Co-sputtering Process Research Articles

Microstructural characterization of chemical bath deposited and sputtered Zn(O,S) buffer layers

The present work aims at investigating the microstructure of Zn(O,S) buffer layers relative to their deposition route, namely either chemical bath deposition (CBD) or RF co-sputtering process (PVD) under pure Ar. The core of the study consists of cross-sectional transmission electron microscopy (TEM) characterization of the differently grown Zn(O,S) thin films on co-evaporated Cu(In,Ga)Se2 (CIGSe) absorbers. It shows that the morphology of Zn(O,S) layer deposited on CIGSe using CBD process is made of a thin layer of well oriented ZnS sphalerite-(111) and/or ZnS wurtzite-(0002) planes parallel to CIGSe chalcopyrite-(112) planes at the interface with CIGSe followed by misoriented nanometer-sized ZnS crystallites in an amorphous phase. As far as (PVD)Zn(O,S) is concerned, the TEM analyses reveal two different microstructures depending on the S-content in the films: for [S]/([O]+[S])=0.6, the buffer layer is made of ZnO zincite and ZnS wurtzite crystallites grown nearly coherently to each other, with (0002) planes nearly parallel with CIGSe-(112) planes, while for [S]/([O]+[S])=0.3, it is made of ZnO zincite type crystals with O atoms substituted by S atoms, with (0002) planes perfectly aligned with CIGSe-(112) planes. Such microstructural differences can explain why photovoltaic performances are dependent on the Zn(O,S) buffer layer deposition route.

Investigation on the structural and mechanical properties of anti-sticking sputtered tungsten chromium nitride films

Tungsten chromium nitride (WCrN) thin films are prepared by dual-gun co-sputter process. As the surface coatings on the molding die for glass forming, WCrN films show less deterioration at high temperature than the conventional CrN coating. WCrN thin films are deposited via the reactive co-sputtering of Cr/W targets. The working pressure is kept at 2.66Pa and the argon/nitrogen ratio is 10. Applied power of chromium is fixed and the applied power of tungsten is varied. Experimental results indicate that the atomic ratio of tungsten in the films increases with the applied power of tungsten. The dominant crystalline phase is chromium nitride when the tungsten target power is below 100W, while tungsten nitride dominates in the film structure when the tungsten target power is beyond 200W. A dense structure with much finer particles is developed as the tungsten power is 200W. As the power is increased to 300W, the particles become coarser in size. The film roughness exhibits a decreasing trend at low tungsten power and then increases as the tungsten power increased up to 300 and 400W, presumably due to the phase change from chromium nitrides to tungsten nitrides. Further annealing of the WCrN thin films is simulated as the glass molding condition to check the anti-sticking property which is a critical requirement in molding die surface coating application. The WCrN thin film coating shows good anti-sticking property at 400°C annealing when the tungsten target power is 200W.

Post-annealing Effect on Microstructures and Thermoelectric Properties of Bi0.45Sb1.55Te3 Thin Films Deposited by Co-sputtering

p-Type Bi0.45Sb1.55Te3 thermoelectric (TE) thin films have been prepared at room temperature by a magnetron cosputtering process. The effect of postannealing on the microstructure and TE properties of Bi0.45Sb1.55Te3 films has been investigated in the temperature range from room temperature to 350°C. x-Ray diffraction analysis shows that the annealed films have polycrystalline rhombohedral crystal structure, and the average grain size increases from 36 nm to 64 nm with increasing annealing temperature from room temperature to 350°C. Electron probe microanalysis shows that annealing above 250°C can cause Te reevaporation, which induces porous thin films and dramatically affects electrical transport properties of the thin films. TE properties of the films have been investigated at room temperature. The hole concentration shows a trend from descent to ascent and has a minimum value at the annealing temperature of 200°C, while the Seebeck coefficient shows an opposite trend and a maximum value of 245 μV K−1. The electrical resistivity monotonically decreases from 19.8 mΩ cm to 1.4 mΩ cm with increasing annealing temperature. Correspondingly, a maximum value of power factor, 27.4 μW K−2 cm−1, was obtained at the annealing temperature of 250°C.

