Changes In Film Composition Research Articles

Growth and Modification of Organosilicon Films in PECVD and Remote Afterglow Reactors

AbstractSummary: Five hundred nanometer thick organosilicon coatings are prepared on Si substrates in parallel by the plasma‐assisted polymerisation of hexamethyldisiloxane (HMDSO) in an RF‐inductively coupled plasma (RFICP) and distributed electron cyclotron resonance plasma (DECRP) at low pressure (0.27 Pa) and of tetramethyldisiloxane (TMDSO) premixed with oxygen in an N2 microwave induced remote afterglow (MIRA) at 560 Pa. The structure of these different films is analyzed by different techniques, such as Fourier‐transform infrared spectroscopy, Rutherford backscattering spectrometry, atomic force microscopy, ellipsometry, and contact angle measurements. Results of the film composition (at least 30% carbon content), optical properties, and morphology indicate a low cross‐linking degree accompanied by short chain length for RFICP and DECRP films, in contrast to a high‐molecular‐weight structure observed for the MIRA film. Carbon removal is achieved within the same plasma reactors by further oxygen‐containing plasma treatment performed in the RF‐ICP (3.33 Pa), DECRP (0.27 Pa, −200 V biased substrate), and MIRA (N2/O2 (98.7:1.3, 560 Pa)) reactors. The same measurements are carried out on the treated samples in order to detect the main changes in film composition, optical properties, and morphology. The evolution of surface energy is also studied. The results are discussed according to film structure and process specificity.O/Si and C/Si elemental ratios calculated from RBS analysis for an as‐deposited RF‐inductively coupled plasma coating (RFICP) and films post‐treated by N2/O2 microwave induced remote afterglow (MIRA), O2 RFICP and O2 distributed electron cyclotron resonance plasma (DECRP, biased sample) processes.imageO/Si and C/Si elemental ratios calculated from RBS analysis for an as‐deposited RF‐inductively coupled plasma coating (RFICP) and films post‐treated by N2/O2 microwave induced remote afterglow (MIRA), O2 RFICP and O2 distributed electron cyclotron resonance plasma (DECRP, biased sample) processes.

In situ and ex situ characterisation of oxide films formed on strained stainless steel surfaces in high-temperature water

A possible approach in describing the role of the environment in the phenomena behind initiation and propagation of a stress corrosion crack is to assume that the transport of matter and charge through the oxide film on the material is one of the rate-controlling factors. Straining of the bulk material may affect the transport rates of ionic defects, such as vacancies and interstitials, through the oxide film. The aim of the present work has been to verify the applicability of combined slow strain rate tests (SSRT) and contact electric resistance (CER) measurements to assess the influence of strain on the electric properties of oxide films on AISI 316L stainless steel with or without prior cold work in simulated boiling water reactor (BWR) coolant conditions. The SSRT-CER measurements have been combined with ex situ characterisation of the oxide films after experiments using electron spectroscopy for chemical analysis (ESCA) and scanning electron microscopy (SEM). The results suggest that the effect of strain on the resistance of the oxide films seems to correlate with the effect of the same parameter on the Cr(III) concentration in the inner layer of the oxide. In addition, important differences between the concentration of Ni and Fe in the outer layer formed on stressed and unstressed surface have been observed. Based on the mixed-conduction model for oxide films, an attempt is made to evaluate the effect of straining on the electric properties of the oxide films and to correlate these effects with the changes in film composition and structure.

Effect of Thermal Treatment on Carbon-Doped Silicon Oxide Low Dielectric Constant Materials

Carbon-doped silicon oxide (SiOCH) low dielectric constant (low-k) material is a good candidate for advanced interconnect technology. Good thermal stability of the dielectric is required due to the many thermal processes involved during IC fabrication. The thermal stability of tetramethylcyclotetrasiloxane (TMCTS) based plasma-enhanced chemical vapor deposition (PECVD) carbon doped low-k material with annealing temperature from 400 to 800 degrees C in N2 was studied. The thermal stability temperature of TMCTS based carbon doped low-k material is 600 degrees C. Above 600 degrees C annealing, the thermal energy can break Si-CH3, Si-C, Si-H, and C-H bonds leading to outgasing, which results in film composition change, weight loss, and thickness shrinkage. Film composition changes, especially carbon loss and oxygen incorporation, can degrade its reliability extremely. Carbon is desorbed in the form of CH4, CO, and other hydrocarbon.

