Ion Etching Rate Research Articles

Ion energy dependence of dry etch damage depth in Ga2O3 Schottky rectifiers

The β-polytype of Ga2O3 has a high critical electric field strength (∼8 MV.cm−1) and can be grown as large diameter (6 in.) single crystal boules by inexpensive melt-growth techniques. This makes it promising for next generation power electronics and solar-blind UV photodetectors. Since wet etching is not feasible for patterning such devices due to the chemical inertness of Ga2O3, attention is focused on dry etching, with the attendant issue of surface modification due to chemical or ion-induced changes. In this work, we demonstrate that dry etch damage in β-Ga2O3 is manifested by a reduction in near-surface carrier concentration, possibly due to the introduction of Gav acceptor states. The depth to which the carrier density is affected depends on the interplay between ion energy and etch rate, with faster etch rates reducing the depth of the remaining damaged region. The maximum damage depth observed experimentally from capacitance-voltage profiling on Schottky rectifiers was ∼ 110 nm, well beyond the range of the ions in the Inductively Coupled Plasmas and emphasizing that rapid diffusion of point defects occurs into the sample during the etch step. Using Schottky rectifier structures as a platform to understand the effect of dry etch damage on device parameters, we found that on-state resistance was more affected than ideality factor or breakdown voltage, with a large increase (5x) for ion energies ≥ 325 eV. Reverse current density characteristics showed the presence of trap-assisted space-charge-limited conduction in the damaged layers. The implications for high power rectifier fabrication are discussed.

A Study on the Improvement of Etch Uniformity in an Ion Beam Etcher with a Magnetized Inductively Coupled Plasma Source

A magnetized inductively coupled plasma ion beam etcher (MICP-IBE) was designed by employing electromagnets around the etcher (IBE). A magnetic field can be set up such that the magnitude of the magnetic flux density on the screen grid increases or decreases with the radial distance from the screen grid center. Four different types of magnetic field conditions were considered. The plasma densities and electron temperatures were measured as functions of radial distance from the screen grid center under each condition. In addition, ion flux was measured with respect to radial distance from the substrate center using ion energy analyzer (IEA), after which the uniformity characteristics of the ion flux in the substrate were investigated. The dry etching characteristics of CoFeB, a typical alloy being used in the magnetic memory device, were investigated. The uniformity characteristics of the ion flux and the etch rate can be improved with the proper design of magnetic field conditions; however, the improvement was confirmed to be limited. In this respect, a new screen and acceleration grid were designed that have different grid hole densities with radial distance from the grid center (hereafter referred to as the proposed grid). Using the proposed grid, the ion flux and etch rate of CoFeB were measured with respect to radial distance from the substrate center, to see if the radial etch rate uniformity can be improved further. The CoFeB etch rate non-uniformity in the proposed grid (11.65%) was lower than that for the conventional grid (17.5%).

RIE for structuring E-field processed glasses

We present studies of reactive ion etching of glasses modified by electric field applied to the glasses at elevated temperature. Voltage dependence of the thickness of the modified glass layers is revealed. Secondary ion mass spectrometry data are used to establish the relation between the ion etching rate of the electric field modified glasses and their local composition resulted from the modification. Using structured anodic electrodes allows formation of nanoscale relief structures on the glass surface because of the volume relaxation of the modified regions. This is thermal electric field imprinting procedure. It is shown that the reactive ion etching allows effective deepening the glass surface relief formed in the course of the imprinting. The reactive ion etching allows keeping a high lateral resolution of the surface relief formed in the imprinting. The formation of gratings with micron-scale periodicity is demonstrated.

Ion excitation and etching effects on top-surface properties of sp2 nanocrystallited carbon films

We proposed the low energy ion irradiation effects (ion excitation and ion etching) on the formation and the top-surface properties of sp2 nanocrystallited carbon films in electron cyclotron resonance (ECR) plasma sputtering system. In this work, the ion etching rate during film deposition was measured and a threshold voltage for physical etching was found to be about 35 V. Below the threshold voltage, the film growth was induced by ion excitation effect (ion exciting electrons of top-most atoms), as a result, the sp2 dominant nanocrystallite size in the films was large. When the ion energy exceeded the threshold voltage, the film growth was induced by ion etching effect (ion breaking covalent bond), and the nanocrystallite size was small confirmed by the transmission electron microscopy (TEM) observation and Raman analysis. Furthermore, the top-surface properties of sp2 nanocrystallite carbon films prepared with different ion irradiation effects were examined by using the atomic force microscopy (AFM). Results showed that the ion etched carbon films had smaller surface roughness, scratch depth and adhesive force compared with the ion excited carbon films. These findings shed light on the fabrication and applications of carbon based nanostructured materials.

