Thin Solid Films

Published by Elsevier
Online ISSN: 0040-6090
Publications
Article
(1-x)Pb[Yb(1/2)Nb(1/2)]O(3)-xPbTiO(3) (PYbN-PT, x=0.5)(001) oriented thin films were deposited onto LaNiO3 (LNO)/Si(001) substrates by sol-gel processing. The crystallographic texture of the films was controlled by the annealing temperature and heating rate. Highly (001) oriented LNO thin films were prepared by a simple metal organic decomposition technique, and the samples were annealed at 700 °C and 750 °C using a rapid thermal annealing process and furnace, respectively. X-ray diffraction analysis revealed that the films of PYbN-PT were highly (001) oriented along LNO/Si substrates. The degree of PYbN-PT orientation is dependent on the heating rate and annealing temperature. Annealing heating rate of 10 °C/s and high annealing temperature near 750 °C produce the greatest degree of (001) orientation, which gives rise to improved dielectric properties.
 
Article
The optical properties and electrical conductivity of highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) are reported as a function of the processing additive conditions. The addition of dimethyl sulfoxide (DMSO) increases the conductivity and modifies the dielectric response as observed from the ellipsometric studies. Also the surface roughness and morphology change with the composition of PEDOT:PSS:DMSO and film deposition conditions. The real part of the dielectric function becomes negative in highly conducting samples, indicating the presence of delocalized charge carriers. The real and imaginary parts of the refractive index were determined as a function of wavelength. The results are consistent with the increase in conductivity upon the addition of DMSO.
 
Article
We present a titanium-silicon oxide film structure that permits polarization modulated infrared reflection absorption spectroscopy on silicon oxide surfaces. The structure consists of a ~6 nm sputtered silicon oxide film on a ~200 nm sputtered titanium film. Characterization using conventional and scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy and X-ray reflectometry is presented. We demonstrate the use of this structure to investigate a selectively protein-resistant self-assembled monolayer (SAM) consisting of silane-anchored, biotin-terminated poly(ethylene glycol) (PEG). PEG-associated IR bands were observed. Measurements of protein-characteristic band intensities showed that this SAM adsorbed streptavidin whereas it repelled bovine serum albumin, as had been expected from its structure.
 
Article
Titanium layers are used to promote adhesion between polymer substrates for flexible electronics and the Cu or Au conducting lines. Good adhesion of conducting lines in flexible circuits is critical in improving circuit performance and increasingcircuit lifetime. Nominally 50 nm thick Ti films on polyimide (PI) are investigated by fragmentation testing under uniaxial tensile load in the as-deposited state, at 350 °C, and after annealing. The cracking and buckling of the films show clear differences between the as-deposited and the thermally treated samples, cracks are much straighter and buckles are smaller following heat treatment. These changes are correlated to a drop in adhesion of the samples following heat treatment. Adhesion values are determined from the buckle dimensions using a total energy approach as described in the work of Cordill et al. (Acta Mater. 2010). Cross-sectional transmission electron microscopy of the Ti/PI interface found evidence of a ~ 5 nm thick interlayer between the largely columnar Ti and the amorphous PI. This interlayer is amorphous in the as-deposited state but nano-crystalline in those coatings tested at elevated temperature or annealed. It is put forward that this alteration of the interfacial structure causes the reduced adhesion.
 
Article
The adsorption of tobacco mosaic virus (TMV) on self-assembled and Langmuir-Blodgett monolayers was investigated using total internal reflection fluorescence (TIRF) spectroscopy and scanning force microscopy (SFM). Substrates were chosen to probe electrostatic, hydrophobic and surface fluidity effects on TMV adsorption. Positively charged and hydrophobic surfaces demonstrated similar initial rates of TMV adsorption; however, their respective surface TMV coverages differed greatly. Likewise, positively charged surfaces which differed primarily in surface fluidity exhibited similar adsorption rates for TMV, but different TMV surface coverages. In contrast, virus adsorption to negatively charged and zwitterionic substrates was negligible. To elucidate these differences in adsorption behavior, SFM was used to image the distribution and the aggregation state of adsorbed TMV.
 
Article
This paper presents experimental evidence that thin (< approximately 200 nm) boron coatings, deposited with a (vacuum) cathodic arc technique on pre-polished Co-Cr-Mo surfaces, could potentially extend the life of metal-on-polymer orthopedic devices using cast Co-Cr-Mo alloy for the metal component. The primary tribological test used a linear, reciprocating pin-on-disc arrangement, with pins made of ultra-high molecular weight polyethylene. The disks were cast Co-Cr-Mo samples that were metallographically polished and then coated with boron at a substrate bias of 500 V and at about 100 degrees C. The wear tests were carried out in a saline solution to simulate the biological environment. The improvements were manifested by the absence of a detectable wear track scar on the coated metal component, while significant polymer transfer film was detected on the uncoated (control) samples tested under the same conditions. The polymer transfer track was characterized with both profilometry and Rutherford Backscattering Spectroscopy. Mechanical characterization of the thin films included nano-indentation, as well as additional pin-on-disk tests with a steel ball to demonstrate adhesion, using ultra-high frequency acoustic microscopy to probe for any void occurrence at the coating-substrate interface.
 
