2011

Robert Baumann

Slide 1/15

Determining the Impact of Alpha-

Particle-Emitting Contamination from

the Fukushima-Daiichi Disaster on

Japanese Semiconductor

Manufacturing Sites

Dr. Robert C. Baumann

Texas Instruments Fellow / IEEE Fellow

2011

Robert Baumann

Slide 2/15

What happened at Fukushima-Daiichi?

Are beta and gamma emitters a concern for Silicon devices?

Did any alpha-emitters get out?

Did they disperse? If so, how far and in what concentrations?

What is the size distribution of particulates? Can they breach clean

room filters?

Can we detect any activity on wafers exposed during the disaster?

Summary of analysis – Did the nuclear incident impact

manufacturing in Japan from an SER risk point-of-view?

Questions to be Addressed

2011

Robert Baumann

Slide 3/15

From http://cryptome.org/eyeball/daiichi-npp/daiichi-photos.htm

Tokyo

Mihomura

Aizuwakamatsu

FukushimaDaiichi

~ 100km

~ 160km

JAPAN

Tokyo

Mihomura

Aizuwakamatsu

FukushimaDaiichi

~ 100km

~ 160km

JAPAN

Fukushima-Daiichi Power Plant

東日本大震災東日本大震災東日本大震災東日本大震災 “Higashi Nihon Daishinsai” (East Japan Great Earthquake Disaster)

Friday, 11 March 2011, 2:46:23 PM JST, 6 minutes, Magnitude: 9.0

Tsunami: Yes. Up to 40.5 m (133 ft) Land subsidence: 0.29m to 1.2m (Japan got smaller!)

Global Impact: NASA’s JPL determined that the Earth’s rotation was slowed so that days are

1.8 microseconds shorter. Changed Earth’s axis (tilt) by 10 - 25 cm!

Fukushima-Daiichi Nuclear Power Plant run by the Tokyo

Electric Power Company, consisted of 6 light boiling water reactors (BWRs) generating 4.7 GW.

2011

Robert Baumann

Slide 4/15

What Exactly Happened?

From:http://en.wikipedia.org/wiki/File:Fukushima_I_nuclear_accidents_diagram.svg

The loss of offsite power (earthquake) and onsite AC

power (tsunami), combined with the rapid discharge of the DC batteries led to a complete station blackout.

Blackout disabled the Emergency Core Cooling System

which led to fuel and containment overheating and

damage.

Rapid oxidation at high temperatures (usual core temp 250C, w/o cooling > 2000C) and generation of large

amounts of H2 led to the explosion/destruction of the outer building structures at Units 1 and 3.

Venting of hydrogen into buildings 2 and 4 is assumed

to be the cause of the subsequent fires and explosions in those structures. Units 5 & 6 were undamaged and

were off line prior to the disaster.

Apparently explosions destroyed outer building only

and core and containment structures were fairly well maintained.

Spent fuel pools appear to have remained underwater

despite earlier fears of air exposure. But several of the cores appear to have partially melted.

http://mitnse.com/2011/08/07/updated-mit-faculty-report-on-fukushima/fukushima-lessons-learned-mit-nsp-025_rev1/

2011

Robert Baumann

Slide 5/15

235U

nucleus

neutron Fission

Fragment

Fission

Fragment

neutron

neutron

The dominant process is the nuclear

fission of 235U creating more

neutrons and energetic fission

fragments. In a typical nuclear fission

reaction, 187 MeV is released in the

form of kinetic energy from the

fission products, from the fission

neutrons, instantaneous gamma

rays, and gamma rays from the

capture of neutrons. Natural

radioactive decay is continuously

occurring (a, b, and g emission) as is

neutron capture (creating new

isotopes) and beta and gamma

emission from fission products. Thus

a lot of kinetic energy is being

converted to heat even with the

reactor “off”.

[http://en.wikipedia.org/wiki/Decay_heat]

Nuclear Fission Basics

2011

Robert Baumann

Slide 6/15

From http://en.wikipedia.org/wiki/File:Reaktor.svg

The removal of the decay heat is a significant reactor safety concern. Failure to remove

decay heat may cause the reactor core temperature to rise to dangerous levels.

(typical spent nuclear fuel generates about 10 kW of decay heat per ton of fuel)

http://en.wikipedia.org/wiki/Decay_heat

Problems with losing your cool

2011

Robert Baumann

Slide 7/15

0.01

0.1

1

10

0 5 10

Incident Particle Energy (MeV)

dE

/dx

(fC

/µm

) in

Sili

co

n

electrons (-β particles and from γphoton interactions)

α particles

16 fC/µm

0.18 fC/µm

Which radiations matter?

For silicon devices, alpha-particle emitting

contamination is the biggest concern.

90 110 15013070 170

0.02

0.04

0.06

0.08

137Cs

134Cs

Yie

ld F

raction

Mass Number of Fission Fragment

134I

131I

For humans, the β− and γ− emitting fission fragments are a major concern.

