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First Principles Studies on High-k Oxides and Their Interfaces with Silicon and Metal Gate. Feng Yuan Ping ( 冯元平 ) Department of Physics National University of Singapore email@example.com. www.mrs.org.sg. G. S. D. Outline. Introduction Oxygen vacancy in HfO 2 and La 2 Hf 2 O 7
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Feng Yuan Ping (冯元平)
Department of Physics
National University of Singapore
HK OxideWhy High-k oxides ?
Rober Chau, Intel
Wang et al. APL 78, 1604 (2001)
Wang & Ong, APL 80, 2541 (2002)
Among other problems, oxide has too many charge traps, and the threshold voltage (Vth) shifts from CMOS standards.
Power law shift!
Time evolution of threshold voltage Vthunder static and dynamic stresses of
different frequencies, for (a) n-MOSFET, and (b) p-MOSFET. The Vthevolution
has a power law dependence on stress time.
C. Shen, H. Y.Yu, X. P. Wang, M. F. Li, Y.-C. Yeo, D. S. H. Chan, K. L. Bera, and D. L.
Kwong, International Reliability Physics Symposium Proceedings 2004, 601.
Formation energies for (a) interstitial H and H2 molecules, and (b) the VO-H complex.
J. Kang et al., APL, 84, 3894 (2004).
J. Kang, E.-C. Lee and K. J. Chang, PRB, 68, 054106 (2003)
Vg > 0
Vg < 0
(b)Charge Trapping Mechanism
Negative bias for p-MOSFET
Holes are injected to HK
V0 V+ (meta-stable) V++
Positive bias for n-MOSFET
Electrons are injected to HK
V0 V- (meta-stable) V--
In both cases, when the gate bias is removed,
no charges are injected to HK,
all charges in the O traps will be de-trapped,
the gate dielectric remains neutral
Experimental and simulation results for n-MOSFET
A. S. Foster, et al. PRB 65, 174117 (2002)
Formation energy for neutral vacancy: 9.36 eV (O3) & 9.34 eV (O4)
Present calculation: 9.33 eV (relative to O atom)
X. P. Wang et al. VLSI2006
Charge trapping induced Vth shift under constant voltage stress for HfO2, HfLaO with 15% and 50% La gate dielectric NMOSFETs.
Work function of several elemental metals in vacuum, on a scale ranging from the positions of the conduction band to the valence band of silicon.
Metal work functions are generally dependent on the crystal orientation and on the underlying gate dielectric.
Very small lattice mismatch (<2%)
Supercells for the Ni-m-ZrO2 interfaces,
The interface is formed using c-ZrO2(001) and fcc Ni(001) surfaces.
Spin resolved and atomic site-projected density of states (PDOS) for (a) Ni-Pt-ZrO2 interface and (b) Ni-Al-ZrO2 interface, with half monolayer of metal insertion. The PDOS for the Ni in the bulk region (Ni-bulk), interface metal m (Pt or Al), interface oxygen (O-Int.), and oxygen in the bulk region (O-bulk) are shown.
Average electrostatic potential at the cores (Vcore) of Ni (filled dark circle) and Zr (open circle) as a function of the distance from the interface for Ni-m-ZrO2 interfaces (m= Au, Ru, Ti) with half monolayer metal insertion.
Breaks were introduced in the vertical axis (Vcore) between - 41 eV and -36 eV.
Range of tuning: 2.8 eV!
n-SBHs of Ni-m-ZrO2 interfaces are shown as a function of electronegativity (Mulliken scale) of m. The straight line is a least-squares fit to data points shown in filled squares (Al and W were not included).
Work functions of Ni(001) with half monolayer of metal m coverage are shown as a function of electronegativity (Mulliken scale) of m. The straight line is a least-squares fit to data points shown in filled squares.
Ni m OMechanism?
Penetration of electronic density of the gap states into the ZrO2 of Ni-m-ZrO2 interfaces. Position of the surface oxygen is set to z = 0 Å.
3.2Interface bonding dependent SBH: experimental evidence (in-situ XPS)
Afanas'ev et al. JAP 91, 3079 (2002).
Y F Dong Physics Department, NUS
Y Y Sun Physics Department, NUS
S J Wang Institute of Materials Research & Engineering
A Huan Institute of Materials Research & Engineering
M F Li Dept of Electrical & Computer Engineering, NUS Institute of Microelectronics