Inductively Coupled Plasma Etching Research Articles

Fabrication of the hexagonal Si nanorod arrays using the template of polystyrene nanospheres in monolayer dispersion

Silicon etching is an essential fabrication step in micro-/nanoelectromechanical systems. In this article, the inductive coupled plasma etching technology using monolayer polystyrene nanospheres as the template provides a feasible top-down dry etching method in silicon substrates. The size of the polystyrene nanosphere templates coated on the silicon substrate was adjusted using O2 plasma etching, and the subsequent inductive coupled plasma etching process was applied to produce the silicon nanorods by alternatively employing etching gas SF6 and protective gas C4F8. The O2 plasma etching time on the template and the SF6/C4F8 flow rate for etching Si substrate were optimized in order to obtain the silicon nanorod structures in the hexagonal morphologies with good verticality, uniformity, and periodicity.

Effect of Inductively Coupled Plasma Etching in p-Type GaN Schottky Contacts

The effects of inductively coupled plasma (ICP) etching damage on the electrical characteristics of low-Mg-doped p-GaN Schottky contacts were evaluated. The ICP etching greatly reduced the memory effect in the current–voltage characteristics and the difference between the depletion layer capacitances before and after forward current injection. These reductions indicate that acceptor-type interfacial defects were passivated by H atoms during ICP etching. Additionally, photoresponse (PR) measurements revealed that Schottky barrier height was increased from 2.08 to 2.63 eV by the etching. Because of the surface state change, the Fermi level position would be moved toward the conduction band edge slightly by the etching. After annealing, the memory effect and the capacitance change were partially restored, and the PR spectra showed less variation. Absorbed H atoms on the p-GaN surface might be released by annealing.

Geometry of nanopore devices fabricated by electron beam lithography: Simulations and experimental comparisons

Fabrication of solid-state nanopore sensors for individual biomolecule analysis is a growing topic of interest. A number of recent studies demonstrate that engineered nanopore devices (ENDs) can be fabricated by electron beam lithography (EBL) with high density (on the order of 10 devices per cm2). The internal pore geometry of ENDs is a critical characteristic of the devices, and often obtained by some combination of SEM, TEM, AFM, and conductance measurements. However, experimental data alone is not sufficient to understand the nanopore geometry under a broad set of fabrication conditions. It is necessary to also examine the physical basis underlying the EBL-based fabrication of ENDs. In this work, the internal pore geometry of ENDs is calculated from electron energy distributions in EBL while investigating the effects of dose, operating blur, substrate, and dosing pattern. The photoresist is ZEP-520 on silicon or silicon nitride substrates. It is found that higher beam blur and lower dose cause a greater degree of pore tapering, with the most prominent tapering observed in sub-10nm pores. Nanopores in silicon nitride tapered more than those in silicon. The results also demonstrate that a combination of blur and dose can be chosen to achieve a target tapering angle and pore size at a given depth in the substrate. Because the pore tapering angle is non-uniform, the ICP (inductively coupled plasma) etch depth may also be used to tune pore size and geometry following EBL. The resist sensitivity is shown to increase with beam blur for pore sizes larger than 10nm. By comparing to our experimental data, it is found that beam intensity measured by the EBL instrument may not translate to the operating blur, as is often assumed in EBL simulations. Secondary electrons were found to be responsible for pore tapering and beam broadening in the resist.

ICP Etching of 4H-SiC Substrates

Due to its inert chemical nature, plasma etching is the most effective technique to pattern SiC. In this paper, dry etching of 4H-SiC substrate in Inductively Coupled Plasma (ICP) has been studied in order to evaluate the impact of process parameters on the characteristics of etching such as etch rate and trenching effect. Key process parameters such as platen power and ICP coil power prove to be essential to control the SiC etch rate. On the other hand, the ICP coil power and the working pressure mainly master the trenching effect. Our results enlighten that high etch rate with minimal trenching effect can be obtained using high ICP coil power and low working pressure.

