

Black silicon morphologies using conventional RIE processing

We report on the use of conventional non-Bosch, non-cryogenic Reactive Ion Etching (RIE) processing to produce a range of low optical reflection morphologies on <100> silicon wafer. Tapered structures and nano dendritic-pillars are patterned into silicon over a pressure range of 550 - 700 mTorr at various run times. Low pressure RIE conditions yield tapered profiles while at higher pressures nano-pillars are produced. The optimized condition of 650 mTorr for 20-30 minutes yields uniform distribution of nano dendritic pillars resulting in a low average reflectance of 4.2% – without an additional antireflective coating. A simple kinetic Monte-Carlo model shows that nano-dendritic structures can be formed due to low etching rate of side walls and evolve into tapered structures over a longer run time. Refractive index profiles built from our simulated patterns and surface morphology of the samples yield calculated reflectance curves that correlate well with experimental results.

Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks

A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10−10 M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates.

Formation of a wedge-shaped element on an end face of a microstrip optical waveguide designed to minimize loss when coupling with an optical fiber

We have investigated a method for forming microstrip optical waveguides of variable cross section designed for coupling a planar waveguide with an optical fiber. The method is based on the use of combined reactive-ion etching of polymer cladding and photoresist. It is shown that butt expansions and a microstrip waveguide can be formed in one technological process. The influence of the conditions of reactive-ion etching on the quality of the waveguide optical surface is analyzed.

Development of Double-Textured ZnO:B Substrates for Improving Microcrystalline Silicon Solar Cell Performance

Zinc oxide (ZnO) films are widely used as front transparent conductive oxide films in thin-film silicon solar cells. Double-textured B-doped zinc oxide (W-textured ZnO:B) substrates, which are formed by reactive ion etching (RIE) and metal-organic chemical vapor deposition, have a high haze ratio over a wide wavelength range. In this study, we have investigated the RIE conditions necessary to modify the surface morphology and the optical properties of a glass substrate. By increasing the pressure during the RIE process, the surface morphology of etched glass was changed from circular to ellipsoidal shapes, and its texture size increased. A newly developed W-textured ZnO:B substrate fabricated using the modified glass exhibited a higher haze ratio than a conventional W-textured ZnO:B substrate and achieved a higher short-circuit current in microcrystalline silicon solar cells without significant deterioration of open-circuit voltage and fill factor.

Resist-free antireflective nanostructured film fabricated by thermal-NIL.

Resist-free antireflective (AR) nanostructured films are directly fabricated on polycarbonate (PC) film using thermal-nanoimprint lithography (T-NIL) and the moth-eye shape of AR nanostructure is elaborately optimized with different oxygen reactive ion etching conditions. Anodic aluminum oxide (AAO) templates are directly used as master molds of T-NIL for preparation of AR nanostructures on PC film without an additional T-NIL resist. AR nanostructures are well arranged with a period of about 200 nm and diameter of about 150 nm, which corresponds to those of the AAO template mold. The moth-eye AR nanostructures exhibit the average reflectance of 2% in wavelength range from 400 to 800 nm. From the results, highly enhanced AR properties with simple direct imprinting on PC film demonstrate the potential for panel application in the field of flat display, touch screen, and solar cells.

Textured conducting glass by nanosphere lithography for increased light absorption in thin-film solar cells

Nanoscale surface texturing in thin-film solar cells has been shown to enhance device efficiency by increasing light absorption through reduced reflectance and increased light scattering across a broad range of wavelengths and angles. However, light trapping in the industrial thin-film cells is still sub-optimal and creating optimized nanoscale texture over a large area remains challenging. In this article, we present a well-controlled low-cost process to fabricate a periodic nanocone texture optimized for maximum light absorption in thin-film microcrystalline silicon solar cells. The texture is fabricated using nanosphere lithography with the period controlled by the nanosphere diameter and the texture shape and aspect ratio controlled by the reactive ion etching conditions. Finite-difference time-domain optical simulations are used to optimize the texture in the state-of-the-art microcrystalline cells, and optical absorption measurements show that the same cells fabricated on the optimized nanocone-textured substrates exhibit a relative short-circuit current increase of close to 30% compared to a reference state-of-the-art cell with a randomly textured zinc oxide layer. This nanocone texturing technique is compatible with standard thin-film cell fabrication processes and can also be used for other thin-film cells (CIGS, CdTe, CZTS, etc) to maximize light absorption and minimize layer thickness enabling more efficient carrier collection and lower overall cost.

Fabrication of size-tunable antireflective nanopillar array using hybrid nano-patterning lithography

This study developed a novel and inexpensive method for fabricating size-tunable tapered antireflective nanopillars on a polycarbonate (PC) film using hybrid nano-patterning lithography consisting of nanosphere lithography (NSL) and nanoimprint lithography (NIL). The optical properties of the antireflective surfaces can be controlled by the CrN nanomold morphologies resulting from the different reactive ion etching conditions. The nanomold surface of CrN nanohole arrays has a low surface energy at the interface and has an anti-sticking property that can be applied in the problem of the sticking during demolding. A high-performance antireflective tapered nanopillar layer was successfully imprinted on a PC film surface using a contactless gas assisted pressing process along with a CrN nanomold prepared by NSL. The optical properties of antireflective characteristic of the PC tapered nanostructures were analyzed. Such antireflective surfaces are promising for fabrication of high light transmittance and antireflective optical materials to be used in many important fields.

