ICP Power Research Articles

Morphology of films deposited on the sidewall during the Bosch process using C4F8 plasmas

In the Bosch process, C4F8 plasmas are used to deposit passivation films. In this study, the passivation films were deposited in micro-scale trenches by changing the C4F8 flow rate, ICP power, and pressure, and their cross sections were observed by scanning electron microscopy. The results showed that the morphology of the passivation film and its relative deposition rate at each depth varied depending on the plasma discharge conditions. There is a correlation between the C–CF x bond content and the morphology of passivation films, with high C–CF x bond content resulting in smooth morphology and low C–CF x bond content resulting in a rough morphology. Furthermore, it was found that ion bombardment reduced the roughness of the passivation film. Through these experiments, we also found the possibility of controlling the deposition rate of the passivation film at each trench depth by adjusting the plasma discharge conditions.

Wet and dry etching of ultrawide bandgap LiGa5O8 and LiGaO2

Crystalline thin films of LiGa5O8 have recently been realized through epitaxial growth via mist-chemical vapor deposition. The single crystal, spinel cubic LiGa5O8 films show promising fundamental material properties and, therefore, make LiGa5O8 a potential enabling material for power electronics. In this work, chemical resistance and etch susceptibility were investigated for the first time on crystalline LiGa5O8 thin films with various wet chemistries. It was found that LiGa5O8 is very chemically resistive to acid solutions, with no apparent etching effects observed when placed in concentrated acid solutions of HCl, H2SO4, HF, or H3PO4 at room temperature. In contrast, orthorhombic (010) LiGaO2 shows effective etching in HCl solutions at varying dilution concentrations, with etch rates measured between 8.6 [1000:1 (DI water: HCl concentration)] and 6092 nm/min (37 wt. % HCl). The inductively coupled plasma reactive ion etching (ICP-RIE) of LiGa5O8 using BCl3/Ar and CF4/Ar/O2 gas chemistries was investigated. The etching rate and surface morphology of etched surfaces were examined as a function of RIE and ICP power. Using a CF4/Ar/O2 gas chemistry with an RIE power of 75 W and an ICP power of 300 W resulted in smooth etched planar surfaces while maintaining an etch rate of ∼24.6 nm/min. Similar dry etching studies were performed for LiGaO2. It was found that the BCl3/Ar gas chemistry was better suited for LiGaO2 etching, with similar surface morphology quality being obtained after etching as prior etching when a RIE power of 15 W and an ICP power of 400 W is utilized.

Boosting the Performance of on-Chip Vertically-Aligned Carbon Nanotube Supercapacitors Via Solvent-Free Radiofrequency Nitrogen Plasma Treatment