Fabrication of silicon nanopore arrays using a combination of dry and wet etching

This paper presents a novel method for the fabrication of silicon nanopore arrays. The proposed method is based on inductive coupled plasma (ICP) etching and a two-step anisotropic wet etching, and can be used to fabricate individual nanopores, and massive nanopore arrays, with lower cost and less time compared with conventional fabrication processes. To optimize this nanopore fabrication process, the size of the ICP etch window was determined in a series of ICP experiments, and a theoretical analysis of the two-step wet etching was conducted. A nanopore array with an average feature size of 130 nm and a rectangular nanopore with a feature size of 38 nm were successfully obtained using this method. These results indicate the potential of this method for the large-scale production arrays of nanopores with desired sizes and shapes.

Electroluminescence from InGaN/GaN multi-quantum-wells nanorods light-emitting diodes positioned by non-uniform electric fields

We report that the nanorod light-emitting diodes (LEDs) with InGaN/GaN multi-quantum-wells (MQWs) emitted bright electroluminescence (EL) after they were positioned and aligned by non-uniform electric fields. Firstly, thin film LED structures with MQWs on sapphire substrate were coated with SiO(2) nanospheres, followed by inductively-coupled plasma etch to create nanorod-shapes with MQWs, which were transferred to the pre-patterned SiO(2)/Si wafer. This method allowed us to obtain nanorod LEDs with uniform length, diameter and qualities. Dielectrophoretic force created by non-uniform electric field was very effective at positioning the processed nanorods on the pre-patterned contacts. After aligned by non-uniform electric field, we observed bright EL from many nanorods, which had both cases (p-GaN/MQWs/n-GaN or n-GaN/MQWs/p-GaN). Therefore, bright ELs at different locations were observed under the various bias conditions.

Antireflective disordered subwavelength structure on GaAs using spin-coated Ag ink mask

We present a simple, cost-effective, large scale fabrication technique for antireflective disordered subwavelength structures (d-SWSs) on GaAs substrate by Ag etch masks formed using spin-coated Ag ink and subsequent inductively coupled plasma (ICP) etching process. The antireflection characteristics of GaAs d-SWSs rely on their geometric profiles, which were controlled by adjusting the distribution of Ag etch masks via changing the concentration of Ag atoms and the sintering temperature of Ag ink as well as the ICP etching conditions. The fabricated GaAs d-SWSs drastically reduced the reflection loss compared to that of bulk GaAs (>30%) in the wavelength range of 300-870 nm. The most desirable GaAs d-SWSs for practical solar cell applications exhibited a solar-weighted reflectance (SWR) of 2.12%, which is much lower than that of bulk GaAs (38.6%), and its incident angle-dependent SWR was also investigated.

Efficient and reliable green organic light-emitting diodes with Cl2 plasma-etched indium tin oxide anode

The effects of brief etching with Cl2-based inductively coupled plasma (ICP) on the surface chemistry and properties of indium-tin-oxide (ITO) were investigated. Due to the low volatility of InClx, Cl2, and Cl2/BCl3 ICP etching created stable In-Cl polar bonds at the ITO surfaces, raising its work function by up to 1.0 eV. Green phosphorescent organic light-emitting diodes (OLEDs) built on ICP-etched ITO/glass substrates exhibited a brightness of 1.4 × 104 cd/m2 and a current efficiency of 70 cd/A at 20 mA/cm2, which were 40% higher than those of similar OLEDs with an O2 plasma-treated ITO anode. The OLEDs with plasma chlorinated ITO also showed better stability and reliability. These results suggest that brief chlorine plasma etching can result in stable chlorinated ITO surfaces with a high work function, leading to more balanced charge injection and performance enhancement of OLEDs.

