XPS study on composition and structure of epitaxial KTa1−xNbxO3 (KTN) thin films prepared by the sol-gel process

Epitaxial KTN (x=0.35) thin films were prepared on (100) SrTiO₃ substrates by the sol-gel process. In this paper, wide and narrow scans of XPS analysis were studied on the surface of the KTN thin films before and after Ar⁺ sputtering for 10 min. The results show that no impurity or residual carbon was observed in the films, except for some carbon contamination caused by handling and pumping oil on the surface of the films. The chemical composition of the films is in good agreement with the stoichiometry of the starting materials, as demonstrated by the ICP results. The valence states of the ions indicated that the films are KTN with a perovskite structure. XPS spectra of the films after Ar⁺ sputtering differ considerably from those of the as-grown films, which may be attributable to the preferred sputtering of potassium and to new valence states produced during the Ar⁺ bombardment. In addition, it was confirmed by the angle resolution XPS results that the chemical composition was well-distributed and that no other phase was observed apart from KTN in the near surface region of the films.     

XPS study of the surface composition modification of nc-TiC/C nanocomposite films under in situ argon ion bombardment

X-ray Photoelectron Spectroscopy (XPS) is commonly used to study the chemical composition of TiC/C nanocomposite films. Nevertheless, XPS remains a surface analysis technique and the obtained chemical information can be strongly affected by the surface oxidation and carbon contamination of the nanocomposite samples due to their exposure to air. Generally, an erosion stage is performed before XPS analysis using argon ion bombardment to remove the surface contamination. Since ion bombardment is likely to modify the surface chemical composition of the films, the question of whether XPS results are really representative of the bulk nanocomposite material can be addressed. Therefore, this study is devoted to the effect of ion bombardment on the surface chemical composition of nanocomposite films. TiC_x and TiC_xO_y films were grown by a hybrid plasma process combining Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition. Then, the samples were transferred to the XPS system where an in situ study of the modification of the surface chemical composition under argon ion bombardment was performed. XPS results are compared to Energy Dispersive X-ray analysis.     

Preparation and characterization of ZnS thin films by the chemical bath deposition method

ZnS thin films prepared on quartz substrates by the chemical bath deposition (CBD) method with three type temperature profile processes have been investigated by X-ray diffraction, scanning electron microscope, energy dispersive X-ray analysis and light transmission. One is a 1-step growth process, and the other is 2-steps growth and self-catalyst growth processes. The surface morphology of CBD-ZnS thin films prepared by the CBD method with the self-catalyst growth process is flat and smooth compared with that prepared by the 1-step and 2-steps growth processes. The self-catalyst growth process in order to prepare the particles of ZnS as initial nucleus layer was useful for improvement in crystallinity of ZnS thin films prepared by CBD. ZnS thin films prepared by CBD method with self-catalyst growth process can be expected for improvement in the conversion efficiency of Cu(InGa)Se₂-based thin film solar cells by using it for the buffer layer.     

A low temperature process for the reactive formation of Si3N4 layers on InSb

Standard chemical vapour deposition (CVD) processes for the deposition of silicon nitride films require working temperatures of 275°C or above which are liable to cause surface degradation of III–V semiconductors such as InSb. In this paper, a room temperature CVD process yielding Si₃N₄ layers with electrical characteristics that are comparable with those obtained by conventional processes is presented. The film density and the adherence to the InSb substrates could be significantly improved using a special electrode configuration and an in situ sputter etch prior to film deposition.     

A review of the specific role of oxygen in irreversible photo- and thermally induced changes of the optical properties of thin film amorphous chalcogenides

Recent results concerning the influence of oxygen on the photo- and thermally induced changes of optical properties of thin amorphous chalcogenides are summarized. It is shown that interaction of the surface of thin films with oxygen considerably affects the shift of the optical gap. The influence of oxygen is perhaps twofold. It behaves probably like a “catalyzer in the process of oxygen-assisted bond reconstruction” as proposed by Spence and Elliott [Phys. Rev. B 39 (1989) 5452], but it also enters directly into the film network forming strong covalent bonds with germanium and chalcogen atoms, respectively. Hence, the presence of oxygen during illumination or annealing of thin amorphous chalcogenide films most probably affects (i) the density of dangling and homopolar bonds, respectively, (ii) and actual chemical composition of the surface layer making this one oxygen rich (in normally deposited thin films) but also, chalcogen poor (in some obliquely deposited thin films). The role of oxygen in the case of illumination or annealing of amorphous chalcogenide films is of considerable importance and should not be neglected.     