Article
In this work, we report low-loss single-mode integrated optical waveguides in the near ultra-violet and visible spectral regions with aluminum oxide (Al(2)O(3)) films using an atomic layer deposition (ALD) process. Alumina films were deposited on glass and fused silica substrates by the ALD process at substrate/chamber temperatures of 200 °C and 300 °C. Transmission spectra and waveguide measurements were performed in our alumina films with thicknesses in the range of 210 - 380 nm for the optical characterization. Those measurements allowed us to determine the optical constants (n(w) and k(w)), propagation loss, and thickness of the alumina films. The experimental results from the applied techniques show good agreement and demonstrate a low-loss optical waveguide. Our alumina thin-film waveguides is well transparent in the whole visible spectral region and also in an important region of the UV; the measured propagation loss is below 4 dB/cm down to a wavelength as short as 250 nm. The low propagation loss of these alumina guiding films, in particular in the near ultra-violet region which lacks materials with high optical performance, is extremely useful for several integrated optic applications.
 
Article
Hydrogen silsesquioxane (HSQ) is a material with the potential for studying the effect of surface stiffness on stem cell differentiation. Here, the effects of electron beam dose on the topography and the mechanical properties of HSQ obtained with or without trimethylamine (TMA) development are characterised by atomic force microscopy imaging and indentation. A correlation between the surface stiffness (uniform across the sample) and electron beam exposure is observed. Surface roughness of HSQ samples developed in TMA decreases exponentially with increasing electron beam exposure. Surface coating with plasma polymerised allylamine (ppAAm) leads to an overall decrease in stiffness values. However, the increase in surface stiffness with increasing electron beam exposure is still evident. The ppAAm coating is shown to facilitate human mesenchymal stem cell adhesion.
 
Article
Undoped and boron-doped nanocrystalline (NCD) diamond films were deposited on mirror polished Ti-6Al-4V substrates in a Microwave Plasma Assisted Chemical Vapor Deposition system. Sliding wear tests were conducted in ambient air with a nanotribometer. A systematic study of the tribological properties for both undoped and boron-doped NCD films were carried out. It was found for diamond/diamond sliding, coefficient of friction decreases with increasing normal loads. It was also found that the wear rate of boron-doped NCD films is about 10 times higher than that of undoped films. A wear rate of ~5.2×10(-9) mm(3)/Nm was found for undoped NCD films. This value is comparable to the best known value of that of polished polycrystalline diamond films. Although no surface deformation, film delamination or micro-cracking were observed for undoped films, boron-doped NCD film undergoes a critical failure at a normal stress of 2.2 GPa, above which surface deformation is evident. Combined with high hardness and modulus, tunable conductivity and improved open air thermal stability, boron-doped nanocrystalline diamond film has tremendous potentials for applications such as Atomic Force Microscope probes, Micro-Electro-Mechanical System devices and biomedical sensors.
 
Article
A fully integrated, wireless neural interface device is being developed to free patients from the restriction and risk of infection associated with a transcutaneous wired connection. This device requires a hermetic, biocompatible encapsulation layer at the interface between the device and the neural tissue to maintain long-term recording/stimulating performance of the device. Hydrogenated amorphous silicon carbide (a-SiC(x):H) films deposited by a plasma enhanced chemical vapor deposition using SiH(4), CH(4), and H(2) precursors were investigated as the encapsulation layer for such device. Si-C bond density, measured by Fourier transform infrared absorption spectrometer, suggests that deposition conditions with increased hydrogen dilution, increased temperature, and low silane flow typically result in increase of Si-C bond density. From the variable angle spectroscopic ellipsometry measurement, no dissolution of a-SiC(x):H was observed during soaking tests in 90°C phosphate buffered saline. Conformal coating of the a-SiC(x):H in Utah electrode array was observed by scanning electron microscope. Electrical properties were studied by impedance spectroscopy to investigate the performance of a-SiC(x):H as an encapsulation layer, and the results showed long term stability of the material.
 
Article
In this work the structure of ternary Ga x In1 - x P nanowires is investigated with respect to the chemical composition and homogeneity. The nanowires were grown by metal-organic vapor-phase epitaxy. For the investigation of ensemble fluctuations on several lateral length scales, X-ray diffraction reciprocal space maps have been analyzed. The data reveal a complicated varying materials composition across the sample and in the nanowires on the order of 20%. The use of modern synchrotron sources, where beam-sizes in the order of several 10 μm are available, enables us to investigate compositional gradients along the sample by recording diffraction patterns at different positions. In addition, compositional variations were found also within single nanowires in X-ray energy dispersive spectroscopy measurements.
 
Article
Multinary Ti-Al-N thin films are used for various applications where hard, wear and oxidation resistant materials are needed. Here, we study the effect of Zr addition on structure, mechanical and thermal properties of Ti(1-x)Al(x)N based coatings under the guidance of ab initio calculations. The preparation of Ti(1-x-z)Al(x)Zr(z)N by magnetron sputtering verifies the suggested cubic (NaCl-type) structure for x below 0.6-0.7 and z ≤ 0.4. Increasing the Zr content from z = 0 to 0.17, while keeping x at ~ 0.5, results in a hardness increase from ~ 33 to 37 GPa, and a lattice parameter increase from 4.18 to 4.29 Å. The latter are in excellent agreement with ab initio data. Alloying with Zr also promotes the formation of cubic domains but retards the formation of stable wurtzite AlN during thermal annealing. This leads to high hardness values of ~ 40 GPa over a broad temperature range of 700-1100 °C for Ti(0.40)Al(0.55)Zr(0.05)N. Furthermore, Zr assists the formation of a dense oxide scale. After 20 h exposure in air at 950 °C, where Ti(0.48)Al(0.52)N is already completely oxidized, only a ~ 1 μm thin oxide scale is formed on top of the otherwise still intact ~ 2.5 μm thin film Ti(0.40)Al(0.55)Zr(0.05)N.
 
