锡薄膜等温氧化研究

采用电子束蒸发制备金属锡薄膜,将其在250—400℃温度范围内进行等温氧化,研究锡薄膜的热氧化动力学机制.采用台阶仪、扫描电子显微镜、俄歇电子能谱仪和X射线衍射仪等方法研究锡薄膜氧化过程中厚度、组分、结构等演变.实验结果表明,在250—400℃温度范围内,锡膜氧化后氧化层按抛物线规律生长;转变活化能为0.34eV;锡膜氧化受到氧扩散机制的控制.研究得到氧化层的生长首先从形成SnO相开始,随着氧化的深入,SnO相分解形成Sn₃O₄相,最后转变为SnO_{2< 关键词：}     

Optical characterization of thin thermal oxide films on copper by ellipsometry

A complete optical characterization in the visible region of thin copper oxide films has been performed by ellipsometry. Copper oxide films of various thicknesses were grown on thick copper films by low temperature thermal oxidation at 125 °C in air for different time intervals. The thickness and optical constants of the copper oxide films were determined in the visible region by ellipsometric measurements. It was found that a linear time law is valid for the oxide growth in air at 125 °C. The spectral behaviour of the optical constants and the value of the band gap in the oxide films determined by ellipsometry in this study are in agreement with the behaviour of those of Cu₂O, which have been obtained elsewhere through reflectance and transmittance methods. The band gap of copper oxide, determined from the spectral behaviour of the absorption coefficient was about 2 eV, which is the generally accepted value for Cu₂O. It was therefore concluded that the oxide composition of the surface film grown on copper is in the form of Cu₂O (cuprous oxide). It was also shown that the reflectance spectra of the copper oxide–copper structures exhibit behaviour expected from a single layer antireflection coating of Cu₂O on Cu. Received: 19 July 2001 / Accepted: 27 July 2001 / Published online: 17 October 2001     

A study of the oxidation of tantalum nitride by ellipsometry and auger electron spectroscopy

Ellipsometry and Auger electron spectroscopy in conjunction with in-situ ion sputtering have been used to study the thermal and anodic oxidation of thin tantalum nitride (Ta₂N) resistor films which are used in microelectronic circuits. In addition, the effects of thermal oxidation on the resistor-conductor contact resistance and conductor adhesion have been investigated.Thermal oxide thickness and stoichometry were estimated by Auger electron spectroscopy. A more accurate determination of oxide thickness was obtained by using multiple angle-of incidence ellipsometry. The thermal oxide was found to demonstrate a parabolic growth rate, in agreement with other workers. It was determined that the contact resistance should not be adversely affected by oxidation of the tantalum nitride at room temperature for storage times of several months; no significant decrease in the conductor adhesion was observed for oxide thicknesses up to 8 nm.A significant difference in the stoichiometry and refractive index of the thermally and anodically oxidized films was found, however. Depletion of the nitrogen from the surface of the anodically oxidized Ta₂N films resulted in an increase in the refractive index of the anodic oxide layer to a value close to that of pure Ta₂O₅.     

Influence of oxidation time on semiconductive behaviour of thermally grown oxide films on AISI 304L

The oxide films formed on AISI 304L stainless steel at 300 °C in the oxidation time range between 2 and 4 h have been studied by photoelectrochemistry. Photocurrents were investigated as a function of the wavelength of the incident light and the electrode potential. The investigation allowed the determination of the semiconductive properties of the oxides. The oxide films showed n-type behaviour. A duplex structure of the oxide films has been suggested on the basis of the photocurrent spectra, with an internal oxide layer having an optical gap (E_g2 = 2.16-2.3 eV) depending on the applied potential and oxidation time, higher to that of the external oxide layer (E_g1 ≈ 1.9 eV). Significant variations in the amplitude of the photocurrent were detected as a function of the applied potential and the oxidation time.     

Local Anodic Oxidation of Thin GeO Films and Formation of Nanostructures Based on Them

The process of local anodic oxidation of thin GeO films has been studied using an atomic force microscope. The electron-probe microanalysis showed that oxidized areas of a GeO film were germanium dioxide. The effect of the voltage pulse duration applied to the probe–substrate system and the atmospheric humidity on the height of the oxide structures has been studied. The kinetics of the local anodic oxidation (LAO) in a semi-contact mode obeys the Cabrera–Mott model for large times. The initial growth rate of the oxide (R₀) significantly increases and the time of starting the oxidation (t₀) decreases as the atmospheric humidity increases by 20%, which is related to an increase in the concentration of oxygen-containing ions at the surface of the oxidized GeO film. It was shown that nanostructures in thin GeO layers can be formed by the LAO method.     

