T. L. Tan

Oxygen rich p-type ZnO thin films using wet chemical route with enhanced carrier concentration by temperature-dependent tuning of acceptor defects

This paper reports the temperature-dependent tailoring of acceptor defects in oxygen rich ZnO thin films, for enhanced p-type conductivity. The oxygen rich p-type ZnO thin films were successfully grown by pulsed laser deposition on silicon substrate at different postdeposition annealing temperatures (500–800 °C). The oxygen rich ZnO powder was synthesized by wet chemical method using zinc acetate dihydrate [Zn(CH3COO)2·2H2O] and potassium hydroxide (KOH) as precursors. The powder was then compressed and sintered to make pellets for pulsed laser deposition system. The x-ray diffraction analysis exhibits an improved crystallinity in thin films annealed at elevated temperatures with a temperature-dependent variation in lattice constants. An analysis of Auger Zn L3M4,5M4,5 peak reveals a consistent decrease in interstitial zinc (Zni) exhibiting its temperature-dependent reversion to zinc lattice sites. Room temperature photoluminescence of the p-type ZnO shows a dominant deep level emission peak at ∼3.12 eV r...

Enhanced indirect ferromagnetic p-d exchange coupling of Mn in oxygen rich ZnO:Mn nanoparticles synthesized by wet chemical method

This paper investigates the ferromagnetism in ZnO:Mn powders and presents our findings about the role played by the doping concentration and the structural defects towards the ferromagnetic signal. The narrow-size-distributed ZnO:Mn nanoparticles based powders with oxygen rich stoichiometery were synthesized by wet chemical method using zinc acetate dihydrate and manganese acetate tetrahydrate as precursors. A consistent increase in the lattice cell volume, estimated from x-ray diffraction spectra and the presence of Mn 2p3/2 peak at � 640.9eV, in x-ray photoelectron spectroscopic spectra, confirmed a successful incorporation of manganese in its Mn 2þ oxidation state in ZnO host matrix. Extended deep level emission spectra in Mn doped ZnO powders exhibited the signatures of oxygen interstitials and zinc vacancies except for the sample with 5 at. % Mn doping. The nanocrystalline powders with 2 and 5 at. % Mn doping concentration were ferromagnetic at room temperature while the 10 at. % Mn doped sample exhibited paramagnetic behavior. The maximum saturation magnetization of 0.05emu/g in the nanocrystalline powder with 5 at. % Mn doping having minimum defects validated the ferromagnetic signal to be due to strong p-d hybridization of Mn ions. V C 2012 American Institute of Physics. [doi:10.1063/1.3679129]

Electromigration-induced extrusion failures in Cu/low-k interconnects

Electromigration experiments were conducted to investigate the thresholds required for electromigration-induced extrusion failures in Cu/low-k interconnect structures. Extrusions at the anode were observed after long periods of void growth. Characterization of failure sites was carried out using scanning and transmission electron microscopy, which showed that failures occurred through delamination at the interface between the silicon-nitride-based capping layer diffusion barrier and the underlying Cu, Ta liner, and interlevel dielectric (ILD) materials. This interface is subjected to near tensile (mode I) loading with a mode mixity angle between 4° and 7°, estimated using finite-element-method analysis, as electromigration leads to a compressive stress in the underlying Cu. Comparisons of the fracture toughness for interfaces between the capping layer and individual underlayer materials indicate that the extrusion process initially involves plane-strain crack propagation. As Cu continues to extrude, the c...

Neon soft x-ray emission studies from the UNU-ICTP plasma focus operated with longer than optimal anode length

The UNU-ICTP plasma focus with a significantly longer than conventional anode can still be a reasonably good neon soft x-ray (SXR) source. The highest average neon SXR yield of 3.3 J was achieved at 3 mbar. The time difference between the two first peaks of the voltage probe signal at the radial collapse phase was found to be inversely related to the SXR yield, i.e. the smaller the time difference, the higher the yield and vice versa. The estimation of average current sheath speeds using the shadowgraphic method coupled with laser and focus peak timing signals showed that the average axial rundown speed is similar to the one obtained for the optimal anode length but the average radial compression speed is decreased significantly. The range of pressure for a good neon SXR yield, however, has become much narrower, making efficient plasma focus operation a very sensitive function of the filling gas pressure for longer than the optimal anode length.

