Structural investigation of bulk and thin film PLZT using X-ray absorption spectroscopy

Thin film electro-optic and non-linear optical materials are of interest for applications in high-speed integrated optical devices. Materials of the system Pb_1−x/100La_x/100(Zr_y/100 Ti_1−y/100)_1−x/400O₃ or PLZT x/y/(100−y) are attractive since they can be integrated into Si and GaAs substrates using suitable deposition techniques. In this investigation we examine the structural properties of r.f. magnetron sputter-deposited PLZT using X-ray absorption near-edge spectroscopy (XANES). For XANES analysis, four samples were selected: (1) a highly oriented PLZT 28/0/100 film of ≈ 4500 Å deposited on SiO₂; (2) a highly oriented PLZT 28/0/100 film of ≈ 4500 Å deposited on a 2 ωm SiO₂ buffer layer over a Si(100) substrate; (3) a highly oriented PLZT 28/0/100 film of ≈4500 Å deposited on Al₂O₃ (1 02); and (4) a commercial ceramic wafer of PLZT 9/65/35. The XANES experiments were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) using electron yield and fluorescence techniques. Data was taken at the Ti K-edge (4966.4eV) and compared to reference spectra. Of the reference spectra, the Ti K-edge spectra of the PLZT most closely resemble perovskite (SrTiO₃). The surface and bulk thin film are similar and all the 28/0/100 spectra resemble the spectra of 9/65/35, indicating similar cubic perovskite structures for these materials.     

Thin film interaction between low-k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer

The interaction between low-k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer has been studied using four-point-probe sheet resistance measurement, X-ray diffraction, conventional Rutherford backscattering spectrometry (RBS), nuclear resonance analysis (NRA), elastic recoil detection (ERD), secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS). The conventional intermetal dielectrics SiO₂ and plasma-enhanced tetraethylorthosilicate (PETEOS) have been studied also for the purpose of comparison with HSQ. In the low temperature regime (300–550°C), a considerable amount of oxygen atoms, from various sources, diffuses into Ti film to form a Ti(O) solid solution, raising the resistivity of Ti significantly and causing the expansion of the Ti lattice. A good correlation between the oxygen composition in the Ti film, the sheet resistance variation of Ti and the change of Ti lattice parameter C₀ have been observed. At the same temperature, there are more oxygen atoms incorporated into the Ti film in Ti/HSQ than those for Ti/PETEOS, suggesting that additional HSQ-related oxygen sources, such as the moisture uptake and the conversion reaction of HSQ, may be attributed to this. In the high temperature regime (550–700°C), HSQ reacts with Ti to form a final TiO/Ti₅Si₃/HSQ stack structure. It is assumed that a few competing reactions occur in this regime. At 550–650°C, HSQ reacts directly with Ti; in the meantime, part of HSQ undergoes conversion reactions, with the reaction products SiO₂ and SiH₄ reacting with Ti to form Ti silicide. At 650–700°C, HSQ is almost completely converted into SiO₂, so the dominant mechanism is Ti reaction with SiO₂. Before HSQ is completely turned into SiO₂, the Ti/HSQ system is more reactive than both Ti/PETEOS and Ti/SiO₂. The initiating temperature for the Ti/HSQ reaction exhibits no obvious Ti thickness dependence.     

Growth mechanism of stress corrosion cracking in high strength steel

Stress corrosion crack growth rates are measured at sveral stress intensity levels for low-tempered 4340 steel in 0.1N H₂SO₄ solution. The characteristics of the growth rates are divided into three regions of stress intensity factors: Region I near K_1SCC; Region III near unstable fracture toughness, K_1SC; and Region II, which lies between the two. K_1SCC is the value of K at which no crack growth can be detected after 240 hr.

In order to explain these experimental results, the crack initiation analysis reported in a previous paper is extended to the growth rates. A detached crack initiates and grows at the tip of an already existing crack. When the detached crack reaches the tip of the main crack, the process repeats as a new existing crack.

A relationship between crack growth rate, v, and stress intensity factor, K, is obtained as a function of b/a and a = b + d, where b is the distance from the tip of the main crack to the detached crack, and d is the ydrogen atom saturated domain.

