Reactive Ion Etching Technique Research Articles

Polymer peel‐off mask for high‐resolution surface derivatization, neuron placement and guidance

We present a dry lift-off method using a chemically resistant spin-on plastic, polyimide, to pattern surfaces with high accuracy and resolution. Using well-known lithographic and reactive ion etching techniques, the spin-on polymer is patterned over a silicon dioxide surface. The plastic efficiently adheres to the silicon dioxide surface during the chemical modification and is readily lifted-off following the derivatization process, permitting highly reliable surface derivatization. The verticality of the reactive ion etch enables sub-micrometer features to be patterned, down to 0.8 µm. The technique is used to pattern neurons on silicon dioxide surfaces: efficient neuron placement over a 4 mm area is shown for patterns larger than 50 µm while process guidance is shown for 10 µm patterns.

Fabrication of obliquely-aligned single crystalline diamond nanostructures and their arrays

The polycrystalline diamond film on silicon substrates is used as a starting material to fabricate three different single crystalline nanostructures by employing the bias-assisted reactive ion etching technique in hydrogen plasma. The gold layer was sputtered on the top of the films as an etching mask to produce the high-density arrays of nanocones, nanopillars and nanofibers. The well-aligned nanostructures are uniformly distributed over large surface areas, and have a tilted angle of 60° to the substrate. Meanwhile, Raman measurement confirms that no stress is introduced into the nanostructures during the etching process. The nanostructures with the unique morphologies have potential applications in various diamond-based devices.

Novel Projection Display Pixels Using Micro Vessel Structures

In this paper Electrochromic based micro-mirrors fabrication has been investigated on silicon substrates using a highlyprogrammable deep reactive ion etching technique. Silicon based micro structures have been used as micro containers for Li+ based electrolyte.Covering these micro vessels with WO3 coated ITO electrodes as electrochromic layer, leads to transparent or opaque interfaces which later will be used as image pixels. Passive addressing of micro-mirrors if feasible between mentioned ITO electrodes on top and silicon n+ doped lines at the bottom of micro structures. Desired image can be achieved by addressing each or a cluster of pixels.

Effective improvement in the distribution of single crystalline diamond nanorods fabricated from the randomly-oriented polycrystalline films

By using the bias-assisted reactive ion etching technique and the etching masks of Au nanodots, the high-density single crystalline diamond nanorods have been obtained from the polycrystalline diamond films with randomly-oriented grains grown on silicon substrates. The inhomogenous distribution of the nanorods mainly results from the existence of grain boundaries in the films, and can be effectively improved by adding the graphite sheet under the substrate. Furthermore, the fabrication mechanism of the nanorod array is carefully investigated in this paper. The morphological evolution is observed by using a scanning electron microscopy technique. Raman measurements are carried out to monitor the phase change during the etching process. It is found that the non-diamond phases are present during the experimental process, and then are completely removed away in the end.

Design and Fabrication of Silicon Oxynitride Based Evanescent Optical Waveguide Sensor for Rapid Detection of Adulteration in Petrol

In this paper we report on the design and fabrication of an Evanescent Optical Waveguide Sensor (EOWS) using silicon oxynitride (SiON) as the core layer on silica-silicon wafer and its implementation for rapid detection of adulterant traces in pure petrol incorporating composite planar waveguide geometry. The embedded waveguide of length ∼ 10,000μm and core width ∼ 50μm was fabricated using standard Plasma Enhanced Chemical Vapour Deposition (PECVD) technologies and Reactive Ion Etching (RIE) technique. The main aim of this work is to encompass an abrupt choice to the time-consuming existing adulteration detection methods which generally requires some time to give the consequence. Using Simple Effective Index Method (SEIM), the theoretical predictions and experimental results at wavelength 632.8nm are analyzed and presented, which demonstrated that the sensitivity of the proposed EOWS is ∼40 times more than that of the existing planar waveguide sensors and also 20 times more than that of asymmetric waveguide structure thereby allowing rapid detection of adulterant traces in pure petrol without involving the use of chemicals. It is found that the sensor structure is polarization independent and advantages include high sensitivity, easy fabrication and more importantly, requirement of very minimal amount of sample volume for detecting adulteration.

