Ar Sputtering Gas Research Articles

Influence of oxygen content on the properties of In2(OxS1−x)3 used as buffer material in Cu(In,Ga)Se2 solar cells

We investigate magnetron-sputtered In2(OxS1−x)3 compounds acting as an alternative buffer system to the solution-grown CdS or Zn(O,S) buffer layers in Cu(In,Ga)Se2 (CIGS) thin-film solar cells. The influence of the oxygen content on the solar cell performance, microstructure of the mixed systems, bandgap, and band offsets to CIGS is investigated experimentally and also characterized by calculations based on density functional theory. Samples in a series with different chemical compositions ranging from In2S3 to In2O3 are either directly deposited from ceramic targets or from a pure In2S3 target by reactive sputtering by adding O2 in the Ar sputtering gas. The binary compounds In2S3 and In2O3 sputtered at 220 °C substrate temperature from ceramic targets exhibit a crystalline structure, whereas the ternary In2(O,S)3 compounds are either nanocrystalline in the case of In2(O0.25S0.75)3 or amorphous for In2(O0.5S0.5)3 and In2(O0.75S0.25)3. For [O]/([O] + [S]) ratios above 0.25, the cell efficiencies decrease drastically, mainly due to lower open-circuit voltages (VOC). This behavior can be explained by an increase of the negative conduction band offset between the CIGS absorber and the oxygen-rich In2(OxS1−x)3 or In2O3 buffer, resulting in pronounced VOC losses. Adding oxygen to In2S3 with optical bandgap energies of around 2 eV results in a bowing of the values to below 2 eV and finally reaching values of around 2.7 eV for In2O3 if an indirect band transition is assumed. In summary, our results reveal that pronounced oxygen incorporation in In2S3 is not beneficial in terms of CIGS device efficiency because oxygen is electronically inactive and poorly miscible.

Raman scattering studies of Si/B4C periodic multilayer mirrors with an operating wavelength of 13.5 nm

In order to obtain mirrors with a minimum value of residual stress, periodic multilayer mirrors composed of Si/B4C were deposited by magnetron sputtering with change in pressure of sputtering Ar gas. The microstructure and phase of Si and B4C was manipulated by the pressure of Ar gas which overall affected the stress in the mirrors. The minimum stress was obtained at higher pressure of sputter Ar gas, which showed the formation of amorphous boron, amorphous B4C, free carbon atoms and amorphous carbon structure in the B4C layers, investigated by Raman scattering spectroscopy. In Raman spectroscopy, a transverse optical (TO) mode of amorphous Si was shifted to lower frequency with increase in Ar gas pressure, which indicated relaxation of stress, also confirmed by the curvature measurement of mirrors. However, in the case of high residual stress, the amorphous B4C was a prominent phase in this layer and the frequency of the TO mode of amorphous Si was blue-shifted. Microstructure and stress affected the interfaces and modulation of the periodicity of the Si/B4C mirrors, investigated by secondary ion mass spectroscopy, which influenced the reflectivity of the mirrors.

Giant spin Hall effect in half-Heusler alloy topological semimetal YPtBi grown at low temperature

Half-Heusler alloy topological semimetal YPtBi is a promising candidate for an efficient spin source material having both large spin Hall angle θSH and high thermal stability. However, high-quality YPtBi thin films with low bulk carrier density are usually grown at 600 °C, which exceeds the limitation of 400 °C for back end of line (BEOL) process. Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films grown at lower growth temperature down to 300 °C. Although both effective spin Hall angle and spin Hall conductivity degraded with lowering the growth temperature to 300 °C due to degradation of the interfacial spin transparency, they were recovered by reducing the sputtering Ar gas pressure. We achieved a giant θSH up to 7.8 and demonstrated efficient spin–orbit torque magnetization switching by ultralow current density of ∼105 A/cm2 in YPtBi grown at 300 °C with the Ar gas pressure of 1 Pa. Our results provide the recipe to achieve giant θSH in YPtBi grown at lower growth temperature suitable for BEOL process.

