A Self-Aligned Epitaxial Regrowth Process for Subfor Sub

2010 Materials Research Society Spring Meeting, April 7, San Francisco

A Self-Aligned Epitaxial Regrowth Process for Sub 100 nm III V FETsfor Sub-100-nm III-V FETs

Mark Rodwell

A. D. Carter, G. J. Burek, M. A. Wistey*, B. J. Thibeault, A. Baraskar, U. Singisetti, J C S St A C G d C P l t

Mark. Rodwell, University of California, Santa Barbara

J. Cagnon, S. Stemmer, A. C. Gossard, C. PalmstrømUniversity of California, Santa Barbara*Now at Notre DameB Shi E Ki P C M I tB. Shin, E. Kim, P. C. McIntyreStanford UniversityY.-J. LeeI t lIntelB. Yue, L. Wang, P. Asbeck, Y. TaurUniversity of California, San Diego

III-V MOS: What is needed ?

True MOS device structures at 10 nm gate lengths10nm gate length, < 10nm electrode spacings, < 10nm contact widths

True MOS device structures at ~10 nm gate lengths

< 3 nm channel, < 1 nm gate-channel separation, < 3nm deep junctions, g p , p jFully self-aligned processes: N+ S/D, S/D contacts

D i t >> 1 A/ i @ 1/2 V lt VDrive currents >> 1 mA/micron @ 1/2-Volt Vdd.Low access resistances. Density-of-states limits.

Dielectrics: < 0.6 nm EOT , Dit < 1012 /cm2-eV y

impacts Ion, Ioff , ...

...and the channel must be grown on SiliconLow dielectric Dit must survive FET process.

pacts on, off ,

FET FETs

FET Scaling Laws GL

Changes required to double device / circuit bandwidth.

laws in constant voltage limit:

g q

laws in constant-voltage limit: GW widthgateFET parameter change

gate length decrease 2:1current density (mA/m), gm (mS/m) increase 2:1channel 2DEG electron density increase 2:1electron mass in transport direction constantelectron mass in transport direction constantgate-channel capacitance density increase 2:1

dielectric equivalent thickness decrease 2:1channel thickness decrease 2 1channel thickness decrease 2:1channel density of states increase 2:1

source & drain contact resistivities decrease 4:1

Current densities should doubleCharge densities must double

Semiconductor Capacitances Must Also Scale

)( VV motion)onalunidirecti(

oxc)( thgs VV )(

inversiondepth /Tc

2*2 2/

qEE wellf /)(

22 2/ gmqcdos

)2/()()(chargechannel 2* gmEEqVVcqn llfllfd )2/()()(charge channel gmEEqVVcqn wellfwellfdoss

scale. both alsomust states ofdensity & thicknessInversion

Calculating Current: Ballistic LimittoappliedvoltagevoltageFermiChannel c

vv )3/4(velocityelectronmean

2/* through velocity Fermidetermines

toapplied voltagevoltageFermiChannel2ffff

dos

vmqVEv

c

fvv )3/4(velocity electronmean

thgsequivdos

cfdos VVcc

ccVVc

s :charge Channel

minima band of # theis where, )/*(2/* ,22 gmmgcgmqc oodosdos

dosequiv cc

2/3

2/3,

2/1

V 1)/*()/(1)/*(

mmA 84

thgs

ooxodos

o VVmmgcc

mmgJ

Do we get highest current with high or low mass ?