Characterization of SnO2 obtained from the thermal oxidation of vacuum evaporated Sn thin films

Tin oxide has been prepared by thermal oxidation of evaporated tin thin films onto pyrex glass substrates. Films oxidation was achieved in air at a temperature of 600 °C with varied duration from 20min to 3 h. Structural, optical and electrical properties of the films were characterized by means of X-ray diffraction, UV–vis spectroscopy and electrical resistivity measurements respectively. The X-ray analysis revealed the transformation of Sn into SnO₂ with preferential orientation along (101) plans. No intermediate phases such as SnO and Sn₃O₄ were evidenced. It was also found that the SnO₂ crystallites orientation changed with the annealing time due to the strain energy effect. Both band gap energy and electrical resistivity decrease with annealing time due to the crystalline quality improvement and films densification. We have noticed that oxidation at 600 °C for 3 h leads to transparent and conductive films with suitable properties for photovoltaic applications.     

Fabrication of cuprous and cupric oxide thin films by heat treatment

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were prepared by thermal oxidation of copper films coated on indium tin oxide (ITO) glass and non-alkaline glass substrates. The formation of Cu₂O and CuO was controlled by varying oxidation conditions such as, oxygen partial pressure, heat treatment temperature, and oxidation time. The microstructure, crystal direction, and optical properties of copper oxide films were measured with X-ray diffraction, atomic force microscopy, and optical spectroscopy. The results indicated that the phase-pure Cu₂O and CuO films were produced in the oxidation process. Optical transmittance and reflectance spectra of Cu₂O and CuO clearly exhibited distinct characteristics related to their phases. The electrical properties indicated that these films formed ohmic contacts with Cu and ITO electrode materials. Multilayers of Cu₂O/CuO were fabricated by choosing the oxidation sequence. The experimental results in this paper suggest that the thermal oxidation method can be employed to fabricate device quality Cu₂O and CuO films that are up to 200–300 nm thick.     

Optical constants of thin oxide films on titanium

Thin oxide films on titanium formed by heating were studied by the ellipsometric method. To obtain the complex refractive index and film thicknesses, the ellipsometric measurements were performed by means of the immersing method: each sample was measured first in air and then in a liquid of known refractive index (in our case CCl₄). The optical constants and the oxide film thickness were computed by means of a computer from two pairs of ellipsometric values. To state the optical constants of clean titanium surface the graphic-computational method was proposed and applied. The measurements were carried out at two wavelengths on oxide films grown in air and dry oxygen by thermal oxidation at temperatures from 150 to 700 °C. It has been shown that when increasing the film thickness the refractive index of the film decreases, whereas the absorption coefficient is independent on the film thickness. Optical constants of oxide films growing in dry oxygen are smaller than those growing in air.     

Preparation and characterization of p-type transparent conducting tin-gallium oxide films

p-Type transparent conducting tin-gallium oxide (TGO) films were successfully fabricated on quartz substrates by DC magnetron sputtering of GaSn alloy films followed by thermal oxidation. XRD characterization indicated that the TGO films maintain rutile structure of the tin oxide (SnO₂). UV-vis transmittance spectra indicated that the films have a transmittance higher than 85% in the visible region, with an optical band-gap around 3.8 eV. Hall effect measurement showed that electrical properties of the TGO films were dependent on oxidation temperature. Oxidation at too high or low temperature was unfavorable for p-type conduction. It is found that the optimum oxidation temperature for highest hole concentration (8.84 × 10¹⁸ cm⁻³) was in the range of 600-650 °C.     

Investigation of oxidation process and properties of indium and tin-based thin-film heterostructures

Solid-phase processes in thin films (～200 nm) based on tin and indium oxides (ITO structures) prepared by magnetron sputtering from a composite target (93 at % In and 7 at % Sn) and by layer-by-layer deposition of In/Sn/Si and Sn/In/Si structures from two magnetrons in a single vacuum cycle have been investigated in the work under their oxidation in an oxygen flow. Two ways of optically transparent semiconductor film formation have been compared using near-edge fundamental absorption spectroscopy, x-ray diffraction analysis, and electron microscopy and dynamics of the change in their optical and structure properties has been studied. In the case of oxidation of the layer-by-layer deposited structures, the heterogeneous phase composition of the film is confirmed both by the XRD data and by the optical results. Only wide-band-gap phases with an energy of direct transitions of 3.5–3.6 eV have been found in the films prepared by magnetron sputtering from a composite target after their oxidation. These wide-band-gap phases are associated with In₂O₃ oxide and a tin-doped indium oxide compound.     