2011

Robert Baumann

Slide 8/15

1.3E-063.8E-021.8E+01α0.004%244Cm

1.5E-102.8E-062.46E+05α0.006%234U

1.8E-071.6E-034.4E+02α0.012%241Am

1.6E-103.2E-072.1E+06α0.049%237Np

1.0E-091.8E-063.8E+05α0.056%242Pu

1.6E-061.6E-034.3E+02β, α∗0.102%241Pu

2.2E-071.0E-046.7E+03α0.212%240Pu

1.5E-072.9E-052.4E+04α0.520%239Pu

1.4E-103.0E-082.3E+07α0.460%236U

7.9E-129.8E-107.0E+08α0.800%235U

β3.481%Fiss. frag.

1.5E-101.6E-104.5E+09α94.300%238U

% Specific Activity

Activity (year

-1)

Half-life (years)

Type%

AbundanceIsotope

1.3E-063.8E-021.8E+01α0.004%244Cm

1.5E-102.8E-062.46E+05α0.006%234U

1.8E-071.6E-034.4E+02α0.012%241Am

1.6E-103.2E-072.1E+06α0.049%237Np

1.0E-091.8E-063.8E+05α0.056%242Pu

1.6E-061.6E-034.3E+02β, α∗0.102%241Pu

2.2E-071.0E-046.7E+03α0.212%240Pu

1.5E-072.9E-052.4E+04α0.520%239Pu

1.4E-103.0E-082.3E+07α0.460%236U

7.9E-129.8E-107.0E+08α0.800%235U

β3.481%Fiss. frag.

1.5E-101.6E-104.5E+09α94.300%238U

% Specific Activity

Activity (year

-1)

Half-life (years)

Type%

AbundanceIsotope

What makes up “spent” fuel?

2011

Robert Baumann

Slide 9/15

1 2 3 4 5 6 7 8

Measurement Location

10-8

10-6

10-4

10-2

10 0

10 2

Activity (

Bq

/m3)

Sum Detected

Activity

238Pu activity

239Pu activity

234U activity

235U activity

238U activity

Natural Outdoor Radon Background

1 2 3 4 5 6 7 8

Measurement Location

10-8

10-6

10-4

10-2

10 0

10 2

Activity (

Bq

/m3)

Sum Detected

Activity

238Pu activity

239Pu activity

234U activity

235U activity

238U activity

Natural Outdoor Radon Background

Riverside, CA86798

Anaheim, CA86497

San Fran., CA80636

Seattle, WA74735

Hawaii, HI58994

Alaska, AK45773

Guam, GU27202

Saipan, CNMI25451

Location Distance (km)* Num.

Riverside, CA86798

Anaheim, CA86497

San Fran., CA80636

Seattle, WA74735

Hawaii, HI58994

Alaska, AK45773

Guam, GU27202

Saipan, CNMI25451

Location Distance (km)* Num.

Pu and U isotope signals

were detected in U.S.

locations after the

Fukushima-Daiichi

accident.

Levels were > 105 times

LOWER than natural

background activity, BUT

they confirm that alpha-

emitting contamination

escaped containment and

was widely dispersed.

Based on raw data from

Adapted from EPA RadNET 4/16/11.

EPA report confirms release

2011

Robert Baumann

Slide 10/15

From TEPCO press release (May 3, 2011)

238Pu

239Pu

240Pu

234U

235U

238U

241Am

242Cm

243Cm

244Cm

0.21 0.063 0.063 7.2 0.32 8.2 0.027 2.4 0.19 0.19

ND - 0.15 ND - 0.15

Detected Soil Activity 500m from Reactors (Bq/kg dry soil)

Ratio of nuclides same as spent fuel

in reactors 1 and 3

Soil background

levels in Japan

Early TEPCO press releases claimed no actinide isotopes above background

levels. Later soil activity measurements reveal non-background U/Pu/Am/Cm

contamination from nuclear fuel - confirming release of contamination from the

incident.

Higher concentrations of contamination are possible further away from plant

due to wind action but Gaussian plume models cannot accurately predict

distribution due to lack of timely air measurements for actinide contamination.

TEPCO report confirms release

2011

Robert Baumann

Slide 11/15

EXPLOSIVE & BUOYANT RISE

WIND Wet

deposition

Dry

deposition resuspension

POWER

PLANT

PLUME

IMPACTION

TURBULENT MIXING

Absorption by soil, vegetation, bodies of water

MOUNTAIN

CLOUD

Dissolved volatiles and non volatiles

WASTE HEAT

EXPLOSIVE & BUOYANT RISE

WIND Wet

deposition

Dry

deposition resuspension

POWER

PLANT

PLUME

IMPACTION

TURBULENT MIXING

Absorption by soil, vegetation, bodies of water

MOUNTAIN

CLOUD

Dissolved volatiles and non volatiles

WASTE HEAT

Based the complexity of the dispersion process and the

lack of ground-level data, it is impossible to model realistic

dispersion of alpha-emitting particulates.

