Si/SiGe(C) Heterostructures
description
Transcript of Si/SiGe(C) Heterostructures
Si/SiGe(C) Heterostructures
S. H. Huang
Dept. of E. E., NTU
OUTLINE
• Introduction
• Strain Effects
• Device Performance
• Fabrication technologies
Introduction •The Si/SiGe:C heterostructures add the colorful
creativity in the monotonic Si world.
•The Si/SiGe heterojunction bipolar transistors have the
cutoff frequency of 300 GHz and maximum oscillation
frequency of 285GHz with carbon incorporation in the
base. (IBM)
Device Figure of Merit Growth Technique
Strained NMOSFET Peak effective electron mobility 800 cm2/Vs [6] relaxed buffer
Strained PMOSFET Peak effective hole mobility 2700 cm2/Vs [5] relaxed buffer
Npn-HBT fT=210GHz [1], fmax=285GHz [2] Pseudomorphic
Pnp-HBT fT=59GHz at RT, fT=61GHz at 85K [12] Pseudomorphic
Heterojunction Phototransistors
1.47 A/W at 850 nm, bandwidth=1.25 GHz [13] Pseudomorphic
n-MODFET Gm=460ms/mm fT=76GHz fmax=107GHz at RT [14] Gm=730ms/mm fT=1
05GHz fmax=170GHz at 50K
relaxed buffer
p-MODFET Gm=300ms/mm fT=70GHz fmax=135GHz at RT[15] relaxed buffer
n-RTD P/V7.6 at RT [7], 2 at 4.2K [8] relaxed buffer
p-RTD P/V=1.8 at RT, 2.2 at 4.2K[9] Pseudomorphic
Detector (IR) 1.3μm , 1.5μm[16] quantum dots
Detector (LWIR) Schottky barrier:λc=10μm[17] Pseudomorphic
LED 1.3μm , 1.5μm at RT[18,19] Pseudomorphic
Table I: The recent performance of electronic and optoelectronic devices based on SiGe technology. The last column indicates the growth techniques to achieve the device quality material
: SiGe virture atoms
: Si atoms
The strained SiGe grown on (100) Si. The misfit dislocation is the missing bond between Si and SiGe atoms.
strained Si or Ge
relaxed SiGe
Simisfit dislocation
threading dislocation
The misfit dislocation and threading dislocation. The misfit dislocation is at the Si/SiGe interface, and threading dislocation ends at the surface of the epilayers.
20 nm
(a)
GeSi spacer
GeSi spacer
GeSi cap
SiO 2
p-type Si substrate
Si buffer layer ~ 50nm
~100nm ~2nm
~6nm
(b)
(a) TEM photo of multi-layer Ge dots. The spacer thickness is ~20nm. The SiO2 dots are also formed above the Ge do
ts. (b) The strain field in Si layers.
Composite dots with fine structures such as Ge/Si/Ge composite dots
AFM picture of (a) composite dots and (b) conventional dots. The composite dots has larger coverage area.
(a) (b)
0.0 0.2 0.4 0.6 0.8 1.00.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
strained SiGe
relaxed SiGe
Ge mole fraction
E n
e r
g y
( e
V )
2.42.22
1.8
1.6
1.4
1.2
1
w a
v e l e
n g
t h ( m
)
The bandgap of strained Si1-xGex on (001) Si substrate and relaxed band gap of Si
1-xGex alloys. The showdow areas indicate the optical communication bandwidth of 1.3 and 1.5 m.
0.00 0.05 0.10 0.15 0.200
100
200
300
400 NA=1016cm-3
T=300K
Ho
le M
ob
ility
(cm
2 /Vs)
Ge Mole Fraction
Theoretical mobility Experimental Data
Theoretical values of the hole mobility in relaxed SiGe alloys at 300K and doping concentration of NA=1016cm-3 with experimental results of Gaworzewski
0.0 0.1 0.2 0.3 0.4
100
1000
NA=1019cm-3
NA=1018cm-3
NA=1017cm-3
NA=1015cm-3
Maj
ori
ty H
ole
Mo
bili
ty(c
m2 /V
s)
Ge Mole Fraction
in-plane out-of-plane
The in-plane and out-of-plane majority hole mobility of SiGe strained alloys for different doping concentration .
0.00 0.05 0.10 0.15 0.20 0.25 0.30100
150
200
250
300
350
NA=1020cm-3
NA=1019cm-3
NA=1018cm-3
Min
ori
ty E
lect
ron
Mo
bili
ty (
cm2 /V
s)
Ge Mole Fraction
out-of-plane in-plane
In-plane and out-of-plane minority electron mobilities of SiGe alloys at different doping level at 300K.
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.51000
1200
1400
1600
1800
2000
2200
2400
E
lect
ron
mo
bili
ty (
cm2 /V
s)
Strain () (%)
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
500
1000
1500
2000
2500
(H
ole
mo
bili
ty c
m2 /V
s)
Strain () (%)
The in-plane electron and hole mobility of strained Si.
0 10 20 30 40 501.0
1.5
2.0
2.5
Mo
bili
ty E
nh
ance
men
t F
cto
r
Substrate Ge content (%)
Electron[Takagi et al.] Hole[Oberhuber et al.]
The calculated electron and hole mobility enhancement factor in MOS inversion layers of strained Si.
-5 -4 -3 -2 -1 0 1 2 3102
103
104
E
lect
ron
mo
bili
ty (
cm2 /V
s)
Strain
in-plane
-5 -4 -3 -2 -1 0 1 2 3 4 5103
104
105
Ho
le M
ob
ility
(cm
2 /Vs)
Strain (%)
in-plane
Electron and hole mobility in strained Ge .
