Thin Solid Films (v.475, #1-2)

Preface by Jeon G. Han (xi).

Committee (xii-xiii).

This article is focused on emission spectroscopy whose the main interest is in a non intrusive diagnostics, allowing a control and a piloting of the surface treatment process. To analyse a given plasma process, the emission spectroscopy must be coupled to the plasma kinetic equations. These mechanisms are described for a PVD process with a RF-activated magnetron DC cathode where it is shown how to follow the metal ionization degree with the example of Cu sputtering. In a second part of the article, it is shown how to measure the absolute densities of N- and O-atoms by NO titration in flowing N2 and O2 post-discharges, with applications to the activation of elastomers and to the sterilization of oral bacteria. In a chosen N2–O2 flowing microwave post-discharge, it has been obtained a decrease of 12 log (when 6 log is necessary for sterilization) for E. coli bacteria after a treatment time of 15 min.
Keywords: Post-discharges; Cathode magnetron sputtering; Emission spectroscopy;

Two-dimensional images of optical emission intensities from plasmas, captured by an intensified charge coupled device (ICCD) camera at the viewing window of a plasma chamber, could be interpreted as the spatial distributions of excited species or ions. We report the use of ICCD images for the optical emission study of a pulsed D.C. plasma for TiN coatings by an unbalanced magnetron sputtering. The images through specific pass filters discerned the differences of the optical emission distribution of corresponding species. The Abel inversion was performed to convert the line-integrated intensity values, measured by ICCD, to the emissivity data. For the calibration of intensity measurement with an ICCD, the ratio of heights among the peaks in a spectral graph measured by a monochromator was used as the reference data. Especially the comparison between N2 and Ti emission images of the region near the substrate surface is noticeable. The significant increase in the ratio of N2 to Ti intensity with increasing nitrogen gas flow rate implied the transition of deposition mode.
Keywords: Spatially resolved optical emission; Pulsed D.C. plasma; TiN deposition; Unbalanced magnetron sputtering; Abel inversion;

Characterization of hydrogen plasma with a fiber optics catalytic probe by U. Cvelbar; M. Mozetič; I. Poberaj; D. Babič; A. Ricard (12-16).
The most important parameter in reactive hydrogen plasma is the density of neutral hydrogen atoms. The density can be measured by different means including a variety of optical emission and absorption spectroscopy methods, titration and catalytic probes. Recently, it was shown that catalytic probes have some advantages over the other methods. The main advantage is the ability for real time measurement of the atom density. A catalytic probe was used to measure the H density in an afterglow of a plasma reactor. Plasma was created in a mixture of argon and hydrogen. At a constant H2 and Ar flow rates, the H density was found to increase with increasing power. At a low concentration of hydrogen in the gas mixture, saturation in the H density was observed. The lower the hydrogen concentration the lower the power at which the saturation was observed. At high hydrogen concentrations, no H saturation was observed. The results were explained with collision phenomena in ionized gases and heterogeneous recombination of H atoms on surfaces.
Keywords: Hydrogen plasma; Plasma characterization; H density; Catalytic probe; FOCP;

We present a computational study on the plasma generation and film deposition in a circular type DC magnetron sputtering system. Design optimization of a large-area magnetron sputtering system needs a precise multi-scale simulation considering a target erosion by magnetron plasma, a macrofilm deposition by collisional transport, and a micro-deposition topography by collisionless transport. Our multi-scale simulation consists of particle-in-cell and Monte Carlo collision method (PIC-MCC) magnetron plasma simulation and Monte Carlo macro/microfilm deposition simulation. Thompson energy distribution and cosine angular distribution are used for the kinetic energy distribution and for the angular flux distribution of the sputtered atoms, respectively. A variable hard sphere (VHS) model is used to calculate the collision cross section of sputtered atoms and an equi-volume rate model (EVRM) is used to represent evolving film surface.The target erosion profiles are expected from the ion current density distribution on the sputter target simulated by two-dimensional PIC-MCC magnetron plasma simulator, and these profiles are compared with the experimental results. We present a discussion about the optimum detection range for the quasi-steady state of magnetron plasma in PIC-MCC simulation. Macro/microfilm deposition simulator predicts the macrofilm uniformity over the wafer and the micro-deposition topography in the micro-holes. Finally, we present a new algorithm, which can generate an asymmetric angular flux distribution, based on Monte Carlo method for microfilm deposition simulation.
Keywords: Computer simulation; Particle-in-cell; Monte Carlo collision; Plasma processing and deposition; Sputtering;

Interaction of a plasma with a hole on a solid wall bounding that plasma was investigated by measuring the energy and angular distribution of ions extracted through a hole in contact with a high density deuterium plasma. Experiments were conducted by varying the ratio of the hole diameter to the sheath thickness (d/l) and the hole aspect ratio. In contrast to reported studies, holes with diameter larger than as well as smaller than the local sheath thickness were used. At one extreme, when d/l≪1, the plasma was not perturbed by the presence of the hole. The ion energy distribution (IED) had multiple peaks and the ion angular distribution (IAD) was Gaussian, peaking at zero angle with respect to the surface normal. At the other extreme, when d/l≫1, the plasma “leaked” through the hole. The IED had a single peak with a shoulder and the IAD was quite broad extending up to 30° off normal. The IAD was not affected by varying power and pressure suggesting that the plasma leaked completely out of the hole. When d/l≈1, the shape of the IED and IAD was in-between the two extremes mentioned above.
Keywords: Plasma molding; Sheath; Ion energy distribution; Ion angular distribution;

We have investigated and compared the characteristics of Ru etching by employing O2/Cl2 inductively coupled plasma (ICP) and helicon plasma. We have studied the variation of Ru etch rate and the Ru to SiO2 etch selectivity with varying the gas flow ratio, the bias power, and the total gas flow rate. With optimizing the process for two different plasma sources, we have obtained higher etch rate of Ru electrode by using ICP, compared to by using helicon plasma. We demonstrated the etching slope of greater than 85° in terms of real pattern, using ICP. X-ray photoelectron spectroscopy (XPS) revealed that the Ru surface etched using ICP contained less amount of O element than using helicon plasma.
Keywords: Etching; Ruthenium; Plasma processing and deposition;

Ar cluster was generated by an adiabatic expansion using a converging–diverging Laval nozzle at the pressure 5–7 bar and at room temperature. The size distribution of the cluster was estimated by a time-of-flight (TOF) spectroscopy and the mean size of the cluster at 5 bar was about 500 molecules. Ar cluster was ionized by electron impact and then irradiated on Si(100) and GaAs(100) semiconductor crystal surfaces at the very low fluence to investigate the interaction of cluster with the solid surface. From the isolated cluster impact at the acceleration 15–25 keV, nanoprotrusion with a few tens and hundreds of nanometer diameter and a few nanometer height was observed. This formation of out-grown nano-structure instead of inward crater is predicted due to the increase of the local pressure up to 10–100 GPa and local heating 104–105 K in ps by an impingement of cluster ion beam and re-bounce of liquid medium from the solid and subsequently quenching effect. In addition, the change of Si (100) surface roughness was investigated with the variations of Ar cluster ion dose, and from which phenomenological ESE model of cluster ion impact with solid surface, i.e., surface embossment(E), surface sputtering/smoothing(S), and surface etching(E), is proposed to happen in sequence.
Keywords: Cluster; Laval nozzle; Time-of-flight; Isolated cluster impact; Nanoprotrusion; Crater; Surface roughness; Ion dose; Surface embossment; Surface sputtering/smoothing; Surface etching;

Fabrication of Si nano-pillar array through Ni nano-dot mask using inductively coupled plasma by Mun Ja Kim; Jin Seung Lee; Seong Kyu Kim; G.Y. Yeom; Ji-Beom Yoo; Chong-Yun Park (41-44).
We formed Si nano-pillar array using inductively coupled plasma (ICP) etching of Si with Ni nano-dot mask. For the formation of Ni nano-dot mask, Ni was deposited on Si substrate using sputtering. Through rapid thermal annealing (RTA) of Ni layer at 700 °C, Ni nano-dot array was formed on Si substrate. Effects of etching parameters such as rf power, bias voltage and gas composition on the morphologies of Si nano-pillar array were investigated. Optimum etching of Si with Ni nano-dot mask was obtained under the bias voltage of −90 V, power of 1500 W and gas composition of CF4 (70%) and sulfur hexafluoride (SF6; 30%). Si nano-pillar array with a diameter smaller than 50 nm and aspect ratio larger than 10 was formed.
Keywords: Si nano-pillar; Ni nano-dot; Photonic crystal;