Effect of reactive gas condition on nonpolar AlN film growth on MnS/Si (100) by reactive DC sputtering

The effects of reactive gas flow conditions on nonpolar AlN film growth on MnS/Si (100) substrates using reactive DC magnetron sputtering were investigated. During AlN deposition at a substrate temperature of 750 °C, the MnS surface can be unintentionally nitrided, resulting in a decrease in the crystallinity of the AlN. Low-temperature growth of the AlN layer at 300 °C prevents this nitridation and results in the crystallization of nonpolar AlN. A N2 flow equal to 30% of the Ar sputtering gas flow was found to improve the crystallinity of the nonpolar AlN and to reduce nitrogen defects, which play an important role in interfacial reactions. Nitrogen defects promote the formation of alloys such as AlMn and MnSi that degrade the interface and can significantly decompose the MnS. A higher proportion of N2 improves the nonpolar AlN crystallinity, reduces the concentration of defects and suppresses reactions at the AlN/MnS interface.

Optical properties of Mo and amorphous MoOx, and application to antireflection coatings for metals

To form antireflection (AR) coatings to hide metal architecture in display technologies, we deposited thin films of metal Mo and oxide MoOx by sputtering targets of various compositions using pure Ar sputter gas. The optical constants [n,k] of these samples were measured by the direct numerical solution of reflectance and transmittance at each wavelength point measured. We find that 50 nm films are uniform in the growth direction, but for thicker 100 nm samples, evidence exists for nonuniform growth, where the top 20 nm appears to be metal rich. From these [n,k], negative Tauc bandgap energies show these oxides are semi-metals. We then identified the specific composition (x) that optimizes the AR response for a host of metals (Al, Cu, Ag, Au). Finally, two methods were used to understand why these MoOx materials function well as AR media, including (i) using phasor rays and (ii) developing a universal expression for the AR condition that applies to both dielectric and metal substrates. In (i), we find two characteristics for AR of metals: (a) its optical thickness should be roughly π3, not the π2 for dielectrics, since for MoOx, their [r^ij,t^ij] Fresnel phases differ from the usual [180°, 0°] of dielectrics; and (b) the medium incorporates a k-dominant strategy whose function is to absorb the energy that is reflected at the AR/metal interface. In (ii), the universal AR condition is found to be r^01+r^12z^=0. For dielectrics, this reduces to the well-known nAR=nairnsub condition. However, for metals, a concise analytic expression is lacking since this expression is highly nonlinear but is easily solved by numerical methods.

Fabrication of SnO2 by RF magnetron sputtering for electron transport layer of planar perovskite solar cells

The requirements of electron transport layer (ETL) for high efficiency Perovskite solar cells (PSCs) are, for example, appropriate band energy alignment, high electron mobility, high optical transmittance, high stability, and easy processing. SnO2 has attracted more attention as ETL for PSCs because it has diverse advantages, e.g., wide bandgap energy, excellent optical and chemical stability, high transparency, high electron mobility, and easy preparation. The SnO2 ETL was fabricated by RF magnetron sputtering technique to ensure the chemical composition and uniform layer thickness when compared to the use of chemical solution via spin-coating method. The RF power was varied from 60 - 150 W. The Ar sputtering gas pressure was varied from 1 × 10−3 - 6 × 10−3 mbar while keeping O2 partial pressure at 1 × 10−4 mbar. The thickness of SnO2 layer decreases as the Ar gas pressure increases resulting in the increase of sheet resistance. The surface morphology and optical transmission of the SnO2 ETL were investigated. It was found that the optimum thickness of SnO2 layer was approximately 35 - 40 nm. The best device shows Jsc = 27.4 mA/cm2, Voc = 1.03 V, fill factor = 0.63, and efficiency = 17.7%.

