Co-sputtered Films Research Articles

Formation of C54 TiSi 2 in a cosputtered (Ti+Si) blanket film in the presence of a TiN capping layer

Formation of C54 TiSi 2 was investigated in cosputtered (Ti+Si) films with and without a TiN capping layer following rapid thermal annealing (RTA). The first phase observed in the specimens was Ti 5Si 3 regardless if a TiN overlayer was present. Free energy calculations indicate the preference of Ti 5Si 3 formation as the first phase. C54 TiSi 2 started to form at lower temperatures in the specimens capped with TiN. Its formation also occurred at shorter annealing times at some given temperature. The influence of a TiN capping layer on enhancing C54 TiSi 2 formation is attributed to the stress induced by this layer into the (Ti+Si) film. The X-ray diffraction (XRD) method was used to evaluate the stress in the TiN film. Free energy values also indicate that C54 TiSi 2 formation is favored in capped samples.

Iron silicide formed in a-Si:Fe thin films by magnetron co-sputtering and ion implantation

Thin films containing iron silicides are prepared by two methods. The first one consists in depositing a-Si:H:Fe thin films by magnetron co-sputtering followed by rapid thermal annealing (RTA). The second one is ion implantation of Fe in a-Si:H thin films and RTA treatment. The samples are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Rutherford back-scattering (RBS). FTIR spectra show absorption bands typical for β-FeSi 2 at 263, 293, 308, 345 and 425 cm −1. It is shown that the optimal concentration of Fe in the co-sputtered films to obtain β-FeSi 2 is 35–40% and the optimal RTA temperature is 900°C. XPS spectra show that β-FeSi 2 is formed in as-deposited and annealed co-sputtered a-Si:H:Fe and implanted a-Si:H thin films.

Microstructure, chemistry, and tribological performance of MoSx/WSey co-sputtered composites

Co-sputtered thin films have been deposited from MoS2 and WSe2 targets in order to investigate the relationships between tribological behavior and film microstructure. The stoichiometries of pure films for the sputtering conditions used, were found to be MoS1.6 and WSe1.5 as measured by wavelength dispersive x-ray analysis. The mechanical properties of the composite films were investigated by pin-on-disk wear testing in 50% relative humidity air as a function of WSe2 concentration. X-ray diffraction measurements indicate that the microstructure is strongly affected by the inclusion of WSe2 and there is a strong correlation between microstructure and tribological performance. X-ray and Raman measurements indicate a large increase in the c axis of the MoS2, which may be due to intercalation. X-ray photoelectron spectroscopy measurements show no evidence that either Se or W chemically substitutes into the MoS2 structure.

Microstructure and tribological performance of MoSx/Au co-sputtered composites

Co-sputtered thin films of MoSx with Au have been deposited in order to investigate the relationships between tribological behavior and film microstructure. The mechanical properties of the composite films were investigated by pin-on-disk wear testing in 50% relative humidity air as a function of Au concentration. X-ray diffraction measurements indicate that the microstructure is strongly affected by the inclusion of Au and that there is a strong correlation between microstructure and tribological performance.

Mechanical and tribological performance of MoS 2 co-sputtered composites

Co-sputtered films of MoS 2 with Au, Ti, Cr or WSe 2, respectively, have been deposited in order to investigate the relationships between dopant and tribological and mechanical behaviour. The alloying constituents were selected based on possible chemical effects, for example substitution in the MoS 2 structure, intercalation, edge-bond passivation, and with and without simultaneous oxygen gettering of the sputtering environment. The mechanical properties of the composite films were investigated by pin-on-disk sliding wear testing and linear, oscillating wear testing both in 50% relative humidity air, microscratch and indent adhesion characterisation, and nanoindentation hardness as a function of the dopant element(s) and concentration. All of the dopants investigated exhibited superior tribological and mechanical behaviour compared to the pure MoS x films. In tribological tests, results indicate a significant improvement in the lifetime, mean friction coefficient, and friction ‘noise’ of the films. Tribological performance was found to be strongly related to both the dopant element and dopant concentration. The best dopant for improved performance was found with WSe 2 followed by Au, Ti, and Cr.