Supercapacitors are essential components for energy storage devices in many fields, including renewable energy systems, electric vehicles, and portable electronics [1]. Carbon nanotube arrays have shown great promise for use in supercapacitors due to their high surface area and excellent electrical conductivity. However, the specific capacitance of these arrays needs to be increased to improve the overall energy storage capacitance of the supercapacitor.This study presents an innovative approach to enhance the specific capacitance of on-chip vertically-aligned carbon nanotube (VACNT) structures for the development of high-performance supercapacitors. The proposed technique involves employing a solvent-free radiofrequency (RF) nitrogen plasma treatment to dope nitrogen onto VACNT surfaces. The plasma doping process utilizes reactive ion etching-induced coupled plasma (RIE-ICP) to optimize the parameters for nitrogen incorporation [2]. The nitrogen plasma treatment introduces nitrogen-containing functional groups, thereby improving their specific capacitance. The dry process is compatible with semiconductor fabrication and can be integrated into existing manufacturing techniques [1]. This study provides a promising avenue for tailoring the nitrogen doping process to achieve desired performance enhancements for on-chip VACNT supercapacitors.The plasma doping process involves the generation of reactive nitrogen species in the plasma, which subsequently interact with the VACNT surfaces. Under the influence of the RF electric field, nitrogen gas molecules are ionized and can react with the carbon atoms of the VACNTs, resulting in the formation of nitrogen-containing functional groups and the substitution of carbon atoms with nitrogen atoms within the carbon lattice [3].The improved capacitance can be attributed to the incorporation of nitrogen functional groups and to the modification of the electronic properties of the carbon nanotubes, including additional charge carriers, leading to an increase in electrical conductivity [4] and introduction of the pseudocapacitance effect [5]. There are various types of nitrogen species in the carbon lattice, such as pyridinic, pyrrolic, and graphitic nitrogen. Among these, pyridinic and pyrrolic nitrogen are known to be more electrochemically active [5], contributing to the enhanced specific capacitance. The increased electrical conductivity stems from the introduction of nitrogen dopants, which alter the electronic structure of the VACNTs, creating localized states near the Fermi level and thus facilitating charge transport [4].The level of nitrogen doping depends on several process factors, including the plasma power, gas pressure, and treatment duration. Higher plasma power generates a larger number of reactive nitrogen, while lower gas pressure results in a higher ionization efficiency. Furthermore, a longer treatment duration increases the chance of nitrogen incorporation into the VACNT structures [3]. By carefully controlling these parameters during the nitrogen plasma treatment, it is possible to tailor the nitrogen doping process to achieve the desired performance enhancement for on-chip VACNT supercapacitors.The treatment is performed in a chamber with a pressure of 10 Pa, a nitrogen gas flow rate of 10 sccm, an ICP power of 200W, and a bias voltage of -120 V. We report a specific capacitance of modified VACNTs of 18 mF/cm2(Figure 1), nearly twice that of pristine samples (Figure1(B)), for dense arrays of 1012 CNTs/ cm2. XPS result confirms 11.76% nitrogen content and 13% oxygen content in treated samples (N-VACNTs), aligning with previous studies on wet process nitrogen-doped carbon nanotubes [5]. Oxygen content also plays a crucial role in VACNT-based supercapacitor performance, improving surface wettability which will reduce the resistance between electrode and electrolyte [6, 7]. However, excessive oxygen content can negatively affect VACNT supercapacitor lifetime. By finding the trade-off between nitrogen and oxygen content, we optimized the doping process, enhancing specific capacitance, stability (Figure 2), and lifetime for on-chip VACNT structures.In conclusion, our study demonstrates that the solvent-free RF nitrogen plasma treatment can effectively enhance the specific capacitance of on-chip VACNT structures by up to 100%, making them suitable for integration into high-performance on-chip supercapacitor.

Analysis of cerium-substituted yttrium iron garnets by inductively coupled plasma atomic emission spectrometry with preliminary microwave decomposition

An analytical procedure for inductively coupled plasma atomic emission (ICP-AES) analysis of iron garnets of the composition Y3 – xCexFe5 – yGayO12, where x = 0.4 – 0.5 and y = 2.4 – 2.6 with preliminary microwave decomposition of the sample is described. The compositions of acid mixtures (HCl/HNO3), as well as modes of microwave heating (holding time and temperature), providing complete dissolution of the samples are proposed. In addition to optimized sample preparation, conditions for ICP-AES analysis of cerium-doped yttrium iron garnets were studied. The effect of matrix components (Y, Ce, Fe, Ga) on the determination of doping elements was revealed and studied. The operating parameters of the spectrometer (ICP power and nebulizer flow rate) have been substantiated, which make it possible to reduce the matrix effect of Fe, Ga, Y, Ce on the elements Na, Mg, Al, Si, P, K, Ca, Sc, Cr, Mn, Co, Ni, Cu, Zn, Se, Cd, Sn, Te, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb in iron yttrium garnets by the ICP-AES. ICP-AES measurements were performed in the axial and radial mode for trace elements and in the radial mode for matrix elements. The limits of quantification (LOQs) of most elements ranged within n × 10–5 – n × 10–4 wt.%. The accuracy is confirmed by the spike recovery test. The relative standard deviation is in the range of 1 – 5% depending on the selected plasma view mode and the analyzed analytes. The developed method makes it possible to determine macro- and microcomponents in yttrium iron garnets in a wide range of concentrations with a high accuracy.

