Structural roughness and interface strain properties in Si/SiO2/Poly-Si1−x Ge x tri-layer system with ultrathin oxide

We have explored the microstructure and local interface strain in the poly-Si_1-xGe_x/SiO₂/Si tri-layer system with ultrathin oxides. High-resolution transmission electron microscopy (HRTEM) and high-resolution X-ray diffraction rocking curves (HR-RC) and two-dimensional reciprocal space mapping (2D-RSM) were the main characterization tools. The poly-Si_1-xGe_x/SiO₂/Si structures have x=0, 0.2, and 0.35 for ultrathin oxides (2.0–3.0 nm). The result shows that for the adopted growth process, the poly grain size depends very strongly on the Ge concentration, and it increases with increasing Ge mole fraction. In turn, this increase of the grain size in the poly-Si_1-xGe_x/SiO₂/Si reduces the strain in the film, which then affects the interface strain at the lower SiO₂/Si interface. In addition, the presence of defects at the SiO₂/Si interface was found to be greater for samples with no local interface strain.     

Native oxide consumption during the atomic layer deposition of TiO2 films on GaAs (100) surfaces

The consumption of the surface native oxides is studied during the atomic layer deposition of TiO₂ films on GaAs (100) surfaces. Films are deposited at 200 °C from tetrakis dimethyl amido titanium and H₂O. Transmission electron microscopy data show that the starting surface consists of ~2.6 nm of native oxide and X-ray photoelectron spectroscopy indicates a gradual reduction in the thickness of the oxide layer as the thickness of the TiO₂ film increases. Approximately 0.1-0.2 nm of arsenic and gallium suboxide is detected at the interface after 250 process cycles. For depositions on etched GaAs surfaces no interfacial oxidation is observed.     

Inspection of intermediate stress-induced electronic traps in Si/Al2O3 system

The physical characteristics of device-grade thin silicon film at (1 0 0) grown on α-Al₂O₃ substrate using the chemical vapour deposition (CVD) technique has been studied in this paper. Its thickness, crystalline structure, elemental inter-diffusion in the interface region and the quality were characterized by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), core level X-ray photoelectron spectroscopy (XPS) and nuclear resonance reaction ²⁷Al(p,γ)²⁸Si, respectively. The results of stoichiometric defect profile and individual silicon suboxide (such as SiO, and Si₂O₃ components with respect to the metallic Si element) formation in the intermediate region were observed. The deep traps located around E_c=0.26eV, in ∼500 nm thick n-type Si films, were attributed to the defects caused by the strain of the silicon lattice. Raman spectroscopy was used to evaluate the compressive stress in the Si film.     

Structure and formation process of (K,Na)-clinoptilolite

In order to synthesize (K,Na)-clinoptilolite, a (K,Na)-aluminosilicate slurry with a seed crystal was stirred at 30 °C for 4 days and then hydrothermally treated under homogeneous mixing conditions at 120 °C for 14 days. The Si/Al:(Na+K)/Si:K/(Na+K):H₂O/Al molar ratio of the starting materials was 6.0:0.42:0.5:52.5. The formation process of (K,Na)-clinoptilolite was investigated by a variety of techniques. When the materials were hydrothermally treated up to 6 days, amorphous (K,Na)-aluminosilicate was formed. After the hydrothermal treatment for 8 days, irregular particles due to the amorphous (K,Na)-aluminosilicate disappeared and plate-like particles of (K,Na)-clinoptilolite were formed, indicating that the amorphous aluminosilicate crystallized as clinoptilolite. In addition, (Na+K)/Al molar ratio in the materials varied from 1.2 to 1.0, accompanying the decrease of cation exchange capacity. During the crystallization, the wavenumber of external linkages of TO bonds shifted to higher values, implying that the SiOSi and SiOAl bonds were formed.     

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.     

Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO2 films

HfO₂ thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O₂/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO₂ grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiO_x suboxide layer at the HfO₂/Si interface is unavoidable. The HfO₂ thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O₂/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO₂, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO₂ to form HfO₂, leaving Si-Si bonds behind.     

