Nivedita Biswas

Permittivity enhancement of aluminum oxide thin films with the addition of silver nanoparticles

Multilayer reactive electron-beam evaporation of thin aluminum oxide layers with embedded silver nanoparticles (Ag-nps) has been used to create a dielectric thin film with an enhanced permittivity. The results show a frequency dependent increase of the dielectric constant κ. Overall stack κ of the control sample was found to be 7.7–7.4 in the 1kHz–1MHz range. This is in comparison with κ=16.7–13.0 over the same frequency range in the sample with Ag-nps. Capacitance-voltage and conductance-voltage measurements indicate the presence of charge capture resulting from the Ag-nps. The authors attribute this dielectric constant enhancement to dipole and space charge polarization mechanisms.

Electrical characteristics of metal-oxide-semiconductor capacitors on p-GaAs using atomic layer deposition of ultrathin HfAlO gate dielectric

Properties of ultrathin HfAlO gate dielectrics on sulfur-passivated p-GaAs were investigated using capacitance-voltage and current-voltage measurement techniques and angle-resolved x-ray photoelectron spectroscopy. By optimizing the individual layer thickness of atomic-layer deposited Al2O3 and HfO2 and the postdeposition anneal (PDA) conditions, a low equivalent oxide thickness of 1.6 nm, low gate leakage of 2.6×10−3 A/cm2 at Vg=Vfb−1 V, and excellent frequency dispersion characteristics were obtained. No interfacial As–O bonding and only a small amount of Ga–O bonding were detected after PDA at 500 °C. These results reveal a good quality dielectric interface on GaAs without an additional interface passivation layer.

Work function tuning of nickel silicide by co-sputtering nickel and silicon

Co-sputtered nickel silicide films were evaluated on thin layers of SiO2 gate dielectrics. Work function values ranging from 4.86eV for Ni rich films to 4.3eV were observed at 400°C and were found to be a strong function of the Ni and Si ratio in the films. Phase analysis indicated the presence of different phases of NixSiy for varying concentrations of Ni and Si. High-temperature characteristics, leakage, and change in equivalent oxide thickness values were also evaluated for selected conditions. Rutherford backscattering, x-ray diffraction, Auger electron spectroscopy and high-resolution transmission electron microscopy were used for material analyses.

Evaluation of Fermi level pinning in low, midgap and high workfunction metal gate electrodes on ALD and MOCVD HfO/sub 2/ under high temperature exposure

The workfunction behavior and stability of several candidate metal gate electrodes on HfO/sub 2/ was carefully examined and correlated with processing parameters such as anneal temperatures and oxygen exposures. Transition metals and their nitrides, binary metal alloys and refractory metals were studied on MOCVD HfO/sub 2/ dielectrics of varying thicknesses. Binary low work function Mo-Ta alloys were also investigated on HfO/sub 2/.

Electrical and physical analysis of MoTa alloy for gate electrode applications

This article presents Mo x Ta v as a potential candidate for dual metal complementary metal oxide semiconductor (CMOS) applications. The electrical characterization results of MoTa alloy indicates that the effective work function can be controlled to around 4.3 eV on SiO 2 and is suitable for n-type MOS gate electrode application. The MoTa alloy forms a solid solution instead of an intermetallic compound. We report that the MoTa solid solution can achieve low work function values and is stable up to 900°C. X-ray diffraction results indicated only a single MoTa alloy phase. X-ray photoelectron spectroscopy analysis confirmed that no Mo-Ta compound bonding formed within the MoTa alloy. Moreover, from Auger electron spectroscopy and Rutherford backscattering spectroscopy analysis, MoTa was found to be stable on SiO 2 under high-temperature anneals and no metal diffusion into substrate Si channel was detected. This indicates that Mo x Ta y is a good candidate for CMOS metal gate applications.