Self-organized lamellar structured tantalum–nitride by UHV unbalanced-magnetron sputtering by G.R. Lee; J.J. Lee; C.S. Shin; I. Petrov; J.E. Greene (45-48).
The effect of crystal orientation and microstructure on the mechanical properties of TaN x was investigated. TaN x films were grown on a SiO2 substrate by ultrahigh vacuum unbalanced magnetron sputter deposition in mixed Ar/N2 discharges at 20 mTorr (2.67 Pa) and at 350 °C.Unlike the Ti–N system, in which TiN is the terminal phase, a large number of N-rich phases in the Ta–N system could lead to layers which had self-organized nanosized lamella structure of coherent cubic and hexagonal phases, with a correct choice of nitrogen fraction in the sputtering mixture and ion irradiation energy during growth. The preferred orientations and the microstructure of TaN x layers were controlled by varying incident ion energy E i (=30–50 eV) and nitrogen fractions f N2 (=0.1–0.15). TaN x layers were grown on (0002)-Ti underlayer as a crystallographic template in order to relieve the stress on the films.The structure of the TaN x film transformed from B1-NaCl δ–TaN x to lamellar structured B1-NaCl δ-TaN x + hexagonal ɛ-TaN x or B1-NaCl δ-TaN x +hexagonal γ-TaN x with increasing ion energy at the same nitrogen fraction f N2 . The hardness of the films also increased by the structural change. At the nitrogen fraction of 0.1–0.125, the structure of the TaN x films was changed from δ-TaN x +ɛ-TaN x to δ-TaN x +γ-TaN x with increasing ion energy. However, at the nitrogen fraction of 0.15, the film structure did not change from δ-TaN x +ɛ-TaN x over the whole range of the applied ion energy. The hardness increased significantly from 21.1 to 45.5 GPa with increasing ion energy.
Keywords: TaN; Sputtering; Lamellar; Stress; Hardness;

Formation of fullerene dimers in pair-ion plasma by W. Oohara; H. Iwata; D. Date; R. Hatakeyama (49-53).
Positive and negative fullerene ions are produced coincidentally with impact ionization and attachment of electrons, and the generation of single pair-ion plasma is achieved. Because negative ions are accelerated by the electric field formed between a cathode and a grounded grid, they collide with positive ions, yielding the collision products as dimers. When the cathode setup is modified, double pair-ion plasmas are generated on each side and are miscible with each other. Both the ions are accelerated in the opposite direction by the electric field formed between two cathodes which can be diversely biased, and collide with each other, yielding effectively the collision products. This novel method without catalysts or nonallotropic fullerene derivatives has prospects of mass production of fullerene-fusion materials.
Keywords: Pair-ion plasma; Fullerene; Dimer; Mass production;

Characteristics of RuO2–SnO2 nanocrystalline-embedded amorphous electrode for thin film microsupercapacitors by Han-Ki Kim; Sun-Hee Choi; Young Soo Yoon; Sung-Yong Chang; Young-Woo Ok; Tae-Yeon Seong (54-57).
The characteristics of RuO2–SnO2 nanocrystalline-embedded amorphous electrode, grown by DC reactive sputtering, was investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM), and transmission electron diffraction (TED) examination results showed that Sn and Ru metal cosputtered electrode in O2/Ar ambient have RuO2–SnO2 nanocrystallines in an amorphous oxide matrix. It is shown that the cyclic voltammorgram (CV) result of the RuO2–SnO2 nanocrystalline-embedded amorphous film in 0.5 M H2SO4 liquid electrolyte is similar to a bulk-type supercapacitor behavior with a specific capacitance of 62.2 mF/cm2 μm. This suggests that the RuO2–SnO2 nanocrystalline-embedded amorphous film can be employed in hybrid all-solid state energy storage devises as an electrode of supercapacitor.
Keywords: RuO2; SnO2; Nanocrystalline; Capacitance; Supercapacitor;

Electromigration is now a primary concern regarding reliability of ultralarge scale integrated circuits (ULSI) because of increasing current density in miniatured devices. Effects of rapid thermal annealing (RTA) treatment on the microstructural parameters on the electromigration resistance of electroplated Cu films were determined using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis techniques. Also electron backscattered diffraction (EBSD) patterns were used to characterize the texture of the Cu thin films.It has been found that the electromigration resistance of the electroplated Cu film is enhanced with increasing the annealing temperature in the temperature range from 200 to 500 °C. Nitrogen is more favorable than vacuum as RTA atmosphere since nitrogen atmosphere offers lower resistivity and smoother film surface. Also the dependence of the bamboo structure on the annealing temperature and the line width of the Cu interconnect is discussed. If the line width is a quarter micron, a bamboo structure will be obtained by the RTA treatment at temperatures higher than 500 °C. On the other hand, if it is less than 0.1 μm, RTA at any temperature above 200 °C will result in the bamboo structure.
Keywords: Electroplated copper; Rapid thermal annealing (RTA); Electromigration; Grain size; Preferred orientation;

Reduction of TiO2 assisted by a microwave plasma at atmospheric pressure by S. Huet; T. Belmonte; J.M. Thiébaut; S. Bockel; H. Michel (63-67).
The reduction of rutile-TiO2 thin foils by microwave plasma created in a resonant cavity at atmospheric pressure gives a TiO/Ti2O3/Ti3O5 sequence at 973 K for a 5%H2–He mixture. The efficiency of the reduction process is strongly affected by a slight change of the gas composition. The intensity of the Hα transition measured by optical emission spectroscopy was used to determine experimental conditions where the temperature of the substrate could be adjusted between 980 and 1090 K without changing the hydrogen concentration close to the surface substrate. In these conditions, no titanium layer could be detected by grazing angle X-ray diffraction. A TiO/Ti2O3 sequence is observed with an anatase–rutile transition that occurs above a treatment temperature of 1020 K. The overall reduction rate is close to 1 μm h−1 under the chosen conditions. The evolution of the thickness of the Ti2O3 layer below 1060 K demonstrates that the deoxidation mechanism is not simply related to the atomic hydrogen concentration in the gas phase.
Keywords: Surface treatment; Atmospheric pressure plasma; Titanium dioxide reduction;

Technologies for flexible electronics have been developed to make electronic or microelectromechanical (MEMS) devices on inexpensive and flexible organic substrates. In order to fabricate the interconnect lines between device elements or layers in flexible electronic devices, metallization on the flexible substrate is essential. In this case, the width and conductivity of metallization line are very important for minimizing the size of device. Therefore, the realization of metallization process with the scale of a few micrometers on the flexible substrate is required. In this work, micro-scale metallization lines of Cu were fabricated on the flexible substrate by electroplating using the patterned mask of a negative-tone SU-8 photoresist. Polyimide surface was treated by O2/Ar atmospheric plasma for the improvement in adhesion between Cr layer and polyimide and in situ sputter deposition of 100-nm-thick Cu seed layers on the sputter-deposited 50-nm-thick Cr adhesion layer was followed. SU-8 photoresist was spin-coated and patterned by photolithography. Electroplating of Cu line, removal of SU-8, and selective wet etch of Cr adhesion and Cu seed layers were carried out. Gap between the Cu lines was successfully filled by spin-coating of polyimide. Micro-scale Cu metal lines with gap filling on the polyimide substrate with a thickness of 6–12 μm and an aspect ratio of 1–3 were successfully fabricated.
Keywords: Cu metallization; Electroplating; Polyimide; Gap filling; Flexible electronics;

Computational fluid dynamics (CFD) has been extended to the fields of the electric and electronics as well as the mechanics because of increasing of computer power and developing of numerical schemes. The thermal plasma inevitably established by separating the contacts makes a complex interaction with surroundings, it is not easy to analyze the phenomena neither experimentally nor theoretically. Nowadays, the operating energy used to move the contacts is required as low as possible, because it is the key factor to compact the integral system and to increase the reliability. Therefore, it is indispensable to analyze the thermal plasma conditions of circuit breakers using CFD. The thermal plasma characteristics could be obtained with computing flow field and electromagnetic field simultaneously. In this paper, we have simulated the switching process of the thermal expansion SF6 gas circuit breaker (GCB) that is combination of two interruption techniques, the self-expansion by the arc itself and the arc rotation by coils. In order to calculate the governing equations describing the dominant physical processes accurately, the commercial CFD code, PHOENICS, which is customized to allow the inclusion of arc plasma modeling by Fortran subroutines externally has been used. Through this work, we have found that the energy produced by the arc causes the pressure-rise in the chamber during high current period. And as the current falls near current zero, furthermore, the gas flows back from this region over the arc and should extinguish the arc just after current zero. The results have been compared with various dimensions and verified with the measured arc voltage.
Keywords: SF6 Thermal Plasma; Numerical Modeling; CFD; Switching Process;

The effect of SiCl4 additive gas on the Cl-based Al plasma etch procedure by D.W. Kim; M.Y. Jung; Seong S. Choi; J.W. Kim; J.H. Boo (81-85).
The influences of both SiCl4 additive gas and the magnitude of bias voltage on the anisotropic etch profile of aluminum pattern and the deterioration of photoresist (PR) mask layer have been studied by varying etching conditions. Using Cl2 gas as a primary etchant, the ratio of SiCl4 flow rate to Cl2 and the ion energy bombarded onto the surface were changed systematically. When a small amount of additive gas was added, undercut profile in Al layer was not observed even in the lowest bias voltage measured in this experiment. With the optimized etching condition, the PR deterioration usually reported during metal etching was not observed at all, which allows the complete PR strip without any additional process.
Keywords: Chlorine; Anisotropic plasma etching; Ion-assisted physical etching; Bias voltage;

