Intrinsic Threshold Voltage Instability of the HFO2 NMOS Transistors

Bersuker, G.; Sim, J.H.; Park, C.S.; Young, C.D.; Nadkarni, S.; Choi, Rino; Lee, B.H.

doi:10.1109/relphy.2006.251213

Cited by 33 publications

(32 citation statements)

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“…1), thermal ionization energies of these defects differ by 0.2 eV. These values are consistent with 0.35, 0.5 eV activation energies extracted from thermal de-trapping kinetics measurements 11,12,13 . On the other hand, very large de-trapping energies for the V + and V 0 vacancies rule out these species as possible shallow electron traps.…”

supporting

confidence: 87%

“…The results of trap discharging measurements 11,12,13 are consistent with thermal ionization of negatively charged V − and V 2− oxygen vacancies. These results further support the common assumption that oxygen vacancies are likely candidates for intrinsic electron traps in these devices and suggest that negative oxygen vacancies can be responsible for V t instability.…”

mentioning

confidence: 57%

“…To relate these energies to experimental data we distinguish optical absorption/reflection type measurements involving Frank-Condon type (vertical) excitations, and electrical thermal de-trapping measurements, where phonon-assisted electron excitations are accompanied by strong lattice relaxation. We focus on the results of so called de-trapping electical measurements 11,12,13 which are interpreted in terms of thermal ionization of shallow electron traps and demonstrate that the interpretation is consistent with thermal ionization of negative V − and V 2− vacancies.Our periodic non-local density functional calculations were carried out using atomic basis set and a B3LYP hybrid density functional 14 implemented in the CRYS-TAL03 code 15 . This method reproduces band gaps of a range of transition metal oxides 16 and allows us to carry out geometry optimization of defect structures, calculate defect electronic properties and excitation energies within the same method.…”

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confidence: 98%

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confidence: 98%

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Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

Gavartin

Ramo

Shluger

et al. 2006

Applied Physics Letters

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332

191

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We calculated the optical excitation and thermal ionization energies of oxygen vacancies in mHfO2 using atomic basis sets, a non-local density functional and periodic supercell. The thermal ionization energies of negatively charged V − and V 2− centres are consistent with values obtained by the electrical measurements. The results suggest that negative oxygen vacancies are the likely candidates for intrinsic electron traps in the hafnum-based gate stack devices.Hafnium based oxides are currently considered as a practical solution satisfying stringent criteria for integration of high-k materials in the devices in future technology nodes. However, high-k transistor performance is often affected by high and unstable threshold potential 1 , V t , and low carrier mobility 2 . These effects are usually attributed to a high concentration of charge traps and scattering centers in the bulk of the dielectric and/or at its interface with the silicon channel. Although the reported trap densities vary greatly with fabrication techniques, the majority of data point to existence of a specific intrinsic shallow electron centre common to all HfO 2 based stacks while some extrinsic defects, such as Zr substitution in HfO 2 , have also been considered 3 .Oxygen vacancies are dominating intrinsic defects in the bulk of many transition metal oxides including HfO 2 and ZrO 2 , and are thought to be also present in high concentrations in thin films. However, in spite of numerous experimental studies, evidence relating oxygen vacancies to measured characteristics of interface traps in high-k stacks is still mostly circumstantial. Therefore, accurate theoretical characterization of these defects is highly desirable.Previous theoretical calculations of oxygen vacancy in HfO 2 and ZrO 2 reported the ground state properties obtained within local or semilocal approximations to density functional theory (DFT) methods (see 4,5 for a review). This approach, however, significantly underestimates band gaps, which hampers determining energies of defect levels with respect to the band edges and precludes identifying shallow defect states 5,6,7 . As a result, most of the early local DFT calculations (except, perhaps, ref. 8 ) failed to predict unambiguosly negative charge states of oxygen vacancy in HfO 2 . Significant improvement was achieved by Robertson et al. 4,9,10 who used screened exchange approximation to predict vacancy energy levels including V − charge state. However, these calculations were performed using a small periodic supercell and therefore corresponded to extremely high vacancy concentrations. The quality of the functional used is also largely unknown and needs independent verification.In this work we used much bigger supercells and a nonlocal functional to calculate optical excitation and thermal ionization energies of oxygen vacancies in five charge states. To relate these energies to experimental data we distinguish optical absorption/reflection type measurements involving Frank-Condon type (vertical) excitations, and electric...

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supporting

confidence: 87%

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confidence: 57%

mentioning

confidence: 98%

mentioning

confidence: 98%

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Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

Gavartin

Ramo

Shluger

et al. 2006

Applied Physics Letters

Self Cite

332

191

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“…Proper analysis techniques can provide information on charge trapping [32, 70-74, 81, 83, 85] and the effect on device performance, separation of fast and slow trapping processes [20,32,50,54,55,74,86], and bias temperature instability [50,[87][88][89][90].…”

Section: Applicationsmentioning

confidence: 99%

The Pulsed I_d-V_gmethodology and Its Application to the Electron Trapping Characterization of High-κ gate Dielectrics

Young¹,

Heh

Choi

et al. 2010

JSTS:Journal of Semiconductor Technology and Science

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Intrinsic Charge Trapping and Reversible Charge Induced Structural Modifications in a‐Si₃N₄

Hückmann,

Cottom,

Meyer

2023

Advanced Physics Research

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Amorphous silicon nitride (a‐Si3N4) is an essential material for a wide variety of electronic devices, ranging from its use in dielectric layers to its paramount importance for memory applications. In particular, the latter has triggered the interest in charge trapping, for which so‐called N‐ and K‐centers have been identified in experiments – with the atomistic configuration still subject of vigorous debate. Here, the range of hole and electron traps in stoichiometric a‐Si3N4 are revealed by combining atomistic calculations at different levels of theory. The variety of sites within the amorphous network are characterized by introducing a statistical sampling method to quantify the statistical completeness of structural models obtained from a melt‐quench procedure, in combination with a powerful local descriptor inspired by Tolman's angle. Hole trapping is dominated by two‐coordinate N‐centers, resulting in shallow hole traps. In contrast, electron trapping exhibits more nuanced behavior, encompassing both intrinsic polaronic trapping and the previously identified K‐center type trapping (silicon dangling bond *SiN3). Intrinsic polaronic trapping originates from distorted SiN4 tetrahedra. Structural relaxation of the intrinsic polaron sites results in significant elongation of a Si‐N bond and reversible generation of *SiN3 and N3Si‐SiNx ∈ {3, 4} defects.

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Intrinsic Threshold Voltage Instability of the HFO2 NMOS Transistors

Cited by 33 publications

References 2 publications

Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

The Pulsed I_d-V_gmethodology and Its Application to the Electron Trapping Characterization of High-κ gate Dielectrics

Intrinsic Charge Trapping and Reversible Charge Induced Structural Modifications in a‐Si₃N₄

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Intrinsic Threshold Voltage Instability of the HFO2 NMOS Transistors

Cited by 33 publications

References 2 publications

Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

The Pulsed Id-Vgmethodology and Its Application to the Electron Trapping Characterization of High-κ gate Dielectrics

Intrinsic Charge Trapping and Reversible Charge Induced Structural Modifications in a‐Si3N4

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The Pulsed I_d-V_gmethodology and Its Application to the Electron Trapping Characterization of High-κ gate Dielectrics

Intrinsic Charge Trapping and Reversible Charge Induced Structural Modifications in a‐Si₃N₄