An empirical X-ray K-Ratio framework for thickness measurement of 2D Si and SiO₂ thin films and SiO2 layer on Si substrate.

Determination of thin film thickness is ultimate important in many technology area, particularly those of optics and microelectronics. There are numerous ways to measure thin film thickness, many of them need after measurement numerical calculations, namely, some physical constants of the film: refractive index, absorption coefficient, or electrical conductivity, etc., need to be known beforehand in order to- carry out the calculation which. relates a certain measured physical quantity of the film: transmission spectrum, electrical resistance etc., to these constants and film thickness. The accuracy of these constants is crucial to the accuracy of the film thickness deduced from the calculation. Unfortunately, physical constants of thin films are always different significantly from those of bulk materials. The use of bulk value in the calculation inavoidably lead to inaccurate film thickness determination. There are some methods which directly measure the film thickness without numerical process and knowledge of other physical constants of the film. Among those methods, surface profile determination by stylus mechanically or by interferometry optically are frequently used. A film edge has to be created, the edge height measured directly by stylus profile or interference pattern is equal to the film thickness. There are some disadvantages for these methods, stylus may scratches the film and substrate which are soft, the range of film thickness which can be determined is limited by the optical wavelength in the interference method.

Instrument-invariant method of film thickness determination by means of substrate-to-film X-ray peak intensity ratioing

A method for thickness determination of thin films of amalgamable metals by total-reflection X-ray fluorescence

Silicon dioxide films deposited by electron cyclotron resonance chemical vapor deposition have been characterized using Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, and ellipsometry. A commercially available reactor was used to generate a high-density plasma at low total gas pressures (3–4 mTorr). A gas mixture of Ar, O2, and SiH4 was used to deposit SiO2 films on 200 mm Si substrates at temperatures less than 450 °C for interlayer dielectric applications. The dielectric constant of the films was measured using metal oxide semiconductor capacitors. Relationships between the dielectric constant and the refractive index, Si–OH content, and film stoichiometry were investigated using a model based on the Clausius–Mosotti equation. During the study, the O2 and SiH4 gas flows were adjusted to vary the film properties. Silicon dioxide was deposited over a wide range of O2 and SiH4 gas flow conditions. For SiO2 films, the dielectric constant was strongly correlated with the Si–OH content. At low O2/SiH4 gas flow ratios, suboxide films were deposited and the dielectric constant increased in relation to the refractive index. A low-temperature, postdeposition anneal was investigated as a means to reduce the Si–OH content and dielectric constant of the films. Modeling results indicate that the dielectric constant of SiO2 films can be predicted using measurements of the film thickness, refractive index, and Si–OH content, thus providing a nondestructive technique for monitoring the dielectric constant.

One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the α-phase Si(111)√3 × √3R30°-Bi at a low substrate temperature of 200 °C. Si films have been studied in situ by reflection electron energy loss spectroscopy (REELS) and Auger electron spectroscopy, as a function of the electron beam incidence angle α and low-energy electron diffraction (LEED), as well as ex situ by grazing incidence X-ray diffraction (GIXRD). Scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) were also reported. The REELS spectra, taken at the Si K absorption edge (~1.840 KeV), reveal the presence of two distinct loss structures attributed to transitions 1s→π* and 1s→σ* according to their intensity dependence on α, attesting to the sp2-like hybridization of the silicon valence orbitals in both thin and thick Si films. The synthesis of a silicon allotrope on the α-phase of Si(111)√3 × √3R30°-Bi substrate was demonstrated by LEED patterns and GIXRD that discloses the presence of a Si stack of 3.099 (3) Å and a √3 × √3 unit cell of 6.474 Å, typically seen for multilayer silicene. STM and STS measurements corroborated the findings. These measurements provided a platform for the new √3 × √3R30° Si allotrope on a Si(111)√3 × √3 R30°-Bi template, paving the way for realizing topological insulator heterostructures from different two-dimensional materials, Bi and Si.

