Glow Discharge Sputtering Research Articles

Investigation of glow-discharge-induced morphology modifications on silicon wafers and chromium conversion coatings by AFM and rugosimetry

The effect of radiofrequency glow-discharge sputtering on the sample surface in terms of modifications in the surface morphology were investigated in this work by using atomic force microscopy (AFM) and rugosimetry measurements. The influence of GD operating parameters (e.g. rf power, discharge pressure and sputtering time) on surface roughening was investigated using two different types of samples: mirror-polished and homogeneous silicon wafers and chromate conversion coatings (CCCs). Surface morphology changes produced by GD sputtering into the sample surface were carefully investigated by AFM and rugosimetry, both at the original sample surface and at the bottom of GD craters using different GD experimental conditions, such as the sputtering time (from 1 s to 20 min), rf forward power (20-60 W for the Si wafer and 10-60 W for the CCC), and discharge pressure (400-1,000 Pa for the Si wafer and 500-1000 Pa for the CCC). In the present study, GD-induced morphology modifications were observed after rf-GD-OES analysis, both for the silicon wafers and the CCC. Additionally, the changes observed in surface roughness after GD sputtering were found to be sample-dependent, changing the proportion, shape and roughness of the micro-sized patterns and holes with the sample matrix and the GD conditions.

Electrical and Optical Characteristics of High-Power Pulsed Sputtering Glow Discharge

Droplet-free metal-plasma sources are promising for enhanced adhesion of deposited films with a smooth surface. High-power pulsed sputtering (HPPS) plasma is an arc-free discharge and a glow-discharge plasma with instantaneous power consumption of several tens of kilowatts, although the average power is the same as conventional sputtering discharge systems. Sputtered metallic species are significantly ionized. In this paper, two metal-plate cathode targets are positioned in parallel to form a gap. A magnetic field with a strength of 0.3 T is oriented parallel to the electric field, and a Penning discharge is generated at the gap. When a negative pulse voltage is applied to the two targets with the same polarity, a glow plasma is generated at the gap. Gas ions are first produced and accelerated toward the target, where metals are sputtered and simultaneously ionized. The plasma source is compact in size (60 times 60 times 60 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), with a gap length of 10 mm. The pulsed voltage is rectangular in shape, with amplitude ranging from -600 to -1500 V and pulse-widths of 30 and 100 mus. The repetition rate of the applied pulse is 625 Hz. Electrical and optical characteristics are investigated to determine fundamental characteristics of the HPPS glow metal plasma, and the plasma density are estimated using an electrode immersed in the HPPS glow plasma. The electrode is set nearby the plasma source. With a current-limiting resistor of 10 Omega and an applied voltage of -1200 V, the peak discharge current is approximately 76 A, which results in a peak instantaneous power consumption of approximately 30 kW at an argon gas pressure of 2 Pa. In this case, the consumed energy per pulse is 0.8 J, which corresponds to an average power of 500 W at a repetition rate of 625 Hz. The peak power density at the target surface is approximately 1.3 kW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The ion density at the holder-electrode set, positioned near the HPPS plasma source, is estimated to be on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , and it is time dependent. Optical emissions from titanium ions with a charge of +1 and excited titanium atoms are observed. Emissions are also observed from argon atoms and ions. Ions are extracted at the holder electrode. It is found that the titanium-ion spectrum intensity is proportional to the argon-ion spectrum intensity. The waveform of the ion current has a sharp peak at the initial stage followed by a stationary state. Thus, the holder electrode is immersed in the plasma, and a transient ion sheath is formed around the holder electrode. It can be shown that the stationary ion current is proportional to the ion density at the surface of the holder electrode.

Voltage–current characteristics of a high-power pulsed sputtering (HPPS) glow discharge and plasma density estimation

A droplet-free metallic plasma source is promising for enhanced adhesion of films with a smooth coating surface. This paper concerns the study of a highly ionized metallic plasma source using a pulsed Penning discharge designed with a magnetic field oriented parallel to an electric field. Such a plasma is called a high-power pulsed sputtering (HPPS) glow discharge plasma. This technology is related to so-called high-power impulse magnetron sputtering (HIPIMS), though the interaction of the magnetic and electric field in the HPPS glow plasma is different from the HIPIMS plasma.The titanium metallic species are sputtered by energetic argon ion bombardment, causing their ionization in as short as a few microsecond. The typical electrical characteristics are as follows: a peak current of 45A (0.9A/cm2), a peak power of 18kW (0.8kW/cm2), and an average power of 1kW. The target voltage is approximately 400V at 30μs for glow currents of 30–120A. A negative pulse voltage is applied to the substrate holder electrode to extract ions from the magnetically confined HPPS glow plasma. Using the recovery characteristics of the voltage applied to the substrate, the ion density at the substrate surface is estimated to be on the order of 1016–17m−3 for a singly charged titanium plasma.