The experimental data are in good agreement with the theoretical values in Region II when a = 0.02 mm, b/a = 0.8, c₁/c₀ = 2.8 for 200°C tempered specimens and a = 0.015 mm, b/a = 0.7, c₁/c₀ = 3.0, ρ_b = 0.055 mm for 400°C tempered specimens, where ρ_b is a fictitious notch radius. The plateau part in Region II for 400°C tempered specimens is also successfully explained by the present theory. For Region III, the value of b/a will be almost equal to 1 because v → ∞ for b/a → 1. On the other hand, for Region I, b/a will be zero, since the value of v becomes negligibly small and no crack growth is observable.     

Cu/Ti3SiC2体系润湿性及润湿过程的研究

采用座滴法研究了温度及Ti₃SiC₂的两个组成元素Si和Ti对Cu/Ti₃SiC₂体系润湿性的影响。结果表明, Cu与Ti₃SiC₂之间有良好的润湿性, 且润湿过程属于反应性润湿。随着温度的升高, Cu与Ti₃SiC₂间的反应区扩大, 反应层深度增加, 润湿角减小, 温度超过1250℃后反应明显加快, 至1270℃时润湿角降至15.1°。物相分析与微观结构研究表明, Cu/Ti₃SiC₂界面区域发生了化学反应, 反应产物主要为TiC_x和Cu_xSi_y, 同时发生元素的互扩散, 形成反应中间层, 改变体系的界面结构, 促进了Cu和Ti₃SiC₂基体的界面结合, 从而改善了体系的润湿性。在Cu中添加Si抑制了Ti₃SiC₂的分解, 而添加Ti阻碍了Cu向Ti₃SiC₂的渗入, 均不利于Cu/Ti₃SiC₂体系润湿性的改善。     

Optical absorption and emission properties of Er doped mixed alkali borosilicate glasses

This paper presents the optical absorption and luminescence properties of Er³⁺ doped mixed alkali borosilicate glasses: 59.5SiO₂ · 20B₂O₃ · xLi₂O · (20 − x)Na₂O · 0.5Er₂O₃ and 59.5SiO₂ · 20B₂O₃ · xLi₂O · (20 − x)K₂O · 0.5Er₂O₃, with x = 0, 4, 8, 12, 16 and 20 mol%. The variations of Judd–Ofelt intensity parameters (Ω₂, Ω₄, and Ω₆), hypersensitive transition intensities, total radiative transition probability (A_T), radiative lifetimes (τ_R), integrated absorption cross-sections (Σ) and stimulated emission cross-sections (σ_p) as a function of x are discussed in detail. The changes in Ω₂ and intensities of hypersensitive transitions are attributed to optical basicity changes in the host glass matrix, which leads to variations in the covalency of the Er–O bond. The luminescence properties are reported for certain transitions, and the emission cross-section is high at x = 8–12 in the case of lithium sodium glass, whereas in lithium potassium glass it is high at x = 8.     

Silicide formation and phase separation from Cu/Nb and Nb/Cu bilayers on silicon

Electron beam evaporation was used to produce Nb/Cu and Cu/Nb bilayers on silicon. The phase sequence and morphology were investigated as a function of annealing temperature in the temperature range between 200 °C and 800 °C, using Auger electron spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and transmission electron microscopy. Independently of the sequence of deposition, the phases Nb₃Si and Nb₅Si₃ are the two first niobium phases to be formed as a very thin layer at the Nb---Si interface. However, there is evidence that the reaction between niobium and silicon depends strongly on the presence of copper at the Nb---Si interface. The unusual coexistence of Nb₅Si₃, NbSi₂ and niobium phases was also observed. The formation of the ternary phase Nb₅Cu₄Si₄ was detected after annealing Cu/Nb at 700 °C and Nb/Cu at 800 °C. In the latter case the NbSi₂ and Cu₃Si+Cu₄Si phases were formed through a layered growth process.     

Diffusion barrier properties of sputtered TaNx between Cu and Si using TaN as the target

TaN_x films sputtered from a TaN target were used as diffusion barriers between Cu thin films and Si substrates. Material characteristics of TaN_x films and metallurgical reactions of Cu/TaN_x/Si systems annealed in the temperature range 400–900 °C for 60 min were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, cross-sectional transmission electron microscopy, and sheet resistance measurements. We found that the deposition rate decreased with increasing bias. TaN, β-Ta, and Ta₂N phases appeared and/or coexisted in the films at specific biases. A step change in N/Ta ratio was observed whenever a bias was applied to the substrate. After depositing a copper overlayer, we observed that the variation percentage of sheet resistance for Cu (70 nm)/TaN_x (25 nm, x=0.37 and 0.81)/Si systems stayed at a constant value after annealing up to 700 °C for 60 min; however, the sheet resistance increased dramatically after annealing above 700 and 800 °C for Cu/TaN_0.37/Si and Cu/TaN_0.81/Si systems, respectively. At that point, the interface was seriously deteriorated and formation of Cu₃Si was also observed.     

