A comparative capacitance voltage method is used to investigate the equivalent thickness reduction during post metallization annealing of thermally grown ultrathin (∼15-27 Å) oxides. It is found that a double layered dielectric consisting of a thin Al2O3—SiO2 sandwich is appropriate to describe both the increased capacitance and the nearly unaltered current after anneal. It is further shown that the impact of initial thickness and method of growth — in a conventional furnace or by rapid thermal oxidation — on the equivalent thickness reduction is negligible.

We directly observed self-control crystallization of epitaxial BaTiO3 films during alternate depositions of BaO and TiO2. When TiO2 (or BaO) was supplied excessively, surface crystallinity and smoothness degraded due to three-dimensional (3D) growth. However, when the following BaO (or TiO2) was supplied onto the rough TiO2 (or BaO) surface, the surface smoothness was recovered drastically. It was found that a single phase BaTiO3 film grew by repeating the alternate deposition cycle of excessive supply of both BaO and TiO2. The mechanism of this phenomenon was discussed.

In this paper we report the fabrication and characterization of Ag/(Ba,Sr)TiO3 /LaNiO3/LaAlO3 capacitors. All the films, including the top (silver) and bottom (LaNiO3) electrodes, were deposited using a pulsed laser deposition technique. The electrical and dielectric properties of (Ba,Sr)TiO3 capacitors were found to improve significantly by means of silver doping. For example, the leakage current density of a Ag/Ag-doped-(Ba,Sr)TiO3 /LaNiO3/ capacitor was about an order of magnitude lower and dielectric constant was ∼40 % higher than that of a Ag/(Ba,Sr)TiO3 /LaNiO3/capacitor over a range of biases. The improvement in the electrical properties of (Ba,Sr)TiO3 films is believed to be caused by a double role of silver. The first one is associated with the reduced oxygen vacancies due to improved oxygenation of BST films in presence of silver and the second one is associated unpinning effect of domain walls again in presence of silver.

Tantalum oxide films were grown by chemical vapor deposition using an alternating supply of tantalum pentaethoxide and ammonia. The supply of one source was followed by a purge with argon gas before introducing the other source onto the substrate in order to prevent gas-phase reactions. At substrate temperature between 250-275 °C the film growth depended only on the number of source supply cycles (0.15 nm/cycle) and did not depend on the substrate temperature nor supply time of the sources. As-deposited films were amorphous, however, were crystallized after annealing at 800 °C in oxygen atmosphere by rapid thermal process. Annealed films showed increased dielectric constant and decreased leakage current density, which were 13.3 and 6.6 μA/cm2 at 1 MV/cm, respectively, for a 15-nm-thick film after annealing at 800 °C for 10 minutes.

The effects of vacuum and inert gas annealing of ultra-thin (20Å) CVD Ta2O5 films deposited on Si substrates, with and without oxynitride interface layer, on the Ta2O5/Si interface stability were examined extensively by means of in-situ X-ray Photoelectron Spectroscopy (XPS), ex-situ Time-of-Flight Secondary Ion mass Spectrometry (ToF-SIMS), and Temperature Programmed Reaction (TPR). When annealed to 680 °C for up to 50 min, changes in ∼ 20Å Ta2O5 films formed on Si(100) are negligible, but annealing to 820 °C for 10 min in vacuum, Ar or N2 produces major chemical restructuring. SiO is formed at the Ta2O5 - Si(100) interfaces and becomes incorporated into the tantalum oxide. A reduced form of Ta, attributed to TaSix, forms at the buried interface. Extending the annealing time to 20 min produces no further changes. SiO desorbs during annealing at 1000 °C. Nitriding Si prior to forming the Ta2O5 film deposition inhibits these processes.

