Highly textured Gd2Zr2O7 films grown on textured Ni-5 at.%W substrates by solution deposition route: Growth, texture evolution, and microstructure dependency

Growth, texture evolution and microstructure dependency of solution derived Gd₂Zr₂O₇ films deposited on textured Ni-5 at.%W substrates have been extensively studied. Influence of processing parameters, in particular annealing temperature and dwell time, as well as thickness effect on film texture and morphology are investigated in details. It is found that a rotated cube-on-cube epitaxy of Gd₂Zr₂O₇< 110>//NiW<100> in-plane texture forms as soon as the (004) out-plane texture appears, implying that epitaxial growth dominates the crystallization processes. Thermal energy plays an important role in minimizing the difference of interfacial energy along two directions in the anisotropic metallic substrate. Growth of Gd₂Zr₂O₇ films displays an ultrafast kinetics under optimized conditions. Independency of sharp epitaxial (004) and polycrystalline (222) orientation is revealed from further synchrotron diffraction studies. Fully covered films with a broad thickness range exhibit a high degree of biaxial orientation, similar surface morphology with crack free and nano-size grains microstructure, seemingly independent of neither heat treatment nor thickness. Particularly, we compared the porosity of the film surface and body according to surface or cross-sectional observation and Rutherford Backscattering Spectrometry analysis, pointing to inhomogeneous structure through film thickness, i.e., dense in the surface layer but porous in the body. This is attributed to trapped gas generated during either decomposition or crystallization in the thicker films. This work not only demonstrates a route for producing textured Gd₂Zr₂O₇ buffer layers with dense structure directly on technical substrates, but also provides some fundamental understandings related to chemical solution derived films grown on metallic substrates.     

Preparation and characterization of indium doped CdS0.2Se0.8 thin films by spray pyrolysis

The CdS_0.2Se_0.8 and indium doped CdS_0.2Se_0.8 thin films have been deposited onto the amorphous glass and fluorine doped tin oxide coated glass substrates by spray pyrolysis. The doping concentration of indium has been optimized by photoelectrochemical characterization technique. The structural, surface morphological, optical and electrical properties of CdS_0.2Se_0.8 and indium doped CdS_0.2Se_0.8 thin films have been studied. X-ray diffraction studies reveal that the films are polycrystalline in nature with hexagonal crystal structure. Scanning electron microscopy studies reveal that the grains are uniform with uneven spherically shaped, distributed over the entire substrate surface. The complete surface morphology has been changed after doping. In optical studies, the transition of the deposited films is found to be direct allowed with optical energy gaps decreasing from 1.91 to 1.67 eV with indium doping. Semiconducting behavior has been observed from resistivity measurements. The thermoelectric power measurements reveal that the films exhibit n-type conductivity.     

Biaxial CdTe/CaF2 films growth on amorphous surface

A continuous and highly biaxially textured CdTe film was grown by metal organic chemical vapor deposition on an amorphous substrate using biaxial CaF₂ nanorods as a buffer layer. The interface between the CdTe film and CaF₂ nanorods and the morphology of the CdTe film were studied by transmission electron microscopy (TEM) and scanning electron microscopy. Both the TEM and X-ray pole figure analysis clearly reveal that the crystalline orientation of the continuous CdTe film followed the {111}<121> biaxial texture of the CaF₂ nanorods. A high density of twin faults was observed in the CdTe film. Furthermore, the near surface texture of the CdTe thin film was investigated by reflection high-energy electron diffraction (RHEED) and RHEED surface pole figure analysis. Twinning was also observed from the RHEED surface pole figure analysis.     

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al₂O₃) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 °C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al₂O₃-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance, AC conductivity and activation energy were determined and the results are discussed.     

