InAlAs/InGaAs/InP DHBTs with Polycrystalline InAs Extrinsic Emitter Regrowth
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Transcript of InAlAs/InGaAs/InP DHBTs with Polycrystalline InAs Extrinsic Emitter Regrowth
InAlAs/InGaAs/InP DHBTs with Polycrystalline InAs Extrinsic
Emitter Regrowth
D. Scott, H. Xing, S. Krishnan, M. Urteaga, N. Parthasarathy and M. Rodwell
University of California, Santa Barbara
[email protected] 805-893-8044, 805-893-3262 fax
Advantages of InP vs. SiGe HBTs
InP HBT Material Properties:
• Available lattice-matched materials allows for emitter bandgap wider than base, allowing for higher base doping and lower base sheet resistance
• Electron velocities reported as high as 4107 cm/s
InP HBT Processing Technology :
• High topography mesa structure allows for small-scale integration
• Base-emitter junctions defined by etching and depositing a self-aligned base metal results in low yield and limits emitter scaling
Si/SiGe HBT Material Properties:
• Allowable lattice mismatch limits Ge:Si alloy ratio resulting in smaller emitter-base bandgap difference and higher base sheet resistance
• 4:1 lower electron velocity is seen in silicon
Si/SiGe Processing Technology :
• Planar process using silicon CMOS technology allows for VLSI
• Self-aligned base-emitter junctions are diffused, extrinsic base and emitter wider than the active junction allows for high degree of scaling
Evolution Cbc Reduction in III-V HBTs
Emitter
Collector
S.I. Substrate
Subcollector
Base
Emitter
Collector
S.I. Substrate
Subcollector
Base
Emitter
Collector
S.I. Substrate
Subcollector
Base
Emitter
Collector
Mesa HBT Cbc Reduction HBT
Transferred Substrate HBTHighly Scaled HBT
UCSB Highly Scaled HBT
UCSB has demonstrated laterallyscaled HBTs with emitters written by e-beam lithography.
These HBTs show problems with:
• High emitter resistance, Rex
• Low yield
These devices demonstrated lower than predicted values of f despite aggressive thinning of the epitaxial layers.
cbjeecbexcollectorbase CCqIkTCRf
/
2/1
Si/SiGe HBT Process Advantages
•Highly scaled
• very narrow active junction areas
• very low device parasitics
• high speed
• Low emitter resistance using wide n+ polysilicon contact
• Low base resistance using large extrinsic polysilicon contact
• High-yield, planar processing
• high levels of integration
• LSI and VLSI capabilitiesPublished Si/SiGe HBT f as high as 210 GHz
InP-based HBT f as high as 341 GHz
Polycrystalline n+ InAs
6 1018
8 1018
1 1019
1.2 1019
1.4 1019
1.6 1019
1.8 1019
2 1019
2.2 1019
945 950 955 960 965 970 975 980 985
Poly InAs:Si Doping vs. Temp01/28/2002
y = 1.13477e+05 * e^(3.35301e-02x) R= 9.99672e-01
Dopi
ng
Temp
Polycrystalline InAs grown on SiNx Hall measurements as high as:
• Doping = 1.3 1019 cm-3, Mobility = 620 cm2/V•s
• Results in doping-mobility product of 81021 (V •s •cm)-1
Compare these numbers to InGaAs lattice matched to InP:
• Doping = 1.0 1019 cm-3, Mobility = 2200 cm2/V•s
• Results in doping-mobility product of 221021 (V •s •cm)-1
Polycrystalline InAs has potential as an extrinsic emitter contact!
Base-Collector Template for Regrown Emitter HBT
Base-collector templateas-grown
Base-collector templateprior to regrowth
Regrown Emitter Fabrication Process
Regrowth Emitter/capetch
Base/collectoretch
Metalization
Large-area Small-emitter HBTs
First Attempt Results
0 100
1 10-3
2 10-3
3 10-3
4 10-3
5 10-3
6 10-3
0 0.5 1 1.5 2
First Attempt Regrown Emitter HBTCommon Emitter Curves, Ib = 500 uA, 6 steps
Ic (
A)
Vce (V)
SiNx
Regrown area
Regrown area very roughTransistor action!!