Structural study of (50 − x)Na2O-xCuO-10Bi2O3-40P2O5 glasses

(50−x)Na₂O-xCuO-10Bi₂O₃-40P₂O₅ glasses (0≤x≤25) were prepared by melting at 900-1100°C mixtures of Na₂CO₃, Bi₂O₃, CuO and (NH₄)₂HPO₄. DSC measurements give the variation of glass transition temperature T_g from 318 (x=0) to 378°C (x=25). FTIR spectroscopy shows the evolution of the phosphate skeleton: (PO₃)_∞ chains for 60Na₂O-40P₂O₅ to P₂O₇ groups in the glass containing Bi₂O₃ or both Bi₂O₃ and CuO. When bismuth and copper oxides replace Na₂O, phosphate chains are depolymerized by the incorporation of Bi₂O₃ and CuO through POBi and POCu bonds. P₂O₇ groups are predominant structural units in the richest CuO glass. The variation of T_g also supports these results.     

Silicate formation at the interface of Pr-oxide as a high-K dielectric and Si(001) surfaces

The composition and chemical bonding of the first atoms across the interface between Si(001) and the dielectric determine the quality of dielectric gate stacks. An analysis of that hidden interface is a challenge as it requires both, high sensitivity and elemental and chemical state information. We used X-ray absorption spectroscopy in total electron yield and total fluorescence yield at the Si2p and the O1s edges to address that issue. We report on results of Pr₂O₃/Si(001) as prepared by both, epitaxial growth and metal organic chemical vapor deposition (MOCVD), and compare to the SiO₂/Si(001) system as a reference. We find evidence for the silicate formation at the interface as derived from the characteristic features at the Si2p and the O1s edges. The results are in line with model experiments in which films of increasing film thickness are deposited in situ on bare Si(001) surfaces.     

Crystal chemistry of β-Si3N4 solid solutions containing metal oxides

Phase equilibrium diagrams of Si₃N₄-metal oxides systems were reviewed. It was found that the solid solubility limits of different metal oxides in β-Si₃N₄ depends on the size and charge of the metal elements. A misfit factor was suggested to present these variables numerically. For some compositions in the systems Si,Al/N,O, Si, Be/N,O, Si,Al,Be/N,O and Si,Be,Mg/N,O the misfit factors were computed and plotted against the solubility limits. It was found that substantial amount of foreign atoms can be accommodated in the β-Si₃N₄ lattice when the misfit factor is small. When the misfit factor becomes larger, only small amount of foreign atoms enter the lattice. The results suggested that this method can be used to estimate the solid solubility limits of one or more metal oxides and nitrides in β-Si₃N₄.     

Dependence of hydrogen and oxygen incorporation on deposition parameters in photochemical vapor deposited mercury free silicon nitride films

Silicon nitride films have been deposited on p-type Si (100) by mercury-sensitized photo-chemical vapor deposition (photo-CVD) method varying deposition pressure and substrate temperature. Energy dispersive X-ray fluorescence spectra of the samples show that the incorporation of mercury in the films, if any, is below 20 ppm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy studies show the incorporation of oxygen and hydrogen in all the films, which is a function of the deposition parameters. Higher substrate temperature favors the formation of SiH bonds and reverse is the case for the formation of SiNH bonds. The sample deposited at low temperature (170 °C) shows the presence of less unreacted silicon (4%) in comparison to the sample (12.5% unreacted silicon) deposited at higher deposition temperature (250 °C), but the variation of pressure shows no significant change in terms of the unreacted silicon. The incorporated hydrogen and oxygen passivate surface defects thereby influencing interface electronic state densities (D_it) and fixed insulating charges (Q_ss).     

R.F. plasma annealing of as-grown defects in the Si/SiO2 system

The annealing effect of an r.f. hydrogen plasma on the interface properties in Si/SiO₂ systems was investigated. The fixed oxide charge is found to be sensitive to the low temperature plasma annealing. Annealing is more effective at higher temperatures and when applied to metallized structures. With bare oxides the generation of slow states is observed whose concentration depends on the substrate temperature. A final 450 °C hydrogen anneal gives very low fixed charge densities. Comments on the annealing mechanism are also given.     