Microstructural size effects on the hardness of nanocrystalline TiN/amorphous-SiNx coatings prepared by magnetron sputtering

It has been postulated that equiaxed nanocrystalline (<10 nm) TiN grains embedded in a thin amorphous silicon nitride (a-SiN_x) phase are a prerequisite to obtain ultrahard TiN/a-SiN_x coatings. The present study correlates hardness and microstructure of TiN/a-SiN_x coatings with Si contents between 0 and 17 at.%. The coatings have been deposited by magnetron sputtering in industrial-scale physical vapour deposition systems. Transmission electron microscopy studies revealed that increasing the silicon content causes the TiN grain size to decrease. This is accompanied by a change in grain morphology: At Si contents lower than 1 at.% TiN grains become columnar, while at Si contents higher than 6 at.% equiaxed grains with diameters of 6 nm form. For silicon contents between 1 and 6 at.%, a transition region with nanocrystalline columnar grains exists. This nanocrystalline columnar microstructure causes maximum hardness values of more than 45 GPa for TiN/a-SiN_x coatings as determined by nanoindentation. The elongated and equiaxed nanocrystalline TiN grains exhibit almost theoretical strength as dislocation-based deformation mechanisms are constrained.     

Texture and microstructure of Cr2O3 and (Cr,Al)2O3 thin films deposited by reactive inductively coupled plasma magnetron sputtering

Cr₂O₃ and (Cr,Al)₂O₃ films were grown using reactive dc and inductively coupled plasma magnetron sputtering at substrate temperatures of 300-450 °C. For pure chromia, α-Cr₂O₃ films with fiber texture were grown; the out-of-plane texture could be controlled from < 0001> to < 101?4>. The former texture was obtained as a consequence of competitive growth with no applied bias or inductively coupled plasma, while the latter was obtained at moderate bias (− 50 V), probably due to recrystallization driven by ion-bombardment-induced strain. By reactive codeposition of Cr and Al, a corundum-structured metastable solid solution α-(Cr,Al)₂O₃ with Cr/Al ratios of 2-10 was grown with a dense, fine-grained morphology. Hardness and reduced elastic modulus values were in the ranges 24-27 GPa and 190-230 GPa, respectively.     

Structural and optical studies of nanocrystalline V2O5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T_S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V₂O₅ films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V₂O₅ films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.     

Development of TiSiN CVD process using TiCl4/SiH4/NH3 chemistry for ULSI anti-oxidation barrier applications

CVD-TiSiN may be promising material for O₂ diffusion-barrier films in ultra-large scale integrated (ULSI) circuit applications, especially for dynamic random-access memory (DRAM) capacitors. We developed a method for introducing Si into TiN, which is a common material used for diffusion-barrier films. TiSiN films were deposited by reacting TiCl₄, SiH₄, and NH₃ in a hot-wall CVD reactor. We measured TiSiN film deposition rates, composition, crystal structure, and resistivity as a function of SiH₄ partial pressure. Adding Si to TiN converts the TiN film structure from columnar grains to columnar-free structure films, thereby effectively removing the diffusion paths for O₂. The resistivity of TiSiN films was increased by adding SiH₄ to the reactant gas. With an increase in SiH₄ partial pressure up to P_SiH4=0.8 Torr, the resistivity gradually increased, but for P_SiH4=1.2 Torr, the phase present in the film was almost SiN and its resistivity jumped up. TiSiN film rapid thermal annealing was performed to evaluate the anti-oxidation performance at the temperature range from 400 to 600 °C in 100 Torr of O₂. For an increase the Si concentration up to 4.4 at.% improved anti-oxidation performance of TiSiN films. Flow modulation chemical vapor deposition (FMCVD) was used to create TiSiN films with low Cl concentration and improved anti-oxidation performance.     

Effect of Li doping on the structural, optical and electrical properties of spray deposited SnO2 thin films

Studies on spray deposited transparent conducting Li doped SnO₂ thin films are scarce. Li (0 to 5 wt.%) doped SnO₂ thin films spray deposited onto glass substrates at 773 K in air from chloride precursors were studied for their structural, optical and temperature dependent electrical behaviors. X-ray diffraction patterns indicated single phase with polycrystalline nature. Systematic variation in surface morphology on Li doping was examined by scanning electron microscopy and atomic force microscopy. Film thickness, optical band gap (direct and indirect), sheet resistance and figure of merit were computed from spectral transmittance and temperature dependent resistivity data. Lithium doping was found to decrease the value of sheet resistance by an order in magnitude. Activation energy was computed from temperature dependent electrical resistivity data measured in the range 300 to 448 K. The 4 wt.% Li doped SnO₂ film was found to have a high value of figure of merit among other films. The results are discussed.     

