We present a combined electrical and modeling study to determine the tunneling electron effective mass and electron affinity for HfO 2 . Experimental capacitance-voltage (C-V) and current-voltage (I-V) characteristics are presented for HfO 2 films deposited on Si(100) substrates by atomic layer deposition (ALD) and by electron beam evaporation (e-beam), with equivalent oxide thicknesses in the range 10-12.5 Å. We extend on previous studies by applying a self-consistent 1D-Schrödinger-Poisson solver to the entire gate stack, including the inter-layer SiO x region -and to the adjacent substrate for non-local barrier tunnellingself-consistently linked to the quantum-drift-diffusion transport model. Reverse modeling is applied to the correlated gate and drain currents in long channel MOSFET structures. Values of (0.11 ± 0.03)m o and (2.0 ± 0.25) eV are determined for the HfO 2 electron effective mass and the HfO 2 electron affinity, respectively. We apply our extracted electron effective mass and electron affinity to predict leakage current densities in future 32 nm and 22 nm technology node MOSFETs with SiO x thicknesses of 7-8 Å and HfO 2 thicknesses of 23-24 Å.
High dielectric constant hafnium oxide films were formed by electron beam ͑e-beam͒ evaporation on HF last terminated silicon ͑100͒ wafers. We report on the influence of low energy argon plasma ͑ϳ70 eV͒ and oxygen flow rate on the electrical, chemical, and structural properties of metal-insulator-silicon structures incorporating these e-beam deposited HfO 2 films. The use of the film-densifying low energy argon plasma during the deposition results in an increase in the equivalent oxide thickness ͑EOT͒ values. We employ high resolution transmission electron microscopy ͑HRTEM͒, x-ray photoelectron spectroscopy ͑XPS͒, and medium energy ion scattering experiments to investigate and understand the mechanisms leading to the EOT increase. We demonstrate very good agreement between the interfacial silicon oxide thicknesses derived independently from XPS and HRTEM measurements. We find that the e-beam evaporation technique enabled us to control the SiO x interfacial layer thickness down to ϳ6 Å. Very low leakage current density ͑Ͻ10 −4 A / cm 2 ͒ is measured at flatband voltage +1 V into accumulation for an estimated EOT of 10.9Ϯ 0.1 Å. Based on a combined HRTEM and capacitance-voltage ͑CV͒ analysis, employing a quantum-mechanical CV fitting procedure, we determine the dielectric constant ͑k͒ of HfO 2 films, and associated interfacial SiO x layers, formed under various processing conditions. The k values are found to be 21.2 for HfO 2 and 6.3 for the thinnest ͑ϳ6 Å͒ SiO x interfacial layer. The cross-wafer variations in the physical and electrical properties of the HfO 2 films are presented.
We correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface in metal-oxide-semiconductor (MOS) structures using synchrotron photoelectron emission spectroscopy (PES), cathodoluminescence and high-temperature capacitance-voltage measurements. The influence of the wet chemical pretreatments involving (1) HCl+HF etching or (2) NH4OH(aq) exposure prior to atomic layer deposition (ALD) of Al2O3 were investigated on n-type GaN (0001) substrates. Prior to ALD, PES analysis of the NH4OH(aq) treated surface shows a greater Ga2O3 component compared to either HCl+HF treated or as-received surfaces. The lowest surface concentration of oxygen species is detected on the acid etched surface, whereas the NH4OH treated sample reveals the lowest carbon surface concentration. Both surface pretreatments improve electrical characteristics of MOS capacitors compared to untreated samples by reducing the Al2O3/GaN interface state density. The lowest interfacial trap density at energies in the upper band gap is detected for samples pretreated with NH4OH. These results are consistent with cathodoluminescence data indicating that the NH4OH treated samples show the strongest band edge emission compared to as-received and acid etched samples. PES results indicate that the combination of reduced carbon contamination while maintaining a Ga2O3 interfacial layer by NH4OH(aq) exposure prior to ALD results in fewer interface traps after Al2O3 deposition on the GaN substrate.
We report a new analysis of electron mobility in HfO 2 / TiN gate metal-oxide-semiconductor field effect transistors ͑MOSFETs͒ by investigating the influence of HfO 2 thickness ͑1.6-3 nm͒, temperature ͑50-350 K͒, and oxide charge ͑ϳ1 ϫ 10 11 -8ϫ 10 12 cm −2 ͒ in the high inversion charge region. The fixed oxide charge and interface state densities are deliberately increased using negative-bias-temperature stress, allowing the determination of the Coulomb scattering term as a function of temperature for various oxide charge levels. The temperature dependence of the Coulomb scattering term is consistent with the case of a strongly screened Coulomb potential. Using the experimentally determined temperature dependence of Coulomb scattering term, a model is developed for the electron mobility, including the effects oxide charge ͑ C ͒, high-k phonon ͑ Ph-Hk ͒, silicon phonon ͑ Ph-Si ͒, and surface roughness scattering ͑ SR ͒. The model provides an accurate description of the experimental data for variations in HfO 2 thickness, temperature, and oxide charge. Using the model the relative contributions of each mobility component are presented for varying oxide charge and high-k thickness. Scaling of the HfO 2 physical thickness provided a reduction in the oxide charge and high-k phonon scattering mechanisms, leading to an increase in electron mobility in HfO 2 / TiN gate MOSFETs.
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