Large-Scale Synthesis of Colloidal Si Nanocrystals and Their Helium Plasma Processing into Spin-On, Carbon-Free Nanocrystalline Si Films.

This paper describes a simple approach to the large-scale synthesis of colloidal Si nanocrystals and their processing into spin-on carbon-free nanocrystalline Si films. The synthesized silicon nanoparticles are capped with decene, dispersed in hexane, and deposited on silicon substrates. The deposited films are exposed to nonoxidizing room-temperature He plasma to remove the organic ligands without adversely affecting the silicon nanoparticles to form crack-free thin films. We further show that the reactive ion etching rate in these films is 1.87 times faster than that for single-crystalline Si, consistent with a simple geometric argument that accounts for the nanoscale roughness caused by the nanoparticle shape.

Polishing superhard material surfaces with gas-cluster ion beams

We have studied the influence of bombardment with accelerated gas-cluster ions on the surface topography of silicon carbide and diamond. Atomic-force microscopy shows that exposure to 10-keV gas-cluster ions at a total dose above 1016 cm–2 leads to smoothing of the surface relief. The ion-etching rate and efficiency of the surface relief smoothing as dependent on the thickness of removed layer have been estimated. Raman-spectroscopy data show that surface irradiation with gas-cluster ions does not introduce defects into the crystalline structure of irradiated material.

A gyroscope fabrication method for high sensitivity and robustness to fabrication tolerances

MEMS gyroscopes have favorable characteristics, including small size, high throughput, and low cost. The performance of MEMS gyroscopes depends on the displacement sensitivity of the capacitors. In this paper, we describe the fabrication of 300-µm-thick gyroscopes that can provide high displacement sensitivity and are robust to fabrication tolerances, i.e. deep reactive ion etch (DRIE) rate uniformity. When thick structures are perforated using DRIE to achieve high-aspect-ratio features, footing is commonly observed. However, we describe a fabrication method that circumvents problems associated with footing and side-wall etching, so that the gyroscopes can have uniform dimensions and small variations across the wafer. Using a post-fabrication translation approach, the position of capacitors is modified following DRIE, and the gap in the gyroscopes can be reduced to 3 μm, which leads to an aspect ratio of 100. Using this method, we fabricated MEMS gyroscopes that can overcome the DRIE aspect ratio limit and have capacitors with higher sensitivities than those of other gyroscopes, which typically employ substrates that are less than 100 µm thick. The gyroscope had a resonant frequency of 9.91 kHz, a quality factor of 2500 and a sensitivity of 23 mV/[deg/s].

Evaluation of the thickness and roughness of homogeneous surface layers on spherical and irregular powder particles

The present study describes the development of a theoretical model for estimating the thickness of homogeneous surface layers on spherical and irregular shaped powder particles using the XPS depth profiling. As opposed to flat surfaces, such an approach for substrates of specific geometry is not straightforward. One needs to consider those geometrical factors associated with the experimental setup and sample's roughness, which impose an angle dependence on the photoelectrons peak intensity, X‐ray flux and ion etch rate over the surface in question in order to evaluate it. The novelty of the current model lies in the introduction of geometrical freedom in connection to the experimental arrangement, which can be tailored to match the needs of contemporary instruments. The model was evaluated experimentally by analyzing the surface oxide layers on metal powder grades of different morphology. Complementary analytical techniques such as high resolution (HR) SEM and focused ion beam (FIB) were used in combination to further characterize the surface layers prior to the XPS investigations. The results reveal that the estimation of the oxide/metal interface from the measured relative metal intensity signal as function of etch depth using the model is in extremely good agreement with the corresponding values from direct measurement of HR SEM on FIB cross‐sectioned powder samples. The model deviates slightly only for the irregular shaped powder, which can be regarded as means for quantification of surface roughness of the material. The model is used as a basis for a computer software that estimates the thickness of surface layers for powdered materials. Copyright © 2014 John Wiley & Sons, Ltd.