Self-patterned Nano Structures in Structurally Gradient Epitaxial La0.5Ba0.5CoO3 Films

Highly epitaxial La_0.5Ba_0.5CoO₃ (LBCO) thin films with sharp interface and a thickness of 200 nm were epitaxially grown on (001) SrTiO₃ substrates using pulsed laser deposition. High-resolution transmission electron microscopy and electron diffraction analysis revealed that the films have a triple-layered structure. The first layer, close to the film/substrate interface, has a thickness of ~ 6 nm and is a defect free single crystal disordered cubic structure (a = 3.882 Å) which has a lattice mismatch of − 0.59% with respect to the substrate. The second layer which dominates the film structure has a single crystal disordered cubic structure (a = 3.854 Å) which has a lattice mismatch of − 1.31% with respect to the substrate. The third layer located on the top of the film has a thickness of several nanometers and consists of 112-type ordered tetragonal structure. The cubic structures in the first and second layer have an orientation relationship of (001)_LBCO//(001)_STO and < 100 > _LBCO//< 100 > _STO with respect to the substrate. Self-patterned 3-dimensional nano structures with a dimension range from 2 to 10 nm were formed in the second and third layers. These nano structures were formed by the enclosure of anti-phase boundary planes which are parallel to the {100} of the cubic structure. Epitaxial LBCO thin films with such nano structures are hard ferromagnetic with a large coercive field value and magnetoresistance effect value (~ 24%), and exhibit semiconductor behavior at temperatures < 300 K.     

Alteration of internal stresses in SiO2/Cu/TiN thin films by X-ray and synchrotron radiation due to heat treatment

A break of wiring by stress-migration becomes a problem with an integrated circuit such as LSI. The present study investigates residual stress in SiO₂/Cu/TiN film deposited on glass substrates. A TiN layer, as an undercoat, was first deposited on the substrate by arc ion plating and then Cu and SiO₂ layers were deposited by plasma coating. The crystal structure and the residual stress in the deposited multi-layer film were investigated using in-lab. X-ray equipment and a synchrotron radiation device that emits ultra-high-intensity X-rays. It was found that the SiO₂ film was amorphous and both the Cu and TiN films had a strong {1 1 1} orientation. The Cu and TiN layers in the multi thick (Cu and TiN:1.0 μm)-layer film and multi thin (0.1 μm)-layer film exhibited tensile residual stresses. Both tensile residual stresses in the multi thin-layer film are larger than the multi thick-layer film. After annealing at 400 °C, these tensile residual stresses in both the films increased with increasing the annealing temperature. Surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat-treatment.     

Highly (100)-oriented CeO2 films prepared on amorphous substrates by laser chemical vapor deposition

CeO₂ films were prepared on amorphous silica substrates by laser chemical vapor deposition using cerium dipivaloylmethanate precursor and a semiconductor InGaAlAs (808 nm in wavelength) laser system. The laser spot size was about 20 mm, which was sufficient to cover the whole substrate. Highly (100)-oriented CeO₂ films were obtained at extraordinary high deposition rates ranging from 60 to 132 μm/h. Films exhibited a columnar feather-like structure with a large number of nano-sized voids, and a surface morphology consisting of either nearly flat or pyramidal top-ending columns depending on the laser power. Nearly flat top-ending columns could be fairly (100)-oriented at the top and (111)-oriented laterally.     

