Thermal stability of hafnium silicate dielectric films deposited by a dual source liquid injection MOCVD

The hafnium and silicon precursors, Hf(NMe₂)₄ and Bu^tMe₂SiOH, have been investigated for the MOCVD of high- hafnium silicate, (HfO₂)_1–x –(SiO₂) _x films for gate dielectric applications. Control of the silica concentration in the hafnium silicate can be achieved by varying the relative precursor ratios up to a saturation level of 35–40% SiO₂. The thermal stability of the resulting hafnium silicate films in air has been investigated using medium energy ion scattering. Internal oxidation of the underlying silicon substrate is discernable when the films are annealed in dry air for 15 min over the temperature range 800–1000 °C.     

Electrical properties of r.f. magnetron sputtered BaxSr1−xTiO3 films on multi-layered bottom electrodes for high-density memory application

Ba_xSr_1–xTiO₃ (BST) thin films have been deposited by r.f. magnetron sputtering on silicon and platinum-coated silicon substrates with different buffer and barrier layers. Electrical properties of BST films have been evaluated using both metal–insulator–semiconductor (MIS) and metal–insulator–metal (MIM) structures. MIS capacitor C–V and G–V characteristics have been utilized to determine the fixed charge density, interface trap density and the trap distribution in the silicon bandgap. BST films deposited on Si/SiO₂/SiN/Pt and Si/SiO₂/Ti/TiN/Pt multilayer bottom electrodes have been used for the fabrication of MIM capacitors. The role of bottom electrode, processing temperature and Ba to Sr ratio on the electrical properties of Ba_xSr_1–xTiO₃ films have been investigated. Current–voltage behavior has indicated an ohmic nature at lower voltages and Poole–Frenkel conduction at higher voltages. Deposited films have shown an excellent time-dependent dielectric breakdown under constant-current stressing.     

Kinetic and electrical characterization of thin silicon oxide films obtained by electron cyclotron resonance plasma

We report the use of ECR plasma to grow and deposit silicon oxides ranged between 2.5 and 10 nm with rates between 0.04 and 2.0 nm s^–1. The thickness of the films, well grown or deposited, were characterized by means of a spectroscopic ellipsometer, operating in the 1.5–4.5 eV range. Uniformities of thin oxide films were better than 4% on 3 silicon wafers, and ranged from 4% to 6% between different runs. The concentrations of the different chemical species during the first stages of the plasma formation were followed by optical emission spectroscopy to give some insight into the origin of the properties of the different thin SiO _x films. FT-IR spectra show bands with larger FWHM in ECR oxides than in the thermal ones, but the main peak positions were close to one another in the spectra of the three kinds of oxides. The observed mode strength for the LO₄-TO₄ pair of each spectrum is the main aspect that distinguishes the deposited from the grown film, indicating unequal degrees of disorder in both oxides. C–V measurements were performed in MOS capacitors. In the as-deposited SiO _x films a positive net oxide charge density similar to the one in the thermal SiO₂ films is observed. It is worth noting that a post-metallization anneal causes a reduction of the initial net charge density and even a sign change, depending on the treatment conditions.     

Characterization of (Pb,La) TiO3 thin films prepared by the sol-gel method

Pb_(1–1.5x)La_xTiO₃ thin films were synthesized by the sol-gel spin-coating technique. The films became crystallized when the spin-coated films were annealed at 600 °C and at higher temperature, and became amorphous when annealed at 550 °C. The breakdown voltage, V _B, was recorded at around 30 V for 600–650 °C annealed films and varied only slightly with the composition. The V _B value of the amorphous films was observed to be higher than that of the crystalline films. The ferroelectric properties of both the amorphous and crystalline films were found to be similar. The dielectric constant, charge storage density and optical index of refraction of the films were _r =5–20, Q _c=0.12–0.54 C cm^–2 and n=1.6–2.3, respectively. They all increased moderately with La³⁺ content in the films. One possible reason why the ferroelectric properties are not modified as the amorphous films crystallize, may be that the octahedra are equilateral, whether the films are amorphous or crystalline. Additionally, a possible cause which lowers the breakdown voltage in crystalline film, is the formation of lead vacancies due to lead loss. The electrical properties of films coated on bare silicon become significantly lowered due to interdiffusion between films and substrate. The diffusion of Si⁴⁺ ions into-the films can be prevented by coating SrTiO₃ on the silicon substrate as a buffer layer. The charge storage capacity consequently becomes substantially enhanced.     

