Hydrogen 2007 1

Studying the Effect of Molecular Hydrogen on Silicon Device Radiation Response

Using Gated Bipolar Transistors

Jie Chen, David Wright, and Hugh BarnabyElectrical Engineering, ASU, Tempe, Az

Hydrogen 2007 2

Topics of Discussion

• Motivation for the study

• Background

• Initial experimental results

• Modeling the effect of molecular hydrogen

• Recent experimental results

• Experimental data vs. model

• Summary

Hydrogen 2007 3

Motivation of Study

1.E-09

1.E-08

1.E-07

1.E-06

-100 -80 -60 -40 -20 0Vg (V)

Ib (A

)

sealed @ 30kradunsealed @ 30Krad after 8 days

Previous experiments showed 3x increase in Nit in devices in sealedpackages compared toun-sealed ones.

ΔNot (cm-2) ΔNit (cm-2)

Unsealed ~1.7x1011 ~0.8x1011 0.00005% H2

Sealed ~1.4x1011 ~2.5x1011 1.3% H2

Sealed package

Unsealed package

Hydrogen 2007 4

Post-irradiation annealing in H2

After Mrstik & Rendell, IEEE Trans. Nucl. Sci., 1991

• MOSFETS exposed to 10Mrad and 1Mrad 10KeV x-rays.

• Post-irradiation annealing in 100%, 10%, and 1% H2 environment.

• Results show increase in Nit after annealing in H2.

Increase in Nit

Increase in Nit

Hydrogen 2007 5

Earlier Experiments

NAVSEA Crane performed HDR testing performed at NAVSEA on devices in 100% H2

1.E-09

1.E-08

1.E-07

1.E-06

-100 -80 -60 -40 -20 0Vg (V)

Ib (A

)

preradIrrad in airIrrad in 1.3% H2Irrad in 100% H2

0

5E+10

1E+11

1.5E+11

2E+11

2.5E+11

0 10000 20000 30000 40000

Total Dose (rad)

del N

it (c

m̂-2

)

Air (unsealed)1.3% H2 (sealed)100% H2 (unsealed)

Increase in Nit

Hydrogen 2007 6

Interface Trap Formation:2 stage model

Si-SiO2

interface

-+

-

+

-

+H

-

+fH

tox

Ionizing radiation

H

xd

H

DH volume

fp

H+

H+

- protons

- Si-H (NSiH)

- dangling bond (Nit)

H

H+

fH- proton flux

- hydrogen defect (D’H)

H+

HDH DH p

f HN fx t

it itSiH it it H

it

N N (t)N N (t) σ ft

After Mclean TNS 1980Rashkeev et al. TNS 2002

Hydrogen 2007 7

Model:Impact of Molecular H2

Si-SiO2interface

-+

-

+

-

+H

-

+fH

tox

Ionizing radiation

H

xd

H

D’H volume

fp

H+

H+

H+

Si-SiO2interface

-+

-

+

-

+H

-

+fH

tox

Ionizing radiation

H

xd

H

D’H volume

fp

H+

H+

H+

Empty D centers

HH

HH

H2 molecules

Molecular hydrogen reacts with empty D centers to generate more DH centers

2DH2DH2

HH

DHcenters

H

H

H

H2 transportinto material

21

H2

21H1

DH2

2

Nk1Nk

N

Rad-inducedholes

Hydrogen 2007 8

1D Analytical Model

2

2

12

1 212

2

21

oDH DH SiH it g y oH

it

H

x

k ( )N ( N Dk f t t )

NN

N/

k ( )

Note: final 1D model assumes steady state, no Nit saturation or annealing

21

H2

21H1

DH2

2

Nk1Nk

N

Equil. H2 - DH model Steady state hole transport

oxygp tfkDf (fp > 0 for all x)

HDH DH p

f HN fx t

Proton continuity

it itSiH it it H

it

N N (t)N N (t) σ ft

Trap continuity

Final Model

*

Hydrogen 2007 9

Latest Experiments

• GLPNP devices used are designed by NAVSEA Crane and fabricated using National’s standard linear bipolar IC process

• Using only devices with no-passivation (Wafer #4) for simplicity (one less parameter in modeling)

• 10%, 0.1%, 0.01%, 50% H2 ambient concentrations, as well as re-examination of 1% and 100% data points

GLPNP with no passivation

Hydrogen 2007 10

Experimental Details

• 4 device samples for each H2 concentration

• De-seal lids at least 3 days prior to soaking

• 10-5 torr vacuum before filling of H2

• >48hrs soaking before irradiation

• Gamma HDR test to 30Krad at 18 rad/s

• Pb shield used during irradiation

• Devices grounded during irradiation

• Soaking temperature: 72 deg F

• Irradiation temperature: 72 deg F H2 Chamber (Soaking & Irradiation)

Hydrogen 2007 11

Latest Experimental Results• Characterization performed using Agilent 4156 SPA. Gate Sweep (GS),

Subthreshold Sweep (SS), and Gummel are performed.

• Gate Sweep: VG = 80V to -100V, VBE = 0.5V, VC = 0V

Hydrogen 2007 12

Latest Experimental Results• Subthreshold Sweep: Vg = 10V to -100V, VE = -0.1V as the drain of the

pMOSFET, VC = 0V, VB = 0V.

Hydrogen 2007 13

1D model fit to data

• ASU results indicated monotonic increase of Nit vs ambient H2 concentration, agrees with the predictions of the model.

• Saturation at high H2 and low H2 concentration agrees with the predictions of the model,

• Crane’s 100% data is different than ASU’s 100% data. The difference may be due to differences in dose, dose rate, environmental factors, etc.

Re-fit of the data with the analytical model

Hydrogen 2007 14

Continuing work

• Post-irradiation annealing studies

• Effect of high pressure H2 environment

• Model refinement

• Relate dose-rate effects to the reaction processes of hydrogen species in SiO2

• Effect of H2 under low temperature exposure