Effect of deposition pressure on microstructure and properties of hydrogenated carbon nitride films prepared by DC-RF-PECVD

Hydrogenated carbon nitride (a-CN:H films) were deposited on n-type (1 0 0) silicon substrates making use of dual direct current radio frequency plasma enhanced chemical vapor deposition (DC-RF-PECVD), at working pressure of 2–20 Pa, using a mixed gas of CH₄ and N₂ as the source gas. The growth rate, composition, bonding structure of the deposited films were characterized by means of XPS and FTIR, and the mechanical properties of the deposited films were investigated by nano-indentation test. It was found that the parameters for the DC-RF-PECVD process had significant effects on the growth rate, structure and properties of the deposited films. The growth rate of the deposited films increased at first with increasing deposition pressure, then saturated with further increase of the deposition pressure. The N/C ratio inside the deposited films increased with increasing working pressure except that it was as much as 0.50 at a working pressure of 5.0 Pa. The nano-hardness of the films decreased with increasing deposition pressure. CN radicals were remarkably formed in the deposited films at higher pressures, and their contents are related to the nitrogen concentrations in the deposited films.     

Influence of the nitrogen flow rate on the order and structure of PECVD boron nitride thin films

Three sets of boron nitride (BN) thin films are deposited with different N₂/B₂H₆ flow ratios (r = 4, 10 and 25) by plasma enhanced chemical vapor deposition (PECVD). The variations of physical properties in different deposition sets are analyzed by optical (XPS, FTIR, UV–visible spectroscopies), mechanical and electrical measurements. The films are considered to be deposited in a turbostratic phase (t-BN). Evolution of bonding configurations with increasing r is discussed. Relatively higher nitrogen flow rate in the source gas mixture results in lower deposition rates, whereas more ordered films, which tend to reach a unique virtual crystal of band gap 5.93 eV, are formed. Anisotropy in the film structure and film inhomogeneity along the PECVD electrode radial direction are investigated.     

Transition between amorphous and crystalline phases of SiC deposited on Si substrate using H3SiCH3

This paper presents a study of the transition between amorphous and crystalline phases of SiC films deposited on Si(1 0 0) substrate using H₃SiCH₃ as a single precursor by a conventional low-pressure chemical vapor deposition method in a hot-wall reactor. The microstructure of SiC, characterized by X-ray diffraction and high-resolution transmission electron microscopy, is found to vary with substrate temperature and H₃SiCH₃ pressure. The grain size decreases with increasing MS pressure at a given temperature and also decreases with reducing temperature at a given MS pressure. The deposition rates are exponentially dependent on the substrate temperature with the activation energy of around 2.6 eV. The hydrogen compositional concentration in the deposited SiC films, determined by secondary ion mass spectrometry depth profiling, is only 2.9% in the nanocrystalline SiC but more than 10% in the amorphous SiC, decreasing greatly with increasing deposition temperature. No hydride bonds are detected by Fourier transform infrared spectroscopy measurements. The chemical order of the deposited SiC films improves with increasing deposition temperature.     

Deposition of microcrystalline Ge films using hot-wire technique without toxic gases

To investigate the deposition of Ge films without toxic gas such as germane, we have studied the Ge films prepared by the hot-wire technique, which utilize the reaction between a Ge target and hydrogen atoms generated by the hot-wire decomposition of H₂ gas. The films deposited on Si substrate were microcrystalline Ge films and the mean crystallite size of the films increased from 13.3 to 24.8 nm with increasing the substrate temperature from 300 to 500 °C. Moreover, the deposition rate of Ge films deposited on Si substrate was higher than that of Ge films deposited on Corning 1737 substrate. It was found that the substrate temperature and the kind of substrate are key parameters for the preparation of microcrystalline Ge films by the hot-wire technique.     

Effect of N2/CH4 flow ratio on microstructure and composition of hydrogenated carbon nitride films prepared by a dual DC-RF plasma system

