Rf Magnetron Discharge Research Articles

Effects of power on ion behaviors in radio-frequency magnetron sputtering of indium tin oxide (ITO)

This study delves into ion behavior at the substrate position within RF magnetron discharges utilizing an indium tin oxide (ITO) target. The positive ion energies exhibit an upward trajectory with increasing RF power, attributed to heightened plasma potential and initial emergent energy. Simultaneously, the positive ion flux escalates owing to amplified sputtering rates and electron density. Conversely, negative ions exhibit broad ion energy distribution functions (IEDFs) characterized by multiple peaks. These patterns are clarified by a combination of radiofrequency oscillation of cathode voltage and plasma potential, alongside ion transport time. This elucidation finds validation in a one-dimensional model encompassing the initial ion energy. At higher RF power, negative ions surpassing 100 eV escalate in both flux and energy, posing a potential risk of sputtering damages to ITO layers.

Time-Resolved Analysis of the Electron Temperature in RF Magnetron Discharges with a Pulsed Gas Injection

Pulsed gas injection in a plasma can affect many fundamentals, including electron heating and losses. The case of an asymmetric RF magnetron plasma with a pulsed argon injection is analyzed by optical emission spectroscopy of argon 2p-to-1s transitions coupled with collisional-radiative modeling. For a fully detailed population model of argon 2p levels accounting for direct and stepwise electron-impact excitation in optically thick conditions, a rapid decrease in the electron temperature, Te, is observed during each gas injection with the sudden pressure rise. The opposite trend, with unrealistic Te values before and after each pulse, is observed for analysis based on simple corona models, thus emphasizing the importance of stepwise excitation processes and radiation trapping. Time-resolved electron temperature variations are directly linked to the operating parameters of the pulsed gas injection, in particular the injection frequency. Based on the complete set of data, it is shown that the instantaneous electron temperature monotonously decreases with increasing pressure, with values consistent with those expected for plasmas in which charged species are produced by electron-impact ionization of ground state argon atoms and lost by diffusion and recombination on plasma reactor walls.

Deposition of Metal Films on Microparticles Trapped in RF Magnetron Discharge

The technique for a metal film deposition on spherical microparticles in an RF plasma trap is presented. Both the particle confinement and the electrode sputtering are performed by a single RF magnetron discharge. The samples of a coated spheres are obtained and examined. The technique allows confining the particles near to the sputtered region close to the border zone of ballistic bombardment by sputtered atoms.

Electrical Potential and Topography of the Surface of a Calcium-Phosphate Coating Deposited with RF-Magnetron Discharge

Abstract—Research into the correlations of the surface electric potential of electret calcium-phosphate coatings formed by RF-magnetron sputtering and the surface topography are performed. It is determined that the electric potential over the coating surface has irregular distribution. The highest value of the potential is localized in the region near structural elements (vertices) with a higher peak sharpness value. The spots on the coating surface having a maximum potential within the range of 670–900 mV correspond to a profile of points with heights in the range of 77−326 nm. The higher values of the electron work function of the surface of the coating as compared to a titanium surface without the coating correspond to enhancement of the adhesion effect of osteoblasts and osteoclasts to the surface of the calcium-phosphate coatings.

Azimuthal inhomogeneities of axially symmetric rf discharge plasma in arc-shaped magnetic field

An axially symmetrical rf magnetron discharge in argon with a small admixture of air and in air was studied. The plane loaded electrode was equipped with a ring-shaped dielectric insert. Design features of the electrode and of the magnetic system allow the discharge ring to be located in the region where the electric and magnetic field lines are not perpendicular to each other. It has been revealed that in this case the glowing plasma ring is sectionalized. Up to 10 long-living plasma bunches were observed. They equidistantly locate along the discharge ring and may either rotate around the discharge axis or remain motionless. Both the discharge power and the working gas pressure are quite different from those proper to dc and high-power impulse magnetron sputtering discharges with spokes.