Plasma etching of (Ba,Sr)TiO3 thin films using inductively coupled Cl2/Ar and BCl3/Cl2/Ar plasma by Gwan-Ha Kim; Kyoung-Tae Kim; Dong-Pyo Kim; Chang-Il Kim (86-90).
BST thin films were etched with inductively coupled plasmas. A chemically assisted physical etch of BST was experimentally confirmed by ICP under various gas mixtures. After a 20% addition of BCl3 to the Cl2/Ar mixture, resulting in an increased the chemical effect. As increases of RF power and substrate power, and decrease of working pressure, the ion energy flux and chlorine atoms density increased. The maximum etch rate of the BST thin films was 90.1 nm/min, and at the RF power, substrate power, and working pressure were 700 W, 300 W, and 1.6 Pa, respectively. It was proposed that sputter etching is dominant etching mechanism while the contribution of chemical reaction is relatively low due to low volatility of etching products.
Keywords: ICP; (Ba,Sr)TiO3; Etching; OES; Langmuir probe;

Spatially resolved optical emission spectroscopy of pulse magnetron sputtering discharge by Yong M. Kim; Min J. Jung; Soo G. Oh; Jeon G. Han (91-96).
The spatially resolved optical emission spectroscopy of various species of a pulse DC unbalanced magnetron sputtering is studied. Ar–N2 gas mixtures are used. Emission lines corresponding to titanium cathode and gas discharge species are considered. In this study, the two-dimensional (2-D) emission profiles of the lines are measured by an ICCD camera during TiN coatings. It turns out that the 2-D emission profiles of the various lines behave differently. As a result, we obtained the surface roughness value of RMS 2.3 nm at higher pulse frequency and 3.8 nm at lower pulse duty cycle.
Keywords: Pulsed plasma; Reactive magnetron sputtering; Spatially resolved OES;

Strain effect on dielectric property of SrTiO3 lattice: first-principles study by Leejun Kim; Juho Kim; Donggeun Jung; Jaichan Lee (97-101).
We performed first-principles calculations and obtained information on dielectric response and zone center optical phonon of strained SrTiO3. The dielectric response and zone center optical phonon of SrTiO3 lattice under a strained state are calculated by density functional theory within the local density approximation. After the structural analysis SrTiO3 lattice, the zone center optical phonon frequency was calculated by the frozen phonon method. The first-principles calculation showed that lattice distortion strongly affects the lattice dynamic property (e.g., optical phonon) and dielectric property of the strained SrTiO3 lattice. As the SrTiO3 lattice was progressively distorted from unstrained state to c/a=0.985, the optical phonon frequency was softened. As a result, the dielectric constant increased and reached 960. When the SrTiO3 layer was deformed further over c/a=0.985, the dielectric constant decreased again. Therefore, the first-principles calculation showed that a maximum dielectric constant exists at a certain degree of lattice distortion (c/a=0.985), which leads to good agreement with experimental results (i.e., the dielectric behavior of strained SrTiO3 lattice).
Keywords: SrTiO3; Artificial lattice; Strain; First-principles calculation; Optical phonon; Börn effective charge; Dielectric constant;

In reactive sputtering, the introduction of reactive gas would create a hysteresis transition from metal to compound mode in both the target and the substrate. The hysteresis transition is characterized by a sudden change in partial pressure, sputtering rate and fraction of compound formation, etc. Therefore, the stability is an important issue of process control. In this paper, a mathematical model with variable sticking coefficients based on surface kinetics is introduced to study the process stability. The variable sticking coefficient represents different mechanisms for surface reactions from the type of Langmuir to precursors. To facilitate the analysis, several nondimensional parameters are introduced and used for formulation. Results show that, when the chemical reaction on a substrate is moderate, a higher sputtering yield of the compound leads to a more stable steady-state at lower inflow rates. However, when the ratio of sputtering yield (compound/metal) is zero, there is no hysteresis transition because of the deposition of pure metal (single phase) on the substrate. For different sticking mechanisms, the precursor type is found to make the surface easier to saturate with compound due to its higher default sticking coefficient and the lower pressure and inflow rate for the hysteresis transition.
Keywords: Reactive sputtering; Langmuir kinetics; Sticking coefficient; Stability; Hysteresis;

Fluorinated amorphous carbon films were deposited on a p-type silicon substrate by using an inductively coupled plasma chemical vapor deposition with mixture of carbon tetrafluoride and methane gases. The structural properties of fluorinated amorphous carbon films as a diamond-like carbon were studied by Raman spectra, Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra as a function of the flow rate ratio of precursors. The variation of the fluorine contents of fluorinated amorphous carbon films was investigated by X-ray photoelectron spectroscopy. From these chemical results, the correlation between the dielectric constant and the variation of the bonding structure as a function of the flow rate ratio was researched.
Keywords: Low-k materials; a-C:F films; Diamond-like carbon; Resonance effect; Inductive effect; Diels–Alder reaction;

Planar magnetron (PM) power and ICP-RF power dependences of the optical emission intensities of excited atomic and ionic species in the reactive ionized sputter-deposition of magnesium oxide (MgO) thin films were investigated. With the increase in PM power at constant ICP-RF power, Mg I emission intensity increased and Ar I emission intensity gradually decreased. With the increase in ICP-RF power at constant PM power, the Mg I emission intensity increased at lower ICP-RF power and then gradually decreased at higher ICP-RF power; on the contrary, Ar I emission intensity monotonically increased. Emission intensity of atomic oxygen was negligibly small compared with those of Mg I and Ar I under the metallic sputtering mode condition.
Keywords: Inductively coupled plasma; Sputtering; Magnesium oxide; Optical emission;

A fluid model including an electron beam of hot electrons is presented and used to describe the transport of charged particles in a 13.56-MHz O2 plasma. An increase in the electron density when the RF power increases is observed from Langmuir probe measurements. The calculated evolution of the electron number density shows a reasonable agreement if the secondary emission coefficient is chosen equal to 10−4 on a steel (316L) electrode. The values of the plasma potential increase with increasing RF power from 30 to 35 V at 0.5–0.6 Torr, in the range 100–300 W. Surprisingly, the electron temperature decreases with increasing applied RF power. No clear explanation for this behavior is available yet.
Keywords: Plasma modeling; Langmuir probes; Radiofrequency; Oxygen plasma;

Influence of electrode size on the generation of low-pressure coaxial ECR microplasmas by M. Kumamoto; H. Inoue; M. Matsushita; H. Fujiyama (124-127).
Electrode structure and size are the most important factors, as much as the operating pressure is, in the generation of low-pressure coaxial electron cyclotron resonance (ECR) microplasmas. The experimental results will be presented showing the influence of these on the generation of low-pressure coaxial ECR microplasmas. The discharge conditions for various magnetic field were investigated in three types of coaxial electrodes when the gap length was fixed to 3.5 mm. With increasing magnetic field, a breakdown occurred at the “breakdown magnetic field” and vanished at the “maximum trapping magnetic field”. Comparing the plasma discharge region of the three types of coaxial electrodes, it was found that microplasma generation is easier for an electrode with a longer axial length of plasma generation point and a shorter inner electrode radius because initial electrons can be confined axially. Furthermore, the surface electric field strength of the inner electrode with shorter radius is stronger.
Keywords: Breakdown magnetic field; Maximum trapping magnetic field; Plasma discharge region;

Oxidation of the hydrogen terminated silicon surfaces by oxygen plasma investigated by in-situ infrared spectroscopy by Masanori Shinohara; Teruaki Katagiri; Keitaro Iwatsuji; Yoshinobu Matsuda; Hiroshi Fujiyama; Yasuo Kimura; Michio Niwano (128-132).
We have investigated oxidation process of hydrogen terminated Si surfaces by oxygen plasma using infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry. We have measured IRAS spectra in the Si–H stretching vibration regions of the hydrogen-fluoride acid (HF) treated Si surface and the hydrogen (H) plasma treated Si(100) surface during the oxygen plasma exposure in order to elucidate a plasma oxidation process. IRAS data demonstrated that the densities of hydride species rapidly decrease on the HF-treated surface by the oxygen plasma exposure; on the other hand, they slowly decrease on the H-plasma treated surface by the exposure. IRAS data also demonstrated that dihydride (SiH2) species are more rapidly removed on the HF-treated surface by the oxygen plasma exposure than monoohydride (SiH) species. More hydride species are left on the H-plasma treated surface after the exposure to oxygen plasma than on the HF-treated surface because the H-plasma treatment makes Si surfaces rougher and more hydrogen insert into the subsurface regions than the HF treatment does. Oxygen plasma is hard to oxidize the H-plasma treated surface compared with the HF-treated surface.
Keywords: Oxygen plasma; Si(100) surface; Infrared absorption spectroscopy; Hydride species;

