Structural investigation of silicon films chemically vapour deposited onto amorphous SiO2 substrates

The influence of substrate temperature and the silane-to-nitrogen ratio on the structure of silicon films 0.5–0.6 μm thick deposited onto amorphous SiO₂ substrates was investigated by X-ray diffraction. The investigations were carried out for silicon films deposited at various temperatures in the range 500–750 °C and with various silane-to-nitrogen ratios in the range 3.04 × 10^-4-2.84 × 10^-3 by volume. The silicon films deposited at 500 °C were amorphous while the films deposited at 550 °C were randomly oriented polycrystalline. The films deposited in the temperature range 600–700 °C were polycrystalline with a preferred orientation that changed from 〈110〉 through 〈100〉 to 〈111〉. The structure of the films deposited at 750 °C was randomly oriented polycrystalline. Investigations of the influence of the silane-to-nitrogen ratio on the silicon film structure revealed that the structure of films deposited at a substrate temperature of 500 °C was independent of the silane-to-nitrogen ratio. The structure of the films deposited at 600 °C depended on the silane-to-nitrogen ratio and changed from polycrystalline with a 〈110〉 preferred orientation to randomly oriented polycrystalline when the ratio was increased. The structure of films deposited at 700 °C also depended on the silane-to-nitrogen ratio and changed from randomly oriented polycrystalline to polycrystalline with double preferred orientation (〈100〉 and 〈111〉) when the ratio was increased.     

Effects of the Ar–N2 sputtering gas mixture on the preferential orientation of sputtered Ru films

We have investigated the influence of N₂ addition to the Ar sputtering gas on the crystal orientation of sputtered Ru films. An rf magnetron sputtering apparatus with a Ru target (99.9%) and a glass substrate heated to 100 °C or 300 °C was used for the deposition. The crystal structure, chemical composition and electrical properties of the resultant films were investigated. X-ray diffraction (XRD) revealed the dominant orientation at 0% N₂ to be the c-axis. With increasing proportion of N₂ in the sputtering gas at a substrate temperature of 100 °C, the intensity of the (002) peak decreased, finally disappearing at 50% N₂. This c-axis-suppressed Ru film sputtered at 50% N₂ was found to contain nitrogen by Auger electron spectroscopy (AES), but by annealing the film in vacuum at 400 °C, the nitrogen in the film was completely removed. The film orientation remained the same as before annealing. Thus, we have demonstrated a new method for depositing Ru films with a controlled preferential orientation of either c-axis oriented or c-axis suppressed.     

Effect of crystallographic orientations on electrical properties of sputter-deposited nickel oxide thin films

Nickel oxide thin films of various preferred orientations were deposited by radio-frequency (RF) magnetron sputtering process in different gas ratios of oxygen atmosphere at RF power 200 W on unheated and heated for (673 K) substrates. The relationships among substrate temperature, preferred orientation and electrical properties of the NiO films were investigated. The resulting films were analyzed by grazing-incidence X-ray diffraction, high-resolution transmission electron microscopy (HR-TEM), and ultrahigh resolution scanning electron microscopy (HR-SEM). The electrical properties were measured using four probe and Hall effects measurements. The results show that films deposited at room temperature with the ratio of oxygen varying from 0 to 100% develop a (111) preferred orientation. At temperature of 673 K, while the (111)-orientated film was obtained under a low ratio of oxygen (<50% O₂), a (200) preferred orientation was developed under 100% oxygen. The lowest sheet resistance 0.01 MΩ/□, resistivity 0.83 Ω-cm and higher carrier density 7.35 × 10¹⁸ cm⁻³ could be obtained on (111) preferred orientation samples prepared on unheated substrates in pure oxygen atmosphere. The relationship between preferred orientation and electrical properties was proposed in this paper.     