Enhanced electrical properties of PZT thick films prepared by sol–gel technique through step-by-step crystallization process

[Pb(Zr_xTi_1-x)O₃: PZT] films at morphotropic phase boundary composition (x = 0.52) were deposited on bare Si, ZrO₂/Si and Pt/Ti/SiO₂/Si substrates by sol–gel spin on technique. Films deposited on the bare Si and ZrO₂/Si substrates had low degree of crystallization and micro cracks. Well crystallized films with smooth microstructure were obtained on Pt/Ti/SiO₂/Si substrates. Further, the thickness of the films on Pt/Ti/SiO₂/Si substrate was increased up to ~1 μm by step-by-step crystallization process. The single perovskite phase of the above films was confirmed with X-ray diffraction analysis. Films had enhanced dielectric properties at room temperature and the dielectric constant values were comparable to those of bulk values at Curie temperature (T_c) from the temperature dependent dielectric measurements. Films exhibit higher remnant polarization (P_r) and lower coercive field (E_c) values. Further, capacitance–voltage (C–V), current–voltage (I–V) measurements and rough estimation of piezoelectric coefficient of the films were carried out.     

Synthesis and characterization of HfO2 and ZrO2 thin films deposited by plasma assisted reactive pulsed laser deposition at low temperature

A plasma assisted reactive pulsed laser deposition process was demonstrated for low-temperature deposition of thin hafnia (HfO₂) and zirconia (ZrO₂) films from metallic hafnium or zirconium with assistance of an oxygen plasma generated by electron cyclotron resonance microwave discharge. The structure and the interface of the deposited films on silicon were characterized by means of Fourier transform infrared spectroscopy, which reveals the monoclinic phases of HfO₂ and ZrO₂ in the films with no interfacial SiO_x layer between the oxide film and the Si substrate. The optical properties of the deposited films were investigated by measuring the refractive indexes and extinction coefficients with the aid of spectroscopic ellipsometry technique. The films deposited on fused silica plates show excellent transparency from the ultraviolet to near infrared with sharp ultraviolet absorption edges corresponding to direct band gap.     

Microstructure and properties of a composite system for dental applications composed of glass-ceramics in the SiO2–Li2O–ZrO2–P2O5 system and ZrO2-ceramic (TZP)

The objective of the study was to develop a biocompatible composite system which was composed of TZP-ceramic (tetragonal zirconia polycrystals, ZrO₂ stabilized with 3 mol% Y₂O₃) and two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type. The metal-free composite system would satisfy the translucency, the biocompatibility and the strength requirements of dentistry. The two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type with a content of 15 and 20 wt% ZrO₂ respectively, were chemically and physically adapted to TZP-ceramic. The glass-ceramics were used as a dentin buildup material. The TZP-ceramic had the function of a root post. The shape of the post was cylindrical with a conical tip. The composite system was easy to process through viscous flow of the glass-ceramic at 900 and 1000°C, respectively. The microstructure and the mechanical properties of two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type were examined therefore.     

Phase Composition of Films Deposited by ZrB2 RF Magnetron Sputtering

X-ray diffraction and electron-microscopic studies demonstrate that the conditions of ZrB₂ rf magnetron sputtering (primarily, the argon pressure) have a significant effect on the thickness, phase composition, and structure of the growing films. The films deposited on silicon substrates at low argon pressures (0.15–0.18 Pa) consist of zirconium diboride and a very thin zirconia layer. At higher argon pressures, from 0.21 to 0.42 Pa, the film thickness is larger, and the film is composed of four layers: ZrB₂/ZrB/ZrO₂/B₂O₃. Increasing the argon pressure to 0.47 Pa, reduces the deposition rate and the thickness of the zirconia layer. The resultant films contain neither ZrB nor B₂O₃. At still higher argon pressures, up to 0.65 Pa, film thickness continues to decrease because of the reduction in the thickness of the ZrB₂ layer. The substrate temperature influences the structural perfection of the growing films. Other sputtering parameters influence the argon pressure and, accordingly, the phase composition of the films. At deposition temperatures of 60–70°C, there are certain orientational relationships between the films and single-crystal substrates. On glass-ceramic substrates, the deposition rate is substantially faster, and the deposits consist of randomly oriented crystallites.     

Studies on the radiopacity of experimental dental composite resins containing admixed SiO2−ZrO2 fillers

To produce radiopaque silica (SiO₂)-based fillers, zirconia (ZrO₂) powders were mechanically added to SiO₂ powders with ZrO₂ content up to 40 wt%. We evaluated the radiopacity of experimental composite resins consisting of (Bis-GMA + TEGDMA + CQ + DMAEMA) monomer mixture (25 wt%) and admixed SiO₂–ZrO₂ fillers (75 wt%), and compared their radiopacity with those of human dentin and enamel. It became confirmed that the radiopacity of experimental composite resins increased linearly with zirconium content, while the composite resin containing 80 wt% SiO₂-20 wt% ZrO₂ filler possessed radiopacity similar to that of human enamel. It was proved that the radiopacity of the composites could be precisely controlled by adjusting ZrO₂ content in SiO₂–ZrO₂ fillers.     