Co-sputtered Ru-Ti alloy electrodes for DRAM applications

Co-sputtered Ru-Ti alloy films were studied for use as a bottom electrode for ferroelectric/paraelectric thin film capacitors. The Ru/Ti ratio in the alloy was found to strongly affect the resistivity, structure formation and thermal stability. The resistivity of the as-deposited films decreases and approaches that of pure Ru metal films as the amount of Ru atoms increases. From X-ray diffraction measurements, it was found that the RuTi phase has formed for the as-deposited sample. The resistivity of alloy thin films is thermally stable as the Ru composition varies from 0.68 to 0.81. It may be due to RuTiO 2 formation at the surface and play an important role in preventing further oxidation of the Ru-enriched layer. This oxide also exhibits conductive behavior. On the other hand, the interface between Ru-enriched alloys and Si substrate was still sharp for the sample treated by rapid thermal processing at 600 °C for 1 min. The alloy film with high Ru composition shows excellent thermal stability and barriers against interdiffusion of Si and oxygen.

XPS characterization and optical properties of Si/SiO 2, Si/Al 2O 3 and Si/MgO co-sputtered films

Si/SiO 2, Si/Al 2O 3 and Si/MgO co-sputtered films were prepared by placing 6 or 12 Si plates (5×15 mm) on an SiO 2, Al 2O 3 or MgO target 100 mm in diameter during deposition. X-ray photoelectron spectroscopic (XPS) analysis of these films revealed that the main low valency Si state was SiO x (0< x<2) for Si/SiO 2, and Si for Si/Al 2O 3 and Si/MgO under the same preparation conditions. Although the Si/SiO 2 films maintained a homogeneous Si component profile even after heat treatment at 820°C, heat treatment above 700°C for Si/Al 2O 3 and above 300°C for Si/MgO resulted in an inward diffusion of Si. The Si/SiO 2 co-sputtered film had a stronger photoluminescence (PL) intensity at about 1.7 eV than the other two co-sputtered films from Ar ion laser excitation at 514.5 nm. The weak PL observed for Si/Al 2O 3 and Si/MgO is deduced to be due to the low content of SiO x where electrons and holes recombine and PL is emitted.

Co-sputtered Thin Films Consisting of Cobalt Nano-Grains Embedded in Graphite-like Carbon and Their Magnetic Properties

The microstructure and the magnetic properties of co-sputtered cobalt-carbon thin films were analyzed. Cobalt-carbon thin films consisting of nano-crystalline cobalt grains separated by graphite-like carbon were obtained after subsequent annealing. The phase of the cobalt grains depended on the carbon concentration; a hexagonal close-packed phase and a heavily faulted close-packed phase were observed. The grain size ranged from 4 to 20 nm. The in-plane magnetic hysteresis loops measured at room temperature showed that the coercivity and the squareness were drastically changed with the carbon concentration. These changes can be related to a change in the magnetocrystalline anisotropy of the cobalt grains due to a difference in the phase and/or size effect that can be explained by the presence of superparamagnetic particles. The highest coercivity (660 oersteds) was measured in a film with a large grain size as well as a hexagonal close-packed cobalt phase. The annealing temperature was found to have an optimum value; the magnetic properties were improved upon annealing due to carbide decomposition, but at high annealing temperatures, coalescence of the grains resulted in sample degradation.

Co-sputtered films within the quasi-binary system TiN-TiB 2

Ti-B-N films with a gradient in the chemical composition were deposited onto austenitic stainless steel and molybdenum sheets by means of unbalanced dc magnetron co-sputtering using a separated TiN/TiB 2 target. Different energetic contributions necessary for film growth were investigated adjusting suitable deposition parameters. Film microstructure was characterized by means of scanning (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD), as well as glancing angle X-ray diffraction (GAXRD) and electron probe microanalysis (EPMA). Coating hardness was measured using a depth sensing nanoindenter. The microstructure of the films appears featureless using SEM fracture cross sections. The grain size determined from TEM investigations ranged between 3 and 5 nm. The composition of the films was found to lie on the quasi-binary section TiN-TiB 2 within the ternary system Ti-B-N. Coatings consisted of nanocrystalline fcc and hcp Ti-B-N phases. Microstructure as well as chemical composition of the films do not seem to be influenced by varying the deposition parameters used in this investigation. Contrarily, the hardness was strongly influenced by varying the ion bombardment. Hardness values exceeding 50 GPa were obtained for Ti-B-N films.

