Ar Addition Research Articles

Plasma-assisted pre-treatment for PACVD TiN coatings on tool steel

Ti-based hard coatings are widely used to protect tools from early failure caused by wear and corrosion. In recent years, plasma-assisted chemical vapor deposition (PACVD) was introduced as a suitable technique to deposit hard coatings onto tools of complex geometry. In addition, PACVD offers the possibility of combining pre-treatment steps such as sputter cleaning and nitriding with coating deposition in the same chamber. Although PACVD coatings have been successfully applied to a variety of applications, deposition on tool steels with high chromium content may cause adhesion problems. Therefore, the aim of this work was to investigate the influence of different gas compositions during pre-treatment on the adhesion of PACVD TiN coatings on a cold work tool steel containing 11.5 wt.% chromium. For plasma-assisted etching and nitriding, mixtures of H 2, N 2 and Ar were used. The efficiency of different pre-treatment steps has been characterized using TiN-coated as well as pre-treated uncoated samples. The phases formed in the near-surface region of the tool steel after pre-treatment were characterized by X-ray diffraction (XRD). The adhesion of 3.5-μm-thick TiN coatings was characterized using the VDI indentation test. The results obtained are correlated with the chemical composition at the interface characterized by secondary ion mass spectrometry (SIMS). The best adhesion quality value of HF 1 was achieved for coatings pre-treated in an atmosphere containing 40 vol.% N 2, whereas more or less nitrogen resulted in decreasing adhesion. Increasing nitrogen content promoted the formation of a CrN phase in the near-surface region of the tool steel. No compound layer was formed, but the diffusion layer varied in thickness, which can be related to the adhesion quality value. With Ar addition, adhesion generally deteriorated.

On mechanisms of argon addition influence on etching rate in chlorine plasma

Parameters of Cl 2/Ar plasma were investigated aimed to understand the mechanism of Ar addition influence on etching rate acceleration. Analysis was carried out on the base of combination of experimental methods and plasma modelling. It was found that the addition of Ar to chlorine under a constant total pressure condition cause changes in plasma electro-physical properties (EEDF, mean electron energy) due to the ‘transparency’ effect. Direct electron impact dissociation of Cl 2 molecules was found as the main source of chlorine atoms while the contributions of dissociative attachment and stepwise dissociation involving Ar metastable atoms are negligible. It was supposed that the main reason of etching rate increasing in Cl 2/Ar mixture plasma is connected with simultaneous action of Ar on volume chemistry and the heterogeneous stage of etching process.

Plasma-induced damage in PZT thin films etched by inductively coupled plasma

We investigated the etching damage induced by Ar/(Cl 2+CF 4) plasma and improvement in etching damage by O 2 annealing. PZT thin films were etched for 1 min in an ICP using a gas mixture of Cl 2 80%/CF 4 20% with 20% Ar addition. The etching conditions were fixed at a substrate temperature of 30 °C, RF power of 700 W, DC bias voltage of −200 V and a chamber pressure of 15 mTorr. To improve the ferroelectric properties of PZT thin films after etching, the samples were annealed for 10 min at 600 °C in O 2 atmosphere. After O 2 annealing, the remanent polarization-on-fatigue property was recovered to the characteristics of the as-deposited film. According to X-ray diffraction (XRD) analysis, an increase in (100) and (200) phases showed the improvement in structure of the PZT thin films after the O 2 annealing process. In addition, transmission electron microscope (TEM) images showed that the etched PZT surface is damaged by the bombardment of energetic particles, but that the damaged surface can be recovered by O 2 annealing. The results of electron probe microanalysis (EPMA) and Auger electron spectroscopy (AES) showed that O 2 annealing supports the substitution of oxygen vacancies on the PZT surface by O atoms. This decrease in oxygen vacancies improves the fatigue characteristics of PZT thin films.