Nano-structural characteristics of Ti/glass and Ti/Mo films as a function of deposition rate and angle of incidence

Titanium films of 90 nm thickness were deposited under UHV condition at different deposition rates, ranging from 0.3 to 10.2 Å s^− 1, at room temperature on glass and Mo substrates at two incidence angles of 8.5° and 45°. The samples were analyzed using XRD and AFM techniques. The grain sizes were obtained from AFM images, while the crystallite sizes and preferred orientation of the films were obtained from XRD profiles. Results show that Ti/glass films at 8.5° angle of incidence show (002) preferred orientation, while at 45° incidence angle, at lower deposition rates, films show an almost amorphous structure, which develops to a strong (002) preferred orientation for deposition rate of 1.6 Å s^− 1, and again at much higher deposition rate of 10.2 Å s^− 1 it changes to an amorphous structure. Ti/Mo films deposited at 45° incidence angle showed (101) preferred orientation.     

Structural and electrical properties of RuO2 thin films prepared by rf-magnetron sputtering and annealing at different temperatures

Conductive ruthenium oxide (RuO₂) thin films have been deposited at different substrate temperatures on various substrates by radio-frequency (rf) magnetron sputtering and were later annealed at different temperatures. The thickness of the films ranges from 50 to 700 nm. Films deposited at higher temperatures show larger grain size (about 140 nm) with (200) preferred orientation. Films deposited at lower substrate temperature have smaller grains (about 55 nm) with (110) preferred orientation. The electrical resistivity decreases slightly with increasing film thickness but is more influenced by the deposition and annealing temperature. Maximum resistivity is 861 μΩ cm, observed for films deposited at room temperature on glass substrates. Minimum resistivity is 40 μΩ cm observed for a thin film (50 nm) deposited at 540°C on a quartz substrate. Micro-Raman investigations indicate that strain-free well-crystallized thin films are deposited on oxidized Si substrates.     

Adhesion enhancements and internal stress in MgF2 films deposited with ion beam assistance

We performed adhesion measurements using a dynamically loaded scratch tester to evaluate MgF₂ coatings deposited onto heated and unheated fused silica substrates. Resistance evaporation at 5 Å s^-1 with Ar⁺ ion beam assistance improved the relative adhesive strength of films deposited onto unheated substrates by over an order of magnitude compared with the results for heated substrates without ion beam assistance. Additional experiments were performed to measure internal stress in MgF₂ films on specially masked BK-7 glass substrates using modulated transmission ellipsometry. We found that ion-assisted deposition can reduce internal stress to approximately 450 kgf cm^-2 (tensile) in films 2300 Å thick. The great potential for stress relaxation in MgF₂ films deposited with ion assistance is suggested by these measurements, but additional work with films of higher purity may be required to identify the relative contributions of stress relief, substrate cleaning and chemical bonding to improved adhesion.     

Effects of substrate temperature and substrate material on the structure of reactively sputtered TiN films

Stoichiometric TiN films were reactively magnetron sputtered in an Ar-N₂ atmosphere. The films were deposited at various substrate temperatures in the range 200–650°C onto two types of substrate material, high speed steel and stainless steel. The microstructure of the films obtained was investigated by the use of a transmission electron microscope and the morphology was studied in a scanning electron microscope. Measurements of the hardness were also performed. The analysis of the microstructure shows that the growth of the film is markedly influenced by the substrate material. In particular, the high speed steel substrates were found to have a considerable influence on the microstructure. The vanadium carbide particles in these steels, which have a good lattice match to TiN, stimulate a localized epitaxial growth to occur on these carbide particles. This results in a microstructure consisting of large grains surrounded by small grains. The shape of the large grains is influenced by the temperature. In the development of these large grains cracks and/or voids occur in and around the grains at substrate temperatures above 400°C and the hardness drops by about 20%. No large grains were found on films deposited onto stainless steel and their hardness increases slightly with temperature. High hardness for films deposited onto the high speed steel substrate at temperatures above 400°C can also be obtained if a substrate bias is used. Ion bombardment during film growth suppresses the formation of the large grains with voided or cracked boundaries because of a continuous renucleation process. The formation of the different microstructures is discussed in terms of surface energy minimization and thermally activated processes as surface and grain boundary migration.     

