Growth and in-situ electrical characterization of ultrathin epitaxial TiN films on MgO

We examine the properties of ultrathin TiN films grown by reactive dc magnetron sputtering on single-crystalline MgO(100) substrates at growth temperatures ranging from 30 to 650 °C. The resistance of the films is measured in-situ, during growth, to study the thickness at which the films coalesce and become structurally continuous. Both the in-situ resistance measurements and X-ray diffraction measurements show a clear transition from polycrystalline growth to epitaxial (100) growth well below typical TiN growth temperatures, or between 100 and 200 °C. The coalescence and continuity thicknesses are 1.09 ± 0.06 nm and 5.5 ± 0.5 nm, respectively, at room temperature but reach a minimum of 0.08 ± 0.02 nm and 0.7 ± 0.1 nm, respectively, at 600 °C. A large drop in resistivity is seen with increasing growth temperature and the resistivity reaches 16.6 μΩ cm at 600 °C. Achieving epitaxy at such a low temperature and a low continuity thickness is important in a variety of applications such as device interconnects and metal-oxide-semiconductor devices.     

Morphology of TiN thin films grown on SiO2 by reactive high power impulse magnetron sputtering

Thin TiN films were grown on SiO₂ by reactive high power impulse magnetron sputtering (HiPIMS) at a range of temperatures from 45 to 600 °C. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. Structural characterization was carried out using X-ray diffraction and reflection methods. The HiPIMS process produces denser films at lower growth temperature than does dcMS. Furthermore, the surface is much smoother for films grown by the HiPIMS process. The [200] grain size increases monotonically with increased growth temperature, whereas the size of the [111] oriented grains decreases to a minimum for a growth temperature of 400 °C after which it starts to increase with growth temperature. The [200] crystallites are smaller than the [111] crystallites for all growth temperatures. The grain sizes of both orientations are smaller in HiPIMS grown films than in dcMS grown films.     

Effect of carbon additive on microstructure evolution and magnetic properties of epitaxial FePt (001) thin films

FePt:C thin films were deposited on CrRu underlayers by DC magnetron co-sputtering. The effects of C content, FePt:C film thickness and substrate temperature on the microstructural and magnetic properties of the epitaxial FePt (001) films were studied. Experimental results showed that even with 30 vol.% C doping, the FePt films could keep a (001) preferred orientation at 350 °C. When a FePt:C film was very thin (< 5 nm), the film had a continuous microstructure instead of a granual structure with C diffused onto the film surface. With further increased film thickness, the film started to nucleate and formed a column microstructure over continuous FePt films. A strong exchange coupling in the FePt:C films was believed to be due to the presence of a thin continuous FePt layer attributed to the carbon diffusion during the initial stage of the FePt:C film growth. Despite the presence of a strong exchange coupling in the FePt:C (20 vol.% C) film, the SNR ratio of the FePt:C media was about 10 dB better than that of the pure FePt media. The epitaxial growth of the FePt:C films on the Pt layers was observed from high resolution TEM cross sectional images even for the films grown at about 200 °C. The TEM images did not show an obvious change in the morphology of the FePt:C films deposited at different temperatures (from 200 °C to 350 °C), though the ordering degree and coercivity of the films increased with increased substrate temperature.     

High-temperature growth and in-situ annealing of MgZnO thin films by RF sputtering

We report the effect of growth temperature and annealing on microstructural, elemental and emission properties of as-grown and in-situ annealed MgZnO thin films, containing ∼ 10 at. % Mg, grown at high temperature by RF sputtering. Microstructural analysis carried out by TEM reveals formation of thin oxide layer with increased layer thickness on growth temperature, in the interface between Si substrate and MgZnO thin film. Irrespective of growth temperature, increase in Mg mole fraction with increase in thickness of MgZnO thin film is observed from EDX and AES spectroscopy, and a maximum of 14 at. % Mg is observed at 800 °C. The photoluminescence investigation shows blue shift of 104 meV in MgZnO film grown at 800 °C, compared to the film grown at 600 °C, which is due to the enhancement of the Mg incorporation at higher temperature. In addition, annealing at the growth temperature enhanced the intensity ratio of the UV/deep level emission and increased the grain size. Thermal treatment in a vacuum improved the emission efficiency and changed the origin of the point defects.     