[ ]

−−

−=

)(2

h

)(2

y exp

)()(

/exp),(

2

2

2

2

xxxyv

vxSyxc

zyzywx

wxo

σσσσπ

λ

Can we model the dispersion?

2011

Robert Baumann

Slide 12/15

After G. Kaurov, et al., “Physiochemical Characteristics of Uranium Microparticles Collected at Nuclear Fuel Cycle Plants”, International Atomic Energy Agency-SM-367/10/05/P

The morphologies and sizes of uranium

micro-particles collected from reactors spent fuel assemblies.

Particles down to 0.2 µm have been documented,

With the bulk being in the 1-2 µm range

What about the U/Pu dust?

After C.W. Fort, R. Douglas, R. Gauntt, and A.R. McFarland, “Particle Size Distribution of Yellowcake Emissions at the United Nuclear Churchrock Uranium Mill”, EPA, ORP/LV-80-1, Jan. 1980, p.20.

HEPA Filter (High Efficiency Particulate Air) -

Remove particles 0.3 micron or larger with a 99.97 to 99.9995% particle-collective efficiency.

ULPA Filter (Ultra-Low Penetration Air ) - Remove particles 0.12 micron or larger at 99.9995% particle-

collective efficiency.

2011

Robert Baumann

Slide 13/15

Alpha Counting Detailspositive high

voltageIonization detector

Discriminator

& Counter

wafer sample

emittedalpha flux

++++++++++++++ Amp

62.74%0.000180.000720.000134950Full process 8LM Cu wafer 2

96.78%0.000280.000370.000134950Full process 8LM Cu wafer

-0.000040.000340.000124950Bare silicon wafers (C027)

-0.000070.000340.000124950diborane based W process

-0.000110.000340.000124950C021 Alternate dielectric

96.41%0.000270.000360.000134950C021 Interlevel dielectric

99.96%0.000390.000350.000124950C027 Interlevel Dielectric

-0.000000.000330.000124950C027 Barrier Layer

91.47%0.000360.000540.000194950ECD Cu 10um

conf. averageMDA95CDL95DetectorSample Description

P10 gas

Mylar

window

Two sets of 8” wafer samples

were obtained from each

Of the two sites:

8 exposed wafers from Miho

8 sealed wafers from Miho

8 exposed wafers from Aizu

8 sealed wafers from Aizu

Counts α events

ignores β events

2011

Robert Baumann

Slide 14/15

Alpha Counting Results

εσ

A

t

B

t

G

nnLODBG

22+

==

Methodology and reporting is compliant with the new JEDEC Standard JESD221 (May 2011)

“Alpha Radiation Measurement in Electronic Materials”

Counter Identification 4950

Minimum Discriminator Energy 1.00 MeV

P10 Flow Rate 200 cc/min

Sample/Electrode distance < 2 mm

Counter Efficiency 84 %

Counter Active Area (cm2) 3600 cm2

Sample Active Area (cm2) 2512 cm2

Confidence Interval (%) 90 %

Miho Aizu

Background Count (B) 1439 1497

Background Count Time (hours) 168 168

Gross (sample + background) Count 1504 1388

Gross Count Time (hours) 168 168

Raw Alpha Emissivity (� /cm2-hr) 0.00018 -0.00031

Std. Deviation of Emissivity (� /cm2-hr) 0.00016 0.00015

Detection Limit (a/cm2-hr)

at 90% confidence interval 0.00026 0.00025

Ultra Low Alpha Material Emission

Standard (a/cm2-hr)

Counting Results

< 0.002

Tray & chamber were running a bit hot

(1.6x higher than usual) and thus we used our unexposed wafers as

background (since they blocked the same area of tray). Note that for null

results it is not uncommon to get negative raw emissivities BUT usually

these are within 1 standard deviation while in the Aizu case we are 2 std devs.

Lower. After detecting the high background for the trays and the

chamber we sent the detector out for

service and will redo the test once background is back to normal but we do

not expect that we will see a different result.

2011

Robert Baumann

Slide 15/15

Conclusions• The first report of alpha-particle counting from wafers exposed to atmosphere

(AF > 100x) during and after the disaster confirm that no alpha emission was

observed in any of the samples.

• All wafer samples were below the limit of detection (LOD) and LOD was ten

times below the emission level of ULA materials specified for minimizing

alpha-particle soft errors. Background was about 1.6x higher than previous

runs done a few years ago – detector needs servicing.

• These results prove that semiconductor manufacturing, at least at these two

sites, was NOT impacted by contamination released from the Fukushima

Daiichi plant. Products manufactured at these facilities will NOT exhibit any

increase in alpha-induced SER.

• The SER reliability performance of semiconductor devices manufactured in

Japan is not impacted in any measurable way.