Thermal Plasma Chemical Vapor Deposition of Superhard Nanostructured Si-C-N Coatings

AbstractA triple torch plasma reactor was used to synthesize Si—C—N composite films via the thermal plasma chemical vapor deposition process. The argon-nitrogen plasma provided atomic nitrogen to carbon- and silicon-based reactants, which were injected through a central injection probe and ring configuration. Films were deposited with variations of the total nitrogen flow through the torches (1.5-4.5slm), reactant mixture (silicon tetrachloride and acetylene or hexamethyldisilazane) and substrate material (silicon and molybdenum). Micro X-ray diffraction was used to determine that both α-Si3N4 and β-Si3N4 were dominant in most of the depositions. Composites of silicon nitride and silicon carbide were synthesized on molybdenum. The bonding of amorphous phases was investigated using Fourier transform infrared spectroscopy, which indicated the presence of N—H, CHx and CΞ in various films. Indentation tests on the polished film cross-sections determined that large variations in hardness and elastic modulus existed for minor changes in film composition. Correlations between indentation results and scanning electron and optical microscope images showed that the mechanical properties greatly depend on the film morphology; the denser, smoother, and more crystalline films tended to display enhanced mechanical properties.

Novel Wide-Band-Gap Ag(In1-xGax)Se2 Thin Film Solar Cells

AbstractAg(In1-xGax)Se2 thin films have been deposited on Mo-coated soda-lime glass substrates by the three-stage process using a molecular beam epitaxy (MBE) system. We found a remarkable decrease in the substrate temperature during the 2nd stage in which the film composition changes to a Ag excess. A single phase chalcopyrite AIGS thin film with a slightly Ag poor composition was obtained by using the temperature monitoring composition method. The cell performance of the AIGS thin film solar cell was found to strongly depend on the Ga/(In+Ga) and Ag/(In+Ga) atomic ratios.A high efficiency wide-gap (Eg=1.7eV) Ag(In0.2Ga0.8)Se2 thin film solar cell with a total-area efficiency of 9.3% (10.2% active area efficiency), Voc = 949mV, Jsc = 17.0 mA/cm2, FF = 0.577, and total area = 0.42 cm2 was achieved. The junction formation mechanism of AIGS devices is discussed based on electron beam induced current (EBIC) and scanning capacitance microscopy (SCM) analyses.

Corrosion studies in support of lead-bismuth cooled FBRs

The performance of structural materials in lead or lead-bismuth eutectic (LBE) systems is evaluated. The materials evaluated included several US steels (austenitic steel [316L], carbon steels [F-22, Fe-Si], ferritic/martensitic steels [HT-9 and 410]), and several experimental Fe-Si-Cr alloys that were expected to demonstrate corrosion resistance. The materials were exposed in either a dynamic corrosion cell for periods from 100 to 1,000 h at temperatures of 400, 500, 600 and 700°C, depending on material and exposure location. Weight change and optical SEM or X-ray analysis of the specimen were used to characterize oxide film thickness, corrosion depth, microstructure, and composition changes. The tests conducted with stainless steels (410, 316L and HT-9) produced mass transfer of elements (e.g., Ni and Cr) into the LBE, resulting in degradation of the material. With Fe-Si alloys a Si rich layer (as SiO 2) is formed on the surface during exposure to LBE from the selective dissolution of Fe.

Transpassivation of Fe–Cr–Ni stainless steels

A transpassivation model was proposed for Fe–Cr–Ni stainless steels. In this model, the important steps and processes involved in transpassivation were illustrated. With some reasonable assumptions, transpassivation behaviours were predicted, such as the changes in film composition, film thickness, anodic current density and AC impedance spectrum in transpassive and secondary passive regions. It was demonstrated that these theoretical predictions were in good agreement with experimentally observed transpassivity of Fe–Cr–Ni stainless steels.

