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.