Synthesis of DLC films by PECVD combined with hollow cathode sputtering

The mechanical and electrical properties of aluminium-doped diamond-like carbon (DLC) thin films obtained with a hybrid method combining hollow magnetron discharge sputtering and plasma-enhanced chemical vapour deposition (PECVD) are reported. The ratio between the mass flows of methane reactive gas and argon inert gas was found to have a big influence on the properties of doped DLC films. For low mass flow of methane gas the cathode surface was kept in a metallic state. By increasing methane mass flow the cathode surface became to be covered with DLC and the behaviour of the discharge changed, influencing the properties of deposited films. The lowest resistivity (10⁻⁴ Ω cm) of thin films was obtained in the metallic state of the cathode but without DLC character, as indicated by Raman measurements. The resistivity increased in the intermediate mode (0.01 Ω cm) and attained higher value (1 Ω cm) in the poisoned state of the cathode. These films presented DLC character, with D and G bands, as revealed by Raman measurements.     

Low temperature (< 100 °C) deposited P-type cuprous oxide thin films: Importance of controlled oxygen and deposition energy

With the emergence of transparent electronics, there has been considerable advancement in n-type transparent semiconducting oxide (TSO) materials, such as ZnO, InGaZnO, and InSnO. Comparatively, the availability of p-type TSO materials is more scarce and the available materials are less mature. The development of p-type semiconductors is one of the key technologies needed to push transparent electronics and systems to the next frontier, particularly for implementing p-n junctions for solar cells and p-type transistors for complementary logic/circuits applications. Cuprous oxide (Cu₂O) is one of the most promising candidates for p-type TSO materials. This paper reports the deposition of Cu₂O thin films without substrate heating using a high deposition rate reactive sputtering technique, called high target utilisation sputtering (HiTUS). This technique allows independent control of the remote plasma density and the ion energy, thus providing finer control of the film properties and microstructure as well as reducing film stress. The effect of deposition parameters, including oxygen flow rate, plasma power and target power, on the properties of Cu₂O films are reported. It is known from previously published work that the formation of pure Cu₂O film is often difficult, due to the more ready formation or co-formation of cupric oxide (CuO). From our investigation, we established two key concurrent criteria needed for attaining Cu₂O thin films (as opposed to CuO or mixed phase CuO/Cu₂O films). First, the oxygen flow rate must be kept low to avoid over-oxidation of Cu₂O to CuO and to ensure a non-oxidised/non-poisoned metallic copper target in the reactive sputtering environment. Secondly, the energy of the sputtered copper species must be kept low as higher reaction energy tends to favour the formation of CuO. The unique design of the HiTUS system enables the provision of a high density of low energy sputtered copper radicals/ions, and when combined with a controlled amount of oxygen, can produce good quality p-type transparent Cu₂O films with electrical resistivity ranging from 10² to 10⁴ Ω-cm, hole mobility of 1-10 cm²/V-s, and optical band-gap of 2.0-2.6 eV. These material properties make this low temperature deposited HiTUS Cu₂O film suitable for fabrication of p-type metal oxide thin film transistors. Furthermore, the capability to deposit Cu₂O films with low film stress at low temperatures on plastic substrates renders this approach favourable for fabrication of flexible p-n junction solar cells.     

Study of Cu diffusion behavior in low dielectric constant SiOC(-H) films deposited by plasma-enhanced chemical vapor deposition

Carbon doped silicon oxide (SiOCH) thin films deposited using plasma-enhanced chemical vapor deposition (PECVD) are commonly used in multilevel interconnect applications. To enhance the electrical performance, the deposited SiOC(-H) films were annealed in a vacuum at various temperatures ranging from 250 to 450 °C. A Cu electrode was then deposited using thermal evaporation. The drift rate of Cu⁺ ions in the SiOC(-H) films with the Cu/SiOC(-H)/p-Si(100)/Al metal-insulator-semiconductor (MIS) structures after annealing was evaluated by C-V measurements with a flatband shift caused by bias-temperature stress (BTS). The samples were stressed at different temperatures of 150 to 275 °C and electric fields up to 1.5 MV/cm to examine the penetration of Cu⁺ ions into the SiOC(-H) films. The Cu⁺ ion drift diffusion behavior was observed by high-resolution transmission electron microscopy and depth profile analysis of the Auger electron spectra. The drift diffusion experiments suggested that the Cu⁺ ion drift rate in the of SiOC(-H) films increased with increasing annealing temperature. A thermal stress and BTS were used to evaluate the impact of Cu penetration on the dielectric properties of the SiOC(-H) films.     