Thin Film Self-Assembly of Poly(trimethylsilylstyrene-b-d,l-lactide) with Sub-10 nm Domains

Integrating block copolymer self-assembly with existing lithography processes to enhance their patterning capability is a promising approach for manufacturing a variety of semiconductor devices and next-generation magnetic storage media. Sub-10 nm block copolymer domains are specifically targeted in many of these applications, yet there are relatively few block copolymers that can achieve these dimensions. Here the synthesis and self-assembly characteristics of a new block copolymer poly(trimethylsilylstyrene-b-d,l-lactide) (PTMSS-b-PLA) capable of forming domains as small as ∼5 nm are described. Several lamellar and cylinder forming diblocks were synthesized with bulk domain periodicities of 12–15 nm which are among the smallest domains yet reported for any neat block copolymer. Such small domains are possible because this new material has a large segment–segment interaction parameter which is an order of magnitude higher than poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and twice as large as poly(styrene-b-dimethylsiloxane) (PS-b-PDMS), two commonly studied polymers for these applications. Furthermore, the PTMSS-b-PLA blocks have glass transitions well above room temperature with a large reactive ion etch rate contrast between them (∼28) which is at least 4 times greater than PS-b-PMMA due to incorporation of a trimethylsilyl group into the styrene monomer.

Formation technology of through metallized holes to sources of high-power GaN/SiC high electron mobility transistors

The technology of through metallized holes to sources of high-power GaN/SiC high electron mobility transistors is studied. The dependences of the reactive ion etch rate of SiC in the inductively coupled plasma discharge on the pressure of the SF6/O2/Ar gas mixture (5–40 mTorr), the high-frequency power applied to the bottom electrode (200–300 W), the working gas flow ratio (5 : 1 : (0–10)), and the bottom electrode temperatures (5–50°C) are studied. Based on these dependences, the hole etching process on 76-mm-diameter SiC substrates 50 and 100 μm thick is developed. The process features smooth etched-surface morphology, a high rate (1 μm/min), and low high-frequency power deposited into the inductively coupled plasma discharge (1000 W). The developed process of hole etching in SiC substrates is characterized by the selectivity coefficient S = 12 and the anisotropy coefficient A = 13. Films based on NiB are recommended as masks for etching through holes into SiC substrates. The processes of through-hole metallization by the electrochemical deposition of Ni and Au layers are developed.

Maskless and Resist-Free Rapid Prototyping of Three-Dimensional Structures Through Electron Beam Induced Deposition (EBID) of Carbon in Combination with Metal-Assisted Chemical Etching (MaCE) of Silicon

In this work, we introduce a maskless, resist-free rapid prototyping method to fabricate three-dimensional structures using electron beam induced deposition (EBID) of amorphous carbon (aC) from a residual hydrocarbon precursor in combination with metal-assisted chemical etching (MaCE) of silicon. We demonstrate that EBID-made patterned aC coating, with thickness of even a few nanometers, acts as a negative "mask" for the etching process and is sufficient for localized termination of the MaCE of silicon. Optimal aC deposition settings and gold film thickness for fabrication of high-aspect-ratio nanoscale 3D silicon structures are determined. The speed necessary for optimal aC feature deposition is found to be comparable to the writing speed of standard Electron Beam Lithography and the MaCE etching rate is found to be comparable to standard deep reactive ion etching (DRIE) rate.

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter

Highly electronegative plasmas were produced in Ar/SF6 gas mixtures in a dc discharge with multipolar magnetic confinement and transversal magnetic filter. Langmuir probe and mass spectrometry were used for plasma diagnostics. Plasma potential drift, the influence of small or large area biased electrodes on plasma parameters, the formation of the negative ion sheath and etching rates by positive and negative ions have been investigated for different experimental conditions. When the electron temperature was reduced below 1 eV the density ratio of negative ion to electron exceeded 100 even for very low amounts of SF6 gas. The plasma potential drift could be controlled by proper wall conditioning. A large electrode biased positively had no effect on plasma potential for density ratios of negative ions to electrons larger than 50. For similar electronegativities or higher a negative ion sheath could be formed by applying a positive bias of a few hundred volts.