2/1*2/3A VV

Drive Current Versus Mass, # Valleys, and EOT

2/3*

,

*

)/()/(1 where,

V 1mmA84

oequivodos

othgs

mmgccmmgK

VVKJ

0 35

0 25

0.3

0.35g=2g=1

InGaAs <--> InP Si

)/c/c(c 111

0.15

0.2

0.25

K

0.4 nm0.3 nm

/EOTε)/c/c(c oxequiv

2SiO

depth

11

0.05

0.1

0.15

EOT 1 0EOT i l d th f ti d th t

0.6 nm

0.4 nm

0

0.05

0.01 0.1 1m*/m

EOT=1.0 nmEOT includes the wavefunction depth term (mean wavefunction depth*

SiO2 /

semiconductor )

Standard InGaAs MOSFETs have superior Id to Si at large EOT.Standard InGaAs MOSFETs have inferior Id to Si at small EOT.

m /mo

2/12/12/1 L

Transit Delay versus Effective Mass

,

0272

*1* whereVolt1cm/s 1052.2

oeq

odos

thgs

gch m

mgcc

mmK

VVL

K

1 5EOT=1.0 nm 0.6 nm

1.5

elay

K2

0.6 nm

1 nm0.4 nm

1

d tra

nsit

de 0.4 nm

)/c/c(c oxequiv1

depth11

0.5

norm

aliz

ed

EOT i l d f ti d th t

g=1, isotropic bands

g=2, isotropic bands

/EOTεoxequiv

2SiO

dept

00 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

m*/m

EOT includes wavefunction depth term (mean wavefunction depth*

SiO2 /

semiconductor )

m*/mo

Low m* gives lowest transit time, lowest Cgs at any EOT.

III-V MOSFETs for VLSI: Why and Why Not.

Lower mass → Higher Carrier Velocity→ lower input capacitanceimproved gate delay in transistor-capacitance-limited gatesnot relevant in wiring-capacitance-limited gates (i.e. most of VLSI)

More importantly: potential for higher drive currentimproved gate delay in wiring-capacitance-limited gates (VLSI)

But this advantage is widely misunderstood in community

improved gate delay in wiring-capacitance-limited gates (VLSI)

But this advantage is widely misunderstood in communityInGaAs channels→ higher Id / Wg than Si only for thick dielectrics

....LOWER Id / Wg than Si for thin dielectricsbreak-even point is at ~0 5 nm EOTbreak-even point is at ~0.5 nm EOT

We will introduce (DRC2010) candidate III-V channel designsproviding higher Id / Wg than Si even for small EOT

Contacts: Low Resistivity, High Current Density

sidewall

metal gategate dielectric

source contact drain contact

b t t

barrier

quantum well / channelN+ source N+ drain

10)/( current, drive onimpact 10% For

hDDSD VVRI

substrate

V3.0)(@mmA/5.1~/Target

1.0)/(

thDDgD

thDDSD

VVWI

VVRI

m 20)(@g

gs

thDDgD

WR

)(!20t tid10 2 )(!m2.0contact widenm 10 2 c

contacts refractorymmA/ 150contact indensity current 2

F h 2 1 d ti i t l th

FET: Key Regions, Key Challenges

For each 2:1 reduction in gate length: gate dielectric:2:1 reduction in thicknesslimit: tunneling→high-Klimit: tunneling→high Klimit (high-K): defects

contacts:4:1 reduction in contact resistivity channel :

2:1 increase in electron density @ same voltage 2:1 shallower4:1 higher J

2:1 increase in electron density @ same voltage limit: # available electron states / area / energy"density of states bottleneck"; perceived to be fundamental

Hi hl S l d FETHighly Scaled FETP FlProcess Flows

Scalable nm III-V MOSFET: what is needed

True MOS device structures at 10 nm gate lengths10 nm gate length, < 10nm electrode spacings, < 10nm contact widths

True MOS device structures at ~10 nm gate lengths

< 3 nm channel, < 1 nm gate-channel separation, < w nm deep junctions, g p , p jFully self-aligned processes: N+ S/D, S/D contacts

InGaAs MOSFET with N+ Source/Drain by MEE Regrowth1

HAADF-STEM1*

InGaAsregrowth

Interface

InGaAs

regrowth

2 nm

* TEM by J. Cagnon, Susanne Stemmer Group, UCSB

Self-aligned source/drain defined by MBE regrowth2

Self aligned in situ Mo contacts3Self-aligned in-situ Mo contacts3

Process flow & dimensions selected for 10-30 nm Lg design;1Singisetti, ISCS 20082Wistey, EMC 20083Baraskar, EMC 2009