Thickness dependence of structure and optical properties of silver films deposited by magnetron sputtering

A series of silver films with different thickness were prepared under identical conditions by direct current magnetron sputtering. The optical properties of the silver films were measured using spectrophotometric techniques and the optical constants were calculated from reflection and transmission measurements made at near normal incidence. The results show that the optical properties and constants are affected by films' thickness. Below the critical thickness of 17 nm at which Ag film forms a continuous film, the optical properties and constants vary significantly as the thickness of films increases and then tends to a stable value which is reached at 41 nm. X-ray diffraction measurements were carried out to examine the structure and stress evolution of the Ag films as a function of films' thickness. It was found that the interplanar distance of (111) orientation decreases when the film thickness increases and tends to be close to that of bulk material. The compressive strains also decrease with increasing thickness.     

Ru thin film grown on TaN by plasma enhanced atomic layer deposition

Ru thin films were sequentially deposited onto TaN (5 nm) by plasma enhanced atomic layer deposition using Ru(EtCp)₂ and NH₃ as precursors. The effect of growth temperature on the electrical resistivity and morphology of the Ru films were studied. It was found that the Ru films can achieve a low resistivity of 14 µΩ cm and a low root-mean-square roughness at a growth temperature of 270 °C. The thickness of the underlying TaN film was found to affect the Ru film growth. The oxidation of the very thin TaN film was correlated with the island growth of Ru. Ex and in-situ X-ray diffraction was employed to verify the copper diffusion barrier properties of a Ru (3 nm)/TaN (5 nm) bi-layer structure.     

Effects of substrate temperature and post-deposition anneal on properties of evaporated cadmium telluride films

The effects of substrate temperature and post-deposition heat treatment steps on the morphology, structural, optical and electrical properties of thin film CdTe layers grown by vacuum evaporation were investigated. Scanning electron microscopy and X-ray diffraction (XRD) techniques were employed to study the structural changes. It was observed that the grain sizes and morphologies of as-deposited layers were similar for substrate temperatures of − 173 °C and − 73 °C. However, CdTe films produced at a substrate temperature of 27 °C had substantially larger grain size and clearly facetted morphology. Annealing at 200-400 °C in air did not cause any appreciable grain growth in any of the films irrespective of their growth temperature. However, annealing at 400 °C reduced faceting in all cases and initiated fusing between grains. XRD studies showed that this behavior after annealing at 400 °C coincided with an onset of a degree of randomization in the originally strong (111) texture of the as-grown layers. Optical band gap measurements showed sharpening of the band-edge upon annealing at 400 °C and a band gap value in the range of 1.46-1.49 eV. Resistivity measurements indicated that annealing at 400 °C in air forms a highly resistive compensated CdTe film. All results point to 400 °C to be a critical annealing temperature at which optical, structural and electrical properties of CdTe layers start to change.     

The effect of substrate temperature on the oxidation behavior of erbium thick films

The effect of substrate temperature on the oxidation behavior of erbium thick films, fabricated by electron-beam vapor deposition (EBVD), was investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The erbium thick film is black when it is deposited at substrate temperature below 450 °C and turns gray at higher substrate temperature in a vacuum pressure of approximately 1.5 × 10⁻⁶ Torr, which indicates that the thickness of erbium oxide layer formed on the surface of erbium films increases with the decreasing substrate temperature. XPS depth profile results demonstrate that the thickness of the surface erbium oxide layer of erbium film deposited at substrate temperature of 550 and 350 °C are about 50 and 75 nm, respectively. The thicker oxide layer at lower substrate temperatures may be attributed to grain size and the dynamic vacuum condition around the substrates. Other possible factors involved in the oxidation behavior are also discussed.     