We have fabricated very thin TiO2 film (Teq∼20Å) by RTP oxidation of sputtered Ti in NO ambient on nitrogen passivated Si substrates. The leakage current is about two orders magnitude lower than SiO2 of identical Teq. Results show that NO passivation layer prior to sputtering is critical in reducing the leakage current. XPS results show that the temperature RTP NO oxidation of sputtered Ti is very important for achieving high quality TiO2 films. high oxidation temperature an SiO2 layer is formed at the interface between TiO2 and Si and the leakage current is approaching to that of SiO2.

The thermal and chemical stability of thin CVD iridium films deposited on thin CVD tantalum pentoxide (Ta2O5) films on Si(100) have been investigated by means of in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Angle Resolved XPS (ARXPS). It was found that upon annealing in vacuum at 800 °C for more than 1 min, tantalum oxide at the Ir-Ta2O5 interface was decomposed and formed metallic tantalum which diffused through Ir, while changes in iridium film itself were negligible. When annealed at 750 °C within 15 minutes, intermediate partially oxidized Ta was formed and coexisted with metallic and oxidized Ta. A portion of metallic Ta near Ir-vacuum interface was subsequently oxidized when the films were exposed in air.

In this paper, we report the effect of vacuum ultraviolet (VUV) annealing of tantalum oxide films deposited on Si (100) and quartz at room temperature by photo-induced chemical vapour deposition using excimer lamps. The influences of annealing pressure and temperature on the structural and optical properties have been studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR) and UV spectrophotometry. Under optimum annealing conditions, the refractive index of the films was found to be around 2.15, while a dielectric constant of 24, a breakdown field of 2.3 MV/cm and an optical transmittance in the visible region of the spectrum greater than 85% were obtained.

As deposited tantalum pentoxide (Ta2O5) films are amorphous. The films will remain amorphous after O2 or N2O plasma annealing at low temperature. High temperature annealing will produce polycrystalline films where grain boundaries can generate leakage current. Previously, we have shown that N2O plasma annealing is superior to O2 plasma annealing in terms of leakage current reduction for AI/Ta2O5/Si capacitors. However, for TiN/Ta2O5/Si capacitors, the leakage current tends to be higher at low bias voltage for N2O plasma annealing compared to O2 plasma annealing. By adding an 02 plasma annealing step and then comparing TiN/Ta2O5/Si capacitors with two step O2/N2O plasma annealing with respect to similar structures with two step O2/O2 plasma annealing, it can be easily seen that TiN/Ta2O5/Si capacitors with two step O2/N2O plasma annealing have lower leakage current compared to similar structures with two step O2/O2 plasma annealing throughtout the voltage range tested.

The characterisation of the physical and chemical properties of tantalum pentoxide (Ta2O5) films, deposited on silicon using a newly developed low temperature deposition technique - ultraviolet assisted injection liquid source chemical vapour deposition (UVILSCVD), is reported. The effect of deposition parameters including substrate temperature, oxidising agent (N2O) flow, precursor carrier gas (Ar) flow, number of drops of precursor injected and precursor solution concentration is discussed. Spectroscopic ellipsometry (SE) was used to determine the refractive index and thickness of the Ta2O5 films. The film thickness was observed to increase with temperature, number of injected drops and precursor solution percentage, while the refractive index was found to be most sensitive to temperature. SIMS measurements showed good agreement with extracted thickness values. Fourier transform infrared spectroscopy was used to identify and monitor Ta2O5 (pentoxide), TaO2 and TaO (suboxide) formation via curve fitting analysis of spectral features. Results showed increased suboxide formation as a function of increasing pressure and as a function of decreasing N2O flow, precursor solution concentration and number of drops injected. The summation of the areas under peaks characteristic of the tantalum-oxygen bonding correlated well with the thicknesses determined by spectroscopic ellipsometry. The FTIR spectra revealed a dramatic increase in the proportion of suboxide in the absence of the oxidising gas.