Effect of substrate temperature on the surface and interface oxidation of NiTi thin films

NiTi shape memory alloy thin films are deposited on pure Cu substrate at substrate ambient temperatures of 300 °C and 450 °C. The surface and interface oxidation of NiTi thin films are characterized by X-ray photoelectron spectroscopy (XPS). After a subsequent annealing treatment the crystallization behavior of the films deposited on substrate at different temperatures is studied by X-ray diffraction (XRD). The effects of substrate temperature on the surface and interface oxidation of NiTi thin films are investigated. In the film surface this is an oxide layer composed of TiO₂. The Ni atom has not been detected on surface. In the film/substrate interface there is an oxide layer with a mixture Ti₂O₃ and NiO in the films deposited at substrate temperatures 300 °C and 450 °C. In the films deposited at ambient temperature, the interface layer contains Ti suboxides (TiO) and metallic Ni.     

Dynamics of oxide phases on the surface of single- and polycrystalline Pb1 − x Sn x Te films upon their investigation by the raman light scattering method

We have studied Raman spectra of single- and polycrystalline Pb_{1 ? x} Sn _x Te (0 ≤ x ≤ 1) films on different substrates in relation to the intensity of the laser action. The composition of oxide phases on the surface of lead-tin telluride films has been described, and their modification as a result of photostimulated oxidation of the surface during measurements of spectra has been analyzed. We have shown that, for films with a small mole fraction of tin telluride (x ≤ 0.26), irrespective of the crystalline state, predominant oxidation of tellurium with the formation of the compound TeO₂ takes place during the laser action. In films with a high content of tin, at a laser-action intensity higher than 1000 μW, tellurium dioxide TeO₂ on the surface is replaced with tin dioxide SnO₂.     

Vanadium oxide thin films deposited on indium tin oxide glass by radio—frequency magnetron sputtering

Highly oriented VO₂(B), VO₂(B) + V₆O₁₃ films were grown on indium tin oxide glass by radio-frequency magnetron sputtering. Single phase V₆O₁₃ films were obtained from VO₂(B) +V₆O₁₃ films by annealing at 480℃ in vacuum. The vanadium oxide films were characterized by x-ray diffraction and x-ray photoelectron spectra (XPS). It was found that the formation of vanadium oxide films was affected by substrate temperature and annealing time, because high substrate temperature and annealing were favourable to further oxidation. Therefore, the formation of high valance vanadium oxide films was realized. The V₆O₁₃ crystalline sizes become smaller with the increase of annealing time. XPS analysis revealed that the energy position for all the samples was almost constant, but the broadening of the V_2p3/2 line of the annealed sample was due to the smaller crystal size of V₆O₁₃.     

The reactions of nitric oxide with nickel films as studied by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been employed to study the reactions between nitric oxide and freshly deposited nickel films. When the nickel surface is treated with NO at pressures of less than 1 · 10^?4 torr for 60 s (6000L), the NO is dissociatively adsorbed with no oxidation of the nickel surface. When treated with 0.40 torr of NO that has been exposed to varying degrees of oxidation, the nickel surface is oxidized and species such as NO₃^?, NO₂^?, NO and N₂ may be found on the surface. The species found are determined by the extent of oxidation of NO.     

Formation of ZnO and Zn1−xCdxO films on CdTe/CdZnTe single crystals

In this work we report on the properties of ZnO and Zn_1−xCd_xO films formed on top of CdTe and CdZnTe single crystals. The films have been obtained by thermal evaporation of Zn metal films and further oxidation in atmospheric conditions. The structural and compositional characteristics of the films have been analysed by means of scanning electron microscopy and energy-dispersive X-ray analysis. The chemical composition of the films as a function of growth parameters has been obtained. It has been possible to demonstrate by Raman spectroscopy the formation of both ZnO and Zn_1−xCd_xO films. The possible inter-diffusion effects between the films and the substrate, derived from the oxidation process, have been discussed. It has been possible to check by means of photoluminescence, the optical quality of the ZnO and Zn_1−xCd_xO films, also regarding to the presence of local changes. Differences between the optical spectra obtained from various ZnO films grown on top of CdTe and CdZnTe substrates enabled the determination of compositional differences introduced by the substrate when the deposition parameters are modified.     

