Ion Implantation for Fabrication of Semiconductor Materials & … · 2019. 6. 6. · 3 Current Scientific MAM-A.5 Health Physics Society: Jan 2008 Overview of Ion Implantation: System

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Current ScientificHealth Physics Society: Jan 2008MAM-A.5

Ion Implantation for Fabrication ofSemiconductor Materials & Devices

Michael I. Current: Current Scientific, San Jose [email protected]

Nicholas R. White: Albion Systems, Manchester [email protected]

1. Overview of ion implantation for semiconductors

2. Radiation issues: Plasma Immersion (x-rays)8 to 12 MeV Boron (neutrons)

3. Toxic materials: molecular ions

4. Summary

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Applications for Semiconductors

Ion Implantation Dose & Energy

0.1

1

10

100

1000

10000

1.E+10 1.E+11 1.E+12 1.E+13 1.E+14 1.E+15 1.E+16 1.E+17 1.E+18 1.E+19

Ion Dose (atoms/cm2)

Ato

m E

nerg

y (k

eV)

Channel(Vth)

Steep Retrograde Channel (Vth)

Mid-well(Vpunch thru)

Deep-well(Latch up, SER)

Super-deep-well(CCDs)

SIMOX(SOI)

H-cut(Laminatedmaterials)

Halo(Vth, SCE)

SD Extension(Vth, Ids)

S/D Contact(Ids)

Poly-Si Gate(Vth, Ids)

Doping of transistors:Ions: B, BF2, B10H14, B18H22As, P, Sb, In, (Si, Ge, He, F, C)

Energy Range:0.2 keV to 3 MeV (8 MeV)

Dose Range:1e11 ions//cm2 (threshold)5e16 ions/cm2 (poly-gate)

Lamination and SOI:H-cut: 5e16 H/cm2

SIMOX: 2e17 to 5e18 O/cm2

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Overview of Ion Implantation:System Sales

• Implantation system sales is arobust, global business now at~$1.5 B/year.

• Average selling price is $3 to5 M/tool with hundreds ofmachines shipped per year.

• Since 1970, >7,000 commercialimplanters have been shippedfor semiconductor fabrication.

• Most of them are still in use.

Ion Implantation Systems: Worldwide

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2000 2002 2004 2006 2008 2010 2012

Year

Syst

em S

ales

, US$

M

TotalsHigh Current

Medium Current

High Energy

High Dose

Source: Dataquest

BushRecession

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Plasma Immersion Ion Implantation

Varian PLAD

positive ion electron neutral

V

plasma

sheath

- +

wafer target

TimeW

afer

Cur

rent

H2 plasma, 19 µs, 300 A(peak)

SiGen, 1999

19 us

• “Simple” plasma-wafer system

• Excellent for high-dose, low-energy

• Doping (poly-Si gates); H-cut

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Secondary Electrons

(-V)

Ar+

• Copious ion current (100’s A)yields lots of secondary electronsfrom the wafer and platen.

• Secondary yield increases withwafer bias.

• Secondary electrons areaccelerated by the wafer bias.

• Fast secondaries generate x-raysslowing down in groundedchamber walls.

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Plasma Immersion: X-ray Suppression

IonPlasmaSource

Wafer

Mass Filter(optional)

Vextraction

Vacceleration

+

+

++

+

+ ++

Ion Shower

Wafer

IonPlasmaSource

Vpulse

-

Ion Plasma

+ + + ++

Plasma Immersion(with enclosure)

+

++

+

Plasma Immersion

Wafer

Vpulse

-

IonPlasmaSource

Ion Plasma

+ + + ++

• Mass filters in ionshowers (left) andfloating enclosures inPIII (right) suppressx-ray generation athigh bias (~100 kV)operation.

• Many commercialPIII systems operateat <5 kV with modestshielding (center).

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Very-High Energy Doping: Cameras

•“Routine” CMOS wells for logic,DRAM & FLASH use ion energiesfrom 0.5 to ~3 MeV.

• Deep wells for high-performanceCCD & CMOS imagers would likeprofile depths of ~10 um or more.

• Range of 8 MeV B is ~10 um.

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Tandem Accelerators

Varian Kestrel IIIon source

Mass selection

HV

Charge state(energy)selection

Charge exchange channel

Negative ion path

Positive ion path

Spinning& scanningwafer wheel

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12 14 16

Final Energy, MeV

Frac

tion

in c

harg

e st

ate,

%

Boron 1Boron 2Boron 3Boron 4

B+ B+2

B+3

B+4

2 MV

• Tandem accelerators“multiply” the terminalvoltage by chargeexchanges at the HV.

