Transcript Strained Silicon MOSFET

Strained Silicon MOSFET
R91943037
Jie-Ying Wei
Department of Electrical Engineering and
Graduate Institute of Electronics Engineering
National Taiwan University, Taipei, Taiwan, R.O.C.
Cubic Lattice at Equilibrium
Lattice constant for a Si1-xGex
alloy as a function of x
Critical thickness of Si1-xGex layers
as a function of Ge fraction
The size change of each valley in a constant
energy surface diagram indicates a
shift up(smaller) or down(larger) in energy
LH：light hole band HH：heavy hole band
SO：spin-orbit band
Sub-bands in an MOS inversion layer. Additional
energy separation reduces inter-valley scattering
Band Alignment
Surface Channel MOSFET Structure
Extraction
• Mobility
• Band Offsets
Mobility
eff
Eeff
L
gD
W
1
Qinv
;
Qb
Qinv
;
s
gD : from
Qb , Qinv
1
2
1
3
dID
at small VDS ;
dVDS
: from split C
for electron;
for hole;
V;
Split C-V measurement configuration
Measured split C-V capacitance from
a surface strained-Si n-MOSFET
grown on a relaxed-Si0.7Ge0.3
VT :the intersection of the CGC and CGB curves
Gate-channel capacitance curve CGC
Gate-bulk capacitance curve CGB
When VGS < V FB , holes begin to accumulate at the
Si/SiGe interface, confined by the valence band offset.
The hole confinement causes the observed plateau at
C’OX in CGB curve.
Effective mobility of surface-channel, strained-Si
n-MOSFET at room temperature (Na=2E16)
Peak mobility enhancement ratio at room
temperature as a function of apparent Ge
fractions in the buffer layer
Transconductance for W*L = 5*10 µm strained-Si
n-MOSFETs
Performance saturation with Ge fractions x > 0.2
Extraction
• Mobility
• Band Offsets
Full C-V characteristics of a surface strained-Si
n-MOSFET (on relaxed Si0.7Ge0.3)
compared to a CZ Si control
Some parameters
• Qf : match the flatband voltages between the
measured data and the theoretical curves
• ΔEC = ΔVT since the thickness of the Si
channel(10nm) is less than the Debye length
of the material(20nm)
• ΔEV : the difference between Va and V’a is
not straight-forward, so simulation of the
theoretical curve is required
Threshold voltage shift (ΔVT )
as a function of Ge fraction x
Two major assumptions in band offset
extraction using SEDAN simulation
• All material properties, other than the
bandgap, in strained-Si and relaxed SiGe
are identical to bulk Si.
The results may be affected by
1. the material dielectric constant
2. the electron affinity
3. the density-of-state (DOS) effective mass
• Data of Braunstein, at al. is accurate for the
bandgap of relaxed SiGe.
The results were identical, except for a shift in the flatband voltage
Strained-Si band parameters and channel
thickness extracted from C-V measurments
Bandgap of strained-Si grown
on a relaxed SiGe buffer layer
IEDM 2002
1. Strained Silicon MOSFET Technology
2. Low Field Mobility Characteristics of
Sub-100nm Unstrained and Strained Si
MOSFETs
Strained Silicon MOSFET Technology
Schematic illustration a surface-channel
strained-Si n-MOSFET
Effective mobility enhancement ratios
Mobility behavior in strained Si(20% Ge) and
unstrained Si n-MOSFETs as a function of doping
Comparison of hole mobility enhancement
ratios in strained Si p-MOSFETs as a function
of vertical effective field, Eeff
Low field Mobility Characteristics of Sub100nm Unstrained and Strained Si MOSFETs
Leff
eff
Rtotal
2
d ID
Leff
Qinv
RFET
Rext
1
Qinv
d VD
d R total
d L eff
Leff
Qinv
gD
2
Qinv
Rext
The slopes of the lines were used to
calculate mobility
Comparison of mobility extracted on long channel and short
channel devices using the conventional and dR/dL method
Mobility enhancement factor as
a function of temperature
Reference
1. Jeffrey John Welser “ The application of strainedsilicon/relaxed-silicon germanium
heterostructures to metal-oxide-semiconductor
field-effect transistors”
2. Kern Rim “Application of silicon-based
heterostructures to enhanced mobility metaloxide-semiconductor field-effect transistors”
3. J.L. Hoyt, IEDM 2002
4. K. Rim, IEDM 2002