Analytical solution for polish-rate decay in chemical–mechanical polishing

An analytical solution to the population balance for the heights of pad asperities worn down during chemical–mechanical polishing of silicon wafers is used to calculate the chemical–mechanical removal-rate decay. This analytical solution is compared with experimental data from Journal of Electronic Materials, 25, No. 10 (1996) 1623–1627 by Stein et al. The model results agree with the experimental removal-rate decay results.     

Preparation of non-spherical silica composite abrasives by lanthanum ion-induced effect and its chemical–mechanical polishing properties on sapphire substrates

Chemical–mechanical polishing is the only technology that can provide a global planarization, and has become widely accepted. Abrasives are one of the important factors influencing chemical–mechanical polishing. In order to improve surface planarization and increase material removal rate of sapphire substrates, non-spherical silica composite abrasives were synthesized by lanthanum ion-induced effect-assisted growth method. Scanning electron microscopy showed the morphologies of non-spherical silica composite abrasives were peanut-shaped, chemical–mechanical polishing tests displayed the material removal rate of the non-spherical silica composite abrasives increased by 32.6% compared with spherical silica composite abrasives, Ambios Xi-100 surface profiler indicated the best surface roughness of sapphire substrate was 1.540 nm, and the element compositions of solids after polishing were analyzed by X-ray photoelectron spectroscopy, which investigated the interactions between abrasives and sapphire substrates. Non-spherical silica composite abrasives may lead to more solid-chemical reactions with sapphire substrates, and higher material removal rate may be also attributed to the mechanical grinding effect enhanced owing to the unique shape to achieve the purpose of material removal.     

A study on electrodeposited Co–Mo alloys thin films

Cobalt–Molybdenum (Co–Mo) induced electrodeposition has been studied from a sulphate bath on Ru electrodes at pH 4. The conditions of electrodeposition of Co–Mo alloys were determined using the cyclic voltametry at different ions concentration ratios. The theoretical model of Scharifker-Hills was used to analyse the current transients for studying the first stage of nucleation of Co–Mo alloys. The electrodeposited coatings were analysed by scanning electron microscopy, X-rays diffraction and alternating gradient force magnetometer techniques. The cyclic voltametry shows that the codeposition of Co–Mo alloys was accompanied by concurrent reactions such as the formation of the molybdenum oxides and the hydrogen evolution reaction. For the electrodeposited Co–Mo, the nucleation is in good agreement with the instantaneous nucleation and three-dimensional (3D) diffusion-limited growth. Co–Mo thin films of an hcp structure have been obtained, and the electrodeposition parameters such as the applied potential have a great influence on the structure, morphology and magnetic properties.     

Microstructure and mechanical properties of nanolayered W/W–C thin films

The present study reports on the mechanical and structural properties of W/W–C multilayered thin films with bilayer periods Λ ranging from 2.5 to 100 nm. Films were grown by reactive sputtering radio frequency on Si (100) substrate. X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD) and X-ray reflectivity were used to globally characterise the multilayers structure. Hardness and Young modulus have been determined using nanoindentation with a Berkovich tip. The XRD and the GIXRD diagrams revealed the presence of three phases: WC_1−x randomly oriented, W₂C with (100) preferred orientation and W with (110) preferred orientation. An increase in hardness is observed with decreasing period Λ, reaching a maximum value of ~26 GPa at Λ = 2.5 nm.     

Influences of film composition and annealing on the mechanical and electrical properties of W–Mo thin films

In this article, the mechanical and electrical characteristics of co-sputtered W–Mo thin films investigated for the application to microelectromechanical systems are described. W–Mo thin films with various compositions were deposited by co-sputtering onto a cover glass and silicon oxide (SiO _x ) film-coated Si wafer. The internal stress measured by Newton-ring method depended on film composition and Ar pressure, but were independent on annealing at 623 K. The hardness gradually decreased with an increase in Ar pressure, whereas the effective Young’s modulus stayed constant throughout Ar pressures ranging from 0.2 to 0.4 Pa. Both the mechanical properties showed no dependences of film composition and annealing. The resistivity was proportional to Ar pressure, but was not related to film composition. Annealing slightly affected the resistivity. Auger spectroscopy clarified that, by annealing, an oxide layer of approximately 10 nm thick was produced on the top surface, but film composition did not change. From the experimental results obtained, annealing at 623 K did not affect the mechanical and electrical properties of W–Mo films. This indicates that the co-sputtered film is very stable at temperatures ranging from RT to 623 K. By controlling Ar pressure, stress-free W–Mo films with superior mechanical characteristics and low resistivity can be produced regardless of film composition.     

