Anisotropic Etching Of Silicon Research Articles

Silver Dendrite‐Coated Silicon Pyramid Substrate as Surface‐Enhanced Raman Scattering Probe for Detecting Glucose

Raman spectroscopy offers a rapid and nondestructive method for qualitatively and quantitatively analyzing the molecular structure of substances. Herein, a facile and cost‐effective approach for the preparation of three‐dimensional (3D) surface‐enhanced Raman scattering (SERS) substrates is proposed, in which pyramid structures are fabricated using silicon anisotropic wet etching and silver dendrites are decorated on these silicon pyramid (PSi) substrates by immersing them in a mixture of hydrofluoric acid and silver nitrate for several minutes. The 3D SERS substrates, based on PSi coated with Ag dendrites, reveal high‐performance SERS enhancement (with an analytical enhancement factor reaching 3.54 × 1010) and can detect rhodamine 6G (R6G) in the presence of chemical enhancer (lithium chloride) at low concentrations down to 10−11 m. For glucose detection, 2‐thienylboronic acid is employed to faciliate glucose attachment to the substrate surface, achieving a detection limit as low as 10−6 m. The substrate exhibits good repeatability with a relative standard deviation of 11.223%, as well as reusability and long‐term stability for detection. The results also highlight the excellent sensitivity of the PSi‐based SERS substrate, which is expected to be instrumental in biochemical analysis and holds significant potential for developing noninvasive glucose sensor for diabetic patients using saliva samples.

Deep-reactive ion etching of silicon nanowire arrays at cryogenic temperatures

The pursuit of sculpting materials at increasingly smaller and deeper scales remains a persistent subject in the field of micro- and nanofabrication. Anisotropic deep-reactive ion etching of silicon at cryogenic temperatures (cryo-DRIE) was investigated for fabricating arrays of vertically aligned Si nanowires (NWs) of a large range of dimensions from micrometers down to 30 nm in diameter, combined with commonly used wafer-scale lithography techniques based on optical, electron-beam, nanoimprint, and nanosphere/colloidal masking. Large selectivity of ∼100 to 120 and almost 700 was found with resists and chromium hard masks, respectively. This remarkable selectivity enables the successful transfer of patterned geometries while preserving spatial resolution to a significant extent. Depending on the requirements by applications, various shapes, profiles, and aspect ratios were achieved by varying process parameters synchronously or asynchronously. High aspect ratios of up to 100 comparable to the best result by metal-assisted wet-chemical etching and sub-μm trenches by DRIE were obtained with NW diameter of 200 nm, at an etch rate of ∼4 μm/min without being collapsed. At the same time, low surface roughness values were maintained on the NW top, sidewall, and bottom surface of ∼0.3, ∼13, and ∼2 nm, respectively, as well as high pattern fidelity and integrity, which were measured using angle-resolved Fourier microscopy, combined atomic force, and scanning electron microscopy on selected NWs. This work establishes the foundation in the controllable development of Si nanoarchitectures, especially at sub-100 nm structures, for energy-harvesting and storage, damage-free optoelectronics, quantum, photovoltaics, and biomedical devices.

Modern Scanning Electron Microscopy. 2. Test objects for Scanning Electron Microscopy

The review of the test objects intended for calibration of scanning electron microscopes and researches to secondary electronic emission of a relief surface of a solid state in scanning electron microscope is carried out. The test objects are divided on two parameters – kind of a relief and structure of a relief. By the form of relief the test objects are divided on single, pitch and periodic. On a structure of a relief of the test objects are divided into objects with a rectangular structure and objects with a trapezoid structure with the large and small corners of an inclination of lateral walls. The examples of such the test objects are given. Their characteristics and methods of certification of parameters are described. The advantages and lacks of the test objects are considered. Is shown, that the best characteristics have the tests objects representing pitch structures consisting of trapezoid trenches with the large corners of an inclination of lateral walls. The test objects are created in monosilicon with of a surface orientation by {100} by method liquid anisotropic etching of silicon. These test objects allow defining all characteristics scanning electron microscopes, influencing on measurement of the linear sizes of relief structures used in microelectronics and nanotechnology. With their help it is possible to carry out correlation measurements, which raise accuracy of calibration scanning electron microscopes up to ten times.