Generation of RF plasma assisted high power pulsed sputtering glow discharge without using a magnetic field

High power pulsed sputtering plasma is an emerging technology used to modify the surfaces of industrial components and biomedical parts. The characteristic feature of the plasma is that metallic species are highly ionized and charged particles are magnetized. In order to use the plasma source in a variety of material processing applications, it is desirable that the glow is generated without a magnetic field. In this paper, a sputtering of metallic species is enhanced by a pulsed dc voltage applied to a pair of electrodes immersed in an RF plasma.Sputtered metallic species are ionized as follows: first, a 200kHz-RF (radio frequency, output voltage: 3kV and duration: 200μs) argon plasma is generated. Then, a pulsed dc (direct current) voltage is applied to a pair of electrodes (of 60mm diameter and 75mm long) set in the RF plasma to accelerate argon ions toward the cathode (sputter target). The applied voltage ranges from 0.8 to 1.4kV with negative polarity. The argon gas pressure is 2.7Pa. The pulse width is 60μs. In a typical example, the induced current through the electrode is 45A with a voltage of 1000V. The instantaneous consumed power of 45kW and the energy consumed per pulse is 2.7J, corresponding to an average power of 216W at a repetition rate of 80Hz.

The effect of glow discharge sputtering on the analysis of metal oxide films

The potential of radiofrequency glow discharge optical emission spectrometry (rf-GD-OES) for the quantification and the solid-state speciation of metal oxide films has been investigated in this work. Two types of oxide coatings, an iron oxide film deposited on silicon and a chromate conversion coating (CCC), were studied at 700 Pa of pressure and 30 W of forward power. The metal to oxygen ratios in the quantitative depth profiles (Fe/O and Cr/O, respectively) were used to evaluate the oxidation states of iron and chromium in the oxide films, demonstrating the capability of GD-OES technique for depth-resolved solid-state speciation. Furthermore, the effect of glow discharge sputtering on the samples surface in terms of modifications in the surface morphology and species transformations, were investigated by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The iron and chromium oxidation states were carefully studied by XPS at the original samples surface and at the bottom of GD craters, and a systematic reduction of metal elements was observed after rf-GD-OES analysis. In the case of thin oxide films, preferential sputtering can be considered as a critical factor since oxygen atoms can be preferentially sputtered, leaving a metal-enriched surface and, therefore, promoting the reduction of metal elements. In the present study preferential sputtering was found to be sample dependent, changing the proportion of the metal reduction in the oxide film with its composition. Additionally, alternative sputter-depth-profiling techniques such as secondary ion mass spectrometry (SIMS), femtosecond laser ablation (fs-LA), and XPS ion gun were used for the analysis of the CCC in order to evaluate the reduction of Cr 6+ to Cr 3+ depending on the sputtering mechanism.

Calculation of the flow of sputtered atoms returning to a target with a surface relief during sputtering in glow discharge

A model is constructed that describes the transport of a sputtered substance near a target with a relief surface that is sputtered in glow discharge. For a periodic relief with small amplitude, distribution of a return flow of sputtered atoms from a discharge gap is calculated by a perturbation method. It is shown that nonuniform repeated deposition of the substance sputtered from the target could be one of the causes of formation of a relief on its surface.

Generation of droplet‐free high‐power pulsed sputtering (HPPS) glow plasma with several tens of kilowatts

AbstractA droplet free metallic plasma source is promising for enhanced adhesion of films with a smooth coating surface. This paper concerns a highly ionized metallic plasma source using a pulsed Penning discharge. A high‐power pulsed sputtering (HPPS) glow discharge plasma is generated using electric‐ and magnetic‐field interactions. The metallic species are sputtered by the energetic argon ion bombardment, followed by their ionization in as short as approximately 3 μs. The plasma source is compact in size (approximately 60 × 60 × 60 mm3) and the plasma is arc‐free. The glow plasma is generated at a gap with a length of 10 mm. The magnetic field at the gap is approximately 0.3 T. A pulsed power source with a rectangular‐shaped voltage‐output is used. Fundamental electrical and optical characteristics are obtained. The glow voltage and current are approximately –0.43 kV and 37 A at 30 μs, respectively, which corresponds to a peak power of approximately 16 kW, where the applied voltage –1.2 kV and a current limiting series resistance is 20 Ω. The consumed energy is approximately 0.41 J, which corresponds to an average power of 250 W at a repetition rate of 625 Hz. The power and energy are changed by circuit conditions. In order to increase the consumed power, the current limiting‐resistance is decreased to be 3 Ω, the peak power is increased to approximately 70 kW with a power density of 2.9 kW/cm2, where a current density is 4.5 A/cm2. The ambient gas is argon at a pressure of 2 Pa. In the emission spectra, singly‐ and doubly‐ionized titanium ions are observed, following the generation of argon ions, which shows the ionization of sputtered titanium species. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Plasma Deposition of Silver Nanoparticles onto Stainless Steel for the Prevention of Fungal Biofilms: A Case Study on Saccharomyces cerevisiae

