Microanalyses on the hydrogen permeated 70% SiCC films

SiCC films with content of 70% SiC were deposited by rf magnetron sputtering on stainless steel or NaCl substrate followed by argon ion bombardment. Samples were then submitted to hydrogen permeation at 3.23×10⁷ Pa and 500 K for 3 h. Secondary ion mass spectroscopy (SIMS) was used to analyze hydrogen concentration with depth and to check the formation of hydrogen related bonds in the SiCC films with IR measurement. Auger electron spectra (AES) and X-ray photoelectron spectra (XPS) were carried out to check the effects of hydrogen participation on shifts of chemical bonding states of C, Si and O contamination.     

Investigation of alumina-silica films deposited by pulsed injection metal-organic chemical vapour deposition

This work is devoted to deposition of alumina-silica films using an innovative pulsed injection metal organic chemical vapour deposition technique and aluminium tri(iso-propoxide) (Al(i-OPr)₃) and tetraethoxysilane (TEOS) as precursors. The deposited aluminium silicate films have been characterised by scanning electron microscopy, infrared spectroscopy, X-ray diffractometry and capacitance-voltage (C-V) measurements. The investigation of the deposition at different Si/Al ratios and substrate temperatures has shown that the growth rate increases with the increase of Al(i-OPr)₃ proportion in solution and decreases as the proportion of TEOS increases. We have also shown that aluminium content in the film increases at lower deposition temperatures while silicon content increases at higher temperatures. The permittivity of the films determined from C-V measurements decreases with increasing substrate temperature. It was found that films deposited at substrate temperatures of 600 or 700 °C and with the highest Si/Al ratio have the lowest dielectric permittivity. This research should be useful for further development of MOCVD technology for the deposition of aluminosilicate-based dielectric materials with controlled dielectric permittivity.     

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.     

Hot-wire chemical vapor deposition of WO3−x thin films of various oxygen contents

We present the synthesis of tungsten oxide (WO_3−x) thin films consisting of layers of varying oxygen content. Configurations of layered thin films comprised of W, W/WO_3−x, WO₃/W and WO₃/W/WO_3−x are obtained in a single continuous hot-wire chemical vapor deposition process using only ambient air and hydrogen. The air oxidizes resistively heated tungsten filaments and produces the tungsten oxide species, which deposit on a substrate and are subsequently reduced by the hydrogen. The reduction of tungsten oxides to oxides of lower oxygen content (suboxides) depends on the local water vapor pressure and temperature. In this work, the substrate temperature is either below 250 °C or is kept at 750 °C. A number of films are synthesized using a combined air/hydrogen flow at various total process pressures. Rutherford backscattering spectrometry is employed to measure the number of tungsten and oxygen atoms deposited, revealing the average atomic compositions and the oxygen profiles of the films. High-resolution scanning electron microscopy is performed to measure the physical thicknesses and display the internal morphologies of the films. The chemical structure and crystallinity are investigated with Raman spectroscopy and X-ray diffraction, respectively.     

Investigation of the aluminum oxide/Si(1 0 0) interface formed by chemical vapor deposition

Thin films of aluminum oxide were deposited using trimethylaluminum and oxygen. The deposition rate was found to decrease with increasing temperature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the film/substrate interface. When dry O₂ was used during deposition, the film/substrate interface was free of any silicon dioxide or aluminum silicate phase. On annealing the as-deposited films in Ar, a layer of silicon dioxide film formed at the interface. XPS results indicated that the O/Al ratio in the as-deposited films was higher than that in stoichiometric Al₂O₃. However, the ratio was found to decrease in the annealed samples suggesting that excess oxygen present in the deposited films is responsible for the formation of interfacial silicon dioxide layer. Interfacial phase formation was observed in the as-deposited samples, when small amounts of ozone along with oxygen were used as the oxygen precursor.     

Flash-lamp-crystallized polycrystalline silicon films with high hydrogen concentration formed from Cat-CVD a-Si films

We investigate residual forms of hydrogen (H) atoms such as bonding configuration in poly-crystalline silicon (poly-Si) films formed by the flash-lamp-induced crystallization of catalytic chemical vapor deposited (Cat-CVD) a-Si films. Raman spectroscopy reveals that at least part of H atoms in flash-lamp-crystallized (FLC) poly-Si films form Si-H₂ bonds as well as Si-H bonds with Si atoms even using Si-H-rich Cat-CVD a-Si films, which indicates the rearrangement of H atoms during crystallization. The peak desorption temperature during thermal desorption spectroscopy (TDS) is as high as 900 °C, similar to the reported value for bulk poly-Si.     

