Device Research Conference 2007
Erik Lind, Adam M. Crook, Zach Griffith, and Mark J.W. RodwellDepartment of Electrical and Computer EngineeringUniversity of California, Santa Barbara, CA, 93106-9560, USA
Xiao-Ming Fang, Dmitri Loubychev, Ying Wu, Joel M. Fastenau, and Amy LiuIQE Inc. 119 Bethlehem, PA 18015, USA
[email protected], 805-893-3273, 805-893-3262 fax
560 GHz ft, fmax InGaAs/InP DHBT in a novel dry-etched emitter process
Latest UCSB DHBT w/ refractory emitter metal
Scalable below 128 nm width
New refractory metal emitter technology 250 nm emitter width
0
5
10
15
20
25
30
109 1010 1011 1012
109
1010
1011
1012
Gai
ns (d
B)
Frequency (Hz)
U
H21
MAG/MSG
Ie=22 mA, V
ce=1.45V
Je=16 mA/m2, V
cb=0.4V
ft, f
max=560 GHz
First RF resultsSimultaneously 560 GHz ft & fmax
BVceo = 3.3V
Standard figures of merit / Effects of Scaling
Small signal current gain cut-off frequency (from H21)
cbcexcbjec
Bcb CRRCC
qITnk
f
21
effcbCRffeffbb ,,
max 8
VIC
c
cb
Charging time for digital logic
•Power gain cut-off frequency (from U)
Thinning epitaxial layers (vertical scaling) reduces base and collector transit times… But increases capacitances
Reduce Rbb and Ccb, through lateral scaling
More efficient heat transfer
e
e
InP
ceee
WL
KVWJT ln
emitter 500 250 125 nm width 16 9 4 m2 access
base 300 150 75 width, 20 10 5 m2 contact
collector 150 100 75 nm thick, 5 10 20 mA/m2 current density5 3.5 3 V, breakdown
f 400 500 700 GHzfmax 500 700 1000 GHz
power amplifiers 250 350 500 GHz digital clock rate 160 230 330 GHz(static dividers)
What parameters are needed for THz HBTs?
✓✓
✓✓
✓
✓✓ c<1 m2 U. Singisetti
DRC 2007
Ohmic contacts and epitaxial scaling good for 64nm HBT node!
Develop technology suitable for aggressive lateral scaling
TiW emitter dry etch formation
TiW
Cr
• Lift-off no good at <300 nm!• Dry etching – very high aspect ratio• Optical Lithography
O2 plasmaICP Cl2O2 etch
Mask Plate
SiO2
ICP SF6/Ar etch
•Refractory Ti0.1W0.9 is thermally stable
• c < 1m2 possible – no degradation of contact resistance for anneals up to 400C
TiW dry etching results• 250-300 nm emitters routinely formed• Demonstrated scalability down to 150 nm • ~ 50-100 nm tapering during etch sets scaling limit
•Emitter metal height ~ 500-600 nm
150 nm
Wet etch does not scale
{111}A planes – slow{101}A planes – fast
InGaAs etch ~ 30-40nmInP etch ~ 40 nm
Minimum emitter width ~ 150 nm!
Collector
Base
baseInP emitter
InGaAs emitter
TiW metal
Hybrid dry/wet etch• Anisotropic dry etch InGaAs, part of InP emitter, Cl2N2
• Formidable problem – InClx formation• Extensive UCSB know how on dry etching• Solution – low power ICP etch @ 200C, low Cl2 concentration• Short InP wet etch
TiW
InGaAs
InP
InGaAs Base
Current UCSB TiW emitter process
SiO2
TiW
InGaAs n++
InGaAs p++ Base
InP n
CrSF6/Ar ICP Cl2/N2 ICPSiNx sidewall
Wet EtchHCl:H3PO4
BHF
Ti
a b c d e
InGaAs p++ Base InGaAs p++ Base InGaAs p++ Base InGaAs p++ Base
InP nInGaAs n++ InGaAs n++
• 5 nm Ti layer for improved adhesion• 25 nm SiNx sidewalls protects Ti/TiW during Cl2 and BHF etch, improves adhesion• Standard triple mesa• BCB pasivation
Emitter prior to InP wet etch
Layer structure -- 70 nm collector DHBTThickness
(nm) Material Doping cm-3 Description
30 In0.53Ga0.47As 51019 : Si Emitter cap
10 In0.53Ga0.47As 41019 : Si Emitter
60 InP 31019 : Si Emitter
10 InP 1.21019 : Si Emitter
20 InP 1.01018 : Si Emitter
22 InGaAs 5-91019 : C Base
5.0 In0.53Ga0.47 As 21017 : Si Setback
11 InGaAs / InAlAs 21017 : Si B-C Grade
3 InP 6.2 1018 : Si Pulse doping
