A (partial, biased?) history of the MOSFET
from a physicist’s perspective
(i.e., A brief history of sand)
M. Fischetti
October 2, 2009
Department of Electrical and Computer Engineering
This talk: Void where prohibited, limitations and restrictions apply
 Technology (i.e., how do we make them?) vs. electronic operation (i.e., how do they work
and how do we make them better?)
 Too much to cover
 Talk about what I know
 Major omissions (that is, a disclaimer*):
• Doping: Diffusion (theory and technology), ion implantation, high-doping effects
• Lithography, possibly a “technology enabler”: Optical, contact, phase-shift, X-ray…
• Metallization: Deposition/growth, DAMASCENE, electromigration
• Etching: Wet vs. dry, RIE, plasma
• Film growth: Epitaxy, CVD, PE-CVD, MBE, ALD,…
• Contacts: Silicides, salicides, FUSI,…
• Layout issues: Isolation (deep/shallow trenches), cross-talk, latch-up, design rules,
DRAM/SRAM design, power,…
• …
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History of the MOSFET? What’s that?
 Thanks to Jiseok Kim for having put me on the spot….
It’s OK… I wish him good luck in getting his PhD wherever ELSE he may wish to get it….
 I’m not sure what he meant by “history”… So, let’s start from the beginning….
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The main character of our story: The MOSFET
 No other human artifact has been fabricated in larger numbers (except perhaps nails?)
 “…some consider it one of the most important technological breakthroughs in human
history…” (Wikipedia, the source of all human knowledge)
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Timeline I
Technology
Physics/Simulations
1925: Julius Edgar Lilienfeld’s MESFET patent
1935: Oskar Heil’s MOSFET patent
194?: Unpublished Bell Labs MESFET
1947: Ge BJT (Bardeen, Brattain, Shockley, Bell Labs)
1954: Si BJT (Teal, Bell Labs)
1955: Si, Ge conduction band (Herring&Vogt)
1960: MOSFET (Atalla&Khang, Bell Labs)
Deformation-potential, high-field (Bardeen&Shockley)
1961: Integrated circuit (Kilby, TI)
1957: BTE in semiconductors – impurities (Luttinger&Kohn),
1963: CMOS (Sah&Wanlass, Fairchild)
phonons (Price, Argyles)
1964: Commercial CMOS IC (RCA)
1964: Band structure calculations (Hermann)
1965: DRAM (Fairchild)
Monte Carlo for semiconductors (Kurosawa)
1968: Poly-Si gate (Faggin&Klein, Fairchild)
1965: Linear-parabolic oxidation model (Deal&Grove)
1968: 1-FET DRAM cell (Dennard, IBM)
1966: Observations of 2DEG (Fowler, Fang, Stiles, Stern,..)
1971: UV EPROM (Frohman, Intel)
1967: Conductance technique (Nicollian&Goetzberger)
1971: Full CPU in chip, Intel 8008 (Faggin, Intel)
1974: Digital watch
1974: DDE device simulator (Cottrell&Buturla)
1974: Scaling theory (Gänsslen&Dennard, IBM)
1975: Quantum Hall Effect predicted (Ando)
1978: Use of ion implanter
1978: Flotox EEPROM (Perlegos, Intel)
1979: Quantum Hall Effect observed (von Klitzing)
1980: Ion-implanted CMOS IC
1981: Identification of native Nit: Pb-centers (Poindexter)
1980: Plasma etching
Full-band MC (Shichijo&Hess)
1984: Scaling theory <0.25 μm (Baccarani, U. Bologna)1982: Fractional QHE observed (Störmer&Tsui, Laughlin)
1986: 0.1 μm Si MOSFET (Sai-Halasz, IBM)
1988: Full-band MC device simulator (MVF&Laux)
1991: CMOS replaces BJT also at high-end
1992: NEGF device simulator (Lake, Klimeck, et al.)
1993: DGFET scalable to 30 nm (theory, Frank et al.)
2007: Non-SiO2 (HfO2–based) MOSFET (Intel)
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Timeline II
Feature size
1975: 20 μm (tOX≈250 nm)
Main Problems
↑
SiO2 growth and instability: Ions, traps, interface
1980: 10 μm (tOX≈150 nm)
1985: 5 μm (tOX≈70 nm)
SiO2 instability during operation: electron trapping, NBTI
Hot electron effects: oxide trapping, VT shift, breakdown
1990: 1 μm (tOX≈15 nm)
Scaling: Short-channel effects (SCE), oxide, dopants
↓
1995: 0.35 μm (tOX≈8 nm)
2000: 0.18 μm (tOX≈3 nm)
….life is good…
2005: 65 nm (tOX≈1.4 nm)
2010: 32 nm (tOX≈1.2 nm?)