I–V characteristics of the Langmuir probe in flowing afterglow plasmas

The specific features of the probe I–V characteristics in flowing-afterglow plasmas are studied experimentally and in theory. As it was found at a probe potential equal to the plasma one, V=0, an electron concentration in a probe vicinity (and a probe current) is decreased due to a predominant outflow of the electrons into an electrical circuit of the probe from the probe vicinity. The expression allowing one to reconstruct the undisturbed-by-probe electron concentration from only experimental data is derived. The reconstructed values of the electron concentration enable one to find from the experiments the semiempiric expressions allowing to describe quantitatively the behavior of the probe I–V characteristics at the electron-attracting as well as at the ion-attracting potential, respectively. The expressions found (both for electron-attracting and ion-attracting potential) include the “separating length,” which merely is the Langmuir length with a factor equal to the square root of the electron mass over the ion mass ratio for two-component plasma. The intermediate part of the probe I–V characteristics is discovered for probes operating with afterglow plasmas. This intermediate part is described in terms of the experimental parameter L0 having a dimension of the length (presumably electron-orbital length). The value of the parameter L0 does not depend on plasma parameters to within the ranges of plasma parameter variations for experimentally investigated plasmas as it was found. The experiments were performed with two cylindrical probes of 10 and 25 μm diam and ∼3 mm lengths in the experimentally investigated ranges of the afterglow plasma parameters: 105 cm−3<n<1010 cm−3, 0.017 eV<kT<0.3 eV, and 0.5 Torr⩽p⩽2 Torr of He gas pressure (corresponding to 950 μm⩾λTe⩾240 μm electron mean-free path) with (or without) Ar addition.

Effect of helium/argon gas ratio in a He-Ar-Cu + IR hollow-cathode discharge laser: modeling study and comparison with experiments

The He-Ar-Cu+ IR laser operates in a hollow-cathode discharge, typically in a mixture of helium with a few-% Ar. The population inversion of the Cu+ ion levels, responsible for laser action, is attributed to asymmetric charge transfer between He+ ions and sputtered Cu atoms. The Ar gas is added to promote sputtering of the Cu cathode. In this paper, a hybrid modeling network consisting of several different models for the various plasma species present in a He-Ar-Cu hollow-cathode discharge is applied to investigate the effect of Ar concentration in the gas mixture on the discharge behavior, and to find the optimum He/Ar gas ratio for laser operation. It is found that the densities of electrons, Ar+ ions, Arm* metastable atoms, sputtered Cu atoms and Cu+ ions increase upon the addition of more Ar gas, whereas the densities of He+ ions, He2+ ions and Hem* metastable atoms drop considerably. The product of the calculated Cu atom and He+ ion densities, which determines the production rate of the upper laser levels, and hence probably also the laser output power, is found to reach a maximum around 1–5 % Ar addition. This calculation result is compared to experimental measurements, and reasonable agreement has been reached.

The effect of argon on the electron field emission properties of α-C:N thin films

Amorphous carbon nitride (α-C:N) thin films were synthesized on silicon as electron emitters by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) system in which a negative dc bias was applied to the graphite substrate holder and a mixture of C 2H 2 and N 2 was used as precursors. The addition of Ar combined with the application of a negative dc bias can increase nitrogen content (N/C) measured by X-ray photoelectron spectroscopy (XPS), eliminate the dangling bonds in the film determined by Fourier transform infrared (FTIR) spectroscopy, decrease the film thickness measured by field emission scanning electron microscope (FE-SEM), increase the film roughness measured by atomic force microscope (AFM) and raise the graphitic content examined by Raman spectroscopy. The result shows that the onset emission field of α-C:N with Ar addition to the precursors can be as low as 4.5 V μm −1 compared with 9.5 V μm −1 of the film without the addition of Ar.

Effects of Ar and O2 additives on SiO2 etching in C4F8-based plasmas

Gas mixtures based on C4F8 are promising for the development of high-performance SiO2 plasma etching processes. Measurements of important gas phase species, thin film etching rates and surface chemistry changes were performed for inductively coupled plasmas fed with C4F8/Ar and C4F8/O2 gas mixtures. The addition of Ar to C4F8 causes a strong increase of the plasma density relative to that of pure C4F8 (by up to a factor of 4× at 90% Ar). For O2 addition the changes in plasma density are small up to 90% O2 relative to pure C4F8. Infrared laser absorption spectroscopy was used to determine the absolute densities of neutral CF, CF2 and COF2 radical species as a function of the gas composition. The densities of CF and CF2 were enhanced for certain operating conditions when Ar was added to C4F8 as long as the amount of Ar remained below 20%. For instance, the partial pressure of CF was 0.1 mTorr for a 20 mTorr 1400 W source power discharge for pure C4F8, and increased to 0.13 mTorr at 20% Ar. Above 20% Ar it decreased, roughly following the gas dilution. The CF2 partial pressure was about 5 mTorr for the same conditions, and increased by about 10% at 20% Ar. Above 20% Ar the CF2 partial pressure decreased roughly linearly with the amount of Ar added, to about 2 mTorr at 50% Ar. Of particular interest was the analysis of the difference in behavior of CF, CF2 and COF2 partial pressures over SiO2 and Si surfaces, with and without rf bias power (in the latter case a self-bias voltage of −100 V was used). For pure C4F8 discharges at 20 mTorr and 1400 W inductive power without rf bias the partial pressures of CF, CF2 and COF2 radicals are comparable over SiO2 and Si surfaces. Upon applying a rf bias, the CF2 partial pressure over a SiO2 surface is reduced much more strongly than for a Si surface. The overall reduction appears to be consistent with the relative SiO2/Si etch rate ratios observed for these conditions. These results indicate that CF2 is consumed during the etching of SiO2 and Si. We also measured fluorocarbon deposition rates without rf bias and etching rates of blanket SiO2, silicon, resist and deposited fluorocarbon films as a function of the rf bias and feed gas composition. Important differences in the response of the etching rates of those materials upon the addition of O2 and Ar to C4F8 were observed. In particular, we show that the SiO2/Si and SiO2/resist etching selectivities can be doubled by adding up to 90% Ar to C4F8, without inducing an unacceptably large reduction of the SiO2 etching rate. The change in etch rate ratios is at least in part due to strong surface chemical changes seen for Ar-rich fluorocarbon gas mixtures. The surface chemical changes of Si and SiO2 surfaces were investigated by real-time ellipsometry and x-ray photoelectron spectroscopy. A strong reduction of the fluorine content of the fluorocarbon steady-state layer and an increase in thickness is seen when up to 90% Ar was added to C4F8, and this coincides with an increase of the SiO2/Si etching selectivity. The change in fluorocarbon surface chemistry can be explained by the strongly increased ion/neutral flux ratio that is characteristic of Ar-rich C4F8/Ar gas mixtures.

