2011 5 May ISCS Jain Presentation

8/12/2019 2011 5 May ISCS Jain Presentation

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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

Documents

2011 5 May ISCS Jain Presentation