Inductively coupled plasma etching of LiTaO3 in CHF3/Ar plasmas

CHF3/Ar plasma was used to etch LiTaO3 crystal by inductively coupled plasma technology. The etched crystals under different process parameters were analyzed by surface profilometer and characterized by atomic force microscopy and scanning electron microscope. It was shown that ICP power, RIE power, and total gas flow rate had similar effects on etching rate and selectivity, while Ar/(Ar + CHF3) gas ratio had opposite effects on etching rate and selectivity, with better etching rate and selectivity at the ratio of 0.2. Our work gives a fundamental instruction for the fabrication of LiTaO3 based devices.

Low-Temperature Deposition of High-Quality SiO2 Films with a Sloped Sidewall Profile for Vertical Step Coverage

SiO2 is one of the most widely used dielectric materials in optical and electronic devices. The Josephson voltage standard (JVS) chip fabrication process has rigorous requirements for the deposition temperature and step-coverage profiles of the SiO2 insulation layer. In this study, we deposited high-quality SiO2 insulation films at 60 °C using inductively coupled plasma-chemical vapor deposition (ICP-CVD) to fulfill these requirements and fabricate JVS chips simultaneously. SiO2 films have a high density, low compressive stress, and a sloped sidewall profile over the vertical junction steps. The sidewall profiles over the vertical junction steps can be adjusted by changing the radio frequency (RF) power, ICP power, and chamber pressure. The effects of sputtering etch and sloped step coverage were enhanced when the RF power was increased. The anisotropy ratio of the deposition rate between the sidewall and the bottom of the film was lower, and the sloped step coverage effect was enhanced when the ICP power was increased, or the deposition pressure was decreased. The effects of the RF power on the stress, density, roughness, and breakdown voltage of the SiO2 films were also investigated. Despite increased compressive stress with increasing RF power, the film stress was still low and within acceptable limits in the device. The films deposited under optimized conditions exhibited improved densities in the Fourier transform infrared spectra, buffered oxide etch rate, and breakdown voltage measurements compared with the films deposited without RF power. The roughness of the film also decreased. The step-coverage profile of the insulation layer prepared under optimized conditions was enhanced in the junction and bottom electrode regions; additionally, the performance of the device was optimized. This study holds immense significance for increasing the number of junctions in future devices.

ICP etching of GaN microstructures in a Cl2–Ar plasma with subnanometer-scale sidewall surface roughness

Substrate temperature, RF power, and ICP power were investigated for their effects on GaN micropillar sidewall roughness and etch characteristics. Elevated substrate temperature was shown to improve the sidewall etch morphology at low RF powers (reduced physical bombardment) and low ICP powers (lower plasma densities). Increased lateral etching is observed with both increased ICP power and substrate temperature, which both act to increase the chemical component of the etch. Etch conditions with a high chemical driving force resulted in faceting along the a-plane on the sidewalls. This faceting produced extremely smooth surfaces with root-mean-square roughness (Rq) as low as 0.20 nm which is comparable to typical epitaxy-ready surfaces and smaller than the a-plane lattice spacing of 0.3186 nm. The smooth surfaces produced in this study enable possibilities for laser facets or for new device structures that require high quality surfaces for GaN regrowth.

Direct inductively coupled plasma optical emission spectrometry for analysis of waste samarium-cobalt magnets

An analytical procedure for direct determination of Al, Mg, Ti, Cr, Mn, Nb, La, Nd, Eu, Gd, Tb, Dy, Tm, Yb, Lu, Hf, Ni, Cu, Fe, Zr Sm and Co by ICP-OES in waste samarium-cobalt magnets has been developed. The significant influence of the matrix on all determinable components has been shown. The influence of operation parameters (ICP power and nebuliser flow rate) on the matrix effect has been studied using two plasma observation modes (axial and radial). For the first time, the optimal conditions for ICP-OES analysis of waste samarium-cobalt magnets has been substantiated (ICP power 1400 W, nebuliser flow rate 0.5–0.6 L/min). The analytical capabilities of the method have been evaluated using spike recovery test, certified reference materials and comparison with ICP-MS. ICP-OES measurements were performed in the axial mode for trace elements (with concentrations of n·10−4-n·10−2 % wt.) and in the radial mode for matrix elements and analytes (with concentrations higher than n·10−2 % wt.). The limits of quantification (LOQs) were in the range of n·10−5 wt% for Mn, Zr and Yb and n·10−4 wt% for Al, Mg, Ti, Cr, Hf, La, Ni, Cu, Tb, Lu, Nb, Fe, Nd, Eu, Gd, Dy and Tm. RSD ranged from 0.2 to 10.6%.