Structure evolution and ferroelectric properties of Bi3.4Yb0.6Ti3O12 thin films crystallized under a moderate temperature

Ytterbium-doped Bi₄Ti₃O₁₂ (Bi_3.4Yb_0.6Ti₃O₁₂, BYT) ferroelectric thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by chemical solution deposition (CSD). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. Structure evolution and ferroelectric properties of the as-prepared thin films annealed under different temperatures (600 °C-750 °C) were studied in detail. Additionally, the mechanism concerning the dependence of electrical properties of the BYT ferroelectric thin films on the annealing temperature was discussed.     

Epitaxial growth and properties of cubic Zn0.7Mg0.3O films on TiN-buffered Si(100) substrates by in situ pulsed laser deposition

A novel cubic Zn_0.7Mg_0.3O film on silicon substrate is conducted by KrF excimer pulsed-laser ablation system. By introducing a thin TiN buffer, layer-by-layer growth of cubic Zn_0.7Mg_0.3O film epilayer has been realized. The overall growth process was monitored in situ by reflection high-energy electron diffraction (RHEED) method. It was found that the crystallinity and surface morphology of the Zn_0.7Mg_0.3O films were strongly affected by the TiN buffer layer. The Zn_0.7Mg_0.3O film obtained at an optimal buffer layer exhibited high quality and good surface. For the metal-insulator-metal (MIM) structure of Pt/Zn_0.7Mg_0.3O (200 nm)/TiN (20 nm)/Si (400 μm) prepared at the optimal growth conditions achieved a very low leak current density of ∼10⁻⁶ A cm⁻² at an electric field of 9 × 10⁵ V cm⁻¹ and the permittivity (?_r) of about 8.1, agreed well with that of acquired MgO film and MgO single crystal.     

Role of substrate temperature on the structural, morphological and optical properties of CuGaSe2 thin films grown by Pulsed Electron Deposition technique

CuGaSe₂ (CGS) thin films were grown on uncoated and Mo-coated soda lime glass by Pulsed Electron Deposition (PED) technique at substrate temperatures comprised between 25 °C and 475 °C. X-ray diffraction analysis reveals that CGS samples exhibit a noteworthy crystal quality even at low growth temperature, T_g = 100 °C, whereas the out-of-plane preferential orientation of CGS chalcopyrite phase switches from < 220 > to < 112 > by increasing the substrate temperature. Annealing treatments seem to enhance the crystallinity of the film and to release the residual strain energy. Visible/near-infrared absorbance spectra show a monotonic decrease of CGS optical bandgap (from 1.75 to 1.65 eV) by enhancing the substrate temperature. Yet the morphology of CGS films strongly depends on T_g, which promotes the formation of larger columnar grains perpendicular to the growth plane. Grain dimensions of ~ 2 μm are achieved when CGS films are grown at high temperature (> 400 °C) on Mo-coated glass. The results indicate that PED is a promising growth technique for achieving good-quality CGS that can be useful as absorber layers in thin film solar cells.     

Y2O3 stabilized ZrO2 thin films deposited by electron-beam evaporation: Optical properties, structure and residual stresses

This paper describes the preparation and the characterization of Y₂O₃ stabilized ZrO₂ thin films produced by electric-beam evaporation method. The optical properties, microstructure, surface morphology and the residual stress of the deposited films were investigated by optical spectroscopy, X-ray diffraction (XRD), scanning probe microscope and optical interferometer. It is shown that the optical transmission spectra of all the YSZ thin films are similar with those of ZrO₂ thin film, possessing high transparency in the visible and near-infrared regions. The refractive index of the samples decreases with increasing of Y₂O₃ content. The crystalline structure of pure ZrO₂ films is a mixture of tetragonal phase and monoclinic phase, however, Y₂O₃ stabilized ZrO₂ thin films only exhibit the cubic phase independently of how much the added Y₂O₃ content is. The surface morphology spectrum indicates that all thin films present a crystalline columnar texture with columnar grains perpendicular to the substrate and with a predominantly open microporosity. The residual stress of films transforms tensile from compressive with the increasing of Y₂O₃ molar content, which corresponds to the evolutions of the structure and packing densities.     

