Halo Doping: Physical Effects and Compact Modeling yIntroduction yCompact modeling of halo doping...
Transcript of Halo Doping: Physical Effects and Compact Modeling yIntroduction yCompact modeling of halo doping...
Halo Doping: Physical Halo Doping: Physical Effects and Compact Effects and Compact
ModelingModeling
S. Mudanai, W. Shih, R. Rios, S. Mudanai, W. Shih, R. Rios,
P. Packan and S.W. LeeP. Packan and S.W. Lee
OverviewOverview
IntroductionIntroduction
Compact modeling of halo Compact modeling of halo doping for threshold voltagedoping for threshold voltage––Mobility artifactMobility artifact
Mechanism of output resistance Mechanism of output resistance degradationdegradation
Compact modeling requirementsCompact modeling requirements
IntroductionIntroductionScaling requires the use of Scaling requires the use of Halo implants for control of Halo implants for control of short channel devicesshort channel devices
–– Halo implant profile Halo implant profile optimized for best optimized for best performance for the digital performance for the digital devicesdevices
Non-uniform doping along the channel leads to
– Reverse short channel effect
– Long channel DIBL
– Degradation of output resistance at longer lengths
Gate
Source Drain
Halo Doped region
Low doped centre
Netdoping
Halo doping effectsHalo doping effects
L
LHalo LHalo
Dop
ing
con
cent
ratio
n
NHalo
Nbulk
L
2LHalo
Dop
ing
con
cent
ratio
n
NHalo
Dop
ing
con
cent
ratio
n
L
2LHaloNHalo
In compact models RSCE is modeled by using In compact models RSCE is modeled by using a length dependent doping concentration.a length dependent doping concentration.
–– Match the Match the subthresholdsubthreshold current across the current across the 3 transistors to extract an equivalent 3 transistors to extract an equivalent doping.doping.
The core quantities in a compact model are The core quantities in a compact model are calculated assuming a uniform doping.calculated assuming a uniform doping.
Bulk
Halo
Halo
Halo implant effects: linear Halo implant effects: linear regionregion
IV characteristics are not IV characteristics are not the same.the same.On region current for halo On region current for halo device is higher than the device is higher than the uniformly doped deviceuniformly doped device
0.1um0.1um
Dop
ing
con
cent
ratio
n
2e18
3e17
1.0um0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Vgs(V)
Ids(
mA
/m
)
1.4e+18cm-33e+17cm-3
2e+18cm-3
3-Transistor modelHalo transistors=0.1umHalo doping = 2e+18cm-3Bulk doping = 3e+17cm-3
Bulk
Halo
HaloEquivalentDopinguniformSame vt
Mobility artifactMobility artifact
1
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
1.45
0.1 1 10 100
Channel length (micron)
Idlin
(hal
o)/Id
lin(u
nifo
rm)
Nhalo=2e18;Nbulk=3e17
Nhalo=1e18;Nbulk = 3e17
Modeling of the nonModeling of the non--uniform doping along uniform doping along the channel with the channel with ““averagedaveraged”” doping doping requires an increase in requires an increase in ““mobility parametermobility parameter””used.used.
This required increase is This required increase is –– a function of channel a function of channel
length.length.
–– a function of difference a function of difference in the bulk and halo in the bulk and halo doping.doping.
Bulkthgs
BulkHalo
thgs
Halo
dsoxds
VVL
VVL
WVCI
−+
−
≈ 2µ
Long channel DIBLLong channel DIBL
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
distance along the channel (micron)
Chan
nel p
oten
tial (
V)
Vds = 1.2V
Vds = 0.05V
2-D device simulation
Numerical device simulation
Occurs due to barrier reduction on the drain side.Occurs due to barrier reduction on the drain side.Most compact models use a term proportional to Most compact models use a term proportional to vdsvds in in their DIBL formulations to describe this effect.their DIBL formulations to describe this effect.
Halo Implant effects: Halo Implant effects: saturation regionsaturation region
Output resistance Output resistance
degradation in saturation.degradation in saturation.