Fabrication and reflection properties of silicon nanopillars by cesium chloride self-assembly and dry etching

Cesium chloride (CsCl) self-assembly has been successfully used to fabricate different average diameter CsCl nanoislands ranging from 50nm to 1μm through controlling CsCl film thickness, relative humidity and developing time. By process control of inductively coupled plasma (ICP) etching, the silicon nanopillars with different high aspect ratio (2–6), morphologies from column to cone, and diameters from 150 to 800nm have been made by dry etching with the structure mask of CsCl nano hemispheres. The reflectivity of the silicon nanopillars has also been measured for wavelength from 400 to 1000nm and shows the best antireflection under 5% by native silicon nanopillars with 200nm average diameter after 40min ICP etching. With a layer of SiO2 on silicon nanopillars by thermal oxidation process, the reflectivity reaches to below 2.5% at a large range of wavelength from 400 to 1000nm.

Interface Properties of Al2O3/n-GaN Structures with Inductively Coupled Plasma Etching of GaN Surfaces

The effects of the Cl2-based inductively coupled plasma (ICP) etching of GaN on the interface properties of Al2O3/GaN structures prepared by atomic layer deposition (ALD) were investigated. We used n-GaN layers grown on freestanding n+-GaN substrates with low dislocation density. The ICP etching caused slight disorder of the chemical bonds at the GaN surface and monolayer-level interface roughness at the Al2O3/GaN interface, resulting in poor capacitance–voltage (C–V) characteristics due to high-density interface states including nitrogen-vacancy (VN) related levels. The postannealing process in N2 at 400 °C drastically improved the C–V characteristics, probably owing to the partial recovery of the VN-related defects and the increased ordering of chemical bonds in the GaN surface region.

Global Model of <formula formulatype="inline"><tex Notation="TeX">$\hbox{Cl}_{2}\hbox{/Ar}$</tex> </formula> High-Density Plasma Discharge and 2-D Monte-Carlo Etching Model of InP

A multiscale approach has been developed in order to simulate the etch process of InP in an inductive coupled plasma (ICP) Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar plasma discharge. The model consists of three modules: a global kinetic model of the Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar plasma discharge, a sheath model, and a 2-D Monte-Carlo etching model. The densities and the fluxes of all neutral and charged species considered in the reaction scheme as well as the electron temperature are calculated from the global model. The angular and energy distribution functions of ions are computed from the sheath model. The output parameters of both the global kinetic model and the sheath model in terms of particle fluxes, ion angular distribution function and ion energy distribution function are used as input parameters in the 2-D etching model. The latter allows tracking in time the evolution of the etched surface. The ultimate goal of the multiscale approach is to predict the etch rate, the etched surface chemical composition, and the etch profile as a function of the operating conditions (power, pressure, gas flow rates, etc). In this paper, the results from the global model are first compared to the measurements carried out in the ICP etching tool, showing a satisfactory agreement. The etching model is then used to simulate the etching of narrow trench and small-diameter hole in InP. The mechanisms involved in the development of undercut below the mask and in the bowing effect are analyzed. The comparison between simulated and experimental etch profiles evidences the important role of Cl adsorption probability on the development of the undercut, and the significant impact of the redeposition of the etched species on the etch rate variation and on the narrowing in the bottom of the etched hole/trench.

Effect of Cl2- and HBr-based inductively coupled plasma etching on InP surface composition analyzed using in situ x-ray photoelectron spectroscopy

A Cl2-HBr-O2/Ar inductively coupled plasma (ICP) etching process has been adapted for the processing of InP-based heterostructures in a 300-mm diameter CMOS etching tool. Smooth and anisotropic InP etching is obtained at moderate etch rate (∼600 nm/min). Ex situ x-ray energy dispersive analysis of the etched sidewalls shows that the etching anisotropy is obtained through a SiOx passivation mechanism. The stoichiometry of the etched surface is analyzed in situ using angle-resolved x-ray photoelectron spectroscopy. It is observed that Cl2-based ICP etching results in a significantly P-rich surface. The phosphorous layer identified on the top surface is estimated to be ∼1–1.3-nm thick. On the other hand InP etching in HBr/Ar plasma results in a more stoichiometric surface. In contrast to the etched sidewalls, the etched surface is free from oxides with negligible traces of silicon. Exposure to ambient air of the samples submitted to Cl2-based chemistry results in the complete oxidation of the P-rich top layer. It is concluded that a post-etch treatment or a pure HBr plasma step may be necessary after Cl2-based ICP etching for the recovery of the InP material.

