Electron Probe Microanalysis of HfO2 Thin Films on Conductive and Insulating Substrates

Quantitative electron probe microanalysis of highly insulating materials is a complicated problem, partially solved by coating samples with grounded thin conductive layers or using novel scanning electron microscopy (SEM) techniques, such as low-voltage and/or variable pressure SEM. In this work, some problems of quantitative X-ray microanalysis of thin HfO₂ films, in particular the possibility to determine mass thickness correlated to the density of the layer material, are discussed. For comparison, Al₂O₃, Ta₂O₅ and TiO₂ films grown onto both semiconductive Si and insulating quartz substrates were also analysed. All the films studied were synthesized by atomic layer deposition method.     

Time-resolved streak camera system with solid state laser and optical parametric generator in different spectroscopic applications

Apparatus to study time-evolution of emission spectra over very wide time and spectral range is described. Excitation part of the equipment consists of solid state Nd:YAG laser and optical parametric generator. The heart of the detection system consists of spectrograph and streak camera. The significance of optics and electronics built in the system for proper, fast and convenient measurements is underlined. The results of donor-acceptor energy transfer in a rigid polyvinyl alcohol matrix serve here as an example of application our equipment to study complex systems.     

Pressure and temperature dependence of the emission in BaF2:Eu and SrF2:Eu

The 4f⁶5d¹(e)→4f⁷ emission (normal) of Eu²⁺ in SrF₂ and normal and anomalous emissions of Eu²⁺ in BaF₂ are studied as a function of pressure and temperature. Although in BaF₂ both emissions (anomalous and normal) shift with pressure in the same spectral direction (a red shift), the anomalous emission converts to the normal emission when the pressure increases to 33 kbar. Considering the dependence of BaF₂:Eu²⁺ luminescence on the pressure and temperature we have found that spectral transformation takes place due to a smooth pressure-induced level crossing at approximately the same pressure as the phase transition.     

Cr-related centers in Gd3Ga5O12 polycrystals

The luminescence excitation spectra, emission spectra under photo- and X-ray excitation, luminescence decay kinetics and thermostimulated luminescence (TSL) of Gd₃Ga₅O₁₂ garnet (GGG) polycrystalline samples have been investigated. It was established that the spectrum of Cr³⁺ ion emission were present in all TSL peaks. The activation energies of traps that are responsible for appearance of TSL in the region 295-600 K were estimated. It is shown that delocalization of electrons from the Cr³⁺e traps leads to the appearance of thermoluminescence (TL) glow peak at 390 K. The nature of other TSL peaks is discussed. The influence of visible light on the TSL intensity of the preliminary X-ray-irradiated samples is shown.     

High Pressure Spectroscopy of Ti Doped Al2O3 and YAIO3 Host Crystals

We report high-pressure luminescence spectroscopy studies of Ti^3? in Al₂O₃ and YAlO₃. High-pressure luminescence spectra were measured for Al₂O₃:Ti^3? up to 90kbar and for YAlO₃:Ti^3? up to 181 kbar. In both cases, a blue shift of the luminescence peak with pressure was observed and is attributed to an increase in the octahedral crystal-field strength (10 Dq) with pressure. In the case of YAlO₃;Ti^3?, an additional luminescence peak was observed at 181 kbar and below ～ 200 K, and is attributed to a metastable state. The metastability of the ²E excited state was induced by pressure that removes the equivalency of three energy minima of the ²E state coupled to the ? mode.     

Atomic layer deposition of Al2O3, ZrO2, Ta2O5, and Nb2O5 based nanolayered dielectrics

Ta₂O₅, Ta-Nb-O, Zr-Al-Nb-O, and Zr-Al-O mixture films or solid solutions were grown on Si(1 0 0) substrates at 300 °C by atomic layer deposition. The equivalent oxide thickness of Ta₂O₅ based capacitors was between 1 and 3 nm. In Zr-Al-O films, the high permittivity of ZrO₂ was combined with high resistivity of Al₂O₃ layers. The permittivity, surface roughness and interface charge density increased with the Zr content and the equivalent oxide thickness was between 2.0 and 2.5 nm. In the Zr-Al-Nb-O films the equivalent oxide thickness remained at 1.8-2.0 nm.     

