D2.3 - Gate oxide process impact on RNCE for advanced CMOS

ESSDERC ‘02

Gate Oxide Process Impact on RNCE Gate Oxide Process Impact on RNCE for Advanced CMOS for Advanced CMOS TTransistorsransistors

F.Arnaud*, M.Bidaud***STMicroelectronics, Central R&D, 850 rue J.Monet 38926 Crolles, FRANCE

**Philips Semiconductors, 850 rue J.Monet 38926 Crolles, FRANCE

Sept. 2002 / Firenze / Italy 2ESSDERC ‘02

F.Arnaud and M.Bidaud

OutlineOutline

IntroductionParasitic effect of gate oxidation stepsExperimental matrix desciptionReverse Narrow Channel Effect (RNCE)– Threshold Voltage– Body Factor

Edge current tool– Theory and test structure– Measurement and temperature effect

Conclusions



Introduction Introduction (1/2)(1/2)

0

1

2

3

4

5

6

Technology node

EO

T (n

m)

EOT= Equivalent Oxide Thickness

EOT reduction best process way to enhance Ion/Ioff compromize



Introduction Introduction (2/2)(2/2)

MOSFET mobility degradation at low electric field

Gate leakage reduction w.r.t. pure oxide at same EOT

N.B.T.I. degradation due to nitrogen at Si-SiO2interface

Inihibition of P+ gate Boron diffusion inisdeP-channel

RisksAdvantages

Oxynitride introduction for advanced gate material induced:

This work: we studied the impact of gate oxidation mode on RNCE



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Conclusions



Dopants Dopants segregation phenomena segregation phenomena (1/2)(1/2)

After gate oxidation stepsBefore gate oxidation steps

> 5.1017 at/cm3

< 5.1017 at/cm3

STIActive area

Uniform Channel doping

> 5.1017 at/cm3

< 5.1017 at/cm3

STIActive area

Final Channel doping

☹ Gate oxidation process induced a Channel-Boron pumping toward the trench oxide

This parasitic effect is called dopants segregation effect



Dopants Dopants segregation phenomena segregation phenomena (2/2)(2/2)

Dopants segregation consequencies:

Bulk doping reduction Nb Nbeff

Vth of narrowest transistor reduction

SRAM leakage static consumption increase

Parasitic ‘’ hump’’ effect with back bias

Segregation coefficient:

meff = m0 . Exp (- Ea/k.T)

meff depends strongly on gate oxidation characteristic (T°, time, ambient …)



RNCE RNCE and Iand IedgeedgeNarrow deviceLarge device

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

0.1 1 10

Wg (µm)

Vth

/Vth

(w=1

0µm

) ra

tio

S DG

S DG

Parasitic area

Vthchannel > Vth

parasitic

Iofftransistor = Ichannel.Wg + 2.Iedge



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Conclusions



Experimental matrixExperimental matrix

141.6RTN 950°CDPN 35sNO anneal 1000°C/15s

RTN + DPN + Anneal

101.8RTO 900°CDPN 35sNO anneal 1000°C/15s

RTO + DPN + Anneal

81.65RTO 900°CDPN 35s

RTO + DPN

41.8RTO 900°CRTN 950°C

RTO + RTN

02.0Pure oxideRTO 900°C

RTO

NitrogenConc.(%)

EOT*(nm)

Process featuresGate oxideProcess

* All the EOT values have been extracted from C-V curve fitting by Schrödinger-Poisson method



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Conclusions



RNCE RNCE experimental resultsexperimental results

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

0.1 1 10

Wg (µm)

Vth

/Vth

(w=1

0µm

) ra

tio

RTORTO+RTNRTO+DPNRTO+DPN+AnnealRTN+DPN+Anneal

☹ pure oxide process is the worst option in term of RNCE

☺ oxynitride solutions reduce strongly the Vth-Wg roll down



Body Body Factor method Factor method descriptiondescription

( )BBSBbthth VKVV Ψ−+Ψ⋅=− .2.20

ox

subscB C

NqK ...2 ε=ox

subsc

ox

BB

Nq

T

KK

εε

ε

.

...2

0

* ==

1.E-12

5.E-06

1.E-05

2.E-05

2.E-05

3.E-05

3.E-05

4.E-05

4.E-05

5.E-05

5.E-05

0 0.2 0.4 0.6 0.8 1 1.2

Vgate (Volt)

Idra

in (A

/µm

)

0.E+00

1.E-04

2.E-04

3.E-04

4.E-04

5.E-04

6.E-04

7.E-04

8.E-04

9.E-04

Gm

(S)

Threshold

current Ith 1.E-06

1.E-05

1.E-04

1.E-03

0 0.05 0.1 0.15 0.2 0.25 0.3

Vgs (Volt)

Id (A

)

Ith

Vth @VBS



Body Body Factor experimantal resultsFactor experimantal results

Pure oxide process increases the Boron segregation close to STI edge

Agressive nitridation options limit the dopants concentration reduction

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

0.1 1 10

Wg (µm)

Kb* /K

b* (w=1

0µm

) ra

tio




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Conclusions



Edge current Edge current extraction extraction methodmethod

Iofftransistor = Ichannel.Wg + nedge.Iedge

Nedge= 2 Nedge= 6 Nedge= 12

Ioff = 0.0519.Nedge + 0.7865R2 = 0.9965

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60

Nedge (number)

Tota

l Iof

f (nA

)

Slope = edge component

Intercept = channel component



Edge current experimental resultsEdge current experimental results

0

0.5

1

1.5

2

2.5

3

3.5

4

25°C 50°C 75°C 100°C

Temperature (°C)

I edg

e / I

cha

nnel

rat

ioRTORTO+RTNRTO+DPNRTO+DPN+AnnealRTN+DPN+Anneal

Thanks to a lower Boron segregation inside STI edge parasitic current is reduced by using NO process for gate material



Edge current and Edge current and T° T° behaviour behaviour (1/2)(1/2)

16

17

18

19

20

21

22

0 0.1 0.2 0.3

Substrate depth (µm)

Dop

ant c

once

ntra

tion

(at/c

m3)

Channel (Boron)SD (Arsenic)

Nj = Junction concentration

Process oxidation modulates the segregation

Segragation modulate Nj

Nj generates a direct tunneling leakage (junction leakage)

Direct tunneling is unsensitive to the temperature

Nj modulates the Off-current

Activation Energy (Ea) of Iedge current is extracted versus T°

More the Ea is high more the segregation is strong



Edge current and Edge current and T° T° behaviour behaviour (2/2)(2/2)

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

30 32 34 36 38 40

1/Kb.T (1/eV.K)

I edg

e (A

/edg

e)


283RTN+DPN+ anneal

384RTO+DPN+ anneal

312RTO+DPN

288RTO+RTN

398RTO

Ea (meV)Process

Higher is the nitridation part

lower is the Ea

and lower is the dopants segregation



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Conclusions



ConclusionsConclusions

The strong interest of oxynitride process (Rapid Thermal Nitridation and Decoupled PlasmaNintridation) to reduce RNCE has been demonstratedBoth Vth-Wg roll down and parasitic edge current have been decreasedBody Factor method and T° measurement put in evidence the role of NO-gas during gate oxidation stepsNitridation option is a safety solution for SRAM cell leakage control, especially for Low Power Applications

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D2.3 - Gate oxide process impact on RNCE for advanced CMOS