The effect of sputtering Ar gas pressure on optical and electrical properties of flexible ECD device with WO3 electrode deposited by RF magnetron sputtering on ITO/PET substrate

In this study, the electro-optical properties of a flexible electrochromic device (ECD) with WO3 film were investigated according to the pressure of Ar gas during RF magnetron sputtering process. The ECD was fabricated using WO3 film as the cathode electrode and NiO as the anode electrode. Both electrodes were deposited using RF magnetron sputtering over indium tin oxide coated on polyethylene terephthalate film (PET/ITO). The electrolyte for the ECD used the lithium percolate mixed with poly methyl methacrylate and propylene carbonate to form the gel type electrolyte. The sputtering time was controlled while measuring with a thickness/rate monitor (Sycon STM-100) to have the identical WO3 film thickness at different Ar pressures. Also, argon working gas pressure in sputtering chamber was varied at 5 mTorr, 10 mTorr, and 15mTorr, respectively. The deposition rate of WO3 film was 14 nm/min for Ar gas pressure 5 mTorr then after the pressure was increased until 15 mTorr the deposition rate was 8.6 nm/min. The sputtering process was operated until the thickness of the WO3 film reach 250 nm. In order to investigate electro-optical properties of the ECD, such as coloration efficiency (CE), transmittance of bleached state (Tb), transmittance of coloured state (Tc), optical modulation, bleaching time, and coloration time were analyzed. The ECD with Ar pressure at 5 m Torr for WO3 film shows the coloration efficiency was 57.58 cm2C-1, Tb was 17%, Tc was 5%. Also, the bleaching time was 15 s, and coloration time was 30 s. When the sputtering pressure was increased to 15 mTorr, the ECD showed the better optical properties but the bleaching time and coloration time was rise to 50 s, and 58 s, respectively. The ECD at 15mTorr show the higher optical modulation of 55%.

Optical, electrical, and structural properties of Ta-doped SnO2 films against substrate temperature using direct current magnetron sputtering

Ta-doped SnO2 (TTO) films were deposited at 3 × 10−3 Torr pressure from the 6 wt. % Ta2O5-doped SnO2 target at temperatures of 30–500 °C in Ar sputtering gas. The Ta dopants in the SnO2 host lattice were detected via X-ray photoemission, EDX mapping, and photoluminescence spectra. The Ta5+–Sn4+ substitution formed the OOx at VOxsites in the host lattice and the substitution occurred at deposition temperatures greater than 200 °C. The substitution leads to a decrease in the amount of VOx in the SnO2 lattice corresponding to the preferred rutile SnO2 (110) lattice reflection in the X-ray diffraction patterns. The ultraviolet-visible transmittance in visible light was approximately 80%. The lowest resistivity achieved was 2.0 × 10−3 Ω.cm, with a carrier concentration of 1.28 × 1020 cm−3 and carrier mobility of 24.5 cm2V−1s−1. The integration of the TTO-400 film with (n- and p-) Si exhibited an excellent photoelectric effect.

Tribological performance of DLC coatings deposited by DOMS in mixed Ar-Ne discharges

Several authors have reported that partially or even totally replacing the conventional Ar sputtering gas with Ne in HiPIMS plasmas results in significant improvement of mechanical and tribological properties of the DLC coatings. In this work, the tribological properties of the produced DLC films with different substrate biasing and Ne contents in discharge gas were evaluated. The tribological properties of the DLC films were evaluated on a reciprocating sliding machine. All DLC films showed no sign of failure after the tribological tests. The higher wear resistance of DLC films produced in Ar-Ne discharges is reached with only a small increase of the coefficient of friction. The conjunction of the low friction coefficient (between 0.10 and 0.18) and specific wear rate (between 4 × 10−17 and 7 × 10−17 m3/Nm) obtained by the DLC films (either deposited with −80 V of biasing or with Ne) in this work, is possible to affirm that these films are good candidates to replace the CrN films used in many applications of the automotive industry.

Roles of Atomic Nitrogen/Hydrogen in GaN Film Growth by Chemically Assisted Sputtering with Dual Plasma Sources.

The growth of sputtered GaN at low temperature is strongly desired to realize the dissemination of low-cost GaN high electron mobility transistor devices for next-generation communication technology. In this work, the roles of atomic nitrogen (N)/hydrogen (H) in GaN film growth on AlN/sapphire substrates by chemically assisted dual source sputtering are studied at a low growth temperature of 600 °C under a pressure of 2 Pa using vacuum ultraviolet absorption spectroscopy. The lateral growth was strongly enhanced with an appropriate H/N flux ratio of 1.9 at a GaN growth rate of ∼1 μm h–1. X-ray photoelectron spectroscopy measurements indicated that N removal from the grown GaN surface by atomic hydrogen promoted the migration of Ga. A smooth GaN surface was achieved at a suitable N/Ga supply ratio of 53 and a H/N ratio of 1.9 with the addition of 0.5% chlorine to the Ar sputtering gas.

