Q. Fang

Spectroscopic ellipsometry characterization of nitrogen-incorporated HfO2 gate dielectrics grown by radio-frequency reactive sputtering

Spectroscopic ellipsometry with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of nitrogen-incorporated HfO2 films on Si(100) substrates grown by radio-frequency reactive sputtering using different N2∕(N2+O2+Ar) gas ratios from 20% to 50%. Excellent agreement has been found between the experimental and the simulated spectra, in which an empirical dielectric dispersion relation based on Tauc-Lorentz model has been successfully adopted. Increases in the refractive index n and the extinction coefficient. k, with increases in nitrogen-incorporation content are observed due to the nitrogen-incorporation-induced higher packing density. The change of the complex dielectric functions and reduction in the optical band gap with an increase in nitrogen concentration resulting from the effect of the nitrogen-incorporation on the structure are discussed in detail.

Investigation of TiO2-doped HfO2 thin films deposited by photo-CVD

Abstract TiO 2 -doped HfO 2 thin films, as potential replacements for SiO 2 as high- k gate dielectric material, have been grown by photo-induced CVD using 222 nm excimer lamps at a temperature of 400 °C. Vaporised titanium isopropoxide and hafnium (IV) tetra- t -butoxide were used as the precursors. Films from approximately 45–70 nm in thickness with refractive indices from 1.850 to 2.424 were grown with various Ti:Hf ratios. The as-deposited films were found to be amorphous by X-ray diffraction when the Ti/(Ti+Hf) value was up to 33%, while the crystalline TiO 2 anatase phase formed when the Ti/(Ti+Hf) was 41%. We also found that the refractive index increased sharply when the Ti/(Ti+Hf) was over 25%. Fourier transform infrared spectroscopy, XPS and TEM were also used to monitor as well as the presence of Ti, interface and microstructure of the films on Si-substrate. The effect of UV-annealing on the electrical properties of these films will also be discussed.

Development of an electrically tuneable Bragg grating filter in polymer optical fibre operating at 1.55 µm

We present a thorough study on the development of a polymer optical fibre-based tuneable filter utilizing an intra-core Bragg grating that is electrically tuneable, operating at 1.55 νm. The Bragg grating is made tuneable using a thin-film resistive heater deposited on the surface of the fibre. The polymer fibre was coated via the photochemical deposition of a Pd/Cu metallic layer with the procedure induced by VUV radiation at room temperature. The resulting device, when wavelength tuned via Joule heating, underwent a wavelength shift of 2 nm for a moderate input power of 160 mW, a wavelength to input power coefficient of -13.4 pm mW-1 and time constant of 1.7 s-1. A basic theoretical study verified that for this fibre type one can treat the device as a one-dimensional system. The model was extended to include the effect of input electrical power changes on the refractive index of the fibre and subsequently to changes in the Bragg wavelength of the grating, showing excellent agreement with the experimental measurements.

Electrical property improvements of yttrium oxide-based metal-insulator-metal capacitors

We investigate the effects of the thickness reduction and specific postannealing treatments in order to improve the electrical properties of yttrium oxide-based metal-insulator-metal (MIM) capacitors. The films were grown on Si∕TiSi2∕TiN substrates at 350°C by a low temperature process (pulsed liquid injection plasma-enhanced metal organic chemical vapor deposition). Although the thickness reduction leads to an increase of the capacitance density, the other electrical characteristics (the voltage linearity, the leakage currents, and the voltage breakdown) are seriously deteriorated due to the augmentation of the electric field. Low thermal budget annealing posttreatments (⩽450°C) were carried out in a gas flux (Ar, O2, and H2) and under an ultraviolet (UV) radiation (O2 and N2). We demonstrate that the UV-O2 annealing treatment is particularly efficient in improving the voltage linearity, the leakage currents, and the electric field breakdown. The improved electrical properties after the UV-O2 annealing c...