Conference Paper
Amorphous Ta-Si-N films of about 500 nm thickness were reactively sputter deposited on Si substrates using DC magnetron sputtering from TaSi<sub>0.1</sub>, TaSi<sub>0.4</sub> and TaSi<sub>0.6</sub> targets. The film properties were characterized by sheet resistance measurement and X-ray diffraction. With increasing amounts of nitrogen in the sputtering gas, the film resistivity increased. Surface erosion of the multiphase target material was analyzed by SEM. Particulate emission is minimized with increasing density and refined microstructure of the target material
 
Conference Paper
The concept of treating interconnections as a device and designing them while keeping both materials and structures in mind is presented. An example using molybdenum and copper is demonstrated. Copper introduces new problems such as diffusion in addition to the traditional problems for interconnections such as adhesion. A new structure called a sidewall barrier is presented and used as part of a copper interconnection. This structure can be combined with a multilayer thin film resulting in a completely encapsulated interconnection. The technique is versatile enough that almost any material including dielectrics can be used as the encapsulation material and the sidewall barrier can be either on the outside of a feature or the inside of a space. Several potential metals (Mo, TiN, W) for encapsulating copper are examined and molybdenum is chosen and used. Electromigration measurements of bilayered copper films reveal that there are problems with TiN and tungsten barriers. Copper oxidation, stress, electromigration, hillock growth, resistivity, diffusion and adhesion are all studied
 
Conference Paper
An experimental investigation is presented on the influence of the laser excitation on the photoluminescence (PL) linewidth in silicon-doped InAlAs layers grown lattice-matched to InP substrates by molecular beam epitaxy (MBE). It was observed that the linewidth decreases with increasing laser excitation power. A model describing an unbalanced migration of photo-generated charge carriers due to the presence of clusters is proposed to explain the effect of the linewidth reduction. Also, the trend of the linewidth decrease becomes more pronounced in InAlAs samples with higher silicon doping concentrations. These samples have broader linewidths which is the result of poorer alloy quality due to the presence of disorder. A similar trend of linewidth reduction was also observed at higher measurement temperatures of 15 and 30 K. Our results show that such measurement of linewidth vs. laser excitation power can be used as a supplementary method for InAlAs material characterization
 
Conference Paper
Vertical p-MOS transistors with channel length of 130 nm have been fabricated using selective epitaxial growth (SEG) to define the channel region. The vertical layout offers the advantages of achieving short channel lengths and high integration densities while still using optical lithography to define lateral dimensions. Compared to other vertical concepts, this layout has reduced gate to source/drain overlap capacitances which is necessary for high speed applications. The use of SEG instead of blanket epitaxy avoids the deterioration of the Si-SiO2 interface due to reactive ion etching (RIE) and reduces punch-through due to facet growth. First nan-optimized p-channel MOSFETs With a 12-nm gate oxide show a transconductance of 90 mS/mm. The cut-off frequencies of this device turned out to be f(T) = 2.3 GHz and f(max) = 1.1 GHz.
 
Conference Paper
The objects of this study were SnTe films grown by thermal evaporation in vacuum on [001]KCl substrates. The dependences of the Seebeck coefficient S and the Hall coefficient R<sub>H</sub> on the SnTe film thickness (d = 5 - 700 nm) were obtained at room temperature. Distinct oscillations in the d-dependences of S and R<sub>H</sub> were observed and attributed to the size quantization in SnTe thin films. The discrepancy between the experimentally determined oscillation period Δd and the theoretical Δd estimated using the model of a quantum well with infinitely high walls is explained by an oversimplification of the model. The monotonic component of the d-dependences of S and R<sub>H</sub> changes with increasing thickness up to d∼100 nm, and then remains constant. It is suggested that this behavior can result from the dependence of the equilibrium concentration of non-stoichiometric cation vacancies on the SnTe film thickness.
 
Conference Paper
DC and low-frequency-noise characteristics Of SiGe HBTs with a raised-emitter structure, fabricated by epitaxial growth of phosphorous-doped Si layers, were investigated. Experimental results indicate unexpected emitter-size dependencies of both base current and low-frequency noise, because mono-poly interfacial native oxides close to the intrinsic emitter-base junction are localized at the emitter periphery. The raised mono-Si emitter SiGe HBT with a scaled emitter exhibits low-frequency noise that is about ten times smaller than a conventional poly-Si emitter SiGe HBT (c) 2008 Elsevier B.V. All rights reserved.
 
Conference Paper
A simple model of thermal dissociation of hydrogen from silicon dangling bonds (P<sub>b</sub> centers) and their hydrogen passivation with vacuum annealing is suggested. It takes into account the reactions occurring for hydrogen with defect states at the interface of the Si/SiO <sub>2</sub> structure as well as the diffusion process for atomic and molecular hydrogen. The reaction kinetic coefficients were calculated in diffusion approximation. Excellent agreement of calculations with experimental data was obtained in the temperature range (480-700°C), and oxide thickness of (200-1024 Å) for the (111) and (100) interfaces
 
Conference Paper
For more than a decade, considerable effort has been put into the development of light emitting devices based on evaporated layers of organic semiconductors. To date, the properties of matrix displays consisting of organic light emitting diodes (OLEDs) basically meet automotive and consumer product requirements. OLED matrix displays offer high contrast, wide viewing angle and a broad temperature range at low power consumption. In contrast to polymer devices, OLEDs are processed in ultrahigh vacuum systems. The organic source materials are sublimated from effusion cells. Due to the sensitivity of organic thin films, device structuring by conventional etching techniques is not feasible and alternative structuring techniques were developed. Electrical current in organic devices is limited by the low conductivity of organic semiconductors and by energy barriers at the metal-organic semiconductor interface. Photoelectric measurements facilitate the determination of barrier height differences between various electrode set-ups. Further insights into the energy band alignment at organic heterointerfaces are gained by ultraviolet photoelectron spectroscopy (UPS). In addition to widely employed electrical (I-V, C-V) and optical (PI) measurements, thermally stimulated current (TSC) and luminescence (TSL) allow the characterization and a more detailed understanding of carrier traps and charge transport in organic devices. Energy transfer in a doped OLED emitting layer can be investigated by time-resolved photoluminescence measurements
 