Corrosion Studies in Support of Medium-Power Lead-Alloy-Cooled Reactor

The performance of structural materials in lead or lead-bismuth eutectic (LBE) systems is evaluated. The materials evaluated included refractory metals (W, Mo, and Ta), several U.S. steels [austenitic steel (316L), carbon steels (F-22, Fe-Si), ferritic/martensitic steels (HT-9 and 410)], and several experimental Fe-Si-Cr alloys that were expected to demonstrate corrosion resistance. The materials were exposed in either an LBE rotating electrode or a dynamic corrosion cell for periods from 100 to 1000 h at temperatures of 400, 500, 600, and 700°C, depending on material and exposure location. Weight change and optical scanning electron microscopy or X-ray analysis of the specimen were used to characterize oxide film thickness, corrosion depth, microstructure, and composition changes. The results of corrosion tests validate the excellent resistance of refractory metals (W, Ta, and Mo) to LBE corrosion. The tests conducted with stainless steels (410, 316L, and HT-9) produced mass transfer of elements (e.g., Ni and Cr) into the LBE, resulting in degradation of the material. With Fe-Si alloys a Si-rich layer (as SiO2) is formed on the surface during exposure to LBE from the selective dissolution of Fe.

Characterization of perivascular poly(lactic-co-glycolic acid) films containing paclitaxel

The objectives of this study were to investigate the use of poly(lactic-co-glycolic acid) (PLGA) for the formulation of paclitaxel loaded films and to characterize these films for potential application as perivascular “wraps” to prevent restenosis. Films were manufactured from PLGA blended with either methoxypolyethylene glycol (MePEG) or a diblock copolymer composed of poly( d, l-lactic acid)-block-methoxypolyethylene glycol, PDLLA-MePEG (diblock) by solvent evaporation on teflon discs. Elasticity was determined by gravimetric stress/strain analysis. Thermal analysis was determined using differential scanning calorimetry (DSC). Changes in film composition and degradation in aqueous media were determined using gel permeation chromatography (GPC). Paclitaxel release from films was measured by incubation of the films in phosphate buffered saline (PBS) with drug analysis by HPLC methods. The addition of MePEG or diblock to PLGA caused a concentration dependent increase in the elasticity of films, due to plasticizing effects. DSC analysis showed that MePEG and diblock caused a concentration dependent decrease in the glass transition temperature ( T g) of PLGA indicating miscibility of the polymers. When placed in aqueous media, more than 75% of MePEG dissolved out of the PLGA films within 2 days, whereas diblock partitioned slowly and in a controlled manner out of the films. Paclitaxel release from PLGA/MePEG films was very slow with less than 5% of the encapsulated drug being released over 2 weeks. The addition of 30% diblock to paclitaxel loaded PLGA films caused a substantial increase (five- to eight-fold) in the release rate of paclitaxel. PLGA films containing 30% diblock and either 1% or 5% paclitaxel were partially or completely degraded following perivascular implantation in rats.

Film strain and compositional changes in thermally nitrided silicon dioxide thin films

The nature of the Si–O bonds, composition, and film strain changes in thermally nitrided silicon dioxides in NH 3 at 1000 °C and 1 atm is investigated with Fourier transform infrared spectroscopy and spectroscopic ellipsometry. Shifts of the transverse optical and longitudinal optical phonons of O in Si–O–Si bridging bonds are the results of both compositional and strain within the silicon dioxide matrix. Red shifts during the initial nitridation period are followed by blue shifts at longer nitridation times. Red shifts can be explained by nitrogen incorporation and strain accumulation, while bulk film strain relaxation in nitrided oxides is most likely responsible for the blue shifts.