Structural and optical characterization of β-FeSi2 layers on Si formed by ion beam synthesis

Structural and optical properties have been investigated for surface β-FeSi₂ layers on Si(100) and Si(111) formed by ion beam synthesis using ⁵⁶Fe ion implantations with three different energies (140–50 keV) and subsequent two-step annealing at 600 °C and up to 915 °C. Rutherford backscattering spectrometry analyses have revealed Fe redistribution in the samples after the annealing procedure, which resulting in a Fe-deficient composition in the formed layers. X-ray diffraction experiments confirmed the existence of /gb-FeSi₂ by annealing up to 915 °C, whereas the phase transformation from the β to phase has been induced at 930 °C. In photoluminescence measurements at 2 K, both β-FeSi₂/Si(100) and β-FeSi₂/Si(111) samples, after annealing at 900–915 °C for 2 h, have shown two dominant emissions peaked around 0.836 eV and 0.80 eV, which nearly coincided with previously reported PL emissions from the sample prepared by electron beam deposition. Another β-FeSi₂/Si(100) sample has shown sharp emissions peaked at 0.873 eV and 0.807 eV. Optical absorption measurements at room temperature have revealed the allowed direct bandgap of 0.868–0.885 eV as well as an absorption coefficient of the order of 10⁴ cm⁻¹ near the absorption edge for all samples.     

Effect of temperature gradients and stress levels on damage of C/SiC composites in oxidizing atmosphere

Strain response of a C/SiC composite, which is cycled with ΔT₁ of 500 °C at 50 MPa, ΔT₂ of 400 °C at 100 MPa and ΔT₃ of 300 °C at 150 MPa, was investigated. Measured thermo-elastic strain ranges are found to retain 0.209% for ΔT₁, 0.168% for ΔT₂, and 0.122% for ΔT₃, independent upon the applied stress level. Non-linear variations of thermal cycling creep strain can reflect damage evolutions of the composites by changing its rate, which depends on temperature gradient and applied stress. After 104 thermal cycles, strength, modulus, and failure strain of the composites retain 60.29%, 84.2%, and 59% of the initial properties, respectively. The coating cracks of the cycled specimens are observed to be perpendicular to the applied stresses and arranged at relatively regular spacing, through which the fibers are oxidized superficially.     

Structural characterization of ion-beam-induced epitaxially crystallized thin layers of III–V and IV–IV semiconductors

Structural properties of ion-beam-induced epitaxial crystallization (IBIEC) for amorphous layers of GaAs on GaAs(100), BP on BP(100) and Si_1−xGe_x and Si_1−x−yGe_xC_y on Si(100) have been investigated. Crystallization was induced by ion bombardment with 400 keV Ne, Ar or Kr at 150 °C for GaAs and at 350 °C for BP. Epitaxial crystallization up to the surface was observed both in GaAs and BP at temperatures much below those required for the solid phase epitaxial growth (SPEG). The growth rate per nuclear energy deposition density has shown a larger dependence on ion dose rate in cases of heavier ion bombardments both for GaAs and BP. Crystallization of a-GaAs with ions whose projected ranges are within the amorphous layer thickness was also observed at 150 °C. Epitaxial crystallization of Si_1−xGe_x and Si_1−x−yGe_xC_y layers (x = 0.13 and y = 0.014 at peak concentration) on Si(100) formed by high-dose implantation of 80 keV Ge and 17 keV C ions has been observed in the IBIEC process with 400 keV Ar ion bombardments at 300–400 °C. Crystalline growth by IBIEC has shown a larger growth rate in Si_1−x−yGe_xC_y/Si} than in Si_1−xGe_x/Si} with the same Ge concentration for all bombardments under investigation. X-ray rocking-curve measurements have shown a strain-compensated growth in Si_1−x−yGe_xC_y/Si}, whereas Si_1−xGe_x/Si} samples have shown a growth with strain accommodation.     

