Transcript ALD Oxides Ju Hyung Nam, Woo Shik Jung, Ze Yuan, Jason Lin.

ALD Oxides
Ju Hyung Nam, Woo Shik Jung,
Ze Yuan, Jason Lin
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Outline
• Materials:
– Al2O3
– HfO2
– ZrO2
– TiO2
• For each material:
– ALD Chemistry
– Physical Characterization
– Electrical Characterization
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Al2O3
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Chemistry
• Precursors: Trimethylaluminium (TMA, (CH3)3Al), H2O
• Reaction: 2Al(CH3)3 + 3H2O -> Al2O3 + 6CH4
• Composed of two half-reactions:
– A) AlOH* + Al(CH3)3 -> AlOAl(CH3)2* + CH4
– B) AlCH3* + H2O -> AlOH* + CH4
– (*: surface species)
Figure:
http://informationengineers.bl
ogspot.com/
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Deposition rate: on Si
Al2O3 thickness vs. cycles
250
200 o C
Linear fit to 200 o C
Thickness (Ang)
200
150
 0.99834x + 6.113
100
50
0
0
50
100
150
200
250
Cycles
• Found depositio rate @ 200 oC: ~0.99 A/cycle
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Deposition rate: on Si
Deposition thickness vs. temperature (100 cycles)
120
115
110
Thickness (A)
105
100
95
90
85
80
75
160
170
180
190
200
210
220
230
240
o
Temperature ( C)
• Deposition rate decreases with temperature increase
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MOSCAP Fabrication
• Process flow: Si substrate diff clean → Al2O3 deposition → Al
deposition → patterning (Karlsuss) → wet etch → FGA annealing
• Annealing treatments appear necessary
FGA annealing (200 oC, 150 cycles)
-3
4
x 10
wo FGA
FGA
Capacitance (@ 1 MHz) (F/m 2)
3.5
Hysteresis (V)
Cycles
Befer FGA
After FGA
50
1.12
0.26
2
100
0.172
0.031
1.5
150
0.153
0.026
3
2.5
∙FGA done at: 325 oC, 30 min
1
0.5
0
-4
-3
-2
0
-1
DC bias (V)
1
2
3
Hysteresis before & after annealing
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Dielectric Constant
• Dielectric constant is extracted from accumulation capacitance &
measured dielectric thickness
0.01
Cycles
Dielectric Constant (k)
50
6.30
0.007
100
6.77
0.006
150
6.74
0.005
200
6.76
50 cycles
100 cycles
150 cycles
0.009
Capacitance (@ 1 MHz) (F/m 2)
0.008
0.004
∙Deposition temperature: 200 oC
0.003
0.002
0.001
0
-4
-3
-2
-1
0
DC bias (V)
1
2
3
Extracted dielectric constant: ~6.75
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Fixed Charge
• Due to the fixed charge along the high-k/Si interface, flat band
voltage (Vfb) shifts with Al2O3 thickness.
• Fixed charge density can be estimated from Vfb shift.
V fb  ms  Q f 
t

