Changhwan Shin Department of Electrical Engineering and Computer Sciences
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Transcript of Changhwan Shin Department of Electrical Engineering and Computer Sciences
Suppression of Random Dopant-Induced Threshold Voltage
Fluctuations in Sub-0.1μm MOSFET’s with Epitaxial and δ-Doped ChannelsA. Asenov and S. Saini, IEEE Trans. on Electron Devices, Aug 1999
Changhwan ShinDepartment of Electrical Engineering and Computer Sciences
University of California, Berkeley, CA 94720
March 2, 2009
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Outline
Introduction» Bulk MOSFET and its scaling challenges
» Random Dopant Fluctuations (RDFs)
MOSFET design to suppress the RDFs» Adjusting the channel doping profile
Summary
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Outline
Introduction» Bulk MOSFET and its scaling challenges
» Random Dopant Fluctuations (RDFs)
MOSFET design to suppress the RDFs» Adjusting the channel doping profile
Summary
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Incommensurate gains in ION with scaling» limited carrier mobilities
strain Si to enhance eff
» parasitic resistanceuse metallic (silicide) source/drain extensions
Bulk-Si MOSFET Scaling Challenges
Substrate
Gate
Source DrainLeff Nsub
XJ
LgTox
Performance variation
Leakage» drain current
reduce Tox,eq and Xj
» gate currentuse high- gate dielectric
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Sources of Variability Sub-wavelength lithography:
» Resolution enhancement techniques are costly and increase process sensitivity
Statistical dopant fluctuations» Atomistic effects become significant in nanoscale FETs
Design
Mask
Wafer
250nm250nm 180nm180nm
OPCOPC
90nm and Below90nm and Below
PSM
0°
180°
PSMPSM
0°
180°
0°
180°
OPC0°
180°OPCOPCOPC
0°
180°
A. Asenov, Symp. VLSI Tech. Dig., p. 86, 2007
SiO2Gate
A. Brown et al., IEEE Trans. Nanotechnology, p. 195, 2002
Source Drain
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Outline
Introduction» Bulk MOSFET and its scaling challenges
» Random Dopant Fluctuations (RDFs)
MOSFET design to suppress the RDFs» Adjusting the channel doping profile
Summary
Random Dopant Fluctuations (RDFs)
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“Intrinsic” variation in MOSFET parameters» Arising from the small number of discrete dopants and
their random position in the channel depletion regions
SiO2Gate
A. Brown et al., IEEE Trans. Nanotechnology, p. 195, 2002
Source Drain
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Outline
Introduction» Bulk MOSFET and its scaling challenges
» Random Dopant Fluctuations (RDFs)
MOSFET design to suppress the RDFs» Adjusting the channel doping profile
Summary
MOSFET designs to suppress RDFs
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Fluctuation-resistant architectures via appropriate tailoring of the channel doping profile» Thin, low doped layer in the channel
Radical solutions» Un-doped channel MOSFET (UTB, FinFET, DG, gate-all-
around)» More demanding of technological modification
Conventional Epitaxial Epitaxial w/ δ-doping
3D atomistic simulation results
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Epitaxial MOSFET» σVt is evaluated via 3D atomistic simulator
Results» σVt dramatically reduced for the first 10nm of epilayer
» Maximum depi should be considered with Tox, Xj, Leff
» Leff/depi > 5
» Boron diffusion into epi-layer; tolerable up to 1017cm-3
» Dependence of σVt on the back-doping; Screening effect The holes in the heavily doped region screen the charge of the discrete random acceptors in the thin depletion layer
3D atomistic simulation results
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Epitaxial MOSFET with the delta doping
Results» If the δ-doping is only partially depleted (i.e. depi is deep
enough, or screen effect is valid), the doping concentration NA
b increase will result in σVt reduction.
» Additional degree of freedom in tailoring the threshold voltage
Conventional Epitaxial Epitaxial w/ δ-doping
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Outline
Introduction» Bulk MOSFET and its scaling challenges
» Random Dopant Fluctuations (RDFs)
MOSFET design to suppress the RDFs» Adjusting the channel doping profile
Summary
Summary
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Fundamental issue; RDFs in deep sub-micron MOSFET
3D statistical atomistic simulations to study RDFs
Random dopant-induced threshold voltage fluctuations can be significantly suppressed in MOSFET’s with low-doped epitaxial channels.
Q & A
Thank you for your attention!!!
Questions?