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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)