• >8 MeV ions areproduced with B+3 ionsand a 2 MV terminal.

• >10 MeV B+4 are alsoproduced.

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The Wrong Kind of Tandem

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2 MV Tandem Implanter

Clean room interface

Negative ionsource &injection

SF6 enclosure

2 MV terminal (inside enclosure)

Final ion selection

Beam scanningWafer chamber

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Coulomb Barrier

Coulomb Barriers for Boron-11 and Phosphorus-31

1

10

100

0 5 10 15 20

Target Atomic Number

Cou

lom

b B

arrie

r, La

b Fr

ame,

MeV

Boron CBPhos CB

2D

1H3He

4He

6Li 9Be10B 12C

7Li11B 13C

N O F Ne Na Mg Al Si P S Cl

• Coulomb repulsion is 1storder threshold fornuclear reactions,generating neutrons,gammas, etc.

• 31P CB’s are >40 MeV.

• 11B CB’s are <10 MeV forlight (AMU <15) targets.

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Neutron GenerationModel Target (IC wafer)

Si wafer with 50% resist (C )coverage.

Operation Mode

50% beam on wafer.

* C target material is theprimary neutrongeneration concern.•12 MeV B with 1 particle-uA at1 m from the wafer producesneutrons at >1,000 uSv/hr.

• Safe limit is 0.6 uSv/hr. 12 MeV B

Natural

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Neutrons: Boron on Carbon (Photoresist)

+ + nEC or β+, 2.6 yrs

11B 22Na*12C

22Ne γ (1.2745 MeV)

0.6 uS/hr

1 p-uA

• Neutron generationmeasured in forwarddirection.

• Some data collected 12Cions into solid B targets.

• Gy to Sv conversion = 10.

• Neutron generation ratedrops ~1 decade per MeVbelow 12 MeV.

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Operating Conditions

• Safe (<0.6 uSv/hr)operational beam currentsdrop ~1 decade/MeV at ~8MeV B into 50% PR coveredIC wafers.

• 0.1 p-uA of B is sufficientfor ~20 300 mm wafers/hourat 1e11 B/cm2.

• Higher currents (andthroughputs) are possiblewith shielded, licensedoperations.

Safe Boron Currents for PR Masked Si Wafers

0.01

0.1

1

10

100

5 6 7 8 9 10 11

Boron Energy (MeV)

Bo

ron

Cu

ren

t (p

art

icle

-mic

ro-A

)

<0.6 u-Sv/hr

Shielded, radiation licensed operation

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2 MV Terminal Tandem ImplanterSafety Features for 8 MeV Operation:

• Heavy metal beamstop target for10 MeV B+4 ions.

• Ludlam neutron monitor linked toalert and shutdown systems. Samplingtimes adjusted to avoid false warningsat ~0.6 uS/hr.

• Interlocked wall enclosure at >1 mfrom wafers and beamstops.

• Injection magnet field monitored toprevent deuterium beam injection.

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Large Molecular and Cluster Ions• 30 nm Lgate requires 15 to 10 nm SDExtension junction depth.

• Sub-keV B doping favors the use oflarge molecular or cluster ions.

• New ions are: B10H14, C2B10H12, B18H22and “massive” (~10k) clusters.

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Toxic Source Materials

• New molecular ions( ) are as toxic as the“old” materials.

• Handling andabatement proceduresare not relaxed.

• Even Carboranebreaks up into toxiccomponents (Diborane,etc.) in the beamlineand pumps.

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Safety for Ion Implantation

• Ion implantation for fabrication of materials (SOI wafers) & ICdevices is a robust, global business.

• Ion implantation equipment operates with significant risks forhigh-voltages & currents, toxic materials, high-vacuum, highmechanical energy, & ionizing radiation.

• Safe operations is a key factor in the design, fabrication,installation, operation, maintenance & shut-down of implanters.

• New source materials, new system designs & new operatingregimes continually challenge the safety needs of the industry.

• Safety training of engineers, operators and maintenance in newenvironments (China, India, etc.) is particularly challenging.

[email protected] [email protected]

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Ion Implantation for Fabrication of Semiconductor Materials & … · 2019. 6. 6. · 3 Current Scientific MAM-A.5 Health Physics Society: Jan 2008 Overview of Ion Implantation: System