Drain saturation voltage Drain saturation voltage
((VdsatVdsat) for the uniformly ) for the uniformly
doped device is slightly doped device is slightly
higher than the higher than the VdsatVdsat for for
the halo doped device.the halo doped device.
Higher drive in saturation Higher drive in saturation
region for the halo device.0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
6.E-05
7.E-05
0 0.5 1 1.5Vds(V)
Ids(
A)
Halo doped device
Uniformly doped deviceVdsatHalo Vdsat uniform
Numerical device simulationSame linear Vth
region for the halo device.
The halo device pinch –off region occursin the halo implant region, since that regionis closest to the drain and has a thresholdvoltage higher than the uniformly doped region α
VthVgsVdsat −=
22--d device simulation: d device simulation: potential profile potential profile
0.20.30.40.50.60.70.80.9
11.11.2
0 0.2 0.4 0.6 0.8 1
Distance along the channel(um)
Cha
nnel
pot
entia
l (V) Vds =1.2
Vds=0.5Vds=0.2
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1
Distance along the channel (um)
Cha
nnel
pot
entia
l(V)
Vds = 1.2Vds=0.5Vd=0.2
UNIFORM Doping Halo Doping
0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
6.E-05
7.E-05
0 0.5 1 1.5Vds(V)
Ids(
A)
Halo doped device
Uniformly doped device
Uniform doping: In saturation additional drain bias is dropped in the pinch off regionnear the drainHalo doping: In saturation channel potential continues to increase in the bulk doped part,as though it was still in linear region.
22--T equivalent circuitT equivalent circuit22--d device simulations have shown that the d device simulations have shown that the Rout degradation occurs because of drain Rout degradation occurs because of drain side barrier modulation and the source side side barrier modulation and the source side barrier does not play a role.barrier does not play a role.
Vg
Vs
Vd
Vs
Vg
Vd
Lh
L-Lh
Vd’
Halo
Bulk
22--T equivalent circuitT equivalent circuit
Halo Dopedregion
Low doped region
SourceDrain
I II III
Vd’
Vdsathalo Vds2
Potentialdrop
Vds1
Vds3
Vds1: Linear region Vds1: Linear region VdVd’’ resistive potential divider resistive potential divider Halo/Bulk.Halo/Bulk.
Vds2/3: Saturation region Vds2/3: Saturation region VdVd’’ potential divider of potential divider of VdsatVdsathalohalobetween Region II and region Ibetween Region II and region I
Increasing the drain bias increases the length of Region III, Increasing the drain bias increases the length of Region III, reducing the length of region II reducing the length of region II increasing increasing VdVd’’
1. Pinch-off points moves closer to the source of the Halo
2. Barrier reduction already accounted through the long channel DIBL modelPinch
off
22--Tequivalent circuit Tequivalent circuit --simulationsimulation
0
0.005
0.01
0.0 0.5 1.0VDS(V)
IDS(
mA
/um
)Uniform doping 1.3e18
composite circuit with CLM
composite circuit without CLM
The halo doped transistor of length Lhalo is simulated with and without channel length modulation.
Vs
Vg
Vd
Lh
L-Lh
Vd’
Halo
Bulk
Vg
Vs
Vd
Equivalentdoping
22--T equivalent circuit T equivalent circuit -- simulationsimulation
GmHalo
Gmeq
GmBu
lk
GdsHal
o
GdsBul
k
Routeq
Vd
Vd’
Vd+
-Vgd’
+
-
Vg
+
-
Vg
The intermediate node The intermediate node voltage continues to voltage continues to increase in saturation. increase in saturation. This results in increasing This results in increasing current in saturation.current in saturation.
Vs
Vg
Vd
Lh
L-Lh
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Vds(V)
Vd's
(V)
Composite circuit with CLM
Composite circuit without CLM
Vd’
So why does adding Halo So why does adding Halo implant make Rout worse ?implant make Rout worse ?