AbstractA silver nanoparticle composite film was deposited onto stainless steel to reduce the adhesion strength of the model yeast S. cerevisiae. Deposition was carried out under cold‐plasma conditions, combining RF glow discharge and silver sputtering. Shear‐flow‐induced detachment experiments demonstrated the film's anti‐adhesive properties. However, the surface tended to undergo some chemical changes after use, such an increase in hydrophilicity. XPS analysis confirmed the presence of metallic silver for the native plasma‐modified surface and revealed silver oxidation after use. The silver content was also lowered, due to the progressive release of ionic silver from the composite into the medium.magnified image

A study on double glow plasma surface metallurgy Mo–Cr high speed steel of carbon steel

Double glow plasma surface metallurgy and heat treatment technology that generated excellent properties reinforcing layer on the surface of Q235 steel was introduced. Using this technology, the alloying elements of Mo, Cr, C can be obtained on the surface of Q235 steel. The content of constituent elements was near or equal to metallurgic high speed steel (HSS). The fundamental principle is that alloying elements Mo, Cr are penetrated into the Q235 steel in a vacuum chamber by glow discharge sputtering so that the content of alloyed layer content was about 20% Mo and 10% Cr on the surface of Q235 steel. Then after ultra-saturated carbonization alloyed constituent was similar to molybdenum HSS with surface carburizing of more than 2.0%. After quenching + low tempering; quenching + cryogenic treatment for 2 h + low tempering; quenching + cryogenic treatment for 16 h + low tempering, it was found that the surface hardness of cryogenic treatment was up to 1600 HV much higher than that without cryogenic treatment. The abrasion test results indicate that carbonization + quenching + low tempering, infiltration of Mo–Cr + carbonization + quenching + infiltration of Mo–Cr + carbonization + quenching + cryogenic processing for 2 h + low tempering and infiltration of Mo–Cr + carbonization + quenching + cryogenic processing for 16 h + low tempering the relative wear resistance was higher by one order in magnitude.

Frication Property of Mo-Cr-Infiltrated Steel Layer by Plasma Surface Metallurgy

Introduced in this article is the technique to acquire a high performance strengthened layer on carbon steel samples, namely, plasma alloying on the surface of Q235 steel and heat treatment technology. With this technique the alloying elements of Mo, Cr, and C can be obtained on the surface of Q235 steel samples. The content of the constituent elements is approximately up to high speed steels (HSS). The surface property required for the HSS after hardening and low tempering is attained. In the test, the alloying elements Mo and Cr were penetrated into the Q235 steel samples by glow discharge sputtering so that the content of the alloyed layer on the surface of the Q235 steel samples was about 20% Mo and 10% Cr. Two kinds of experiments were conducted. One was to carry out ultra-saturated carburization. The alloyed layer's composition was similar to molybdenum HSS with surface carburizing of more than 2.0%. The carbides of the alloyed layer were compact, uniform and disperse without a coarse eutectic ledeburite structure. The another was ion nitriding after the alloying elements of Mo and Cr were penetrated. The first process included hardening with low tempering and hardening with cryogenic treatment for 2 hr and low tempering. The second one was ion nitriding only. It was found that the surface hardness after cryogenic treatment is up to 1600 HV, much higher than that without cryogenic treatment. The abrasion test results indicate that, without the penetrated alloy elements Mo and Cr and without cryogenic treatment and ion nitriding, the friction coefficient is lower by one order of magnitude. The change in relative resistance is similar to the change in the friction coefficient, but without a proportional relationship.

