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High performance 110 nm InGaAs/InP DHBTs in dry-etched in-situ refractory emitter contact technologyVibhor Jain, Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark RodwellECE Department, University of California, Santa Barbara, CA 93106-9560
Zach Griffith, Miguel UrteagaTeledyne Scientific & Imaging, Thousand Oaks, CA 91360
Sebastian T BartschNanoelectronics Device Laboratory, EPFL, Switzerland
D Loubychev, A Snyder, Y Wu, J M Fastenau, W K LiuIQE Inc., 119 Technology Drive, Bethlehem, PA 18015
[email protected], 805-893-3273
Outline
• HBT Scaling Laws
• Fabrication– Challenges
– Process Development
• DHBT Epitaxial Design
• Results– DC & RF Measurements
• Summary
2
Ohmic contacts
Lateral scaling
Epitaxial scaling
Bipolar transistor scaling laws
To double cutoff frequencies of a mesa HBT, must:
(emitter length Le)
We
Tb TcWbc
Keep constant all resistances and currentsReduce all capacitances and transit delays by 2
RCf tr
2
1
exitbnbb vTDT 22satcc vT 2
eex AR /contact
contacts
contactsheet 612 AL
W
L
WR
e
bc
e
ebb
cccb /TAC 2
cbmax, /)( cbieeffc TVAvI
effcbeffbb CR
ff
,,max 8
3
InP Bipolar transistor scaling roadmap
Emitter
256 128 64 32 Width (nm)
8 4 2 1 Access ρ (Ω·µm2)
Base
175 120 60 30 Contact width (nm)
10 5 2.5 1.25 Contact ρ (Ω·µm2)
Collector 106 75 53 37.5 Thickness (nm)
Current density 9 18 36 72 mA/µm2
Breakdown voltage 4 3.3 2.75 2-2.5 V
fτ520 730 1000 1400 GHz
fmax850 1300 2000 2800 GHzPe
rfor
man
ceD
esig
n
Evan Lobisser et al, IPRM 2009 4
Sub-200 nm HBT node: Fabrication Challenges - I
Emitter yield drops during base contact, subsequent lift-off steps
High stress in emitter metal stack
Poor metal adhesion to InGaAs
5
Need for low stress, high yield emitters
Fallen emitters
Sub-200 nm HBT node: Fabrication Challenges - II
Undercut in emitter semiconductor
Helps in Self Aligned Base Liftoff
Narrow emitters need controlled semiconductor undercut
Thin semiconductor
To prevent short, base metal needs to be thinned
Higher base metal resistance
Solution: Undercut in the emitter metal to act as a shadow mask6
Slow etch plane
InP Wet Etch
Fast etch plane
Composite Emitter Metal Stack
TiW
W
• W/Ti0.1W0.9 metal stack
• Low stress
• Refractory metal emitters
• Vertical dry etch profile
W emitter
Erik Lind
Evan LobisserTiW emitter
7
Junction Width via SEM, TEM
W
TiW
BC
SiNx
BCB
M1
200 nm
110 nm100 nm
100 nm emitter metal-semiconductor junction
110 nm emitter-base junction 8
In-situ Emitter Contact
• Highly doped n-InGaAs regrown on IQE InGaAs and in-situ Mo deposited • Active carriers ~ 5×1019 cm-3
• In-situ Mo deposition on n-InGaAs - c ~ 1.1 .m2 *
• In-situ deposition repeatable contact resistivity
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30
Res
ista
nce
(
)
Gap spacing (m)
In-situ Mo contacts*
c ~ 1.1 .m2
* A. Baraskar et al., J. Vac. Sci. Tech. B, 27, 4, 2009
9
Process flow
Regrown InGaAs emitter cap
In-situ Mo dep
W/TiW/SiO2/Cr dep
SF6/Ar etch
SiNx Sidewall
SiO2/Cr removal
InGaAs Wet Etch
Second SiNx Sidewall
InP Wet Etch
Base Contact Lift-off
W/TiW interface acts as shadow mask for base lift off
Base and collector formed via lift off and wet etch
BCB used to passivate and planarize devices
10Self-aligned process flow for 110 nm DHBT
Mo
base
N- collector
InP substrate
sub collector
emitteremitter cap
n+ InGaAs
n InP
emitter capemitter
base
SiO2/Cr
TiW
MoW
SiN (SW)
emitterbase base base
Epitaxial Design
T(nm) Material Doping (cm-3) Description
10 In0.53Ga0.47As 51019 : Si Regrown Cap
10 In0.53Ga0.47As 51019 : Si Emitter Cap
10 InP 41019 : Si Emitter
10 InP 11018 : Si Emitter
30 InP 81017 : Si Emitter
