Impact of oxygen vacancies on high-κ gate stack engineering (original) (raw)
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The effect of interfacial layer properties on the performance of Hf-based gate stack devices
Journal of Applied Physics, 2006
The influence of Hf-based dielectrics on the underlying SiO 2 interfacial layer ͑IL͒ in high-k gate stacks is investigated. An increase in the IL dielectric constant, which correlates to an increase of the positive fixed charge density in the IL, is found to depend on the starting, pre-high-k deposition thickness of the IL. Electron energy-loss spectroscopy and electron spin resonance spectra exhibit signatures of the high-k-induced oxygen deficiency in the IL consistent with the electrical data. It is concluded that high temperature processing generates oxygen vacancies in the IL responsible for the observed trend in transistor performance.
Physical model of BTI, TDDB and SILC in HfO2-based high-k gate dielectrics
International Electron Devices Meeting, 2004
The microscopic mechanism of the degradation occurring in HfO2-based high-k/IL dual layer gate insulator has been investigated. The hole-injection-induced release of hydrogen from Si-H terminations causes IL-breakdown. This mechanism accelerates NBTI. Defects due to electron-trapped oxygen vacancies are the origin of trap-assisted tunneling, causing SILC in the electron current and PBTI.
SiO 2 Free HfO 2 Gate Dielectrics by Physical Vapor Deposition
— HfO 2 layers, 25-Å thick, were grown by cyclic Hf sputter deposition and room temperature oxidation steps on chemically oxidized Si(001). Subsequent in situ annealing and TiN deposition yield a high-κ gate-stack for which the original 8-Å-thick SiO 2 layer is eliminated, as confirmed by transmission electron microscopy. Transistors fabricated with this gate-stack achieve an equivalent oxide thickness in inversion T inv = 9.7 Å, with a gate leakage J g = 0.8 A/cm 2. Devices fabricated without in situ annealing of the HfO 2 layer yield a T inv which increases from 10.8 to 11.2 Å as the oxidation time during each HfO 2 growth cycle increases from 10 to 120 s, also causing a decrease in J g from 0.95 to 0.60 A/cm 2 , and an increase in the transistor threshold voltage from 272 to 294 mV. The annealing step reduces T inv by 1.5 Å (10%) but also increases the gate leakage by 0.1 A/cm 2 (30%), and causes a 61 mV reduction in V t. These effects are primarily attributed to the oxygen-deficiency of the as-deposited HfO 2 , which facilitates both the reduction of an interfacial SiO 2 layer and a partial phase transition to a high-κ cubic or tetragonal HfO 2 phase. Index Terms— HfO 2 , high-k dielectrics, interface scavenging, MOSFET, physical vapor deposition (PVD), SiO 2 interlayer.
Microelectronic Engineering, 2007
We studied the leakage current mechanism in Ru-gated MOS capacitors with ultrathin Hf x Si 1-x O y gate dielectrics grown by atomic vapour deposition (AVD ® ). The dielectrics were annealed by rapid thermal annealing in oxygen atmosphere at temperatures ranging from 700 to 1000 °C. Temperature dependent current-voltage characteristics exhibit trap-assisted tunneling through the Hf-silicate film annealed at 700 °C. The energy trap level is 2 eV below the dielectric conduction band edge. On the other hand, direct tunneling was found to control the leakage current through gate dielectrics annealed at 800 and 900 °C. Based on a microstructural study, the trap level was attributed to hafnia oxygen vacancies in the Hf-silicate.
Oxygen related defects and the reliability of high-k dielectric films in FETs
2013 International Semiconductor Conference Dresden - Grenoble (ISCDG), 2013
The interaction between oxygen vacancies and dopant atoms in HfO 2 dielectric were studied using first principles total energy calculations. Beside La dopants also the influence of fluorine and nitrogen atoms has been studied. La dopants in the vicinity of a neutral oxygen vacancy (VO) are more stable compared to the La defects far from VO centers. Furthermore, La atoms lead to a shift of the defect states of oxygen vacancies towards the conduction band edge. A similar but more pronounced effect can be observed by fluorine and nitrogen atoms filling the VO centers. These elements may therefore contribute to the reduction of the gate leakage current and improvement of the device reliability.
Interfacial oxide determination and chemical/electrical structures of HfO2/SiOx/Si gate dielectrics
Solid-State Electronics, 2004
An expression that can be used to determine the thickness of an interfacial oxide layer between a high-K dielectric and Si substrate has been derived using the photoelectron intensity ratio of high resolution X-ray photoelectron spectroscopy (HRXPS). Experimental results show the interfacial silicon oxide thickness obtained with the expression fits very well with Ellipsometer measurements. We also studied the formation of an interfacial layer between a high-k HfO 2 film and a Si substrate as well as its thermal stability. The results have revealed that: (i) the interfacial oxide formation requires the existence of thermally energized oxygen in an environment to break the H-Si bonds first for hydrogen terminated Si surface and (ii) the thermodynamic stability of the oxide interfacial layer depends on its initial formation process. The valence band structures of Si, SiO 2 , and HfO 2 have been analyzed using HRXPS and an energy band diagram of HfO 2 /SiO 2 /Si has been constructed.