B.J. O'Sullivan

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.

Interface states and Pb defects at the Si(100)/HfO2 interface

Defects present at the Si(100)/HfO 2 interface are analyzed using a combination of electron spin resonance (ESR) and frequency-dependent impedance analysis. The 3.4 nm HfO 2 layers were formed by injection metalorganic chemical vapor deposition on boron-doped silicon (100) substrates. ESR spectra indicate the presence of P b 0 defects ((5.0 ′ 0.4) × 10 1 2 cm - 2 ), while analysis of the low-frequency (20 Hz) capacitance-voltage (CV) response indicates a defect density of (5.8 ′ 1.1) X 10 1 2 cm - 2 , between 0.1 and 0.56 eV above the valence bandedge (E v ), with the peak density located at E v + 0.28 eV. Analysis of conductance data reveals an interface state density of (8.4 ′ 2.1) X 10 1 2 cm - 2 , with a peak density observed at E v + 0.27 eV. These results provide a link between the density of P b centers measured by ESR, and the electrical active defects measured from CV and conductance analysis. This provides an explanation for the nonideal, frequency-dependent features in the region between accumulation and strong inversion for high-K MOS structures.

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.

Characteristics of tantalum pentoxide dielectric films deposited on silicon by excimer-lamp assisted photo-induced CVD using an injection liquid source

Abstract We report the physical and electrical characteristics of the first tantalu pentoxide dielectric films as deposited by the new technique of low pressure ultraviolet-assisted injection liquid source (UVILS) chemical vapour deposition (UVILS-CVD) using the precursor tantalum tetraethoxy dimethylaminoethoxide (Ta(OEt) 4 (dmae)). The films as deposited exhibit high leakage currents due to carbon impurities. Significant porosity is found at deposition temperatures below 350°C. Conventional CV characteristics are exhibited by thick (200 A to 1000 A) as-deposited films, with dielectric constants of 17.4 to 24.