Combined effects of argon addition and substrate bias on the formation of nanocrystalline diamond films by chemical vapor deposition

The article reports combined effects of Ar addition and substrate bias on the grain size, microstructure, and growth rate of the diamond films prepared in microwave plasma-enhanced chemical vapor deposition. The nanocrystalline diamond (NCD) films with grain size of 50–100 nm, characterized by Raman spectra, scanning and transmission electron microscopy, were produced at 90–99 vol % Ar concentration under −50 V substrate biasing. The growth rate of the NCD films was 0.7–0.8 μm h−1, larger apparently than those grown by only Ar addition or by substrate bias effect alone. The NCD formation by various mechanisms is discussed, and a revised C2 insertion mechanism by the promotion of H+ ions is proposed to interpret the higher growth rate of the NCD films.

Parametric reactive ion etching of InP using Cl2 and CH4 gases: effects of H2 and Ar addition

The etching characteristics of InP by reactive ion etching (RIE) using Cl2 and CH4 gases were investigated systematically as functions of various etching parameters. The etching parameters, such as Cl2 flow rate, CH4 flow rate, rf power and process pressure, were varied. The effects of H2 or Ar addition to the Cl2 and the CH4 discharges were compared. The etch rates of SiO2 mask during Cl2 RIE process were also measured. The etched profiles, sidewall roughness and surface morphology were observed by scanning electron microscopy and by atomic force microscopy. Auger electron spectroscopy was used to examine the elemental composition of etched surfaces and to evaluate contamination. The possible mechanism for these etching phenomena is discussed. The results suggest that a CH4/H2 gas mixture is the most promising for achieving ideal etching profiles (i.e., anisotropy, good surface morphology, smooth sidewall roughness) for optoelectronic device applications.

Growth of faceted, ballas-like and nanocrystalline diamond films deposited in CH 4/H 2/Ar MPCVD

The influence of Ar addition to CH 4/H 2 plasma on the crystallinity, morphology and growth rate of the diamond films deposited in MPCVD was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. X-Ray diffraction patterns indicate that diamond films of strong (111) and weak (400) texture are produced in these samples. Faceted diamond gradually turns into ballas-like diamond with graphitic inclusions when the Ar concentration increases to above 30 vol.%, as indicated by Raman spectra. As the Ar concentration goes above 90 vol.%, nanocrystalline diamond films are formed, characterized by a 1150-cm −1 peak in the Raman spectra and morphology observation. Diamond growth by CH 3 or by C 2 mechanism is proposed to interpret the change in the growth rate of diamond films with the variation of Ar content in the plasma.

Structure and mechanical properties of argon assisted carbon nitride films

This paper reports on the effects of Ar dilution on the structure, bonding and tribological properties of nitrogen-doped amorphous carbon films (a-C:H:N) deposited by r.f. glow discharge from CH 4–N 2 and CH 4–N 2–Ar mixtures on silicon substrates. For different N 2 fractions, film structure and chemical composition were examined using Raman spectroscopy, X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS). The mechanical and tribological properties were investigated by scratch testing and a tribometer in a ball-on-disk configuration. Results indicate that, as argon is introduced in the gas mixture, progressive graphitization of the films occurs and the mass density decreases. The behavior of the adhesive strength, as a function of nitrogen content, achieved with Ar addition is of the same order as those reported for CN x films. However, at a fixed nitrogen partial pressure, films obtained without Ar dilution show better adhesion and a denser sp 3 bonded carbon network.