Measurement of pressure drop and flow resistance in microchannels with integrated micropillars

In the present study, we investigate single phase fluid flow through microchannels with integrated micropillars to calculate the pressure drop and flow resistance. The microchannels, which contain micropillars arranged in square and staggered arrangement, are fabricated in silicon substrate using standard photolithography and deep reactive ion etching (DRIE) techniques. The DRIE technique results in precise and accurate fabrication with smooth and vertical wall profiles. Pressure drop measurements are performed on microchannels with integrated micropillars under creeping flow regime over a range of water flow rates from 50 to 600 μl/min. It is observed that the pressure drop varies linearly with increasing flow rates. Flow resistance ( $$\Updelta P/Q$$ ) is calculated using the pressure drop values and is found to be decreasing as the Darcy number ( $$\sqrt{K/h^2}$$ ) increases. In general, the square arrangement of pillars offers higher resistance to flow than their staggered counterparts. It is observed that the existing theoretical models fail to accurately predict the permeability of the microchannel with integrated micro-pillars, particularly for cases where the micropillars have smooth and accurate geometric conformity, as obtained in the microfabricated structures used in the present study.

Hybrid integration of waveguide photodetectors with silicon-on-insulator micro-ring resonator on silicon substrate

To integrate compound semiconductors with foreign substrates can lead to superior or novel functionalities. The design and fabrication of heterogeneously integrated waveguide photodetectors with Silicon-on-Insulator micro-ring resonator are reported in this paper. The micro-ring resonator was fabricated by utilizing electron beam lithography and inductively-coupled-plasma reactive ion etching technique, which is used for wavelength selectivity. The waveguide photodetectors fabricated by wet etching were used for light detection. The free spectral range (FSR) of the hybrid integrated device was about 24nm, and the dark current of 7.9nA was achieved at the reverse bias voltage of 2.0V. The measured response of the photodetector at through port was 0.538μA/W at the wavelength of 1556nm and a reverse bias of 1V.

Boron filling of high aspect ratio holes by chemical vapor deposition for solid-state neutron detector applications

A multiple deposition and etching process has been developed to enable high fill factor boron deposition in high aspect ratio holes fabricated in a (100) silicon substrate. The boron deposition was carried out using low-pressure chemical vapor deposition and the etching was done by inductively coupled plasma reactive ion etching technique. The boron deposition processes were carried out under different conditions in order to find a baseline process condition. The boron etching processes done under different conditions with the photoresist as the mask are also discussed. Finally, the fabricated neutron detector with the highest fill factor was characterized for the thermal neutron detection efficiency.

Hydrodynamic chromatography separations in micro‐ and nanopillar arrays produced using deep‐UV lithography

We report on a series of hydrodynamic chromatography separations conducted in micropillar array columns with an interpillar distance spacing of, respectively, 1.00, 0.70, and 0.47 μm. The columns have been produced using state-of-the-art deep-UV lithography and deep reactive ion etching techniques. Despite the fact that the efficiency was smaller than theoretically possible (due to fabrication limitations and significant injection and detection band broadening), it was nevertheless possible to separate mixtures of fluorescein isothiocyanate (used as the t(0) -marker) and 20- and 40-nm polystyrene beads. With the smallest interpillar distance, a resolution of R(s) = 0.5 between the 20- and 40-nm particles could be obtained in 90s over a column length of 4 cm. The selectivity obtained in the pillar array columns was found to be very similar to that observed in packed-bed columns. By detecting the fluorescent signals in a 90-μm-deep detection groove at the end of the column, the signal-to-noise ratio could be enhanced up to 150 times.

Nanowire FET Biosensors on a Bulk Silicon Substrate

A biosensor based on a nanowire field-effect transistor is demonstrated on a bulk silicon wafer for low-cost applications. The silicon nanowire is fabricated using a simple reactive-ion etching technique known as the Bosch process. The sensor operation of the fabricated device is confirmed as a proof of concept by detecting the negatively and positively charged polymers on the nanowire surface in real time. The drain current of the device is clearly modulated by the charge polarity of the polymers. In addition, the specific binding of the antigen and the antibody for avian influenza is also detected by a real-time label-free electrical method for practical applications. Control experiments support that a charged species only on the nanowire surface leads to a significant change in the drain current of the sensor. The proposed approach in bulk nanowire biosensors paves the way for the application of complementary metal–oxide–semiconductor technology for low-cost and miniaturized biosensors without external transducers; this approach is attractive in disposable and portable applications.

