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(In)GaAs MOS and MOSFETs
林耕雍
2018/10/04
1
Outline• Introduction
• Metal-oxide-semiconductor (MOS) structure
• MOS capacitor analysis
• MOS field-effect transistors (MOSFETs)
• High dielectric constant (κ) oxides on (In)GaAs• High carrier mobility materials
• High-κ oxides
• In-situ preparation of oxide/semiconductor interfaces
• High-κ on (In)GaAs MOSCAPs and MOSFETs• MBE-HfO2, Y2O3 and ALD-Y2O3 on GaAs MOSCAPs
• ALD-HfO2 and Al2O3 on In0.53Ga0.47As MOSFETs
• Common gate MBE-Y2O3 for Ge, GaSb and In0.53Ga0.47As MOSCAPs and MOSFETs
2
Semiconductor band structure
Si band structure
3
Doped Si: Boron (p-type), Phosphorous (n-type)
Doping in semiconductor
4
Fermi level in semiconductor
Intrinsic
n-type
p-type
n >> p
n << p
n〜 p
carrier conc.
5
Semi. substrate
(silicon)
Gate electrode (metal or polysilicon)
Oxidetox
C= ε0 εi A/tox
• MOSFET-like structure
• Easy fabrication
• Interfacial information acquired prior
to device (MOSFET) processing
Advantages
Metal-oxide-semiconductor structure
MOS structure (capacitor/diode) :
Back (Ohmic) contact
6
Operation principle of MOS capacitor
Fermi level alignment when
𝑉𝐺 = 0 (equilibrium)
Flat band condition (ideal) :
𝑉𝐺 = 𝑉𝐹𝐵 = 0 𝑤ℎ𝑒𝑛 𝜙𝑚𝑠 = 0
n-type
p-type
7
Operation principle of MOS capacitor
Flat band condition (ideal) :
𝑉𝐺 = 𝑉𝐹𝐵 = 0accumulation
depletion
inversion
8
Schematics of an MOS capacitor under different bias modes
Operation principle of MOS capacitor
accumulation ofmajority carriers
depletion ofmajority carriers
accumulation ofminority carriers
9
MOS capacitance-voltage (C-V) measurement :
qC
V
MOS capacitor analysis
differential capacitance :
at some voltage V
small amplitude ac signal (100 Hz to 1 MHz) on staircase dc bias
10
MOS small-signal capacitance model :
oxC oxCoxC
depC
Accumulation Depletion Inversion
ox
oxox
tC
d
Sidep
XC
incremental charge
located at
semiconductor surface
Incremental charge
located at bottom edge
of depletion region
MOS capacitor analysis
Incremental charge
located at
semiconductor surface
oxide capacitance
11
• CG = Cox in the accumulation and
inversion regions of operation.
• CG is smaller, and is a non-linear
function of VGB in the depletion region
of operation.
max,
min,
min,
min,
min
where
d
Sidep
depox
depox
XC
CC
CCC
MOS capacitor analysisMOS capacitance-voltage (C-V) curve :
12
p-type substrate
Accumulation
h h h h
Vg < VFB
Vg < VFB
Cox=εox/tox
Hole
-4 -3 -2 -1 0 1 2 3 4
0
20
40
60
80
100
120
140
160
180
200
Low freq
High freq
Cap
acito
r(F
)
Vg(V)
Accumulation
MOS capacitor analysisMOS capacitance-voltage (C-V) curve :
Simulation of C-V curve
13
p-type substrate
Depletion
h h h h
Increasing
Vg > VFB
Vg > VFB
Negative
space charge
-4 -3 -2 -1 0 1 2 3 40
20
40
60
80
100
120
140
160
180
200
Low freq
High freq
Capacitor(
F)
Vg(V)
MOS capacitor analysisMOS capacitance-voltage (C-V) curve :
Simulation of C-V curve
Depletion
14
Increase
Vg > Vt
P-type substrate
Inversion
Vg > Vt
Inversion layer
-4 -3 -2 -1 0 1 2 3 4
0
20
40
60
80
100
120
140
160
180
200
Low freq
High freq
Cap
acito
r(F
)
Vg(V)
MOS capacitor analysisMOS capacitance-voltage (C-V) curve :
e- e- e- e-
Inversion
Simulation of C-V curve
15
• Low frequency
Charge equilibrium maintains at all times. The capacitance isthe ratio of the change in charge to the change in gate voltage,measured while the capacitor is in equilibrium.