Study on Mn-induced Jahn–Teller distortion in BiFeO3 thin films

Present work reports Raman spectroscopy study of single-phase Mn-doped BiFeO₃ [BiFe_1?x Mn _x O₃ (0 ≤ x ≤ 0.20)] polycrystalline thin films carried out in backscattering geometry. De-convolution of Raman spectra showed a gradual transition in the crystal symmetry from rhombohedral (?R) to multiphase [rhombohedral (?R) + tetragonal (?T)] structure with increasing Mn doping concentration in BiFe_1?x Mn _x O₃ (BFMO) thin films. X-ray diffraction (XRD) along with Le-Bail extraction refinement confirms that the structural symmetry lowering in BFMO thin films occurs at about 10 % Mn doping concentration. A blue shift is observed in the direct energy band gap of BFMO thin films from 2.53 to 2.87 eV (at T = 295 K) and is attributed to the local symmetry lowering and local induced strain in Fe³⁺ environment resulted from Jahn–Teller distortion in (MnFe)³⁺O₆ octahedral unit. Second-derivative analysis of FTIR spectra in the spectral regions (420–470) cm^?1 and (480–680) cm^?1 further indicates the favourable structure distortion leading to the simultaneous exhibition of enhanced ferromagnetic and ferroelectric properties owing to Mn substitution in host BiFeO₃ lattice.     

Effects of Mg doping on sol–gel derived nanocrystalline hydroxyapatite thin films

Abstract

Both pure and Mg doped thin films were fabricated by sol–gel dip coating. The films were sintered either at 800 or 1000°C. The average grain size of the films was significantly affected by Mg substitution in the hydroxyapatite (HA) structure and change in the sintering temperature. The grains were considerably larger in the films sintered at higher temperatures. In addition, Mg doped films contained significantly larger grains compared to undoped HA films. Mg doping also caused rodlike grains at 800°C, and led to whitlockite (β-TCP) formation at 1000°C. The ratio of the existing phases was estimated as β-TCP/HA=27 : 73. All the films had rough surfaces with high porosity. It was also observed that undoped films had higher surface roughness than Mg doped ones.     

A selective ethanol gas sensor based on spray-derived Ag–ZnO thin films

A simple and cost-effective spray pyrolysis technique was employed to synthesize silver-doped zinc oxide (Ag–ZnO) thin films on the glass substrates from aqueous solutions of zinc acetate and silver nitrate precursors at 450 °C. The effects of Ag doping on structural, morphological, and gas-sensing properties of films were examined. The X-ray diffraction spectra of the Ag–ZnO films showed the polycrystalline nature having hexagonal crystal structure. Scanning electron microscopy (SEM) images of the pure ZnO films revealed the uniform distribution of the spherical grains (~80 nm size). Tiny Ag nanoparticles are clearly visualized in the SEM of Ag–ZnO films. The investigation of the effect of Ag doping on the gas-sensing properties of the Ag–ZnO revealed that the 15 % Ag-doped ZnO sample has the highest gas sensitivity (85 %) and excessive Ag doping in ZnO degraded the gas sensitivity. A possible mechanism of Ag–ZnO-based sensor sensitivity to the target gas is also proposed.     

Influence of precursor source on sol–gel deposited ZnO thin films properties

Zinc oxide thin films were deposited by sol gel technique on glass substrates using different precursors (zinc acetate, zinc nitrate and zinc chloride). In the present work we investigate the precursor nature influence on structural, morphological, optical, electrical properties and photocatalytic activity of ZnO thin films. For this purpose we have used X-rays diffraction (XRD), atomic force microscopy (AFM), UV–visible spectroscopy and Hall effect measurements for films characterization. The obtained results indicated that ZnO films properties are strongly influenced by the nature of the used precursor as reactant. Films photocatalytic activity was evaluated by the photo-degradation of methylene blue (MB) dissolved in aqueous solution under UV-A light. The obtained results indicated that ZnO thin films prepared from zinc acetate are more efficient than those prepared from zinc nitrate and zinc chloride.     