A Novel Coplanar-Waveguide Band-Pass Filter Utilizing the Inductor–Capacitor Structure in 0.18 µm Complementary Metal–Oxide–Semiconductor Technology for Millimeter-Wave Applications

A low-insertion-loss V-band complementary metal–oxide–semiconductor (CMOS) band-pass filter is demonstrated. The proposed filter architecture has the following features: the low-frequency transmission-zero (ωz1) and the high-frequency transmission-zero (ωz2) can be tuned individually by adjusting the value of the series capacitor (Cs) and the size of the built-in inductor–capacitor (LC) resonator, respectively. The folded short-stub technique is used to reduce the chip size of the filter. To reduce the silicon substrate loss, the CMOS-process-compatible backside inductively-coupled-plasma (ICP) deep trench technology is used to selectively remove the silicon underneath the filter. After the ICP etching, the filter achieves insertion-loss (1/S21) lower than 3 dB over the frequency range of 46.5–85.5 GHz. The minimum insertion-loss is -1.8 dB at 60 GHz.

Towards High-Resolution X-Ray Imaging Using a Structured Scintillator

Structured scintillators, by light-guiding secondary emitted visible photons to a pixel in a CCD or CMOS image sensor, improve the lateral resolution of X-ray imaging detectors. In this work we have fabricated pore arrays in a silicon wafer and subsequently filled them with CsI(Tl) by a melting process. The goal was to down-scale the pore geometry for increased resolution. The results show that although pore depth must be reduced to comply with achievable aspect ratio of the Inductively Coupled Plasma (ICP) etching, melting into the pores is possible. The time and temperature has, however, to be optimized to prevent thallium loss during the melting. By correlating light yield measurements with the X-ray absorption in samples of various geometries, we find that the efficiency is slightly reduced for pore diameters approaching one micron. Nevertheless, the increased absorption in deep pores will lead to a significantly improved quantum efficiency compared to thin films currently used to achieve the same lateral resolution.

Deep anisotropic LiNbO3 etching with SF6/Ar inductively coupled plasmas

A SF6/Ar inductively coupled plasma (ICP) technique was investigated to improve etching of proton exchanged LiNbO3. The influences of He backside cooling, power, and gas flows on characteristics such as etching rate, sidewall slope angle, and surface roughness were investigated. Total gas flow is a key parameter that affects etching results, and an optimized gas flow (50 sccm) was used for lengthy etching processes (30 min). Deep (&amp;gt;3 μm) and highly anisotropic etching, as well as ultra smooth LiNbO3 surfaces were achieved in a single-step run. The authors’ proposed method has achieved the deepest, most vertical, minimal residue structure yet reported for single-step ICP etching.

Characteristics of GaN thin films by inductively coupled plasma etching with Cl2/BCl3 and Cl2/Ar

GaN thin films were etched by inductively coupled plasma (ICP). The effects of BCl3 and Ar with different Cl2 fraction are studied and compared. The ICP power and RF power are also altered to investigate the different effects by using Cl2/BCl3 or Cl2/Ar as etching gases. The etch rate and surface morphology of the etched surface are characterized by using surface profiler, scanning electron microscopy and atomic force microscopy. The root-mean-square roughness values are systematically compared. It is found that the etch rates of Cl2/Ar are higher than that of the Cl2/BCl3 in the Cl2 fraction ranging from 10 to 90%. When the ICP power is increased, the RMS roughness of GaN surface after ICP etching shows reverse trend between Cl2/BCl3 and Cl2/Ar gas mixture. The results indicate quite different features using Cl2/BCl3 and Cl2/Ar for GaN ICP etcing under the same conditions.

