MSE 510
Part 6: High Dielectric Constant (k), Gate Electrode, & Channel
Materials
SiO2 gate oxide is approaching physical limits
Thickness & Current
+V
gate
VSource
VDrain
W
M
+
poly-crystalline
Si
O
Source Contact
Insulator
S
n++ Poly Si
Gate Contact
or Electrode
Drain Contact
Insulator
SiO2 - Gate oxide
n+source - - - - - - - - - - - - - - n+drain
channel
p-Si Wafer
Crystalline Si
Cox 
t EOT 
Knowlton
tox
 o kox A
tox
kox
thigh  k
khigh  k
Frank, Dennard, Nowak, Soloman, Wong & Taur, Proc. IEEE Circuit & Devices , 89 (2001) 259
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M. Houssa et al., Materials Science and Engineering R, 51 (2006) 37-85
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High Dielectric Constant (k) Materials
Bandgap versus Dielectric Constant (k)
e Hik  Ec  e Si
Trend: As k ↑, Eg ↓
Knowlton
Robertson, MRS Bulletin (March 2002) p. 217
 e Hik  e Si  Ec
Robertson, J. Vac. Sci. Technol. B, 18(3), May/Jun 2000
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High Dielectric Constant (k) Materials
Band Offsets: High k on Si
Aspects to Consider:
1. Eg
2. Ec & Ev
3. meff
Recall in Barrier Region:
  e kx
So:
J   *  e 2 kx
2meff (V  Ee )
k

 k  meff
 meff , J 
e Hik  Ec  e Si
 e Hik  e Si  Ec
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MSE 510
Robertson, MRS Bulletin (March 2002) p. 217
J    g (k )T  k   f leftSide  E f   f rightSide  E f   dk
1 E
pˆ
& g 
where p  m g &  g 
 k
m
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High Dielectric Constant (k) Materials
Band diagrams of MOS – compare SiO2 to high k materials
SiO2; κ~3.9
HfO2; κ~25
PbZr(0.53)Ti(0.47)O3
κ~200
Low S/C doping
Knowlton
Southwick & Knowlton, IEEE TDMR, 6(2), (2006) 136-145
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High Dielectric Constant (k) Materials
Need to consider the
Thermodynamics of the
materials system
Ellingham diagram
G –vs- Temperature
The more negative G
is, the more stable the
materials system is.
Example:
Grow Y2O3 on Si, Si will
steal oxygen from Y2O3
to form interfacial layer
(IL) of SiO2. Why?
Y 2O 3
SiO2
Al2O3
GSiO2  GY2O3
 SiO2 more stable than Y2O3
R. DeHoff, Thermodynamics of Materials, (Prentice Hall, 1996) Ch. 11, fig. 11.4
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MSE 510
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High Dielectric Constant (k) Materials
Interfacial layer (IL) of SiO2 Present for HfO2
EOT WRT tS i O 2 & tH f O 2
TiN
3.5
3
SiO2
IL
EOT nm
HfO2
2.5
tIL
2
1.5
1
0.5
0
Crystalline
Si Channel
0
2
4
6
8
10
tH f O 2 nm 
tox ,eff  t IL 
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k IL
khigh  k
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thigh  k
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MSE 510
High Dielectric Constant (k) Materials
EOT:
7 nm HfO2 & 1nm SiO2:
EOT ~ 2 nm
8 nm HfO2:
EOT ~ 1.25 nm
Southwick & Knowlton, IEEE TDMR, 6(2), (2006) 136-145
Knowlton
MSE 510
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High Dielectric Constant (k) Materials - NVM
Floating Gate NVM Versus SONOS (SiO2-Si3N4-SiO2-Si) NVM
SONOS Advantages over Floating Gate:
Replace poly-Si floating gate with Si3N4
Stored charge lies in defect (bound) states below Si3N4 conduction band
Improved endurance - single defect will not cause the discharge/leakage of carriers
Can reduce Thickness of TO
Si3N4 thinner than floating gate Poly Si
Carriers not “Floating” around
Minimizes interaction with neighboring memory cells
Thus, can scale down memory cell size
BL = Blocking Layer
CTL = Charge Trapping Layer
TL = Tunnel Layer
BL
CTL
TL
Knowlton
Todd Wallinger, SONOS Eases Non-Volatile Memory Integration in SoC, Semiconductor International (2007)
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High Dielectric Constant (k) Materials - NVM
BL
CTL
TL
BL
Poly
Si
CTL
TL
Floating Gate
Flat Band
Condition
BL TL
Poly
Si
Si
Si
Energy Band