Deposition of diamond-like carbon films on the inner surface of narrow stainless steel tubes

Diamond-like carbon (DLC) films were deposited on the inner surface of 304-type stainless steel tube with an inner diameter of 10 mm by DC glow discharge plasma. The influence of the deposition time, pressure and the ratios of CH₄ in CH₄/Ar gas mixture on the DLC film deposition were investigated. The images of Scanning Electron Microscopy (SEM) show that the DLC films are featureless and free of porosity. Fibre-like structure was recognized on the film surface by Atomic Force Microscopy (AFM). The film deposition rate decreases with increasing the deposition time. Relative higher deposition rate (40 nm/min) can be obtained at 20-30 Pa, higher and lower pressure will significantly decrease the deposition rate. Raman spectrum analysis shows that the films deposited in 30 min at 20-30 Pa have more sp³ content. The corrosion resistance of the films was measured by potentiodynamic polarization test. The DLC films deposited on the inner surface of the 304-type stainless steel tube significantly improve its corrosion resistance.     

Structural, optical and electrical properties of reactively sputtered Ag2Cu2O3 films

Ag₂Cu₂O₃ thin films were deposited on glass substrates by RF magnetron sputtering of an equiatomic silver-copper target (Ag_0.5Cu_0.5) in reactive Ar-O₂ mixtures. The reactive sputtering was done at varying power, oxygen flow rate and deposition temperature to study the influence of these parameters on the deposition of Ag₂Cu₂O₃ films. The film structure was determined by X-ray diffraction, while the optical properties were examined by spectrophotometry (UV-vis-NIR) and photoluminescence. Furthermore, the film thickness and resistivity were measured by tactile profilometry and 4-point probe, respectively. Additional mobility, resistivity and charge carrier density Hall effect measurements were done on a few selected samples. The best films in terms of stoichiometry and crystallography were achieved with a sputtering power of 100 W, oxygen and argon flow rates of 20 sccm (giving a deposition pressure of 1.21 Pa) and a deposition temperature of 250 °C. The optical transmittance and photoluminescence spectra of films deposited with these parameters indicate several band gaps, most prominently, a direct one of around 2.2 eV. Electrical characterization reveals charge carrier concentrations and mobilities in the range of 10²¹-10²² cm^− 3 and 0.01-0.1 cm²/Vs, respectively.     

Magnetization and crystal structure of RF-sputtered nanocrystalline CuFe2O4 thin films

Cu-ferrite films were deposited on glass substrates by RF-magnetron sputtering in pure Ar and mixture of (Ar + O₂) environment. The XRD studies of the as-deposited films indicate nanocrystalline cubic spinel structure. The observed increase in the intensity of (400) line at the expense of (220) line with increase in O₂ content is ascribed to the change in distribution of Cu and Fe-ions among tetrahedral A-site and octahedral B-sites. The highest saturation magnetization (M_S) of 264 emu/cm³ (in-plane) and 188 emu/cm³ (out of-plane) was obtained for the as-deposited films in pure Ar. The high deposition rate in reducing atmosphere leads to the formation of Cu⁺ ions which prefer occupation of the A-site in the spinel structure displacing Fe³⁺ cations to occupy the B-sites giving rise to the change in cation distribution among A and B-sites and consequently leading to high value of M_S. The decrease in M_S value with increase in oxygen content is ascribed to the decrease in film growth rate and Cu⁺ concentration which allow the cations to take up their preferable sites. The observed change in the film properties with environment is due to the presence of multivalent copper and iron ions with differing site preferences.     

Structural and optical characterizations of chemically deposited cadmium selenide thin films

Synthesis of cadmium selenide thin films by CBD method has been presented. The deposited film samples were subjected to XRD, SEM, UV-vis-NIR and TEP characterization. X-ray diffraction analysis showed that CdSe film sample crystallized in zinc blende or cubic phase structure. SEM studies reveal that the grains are spherical in shape and uniformly distributed all over the surface of the substrates. The optical band gap energy of as deposited film sample was found to be in the order of 1.8 eV. The electrical conductivity of the film sample was found to be 10⁻⁶ (Ω cm)⁻¹ with n-type of conduction mechanism.     