Effects of growth temperature and film thickness on the electrical properties of Ba0.7Sr0.3TiO3 thin films grown on platinized silicon substrates by pulsed laser deposition

Barium strontium titanate Ba_0.7Sr_0.3TiO₃ (BST) thin films, with different growth temperatures (T_g) as well as different film thicknesses, have been prepared on Pt/Ti/SiO₂/Si substrates by a reactive pulsed laser deposition method. We observed strong dependences of dielectric properties, such as the Curie-Weiss temperature, dielectric constant, loss tangent, dielectric tunability and leakage current, on the T_g and the BST film thickness. With increase of T_g from 630 to 750 °C, the dielectric constant gradually increases due to the increase in the crystallinity and the grain size. However, the dielectric tunability, loss tangent and leakage current characteristics drastically degrade when the T_g increases up to 750 °C, due to the diffuse and rough interface. The BST film grown at 690 °C shows the best overall dielectric properties with a figure-of-merit of 33 (at 400 kV/cm). These results suggest that film growth process could be optimized by systematically investigating the structure-property relationships. Furthermore, as the BST film thickness increases from 250 to 560 nm, the dielectric properties are remarkably enhanced. The film thickness effect is attributed to the interfacial low-dielectric layers (the so-called “dead layer”) between the BST film and both metal electrodes, which is well explained in terms of a series capacitor model. The thickness and the average dielectric constant for the dead layer are experimentally estimated to be 1.9 nm and 20.3, respectively, in Pt/BST/Pt capacitors.     

Femtosecond laser deposited zinc oxide film and its optical properties

Zinc oxide (ZnO) thin films have been grown on Si (100) substrates using a femto-second pulsed laser deposition (fsPLD) technique. The effects of substrate temperature and laser energy on the structural, surface morphological and optical properties of the films are discussed. The X-ray diffraction results show that the films are highly c-axis oriented when grown at 80 °C and (103)-oriented at 500 °C. In the laser energy range of 1.0 mJ-2.0 mJ, the c-axis orientation increases and the mean grain size decreases for the films deposited at 80 °C. The field emission scanning electron microscopy indicates that the films have a typical hexagonal structure. The optical transmissivity results show that the transmittance increases with the increasing substrate temperature. In addition, the photoluminescence spectra excited with 325 nm light at room temperature are studied. The structural properties of ZnO films grown using nanosecond (KrF) laser are also discussed.     

Substrate temperature dependent morphology and resistivity of pulsed laser deposited iridium oxide thin films

Iridium oxide (IrO₂) thin films were deposited on Si (100) substrates by means of pulsed laser deposition technique at various substrate (deposition) temperatures ranging from 250 to 500 °C. Effects of substrate temperature on the crystalline nature, morphology and electrical properties of the deposited films were analyzed by using X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and four-point probe method. It was found that the above properties were strongly dependent on the substrate temperature. The as-deposited films at all substrate temperatures were polycrystalline tetragonal IrO₂ and the preferential growth orientation changed with the substrate temperature. IrO₂ films exhibited fairly homogeneous thickness and good adhesion with the substrate, the average feature size increases with the substrate temperature. The room-temperature resistivity of IrO₂ films decreased with the increase of substrate temperature and the minimum resistivity of (42 ± 6) μΩ cm was obtained at 500 °C. The resistivity of IrO₂ films correlated well with the corresponding film morphology changes.     

Depth dependence of structural quality in InN grown by metalorganic chemical vapor deposition

Rutherford backscattering and channeling is combined with X-ray diffraction to study the depth dependence of crystalline quality in InN layers grown by metalorganic chemical vapor deposition on sapphire substrate. The poorest crystalline quality in InN layer is produced at the intermediate region over 100 nm away from the InN/sapphire interface. With increasing layer thickness the crystalline quality improves to a certain degree dependent on the growth temperature. The InN sample grown at 450 °C is found to be more homogeneous than the sample grown at 550 °C. The difference in the defect profile is explained by the temperature-dependent growth modes. The inhomogeneity of structural quality and related properties such as carrier concentration and strain field is possibly the reason to observe a high energy wing in PL spectrum of the InN sample grown at 550 °C.     