The gate tunneling current in ultrathin gate dielectric NMOSFETs with positive gate bias is due to the tunneling of electrons from the conduction and valence bands of the substrate. Valence-band electrons tunnel from the substrate of NMOS devices when the valence-band edge in the substrate rises above the conduction-band edge in the substrate. This paper reports experimental trends in the contribution of valence-band electrons tunneling to the gate current of NMOSFETs with gate oxides composed of pure SiO2. The large gate tunneling current can be reduced by replacing the conventional SiO2 gate dielectric with alternative dielectrics with larger dielectric constants. This paper reports the effect of replacing SiO2 with alternative dielectrics on the contribution of valence-band electron tunneling to the gate current. Simulations are carried out for composite SiO2/Ta2O5 gate dielectric structures.

Ba0.5Sr0.5TiO3 (BST) is one of the high-k candidates for replacing SiO2 as the gate dielectric in future generation devices. The biggest obstacle to scaling the equivalent oxide thickness (EOT) of BST is an interfacial layer, SixOy, which forms between BST and Si. Nitrogen (N2) implantation into the Si substrate has been proposed to reduce the growth of this interfacial layer. In this study, capacitors (Pt/BST/Si) were fabricated by depositing thin BST films (50Å) onto N2 implanted Si in order to evaluate the effects of implant dose and annealing conditions on EOT. It was found that N2 implantation reduced the EOT of RF magnetron sputtered and Metal Oxide Chemical Vapor Deposition (MOCVD) BST films by ∼20% and ∼33%, respectively. For sputtered BST, an implant dose of 1×1014cm−;2 provided sufficient nitrogen concentration without residual implant damage after annealing. X-ray photoelectron spectroscopy data confirmed that the reduction in EOT is due to a reduction in the interfacial layer growth. X-ray diffraction spectra revealed typical polycrystalline structure with (111) and (200) preferential orientations for both films. Leakage for these 50Å BST films is on the order of 10−8 to 10−5 A/cm2—lower than oxynitrides with comparable EOTs.

A large-area pulsed laser deposition (PLD) technique was used to uniformly grow tantalum pentoxide (Ta2O5) films on silicon wafers of 75 mm diameter. A KrF excimer laser beam was focused onto a 90 mm diameter Ta2O5 target to induce its ablation in oxygen gas ambient. The large-area coverage was obtained by rastering the laser beam over the radius of the rotating target, while the substrate was rotated simultaneously.

The tantalum oxide films were characterized in terms of uniformity of thickness, composition, structure, and optical properties across the substrate. Average deviations typically below 1% were achieved in thickness, composition, indices of refraction and optical energy band-gap. Identical X-ray diffraction spectra were obtained at the center, middle of radius and edge of the wafers.

Ultrathin silicon oxide/nitride/oxide films on silicon prepared by the usual route -thermal growth of an oxide followed by deposition of a nitride layer by chemical vapor deposition, and finally a reoxidation step - were characterized using isotopic substitution of N and O and depth profiling with sub-nanometric resolution. The redistribution of N and O during the oxide/nitride/oxide film processing was investigated by: i) 15N and 18O depth profiling by means of narrow nuclear resonance, and ii) 16O profiling using step-by-step chemical dissolution associated with areal densities determinations by nuclear reaction analysis. It was observed that the reoxidation step, here performed varying temperature and time, induces atomic transport of O and N thus resulting in oxide/nitride/oxide structures which are not stacked layered ones, but rather silicon oxynitride ultrathin films, in which the N concentration presents a maximum in the bulk and is moderate in the near-surface and near-interface regions.

Reflection-absorption infrared data are presented for H8Si8O12 clusters chemisorbed to Si(100)-2×1 and evaporated gold surfaces. Peak assignments and the implications of the local symmetry imposed upon the cluster by the surface are discussed.

Local electronic states at nanometer-thick silicon oxide and nitride films on Si can be studied on an unprecedented scale using low - energy cathodoluminescence spectroscopy to observe optical transitions of defect bonding arrangements at ultrathin film interfaces prepared by low -temperature plasma deposition. Our results illustrate significant differences in the dependence of specific defects at the oxide versus nitride interfaces on thermal annealing and hydrogenation.