Effect of substrate on microstructure and mechanical properties of sol–gel prepared (K,Na)NbO3 thin films

Lead-free ferroelectric (K, Na)NbO₃ (KNN) thin films (～200 nm thickness) were prepared using a modified sol–gel method by mixing K and Na acetates with the Nb–tartarate complex, deposited by spin-coating method on Pt/Al₂O₃ and Pt/SiO₂/Si substrates and sintered at 650 °C. Pure perovskite phase of K_0.65Na_0.35NbO₃ in film on silicon were revealed, while film on alumina contained also small amount of secondary pyrochlore Na₂Nb₈O₂₁ phase. Homogenous microstructure of film on Si substrate was smoother with the lower roughness (～7.4 nm) and contained spherical (～50 nm) particles. The mechanical properties of films were characterized by nanoindentation. The modulus and hardness of KNN films were calculated from their composite values of film/substrate systems using discontinuous and modified Bhattacharya model, respectively. The KNN film modulus was higher on alumina substrate (91 GPa) in comparison with silicon substrate (71 GPa) and values of film hardness were the same (4.5 GPa) on both substrates.     

Effect of B content on thermal stability of nanocomposite Ti–B–N thin films

Abstract

Ti–B–N thin films with different B contents were deposited on Si (100) at room temperature, followed by vacuum annealed at 400, 600, 800 and 1000°C for 1 h respectively. Effect of boron content on thermal stability was investigated using X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and nanoindentation measurements. The results indicated that incorporation of B into TiN produced a nanocomposite structure, which had a positive effect on microstructure stability. A high B content resulted in an elevated recrystallisation temperature. The hardness stability was not consistent with that of microstructure, and depended on phase configuration and composition. The films with a high as deposited hardness showed high hardness stability. Excessive or lack of amorphous phase decreased hardness stability. The residual stress value was decreased with increasing annealing temperature owing to recovery of amorphous matrix, and crystallisation of amorphous phase made its direction transform from compression to tension.     

Microhardness properties of Cu–W amorphous thin films

Pure copper, pure tungsten and amorphous Cu₅₀W₅₀ and Cu₆₆W₃₄ alloy films were deposited by the direct current magnetron sputtering technique on cooled glass substrates. The film microhardness has been investigated as a function of alloy composition and substrate potential bias during deposition. The microhardness exhibited a maximum at Cu concentrations close to 50 at%, similar to the case of completely miscible binary alloys. The ion bombardment caused by the negative substrate polarization increased the film microhardness. The annealing of the amorphous Cu–W films up to 250 °C in vacuum increased the film microhardness by 10–20% apparently owing to the formation of the W(Cu) crystalline phase dispersed within a predominantly amorphous film matrix.     

Influence of annealing on ZnO films grown by metal–organic chemical vapor deposition

Zinc oxide (ZnO) films were deposited on silica glass substrates using metal–organic chemical vapor deposition (MOCVD) with diethyl zinc (DEZn) as the Zn precursor and ethanol as the oxygen source. Annealing was performed at 600°C for 1 h in air. The X-ray diffraction (XRD) patterns of the samples show sharp diffraction peaks for ZnO (0002), which indicates that the films are highly c-axis oriented. The films were also characterized by measuring the optical transmission spectrum, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The XPS spectra showed that the ZnO films changed from O-rich to Zn-rich after being annealed.     

Mechanical properties of nanocomposite metal–ceramic thin films

Thin film composites consisting of metallic nanocrystals embedded in an insulating host have been synthesized using alternating-target pulsed laser deposition of Ni and Al₂O₃ on silicon (100) substrate. The evaluation of structural quality of the thin film composites using high resolution transmission electron microscopy and scanning transmission electron microscopy with atomic number contrast has revealed the formation of a biphase system with thermodynamically driven segregation of Ni and alumina during pulsed laser deposition. The best hardness values of the thin film composites, measured using nanoindentation techniques, were found to be 20–30% larger than pure alumina films fabricated under identical conditions. Fracture toughness measurements of the composite showed slight toughening due to embedding of Ni nanoparticles.     