Hydrogenated carbon nitride (a-CN:H) films were deposited on n-type (1 0 0) silicon substrates making use of direct current radio frequency plasma enhanced chemical vapor deposition (DC-RF-PECVD), using a gas mixture of CH₄ and N₂ as the source gas in range of N₂/CH₄ flow ratio from 1/3 to 3/1 (sccm). The deposition rate, composition and bonding structure of the a-CN:H films were characterized by means of X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectrometry (FTIR). The mechanical properties of the deposited films were evaluated using nano-indentation test. It was found that the parameter for the DC-RF-PECVD process had significant effects on the growth rate, structure and properties of the deposited films. The deposition rate of the films decreased clearly, while the N/C ratio in the films increased with increasing N₂/CH₄ flow ratio. CN radicals were remarkably formed in the deposited films at different N₂/CH₄ flow ratio, and their contents are related to the nitrogen concentrations in the deposited films. Moreover, the hardness and Young’s modulus of the a-CN:H films sharply increased at first with increasing N₂/CH₄ flow ratio, then dramatically decreased with further increase of the N₂/CH₄ flow ratio, and the a-CN:H film deposited at 1/1 had the maximum hardness and Young’s modulus. In addition, the structural transformation from sp³-like to sp²-like carbon-nitrogen network in the deposited films also was revealed.     

Large grain μc-Si:H films deposited at low temperature: Growth process and electronic properties

We have studied structural and electronic properties of μc-Si:H films deposited from SiH₄ + H₂ and SiH₄ + H₂ + Ar gas mixtures. The use of Ar containing gas mixtures for depositions allows us to increase deposition rate by a factor of two and to obtain films with an important fraction of large grains in comparison with SiH₄ + H₂ gas mixtures. Electronic properties of fully crystallized films become more intrinsic with the increase of large grain fraction. Deposition of highly p- and n-doped μc-Si:H layers from the dopant/SiH₄ + H₂ gas mixture at a temperature of 175 °C is possible without any remarkable changes in crystallinity in comparison with undoped films deposited with the same discharge conditions.     

A narrow process window for the preparation of polytypes of microcrystalline silicon carbide thin films by hot-wire CVD method

Effects of deposition conditions on the structure of microcrystalline silicon carbide (μc-SiC) films prepared by hot-wire chemical vapor deposition (hot-wire CVD) method have been investigated. It is found from X-ray diffraction patterns of the film that a diffraction peak from crystallites from hexagonal polytypes of SiC is observed in addition to those of 3 C-SiC crystallites. This result is obtained in the film under a narrow deposition conditions of SiH₃CH₃ gas pressure of 8 Pa, the H₂ gas pressure of 80–300 Pa and the total gas pressure of 40–300 Pa under fixed substrate and filament temperatures employed in this study. Furthermore, the grain size of hexagonal crystallites (about 20 nm) on c-Si substrates becomes larger than that of 3 C-SiC crystallites (about 10 nm) for the films deposited under the total gas pressure of 36–88 Pa. The fact that microcrystalline hexagonal SiC can be deposited under limited deposition conditions could be interpreted in the context of a result for c-SiC polytypes prepared by thermal CVD method.     

Evolution from (110) Fe to (111) Fe3O4 thin films grown by magnetron sputtering using Fe2O3 target

Fe and Fe₃O₄ thin films were grown by radio frequency magnetron sputtering. Fe₂O₃ was used as the target and hydrogen was introduced together with Argon gas to provide a certain reducing atmosphere. By varying H₂/Ar flow ratio, the changes in composition and structure of the thin films from (110) Fe to (111) Fe₃O₄ were observed by X-ray diffraction. The valence states of Fe in the thin films were analyzed by X-ray photoelectron spectroscopy. Magnetization measurements indicate that the Fe thin films grown with low H₂/Ar flow ratios possess large coercive force. It was ascribed to the increasing boundary density and the increasing amount of Fe oxides such as FeO distributed at the boundary.     

Role of annealing environment and partial pressure on structure and optical performance of TiO2 thin films fabricated by rf sputter method

Influences of the different annealing ambient (in air, 1 bar, 2 bar, 3 bar and 4 bar oxygen partial pressure) on the titanium dioxide (TiO₂) thin films deposited on soda lime glass by standard radio frequency (rf) magnetron reactive sputtering method at 100 watt were investigated by means of X–ray diffractometer (XRD), ultra violet spectrometer (UV–vis), and Scanning Electron Microscopy (SEM). It was found that either optical properties or energy band gaps of the films enhanced with increase in the oxygen partial pressure up to 3 bar. The energy band gaps of the films (except for the film annealed in 4 bar oxygen partial pressure) became larger than the film annealed in atmospheric pressure. The best transmission was observed for the thin film annealed in 3 bar oxygen partial pressure. Moreover, not only was grain–like structure found to be more dominant than dot–like structure but also growth of anatase phase was observed instead of that of the rutile phase with increasing oxygen partial pressure up to 3 bar. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of thermoannealing on crystallinity and optical properties of Sb2S3 thin films