Spectro-ellipsometric studies of Au/SiO2 nanocomposite films by Sunghun Cho; H. Lim; K.S. Lee; T.S. Lee; B. Cheong; W.M. Kim; Soonil Lee (133-138).
Au/SiO2 nanocomposite films in which Au nanoparticles were embedded in SiO2 matrix were fabricated via alternating sputtering of SiO2 and Au layers. In particular, we kept the nominal thickness of the Au layers below the threshold for the continuous layer formation whereas that of SiO2 layers was sufficient to form continuous layers. Transmission electron microscopy (TEM) images revealed that the Au nanoparticles were spherical in shape and that their average size was linearly proportional to the nominal thickness of Au layers. To account for the absorption variation of the composite films, including the absorption peak around 530 nm due to the surface plasmon resonance (SPR), we used Maxwell–Garnett effective medium theory (EMT) together with the modified Drude model. As it turned out, the combination of the modified Maxwell–Garnett effective medium theory and the aforementioned modification of the Drude model, which took the size of Au nanoparticles into consideration, were sufficient to model the variable–angle spectroscopic ellipsometry spectra. The values of the fitting parameters, such as film thickness, volume fraction of Au, and the diameter of Au nanoparticles, extracted from the modeling procedure were in good agreement with the results of TEM and spectrophotometer measurements.
Keywords: Nanocomposite film; Alternating sputtering; Optical property; Surface plasmon resonance;

We investigated the effects of charge trapping on the asymmetrical increase in the memory window of metal–ferroelectric–insulator–semiconductor (MFIS) devices. We suggest that defect centers located at the ferroelectric–insulator interface play important roles in generating the asymmetrical increase in the memory window: Electron trapping at/near the SBN (or SBT)–Y2O3 interface via avalanche electron injection from the Si substrate results in the preferential domain switching, causing the asymmetrical increase in the memory window.
Keywords: Nonvolatile memory; MFIS; SBN; SBT; Y2O3; Charge trapping;

Deposition behaviors of Ti films on a sharp tip were examined by a computer simulation using two modules: the conventional physical vapor deposition (PVD) and ionized PVD modules in PVD-Pro 3.2. The modeling results of Ti film growth on a sharp tip through the conventional PVD showed that as the process parameters of target–substrate distance, Ar gas pressure and input power were changed, the energy of sputtered particles was changed but the film morphology on the sharp tip was hardly controlled. The results for the ionized PVD modeled as a function of the ion-to-neutral flux ratio and incident energy showed that the most influential factor for the film deposition during ionized PVD was ion-to-neutral ratio and the morphology of Ti films on the sharp tip was controllable with increasing the directionality of depositing particles.
Keywords: Computer simulation; Ionized physical vapor deposition; Sputter deposition; Sharp tip; Ti thin film;

The effect of the CH4 plasma treatment on deposited SiOC(–H) films with low dielectric constant prepared by using TMS/O2 PECVD by Chang Sil Yang; Young Hun Yu; Heon-Ju Lee; Kwang-Man Lee; Chi Kyu Choi (150-154).
The low dielectric SiOC(–H) films can be damaged by oxygen plasma during photoresist stripping. In this work, we have studied the CH4 plasma treatment to improve the characteristics of the SiOC(–H) film. Posttreated SiOC(–H) film in CH4 plasma showed the decreased leakage current density of 1 A/cm2, which was lower two to three orders of magnitude than that of nontreated SiOC(–H) film. Unlike the nontreated SiOC(–H) films, Fourier transform infrared (FT-IR) absorbance spectrum of posttreated SiOC(–H) film remained almost unchanged after O2 ashing. The dielectric constant of the treated SiOC(–H) film also did not change much. The CH4 plasma treatment can provide additional hydrogen and carbon to passivate the inner structure of SiOC(–H) films. Therefore, the properties of SiOC(–H) films are significantly enhanced by CH4 plasma treatment.
Keywords: Low-k; O2 ashing; Plasma treatment; Breakdown voltage;

TiO2 thin films were prepared by using a reactive DC magnetron sputtering method with Ar ion-beam assistance. The effect of the Ar ion-beam current on the structural and optical properties of the reactive magnetron sputtered TiO2 thin films was studied. The as-deposited films were subjected to annealing with the atmospheric environment, and the change of film properties after annealing was investigated. When the Ar ion-beam assistance was applied, the deposited TiO2 thin films were found to induce a higher deposition rate, a higher packing density and refractive index, a lower extinction coefficient, and a smoother surface than that of the film deposited without ion-beam assistance. The structures of all as-deposited films were amorphous. In the annealing process, the ion-beam-assisted TiO2 thin films had a phase transition from amorphous to anatase polycrystalline with a strong TiO2 anatase (101) peak at a temperature of 400 °C. At above 400 °C, the refractive index of deposited films increased by an anatase structure and the extinction coefficient increased due to a reduction in the oxidation of TiO2 thin films.
Keywords: Ion-beam deposition; DC; Magnetron; Reactive sputtering; Titanium oxide;

Structural and electrical characteristics of R.F. magnetron sputtered ZnO films by D.J. Kang; J.S. Kim; S.W. Jeong; Y. Roh; S.H. Jeong; J.H. Boo (160-165).
We investigated the effects of both bottom electrodes and processing parameters on the physical and electrical properties of ZnO films deposited by R.F. magnetron sputtering. We found that the preferential c-axis growth of deposited ZnO films depends on the type of bottom electrode: Both Al and Au bottom electrodes enhance the growth of c-axis orientation in ZnO films, while no clear evidence for any preferential growth was observed in case of Cu and Si. The resistivity of ZnO films deposited on Au and Al bottom electrodes was greater than 106 Ω cm. The ranges of dielectric constant of Al/ZnO and Au/ZnO samples were 8–14 and 13–16, respectively. Dissipation factors change from 0.02 to 0.05. In general, as c-axis orientation enhances, dielectric constant and dissipation factor increase and decrease, respectively.
Keywords: ZnO thin films; c-axis orientation; FBAR;

Characterization of BLT thin films using MgO buffer layer for MFIS-FET by Kyoung-Tae Kim; Jung-Mi Lee; Sang-Hun Song; Chang-Il Kim (166-170).
The BLT thin film and MgO buffer layer were fabricated using a metalorganic decomposition method and the DC sputtering technique. The MgO thin film was deposited as a buffer layer on SiO2/Si and Bi3.25La0.75Ti3O12 (BLT) thin films were used as a ferroelectric layer. The electrical of the metal ferroelectric insulator semiconductor (MFIS) structure were investigated by varying the MgO layer thickness. Transmission electron microscopy (TEM) shows no interdiffusion and reaction that suppressed by using the MgO film as a buffer layer. The width of the memory window in the CV curves for the MFIS structure decreased with increasing thickness of the MgO layer. Leakage current density decreased by about three orders of magnitude after using MgO buffer layer. The results show that the BLT and MgO-based MFIS structure is suitable for non-volatile memory FETs with large memory window.
Keywords: MFIS; BLT; MgO; Memory window;

We have synthesized the titanium dioxide (TiO2) powders with the similar structure as a commercially available Degussa P-25 TiO2 powder for TiO2-based photocatalysts. To improve the photocatalytic activity, electronic modification on the TiO2-based photocatalysts by chemical solution deposition (CSD) coating was also carried out with metal oxides such as Fe2O3 and Al2O3. The structural and compositional changes as well as optical characteristics are mainly investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy, and ellipsometry measurements. In addition, electron spin resonance (ESR) studies have also been carried out to verify the existence of paramagnetic species such as OH and H2O radicals on UV-irradiated TiO2-based photocatalysts. ESR data showed that the hydroxy radicals could decompose organic pollutants into harmless products because they have high oxidizing power. From the reduction test of nitrobenzene, it is found that the photocatalytic effect of TiO2-based photocatalysts coated with Fe2O3 is twice better than that of commercially available noncoated TiO2 photocatalysts. In the case of photocatalytic oxidation reaction of phenol under UV irradiation, moreover, the experimental results showed a consistency with ESR data indicating that TiO2 coated with metal oxides would be one of the most effective photocatalysts.
Keywords: TiO2-based photocatalysts; Surface modification; Chemical solution deposition; Photocatalytic reduction–oxidation reaction; Electron spin resonance analysis;

The production of large volume fluorocarbon plasmas by surface-wave at high pressure (200–3600 Pa) has been achieved. To this end, a microwave launcher made of slot antennae and of an air layer between the antennae and the quartz plate has been used. The influence of the shape of the antennae and of the thickness of the air layer has been studied in terms of homogeneity of the plasma on the quartz plate, as the applied power was varied, and simple models allowed for the understanding of the observed trends.For the configuration enabling the best balance between pressure and homogeneity, fluorocarbon polymer films have been deposited on silicon substrates for different reactive gas mixtures (CF4+C4F8) in argon. The water-repellency property of the deposited polymer films has been determined by contact angle measurements, and linked to observations of the gas phase by OES measurements in the visible spectral range. The absence of film when pure CF4 was used as a reactive gas is explained by the presence of oxygen in the discharge, which is probably released in the gas phase through etching of the quartz plate.
Keywords: PACVD; Fluorocarbon plasma; Microwave; Slot antenna; Water repellency;