Si1-xGex
Wafer A
Si1-xGex
Wafer A
Wafer B
Si1-xGex
Wafer B
Si1-xGex
Wafer B
Wafer AH+ H+ H+ H+H+ H+ H+
1). Hydrogen implantation
2). Hydrophilic bonding at low temperature
3). Splitting annealing
4). Polishing
Smart-cut and layer transfer process flow for making strained Si on SiGe-on-insulator material.
Cross-section TEM picture of relaxed SiGe on SOI using the smart-cut method.
elec
tron
ener
gy
n-emitterp-base
n-colledtor
Ev
Ec
VCB
Δ EG
Si
SiGe
Δ Vp
Si SiSior
SiGe
distance
Δ Vn
VBE
Band diagram of typical SiGe HBT. In forward active region, the base-emitter junction is forward-biased (VBE) and the base-collector junction reverse-biased (VCB)
Ec
Φ p
Ev
lin. gradedSiGe profile
Compositionally graded Si1-xGex can build an
electrical field in the base of Si/SiGe HBTs.
DrainSource
Gate
n+n+
n ploly Si+
SiO2
strained-Si
Relaxed Si1-xGex
GradedbufferRelaxed Si1-yGey
y=0.05 to x
60-100 AO
0.25-0.6μ m
1.5μ m
(a)
DrainSource
Gate
n+n+
n ploly Si+
SiO2
strained-Si
Relaxed Si1-xGex
GradedbufferRelaxed Si1-yGey
y=0.05 to x
60-100 AO
0.25-0.6μ m
1.5μ m
strained-Si 130-200 AO
(b)
Device structures for strained Si NMOSFETs with (a) Si on the surface, (b) Si buried channel.
0.0 0.1 0.2 0.3 0.4 0.5 0.60
400
800
1200
1600W X L =21X90 m
VDS
=40mV 290K
Control-Si
Strained-Si (Surface)
Strained-Si (Buried)
eff(c
m2 /V
.s)
Eeff
(MV/cm)
Effective low-field mobility versus effective field for different NMOSFETs. The surface channel strained-Si mobility shows a fairly constant mobility enhancement compared with that of control-Si device, while the buried strained-Si mobility peaks at low fields but decreases rapidly at higher fields.
0 500 1000 15000
200
400
600
800
1000
110%
Str. Si/ Relx. SiGe 13% Str. Si/ Relx. SiGe 28% Str. Si/ Str. SiGe 30%/ Relx. SiGe 13%
Eff
ecti
ve E
lect
ron
mo
bili
ty (
cm2 /V
s)
Effective Filed (KV/cm)
Control Universal mobility
NMOSFET effective mobility vs vertical effective field.
100 200 300 400 500 600 700 800 900 100011000
20
40
60
80
100
120
140
Eff
ecti
ve H
ole
mo
bili
ty (
cm2 /V
s)
Effective Filed (KV/cm)
Str. Si/Str. SiGe 13% Str. Si/Str. SiGe 28% Str. Si/Str. SiGe 30%/ Relx. SiGe 13% Control Universal mobility
PMOSFET effective mobility vs vertical effective field.
Gate Oxide
Strained Si 7nm
Strained SiGe 30% 15nm
Relaxed SiGe Buffer
"BC"DeviceEpi Layer StructureStr.Si/Str.SiGe/Rlx.SiGe
EV
Schematic diagram of a buried strained-SiGe PMOSFET. Most current flow is in the strained SiGe channel.
Si-channel
Si-cap
Si1-xGex
n doping+
Si1-xGex
spacer
relaxed Si1-xGex buffer
Si-substrate
(a)
Si1-xGex channel
Si-cap
p doping+
Si spacer
Si buffer
Si-substrate
(b) (c)
Ge-channel
Si-cap
Si1-xGex
p doping+
Si1-xGex
spacer
relaxed Si1-xGex buffer
Si-substrate
Typical layer sequences: (a) NMODFETs with Si-channel on relaxed-SiGe buffer, (b) PMODFET with SiGe channel and (c) PMODFET with Ge channel on relaxed-SiGe buffer.
0.1 1102
103
IBM (B)y=0.3
IBM (A)y=0.3
CNETx=1 y=0.7
DCx=1 y=0.7
DCx=1 y=0.7
IBM (B)x=0.8 y=0.3
IBM (A)x=0.8 y=0.3
Eff
ecti
ve M
ob
olit
y (c
m2/
Vs)
Eeff
(MV/cm)
Hole mobility Electron mobility
Available experimental data [71-75] at 300K for effective electron and hole mobility in MODFET. “A” denotes modulation doping above strained Si channel, “B” denotes doping supply layer below strained silicon channel, x is the Ge fracion in the channel, and y is Ge fraction in the buffer layers.
0.0 0.2 0.4 0.6 0.8 1.010-2
10-1
100
101
102
103
strained SiGe
1550 nm
1300 nm
820 nm
A b
s o
r p
t i o
n
l e n
g t
h ( m
)
Ge mole fraction
The absorption length at 820, 1300, and 1550 nm vs Ge mole fraction. The absorption length decreases as the Ge mole fraction increases. For the large Ge fraction, the shadowed areas indicate the uncertainty of the estimation.
The structure of 5-layer Ge quantum dot devices prepared by UHV/CVD
p-Si sub
Si buffer layer 50 nm
Active region ( × 4 )
Wetting layer 2 nm
Si spacer 50nm
Ge dotSi cap 3 nm