Study of optical and structural properties of Cu2ZnSnS4 thin films

Cu₂ZnSnS₄ is a promising semiconductor to be used as absorber in thin film solar cells. In this work, we investigated optical and structural properties of Cu₂ZnSnS₄ thin films grown by sulphurization of metallic precursors deposited on soda lime glass substrates. The crystalline phases were studied by X-ray diffraction measurements showing the presence of only the Cu₂ZnSnS₄ phase. The studied films were copper poor and zinc rich as shown by inductively coupled plasma mass spectroscopy. Scanning electron microscopy revealed a good crystallinity and compactness. An absorption coefficient varying between 3 and 4 × 10⁴cm^− 1 was measured in the energy range between 1.75 and 3.5 eV. The band gap energy was estimated in 1.51 eV. Photoluminescence spectroscopy showed an asymmetric broad band emission. The dependence of this emission on the excitation power and temperature was investigated and compared to the predictions of the donor-acceptor-type transitions and radiative recombinations in the model of potential fluctuations. Experimental evidence was found to ascribe the observed emission to radiative transitions involving tail states created by potential fluctuations.     

Growth of Cu2ZnSnS4 thin films using sulfurization of stacked metallic films

We fabricated Cu₂ZnSnS₄ (CZTS) thin films through sulfurization of stacked metallic films. Three types of Cu-Zn-Sn metallic films, i.e., Cu-rich, Cu-correct and Cu-poor precursor films were sputtered onto Mo-coated glass. The sulfurization of stacked Cu-Zn-Sn alloy films was performed at a relatively high temperature, 570 °C, with S-powder evaporation. CZTS films from Cu-rich and Cu-correct precursors showed a Cu_2 − xS phase on the film surface, while CZTS films from Cu-poor precursors didn't show the Cu_2 − xS phase. However, all films didn't exhibit any extra secondary phase and exhibited good crystalline textures even with Cu-ratio differences in metallic precursor films. Fabricated CZTS films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Raman scattering measurements. SEM cross-section images of CZTS films showed that Cu-poor CZTS films were grown with more smooth film surface compared with other types of CZTS films.     

Magnetron sputter deposition of low-stress, carbon-containing cubic boron nitride films using Ar―N2―CH4 gas mixtures

Cubic boron nitride (c-BN) films produced by PVD and plasma-assisted CVD techniques typically exhibit undesired high compressive stresses. One of the effective and feasible methods to reduce stress and hence improve film adhesion has been a controlled addition of a third element into the film during deposition. In the present study, BN films were grown on to silicon substrates using reactive magnetron sputtering with a hexagonal BN target. An auxiliary flow of methane was mixed into argon and nitrogen as the working gas. The deposition was conducted at various methane flow rates at 400 °C substrate temperature, 0.2 Pa total working pressure, and − 250 V r.f. substrate bias. The microstructure of the deposited films was then examined in dependence of the methane flow rate. With increasing methane flow rate from 0 to approx. 2.0 sccm, the fraction of the cubic BN phase in the deposited films decreased gradually down to approx. 75 vol.%, whereas the film stress was reduced much more rapidly and almost linearly in relation to the methane flow rate. At 2.1 sccm methane, the stress became approx. 3 times reduced. Owing to the significantly decreased film stress, adherent, micrometer thick, cubic-phase dominant films can be allowed to form on silicon substrate. The microstructure of the films will be illustrated through FTIR and XRR.     

Enhanced crystal grain size by bromine doping in electrodeposited Cu2O

Extremely large crystal grains are obtained by bromine doping in electrodeposited Cu₂O on indium tin oxide (ITO) substrate through an acetate bath. The grains are as large as 10,000 μm² in area, or ~ 100 μm in linear dimension, while the film is only 1-5 μm thick. The enhanced grain size is explained by the effect of over-potential for the Cu²⁺/Cu⁺ redox couple on nucleation density of Cu₂O on ITO substrate. The over-potential is a function of several deposition conditions including solution pH, deposition potential, deposition temperature, bromine precursor concentration, and copper precursor concentration. In addition, undoped Cu₂O displays a high resistivity of 100 MΩcm. Bromine doping in Cu₂O significantly reduces the resistivity to as low as 42 Ωcm after vacuum annealing. Br-doped Cu₂O shows n-type behavior.     