Effects of Boron and Nitrogen Contents on the Microstructures and Mechanical Properties of Cr-B-N Nanocomposite Thin Films

Two series of Cr–B–N nanocomposite thin films with various nitrogen and boron contents were deposited by a co-sputtering process using a bipolar asymmetric pulsed DC reactive magnetron sputtering system, respectively. The crystalline structures and BN bonding nature of thin films were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The cross sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanoindentation technique was used to evaluate the hardness and elastic modulus of thin films. The hardness, elastic modulus and H/E ratio increased with increasing nitrogen content, and decreased with increasing boron content. The optimal mechanical properties were achieved on the Cr-3.7 at.% B-54.6 at.% N thin film with a very fine and dense columnar structure.

Characterization of non-stoichiometric co-sputtered Ba0.6Sr0.4(Ti1 − x Fe x )1 + x O3 − δ thin films for tunable passive microwave applications

The fabrication of novel iron-doped barium strontium titanate thin films by means of radio frequency (RF) magnetron co-sputtering is shown. Investigations of the elemental composition and the dopant distribution in the thin films obtained by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and time-of-flight secondary ion mass spectroscopy reveal a homogeneous dopant concentration throughout the thin film. The incorporation of the iron dopant and the temperature-dependent evolution of the crystal structure and morphology are analyzed by electron paramagnetic resonance spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, and scanning electron microscopy. In summary, these results emphasize the RF magnetron co-sputter process as a versatile way to fabricate doped thin films.

Microstructure and mechanical property evaluation of pulsed DC magnetron sputtered Cr–B and Cr–B–N films

CrB2 and four Cr–B–N films with high Cr/B ratio and various nitrogen contents were deposited by a co-sputtering process using a bipolar asymmetric pulsed DC reactive magnetron sputtering system. The structures and BN bonding nature of the thin films were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The surface and cross sectional morphologies of the thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface roughness of the thin films was explored by atomic force microscopy (AFM). Nanoindentation, microscratch and ball-on-disk wear techniques were used to evaluate the hardness, and tribological properties of the thin films, respectively.The microstructure of the Cr–B–N thin films changed from a coarse columnar structure to a glassy and featureless morphology as the nitrogen content increased from 15.2at.% to 54.5at.%, whereas the corresponding structure developed from an amorphous state to a nanocomposite structure consisting of CrN nanograins and amorphous BN phases. It was found that high hardness, good tribological and brittle properties were obtained for the CrB2 coating. The hardness and elastic modulus of the Cr–B–N thin films decreased with increasing nitrogen content until the nanocomposite structure of nanocrystalline CrN grains and an amorphous BN matrix was formed. However, the hardening effect induced by the nanocomposite structure was limited due to the fact that the small CrN nanograins were surrounded by a thick intergranular soft amorphous BN layer. On the other hand, the fracture toughness and resistance against elastic strain to failure of the Cr–B–N coatings were effectively enhanced by the addition of nitrogen.

Structural characterization and electrochemical behavior of titanium carbon thin films

In the present work we report the results concerning the synthesis of Ti–C films obtained by a co-sputtering process of both titanium and graphite targets. The titanium content within the coatings has been adjusted in a wide range, allowing different structures of the films, to be formed. The chemical composition of the films was determined by X-ray photoelectron spectroscopy (XPS). Phase structure was analyzed by grazing angle X-ray diffraction (GXRD), while the morphology and microstructure were investigated by scanning electron microscopy (SEM). The possibility of using the resulting materials for electrochemical applications was also examined. For these purposes, the Ti–C films used as electrodes were investigated in terms of both reactivity and stability. Electrochemical investigations were carried out by using cyclic voltammetry and spectroscopy electrochemical techniques.

Structural and photoluminescence properties of superlattice structures consisting of Sn-rich SiO 2 and stoichiometric SiO 2 layers