Conference Paper
The factors affecting adhesion are reviewed, and it is shown that the structure of the interfacial region is probably a controlling factor in film adhesion. Nucleation, film growth and surface effects control the structure of the interfacial region and may determine the adhesion obtained. The adhesion stability of a metallization system may be determined by processing and service requirements. Specific metallization systems in common use in the microelectronics industry are discussed together with their applications and limitations.
 
Conference Paper
Ge on Si p-i-n photodetectors with areas which are compatible with commercially-available receivers have been fabricated and tested. A dark current density of 6 mA/cm(2) at -1 V bias has been measured at room temperature; when heated to 85 degrees C, the measured dark current increases by a factor of nine. A responsivity of 0.59 A/W at 850 nm has been measured from these Ge detectors, which matches or exceeds commercially available GaAs devices. We have measured bandwidths approaching 9 GHz at -2 V bias from 50 pm diameter Ge detectors.
 
(a) and (b) X-ray diffraction pattern of highly textured c-axis oriented epitaxial Zn 1 − x Mn x O films grown on (0001) sapphire substrate shown in different panels for x = 0.05 and 0.18, respectively. Inset of Fig. 1(b) shows the XRD pattern for x = 0.10 film in a magnified scale showing absence of any impurity peak or polycrystalline film peak.
(a) Bright field cross-sectional TEM image of Zn 0.82 Mn 0.18 O film and sapphire substrate interface (atomically sharp). Inset shows the SAD patterns taken in the [2-1-10] f zone at a film-substrate interface indicating highly textured film of good single crystalline quality. (b) High resolution cross-sectional (10-10) TEM micrograph of Zn 0.82 Mn 0.18 O epitaxial film clearly shows a highly textured film along with excellent epitaxy with the substrate. (c) Fourier filtered TEM micrograph of Zn 0.82 Mn 0.18 O film grown on (0001) sapphire substrate using opposite {10-10} f 11 {11-20} s reflections showing the match of the corresponding planes. Misfit dislocations at the interface are indicated by the circles with arrow. It clearly shows that every 5th or 6th plane of (2-1-10) sapphire substrate terminates at the interface.
DC-magnetization as a function of temperature [M(T)] of Zn 0.95 Mn 0.05 O film at magnetic fields of H = 2.5, 5, 10, 20 and 50 mT in (a) field-cooled (FC) and (b) zero-field-cooled (ZFC) conditions. M(H) plot in the low field regime for both FC and ZFC conditions are shown in the insets.
Optical absorbance spectra of Zn 1 − x Mn x O (x = 0.01, 0.05, 0.12, 0.18, and 0.25) thin films measured at room temperature. The shifting of the absorbance spectra at a lower wavelength side is mainly due to increase of the ZnO band gap with the increase of Mn ion concentration (x). (αhc / λ) 2 vs (hc / λ) plot (from which band gap are estimated) is shown in inset of Fig. 8.
Article
We report here microstructural, magnetic and optical properties of high quality epitaxial thin films of diluted magnetic semiconductor Zn1 − xMnxO (0.01 ≤ × ≤ 0.25) grown on (0001) sapphire substrate (α-Al2O3) by pulsed laser deposition technique. Seven (01-10) planes of ZnMnO film are found to match with six (-12-10) planes of sapphire substrate through excellent domain matching epitaxy by 30° rotations of ZnMnO unit cell about c-axis with respect to the sapphire unit cell. From high resolution transmission electron micrograph image the misfit dislocations are observed at the interface of sapphire and ZnMnO film growth plane. The insulating Zn0.82 Mn0.18 O epitaxial thin film showed ferromagnetic behavior (hysteretic) with coercive field ∼ 6.2 mT, and a maximum saturation moment of 0.42 μB/Mn+2 ion at a field of 0.5 T at the lowest attainable temperature (T = 10 K). The strong concave behavior of magnetization as a function of the temperature curves in this strongly insulating ferromagnetic diluted magnetic semiconductor film has been best explained through non-mean-field polaron-percolation-theory. The increase of band gap from bulk ZnO with dopant concentration (x), observed from absorbance spectra, has been attributed to the sp-d spin — exchange interaction between the band electrons and localized d electrons of Mn+2 ions of Zn1 − xMnxO films in the presence of tetrahedral crystal field interaction.
 
Article
Amorphous tantalum oxide thin films were deposited by reactive r.f. magnetron sputtering onto silicon[001] substrates. Growth temperature, oxygen partial pressure and total gas pressure have been varied for optimizing thin film density. The as-deposited films were annealed in atmosphere at 700°C and transformed into a polycrystalline state. The thin films were analyzed by glancing-angle-of-incidence X-ray diffraction, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared (NIR) to vacuum-ultra-violet (VUV) spectral region for photon energies from 1 to 8.5 eV, and in the infrared (IR) region from 0.03 to 1 eV. We present the IR dielectric functions of amorphous and polycrystalline tantalum oxide, which were obtained by analyzing the experimental ellipsometric data with Lorentzian lineshapes for each phonon resonance absorption. We observe a shift of the characteristic phonon absorption in tantalum oxide to lower frequencies upon sample annealing. The optical properties in the NIR to VUV were analyzed by using a parametric model approach. The dielectric functions obtained thereby were further locally fitted by Lorentzian lineshapes in order to analyze critical point structures due to electronic band-to-band transitions.
 