We established the number of Si 2p photoelectrons emanating from a Si(100) substrate covered with a silicon–oxide film as a function of azimuthal and polar angles using the oxide film thickness as a parameter. The elastic and inelastic scattering cross sections of Si 2p photoelectrons in silicon oxide were deduced by reproducing the experimental results with Monte Carlo simulation for the path of Si 2p photoelectrons in silicon oxide. Based on the simulation, we found that the elastic scattering of Si 2p photoelectrons in silicon oxide could effectively be neglected in several specific directions. We also found that an emitting direction different to these specific directions is indispensable when precisely determining the thickness using XPS with a large receiving angle.

When the MOSFET with the SiO2 gate dielectric is scaled down to the nanosize, the leakage current becomes very large and the dopant can easily diffuse to the channel region to degrade the device's performance and reliability [1]. To solve these problems, a physically thicker high dielectric constant (high-k) film with the same equivalent oxide thickness (EOT) as the SiO2 film is used. For the conventional floating gate (FG) memory device, a poly-Si layer is embedded in the silicon dioxide (SiO2) gate dielectric to trap charges. Because of the large band offsets between Si and SiO2, a large operating voltage is required to achieve the acceptable write/erase efficiency and the tunnel oxide layer has to be thick enough to retain the trapped charges [2]. Since the high-k dielectric has lower band offsets with Si than the SiO2 film has, it can be used as the tunnel oxide to solve the above power consumption and charge retention problems. Separately, it has been proved that the Zr-doped HfO2 (ZrHfO) has better bulk and interface properties, such as a higher crystallization temperature, lower interfacial layer thickness, and lower interface density of states, than the undopd HfO2 has [3]. Also, the memory functions of the nc-ZnO or nc-MoOx embedded capacitor are affected by light exposure [4,5]. In this study, MOS capacitors made of the AlOx embedded ZrHfO high-kgate dielectric are fabricated and studied for the light wavelength effects on the memory functions.

The crystallization and distribution the features of Pt, Pd and Pt/Pd nanoparticles in spin-on glass SiO2 films were studied within a wide range of the dopant concentrations in silica sol (from 10 to 80 mol.% Pt, Pd or Pt/Pd per 100 mol.% Si). The grazing incidence X-ray diffraction (GIXRD) characterization revealed that the formation of 4–8 nm sized crystalline Pt, Pd and Pt/Pd nanoparticles in SiO2 films began at the dopant concentrations of at least 10 mol.% Pt and/or Pd per 100 mol.% Si. The nanoparticles obtained from sols with the lower Pt, Pd or Pt/Pd concentrations were characterized by an amorphous structure. The dopants distribution over the film thickness (~21–47 nm) was studied using X-ray reflectometry. The effect of the dopant concentration, spin-coating modes and heat treatment temperature on the film thickness was characterized. When only one of the dopants (Pt or Pd) was introduced into the silica sol, the resulting nanoparticles were preferentially localized close to the film surface. When dopants were used together, the Pt/Pd nanoparticles were distributed more evenly.

Heteroepitaxial CaF2/Si and Si/CaF2/Si structures have been formed by conventional vacuum deposition of CaF2 and Si. Optimum conditions for obtaining good epitaxial films have been investigated by changing Si substrate orientations, film thicknesses, and substrate temperatures during film deposition. It has been found from Rutherford backscattering and channeling spectroscopy (RBS) that the crystalline quality of CaF2 films grown on Si (111) and (110) substrates is excellent, but that the quality of the films on Si (100) is much worse. It has also been found from RBS and TEM (transmission electron microscopy) that single-crystalline Si films are formed on the CaF2/Si (111) structure at substrate temperature of 700°C. Finally, etching characteristics ofCaF2 and Si films have been studied. It has been shown that the CaF2 and Si films are selectively etched by the wet and dry plasma processes.

Heteroepitaxial CaF2/Si and Si/CaF2/Si structures have been formed by conventional vacuum deposition of CaF2 and Si. Optimum conditions for obtaining good epitaxial films have been investigated by changing Si substrate orientations, film thicknesses, and substrate temperatures during film deposition. It has been found from Rutherford backscattering and channeling spectroscopy (RBS) that the crystalline quality of CaF2 films grown on Si (111) and (110) substrates is excellent, but that the quality of the films on Si (100) is much worse. It has also been found from RBS and TEM (transmission electron microscopy) that single-crystalline Si films are formed on the CaF2/Si (111) structure at substrate temperature of 700°C. Finally, etching characteristics ofCaF2 and Si films have been studied. It has been shown that the CaF2 and Si films are selectively etched by the wet and dry plasma processes.