Sb₂S₃ thin films are obtained by evaporating of Sb₂S₃ powder onto glass substrates maintained at room temperature under pressure of 2×10^‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb₂S₃ thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E₀, dispersion energy, E_d) were determined. The static refractive index n(0), static dielectric constant, ε_∞, and optical band gap energy, E_g, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of oxygen partial pressure on physical properties of nano‐crystalline silver oxide thin films deposited by RF magnetron sputtering

Nano‐crystalline silver oxide films were deposited on glass and silicon substrates held at room temperature by RF magnetron sputtering of silver target under different oxygen partial pressures. The influence of oxygen partial pressure on the structural, morphological, electrical and optical properties of deposited films was investigated. Varying oxygen partial pressure during the sputter deposition leads to changes of mixed phase of Ag₂O and Ag to a single phase of Ag₂O and to AgO. The X‐ray diffraction and X‐ray photoelectron spectroscopy results showed the formation of single phase Ag₂O with cubic structure at oxygen partial pressures of 2x10^‐2 Pa while the films deposited at higher oxygen partial pressure of 9x10^‐2 Pa showed the formation of single phase of AgO with monoclinic structure. Raman spectroscopic studies on the single phase Ag₂O showed the stretching vibration of Ag‐O bonds. Single‐phase Ag₂O films obtained at oxygen partial pressure of 2x10^‐2 Pa were nano‐crystalline with crystallite size of 20 nm and possessed an electrical resistivity of 5.2x10^‐3 Ωcm and optical band gap of 2.05 eV. The films deposited at higher oxygen partial pressure of 9x10^‐2 Pa were of AgO with electrical resistivity of 1.8x10^‐2 Ωcm and optical band gap of 2.13 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermodynamic analysis of gas phase chemistry in hot wire chemical vapor deposition of a-Si:H and μc-Si:H

Gas phase reactions amongst filament-generated radicals play a crucial role in growth and properties of films deposited by hot wire chemical vapor deposition (HWCVD) technology. Gas phase species of interest are SiH₄, H₂, Si, H, SiH₃, SiH₂ and SiH. Partial pressures of these species for different sets of deposition conditions have been determined from the standard Gibbs free energy data. Equilibrium concentrations of the film forming precursors have been determined. The effect of the various process parameters on the equilibrium concentration of the precursors has been studied. H, Si and SiH are found to be the dominant species in gas phase above a filament temperature of 2300 K. However SiH₃ and SiH₂ concentration peaks are between 1900 and 2300 K, of the filament temperature.     

The influence of N2 flow rate and substrate temperature on Ti1‐xAlxN thin films

Titanium aluminium nitride (Ti_1‐xAl_xN) films have been deposited on silicon (111) substrate at a N₂ flow rate of 2 sccm and 20 sccm and at a substrate temperature of 773 K and at a N₂ flow rate of 2 sccm and at a substrate temperature of 873 K by reactive DC magnetron sputtering technique. The effect of N₂ flow rate and substrate temperature on the grain size and surface roughness of the deposited films have been investigated. The films have been analysed by X‐ray diffraction (XRD) and atomic force microscopy (AFM). The films were found to be nanocrystalline. While the grain size of the films decreases with increasing N₂ flow rate and decreases with increasing substrate temperature, the surface roughness of the films decreases with increasing N₂ flow rate and increases with increasing temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TiO2 thin films as sensing gas materials

TiO₂ thin films were prepared by DC reactive magnetron sputtering on heated Si, quartz and glass substrates using O₂ and water vapor as reactive gases. The percentage of anatase and rutile as well as the grain size strongly depend on the deposition conditions, as revealed by X-ray diffraction patterns. The films deposited on Si substrates are pure rutile, while a mixed anatase/rutile structure occurs in the films deposited on glass and quartz substrates. Smaller grain rutile and anatase films were prepared in a water vapor atmosphere, in contrast to the films grown in oxygen. The former choice considerably increases the sensing properties of titanium dioxide films. The gas sensitivity was investigated for some reducing gases (methane, acetone, ethanol and liquefied petroleum gas) and the optimum operating temperatures were found.     

Structural and optical properties of TiO2:SnO2 thin films prepared by sol gel method

ABSTRACT

TiO₂:SnO₂ thin films were deposited on glass substrates, by using sol gel spin coating method with different ratio (3%, 5% and 7%) at 3200 rpm, to study their effect on different properties of TiO₂: SnO₂ thin films. The structural and optical properties of films have studied for different ratio. These deposited films have been characterized by various methods such as X-Ray Diffraction (XRD), Ultra Visible spectroscopy. The (XRD) can be used to identify crystal structure of as deposited films. The Transmission spectra have shown the transparent and opaque parts in the visible and UV wavelengths.     

