improved regrowth of self-aligned ohmic contacts for iii-v fets north american molecular beam...
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3 Wistey, NAMBE 2009 Motivation for Regrowth: Scalable III-V FETs Classic III-V FET (details vary): Channel Bottom Barrier InAlAs Barrier Top Barrier or Oxide Gate Low doping Gap SourceDrain Large Rc { Large Area Contacts { III-V FET with Self-Aligned Regrowth: Channel In(Ga)P Etch Stop Bottom Barrier High-k Gate n+ Regrowth High Velocity Channel Implant: straggle, short channel effects Advantages of III-V’s Disadvantages of III-V’s Small R access Small Rc Self-aligned, no gaps High doping: cm -2 avoids source exhaustion 2D injection avoids source starvation Dopants active as-grown High mobility access regions High barrier Ultrathin 5nm doping layer }TRANSCRIPT
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Improved Regrowth of Self-Aligned Ohmic Contacts for III-V FETs
North American Molecular Beam Epitaxy Conference (NAMBE),8-11-2009
Mark A. Wistey
Now at University of Notre [email protected]
A.K. Baraskar, U. Singisetti, G.J. Burek, M.J.W. Rodwell, A.C. GossardUniversity of California Santa Barbara
P. McIntyre, B. Shin, E. KimStanford University
Funding: SRC
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2Wistey, NAMBE 2009
Outline: Regrown III-V FET Contacts
•Motivation for Self-Aligned Regrowth
•Facets, Gaps, Arsenic Flux and MEE
•MOSFET Results•Conclusion
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3Wistey, NAMBE 2009
Motivation for Regrowth: Scalable III-V FETs
Classic III-V FET (details vary):
ChannelBottom BarrierInAlAs Barrier
Top Barrier or Oxide
Gate
Low doping
GapSource Drain
Large Rc {
Large Area Contacts{III-V FET with Self-Aligned Regrowth:
ChannelIn(Ga)P Etch Stop
Bottom Barrier
High-k
Gate
n+ Regrowth
High Velocity Channel
Implant: straggle,short channel effects
• Advantages of III-V’s
• Disadvantages of III-V’s
Small Raccess
Small RcSelf-aligned, no gaps
High doping: 1013 cm-2 avoids source exhaustion
2D injection avoids source starvation
Dopants active as-grown
High mobilityaccess regions
High barrier
Ultrathin 5nm doping layer}
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4Wistey, NAMBE 2009
MBE Regrowth: Bad at any Temperature?
• Low growth temperature (<400°C):
–Smooth in far field–Gap near gate (“shadowing”)–No contact to channel (bad)
Gate
200nm Gap
Source-DrainRegrowth
SEMs: Uttam Singisetti
Metals
Channel
SiO2
high-k Gate
Source-DrainRegrowth
Regrowth: 50nm InGaAs:Si, 5nm InAs:Si. Si=8E19/cm3, 20nm Mo, V/III=35, 0.5 µm/hr.
•High growth temperature (>490°C):– Selective/preferential epi on InGaAs– No gaps near gate
– Rough far field – High resistance
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5Wistey, NAMBE 2009
560C
490C460C
SiO2 dummy
gate
SiO2 dummy
gate
540C
No gaps, but
faceting next to gates
Gap
High Temperature MEE: Smooth & No Gaps
Smooth
regrowth
Note faceting: surface kinetics, not shadowing.
In=9.7E-8, Ga=5.1E-8 Torr
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Wistey NAMBE 2009 6
Shadowing and Facet Competition
[111]
[100]
Fast surface diffusion = slow facet
growth
Slow diffusion = rapid facet growth
Shen & Nishinaga, JCG 1995
[111] faster[100] faster
• Shen JCG 1995 says:Increased As favors [111] growth
SiO
2
[111]
[100]
Slow diffusion =fast growth
Fast surface diffusion =
slow facet growth
SiO
2
Good fill next to gate.
• But gap persists
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Wistey NAMBE 2009 7
Gate Changes Local Kinetics
[100]
2. Local enrichment of III/V ratio
4. Low-angle planes grow insteadsidew
all
1. Excess In & Ga don’t stick to SiO2
• Diffusion of Group III’s away from gate
3. Increased surface mobility
Gate
SiO2 or SiNx
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Change of Faceting by Arsenic Flux
SiO2WCr
Increasing As flux
Original Interface
InAlAsmarkers
InGaAs
0.5x10-6
1x10-6
2x10-6
5x10-6
• Lowest arsenic flux → “rising tide fill”
• No gaps near gate or SiO2/SiNx
• Tunable facet competition
(Torr)
Growth conditions: MEE, 540*C, Ga+In BEP=1.5x10-7 Torr, InAlAs 500-540°C MBE.
• InGaAs layers with increasing As fluxes, separated by InAlAs.
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Control of Facets by Arsenic Flux
SiO2WCr
Increasing As flux
Original Interface
InAlAsmarkers
InGaAs
0.5x10-6
1x10-6
2x10-6
5x10-6
• Lowest arsenic flux → “rising tide fill”
• No gaps near gate or SiO2/SiNx
• Tunable facet competition
(Torr)
Growth conditions: MEE, 540*C, Ga+In BEP=1.5x10-7 Torr, InAlAs 500-540°C MBE.
• InGaAs:Si layers with increasing As fluxes, separated by InAlAs.
[111]
[100]
SiO
2
Filling[11
1]
[100]
SiO
2
[111]
[100]
SiO
2
Conformal
Faceting
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Low-As Regrowth of InGaAs and InAs
4.7 nm Al203, 5×1012 cm-2 pulse dopingIn=9.7E-8, Ga=5.1E-8 Torr
SEMs: Uttam Singisetti
InGaAs regrowth (top view)
• Low As flux good for InAs too.
• InAs native defects are donors. Bhargava et al , APL 1997
• Reduces surface depletion.
InAsregrowth
InGaAs InAs
• No faceting near gate• Smooth far-field too
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11Wistey, NAMBE 2009
InAs Source-Drain Access Resistance4.7 nm Al203, InAs S/D E-FET.
• Upper limit: Rs,max = Rd,max = 370 Ω−μm.• Intrinsic gmi = 0.53 mS/μm• gm << 1/Rs ~ 3.3 mS/μm (source-limited case)
➡ Ohmic contacts no longer limit MOSFET performance.
740 Ω-µm
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Conclusions
• Reducing As flux improves filling near gate• Self-aligned regrowth: a roadmap for scalable III-V FETs
–Provides III-V’s with a salicide equivalent• InGaAs and relaxed InAs regrown contacts
–Not limited by source resistance @ 1 mA/µm–Results comparable to other III-V FETs... but now scalable
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Acknowledgements
• Rodwell & Gossard Groups (UCSB): Uttam Singisetti, Greg Burek, Ashish Baraskar, Vibhor Jain...
• McIntyre Group (Stanford): Eunji Kim, Byungha Shin, Paul McIntyre
• Stemmer Group (UCSB): Joël Cagnon, Susanne Stemmer
• Palmstrøm Group (UCSB): Erdem Arkun, Chris Palmstrøm
• SRC/GRC funding• UCSB Nanofab: Brian Thibeault, NSF