Characterization of GaSb thin films with excess Ga grown by RF magnetron sputtering

Understanding the behavior of excess Ga is important for fabrication methods that employ the sputtering of GaSb-based materials. This is due to the comparatively low vapor pressure of Ga, which can result in GaSb becoming Ga-rich under experimental conditions. In this study, the growth and characterization of nonstoichiometric polycrystalline GaSb thin films with excess Ga, grown by RF magnetron sputtering, are reported. Ga content was adjusted by mixing N2in the Ar sputtering gas. The structural properties indicate that the grown thin films maintain the zinc blend structure of GaSb, and have an induced tensile strain along a direction parallel to the substrate. Excess Ga segregates towards the film surface and forms micro/nanoclusters. The internal tensile strain and the Ga cluster formation have little effect on the intrinsic properties of GaSb. These findings could lead to the fabrication of GaSb-based thin films using sputtering with excellent mass productivity.

Effects of substrate self-bias and nitrogen flow rate on non-polar AlN film growth by reactive sputtering

The effects of the N2 gas flow ratio and the substrate self-bias of reactive sputtering on the polarity of AlN film on various planar sapphire substrates were investigated to obtain a non-polar oriented AlN film. On a c-plane sapphire substrate, substrate self-bias enhanced c-plane AlN growth and Al termination at the surface, as confirmed by X-ray diffraction (XRD) and time-of-flight low-energy atom scattering spectroscopy. In addition, the AlN film deposited at an N2 gas:Ar sputtering gas ratio of 14% with substrate self-bias had high crystallinity with an XRD ω-rocking curve of 17 arcsec for the 0002 diffraction. In contrast, the AlN films on a- and r-plane sapphire substrates had semi-polar and non-polar plane orientations, respectively. However, on the a-plane sapphire substrate, the c-plane-orientated AlN phase was also observed, which was increased under substrate self-bias condition and an N2 flow rate below 30%. Preferable conditions for non-polar AlN growth by reactive sputtering were non-substrate self-bias and a high N2 flow rate of 30% or more.

Fabrication and Morphological Control of a Palladium Film with a Three-Dimensional Nano-Network Structure as a Hydrogen Gas Sensing Material using Organic Acid Chelation

ABSTRACTNano-porous palladium (Pd) thin films could potentially be applied to hydrogen gas sensing materials with high sensitivity and selectivity. In our previous study, a nano-porous Pd film was fabricated with a three-dimensional network structure from an AlPd mother alloy film by a dealloying method using the chelating ability of an organic acid. This process was simple and environmentally friendly because it only required organic acid in a ppm concentration, and did not exhaust a strong acid waste solution, including heavy metal ions. This method was modified to improve the Pd purity of the dealloyed specimen, reaction rate, and morphology control. In this study, the existence of a composition undulation pattern was shown in the AlPd mother alloy film, and its effects on the morphology of the dealloyed specimen were evaluated. Furthermore, this pattern could be controlled by N2 gas addition to the Ar sputtering gas during the preparation of the AlPd mother alloy film.