Structural, chemical, and electrical characterisation of reactively sputtered WSx thin films

WS_x films were sputter-deposited on Si, SiO₂/Si, and glass substrates from a WS₂ target in an Ar/H₂S atmosphere. Their structure, morphology, chemical composition, and electrical properties were investigated as a function of deposition parameters such as working pressure and H₂S fraction. Films could be grown in the composition range WS_0.3−WS_3.5. Crystallisation was achieved at substrate temperatures T_s > 70 °C and compositions 0.7 ≤ x ≤ 1.95. While the first 5–50 nm near the interface exhibited a basal orientation (c), further growth resulted in the formation of edge-oriented platelets (c) giving rise to a porous, lamellar microstructure. The crystalline structure was mainly turbostratic, while some degree of ordered stacking was present in samples grown at high substrate temperature (600 °C). Resistivity measurements showed a semiconductor-type temperature dependence characterised by activation energies up to 95 meV. Sheet resistance was found to be nearly independent of film thickness, suggesting that the main carrier transport takes place in an interfacial layer of about 20 nm in thickness.     

Growth, selectivity and adhesion of CVD-deposited copper from Cu (hexafluoroacetylacetonate trimethylvinylsilane) and dichlorodimethylsilane

Copper films have been deposited by low-pressure (1–20 mTorr) chemical vapour deposition using Cu¹⁺ (hexafluoroacetylacetonate) trimethylvinylsilane onto SiO₂ patterned substrates having seed layers of W, TiN and Al. Blanket deposition is observed for all growth temperatures in the range 140 °C ≤ T_g ≤ 240 °C. However, depending on the initial substrate seed layer and pre-treatment, the relative strength of the copper-oxide and copper-seed layer bond can be dramatically altered particularly when growth is carried out in the presence of dichloromethylsilane (DCDMS). The degree of selectivity as well as film morphology is also found to be sensitive to the initial pre-treatment, growth temperature and flow rate of DCDMS.     

Microstructure and strength of diffusion-bonded joints of TiAl base alloy to steel

Diffusion bonding of TiAl-based alloy to steel was carried out at 850–1100 °C for 1–60 min under a pressure of 5–40 MPa in this paper. The relationship of the bond parameters and tensile strength of the joints was discussed, and the optimum bond parameters were obtained. When products are diffusion-bonded, the optimum bond parameters are as follows: bonding temperature is 930–960 °C, bonding pressure is 20–25 MPa, bonding time is 5–6 min. The maximum tensile strength of the joint is 170–185 MPa. The reaction products and the interface structures of the joints were investigated by scanning electron microscopy (SEM), electron probe X-ray microanalysis (EPMA) and X-ray diffraction (XRD). Three kinds of reaction products were observed to have formed during the diffusion bonding of TiAl-based alloy to steel, namely Ti₃Al+FeAl+FeAl₂ intermetallic compounds formed close to the TiAl-based alloy. A decarbonised layer formed close to the steel and a face-centered cubic TiC formed in the middle. The interface structure of diffusion-bonded TiAl/steel joints is TiAl/Ti₃Al+FeAl+FeAl₂/TiC/decarbonised layer/steel, and this structure will not change with bond time once it forms. The formation of the intermetallic compounds results in the embrittlement of the joint and poor joint properties. The thickness of each reaction layer increases with bonding time according to a parabolic law. The activation energy Q and the growth velocity K₀ of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC in the diffusion-bonded joints of TiAl base alloy to steel are 203 kJ/mol and 6.07 mm²/s, respectively. Careful control of the growth of the reacting layer Ti₃Al+FeAl+FeAl₂+TiC can influence the final joint strength.     

Low temperature plasma-assisted oxidation and thin-film deposition processes for forming device-quality SiO2/Si and composite dielectric-SiO2/Si heterostructures

In the high-temperature thermal oxidation of Si, the SiO₂/Si interface is continuously regenerated as the bulk oxide grows. This paper describes an alternative low temperature, 200–300 °C, plasma-assisted process that optimizes electrical properties of SiO₂/Si interfaces and bulk SiO₂ layers by separately controlling interface formation and bulk oxide deposition. Composite dielectrics, oxide/nitride (ON) and oxide (ONO), have been fabricated by extending the low temperature plasma-assisted processes to include deposition of Si₃N₄ films. The electrical properties of SiO₂/Si structures formed by the two-step, low temperature oxidation-deposition process are essentially the same as those of SiO₂/Si structures formed by high temperature, 850–1050 °C, thermal oxidation. The electrical properties of devices incorporating ON and ONO composite dielectrics are degraded with respect to the SiO₂/Si structures, but are similar to those of composite dielectrics formed by combinations of high temperature processing.     