• High frequency
Under this condition, one finds that the charge in the inversionlayer does not change from the equilibrium value at the applieddc voltage. The high frequency capacitance therefore reflectsonly the charge variation in the depletion layer and the (rathersmall) movement of the inversion layer charge.
low frequency- dVg is slow enough to change Qinv
Frequency dependence :
MOS capacitor analysis
high frequency- dVg is too fast to change Qinv
16
MOS capacitor analysisFrequency dependence :
17
Oxide
Semiconductor
Qm mobile oxide charge
Qot oxide trapped charge
Qf fixed oxide charge
Qit interface trapped charge
Non-ideal effects in MOS capacitorCharges in oxide layer :
18
Vg
Dit
C
V
Dit = 0
Dit is not 0
For the same Vg, the surface potential with Dit is smaller.
The C-V curve is lengthened.
Non-ideal effects in MOS capacitorInterface trapped charge Qit :
Interfacial traps(Si dangling bonds)
19
Non-ideal effects in MOS capacitorInterface trapped charge Qit :
Gate
+ + + +
- - - -
but
Gate
+ + + +
Nothing !!
Interface trapsOxide
Semiconductor
Oxide
Semiconductor
- Peaks in CLF-V curve
Ctrap from charging-discharging
- Distortion in CHF-V curve
Interface charges Qit varied with Vgb
20
MOS field-effect transistor
P-type semiconductor
N+ N+
Body (B)
Gate (G)Drain (D)Source (S)
Metal
Oxide
self-aligned process
gate patterning
S/D imp./activ.
S/D contact metal
Pad metal
Dimensional scaling
High-mobility semiconductors
High-𝜅 dielectrics
But, the most important issue is the interface quality!
MOSFET ID-VG
21
• High-speed and low-power logic devices
Material
Property
IV III-V
Si Ge GaAs In0.53Ga0.47As InAs GaSb InSb
Electron Mobility
(cm2/V∙s)1,400 3,900 8,500 12,000 40,000 3000 77,000
Hole mobility
(cm2/V∙s)450 1,900 400 450 500 1000 1250
Bandgap (eV) 1.11 0.67 1.42 0.74 0.36 0.72 0.17
S. Takagi and M. Takenaka,
ECS (2011)
High carrier mobility materials
22
High dielectric constant oxides
Dielectrics SiO2 Al2O3 HfO2 Gd2O3 Y2O3 La2O3
Dielectric constant 3.9 9 20 14 15-24 30
Band gap (eV) 8.9 8.7 5.7 5.8 5.8 4.3
Conduction band
offset to GaAs (eV)3.3 3.2 1.51 1.55 2.2 2.4
Valence band offset
to GaAs (eV)4.2 4.1 2.79 2.85 2.1 0.5
23
In-situ prepared oxide/semi. interfaces
@ ITRI24
Direct Deposition of High-k Oxides
Molecular-beam-deposited and ALD
oxides
Interfacial layer free !!
L. K. Chu, et al., Appl. Phys. Lett. 94, 202108 (2009).
W. C. Lee, et al., J. Cryst. Growth, 311, 2187 (2009).
L. K. Chu, et al., J. Cryst. Growth, 311, 2195 (2009).
T. D. Lin, et al., J. Cryst. Growth,
301, 386 (2007).