Growth and Process Improvements
SiNx
Regrown area
SiNx
Regrown area
First attempt at the base-emitter junction withoutRHEED or pyrometer
Second attempt with improvedpre-regrowth processing andRHEED/pyrometer features
added to the wafer
Growth and Process Improvements
First attempt at the base-emitter junction withoutRHEED or pyrometer
Second attempt with improvedpre-regrowth processing andRHEED/pyrometer features
added to the wafer
Base-emitter Regrowth SEM Detail
Base-emitter Regrowth SEM
2 μm emitter regrowth30K magnification
1 μm emitter regrowth55K magnification
Second Attempt DC Results
Common-emitter gain, β > 15
Unintended InAlAs Layer (>50Å)
• wide-bandgap layer acts as a current block from emitter to base
• reduces common-emitter gain
• may account for the dip in common-emitter curves
0.0 100
2.0 100
4.0 100
6.0 100
8.0 100
10 100
0 0.5 1 1.5 2 2.5 3 3.5 4
Regrown Common-Emitter Curves
AE = 0.8 x 15 um 2 I
b = 100uA/step
I c (m
A)
Vce
(V)
Base-emitter Current Leakage
0.0 100
2.0 10-3
4.0 10-3
6.0 10-3
8.0 10-3
1.0 10-2
0 0.5 1 1.5 2
Regrown Base-Emitter Diode for 1x15 um2 Emitter
Tight Alignment
Less Tight Alignment
Ib (
am
ps)
Vbe (volts)
Evidence of resistance seen in the base-emitter diode
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
0 0.2 0.4 0.6 0.8 1 1.2
Gummel for 1x15 um2 Emitter
Ic, I
b (
mA
)
Vbe (volts)
Ib
Ic
Evidence of base-emitter leakage seen in Gummel
Third Attempt DC Results
Common-emitter gain, β > 20
0.0 100
2.0 100
4.0 100
6.0 100
8.0 100
1.0 101
0 1 2 3 4
Regrown Common-Emitter Curves
AE = 0.8 x 15 um 2 I
b = 100uA/step
I c (m
A)
Vce
(V)
Third Attempt DC Results
0 100
2 10-3
4 10-3
6 10-3
8 10-3
10 10-3
-1 -0.5 0 0.5 1
1x15 um2 Base-Emitter Diode
I E (
A)
VBE
(V)
InGaAsbase
InP collector
InGaAsbase
InP collector
Base-collector band diagram withthe incorrect base-collector grade.This mistake may account for the
oscillations seen in the HBT I-V curve.
Base-collector band diagram withthe corrected base-collector grade.
A thin, heavily-doped layer wasinserted between the grade and
collector to pull the conduction banddown at the grade-collector junction.
Base-collector Grade Design Error
Regrowth with Buried Base Contact
InP HBTs with polycrystalline InAs extrinsic emitter regrowth
Objective:• Emulate high-yield 0.2 um SiGe emitter process• Polycrystalline extrinsic emitter wide contact for low resistance
Future Work:• RF devices need to be designed and demonstrated
• GaAsSb based DHBTs should be demonstrated
• Higher scaling in the regrown emitters needs to be examined
Growth Related Work:• A low-resistance p-type polycrystalline contact needs to be verified• Regrowth of the base will need to be explored to obtain a fully planar
HBT completely analogous to the Si/SiGe HBT
InP HBTs with polycrystalline InAs extrinsic emitter regrowth
Objective: Emulate high-yield 0.2 um SiGe emitter process Polycrystalline extrinsic emitter wide contact for low resistance
Future Work (short-term): Improve DC characteristics. Improve base capping layer to lower extrinsic base resistance GaAsSb base layers for higher carbon incorporation Deep submicron scaling of regrown emitter. RF device demonstration
Future work (long-term): full SiGe-like process flow for submicron InP HBT regrown emitter, regrown extrinsic base over buried dielectric spacer for Ccb reduction
Future Work
DC Device Work:• DC characteristics should be demonstrated without the design errors• Improvements will be made to the base capping layer to lower
extrinsic base resistance• GaAsSb based DHBTs should be demonstrated• Higher scaling in the regrown emitters needs to be examined
RF Device Work:• RF devices need to be designed and demonstrated
Growth Related Work:• A low-resistance p-type polycrystalline contact needs to be verified• Regrowth of the base will need to be explored to obtain a fully planar
HBT completely analogous to the Si/SiGe HBT