Reactive Ion Etching Of Silicon Research Articles

Mechanism of Improving Etching Selectivity for E-Beam Resist AR-N 7520 in the Formation of Photonic Silicon Structures

The selectivity of the reactive ion etching of silicon using a negative electron resist AR-N 7520 mask was investigated. The selectivity dependencies on the fraction of SF6 in the feeding gas and bias voltage were obtained. To understand the kinetics of passivation film formation and etching, the type and concentration of neutral particles were evaluated and identified using plasma optical emission spectroscopy. Electron temperature and electron density were measured by the Langmuir probe method to interpret the optical emission spectroscopy data. A high etching selectivity of 8.0 ± 1.8 was obtained for the etching process. The optimum electron beam exposure dose for defining the mask was 8200 pC/m at 30 keV.

A High-Aspect-Ratio Deterministic Lateral Displacement Array for High-Throughput Fractionation.

Future industrial applications of microparticle fractionation with deterministic lateral displacement (DLD) devices are hindered by exceedingly low throughput rates. To enable the necessary high-volume flows, high flow velocities as well as high aspect ratios in DLD devices have to be investigated. However, no experimental studies have yet been conducted on the fractionation of bi-disperse suspensions containing particles below 10 µm with DLD at a Reynolds number (Re) above 60. Furthermore, devices with an aspect ratio of more than 4:1, which require advanced microfabrication, are not known in the DLD literature. Therefore, we developed a suitable process with deep reactive ion etching of silicon and anodic bonding of a glass lid to create pressure-resistant arrays. With a depth of 120 µm and a gap of 23 µm between posts, a high aspect ratio of 6:1 was realized, and devices were investigated using simulations and fractionation experiments. With the two-segmented array of 3° and 7° row shifts, critical diameters of 8 µm and 12 µm were calculated for low Re conditions, but it was already known that vortices behind the posts can shift these values to lower critical diameters. Suspensions with polystyrene particles in different combinations were injected with an overall flow rate of up to 15 mL/min, corresponding to Re values of up to 90. Suspensions containing particle combinations of 2 µm with 10 µm as well as 5 µm with 10 µm were successfully fractionated, even at the highest flow rate. Under these conditions, a slight widening of the displacement position was observed, but there was no further reduction in the critical size as it was for Re = 60. With an unprecedented fractionation throughput of nearly 1 L per hour, entirely new applications are being developed for chemical, pharmaceutical, and recycling technologies.

An examination of the performance of molecular dynamics force fields: Silicon and silicon dioxide reactive ion etching

Classical molecular dynamics (MD) simulations of plasma-surface interactions were performed of physical sputtering and reactive ion etching (RIE), with predictions based on several force fields. In this paper, we focus mainly on SiO2 but include some results for Si substrates as well. We compare predictions from these MD simulations to experimental studies of SiO2 physical sputtering (by Ar+ ions), RIE of Si, and RIE of SiO2 (both using F atoms and Ar+ ions). MD results using different published force fields are compared to reported yields from published vacuum beam experiments. The near-surface depth profiles predicted using different force fields are compared. One motivation for the present study is to document the nature and magnitude of differences in the predictions for selected systems and conditions of practical interest.

Controlling Silicon Etching Parameters in RF CHF3 Plasma by Optical Emission Spectroscopy

The processes of plasma-chemical and reactive-ion etching of silicon in trifluoromethane (CHF3) are studied using optical emission spectroscopy. The dependences of the radiation intensities of atoms and mol-ecules on the etching time, input power, and pressure of the plasma-forming gas are obtained and analyzed.

Plasma-Chemical and Reactive-Ion Etching of Silicon in Tetrafluoromethane with Argon

Plasma-Chemical and Reactive-Ion Etching of Silicon in Tetrafluoromethane with Argon

Plasma Parameters and Kinetics of Reactive-Ion Etching of Silicon in a C6F12O + Ar Mixture

Plasma Parameters and Kinetics of Reactive-Ion Etching of Silicon in a C6F12O + Ar Mixture

Surface engineering of standing hollow circular cylinder ordered arrays (HCCA) and used as platform for excellent SERS substrate