We compare the nanostructural and photoluminescence (PL) properties of Sn-rich silicon oxide (SiO 2) single layer and superlattice structures grown by a co-sputtering process. The superlattice structure consists of alternating thin Sn-rich SiO 2 and stoichiometric SiO 2 layers. Both transmission electron microscopy (TEM) and X-ray diffraction studies demonstrated the formation of β-Sn nanocrystals in the single layer structure after annealing at 600 °C, whereas no β-Sn nanocrystals were found in the superlattice structure. Sn oxide nanoparticles of ~ 3.0 nm in diameter were also observed by TEM in both structures. UV-violet PL enhancement around 3.2 eV was observed at room temperature from the superlattice structure compared with the single layer after annealing at the same temperature. The PL property is attributed to the triplet–singlet transition of the oxygen vacancy typical for Sn-related defects in the Sn-rich SiO 2 films. The formation of Sn oxide nanoparticles also contributes to PL in this region with its near band edge emission and defect centre emission. The enhancement of the UV-violet PL is due to the pronounced difference in the nanostructural properties between the two structures. The formation of β-Sn nanocrystals in the single layer can significantly reduce the number of the Sn-related defect centres, hence reducing the PL intensity. On the other hand, the precipitation of Sn nanocrystals is strongly suppressed in the superlattice structure and so also their effect on reducing PL intensity. In addition, more pronounced interface diffusion of Sn atoms to SiO 2 barrier layers in the superlattice structure causes more Sn-related defect centres near the layer interfaces so as to increase PL emission further.

Effect of Cr incorporation on the structural and optoelectronic properties of TiO 2:Cr deposited by means of a magnetron co-sputtering process

In this work, we report on the effect of Cr incorporation on the microstructural and optical properties of TiO 2:Cr thin films deposited by the RF-magnetron sputtering method. The structural, morphological, chemical bonding and optoelectronic properties of the sputter-deposited TiO 2:Cr films were systematically investigated, as a function the incorporated Cr content, by means of various techniques including X-ray diffraction (XRD), atomic force microscopy (AFM), Fourier-Transform Infra-Red (FTIR) absorption, X-ray Photoelectron Spectroscopy (XPS) and ellipsometry. The Cr incorporation into the TiO 2 films was controlled by adjusting the RF power ( P Cr) on the Cr target during the co-sputtering process of TiO 2 and Cr. We were thus able to demonstrate that by varying P Cr from 8 W to 150 W, the Cr content of the TiO 2:Cr films can be fairly controlled from ∼2 at.% to ∼18 at.% and their associated bandgap engineered from 3.3 eV to 1.5 eV. The room-temperature deposited TiO 2:Cr are mainly amorphous with the presence of some TiO 2 nanocrystallites, and their density increases as their Cr content is increased. The Cr inclusions were found to coexist under both metallic and oxidized forms in the films. By subjecting the TiO 2:Cr films to post-annealing treatment (at 550 °C), their crystalline structure was found to be sensitive to their Cr content. Indeed, an anatase-to-rutile phase transformation has been pointed out to occur at a Cr content of ∼7 at.%. Likewise, the Cr-content dependence of the bandgap of annealed TiO 2:Cr films undergoes a transition around the 7 at.% of Cr. Our results demonstrate the ability to control the Cr-content of TiO 2:Cr films, which leads to tune their optoelectronic properties, such as bandgap or optical absorption edge.

Using co-sputtered platinum or palladium activated tungsten oxide films to detect reducing gases

WO3, activated by 1% Pt or 1% Pd, was deposited by radio frequency co-sputtering process. The as-sputtered films were thermally-treated at 450°C for 24h after co-sputtering. The microstructure, crystal structure and chemical composition of the as-sputtered and thermally-treated films were analyzed by SEM, XRD and XPS. The sensing characteristics of the Pt or Pd activated WO3 films, as well as the pure WO3 films, were characterized with 25-200ppm H2, 25-200ppm CO and 0.62-5ppm NH3 at 50-300°C in air with different humidity.

Transparent Ga and Zn co-doped In 2O 3 electrode prepared by co-sputtering of Ga:In 2O 3 and Zn:In 2O 3 targets at room temperature

This study examined the characteristics of Ga:In 2O 3 (IGO) co-sputtered Zn:In 2O 3 (IZO) films prepared by dual target direct current (DC) magnetron sputtering at room temperature in a pure Ar atmosphere for transparent electrodes in IGZO-based TFTs. Electrical, optical, structural and surface properties of Ga and Zn co-doped In 2O 3 (IGZO) electrodes were investigated as a function of IGO and IZO target DC power during the co-sputtering process. Unlike semiconducting InGaZnO 4 films, which were widely used as a channel layer in the oxide TFTs, the co-sputtered IGZO films showed a high transmittance (91.84%) and low resistivity (4.1 × 10 − 4 Ω cm) at optimized DC power of the IGO and IZO targets, due to low atomic percent of Ga and Zn elements. Furthermore, the IGO co-sputtered IZO films showed a very smooth and featureless surface and an amorphous structure regardless of the IGO and IZO DC power due to the room temperature sputtering process. This indicates that co-sputtered IGZO films are a promising S/D electrode in the IGZO-based TFTs due to their low resistivity, high transmittance and same elements with channel InGaZnO 4 layer.

