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

dennis@umail.ucsb.edu 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