Solid state doping of CdxHg1-xTe epitaxial layers with elements of V group

Presented here are the results of studying the controlled doping with elements of V group of the periodic table, arsenic As and antimony Sb, of narrow gap CdxHg1−xTe epitaxial layers during the isothermal growth from the vapour phase by the evaporation- condensation-diffusion method. Three types of impurity sources have been used for solid state doping: homogeneously doped with As(Sb) single crystal substrates of CdTe, As doped buffer CdyHg1−yTe (y > x) epitaxial layers obtained by RF sputtering in mercury glow discharge onto undoped CdTe substrates, and As(Sb) implanted undoped CdTe substrates. The results of comparative analysis of galvano-magnetic measurements and SIMS spectra indicated very high, practically nearly ~100 %, electrical activity of dopants in the CdxHg1−xTe epitaxially grown layers.

Surface Modification of Magnesium Alloy by Mg2Si Coating Technology

Surface modification technology on magnesium alloys has been developed by using Mg-Si thin films via a glow discharge sputtering process, in employing Mg2Si bulky materials fabricated by powder metallurgy (PM) process as targets. This is because Mg2Si sintered materials have high hardness and Young’s modulus, in particular, a superior corrosion resistance to the conventional stainless steel. The Mg-Si thin film, having 1-2µm thickness, deposited on the AZ31 substrate improved the mechanical properties, wear and corrosion resistance compared to the conventional magnesium alloys. In particular, the effect of crystalline/amorphous structures of Mg-Si thin films on these properties was investigated in detail.

Computer simulations of crater profiles in glow discharge optical emission spectrometry: comparison with experiments and investigation of the underlying mechanisms

The crater profiles obtainable with glow discharge sputtering are calculated for a wide range of current–voltage conditions, and comparison is made with experimental data for exactly the same geometry and conditions. The agreement is fairly good, except at high electrical current and low voltage. This good agreement suggests that the model takes into account the correct underlying mechanisms responsible for the crater shape, and that it can be used to predict optimum conditions for flat crater profiles. It is concluded from the model that the characteristic crater shape is determined by the electric potential distribution in front of the cathode, the radial distribution of fluxes and energies of the species bombarding the cathode, as well as the redeposition of sputtered atoms at the cathode surface, which is in correspondence to previous findings.

High temperature arsenic doping of CdHgTe epitaxial layers

AbstractExperimental results on solid‐state arsenic doping of the n‐type bulk and ISOVPE epitaxial CdXHg1‐XTe (X = 0.19 ÷ 0.3) alloys are presented. The arsenic doped thin epitaxial CdxHg1‐xTe films (nAs ≈ 5 · 1016 ÷ 1 · 1020 cm‐3; d = 2 ÷ 5 μm) obtained by RF sputtering in a mercury glow discharge were used as As diffusion sources. The arsenic diffusion and activation were carried out at temperatures T = 500 ÷ 600 °C under Hg vapour pressure. Immediately after the high temperature treatment all samples were annealed to annihilate point defects. The SIMS analysis was used for determination of the quantitative admixture distribution of As in the diffusion area. The arsenic electrical activity has been evaluated by means of differential Hall, resistivity and thermoemf measurements. The analysis of experimental data obtained as well as their comparison with previously obtained results has been performed. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Radiofrequency GDOES: a powerful technique for depth profiling analysis of thin films

AbstractPreviously, glow discharge optical emission spectroscopy (GDOES), both d.c. and r.f. has been used for depth profiling analysis of thick films several tens of microns thick, utilizing its high sputtering rates of &gt;1 µm min−1. Through selected examples, it is demonstrated here that r.f. GDOES also has enormous potential for depth profiling analysis of ultrathin films &lt;10 nm thick, where AES and SIMS have dominant roles. The significant features of r.f. GDOES enabling such analysis arise from the nature of r.f. glow discharge sputtering where samples, both conducting and non‐conducting, are sputtered very stably with Ar+ ions of low energies (&lt;50 eV) and high current fluxes (of the order of 100 mA cm−2). The low Ar+ energy ensures that film sputtering proceeds without significant formation of altered layers, which is a prerequisite for successful depth profiling analysis of ultrathin films at high depth resolution. The high current fluxes allow sputtering to proceed at very high rates of &gt;1 µm min−1, thereby extending the limit of film thickness for analysis to 100 µm. Thus r.f. GDOES, with its unique ability to accommodate depth profiling analysis of films of a very wide thickness range, is expected to play an important role in the field of practical surface analysis. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Surface characterization and depth profile analysis of glasses by r.f. GDOES

