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InGaAs/InP DHBTs in a planarized,etch-back technology for base contacts
Vibhor Jain, Evan Lobisser, Ashish Baraskar, Brian J Thibeault,Mark RodwellECE Department, University of California, Santa Barbara, CA 93106-9560
D Loubychev, A Snyder, Y Wu, J M Fastenau, W K LiuIQE Inc., 119 Technology Drive, Bethlehem, PA 18015
[email protected], 805-893-3273
International Symposium on Compound Semiconductors 2011
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Outline
HBT Scaling Laws Refractory base ohmics
Fabrication
DHBT Epitaxial Design and Results Summary
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Ohmic contacts
Lateral scaling
Epitaxial scaling
Bipolar transistor scaling laws
To double cutoff frequencies of a mesa HBT, must:
(emitter length Le)
We
Tb Tc
Wbc
Keep constantall resistances and currentsReduce all capacitances and transit delays by 2
RC
f
tr
2
1
exitbnbb vTDT 22
satcc 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
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InP bipolar transistor scaling roadmap
Emitter
256 128 64 32 Width (nm)
8 4 2 1 Access (m2)
Base
175 120 60 30 Contact width (nm)
10 5 2.5 1.25 Contact (m2)
Collector 106 75 53 37.5 Thickness (nm)
Current density 9 18 36 72 mA/m2
Breakdown voltage
4 3.3 2.75 2-2.5 V
f
520 730 1000 1400 GHz
fmax 850 1300 2000 2800 GHzPerforma
nce
Design
Rodwell, Le, Brar, Proceedings of IEEE, 2008
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Pd contacts diffuse in base (p-InGaAs)
Contact resistance for thin base Limits base thickness
Scaling Limitation
100 nm InGaAs grown in MBE
15 nm Pd diffusion
Need for non-diffusive, refractory base metal
Contact diffusionTEM by E Lobisser
Ashish Baraskar
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Refractory base ohmics
Doping Metal Type c( -m2)1.5E20 Mo As deposited 2.5
1.5E20 Ru/Mo As deposited 1.3
1.5E20 W/Mo As deposited 1.2
1.5E20 Ir/Mo As deposited 1.0
2.2E20 Ir/Mo As deposited 0.62.2E20 Ir/Mo Annealed 0.8
Ashish Baraskar et al., EMC 2010
Refractory metal base contacts
Require a blanket deposition and etch-back process
Ashish Baraskar et al., Int. MBE 2010
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W
Mo
InGaAs
p+ InGaAs Base
Ti0.1W0.9
InP
W
Mo
InGaAs
p+ InGaAs Base
Ti0.1W0.9
InP
SiNx
Base process flowII
Lift-off Ti/Au
Low base metal resistance
Blanket SiNx mask
Etch base contact metal in the field
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Base Planarization
Planarization: Emitter projectingfrom PR for W dry etch
Etch Back
Planarization Boundary
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Epitaxial Design
T(nm) Material Doping (cm-3) Description
10 In0.53Ga0.47As 81019 : Si Emitter Cap15 InP 51019 : Si Emitter 15 InP 21018 : Si Emitter 30 InGaAs 9-51019 : C Base4.5 In0.53Ga0.47 As 91016 : Si Setback
10.8 InGaAs / InAlAs 91016 : Si B-C Grade3 InP 6 1018 : Si Pulse doping
81.7 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 = 25 mA/m2-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
0 50 100 150 200
Energy(eV)
Distance (nm)
Emitter
Collector
Base
Low Base doping Good refractory ohmics not possible
Pd/W contacts used
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Results - DC Measurements
BVceo = 2.4 V@ Je = 1 kA/cm2
= 26
JKIRK= 21 mA/mm2
@Peak f,fmax
Je = 17.9 mA/mm2
P = 30 mW/mm2
Gummel plot
Common emitter I-V
0
10
20
30
0 0.5 1 1.5 2 2.5
Je(mA/m
2)
Vce
(V)
P = 25 mW/mm2
Peak f/f
max
Ib= 200 mA
Ib,step
= 200 mA
10-7
10-5
10-3
10-1
0 0.2 0.4 0.6 0.8 1
Ic,
Ib(A)
Vbe
(V)
Ic
Ib
Solid Line: Vcb
= 0 V
Dashed Line: Vcb
= 0.7 V
nc= 1.76
nb= 3.29
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Equivalent Circuit
Hybrid- equivalent circuit from measured RF data
Rex = 6 m2Ccb,x = 4.48 fF
Ccb,i = 1.3 fF
Rcb = 17 kRc = 1.7
Rex = 4.7
Rbe = 42
Rbb = 24
Cje + Cdiff= (15 + 241) fF gmVbee-j
0.73Vbeexp(-j0.15ps)
Base
Emitter
Col
Ccg = 6.8 fF
Ccb,x = 4.48 fF
Ccb,i = 1.3 fF
Rcb = 17 kRc = 1.7
Rex = 4.7
Rbe = 42
Rbb = 24
Cje + Cdiff= (15 + 241) fF gmVbee-j
0.73Vbeexp(-j0.15ps)
Base
Emitter
Col
Ccg = 6.8 fF
S21/12
S12x5
S11S22
--- : Measuredx : Simulated
S21/12
S12x5
S11S22
--- : Measuredx : Simulated
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TEM
Large undercut in base mesa
Pd/W adhesion issue High Rbb Low fmax 0.1 m
Pd/W adhesion issue
Large mesa undercut
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Summary
Demonstrated a planarized, etch back process forrefractory base
contacts Demonstrated DHBTs with peak f/ fmax = 410/690 GHz Higher base doping, thinner base and refractory base ohmics
needed to enable higher bandwidth devices
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Questions?
hank You
This work was supported by the DARPA THETA program under HR0011-09-C-006.
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