Control of crystallographic orientation of LiNbO3 films grown by electron-cyclotron resonance plasma sputtering on TiN films

We investigated the orientation of domains in LiNbO₃ (LN) thin films grown by electron-cyclotron resonance plasma sputtering on TiN films with various crystalline states. Deposition at 400 °C on an amorphous TiN produced partially crystallized and apparently c-axis-oriented LN. When TiN crystallized at 460 °C to become polycrystalline grains, the roughened surface randomized the orientation of LN. At 600 °C, the reaction of TiN with oxygen atoms supplied from the plasma created a TiO_x layer. Rapid thermal annealing of amorphous LN films at 460 °C was the best solution for removing these disorientation factors, but annealing of amorphous LN on poly-crystalline TiN yielded no c-axis-oriented domains.     

Effects of nitrogen partial pressure on microstructure,morphology and N/Ti ratio of TiN films deposited by reactive magnetron sputtering

Abstract

TiN films were deposited on Si(111) substrates at different nitrogen partial pressures with reactive magnetron sputtering. The crystal structure and preferred growth orientation of the films were determined using X-ray diffraction (XRD) analysis. Their morphology and composition were analysed using field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). It is found that with the increase in nitrogen partial pressure, the growth of TiN films varies from the {111} preferred orientation to the {100} preferred orientation and the deposition rate of TiN films decreases. When the {111} preferred orientation is presented, TiN films reveal a kind of surface morphology of triangular pyramid with right angles; while the {100} orientation is dominant, TiN films characterise another kind of domelike surface morphology. Furthermore, the N/Ti ratio of the TiN films first increases, then decreases and increases again as nitrogen partial pressure enlarges.     

Fabrication of low-resistivity and gold-colored TiN films by halide chemical vapor deposition with a low [NH3]/[TiCl4] flow ratio

This work describes the preparation of titanium nitride (TiN) films on Si (111) substrates by atmospheric pressure halide chemical vapor deposition (AP-HCVD). Various TiN films were obtained by exploiting TiCl₄ + NH₃ gas chemistry with flow ratios [NH₃]/[TiCl₄] from 0.2 to 1.4, and deposition temperatures (T_d) from 600 to 900 °C. When T_d = 800 °C gold-colored films with electrical resistivities of under 100 μΩ cm were formed at almost all of the investigated [NH₃]/[TiCl₄] flow ratios. In particular, a lowest resistivity of about 23.7 μΩ cm, which is quite close to that of bulk TiN, was achieved using an [NH₃]/[TiCl₄] flow ratio of 0.3. Atomic force microscopy indicated that the root mean square surface roughness of that film was only about 5.1 nm. Under the same [NH₃]/[TiCl₄] flow ratio as above, X-ray diffraction analyses revealed the presence of a cubic TiN phase with a preferred orientation of (200) for T_d ≤ 800 °C, while additional (111) and (220) orientations emerged when the film was deposited at 900 °C. In conclusion, a low resistivity (< 100 μΩ cm) TiN film can be formed by AP-HCVD with very low [NH₃]/[TiCl₄] flow ratios 0.3-1.4.     

Crystallography of TiSi2 (C54) epitaxy on (111)Si and (001)Si surfaces

Following the success in understanding the textures in TiSi₂ (C49) epitaxy on (001)_Si surface using the edge-to-edge matching model that was originally developed for predicting the crystallographic features of diffusion-controlled phase transformations in solids, the present work applies this model to understand the in-plane texture in TiSi₂ (C54) thin films on Si single crystal surfaces and to explain why its epitaxial growth is more favoured on (111)_Si than on (001)_Si. Based on the actual atomic spacing along the matching directions across the interface between the thin films and the substrate, the model predicts most of the experimentally observed orientation relationships (ORs) and that the preferred order among the different systems is C49/(001)_Si system > C54/(111)_Si system > C49/(111)_Si system ≅ C54/(001)_Si system. The model has strong potential to be used to develop new thin film materials.