MACRODROPLET REDUCTION AND GROWTH MECHANISMS IN CATHODIC ARC PHYSICAL VAPOR DEPOSITION OF TiN FILMS

Cathodic arc physical vapor deposition (CAPVD) a technique used for the deposition of hard coatings for tooling applications has many advantages. The main drawback of this technique is the formation of macrodroplets (MDs) during deposition resulting in films with rougher morphology. The MDs contamination and growth mechanisms was investigated in TiN coatings over high-speed steel, as a function of metal ion etching, substrate bias, and nitrogen gas flow rate; it was observed that the latter is the most important factor in controlling the size and number of the macrodroplets.

Formations of conic surfaces on diamond films induced by hot filament assisted double-bias hydrogen plasma

The hot filament assisted double-bias hydrogen has been employed for the surface fabrication of the as-formed chemical vapor deposited diamond films on the nanometer scale. Diamond cone arrays are successfully prepared through hydrogen plasma etching. The intrinsic columnar structure of the diamond films leads to the unevenly distributed ion etching rate, which plays an important role in the cone formation. Simultaneously, the carbon-containing species sputtered out may re-deposit on the surface. The evolvement of the characteristic surface is thus determined by the competition between the ion etching and the carbon deposition. The application of grid electrode influences the discharge characteristics at the substrate region. By controlling the grid current, the surface structure of diamond films may be significantly tuned. Moreover, by introducing small amounts of methane in the etching process, the increased concentration of carbon-containing species enhances the secondary diamond nucleation on the film surface, which further promotes the uniformity of the diamond cone arrays.

Characterisation and application of BPR-100 thick photoresist

BPR-100 thick photoresist was characterised by spin speed, exposure time, ultra-violet light (UV) absorption, development time and reactive ion etching (RIE) rates. This photoresist has been found to be highly stable in chemical baths and as a mask for RIE. The thickness of the resist varies with spin speed from 15 to 90 µm with a single spin. Optical and scanning electron microscopy images show vertical sidewalls and crack-free resist surfaces with a production-type reproducibility. An aspect ratio of 3:1 was achieved under optimum conditions.

Plasma Etch Rates of Porous Silica Low-k Films with Different Dielectric Constants

The reactive ion etch rates of porous silica films with different dielectric constants (k-values) or film densities were measured by varying wafer bias and gas ratio for Ar/C5F8/O2 plasma. Both the etch rates of porous silica films and the optical emission intensities from the etching products (SiF) increased with wafer bias power. Etch rate increased with decreasing k-value of porous silica, whereas SiF emission intensity was maintained constant regardless of k-value, indicating that the amount of etching products escaping from the porous silica surface to the gas phase remained unchanged. From this result it is concluded that mass etch rate, defined as the weight of a porous silica film etched from a unit area per unit time, is constant for Ar/C5F8/O2 plasma.

Effect of dynamic vulcanization on co‐continuous morphology

AbstractThis study examines the effect of dynamic vulcanization on the co‐continuous morphology in ethylene‐propylene‐diene terpolymer (EPDM)/polypropylene (PP) blends using a technique of morphology investigation involving focused ion beam (FIB) etching of the sample surface, followed by topological investigation of the sample surface using tapping mode atomic force microscopy (TMAFM). The FIB ion etching rates of EPDM and PP are distinctly different, and these differences create a significant topological contrast between the phases when subsequently analyzed by atomic force microscopy. This approach allows for the high‐resolution observation of dispersed EPDM, and phases as small as 100 nm, are clearly identified. Since it is shown that the etching rates of noncrosslinked and crosslinked EPDM are similar, it was necessary to selectively remove the noncrosslinked EPDM phase by solvent dissolution. This combination of techniques then allows for the clear distinction of polypropylene, as well as noncrosslinked and crosslinked EPDM phases in the blend. The high‐resolution micrographs together with the continuity data, surprisingly, indicate that a noncrosslinked co‐continuous EPDM phase (α‐network) transits to a finer network of crosslinked EPDM (β‐network) after dynamic crosslinking. It is suggested that this β‐network is produced as a result of the viscosity mismatch between the noncrosslinked and crosslinked EPDM melt occurring at the outer envelope of the α‐network during dynamic crosslinking. As the crosslinked material pulls away from the noncrosslinked material under dynamic melt mixing conditions, it creates a smearing effect. It is shown that the initial α‐network maintains its continuity and demonstrates a diminished pore diameter as crosslinking proceeds. Furthermore, when the noncrosslinked material is extracted almost no crosslinked phase (<1%) is found to be present in the extract. These results strongly indicate that the crosslinking proceeds initially at the outer envelope of the EPDM phase, and works its way toward the center. © 2006 American Institute of Chemical Engineers AIChE J, 2006