Preparation and characterization of Cu(In,Ga)(Se,S)2 films without selenization by co-sputtering from Cu(In,Ga)Se2 quaternary and In2S3 targets

In this study, Cu(In,Ga)(Se,S)2 (CIGSS) thin films were deposited onto a bi-layer Mo coated soda-lime glass by co-sputtering a chalcopyrite Cu(In,Ga)Se2 (CIGS) quaternary alloy target and an In2S3 binary target. A one-stage annealing process was performed to form CIGSS chalcopyrite phase without post-selenization. Experimental results show that CIGSS films were prepared by the proposed co-sputter process via CIGS (70W by radio frequency) and In2S3 (30W by direct current) with a substrate temperature of 373K, working pressure of 0.67Pa, and one-stage annealing at 798K for 30min. The stoichiometry ratios of the CIGSS film were Cu/(In+Ga)=0.92, Ga/(In+Ga)=0.26, and Se/(S)=0.49 that approached device-quality stoichiometry ratio (Cu/(In+Ga)<0.95, Ga/(In+Ga)<0.3, and (Se/S)≈0.5). The resistivity of the sample was 14.8Ωcm, with a carrier concentration of 3.4×1017cm−3 and mobility of 1.2cm2V−1s−1. The resulting film exhibited p-type conductivity with a double graded band-gap structure.

Multi-band silicon quantum dots embedded in an amorphous matrix of siliconcarbide

Silicon quantum dots embedded in an amorphous matrix of silicon carbide were realized bya magnetron co-sputtering process and post-annealing. X-ray photoelectron spectroscopy,glancing x-ray diffraction, Raman spectroscopy and high-resolution transmission electronmicroscopy were used to characterize the chemical composition and the microstructuralproperties. The results show that the sizes and size distribution of silicon quantum dots canbe tuned by changing the annealing atmosphere and the atom ratio of silicon and carbon inthe matrix. A physicochemical mechanism is proposed to demonstrate this formationprocess. Photoluminescence measurements indicate a multi-band configuration due to thequantum confinement effect of silicon quantum dots with different sizes. ThePL spectra are further widened as a result of the existence of amorphous siliconquantum dots. This multi-band configuration would be extremely advantageousin improving the photoelectric conversion efficiency of photovoltaic solar cells.

Tuning macro-twinned domain sizes and the b-variants content of the adaptive 14-modulated martensite in epitaxial Ni–Mn–Ga films by co-sputtering

In order to obtain modulated martensite in our epitaxial Ni–Mn–Ga films, we tuned the composition by using a co-sputtering process. Here we present how the composition affects the variant distribution of the 14-modulated martensite at room temperature. The nature of such modulated martensites is still strongly debated for magnetic shape memory alloys. It has been very recently demonstrated that the modulated martensites in Ni–Mn–Ga are adaptive phases. The results presented here corroborate this theory for the first time, for three different compositions. Moreover, we demonstrate with the help of the adaptive modulations theory that b-variants of the 14-modulated martensite form close to the free surface of the film to release the stress induced by branching of macro-twinned domains during the martensitic transformation on a rigid substrate. At room temperature, the content of such b-variants is found to strongly decrease when the macro-twinned domain sizes increase.

Characterization of Sn and Si nanocrystals embedded in SiO2 matrix fabricated by magnetron co-sputtering

Sn and Si nanocrystals were prepared by depositing Sn–Si-rich SiO2 films using a co-sputtering process and a subsequent annealing. The microstructure and optical properties of Sn and Si nanocrystals were characterized by scanning electron microscopy (SEM), Raman spectra, X-ray diffraction and photoluminescence spectra. The crystallization of Sn has started at the annealing temperature of 400°C, and was accomplished at 700°C. However, the phase of amorphous Si starts to transform into nanocrystal Si when the annealing temperature is higher than 700°C. These results illustrate that Sn existence as an element may played an important role in lowering the crystallization temperature of Si, and the crystallization rate of Si will be enhanced when Sn atom serves as the nucleation centre. Because quantum confinement effects are expected at relatively large radius for nanocrystal Sn, the redshift of high-energy PL peak may result from quantum confinement effects of nanocrystal Sn. However, the low-energy PL peak may be attributed to defects.