Physical and dispersive optical characteristics of ZrON/Si thin-film system

To date, the complex evaluation of physical and dispersive optical characteristics of the ZrON/Si film system has yet been reported. Hence, ZrON thin films have been formed on Si(100) substrates through oxidation/nitridation of sputtered metallic Zr in N₂O environment at 500, 700, and 900 ^°C. Physical properties of the deposited films have been characterized by X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, reflection high-energy electron diffraction (RHEED), and spectroscopic ellipsometry (SE). It has been shown that ZrON/Si thin films without optical absorption can be prepared by oxidation/nitridation reaction in N₂O environment at 700–900 ^°C.     

The thermal oxidation of silicon the special case of the growth of very thin films

The thermal oxidation of silicon is generally modelled by Deal and Grove's theory based on the assumption that the oxygen molecules dissolve in silicon in interstitial positions and migrate to the Si-SiO₂ interface where they react with the silicon substrate. Experimental results for oxidation in dry oxygen agree with this theory only for thick oxide films. The growth of very thin oxide films exhibits particular features which are discussed in this paper. For these films, the growth mechanism is different from that of thick films; this difference is possibly associated with the transport of oxygen atoms through the silica network. The effect of hydrogenated impurities is also discussed.     

Structural and photoluminescence properties of SnO2 obtained by thermal oxidation of evaporated Sn thin films

Tin oxide films have been prepared by oxidation of Sn thin films deposited by thermal evaporation method onto glass substrates. The oxidation of films was done, in air at a temperature of 500 °C, from 20 to 120 min. The oxidized films were characterized by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), photoluminescence spectroscopy (PL) and surface profilometer. The XRD patterns show that the crystalline structure of the oxidized Sn films improves with the annealing time. The tetragonal SnO₂ phase (cassiterite) was obtained after 120 min of annealing with grains sizes between 15 and 20 nm. The thickness of oxide films, as function of the annealing time, follows a parabolic law. The O/Sn atomic ratio increases with the annealing time indicating an improvement of the films quality. Tin interstitials defects density, calculated from PL spectra using Smakula's formula, was found to decrease with the increasing annealing time. Tin interstitials defects density was found proportional to the increasing oxygen density (deduced from RBS). A fit of this proportionality allowed us to quantify the tin cations and oxygen anions diffused through the oxide films.     

Gadolinium oxide high-k gate dielectrics prepared by anodic oxidation

The growth and properties of gadolinium oxide (Gd₂O₃) films prepared by anodic oxidation were investigated. Uniform Gd₂O₃ thin film with good oxide quality was obtained. The X-ray diffraction (XRD) pattern of the Gd₂O₃ films showed that they had a poly-crystalline structure. The dielectric constants of Gd₂O₃ films oxidized at 30 and 60 V are 9.4 and 12.2, respectively. The equivalent oxide thickness (EOT) of the Gd₂O₃ stacked oxide is in the range of 5.8-9.4 nm. The MOS capacitor with Gd₂O₃ exhibits interesting electrical properties. Longer oxidation time reduced the leakage current density for 30 V anodic oxidation but increased the leakage current density for 60 V anodic oxidation. This work reveals that Gd₂O₃ could also be an alternative dielectric for Si substrate and therefore, might pave the way to fabricate CMOS devices in the future.     

A nanogravimmetric investigation of the charging processes on ruthenium oxide thin films and their effect on methanol oxidation

The charging processes and methanol oxidation that occur during the oxidation-reduction cycles in a ruthenium oxide thin film electrode (deposited by the sol-gel method on Pt covered quartz crystals) were investigated by using cyclic voltammetry, chronoamperometry and electrochemical quartz crystal nanobalance techniques. The ruthenium oxide rutile phase structure was determined by X-ray diffraction analysis. The results obtained during the charging of rutile ruthenium oxide films indicate that in the anodic sweep the transition from Ru(II) to Ru(VI) occurs followed by proton de-intercalation. In the cathodic sweep, electron injection occurs followed by proton intercalation, leading to Ru(II). The proton intercalation/de-intercalation processes can be inferred from the mass/charge relationship which gives a slope close to 1 g mol⁻¹ (multiplied by the Faraday constant) corresponding to the molar mass of hydrogen. From the chronoamperometric measurements, charge and mass saturation of the RuO₂ thin films was observed (440 ng cm⁻²) during the charging processes, which is related to the total number of active sites in these films. Using the electrochemical quartz crystal nanobalance technique to study the methanol oxidation reaction at these films was possible to demonstrate that bulk oxidation occurs without the formation of strongly adsorbed intermediates such as CO_ads, demonstrating that Pt electrodes modified by ruthenium oxide particles can be promising catalysts for the methanol oxidation as already shown in the literature.