Transparent SiOxCyHz Barrier Film Prepared by Roll to Roll PECVD

This paper uses plasma-enhanced chemical vapor deposition (PECVD) to successfully fabricate silicon oxide films on silicon dioxide substrates for supporting layers of uncooled infrared focal plane array microbridge structures. In this paper, the thickness, refractive index, growth rate, and other parameters of the films were measured using the XP-2 step meter and ellipsometer. At the same time, atomic force microscopy (AFM) was used to study the surface morphology of the films. The experimental results show that deposition temperature and ICP power are the main factors affecting the growth rate of thin films. Deposition temperature is a crucial factor affecting the surface morphology of thin films.

A Review: Inductively Coupled Plasma Reactive Ion Etching of Silicon Carbide

The inductively coupled plasma reactive ion etching (ICP-RIE) is a selective dry etching method used in fabrication technology of various semiconductor devices. The etching is used to form non-planar microstructures—trenches or mesa structures, and tilted sidewalls with a controlled angle. The ICP-RIE method combining a high finishing accuracy and reproducibility is excellent for etching hard materials, such as SiC, GaN or diamond. The paper presents a review of silicon carbide etching—principles of the ICP-RIE method, the results of SiC etching and undesired phenomena of the ICP-RIE process are presented. The article includes SEM photos and experimental results obtained from different ICP-RIE processes. The influence of O2 addition to the SF6 plasma as well as the change of both RIE and ICP power on the etching rate of the Cr mask used in processes and on the selectivity of SiC/Cr etching are reported for the first time. SiC is an attractive semiconductor with many excellent properties, that can bring huge potential benefits thorough advances in submicron semiconductor processing technology. Recently, there has been an interest in SiC due to its potential wide application in power electronics, in particular in automotive, renewable energy and rail transport.

Changes of Crystal Structure and Microstructure of MoN Coatings in Accordance with Inductively Coupled Plasma Power

Nano-crystalline MoN coatings were prepared by inductively coupled plasma magnetron sputtering (ICPMS) according to changing the plasma power from 0 to 200 W. The properties of the coatings were analyzed by X-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, a nano-indentation tester, and a semiconductor characterization system. As the ICP power increased, the crystal structure of the MoN coatings was changed from a mixed phase of γ-Mo2N and α-Mo to a single phase of γ-Mo2N. The residual stress of the MoN coatings was also converted from tensile stress to compressive stress according to the increasing ICP power. As a result, the coatings deposited by the ICPMS have a very compact microstructure with high hardness: the nano-indentation hardness reached up to 27.1 GPa. The electrical resistivity of the coatings was decreased from 691.6 to 325.9 μΩ·cm as the ICP power increased as well.

Low Resistivity Hafnium Nitride Thin Films Deposited by Inductively Coupled Plasma Assisted Magnetron Sputtering in Microelectronics.

Hafnium nitride (HfN) thin films with low electrical resistivity were obtained by inductively coupled plasma assisted magnetron sputtering as a function of ICP power. Microstructural, crystallographic and sheet resistance characterizations of HfN films were performed by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and 4 point probe method. The results show that ICP has significant effects on coating's microstructure, structural and electrical properties of HfN films. With an increase in ICP power, thin film microstructure evolved from a porous columnar structure to a highly dense one. HfN thin films with different crystal structure and phases were obtained as a function of ICP power. The minimum resistivity of 125 µΩ-cm, the smoothest surface morphology with Ra roughness of 5.9 nm were obtained for the HfN films deposited at ICP power of 200 W.

High-Quality Etching of GaN Materials with Extremely Slow Rate and Low Damage

High-quality gallium nitride etching is highly desirable in electronic device fabrications. For the GaN base devices, the electronic properties largely depended on the etching induced surface damages. To overcome this, a controllable GaN etching method was developed using inductively coupled plasma reactive ion etching (ICP-RIE) by controlling radio frequency (RF) power, and DC bias. The etching rate, DC bias, and root-mean-square surface roughness were measured as a function of bias power under different RF, 40 and 13.56 MHz. The effects of ICP power and chlorine to argon percentage were systematically studied. An extremely slow etching rate and low-damage surface were achieved by reducing DC bias power to 25 W under RF 40 MHz. Ni|Au Schottky diodes were fabricated and characterized. The diode fabricated on the 40-MHz RF etching GaN surface has a much lower ideality factor and higher barrier height than non-etched GaN and RF 13.56 MHz etching GaN.