Properties of atomic layer deposited HfO2 thin films

The growth, composition and morphology of HfO₂ films that have been deposited by atomic layer deposition (ALD) are examined in this article. The films are deposited using two different ALD chemistries: i) tetrakis ethylmethyl amino hafnium and H₂O at 250° and ii) tetrakis dimethyl amino hafnium and H₂O at 275 °C. The growth rates are 1.2 Å/cycle and 1.0 Å/cycle respectively. The main impurities detected both by X-ray Photoelectron Spectroscopy and Fourier transform infrared spectroscopy (FTIR) are bonded carbon (~ 3 at.%) and both bulk and terminal OH species that are partially desorbed after high temperature inert anneals up to 900 °C. Atomic Force Microscopy reveals increasing surface roughness as a function of increasing film thickness. X-ray diffraction shows that the morphology of the as-deposited films is thickness dependent; films with thickness around 30 nm for both processes are amorphous while ~ 70 nm films show the existence of crystallites. These results are correlated with FTIR measurements in the far IR region where the HfO₂ peaks are found to provide an easy and reliable technique for the determination of the crystallinity of relatively thick HfO₂ films. The index of refraction for all films is very close to that for bulk crystalline HfO₂.     

Preparation of aluminum doped zinc oxide films and the study of their microstructure, electrical and optical properties

Aluminum doped zinc oxide (AZO) polycrystalline thin films were prepared by sol-gel dip-coating process on optical glass substrates. Zinc acetate solutions of 0.5 M in isopropanol stabilized by diethanolamine and doped with a concentrated solution of aluminum nitrate in ethanol were used. The content of aluminum in the sol was varied from 1 to 3 at.%. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 300 °C and 500 °C for 1 h. The coatings have been characterized by X-ray diffraction, UV-Visible spectrophotometry, scanning electron microscopy, and electrical resistance measurement. The ZnO:Al thin films are transparent (∼ 90%) in near ultraviolet and visible regions. With the annealing temperature increasing from 300 °C to 500 °C, the film was oriented more preferentially along the (0 0 2) direction, the grain size of the film increased, the transmittance also became higher and the electrical resistivity decreased. The X-ray diffraction analysis revealed single-phase ZnO hexagonal wurtzite structure. The best conductors were obtained for the AZO films containing 1 at.% of Al, annealed at 500 °C, 780 nm film thickness.     

Effect of growth temperature on the structural and transport properties of magnetite thin films prepared by pulse laser deposition on single crystal Si substrate

Magnetite (Fe₃O₄) thin films are prepared by pulsed laser deposition using an α-Fe₂O₃ target on silicon (111) substrate in the substrate temperature range of 350 °C to 550 °C. X-ray diffraction (XRD) measurement shows that the film deposited at 450 °C is a single phase Fe₃O₄ film oriented along [111] direction. However, the film grown at 350 °C reveals mixed oxide phases (FeO and Fe₃O₄), while the film deposited at 550 °C is a polycrystalline Fe₃O₄. X-ray photoelectron spectroscopy study confirms the XRD findings. Raman measurements reveal identical spectra for all the films deposited at different substrate temperatures. We observe abrupt increase in the resistivity behavior of all the films around Verwey transition temperature (T_V) (125 K-120 K) though the transition is broader in the film deposited at 350 °C. We observe that the optimized temperature for the growth of Fe₃O₄ film on Si is 450 °C. The electrical transport behavior follows Shklovskii and Efros variable range hopping type conduction mechanism below T_V for the film deposited at 450 °C possibly due to the granular growth of the film.     

Deposition of WNxCy thin films for diffusion barrier application using the dimethylhydrazido (2) tungsten complex (CH3CN)Cl4W(NNMe2)

Tungsten nitride carbide (WN_xC_y) thin films were deposited by chemical vapor deposition using the dimethylhydrazido (2⁻) tungsten complex (CH₃CN)Cl₄W(NNMe₂) (1) in benzonitrile with H₂ as a co-reactant in the temperature range 300 to 700 °C. Films were characterized using X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy and four-point probe to determine film crystallinity, composition, atomic bonding, and electrical resistivity, respectively. The lowest temperature at which growth was observed from 1 was 300 °C. For deposition between 300 and 650 °C, AES measurements indicated the presence of W, C, N, and O in the deposited film. The films deposited below 550 °C were amorphous, while those deposited at and above 550 °C were nano-crystalline (average grain size < 70 Å). The films exhibited their lowest resistivity of 840 µΩ-cm for deposition at 300 °C. WN_xC_y films were tested for diffusion barrier quality by sputter coating the film with Cu, annealing the Cu/WN_xC_y/Si stack in vacuum, and performing AES depth profile and XRD measurement to detect evidence of copper diffusion. Films deposited at 350 and 400 °C (50 and 60 nm thickness, respectively) were able to prevent bulk Cu transport after vacuum annealing at 500 °C for 30 min.     