Sputter deposition of semicrystalline tin dioxide films

Tin dioxide is emerging as an important material for use in copper indium gallium diselenide based solar cells. Amorphous tin dioxide may be used as a glass overlayer for covering the entire device and protecting it against water permeation. Tin dioxide is also a viable semiconductor candidate to replace the wide band gap zinc oxide window layer to improve the long-term device reliability. The film properties required by these two applications are different. Amorphous films have superior water permeation resistance while polycrystalline films generally have better charge carrier transport properties. Thus, it is important to understand how to tune the structure of tin dioxide films between amorphous and polycrystalline. Using X-ray diffraction (XRD) and Hall-effect measurements, we have studied the structure and electrical properties of tin dioxide films deposited by magnetron sputtering as a function of deposition temperature, sputtering power, feed gas composition and film thickness. Films deposited at room temperature are semicrystalline with nanometer size SnO₂ crystals embedded in an amorphous matrix. Film crystallinity increases with deposition temperature. When the films are crystalline, the X-ray diffraction intensity pattern is different than that of the powder diffraction pattern indicating that the films are textured with (101) and (211) directions oriented parallel to the surface normal. This texturing is observed on a variety of substrates including soda-lime glass (SLG), Mo-coated soda-lime glass and (100) silicon. Addition of oxygen to the sputtering gas, argon, increases the crystallinity and changes the orientation of the tin dioxide grains: (110) XRD intensity increases relative to the (101) and (211) diffraction peaks and this effect is observed both on Mo-coated SLG and (100) silicon wafers. Films with resistivities ranging between 8 mΩ cm and 800 mΩ cm could be deposited. The films are n-type with carrier concentrations in the 3 × 10¹⁸ cm^− 3 to 3 × 10²⁰ cm^− 3 range. Carrier concentration decreases when the oxygen concentration in the feed gas is above 5%. Electron mobilities range from 1 to 7 cm²/V s and increase with increasing film thickness, oxygen addition to the feed gas and film crystallinity. Electron mobilities in the 1-3 cm²/V s range can be obtained even in semicrystalline films. Initial deposition rates range from 4 nm/min at low sputtering power to 11 nm/min at higher powers. However, deposition rate decreases with deposition time by as much as 30%.     

Field emission properties of composite nano-Au/DLC films prepared by CVD technique

Nanocrystalline gold incorporated diamond-like carbon (nano-Au/DLC) films were deposited by capacitively coupled plasma (CCP) r.f. chemical vapour deposition (CVD) technique. Gold content in the DLC matrix was controlled by the amount of argon in the argon + methane mixture in the plasma. Field emission properties of these films were studied critically. Bonding environment (sp²/sp³ ratio) in these films was obtained from Raman measurements. Modification of the surface with the incorporation of gold nanocrystallites and associated modulation of sp²/sp³ ratio in the films culminated in improved field emission properties. Fowler-Nordheim model was used to ascertain the work function (?) which varied between 19 and 64 meV. The field factor (β) varied between 172 and 1050.     

Thin films preparation by rf-sputtering of copper/iron ceramic targets with Cu/Fe = 1: From nanocomposites to delafossite compounds

In the Cu-Fe-O phase diagram, delafossite CuFeO₂ is obtained for the Cu^I oxidation state and for the Cu/Fe = 1 ratio. By decreasing the oxygen content, copper/spinel oxide composite can be obtained because of the reduction and the disproponation of cuprous ions. Many physical properties as for instance, electrical, optical, catalytic properties can then be affected by the control of the oxygen stoichiometry.In rf-sputtering technique, the bombardment energies on the substrate can be controlled by the deposition conditions leading to different oxygen stoichiometry in the growing layers.By this technique, thin films have been prepared from two ceramic targets: CuFeO₂ and CuO + CuFe₂O₄. We thus synthesized either Cu⁰/Cu_xFe_1−xO₄ nanocomposites thin films with various Cu⁰ quantities or CuFeO₂-based thin films.Two-probes conductivity measurements were permitted to comparatively evaluate the Cu⁰ content, while optical microscopy evidenced a self-assembly phenomenon during thermal annealing.     

Effect of annealing on the electrodeposited Cu2O films for photoelectrochemical hydrogen generation

Cu₂O films were electrodeposited on stainless steel substrates followed by Ar annealing for photoelectrochemical hydrogen generation. Plating variables including time and pH for the plating bath were explored to obtain desirable film qualities. X-ray diffraction (XRD) patterns indicated that the as-deposited Cu₂O films exhibited preferred orientations in (200) and (111) planes from the plating bath of pH 9 and pH 11, respectively. Images from scanning electron microscope (SEM) revealed pyramid-like grains in 1 µm size for the Cu₂O films from pH 9 plating bath and large plate-like grains in 3-8 µm size from pH 11 plating bath. Identical results from SEM and XRD were obtained from the Cu₂O films at longer plating time. After annealing at 350 °C for 30 and 60 min, the Cu₂O phase was nicely maintained but SEM images demonstrated coarser grains. Photoelectrochemical activity for H₂ generation was obtained on the Cu₂O films before and after annealing by recording relevant photoelectrochemical currents at − 0.3 V in 0.5 M aqueous Na₂SO₄ solution. For the Cu₂O films from both baths, substantial increments in photoelectrochemical current were observed for the annealed samples as opposed to as-deposited ones. The largest photoelectrochemical current was obtained at 0.143 mA/cm² from the Cu₂O film of pH 9 plating bath with 60 min annealing, which exhibited a 560% increase over the as-deposited sample. We attributed the enhanced photoelectrochemical current to the improved crystallinity and reduced defects for the annealed Cu₂O films.     

