Gate Last Indium-Gallium-Arsenide MOSFETs with Regrown Source-Drain Regions and ALD Dielectrics
- Degree Grantor:
- University of California, Santa Barbara. Electrical & Computer Engineering
- Degree Supervisor:
- Mark Rodwell
- Place of Publication:
- [Santa Barbara, Calif.]
- University of California, Santa Barbara
- Creation Date:
- Issued Date:
- Engineering, Electronics and Electrical and Engineering, Materials Science
- Dissertations, Academic and Online resources
- Ph.D.--University of California, Santa Barbara, 2013
III-V-based MOSFETs have the potential to exceed the performance of silicon-based MOSFETs due to the semiconductor's small electron effective mass. Modern silicon-based MOSFETs with 22 nm gate lengths utilize high-k gate insulators and non-planar device geometries to optimize device performance. III-V HEMT technology has achieved similar gate lengths, but large source-drain access resistances and the lack of high-quality gate insulators prevent further device performance scaling. Sub-22 nm gate length III-V MOSFETs require metal-semiconductor contact resistivity to be less than 1 ohm-micron squared, gate insulators with less than 1 nm effective oxide thickness, and semiconductor-insulator interface trap densities less than 2E12 per square centimeter per electron volt.
This dissertation presents InGaAs-based III-V MOSFET process flows and device results to assess their use in VLSI circuits. Previous III-V MOSFET results focused on long (>100 nm) gate lengths and ion implantation for source-drain region formation. Scaling III-V MOSFETs to shorter gate lengths requires source-drain regions that have low sheet resistance, high mobile charge densities, and low metal-semiconductor contact resistance. MBE- and MOCVD-based raised epitaxial source-drain regrowth meet these requirements. MBE InAs source-drain regrowth samples have shown 0.5 to 2 ohm-micron squared metal semiconductor contact resistivities. MOCVD InGaAs source-drain regrowth samples have shown < 100 ohm-micron single-sided access resistance to InGaAs MOSFETs.
Gate insulators on III-V materials require large conduction band offsets to the channel, high dielectric permittivities, and low semiconductor-insulator interface trap densities. An in-situ hydrogen plasma / trimethylaluminum treatment has been developed to lower the gate semiconductor-insulator interface trap density. This treatment, done immediately before gate insulator deposition, has been shown to lower MOS capacitor interface trap densities by more than a factor of two.
Devices using gate-first MBE regrowth, gate-last MBE regrowth, and gate-last MOCVD regrowth were fabricated and resulting devices characterized. 65 nm gate length gate-first MBE regrowth devices employing a 2.2 nm EOT Al 2O3 gate insulator show peak transconductances of 0.3 mS/micron at 1 V Vds. Gate-first FET performance scaling is limited by processed-induced damage and ungated access regions. 64 nm gate length gate-last MBE regrowth devices employing a 1.21 nm EOT Al2O 3 / HfO2 bi-layer gate insulator show peak transconductances of 1.4 mS/micron at 0.5 V Vds. Other gate-last MBE samples had long channel subthreshold swings as low as 117 mV/dec. 48 nm gate length gate-last MOCVD MOSFETs employing a 0.8 nm EOT HfO2 gate insulator and digital channel etching show peak transconductances of 2 mS/micron at 0.5 V Vds, with long channel devices having 97 mV/dec subthreshold swing.
- Physical Description:
- 1 online resource (230 pages)
- UCSB electronic theses and dissertations
- Catalog System Number:
- Andrew Carter, 2013
- In Copyright
- Copyright Holder:
- Andrew Carter
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