AbstractThe characterization of surfaces, interfaces and interphases in glasses is analytically challenging and may benefit from recent developments in radiofrequency glow discharge optical emission spectroscopy (r.f. GDOES) applied to non‐conductive materials. Thus, the main thrust of this study is to evaluate the potential of r.f. GDOES for the characterization of glass surfaces, physical heterogeneities such as discrete layers and continuous interphases and the distribution of elements in glass materials. Model glasses with increasing structural and chemical complexity thus were analysed using a Jobin Yvon GDOES system (5000 RF): the glasses included a multilayered glass (triple‐coated glass), two photoreactive glasses (with potential chemical diffusion gradients) and acid‐leached glass with an alteration layer. Concurrently, surface characterization of the glasses was conducted using scanning electron microscopy or transmission electron microscopy with energy‐dispersive x‐ray imaging to assess the chemical and physical gradients in the materials and to investigate the glow discharge sputtering process. From this the capability of r.f. GDOES for elemental depth profiling in glass materials is established. However, although the sputtering rates for glass are greatly reduced compared with conductive materials (∼2 nm s−1 compared with 50–150 nm s−1 for metals), r.f. GDOES offers good spatial depth resolution (nm) and elemental sensitivity for several applications, such as the characterization of interfaces or interphases and the determination of chemical gradients in glasses. Furthermore, the technique distinguishes submicrometre discrete layers in the coated glass, and the diffusion of elements within glass matrices may be monitored. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Target surface condition during reactive glow discharge sputtering of copper

During reactive glow discharge sputtering of copper in an argon/nitrogen plasma, we noticed an abrupt change of the target voltage and the deposition rate when the nitrogen concentration in the plasma exceeds a critical value. To explain this behaviour, the target surface after reactive glow discharge sputtering was examined by x-ray photoelectronspectroscopy (XPS). An experimental arrangement was constructed that allows direct transfer of the glow discharge cathode to the XPS analysis chamber without air exposure. These XPS measurements revealed that several different chemical states of nitrogen are present in the layer that forms on the target surface. The relative concentration of these different states changes when the critical nitrogen concentration in the plasma is exceeded.

Powered automatic measuring system for Langmuir probe plasma analysis

Langmuir probe analysis of a sputtering glow discharge leads to errors in measurements due to contamination of the probe surface by the sputter deposition from the target. An automatic Langmuir probe system using a personal computer has been designed. The design details and performance evaluation of this system are discussed in this article.

On glow-discharge sputtering of iron and steels in a commercial deposition plant

The sputtering rates of iron films and various steels exposed to argon–hydrogen pulsed-DC glow discharges in a commercial plasma-assisted chemical vapour deposition plant have been studied experimentally. The sputtering rate of iron was obtained from measurements of the film thickness before and after glow-discharge exposure, using Rutherford backscattering spectrometry, and the sputtering rates of the steels were obtained from shifts of positions of implanted Xe markers in Rutherford backscattering spectra. Through anode-catcher experiments, the dependence of the sputtering rate on the oxygen partial pressure was measured. To investigate any influence of the background oxygen pressure on the plasma (the cathode ion bombardment), energy spectra of the ions hitting the cathode were also recorded. With finite oxygen background pressures, iron sputtering rates much smaller than the ones corresponding to sputtering yields of iron oxides were measured. In fact, due to these low rates, it was only possible to establish upper limits to the iron and steel sputtering rates in glow discharges in the commercial chamber.

Modeling the Optical Quantum Efficiency of Thin Film Amorphous Silicon Solar Cells

ABSTRACTThe optical quantum efficiency and spectral response of p-i-n thin film amorphous silicon (a-Si:H) solar cells have been modeled using software based on optical admittance analysis. The optical constants of a-Si:H and Indium Tin Oxide (ITO) thin film layers have been measured by Variable Angle Spectroscopic Ellipsometry (VASE) and used as inputs into the optical admittance analysis program in order to model cells constructed from these films.Amorphous silicon thin films and p-i-n assemblies have been deposited by glow discharge and reactive sputtering techniques. The optical constants of doped and intrinsic a-Si:H thin films were determined by VASE and the film thickness verified by Scanning Electron Microscopy studies. The optical constants of commercially available transparent conducting oxide (TCO) coated substrates have also been determined by VASE.The experimental transmission spectra of p-i-n assemblies are compared with transmission spectra that have been modeled using the measured optical constants. Results of modeling different a-Si:H solar cell structures using these materials are presented, including a study of the optimal TCO layer thickness for p-i-n a-Si:H solar cells. This work shows that optical admittance modeling gives a good prediction of the optical behavior of p-i-n assemblies, but that accurate measurements of the optical constants of the component films are required in order to model effectively the optical quantum efficiency and photocurrent.