Transcript Presentation title

Electrical Evaluation of Electron
Traps in Hf-based Gate Stacks
G. Bersuker
C. Young
D. Heh
R. Choi
Pulse Id-Vg Technique
Example
PW
450
Vg
Gate
tp= tr+PW
Vg
400
Gate
350
High-
High-
IL
IL
Id
Id
tp<<τc
tp>τc
Drain Current[A]
tr
Id Degradation
 Id
250
200
150
tp << c
Vg = -1 to 2 V
tp ~ 37 ns
Vg = -1 to 2 V
tp ~ 6 ms
100
50
Note: Time Scale Difference
0
25 30 35 40 45 50 55 60 65
Time [ns]
3 4 5 6 7 8 9 10
Time [ms]
Detectable trapping was not observed until tp  100 s for the
gate stacks in this study
The Vt is calculated as in:
Bersuker et al, 2004 Spring MRS, APL 2005
02/16/05
tp >> c
Ultra-Short pulse measurement allows determination
of the “onset of trapping”
–
•
b)
300
I d
Vt 
 Vg  Vt 
Id
•
a)
Drain Current * EOT[A*nm]
700
600
Chem Ox/3 nm IN HfO2/TiN
Vd = 100mV
500
400
300 EOT =o1.15 nm
N2, 600 C
200
DC
Pulse
100
0
0.0
•
02/16/05
0.4
0.8
1.2
1.6
Gate Voltage [V]
2.0
Drain Current * EOT [A*nm]
Pulse v DC Id-Vg
700
600
Chem Ox/3 nm IN HfO2/TiN
Vd = 100mV
500
400
300
EOT = 1.07 nm
o
NH3, 700 C
200
DC
Pulse
100
0
0.0
0.4
0.8
1.2
1.6
2.0
Gate Voltage [V]
Ramped pulse Id-Vg done with tr = tf = 2 ns and
PW = 35 ns
Pulse Mobility
Closed symbols: NH3 PDA
IN (Inorganic)
OR (Organic)
Open symbols: N2 PDA
200
2
Pulse Mobility [cm /V*sec]
250
150
100
EOT
50
1.15 nm
1.07 nm
0.85 nm
0.81 nm
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Effective Field [MV/cm]
•
02/16/05
Pulse mobility extraction using Pulse Id-Vg in
conjunction with NCSU CVC and Mob2d
Charge Trapping Model
• Fast process: direct resonance tunneling of injected
electrons into the traps
• Slow process: migration of trapped electron to
unoccupied traps
C B
00
V
V
Gate
High-k
High
-
A
A
VV00
Si
SiO22
Electrode
02/16/05
High-k
SiO2
300
20
77K
150K
15
225K
250
298K
200
150
0
PW = 100 s
tr/f =100ns,
PW=100s
50
100 150 200
Time [s]
T= 298-150K
10
5
0
250
0
Vg= 1.8 V
5
10
15
Pulse Time [s]
n
J
 p ( N 0  n ); p 
 ( Et  EF )
t
q
n=N0(1-e-pt)
Trap capture cross-section & density:
02/16/05
σ  E-14 cm2, N0  E14/cm2
Flux
350
tr = t = 100 ns
f
 I d[ A]
Current [A]
Fast Electron Trapping Process
Delta Vt (V)
Slow Electron Trapping Process
0.02
Delta Vt (V)
298K
Fast trapping component
is subtracted
225K
0.01
150K
0
0
0.02
200
400 600 800
Time (sec)
Vgg =1.95V
=1.95V
77K
1000 1200
298K
298K
225K
225K
0.01
0
02/16/05
Vg =1.80V
150K
150K
77K
77K
0
200
400 600 800 1000 1200
Time (sec)
N
 N 1  e 
 pi t
i  a ,b , c
0i
p i   i N0 exp(  Ei / kT )
N0=109–1010 cm-2
Spin Inside the Sphere (e)
Nature of Bulk Traps: O vacancies
1
Zr3+
V– (4)
r =const(r)
0.8
0.6
0.4
0.2
0
0
1
2
3
Radius (A)
O
Hf
V0
Negative oxygen vacancies
