ELECTRICAL AND OPTICAL DEFECT SPECTROSCOPY ON HIGH-K MATERIALS P. Scharf1, A. Schmid1, F. Kersten1, T. Nestler1,2, J. Beyer1 and J. Heitmann1 1
Institute of Applied Physics, TU Bergakademie Freiberg, 09599 Freiberg 2 Institute of Experimental Physics, TU Bergakademie Freiberg, 09599 Freiberg
Motivation & Introduction
Samples & Preparation
• shrink of devices for integrated circuits • lower gate oxide thickness required problem: high leakage currents
• MIS- and MIM-samples
solution: replace SiO2 by high-k materials • increased gate capacitance and reduced leakage currents kZrO2= 25 [2] kAl2O3= 7-12 [3] • characterization of defects introduced by high-k materials is important
• Al2O3 by Atomic Layer Deposition (ALD) [4]: => precursors: TMA + H2O => thickness: 5 - 95 nm • ZrO2 by sol-gel-process [5]: => spin coated zirconium n-propoxide => thickness: 10 - 50 nm
transistor, 45 nm technology [1]
Setup
Electrical Characterization • current voltage measurements (IV) => leakage current => temperature range: 25 - 420 K
top contacts dielectric titanium nitride substrate
Optical Stimulation • defect stimulation by tunable infrared laser • additional current flow by excitation of interface or oxide traps
SMU
A
-
• capacitance voltage measurements (CV) => Si surface potential and dielectric field => interface trap density
cryostat
h
EF EVB h
Qit
VBias
Ti
Results
10
-8
10
-9
10
-10
10
-11
10
-12
10
-13
10
-14
24 nm ZrO2 -1.0
-0.8
-0.6
-0.4
-0.2
I A1 exp t I 0 • charge extraction by: Q I dt ~ 1011 cm-2
• strong temperature dependency • possible Poole-Frenkel (PF) behavior (φB = 0.3 - 0.4 eV)
0.0
voltage [V]
• IR laser light leads to trap excitation in ZrO2 • current follows exponential model:
• leakage current is dominated by defects
1x10
10
-7
10
-8
10
-9
10
-10
10
-11
EF
VBias
p-Si
Ti
high-k
TiN
30 nm Al2O3
• leakage current below 1 MV is T dependent and
PF
dominated by defects (PF) • barrier φB ~ 0.4 eV [6] • leakage current at high field is dominated by direct and Fowler-Nordheim tunneling
125°C 100°C 75°C 50°C 25°C
-1
0
1
2
3
oxide field E [MV/cm]
-11
-22
1300nm
-24
5x10
-5x10
-12
laser excitation
1400nm
Ti
TiN
1600nm
1700nm
1 eV
0 Off
Off
Off
-12
3.9 eV
3.2 eV
2.9 eV
Off
-11
0
500
1000
1500
2000
-26
EVak
1500nm
Off
-1x10
Al2O3
4.2 eV
-28
ln (J/E)
10
-7
285K 233K 183K 134K 85K 25K
-6
h
ALD Al2O3
8.8 eV
-6
10 2
10
current density [A/cm ]
-5
current [A]
current density [A/cm²]
10
high-k
φB
ECB
sample
Sol-Gel ZrO2
micrograph of sol-gel film [5]
-30 -32 -34
EF
-36 -38
2500
30 nm Al2O3 0.0
125°C 100°C 75°C
0.5
1.0 1/2
time [s]
oxide field E
50°C 25°C
1.5
2.0
1/2
[(MV/cm) ]
Summary • strong temperature dependency of the leakage current for Al2O3 and ZrO2 samples • leakage current in ZrO2 is dominated by PF emission • leakage current in Al2O3 is dominated by PF emission at fields below 1 MV and tunneling at higher fields
[1] Intel Corporation , www.intel.com, requested on 21.03.2014 [2] J. Robertson, J. Vac. Sci. Technol. B18, 1785 (2000) [3] G. D. Wilk et. al., J. Appl. Phys. 89, 10 (2001)
• principle of laser assisted IV measurement for defect spectroscopy was shown • relaxation time constants and currents depend on the excitation wavelength of the laser • resulting charge density of 1011 cm-2 for the ZrO2 sample
[4] F. Kersten et. al., Energy Procedia 38, ( 2013 ) [5] T. Nestler, Master Thesis, TU Freiberg, (2012) [6] A. Schmid et.al., ECS Transactions, accepted (2014)
M. Sc. Patrick Scharf TU Bergakademie Freiberg | Institut für Angewandte Physik | Leipziger Straße 23 | 09599 Freiberg | Telefonnummer: 03731 / 39-2731 |
[email protected] | DPG-Frühjahrstagung | 30.03. – 04.04.2014