Effect of Ar addition to an O2 plasma in an inductively coupled, traveling wave driven, large area plasma source: O2/Ar mixture plasma modeling and photoresist etching

We report on the effect of Ar addition to an O2 plasma on photoresist etching in an inductively coupled, traveling wave driven, large area plasma source (LAPS). We also develop a simplified spatially varying O2/Ar mixture discharge model corresponding to the LAPS in a two-dimensional geometry in order to account for the effect of Ar addition. A photoresist etch kinetics model and spatially varying O2/Ar mixture discharge model are used to explain the experimental data. We find that the addition of 50% Ar increases the plasma density and etch rate approximately by a factor of 2. From the simulation we find that argon metastables (Ar*) play an important role in the mixture plasma. The simulation predicts an enhancement in O-atom density due to Ar addition, even in the presence of dilution of the feed gas. The experimental data and predicted etch rates from the simulation are generally in good agreement, indicating that the increase in the etch rate with Ar addition is due to both the increase in the plasma density and the enhancement in O-atom density attributable to the dissociation of O2 by Ar*.

Addition of Ar to Xe/Ne and Xe/He mixtures: radiation characteristicsand discharge onset voltage for an application of plasma displaytechnology

The influence of Ar addition to conventional Plasma Display Panelgases, Xe/Ne and Xe/He mixtures, on the radiation characteristics and thedischarge onset voltage is studied using a Boltzmann equation method coupledwith rate equations for electrons and excited species. When Ar is added toXe/Ne mixtures, the efficiency of ultraviolet light radiation from Xe(1s2,4) and Xe2* increases 7-17% for E/p0 between 3 and100 V cm-1 Torr-1. In Xe/He mixtures, the efficiency increases over20% for E/p0<10 V cm-1 Torr-1. In addition, the visible lightradiation of the 600 nm band from excited Ne, which makes the contrast worse,is effectively reduced. On the other hand, the discharge onset voltageincreases with Ar addition because of a decrease in the effective secondaryelectron emission coefficient.

New combination of four-component gas He–Ne–Xe–Ar for high efficiency plasma display panel

The improvement of luminous efficiency is one of the most important issues in making a plasma display into a large flat panel device. Accordingly, a new combination of a four-component gas, He–Ne–Xe–Ar, is proposed in order to achieve a high luminous efficiency in color plasma display panels (PDP). The densities of 32 species and electron temperature were calculated using a zero-dimensional simulation. The results were then compared with measurements of brightness and luminous efficiency to identify the optimum mixing condition of He(7): Ne(3)–Xe(4%)–Ar gas for a color PDP. The reaction mechanism was computationally analyzed to comprehend the discharge mechanism in He–Ne–Xe–Ar as well as in He–Ne–Xe. By simulation, the maximum peak point of the Xe*(1S4) state was obtained between a 0.1% and 0.5% Ar mixing ratio and the maximum luminous efficiency was measured with a 0.3% Ar mixing ratio in the PDP. As a result, the luminous efficiency was considerably improved (about 20%) with a 0.3% Ar addition, compared with the conventional He–Ne–4% Xe mixing gas.

The influence of Ar addition on the structure of an a-SiOCF film prepared byplasma-enhanced chemical vapour deposition

The preparation of a-SiOCF films from Si(OC2H5)4, C4F8 and/or Arusing a plasma-enhanced chemical vapour deposition method is reported. Thechemical bonding structures of the films are analysed by high-resolution x-rayphotoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR)spectroscopy. The results show that the films contain F-Si-O-Si, Si-OH,Si-O-Si, C-CF and C-F configurations. However, as for the film deposited fromthe feeding gases with Ar, a C-C configuration is also included in addition tothe above-mentioned configurations. This indicates that the existence of Ar inthe plasma leads to the formation of a fluorocarbon structure with a high degree ofcross-linking. No evidence reveals the presence of a Si-C bond in thefilm, so it is believed that the fluorocarbon is perhaps embedded into thematrix of SiOF.