Article
The present investigation is devoted to the further study of the two-temperature evaporation–condensation–diffusion (ECD) method. Experiments have been performed to determine the Hg vapour pressure influence on rates of HgTe evaporation and condensation, morphological peculiarities of the initial stages of Hg1−xCdxTe layer growth, and interdiffusion in the HgTe–CdTe system. It is shown that the classical ECD method for Hg vapour pressures higher than 4 atm becomes inefficient due to the several reasons discussed in this paper. We suggest a two-stage epitaxy process for Hg1−xCdxTe and other solid solutions. In the first stage, a structurally perfect layer with a desired thickness is formed at low Hg pressure. In the second stage, the Hg vapour pressure is fixed. This provides the necessary composition of the layer surface. High-quality Hg1−xCdxTe layers with the surface composition xs up to 0.5 are reproducibly obtained by this proposed technique.
 
Article
Nanocrystalline nickel ferrite with different concentration of Ni and Zn (NixZn1 − xFe2O4 where x = 0.1, 0.3, 0.5) were synthesized using chemical co-precipitation method. The effect of doping ion concentration on physical properties like crystalline phase, crystallite size, particle size, and saturation magnetization are investigated. The X-ray diffraction pattern confirms the synthesis of single crystalline NixZn1 − xFe2O4 nanoparticles. The lattice parameter decreases with increase Ni content resulting in reduction of lattice strain. HRTEM images revealed that the as-prepared nanoparticles were crystalline with particle size distribution in 10–30 nm range. The saturation magnetization show the superparamagnetic nature of sample for x = 0.1 and x = 0.3 whereas for x = 0.5, the material is ferromagnetic. The saturation magnetization value is 23.95 emu/gm for Ni0.1Zn0.9Fe2O4 sample and it increases with increase in Ni content.
 
Article
Virtual substrates with relaxed SiGe buffers on Si substrates are needed for strain adjusted heterodevices with high Ge content. We have investigated the degree of relaxation in thin (<0.1 μm) SiGe layers grown by solid source molecular beam epitaxy (MBE) using a special low temperature growth step. Full relaxation (100%) of layers with a low temperature growth stage was achieved. X-Ray data suggest that SiGe buffers grown using this method are fully relaxed (100%), when appropriate values of Ge content, thickness and growth temperature are chosen. A typical sample with 28% Ge at total thickness of 70 nm and low temperature growth stage with 200°C heater temperature is shown. TEM data indicate that the misfit dislocations are confined within the virtual substrate. Furthermore, the surface is smooth and free from strain-induced undulations and crosshatch.
 
Article
This work is aimed at the practical effect of Ti-rich TiN as a Co-salicide capping layer on Gate-Induced Drain Leakage (GIDL) variation on High Voltage (HV) transistors in embedded Flash memory devices. It is reported that Ti-incorporating capping layer into Co film may reduce GIDL of HV transistor dramatically by ∼2 order magnitude of leakage at Vdd > 8 V of drain bias, resulting in better yield and reliability performance. This is due to the removal of contaminated silicon oxide from the reaction between diffused Ti and interfacial contaminated oxide at the Co/Si interface during salicide process. I–V measurement to define the leakage behavior and transmission electron microscopy (TEM) with element mapping analysis to investigate the Co/Si interface of S/D junction area have been carried out. Furthermore, we verified that Ti-rich TiN layer with the advantages of both Ti and TiN film could suppress GIDL with a larger process window due to the minimization of the sensitivity of Co-salicide process to Si-surface condition as well as provided a good junction leakage uniformity and contact resistance (Rc), concurrently.
 
Article
The influence of residual stress state and composition on the mechanical properties of arc evaporated TiCxN1−x thin films have been investigated. By controlling the flow ratios of the reactive gases, N2 and CH4, films with compositions x=0 (TiN), x∼0.15, and x∼0.45 have been grown on cemented carbide substrates. The residual stress state was altered through variations in the negative substrate bias over the range 20 V≤Vs≤820 V. The intrinsic stress, σint, measured by the X-ray diffraction (XRD) sin2ψ method was compressive and increased with decreasing Vs and increasing x. The latter behavior is suggested to be due to increased effective stability of defect complexes when the carbon content increases. Maximum stress level was between −6 and −7 GPa and limited by interior cracking of the films. The increase in intrinsic stress was accompanied by an increase in XRD peak broadening due to inhomogeneous strains. The hardness, H, and Young’s modulus, E, of as-deposited films were measured using the nanoindentation technique. Apparently linear correlations between σint and H were found for each film composition where H increased with x. The maximum H, 44 GPa, was thus obtained for the x∼0.45 film with σint=−5.5 GPa. The lowest hardness for this composition was 35 GPa for a film with σint=−2.7 GPa. For the TiN films, a similar variation in hardness of 33 GPa at σint=−5.8 to 26 GPa at σint=−1.2 GPa was obtained. E was constant at ∼610 GPa for most of the films, with a slight decrease in the films with the lowest σint values.
 