Silicon dioxide (SiO2) thin films were deposited at room temperature by 193-nm ArF excimer laser ablation of silicone in oxygen atmosphere. Only the side chains of the target were photo-dissociated during ablation to deposit Si-O bonds on a substrate in high laser fluence at about 10 J/cm2. Oxygen gas worked to oxidize the Si-O bonds ejected from the target to from SiO2 thin films at the gas pressure of 4.4 X 10-2 Torr, in addition to reducing the isolated carbon mixed into the films. We also found that the deposited rate could control refractive index of the films. The refractive index of the film deposited at 0.05 nm/pulse is greater than that of the film at 0.1 nm/pulse. Thus, a 0.2-micrometers thick SiO2 cladding film deposited at 0.1 nm/pulse was firstly formed on the whole surface of a 100- micrometers -thick polyester film, and then a 0.6 micrometers -thick SiO2 core film at 0.05 nm/pulse was fabricated in a line on the sample. The sample functioned as a waveguide device for a 633-nm line of He-Ne laser.

Catalytic microstructured reactors are becoming widely recognized for their unique properties, such as high surface–to–volume ratios, isothermal conditions due to high heat transfer rates, enhanced safety, and potential applications in chemistry and in chemical industry. The efficient use of microreactors requires shaping of the catalyst usually by deposition of thin catalytic films on microchannel walls. Thin films with large internal surface area can considerably enhance the catalytic surface in the absence of internal mass transfer limitations in the porous structure. As the diffusion of large organic molecules in the porous network is much slower as compared to that observed in gas phase reactions, the maximum catalytic film thickness to avoid internal mass transfer limitations is estimated to be ca. 3 µm. Mesoporous titania thin films doped with metal nanoparticles attract considerable attention in catalysis due to their large surface areas, narrow pore (and particle) size distribution, and favorable surface properties. To obtain the mesostructured materials with required properties it is important to control accurately the synthesis conditions during the preparation of mesoporous catalytic films. Mesoporous films doped with metal nanoparticles were successfully used in a number of reactions, such as reduction of hydrogen peroxide, hydrogenation of acetylene alcohols and ??,??-unsaturated aldehydes and others. Due to a strong metal support interaction between catalytic nanoparticles (Au, Ag, Pd, Pt) and the support, mesostructured titania can prevent metal nanoparticles aggregation and thus improve catalyst stability. This thesis is devoted to preparation of noble metal doped titania films, deposited on the flat plates and within the fused silica microcapillaries. The mesoporous titania coatings were synthesized via the sol–gel method combined with evaporation induced self assembly, which is based on the self–assembling of the structures in the presence of ionic surfactants or block–copolymers. The catalytic films were obtained via direct adding of metal nanoparticles into the titania sol or by adsorption of the metal-organic compounds onto the mesostructured titania films. The catalytic films properties, such as thickness, porosity, particle and pore sizes, and structure, were investigated by a number of techniques (TEM, SEM, ellipsometry, IR, XRD, XPS). The particle size in a nanostructured catalyst, the pore size and the thickness of the mesoporous support can be independently controlled via a one-pot evaporation induced self assembly synthesis. Titania films doped with Au or Pt-Sn nanoparticles were tested in a model reaction of citral hydrogenation into unsaturated alcohols (UCOL). Citral (3,7-dimethyl-2,6-octadienal) is considered as an interesting model molecule since it has three hydrogenation targets: a carbonyl group, a C=C bond conjugated with the carbonyl group, and an isolated C=C bond. However, the citral hydrogenation reaction attracts not only scientific, but also practical interest, since the hydrogenation is an important step in many fine chemical processes. The synthesis of mesoporous TiO2 and Au/TiO2 films is described in Chapter 2. The influence of synthesis parameters, such as the ratio of templating agent/Ti-precursor and pH of initial sol on the structure of the films was studied. The films have been investigated by a number of physico-chemical methods in order to characterize the properties of the mesoporous films. It was found that highly ordered hexagonal mesostructures can be obtained at a certain range of pH values (1.5-1.8) and template/Ti ratios (0.006-0.009). The thickness of the mesoporous titania films was increased from 300 to 1000 nm by a deposition of multi-layer coatings. Gold nanoparticles with an average size of 4.5 nm were embedded in the mesoporous titania films by condensation of metal oxide species via self-assembly in the presence of a known amount of stabilized gold colloids. The complete surfactant removal was achieved at 573 K under a residual pressure of 10 mbar within 4 hrs without destroying the film structure. Under these conditions the Ti4+ sites were reduced to Ti3+ which might be responsible for a high selectivity to UCOL in the hydrogenation of citral over Au-containing supported catalysts. A 