M. Hong, et al., J. Vac. Sci. Technol. B 14(3), 2297 (1996), and Appl. Phys.
Lett. 76, 312 (2000).
T. D. Lin, et al., Appl. Phys. Lett.
93, 033516 (2008).
W. C. Lee, et al., J. Cryst. Growth,
278, 619 (2005).
ALD- and MBD-HfO2 on (In)GaAs
ALD- and MBD-Y2O3
on GaSb
ALD- and MBD-Y2O3
on (In)GaAs
R. L. Chu, et al., Appl. Phys. Lett.
105, 182106 (2014).
S. Y. Wu, et al, MEE 147, 310 (2015), and P.
Chang et al, Appl. Phys. Express 4 114202 (2011).
T. D. Lin, et al., Appl. Phys. Lett.
103, 253509 (2013).
25
GaAs MOSCAPs process flow
MBE prepared GaAs(001)-4×6 surface
Deposition of ALD-Al2O3/Y2O3
Post deposition annealing
(900oC 60s N2 for Y2O3 samples)
100nm Ni metal gate formation
Ti/Au as back contact electrodes
Y2O3/GaAs
GaAs-P+/N+
GaAs-Be/Si-doped
26
GaAs MOS capacitor structure
Amorphous MBE-HfO2 for GaAs passivation
CV characteristics
27
• Amorphous thin HfO2
intended to prevent multi-
domain HfO2 crystal when
annealed > 600oC
• Thermal stability > 900oC
• Dit < 1 x 1012 eV-1cm-2
min. 1.3 x 1011 eV-1cm-2
H. W. Wan, et al., MEE 178, 154 (2017)
JE characteristics & STEM image
900oC-annealed
sample
Single crystalline MBE-Y2O3 for GaAs passivation
RHEED: GaAs (001)-4x6
RHEED: MBE-Y2O3(110)
CV characteristics
– Comparison with ALD-Al2O3 passivation
MBE-Y2O3 passivation
ALD-Al2O3 passivation
28
• Single crystalline
Y2O3(110) on GaAs(001)
similar to structure of
Gd2O3(110) on GaAs(001)
• Thermal stability > 900oC
• Dit ~(3-5) x 1011 eV-1cm-2
H. W. Wan, K. Y. Lin, et al., JCG 477, 179 (2017)
Y2O3(110)
1.0 nm
Y2O3(110)
2.3 nm
GaAs(001)
surface[𝟏𝟏 𝟎] [𝟏𝟏𝟎] 4x 6x
S. Y. Wu, M. Hong, et al, Microelectron. Eng. 147, 310-313 (2015)
K. Y. Lin, L. B. Young, M. Hong, et al, Microelectron. Eng. 178, 271-274 (2017)
A B
[𝟎𝟎𝟏]
[𝟎𝟎𝟏]
[𝟏 𝟏𝟎]
[𝟏 𝟏𝟎]
C
[𝟏 𝟏𝟏]
[𝟏 𝟏𝟏]
GaAs(001)
ALD-Y2O3(110)
ALD-Al2O3
(004) 0.14 nm
29
Single crystalline ALD-Y2O3 for GaAs passivation
RHEED:
ALD-Y2O3(110) on GaAs (001)-4x6
TEM
-4 -3 -2 -1 0 1 2 30.0
0.5
1.0
1.5
QSCV
(1mV/sec)
QSCV
for calculation
Freq. disp. ~6.6%(1.6% /decade)
1 MHz
Ca
pa
cit
an
ce
(F
2/c
m)
100 Hz
Gate bias (V)
-4 -3 -2 -1 0 1 2 30.0
0.5
1.0
1.5
Gate bias (V)
Ca
pa
cit
an
ce
(F
/cm
2)
QSCV
(1mV/sec)
QSCV
for calculation
Freq. disp. ~6.6%(1.6% /decade)
1 MHz
100 Hz
N2 900°C 60s + FGA
He 900°C 10s + FGA
-3 -2 -1 0 1 2 3 40.0
0.5
1.0
1.5
QSCV
for calculationC
ap
ac
itan
ce
(F
/cm
2)
Gate bias (V)
1 MHz
100 HzFreq. disp. ~18.7%(4.7% /decade)
QSCV
(1mV/sec)
~24.9%
-3 -2 -1 0 1 2 3 40.0
0.5
1.0
1.5
~10.6%
QSCV
(1mV/sec)
QSCV
for calculation
Ca
pa
cit
an
ce
(F
/cm
2)
Gate bias (V)
1 MHz
100 HzFreq. disp. ~10.3%(2.6% /decade)
30