Titanium dioxide (TiO2) thin films were successfully grown on Si(100) and micro cover glass substrates using radio frequency (RF) magnetron sputtering. Highly oriented, crack-free, stoichiometric polycrystalline rutile TiO2 thin film was obtained after annealing at 1000 °C for 1 h. The maximum UV-visible transmittance and hardness of the film were over 90% and 1700 HK0.025, respectively. Different contact angles and crystal growth directions were observed with the various deposition parameters such as annealing temperature, RF power magnitude, and added O2 amounts. These differences were dependent on a phase transition from anatase to rutile phases, reflecting the changes of the crystal structure. In this study, moreover, we found that the transmittance and hardness of the TiO2 thin films were strongly influenced by both the film thickness and the surface roughness. The growth rate was also increased with increasing RF power up to 150 W, and the maximum growth rate observed at 150 W was 1500 nm/h. The most optimum deposition condition for TiO2 thin film growth was determined to be 80 W of RF power, 1000 °C of annealing temperature, 1 h of deposition time, and 30 sccm of O2.
Keywords: TiO2 thin film; RF magnetron sputtering; Phase transition; Deposition parameter effects;

Nanofabrication of InGaAsP periodic 2D columns with square and hexagonal lattices by reactive ion etching by Ji-Myon Lee; Su Hwan Oh; Chul-Wook Lee; Hyunsung Ko; Sahnggi Park; Ki Soo Kim; Moon-Ho Park (189-193).
Two-dimensionally arrayed nanocolumns were fabricated by using a double-exposure laser holography method. The hexagonal lattice was formed by rotating the sample with 60° while the square lattice by 90° before the second laser exposure. The size and period of nanocolumns could be controlled accurately from 80 to 150 nm in diameter and 220 to 450 nm in period for square lattice by changing the incident angle of laser beam. The reactive ion etching (RIE) for a typical time of 30 min using CH4/H2 plasma enhanced the aspect ratio by more than 1.5 with a slight increase of the bottom width of columns. Furthermore, it was observed that a wet etching after reactive ion etching enhanced the photoluminescence intensity of nanocolumns due to the removal of sidewall damage.
Keywords: Photonic crystal; Laser holography; RIE; Damage; Surface lattice;

Surface pretreatment of the underlying film to enhance Ru nucleation is essential in molecular organic chemical vapor deposition (MOCVD) of Ru. In the present work, effects of argon plasma, hydrogen plasma, and palladium sputtering treatments of the Ta–Si–N film surface on Ru nucleation in Ru MOCVD were investigated using scanning electron microscopy (SEM) and Auger electron emission spectrometry (AES) analyses. It was found from the analysis results that palladium sputtering treatment is the most efficient, argon plasma treatment is the next, and hydrogen plasma treatment is the third in enhancing Ru nucleation. Also, the mechanism through which Ru nucleation is enhanced by these pretreatments and why the nucleation enhancing efficiencies of these three pretreatments are different are discussed.
Keywords: Ru MOCVD; Nucleation enhancement plasma treatment; Pd sputtering;

Growth of carbon nitride using microwave plasma CVD by Yukihiro Sakamoto; Matsufumi Takaya (198-201).
An investigation was carried out on the effect of the varying CH4 concentration for the synthesis of carbon nitride using microwave plasma CVD from CH4–N2 gas mixture.Crystalline particles were observed for 1% CH4 concentration. The deposit changed to a film covered with whiskers for 10% CH4 concentration. The composition calculated from the AES spectrum of the deposit at 1% CH4 concentration indicated a nitrogen concentration of 57.5%. In the XRD pattern of the deposit at 1% CH4 concentration, the peaks of α-C3N4 (301), (401) planes were observed. No Raman peak of carbon was observed in Raman spectrum of the deposit for 1% CH4 concentration. C–N and C=N bonded structures were observed in the XPS spectra.
Keywords: Carbon nitride; Microwave; Plasma; CVD; DLC; Crystalline;

Thin films of tantalum nitride (TaN) were deposited on SKD11 tool steel substrate by a D.C. magnetron sputtering system. The influence of the N2/Ar gas ratio of the inlet gases on the structure, hardness, adhesion and wear resistance was investigated. The X-ray diffraction data showed that TaN deposited at low N2/Ar gas ratio, tetragonal β-Ta(330) and hexagonal TaN(101) were observed. Orthorhombic TaN(110) and orthorhombic Ta3N5 were formed with the increase of the N2/Ar gas ratio. High hardness of the films was observed at the low N2/Ar gas ratio. The films deposited at N2/Ar gas ratio of 0.3 showed good adhesion, wear resistance and hardness of Hv0.05 1450. The films deposited with etching time of 30 min at 133.32 Pa gave good adhesion. Thickness of the films decreased with applying the bias voltage. As the bias potential was increased, the hardness of the film increased and then decreased. The films with fine dome structure showed good wear resistance.
Keywords: TaN; D.C. magnetron sputtering; Wear resistance; Adhesion;

Reactive magnetron sputtering of thin films: present status and trends by J. Musil; P. Baroch; J. Vlček; K.H. Nam; J.G. Han (208-218).
This paper gives a critical review of the present state of the knowledge in the field of dc reactive magnetron sputtering of compound films. It analyses (i) the hysteresis effect and the methods of its elimination, (ii) problem of stability of reactive sputtering and (iii) deposition of transparent oxides in the transition mode of sputtering. It shows the conditions under which oxides are reactively sputtered with high deposition rates a D oxide achieving up to approximately 77% of that of a pure metal a D Me, i.e. a D oxide/a D Me≈0.77. A special attention is devoted to the elimination of arcing in sputtering of insulating films using pulsed dual magnetron or sputtering of oxides from a substoichiometric target. Also, the ion bombardment of films growing on insulating or unbiased substrates in dc pulsed magnetron sputtering is discussed in detail. As an example, a new possibility to form superhard single-phase films based on solid solutions using dc reactive magnetron sputtering is shown. At the end, future trends in dc reactive magnetron sputtering are outlined.
Keywords: DC continuous and pulsed reactive magnetron sputtering; Compounds; Deposition rate; Nanocomposites; Film properties;

Influence of the bias voltage on the structure and the tribological performance of nanoscale multilayer C/Cr PVD coatings by Y.N. Kok; P.Eh. Hovsepian; Q. Luo; D.B. Lewis; J.G. Wen; I. Petrov (219-226).
Nanoscale multilayer C/Cr coatings have been deposited by utilising the combined steered cathodic arc/unbalanced magnetron sputtering technique. The coating microstructure and tribological performance have been investigated as a function of the bias voltage, ranging from U b=−65 to −350 V. The XRD results revealed that C/Cr coatings are amorphous at low U b, but became more crystalline when the U b increased to −350 V. High-resolution XTEM analysis indicated coating densification and smoothening as well as formation of novel amorphous nanostructure, in which carbon-rich clusters are surrounded by a Cr-rich matrix, leading to the formation of self-organised multilayer structure as the bias voltage was increased from −65 to −350 V. An increase of the bias voltage from −65 to −350 V resulted in an increase in the hardness from 8 to 25 GPa and Young's modulus, E from 186 to 319 GPa. A pin-on-disc test showed that the friction coefficient was reduced from 0.22 to 0.16 when the bias voltage was increased from −65 to −95 V. However, a further increase in the bias voltage to −350 V led to an increase in the friction coefficient to 0.31. The lowest wear coefficient K c∼6.25×10−17 m3 N−1 m−1 was achieved at U b=−120 V. Standard HSS drills, 8 mm in diameter, coated with C/Cr have been tested using solution annealed AISI 304 stainless steel as the work piece material. An improvement of the lifetime by a factor of ∼9 has been achieved as compared to the uncoated tools. In this test, the C/Cr coating outperformed a number of commercially available PVD coatings, such as TiCN, TiAlCrN and showed similar performance to TiAlCrYN.
Keywords: Sputtering; C/Cr coating; Bias voltage; Tribology; Microstructure;

RETRACTED: Stability improvement of organic light-emitting diode with aluminum cathode deposited by ion beam assisted deposition method by Soon Moon Jeong; Won Hoi Koo; Sang Hun Choi; Sung Jin Jo; Hong Koo Baik; Se-Jong Lee; Kie Moon Song (227-230).
Reason: This article is part of an extreme case of duplicate publication in which the paper, or nearly identical copies of it, has appeared in at least nine other journals. The authors have acknowledged the abuse, which has also been brought to the attention of the responsible administrators at their institutions. Multiple publication represents a flagrant disregard of international copyright law and scientific ethics, it wastes reviewer's and journal staff time, and is also a very poor use of costly journal space which is explicitly reserved for publishing original work. Thin Solid Films takes a strong view on this matter.