Scaling: SCE, insulator
Leakage: Insulator
Power: Alternative devices
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Timeline III
Feature size
Transport Physics
1975: 20 μm
1980: 10 μm
1985: 5 μm
Drift-Diffusion
↓
Hydrodynamic/
Energy transport
1990: 1 μm
1995: 0.5 μm
2000: 0.25 μm
2005: 63 nm
2010: 32 nm
2015: 16 nm ?
↕
Boltzmann
↓
Quantum?
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Transistor prehistory
1935 Heil’s patent
1947 First BJT
1960 Atalla’s MOSFET
Bardeen, Shockley, Brattain (Bell Labs)
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IC Prehistory
1961 Kilby’s first IC
1962 Fairchild IC
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1964 First MOS IC
(RCA)
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Moore’s law prehistory
Gordon Moore
1965: Cost vs time
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Moore’s law 1960-1975
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Moore’s law
Number of transistors/die & feature size vs time
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Microprocessor prehistory
1965: Federico Faggin
1968: Fairchild 8-bit μP
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1971: Intel 8080 μP
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Memory prehistory: DRAM and EPROM
Bob Dennard (1-FET DRAM cell, 1968;
scaling theory with Fritz Gänsslen,1974)
Department of Electrical and Computer Engineering
1971 Frohman’s UV-erasable EPROM
(written by avalanche injection)
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More historical trends
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J. Armstrong (ca.1989)
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Timeline II once more
Feature size
1975: 20 μm (tOX≈250 nm)
Main Problems
↑
SiO2 growth and instability: Ions, traps, interface
1980: 10 μm (tOX≈150 nm)
1985: 5 μm (tOX≈70 nm)
1990: 1 μm (tOX≈15 nm)
SiO2 instability during operation: electron trapping, NBTI
Hot electron effects: oxide trapping, VT shift, breakdown
Scaling: Short-channel effects (SCE), oxide, dopants
↓
1995: 0.35 μm (tOX≈8 nm)
2000: 0.18 μm (tOX≈3 nm)
….life is good…
2005: 65 nm (tOX≈1.4 nm)
2010: 32 nm (tOX≈1.2 nm?)
Scaling: SCE, insulator
Leakage: Insulator
Power: Alternative devices
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SiO2 growth and instability
 Ionic contamination (K, Na): Unrecognized source of early problems
 Fixed traps (oxygen vacancies?), especially near Si-SiO2 interface
 Growth kinetics: Deal & Grove model: linear (reaction-limited) and parabolic (diffusion-limited)
regions; dry and wet oxidation rates
 Interface-state passivation: Al (with H) Post Metallization Anneal (PMA, Peter Balk):
 H2O → H+ + OH Si- + H+ → Si-H
Andrew Grove (left), Bruce Deal (center)
and Ed Snow (left)
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Ed Snow’s cartoon, ca. 1966
about SiO2 instabilities
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SiO2 growth and instability, as-grown and during operation
 CV-plot instabilities (VFB or VT shifts):
 Ions (mainly Na+ and K+, contamination in chambers, handling, gases, etc…)
 Interface states generation (stretch-out, Lai, Feigl, Sandia group, Technion, Siemens,…)
 Electron and hole traps (DiMaria, Young, Feigl):
• Neutral: H2O-related (mainly OH-) in wet oxides, radiation induced in processing,
σ ≈ 10-15 to 10-17 cm2
• Charged-attractive: Ionic contamination, σ ≈ 10-13 cm2 , field-dependent
• Charged-repulsive: Radiation-induced, σ ≈ 10-19 cm2
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SiO2 instability during operation
 Anomalous Positive Charge (APC):
 Caused by electron injection (Avalanche, Fowler-Nordheim) and also hole injection
 Related to Hydrogen: Boron deactivation in p-type substrates (Sah)
 Related to hole back-injection from anode? Dependent on gate-metal workfunction Au vs. Al vs. Mg (MVF&Weinberg, Chenming Hu)
 Occurring at Si-SiO2 interface even under negative bias: Neutral species such as
solitons, H2 diffusion…? (Weinberg).
 Connected to wear-out and breakdown (DiMaria, Stathis)
 Strongly correlated to interface traps (Pb-centers, Lenahan, Poindexter)
 Oxygen deficiency (Revesz)? Broken Si-H bonds (Si-D experiment, Lyding&Hess)?