Mass spectrometry investigation of magnetron sputtering discharges

This paper deals with the mass spectrometric characterization of atoms, radicals and ions generated in the RF magnetron discharges sputtering metal targets in Ne, Ar, Kr and Xe gases. In magnetron discharges different kinds of species such as atoms, radicals and positive and negative ions according to the target material and sputtering gas pressure can be generated. The mass spectrometry of the magnetron discharge, which gives the detailed information on these species, is of key importance for the development of new advanced thin films. The amount of individual atoms, radicals and ions and the ion energy distribution as a function of flow and pressure of the sputtering gas, and the magnetron power is discussed in detail. This article shows (1) the ion distribution functions of gas and sputtered target material ions as a function of sputtering gas pressure, (2) the evolution of the amount of single-ionized and double-ionized atoms of gases and metals generated in the RF discharge during sputtering of Ag films in various inert gases as a function of gas pressure, and (3) the contamination of the sputtered metallic films by the oxygen from a residual gas atmosphere in the deposition chamber at low film deposition rates.

Mass Spectrometric Characterizations of Ions Generated in RF Magnetron Discharges during Sputtering of Silver in Ne, Ar, Kr an.d Xe Gases

The article reports mass spectrometric characterizations of ions generated in RF magnetron discharges generated using silver targets and Ne, Ar, Kr and Xe gases. Both the amount of ions and ion energies in magnetron discharges were investigated. The following ions X+, Ag+, (XAg)+, X2+, Ag2+, X++ and Ag++ were found in the RF discharges; here X = Ne, Ar, Kr, Xe is the inert gas atom and Ag is the silver atom. The amount of individual ions, their energies and ion energy distribution (IED) functions as a function of sputtering gas pressure were measured. It is shown that the sputtering gas pressure strongly influences the generation of ions, their amount and energy in the RF magnetron discharges. The knowledge of the energies and amounts of individual ions is of a key importance in the deposition of thin films with controlled properties using RF magnetron discharges.

Formation of crystalline γ-Al2O3 induced by variable substrate biasing during reactive magnetron sputtering

Reactive magnetron sputtering is a widely used technique to deposit various materials such as oxides and nitrides with a superior control of morphology and stoichiometry. The adjustment of the film properties at a given substrate temperature is believed to be affected by the average energy 〈E〉 per incorporated atom during film growth, which is controlled by the ion-to-neutral ratio in the film forming growth flux and the energy of the incident ions. This concept is tested for alumina growth in an rf-magnetron discharge by keeping 〈E〉, the average energy of the incident ions Eions, and the ion-to-neutral flux ratio constant, but varying only the energy distribution of the incident ions (ion energy distribution–IED). The influence of the IED on film growth is monitored by observing the transition of the films between x-ray amorphous Al2O3 to γ-Al2O3. The results reveal that the substrate temperature necessary for the transition to γ-crystalline films can be lowered by almost 100 °C, when the maximum energy of the incident ions is kept at 100 eV, while maintaining the energy per incorporated atom at 11 eV. This result is compared with TRIM calculations for the collision cascades of impacting ions.

Orbital motion of dust particles in an rf magnetron discharge. Ion drag force or neutral atom wind force

Microparticles with sizes up to 130 μm have been confined and the velocity and diameter of particles in a plasma trap of an rf magnetron discharge with an arc magnetic field have been simultaneously measured. The motion of the gas induced by electron and ion cyclotron currents has been numerically simulated using the Navier-Stokes equation. The experimental and numerical results confirm the mechanism of the orbital motion of dust particles in the magnetron discharge plasma that is associated with the orbital motion of the neutral gas accelerated by electron and ion drift flows in crossed electric and magnetic fields.

Thin Metal Film Deposition on Microparticles Trapped in RF Magnetron Discharge Plasma

AbstractWe present the technique for metal film deposition on spherical microparticles in plasma trap. An RF magnetron discharge was applied both to sputter Ag or Cu electrodes and to confine the microparticles in the immediate proximity to the sputtered area. We estimated the stopping power of Ar buffer gas on the sputtered atoms in van der Waals collisions which provide a main thermalization channel with cross‐section of the order of magnitude larger than for the hard sphere collision model. During our deposition experiments the microparticles were trapped close to the border zone of ballistic bombardment by the sputtered atoms. The deposition rate was of the order of 10−1 nm · s−1, the coatings have continuous surface with uniform thickness. magnified image

RF magnetron discharge model based on power balance

Previously developed theoretical approach to model asymmetrical capacitively coupled RF discharge is applied in the case of RF magnetron discharge. The method is based on deriving theoretical dependence of the FR power dissipated in the discharge on the DC selfbias voltage. These are easily measurable quantities and this experimental data is fitted with the theoretical model. Latter is based on rather broad assumptions and is applicable in large variety of cases. Experiments with Ar and O2 at low pressure are conducted. The data obtained fits perfectly with the model. The dependence of the total ion current, bombarding the target on the discharge conditions (applied power) is derived. The results show that independently on the similarity in the initial data, a substantial difference in the plasma sustaining power in both cases can be distinguished. This fact can be attributed to the presence of a number of vibrational rotational levels in O2 molecules, absent in Ar. The additional power needed to sustain O2 plasma goes for excitation of the vibrational rotational levels.