51 InP 21017 : Si Collector
5 InP 11019 : Si Sub Collector
5 In0.53Ga0.47 As 21019 : Si Sub Collector
300 InP 21019 : Si Sub Collector
Substrate SI : InP
Objective:• Thin collector and base for decreased electron transit time• Collector doping designed for high Kirk threshold, designed for 128 nm node• Setback and grade thinned for improved breakdown
Vbe = 1.0 V, Vcb = 0.0 V
Je = 0, 14, 21 mA/m2-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
80 100 120 140 160 180 200 220 240
Ener
gy (e
V)
distance (nm)
emitterbase
collector
valence band
conduction band
Je = 0mA/m2, 15mA/m2, 30mA/m2
RF & DC data –70 nm collector, 22 nm base InP Type-I DHBT
0
5
10
15
20
25
30
109 1010 1011 1012
109
1010
1011
1012
Gai
ns (d
B)
Frequency (Hz)
U
H21
MAG/MSG
Ie=22 mA, V
ce=1.45V
Je=16 mA/m2, V
cb=0.4V
ft, f
max=560 GHz
0
5
10
15
20
0 0.5 1 1.5 2 2.5 3 3.5 4
BCDHJLBBBB
Vce
(V)
25 mW/m2
Peak fmax
Peak ft
J e (mA
/um
2 )
Aje= 0.25 x 4.5 m2
Ajc= 0.6 x 5 m2
BVceo
~ 3.3 V
Emitter width ~ 250 nm
First reported device with ft, fmax > 500 GHz
BVCEO ~ 3.3 V, BVCBO = 3.9 V (Je,c = 15kA/cm2)
Emitter contact (from RF extraction), Rcont < 5 m2
Base: Rsheet = 780 /sq, Rcont ~ 15 m2
Collector: Rsheet = 11.1 /sq, Rcont ~ 10.1 m2
10-11
10-9
10-7
10-5
10-3
10-1
0
5
10
15
20
25
0.0 0.2 0.4 0.6 0.8 1.0
I c, Ib (A
)
Vce
(V)
Current G
ain
Aje= 0.25 x 4.5m2, A
jc= 0.6 x 5m2
nc= 1.05
nb=2.01
Ic
Ib
RF data –70 nm collector, 22 nm base InP Type-I DHBT
4
5
6
7
8
9
10
3
4
5
6
7
5 10 15 20 25C
cb (f
F)
Ccb /A
je (fF/um2)
Je (mA/m2)
Vcb
= 0.4 V
0.0 V
Aje=0.25 x 5.5 m2 A
jc=0.6 x 6 m2
Figure 2. Common
-emitter I
-V characteristics
Vcb
= -0.1 V
0.1 V
0.2 V
0.3 V
450
475
500
525
550
575
600
10 12.5 15 17.5 20 22.5J
e (mA/m2)
f (GH
z)
Vcb
= 0.4V
0.0V
0.1V
-0.1V
• No detectable increase in Ccb for high Je
• Indicates that Kirk threshold is not reached• Device performance limited by self heating?• Further scaling needed for better thermal performance!
cb
f
c
cb
cbcb
cb
cc
cb
VIQ
VVQ
IIC
Kirk effect increases Ccb
...even in DHBTs
Ccb / Je
Breakdown performance of InP HBTs
1
10
100 1000
InP/GaAsSbInP/InGaAsInP SHBTThis work
Brea
kdow
n volt
age,
BVce
o (V)
f (GHz)
?
Type I DHBT and Type II DHBT – similar BVceo
Type II DHBTs has low fmax due to base resistance
SHBT have substantially lower breakdown
Ec
Ev
Ec
Ev
Type I DHBT
Type II DHBT
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
TeledyneUIUC DHBT NTTFujitsu HEMT
SFU/ETHzUIUC SHBT UCSB NGST Pohang SHBTHRLIBM SiGe
Vitesse
f max
(GH
z)
ft (GHz)
500 GHz400 GHz300 GHz200 GHz maxff
Updated July 2007
600 GHz
Current status of fast transistors
)( ),/( ),/( ),/(
hence , :digital
gain, associated ,F :amplifiers noise low
mW/ gain, associated PAE,
:amplifierspower
)11(
2/) (alone or
min
1max
max
max
max
cb
cbb
cex
ccb
clock
ττVIRVIRIVC
f
m
ff
ff
ffff
:metrics better much
:metrics popular
250-300nm
600nm
300-400nm
Emitter Process will scale to 128 nm & below
• Emitter-base junction has been scaled down to 64 nm• Pure W emitter- no tapering
61 nm emitter-base junction!
Tungsten
Emitter metal peeled off during cross section cleave..
Conclusion
• HBTs @ 128 nm node→ 700 GHz ft, xx GHz fmax feasblechallenges: contact resistivity, robust deep submicron processes
• Dry etch based DHBT emitter process → sub 100 nm junctions feasible
• First RF results: 250nm junctions: simultaneous ft,fmax ~ 560 GHz• 125 nm devices should come soon !
• … THz before next DRC?
This work was supported by DARPA SWIFT program and a Swedish Research Council grant.