Influence of temperature on the microcrystalline structure of thermally evaporated Sb2S3 thin films

Thin films of antimony trisulfide (Sb₂S₃) were prepared by thermal evaporation under vacuum (p=5×10^–5 torr) on glass substrates maintained at various temperatures between 293 K and 523 K. Their microstructural properties have obtained by transmission electron microscopy (TEM). The electron diffraction analysis showed the occurrence of amorphous to polycrystalline transition in the films deposited at higher temperature of substrates (523 K). The polycrystalline thin films were found to have an orthorhombic structure. The interplanar distances and unit‐cell parameters were determined by high‐resolution transmission electron microscopy (HRTEM) and compared with the standard values for Sb₂S₃. The surface morphology of Sb₂S₃ thin films was investigated by scanning electron microscopy (SEM). The optical transmission spectra at normal incidence of Sb₂S₃ thin films have been measured in the spectral range of 400–1400 nm. The analysis of the absorption spectra revealed indirect energy gaps, characterizing of amorphous films, while the polycrystalline films exhibited direct energy gap. From the photon energy dependence of absorption coefficient, the optical band gap energy, E_g, were calculated for each thin films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasma enhanced chemical vapor deposition of ZnO thin films

Zinc oxide thin films were deposited on silicon and corning-7059 glass substrates by plasma enhanced chemical vapor deposition at different substrate temperatures ranging from 36 to 400 °C and with different gas flow rates. Diethylzinc as the source precursor, H₂O as oxidizer and argon as carrier gas were used for the preparation of ZnO films. Structural and optical properties of these films were investigated using X-ray diffraction, reflection high energy electron diffraction, atomic force microscopy and photoluminescence. Highly oriented films with (0 0 2) preferred planes were obtained on silicon kept at 300 °C with 50 ml/min flow rate of diethylzinc without any post annealing. Reflection high energy electron diffraction pattern also showed the crystalline nature of these films. A textured surface with rms roughness ∼28 nm was observed by atomic force microscopy for the films deposited at 300 °C. A sharp peak at 380 nm in the PL spectra indicated the UV band-edge emission.     

The effects of deposition parameters on a-Si:H films fabricated by microwave glow discharge techniques

Hydrogenated amorphous silicon (a-Si:H) films have been fabricated by a novel method of microwave glow-discharge deposition from SiH₄ and H₂, operating at 2.45 GHz. The properties of the deposited films are dependent upon the confinement of the microwave plasma by a magnetic field, and upon the orientation of the substrates with respect to the electric field. The quality of these materials is comparable to that of films deposited in conventional radio-frequency glow-discharge systems.     

Properties of CVD alumina-titania composite films grown at different CO2/H2 inputs

Amorphous alumina-titania (Al₂O₃-TiO₂) films were prepared on silicon substrates by low-pressure chemical vapor deposition (CVD) using a mixture of aluminum tri-sec-butoxide (ATSB) and titanium tetrachloride (TiCl₄) at different CO₂/H₂ inputs (the ATSB/TiCl₄/CO₂/H₂ system). The films had increased Al contents at higher temperatures and CO₂/H₂ inputs. The `splotchy' deposits were observed. The higher compressive internal stress at higher temperature was attributed to the films with a thinner thickness. Higher compressive internal stress and more Al-O bonding resulted in higher specific critical load. Films deposited at low temperature of 350 °C have a defected structure and a higher dielectric property, due to the non-stoichiometric nature at the Ti-rich composition. Resistivity decreased from 10¹¹ to 10⁸-10⁹ Ω cm after annealing. Breakdown voltages increased slightly with substrate temperature and were in the range of 2.3-6.4 MV/cm. Refractive indices were in the range of 1.71-2.28. Greater than 60% transmittance was observed at visible range for all films.     

Formation of ultrasmooth thin silver films by pulsed laser deposition

Ultrasmooth thin silver films have been formed on a quartz substrate with a buffer yttrium oxide layer by pulsed laser deposition. The dependence of the surface morphology of the film on the gas (N₂) pressure in the working chamber and laser pulse energy is investigated. It is found that the conditions of film growth are optimal at a gas pressure of 10^?2 Torr and lowest pulse energy. The silver films formed under these conditions on a quartz substrate with an initial surface roughness of 0.3 nm had a surface roughness of 0.36 nm. These films can be used as a basis for various optoelectronics and nanoplasmonics elements.