Off-axis co-sputtered YBCO and CeO/sub 2/ thin films

We have investigated the properties of off-axis co-sputtered films of YBCO and CeO/sub 2/ having CeO/sub 2/ concentrations up to 43%. Morphology investigations suggest that films with more than 29% CeO/sub 2/ may consist of a new material phase, T/sub c/ and resistance ratio decreased with increasing CeO/sub 2/ concentration. Degradation of T/sub c/, after photoresist processing the films was observed and reversed by a 20 minute oxygen plasma etch. The temperature dependence of the critical current near T/sub c/ showed two power law dependence regions with a crossover near 0.99 T/sub c/ for films having low concentrations of CeO/sub 2/. I/sub C/ 's were decreased by small applied magnetic fields, and for some samples the response was observed to increase at lower temperature. For a sample having 26% CeO/sub 2/, a 40% reduction in critical current was observed for a 2 Gauss applied field. This response indicates that this may be a candidate material for the development of Josephson vortex flow devices.

Giant magnetoresistance and microstructures in CoAg granular films fabricated using ion-beam co-sputtering technique.

The correlation between the GMR effect and the microstructures in ion-beam co-sputtered CoAg granular films was systematically studied. The highest magnetoresistance was observed in ${\mathrm{Co}}_{22}$${\mathrm{Ag}}_{78}$ samples. It is sensitive to the annealing treatment and to the size of the cobalt granules. The microstructures of the sample were studied by a variety of structural techniques. HREM provides a clear two-dimensional image of as-deposited ${\mathrm{Co}}_{22}$${\mathrm{Ag}}_{78}$ samples. Real-time observation of TEM together with FMR indicates that the shapes and sizes of cobalt granules evolve primarily in plane during the annealing process. \textcopyright{} 1996 The American Physical Society.

Fabrication of Si/SiO 2 nanocomposite thin films

Si-rich SiO 2 films were deposited onto Si and quartz substrates by r.f. co-sputtering, and then annealed under vacuum at temperatures between 500 to 900°C for 1 hour. A combination of high resolution transmission electron microscopy, optical ellipsometry, and UV/VIS and FTIR photospectrometry were used to investigate the microstructures and optical properties of the co-sputtered films before and after annealing. The as-deposited films consisted of a fully amorphous SiO x(I < × < 2) structure. After annealing, the films consisted of clusters of crystalline Si with average sizes in the range between 3nm and 8nm embedded in a stoichiometric SiO 2 amorphous matrix.

Fracture in MoS 2 solid lubricant films

The fracture properties of sputter-deposited films of MoS 2 as a function of the additive-controlled microstructure were assessed using brale indentation contact and scanning electron microscopy (SEM). Additives were incorporated as either co-sputtered species (Ni, SbO x ) or as multilayers (Au-20% Pd, Ni). Undoped films were also examined as references. The undoped films and 3% co-sputtered Ni films (deposited at 2.66 Pa argon background pressure) showed zone 2 columnar plate morphologies with porosity. Co-sputtered films having higher concentrations of Ni or SbO x showed zone 1 dense cauliflower morphologies, while the multilayer films (and pure MoS 2 films deposited at 0.266 Pa) exhibited dense, featureless morphologies. The porous zone 2 films generally resisted delamination better than the denser morphologies. High Ni concentrations increased spallation. The presence of SbO x affected fracture propagation and appeared to be more benign than Ni. The presence of multilayers also affected fracture and retarded spallation in dense microstructures. However, many multilayer structures showed significant delamination.

Preparation and properties of CuInSe 2 thin films produced by selenization of co-sputtered Cu-In films

Thin films of CuInSe 2 have been prepared by selenizing co-sputtered Cu-In films with selenium vapor. X-ray diffraction, Auger electron spectroscopy, electrical conductivity and optical transmission measurements were used to characterize the specimens. In very Cu-rich films, Cu-Se segregations were identified and a strong (112) orientation was observed. No preferential crystallite orientation was detected in near-stoichiometric and In-rich films. The conductivity types were p-type for Cu-rich and n-type for near-stoichiometric and In-rich films. Conductivity measurements were performed on several n-type films in the temperature range 77–370 K. All samples showed a thermally activated conductivity for higher temperatures and the variable-range hopping conduction mechanism in the lower temperature range. The dependence of the absorption coefficient on incident photon energy indicates allowed direct transitions with energies in the range 0.96-1.01 eV.