Luminescence of Er-doped amorphous silicon quantum dots by Nae-Man Park; Tae-Youb Kim; Sang Hyeob Kim; Gun Yong Sung; Kwan Sik Cho; Jung H. Shin; Baek-Hyun Kim; Seong-Ju Park; Jung-Kun Lee; Michael Nastasi (231-234).
The role of the size of amorphous silicon quantum dots in the Er luminescence at 1.54 μm was investigated. As the dot size was increased, the Er luminescence intensity was decreased and the temperature quenching was also fast because of the small band gap resulting in the decrease of electron–hole pair energy. Accordingly, the critical dot size, needed to take advantage of the positive effect on Er luminescence, is considered to be about 2.0 nm, below which a small dot is very effective in the efficient luminescence of Er.
Keywords: Er luminescence; A-Si QD; Size effect;

Multilayered thin film structures of Cr–Si have been prepared on top of Al2O3 substrates by RF magnetron sputtering technology, and the electrical and thermodynamic properties of the thin film structures were assessed up to the temperature of 500 °C. The thickness of the Cr–Si film was ranged to about 1 μm, and a post-annealing was carried out to achieve more reliable film structures. In measurements of temperature coefficient of resistance (TCR), chrome-rich films show the metallic properties, whereas silicon-rich films do the semiconductor properties. Optimal composition between chrome and silicon was obtained as 1:2 in the Auger electron spectroscopy analysis, and there is approximately 15% change or less of surface resistance from room temperature to 500 °C. Compared to the conventional heating elements, the thin film heater has additional advantages of extremely low outgassing and high ramping speed in addition to the temperature uniformity.
Keywords: Thin film; Semiconductor processing; Temperature coefficient of resistance; Magnetron sputtering;

The ion beam sputtering deposition is a very promising technique for optical coatings and is an excellent something of the deposition parameters. In this work, the Ta2O5 thin films as the substrate temperature (50–200 °C) were prepared on the silicon wafer (111) and the glass using the single ion-beam sputtering (SIBS) and dual ion-beam sputtering (DIBS). As the substrate temperature increased, the deposition rate of the SIBS and DIBS increased from 1.08 and 1.07 μm to 1.24 and 1.17 μm. The DIBS process at 150 °C deposited films, the refractive index was 2.112. The surface morphologies are found to be improved in the DIBS process and the rms roughness of deposited films was 0.1535 nm, which was smaller than the SIBS (rms=0.1822 nm) process at 150 °C deposited.
Keywords: Dual ion beam sputtering (DIBS); Single ion beam sputtering (SIBS); Ta2O5 thin film; Optical properties;

Nano-oxide layer and magnetic properties in Mn–Ir–Pt-based spin valve multilayers by D.M. Jeon; J.P. Lee; D.H. Lee; S.Y. Yoon; J.H. Kim; D.H. Yoon; S.J. Suh (243-245).
In giant magnetoresistance (MR) spin valve (SV), the thin nano-oxide layer (NOL) has been used for the confinement of conduction electrons, which contributes to spin scattering in film and its interfaces. In this article, we have investigated the effects of NOLs, which were fabricated by a plasma oxidation of Co–Fe layer on the magnetic properties and MR in a Mn–Ir–Pt-based SV. The NOLs were located at the middle of pinned layers and between a free and a metal-capping layer. The adjusted NOL could result in high MR and strong exchange coupling field (H ex). From a high-resolution electron microscopy analysis, the oxide was formed at about 1 nm. For SVs employing an oxide-capping layer, the strong reflectivity at the interface of a free and an oxide-capping layer should lead to the large decrease of an interlayer coupling field, which could possibly improve H ex.
Keywords: Plasma oxidation; Specular spin valve; Giant magnetoresistance; Nano-oxide layer;

Growth and magnetic properties of LPE-grown (EuTbBi)3(FeAlGa)5O12 garnet films by G.Y. Kim; S.G. Yoon; I.S. Chung; S.B. Park; S.J. Suh; D.H. Yoon (246-250).
Using the PbO–B2O3–Bi2O3 flux system, (EuTbBi)3(FeAlGa)5O12 (EuTbIG) films were grown on (GdCa)3(GaMgZr)5O12 (SGGG) substrates for optical devices by the liquid phase epitaxial (LPE) method. The grown films' growth and magnetic domain wall were observed as a function of the Fe2O3/(Al2O3+Ga2O3)(R2) molar ratio by magnetic force microscope (MFM). As the grown films decreased the R2 molar ratio, the saturation magnetization of the grown films showed a tendency to decrease from 250 to 150 Oe. Also, we observed that the R2 molar ratio did not affect the surface morphology and thickness of the grown films, but it did affect the magnetic domain wall.
Keywords: LPE; Fe2O3/(Al2O3+Ga2O3)(R2) molar ratio; Magnetic domain wall; Saturation magnetization;

Characterization of nano-oxide layer in specular spin valve multilayer by D.H. Lee; S.Y. Yoon; J.H. Kim; S.J. Suh (251-255).
To characterize the nano-oxide layer (NOL) in specular spin valve multilayer, naturally oxidized CoFe layer was inserted between pinned CoFe layers. The under-, optimum, and over-oxidized samples were obtained by control of the oxidation time and the oxygen flow rate. The NOL was analyzed to be Fe oxide mainly by X-ray photoelectron spectroscopy (XPS) data. As oxidation increased, the content of Fe oxide and the thickness of the NOL increased and too much thicker NOL was obtained in case of over-oxidation. We concluded that the lower magnetoresistance (MR) ratio and the more slanted magnetization curve than the optimum could be attributed to the Fe oxide as a non-ferromagnetic defect or magnetic discontinuity in case of under-oxidation and the too thick NOL in case of over-oxidation.
Keywords: NOL; MR ratio; XPS; Fe oxide;

Enhancement of ZnO nucleation in ZnO epitaxy by atomic layer epitaxy by Jongmin Lim; Kyoungchul Shin; Hyounwoo Kim; Chongmu Lee (256-261).
Dry cleaning techniques employing argon, oxygen and hydrogen ECR plasma were used, respectively, to remove organic contaminants and native oxides on sapphire and silicon (Si) substrates prior to the growth of the ZnO film by atomic layer epitaxy. The cleaning efficiency was assessed by investigating the nucleation density and the incubation period for ZnO nucleation using scanning electron micrography (SEM) and Auger electron emission spectroscopic analysis (AES). ECR plasma pretreatment increased the ZnO nucleation density and reduced the incubation period for ZnO nucleation. Oxygen ECR plasma pretreatment was found to be more effective in enhancing ZnO nucleation than any other plasma pretreatment, and the effects are more prominent on the sapphire substrate than the silicon substrate. ZnO nucleation on the sapphire substrate is substantially enhanced by treating the substrate surface with oxygen ECR plasma prior to ZnO atomic layer epitaxy (ALE) because the hydroxyl packing density at the substrate surface is increased by oxygen plasma.
Keywords: ZnO; ECR plasma treatment; ALE; Epitaxy;

We have investigated the effect of the oxygen pressure and the deposition temperature on the electrical and optical properties of the Sn-doped indium oxide (ITO) films on quartz glass substrate by pulsed laser deposition (PLD) using a 10 wt.% SnO2-doped In2O3 target. The resistivity and the carrier concentration of the films were decreased due to the decrease of the oxygen vacancy while increasing the oxygen pressure. With increasing deposition temperature, the resistivity of the films was decreased and the carrier concentration was increased due to the grain growth and the enhancement of the Sn diffusion. We have optimized the PLD process to deposit a highly conductive and transparent ITO film, which shows the optical transmittance of 88% and the resistivity of 2.49×10−4 Ω cm for the film thickness of 180 nm.
Keywords: Transparent conducting oxide; PLD; Resistivity; Optical transmittance;

We have synthesized vertically aligned carbon nanotube (CNT) emitters on iron-deposited trenches by thermal chemical vapor deposition of acetylene gas for field emission applications. The trenches patterned with various shapes and sizes were fabricated on silicon oxide/silicon substrates using a conventional lithography method and lift-off process. The vertically well-aligned carbon nanotubes were selectively grown only on iron-deposited trenches. The alignment, selectivity, and structure of carbon nanotube emitters grown on the patterned silicon trenches with various shapes and sizes are investigated. Field emission properties such as turn-on voltage and the emission current are also characterized.
Keywords: Carbon nanotube; Patterned trench; Field emission; Aligned growth; Thermal chemical vapor deposition;