Synthesis and characterization of the open-framework cobalt borophosphate: (C4N2H12)Co[B2P3O12(OH)]

A high yield hydrothermal synthesis of the open-framework cobalt borophosphate (C₄N₂H₁₂)Co[B₂P₃O₁₂(OH)], has been developed. The compound was characterized by single crystal X-ray diffraction methods, thermogravimetric analysis, vibrational (IR and Raman) spectroscopy and magnetic measurements. In the structure Co(II)O₆ octahedra, BO₄ and PO₄ tetrahedra form nine-member rings which in turn are linked to form CoBPO layers parallel to the bc plane. The layers are joined together by another set of PO₄ tetrahedra and the (piperazinium)²⁺ cations occupy the channels running along [1 0 0]. The structure is compared with that of (C₂N₂H₁₀)Co[B₂P₃O₁₂(OH)].     

Reactive sputtering of SiO2-TiO2 thin film from composite Six/TiO2 targets

Coatings of SiO₂-TiO₂ films are frequently used in a number of optical thin film applications. In this work we present results from depositing films with variable Si/Ti ratios prepared by reactive sputtering. The different Si/Ti ratios were obtained by varying the target composition of composite single targets. Compared to co-sputtering this facilitates process control and composition uniformity of the films. Varying the oxygen supply during sputter deposition can result in films ranging from metallic/substoichiometric to stoichiometric oxides. Transmittance spectra of the different films are presented and the optical constants are determined from these spectra. Furthermore, the deposition process, films structure and composition of the films are discussed. The study shows that by choosing the right composition and working in the proper oxygen flow range, it is possible to tune the refractive index.     

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.     

Residual stresses and Raman shift relation in anatase TiO2 thin film

Anatase TiO₂ film (100-1000 nm thick) grown on glass, sapphire (0001), and Si (100) substrates by pulsed dc-magnetron reactive sputtering were evaluated for stress and strain analysis using Raman spectroscopy and curvature measurement techniques. The X-ray analysis revealed that films prepared for this study were purely anatase, and the measurements indicate that the film exhibit that (101) is the preferred growth orientation of the crystallites, especially for the film thicker than 100 nm. Curvature measurements and Raman spectroscopy, with 514.5 nm excitation wavelength, phonon line shift were used for stress analysis. A comparison between Raman lineshapes and peak shifts yields information on the strain distribution as a function of film thickness. The measurements of residual stresses for crystalline anatase TiO₂ thin film showed that all thin film were under compressive stress. A correlation between Raman shifts and the measured stress from the curvature measurements was established. The behavior of the anatase film on three different substrates shows that the strain in film on glass has a higher value compared to the strain on sapphire and on silicon substrates. The dominant 144 cm^− 1E_g mode in anatase TiO₂ clearly shifts to a higher value by 0.45-5.7 cm^− 1 depending on the type of substrate and film thickness. The measurement of the full width at half maximum values of 0.59-0.80 (2θ°) for the anatase (101) peaks revealed that these values are greater than anatase powder 0.119 (2θ°) and this exhibits strong crystal anisotropy with thermal expansion.     

Vacuum-ultraviolet reflectance difference spectroscopy for characterizing dielectrics-semiconductor interfaces

Reflectance difference spectroscopy (RDS) was applied to the characterization of SiO₂/Si, GeO₂/Ge, and high-k/III-V interface structures. We extended the spectral range of RDS to 8.4 eV in order to explore the optical transitions at the dielectrics-semiconductor interfaces as well as to have a high sensitivity to the interface anisotropy. Si surfaces with (110), (113), (331) and (120) orientations showed oxidation-induced RD changes in the vacuum-ultraviolet (VUV) range which were dependent on the surface orientation, oxidation method (dry or wet), and oxidation temperature. The Ge(110) surface also showed characteristic oxidation-induced changes in the VUV range, whereas Al₂O₃ deposition on GaAs(001) and InP(001) surfaces induced only the RD amplitude changes.     