In this paper, we present the results of spectroscopic ellipsometry (SE) studies of Ta2O5 films on Si. Based on these results, we have experimentally determined an effective method for analyzing SE measurements of Ta2O5. A set of CVD-grown Ta2O5 films on silicon – with thicknesses ranging from below 10 nm to approximately 60 nm thick – was investigated by SE in an effort to improve optical film thickness metrology for Ta2O5. The samples were measured across the spectral range 1.5 eV to 6.0 eV by using a well-characterized, high-accuracy rotating-analyzer-type ellipsometer. We present an analysis method, based upon a Tauc-Lorentz parameterization of the optical properties of Ta2O5, that properly describes the SE data. We also demonstrate how optical properties are affected by the presence of an interlayer at the Si/Ta2O5 interface. Our results show small, but meaningful variations in optical parameters resulting from variations in deposition processes and annealing conditions. This work demonstrates that SE can be used successfully to characterize this category of alternate gate dielectrics.

Thin films of high-k dielectric/ferroelectric materials such as BaxSr1−xTiO3 (BST), PbZrxTi1−xO3 (PZT) and SrBi2Ta2O9 (SBT) are currently investigated for integration into high-density CMOS technology. Characterization of these materials by SPM techniques combines imaging of the morphology and microstructure of these films and recording of various electrical parameters at the same local area. Using commercial equipment we have investigated electrical properties such as polarization and leakage current behavior of MOD/MOCVD SBT by applying electrostatic force microscopy (EFM) and conducting atomic force microscopy (CAFM). After applying bias voltages of a few volts across the SBT films between the scanning tip and the lower electrode completely polarized/reverse polarized SBT layers could be observed by EFM. Even single crystallite polarization was imaged. However, unexpectedly some films showed incomplete polarization, which may be caused by local electrical field effects. Images taken by C-AFM displayed enhancement of leakage currents in grain boundary regions, in particular at depressions between adjacent crystallites. The results achieved demonstrate that SPM techniques operated in a variety of imaging and measuring modes, provide a tremendous potential in the elucidation of the microscopic properties of high-k materials.

The objective of this research was to establish a new baseline process for obtaining ultra-thin silicon-oxide gate material in a prototype vertical furnace. Of particular concern was the optimization of a process sequence whereby unpatterned 150 mm diameter wafers ‘see’ the same processing steps prior to gate oxidation as patterned device wafers ‘see’. The figures-of-merit for evaluating process optimization include: i) full-wafer current-voltage (I-V) maps using Hg-gate capacitors; ii) the variation in the current or current density at a given bias voltage, extracted from an I-V map; iii) the variation in electrical oxide thickness that is extracted from full-wafer capacitance-voltage measurements using Hg-gate capacitors; and iv) the variation in optical oxide thickness that is extracted from full-wafer spectroscopic ellipsometry measurements. The results from this research demonstrate that: i) the addition of 1% O2 to the usual N2 gas during the ramp-up cycle in the vertical furnace is necessary to achieve acceptable across-the-wafer oxide-thickness uniformity as determined from both electrical and optical figures-of-merit; and ii) a full-wafer response surface of the current at a given bias voltage is a powerful finger print for process development when the question of variation in as-grown silicon-oxide thickness is at issue.

The N distribution and bonding in five types of oxynitride films have been investigated using SIMS and XPS. Films were grown using N2O, NO-O2 and NH3 gas sources, a remote plasma N source and a Helicon plasma source. The SIMS measurements show different N distributions for each type of sample. XPS measurements show only N≡Si3 bonding in the gas source films, N≡Si3 and O-N-Si2 bonding in the remote plasma sample, and N≡Si3, O-N≡Si2, and O2≡N-Si bonding in the Helicon plasma sample. Angle-resolved XPS measurements show that the O2≡N-Si bonding is deepest in the sample whereas the O-N≡Si2 bonding is associated with a surface oxide.