Growth and characterization of yttrium oxide films by reactive magnetron sputtering

Yttrium oxide (Y₂O₃) is a promising ceramic material for electronic and optical applications due to its excellent properties. The purpose of this study is to characterize the effects of deposition parameters on the structure and composition of Y₂O₃ films. The films are grown on Si substrates by reactive magnetron sputtering at different substrate temperatures and oxygen pressures. The composition and structure of the films are studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It is shown that the Y₂O₃ films deposited by reactive magnetron sputtering are mainly cubic phase and polycrystalline. The films are composed of Y-O, Y-O-Si, and Si-O bonds. Increasing substrate temperature induces the monoclinic to cubic phase transition and results in the formation of oxygen vacancies in the film. The preferred growth orientation of Y₂O₃ film is the (110) plane at low temperature, and it changes to the (111) plane at high temperature. The low temperature is preferable for the formation of Y-O bonds. The oxygen pressure influences on the concentration of Y-O bonds significantly. An optimal oxygen partial pressure for the formation of Y-O bonds exists during the film deposition. In addition, the deposited Y₂O₃ films exhibit excellent mechanical properties.     

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.     

Properties of nanocrystalline SiC:Ge:H alloy deposited by hot-wire chemical vapor deposition using Organosilane and Organogermane

Nanocrystalline hydrogenated silicon carbide: germanium alloy (nc-SiC:Ge:H) films have been deposited by hot-wire chemical vapor deposition at a low substrate temperature of about 300 °C. Germanium incorporation into the films and film structure based on cubic silicon carbide were confirmed by X-ray photoelectron spectroscopy and X-ray diffraction. Optical absorption spectra of the films with a germanium mole fraction of about 2% shifted to lower energies by about 0.2 eV compared with that of nanocrystalline cubic silicon carbide films.     

Influence of deposition temperature on the growth of vacuum evaporated V2O5 thin films

V₂O₅ films were deposited on silicon (111) substrates by vacuum evaporation technique at various deposition temperatures of 300, 473, 573, 623 and 673 K. X-ray characterization revealed that the films deposited at T_s≤473 K are amorphous and the film deposited at T_s≥573 K is polycrystalline. It is interesting to note that the film deposited at T_s=573 K is strongly oriented with (001) planes parallel to the substrate and the degree of preferred orientation towards (001) planes found to decrease with further increase in the deposition temperature. The influence of deposition temperature on the growth of the V₂O₅ films has been studied by Raman scattering spectroscopy. The films deposited on the silicon substrates maintained at 573 K are found to have better structural quality.     

Surface nano-structured silicon carbide thin film produced using hot filament decomposition of ethylene at low temperature on silicon wafer

The structure and spectroscopic properties of nano-structured silicon carbide (SiC) thin films were studied for films obtained through deposition of decomposed ethylene (C₂H₄) on silicon wafers via hot filament chemical vapor deposition method at low temperature followed by annealing at various temperatures in the range 300-700 °C. The prepared films were analyzed with focus on the early deposition stage and the initial growth layers. The analysis of the film's physics and structural characteristics was performed with Fourier transform infrared spectroscopy and Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, and X-ray diffraction. The conditions for forming thin layer of cubic SiC phase (3C-SiC) are found. X-ray diffraction and Raman spectroscopy confirmed the presence of 3C-SiC phase in the sample. The formation conditions and structure of intermediate SiC layer, which reduces the crystal lattice mismatch between Si and diamond, are essential for the alignment of diamond growth. This finding provides an easy way of forming SiC intermediate layer using the Si from the substrate.     