25 In0.53Ga0.47As 7-41019 : C Base
7.5 In0.53Ga0.47 As 91016 : Si Setback
15 InGaAs / InAlAs 91016 : Si B-C Grade
3 InP 5 1018 : Si Pulse doping
74.5 InP 91016 : Si Collector
7.5 InP 11019 : Si Sub Collector
7.5 In0.53Ga0.47 As 21019 : Si Sub Collector
300 InP 21019 : Si Sub Collector
Substrate SI : InP
Vbe = 1 V, Vcb = 0.7 V, Je = 0, 30 mA/m2
Thin emitter semiconductor
Enables wet etching
High collector doping
High Kirk threshold11
En
erg
y (e
V)
Distance (nm)
Collector
Base
Emitter
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
0 50 100 150 200
Results - DC Measurements
BVceo = 2.5 V @ Je = 1 kA/cm2
β = 18
Base ρsheet = 730 Ω/□, ρc < 4 Ω·µm2
Collector ρsheet = 12 Ω/□, ρc = 9 Ω·µm2
0
10
20
30
40
50
60
0 1 2 3
J e (
mA
/um
2)
Vce
(V)
50 mW/m240 mW/m2
Vcb
= 0 V
Aje = 0.11m x 3.5m
Ib = 0.01 mA
Ib,step
= 0.2 mA
10-10
10-8
10-6
10-4
10-2
0 0.2 0.4 0.6 0.8 1
I b, I
c (
A)
Vbe
(V)
Ic
Ib
nc = 1.41
nb = 3.04
Solid Line: Vcb
= 0 V
Dashed Line: Vcb
= 0.7 V
@Peak ft,fmax
Je = 23.1 mA/m2
P = 41 mW/m2
12
Peak ft,fmax
Gummel plot
Common emitter I-V
DUTShort
Results - RF Measurements using Off-Wafer LRRM
Open
G S G
111 ))()(( openshortopenDUTtrans YYYYY
Standard Off Wafer LRRM
Open & Short Pad Cap Extraction
13
* Koolen et al., IEEE BCTM 1991
1-67 GHz RF Data and Extrapolated Cutoff Frequencies
0
10
20
30
40
109 1010 1011 1012
Gai
n (d
B)
freq (Hz)
Aje
= 0.11m x 3.5m
U
H21
MAG/MSG
ft = 400 GHz
fmax
= 660 GHz
Ic = 8.9 mA
Vce = 1.74 V
Je = 23.1 mA/m2
Vcb = 0.7 V
Single-pole fit to obtain cut-off frequencies14
Parameter Extraction
3
4
5
6
7
8
0 5 10 15 20 25 30
Cc
b (
fF)
Je (mA/m2)
Vcb
= 0 V
Vcb
= 0.4 V
Vcb
= 0.7 V
15
150
300
450
600
750
0 5 10 15 20 25 30 35
f max
(G
Hz)
Je (mA/m2)
Vcb
= 0.7 V
Vcb
= 0 V
100
200
300
400
500
0 5 10 15 20 25 30 35
f t (G
Hz)
Je (mA/m2)
Vcb
= 0 V
Vcb
= 0.7 V
Jkirk = 32 mA/m2 (@Vcb = 0.7V)
Ccb/Ic = 0.43 psec/V
Equivalent CircuitCcb,x = 2.97 fF
Ccb,i = 0.99 fF
Rcb = 31 k
Rc = 2.2
Rex = 9.4
Rbe = 126
Rbb = 40
Cje + Cdiff = 8.5 + 43.5 fF gme-j
0.169e(-j0.15ps)
Base
Emitter
Col
Ccg = 3 fF
freq (1.000GHz to 67.00GHz)
S(1,
1)
freq (100.0MHz to 67.00GHz)
S_pa
ram
eter
_Dee
mbe
d_P
NA.
.S11
dS_
para
met
er_D
eem
bed_
PN
A..S
22d
S(2,
2)S(
1,2)
*5S(
2,1)
/5S_
para
met
er_D
eem
bed_
PN
A..S
12d*
5S_
para
met
er_D
eem
bed_
PN
A..S
21d/
5
S21/5S12x5
S11 S22
--- : Measured x : Simulated
freq (1.000GHz to 67.00GHz)
S(1,
1)
freq (100.0MHz to 67.00GHz)
S_pa
ram
eter
_Dee
mbe
d_P
NA.
.S11
dS_
para
met
er_D
eem
bed_
PN
A..S
22d
S(2,
2)S(
1,2)
*5S(
2,1)
/5S_
para
met
er_D
eem
bed_
PN
A..S
12d*
5S_
para
met
er_D
eem
bed_
PN
A..S
21d/
5
S21/5S12x5
S11 S22
--- : Measured x : Simulated
Hybrid- equivalent circuit from measured RF data
Rex ≈ 3.6 m2
16
Microstrip Style TRL Calibration
Ref Plane for TRL
Ref Plane for TRL
t ~ 1 m
h ~ 1 m
w ~ 1.7 m
BCB
A A’
A – A’Metal 1Ref Plane set at device edge
No further de-embedding required
17Collector Metal
140-180GHz RF data
0
5
10
15
1011 1012
Ga
in (
dB)
freq (Hz)
U
H21
Aje
= 0.11m x 3.5m
fmax
= 660 GHzft = 465 GHz
-20dB/decade fit to obtain cut-off frequencies18
Ic = 9.1 mA
Vce = 1.75 V
Je = 23.6 mA/m2
Vcb = 0.7 V
Conclusion
• Demonstrated smallest junction width for a III-V DHBT (110 nm)
• Peak ft/fmax = 465/660 GHz
– Je = 23.6 mA/m2
– Power Density (P) = 41 mW/m2
• High current and power density operation (P > 50 mW/m2)
19
Questions?
Thank You
This work was supported by the DARPA THETA program under HR0011-09-C-0060 and DARPA TFAST under N66001-02-C-8080. A portion of this work was done in the UCSB nanofabrication facility, part of NSF funded NNIN network and MRL Central Facilities supported by the MRSEC Program of the NSF under award No. MR05-20415