Evaluation of nickel and molybdenum silicides for dual gate complementary metal-oxide semiconductor application

Characteristics of NiSi and MoSi via full consumption of undoped silicon layers have been studied. Interaction of nickel (Ni) and molybdenum (Mo) silicides with SiO2 was evaluated in terms of work function and thermal stability. For nickel silicide, the work function values were low for samples annealed at 400 °C even after full consumption of silicon. The work function increased with the anneal temperature and stabilized at 600 °C to close to midgap values. Dielectric interaction as a result of silicide formation was studied using current–voltage characteristics. Low leakage currents in these stacks indicated minimum dielectric damage due to silicided gates. Silicidation of Mo was found to be incomplete as the capacitance–voltage curves were marked with larger EOT values and negative shifts in the flatband voltages even at 700 °C. Auger depth profiling, high resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD) were used for material analysis of the silicided gate stacks.

Characteristics of Ni/Gd FUSI for NMOS Gate Electrode Applications

This letter investigates the work function tuning of nickel/gadolinium (Ni/Gd) fully silicided (FUSI) gate electrodes on HfSiOx dielectrics. It was found that as the percentage of Gd in the Ni/Gd increased from 10% to 30%, the effective work function value after a one-step 450-degC FUSI anneal decreased from 4.75 to 4.35 eV. In addition, the presence of Gd also resulted in lowering of equivalent oxide thickness (EOT) values. The mechanism for a decreased EOT is attributed to the reduction of low-kappa interfacial layers by the presence of Gd in the gate stack. The decrease in work function is attributed to the creation of oxygen vacancies within the high-kappa layer created by the presence of Gd layer.

Influence of oxygen diffusion through capping layers of low work function metal gate electrodes

This letter evaluates Ru and W capping layers for MoTa metal gate electrodes in MOS capacitor applications. The authors report that the oxygen diffusion from the capping layer plays an important role in determining the MoTa alloy effective work function value on SiO/sub 2/. A MoTa alloy metal gate with Ru capping exhibits stable effective work function up to 900/spl deg/C annealing but is not stable with W capping. Auger electron spectroscopy and Rutherford backscattering spectroscopy analyses show minimal oxygen diffusion into MoTa gate stacks with Ru capping while severe oxygen diffusion into the gate is observed with W capping metal after 900/spl deg/C annealing. Current-voltage analysis also demonstrates different barrier heights of MoTa on SiO/sub 2/ with Ru or W capping layer after 900/spl deg/C annealing, confirming the effective work function value change.

Atomic Layer Deposition of Hafnium Dioxide on TiN and Self-Assembled Monolayer Molecular Film

Hafnium dioxide (HfO 2 ) thin films with thicknesses ranging from 20 to 100 A have been grown in a viscous flow reactor using atomic layer deposition (ALD) with tetrakis(dimethylamido)hafnium(IV) and water as the reactants. HfO 2 ALD films are deposited successfully at 200°C on different molecular monolayers. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy analyses show a continuous growth of the HfO 2 layer on the self-assembled monolayer molecules. Electrical properties characterized by current-voltage measurements suggest that three parameters play important roles in determining the physical structure of HfO 2 , namely, the precursor pulse time, the sample exposure time, and the time for purging out an unreacted precursor. ALD conditions for different substrates have been optimized so that excellent electrical properties can be obtained for HfO 2 films on molecules. Transmission electron microscopy of 30 and 60 A ALD HfO 2 on TiN and molecular monolayers shows a continuous deposition of HfO 2 . This process enables the development of a class of molecular electronic devices, solid-state molecular memory devices.

Work function extraction of metal gates with alternate channel materials

The effects of a heterojunction on the effective work function in a metal/high κ gate stack are studied and a new structure developed for the extraction of the work function. It is found that when a Ge/Si heterostructure on silicon is low doped and sufficiently thin, then the work function can be extracted in a manner similar to that on a simple silicon substrate. Modifications to the terraced oxide structure are proposed to remove oxidation effects of the alternate channel materials. The extracted work function of thickness variation of TiN is found to be in agreement with that of TiN on a silicon substrate.