Preferred orientation and interdiffusion in zinc oxide/copper oxide multilayered films

ZnO/CuO and ZnO/ZnO CuO/CuO multilayered films were deposited on Pyrex substrates at <100° C by ion-beam sputtering. The preferred orientation and interdiffusion of these films were examined for films with varying layer repeat lengths (pari thickness). X-ray diffraction analysis showed a preferred ZnO (002) orientation parallel to the surface in annealed ZnO layers of ≈1 to ≈3 nm thickness; no peak was observed for films with a layer repeat length smaller than 1.1 nm. The degree of preferred orientation reduced with increasing layer thickness in ZnO/CuO films and with increasing ZnO CuO thickness in ZnO/ZnO CuO/CuO films. The decay rate of the low-angle X-ray intensity showed that interdiffusivity is largely dependent on the layer repeat length. A smaller layer repeat length gave a larger value of interdiffusivity.     

Role of substrate temperature on the structural,optoelectronic and morphological properties of (400) oriented indium tin oxide thin films deposited using RF sputtering technique

RF sputtering process has been used to deposit highly transparent and conducting films of tin-doped indium oxide onto quartz substrates keeping the RF power constant at 250 W. The electrical, optical and structural properties have been investigated as a function of substrate temperature. XRD has shown that deposited films are polycrystalline and have (400) preferred orientation. Indium tin oxide layers with low resistivity values and high transmittance in the visible region have been deposited. Detailed Analyses based on X-ray diffraction, optical and electrical results are attempted to gain more insight into the factors that are governed by the influence of varying substrate temperature in this investigation. AFM pictures showed uniform surface morphology with very low surface roughness values. It has been observed that ITO films deposited in this study, keeping the substrate temperature at 150 °C, can provide the required optimum electrical and optical properties rendering them useful for developing many optoelectronic devices at a moderate temperature.     

Morphology and texture evolution of nanostructured CaF2 films on amorphous substrates under oblique incidence flux

The morphology and biaxial texture of vacuum evaporated CaF(2) films on amorphous substrates as a function of vapour incident angle, substrate temperature and film thickness were investigated by scanning electron microscopy, x-ray pole figure and reflection high energy electron diffraction surface pole figure analyses. Results show that an anomalous [220] out-of-plane texture was preferred in CaF(2) films deposited on Si substrates at < 200?°C with normal vapour incidence. With an increase of the vapour incident angle, the out-of-plane orientation changed from [220] to [111] at a substrate temperature of 100?°C. In films deposited with normal vapour incidence, the out-of-plane orientation changed from [220] at 100?°C to [111] at 400?°C. In films deposited with an oblique vapour incidence at 100?°C, the texture changed from random at small thickness (5 nm) to biaxial at larger thickness (20 nm or more). Using first principles density functional theory calculation, it was shown that [220] texture formation is a consequence of energetically favourable adsorption of CaF(2) molecules onto the CaF(2)(110) facet.     

Formation and characterization of tungsten silicide layers

Tungsten silicide films formed via furnace annealing were studied. The tungsten layers were deposited either by evaporation or by r.f. sputtering onto Si(100) substrates as well as onto silicon layers deposited in situ. Tungsten deposited at room temperature yields poor silicides owing to the lack of permeability at the interface with silicon. This as well as the formation of voids in the substrate are discussed. Deposition onto substrates heated to 500 °C, however, always allows the formation of a silicide during subsequent annealing.     

Growth of highly c-axis oriented aluminum nitride thin films on β-tantalum bottom electrodes

We have investigated the influence of tantalum (Ta) bottom electrodes on the crystallinity and crystal orientation of aluminum nitride (AlN) thin films. AlN thin films and Ta electrodes were prepared by using rf magnetron sputtering method. The crystal structure of the Ta electrodes was tetragonal (β-Ta, a metastable phase) at room temperature. The crystallinity and orientation of the AlN thin films and Ta electrodes strongly depended on sputtering conditions. Especially, the crystallinity and crystal orientation of the Ta electrodes were influenced by their film thickness and the substrate temperature. When the thickness of the Ta bottom electrodes was 200 nm and the substrate temperature was 100 °C, the AlN thin films indicated high c-axis orientation (the full width at half maximum of rocking curve of 3.9°). The crystal orientation of the AlN film was comparable to that of AlN thin films deposited on face centered cubic (fcc) lattice structure metal, such as Au, Pt and Al, bottom electrodes.     