Thermal evolution and aging of Co-sputtered iron-tin thin films

The composition, structure, magnetic properties and stability of iron-tin thin films produced by co-evaporation with de magnetron sputtering are studied. Rutherford backscattering. Auger electron spectroscopy. X-ray diffraction and conversion electron Mossbauer spectroscopy indicate the formation of a homogeneous solid solution of tin in iron with a concentration well above the limit of equilibrium solid solubility. Measurements with a vibrating-sample magnetometer show that the films present saturation magnetization and remanence similar to those of pure iron, but a much smaller coercivity. Thermal treatment or aging lead to second-phase precipitation, which is accompanied by a growth of coercivity and remanence.

Thin amorphous superconducting niobium-silicon films with high normal state resistivity

We have fabricated co-sputtered niobium-silicon films with thicknesses ranging from 1 nm to 200 nm. Analysis by X-ray diffraction and high resolution TEM shows that the films are amorphous. Due to their stability, the films are suited for the fabrication of reliable devices. The resistive transitions of the films have been studied. The onset for superconductivity takes place at sheet resistances lower than the ‘universal’ value of h/4e 2 .

Amorphous WSi0.45 Metallization for Self-Aligned GaAs MESFETs

ABSTRACTCrystallization temperature (Tc) of amorphous WSix films on GaAs was studied as a function of the Si/W ratio. The highest Tc of 875°C for a 20 min anneal was obtained for co-sputtered WSMi films with the Si/W ratio of 0.45 (31 at.% Si). The WSi0.45 films remained amorphous following implant activation anneal and served as a barrier to Ga and As outdiffusion. Pitting of GaAs under the contact was also prevented. The WSi0.45 composition corresponds to the eutectic point between the W and W5Si3 phases, which was explained by the strong glass-forming tendency of eutectic alloys. Amorpous WSi0.45 films formed stable Schottky contacts to n-GaAs and produced minimum reduction of carrier concentration in the substrate. Therefore, the Si/W ratio of 0.45 is suggested as optimal for the WSix refractory gate metallization in self-aligned GaAs MESFErs.

Co-sputtered Si-Cr resistive films

Si-Cr films of variable composition between pure silicon and pure chromium have been deposited by co-sputtering on to glass substrates and thermally oxidized silicon wafers. In order to assess the applications of the Si-Cr films to thin film resistors, the electrical characteristics of the films have been determined as a function of composition, thickness, thermal treatments, etc.

Short-range order in amorphous co-sputtered Ta-Al thin films

Tantalum-aluminium thin films have assumed considerable technological importance since the discovery in the late 1960's that the films are useful in the fabrication of thin film resistors and capacitors. It is generally claimed that these films, when prepared by co-sputtering Ta and Al, are amorphous over a range of Ta concentrations extending approximately from 15 to 75 at%, and are crystalline beyond this range. Diffuse electron diffraction patterns and ‘mottle pattern’ transmission electron micrographs are typical characteristics of the amorphous phase. In this present study we have attempted to identify any atomic short range order in the amorphous Ta-Al films and to follow the changes in this order as the Ta concentration increases across the amorphous/crystalline transition. The co-sputtered Ta-Al films of ≈100A thickness were examined in a high resolution 4000EX electron microscope (top entry, ±15°(x,y) tilt, Cs = 1.0mm ) at 400kV.

The growth and physical properties of low pressure chemically vapour-deposited films of tantalum silicide on n +-type polycrystalline silicon

Bilayer films of tantalum silicide on n +-type polycrystalline silicon prepared by low pressure chemical vapour deposition (LPCVD) were fabricated from SiH 4 and TaCl 5 in a single standard hot-wall LPCVD reactor. The main advantages over conventional co-sputtered films are reduced wafer handling, improved conformal deposition, increased wafer throughput and the use of only one piece of process equipment. Both films of the bilayer structure are deposited at 575°C and annealing is carried out in the deposition reactor at 900°C. The amorphous deposited silicon films were doped in situ with PH 3. The stoichiometry of the as-deposited tantalumrich Ta 5Si 3 films is shifted to the desired low resistivity TaSi 2 during the annealing process, in which the additional silicon required is supplied from the underlying polycrystalline silicon. The resistivity of annealed LPCVD tantalum silicide films is 60–70μΩ cm which is comparable with that of films prepared by co-sputtering. The peak-to-valley surface roughness of 30 nm is at present typically a factor of 2 larger than that for co-sputtered films. Wet oxidation experiments indicate that there is no large difference in the thermal SiO 2 formation between LPCVD and co-sputtered tantalum silicide.