Enhanced characterization of ITO films deposited on PET by RF superimposed DC magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited on polyethylene terephthalate substrates by RF superimposed DC magnetron sputtering using an ITO target composed of In₂O₃ (90 wt.%):SnO₂ (10 wt.%). The total sputtering power was maintained at 70 W and the power ratio of RF/(RF + DC) was varied from 0 to 100% in steps of 25%. The discharge voltage and deposition rate decreased with increasing RF/(RF + DC) power ratio. The ITO film deposited at a 50% RF portion of the total power showed the lowest resistivity (3.18 × 10^− 4 Ωcm), high transmittance (87.5%) and relatively good mechanical durability, which was evaluated using bending and scratch tests.     

Fluorine doped gallium tin oxide composite films as transparent conductive oxides on polyethylene terephthalate film prepared by electron cyclotron resonance metal organic chemical vapor deposition

The undoped and fluorine doped gallium tin oxide composite films are prepared by an electron cyclotron resonance metal organic chemical vapor deposition. Characteristics of structural, optical and electrical properties of the fluorine doped gallium tin oxide composite thin films are investigated. The four point probe method, atomic force microscopy and X-ray photoelectron spectroscopy are employed to characterize the composite thin films. UV-visible, X-ray diffraction, scanning electron microscope and Hall measurement performed on fluorine doped gallium tin oxide composite are films deposited on polyethylene terephthalate substrates. The diffraction pattern shows the presence of tetragonal structure with (112) special orientation for fluorine doped gallium tin oxide composite films. The doped composite film on F/Ga + Sn mole ratio of 0.35 is observed the lowest electrical resistivity of 3.35 × 10^− 4 Ω cm.     

Effect of catalyst for nickel films for NiSi formation with improved interface roughness

Iodine is an effective catalyst to obtain homogeneous and smooth metal films with good interface properties. We adopted an iodine catalyst during the nickel film deposition by using atomic layer deposition (ALD) with bis(1-dimethylamino-2-methyl-2-butoxide)nickel [Ni(dmamb)₂] precursor and hydrogen reactant gas. The effect of iodine catalyst to nickel nucleation process was studied. The deposited films were silicided by rapid thermal process (RTP) which was performed by varying temperature from 400 °C to 900 °C in nitrogen ambient. The crystalline properties of nickel and nickel silicide films were examined by X-ray diffractometer (XRD) with various deposition temperatures. The interface properties and the surface morphology of nickel silicide films were studied by using Auger electron spectroscopy (AES) depth profile analyses and scanning electron microscopy (SEM). The experimental results showed that the iodine-catalyzed silicide film, which have a clean and smooth interface, exhibit lower resistivity, and lower leakage current density compared to that of non iodine-catalyzed films in implemented n⁺/p junction diode.     

Microstructure and electrical properties of Cu films obtained by chemical vapor deposition of copper(I) pentafluoropropionate complexes with vinyltrialkylsilanes

Copper thin layers were deposited on Si(111) and glass substrates by chemical vapor deposition method using [Cu(OOCC₂F₅)(L)], L = vinyltrimethylsilane (1), vinyltriethylsilane (2) as precursors. Application of multistage depositions of Cu films on a glass surfaces resulted in formation of the metallic membranes. Fabricated crystalline copper layers, which contains some carbon (5-9%) and oxygen (1-5%) impurities, have been characterized by grazing incidence X-ray diffraction and X-ray photoelectron methods. The morphology studies exhibited metallic layers composed of copper grains, their size and packed density depends on deposition parameters. Electrical properties of metallic films were studied by four-point probe, as a function of temperature in 103-333 K range.     

Annealing optimization of silicon nitride film for solar cell application

Hydrogenated films of silicon nitride (SiNx:H) is commonly used as an antireflection coating as well as passivation layer in crystalline silicon solar cell. SiNx:H films deposited at different conditions in Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor were investigated by varying annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in silicon solar cells. By varying the gases ratio (R = NH₃/SiH₄ + NH₃) during deposition, the SiNx:H films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, the silicon wafer with SiNx:H film deposited at 450 °C showed the best effective minority carrier lifetime. The film deposited with the gases ratio of 0.57 shows the best peak of carrier lifetime at the annealing temperature of 800 °C. The single crystalline silicon solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrates (125 mm × 125 mm) were found to have the conversion efficiencies as high as 17.05 %. Low cost and high efficiency single crystalline silicon solar cells fabrication sequence employed in this study has also been reported in this paper.