EFFECT OF METAL ION ETCHING ON THE TRIBOLOGICAL, MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF TiN-COATED D2 TOOL STEEL USING CAE PVD TECHNIQUE

A study has been made on TiN coatings deposited on D2 tool steel substrates by using commercially available cathodic arc evaporation, physical vapor deposition technique. The goal of this work is to determine the usefulness of TiN coatings in order to improve the micro-Vickers hardness, coefficient of friction and surface roughness of TiN coating deposited on tool steel, which is vastly use in tool industry for various applications. A pin-on-disc test was carried out to study the coefficient of friction versus sliding distance of TiN coating at various ion etching rates. The tribo-test showed that the minimum value recorded for friction coefficient was 0.386 and 0.472 with standard deviation of 0.056 and 0.036 for the coatings deposited at zero and 16 min ion etching. The differences in friction coefficient and surface roughness was mainly associated with the macrodroplets, which was produced during etching stage. The coating deposited for 16 min metal ion etching showed the maximum hardness, i.e., about five times higher than uncoated one and 1.24 times to the coating deposited at zero ion etching. After friction test, the wear track was observed by using field emission scanning electron microscope. The coating deposited for zero ion etching showed small amounts of macrodroplets as compared to the coating deposited for 16 min ion etching. The elemental composition on the wear scar were investigated by means of energy dispersive X-ray, indicate no further TiN coating on wear track. A considerable improvement in TiN coatings was recorded as a function of various ion etching rates.

Etching characteristics of LaNiO3 thin films in BCl3∕Ar gas chemistry

La Ni O 3 (LNO) electrode was intensively studied as electrodes because LNO has a pseudocubic perovskite crystal structure with a lattice parameter of 3.84Å. But the etching process of LNO thin films must be developed in order to realize highly integrated ferroelectric random access memories. In this work, we investigated etching characteristics and mechanisms of LNO thin films using inductively coupled BCl3∕Ar plasma (ICP) system. The maximum etch rate of LNO thin films was 41.1nm∕min at a BCl3(20)∕Ar(80) gas mixing ratio. The positive ions and the ion energy distributions were measured with a quadrupole mass spectrometer (QMS). As rf power and dc bias voltage increased and working pressure decreased, the ion energy and etch rates of LNO thin films were increased. A chemically assisted physical etch of LNO was experimentally confirmed by ICP system and QMS measurements.

Sample tilting technique for preventing electrostatic discharge during high-current FIB gas-assisted etching with XeF 2

FIB-induced electrostatic discharge (ESD) is a major limiting factor for achieving successful and efficient circuit modifications of LSI. We have discovered a novel antistatic technique applicable to high-current (nanoampere-order) FIB gas-assisted etching with XeF 2. The method simply utilizes inclined incidence of FIB by sample tilting. The effect of the sample tilting technique on preventing ESD was investigated using a logic LSI device fabricated by 0.13 μm technology and eight-layer copper metallization. The result demonstrated that inclined incidence of 60° prevents ESD even for high-current (12.5 nA) FIB gas-assisted etching with XeF 2. The mechanism of ESD suppression by the sample tilting technique was proposed by taking account of the presence of processing gas molecules and the tilting-angle dependences of ion range, back-scattering yield, secondary-electron yield and etching rate. In the case of FIB irradiation at inclined incidence with XeF 2 gas flow, more secondary-electrons and sputtered particles are ejected with higher energies than those for the case of normal incidence. This leads the ionization probabilities of neutral gases and the sputtered particles to be increased, and results in producing increased low-energy electrons around the FIB processing area. These low-energy electrons suppress the FIB-induced positive charging.