Article
The electrical performance of hydrogen silsesquioxane (HSQ) as the interlayer level dielectric (ILD) has been determined by using two-metal-layered test structures to study the impact of oxide liner thickness on the capacitance reduction. In comparison with SiO2, HSQ test structures formed with SiO2 cap and liner or with SiO2 cap only, have 20–27% lower intraline capacitance while 6–16% reduction was observed for fluorosilicate glass (FSG) relative to SiO2. It was found that the capacitance of SiO2/HSQ ILDs did not vary with oxide liner thickness as expected. Similar effects were observed with via resistance measurement. Analysis of the structure shows that wide variation of SiO2/HSQ/SiO2 stack thickness after oxide Chemical Mechanical Polishing (CMP) step changed the expected contribution of liner thickness on the intraline and interlayer capacitance. This thickness variation also has a strong impact on landed/unlanded via resistance. Therefore, a good control of oxide CMP on the ILD stack is needed to reduce the thickness variation of the liner/HSQ/cap ILD stack which in turn will enhance process yields in the 0.18 μm devices.
 
Article
An overview of the development of advanced Ti and Co self-aligned silicide (SALICIDE) processes for deep-sub micron high performance CMOS technologies at Texas Instruments is presented. SALICIDES are a key factor for scaling of high-performance CMOS devices. They are used to lower sheet resistance of gate and source/drain regions, contact resistance and source/drain series resistance, increasing device performance and lowering RC delays to allow faster operation. Their applicability to deep-sub-micron technologies is determined by the fundamental materials aspects controlling silicide phase formation and evolution, as well as process integration issues such as effect of subsequent processing steps on the silicide films or effects of silicide related process steps on transistor characteristics. The main scaling issues for conventional processes, high resistivity on narrow lines for Ti SALICIDE and high diode leakage on shallow junctions for Co SALICIDE, are addressed. Detailed kinetic studies of the high resistivity to low resistivity phase transformations (TiSi2 C49 to C54 and CoSi to CoSi2) and their dependence on linewidth and film thickness are presented. A nucleation density model is shown to account for the measured linewidth dependence and effect of pre-amorphization implants on the TiSi2 C49 to C54 transformation and explain, as a result, narrow line sheet resistance. This overview covers studies on rapid thermal processing (RTP) for Ti and for Co SALICIDE, pre-amorphization implants and Mo impurities which allowed the first demonstration of low resistivity Ti SALICIDE at 0.10 μm gate lengths, as well as applications to sub-0.18 μm CMOS technologies and integration issues.
 
Article
Relaxor 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (70/30 PMN-PT) and 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (90/10 PMN-PT) thin films have been grown by RF-sputtering on platinum (Pt) and lanthanum nickelate (LaNiO3) bottom electrodes. For both electrodes, macroscopic measurements evidence lower coercive fields, remnant polarizations and piezoelectric coefficients d33 for 90/10 PMN-PT films compared to 70/30 PMN-PT films. For both compositions, coercive fields and remnant polarizations are lower for films grown on LaNiO3 compared to on Pt while piezoelectric coefficients d33 are higher. For each electrode and composition, a similar behavior is revealed for electromechanical activity at the nanoscale when measuring local piezoelectric hysteresis loops; on the other hand, the voltages required for switching the domains are the highest for 90/10 PMN-PT films grown on LaNiO3. The existence of large grain boundaries in the films grown on Pt and the presence of local random fields with polar nano-domains for the 90/10 composition could explain the differences measured in domains switching properties at the macroscale and nanoscale levels.
 
Article
Thin films of La0.7Ca0.3MnO3 (LCMO) have been grown epitaxially on (001) single-crystal substrates of (LaAlO3)0.3–(SrAlTaO6)0.7 by metal-organic deposition. The microstructures of the LCMO films were investigated by transmission electron microscopy (TEM) on cross-sections. High-resolution TEM observations demonstrated a good quality of epitaxy throughout the entire film thickness. For bolometric application, we calculated the temperature coefficients of resistance (TCR) from the temperature dependence of the resistance. Large value of TCR of approximately 22% at 250 K was obtained for the 80 nm thick film.
 
Article
Through the years, 248-nm deep-UV (DUV) photolithography technologies have been used in sub 0.3 μm microelectronics fabrication. In order to fundamentally understand the development behaviors of DUV photoresist and optimize the lithographic process accordingly, the dissolution kinetics of an advanced 248-nm DUV photoresist OCG ARCH2 was studied by varying the concentrations of photo-acid-generator (PAG) and the cooling rate after post exposure bake (PEB). As popularly known, DUV photoresists are very sensitive to airborne contaminations from N-methylpyrrolidone (NMP) or ammonia, etc. As an alternative method for thermal annealing, electron beam (E-beam) was employed to stabilize the DUV Photoresists in order to improve critical dimension (CD) control and post exposure delay (PED) stability. It was observed that E-beam stabilization of DUV photoresist could result in a comparable PED and CD control reported on thermal annealing.
 
Article
Al2O3, AlN and Al composite coating was synthesized on 0.45% C steel sample to improve its corrosion resistance ability by using a plasma source ion implantation and deposition (PSII&D) system. The PSII&D is an extension of PSII by the combination of steady-state gas plasma and pulsed metal plasma. The gas plasma is produced by magnetic multipole filament discharge (or glow discharge) and the metal plasma is produced by pulsed cathodic arc discharge. The electrochemical corrosion test of the coating shows that the corrosion resistance ability of the coated 0.45% C steel sample was greatly improved. The microstructure, surface compositions, depth profile, bonding environment and morphology of the coating were investigated by X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. The results show that the coating is formed by Al2O3, AlN and Al. The improvement in corrosion resistance ability of 0.45% C steel is due to the formation of the composite coating.
 