SiO2 and SiON films were deposited by radiofrequency plasma-enhanced chemical vapor deposition (rf PECVD) technique using SiH4 and N2O as precursor gases. The refractive index (n) decreases to 1.4480 with the increase of the rf bias power from 0 to 75 W and again increases to 1.4486 at the rf bias power of 100 W. A uniform accumulation of fine grains with the root-mean-square (RMS) surface roughness within the area ∼1.5 nm was detected and the grains pack together very densely. The thickness, refractive index, and surface morphology of the films were characterized by prism coupler, scanning electron microscopy (SEM) and atomic force microscopy (AFM).
Keywords: Plasma-enhanced chemical vapor deposition; Silicon dioxide; Silicon oxynitride; Annealing;

Al doped ZnO (AZO) films were synthesized by inductively coupled plasma (ICP) assisted DC magnetron sputtering at low temperatures (<150 °C). A two-turn rf coil was inserted in the process chamber between the substrate and magnetron to generate the ICP. In order to obtain the optimum film properties even at a low temperature, high-density plasma was used to activate the sputtered metals and oxygen. The deposition process could be stabilized by controlling the target voltage in the transition region. The electrical resistivity of the films was ∼10−3 Ω cm, and the optical transmittance in the visible range was >80%. As the working pressure was increased, the visible transmittance of films was increased but the low resistivity processing window became narrower.
Keywords: TCO; Al doped ZnO; Inductively coupled plasma (ICP); Reactive sputtering;

The study of doped DLC films by Ti ion implantation by Liu Cui; Li Guoqing; Chen Wenwu; Mu Zongxin; Zhang Chengwu; Wang Liang (279-282).
Diamond-like carbon (DLC) films were prepared by unbalanced magnetron sputtering. Ti-doped DLC films were obtained by Ti ion implanted into the achieved DLC films using metal vapor vacuum arc (MEVVA). The effects of Ti+ ion implantation on the surface morphology, structure, and tribological properties of the DLC films were investigated by means of atomic force microscopy (AFM), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and friction measurement. The smooth and uniform Ti-doped film with the surface roughness of 0.595 nm was obtained. Raman result revealed that the formation of DLC films and sp2 bonds content increase by Ti+ ion implantation. TEM showed that the nanocrystalline phases of TiC were formed in the films. Ti+ was implanted into the interface between C and substrate, detecting the sputtering depth profiles of the film by XPS; thus, the interface was widened due to reserve diffusion. Tribological test experiment indicated that friction coefficient of the films decreased to approximately 0.15 by Ti+ ion implantation.
Keywords: Diamond-like carbon films; Ion implantation; Ti doped;

PbZrO3 (PZO)/PbTiO3 (PTO) artificial superlattices were fabricated by pulsed laser deposition, and their structural and dielectric properties were investigated. Epitaxial PbTiO3 (PTO) and PbZrO3 (PZO) layers were alternately deposited on La0.5Sr0.5CoO3 (LSCO) (100)/MgO (100) substrate at 500 °C with various stacking periods from 1 to 100 unit cells. The (100) plane spacing (d 100) of the superlattices increased with decreasing the stacking period, and the corresponding dielectric constant was drastically improved. The dielectric constant of the superlattice reached 800 at a stacking period of 1 unit cell/1 unit cell (PZO1/PTO1). With small stacking periods (PZO1/PTO1 and PZO2/PTO2 unit cells), superlattices exhibited the capacitance–voltage hysteresis, i.e., ferroelectric behavior.
Keywords: PZO/PTO artificial superlattices; Pulsed laser deposition; Large dielectric constant; Ferroelectric;

The effect of RF power on tribological properties of the diamond-like carbon films by Won Seok Choi; Jinhee Heo; Ilsub Chung; Byungyou Hong (287-290).
DLC thin films were prepared by radio frequency (RF) plasma-enhanced chemical vapor deposition (PECVD) method on silicon substrates using methane (CH4), hydrogen (H2) and gas mixture. We have checked the influence of varying RF power on DLC film. The Raman spectroscopy shows the diamond-like carbon (DLC) amorphous structure of the films. AFM images show the surface roughness of the DLC film decrease with increasing RF power. Also, the friction coefficients were investigated by atomic force microscope (AFM) in friction force microscope (FFM) mode.
Keywords: Atomic force microscopy; Diamond-like carbon; Friction force microscopy; Surface roughness; Tribology;

Electrochemical behavior of diamond-like carbon films for biomedical applications by Ho-Gun Kim; Seung-Ho Ahn; Jung-Gu Kim; Se Jun Park; Kwang-Ryol Lee (291-297).
Diamond-like carbon (DLC) films have several advantages in biomedical applications such as high hardness, chemical inertness, low friction and electrical insulation. Furthermore, DLC-coated STS 316L films have been reported to have a good biocompatibility. In addition, corrosion resistance is the first consideration for the biomaterials to be used in the body. DLC films have been deposited onto substrates of STS 316L using rf plasma-assisted chemical vapor deposition (PACVD) with benzene (C6H6) or a mixture of C6H6 and silane (SiH4) as process gas. Three kinds of DLC films were prepared as a function of bias voltage and Si incorporation. Corrosion behavior of DLC films was investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS)) and surface analytical techniques (atomic force microscopy (AFM) and scanning electron microscopy (SEM)). The electrolyte used in this test was a 0.89% NaCl of pH 7.4 at temperature of 37 °C. Electrochemical measurements showed that DLC films with higher bias voltage and Si incorporation could improve corrosion resistance in the simulated body fluid environment.
Keywords: DLC; Porosity; Protective efficiency; SEM; EIS;

Characterization of CN x thin films prepared by close field unbalanced magnetron sputtering by Yong Seob Park; Hyun Sik Myung; Jeon Geon Han; Byungyou Hong (298-302).
Carbon nitride (CN x ) film is a material that may successfully compete with DLC coatings, which have high hardness, high wear resistance and a low friction coefficient. Carbon nitride film was prepared on silicon substrate by Close Field UnBalanced Magnetron (CFUBM) sputtering with a graphite target and using nitrogen–argon mixture gas. Parameters were obtained on the deposition rate and investigated effect of total working pressure. The characteristic of the carbon nitride films was analyzed by Raman spectroscopy, energy dispersive X-ray (EDX) analysis, and atomic force microscopy (AFM). The tribological properties are also investigated by hardness measurement.
Keywords: Carbon nitride; CFUBM; Hardness;

Diamond like carbon (DLC) films were synthesized by closed-field unbalanced magnetron sputtering (CFUBM) using carbon targets in Ar and Ar/C2H2 atmosphere. The deposition rate, structure and mechanical properties of these films were studied as a function of applied bias voltage on the substrate during deposition. The film structures were investigated using Raman spectroscopy. The hardness and elastic modulus were measured by nano-indentation tests and the friction coefficient of DLC films was measured by a ball-on-disc type wear tester. Raman analysis showed that sp3/sp2 ratio in DLC films changed with increasing substrate bias voltage. Hydrogenated DLC films deposited at the bias of −200 V exhibited a maximum hardness of 28 GPa and a relatively low friction coefficient of about 0.1.
Keywords: Diamond like carbon (DLC); High rate sputtering; CFUBM;

Amorphous carbon and carbon nitride multilayered films prepared by shielded arc ion plating by K.H. Lee; R. Ohta; H. Sugimura; Y. Inoue; O. Takai; H. Sugimura (308-312).
Multilayered films consisting of amorphous carbon (a-C) and carbon nitride (a-CN) have been prepared by shielded arc ion plating (SAIP). Hardness and wear resistance of the multilayered films were measured with a nanoindenter interfaced with an atomic force microscope (AFM). Friction coefficients of the multilayered films were determined as well against a SUJ2 (SAE 52100) bearing ball using a ball-on-disc tribo-tester. The a-CN films deposited on a hard a-C film prepared at V b=0 or −300 V were harder than the single a-CN films directly deposited on the silicon substrate. The hardness of these layered samples was 4 GPa greater than that of the single layers. The hardness of a-C (60 nm)/a-CN (60 nm, V b=−300 V)/a-C (120 nm) triple layer film was 5 GPa higher than that of the single layered a-C. The wear resistance of the all layers was better than sapphire, although sapphire is harder than the single and double layers. The friction coefficients of the triple layers were low and stable. The triple layer showed the lowest friction coefficient of about 0.1.
Keywords: Amorphous carbon (a-C); Amorphous carbon nitride (a-CN); Multilayer; Shielded arc ion plating (SAIP); Nanoindentation;