Spectroscopic ellipsometry study of the dielectric response of Au-In and Ag-Sn thin-film couples

Optical properties and phase composition of In-Au and Sn-Ag ultra-thin films grown by sequential evaporating and co-depositing of metals in a vacuum were investigated combining X-ray diffraction and spectroscopic ellipsometry methods. The atomic concentration ratios of bilayer and co-deposited samples were the same, i.e. In(Sn):Au(Ag) = 1:2. The XRD patterns indicated creation of AuIn, AuIn₂, Au₃In₂, Au₉In₄ and Ag₃Sn intermetallic compounds at room temperature. The effective complex dielectric functions of the composite layers, , were determined from ellipsometric quantities Ψ and Δ measured in a photon energy range of 0.6-6.5 eV. The free-carrier parameters (unscreened plasma frequency and free-carrier damping) and optical resistivity were evaluated using a semiclassical Drude-Lorentz model of the effective dielectric function. There was noticed a distinct influence of phase composition and surface morphology on the optical constants and conductivity of the samples: ρ_op changed from approximately 15 μΩ cm to 37 μΩ cm for Ag-Sn structures, composed of β-Sn and Ag₃Sn phases, and from 21 μΩ cm to 83 μΩ cm for Au-In multiphase system. Lower resistivity demonstrated diffusive layers formed after deposition of an In(Sn) thin film on the noble metal underlayer.     

Nature of intrinsic luminescence in the glasses of CaO–Ga2O3–GeO2 system

The intrinsic luminescence of glasses of the CaO–Ga₂O₃–GeO₂ system has been investigated. High chemical purity and optical quality glasses, both undoped and doped with transition and rare-earth ions with different compositions, were obtained by high-temperature synthesis. The influences of the basic glass composition, impurities (Cr³⁺, Mn²⁺, Eu²⁺, Nd³⁺, Ho³⁺, Er³⁺, and Ce³⁺) and different kinds of excitation, on the intrinsic luminescence of the CaO–Ga₂O₃–GeO₂ glasses were investigated. The nature and possible mechanisms of the intrinsic luminescence in glasses of this system are discussed. The proposed models of intrinsic luminescence are supported by electron spin resonance spectroscopy.     

Selection of post-growth treatment parameters for atomic layer deposition of structurally disordered TiO2 thin films

Routes to atomic layer-deposited TiO₂ films with decreased leakage have been studied by using electrical characterization techniques. The combination of post-deposition annealing parameters, time and temperature, which provides measurable aluminum–titanium oxide–silicon structures – i.e., having capacitance–voltage curves which show accumulation behavior – are 625 °C, 10 min for p-type substrates, and 550 °C, 10 min for n-type substrates. The best annealing conditions for p-type substrates are 625 °C with the length extended to 30 min, which produces an interfacial state density of about 5–6 × 10¹¹ cm^?2 eV^?1, and disordered-induced gap state density below our experimental limits. We have also proved that a post-deposition annealing must be applied to TiO₂/HfO₂ and HfO₂/TiO₂/HfO₂ stacked structures to obtain adequate measurability conditions.     

Identification of spatial localization and energetic position of electrically active defects in amorphous high-k dielectrics for advanced devices

In this work, we report the use of the conductance transient technique (GTT) to evaluate disordered-induced gap states (DIGS) in gate dielectrics of metal-insulator–semiconductor (MIS) structures. These states are electrically active defects inside the dielectric bulk which are preferentially located at regions near the dielectric/semiconductor interface. Conductance transients occur when the MIS structure is driven from deep to weak inversion, at various frequencies and temperatures, allowing us to obtain contour line maps of defects spatially and energetically distributed inside the dielectric. This method has been applied to evaluate DIGS densities in advanced high-k gate dielectrics, such as HfO₂, Al₂O₃, TiO₂, silicates and other mixtures grown on silicon substrates by atomic layer deposition under different process conditions. Commonly, high DIGS densities involve low interface state densities D_it and vice versa, indicating that there is some kind of interaction or evolution between these two types of defects or traps. An explanation for the dynamics dictating the transformation of interface states to DIGS states is a key point in determining the quality of the dielectric films.