Experimental characterization of the deposition of silicon suboxide films in a radiofrequency magnetron reactive sputtering system

Sputter deposition of silicon suboxide films in a radiofrequency (rf) magnetron discharge using oxygen gas as a reactive species has been studied by a combination of plasma and film characterization techniques. The deposited films are silicon suboxides (SiO x , 0≤ x≤2). Using an energy-resolved mass spectrometer we found an impingement rate of SiO + ions on the deposition surface, which is comparable in magnitude to that of Si +, so a significant contribution of SiO to the Si and O incorporation in the suboxides cannot be ruled out. Increase of the oxygen flow beyond the point of SiO 2 deposition is characterized by a strong decrease of the Si + ion arrival rate on the growth surface. At the same time, the SiO 2 + arrival rate is increased, indicative for the increased oxidized state of the cathode. Number of atoms of the various kinds in the deposited layers have been determined by using Rutherford backscattering (RBS) and Elastic recoil detection (ERD) and correlated with the results of the plasma characterization.

Self-consistent particle-in-cell/Monte Carlo simulation of RF magnetron discharges of oxygen/argon mixture: effects of partial pressure ratio

The characteristics of RF planar magnetron discharges of O/sub 2//Ar mixture are clarified using the particle-in-cell/Monte Carlo method. The simulation is carried out for axisymmetrical magnetic fields. The spatial and temporal behavior of magnetron discharge is examined in detail. The O/sup -/ ions are trapped in the plasma bulk by the time-averaged potential. The O/sup -/ density is governed by a balance of generation and loss of O/sup -/. The positive ions Ar/sup +/, O/sub 2//sup +/, and O/sup +/ are distributed in such a way that the charge neutrality is kept in the plasma bulk. Since the peak point of O/sup -/ density does not coincide with that of electron density, the spatial distributions of Ar/sup +/, O/sub 2//sup +/, and O/sup +/ have two peaks. The number densities of Ar/sup +/ and O/sup -/ ions drastically increase when oxygen is added to the discharge gas Ar, and then saturated. In the case when the mole fraction of oxygen increases, the self-bias voltage on the target decreases. This phenomenon is investigated in detail and a clear physical explanation is presented.

Low-Energy Penning Ionization Gauge Type Ion Source Assisted by RF Magnetron Discharge

The construction and characteristics of a new low-energy Penning ionization gauge (PIG)-type ion source assisted by RF magnetron discharge are described. A two-stage scheme of the ion source is realized by using RF magnetron plasma as the cathodes for the PIG discharge. This scheme permits the independent control of both the ion beam energy and the parameters of discharge plasma in which the ions are produced. A divergent magnetic field configuration provides high current efficiency, reaching 50% under certain conditions. The source produces synthesized ion–electron flow with an ion beam current density of 1.5 mA/cm2 and an ion energy of up to 100 eV under a low working pressure of p=(1-8)×10-4 Torr using inert and reactive gases as the working gas.

Control of plasma parameters and wall sheath voltage in radio frequency magnetron discharge by grid bias

The plasma of a radio frequency (rf) magnetron discharge used for deposition of TiOx thin films was separated by a mesh grid into source (negative glow) and diffusion (deposition) plasmas. Langmuir probes were used to measure the potential, electron density, and electron temperature of both plasmas. While the change of the grid bias affected the diffusion plasma parameters, it did not change the source plasma parameters (except the potential). The use of the biased grid resulted in a decrease of temperature and an increase of density of plasma electrons in the film deposition region. With an increase of the grid biasing potential, the plasma potential increased in order to maintain a negative bias voltage across the grid sheath, the electron temperature increased, and the electron density decreased. The biased-grid-induced change of the plasma potential and the bias voltage across the wall sheath is explained based on the model of the asymmetric double probe, which is formed by the discharge chamber wall and the grid. The effect of the biased grid on the diffusion plasma parameters is discussed accounting for the particle transport phenomena in the system.