SiOxNy Films deposited with SiCl4 by remote plasma enhanced CVD

Silicon oxynitride films have been deposited with SiCl₄ by remote-plasma enhanced chemical vapor deposition (PECVD) at a substrate temperature of 250°C. Different mixtures of O₂ and NH₃ were used to obtain different oxynitride compositions ranging from SiO₂ to an stoichiometry close to that of silicon nitride. Rutherford backscattering spectrometry was used to determine the chemical composition of the SiO_xN_y films. The behavior of the IR absorption spectra as well as the refractive index measured by ellipsometry were used to estimate the effect of the different deposition parameters. It was found that the IR spectra show a shift of the characteristic peak associated with the stretching vibration mode of the Si-O-Si bonds towards lower wavenumbers as the relative concentration of ammonia was increased with respect oxygen. No double peaks associated with silicon oxide and silicon nitride were observed, indicating the formation of an homogeneous alloy. The IR spectra did not show any presence of water or hydrogen related impurities in the film. Also the effect of a hydrogen flow added during the deposition process on the structural characteristics of the deposited films was studied using dielectric spectroscopy and atomic force microscopy measurements showing that the hydrogen flow added during deposition results in a reduction of the film roughness and a planarization effect, which is very interesting for the application of these films in microelectronics devices.     

Carbon incorporation in chemical vapor deposited aluminum oxide films

We report results from an investigation into the nature and extent of carbon incorporation into aluminum oxide thin films deposited from the pyrolysis of dimethylaluminum isopropoxide via high-vacuum chemical vapor deposition. The chemical nature and distribution of carbon in films deposited in the 417-659 °C temperature range were investigated through X-ray photoelectron spectroscopy and Auger electron spectroscopy. Carbon composition increased with increasing deposition temperature, up to approximately 8 at.% at 659 °C. Carbon in films deposited at 477 °C was bonded only to oxygen or carbon, but films deposited above 538 °C also contained metal carbide-like bonding. Carbon content in films deposited on hydrogen-terminated Si (100) substrates increased toward the film-substrate interface, but no silicon-carbon bonding was observed.     

On the nitrogen and oxygen incorporation in plasma-enhanced chemical vapor deposition (PECVD) SiOxNy films

Silicon oxynitride films were deposited by plasma-enhanced chemical vapor deposition at low temperatures using nitrous oxide (N₂O) and silane (SiH₄) as gas precursors. The influence of the N₂O/SiH₄ flow ratio (varied from 0.25 up to 5) and the thickness of the films on the optical and structural properties of the material was analyzed. The films were characterized by ellipsometry, Fourier-transform infrared spectroscopy, Rutherford backscattering spectroscopy and optical absorption. Two distinct types of material were obtained, silicon dioxide-like oxynitrides SiO_2−xN_x and silicon-rich oxynitrides SiO_xN_y (x+y<2). The results demonstrate that in silicon dioxide-like material, the nitrogen concentration can be adequately controlled (within the range 0–15 at.%) with total hydrogen incorporation below 5 at.% and no appreciable SiH bonds. It is also shown that the composition remains uniform through the entire thickness of the films. Furthermore, a linear relation between the refractive index and the nitrogen concentration is observed, which makes this material very attractive for optoelectronic applications. On the other hand, silicon-rich material is similar to amorphous silicon, and presents an increasing concentration of SiH bonds, increasing refractive index and decreasing optical gap, which makes it promising for applications in light-emitting devices.     

Structure of polycrystalline silicon films deposited at low temperature by plasma CVD on substrates exposed to different plasma

Polycrystalline silicon (poly-Si) films were deposited on glass substrates (corning 7059) at 300°C by a plasma enhanced chemical vapor deposition (PECVD) from a SiH₄/SiF₄ mixture. All poly-Si films were prepared under the same deposition conditions on the substrates subjected to nitrogen, hydrogen and/or CF₄ plasma with different gas pressures, just before deposition of the poly-Si films. Effects of such pretreatments for substrates on the structural properties of the resultant poly-Si films have been investigated. The Si film deposited on the substrates without any pretreatments was amorphous. However, formation of a strong 〈110〉 preferentially oriented poly-Si with improved crystallinity was obtained for the films deposited on the glass substrate after plasma pretreatments, which exhibit smoother surfaces. This result was interpreted in terms of a removal of weak Si–Si bonds during nucleation and the subsequent grain growth.     