Sn-containing composite thin films by plasma deposition of tetramethyltin

The time scale of the plasma on- and off-time is important for the control of the film composition in pulsed plasma process. Using low plasma on-times for the preparation of Sn-containing thin films with tetramethyltin (TMT) as precursor, significantly different results about the film chemistry and surface morphology were obtained, in contrast to the findings obtained at high plasma on-times in the literature. Upon changing the plasma on-times from 10 to 1 ms with the off-times below 520 ms and holding the other parameters constant, the surface morphology of the deposited films appeared from round particles of 100 nm at 10/330 through 40 nm at 10/510 in diameter to a tight smooth surface at 1/321 by atomic force microscope (AFM), while a stable particle size was reported at 10 ms on-time and 500–2000 ms off-times by other author. Detailed analysis of Fourier Transform Infrared Spectroscopy (FTIR) revealed that the content of the metal element Sn increased with plasma duty cycle or plasma on-time, in accord to the ‘usual’ plasma deposition mechanism. X-ray reflectometry was used to detect the aging effects under ambient condition on the film smoothness, density and thickness, while changes in film composition were observed by FTIR. In agreement with the morphology observation by AFM, a low roughness was found for the films deposited at low duty cycles. The film thickness increased by 3.6% after exposure to air, while a slight decrease in density was found. Higher density of the deposited substance attributed to higher Sn content was detected under higher plasma duty cycle, which was consistent with the FTIR results. Different deposition/ablation balance and weak Sn–C bond were attributed to the discrepancies.

X-ray photoelectron spectroscopic analyses of corrosion products formed on rock bolt carbon steel in chloride media with bicarbonate and silicate ions

The passivation behavior of Yucca Mountain Repository rock bolt carbon steel in deaerated 3.5% NaCl solution containing SiO 3 2− and HCO 3 − ions was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopic methods. Polarization results indicate that combinations of silicate and bicarbonate anions decrease the passive current density and raise the pitting potential. XPS results indicate the enrichment of silica at passive potentials and the formation of mixed FeCO 3 and silica film at lower potentials. This change in film composition was responsible for the changes in corrosion rate at lower and higher potentials. XPS results also support the thermodynamic data with regard to the occurrence of second oxidation peak observed in the polarization curves to be due to the oxidation of FeCO 3 to Fe 2O 3.

Properties of ITO thin films deposited on amorphous and crystalline substrates with e-beam evaporation

Indium tin oxide (ITO) thin films were deposited using the e-beam evaporation method on amorphous and crystalline substrates under identical conditions. The properties of the films were investigated using optical transmittance, XRD and XPS techniques. It was found that the properties of the films depend strongly on the nature of the substrate surface. Analysis suggests that changes in chemical composition and microstructure of the ITO films deposited on crystalline and amorphous substrates are responsible for the differences in optical properties.

Properties of the Teflon AF1601S Surface Treated with the Low-Pressure Argon Plasma

The stability of the surface properties of Teflon AF films were investigated after their exposure to the low-pressure argon plasma for various times. X-ray photoelectron and infrared spectroscopies, atomic force microscopy, scanning optical microscopy based on chromatic aberration, goniometry (the measurement of water contact angles), as well as electrokinetic method and ellipsometry were used to control changes in the chemical composition and surface properties of Teflon AF films taking place upon their plasma treatment. The stable hydrophilization of the surface of Teflon AF films resulted from plasma treatment was revealed.

Preparation and characterization of semiconducting Zn1−xCdxSe thin films

Abstract The electrodeposition of Zn 1− x Cd x Se polycrystalline semiconducting thin films from aqueous acidic bath without any additives onto tin oxide-coated conducting glass and titanium substrates are described. The influence of deposition parameters on the film formation and deposition mechanism based on cyclic voltammetry is discussed. X-ray diffraction studies showed the polycrystalline wurtzite nature for all the films deposited under the proposed conditions. The optical studies revealed the band gap values in the range between 2.82 and 1.72 eV as the film composition changes from ZnSe to CdSe. It has been observed that the concentration of cadmium salt plays an essential role on the alloy formation. The surface morphological studies and composition analysis were carried out and the results are discussed.

The combined effect of laser fluence and target deterioration in determining the chemical composition of pulsed laser deposited boron carbide films

A series of boron carbide films of 180±30 nm thickness has been deposited by KrF excimer laser ablation of a sintered B 4C target in high vacuum. Rutherford backscattering spectroscopy revealed that the chemical composition of the films grown on Si substrates, at room temperature, at laser fluences tuned between 2 and 14.3 J cm −2 varied depending not only on the actual laser fluence but also on the past record of the B 4C target. Parallel SEM mapping of both film and target surfaces pointed to a correlation between changes in film composition, droplet density and target surface deterioration. This correlation is discussed in detail.