Integrated Fabrication Process of Si Microcantilever Using TMAH Solution With Planar Molybdenum Mask

The anisotropic etching release of a silicon microcantilever structure becomes challenging when it has embedded metal layers. We integrated the anisotropic wet silicon etching and etch-back method for the microcantilever releasing process in a silicon-on-insulator (SOI) wafer using a planar molybdenum (Mo)-based mask. Mo mask, which has good stability on morphology in tetramethylammonium hydroxide (TMAH) etchant as well as electrical characteristics, was employed to protect the metal resistor on the cantilever surface from TMAH etchant during silicon etching. To obtain a planar topography for the Mo mask, we applied a sequence of three etch-back processes using ZEP 520A resist, which has a similar etching rate to the non-doped silicate glass (NSG) layer in the plasma CF <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{4}$</tex-math> </inline-formula> :H <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{2}$</tex-math> </inline-formula> gas (40:1). After surface planarization, the angle of the indentation region (metal edge boundary area) was about 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> (almost flat), thus avoiding cracks in the Mo mask layer. As a result, the cantilever with a metal resistor was successfully released from the silicon substrate by our proposed method. Therefore, this process promises a silicon microcantilever fabrication method without backside alignment masks, relatively low temperature, and complementary metal-oxide semiconductor (CMOS) compatibility for chemical and bio-sensor applications.

Comparative investigation of anisotropic etches for polysilicon nanowire definition in thin film technology

We report a low-cost mass manufacturable route for polysilicon nanowire (NW) fabrication through comparative investigations of spacer etch techniques to realize nanowires from amorphous silicon (α-Si) layer. The process uses thin film technology and mature top-down microelectronics (linewidth > 10 μm). Anisotropic deep silicon etch process using the elevated plasma density of high-density low-pressure systems (HDLP) with a simultaneous flow of etchant SF6 and inhibitor C4F8 delivered nanowires with quarter circle shape. The nanowires are also characterised with significant sidewall striations and noticeable aggregation of polymers. HDLP etch system with a sequential flow of etchant SF6 and inhibitor C4F8 delivered a near rectangular nanowire shape. However, the generally good profile is marred with significant sidewall striations and accumulation of polymers at the tip of the etched sidewall. Shallow etch process using low density plasma in a cheap capacitively coupled reactive ion etch (RIE) equipment with a simultaneous flow of etchant SF6 and inhibitor O2 delivered nanowires with ideal rectangular shape. The nanowires have hardly visible sidewall striations and/or polymer. These results indicate that deep silicon HDLP etch processes albeit advanced and costly are not suitable for good quality nanowire definition using spacer etch from a thin film of α-Si layer. Low density plasma process with simultaneous flow of SF6 and O2 gases in relatively cheap RIE system provides high quality nanowires and hence, provides a simple, low cost, wafer scale mass manufacturable route for high quality polysilicon nanowire fabrication.

Microfluidic Liquid Cell with Silicon Nitride Super-Thin Membrane for Electron Microscopy of Samples in Liquid.

Microfluidic liquid cells have been developed to visualize nanoscaled biological samples in liquid using a scanning electron microscope (SEM) through an electron-transparent membrane (ETM). However, despite the combination of the high-resolution visualization of SEM and the high experimental capability of microfluidics, the image is unclear because of the scattering of the electron beam in the ETM. Thus, this study developed a microfluidic liquid cell with a super-thin ETM of thickness 10 nm. Because the super-thin ETM is excessively fragile, the bonding of a silicon-nitride-deposited substrate and a polydimethylsiloxane microchannel before silicon anisotropic etching was proposed prevented the super-thin ETM from damage and breakage due to etching. With this protection against etchant using the microchannel, the yield of the fabricated super-thin ETM increased from 0 to 87%. Further, the scattering of the electron beam was suppressed using a microfluidic liquid cell with a super-thin ETM, resulting in high-resolution visualization. In addition, T4 bacteriophages were visualized using a super-thin ETM in vacuum. Furthermore, the cyanobacterium Synechocystis sp. PCC6803 in liquid was visualized using a super-thin ETM, and sub-microscopic structures on the surface were observed.

High efficiency echelle gratings for the far ultraviolet.

