Transcript North American Molecular Beam Epitaxy Conference (NAMBE),8-11-2009 Improved Regrowth of Self-Aligned Ohmic Contacts for III-V FETs Mark A.

North American Molecular Beam Epitaxy Conference (NAMBE),8-11-2009
Improved Regrowth of Self-Aligned
Ohmic Contacts for III-V FETs
Mark A. Wistey
Now at University of Notre Dame
[email protected]
A.K. Baraskar, U. Singisetti, G.J. Burek,
M.J.W. Rodwell, A.C. Gossard
University of California Santa Barbara
P. McIntyre, B. Shin, E. Kim
Stanford University
Funding: SRC
[email protected]
Outline: Regrown III-V FET Contacts
•Motivation for Self-Aligned
Regrowth
•Facets, Gaps, Arsenic Flux and
MEE
•MOSFET Results
•Conclusion
Wistey, NAMBE 2009
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Motivation for Regrowth: Scalable III-V FETs
Classic III-V FET (details vary):
{
Source
Large Area Contacts
Gap
Drain
Gate
Large Rc
Top Barrier or Oxide
• Disadvantages
of III-V’s
Channel
Bottom Barrier
InAlAs Barrier
{
• Advantages
of III-V’s
Implant: straggle,
short channel effects
Low
doping
III-V FET with Self-Aligned Regrowth:
High Velocity Channel
Small Raccess
Small Rc
High mobility
access regions
High doping: 1013 cm-2
avoids source exhaustion
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Self-aligned, no gaps
Gate
High-k
n+ Regrowth
High barrier
Channel
In(Ga)P Etch Stop
Bottom Barrier
2D injection avoids
source starvation
5nm
} Ultrathin
doping layer
Dopants active as-grown
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MBE Regrowth: Bad at any Temperature?
200nm Gap
• Low growth temperature (<400°C):
–Smooth in far field
–Gap near gate (“shadowing”)
–No contact to channel (bad)
Gate
Source-Drain
Regrowth
SiO2
Metals
high-k
Channel
• High growth temperature (>490°C):
– Selective/preferential epi on InGaAs
– No gaps near gate
– Rough far field
– High resistance
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Gate
Source-Drain
Regrowth
Regrowth: 50nm InGaAs:Si, 5nm InAs:Si.
Si=8E19/cm3, 20nm Mo, V/III=35, 0.5 µm/hr.
SEMs: Uttam Singisetti
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High Temperature MEE: Smooth & No Gaps
460C
490C
Gap
540C
560C
Smooth
regrowth
SiO2 dummy
gate
SiO2 dummy
gate
In=9.7E-8, Ga=5.1E-8 Torr
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No gaps, but
faceting next
to gates
Note faceting: surface kinetics, not shadowing.
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Shadowing and Facet Competition
SiO2
Shen & Nishinaga, JCG 1995
Fast surface
diffusion =
slow facet
growth
Slow diffusion =
rapid facet growth
SiO2
[100]
Slow
diffusion =
fast growth
Fast surface
diffusion =
slow facet growth
• Shen JCG 1995 says:
Increased As favors [111] growth
[100]
Good fill next to gate.
Wistey NAMBE 2009
• But gap persists
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Gate Changes Local Kinetics
1. Excess In & Ga
don’t stick to SiO2
Gate
sidewall
SiO2 or SiNx
2. Local
enrichment
of III/V ratio
4. Low-angle planes grow
instead
[100]
3. Increased
surface mobility
• Diffusion of Group III’s away from gate
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Change of Faceting by Arsenic Flux
• InGaAs layers with increasing As fluxes, separated by InAlAs.
InAlAs InGaAs
markers
SiO2
Cr
Increasing
As flux
5x10-6
2x10-6
1x10-6
0.5x10-6
(Torr)
W
• Lowest arsenic flux → “rising
tide fill”
• No gaps near gate or SiO2/SiNx
• Tunable facet competition
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Growth conditions: MEE, 540*C, Ga+In BEP=1.5x10-7 Torr, InAlAs 500-540°C MBE.
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Control of Facets by Arsenic Flux
• InGaAs:Si layers with increasing As
fluxes, separated by InAlAs.
Faceting
[100]
SiO2
InAlAs
markers
Increasing
InGaAs As flux
Cr
W
• Lowest arsenic flux → “rising
tide fill”
• No gaps near gate or SiO2/SiNx
• Tunable facet competition
Wistey, NAMBE 2009
Growth conditions: MEE, 540*C, Ga+In BEP=1.5x107 Torr, InAlAs 500-540°C MBE.
Conformal
SiO2
5x10-6
2x10-6
1x10-6
0.5x10-6
(Torr)
[100]
Filling
SiO2
SiO2
[100]
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Low-As Regrowth of InGaAs and InAs
InGaAs
InAs
InAs
regrowth
InGaAs regrowth
(top view)
• No faceting near gate
• Smooth far-field too
• Low As flux good for InAs too.
• InAs native defects are donors.
Bhargava et al , APL 1997
• Reduces surface depletion.
4.7 nm Al203, 5×1012 cm-2 pulse doping
In=9.7E-8, Ga=5.1E-8 Torr
Wistey, NAMBE 2009
SEMs: Uttam Singisetti
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InAs Source-Drain Access Resistance
4.7 nm Al203, InAs S/D E-FET.
740 Ω-µm
• Upper limit: Rs,max = Rd,max = 370 Ω−μm.
• Intrinsic gmi = 0.53 mS/ m
• gm << 1/Rs ~ 3.3 mS/μm (source-limited case)
➡ Ohmic contacts no longer limit MOSFET
performance.
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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
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