Investigating the optimum parameters of a negative photoresist to prepare a V-grooved diffraction grating on Si using photolithography and reactive ion etching techniques

In this study, the deposition parameters of the SU8 2000.5 negative photoresists have been investigated and optimized for the photolithographic technique. Then, applied the inductive coupled plasma reactive ion etching (ICP RIE) to produce V-shaped groove diffraction grating on a silicon substrate. Spin coater (speed: 1000 rpm) was used to coat the photoresist over the Si substrate. The observed photoresist film thickness was measured by ellipsometry and found to be 800 nm. Interestingly, the film exhibited some stability with increasing the spin speed. The thermogravimetric analysis was used to optimize the baking temperature which was found to be ~105 °C. Contrast curves were obtained experimentally and used to optimize the exposure energy along with the images obtained from the field emission scanning electron microscopy (FESEM). The optimized energy fluence was found to be 17 mJ/cm2. It was interesting to observe that the thickness of the photoresists film was increasing with the elevation of the exposure energy fluence. The FESEM images were used to optimize the ICP RIE etching process and the best etching conditions for the Si substrate were ICP power: 150 W, bias power: 100 W, and SF6 gas flow rate: 32 SCCM (standard cubic centimeters per minute), O2 gas flow: 8 SCCM, and Ar gas flow of 8 SCCM. It is worth to mention that well-defined V-shaped grooves were observed with a depth of 2 μm under the same experimental conditions.

Formation of SiO2 hard mask using dry etching and nanosphere lithography

The features of the formation of a SiO2 hard mask using dry etching and nanosphere lithography are considered in the paper. A series of experiments was carried out using a variation of plasma etching parameters such as ICP and RF power, pressure as well as a substrate temperature. As a result, optimal parameters were found to obtain both good selectivity and high etching rate.

Selective etching of p-GaN over Al0.25Ga0.75N in Cl2/Ar/O2 ICP plasma for fabrication of normally-off GaN HEMTs

The article presents the results of development of selective etching of p-GaN over Al0.25Ga0.75N in Cl2/Ar/O2 ICP plasma for fabrication of normally-off p-GaN gate GaN HEMTs using a laser reflectometry system for precise control of the etched material thickness. By optimizing etching process parameters such as oxygen flow, ICP power and chamber pressure, high etching selectivity of p-GaN over Al0.25Ga0.75N were obtained, with values up to 56:1. High etching selectivity and the control of etch rates of p-GaN and Al0.25Ga0.75N layers withing a wide range by changing the ICP process parameters enabled application of developed etching processes in the technology of fabrication of normally-off AlGaN/GaN HEMTs with a p-GaN gate. High threshold voltage of around 1.6 V and current densities up to 400 mA/mm were obtained. Electrical measurements have shown that the shortest 1 min Al0.25Ga0.75N overetch time after selective etching of the p-GaN layer results in best electrical parameters of fabricated devices.

Toward a comprehensive study for multielemental quantitative LA-ICP MS bioimaging in soft tissues

