High k gate dielectrics are required for the sub-65
nm MOS structure because the conventional SiO2 film is too thin (e.g.
2 nm) to minimize the tunneling current and the out diffusion of boron from the
gate. A thick layer can be used with the high k material to lower the parasitic
capacitance. Many issues have to be solved before it is acceptable for the
products. In general, there are three types of high k dielectrics:
1. those with 4 < k < 10
such as SiNx;
2. those with 10 < k <
100 such as Ta2O5, Al2O3, ZrO2,
and HfO2; and
3. those with 100 < k such as
PZT.
The type 2 dielectric film has been routinely used
in transistors, such as TFTs. A thick layer is used to prevent the
top-to-bottom metal shortage, which is a killing factor for the yield. The high
k dielectric material is usually used in combination with a high quality
dielectric interface layer to lower the interface density of states. For
example, in the a-Si:H TFT
case, the N-rich SiNx is exclusively used
as the interface layer. Examples on TFTs with the dual gate dielectric
structure (e.g. SiNx/TaOx and two different types of SiNx/SiNx) are shown as follows.
We are researching on new type of high k dielectric
materials using elements throughout the whole Periodical Table. The goals are
to find new high k thin films that have enhanced dielectric constants and low
leakage currents. We are also working on high-k based new devices, such as the
nonvolatile memories where nanocrystals are embedded
in the dielectric layer. .
Nanocrystals Embedded High-k for
Nonvolatile Memories (see Nonvolatile
Memories for more
information)
- nc-ITO Embedded Zr-doped HfO2
A. Birge, C.-H. Lin, and Y. Kuo, “Memory Functions of Nanocrystalline Indium Tin Oxide
Embedded
Zirconium-Doped Hafnium Oxide MOS Capacitors,” JES 154(10) H887 (2007)
- nc-ZnO
Embedded Zr-doped HfO2
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J. Lu, C.-H. Lin, and Y. Kuo, “Nonvolatile Memories Based on Nanocrystalline
Zinc Oxide Embedded Zirconium-doped
Hafnium
Oxide Thin Films,” ECST 11(4), 509-518 (2007).
- nc-Si Embedded Zr-doped HfO2
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J. Lu, Y. Kuo, J. Yan, and C.-H. Lin, “Nanocrystalline Silicon Embedded Zirconium-Doped Hafnium
Oxide High-k Memory Device,” JJAP 45(34) L901 (2006).
- nc-RuOx
Embedded Zr-doped HfO2 and RuZrHfO
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C.-H. Lin, Y. Kuo, and J. Lu, “Influence of Ru Dopant on the Dielectric Properties of Zr-doped HfO2 High-k Thin Film,” ECST 6(1) 121 (2007).
- nc-RuOx
Embedded Zr-doped HfO2 Reliability
TiN/ ZrHfOx/RuOx/ZrHfOx/p-Si
R. Wan, C.-H. Lin, Y. Kuo, and Way Kuo, “Charge Trapping of Ultra-thin ZrHfOx/RuOx/ZrHfOx High-k Stacks,”
IIRW 2007.
Doping
of TaOx and HfO2 films
- Sub 1 nm EOT Zr-doped
HfO2
J. Yan, Y. Kuo, and J. Lu, “Zirconium-Doped
Hafnium Oxide High-k Dielectrics with Subnanometer
Equivalent Oxide Thickness by Reactive Sputtering,” ESL 10(7), H199 (2007).
- Effects on bulk material properties
JES Letters
(Accepted to appear in 2004)
XRD Patterns of TaOx (a) undoped, (b) Al-doped, (c) Si-doped, (d) Ti-doped films, 700°C, 10 Minutes
- Effects on interface layers
Lu, Kuo, Tewg, and
Schueler, Vacuum, 539-547, 2004.
(Courtesy of B. Foran of
SEMATECH)
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J. Lu, Y. Kuo, and J.-Y. Tewg, JES 153(5) G410 (2006). |
Tewg, Kuo, Lu, and Schueler, “Influence of a 5 Å Tantalum Nitride Interface Layer on Dielectric Properties of Zirconium-Doped Tantalum Oxide High-k Films,”
JES 2005.