Regrown S/D process: key features

Self-aligned & low resistivitySelf aligned & low resistivity...source / drain N+ regions...source / drain metal contacts

Vertical S/D doping profile set by MBEno n+ junction extension below channelabrupt on few-nm scaleabrupt on few-nm scale

Gate-firstgate dielectric formed after MBE growth uncontaminated / undamaged surface

Process flow* * Singisetti et al, 2008 ISCS, September, FrieburgSingisetti et al; Physica Status Solidi C, vol. 6, pp. 1394,2009

Key challenge in S/D process: gate stack etch

R i t id d i i d t fRequirement: avoid damaging semiconductor surface:Approach: Gate stack with multiple selective etches*

SiO2

FIB Cross-section

Damage free channel

Cr

W

P l bl t 10 t l thProcess scalable to ~10 nm gate lengths* Singisetti et al; Physica Status Solidi C, vol. 6, pp. 1394,2009

Challenge in S/D process: dielectric sidewallsidewall

2 1019

2.4 1019

2.8 1019

ratio

n (c

m-3

)

gate source

8 1018

1.2 1019

1.6 1019

10nm SiNctro

n co

ncen

tr

4 1018

0 10 20 30 40 50 60 70 80

20 nm SiN30 nm SiNel

ec

distance (nm) spillover

ns under sidewall:electrostatic spillover from source gateelectrostatic spillover from source, gate

Sidewall must be kept thin:avoid carrier depletion, p ,avoid source starvation

MBE Regrowth→ Gap Near Gate→ Source Resistance

SEMMo+InGaAs

Ti/Au PadSiO2 cap

W / Cr / SiO2 gate

W/Cr gateg

SEM

gGap in regrowth

W / Cr / SiO2 gate

SEM

• Shadowing by gate: No regrowth next to gate

• Gap region is depleted of electronsHigh source resistance because of electron depletion in the gap

MBE growth by Dr. Mark Wistey, device fabrication and characterization by U. Singisetti

Migration Enhanced Epitaxial (MEE) S/D Regrowth*

High T migration enhancedEpitaxial (MEE) regrowth*

No Gap

45o tilt SEM

gateNo Gap Top of SiO2 gate

Side of gate

regrowth interfaceNo Gap

High temperature migration enhanced epitaxial regrowthHigh temperature migration enhanced epitaxial regrowth

*Wistey, EMC 2008Wistey, ICMBE 2008

MBE growth by Dr. Mark Wistey, device fabrication and characterization by U. Singisetti

Regrown S/D III-V MOSFET: Images

SiO2SiO2

WCr

InGaAsregrowth

SiNx

WCr

InGaAsregrowth

SiNx

W

Originalinterface

W

Originalinterface Ti/Au Pad

Mo+InGaAs

Ti/Au Pad

Mo+InGaAs

Cross-section after regrowth, Top view of completed devicebut before Mo deposition

Source Resistance: electron depletion near gate

SiOSiOSiO2

InGaAsregrowth

SiNx

SiO2

InGaAsregrowth

SiNx

WCr

Originalinterface

g

WCr

Originalinterface

g

R1 interfaceinterfaceR1R2

• Electron depletion in regrowth shadow region (R1 )

• Electron depletion in the channel under SiNx sidewalls (R2 )

Regrowth profile dependence on As flux*

SiO2

InGaAsInAlAs

Cr

InGaAs

InGaAsincreasing As flux

W

InGaAs

InGaAs

regrowth f uniform filling

multiple InGaAs regrowths with InAlAs marker layers

surface uniform filling

Uniform filling with lower As flux* Wistey et al, EMC 2009

Wistey et al NAMBE 2009

MBE growth by Dr. Mark Wistey, device fabrication and characterization by U. Singisetti