Temperature dependence of the microstructure and resistivity of indium zinc oxide films deposited by direct current magnetron reactive sputtering

Indium zinc oxide (IZO) films were deposited as a function of the deposition temperature using a sintered indium zinc oxide target (In₂O₃:ZnO = 90:10 wt.%) by direct current (DC) magnetron reactive sputtering method. The influence of the substrate temperature on the microstructure, surface roughness and electrical properties was studied. With increasing the temperature up to 200 °C, the characteristic properties of amorphous IZO films were improved and the specific resistivity was about 3.4 × 10^− 4 Ω cm. Change of structural properties according to the deposition temperature was also observed with X-ray diffraction patterns, transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. IZO films deposited above 300 °C showed polycrystalline phases evolved on the amorphous IZO layer. Very flat surface roughness could be obtained at lower than 200 °C of the substrate temperature, while surface roughness of the films was increased due to the formation of grains over 300 °C. Consequently, high quality IZO films could be prepared by DC magnetron sputtering with O₂/Ar of 0.03 and deposition temperature in range of 150-200 °C; a specific resistivity of 3.4 × 10^− 4 Ω cm, and the values of peak to valley roughness and root-mean-square roughness are less than 4 nm and 0.5 nm, respectively.     

Intrinsic stresses and stress relaxation in TiN/Ag multilayer coatings during thermal cycling

Morphology, structure and thermal behavior of magnetron sputtered TiN/Ag multilayer thin films deposited at 150 °C with a bilayer thickness Λ in the range of 75-600 nm are characterized. The films are thermally cycled and the relationship between bilayer thickness Λ, film structure and stress development is analyzed. The results indicate that the residual stresses in the as-deposited films and the behavior during heating are determined by the morphology and the mechanical properties of the Ag interlayers. The increasing crystallite size of Ag with increasing Λ and the initial porosity in the Ag layer are the reason for significant changes in the stress-temperature behavior. While coatings with Λ = 75 nm behave like a single-phase coating up to 380 °C, coatings with higher Λ show a different behavior when exceeding the deposition temperature, which is related to the densification of the Ag layers. During cooling, all coatings exhibit linear thermo-elastic behavior, where the slope of the stress-temperature curves also depends on Λ.     

High mobility, transparent, conducting Gd-doped In2O3 thin films by pulsed laser deposition

Highly transparent and conducting thin films of gadolinium doped indium oxide, which have high electron mobility, were deposited on quartz substrate to study the effect of growth temperature and oxygen pressure on their structural, optical, and electrical properties. X-ray diffraction study reveals that these films are randomly oriented on the quartz surface. The average particle size of the films grown at 600 °C was calculated to be ∼ 23 nm. The optical transparency of the films increases with an increase in the growth temperature. The film transparency is also found to increase with increased oxygen pressure during deposition. The electrical properties of these films strongly depend on both the growth temperature and the oxygen pressure. Analysis of the electrical data shows that the mobility of the films increases with increase in the growth temperature.     

Influence of substrate temperature on N-doped ZnO films deposited by RF magnetron sputtering

Nitrogen-doped ZnO films were deposited by RF magnetron sputtering in 75% of N₂ / (Ar + N₂) gas atmosphere. The influence of substrate temperature ranging from room temperature (RT) to 300 °C was analyzed by X-ray diffractometry (XRD), spectrophotometry, X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS) and Hall measurements setup. The XRD studies confirmed the hexagonal ZnO structure and showed that the crystallinity of these films increased with increasing substrate temperature (T_s). The optical studies indicate the average visible transmittance in the wavelength ranging 500-800 nm increases with increasing T_s. A minimum transmittance (9.84%) obtained for the films deposited at RT increased with increasing T_s to a maximum of 88.59% at 300 °C (500-800 nm). Furthermore, it was understood that the band gap widens with increasing T_s from 1.99 eV (RT) to 3.30 eV (250 °C). Compositional analyses (XPS and SIMS) confirmed the nitrogen (N) incorporation into the ZnO films and its decreasing concentration with increasing T_s. The negative sign of Hall coefficients confirmed the n-type conducting.