Features of formation of germanium silicate glasses during oxidation of nanostructured films of germanium-doped polycrystalline silicon

Nanostructured films of polycrystalline silicon obtained by joint pyrolysis of monosilane (SiH₄) and monogermane (GeH₄) were oxidized in a medium of dry and wet oxygen. As a result of their oxidation, vitreous films of complex oxides of germanium and silicon, germanium silicate glass (GSG), is formed. It is established that the presence of germanium in the composition of nanostructured films of polycrystalline silicon (NSF PCS) increases their reaction ability with respect to oxidation. Using the methods of IR spectroscopy, XPE spectroscopy, Auger spectroscopy, and thermal analysis, the composition and phase transformation of vitreous oxides formed in the course of oxidation of NSF PCS are investigated. It is shown that the composition and phase transformation of the films of vitreous silicon and germanium oxides depend on the germanium content in the NSF PCS and conditions of their oxidation.     

Comparison study of microstructure, chemical composition and optical properties between resistive heating and electron beam evaporated LaF3 thin films

LaF₃ thin films were deposited by electron beam (EB) and resistive heating (RH) evaporation, respectively. Properties such as microstructure, chemical composition, surface morphology and optical constants of the LaF₃ thin films were characterized by measurements of X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and spectrophotometer, then comparison was made between this two deposition methods. It's found that the microstructure properties of the LaF₃ films deposited by these two methods were different, and slight content of oxyfluoride films was formed during deposition according to the result of chemical composition analysis. The microstructure of LaF₃ bulk materials after interaction with electron beam and resistive heating was also characterized to analyze how the two deposition processes affect the formation of LaF₃ thin films and their microstructure properties. When it was for the laser resistance of the films, although the EB evaporated LaF₃ thin films occupied lower absorption and optical loss than those of the RH films, they showed slightly smaller laser induced damage thresholds at 355 nm, which was thought to be related to their much more rougher surface and higher tensile stress.     

Aerosol assisted chemical vapour deposition of germanium thin films using organogermanium carboxylates as precursors and formation of germania films

Diethyl germanium bis-picolinate, [Et₂Ge(O₂CC₅H₄N)₂], and trimethyl germanium quinaldate, [Me₃Ge(O₂CC₉H₆N)], have been used as precursors for deposition of thin films of germanium by aerosol assisted chemical vapour deposition (AACVD). The thermogravimetric analysis revealed complete volatilization of complexes under nitrogen atmosphere. Germanium thin films were deposited on silicon wafers at 700°C employing AACVD method. These films on oxidation under an oxygen atmosphere at 600°C yield GeO₂. Both Ge and GeO₂ films were characterized by XRD, SEM and EDS measurements. Their electrical properties were assessed by current?Cvoltage (I?CV) characterization.     

Thermodynamic analysis of the growth of germanium-containing films from Ge(C2H5)4 + hydrogen mixtures

Low-pressure (1.33 and 13.3 Pa) chemical vapor deposition (CVD) of GeC _x from tetraethylger-manium + hydrogen mixtures has been analyzed in a wide range of deposition temperatures, 300–1300 K, using thermodynamic modeling. In low-pressure CVD processes, films can be contaminated with impurities, in particular with oxygen, which may originate in the system in question from the residual air pressure in the reactor. Modeling results for the Ge-C-H and Ge-C-H-O-N systems indicate that the presence of oxygen adds significant complexity to the composition of condensed phases. At sufficiently high temperatures (T > 550 K), one can obtain GeC _x films essentially free from oxygen impurities. We have identified deposition conditions (T > 650 K) under which the overall composition of the GeC _x carbon-containing germanium layers remains constant. Experimental data are presented on the growth of germanium-containing films from a gas mixture with GeEt₄: H₂ = 1: 10 in the temperature range 573–823 K by plasma-enhanced CVD. At high deposition temperatures (T > 700 K), the composition of the films was near GeC _x , in agreement with thermodynamic analysis results.     

Interface structure between reactively ion plated TiO2 films and PET substrate

ESCA (electron spectroscopy for chemical analysis) has been used for studying the interface structure between PET (polythylene terephthalate) substrate and TiO₂ films produced from a metal source by reactive rf bias ion plating. The results have been compared with those for films produced by conventional electron beam evaporation. Sequential ESCA analysis and in situ argon sputter profiling have been carried out for the TiO₂ films of varying thicknesses on PET. Bombardment by high energy particles prior to deposition removes surface contamination and activates the PET surface. TiO₂ films are formed on the modified surface, which results in chemical interaction between the film and substrate. A very thin TiC_x layer observed at the interface region shows the presence of this kind of interaction. On the basis of the results, the interface structure is discussed.     