Preparation and properties of ferroelectric Pb1 − xCaxTiO3 thin films produced by the polymeric precursor method

Pb_{1 – x} Ca _x TiO₃ thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO₂/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb_{1 – x} Ca _x TO₃ thin films were granular in structure with a grain size of approximately 60–70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10^–7 A/cm² in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 C/cm² and 150 kV/cm, respectively.     

Phase formation and characteristics of r.f.-sputtered barium-strontium titanate thin films on various bottom layers

(Ba_0.7Sr_0.3)TiO₃ thin films were deposited by r.f.-magnetron sputtering on Pt/Ti/Si, Pt/TiSi₂/Si and Pt/Ti/SiO₂/Si substrates, respectively, and annealed at 650 C for 30s by Rapid Thermal Annealing (RTA). XRD (X-ray diffraction) patterns revealed that the BST films had perovskite structure without preferred orientation. Auger depth profiles of barium-strontium titanate (BST) films on various substrates were performed. In the Pt/Ti/Si and Pt/TiSi₂/Si structures, Si diffused into the BST film, but in the Pt/Ti/SiO₂/Si structure, the diffusion of Si into the BST film was prevented and the interface between the BST film and the electrode was stable. The dielectric constants were about 310–260 (100 kHz–1 MHz).     

Ferroelectric Films of Ba0.7–0.8Sr0.2–0.3TiO3 Solid Solutions Deposited from Carboxylate Solutions

Ferroelectric films of Ba_0.7–0.8Sr_0.2–0.3TiO₃ solid solutions 2–3 m in thickness were deposited onto platinum substrates from carboxylate solutions and characterized by dielectric measurements at 1000 Hz: t _C = 15–16°C, ₂₀ > 1000, tan = 0.04–0.06 in the range 10–100°C. The controllability coefficient of the films in a dc electric field between 36 and 42°C is 1.6.     

Zirconium oxides formed by hydrolytic condensation of alkoxides and parameters that affect their morphology

When zirconium oxides are formed via hydrolytic condensation of zirconium alkoxides, the particle size and morphology of the resultant zirconia is strongly affected by certain parameters during the condensation. These parameters include: the type of alkyl group in the alkoxide, water/alkoxide ratio, molecular separation of species, and the reaction temperature. The particle size and the morphology in turn affect the sintering behaviour and crystalline transformation of ZrO₂, In this work the parameters that affect the formation of ZrO₂ from zirconium alkoxides are investigated. It has been shown that the alkyl groups and molecular separations during the hydrolytic polycondensation have particular significance in the modification of monoclinic tetragonal transformation of the resultant ZrO₂. Tetragonal phase can also be stabilized by copolymerization of ZrO₂ with SiO₂ producing tough ceramic materials.     

Thermal treatment effect on the optical properties of ZrO2 thin films deposited by thermionic vacuum arc

This paper shows the ex situ thermal treatment effects of the ZrO₂ thin films obtained by TVA (thermionic vacuum arc) technique on the optical properties (e.g., transmittance, refractive index and band-gap energy) of ZrO₂ thin films. The crystal structure, surface and optical properties were investigated for ZrO₂ thin films deposited on glass substrates by thermionic vacuum arc (TVA) method. The thermal treatment effect on the optical properties of the thin films was determined. The XRD analysis showed that the deposited ZrO₂ thin films have baddeleyite (monoclinic) and zirconium (hexagonal) structures. The thicknesses and refractive index were determined by interferometric measurements. The thin films were thermal treated at different temperatures (350 °C, 450 °C and 550 °C), and the analysis showed that the optical properties of ZrO₂ deposited thin films were improved by thermal treatment at 450 °C.     

Optical properties of tin diselenide films

SnSe₂ films were deposited on substrates at 300 K by a conventional thermal evaporation technique. The as-deposited films were amorphous and transformed to the crystalline phase on post-deposition annealing above 573 K in an inert atmosphere. The optical properties of the films were investigated, using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the wavelength range 400–2000 nm. The refractive index data fit a single oscillator model with a dispersion parameter 5.149×10^–14 and 5.773×10^–14 eVm² for the amorphous and crystalline films, respectively. The high-frequency dielectric constant of the amorphous films decreased from 9.871 to 7.475 for the crystalline films. The analysis of the spectral behaviour of the absorption coefficient in the intrinsic absorption region revealed an indirect forbidden and a direct allowed transition with energy gaps 0.99 and 2.05 eV for the amorphous films and 0.96 and 2.02 eV for the crystalline films, respectively.     