Comparison of two experimental methods for the mechanical characterization of thin or thick films from the study of micromachined circular diaphragms

The purpose of this study was to compare two experimental methods and evaluate the effectiveness of a set of analytical models in order to measure the initial stress and the Young's modulus value of thin and thick film materials. Two types of experiments were performed on micromachined circular diaphragms: bulge testing and vibrometry. The range of validity and accuracy of the analytical models with respect to the vibration of the diaphragms was discussed from the finite element simulations. It was shown that the a/t ratio should be considered carefully to determine the value of the Young's modulus by vibrometry with an acceptable error. A relative error of approximately ±10% on E was obtained for a/t ≤ 750. For 750 ≤ a/t ≤ 1000, the value of the dimensionless parameter k must also be considered. It has been shown that the residual stress value can be obtained with an accuracy of 10% or less, given that k > 12. As an illustration, experimental methods and models were applied to the characterization of a thick electroplated gold film and a sputter-deposited Inconel thin film. Circular structures were defined by vertical sidewalls etched on the back of a Si wafer using the deep reactive ion etching technique. In addition to analytical models, parametric finite element simulations and a design optimization technique were used to determine the material's mechanical properties. The static deflections of the diaphragms were measured as a function of the applied pressure. The resonant frequencies and mode shapes of the vibrating structures were observed under vacuum by white-light interferometric microscopy. For gold, it was found that E = (53 ± 20) GPa and σ(0) = (180 ± 10) MPa. For Inconel, it was found that E = (157 ± 14) GPa and σ(0) = (172 ± 5) MPa.

Ge_2Sb_15Bi_05Te_5 thin film as inorganic photoresist

A new phase change material Ge2Sb1.5Bi0.5Te5 (GSBT) with good optothermal effect has been developed as an inorganic photoresist. Masks based on the material can be easily fabricated by home-built laser direct writing (LDW) equipment, and as a result mask patterns have been successfully transferred onto Si substrates by reactive ion etching techniques. Experimental results indicate that maximum etching selectivity of Si to GSBT reaches up to 524:1, which is comparable with the traditional organic photoresists, and the high ratio is also explained theoretically. Because of the merits of the inorganic photoresist, it might prove useful in silicon-based microelectronics

Fabrication and characterization of well-aligned and ultra-sharp silicon nanotip array

Well-defined, uniform, and large-area nanoscaled tips are of great interest for scanning probe microscopy and high-efficiency field emission. An ultra-sharp nanotip causes higher electrical field and, hence, improves the emission current. In this paper, a large-area and well-aligned ultra-sharp nanotip arrays by reactive ion etching and oxidation techniques are fabricated. The apex of nanotips can be further sharpened to reach 3-nm radius by subsequent oxidation and etching process. A schematic model to explain the formation of nanotip array is proposed. When increasing the etching time, the photoresist on top of the nanotip is also consumed, and the exposed silicon substrate is etched away to form the nanotip. At the end, the photoresist is consumed completely and a nanotip with pyramid-like shape is developed. The field emission property was measured, and the turn-on field and work function of the ultra-sharp nanotip was about 5.37 V/μm and 4.59 eV, respectively. A nanotip with an oxide layer capped on the sidewall is also fabricated in this paper. Comparing to the uncapped nanotip, the oxide-capped sample exhibits stable and excellent field emission property against environmental disturbance.

The Sub-Micron Hole Array in Sapphire Produced by Inductively-Coupled Plasma Reactive Ion Etching

The sub-micron hole array in a sapphire substrate was fabricated by using nanosphere lithography (NSL) combined with inductively-coupled-plasma reactive ion etching (ICP-RIE) technique. Polystyrene nanospheres of about 600 nm diameter were self-assembled on c-plane sapphire substrates by the spin-coating method. The diameter of polystyrene nanosphere was modified by using oxygen plasma in ICP-RIE system. The size of nanosphere modified by oxygen plasma was varied from 550 to 450 nm with different etching times from 15 to 35 s. The chromium thin film of 100 nm thick was then deposited on the shrunk nanospheres on the substrate by electron-beam evaporation system. The honeycomb type chromium mask can be obtained on the sapphire substrate after the polystyrene nanospheres were removed. The substrate was further etched in two sets of chlorine/Argon and boron trichloride/Argon mixture gases at constant pressure of 50 mTorr in ICP-RIE processes. The 400 nm hole array in diameter can be successfully produced under suitable boron trichloride/Argon gas flow ratio.