Atomic layer deposition of hafnium oxide dielectrics on silicon and germanium substrates

Hafnium oxide films have been deposited at 250 °C on silicon and germanium substrates by atomic layer deposition (ALD), using tetrakis-ethylmethylamino hafnium (TEMAH) and water vapour as precursors in a modified Oxford Instruments PECVD system. Self-limiting monolayer growth has been verified, characterised by a growth rate of 0.082 nm/cycle. Layer uniformity is approximately within ±1% of the mean value. MOS capacitors have been fabricated by evaporating aluminium electrodes. CV analysis has been used to determine the bulk and interface properties of the HfO₂, and their dependence on pre-clean schedule, deposition conditions and post-deposition annealing. The dielectric constant of the HfO₂ is typically 18. On silicon, best results are obtained when the HfO₂ is deposited on a chemically oxidised hydrophilic surface. On germanium, best results are obtained when the substrate is nitrided before HfO₂ deposition, using an in-situ nitrogen plasma treatment.     

Optimizing Single Point Diamond Turning for Mono-Crystalline Germanium Using Grey Relational Analysis

In this paper the results of an experimental study conducted for precision machining of mono-crystalline germanium with single point diamond turning (SPDT) have been reported. The input parameters include the top rake angle, tool overhang, depth of cut, tool feed rate, and rotational speed of the workpiece. The flat profile is generated on a disk of mono-crystalline germanium possessing three performance characteristics: surface roughness (R_a), profile error (P_t), and waviness error (W_a). The process parameters are optimized to obtain the best surface finish with minimum profile and waviness errors by using the Taguchi method. The grey relational analysis is employed for carrying out multiresponse optimization of performance parameters. The best value of surface finish obtained after multiresponse optimization is 10.7 nm having a profile error and a waviness error of 0.202 µm and 0.046 µm, respectively.     

Effect of impinging ion energy on the substrates during deposition of SiOx films by radiofrequency plasma enhanced chemical vapor deposition process

Radiofrequency (13.56 MHz) plasma enhanced chemical vapor deposition process is used for deposition of SiO_x films on bell metal substrates using Ar/hexamethyldisiloxane/O₂ glow discharge. The DC self-bias voltage developed on the substrates is observed to be varied from − 35 V to − 115 V depending on the RF power applied to the plasma. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. The deposited films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, nano-scratch test and thermogravimetric analysis. The characterization results show strong dependency of the SiO_x films properties on the energy of the ions impinging on the substrates during deposition. Analysis of Raman spectra indicates an increase in vitreous silica content and reduction in defective Si-O-Si chemical structure in the deposited SiO_x films with increasing ion energy impinging on the substrates. The increase in inorganic (Si and O) content in the SiO_x films is further confirmed from XPS analysis. The growth of SiO_x films with more inorganic content and defect free chemical structure apparently contribute to the increase in their hardness and scratch resistance behavior. The films show higher thermal stability as the energy of the ions arriving at substrates increases with DC self-bias voltage. The possibility of using SiO_x films for surface protection of bell metal is also explored.     

Surface qualities after chemical–mechanical polishing on thin films

Demands for substrate and film surface planarizations significantly increase as the feature sizes of Integrated Circuit (IC) components continue to shrink. Chemical Mechanical Polishing (CMP), incorporating chemical and mechanical interactions to planarize chemically modified surface layers, has been one of the major manufacturing processes to provide global and local surface planarizations in IC fabrications. Not only is the material removal rate a concern, the qualities of the CMP produced surface are critical as well, such as surface finish, defects and surface stresses. This paper is to examine the CMP produced surface roughness on tungsten or W thin films based on the CMP process conditions. The W thin films with thickness below 1000 nm on silicon wafer were chemical–mechanical polished at different down pressures and platen speeds to produce different surface roughness. The surface roughness measurements were performed by an atomic force microscope (DI D3100). Results show that the quality of surface finish (R_a value) is determined by the combined effects of down pressures and platen speeds. An optimal polishing condition is, then, possible for selecting the down pressures and platen speeds.     

Effects of methane flow rate on the optical properties and chemical bonding of germanium carbon films deposited by reactive sputtering

Amorphous hydrogenated germanium carbon (a-Ge_1−xC_x:H) films were prepared by radio frequency (RF) reactive magnetron sputtering of a pure Ge (111) target in a CH₄ + H₂+Ar mixture and their composition, optical properties, chemical bonding were investigated as a function of gas flow rate ratio of CH₄/(Ar + H₂). The results showed that the deposition rate first increased and then decreased as gas flow rate ratio of CH₄/(Ar + H₂) was increased from 0.125 to 0.625. And the optical gap of the a-Ge_1−xC_x:H films increased from 1.1 to 1.58 eV accompanied with the increase in the carbon content and the decrease in the relative content of Ge–C bonds of the films as the CH₄ flow rate ratio was increased, while refractive index of the films decreased and the absorption edge shifted to high energy. Through the analysis of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, it was found that the formation of Ge–C bonds in the films was promoted by low CH₄ flow rate which is connected with relatively high H₂ concentration and Ge content. Especially in low CH₄ concentration, the formation of sp²-hybridised C–C bonds was suppressed considerably both due to the etching effect on weak bonds of H and the fact that chemical bonding for germanium can be only sp³ hybridization.     