High-performance copper alloy films for barrierless metallization

In this study, we observe useful properties of V1.1- and V0.8N0.4-bearing copper (Cu) films deposited on barrierless silicon (Si) substrates by a cosputtering process. The Cu98.8(V0.8N0.4), or Cu(VNx) for brevity, films exhibit low resistivity (2.9μΩcm) and minimal leakage current after annealing at temperatures up to 700°C for 1h; no detectable reaction occurs at the Cu/Si interface. These observations confirm the high thermal stability of Cu(VNx) films. Furthermore, since these films have good adhesion features, they can be used for barrierless Cu metallization.

Measurement of mechanical and thermal properties of co-sputtered WSi thin film for MEMS applications

In this study, mechanical and thermal properties of the co-sputtered tungsten silicide (WSi) thin film were evaluated to consider the possibility of its use in MEMS applications. WSi film was prepared by co-sputtering and basic micromachining processes, and its mechanical and thermal properties such as Young’s modulus, temperature coefficient of resistance (TCR), strain gauge factor, coefficient of thermal expansion (CTE) and thermal stress were studied. The measurement method was simple and efficient since only one test pattern was used for all measurements. At room temperature, the TCR, gauge factor, CTE and thermal stress were measured to be −670 ppm/°C, 2.8, 32 ppm/°C and 1.76 GPa, respectively. The dependence of these coefficients on temperature was also evaluated experimentally.

Martensite structures and twinning in substrate-constrained epitaxial Ni–Mn–Ga films deposited by a magnetron co-sputtering process

In order to obtain Ni–Mn–Ga epitaxial films crystallized in martensite structures showing Magnetic-Induced Rearrangement (MIR) of martensite variants, a fine control of the composition is required. Here we present how the co-sputtering process might be helpful in the development of Ni–Mn–Ga epitaxial films. A batch of epitaxial Ni–Mn–Ga films deposited by co-sputtering of a Ni-Mn-Ga ternary target and a pure manganese target has been studied. The co-sputtering process allows a precise control of the film compositions and enables keeping the epitaxial growth of Ni-Mn-Ga austenite during deposition at high temperature. It gives rise to tune the content of the MIR-active 14-modulated martensite in the film at room temperature, as well as micro and macro-twinned domains sizes.

Microstructure and Properties of TiAlN/a-C Nanocomposite Coatings Prepared by Reactive Sputtering

TiAlN/a-C nano-composite coatings were synthesized by a reactive co-sputtering process to investigate the effects of sputtering conditions on the microstructure and mechanical properties. Coating films were deposited on square plates of Si and high speed steel (ANSI M2) by the co-sputtering of TiAl (pulsed-d.c. sputtering) and C (d.c. sputtering) targets using a “Facing Target-type Sputtering” system at an atmosphere with a mixture of Ar and N2 but without hydrocarbon gas. The structure of the coatings was investigated by means of XRD, XPS and HRTEM with GIF (Gatan Imaging Filter). Mechanical properties of coating films were measured by a submicron indentation system.Though TiAlN and a-C coatings showed hardness of about 32 and about 10 GPa, respectively, TiAlN/a-C coatings containing 4.6 at% of C showed higher hardness of 43 GPa. The energy filter images depicted that a change of contrast in the zero-loss image corresponded to nanometer-size of Ti agglomerates in Ti map. C1s spectrum in XPS analysis revealed that carbon in the coatings was bounded as C-C and C-N without bonding of Ti-C or Al-C. These results indicated that the TiAlN/a-C nano-composite coatings consisted of complicated mixture of nanocrystalline Ti-Al-N phase and a-C phase (including C-N bonding).

Using Pd/WO 3 composite thin films as sensing materials for optical fiber hydrogen sensors

In this article, a fiber-optic hydrogen gas sensor using composite palladium and tungsten trioxide (WO 3) was proposed and characterized. By magnetron co-sputtering process, Pd/WO 3 composite thin films were deposited on end surface of a single-mode fiber (SMF) and a side-etched multimode fiber (MMF). Modulation of optical power intensity is observed with different hydrogen concentrations. Due to its different sensing principle and structure, improvement of hydrogen sensing response and mechanical stability is reported.