Diagram
Energy Band
Diagram
Si3N4 = CTL
Gate stack scaled down in thickness & cell area
Knowlton
MSE 510
Todd Wallinger, SONOS Eases Non-Volatile Memory Integration in SoC, Semiconductor International (2007)
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High Dielectric Constant (k) Materials - NVM
Flat Band
Condition
BL
TL
Poly Si
Si
Si3N4
Energy Band
Diagram
Gate stack scaled down in thickness & cell area
Knowlton
Todd Wallinger, SONOS Eases Non-Volatile Memory Integration in SoC, Semiconductor International (2007)
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High Dielectric Constant (k) Materials - NVM
Multilayer high k dielectric films for memory applications
SONOS (poly Si–SiO –SiN–SiO –Si)
MANOS (metal–Al2O3–SiN–SiO –Si)
Sanghun et al., IEEE TED 52 (2005) 2654.pdf
TANOS (Si/SiO2/SiN/A2O3/TaN)
Lee et al., Symposium on VLSI Technology Digest of Technical Papers (2006
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Low Dielectric Constant (k) Materials
What About Low-k Dielectric Materials?
What would they be used for?
Cox 
Knowlton
 o kox A
tox
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MSE 510
Engineering a Memory Device – BGE & SP3
Compare and Contrast following Memory Gate Stacks:
Stack #: Metal – BL – CTL – TL -S/C
Stack 1: TiN–SiO2–Si3N4–SiO2–pSi
Stack 2: TiN–Al2O3–Ta2O5–HfO2–pSi
Stack 3: TiN–La2O3–ZnO–ZrO2–pSi
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MSE 510
Knowlton
Soutwick et. al, “An Interactive Simulation Tool for Complex Multilayer Dielectric Devices”, IEEE Transactions on Device & Matls Rel., 11(2), 2011
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Engineering a Memory Device – BGE & SP3
Soutwick et. al, “An Interactive Simulation Tool for Complex Multilayer Dielectric Devices”, IEEE Transactions on Device & Matls Rel., 11(2), 2011
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Engineering a Memory Device – BGE & SP3
Soutwick et. al, “An Interactive Simulation Tool for Complex Multilayer Dielectric Devices”, IEEE Transactions on Device & Matls Rel., 11(2), 2011
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Engineering a Memory Device – BGE & SP3
Soutwick et. al, “An Interactive Simulation Tool for Complex Multilayer Dielectric Devices”, IEEE Transactions on Device & Matls Rel., 11(2), 2011
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Engineering a Memory Device – BGE & SP3
Soutwick et. al, “An Interactive Simulation Tool for Complex Multilayer Dielectric Devices”, IEEE Transactions on Device & Matls Rel., 11(2), 2011
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Engineering a Memory Device – BGE & SP3
Soutwick et. al, “An Interactive Simulation Tool for Complex Multilayer Dielectric Devices”, IEEE Transactions on Device & Matls Rel., 11(2), 2011
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MSE 510
Engineering a Memory Device – BGE & SP3
Soutwick et. al, “An Interactive Simulation Tool for Complex Multilayer Dielectric Devices”, IEEE Transactions on Device & Matls Rel., 11(2), 2011
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MOSFETs – Bandgap Engineering of Channel
Consider: Bandgap, mobility, effective mass,lattice matching, quantum confinement of carriers
Lattice Constants:
aSi = 5.4309 Å
aGe = 5.6577 Å
Knowlton
Cullity, Elements of X-ray Diffraction, 2nd Ed (1978) Appendix 5
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
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MOSFETs – Bandgap Engineering of Channel
Consider: Bandgap, mobility, effective mass, lattice
matching, quantum confinement of carriers
Lattice Constants:
aSi = 5.4309 Å
aGe = 5.6577 Å
Cullity, Elements of X-ray Diffraction, 2nd Ed (1978) Appendix 5
Knowlton IBM RJ Antoniadis et al., Continuous MOFET Performance Inc with Scaling - Strain & Channel Matl (2006)
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