Single crystalline ALD-Y2O3 for GaAs passivation
• Single crystalline
Y2O3 on GaAs
• Thermal stability
> 900oC
• Dit ~(2-3) x 1011
eV-1cm-2
• No mid-gap peak
CV characteristics
0.1 0.3 0.5 0.7 0.9 1.1 1.310
10
1011
1012
1013
By QSCV
He 900oC 10s + FGA N
2 900
oC 60s + FGA
Dit
(eV
-1c
m-2)
E-EV (eV)
0.4 0.5 0.9 1.0 1.110
11
1012
1013
By conductance
MBD-Al2O
3/GaAs(001)
N2 900
oC 60s + FGA
Dit
(e
V-1c
m-2)
E-EV(eV)
Dit distribution
Y. H. Lin, M. Hong, et al, APEX 9, 081501 (2016)T. W. Chang, M. Hong, et al, unpublished (2017)
Y. C. Chang, M. Hong, et al, APL 97, 112901 (2010)In-situ MBE + ALD
14nm/(1nm)
ALD-Al2O3/n-GaAs(001)
with AlN interfacial passivation layerT. Aoki et al., Appl. Phys. Lett., 105, 033513 (2014) High Dit
T. Yang, P. D. Ye, R. M. Wallace et al., Appl. Phys. Lett., 91,
142122 (2007)
ALD-HfO2/Al2O3/GaAs(001)
with NH4OH surface pretreatment
High Dit
ALD-Al2O3/GaAs(001)
with (NH4)2S surface pretreatmentD. Shahrjerdi, et al. Appl. Phys. Lett., 92, 203505 (2008)
High Dit
ALD-Al2O3/n-GaAs(001)
without surface pretreatmentsY. H. Chang, M. Hong et al., Microelectron. Eng., 88, 1101-
1104 (2011)High Dit
31
Ex-situ and in-situ ALD-Al2O3 for GaAs passivation
T. Aoki, et al. Appl. Phys. Lett. 105, 033513 (2014)
ALD-Al2O3/GaAs(001)
with AlN interfacial passivation layer
G. Brammertz et al. Appl. Phys. Lett. 93, 183504 (2008)
ALD-Al2O3/GaAs(001)
with (NH4)2S surface pretreatment
The Dit spectrum shows a midgap peak! 32
Ex-situ ALD-Al2O3 for GaAs passivation
HfAlO/HfO2 (0.8nm)/In0.53Ga0.47As
33
Ultimate CMOS – ALD-HfO2/MBE-In0.53Ga0.47As
T. D. Lin, et al. APL 100, 172110 (2012)
CV characteristics
PDA 800C
Dit distribution CET projection
XPS
• Tetra-valence oxide HfO2
do passivate In0.53Ga0.47As
• Thermal stability > 800oC
• Dit ~(6-20) x 1011 eV-1cm-2
without mid-gap peak
• EOT ~0.9 nm achieved
34
Ultimate CMOS – ALD-Al2O3/MBE-In0.53Ga0.47As
AsOx-free
interface
AsOx
remained
HR-SRPES
Benchmark
Self-aligned inversion-channel device
M. Hong, et al., APL 111, 123502 (2017)
35
Ultimate CMOS – ALD-Al2O3/MBE-In0.53Ga0.47AsM. Hong, et al., APL 111, 123502 (2017)
Common gate MBE-Y2O3 for Ge passivation
-2 -1 0 1 20.0
0.4
0.8
1.2
-2 -1 0 1 2 3-1 0 10.0
0.4
0.8
1.2
Gate bias (V)
100 Hz
500Hz
1k Hz
10k Hz
500k Hz
100 Hz
4k Hz
25k Hz
100k Hz
500k Hz
Gate bias (V)
Al2O3/Y2O3/n-GaSb Al2O3/Y2O3/p-In0.53Ga0.47As Al2O3/Y2O3/n-Ge
C/C
ox
Gate bias (V)
5k Hz
10k Hz
50k Hz
100k Hz
500k Hz
(a) (b) (c)
L.K. Chu et al., J. Crystal Growth 311, 2195 (2009)R.L. Chu et al., Appl. Phys. Lett. 104, 202102 (2014)
Root mean square surface roughness (Rq) is around 3.5 Å in a 1x1 m2 area.