300 nm thick Au-containing film showed an initial TOF of 1.4 s-1 and selectivity towards UCOL as high as 90% in the hydrogenation of citral. Thicker films demonstrated a high selectivity towards the saturated aldehyde (above 55%) and a lower intrinsic catalytic activity (initial TOF of 0.7-0.9 s-1) in the absence of internal diffusion limitations. A new approach for predicting the pore size distribution of mesoporous thin films using ellipsometric porosimetry is described in Chapter 3. The method has been developed taking into account multilayer adsorption and capillary condensation phenomena. The improved Derjaguin - Broekhoff - de Boer model (IDBdB) was applied for determination of the mesopore size on titania and silica films with a thickness of ca. 200 nm deposited on a silicon substrates. This approach eliminates uncertainties related to the application of the statistical film thickness determined via t-plots in previous versions of the DBdB model. The deviation in the surface tension of ethanol in the mesopores from that of a flat interface was described by the Tolman parameter. An empirical expression for the disjoining pressure isotherm has been applied to represent the interaction between the adsorbate and the adsorbent. The parameters in the empirical expression have been obtained by fitting the multilayer region of an experimental isotherm on titania and silica films. Using these parameters, the adsorption and desorption isotherms of ethanol were predicted and adjusted to the experimental data by fitting the Tolman parameter of the model, characterizing the surface tension for a curved surface. The IDBdB desorption model with a positive value of the Tolman parameter of 0.2 nm was found to describe accurately (±1%) the pore diameter in a wide range of mesopores from 2.1 to 8.3 nm what was in a good agreement with results obtained by TEM and XRD. The synthesis and characterization of Pt-Sn/TiO2 powder catalysts and catalytic films is presented in Chapter 4. The processing parameters, such as Pt-Sn precursor types, impregnation techniques, adsorption time, were varied. The resulting catalysts were tested in citral hydrogenation reaction. The selectivity to the desired product (UCOL) was found to be ca. 90% at a citral conversion above 95%. A reaction rate in terms of TOF of 0.2 – 3.3 min-1 was observed in the citral hydrogenation over the Pt-Sn/TiO2 powder catalysts. The highest activity was observed in the case of catalysts prepared by co-impregnation in comparison with the catalysts prepared via organometallic route and successive impregnation, what could be attributed to an intimate contact between the metals. The Pt-Sn/TiO2 films were prepared via i) one-pot synthesis using Pt-Sn colloids or clusters, and ii) adsorption of Pt-Sn clusters into the mesoporous titania films. The activity and selectivity of Pt-Sn/TiO2 films strongly depend on the precursor type and adsorption time (in case of clusters). The highest UCOL yield (72%) was observed in the case of a two layer catalytic film obtained from Pt-Sn clusters solution with adsorption time of 5 hrs. Chapter 5 is focused on the demonstration of the potential of capillary microreactors by the results obtained in a selective hydrogenation of citral to UCOL. The Au/TiO2 sol was impregnated by dip-coating into the fused silica capillary with a length of 10 m and internal diameter of 250 µm. A Pt-Sn/TiO2 wall-coated capillary was made by an impregnation of Pt-Sn clusters into the capillary preliminary coated with a titania layer. Both capillaries were tested in the citral hydrogenation reaction. The influence of the reaction conditions, such as liquid flow, reaction temperature, hydrogen partial pressure, on the catalytic properties was investigated. The detailed analysis of kinetics is presented. The Pt-Sn/TiO2 coated capillary shows better catalytic properties in comparison with the Au/TiO2 coated one. The maximal yield of UCOL was found to be 79 and 29% for Pt-Sn/TiO2 and Au/TiO2 catalysts, respectively. The reaction has first and zero order in hydrogen and citral, respectively. The synthesis and characterization of a new type of catalyst – ZnO nanowires doped with Pd nanoparticles – is presented in Chapter 6. The ZnO nanowires were made by the atomic layer deposition technique. Pd nanoparticles with average sizes of 2.7 and 4.5 nm were impregnated from the Pd colloids solutions. The catalysts were tested in the selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE). The effect of the solvent, hydrogen pressure and reaction temperature on the MBE yield was investigated. ZnO nanowires possess 88% selectivity to MBE at 99% MBY conversion at 5 bar hydrogen pressure and 323K and show no deactivation after 20 runs of the reaction. The Pd/ZnO nanowires catalyst shows 94% yield of MBE in the first run of the reaction. Catalytic tests performed in water and in a methanol–water (3:1 vol.) mixture led to sintering of the Pd particles decreasing both the activity and selectivity. The ZnO NWs were rather stable in water which is promising for further optimization of their activity and stability using highly polar solvents. A kinetic model is proposed to explain activity and selectivity of the ZnO and Pd/ZnO nanowires catalysts. Finally, in Chapter 7 the main conclusions of the previous chapters are summarized.

