Tri-Gate Fully-Depleted CMOS
Transistors: Fabrication,
Design and Layout
B.Doyle, J.Kavalieros, T. Linton, R.Rios
B.Boyanov, S.Datta, M. Doczy, S.Hareland, B. Jin,
R.Chau
Logic Technology Development
Outline of Presentation
•
Introduction
− Different Depleted Substrate Transistor (DST) Architectures
•
Experimental Results
•
Computer Simulation Results
− Dimensional Analysis
− Importance of Corner Effects
•
Tri-Gate Layout Analysis
Transistor Architectures
Single-Gate
Planar
L
Si HSi
g
Si
Gate
Source Drain
~ Lg/3
Double-gate (e.g. FINFET)
WSi Lg HSi Isolation Gate 1 Gate 2 Source DrainTri-gate
Non-Planar
WSi Lg HSi Gate 1 Gate 2 Gate 3 Source DrainTri-gate Transistor
WSi
Lg
Top Gate
Side Gate Side Gate
HSi S/D D/S
Gate
Top Gate
Side Gate
Side Gate
Experimental Tri-Gate Process
•
Starting Si thickness = 50nm
•
BOX thickness ~ 200nm
•
Well implants
•
N
2O sacrificial oxidation
•
Physical Tox = 1.5nm
•
Poly thickness = 100nm
•
Raised source-drain
•
Nickel salicide
Top Gate
Side Gate
60nm NMOS Tri-Gate Transistors
1E-08 1E-07 1E-06 1E-05 1E-04 1E-03 1E-020 0.4 0.8 1.2
Vg (Volts) Id ( µ A/ µ m) Vd=0.05V Vd=1.3V 0.0E+00 2.5E-04 5.0E-04 7.5E-04 1.0E-03 1.3E-03
0 0.4 0.8 1.2
Id (A/µ m) Vg=1.3V Vg=1.1V Vg=0.9V Vd (Volts)
• Idsat = 1.23mA/µm and Ioff = 40nA/um at Vcc = 1.3V
• Subthreshold slope = 72mV/decade
60nm pMOS Tri-Gate Transistors
Gate Voltage (V)
Drain Curren t (A/ µ m) 0.E+00 1.E-04 2.E-04 3.E-04 4.E-04 5.E-04 6.E-04 -0.8 -0.4
Drain Voltage (V)
Drain Current (A/
µ m) 1E-09 1E-08 1E-07 1E-06 1E-05 1E-04 1E-03
-1.2 -0.8 -0.4 0
Vd=1.3V
Vd=0.05V
-1.2 0
• Idsat = 520 µA/um and Ioff = 24nA/um at Vcc = 1.3V
• Subthreshold slope = 69.5mV/decade
Double Gate-like
Understanding Tri-Gate Behavior
• Device simulator
- Full 3D single-carrier solution using DESSIS
device simulator
- Hansch quantum correction model applied - Intel 2.2 Ghz Xeon processor takes about 1
minute/bias point for an 18000 node mesh
• Simulated structures
- Lg=60 nm / HSi=60 nm / WSi=60 nm - Lg=30 nm / HSi=30 nm / WSi=30 nm - Electrical Tox varies from 22 to 34 A
Simulation of L
g=H
Si=W
Si=60nm
1.E-03
Vd=0.05V Vd=1.3V
DIBL=56 mV/V
S/S (0.05V)= 72.5mV/dec
S/S (1.3V)= 76mV/dec
1.E-04
1.E-07 1.E-06
Id (A)
1.E-05
1.E-08
1.E-09
0.0 0.3 0.6 0.9 1.2
Vg (V)
1.0E-03
Simulation of L
g=H
Si=W
Si=30nm
Vd=0.05V Vd=1.0V
DIBL=62 mV/V
S/S (0.05V)= 76mV/dec
S/S (1.3V)= 76mV/dec 1.0E-04
1.0E-05
1.0E-06
Id (A)
1.0E-07
1.0E-08
0.0 0.2 0.4 0.6 0.8 1.0
Vg (V)
Body Scaling Vs DST Architecture
Single-Gate
Double-Gate
Tri-Gate
0
10
20
30
HSi=0.33*Lg
WSi=0.66*Lg Lg =30nm
Lg =20nm
Lg =15nm
(H
si
, W
Si
(nm)
Minimum Body Dimension
Tri-Gate body size more relaxed than single-gate or
Tri-Gate Device Understanding
•
TCAD simulations partitioned
into 3 distinct regions:
Top channel
Sidewall channel
Corners
Components of Current
Vg (V)
Id (A/
µ
m)
1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02
0.0 0.2 0.4 0.6 0.8 1.0
Non-Corner Total
Corner Vd=1.0V
Vd=0.05V
non-Components of Current
0.0% 20.0% 40.0% 60.0% 100.0%
0.0 0.6
Vg (V)
% of Total Curre
n
t
Corner
Non-Corner
Vd=0.05V
Vd=1.0V
80.0%
0.2 0.4 0.8 1.0
Physics of Corner Device
R=8nm
Vg=0.5V, Vd=1.0V Cut at midpoint along channel
Proximity of the two gates at the corner give the nearly-ideal
Physics of Tri-Gate Device
hDensity 1E+18 1E+16 1E+14 1E+12 1E+10 1E+08 1E+06 10000 100 1 Top Gate Si Drain Lg =30nm TS i = 3 0 n m hDensity 1E+18 1E+16 1E+14 1E+12 1E+10 1E+08 1E+06 10000 100 1 Top Gate Si Drain Lg =30nm TS i = 3 0 n m Source hDensity 3E+04(well conc. = 8E+18)
Importance of Corner Profile
1.E-12 1.E-10 1.E-08
0 0.2 0.4 0.6 0.8 1
Vg (V)
Corner Current (A/
µ
m)
R=0 nm R=5 nm R=10 nm R=15 nm R=20 nm R= infinity
Gate
Body
Body
Radius R
1.E-02
1.E-04
1.E-06
Layout Implications:
Fabricating Different Widths
Poly Fins
To meet different required widths for transistors,
Layout Considerations
Planar Transistor
Zeff = Z
Tri-Gate Transistor
Fins
Zeff = 0.6Z
For a given pitch, total current per unit layout-width of the Tri-gate transistor has only 0.60X the channel width of the standard transistor
Spacer-Defined Fins
Fins Fins
Zeff= 0.6Z
Oxide Blocks with nitride spacers
Zeff= 1.2 Z
Litho-defined Fins For the same pitch, # of
spacer-defined fins doubles that of litho-defined fins
Oxide blocks to define spacer-masks for
forming Si fins
Conclusions
• Tri-Gate transistors have been fabricated and achieve excellent drive current with near-ideal DIBL, S/S.
• Tri-Gate corners are responsible for the excellent sub-threshold slope, DIBL characteristics, as well as
relaxing the body dimensions compared to double-gate devices.
• In addition to the corners, the top-gate and sidewall channel regions are important in achieving optimal device performance.