Modern grating manufacturing techniques suffer from inherent issues that limit their peak efficiencies. The anisotropic etching of silicon facilitates the creation of custom gratings that have sharp and atomically smooth facets, directly addressing these issues. We describe work to fabricate and characterize etched silicon echelles optimized for the far ultraviolet (FUV; 90-180 nm) bandpass. We fabricate two echelles that have parameters similar to the mechanically ruled grating flown on the Colorado High-resolution Echelle Stellar Spectrograph sounding rocket. We demonstrate a 42% increase in peak order efficiency and an 83% decrease in interorder scatter using these gratings. We also present analysis on where the remaining efficiency resides. These demonstrated FUV echelle improvements benefit the faint source sensitivity and high resolution performance of future UV observatories.

Разработка чувствительного элемента микромеханического акселерометра

Micromechanical accelerometers have wide range of applications in industry and robotechnics due to the main advantages such like low power consumption, small dimensions and weight, low cost in serial production. Therefore, micromechanical accelerometers research and development received priority. In this work, finite element analysis software was used for modeling the sensitive element, for this method allows providing static and modal analysis. The results of preliminary calculations of the scale factor of the accelerometer that can be assembled based on the developed sensor and sigma-delta transducer, are provided. The article describes the tech-nological process of manufacturing sensitive elements of micromechanical accelerometers. In this case, anisotropic liquid chemical etching of silicon was used, which makes it possible to obtain different profiles of the corresponding crystallographic planes. The results of a study of the influence of technological errors on the geometric dimensions of sensitive elements are provided: the dependence of the value of the lateral undercut of silicon on the accuracy of the angular alignment of the mask with the crystallographic axis of the plate (100) was revealed. The design of the sensitive element of the micromechanical accelerometer has been developed. The performed simulations have proved out the performance of the structure, the calculations have shown the change in the scale factor in the temperature range from –60 to +125 °C, the value of the nominal capacity and capacity with a change in linear acceleration in the range of ± 60 g. In the manufacture of a sensitive element on the basis of the studies carried out, it is possible to ob-tain a lateral undercut of no more than 5 microns at a depth of anisotropic liquid chemical etching of 250 microns for KDB-0,01 plates with an orientation tolerance of ± 30 arc minutes or with a misorientation of the same magnitude allowed during exposure.

Optimization of deep silicon etching process for microstructures fabrication

The paper presents the study of cyclic process of deep anisotropic silicon etching, called Oxi-Etch, in which the steps of etching and oxidation alternate, allowing deep etching of silicon with an anisotropic profile. This process forms typical for cyclic etching process sidewall profile called scalloping. Opportunities for modification and optimization of the process for specific application were investigated. The effects of optimization of the bias voltage and the duration of the etching step on the parameters of the resulting structures, such as the etching depth, wall roughness, and the accuracy of transferring the lithographic size, are considered. Balance between etch rate and scalloping was established.

Single-step alkaline etching of deep silicon cavities for chip-scale atomic clock technology

This paper presents the results of experiments on the development of the technology of MEMS alkali vapor cells for a miniature quantum frequency standard. The classical design of a two-chamber silicon cell containing an optical chamber, shallow filtration channels and a technical container for a solid-state alkali source was implemented in a single-step process of wet anisotropic silicon etching. To prevent the destruction of the filtration channels during etching of the through silicon cavities, the shapes of the compensating structures at the convex corners of the silicon nitride mask were calculated and the composition of the silicon etchant was experimentally found. The experiments results were used in the manufacture of chip-scale atomic clock cells containing vapors of 87Rb or 133Cs isotopes in the neon atmosphere.

A microfabricated ion trap chip with a sloped loading slot to minimize exposing trapped ions to stray charges

A novel microfabricated ion trap chip that can geometrically minimize exposing trapped ions to stray charges on dielectric surfaces is developed. The new design utilizes a sloped loading slot to make the dielectric layers of the loading slot sidewalls invisible to the trapped ions. The designed loading slot is realized by applying silicon anisotropic etching processes, and the ion trap chip that contains the sloped loading slot is fabricated using microelectromechanical system processes. Stray charges induced by injecting an ultraviolet laser on the surface of the fabricated ion trap chip are experimentally characterized by measuring stray electric fields at the location of the trapped ions. The measured results are compared to those of a previous ion trap chip with a vertical loading slot. The magnitude of the measured stray electric field in the axial direction is within 1.5 V m−1 for the proposed ion trap chip, whereas it is approximately 10 V m−1 for the previously reported ion trap chip.