Effect of Ta migration from sidewall barrier on leakage current in Cu/SiOCH low-k dielectrics

Tantalum migration from the anode sidewall barrier was observed in Cu interconnects/SiOCH low-k dielectrics after voltage ramp and constant voltage stress. This phenomenon was found to contribute to leakage current as observed from the current-voltage (I-V) and current-time (I-t) leakage curves. The mechanism of Ta migration is proposed to be due to the ease of Ta oxidation that converts the Ta atoms into ions, which subsequently drift along with the applied electric field and into the SiOCH low-k dielectric. The Ta ionic drift and diffusion into the dielectric led to an increase in leakage current, although the eventual formation of a stable Ta oxide resulted in a leakage saturation.

Delamination-induced dielectric breakdown in Cu/low-k interconnects

Delamination at an interface with the weakest adhesion strength, which is found to be between the SiC(N) capping layer and the SiOCH low- k dielectric, is a potential failure mechanism contributing to time-dependent dielectric breakdown (TDDB) reliability. Bond breaking at that interface is believed to be driven by a field-enhanced thermal process and catalyzed by leakage current through the capping layer based on physical analyses and TDDB measurements. Delamination is found to be easier in terminated tips and corners than in parallel comb lines due to the layout orientation of the Cu lines. Moreover, TDDB activation energy E a can be an indicator of the ease of delamination, whereby a lower E a corresponds to an easier delamination.

Effects of laser energy fluence on the onset and growth of the Rayleigh-Taylor instabilities and its influence on the topography of the Fe thin film grown in pulsed laser deposition facility

The effect of laser energy fluence on the onset and growth of Rayleigh–Taylor (RT) instabilities in laser induced Fe plasma is investigated using time-resolved fast gated imaging. The snow plow and shock wave models are fitted to the experimental results and used to estimate the ablation parameters and the density of gas atoms that interact with the ablated species. It is observed that RT instability develops during the interface deceleration stage and grows for a considerable time for higher laser energy fluence. The effects of RT instabilities formation on the surface topography of the Fe thin films grown in pulsed laser deposition system are investigated (i) using different laser energy fluences for the same wavelength of laser radiation and (ii) using different laser wavelengths keeping the energy fluence fixed. It is concluded that the deposition achieved under turbulent condition leads to less smooth deposition surfaces with bigger sized particle agglomerates or network.

Dielectric degradation mechanism for copper interconnects capped with CoWP

Time-dependent dielectric breakdown (TDDB) reliability of CoWP-capped copper/SiO2 interconnect structures are observed to be better than conventional SiN-capped structures. The activation energy for TDDB (Ea) is higher for CoWP-capped structures (0.66–0.84eV) as compared to SiN-capped ones (0.47eV), and is comparable to the Ea for intrinsic breakdown of SiO2. The TDDB degradation mechanism in CoWP-capped structures is postulated to be dominated by the properties of the intrametal dielectric, as opposed to being influenced by the properties of dielectric cap and associated interfaces. The presence of the dielectric cap lowers the Ea and increases leakage by Poole–Frenkel emission.

Bimodal Dielectric Breakdown Failure Mechanisms in Cu–SiOC Low-

The obtained bimodal VBD failure distribution for Cu/SiOC low-k dielectric is attributed to the two main failure mechanisms that are distinguished by their current-voltage curves and physical failure modes. Type 1 failures show an abrupt increase in leakage current, i.e., an electrical short, without any apparent physical damage. Extrinsic factors such as shorted Cu lines and particle contamination that is already present in between metal lines are believed to be the cause of failure, and this is supported by the temperature independence. On the other hand, Type 2 failure mode follows an intrinsic breakdown mechanism due to its high VBD, temperature dependence of VBD, and visible burn marks, indicating thermal breakdown of the dielectrics in the interconnect system.

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In this paper we observed the characteristics of the electron beam emission from our plasma focus machine filling neon, argon, helium and hydrogen. Rogowski coil and CCD based magnetic spectrometer were used to obtain temporal and energy distribution of electron emission. And the preliminary results of deposited FeCo thin film using electron beam from our plasma focus device were presented.