Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm−1 for the Eg(1) mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm−1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively

Study of interfacial adhesion energy of multilayered ULSI thin film structures using four-point bending test

Adhesion between barrier layers and interconnect metals or dielectrics continues to be a significant concern in the microelectronic industry, with delamination occurring in between the layers leading to device failure. As the sizes of transistors are scaled down to submicron regime, new materials and multilayered thin film structures are applied, which pose a great challenge to quantify the adhesion energy of the interfaces in order to optimize the structures of the multilayered thin films. In this paper, the four-point bending technique is used to quantify the adhesion energy (Gc) between interfaces in multilayered thin film structures for ULSI. An example is presented to demonstrate the applicability of the four-point bending technique for determining the adhesion strength of the SiC/porous polyarylene ether (PAE)/SiC interface. The Gc value obtained is 26.2 J/m2, higher than that of the SiN/PAE interface reported by others, indicating a good adhesion. The resulting fracture surfaces were then characterized by field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) to identify the location of the debonded path. It is found that the crack propagates alternatively between the two PAE/SiC interfaces.Accepted versio

Modulating the optical and electrical properties of all metal oxide solar cells through nanostructuring and ultrathin interfacial layers

The benefits and drawbacks of nanostructuring in all oxide ZnO/Cu2O solar cells were studied. The solar cells were fabricated on fluorine doped tin oxide substrates, with solution processed deposition methods. Both planar ZnO layer and Cu2O were deposited by electrodeposition while ZnO nanorods were grown by chemical bath deposition technique. It is shown that short circuit current (Jsc) of the devices increases with nanostructuring of ZnO due to electrical and optical gains. Despite improving the photocurrent, nanostructuring decreases the Voc of the device due to carrier recombination. The introduction of a thin TiO2 interfacial layer through atomic layer deposition was able to reduce the recombination

The role of ion irradiation in activating silent Raman modes via tuning in plasmonic behaviour and surface disorder of Au/ZnO/Pt NFG system

The perceptible progression of Raman modes of zinc oxide (ZnO) is studied in nanostructures film gap (Au (10 nm)/ZnO (70 nm)/Pt (50 nm)) system with 1.2 MeV Xe ion irradiation. Unattainable silent Raman modes of ZnO turn out to be strongly visible after ion irradiation. The creation of ion-beam–induced lattice disorder, defects, and impurities in a ZnO layer leads to breakdown the translational crystal symmetry that results in the origin of silent modes. The formation of hot-spots in the ZnO layer of the NFG system also supports the enhancement of the intensity of Raman modes. Overall results are attributed to combined effects of lattice disorder, defects, and impurities along with plasmonic effect and explained in the framework of elastic-thermal-spike formation

Analytical modeling of reservoir effect on electromigration in Cu interconnects

Electromigration (EM) in Cu dual-damascene interconnects with extensions (also described as overhangs or reservoirs) ranging from 0 to 120 nm in the upper metal (M2) was investigated by an analytical model considering the work of electron wind and surface/interface energy. It was found that there exists a critical extension length beyond which increasing extension lengths ceases to prolong electromigration lifetimes. The critical extension length is a function of void size and electrical field gradient. The analytical model agrees very well with existing experimental results. Some design guidelines for electromigration-resistant circuits could be generated by the model.Published versio

Structural and optical modification of Ga-doped zinc oxide thin films induced by thermal annealing

236-240<span style="font-size:11.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-bidi-font-family:="" mangal;mso-ansi-language:en-gb;mso-fareast-language:en-us;mso-bidi-language:="" hi"="" lang="EN-GB">Ga doped ZnO (ZnO:Ga) thin films were prepared by the sol-gel spin coating technique. The films are annealed at different temperature varying from 500°C to 900°C in controlled oxygen environment. The effects of annealing temperature on structural, morphological and optical properties of films are investigated. The XRD results show that all deposited films are textured along the (101) direction and exhibits wurtzite phase of ZnO. The AFM images show that the grain size of ZnO films increased with increasing annealing temperature. Red shifting (band gap decreases) of the optical band gap is also observed on increasing the temperature. The observations are explained on the basis of stress and grain growth induced by thermal annealing.</span

Modification of Ta/polymeric low-k interface by electron beam treatment

Polymeric dielectric, porous polyarylene ether (PAE), was introduced in the Cu damascene structures because of its low dielectric constant to reduce resistance-capacitance (RC) delay. One of the requirements of a low-k material includes its good adhesion to the other interconnect materials. In the present study, the adhesion energy (Gc) of the barrier layer Ta/PAE interface was quantitatively measured by a four-point bending technique. The obtained Gc value of the pristine Ta/PAE interface was 5.9 ± 1.1 J/m2. If the PAE was subjected to electron-beam (EB) treatment with low dose (20 μC/cm2) prior to Ta deposition, Gc value increased to 8.1 ± 0.5 J/m2. However, with high-dose (40 μC/cm2) EB treatment, Gc value reduced to 4.0 ± 0.6 J/m2. The adhesion improvement and degradation induced by low- and high-dose EB were correlated to the increase and reduction of the amount of C–Ta bonds at the Ta/PAE interface, respectively. The phenomena were further studied by X-ray photoelectron spectroscopy analysis.Published versio

Effect of electron beam treatment on adhesion of Ta/polymeric low-k interface

Reliability of the Cu/low-k structure is a serious concern since the metal/dielectric interface is generally weak. The adhesion of the Ta/polyarylene ether interfaces with and without electron beam (EB) treatment was investigated by four-point bending test, x-ray photoelectron spectroscopy, and density functional theory. Higher adhesion energy (Gc) was achieved with low-dose EB treatment, attributed to the strong Ta-arene interaction. However, high-dose EB breaks the aromatic rings partially, resulting in fewer available sites for Ta-arene bonding, leading to lower adhesion. It is suggested that the amount of carbon atoms involved in bonding with the metal is the key to improve the Ta/polymer adhesion.Published versio

Reservoir effect and the role of low current density regions on electromigration lifetimes in copper interconnects

Electromigration (EM) in copper dual-damascene interconnects with extensions(also described as overhang regions or reservoirs) in the upper metal (M2) were investigated. It was found that as the extension length increases from 0 to 60 nm, the median-time-to-failure increased from 50 to 140 h, representing a ∼200% improvement in lifetimes. However, further increment of the extension length from 60 to 120 nm did not result in any significant improvement in EM lifetimes. Based on calculations of current densities in the reservoir regions and recently reported nucleation, void movement, and agglomeration-based EM phenomena, it is proposed that there is a critical extension length beyond which increasing extension lengths will not lead to longer EM lifetimes.Published versio