Broadband antireflective silicon carbide surface produced by cost-effective method

A cost-effective method for fabricating antireflective subwavelength structures on silicon carbide is demonstrated. The nanopatterning is performed in a 2-step process: aluminum deposition and reactive ion etching. The effect, of the deposited aluminum film thickness and the reactive ion etching conditions, on the average surface reflectance and nanostructure landscape have been investigated systematically. The average reflectance of silicon carbide surface is significantly suppressed from 25.4% to 0.05%, under the optimal experimental conditions, in the wavelength range of 390-784 nm. The presence of stochastic nanostructures also changes the wetting properties of silicon carbide surface from hydrophilic (47°) to hydrophobic (108°).

Recovery of clean ordered (1 1 1) surface of etched silicon

It is generally known that dry etching induces surface damage, but the structure of etched surfaces has not been studied in detail. Nor has it been established how or whether a clean, ordered surface can be recovered after etching damage. Generally, etching damages the surface by introducing structural disorder and impurities to the surface region. Such damage may be so severe that a clean, ordered surface is not recoverable even after heating up to ∼1400K in UHV. We subjected Si (111) surfaces to different reactive ion etching conditions and/or post-etch treatments and examined their effect on the surface. Low temperature STM revealed that a clean, ordered surface as evidenced by the appearance of large area 7×7 reconstructions can be obtained only under certain etching/post-etch recipes. On the other hand, LEED showing 7×7 diffraction spots but with high intensity background and Auger electron spectroscopy (AES) showing no impurity signal cannot be used as evidence that an ordered surface has been obtained.

Improvement of polycrystalline silicon wafer solar cell efficiency by forming nanoscale pyramids on wafer surface using a self-mask etching technique

The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl2), sulfur hexafluoride (SF6), and oxygen (O2) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120-130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6-10 min to create surface nanostructures by varying the compositions of SF6, Cl2, and O2 gas mixtures in the etching process. The wafers were then treated with acid (KOH:H2O = 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 × 156 mm2) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching.

Fabrication of size-tunable Cr nanodots and nanorings array by modified nanosphere lithography

This Letter is devoted to developing a novel and low-cost strategy for fabricating Cr triangular-shaped nanodot and nanoring array patterns by a distinct magnetron sputtering approach using nanosphere lithography-based technology. The size of polystyrene nanospheres had a direct influence on the size and period of Cr nanorings. The lateral sizes, inner sizes, wall thickness and wall height are controllable by varying the process conditions of reactive ion etching, magnetron sputtering and the lift-off process. The wettability can be manipulated by changing the size of the nanorings. This new approach will surely facilitate further exploration of metal nanorings for potential applications in electro-optic devices.

A simple and fast fabrication of a both self-cleanable and deep-UV antireflective quartz nanostructured surface

Both self-cleanability and antireflectivity were achieved on quartz surfaces by forming heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane self-assembled monolayer after fabrication of nanostructures with a mask-free method. By exposing polymethylmethacrylate spin-coated quartz plates to O2 reactive ion etching (RIE) and CF4 RIE successively, three well-defined types of nanopillar arrays were generated: A2, A8, and A11 patterns with average pillar widths of 33 ± 4 nm, 55 ± 5 nm, and 73 ± 14 nm, respectively, were formed. All the fabrication processes including the final cleaning can be finished within 4 h. All nanostructured quartz surfaces exhibited contact angles higher than 155° with minimal water droplet adhesiveness and enhanced transparency (due to antireflectivity) over a broad spectral range from 350 to 900 nm. Furthermore, A2 pattern showed an enhanced antireflective effect that extends to the deep-UV range near 190 nm, which is a drawback region in conventional thin-film-coating approaches as a result of thermal damage. Because, by changing the conditions of successive RIE, the geometrical configurations of nanostructure arrays can be easily modified to meet specific needs, the newly developed fabrication method is expected to be applied in various optic and opto-electrical areas.PACS codes: 06.60.Ei; 81.65.Cf; 81.40.Vw.

Advanced antireflective nanostructures etched down from nanosilver colloid-transformed island mask

Advanced fabrication methods for antireflective nanostructures are presented via the formation of thermally grown nanosilver islands from continuously deposited colloidal multilayers, followed by a multi-step reactive ion etch (RIE) with optimized gas mixture rate. This process allows the formation of a random array of nanostructures of diameter 150nm or less and height greater than 200nm. The reflectance falls to around 0.7% in the visible region, with reasonably enhanced broadband stability and reduced incidence angle dependence. The tunability of antireflection was investigated with respect to several parameters associated with the nanosilver etch mask fabrication and RIE conditions.

Surface Texturing for Crystalline Silicon Solar Cell Using RIE Equipped with Metal-Mesh

Surface texturing is an important process to enhance light absorption and to improve efficiency of a solar cell. Reactive ion etching (RIE) process is a very effective process and low-cost process, which is applicable during the dry etching processes for thin crystalline silicon solar cells with large areas. In this study, we studied a dry and free mask texturing process on crystalline silicon wafer using SF6/O2plasmas and metal mesh in a RIE system, with special attention to the effect of the metal mesh and RIE conditions on the texture of the silicon surface. In particular, we have found an optimized RIE conditions by increasing the distance between the metal mesh and silicon wafer. We have also found that by increasing the RIE process time, with an optimized SF6/O2ratio, pressure and RF power, it is possible to switch from a random texture, to a nm-size pyramid texture and finally to an um-size pyramid texture. This RIE system textured a crystalline wafer surface that formed about 1~2 μm pyramidal black silicon with 7~10% of reflectivity.