At present, the nonvolatile memory devices based on different kinds of nanocrystals are intensively developed. The important problem for further progress is connected with the optimization of gate multilayer structure. The aim of this work is the investigation of the electrical properties of thin nanocomposite SiO2(Si) films as a medium for the charge storage. The silicon enriched SiOx films were deposited by plasma enhanced chemical vapor deposition (PE CVD) method. The film composition was controlled changing the ratio of the flows of reactive gases SiH4 and N2O in a vacuum chamber. Subsequent thermal annealing led to the phase separation in SiOx films with a formation of nanocomposite SiO2(Si) structure of Si nanocrystals in dielectric matrix. Capacity‐voltage and current‐voltage measurements of MIS structures with gate nanocomposite SiO2(Si) films allowed to optimize the technological conditions of the formation of MIS structures with good charge storage properties. The value and the sign of stored charge were determined from the shift of C‐V characteristics. Analysis of the C‐V characteristics of MIS structures with nanocomposite SiO2(Si) films used equivalent circuit with the capacity of nanocrystals connected in parallel to the capacity of dielectric. The decrease of capacity in the accumulation region caused by nanocrystals was observed. The mechanism of current transport through the SiO2(Si) films was analyzed. It is determined to occur by tunneling through the SiO2 layers between the Si nanocrystals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High quality ceramic thin films were fabricated by thin film deposition process in semiconductor field in order to fabricate high performance carbon/SiO 2 /Al 2 O3 membrane. α-Al 2 O 3 substrate was used as a supporting material. A severe thermal stress and rough surface for active ceramic top layer such as zeolite were observed. To overcome thermal stress, intermediate layer of SiO2 and diamond-like carbon (DLC) thin film were used. SiO 2 and DLC thin films on porous alumina support were deposited using plasma-enhanced chemical vapour deposition (PECVD). Homogeneous and smooth surfaces and interfaces of DLC/SiO 2 /Al 2 O 3 membrane were observed by FESEM. The phases of DLC and SiO 2 thin films were identified by X-ray diffraction pattern. Gas permeabilities of the nanofiltration membrane with DLC/SiO 2 /Al 2 O 3 were observed at various annealing temperatures. Mixed gas permeability of the membrane with 1 μm-thick SiO2 and 2 μm-thick DLC thin film annealed at 200 °C was ∼18 ccm at 1018 mb back pressure.

A novel method using Fourier transform algorithm is proposed to determine each layer thickness of multi-layered thin films from interference oscillation observed in X-ray specular reflection. The peak position in Fourier space gives each layer thickness of the film. The principle of the present technique as well as its applications are described.