TCAD Simulation of Total Ionization Dose Response on DSOI nMOSFET

Co Authors: Li Binhong(IMECAS), Liu Bing(BISLMV), Shen Chen(Cogenda), Song Yanfu(Cogenda), Li Bo(IMECAS), Han Zhengsheng(IMECAS), Luo Jiajun(IMECAS)

Huang YangInstitute of Microelectronics of Chinese Academy of Sciences

1@IMECAS

Contents

2

I. Radiation Environment

II. SOI vs. DSOI

III. TCAD model for DSOI

IV. TID response of DSOI nMOSFET

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Radiation Environment

3

Radiation Effect:

ØTotal Ionization Dose- TID trapped holes in the oxide and interface traps

at the Silicon-oxide interface will affect the

device performance parameters

ØSingle Event Upset-SEUthe state change caused by one single ionizing

particle striking the sensitive node of a device

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SOI vs DSOI

4

Disadvantages: ü the TID effect is even worse in

FDSOI because of the introduction of the buried oxide layer(BOX) and the coupling effect between the front and back gate

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SOIAdvantages:ü good SEU suppression because of the buried

oxide isolation(BOX)

BOX

STI STI

VsourceVgate

Vdrain

VsubFD-SOI

Sub

BOX

STI

STI

Vsource

Vgate

Vdrain

VsubFD-SOI

positive oxide trapped charges

BOX

Body

Gateox

+

+

+

+

++

+

X X X

X X X X

interface traps

SOI vs DSOI

5

With SOI2 (Advantages): •compensation of TID effect VSOI2 controls the positive trapped charges in the oxide•compensate NMOS and PMOS seperatelythe compensation voltages needed for NMOS and PMOS are different•reduction of back-gate effectthe back-gate effect can be suppressed with SOI2 biased at a constant voltage

DSOI has an additional Si layer (SOI2)

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SOI2

STI STISTI

SOI2

N+ N+P NP+ P+

Sub

BOX2

BOX1 BOX1

BOX2

SOI vs DSOI

6

Ø TID Experimental Results of DSOI(0.2μm FD NMOS) ü Irradiation state: OFF ü Irradiation dose rate: 50rad(Si)/sü Irradiation dose: high up to 5Mrad(Si), by 60Co γ-ray

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-0.5 0.0 0.5 1.0 1.5 2.0

10-12

10-10

10-8

10-6

10-4

0Krad(Si) 100Krad(Si) 300Krad(Si) 500Krad(Si) 1Mrad(Si) 2Mrad(Si) 3Mrad(Si) 4Mrad(Si) 5Mrad(Si)

ID (

A)

VG (V)

Vth

Ioff

VSOI2=0V

-0.5 0.0 0.5 1.0 1.5 2.0

10-12

10-10

10-8

10-6

10-4

0 Krad(Si) 500 Krad(Si) 1 Mrad(Si) 2 Mrad(Si) 3 Mrad(Si) 4 Mrad(Si) 5 Mrad(Si)

ID(A

)

VG(V)

VSOI2=-7V

IV shift negatively due to radiation induced holes.By applying VSOI2 properly, IV curves can be recovered.

TCAD model for DSOI

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Ø Software used:Cogenda TCAD device modeling tool(focus on radiation effect simulation)Ø Main characteristics of DSOI(NMOS)FDSOI technology; floating body deviceüSOI1 thickness: 46.7nmüBOX1 thickness:158.7nmüSOI2 thickness: 84nmüBOX2 thickness:156nmüCore gate oxide thickness: 5.6nmüSubstrate: p type, resistivity >1000 ohm-cmüSOI2: n type, resistivity ~10ohm-cmüChannel stop implant: 15nm to 46.7 nm below SOI1 top surface with peak conc. 5e15cm^-3.üVt implant: 0~12nm below SOI1 top surface with peak conc. 1.6e18cm^-3.üLDD implant: peak conc. 9e18cm^-3 at SOI1 top surface. Offset to Poly edge is zero.üS/D implant: 0~15nm below SOI1 top surface with peak conc. 2.0e20cm^-3. Offset spacer distance is 100nm.

SOI2SOI1

VGVS VD VSOI2

TCAD model for DSOI

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ØPhysical models used for TCAD modelingPhysical Model DSOI

Mobility model Lucent

High field saturation model

Impact ionization model Selberherr

Tunneling model BBT model

ü Lucent High Field Mobility Model This model incorporates Philips Unified Mobility model and the Lombardi Surface Mobility model, as well as accounting for Caughey-Thomas model.

low field mobility model

mobility in the (MOS) inversion layer high field velocity saturation

Philips Lombardi

suitable for MOS simulation!

TCAD model for DSOI

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ü Selberherr Impact ionization modelThe generation rate of electron-hole pairs due to the carrier Impact Ionization (II) is generally modeled as:

ionization coefficients Selberherr

default avalanche model

ü Band-to-band tunneling modelMany studies have shown that the combined impact of BBT and positive trapped charge in the buried oxide is a significant factor in the radiation response of floating body FDSOI NMOS.