Herein, we reported a facile and efficient method to mass fabricate special structure of standing hollow circular cylinder ordered arrays (HCCA). The strategy of fabrication of the HCCA is reactive ion etching of silicon covered with monolayer colloidal spheres as mask under the mixture of SF6 and O2 plasma. Based on study of the whole formation process and different factor (such as sample stage, the flow of SF6 and O2, power), we put forward the formation mechanism of HCCA. Research shows that Al sample stage play a crucial effect in formation of such structure. And the presence of O2 and the flow of SF6 are also important factor. Based on HCCA as platform, we can obtain Au@ HCCA structure through sputtering deposition method. The formed Au@HCCA can be used as SERS substrate, and exhibit excellent SERS property using Handheld Raman Spectrometer excited with wavelength of 785 nm. The finite difference time domain (FDTD) simulation results have revealed that SERS “hot spots” are almost distributed at edge site of Au@HCCA. Obviously, such HCCA structure as platform, it can also be applied to a more wide range of fields.

Realization of Three-Dimensionally MEMS Stacked Comb Structures for Microactuators Using Low-Temperature Multi-Wafer Bonding with Self-Alignment Techniques in CMOS-Compatible Processes.

A high-aspect-ratio three-dimensionally (3D) stacked comb structure for micromirror application is demonstrated by wafer bonding technology in CMOS-compatible processes in this work. A vertically stacked comb structure is designed to circumvent any misalignment issues that could arise from multiple wafer bonding. These out-of-plane comb drives are used for the bias actuation to achieve a larger tilt angle for micromirrors. The high-aspect-ratio mechanical structure is realized by the deep reactive ion etching of silicon, and the notching effect in silicon-on-insulator (SOI) wafers is minimized. The low-temperature bonding of two patterned wafers is achieved with fusion bonding, and a high bond strength up to 2.5 J/m2 is obtained, which sustains subsequent processing steps. Furthermore, the dependency of resonant frequency on device dimensions is studied systematically, which provides useful guidelines for future design and application. A finalized device fabricated here was also tested to have a resonant frequency of 17.57 kHz and a tilt angle of 70° under an AC bias voltage of 2 V.

Laboratory X-ray interferometry imaging with a fan-shaped source grating.

The orientation mismatch between the cone beam of an X-ray tube and the grating lines in a flat substrate remains a big challenge for laboratory grating-based X-ray interferometry, since it severely limits the imaging field of view. Here, we fabricated fan-shaped G0 source gratings by modulating the electric field during the deep reactive ion etching of silicon. The gold electroplated fan-shaped G0 grating (3.0 µm pitch) in a 20 keV interferometer improves the uniformity of the field of view with an increase of average visibility from 16.2% to 18.5% and a better angular sensitivity (by a factor 5.8) at the edges.

Deep reactive ion etching of silicon using non-ICP-based equipment

Deep reactive ion etching (DRIE) technology is one of the most important technologies in the processing of microelectronic devices and microelectromechanical system. As a necessary process in semiconductor integration, it has been widely studied in the past decades. It is known that the traditional DRIE process typically uses a plasma etching reactor equipped with inductively coupled plasma (ICP) sources to generate a high-density plasma so as to achieve high aspect ratio trenches with relatively small roughness. A cryogenic temperature control unit is typically employed as well. Here, however, we use a parallel plate RIE with rather simple structure, which is not usually used for DRIE, to obtain high aspect ratio silicon etching. With no ICP sources and no sophisticated temperature control unit, the system and experiment are now much more cost effective. Through the optimization of the processing, the etching rate of silicon can reach 440 nm/min. Finally, a 45 μm deep trench is etched in silicon with good perpendicularity. This method will greatly reduce the equipment related cost, especially for those applications that do not have extremely stringent requirement on the final etching accuracy.

Deep reactive ion etching of ‘grass-free’ widely-spaced periodic 2D arrays, using sacrificial structures

We fabricated two-dimensional arrays of periodic, widely-spaced pillars using deep reactive ion etching of silicon. To avoid the formation of micro-grass in the large open areas we used sacrificial structures surrounding the widely-spaced pillars. The use of sacrificial structures results in a denser pattern where the formation of grass is less likely to happen. We were able to remove the sacrificial structures without damaging the main array of pillars by using a modified Bosch process. The roughness remaining after removal of the sacrificial structures was evaluated using optical profilometry. Using this method, we were able to pattern grass-free arrays of widely-spaced 12 μm diameter pillars of 9:1 aspect ratio, with hexagonal and square distributions.

