Sb counter doping of SiC MOS interface
Claude Ahyi, Yongju Zheng, Chunkun Jiao,Tamara Isaacs-Smith, Sarit Dhar
ARL Workshop August 15 2016
Outline
• Why use counter-doping• Advantages of Sb• Devices characteristics• Threshold voltage stability• Other development of counter doped devices
– Ics– Borosilicate glass
Why use counter doping
Channel with counter doping
Channel with counter doping and trap passivation
Original channel
• Reduces channel electric fieldAttenuates the effects of surface roughness scattering, which results in higher mobility at low field.
• Increases carrier concentration
Wn
P-type SiC
Sharper bending
Less sharp bending
Ec
Ev
Ef
: Implantation width
SiO2
Counter-doping SiC
N type dopants of SiC
SCM measurements made onunpassivated, NO annealed and Sbimplanted AU fabricated samplesshow evidence of counter doping atthe SiO2/SiC interface.
P. Fiorenza et al. CNR Italy
SiO2N SiC
epiN++ SiCsubstrate
Scan direction
0.0E+00
5.0E+17
1.0E+18
1.5E+18
2.0E+18
0 0.05 0.1 0.15
Dopi
ng c
once
ntra
tion
(cm
-3)
Depth (um)
SCM doping profile
Structure of our devices
N+ N+Gate oxide
Poly Si
Counter doping implantP substrate
All dopants are activated at 1550oC for 30min.
G
DS
Field oxide
1E-02
1E-01
1E+00
1E+01
1E+02
1E+17
1E+18
1E+19
1E+20
0 100 200 Si,C
,OIN
TEN
SITY
(arb
itrar
y un
its)
Sb
Con
cent
ratio
n (a
tom
s/cc
)
DEPTH (nm)
Si-> C->O->Sb
. Depth Dose (nm) (at/cm2)
Sb 0-163 3.00E13
1E-02
1E-01
1E+00
1E+01
1E+02
1E+17
1E+18
1E+19
0 100 200 Si,C
,OIN
TEN
SITY
(arb
itrar
y un
its)
Sb
CO
NC
EN
TRAT
ION
(a
tom
s/cc
)
DEPTH (nm)
Si-> C->O->Sb
. Depth Dose (nm) (at/cm2)
Sb 34-173
75% left
24% left
Threshold voltage in counter-doped devices
-2.E-07
0.E+00
2.E-07
4.E-07
6.E-07
8.E-07
1.E-06
-5 0 5 10 15 20 25
Ids (
A)
Vg (V)
Drain Current Change with implant energy
Tox = 63nmAl : 1e17 cm-3 400nmSb :2.5E13cm-2 80 and 100 keVPolySi Gate Phosphorus dopedField Oxide
• For identical counter doping implant doses, there is a higher threshold voltage shift for wider implants.
Effect of Sb counter dopingComparing NO, Sb only , NO+Sb
0
20
40
60
80
100
120
140
160
180
-2 3 8 13
Mob
ility
(cm
2 /Vs
)
Vg (V)
NO
Sb+NO
Sb only
As only
n type
Ec
Ei
EF
Ev
---V EF
n typeEc
Ei
EF
Ev
----V EF-
Low temperature High temperature
Devices with Sb and no N passivation show no evidence of trap passivation using HiLo CV
DLTS study of Sb effect on interface trapping
• Using DLTS there is evidence of a weak trap passivation effect due to Sb. This seems to affect only the O1 traps.
50 100 150 200 250 3000
20
40
60
80
#2 #18
CCDL
TS S
igna
l (m
V)
Temperature (K)
NO-120C = 37 pFen = 465 s-1
Vfb
Vfb + 5V
O1 O2
50 100 150 200 250 3000
20
40
60
80 #25 #7
CCDL
TS S
igna
l (m
V)Temperature (K)
Vfb
Vfb + 5V
Sb + NO-120C = 37 pFen= 465 s-1
O1
O2
DLTS of NO annealed sampleDLTS of NO + Sb sample
Mobility and Vt vs p-well doping for devices with and without Sb
0
2
4
6
8
10
12
14
0
5
10
15
20
25
30
35
40
45
1.00E+16 1.00E+17 1.00E+18
Thre
shol
d Vo
ltage
(V)
Mob
ility
@ 2
.5 M
V/cm
(c
m2 /
Vs)
Channel P doping concentration (cm-3)
Sb counter-dopedmobilityNO only mobility
Sb counter-doped Vt
NO only Vt
0
500
1000
1500
2000
2500
1.00E+16 1.00E+17 1.00E+18
Subt
hres
hold
slop
e (m
V/de
cade
)
Channel P doping concentration (cm-3)
Sb counter dopedsubthreshold slopeNO only subthreshold slope
P well
N+ N+Gate oxide
Poly Si
Counter doping implantP substrate
All dopants activation: 1650oC 30min.
G
DS
Field oxide
Device structure
Counter-doped Pwell mobility and Threshold
0
5
10
15
20
25
30
0 5 10 15 20 25Carr
ier M
obili
ty (c
m2 /
VS)
Gate Voltage (V)
Mobility
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
-10 0 10 20
Dra
in C
urre
nt (A
)
Gate Voltage (V)
Drain Current
Tox = 63nmAl : 1e17 cm-3 400nmSb :2.5E13cm-2 80 keVPolySi Gate Phosphorus doped
• Higher field effect mobility • Positive threshold voltage
1.E-11
1.E-07
2.E-07
3.E-07
4.E-07
5.E-07
6.E-07
7.E-07
-10 0 10 20
Drai
n Cu
rren
t (A)
Gate Voltage (V)
Device Stability
Vth Stability of device with and without P well
Device Stability
0.E+00
1.E-07
2.E-07
3.E-07
4.E-07
5.E-07
6.E-07
0 5 10 15 20
Drai
n Cu
rren
t (A)
Gate Voltage (V)
1.5 MV/cm 225oC
0353d2d09 RT
After 5 min 1.5MV/cm225C
Further developments of Sb counter-doped devices
Integrated Circuits using Sb counter-dopingSingle and multistage differential amplifier(on going)
Boron doped oxide devices:Process
Oxidation1150oC
P-type SiC
n+ n+
P-type SiC
n+ n+SiO2
Boron doping 1000oC in Ar +O2
BN or B2O3 solid source
P-type SiC
n+n+
ArO2
ArO2
Drive in1000oC in Ar
P-type SiC
n+ n+BSG
n+ n+
P-type SiC
BSGgate
Boron doped oxide devices:Results
0
20
40
60
80
100
120
140
160
180
0 5 10 15 20
Axis
Titl
e
Axis Title
comparison of Boron only and Sb+Boron
Boron only
Sb+Boron
Conclusion
• Sb is a convenient channel engineering tool with low impact on trapping and stability of the devices.
• Dose is controllable since it implanted.• Advantage remains for high p well doping.• Compatible with other process including glass formation through dopant
diffusion in the oxide.