Orientation-dependent microwave dielectric properties of Ba0.6Sr0.4TiO3 thin films prepared by sol–gel method

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thin films have been prepared on the (100) LaAlO₃ single-crystal substrates by sol–gel technique. The X-ray diffraction study indicated that the thin films exhibited (100) preferred orientation and random orientation depending upon the concentration of precursor solution. The nonlinear dielectric properties of the BST films were measured using an interdigital capacitor. The temperature dependence of dielectric constant of the BST thin films was measured at 1 MHz in the temperature range from ?100 to 80 °C. The Curie temperature T _c of the films derived from 0.1, 0.2 and 0.3 M was found to be ?18.5, ?32.5 and ?39.9 °C, respectively. The tunability of BST films with the (100) preferred orientation was 30.74 %, which was much higher than that of thin films with random orientation at the frequency of 10 kHz with an applied electric field of 80 kV/cm. The microwave dielectric properties of the BST thin films were measured by a vector network analyser from 1 to 10 GHz.     

Epitaxial growth on MgO on (001) surfaces of silver single-crystal film substrates

The epitaxial growth of evaporated MgO films (<25–4000 Å) on smooth (001) surfaces of silver single-crystal film substrates at a temperature inthe range 25°–200°C has been studied by reflection high energy electron diffraction. At substrate temperatures below 150°C, MgO is oriented with its (111) plane parallel to the surface of the substrate. The (111) orientation is fibrous. At 150°C a major fraction of the deposit is oriented in parallel and at 200°C only the parallel orientation is observed. The deposit initially grows as oriented three-dimensional nuclei. As the film thickness increases to 500 Å, randomly oriented MgO is simultaneously formed at the surface. With further increase in thickness the degree of epitaxial orientation decreases and at 1000 Å a small amount of one- degree (111) orientation appears at the surface. At 4000 Å the surface orientation becomes one-degree (111); the (111) orientation is interpreted as a final growth orientation.     

Growth of copper thin films on sputtered-TiN surfaces by metallorganic chemical vapour deposition from (hfac)Cu(I)(VTMS)

Copper (Cu) films were deposited on sputtered TiN with metallorganic chemical vapour deposition (MOCVD) from (hexafluoroacetylacetonate) Cu^(I) (vinyltrimethylsilane) [(hfac)Cu^(I)(VTMS)] at substrate temperatures of 100–300°C, total pressures of 10–2000 mtorr (1–300 Pa) and bubbler temperature of 50°C with Ar carrier gas. Cu was deposited in the form of discontinuous islands up to the film thickness of about 100 nm on the TiN substrate. The orientation of growing films was changed from random orientation to 〈1 1 1〉 with increasing deposition time and temperature. Increasing temperature increased the surface roughness of the film, and grain coalescence. Resistivity was increased due to the carbon incorporation from the thermal decomposition of Cu precursor. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solid-phase crystallization of β-FeSi2 thin film in Fe/Si structure

Dependence of solid-phase growth of β-FeSi₂ thin films on the crystal orientation of Si substrates has been investigated by using a-Fe (thickness: 20 nm)/c-Si(100), (110) and (111) stacked structures. X-ray diffraction (XRD) measurements suggested that the substrate orientation dependence of the formation rate of β-FeSi₂ was as follows: (100)>(111)>(110). This dependence can be explained on the basis of the lattice mismatch between β-FeSi₂ and Si substrates, i.e., the lattice mismatch between β-FeSi₂(100) and Si(100), β-FeSi₂(110) or (101) and Si(111), and β-FeSi₂(010) or (001) and Si(110) of 1.4-2.0%, 5.3-5.5% and 9.2%, respectively. The substrate orientation dependence of solid-phase growth becomes relatively remarkable for very thin films.     