Surface second harmonic generation of Se–Te–Sb films

We present the first report for the investigation on surface second harmonic generation (SSHG) of thin films of Se_80−xSb_xTe₂₀ (0 ≤ x ≤ 9 at.%) system. SSHG measurements were made using a confocal microscope system and a mode locked Ti:Saphire pulsed laser (785 nm) probe beam with 100 fs pulses. A remarkable difference in the magnitude of the signal generated between the samples with antimony content ≤4 at.% and those containing antimony >4 at.% has been explained based on charge distribution associated with structural changes in these materials for different compositions. The results have been discussed on the basis of relatively isolated atomic events that occur at short length scales mainly due to spatial redistribution of covalent bonds and the rational changes in the electric dipole moment arising from the change in the distribution of the lone pair electrons inherent in chalcogenide glasses. The analysis of the results is supported by the variation of the glass transition temperature obtained from differential scanning calorimetry (DSC) results. The electronic structure has been calculated using the density functional theory (DFT) modified by the generalized gradient approximation (GGA) for the exchange correlation energy.     

Surface morphology and optoelectronic studies of sol–gel derived nanostructured CdO thin films: heat treatment effect

Morphological dependence of the optoelectronic properties of sol–gel derived CdO thin films annealed at different temperatures in air has been studied. After preparing, the films were investigated by studying their structural, morphological, d.c. electrical and optical properties. X-ray diffraction results suggest that the samples are polycrystalline and the crystallinity of them enhanced with annealing temperature. The average grain size is in the range of 12–34?nm. The root mean square roughness of the films was increased from 3.09 to 6.43?nm with annealing temperature. It was observed that the electro-optical characteristics of the films were strongly affected by surface roughness. As morphology and structure changed due to heat treatment, the carrier concentration was varied from 1.13?×?10¹⁹ to 3.10?×?10^19?cm^?3 with annealing temperature and the mobility increased from less than 7 to 44.8?cm² V^?1 s^?1. It was found that the transmittance and the band gap decreased as annealing temperature increased. The optical constants of the film were studied and the dispersion of the refractive index was discussed in terms of the Wemple–DiDomenico single oscillator model. The real and imaginary parts of the dielectric constant of the films were also determined. The volume energy loss increases more than the surface energy loss at their particular peaks.     

Co–Pt–W thin films electrodeposited from sulphate–gluconate baths

Co–Pt–W magnetic thin films were electrodeposited from gluconate baths. Electrochemical characterization (polarization behaviors and transient curves), microstructure and magnetic properties were investigated. It turned out that increase in gluconate concentration and bath pH shifted the deposition potential to more negative potentials. Microstructure of electrodeposited Co–Pt–W thin films was affected by the bath pH and gluconate concentration enormously. Samples obtained from Co–sulphate–gluconate at pH 8.0 and gluconate concentration 0.3 mol L^?1 exhibited single hcp phase with strong (0 0 1) PO. VSM and MFM measurement showed that perpendicular magnetic anisotropy occurred in the Co–Pt–W thin films prepared under these conditions.     

Al–O–N and Al–O–B–N thin films applied on Si–O–C fibers

Protective coatings (Al–O–N and Al–O–B–N) on Si–O–C fibers (Tyranno ZMI) were applied in order to enhance oxidation resistance under severe thermo-mechanical conditions in the 400–600 °C temperature range. The coating process consisted in three steps: (i) the transformation of the Si–O–C fiber surface into microporous carbon; (ii) the impregnation of these carbon microporous layers by an aluminium trichloride (AlCl₃) solution and then, (iii) a final heat treatment under ammonia. Processing parameters were studied in order to select the best conditions. Using these conditions, obtained results have shown that coatings were present around each fiber, with a controlled thickness, and that the mechanical properties of the fibers were preserved. Although, these coatings did not entirely stop the oxygen ingress, it has been shown that they strongly reduced the oxidation of the fiber.