TCAD model for DSOI

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Ø TCAD simulation results vs. experimental resultsDSOI NMOS (W/L=8/1)

Vg=1.8V

Vd=0.95V

Vd=0.1V

Solid lines: simulated curvesDotted lines: experimental curves

Vg=1.5V

Vg=1.2V

Vg=0.6V

Kink effect because of floating body

good correspondence!

TCAD model for DSOI

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Ø TCAD simulation results of DSOI NMOS Suppression of back-gate effect

SOI2 works as a good shield!VSub

BOX2

VGVS VD VSOI2

BOX1

VSub=5V

VSOI2=0VVSOI2=0V, IDVG curves with different Sub voltages.

TCAD model for DSOI

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Ø TCAD simulation results of DSOI NMOS IDVG curves with different VSOI2

Vsoi2=15V, EV and EC

Vsoi2=15V

Vsoi2=-15V

VG/V

ID/AVG=1V

VG=0.2V

VG=-0.6V

-1.0 -0.5 0.0 0.5 1.0 1.5 2.00.0

5.0x10-6

1.0x10-5

1.5x10-5

2.0x10-5

2.5x10-5

3.0x10-5

3.5x10-5

4.0x10-5

4.5x10-5

5.0x10-5

ID

VG

Vsoi2=-15V Vsoi2=-10V Vsoi2=-5V Vsoi2=0V Vsoi2=5V Vsoi2=10V Vsoi2=15V

Vsoi2=-15V

Vsoi2=15V

Experimental Results

TCAD Results

VG=1V

VG=0.2V

VG=-0.6V

front back

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TID response of DSOI NMOSØ TID simulation method of Cogenda

Monte Carlo particle simulation

energetic particle transport

Method proposed by N.L. Rowsey (2012) and I.S. Esqueda (2011)

Easy to implement

Difficult to implement

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TID response of DSOI NMOS

DSOI nMOSFETs are irradiated up to 1Mrad(Si) by 60Co γ-ray at a dose rate of 50rad(Si)/s.

Ø Bias configurations during irradiation and measurementBias applied during irradiation

VG VS VD VSOI2 Vsub

OFF 0V 0V 1.8V 0V 0VBias applied during measurement

Id-Vg curve VG VS VD VSOI2 Vsub

VSOI2=0V Sweep 0V to 1.98V 0V 0.1V 0V 0V

VSOI2=-5V Sweep 0V to 1.98V 0V 0.1V -5V 0V

Irradiation Dose：0rad(Si)、100Krad(Si)、300Krad(Si)、500Krad(Si)、1Mrad(Si)

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~1.8V

~0.6µs

~0.6µs

Ø TCAD simulation results vs. experimental resultsDSOI NMOS (W/L=8/1)

Threshold (Vth): Vg@Id=(0.1μA)x(W/L)

Dose/krad(Si)

Vth shift/V

Irradiation State: OFF VSOI2=0V

Irradiation Dose: 0rad(Si)、100Krad(Si)、300Krad(Si)、500Krad(Si)、1Mrad(Si)、

TID response of DSOI NMOS

TID response of DSOI NMOS

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Ø Simulated trapped holes in the BOX1 layer Source LDD Channel LDD Drain

VS=0V VG=0V VD=1.8V

VSOI2=0V

VSub=0V

Irradiation Dose: 1Mrad(Si)

cutline

cutlineBOX1

front interface

back interface

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IDVG curve is recovered by VSOI2 after 1Mrad(Si)!

TID response of DSOI NMOSØ Compensation of TID effect with VSOI2 Different VSOI2 during measurement

Irradiation Bias: OFF VSOI2=0V

Irradiation Dose: 1Mrad(Si)

Measurement Bias: IDVG curve with VSOI2=0V and VSOI2=-5V respectively

VSOI2=-5V

pre

VSOI2=0V

VD=0.1V

-1.0 -0.5 0.0 0.5 1.0 1.5 2.00.0

5.0x10-5

1.0x10-4

1.5x10-4

2.0x10-4

2.5x10-4

3.0x10-4

3.5x10-4

4.0x10-4

4.5x10-4

5.0x10-4

pre Vsoi2=0V 1Mrad(Si) Vsoi2=0V 1Mrad(Si) Vsoi2=-5

ID/A

VG/V

Shift negatively after 1Mrad(Si)

Shift back after Vsoi2=-5V

Experimental Results

TCAD Results

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TID response of DSOI NMOSØ Compensation of TID effect with VSOI2 Different VSOI2 during measurement

VSOI2=0V

VSOI2=-5V

cutline

cutline

Electrical Field

Electrical Field

BOX1 top

BOX1 top

Source DrainChannel

SummaryØBackground Advantages of DSOI compared with SOI. Successful TID compensation.ØTCAD model for DSOI Physical model. Good correspondence with experimental results.ØTCAD simulation results and explanation TCAD simulation before and after irradiation. Impact of VSOI2 before and after irradiation.

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END

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