Root mean square surface roughness (Rq) is around 1 Å in a 1x1 m2 area.
Ge
36
Common gate MBE-Y2O3 for GaSb passivation
-2 -1 0 1 20.0
0.4
0.8
1.2
-2 -1 0 1 2 3-1 0 10.0
0.4
0.8
1.2
Gate bias (V)
100 Hz
500Hz
1k Hz
10k Hz
500k Hz
100 Hz
4k Hz
25k Hz
100k Hz
500k Hz
Gate bias (V)
Al2O3/Y2O3/n-GaSb Al2O3/Y2O3/p-In0.53Ga0.47As Al2O3/Y2O3/n-Ge
C/C
ox
Gate bias (V)
5k Hz
10k Hz
50k Hz
100k Hz
500k Hz
(a) (b) (c)
R.L. Chu et al., Appl. Phys. Lett. 104, 202102 (2014)R.L. Chu et al., Appl. Phys. Lett. 105, 182106 (2014)
GaSb
37
Common gate MBE-Y2O3 for InGaAs passivation
-2 -1 0 1 20.0
0.4
0.8
1.2
-2 -1 0 1 2 3-1 0 10.0
0.4
0.8
1.2
Gate bias (V)
100 Hz
500Hz
1k Hz
10k Hz
500k Hz
100 Hz
4k Hz
25k Hz
100k Hz
500k Hz
Gate bias (V)
Al2O3/Y2O3/n-GaSb Al2O3/Y2O3/p-In0.53Ga0.47As Al2O3/Y2O3/n-Ge
C/C
ox
Gate bias (V)
5k Hz
10k Hz
50k Hz
100k Hz
500k Hz
(a) (b) (c)
(In)GaAs
P. Chang et al., Appl. Phys. Express 4, 114202 (2011) 38
Common gate MBE-Y2O3 for semiconductors
-2 -1 0 1 20.0
0.4
0.8
1.2
-2 -1 0 1 2 3-1 0 10.0
0.4
0.8
1.2
Gate bias (V)
100 Hz
500Hz
1k Hz
10k Hz
500k Hz
100 Hz
4k Hz
25k Hz
100k Hz
500k Hz
Gate bias (V)
Al2O3/Y2O3/n-GaSb Al2O3/Y2O3/p-In0.53Ga0.47As Al2O3/Y2O3/n-Ge
C/C
ox
Gate bias (V)
5k Hz
10k Hz
50k Hz
100k Hz
500k Hz
(a) (b) (c)
Root mean square surface roughness (Rq) is around 3.5 Å in a 1x1 μm2 area.
Root mean square surface roughness (Rq) is around 1 Å in a 1x1 μm2 area.