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.

Plasma Etching of Silicon at a High Flow and a High Pressure of NF3 in Reactive Ion Etching

Capacitively coupled plasma reactive ion etching of silicon by injecting nitrogen trifluoride (NF3) gas was conducted, and the etching process was studied with a residual gas analyzer and an optical emission spectroscopy. During the etching of silicon by the NF3 plasma, the currents of F+ and SiF+3 ions were obtained from the residual gas analyzer. At the same time, the line intensity of fluorine was measured using optical emission spectroscopy. The ion currents of F+ and SiF+3 and the line intensity of fluorine were highest for etching at high pressure. With the results of this study, the general characteristics of reactive ion etching of silicon by using NF3 plasma were confirmed. In addition, by simply changing the flow rate of NF3, a high NF3 flow rate was found to result in a high etch rate because of the reduced residence time.

Capabilities and Limits to Form High Aspect-Ratio Microstructures by Molding of Borosilicate Glass

This paper presents an experimental study of capabilities to fabricate high aspect-ratio microstructures in glass. The fabrication was done by molding borosilicate glass in deep silicon trenches created by deep reactive ion etching in silicon and releasing the structures by potassium hydroxide (KOH) and Xenon difluoride (XeF2) etching of the Si mold. Subsequent over-etching of the glass can also be used to increase the aspect ratio of the glass structures. By using this molding method, glass structures have been successfully fabricated achieving an aspect ratio of 42:1, a height of 212 $\mu \text{m}$ , and vertical sidewall angle up to 89.7°. We also investigated the effect of molding parameters (heat treatment time, temperature, and pressure) on the process capabilities and limitations for defect free structures. This work demonstrates the capabilities to fabricate high aspect-ratio glass structures that cannot be achieved by conventional etching techniques to date, opening new perspectives for the use of glass in MEMS and microfluidics.

Free-standing La0.7Sr0.3MnO3 suspended micro-bridges on buffered silicon substrates showing undegraded low frequency noise properties

We report on the microfabrication process of free-standing suspended micro-bridges made of La0.7Sr0.3MnO3 (LSMO) thin films of thicknesses in the range of 10–100 nm. LSMO films were epitaxially grown on either SrTiO3 or CaTiO3 buffer layers on silicon substrates by reactive molecular beam epitaxy. The micro-bridges were patterned using standard UV photolithography then etched by ion beam and released using reactive ion etching of silicon in SF6. LSMO suspended micro-bridges 2 and 4 µm wide and of length ranging from 50 to 200 µm could be fabricated with a high fabrication yield (of about 85% as evaluated over 100 fabricated suspended micro-bridges) without degrading the electrical transport properties and in particular the low frequency noise level, as attested by the normalized Hooge parameter. The latter was measured in the 0.55–7.50 × 10−30 m3 range at 300 K, which is comparable to those measured in non-suspended high quality epitaxial LSMO thin films. This fabrication process could be useful for bolometer fabrication where thermal isolation is needed, or for any microelectromechanical systems devices making use of epitaxial functional oxides.

Monte Carlo Simulation of Defects of a Trench Profile in the Process of Deep Reactive Ion Etching of Silicon

A numerical model of the evolution of a 2D profile during cryogenic etching of Si in SF6/O2 plasma is proposed and implemented. To calculate the fluxes of species a Monte Carlo method is used. The etch profile is presented with the help of square cells. The model is meant to investigate diverse defects in a profile of stochastic nature. For this, the state of a model cell is presented as a combination of states of several subcells randomly chosen upon each interaction of the species with the surface, which makes it possible to study small-scale profile defects without loss of calculation performance. They are compared with the experimental data, and good qualitative agreement is observed. Surface defects typical of high aspect ratio cryogenic etching are investigated numerically. They include the depth-dependent sidewall roughness, formation of cavities, trench splitting, and formation of “nanograss.”