Compositional mapping of the argon–methane–hydrogen system for polycrystalline to nanocrystalline diamond film growth in a hot-filament chemical vapor deposition system

The transition in diamond crystal morphology from well-faceted microcrystalline to nanocrystalline phases as a function of increasing argon (Ar) concentration has been studied in a hot-filament chemical vapor deposition (HFCVD) system. The range of Ar concentration in a Ar–methane–hydrogen mixture that permits well-faceted diamond growth is up to 90%. At a concentration of 95.5%, a marked transition into nanocrystalline diamond phase could be observed. Although no graphitic phases were observed by transmission electron microscope and x-ray diffraction up to 95.5% Ar concentration, Raman analyses revealed a proportionate increase in amorphous carbon content with an increase in Ar concentration. The addition of Ar appears to create an electron-rich gas environment because a plasma can be readily discharged by applying a bias to the sample. Analysis of the plasma by optical emission spectroscopy revealed a linear correlation between Ar addition and the occurrence of C2 dimers in the plasma. Our results identified the narrow Ar-methane-hydrogen composition window that is effective for the growth of thick and smooth nanocrystalline diamond in HFCVD.

Influence of the H2 and Ar on the Neon

The experimental results concerning the influence of the H2 and Ar addition to the Ne+1% Xe Penning mixture on the neon optical emission are obtained for two types of discharges: a narrow gap dielectric barrier discharge and the negative glow of a d.c. luminescent discharge. The H2 and Ar contribution to the depletion of the lower level 1s 2 through the Penning collisions and also the hydrogen participation to the feeding of the upper level 2p 1 of the optical transition 2p 1 - 1s 2 of the neon have been demonstrated. As a possible explanation for feeding of the upper level 2p 1 we are favouring the reactive and/or dissociative recombination processes.

Ab initio study of Ar n–HCO + ( n = 0–6): insight into size dependent cluster ion properties

Minimum energy structures, dissociation energies, and harmonic vibrational frequencies are determined for Ar n –HCO + ( n = 0–6) at the MP2/aug-cc-pVDZ level of theory. In all clusters, one Ar atom occupies an energetically preferred bonding site interacting with the hydrogen of HCO + with a linear or near-linear Ar–H–C bond angle. The subsequent Ar atoms add by forming a ring around this Ar–HCO + moiety with the detailed geometry determined largely by Ar/Ar interactions. The positions of the first five Ar atoms can be understood in terms of the crystal structure of solid argon whereas the sixth Ar atom produces a five membered Ar ring which has no analog in the solid phase of argon. Nonmonotonic variations in sequential binding energies of the Ar atoms are rationalized in terms of variations in the Ar n /HCO + interaction energy and the differing number of Ar/Ar interactions involved. The HC stretching frequency (ν 1) is found to undergo a large redshift with the first Ar addition and then to slowly blueshift with subsequent Ar additions in agreement with the experimental results. The identities of two previously unassigned combination bands with ν 1 are established and the experimental assignment of a third combination band with ν 1 is confirmed.

Enhanced diamond film growth by Xe-added microwave plasma CVD

In order to obtain diamond thin films of high quality and favorable electronic properties, we have examined the role of Xe addition to the microwave plasma-assisted {CH4+H2} chemical vapor deposition (CVD) for diamond thin films growth. To make clear effects of Xe addition, we compared the results with those of Ar addition. Effects of Xe addition were evident in the increased growth rate (about 50% increase for 1%-Xe), without degradation of the crystallinity, and in the marked improvement in the transconductance of diamond metal-insulator-semiconductor transistors (MISFETs). Based on the results of the plasma emission spectra, Raman shift and microwave plasma impedance measurements, the prominent effects of Xe addition were attributed to its lower excitation energy, which reduces plasma temperature and it is sufficient for the dissociation of atomic hydrogen and CH3 (precursors for diamond crystallization) but not CH2 radicals.

New combination of a three-component gas, Ne–Xe–Ar, for a high efficiency plasma display panel

The luminous efficiency improvement is a key issue for making a plasma display into a large flat panel device. We suggest a new combination of a three-component gas, Ne–Xe–Ar, to achieve a high luminous efficiency of a color plasma display panel. The densities of 26 species and the electron temperature were calculated by zero-dimensional simulation, and we compared the results of zero-dimensional simulation with a measurement of vacuum ultraviolet (VUV) intensity covering a 140–180 nm wavelength range, in order to find the optimum mixing condition of Ne–Xe–Ar gas in a color plasma display panel. Reaction mechanism was analyzed by a computational work to comprehend the mechanism of discharge in Ne–Xe–Ar as well as Ne–Xe. The maximum peak point of the Xe*(1S4) state was obtained in 0.5% of Ar mixing ratio by simulation and the maximum luminous efficiency was measured at the same point of 0.5% Ar mixing ratio in VUV measurement. The luminous efficiency has been improved considerably (about 30%) with a 0.5% Ar addition, compared with the Ne–4% Xe mixing gas.