Thin SiO2–ZrO2Films Prepared from Solutions

Thin SiO₂–ZrO₂films were prepared from ethanolic solutions of Si(OC₂H₅)₄and ZrOCl₂, and their refractive indices were measured. The storage behavior of the solutions and the reactions underlying the film-formation process were studied.     

Metallo-organic compound-based plasma enhanced CVD of ZrO2 films for microelectronic applications

ZrO ₂ films on silicon wafer were deposited by microwave plasma enhanced chemical vapour deposition technique using zirconium tetratert butoxide (ZTB). The structure and composition of the deposited layers were studied by fourier transform infrared spectroscopy (FTIR). The deposition rates were also studied. MOS capacitors fabricated using deposited oxides were used to characterize the electrical properties of ZrO ₂ films. The films showed their suitability for microelectronic applications.     

In situ grown superconducting YBCO films on buffered silicon substrates for device applications

Thin films of YBa₂Cu₃O_7– (YBCO) have been grownin situ on silicon single-crystal (100) substrate by using SrTiO₃ as a buffer layer. The deposition has been carried out by on-axis rf magnetron sputtering method. The deposition condition have been optimized by studying the plasma characteristics and correlating them with the superconducting performance of the film. Films deposited at substrate temperature in the range of 680–700°C from stoichiometric YBCO targets in an argon + oxygen mixture (31) are superconducting and showc-axis epitaxy. Compositional confirmation has been carried out using Rutherford backscattering. Scanning tunneling microscopy of the films reveal formation of well-defined layered structure with some defects in the initial stages ofin situ growth of the films. Films grown on SrTiO₃ substrates have excellent crystalline quality (XRD), transition temperatureT _c0=81 K and the critical current densityJ _c >2×10⁵ A/cm² for unpatterned films at 77 K. On silicon substrates using buffer layers thein situ deposited YBCO films shows a higher transition width andT _c0 is also slightly less (71 K).     

Influence of high temperature processing of sol-gel derived barium titanate thin films deposited on platinum and strontium ruthenate coated silicon wafers

Thin films of barium titanate (BTO) of 200 nm thickness, derived from an alkoxide-carboxylate sol-gel process, were deposited on Pt/Ti and SrRuO₃/ZrO₂-8%Y₂O₃ coated Si wafers. Films with a dense columnar microstructure were obtained by repeated deposition of thin amorphous layers from low-concentrated sols, and crystallization at 800 °C. This method added 10 nm thickness to the crystalline BTO film in each deposition step. The harsh processing conditions had a negative impact on the platinized silicon wafers, where Pt-Si silicides were formed. This led to diffusion of Si into BTO and interfacial silicate formation. The interfacial silicate layer was the cause of deteriorated dielectric and ferroelectric properties of the BTO layer. Use of SrRuO₃/ZrO₂-8%Y₂O₃/Si substrates solved the problem. No diffusion of Si was observed, and BTO films with good dielectric and ferroelectric properties were obtained.     

Characterization of bi-phased Zr2ON2–ZrO2 coatings deposited by RF magnetron sputtering

The aim of this work is to develop zirconium oxynitride coatings by RF magnetron sputtering on silicon substrates. The film properties were analyzed as a function of oxygen flux percentage in two different inert gas atmospheres namely argon and helium. At low oxygen flux percentage, Zr₂ON₂ and ZrO₂ phases are observed from the structural characterization by X-ray diffraction. The atomic ratio of nonmetallic to metallic atoms (N + O)/Zr content varies from 1.22 to 2.03 for zirconium oxynitride films deposited in argon atmosphere and from 1.43 to 2.33 for films deposited in helium atmosphere. The thickness of the film was measured by surface profiler and the growth rate decreases from 11.33 to 5.1 nm/min for films deposited in argon atmosphere and from 7.01 to 3.75 nm/min for films deposited in helium atmosphere with increase in oxygen flux percentage. The films deposited are hydrophobic and the contact angle was measured by contact angle measuring system. Higher surface roughness and maximum contact angle values of 100° and 103° are observed for films deposited in argon and helium atmosphere respectively at low oxygen flux percentage (2.5%). The surface energy of films was calculated by two methods: Owens-Wendt's geometric mean and Wu's harmonic mean approach. The elevated surface energy values were observed with increase in oxygen flux percentage. The stress measurements of the deposited films were done by sin²ψ X-ray diffraction method which depends on the variation of Zr₂ON₂ and m-ZrO₂ phases.