Photoemission study of the interaction of a Pr 2 O 3 overlayer with Si(100) as a function of annealing temperature

A layer of Pr2O3 with a thickness of about 20 A was grown on Si(100) at room temperature by evaporating Pr in an oxygen ambiance. The interaction of the Pr2O3 overlayer with Si(100) has been investigated in situ after annealing at different temperatures by means of X-ray photoelectron spectroscopy (XPS). The Pr2O3 deposition enhances the oxidation rate of the substrate. The silicon atoms can easily diffuse from the substrate into the Pr2O3 layer, forming a Pr-O-Si silicate as well as SiO2. Annealing facilitates the diffusion of the silicon atoms, leading to the continual growth of the silicate. The intensity of Pr2O3 decreases at temperatures over 590 K and the silicate becomes dominant after annealing at 790 K. Angle-dependent XPS taken after annealing at 1090 K indicates that the silicate moves to the top surface. The amount of SiO2 remains almost constant during annealing.

Electrically tunable Bragg gratings in single-mode polymer optical fiber

We present what is to our knowledge the first demonstration of a tunable fiber Bragg grating device in polymer optical fiber that utilizes a thin-film resistive heater deposited on the surface of the fiber. The polymer fiber was coated via photochemical deposition of a Pd/Cu metallic layer with a procedure induced by vacuum-ultraviolet radiation at room temperature. The resulting device, when wavelength tuned via joule heating, underwent a wavelength shift of 2 nm for a moderate input power of 160 mW, a wavelength to input power coefficient of -13.4 pm/mW, and a time constant of 1.7 s(-1).

Grating based devices in polymer optical fibre

We describe recent research into devices based on fibre Bragg gratings in polymer optical fibre. Firstly, we report on the inscription of gratings in a variety of microstructured polymer optical fibre: single mode, few moded and multimoded, as well as fibre doped with trans-4-stilbenmethanol. Secondly, we describe research into an electrically tuneable filter using a metallic coating on a polymer fibre Bragg grating. Finally we present initial results from attempts to produce more complex grating structures in polymer fibre: a Fabry-Perot cavity and a phase-shifted grating.

Interface of tantalum oxide films on silicon by UV annealing at low temperature

Abstract In previous work, we have grown 4–10 nm Ta 2 O 5 films by photo-induced chemical vapour deposition (photo-CVD) using a special precursor injection system, which exhibited leakage currents as low as 2.19×10 −7 A/cm 2 at 1 MV/cm. However properties of these films are known to deteriorate with decreasing film thickness. UV annealing at low temperatures using an excimer UV source can improve the electrical properties of these films dramatically. In this paper, tantalum pentoxide thin films with thicknesses of approximately 40 nm grown by photo-CVD have been annealed at low temperature using an excimer UV lamp. Film properties have been characterised using ellipsometry, Fourier transform infrared spectroscopy, UV spectrophotometry, capacitance–voltage and current–voltage techniques. After UV annealing, improved leakage current densities as low as 4.0×10 −8 A/cm 2 at 1 MV/cm, and breakdown fields higher than 3.0 MV/cm can be achieved. Investigation of the interfacial SiO x layer formed during deposition and after UV annealing by X-ray photoelectron spectroscopy and TEM reveals that thickness increases with UV annealing time and that the suboxides in the film and at the interface are converted into stoichiometric oxide, leading to an improvement of the electrical properties.

Optical characterization of high-k dielectrics HfO2 thin films obtained by MOCVD

The optical properties of a set of high-k dielectrics HfO2 thin films obtained by two different modified metal organic chemical vapour deposition (MOCVD) techniques were studied using spectroscopic ellipsometry (SE). HfO2 thin films with thickness varying from 10-40 nm were formed over a range of temperatures (300-425°C). After deposition the sample were annealed by Rapid Thermal Annealing (RTP) at 800°C in an oxygen/argon ambient and UV annealing at 400°C in oxygen. The films were analysed physically using XRD and FTIR. The XRD results show that as-deposited HfO2 films microstructure strongly depends on deposition temperature. Both polycrystalline (T>365°C) and amorphous films (T<320oC) were formed. The polycrystalline structure is identified as monoclinic. The SE results demonstrate that as-deposited amorphous HfO2 thin films have a high degree of porosity. After annealing at 800oC in oxygen and in nitrogen ambient, due to the solid phase crystallisation, as-deposited amorphous HfO2 thin films become crystalline and the film porosities are strongly reduced. In addition, an increase of the refractive index and a decrease of the film thickness are also obtained. Optical properties of the as-deposited polycrystalline HfO2 are also improved after annealing and an increase of the refractive index and a decrease of the film thickness is also obtained.