 Negative Bias Temperature Instability (NBTI): No time to discuss, but big issue in high-κ
dielectrics
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Understanding SiO2 degradation: Two approaches
MVF and DiMaria, INFOS 1989
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SiO2 growth and instability: Injection techniques and damage generation
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SiO2 growth and instability: Electronic transport in SiO2
 Electrons:
 Long-standing problems of high-field electron transport in polar insulators
(Karel Thornber’s 1970 PhD Thesis with Richard Feynman)
 LO-phonon scattering run-away connected to dielectric breakdown
 Experimental observations do not show predicted run-away at 2-3 MV/cm
 Umklapp scattering with acoustic phonons keeps electron energy under
control (MVF, DiMaria, Theis, Kirtley, Brorson, 1985)
 Holes: Small polaron (self-trapping) transport (Bob Hughes’ 1977 time-of-flight
experiments explained by David Emin’s 1975 theory).
MVF et al., PR B (1985)
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Hot electron effects in constant-voltage-scaled MOSFETs
 Two problems:
 Understand origin/spectrum of hot carrier
 Understand nature/process of damage generation
 Practical problems:
 Unnecessary and expensive burn-in
 Wall Street “big glitch” in 1994
 Theory:
 Shockley’s “lucky-electron model” widespread in EE community in the ’80s
(publicized by Chenming Hu, UCB): Even the Gods can be wrong at times…
 Full-band models (Sam Shichijo & Karl Hess, MVF&Laux, then others)
 Basic physics of electron scattering, injection into SiO2, etc.
 The mid-1990s “pseudo-full-band” frenzy (Bologna, UNC, Udine, Lille, TUVienna, Aachen,..): Gain without pain… didn’t work…
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Electron injection into SiO2
MVF, Laux, and Crabbé, JAP (1996)
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Timeline III once more
Feature size
Transport Physics
1975: 20 μm
1980: 10 μm
1985: 5 μm
Drift-Diffusion
↓
Hydrodynamic/
Energy transport
1990: 1 μm
1995: 0.5 μm
2000: 0.23 μm
2005: 63 nm
2010: 32 nm
2015: 16 nm ?
↕
Boltzmann
↓
Quantum?
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MVF October 2, 2009
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Electron transport in Si at 3 eV: A big headache
 Effective-mass approximation valid only for E ≈ a few kBT
 Scattering rates at E ≥ {a few kBT} totally unknown
 Moments of the BTE (DDE, Hydrodynamic) not sufficiently accurate
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Electron transport in Si at 3 eV ca. 1992: A depressing picture…
The state-of-the art circa 1992
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A good example of experiments-theory feedback
XPS (McFeely, Cartier, Eklund at the
Brookhaven IBM synchrotron line, 1993)
Carrier separation (DiMaria, 1992)
Cartier et al. APL (1993)
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Electron transport in Si at 3 eV ca. 1994: Much better…
The state-of-the art circa 1994
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MVF et al., JAP (1996)
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Scaling
 Shrink dimensions maintaining aspect-ratio
 Must shrink electrostatic features as well (depletion regions→ doping level and profiles)
↔
1 μm
1980 → 1985 → 1988 → 1991 → 1994
1994 → 1999 → 2003 …
μm 1.3
nm ….
LGATE
μm 2.5
2.5 μm
1.3 μm
μm 0.63
0.63 μm
μm 0.25
0.25 μm
μm 130
130 nm
nm
….
5 μm
GATE = 10 μm
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Scaling




Electrostatic integrity (Well-tempered MOSFET, Antoniadis): SOI, DGFETs, FinFETs, NW-FETs
Reduce power, an example: The tunnel FET n (tFET)
Reduced leakage: High-κ gate-insulators
Improve (or, at least, maintain) performance: Alternative channel materials?
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Scaling – Electrostatic integrity: SOI
22 nm strained-Si nFET: SOI to prevent punch- through,
strained Si to improve performance (B. Doris, IBM, 2006)
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Scaling – Electrostatic integrity: Double gate FET
AIST (2003)
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Scaling – Electrostatic integrity: Multibridge FETs (TEM, SEM)
Samsung Electronics Ltd. (2005)
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Multibridge FETs: Process flow
Samsung Electronics Ltd. (2005)
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Scaling – Electrostatic integrity: FinFETs
Freescale Semiconductors
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Scaling – Electrostatic integrity: Si Nanowire Transistors
KAIST (2007)
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Scaling – Reduce power: The tunnel-FET (tFET)

Stand-by power dissipation approaching “on”
power dissipation… Cannot continue like this!