Kuo, Lu, and Tewg,
JJAP 42 (3), Pt. 2, No. 7A, 2003
ESCA of Ta chemical states of
the deposited TaNx interface layer after 700ºC 10 min O2
annealing.
Kuo, Lu and Tewg, JJAP 42, L769, 2003
- Effects on electric properties
Kuo, Lu and Tewg, JJAP 42, L769, 2003.
AVS
ICMI Meeting, 02/13/02.
k vs. Film Thickness
700°C 10 min annealed
Y. Kuo. SEMATECH, Stacked
Gate Dielectric Meeting Procs.
Y. Kuo, J. Y.
Tewg, and J. Lee. AVS 3rd Natl.
Microelectronics and Interfaces, 133-135, 2002.
Y. Kuo, J. Y. Tewg J. Donnelly, and J. Lee. Proc. 1st Natl. Conf. Semi-conductor Tech., ECS. Vol. 2001-17, 324-327, 2001.
- Decrease of leakage current
Kuo, Lu and Tewg, JJAP 42, L769, 2003.
Leakage vs. Dopant Target Sputtering Power
600°C 60 min annealed
AVS
ICMI Meeting, 02/13/02.
J-E curves of the Zr-doped HfOx films,
including pure HfOx.
J. Yan, Y. Kuo,
W. Luo, et al., IEEE IRW 2.1.1, 2003
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J. Lu, Y. Kuo,
and J.-Y. Tewg, JES 153(5) G410
(2006). |
- Effects on charge trapping VFB, and ∆VFB
Tewg, Kuo, Lu, and Schueler, JJAP 151 (3),
F59-F67, 2004
- Gate electrode effects
Tewg, Kuo, and Lu, “Zirconium-Doped Tantalum Oxide Gate Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten Nitride Gate Electrodes,” JECS 2005.
Tewg, Kuo, and Lu, “Zirconium-Doped Tantalum Oxide Gate
Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten
Nitride Gate Electrodes,” JECS 2005.
Tewg, Kuo, and Lu, “Zirconium-Doped Tantalum Oxide Gate
Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten
Nitride Gate Electrodes,” JECS 2005.
Gate Electrode Material and Annealing Effects on ALD
HfO2
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S. Chatterjee, Y. Kuo,
J. Lu, Microelectron.
- Reliability issues
-
SILC
Applied
voltage generates traps in the oxide, which act as coulombic
scattering centers and as pathways for increased local leakage currents.
Figure
2: (a) Diagram illustrating log(1-[Qo(t)/Qo(0)]) as a function t for different CVS.
(b)The
time dependence of the current density increase observed during constant
voltage stressing @ -2.5 V of 800oC PMA MoN/5nmHfO2/Si
MOS.
Chatterjee,
Kuo, etc., “Effects of Post Metallization Annealing on the Electrical
Reliability of Ultra-thin HfO2 Films with MoN
and WN Gate Electrodes,” 2005 IRPS.
- Time dependent current leakage
Figure 3: Breakdown
phenomena of WN/HfO2 (5 nm)/Si MOS structures during CVS –2.5 V.
Chatterjee, Kuo, etc., 2005
IRPS
- Hysteresis disappear due to breakdown
W. Luo, et al., IEEE IRW 2.1.1, 2003
W. Luo,
et al., IEEE IRW 2.1.1, 2003
Wen Luo, Way Kuo, Yue Kuo,
“Bayesian Approach to Reliability
Projection for High k Dielectric Thin Films,” 2005 IRW proceedings.
For more detailed
information, please see the Publications List.
Graded Gate SiNx Gate Dielectric for a-Si:H TFT
Y. Kuo, JECS, 141(4), 1061, 1994.
Dual SiNx/TaOx
gate dielectric for TFT
Y.
Kuo, JECS, 139(4), 1199, 1992.
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