L.K. Chu et al., J. Crystal Growth 311, 2195 (2009)R.L. Chu et al., Appl. Phys. Lett. 104, 202102 (2014)R.L. Chu et al., Appl. Phys. Lett. 105, 182106 (2014)P. Chang et al., Appl. Phys. Express 4, 114202 (2011)
39
Fabrication process for E-mode MOSFETs
Si-Ge
MBE
oxide
MBE
in-situ
XPS
oxide & metal
MBEIII-V
MBE
in-situ
SPM
in-situ
ALD
40
C. H. Fu, et al., Microelectron. Eng. 147, 330-334 (2015)
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.00
50
100
150
200
250
VG= 0 to -1.5V
step=-0.25V
WG/L
G=
10/1 m/m
I D(A
/m
)
VD (V)
VG= 0 to 2.5V
step=0.5V
WG/L
G=10/1 m/m
0
400
800
1200
1600
n-GaSb p-In0.53Ga0.47As
-3 -2 -1 00
25
50
75
100V
G= 0 to -3V
step=-0.5V
WG/L
G=400/4 m/m
I D(A
/m
)
VD (V)
n-Ge
W/L= 400/4 μm/μm
ID,max= 98 mA/mm
@VG= -3V, VD= -3.5V
Gm,max~ 42 mS/mm
@ VD= -3.5V
μFE= 241 cm2/V∙s
W/L= 10/1 μm/μm
ID,max= 1440 mA/mm
@VG= 2.5V, VD= 2V
Gm,max~ 770 mS/mm
@ VD= 2.5V
μFE= 2100 cm2/V∙s
W/L= 10/1 μm/μm
ID,max= 130 mA/mm
@VG= -1.5V, VD= -1.5V
Gm,max~ 90 mS/mm
@ VD= -1.5V
μFE= 200 cm2/V∙s
n-Ge n-GaSb p-In0.53Ga0.47As
41
Electrical characteristics of MOSFETsC. H. Fu, et al., Microelectron. Eng. 147, 330-334 (2015)
Electrical characteristics of MOSFETsIn0.53Ga0.47As inversion channel nMOSFET
Dielectrics LG
(m)Id, max
(A/m)Id × LG
(A)Gm, max
(S/m)Gm ×LG
(S)S.S. (mV/dec.)
Ion/Ioff μFE (cm2/Vs)a
ALD-Al2O3 0.5 430 215 160 80 240 4×103 1200 Purdue UUHV Al2O3/GGO 1 1050 1050 714 714 - - 1300MOCVD HfAlO 0.25 420 105 45.3 11.3 200 - - NUSALD-Al2O3 0.6 678 406 354 212 194 - -ALD-Al2O3/ HfO2 1 1500 1500 840 840 103 104 1100Not listed 0.03 ~1200 36 2230 66.9 - ~104 1000 IBMAl2O3/Y2O3 1 1440 1440 770 770 97 104 2100 This work
GaSb inversion channel pMOSFET
Al2O3 5 ~0.6 3 - - 250 100 ~270 Stanford UAl2O3 6 4 24 - - 250 103 160 CAS Beijing
Al2O3 2 10 20 - - 400 ~10 25 Tokyo U/NTT
Al2O3/Y2O3 1 130 130 90 90 147 103 200 This work
Ge inversion channel pMOSFET
HfO2/SiON/GeON 5 30 150 - - 102 103 ~300 NUS
HfO2/Si(SiO2) 0.125 1360 170 - - 100 105 358 Leuven
SiO or Al2O3/GeO2 200 0.4 80 - - 120 - 400 Tokyo U
HfO2/GeO2 10 37.8 378 - - 85 103 396 NUS
GGO 1 496 496 178 178 - - 389
Al2O3/GeOx 50 1.5 75 - - - ~102 526 Tokyo U
Al2O3/Y2O3 4 98 392 43 172 - 5×102 241 This work
42
C. H. Fu, et al., Microelectron. Eng. 147, 330-334 (2015)
Thank you for your attention!
43