Preparation and characterization of Ge epitaxially grown on nano-structured periodic Si pillars and bars on Si(001) substrate

The selective epitaxial growth of germanium on nano-structured periodic silicon pillars and bars with 360 nm periodicity on Si(001) substrate is studied to evaluate the applicability of nano-heteroepitaxy on the Ge-Si system for different fields of application. It is found that SiO₂ used as masking material plays the key role to influence the strain situation in the Si nano-islands. To analyze this in detail, X-ray diffraction techniques in combination with theoretical simulations based on the kinematical X-ray scattering from laterally strained nano-structures and finite element method (FEM) calculations of the strain field are applied. The oxide related strain in the Si scales about linearly with the thickness of the SiO₂ mask, but FEM simulations supposing a homogeneous stress distribution in the oxide are not sufficient to describe the local strain distribution in the nano-structures. It is demonstrated that the Ge lattice relaxes completely during growth on the Si nano-islands by generation of misfit dislocations at the interface, but a high structural quality of Ge can be achieved by suited growth conditions.     

Influence of oxidant source on the property of atomic layer deposited Al2O3 on hydrogen-terminated Si substrate

Al₂O₃ thin films were deposited on hydrogen-terminated Si substrate using atomic layer deposition (ALD) technique with tri-methylaluminum (TMA) and an oxidant source of H₂O vapor, O₂ plasma, or O₃. Substrate temperature was maintained at 350 °C when the Al₂O₃ films were grown with the oxidant sources of H₂O vapor and O₃, and with the oxidant source of O₂ plasma, Al₂O₃ films were deposited at the substrate temperature of 200 °C. Growth rates of Al₂O₃ films on HF-cleaned Si surface were saturated at 0.08, 0.14, and 0.06 nm/cycle for H₂O vapor, O₂ plasma, and O₃, respectively. Equivalent oxide thickness (EOT) and leakage current vs. physical thickness of atomic layer deposited Al₂O₃ films grown with various oxidant sources were also measured in this study. To investigate the main cause of different EOT with oxidant sources, interfacial properties were examined by using transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). In the TEM analysis, interfacial layers with the thickness of about 1.7 and 1.3 nm were observed in as-deposited Al₂O₃ films grown using O₂ plasma and O₃. We confirmed that the interfacial layers were mainly composed of SiO_x in the XPS depth analysis. Using angle resolved X-ray photoelectron spectroscopy, effect of annealing on the interfacial structure of Al₂O₃ films grown with O₃ and O₂ plasma was also studied, and we found that after annealing, the peak corresponding to silicon suboxide and Al-silicate disappeared and fully oxidized Si⁴⁺ increased.     

The role of SiO2 buffer layer in the growth of highly textured LiNbO3 thin film upon SiO2/Si by pulsed laser deposition

Highly c-axis-oriented lithium niobate (LiNbO₃) thin films have been grown on Si with optimum thickness of the SiO₂ buffer layer by pulsed laser deposition technique. The amorphous SiO₂ buffer layer was formed on Si (100) wafer by thermal oxidation method. The crystallinity and c-axis orientation of LiNbO₃ films were strongly influenced by the thickness of amorphous SiO₂ buffer layers. The optimum thickness of the amorphous SiO₂ buffer layer was found to be about 230 nm for the growth of highly c-axis-oriented LiNbO₃ films. The achieved films have smooth surface and sharp interface. The prism coupler method indicates that the prepared LiNbO₃ films have great potential for optical waveguide device.     

Physical model and numerical results of dissociation kinetics of hydrogen-passivated Si/SiO2 interface defects

A simple model of thermal dissociation and recovery of hydrogen-passivated silicon defects at the Si/SiO₂ interface, such as P_b - centers, during vacuum thermal annealing has been suggested. his model considers reactions of hydrogen with defect states at the Si/SiO₂ interface and diffusion of liberated atomic and molecular hydrogen in a silicon dioxide film. The rate constants were calculated in diffusion approximation. A good agreement was obtained between the experimental and numerical simulation results for oxides with different thickness (204–1024 Å), grown, both, (111) and (100) samples and annealed in the temperature range (480–700°C).