Quantitative localization of metals in biological tissue sections is critical to obtain insight into metal toxicity mechanisms or their beneficial characteristics. This study presents the development of a quantitative LA-ICP MS bioimaging methodology based on the polymer film strategy and internal standardization. To maximize the number of elements mapped, an aqueous soluble polymer (dextran) was selected. Among the elements studied, the great majority (eight out eleven), i.e., Co, Ni, Cu, Zn, Se, Mo, Cd and Pt, exhibited linear regression after LA-ICP MS analysis of metal-spiked polymer standards. Methodology performances were carefully assessed as a function of the three internal standards (In, Rh and Ir) considered, the analytical operational conditions (ICP power, addition of O2 to ICP, and laser fluency) and the thickness of the biological tissue section. The results indicated that three groups (Co, Mo; Ni, Cu, Pt; and Zn, Se, Cd) of elements could be distinguished from their analytical response as a function of analytical conditions and the internal standard. These different element behaviors appeared to be mainly First Ionization Potential dependent (FIP). For elements with lower FIP (Co, Ni, Cu, Mo and Pt), differential responses due to carbon load in the ICP MS plasma could be efficiently corrected as a function of analytical conditions. Matrix effects were more pronounced for higher FIP elements (i.e., Zn, Cd and Se), and analysis of <10-μm thin sections without the addition of O2 to ICP MS plasma is recommended. LODs are in the range of 0.1–0.5 μg g−1 for Co, Mo, Cu, Ni, Pt and Cd as well as 0.9 and 1 μg g−1 for Zn and Se, respectively. The methodology was validated by means of a homemade metal-spiked kidney homogenate analyzed by LA-ICP MS imaging, and Co, Ni, Cu, Mo, and Pt provided the closest concentrations (5–29% bias) to the target values determined by ICP MS after mineralization. The methodology was applied to two types of clinical human samples undergoing different sample preparation protocols that did not affect internal standard homogeneity in the polymer film. This methodology is the first reported for the quantitative bioimaging of eight elements simultaneously.

Optimization of passivation in AlGaN/GaN heterostructure microwave transistor fabrication by ICP CVD

We have studied the effect of silicon nitride (SiN) dielectric passivating film deposition by inductively coupled plasma chemical vapor deposition (ICP CVD) on the parameters of AlGaN/GaN heterostructure high electron mobility transistors (HEMT). Study of the parameters of the dielectric layers has allowed us to determine the effect of RF and ICP power and working gas flow ratio on film growth rate and structural perfection, and on the current vs voltage curves of the passivated HEMT. The deposition rate changes but slightly with an increase in RF power but increases with an increase in ICP power. Transistor slope declines considerably with an increase in RF power: it is the greatest at minimum power RF = 1 W. In the beginning of growth even at a low RF power (3 W) the transistor structure becomes completely inoperable. Dielectric deposition for HEMT passivation should be started at minimum RF power. We have developed an AlGaN/GaN microwave HEMT passivation process providing for conformal films and low closed transistor drain–source currents without compromise in open state transistor performance: within 15 and 100 mA, respectively, for a 1.25 and 5 mm common T-gate (Ug = –8 V and Ud-s = 50 V).

Reactive ion etching of Ge-Sb-Se ternary chalcogenide glass films in fluorine plasma

Ternary Ge-Sb-Se chalcogenide glass (ChG) is emerging as an attractive material for fabricating micro optical devices due to the excellent optical properties. This paper reports the reactive ion etching (RIE) of ternary ChG films using CHF3 plasma for patterning microstructures. The influences of the etching parameters, including the ICP power, the chamber pressure, and the gas flow rate, on the etching rate and the anisotropy are investigated and optimized. Grass-like residues are found in high chamber pressure, and the formation mechanism is discussed. The results show that high RF power, low gas flow rate, and low chamber pressure are beneficial to achieving high etching rates and improving good anisotropy. The optimized etching parameters can be used as a baseline for patterning Ge-Sb-Se optical microstructures using reactive ion etching.

Micro-trench free 4H-SiC etching with improved SiC/SiO2 selectivity using inductively coupled SF6/O2/Ar plasma

SiC dry etching process for formation of a trenched-gate structure in trench metal-oxide-semiconductor field-effect-transistors employing bottom protection p-well (BPW) has been investigated. SF6/O2/Ar based inductively-coupled-plasma reactive-ion-etching were utilized with various variations in process parameters, such as bias power, ICP power, kind of gas species, working pressure and temperature. The effects of process parameters on trench profiles were analyzed by a cross-sectional scanning electron microscope and profilometer to suppress micro trenches at a bottom corner of the trench and improve SiC/SiO2 etch selectivity. We successfully demonstrated the micro-trench free SiC trench structure with high SiC/SiO2 etch selectivity of 3.7 at bias power of 1 kW, ICP power of 4 kW, SF6/O2/Ar flows of 6/6/8 sccm, working pressure of 15 mTorr and temperature of 20 °C.