Hydrolytic and enzymatic degradation of liquid-crystalline aromatic/aliphatic copolyesters.

Aromatic/aliphatic copolyesters containing hydrophilic moieties in the main chain or side chain were synthesized by bulk polycondensation of aromatic monomers without or with solubilizing substituents and aliphatic monomers. Hydrolytic and enzymatic degradation studies were carried out in vitro at 37 degrees C in pH 7.4 phosphate buffer and in Tris-HCl buffer containing proteinase K. The results indicate that liquid-crystalline aromatic/aliphatic copolyesters are degradable hydrolytically as well as enzymatically. The change in composition and morphology of the polyester films were monitored by nuclear magnetic resonance and scanning electron microscopy. The results suggested that aromatic species and aliphatic moieties could be released into aqueous solution during hydrolytic degradation of aromatic/aliphatic copolyesters with ethyleneoxy groups on the side chain. Modifying aromatic species with hydrophilic groups in aromatic/aliphatic copolyesters was an efficient method to improve degradability and biocompatibility due to improved solubility of degradation products in aqueous solution. Mechanical tests indicated that the copolyesters exhibited good mechanical properties prior to degradation, which can be of relevance for bone tissue engineering.

Corrosive Behavior of Tungsten in Post Dry-Etch Residue Remover

Failure of the tungsten (W) plug has become the main reliability issue in post-metal-etch cleaning due to the interaction between tungsten and the alkanolamine or hydroxylamine ingredients in the cleaning solution, as well as tungsten and chloride from the previous chlorine-based etching process. In our efforts to understand tungsten plug corrosion, the electrochemical behavior of blanket tungsten films in the post-etch resist remover, the EKC265 solution, at 65 °C in the presence of deionized water and Cl- was investigated using Tafel extrapolation, potentiometry, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The corrosion-current density and the open-circuit potential data showed that the basic EKC265 solution was aggressive to tungsten. The addition of chloride ions (Cl-) and the deionized water to the EKC265 solution further increased the corrosion-current density and shifted the open-circuit potential to more negative values. SEM pictures gave visual evidence of changes on the tungsten surface due to corrosion. Pitting was observed in the presence of both deionized water and Cl-. The changes in the chemical composition of tungsten films were evaluated with XPS. It was found that the distribution of oxidation states of tungsten was largely influenced by the chemical treatment in the EKC265-based electrolytes and closely related to the corrosion resistance of tungsten in the electrolytes.

Bright blue phosphors in ZnO–WO3 binary system discovered through combinatorial methodology

We screened bright blue phosphor materials for a ZnO–WO3 binary system. The film was deposited by combinatorial pulsed laser deposition at room temperature and then annealed. The film composition changes continuously in a full-range from ZnO to WO3 on a single substrate. We obtained two results from the distribution of blue emission-intensity observed by cathodoluminescence of the film: (1) not only did the film have a W composition of 50 mol % (stoichiometric ZnWO4 as the well-known blue phosphor material) but also the W composition region from 45 to 60 mol % had the most emissive phase, and (2) two emissive phases other than the ZnWO4, which have not been described in the phase diagram, were found in the W composition region from 10 to 20 mol % and from 65 to 75 mol %.

UV pulsed laser deposition from Al 2O 3–TiC ceramic composites

Ablation of Al 2O 3–TiC targets was performed in ultra high vacuum using a pulsed UV laser (KrF, 248 nm). The ablated material was collected onto Si(1 1 1) substrates to grow thin films. Two sets of experiments were performed with two different fluence values (6 and 15 J cm −2) and, for each set, three different substrate temperatures (approximately 580, 680 and 760 °C). The deposition time was always kept at 50 min. The as-deposited films were investigated by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Structure and chemical composition studies showed that the films consist mainly of amorphous oxides and that the film composition changes periodically along the film depth.