Improved Regrowth of Self-Aligned Ohmic Contacts for III-V FETs

1
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
Dame mwistey_at_nd.edu
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
mwistey_at_nd.edu
2
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)

Large Area Contacts
Gap
Source
Drain
Gate

• Advantages of III-Vs

Large Rc
Top Barrier or Oxide

Channel

• Disadvantages of III-Vs

Bottom Barrier
Implant straggle, short channel effects
InAlAs Barrier
Low doping
Wistey, NAMBE 2009
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MBE Regrowth Bad at any Temperature?
200nm Gap

• Low growth temperature (lt400C)
• Smooth in far field
• Gap near gate (shadowing)
• No contact to channel (bad)

Gate
Source-Drain Regrowth
SiO2
Metals
high-k
Channel
Wistey, NAMBE 2009
SEMs Uttam Singisetti
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High Temperature MEE Smooth No Gaps
490C
460C
Gap
540C
560C
Smooth regrowth
SiO2 dummy gate
No gaps, but faceting next to gates
SiO2 dummy gate
Note faceting surface kinetics, not shadowing.
In9.7E-8, Ga5.1E-8 Torr
Wistey, NAMBE 2009
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Shadowing and Facet Competition
Slow diffusion rapid facet growth
Fast surface diffusion slow facet growth
SiO2
100
111
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Gate Changes Local Kinetics
1. Excess In Ga dont stick to SiO2
2. Local enrichment of III/V ratio
4. Low-angle planes grow instead
SiO2 or SiNx
sidewall
100
Gate
3. Increased surface mobility

• Diffusion of Group IIIs away from gate

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Change of Faceting by Arsenic Flux

• InGaAs layers with increasing As fluxes,
  separated by InAlAs.

Increasing As flux
InAlAs markers
InGaAs
SiO2
5x10-6
2x10-6
Cr
1x10-6
W
0.5x10-6
Original Interface
(Torr)
Growth conditions MEE, 540C, GaIn BEP1.5x10-7
Torr, InAlAs 500-540C MBE.
Wistey, NAMBE 2009
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Control of Facets by Arsenic Flux

• InGaAsSi layers with increasing As fluxes,
  separated by InAlAs.

Faceting
100
InAlAs markers
SiO2
Increasing As flux
111
InGaAs
SiO2
Conformal
5x10-6
2x10-6
Cr
1x10-6
W
0.5x10-6
Original Interface
(Torr)
Filling
Growth conditions MEE, 540C, GaIn BEP1.5x10-7
Torr, InAlAs 500-540C MBE.
Wistey, NAMBE 2009
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Low-As Regrowth of InGaAs and InAs
InGaAs
InAs
InAsregrowth
InGaAs regrowth (top view)

• Low As flux good for InAs too.
• InAs native defects are donors. Bhargava et al ,
  APL 1997
• Reduces surface depletion.

• No faceting near gate
• Smooth far-field too

4.7 nm Al203, 51012 cm-2 pulse doping In9.7E-8,
Ga5.1E-8 Torr
SEMs Uttam Singisetti
Wistey, NAMBE 2009
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InAs Source-Drain Access Resistance
4.7 nm Al203, InAs S/D E-FET.

• Upper limit Rs,max Rd,max 370 O-µm.
• Intrinsic gmi 0.53 mS/µm
• gm ltlt 1/Rs 3.3 mS/µm (source-limited case)
• Ohmic contacts no longer limit MOSFET
  performance.

Wistey, NAMBE 2009
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Conclusions

• Reducing As flux improves filling near gate
• Self-aligned regrowth a roadmap for scalable
  III-V FETs
• Provides III-Vs with a salicide equivalent
• InGaAs and relaxed InAs regrown contacts
• Not limited by source resistance _at_ 1 mA/µm
• Results comparable to other III-V FETs... but now
  scalable

Wistey, NAMBE 2009
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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

Wistey, NAMBE 2009