(Invited) Apprehension of Large Coercive Field in Ferroelectric HfO2 Thin Films

A special feature of ferroelectric HfO2 films is that they have large coercive fields (EC), as large as 1 MV/cm and more. A merit of the large coercive field is that a sufficient memory window is attainable even in ultrathin films. For example, a 2-V-memory window is available by 10-nm-thick Hf-Zr-O ferroelectric film. Compared with the conventional ferroelectric oxide capacitors using Pb(Zr, Ti)O3 and SrBi2Ta2O9 that applies around 100-nm-thick films, the ferroelectric HfO2 films contribute to the scaling of film thickness about one order. It is attractive for the development of high-density non-volatile memories integrated on LSI. On the other hand, the large coercive fields of ferroelectric HfO2 films bring serious concerns such as breakdown and endurance in capacitors. In this work, we studied the influence of large coercive fields on the endurance properties of Hf-Zr-O capacitors. Metal-ferroelectric-metal (MFM) capacitors that consist of TaN/Hf-Zr-O/TaN were prepared on heavily doped Si substrates. TaN electrode films were deposited by DC sputtering, using Ta target and mixture gas of Ar and N2. Hf-Zr-O films were prepared by RF sputtering, using HfO2 and ZrO2 targets and Ar gas. The metal composition was adjusted to Hf : Zr=50 : 50, and the thickness is 10 nm. After deposition of the top TaN film, crystallization anneal was processed in a vacuum condition at 700 degree Celsius. Finally, top electrodes were patterned by photolithography and dry etching. Ferroelectric properties of 10-nm-thick Hf-Zr-O capacitors were investigated by the polarization-voltage measurements. The ECvalue of this capacitor was evaluated to be 1 MV/cm. The electrical breakdown by the DC mode was measured to be about 4 MV/cm. Remnant polarization (Pr) and endurance properties of the capacitors are summarized in the figure. The Pr is faint when the applied electric field is less than the EC. The Pr value increases drastically when the electric fields are set between EC and 2xEC, and then gradually saturates over 2xEc. Thus a larger electric field is favorable for the achievement of large and stable polarization. In contrast, the endurance characteristics show a negative trend with the electric field. The endurance cycle as large as 108 was observed when the electric field is 2xEC, but it decreases drastically with the increment of electric field over 2xEC. It indicates that the capacitors are damaged even when the electric field is much lower than the breakdown field. Although a better endurance is expected at electric field lower than 2xEC, it makes a sacrifice of the Pr value and the stability. This trade-off relationship is considered to be a critical hurdle for the application of ferroelectric HfO2 capacitors. This work was supported by JST CREST Grant Number JPMJCR14F2, Japan. Figure 1

How the sputtering process influence structural, optical, and electrical properties of Zn3N2 films?

Abstract

Thermal stability of the Ti-Zr-Cu-Pd nano-glassy thin films

Nano-glassy thin films consist of nanometer-sized glassy regions (clusters) with a structure corresponding to melt-quenched glasses and amorphous interfacial regions characterized by a reduced density, or locally enhanced free volume, and in many cases a modified chemical composition. Ti-Zr-Cu-Pd nano-glass thin films were synthesized by using direct current (DC) magnetron sputtering on Si substrates. The influence of the sputtering conditions (sputtering power and Ar gas pressure) on the nano- and microstructure of deposited films and on their thermal behavior was analyzed. The thin films were noted to exhibit a homogeneous amorphous structure when sputtered at low Ar pressure (0.2 Pa) and a nano-glass structure with various sizes of the glassy cluster at higher Ar pressures (0.5–0.8 Pa). By raising the Ar pressure, the average size of the glassy clusters was noted to decrease corresponding to an increase of the volume fraction of the interfacial regions. The glass transition and crystallization temperatures were determined by using differential scanning calorimetry (DSC) at heating rates up to 40 Kmin−1. The thermal stability of the thin films was studied by annealing at temperatures above the glass transition and crystallization temperatures. The microstructure of the thin films was studied by means of X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy. The results obtained indicate that the nano-glassy thin films exhibit higher thermal stability than homogeneous glassy thin films. The fact that an increase of the volume fraction of the interfacial component in nano-glassy thin films results in an ultra-stable thermal behavior is indicating that the presence of nano-glassy interfaces impedes crystallization.

Impact of deposition rate, underlayers, and substrates on β-tungsten formation in sputter deposited films