Synthesis, elaboration and characterization of the new material CuIn3S5 thin films

CuIn₃S₅ compound was prepared by direct reaction of high-purity elemental copper, indium and sulphur. CuIn₃S₅ thin films were prepared from powder by thermal evaporation under vacuum (10⁻⁶ mbar) onto glass substrates. The glass substrates were heated from 30 to 200 °C. The powder was characterized for their structural and compositional properties by using X-ray diffraction (XRD) and energy dispersive X-ray (EDAX). The XRD studies revealed that the powder exhibiting P-chalcopyrite structure. From the XRD data, we calculated the lattice parameters a and c. Then, the cation–anion bond lengths l _AC and l _BC are deduced. The films were characterized for their structural, compositional, morphological and optical properties by using XRD, EDAX, atomic force microscopy and optical measurement techniques (transmittance and reflectance). XRD analysis revealed that the films deposited at a room temperature (30 °C) are amorphous in nature, whereas those deposited on heated substrates (≥75 °C) were polycrystalline with a preferred orientation along (112) of the chalcopyrite phase. The surface morphological analysis revealed that the films grown at different substrate temperature had an average roughness between 1.1 and 4.8 nm. From the analysis of the transmission and reflection data, the values of direct and indirect band gap of the films were determined. We found that the optical band gap decreases when the substrate temperature increases.     

Crystallography of epitaxially grown molybdenum on sapphire

Molybdenum thin films were deposited onto (0001), ($\text{1012}$) and (10$\text{12}$) sapphire substrates by electron-beam evaporation in ultrahigh vacuum. The surface morphology and crystallographic orientation of these films were characterized by electron microscope replication and reflection electron diffraction. The effect of the crystallographic plane of the sapphire substrates as well as that of the deposition rate on the crystallographic orientation of the deposited molybdenum films were examined in the temperature range 25°-1000°C. The epitaxial temperature range was 600°-900°C for basal plane substrates and 300°-1000°C for ($\text{1}$012) and (10$\text{1}$2) substrates. The orientation of the deposited film was strongly dependent on that of the sapphire substrate.     

Radio frequency sputtering of CdSe films

We have studied the influence of various substrate and sputtering parameters on the electrical and structural properties of CdSe films. The most important deposition parameters are the substrate temperature and the plasma power density. The condensation rate is determined by both parameters. The power density not only determines the arrival rate of the condensing species on the substrate but (which is even more important for the film quality) it also controls the substrate bombardment by energetic particles (secondary electrons and ions). This bombardment apparently has a big influence on the condensation rate and the structural ordering of the growing film.The film growth was investigated on two different substrates, namely basal- plane-oriented sapphire and silica glass. At substrate temperatures below 400°C the film properties on both kinds of substrates are approximately equal. These films are polycrystalline with a large degree of preferred (0001) orientation (the c axis perpendicular to the substrate). At substrate temperatures above 400°C the mechanism of film growth on the two different substrates is vastly different. The CdSe films on amorphous silica glass become increasingly amorphous with increasing substrate temperature or plasma power density. On the other hand the films on single-crystal sapphire become epitaxial with increasing substrate temperature. The epitaxial relation between substrate and film is as expected, namely (0001) CdSe_∥ on (0001) Al₂O₃.     

射频磁控溅射法制备碲化铅薄膜的X射线衍射分析

采用射频磁控溅射法,在单面抛光的Si(111)衬底上制备了PbTe薄膜,利用X射线衍射法分析了溅射工艺参数如溅射功率、溅射时间、衬底温度以及退火温度对PbTe薄膜的结晶质量的影响。结果表明:在溅射功率为30W,溅射时间为10 min,衬底未加热时制备的薄膜具有最好的〈100〉方向的择优取向性;退火处理可以改善薄膜的结晶质量,并且退火温度越高,薄膜的结晶质量越好。