Article
Textured thin films of γ-In2Se3 and γ-In2(Se,Te)3 have been prepared by alternate thermal evaporation of In and (Se,Te) layers on glass substrates. The crystallization of the as-deposited films was performed by post-deposition heat treatment in neutral atmosphere. Photoconductivity measurements were performed on films of both compounds in order to study the effect of crystalline quality and Te on the photoconductive behaviour of the films. It has been shown for γ-In2Se3 that the photocurrent is higher in films with good texture and large grains than in the films with less better quality. Moreover, the photocurrent is found to be about two orders of magnitude higher in γ-In2(Se,Te)3 films with Te amount up to 10 at.%. On the other hand the variation of the photocurrent with incident photon energy allowed us to determine the energy gap Eg of both compounds and to confirm the Eg lowering by introducing Te.
 
Article
Boron-doped polycrystalline diamond films have been grown on molybdenum substrates by microwave-assisted chemical vapor deposition using a gas mixture of hydrogen and methane. AC impedance of diamond electrode was carried out in a solution of 0.5 M NaCl solution under various DC polarization conditions. Mott–Schottky plots were generated to determine the flatband potential of the boron-doped semiconducting diamond electrode in 0.5 M NaCl solution. It was found to be 0.91±0.2 V vs. R.E. in the frequency range of 1–400 Hz. The flatband potential was found to be higher than 0.91 V when the frequency was higher than 400 Hz and it was found to be lower than 0.91 V when the frequency was lower than 0.1 Hz. The kinetics were faster when a negative bias was applied to the diamond electrode as it was evidenced in the impedance data due to a reduction in the charge-transfer resistance.
 
Article
The microstructures and mechanical properties of hot and cold sputtered Al—1 wt.%Si and Al-1 wt.%Si-0.5 wt.%Cu films were studied. Transmission and scanning electron microscopies were used to examine the grain size, precipitate morphology and surface structure of the films. Stress measurements using a substrate curvature technique and hardness measurements made by nanoindentation were employed to study the mechanical properties. The cold sputtered films show a smaller grain size than the hot sputtered films before and after annealing, whereas the precipitate morphology looked the same after annealing for both films. Stress/temperature curves of AlSi and AlSiCu films are very similar on heating and on cooling above 220 °C. However, below this temperature the tensile stresses in the AlSiCu films increase sharply with decreasing temperature compared with the AlSi films. This effect is normally attributed to precipitation hardening of Al2Cu precipitates which form below 250 °C. However, there is evidence for a second explanation. The steep rise in stress can be caused by the end of diffusional relaxation. Calculations show that the breakdown of thermal activation of diffusional processes occurs in the same temperature range.
 
Article
The important microsectioning techniques developed in the last decade for the direct measurement if diffusion at low temperatures (<0.5 Tm) are briefly reviewed and critically discussed. A powerful variant of these techniques is material removal by r.f. backscattering in an Ar glow discharge which enables tracer profiling to be carried out in steps of about 30 Å or more directly and expeditiously and also independently of the nature of material. The relative merits of the various techniques described are discussed by examining the quality of the recently available low temperature diffusion data for Au.
 
Article
The electromigration resistance of Al-0.5%Cu meander lines was found to increase with increasing grain size s and degree of {111} preferred orientation and with decreasing spread σ in the grain size distribution. This dependence on microstructure can be expressed in terms of the empirical quantity which correlates well with the electromigration lifetime of films obtained by different deposition techniques.
 
Article
The optical properties of amorphous PbZr0.52Ti0.48O3 thin films on vitreous silica and sapphire substrates by the RF magnetron sputtering method have been investigated by transmittance measurements. For a single-layer thin film on the transparent substrate, the inverse synthesis or fitting method with the six fitting parameters was given and used to calculate the optical constants such as the refractive index n, the extinction coefficient k, and the absorption coefficient α. The film thickness d, which was one of the fitting parameters, is simultaneously obtained. According to Tauc's law, the optical transition in amorphous PbZr0.52Ti0.48O3 thin films is direct in nature. The direct band gaps of amorphous PbZr0.52Ti0.48O3 thin films on vitreous silica and sapphire substrates were found to be 3.36 and 3.25 eV, respectively. The dispersions of the refractive index in films were studied by considering a single-oscillator model.
 
Article
The ordinary optical dielectric functions of pulsed-laser-deposition grown wurtzite c-plane MgxZn1−xO (0≤x≤0.53) thin films have been determined by using spectroscopic ellipsometry in the photon energy range from 4.5 to 9.5 eV. The dielectric functions reveal features which resemble those previously detected in uniaxial AlGaN and identified as E1- and E2-type band-to-band transitions with no remarkable dependence of the transition energy on Mg content x. The E1- and E2-type transitions for ZnO are compared with pseudopotential band-structure calculations.
 
Article
To improve the fill factor (FF) over 0.7, the following research has been performed, such as 1) our sulfurization after selenization (SAS) process condition for the Cu(InGa)(SeS)2 (CIS)-based absorber formation is fixed to attain the open-circuit voltage (Voc) of over 0.630 V/cell, 2) thickness of a double buffer structure with both Zn(O,S,OH)x deposited by a chemical-bath deposition (CBD) technique and intrinsic ZnO deposited by a metal–organic chemical vapor deposition (MOCVD) technique is adjusted by optimizing the series resistance (Rs) and the shunt resistance (Rsh), 3) post-deposition annealing in vacuum after CBD is applied to reduce the hydroxide (OH) concentration, and 4) narrower pattern-2 and -3 scribe lines contribute to make the interconnect width less than 200 μm and to keep the short-circuit current density (Jsc) over 34 mA/cm2. As the result, for the first time a FF of over 0.7 has been achieved in our CIS research and development (R&D) since FY1993. This is the biggest contributor to achieve our FY2007 milestone of 15% efficiency with aperture area larger than 800 cm2. We have achieved this milestone in the form of a laminated module.
 