Antireflective Hydrophobic Si Subwavelength Structures Using Thermally Dewetted Ni/SiO2 Nanomask Patterns

We report the disordered silicon (Si) subwavelength structures (SWSs), which are fabricated with the use of inductively coupled plasma (ICP) etching in SiCl4 gas using nickel/silicon dioxide (Ni/SiO2) nanopattens as the etch mask, on Si substrates by varying the etching parameters for broadband antireflective and self-cleaning surfaces. For the fabricated Si SWSs, the antireflection characteristics are experimentally investigated and a theoretical analysis is made based on the rigorous coupled-wave analysis method. The desirable dot-like Ni nanoparticles on SiO2/Si substrates are formed by the thermal dewetting process of Ni films at 900 degrees C. The truncated cone shaped Si SWS with a high average height of 790 +/- 23 nm, which is fabricated by ICP etching with 5 sccm SiCl4 at 50 W RF power with additional 200 W ICP power under 10 mTorr process pressure, exhibits a low average reflectance of approximately 5% over a wide wavelength range of 450-1050 nm. The water contact angle of 110 degrees is obtained, indicating a hydrophobic surface. The calculated reflectance results are also reasonably consistent with the experimental data.

Optimization of Fabrication Process for MEMS Based Microneedles Using ICP Etching Technology

In this paper, optimization of fabrication process for microneedles has been presented. Using inductively coupled plasma (ICP) etching technology, fabrication of out-of-plane hollow silicon microneedles for blood extraction has been carried out. Sharp tip microneedles with length 1100 µm were designed for fabrication. The fabrication of microneedles was not successful because the lumen section was fabricated first and then hole was created for fluid flow. Previously, using same fabrication method successful fabrication of microneedles was done for drug delivery with length 200 µm. This fabrication method is not suitable for long structure. Thus, the alternative microneedle fabrication steps using ICP etching have been developed and presented in this paper. These steps can be more optimized and suitable for sharp tip, long and hollow structure.

Enhanced photo-sensitivity through an increased light-trapping on Si by surface nano-structuring using MWCNT etch mask

We demonstrate an enhanced photo-sensitivity (PS) through an increased light-trapping using surface nano-structuring technique by inductively coupled plasma (ICP) etching on multi-walled carbon nanotube (MWCNT) etch masked Si with hexamethyl-disilazane (HMDS) dispersion. In order for a systematic comparison, four samples are prepared, respectively, by conventional photolithography and ICP etching using MWCNT as a etch mask. MWCNT-etched Si with HMDS dispersion shows the highest RMS roughness and the lowest reflectance of the four. Two test device structures are fabricated with active regions of bare-Si as a reference and MWCNT etch masked Si with HMDS dispersion. The increased light-trapping was most significant at mid-UV, somewhat less at visible and less noticeable at infrared. With an ICP-etched Si using CNT HMDS dispersion, PS is very sharply increased. This result can lead to applications in optoelectronics where the enhancement in light-trapping is important.

Inductively coupled plasma etching of graded-refractive-index layers of TiO2 and SiO2 using an ITO hard mask

Transparent dielectric layers with varying compositions of TiO2 and SiO2, and ITO are deposited on sapphire and Si substrates by using an RF sputter system. Inductively coupled plasma (ICP) reactive ion etching (RIE) of the ITO hard mask is examined under H2, CH4, and Cl2 chemical environments. The slope of the sidewall and the etch residue on the sidewall of the ITO hard mask are controlled by the flow rates of H2, CH4, and Cl2. ICP-RIE dry etch of TiO2 and SiO2 is investigated under fluorinated environments. Comparable etch rates of TiO2 and SiO2 (ratio ≈ 2:1) and high selectivity ≫ 1 over ITO are found. Graded-refractive-index (GRIN) layers, made up of multiple dielectric layers of TiO2 and SiO2, are patterned to form cylindrical pillars by ICP etching using the ITO hard mask. Fluorine containing residues are identified on the TiO2 and SiO2 surfaces. Various etch chemistries are investigated to obtain smooth, vertical, and residue-free sidewalls of the GRIN pillars.