The metastable phase of tungsten, β-W, which is a topologically close packed phase with the A15 (Pm3¯n) structure is of interest for application in spintronic devices based on the spin Hall effect. The deposition of β-W on glass substrates was studied as a function of deposition rate and the pressure of gaseous N2 introduced into the chamber along with the Ar sputtering gas. As the deposition rate is increased by increasing the deposition power, the N2 pressure required to form a given fraction of β-W increased. The variation of fraction of β-W with pressure of N2 for a given deposition rate followed the Langmuir–Freundlich isotherm, in agreement with prior work. The impact of underlayers and substrates on the formation of β-W was examined using 23 underlayers and two single crystal substrates in addition to the glass substrate. The underlayers were B, C, Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W, Fe19Ni81 (permalloy) Co40Fe40B20, Al2O3, and SiO2. The two single crystal substrates were sapphire (Al2O3) and α-quartz (SiO2). The use of such a large number of underlayers and substrates allowed a simple bonding rule to be developed for deposition of β-W versus α-W in the presence of N2. On metallically bonded solids, α-W is formed; on covalently or ionically bonded solids, β-W is formed. Crystallinity of oxide underlayers and substrate is found to have no impact on the formation of β-W. The bonding rule is a reflection of the impact of bond type on N2 adsorption on the depositing surface.

(Zr,Ti,O) alloy films with enhanced hardness and resistance to cracking prepared by magnetron sputtering

The article reports on the effect of (i) the ion bombardment and (ii) the addition of small amount of oxygen into Ar sputtering gas on the structure, microstructure, mechanical properties and macrostress of the (Zr,Ti) alloy films prepared by DC magnetron sputtering. Properties of the (Zr,Ti) alloy films with three different elemental compositions – (1) Zr95Ti5, (2) Zr30Ti70 and (3) Zr5Ti95 were investigated in detail. It was found that (1) the (Zr,Ti) alloy films sputtered at a low value of the negative substrate bias Us=−50V are well crystalline, (2) the (Zr,Ti) alloy films sputtered at high values of the negative substrate bias | Us |≥150V are nanocrystalline, (3) the (Zr,Ti) alloy films, sputtered at all substrate biases Us used in our experiments and ranging from −50 to −250V, exhibit low hardness H<10GPa, low ratio H/E⁎<0.1, low elastic recovery We<60% and low resistance to cracking and (4) the addition of small amount of oxygen in Ar sputtering gas makes it possible to sputter nanocrystalline (Zr,Ti,O) alloy films with high hardness H>10GPa, high ratio H/E⁎≥0.1, high elastic recovery We≥60% and enhanced resistance to cracking; here E⁎ is the effective Young's modulus. The main result of the presented investigation is the demonstration that the incorporation of a small amount of O in a (Zr,Ti) alloy film is a very effective way to increase its hardness and to form the flexible (Zr,Ti,O) alloy films with enhanced resistance to cracking.

Room-temperature rf-magnetron sputter-deposited W-doped indium oxide: decoupling the influence of W dopant and O vacancies on the film properties

Tungsten-doped indium oxide (IWO) thin films were deposited at room temperature using rf-magnetron sputtering. The optical, electrical, and structural properties of the IWO films were studied as functions of the O2-dilution fraction in the Ar sputtering gas. The W-doping level, and contributions of intrinsic oxygen vacancies and W dopant to the free carrier concentration were studied. Windows of optimum deposition conditions are demonstrated where amorphous and smooth-surfaced IWO films are obtained with low resistivity of 3.5 × 10−4 Ω cm, high mobility of 45 cm2 v−1 s−1, and high optical transparency (visible and NIR transparencies of 83 and 80 %, respectively). The observed optoelectronic properties are discussed in light of the underlying electron transport mechanisms.

Influence of deposition pressure, substrate temperature and substrate outgassing on sorption properties of Zr–Co–Ce getter films

Ultrahigh-vacuum conditions for microelectromechanical systems (MEMS) packaging can be achieved and sustained using a nonevaporable getter (NEG) film technology. Better understanding of the processes involved in film deposition, activation, and poisoning could help optimization and engineering of the film properties. In the present work, highly porous ZrCoCe films were deposited on (100) silicon substrates by direct current magnetron sputtering. Film morphology and performance dependence on deposition pressure, substrate temperature and substrate outgassing were investigated. The studies reveal that the pressure of the Ar sputtering gas affects significantly the film structure. High working pressures produce open columnar structures, whereas low pressures produce dense layers. It is demonstrated that the variation of the substrate temperature results in a significant modification of the film morphology. The highest sorption speed obtained for substrate temperature of 150 °C, is clearly correlated with the high specific surface area and porosity of the ZrCoCe film. It has also been confirmed that sorption properties can be improved by substrate outgassing prior to deposition.