Energy: V-  0.5 eV; V-2  0.3 eV; Dimension:  1 nm
02/16/05
4
5
Resonance Injection Points in Pulse
Measurement
Vg = 1.2 V
1.4 V
1.6 V
1.8 V
2.0 V
1.4 nm
2.1 nm
2.8 nm
4
3
2
1
0
Gate Stack Physical Thickness [nm]
•
02/16/05
HfO2-SiO2 offset of 2.3 eV is used for band
alignment (IFIGS model, R. Nemanich, GSEWG
meeting, 02/06)
Electron Trap Profile in High- Layers
50
Interfacial Layer/High-/Anneal ambient
SiO2/MOCVD HfO2/N2
HF-Last/MOCVD HfO2/N2
SiO2/ALD HfO2/N2
30
HF-Last/NH3/ALD HfO2/NH3
12
2
Ntrap [10 /cm ]
40
tr,tf = 100 ns
20
PW = 100 s
10
0
0
1
2
3
4
5
Distance from Gate [nm]
•
•
02/16/05
Electron traps uniformly distributed across the highk film thickness
No significant difference in trap density between
deposition methods and anneal ambients
Frequency Dependent Charge Pumping
measurements
DC I-V
Charge Pumping
•
•
Discharge for 10sec
immediately following
stress, then sense
measurment
Initial CP
...
CP
5 Id-Vg's
between
2-300 sec
with Vt
monitor
Id-Vg
Id-Vg
Id-Vg
CP: Discharge is done immediately after CVS to de-trap any trapped
electrons
DC I-V: Represents DC Id-Vg that are taken intermittently between 0
and 300 seconds
–
02/16/05
Vg
Stress Bias, Vg [V]
Stress Bias, Vg [V]
DisCharge
225-300s
0-2s 2-75s
0 - 300s
10 second discharge at the end of stress cycle
Charge Pumping Energy and Spatial Probing
-6
-5
-4
-3
-2
ALD HfO2
-1
0
1nm SiO2
3
Gate Stack Conduction Bands
Hi- Bulk Traps
1
0.75
0.5
0.25
0
-0.5
0
5
1
F
0
-0.25
10
x(Å)
0
0.25
15
20
Et-Ei (eV)
2
Trap Generation
Region
-1
-2
0.5
12
2 kHz
10
Spatial/energy range probing
by CP at a given frequency
8
x(Å)
6
1 MHz
4
2
0
-0.4
02/16/05
-0.2
0
Et-Ei (eV)
0.2
0.4
Electron Trap Depth profile
70
2
50
10
Nt [10 /cm ]
60
40
1.1nm SiO2/3nm HfO2/TiN
Vstress = 2.4 V
Vamp = 1.4 V
Vbase = -0.7 V
30
–
10
tr, tf = 100 ns
nFET W/L = 10/1 m
0.8
1.0
Probing Depth [nm]
02/16/05
Factors affecting
conversion of
frequency to distance:
–
Initial
After 300s
After 600s
After 900s
20
0
0.0 0.6
•
1.2
Capture cross sections
decrease exponentially
with depth
Recombination rate is
limited by the capture of
holes
Recovery of the Generated Traps
Vbase = -0.6 V
Initial
300 sec
24 hrs
3 days
7 days
10
30
20
10
1nm SiO2/3nm HfO2/TiN
0 3
4
5
10
10
10
nFET W/L = 10/1 m
50
40
2
Nt [10 /cm ]
Vstress = 2.2 V
40
2
Nt [10 /(cycle*cm )]
Vamp = 1.4 V
Vbase = -0.6 V
tr, tf = 100 ns
Vstress = 3.0 V
Initial
After 300s stress
After 600s
After 300s + FGA
After 300s + FGA + 300s
10
30
Vamp = 1.4 V
Frequency [Hz]
6
10
20
10
1nm SiO2/5nm HfO2/TiN
0 3
4
10
10
10
5
Frequency [Hz]
02/16/05
10
6
•
Generated defects
can be passivated
using FGA at 450°C
for 30 min
• Subsequent stress
re-activates
passivated defects