The etching properties of MgO thin films in Cl2/Ar gas chemistry by Sung-Mo Gu; Dong-Pyo Kim; Kyoung-Tae Kim; Chang-Il Kim (313-317).
The metal–ferroelectric–semiconductor (MFS) structure is widely studied for nondestructive readout (NDRO) memory devices, but conventional MFS structure has two critical problems. First, the one that is difficult to obtain ferroelectric films like PZT on Si substrate without interdiffusion of impurities such as Pb, Ti and other elements. Diffusion of Pb or Ti induces increased trap density and Fermi-level pinning. The other one is that PZT/Si structure generates nonferroelectric and low-dielectric constant layer at the interface. In order to solve these problems, the metal–ferroelectric–insulator–semiconductor (MFIS) structure has been proposed with a buffer layer of high dielectric constant such as MgO, Y2O3, and CeO2. Buffer layer candidate should meet the following requirements of low lattice mismatch, low leakage current, low interface-state density, high dielectric constant, chemical stability, and prevention of interdiffusion.In this study, the etching characteristics (etch rate, selectivity) of MgO thin films were etched using Cl2/Ar plasma. The maximum etch rate of 85 nm/min for MgO thin films was obtained at Cl2(30%)/Ar(70%) gas mixing ratio. Moreover, the etch rate was measured by varying the etching parameters such as ICP rf power, dc-bias voltage, and chamber pressure. Plasma diagnostics was performed by Langmuir probe (LP) and optical emission spectroscopy (OES).
Keywords: Etching; MgO; Langmuir; OES;

Fabrication of SiC micro-lens by plasma etching by H.Y. Lee; D.W. Kim; Y.J. Sung; G.Y. Yeom (318-322).
SiC micro-lenses were fabricated by a plasma etching method by controlling the etch selectivities between photoresist and SiC. To etch SiC, inductively coupled plasmas were used with CF4, HCl, and HCl/HBr as the etch gases. When CF4 and HCl were used to etch SiC, the etch selectivities of SiC over photoresist were remained near 0.4 and 0.6, respectively. However, by using HCl/HBr, the selectivity was changed from 0.6 to 1.1. The SiC etch rates for HCl/HBr were in the range from 345 to 500 nm/min. The curvature radius of SiC micro-lenses fabricated with HCl/HBr was in the range from 20 to 27.54 μm and the roughness of the fabricated lenses was in the range from 1.7 to 2.65 nm.
Keywords: SiC; Plasma etching; Micro-lens;

Deposition of TiN thin films using grid-assisting magnetron sputtering by Min J. Jung; Y.M. Kim; Yun M. Chung; S.H. Ahn; J.G. Kim; Jeon G. Han (323-326).
This paper presents a modification to conventional magnetron sputtering systems. The introduction of grid in front of the target increases metal ion ratio. By using optical emission spectroscopy (OES) and observing both Ti neutrals and Ti ions, the relative fraction of ion could be qualitatively extended to grid-attached magnetron sputtering as compared with the conventional magnetron system. And, experimental results clearly demonstrated that a smooth and dense TiN film with a specular reflecting surface and could be produced by grid-attached magnetron with much increased Ti ion fractions as compared to conventional magnetron. From the potentiodynamic polarization test, it was shown that the corrosion current density of TiN deposited by two grid-attached magnetron sputtering was lower than that of TiN deposited by conventional magnetron sputtering.
Keywords: Grid-assisted magnetron sputtering; OES; TiN; Corrosion;

The luminous efficiency of the plasma display panel is investigated in terms of the xenon mole fraction. A theoretical model of the luminous efficiency in a mixed gas is developed, based on the energy balance equation. The luminous efficiency η is expressed as η=exp(−ɛ*/T b), where χ is the gas mixture ratio, T b is the electron breakdown temperature and ɛ* is the xenon excitation energy in eV. As an example, the luminous efficiency in neon gas mixed with xenon is investigated. It is shown that the luminous efficiency η increases monotonically as the xenon mole fraction increases from zero to unity. A preliminary experiment is carried out for neon gas mixed with a small percentage of xenon. The theoretical results agree reasonably well with experimental data. However, the efficiency enhancement dampens significantly when the xenon mole fraction is considerably large.
Keywords: Luminous efficiency; PDP cells; Two-species gas; Xenon mixture;

Formation of nano iridium oxide: material properties and neural cell culture by In-Seop Lee; Chung-Nam Whang; Young-Hee Lee; Gun Hwan Lee; Bong-Joo Park; Jong-Chul Park; Won-Seon Seo; Fu-Zhai Cui (332-336).
Iridium film with the thickness of 30 and 60 nm were formed on both Si wafer and commercially pure (CP) Ti by electron beam evaporation. The thin iridium film showed the identical charge injection capability with the bulk Ir. However, the charge injection value of iridium film was decreased with continuous potential cycling when the deposited iridium became depleted due to the formation of oxide. The number of cycles at which the charge injection value decreased was 800 and 1600 cycles for the 30- and 60-nm-thick Ir film, respectively. FE-SEM observations on the cross section of Ir film clearly showed the thicker iridium oxide was formed with the more potential cycling. Ar ion beam etching to substrates before deposition certainly improved the adhesion strength of Ir film enough to resist to the strain induced by the larger volume occupation of iridium oxide. Swiss 3T3 fibroblasts culture on Ir and Ir oxide showed no cytotoxicity. Also, embryonic cortical neural cell culture on electrode indicated neurons adhered and survived by the formation of neurofilament.
Keywords: Nano iridium oxide; E-beam evaporation; Charge injection; Cortical neural cell; Neurofilament;

Nitrogen-doped titanium oxide photocatalysts, which were reported to be activated by visible light irradiation as well as ultraviolet irradiation, have been prepared by pulsed laser deposition method using Ti, TiO, TiO2 and TiN targets in nitrogen/oxygen gas mixture. As a result, it is found that film properties such as color, crystalline structure and atomic composition rate strongly depend on the target material and nitrogen concentration ratio in the gas mixture. It is also suggested that these films under UV light irradiation exhibit almost the same decomposition ability of methylene blue. However, the photocatalytic activity of the nitrogen-doped TiO2 film prepared using TiN target is higher than that of the other films prepared by Ti, TiO and TiO2 targets under normal fluorescent light irradiation.
Keywords: Pulsed laser deposition; Photocatalyst; Titanium oxide;

Ion shower doping with a main ion source of P2H x using a source gas mixture of PH3/H2 was conducted on excimer-laser-annealed (ELA) poly-Si. The crystallinity of the as-implanted samples was measured using a UV transmittance. The measured value of as-implanted damage was found to correlate well with the one calculated using TRIM-code simulation. The sheet resistance decreases as the acceleration voltage increases from 1 to 15 kV at the moderate doping conditions. It, however, increases as the acceleration voltage increases under the severe doping conditions. Uncured damage after activation annealing seems to be responsible for the rise in sheet resistance. Three different annealing methods were investigated in terms of dopant activation and damage recovery, such as furnace annealing (FA), excimer laser annealing (ELA) and rapid thermal annealing (RTA), respectively.
Keywords: Low-temperature poly-Si; Ion shower doping; Dopant activation; Damage recovery;

This article reports the formation of epitaxial Si film that were formed by directly depositing a Sb-doped n-type epilayer on a p-type substrate by using a DC bais RF magnetron sputter system at a low temperature of 400 °C and a conventional vacuum of 5×10−7 Torr. In addition, the plasma parameters were quantitatively investigated to examine the deposition condition. The electron density (n e) of about 1017 m−3 was obtained at the plasma region under the conditions where gas pressure was 3 mTorr, the power of the RF source was 350 W and the electron temperature (T e) and ion saturation current (I 0) were in the range of 3–4 eV and 1–1.5 mA/cm2, respectively. The p–n junction diode fabricated by the Si epitaxy shows, under optimum conditions, a reverse current density (RCD) as low as 9.5×10−6 mA/cm2 at a reverse bias voltage of 5 V and an ideality factor of 1.05. The reverse current density has a good correlation with the crystallinity of the deposited films, which, in turn, depends on deposition gas pressures and substrate biases.
Keywords: Si epitaxy; RF magnetron sputtering; Electron temperature; Electron density;

Physical and electrical properties of ZrO2 and YSZ high-k gate dielectric thin films grown by RF magnetron sputtering by S.H. Jeong; I.S. Bae; Y.S. Shin; S.-B. Lee; H.-T. Kwak; J.-H. Boo (354-358).
Thin films of ZrO2 were deposited on p-Si(100) substrates using RF magnetron sputtering technique. To investigate the influence of the sputtering parameters, e.g., annealing temperature, different O2-flux, RF power and target to substrate distance on the physical and electrical properties of the as-grown films, systematic investigation using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscope and energy dispersive X-ray (SEM–EDX), C–V, and I–V were carried out in this work. Deposited ZrO2 films had polycrystalline after annealing sample at high temperature. Their silicon oxide (SiO2) layers were formed between high-k film (i.e., ZrO2 and YSZ) and Si substrate either after annealing samples at high temperature or introducing O2-flux the sputtering process step. The high-k thin films have to be deposited amorphous structure without SiO2 interlayers. We also investigated the electrical properties of both the a-ZrO2 and a-YSZ films prepared without O2-flux at room temperature with conditions of various RF power and target to substrate distance. The dielectric constant of amorphous YSZ was determined to be about 24 using metal–insulator–semiconductor (MIS) capacitor structure. The smallest leakage current density of the YSZ film grown at 150 W and at room temperature was obtained to be about 10−10 at 1 V.
Keywords: RF magnetron sputtering; ZrO2 films; YSZ films; High-k gate dielectrics; Leakage current;