Broadband photonic crystal antireflection

Broadband antireflection layers have been fabricated by two dimensional (2D) photonic crystals (PCs) with tapered pillars on the Si substrate. These PCs have been produced by interference lithography and reactive ion etching (RIE) techniques. The effect of depth and the filling factor (FF) of the PCs on the reflectance magnitude and bandwidth has been investigated. The obtained reflectance was less than 1% in the broad spectral range from 400 to 2100 nm. Our numerical simulation shows the PC pillars slope has an essential effect in the reduction of the reflection. However, our results show that the existence of RIE grasses in the PCs, which are created in the RIE process, does not influence the performance of the antireflection layer. This leads to a simpler fabrication process.

Holographic polymer-dispersed liquid crystal memory for optically reconfigurable gate array using subwavelength grating mask

Holographic polymer-dispersed liquid crystal (HPDLC) memory formed by a subwavelength grating (SWG) mask is presented for new optical information processing. The SWG structure in a photomask is formed on the SiO(2) plate using the anisotropic reactive ion etching technique. The configuration contexts for optically reconfigurable gate arrays (ORGAs) are stored in the HPDLC memory by polarization modulation property based on the form birefringence of the SWG plate. The configuration context pattern in the HPDLC memory is reconstructed to write it for the ORGAs under parallel programmability.

Optical Properties Characterization of InGaN/GaN near UV Photodetector with Surface Nano-Structure Fabricated by Nano-Imprinting

An InGaN/GaN-based photodetector with nano-structure on the surface is present. Surface nano-structure was formed by nanoimprint lithography (NIL) and reactive ion etching (RIE) techniques. The NIL technique and nano-structure etching by employing RIE were demonstrated in details. The nano-pattern was designed as regular triangles consisting of columns, whose diameter and period were around 105 and 210 nm, respectively. The height of nano-columns was around 66 nm. The photo-voltage of this type of photodetector had very good wave characteristics with 60° period, and it presented different waveform at different angles and wavelengths of incident light. The periodic characteristics took not only on minimum voltage but also peak voltage. We demonstrated this characteristic by employing Bragg formulation.

Enhanced efficiency for c-Si solar cell with nanopillar array via quantum dots layers

The enhanced efficiency of the crystalline silicon (c-Si) solar cell with nanopillar arrays (NPAs) was demonstrated by deployment of CdS quantum dots (QDs). The NPAs was fabricated by the colloidal lithography and reactive-ion etching techniques. Under a simulated one-sun condition, the device with CdS QDs shows a 33% improvement of power conversion efficiency, compared with the one without QDs. For further investigation, the excitation spectrum of photoluminescence (PL), absorbance spectrum, current-voltage (I-V) characteristics, reflectance and external quantum efficiency of the device was measured and analyzed. It is noteworthy that the enhancement of efficiency could be attributed to the photon down-conversion, the antireflection, and the improved electrical property.

Comparative study on dry etching of polycrystalline diamond thin films

The reactive ion etching (RIE) technique was used to etch polycrystalline diamond thin films. In this study we investigate the influence of process parameters (total pressure, rf power, gas composition) of standard capacitively coupled plasma RIE system on the etching rate of diamond films. The surface morphology of etched diamond films was characterized by Scanning Electron Microscopy and the chemical composition of the etched film part was investigated by Raman Spectroscopy.We found that the gas composition had a crucial effect on the diamond film morphology. The use of CF4 gas resulted in flatter surfaces and lateral-like etching, while the use of pure O2 gas resulted in needle-like structures. Addition of argon to the reactant precursors increased the ion bombardment, which in turn increased the formation of non-diamond phases. Next, increasing the rf power from 100 to 500 W increased the etching rate from 5.4 to 8.6 μm/h. In contrast to this observation, the rise of process pressure from 80 to 150 mTorr lowered the etching rate from 5.6 down to 3.6 μm/h.

Characterisation of a suspended nanowire channel thin-film transistor with sub-100 nm air gap

A novel suspended nanowire (NW) channel thin-film transistor (TFT) with sub-100 nm air gap has been fabricated and characterised. With a simple and low-cost over-etching-time-controlled reactive ion etching technique and a buffered-oxide etch wet-etching process, a suspended NW of 27 nm and an air gap of 10 nm were achieved. The resultant suspended-NW-channel TFTs showed an ultra-low subthreshold swing (52 mV/dec) and considerable hysteresis window (3.7 V). Finally, the impacts of device dimensions on the characteristics of suspended NW TFTs were also investigated.