Chemical/mechanical polishing of diamond films assisted by molten mixture of LiNO3 and KNO3

Chemical/mechanical polishing can be used to polish the rough surface of diamond films prepared by chemical vapor deposition (CVD). In this paper, a mixture of oxidizing agents (LiNO₃ + KNO₃) has been introduced to improve the material removal rate and the surface roughness in chemical/mechanical polishing because of its lower melting point. It had been shown that by using this mixture the surface roughness R_a (arithmetic average roughness) could be reduced from 8-17 to 0.4 μm in 3 h of polishing, and the material removal rate can reach 1.7-2.3 mg/cm²/h at the temperature of 623 K. Pure aluminium is compared with cast iron as the contact disk material in the polishing. Although the material removal rate of aluminiumdisk is lower than that of cast iron, it can eliminate the carbon contamination from the contact disk to the surface of diamond films, and facilitate the analysis of the status of diamond in the chemical/mechanical polishing. The surface character and material removal rate of diamond films under different polishing pressure and rotating speed have also been studied. Graphite and amorphous carbon were detected on the surface of polished diamond films by Raman spectroscopy. It has been found that the oxidization and graphitization combined with mechanical cracking account for the high material removal rate in chemical/mechanical polishing of diamond films.     

Preparation of sols from water-alcohol solutions of tetraethyl orthosilicate and SnCl<Subscript>4</Subscript> and the effect of sol composition on the surface morphology of sol-gel films

We describe a process for the preparation of sols from water-alcohol solutions of tetraethyl orthosilicate and SnCl₄. The kinetics of this process have been studied by measuring the electrical conductivity of the sols, and the optical absorption spectra of the sols have been measured. The surface morphology of films prepared from the sols has been examined by scanning electron microscopy. The results are used to assess the influence of preparation conditions, sol composition, and processes underlying sol formation on the surface morphology of the gas-sensing films prepared from the sols.     

Modeling of plasma CVD on the inner surface of a microchannel

Plasma chemical vapor deposition (P-CVD) of palladium films by a microcapillary plasma has been done successfully by using palladium hexafluoroacetylacetonate (Pd(C₅HF₆O₂)₂) as a precursor. The dependence of the palladium profiles in deposited films and the process completion times on the process parameters is investigated. In addition, the model of the P-CVD is presented and the numerical analysis based on the model is carried out using some assumptions. The model simulation can predict effectively the experimental results. The experimental and calculated results indicate that the gas velocity and current density are the important parameters to decide the palladium profiles of deposited films and the process completion times.     

Fluctuation conductivity of tin films below the superconducting transition temperature

Measurements have been carried out of the temperature dependence of the fluctuation-induced excess electrical conductivity of thin (thickness much less than the Ginzburg-Landau coherence length) superconducting films of tin below the transition temperature. Two types of specimen were investigated: (a) films deposited on a glass substrate held at 300 K and (b) films deposited on a glass substrate at 300 K and then covered by a protective layer of germanium. Special care was taken to ensure sample homogeneity. Analysis of the results shows that the fluctuation parameter, ε_c, is not affected by the germanium layer. Its value is, however, much larger than that predicted by the theory of Kajimura, Micoshiba, and Yamaji.     

Embedding of reduced pressure-chemical vapor deposition grown Ge nanocrystals in a high quality SiO2 matrix for non-volatile memory applications

We have obtained thanks to reduced pressure-chemical vapor deposition germanium nanocrystals in a high quality SiO₂ matrix. A perfect control of (i) the tunnel and control oxide layer thicknesses and (ii) the germanium nanocrystals' density and diameter has been achieved. Scanning electron microscopy was used to (i) determine the nucleation and growth rate of the germanium nanocrystals and (ii) evaluate their morphological stability during their embedding. We have also studied the influence of thin selectively grown Si films in order to passivate the surface of the germanium nanocrystals. X-ray photoelectron spectroscopy has shown that the germanium nanocrystals' surface properties are better with a Si capping. The polycrystalline state of the nanocrystals has been evaluated with X-ray diffraction. Transmission electron microscopy image reveals the lack of germanium diffusion and precipitation in the SiO₂ matrix.