InAs source/drain regrowth

InAsregrowth

Gateregrowth

side of gate

top of gate

M S/D t l ith Mo S/D metal with N+ InAs underneath

Improved InAs regrowth with low As flux for uniform filling1p g gInAs less susceptible to electron depletion: Fermi pinning above Ec

2

1 Wistey et al, EMC 2009 Wistey et al NAMBE 2009.

2Bhargava et al , APL 1997

In-Situ Refractory Ohmics on MBE Regrown N-InGaAs

4

5

)

In-situ Mo on n-InAs In-situ Mo on n-InGaAs6

8

)

2

3

esis

tanc

e (

2

4

esis

tanc

e (

0

1

0 0.5 1 1.5 2 2.5 3 3.5

Re

ρc = 0.6 ± 0.4 Ω·µm2

n = 1×1020 cm-3

ρc = 1.0 ± 0.6 Ω·µm2

n = 5×1019 cm-3

0

2

0 0.5 1 1.5 2 2.5 3 3.5

Re

Gap Spacing (m) Gap Spacing (m)HAADF-STEM*

InGaAsth

Interface

InGaAs

regrowth

2 nm

InGaAs

TEM by Dr. J. Cagnon, Stemmer Group, UCSB

A. Baraskar

Benefits of refractory contacts

100 nm InGaAs grown in MBE

15 nm Pd/Ti diffusion

30 nm Mo

After 250°C anneal, Pd/Ti/Pd/Au diffuses 15nm into semiconductordeposited Pd thickness 2 5nmdeposited Pd thickness: 2.5nm

Refractory Mo contacts do not diffuse measurablyRefractory Mo contacts do not diffuse measurablyRefractory, non-diffusive metal contacts for thin semiconductor layers

A.. Baraskar

Resistivity of MEE Regrowth

15 m TLM width

(mV)

Volta

ge (m

V

~50 nm InAs regrowth has ~22 sheet resistivity50 nm InAs regrowth has 22 sheet resistivityContact resistivity is ~1.2 -m2.

Self-Aligned Contacts: Height Selective Etching*

Mo PR

PR PR

InGaAs

Dummy gateNo regrowth

* Burek et al, J. Cryst. Growth 2009

Fully Self-Aligned III-V MOSFET Process

0 5

0.6

0.7

0.8

mA/m

)

Lg = 200 nm W

g = 8 m

Vgs

: 0 to 4 V in 0.5 V steps

0.2

0.3

0.4

0.5

rain

cur

rent

, ID

(m

0

0.1

0 0.2 0.4 0.6 0.8 1

d

VDS

(V)

Subthreshold characteristics

Lg=0.35 m

10-3

10-2

Lg=1.0 m

325 mV/decade10-5

10-4

290 mV/decadeI d(A)

Vds

=0.1V10-7

10-6

Vd

=0.1V

290 mV/decade

-1 0 1 2 3 4 5

ds

Vds

=1.0 V

10-9

10-8

-1 0 1 2 3 4 5

ds

Vds

=1.0V

1 0 1 2 3 4 5V

gs(V)

1 0 1 2 3 4 5V

gs(V)

10-30 nm Process Development

SiO2 + SiNx Field: SiNx

Cr + SiNx

W + SiNx

Excellent structural yield in sub-100nm process flow

27 nm Self-Aligned InGaAs MOSFETSelf-aligned N+ S/D regrowthg g

shallow , high doping , low sheet Self-aligned Mo in-situ S/D contacts:

lo refractor shallolow , refractory → shallow

HAADF TEM

HAADF TEM

STEM is chemical contrast imaging -> Is the regrowth sinking?

C l iConclusion

III-V MOS

With appropriate design III-V channels can provide > current than Si With appropriate design, III-V channels can provide > current than Si ...even for highly scaled devices

But present III-V device structures are also unsuitable for 10 nm MOSl i l t d iti d j tilarge access regions, low current densities, deep junctions

Raised S/D regrowth process is a path towards a nm VLSI III-V device

(end)