60 mV/dec → ΔVG ≈ 250 mV for Ioff/Ion ≈ 10-4

VT + ΔVG ≥ 0.45 V at 300 K (nFETs)
Must increase slope (i.e., go below 60 mV/dec) if
we want the `Green’ FET (term coined by C. Hu)
Problem: Ion too low in all attempts (DARPA to
IBM, UCB, Stanford,…) so far


InAs Tunnel-FET: structure
(M. Haines, UMass 2009)
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InAs Tunnel-FET: pair generation rate
(M. Haines, UMass 2009)
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Scaling – Reduce leakage
 Off-leakage:
 Accepted value increasing: Ioff/Ion ≈ 10-4 for the 32 nm node (used to be 10-6 or lower!)
 Connected to electrostatic integrity (punch-through, junction leakage, gate leakage)
 Gate leakage:
 C = εox/tox, so if tox has reached its limit (≈ 1nm, too aggressive so far), scale εox:
High-κ insulators such as HfO2, ZrO2, Al2O3, etc.
 Problem: Low mobility in high-κ MOS systems (scattering with interfacial optical phonons)
 Metals with different workfunction needed!
Hi-res TEM from
Susanne Stemmer,
UCSB
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MVF et al., JAP (2001)
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Scaling – Reduce leakage: Gate oxide scaling at Intel
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C. Hu et al., IEDM (1996)
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Scaling – Improve performance
 Taken for granted early on (ca. 1986)
 Slow realization that early optimism was unjustified
MVF and S. Laux, EDL (1987)
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Scaling – Improve performance
 Look for high-velocity, low-effective mass semiconductors… or should we?
 Problems:
 High-energy (≈ 0.5 eV ≈ 20 kBT) DOS and rates identical in most fcc semiconductors
 Low DOS → loss of transconductance
 Low DOS → smaller density in quasi-ballistic conditions → lower Ion
 Low DOS → less scattering in source → source starvation
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Scaling – Improve performance: DOS bottleneck
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MVF and S. Laux, TED (1991)
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Scaling – Improve performance: Strained Si
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MVF and S. Laux, JAP (1996)
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Scaling – Improve performance: Strained Si
IBM 32 nm strained (tensile)
Si nFET on SiGe virtual substrate
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Intel 45 nm strained (compressive)
Si pFET with regrown SiGe S/D
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Why are sub-40 nm devices getting slower?
 Power dissipation → reduce frequency or fry!
 Parasitics play a bigger role (Antoniadis, MIT)
 Higher oxide fields squeeze carriers against interface → increased scattering
(Antoniadis, MIT)
 Intrinsic Coulomb effects!
MVF and S. Laux, JAP (2001)
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Why are sub-40 nm devices getting slower? The effect of e-e interactions
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Sub-32 nm Si CMOS devices: Where do we stand?
 22 nm: Planar (Intel), SOIs (IBM), FinFETs doable but too expensive.
 16 nm: Possibly FinFETs, still Si
 Below 16 nm:
 Ge pFETs and III-V nFETs (IMEC)? A pipedream…
 Ge nFETs still lousy, improvements promised at Dec 2009 IEDM, we’ll see
 III-Vs in the works:
• MIT (del Alamo): Great HEMTs, but huge S/D-gate gap not easily scalable
• SRC/UCSB MOSFETs: Wait and see…
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The future and “post Si CMOS” devices: What do we need?
Three terminal devices (Josephson computers taught us something…!)
At least some gain (preserving signal over billions of devices, beating kBT)
At least a few devices must have high Ion to charge external loads
On/off behavior (Landauer’s water faucet analogy)
Low power, possibly non-charge-switching (spins, QCA,…). BUT: If we use ≈ kBT to
switch, the heat bath will switch for us even if we do not want to…
 Notable historic failures:
 Josephson: Excessively strict tolerances (on insulators), complicated 2-terminal logic
 SETs: No output current (`a slight impedance matching issue’, as someone kindly put
it….)
 Optical computers: Photons are huge! Clumsy 3-terminal devices
 Resonant tunneling diodes and multi-state logic: Non off-off switches, impossible to
control manufacturing tolerances
 High hopes:
 Nanowires: They are just thin and narrow FinFETs
 Long shots:
 Spins and QCA: Low power but no gain
 CNT: No current in single tube, must use many in parallel
 III-Vs: Battle already lost in 1991 (DOS bottleneck),,, why bother again?

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
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And by popular demand… The future of “post-Si CMOS” logic technology
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More slides about the lunatic fringe….
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The lunatic fringe: Exploratory devices
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The lunatic fringe: Exploratory devices
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The lunatic fringe: Exploratory devices
Carbon NanoTube (CNT) FET
IFF-Jülich, Germany (2004)
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CNT Transistors
IFF-Jülich, Germany (2004)
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CNT FET inverter
J. Appenzeller, IBM
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