Low-temperature growth and orientational control in RuO2 thin films by metal-organic chemical vapor deposition

For growth temperatures in the range of 275°C to 425°C, highly conductive RuO₂ thin films with either (110)- or (101)-textured orientations have been grown by metal-organic chemical vapor deposition (MOCVD) on both SiO₂/Si(001) and Pt/Ti/SiO₂/Si(001) substrates. Both the growth temperature and growth rate were used to control the type and degree of orientational texture of the RuO₂ films. In the upper part of this growth temperature range ( 350°C) and at a low growth rate (< 3.0 nm/min.), the RuO₂ films favored a (110)-textured orientation. In contrast, at the lower part of this growth temperature range ( 300°C) and at a high growth rate (> 3.0 nm/min.), the RuO₂ films favored a (101)-textured orientation. In contrast, higher growth temperatures (> 425°C) always produced randomly-oriented polycrystalline films. For either of these low-temperature growth processes, the films produced were crack-free, well-adhered to the substrates, and had smooth, specular surfaces. Atomic force microscopy showed that the films had a dense microstructure with an average grain size of 50–80 nm and a rms. surface roughness of 3–10 nm. Four-probe electrical transport measurements showed that the films were highly conductive with resistivities of 34–40 μΩ-cm (at 25°C).     

Stress variation in epitaxial GaAs films on silicon under thermal treatment

High quality epitaxial GaAs films of 1.8 and 6.3 μm thickness on silicon substrates were examined for lattice distortion, misalignment and curvature by X-ray diffraction (Bond method) at 20–400 °C. These films were deposited by the metal-organic chemical vapour deposition method on the (001) plane of silicon using a buffer layer produced at T_b = 370 or 460 °C. A top layer was then grown at T_t = 560 or 650 °C. The GaAs films contract more strongly on cooling than the substrate, which causes a curvature and a tetragonal distortion below a critical temperature T_c. This temperature varies on thermal treatment at 200–400 °C and approaches T_b, the growth temperature of the buffer layer. The tetragonal distortion can be stabilized, so that T_c approximates T_b, if the GaAs films are annealed for several days at 400 °C.     

Structural, dielectric and optical properties of Ba(Ti, Zr)O3 thin films prepared by chemical solution deposition

Ba(Ti_0.95Zr_0.05)O₃ (BTZ) thin films grown on Pt/Ti/SiO₂/Si(100) substrates were prepared by chemical solution deposition. The structure and surface morphology of BTZ thin films has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). At 100 kHz, the dielectric constant and dissipation factor of the BTZ film are 121 and 0.016, respectively. The ellipsometric spectrum of the BTZ thin film annealed at 730 °C was measured in the range of wavelength from 355 to 1700 nm. Assuming a five-layer model (air/surface roughness layer/BTZ/interface layer/Pt) for the BTZ thin films on platinized silicon substrates, the optical constant spectra (refractive index n and the extinction coefficient k) of the BTZ thin films were obtained.     

Effect of N2O/SiH4 ratio on the properties of low-temperature silicon oxide films from remote plasma chemical vapour deposition

Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 °C) from SiH₄---N₂O. The effect of a gas-phase reaction on the SiO₂ film properties and Si/SiO₂ interface was investigated. As the partial pressure ratio was increased above N₂O/SiH₄ = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N₂O/SiH₄ <4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (Si---OH and Si---H) but when N₂O/SiH₄ >4, the incorporation of Si---OH bond became significant and Si¹⁺, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C---V and I---V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO₂ interface.     

Study on the yield behavior of Al2O3–SiO2(sf)/Al–Si metal matrix composites

As the yield behavior of Al₂O₃–SiO₂(sf)/Al–Si MMCS is concerned, effects of heat treatment and parameters of short fiber, including volume fraction, size, distribution mode, were investigated. Dislocation configurations adjacent to interface between matrix and fiber were observed by TEM. Macro-yield stress (σ_0.2) and micro-yield stress (σ_MYS) vary with parameters of short fiber, and effects of these parameters on σ_0.2 appear to be opposite to those on σ_MYS. This phenomenon was interpreted by thermal residual stress in matrix and dislocation configuration. Suitable quenching followed aging treatment is an effective method to enhance the σ_MYS and the σ_0.2 simultaneously. For the specimen with heat treatment of 550 °C/1 h WQ + 170 °C/6 h (T6) AC, σ_0.2 and σ_MYS reach 200 and 58 MPa, respectively, and they are almost as twice as those as-cast.