Article
Zn2−2xCuxInxS2 (ZCIS) films with 0.78≤x≤1 grown by pulsed laser deposition (PLD) on (001)-oriented GaP substrates were found to crystallize in the tetragonal chalcopyrite-type structure. The thin films are monocrystalline for all compositions under consideration. Among a striking asymmetry of twin distribution, orientation domains extending along all 〈100〉 directions appear additionally. The size of orientation domains decreases with increasing Zn content. As long as the films have tetragonal chalcopyrite-type structure (x>0.78), all domains are ‘infected’ by CuAu-I type ordering independently of their orientation. Beyond the transition from tetragonal chalcopyrite-type to cubic sphalerite-type ZCIS (x<0.78) which seems to coincide with the order–disorder transition too, the films having cubic structure become orientation domain-free, and the CuAu-I type ordering disappears simultaneously. A detailed transmission electron microscope study is presented.
 
Article
α-Fe2O3(0001) films of thickness equal to ∼7 nm and ∼70 nm were epitaxially grown on α-Al2O3(0001) by oxygen plasma-assisted molecular beam epitaxy. The interfaces were characterized using high resolution transmission electron microscopy, electron energy-loss spectroscopy, and X-ray diffraction. The interface exhibited coherent regions separated by equally-spaced misfit dislocations. When imaged from the [2̄110] direction, the dislocation spacing is 7.0±1.1 nm for the 70-nm-thick specimen, and 7.2±0.1 nm for the 7-nm-thick specimen. When imaged from the [011̄0] direction, the dislocation spacing is 4.5±0.1 nm for the 7-nm-thick specimen. The experimentally observed dislocation spacings are approximately consistent with those calculated from the lattice mismatch between α-Al2O3 and α-Fe2O3, implying that the lattice mismatch is accommodated mainly by interface misfit dislocations above the critical thickness, which is less than 7 nm. This conclusion is also corroborated by the measured residual strain of ∼0.5% determined from X-ray diffraction for the 70 nm film. Electron-energy-loss-spectroscopy analysis reveals that the Fe L2,3-edge shows no measurable chemical shift relative to the L2,3-edge of structural Fe+3, indicating complete oxidation of Fe in the as-grown film.
 
Article
The observation of silicon carbide (SiC) surface in the initial stage was carried out in order to understand the variation of surface configurations in a sublimation epitaxy. The surface structures with the nuclei and step flow depend on the process temperature, the process pressure, and the surface polarity. Step-flow configurations were observed at the surface on Si-face. On the other hand, an individual 2D island enlarged nuclei and the coalescenced islands formed on C-face (000-1) 6H-SiC occurred at the relatively low temperature of 1600 °C due to the tensile stress analyzed by Raman spectroscopy.In addition, the nonuniform step-flow behavior on C-face surface was conspicuously exhibited at higher temperature of 1700–2100 °C, but the surface smoothness on C-face was better than that on Si-face. It was confirmed that several hidden parameters including rising rate until the wanted temperature and the final pressure give an effect on the surface configurations, but the decompression rate toward process pressure during temperature-rising stage reveals no change of surface configurations.
 
Article
The growth of thin Cu films on an O-precovered Ru(0001) surface has been studied by low-energy ion scattering, Auger electron spectroscopy and low-energy electron diffraction. During deposition of Cu, the majority of oxygen (about 70%) originally on the clean Ru(0001) surface was found to float out onto the top of the surface of the growing film. This displacement process could be observed up to a Cu coverage of 10 monolayers, which appeared to be independent of the deposition rate, the O precoverage and the substrate temperature. The floating O atoms in the top layer have been determined to be a disordered overlayer by measuring the azimuthal scan dependence at grazing incidence.
 
Article
The incoherent GaN/sapphire interface and microstructure of GaN were observed by high resolution transmission electron microscopy. The most mobile 60° mixed-type dislocation is related to a structural metastability of the Wurtzite GaN film. In spite of the same feature of interband absorption, the photoluminescence mechanism is sensitive to deep level. A strong light emission from the bound exciton of Wurtzite GaN at 358 nm was observed in an n-type GaN sample with the GaN buffer layer. The donor–acceptor pair recombination at 380 nm with LO phonon replicas at 390 and 403 nm and the deep level at 559 nm were observed in both an undoped GaN sample with GaN buffer layer and an n-type GaN sample with AlN buffer layer. This optical behavior is sensitive to the Si doping and the type of buffer layer materials. The deep level emission along the dislocation line is suggested by the local band bending model providing the potential barrier of 0.63 eV by the space charge.
 
Article
Thickness dependency of (001) texture evolution in Fe54Pt46 thin films on an amorphous substrate was investigated using in-house X-ray diffraction or a synchrotron source. The (001) texture was well developed in Fe54Pt46 thin films, especially when its thickness was equivalent to the grain height. The findings show that strain relaxation anisotropy along the film axis, which leads to a (001) crystal (a crystal with a (001) plane parallel to the film plane) that is more stable than others, was large for a low thickness film. In addition, abnormal grain growth was used to explain the abrupt development of a (001) texture. The advantage of multilayered as-deposited structure is also discussed.
 
Top-cited authors
Tadatsugu Minami
  • Kanazawa Institute of Technology
Claes Goran Granqvist
  • Uppsala University
Lars Hultman
  • Linköping University
Hans-Werner Schock
  • Helmholtz-Zentrum Berlin
Syed S Major
  • Indian Institute of Technology Bombay