V fb  
Qf

 t
Q f   
dVfb
dt
• From measured data, dVfb/dt = 3.5 x 107 V/m,
Qf = -1.983 x 10-7 C/cm2
(1.24 x 1012 q/cm2)
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Mobile Charge
• Mobile charge density was calculated from hysteresis
Qmobile = Cox x Vhysteresis
Hysteresis (V)
Mobile charge dnesity (xq/cm2)
Cycles
Befor FGA
After FGA
Before FGA
After FGA
50
1.12
0.26
6.99 x 1012
1.62 x 1012
100
0.172
0.031
6.12 x 1012
1.10 x 1011
150
0.153
0.026
3.82 x 1012
6.49 x 1010
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Temperature Dependency
• As deposition temperature increases, Al2O3 becomes denser, and
dielectric constant also changes.
-3
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Temperature dependency
x 10
160 oC
200 oC
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Temperature (oC) Dielectric Constant (k)
Capacitance (@ 1 MHz) (F/m 2)
240 oC
5
160
7.21
4
200
6.77
3
240
7.41
∙ALD 100 cycles
2
1
0
-4
-3
-2
-1
0
DC bias (V)
1
2
3
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Al2O3 on Ge
• Al2O3 was deposited on epi-Ge
• Growth rate was lower compared to Al2O3 on Si: ~0.9 nm/cycle*
Metal (Al)
Al2O3
epi Ge
Patterning +
Etching
FGA
Si substrate
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MOSCAPs on Ge
0.01
50 cycles, wo FGA
50 cycles, FGA
100 cycles, wo FGA
100 cycles, FGA
0.009
Capacitance (@ 1 MHz) (F/m 2)
0.008
Cycles
Befer FGA
After FGA
50
1.12
0.74
100
0.8
0.23
150
-
0.31
0.007
0.006
0.005
Hysteresis (V)
0.004
0.003
0.002
0.001
0
-4
-3
-2
-1
0
DC bias (V)
1
2
3
Cycles
Dielectric Constant (k)
50
5.08
100
6.21
150
6.42
• Hysteresis: high Dit - annealing treatments appear necessary
• Dielectric constant: ~6.3, lower than Al2O3 on Si
• Fixed charge: Qf = -4.95 x 10-7 C/cm2
(3.09 x 1012 q/cm2)
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HfO2
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ALD of HfO2 - Chemistry
• Precursor : H2O
• Reactant :Tetrakis(dimethylamido)hafnium(IV) [(CH3)2N]Hf
• The surface of Si can be either –H or –OH terminated, although –OH termination is
more favorable
• Nitrogen is used to purge the precursor and the reactant between the steps
• Step 1 – 4 is repeated for in terms of cycles to achieve desired thickness.
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Deposition thickness vs Temperature
• The deposition showed almost linear decrease with temperature until rapid decrease
beyond 250°C.
• The samples were annealed at 300°C for 30min additionally to see if there are change in
thickness due to densification, but found the change negligible.
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• Future ALD process temperature was chosen as 200°C, as the standard recipe suggested.
Surface Roughness of HfO2 films
• Surface roughness was measured using AFM to investigate the film quality in
according to deposition temperature.
• On average, the films showed ~0.2Å(rms) in surface roughness, which is a
comparable value to bare Si surface roughness.
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Deposition rate of HfO2 at 200°C
• Deposition rate of 0.99Å/cycle was observed for deposition at 200°C
• The thickness was measured by using ellipsometry (Woollam)
• Native oxide was also measured (7~10Å) to increase the accuracy of the film
thickness.
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MOSCAP Fabrication
FGA Annealing at
300°C, 30min
Diffusion clean (HF last) Si (WbDiff)
HfO2 deposition at 200°C (Savannah)
Aluminum sputtering 2.5kw, 200sec(Gryphon).
Forming Gas Annealing (FGA) 300°C, 30min
• MOS Capacitor was fabricated to measure the electrical properties of the HfO2.
• Hydrogen in the forming gas should effectively reduce the interface traps between
Si/HfO2 interface, reducing the degree of hysteresis.
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Capacitance – Voltage Characterization
Dielectric Constant
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@ 1MHz
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Average : 15.27
14
13
12
150
200
250
300
Deposition Cycle (cyc)
Average Dielectric Constant : 15.27
Average Doping Concentration: 1.5 x 1016 /cm3
Hysteresis Range: 230mV-285mV
Mobile Charge Range: 8x1011 /1.4x1012 /cm2
• Dielectric Constant (k), doping
type and concentration were
extracted at 1MHz.
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Fixed Charge Extraction
Fixed Charge Type
: Negative
Fixed Charge Density
: 2.94x1012/cm2
Positive Vfb shift
@ 1MHz
Fixed charge type and density
were extracted by normalizing
each CV curve, and observing
the direction and degree of
Vfb shift.
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ZrO2
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ZrO2 Chemistry
• Tetrakis[EthylMethylAmino] Zirconium.
Zr[N(C2H5)(CH3)]4
• XPS confirmation for ZrO2 deposition.
• Precursor temperature, pulse widths for precursor are c
arefully examined.
– Standard recipe will be available in the root of recipe folder.
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ZrO2 Capacitors
Deposition rate at 200C, 100 cycles, ~87A oxide thickness
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Deposition Rate
Deposition rate at 200C, precursor line at 110C pulse time 0.5sec.
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Deposition Temperature
Deposition rate varies with deposition temperature, indication of
instability of phase/property of the deposited film.
Post deposition annealing and will largely influence the property.
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TiO2
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ALD of TiO2
• Tetrakis(dimethylamido)titanium
– [(CH3)2N]4Ti
• Water
– H2O
• Standard recipe is at 200°C
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Physical Characterization (1)
R2 = 0.999
12A native oxide
ALD regime is confirmed, with 0.38A/cycle growth rate.
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Physical Characterization (2)
XPS
AFM
Ti:O ≈ 1:3
RMS: 0.36nm
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Relative Dielectric Constant (k)
k 0
t ox
1
1
1
 
C C1 C 2
C

Depending on which pair of C-V
considered, k = 7.6 to 52.7
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Fixed Charge (QF)
Al / Al2O3 / TiO2 / Si
Al / TiO2 / Al2O3 / Si
Al / Al2O3 / Si
Cannot be +QF
Still requires more study. Current belief is
that the TiO2/Si interface is very defective.
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Mobile Charge (QM)
ΔV = 0.145V
ΔV = 0.093V
From hysteresis, estimate
mobile charge density
• 4.7×1011 cm-2 (Before FGA)
• 2.7×1011 cm-2 (After FGA)
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Thank you
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