Pulsed laser deposition of crystalline ZrC thin films

ZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique under various conditions. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), X-ray diffraction and reflectivity, spectroscopic ellipsometry, and four point probe measurements were used to characterize the properties of the deposited films. It has been found that crystalline films could be grown only by using laser fluences higher than 5 J/cm² and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm² and a substrate temperature of 700 °C, cubic ZrC films (a = 0.469 nm) exhibiting a (200)-texture were deposited under vacuum or low pressure C₂H₂ atmosphere. These films were smooth, with surface roughness values below 1.0 nm and mass densities around the tabulated value of 6.7 g/cm³. AES depth profiling investigations showed oxygen contamination around 7% in the bulk region. Despite the relatively high levels of oxygen contamination, the deposited ZrC films were very conductive. The use of a low C₂H₂ pressure atmosphere during deposition had a small beneficial effect on crystallinity and stoichiometry of the films.     

Size modulation of nanocrystalline silicon embedded in amorphous silicon oxide by Cat-CVD

Different issues related to controlling size of nanocrystalline silicon (nc-Si) embedded in hydrogenated amorphous silicon oxide (a-SiO_x:H) deposited by catalytic chemical vapor deposition (Cat-CVD) have been reported. Films were deposited using tantalum (Ta) and tungsten (W) filaments and it is observed that films deposited using tantalum filament resulted in good control on the properties. The parameters which can affect the size of nc-Si domains have been studied which include hydrogen flow rate, catalyst and substrate temperatures. The deposited samples are characterized by X-ray diffraction, HRTEM and micro-Raman spectroscopy, for determining the size of the deposited nc-Si. The crystallite formation starts for Ta-catalyst around the temperature of 1700 °C.     

Instantaneous cleaning of silicon substrates by mesoplasma for high-rate and low-temperature epitaxy

Homoepitaxial films having properties identical to films deposited on the conventional wet-cleaned substrates have been achieved even in the absence of any substrate pre-treatment through the mesoplasma CVD. X-ray photoelectron spectroscopy reveals that the native oxide layer is effectively removed by exposure of the bare silicon substrates to the Ar-H₂ plasma at exposure times as short as 2 s and temperatures less than 100 °C. Although an exposure to the Ar-H₂ plasma is accompanied by an anisotropic island formation resulting in an increase in rms roughness (~ 5 nm) of the surface, addition of as little as 2 sccm SiH₄ into the plasma reduces the roughness greatly. The absence of Si-H_x peaks in the FTIR spectrum and uniform concentration distribution of H and O atoms across the growth interface observed by SIMS analysis indicate that minimal damage was induced in the silicon film by the hydrogen while attaining high yield of surface cleaning. These suggest that surface interaction with Ar-H₂ plasma at the mesoplasma condition supportively facilitate lateral growth at low temperature in the way of instantaneous surface cleaning and anisotropic Si etching structure favorable for incorporation of the atoms comprising the Si nanoclusters as growth precursors.     

Structure, morphology and electrical characterizations of direct current sputtered ZnO thin films

ZnO thin films were deposited on glass substrates by direct current (DC) sputtering technique at room temperature (RT) to 400 °C with a 99.999% pure ZnO target. Then the samples deposited at RT were annealed in air from the RT to 400 °C. The effects of substrate temperature (T_s) and annealing treatment (T_a) on the crystallization behavior and the morphology have been studied by X-ray diffraction and atomic force microscopy. We also compared the structural properties of samples deposited at 400 °C on glass to those deposited on Pt/silicon substrate. The resistivity, surface roughness and size of the grains have also been studied and correlated to the thickness of ZnO films deposited on Pt/Si substrates. The experimental results reveal that the substrate has a major influence on the structural and morphological properties. For the films deposited on glass, below 400 °C, T_s and T_a have a similar influence on the structure of the films. Moreover, the ZnO samples deposited at RT and annealed in air have poor electrical properties.     

Fabrication of nanocrystalline silicon carbide thin film by helicon wave plasma enhanced chemical vapour deposition

Nanocrystalline cubic silicon carbide thin films have been fabricated by helicon wave plasma enhanced chemical vapour deposition on Si substrates using the mixture of SiH₄, CH₄, and H₂ at a low substrate temperature of 300 °C. The infrared absorption spectroscopy analyses and microstructural characteristics of the samples deposited at various magnetic fields indicate that the high plasma intensity in helicon wave mode is a key factor to the success of growing nanocrystalline silicon carbide thin films at a relative low substrate temperature. Transmission electron microscopy measurements reveal that the films consist of silicon carbide nanoparticles with an average grain size of several nanometers, and the light emission measurements show a strong blue photoluminescence at room temperature, which is considered to be caused by the quantum confine effect of small size silicon carbide nanoparticles.