Reactive magnetron sputtering of tin-doped indium oxide (ITO): influence of argon pressure and plasma excitation mode

Tin-doped indium oxide (ITO) films have been prepared by reactive magnetron sputtering from a metallic alloy target onto unheated substrates. In a systematic study, the influence of the working pressure and the discharge mode (DC, pulsed DC or RF) on the electrical and structural properties of ITO films was investigated. It was found that the RF excitation (13.56 MHz) of a magnetron discharge is the most effective one with respect to the usage of the oxygen for oxidising the sputtered metal atoms on the substrate surface. When varying the working pressure (0.3–3.4 Pa), the oxygen partial pressure for the resistivity minimum of the ITO films is independent of the working pressure for RF excitation. Exciting the plasma by DC, an increasing oxygen amount is necessary in order to prepare low resistant ITO films when increasing the working pressures. This behaviour can be explained by different sources for the input of energetic particles into the growing film for RF and DC excitation. In a DC discharge, most of the energetic particles stem from the target surface (e.g. reflected neutral argon atoms or negative oxygen ions), while in a RF magnetron discharge, the largest part of the energetic particles has its origin in the plasma in front of the substrate. By Rutherford backscattering analysis the chemical composition of the ITO films as a function of the oxygen partial pressure was investigated. Fully oxidised ITO films exhibit an oxygen excess of approximately 15%. Low resistant ITO films show an oxygen-to-metal ratio of approximately 1.5, suggesting a film structure where the tin atoms occupy indium lattice sites. From the XRD analysis, a compressive strain in the ITO films of up to 2% was measured, which seems to be caused by the excess oxygen in the films. Furthermore, the ITO films exhibit a density which is up to 20% lower than that of bulk indium oxide.

Diagnostics by optical absorption of sputtered atom density in magnetron discharges

Densities of sputtered atoms in Ar rf magnetron discharges have been measured by optical absorption. The resonant and self-absorption methods have been used. The first one has given Al and Mg atom densities with an uncertainty of 40% and the second one the order of magnitude of Si atom densities. The Al atom densities are strongly decreasing from 93.7% Al alloy target: (1–5)×1011 cm−3–10.3% Al aluminosilicate glass: (1–2)×109 cm−3. The Si atom density is in the range (3–9)×1010 cm−3 in the aluminosilicate glasses. The Al and Si sputtered atom densities follow the sputtering yields of Al metal and Al, Si oxide targets.

Growth of GaN by molecular-beam epitaxy with activation of the nitrogen by a capacitive rf magnetron discharge

It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 μm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature.

Experimental study of an RF magnetron discharge for thin-film deposition

An investigation by optical emission spectroscopy and Langmuir probe was performed on an RF magnetron discharge used to sputter deposit tungsten and titanium in an argon plasma. The dependence on gas pressure and RF power of some Ti, W and Ar emission line intensities, electron density and temperature are studied in the center of the discharge. A simple model for the excitation process of the Ar, W and Ti atoms allows us to calculate the density of sputtered atoms in the plasma. The variations of electron density as a function of argon pressure and discharge power obtained by probe measurements are well correlated with the Ar (750.4 nm) line intensity. Owing to the transport regime of W and Ti sputtered species across the discharge, the existence of a correlation between the target composition, tungsten and titanium densities in the plasma and film composition on the substrate must be studied carefully.

Infrared studies of room temperature deposition of hydrogenated silicon oxide films in rf magnetron discharges

The properties of a-SiOx:H thin films deposited at low temperature (∼ 50 °C) in a low energy magnetron rf plasma system with Ar/SiH4/O2 gas mixtures are investigated. In the low pressure regime (about 5 mTorr reactive gases), the surface reaction dominates in the film formation process. As the partial pressure ratio (ROS) of oxygen to silane increases, the Si-H related vibrational modes gradually disappear, and the film becomes stoichiometric SiO2 for ROS≥1. High quality oxide film can be deposited due to the low pressure environment and the plasma promoted surface process. In the high pressure regime (tens of mTorr) the deposited SiO2 films contain fine particles (tens of nanometer in size) and are porous (15% void) due to the gas phase homogeneous reaction and aggregation. The infrared absorbance spectra with normal and oblique incidence imply different origins of the half width and the shoulder intensity of the 1070 cm−1 Si-O(s) mode. In comparison with the low pressure dense films, the narrow half width of the high pressure film may be caused by the more ordered local structure which has a narrower distribution of bond angle and length, while the large shoulder intensity may be dominated by the larger (fine particle size) scale disorder.