Adding halo implant Adding halo implant on the drain side on the drain side forces the forces the transistor to transistor to saturate at a lower saturate at a lower VdsatVdsat
Beyond saturation Beyond saturation the high doped the high doped region on the drain region on the drain side acts like a side acts like a scalerscaler of drain bias of drain bias to the bulk doped to the bulk doped transistor
0.0E+00
1.0E-05
2.0E-05
3.0E-05
4.0E-05
5.0E-05
6.0E-05
0 0.2 0.4 0.6 0.8 1 1.2 1.4Vds(V)
Id(A
)
Halo peak = 3e18Halo peak = 1.5e18No halo
Numerical device simulation
Bulk doping = 3e17
Vds
Vdreducing
block
Vgs Bulk transistortransistor
Halo doping variationHalo doping variationAt the same gate bias At the same overdrive
1.0E-06
1.0E-05
1.0E-04
1.0E-03
0 0.5 1 1.5VDS(V)
GD
S(A
/V)
nominal device
halo dopingincreased
1.0E-06
1.0E-05
1.0E-04
1.0E-03
0 0.5 1 1.5
VDS(V)
GD
S(A
/V)
nominal device
increased halodoping
Bulk Halo
Typically compact models do not take into account the barrier between the bulk and halo doped region. Hence, they cannot predict the increased output resistance due to reduced halo implant.
Bulk doping variationBulk doping variationAt the same gate bias, numerical device simulations
2D device simulations: Increasing the bulk doping results in higher threshold voltage resulting in higheroutput resistance.Increasing the bulk doping also results in a reduced barrier between the halo andbulk regions resulting in higher output resistance.
Bulk
Halo
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0 0.2 0.4 0.6 0.8 1 1.2VDS
GD
Snominal device
vt reduced by 100mV
vt increased by 100mV
Gds Gds vsvs LengthLength
1.0E-06
1.0E-05
1.0E-04
1.0E-03
0 0.2 0.4 0.6 0.8 1 1.2
Length(um)
Gds
(A/V
)
Non-uniformlydopeduniformly doped
VDS =0.5 V; VGS =0.6V
22--D device simulations D device simulations were performed with were performed with halo doping and halo doping and uniform doping such uniform doping such that effective that effective VthVth is the is the same.same.
The longer channel The longer channel lengths > 0.1um show lengths > 0.1um show Rout degradationRout degradation
The degradation The degradation reduces with reducing reduces with reducing channel length.channel length.
Rout degradation Rout degradation modelingmodeling
RequirementsRequirements––Function of difference in threshold Function of difference in threshold voltage for the halo and bulk doping.voltage for the halo and bulk doping.
––Capture the results of varying the Capture the results of varying the bulk/halo dopingbulk/halo doping
––Ineffective for very short channel Ineffective for very short channel lengthslengths
––Reflect the Reflect the vdsatvdsat changes with changes with different halo dopingdifferent halo doping
Capacitance modeling in Capacitance modeling in Halo devicesHalo devices
At low frequencies At low frequencies the CV curve of a the CV curve of a halo doped devices halo doped devices exhibits a lower exhibits a lower threshold voltagethreshold voltage–– The centre lower The centre lower
doped region inverts doped region inverts before the source and before the source and drain ends of the drain ends of the channel.channel.
At high frequencies At high frequencies the halo doped the halo doped transistor exhibits a transistor exhibits a pronounced NQS pronounced NQS effect.effect.
0.02.04.06.08.0
10.012.014.016.018.0
0.0 0.5 1.0 1.5Vgs
Cgg
(fF/
m)
Unifrom dopingHalo Doping
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.1 1.0 10.0 100.0Freq(GHz)
CG
G n
orm
aliz
ed to
CG
G @
low
freq
uenc
yhalo dopinguniform doping
ConclusionsConclusions
Compact modeling of halo devices using Compact modeling of halo devices using uniform doping results in a mobility uniform doping results in a mobility artifact.artifact.
22--D numerical device simulations used to D numerical device simulations used to explain output resistance degradation in explain output resistance degradation in long channel deviceslong channel devices
22--T equivalent transistor approach shows T equivalent transistor approach shows that CLM in halo transistor causes Rout that CLM in halo transistor causes Rout degradation.degradation.
Analytical model requirements for compact Analytical model requirements for compact modeling of Rout degradation identified.modeling of Rout degradation identified.