ELECTRICAL AND OPTICAL DEFECT ...

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Summary. • strong temperature dependency of the leakage current for Al. 2. O. 3 and ZrO. 2 samples. • leakage current in ZrO. 2 is dominated by PF emission.
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