On the Operation Modes of Dual-Gate Reconfigurable Nanowire Transistors

We investigate the operation of dual-gate reconfigurable field-effect transistor (RFET) in the programgate at drain (PGAD) and program-gate at source (PGAS) configurations. To this end, dual-gate silicon nanowire (SiNW) FETs are fabricated based on anisotropic wet chemical silicon etching and nickel silicidation yielding silicide-SiNW Schottky junctions at source and drain. Whereas in PGAD-configuration ambipolar operation is suppressed, switching is deteriorated due to the injection through a Schottky-barrier. Operating the RFET in PGAS configuration yields a switching behavior close to a conventional MOSFET. This, howewer, needs to be traded off against strongly non-linear output characteristics for small bias.

Geometry of Structures Developed by Anisotropic Etching in the Nanometer Range

Geometric disadvantages of nanostructure surface developed by anisotropic etching of silicon are discussed. These disadvantages increase uncertainness of its sizes and impeded its using as an etalons for linear measurements. The greatest uncertainness are observed for structures with trapezoid profile. They make up due to defects on sidewalls of etched structures. The surface of a sidewall is proposed to be disposed in the [111] plane and so be absolutely flat. Really parts of a sidewall surface are deflected in stepwise way from the plane [111]. This phenomenon leads to deflection of angles between converging flat sections of etched structure from its known values for silicon. Consequence of this is most drastic to a measure MShps-2K due to its structure, technology of anisotropic etching and absence of required control. Sources of these surface disadvantages induced by anisotropic etching are discussed. Possibilities to decrease disadvantages are evaluated.

Numerical Study of SF6/O2 Plasma Discharge for Etching Applications

SF6/O2 plasma discharge has extensive applications in semi-conductor industry for anisotropic etching of silicon. Herein, a self-consistent fluid model has been used to investigate the capacitive coupled SF6/O2 plasma discharge. A complete set of reactions in gas phase which include electron impact reactions, ion-ion reactions, neutral–neutral reactions and charge transfer reactions in tandem with the primary processes such as dissociation excitation, and ionization were incorporated in the model. The densities of dominant plasma species (both neutral and charged) were calculated. Furthermore, the impact of O2 concentration on the plasma characteristics was studied. The results showed a bell shape distribution for neutral species while uniform distribution for charged species at center of the discharge. Moreover, it was demonstrated that the dominant etching species in the discharge were F, O, S, SF5+, FO, F+, O+, O2+ and S+. With the increase of O2 concentration in the plasma, there is a decrease in the ratio of neutral species (i.e., F/ O) and overall etch rate, signifying that chemical etching is the prominent process for the discharge. In conclusion, the anisotropic etching of Si substrate can be efficiently achieved using the optimum input parameters for SF6/O2plasma discharge.

Facile and scalable fabrication of Ni cantilever nanoprobes using silicon template and micro-electroforming techniques for nano-tip focused electrohydrodynamic jet printing

Electrohydrodynamic jet (E-Jet) printing is a powerful technique for micro/nanostructure fabrication with high resolution and efficiency. However, conventional E-Jet printing are still limited in printing accuracy and ink adaptability due to the nozzle clogging effect. In this paper, we develop a nano-tip focused electrohydrodynamic jet (NFEJ) method to print high-resolution structures. The Ni cantilever nanoprobes with nanoscale radius of curvature (ROC) on their tips were manufactured by a facile and scalable method using silicon template and micro-electroforming technique. Scanning electron microscope was used to analyse the micromorphology of the silicon template with inverted pyramid pits, which was obtained from anisotropic wet etching of silicon. Electroforming mold was obtained by photolithography and plasma etching which divide the top side of Ni film into isolated cantilever pits. Ni cantilever nanoprobes with an average tip ROC of about 48 nm were achieved by the subsequent micro electroforming process. High-resolution droplets array with an average diameter of about 890 ± 93 nm were printed by the NFEJ printing head equipped with these Ni nanoprobes, which verified the practicality of the developed Ni nanoprobes for NFEJ printing.

Anisotropic Etching of Pyramidal Silica Reliefs with Metal Masks and Hydrofluoric Acid.