Microfluidic Chemotaxis Assay through Stable Chemical Gradient

The diffusion-based method can create a non-flow environment for the bacteria, so chemotaxis response can be observed in gradients that evolve only by diffusion, in the absence of flow. Recently, we have reported a convenient and reliable diffusion-based microfluidic device for nonlinear gradient generation. Stable and rapid diffusion of chemicals was successfully generated by direct contact of two fluids manipulated by control of capillary action. In our design, the height of the junction channel is very critical because the junction channel play key roles in diffusion-based gradient generation and physical prevention of bacterial movement toward the chemoeffector channel in analysis of positive chemotactic response. In this study, to improve the height accuracy of the junction channel, we propose a new alternative microfabrication method using thick silicon oxide deposition and reactive ion etching. The height of the junction channel within 1% accuracy could be precisely fabricated by the newly-proposed microfabrication. As a proof-of-concept, we conducted experiments with bacterial chemoeffectors with Pseudomonas aeruginosa PAO1 based on fluorescent observation in a concentration-dependent manner. We easily achieved chemotaxis index of each chemoeffector and it was in a good agreement with our previous result while the variation of chemotaxis index is reduced to be half. We envision that our proposed fabrication will guide microfluidic fabrication to techniques for reproducibility for various field.

Dicing Tape Performance in a Plasma Dicing Environment

Plasma dicing, as a means of isolating individual integrated circuits from within a fully processed semiconductor substrate, is still an emerging technology but is now considered the latest step in the evolution in device singulation. With the trend towards smaller, thinner more robust devices, many chip manufacturers are considering, or already switching, to a plasma dicing approach.[1, 2] The high aspect ratio, deep reactive ion etching of silicon using a Bosch process, leverages some distinct advantages over the more physical methods of device singulation. [3] Although the more established methods of diamond blade saw dicing, various laser based approaches or laser/mechanical hybrid dicing techniques, all introduce an element of heat and in some cases water for cooling purposes, they do not expose dicing tape to the unique conditions within high vacuum plasma. This work investigates how the properties of both dicing tape and adhesive are affected when exposed to the environment of a plasma dicing process used in the semiconductor industry. A preliminary fitness test utilising an aggressive exothermic etching regime was used to establish the compatibility of a range of standard Lintec Adwill dicing tapes. In essence, a measure of base film thermal conductivity and how quickly some of the lower molecular weight volatile components of base film and adhesive materials are boiled off or ‘out-gassed’. Polyvinyl Chloride (PVC) tapes performed less well than Polyethylene terephthalate (PET) tapes and some of the Polyolefin (PO) tapes exhibited the greatest resilience. A design of experiments to measure changes in tensile strength, elongation and adhesive properties were carried out to assess the performance of plasma dicing on PO low adhesion tape. Figure 2 shows that the samples exposed to an SF6 plasma impacted the tape elongation and tensile strength properties. Typically the stretch required for PnP is in the range 1–10 % showing that the plasma dicing does not impact the overall performance of the tape. Further tests employing a die pick-up force measurement system to compare saw diced die with that of plasma diced die, proved the feasibility of this technology. Figure 3 shows that pick-up force measured on plasma diced dies is comparable with saw diced dies.

Surface morphology after reactive ion etching of silicon and gallium arsenide based solar cells

This work aims to study the surface morphology of solar cells before and after reactive ion etching (RIE) at two different pressures. Two types of solar cell based on GaAs and polycrystalline Si were processed and compared. Energy Dispersive X-ray spectroscopy (EDS) was used for the composition analysis of the samples. Raman spectroscopy showed a structural fingerprint of materials before and after processing. Atomic Force Microscope (AFM) demonstrated dimensional topography with high resolution. Optical spectrometer detected changing of reflectance the samples. Experimentally, it has been confirmed that GaAs solar cells have a very high endurance to ion bombardment in comparison to Si cells.

Optical Features of Nanowire Forests Prepared by a Plasma Repolymerization Technique

In this letter, nanowire forests are prepared by using a plasma repolymerization technique. The preparation process involves only a spin-coating step of polyimide and plasma bombardment of the polymer, the entire process is lithography-free, micromachining-compatible, fast, and extremely simple. Moreover, the nanowire forests can further be utilized as nanomasks in reactive ion etching of silicon for nanowire–nanopillar composite forests. Optical features of the nanowire forests and the nanowire–nanopillar composite forests in different wavelength regions are fully investigated. High transmission of the nanowire forests in a visible-light range implies applications of such forests in transparent devices. A specific absorption peak in a range of 8–10 μ m indicates applications of the composite nanoforests in infrared devices for certain substance sensing.