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