This work describes the fabrication of anisotropically etched, faceted pyramidal structures in amorphous layers of silicon dioxide or glass. Anisotropic and crystal-oriented etching of silicon is well known. Anisotropic etching behavior in completely amorphous layers of silicon dioxide in combination with purely isotropic hydrofluoric acid as etchant is an unexpected phenomenon. The work presents practical exploitations of this new process for self-perfecting pyramidal structures. It can be used for textured silica or glass surfaces. The reason for the observed anisotropy, leading to enhanced lateral etch rates, is the presence of thin metal layers. The lateral etch rate under the metal significantly exceeds the vertical etch rate of the non-metallized area by a factor of about 6-43 for liquid and 59 for vapor-based processes. The ratio between lateral and vertical etch rate, thus the sidewall inclination, can be controlled by etchant concentration and selected metal. The described process allows for direct fabrication of shallow angle pyramids, which for example can enhance the coupling efficiency of light emitting diodes or solar cells, can be exploited for producing dedicated silicon dioxide atomic force microscopy tips with a radius in the 50nm range, or can potentially be used for surface plasmonics.

Impact of Ge deposition temperature on parameters of c-Si solar cells with surface texture formed by etching of Si using SiGe islands as a mask

In this paper, the Ge self-assembled islands grown at different temperatures were used as an etching mask for selective anisotropic etching of crystalline silicon (c-Si) in order to form a textured Si surface. The effects of Ge deposition temperature on the texture morphology as well as the parameters of c-Si solar cells fabricated on such structures were studied with the range of temperature from 500 °C to 800 °C. The textures on Si surface with low (<1 μm) etching margin were successfully fabricated for all investigated structures. It was revealed that usage of rapid annealing of Si wafer at 800 °C prior to epitaxial growth along with the low Ge deposition temperature of 500 °C allowed to achieve the relatively high effective carrier lifetime as compared to structures formed at higher (≥700 °C) temperatures thanks to the reduced degradation of Si wafer characteristics. Furthermore, the structure obtained using the lowest deposition temperature of 500 °C exhibited the highest light absorption among all studied samples thanks to the most homogeneous and most pyramidal texture morphology. As a result, the calculated short circuit current density JSC for the sample in which Ge islands were grown at 500 °C was as high as 35.89 mA/cm2. The proposed approach of surface texturing meets the requirements for thin c-Si solar cells due to small etching margin and the obtained results pave the way for increase the efficiency of thin c-Si solar cells by engineering the surface morphology to improve light absorption.

Effect of cations on silicon anisotropic etching process in solutions containing TMAH and TMAH with tensioactive compounds

Almost everything has been written on silicon anisotropic etching in alkaline solutions, however, the difference between etching in pure KOH and TMAH as well as in these solutions containing tensioactive compounds has not been completely elucidated yet. This paper present the results of anisotropic etching of Si(100) and Si(110) in the solutions containing two etching agents, KOH and TMAH. Due to this it is possible to control the effect of concentration of each agent on the course of etching and clarify the effect of cation type (inorganic and organic) on the course of the process. The effect of TMA+ ions on etch rate of Si(100) has already been proven both during etching in pure TMAH as well as after addition of tensioactive compounds to this solution. It results in a change in anisotropy ratio (R(110)/R(100)) in TMAH containing solutions in comparison to solutions based on KOH. As the commonly used KOH concentrations (5–10 M) are larger than those of TMAH 25 % (2.7 M), the concentration range of the studied TMAH solution has been extended to 50 %. The paper describes the properties of those concentrated TMAH solutions, both pure and containing surfactants.

Deep silicon etching for thermopile structures using a modified Bosch process

We present a simple method of deep anisotropic etching of silicon up to 400 μm with nearly vertical sidewall profile for thermopile devices. The method is based on the time-multiplexed etching which is a modified case of the Bosch deep reactive ion etching process. This process is mainly adjusted by chuck power and it is divided into three steps which are zero bias deposition step, high bias polymer removing step, and low bias silicon etching step. Compared with the standard Bosch process, this modified strategy shows advantage of etch rate and selectivity.

Anisotropic plasma etching of Silicon in gas chopping process by alternating steps of oxidation and etching

In the present work a two-stage process for deep anisotropic etching of Silicon based on alternating steps of etching in SF6 plasma and passivation of Silicon surface by oxidation in O2 plasma is proposed. This developed Ox-Etch process has advantages of being free from deposited polymers on sidewalls and does not use cryogenic equipment. Etched structures show anisotropic profile with vertical scalloped walls similar to Bosch and STiGer processes. Selectivity of Silicon etch process with respect to SiO2 mask is up to 120:1. The investigations of etching results depending on process parameters are presented. Main control parameters for Ox-Etch process defining the etch rate and degree of anisotropy are the durations of etch and oxidation steps.