Modulator Design Modulator Design for Plasma Ion for Plasma Ion ImplantationImplantation

Professor Michael Bradley Professor Michael Bradley Dale Heggie, Joel Leslie, Curtis Dale Heggie, Joel Leslie, Curtis

OlsonOlsonMarch 24March 24thth, 2004, 2004

ObjectiveObjectiveConvert an existing vacuum Convert an existing vacuum

chamber into a plasma ion source chamber into a plasma ion source for Ion Implantationfor Ion Implantation

Applications in Materials Applications in Materials ProcessingProcessing

1.1. Electronics IndustryElectronics Industry• Semiconductor dopingSemiconductor doping• IC FabricationIC Fabrication

2.2. Mechanical Mechanical TreatmentTreatment

• Surface hardnessSurface hardness• Frictional PropertiesFrictional Properties

3.3. Biomedical ImplantsBiomedical Implants• Biocompatible materialsBiocompatible materials

Applications in Materials Applications in Materials ProcessingProcessing

1.1. Electronics IndustryElectronics Industry• Semiconductor dopingSemiconductor doping• IC FabricationIC Fabrication

2.2. Mechanical Mechanical TreatmentTreatment

• Surface hardnessSurface hardness• Frictional PropertiesFrictional Properties

3.3. Biomedical ImplantsBiomedical Implants• Biocompatible materialsBiocompatible materials

What’s a plasma??What’s a plasma??

Four States of Four States of MatterMatter

1.1. SolidSolid

2.2. LiquidLiquid

3.3. GasGas

4.4. PlasmaPlasma

Plasma ExamplesPlasma Examples

Neon Neon lightslights

LightninLightningg

SunSun Aurora Aurora

BorealisBorealis

Plasma ExamplesPlasma Examples

Neon Neon lightslights

LightninLightningg

Aurora Aurora BorealisBorealis

PII Material ProcessingPII Material Processing

1.1. Insert sample Insert sample into chamberinto chamber

2.2. Strike a Strike a plasmaplasma

3.3. Apply high Apply high negative negative voltagevoltage

4.4. Ions hit the Ions hit the sample and sample and are implantedare implanted

+ + + + + + +Silicon

-5 kV

PII Material ProcessingPII Material Processing

-5 kV

+ + + +

Characterize the Characterize the effects of implant effects of implant depth and dosedepth and dose

-10 kV-20 kV

Sample MaterialSample Material

Sample HolderSample Holder

Implant ImplicationsImplant Implications

Kinetic energy is Kinetic energy is transferred into transferred into heatheat

Sample Sample overheating from overheating from continuous implantcontinuous implant

Requires pulsed Requires pulsed voltagevoltage

+ + + + + + +

Voltage PulsingVoltage Pulsing

Energy Energy contaminaticontamination from on from rising and rising and falling falling edgesedges

Time

Voltage

Implanting Cooling

+ + + + + + + + +

Final SystemFinal System

+ -

High Voltage Source

Modulator

Vacuum Chamber

Modulator DesignModulator Design

Solid state Solid state transistor transistor modulesmodules

One master One master timer timer

ExpandableExpandable

Time Start

Master Timer

Optical Fiber

+ -

High Voltage Source

To Vacuum

Final System Final System

Circuit PerformanceCircuit Performance

5 switching 5 switching modulesmodules

Excellent Excellent rise and fall rise and fall timestimes

Expandable Expandable without without affecting affecting performanceperformance

TimerTimerHigh VoltageHigh Voltage

Successful ImplantSuccessful Implant

5 switching modules 5 switching modules 1600 V negative 1600 V negative

biasbias 2” Silicon Wafer2” Silicon Wafer Short Nitrogen Short Nitrogen

implantimplant

Special ThanksSpecial Thanks

Dr. Michael BradleyDr. Michael Bradley Dave McColl, P. Eng.Dave McColl, P. Eng. Dr. Ajay SinghDr. Ajay Singh Dr. Akira HiroseDr. Akira Hirose Perry BalonPerry Balon Vic Meyer, Electrical Vic Meyer, Electrical

ShopsShops

Questions???Questions???

Master ControllerMaster Controller

Circuit DescriptionCircuit Description Monostable 555 for Monostable 555 for

implant durationimplant duration Astable 555 for Astable 555 for

pulse frequencypulse frequency FeaturesFeatures

Duty cycle variationDuty cycle variation Implant Time (5, Implant Time (5,

10, 30 seconds)10, 30 seconds) Start ControlStart Control

Circuit DevelopmentCircuit Development

High Voltage Switching UnitsHigh Voltage Switching Units PC Board layout in TraxmakerPC Board layout in Traxmaker Fabricated by Electrical Engineering ShopsFabricated by Electrical Engineering Shops

Vacuum Chamber Vacuum Chamber ResultsResults

• 2 x 102 x 10-7-7 Torr base pressure Torr base pressure• 0.01% impurities from background 0.01% impurities from background

gasgas

Vacuum Chamber Pump Down Curve

1.00E-07

1.00E-06

1.00E-05

1.00E-04

0 0.5 1 1.5 2 2.5

Time (days)

Pre

ssu

re (

To

rr)

Sample HolderSample Holder

Secure silicon Secure silicon wafer inside wafer inside chamberchamber

Thermal Thermal conductivityconductivity AluminumAluminum

Plasma GenerationPlasma Generation

Raise to 2 Raise to 2 mTorr mTorr pressure pressure with with NitrogenNitrogen

Filament Filament generatiogenerationn

Testing Testing

By the Numbers…By the Numbers…

Vacuum ChamberVacuum Chamber• Goal - Base pressure < 1 µTorrGoal - Base pressure < 1 µTorr Result – 2 x 10Result – 2 x 10-7-7 Torr Torr

High Voltage SwitchingHigh Voltage Switching• Goal - < 10 microsecond rise and Goal - < 10 microsecond rise and

fallfall Result – 300 ns rise, 700 ns fallResult – 300 ns rise, 700 ns fall

Switching ProblemsSwitching Problems

• Less than 1% energy contaminationLess than 1% energy contamination

Overall Circuit Overall Circuit PerformancePerformance

• 5 modules at 1600 5 modules at 1600 VoltsVolts

• Expandable without Expandable without affecting performanceaffecting performance

Vacuum ChamberVacuum Chamber

Base pressureBase pressure 1 in 10 000 1 in 10 000

contaminationcontamination

Langmuir ProbeLangmuir Probe

Characterize our Characterize our plasma for accurate plasma for accurate implant dosesimplant doses

Ion saturation Ion saturation current of 12 mAcurrent of 12 mALangmuir Probe Curve

-14-12-10-8-6-4-2024

-40 -30 -20 -10 0

Voltage (V)

Cur

rent

(mA

)

Isat

Vf loat(-5v)

Langmuir Probe Curve

-100

0

100

200

300

400

-40 -30 -20 -10 0 10

Voltage (V)

Cu

rren

t (m

A)

Isat

Vf loat(-5v)

Ion Density of Ion Density of Plasma (~2 x 10Plasma (~2 x 1099 ions/cmions/cm33))

0.57% ionization0.57% ionization

Modulator DesignModulator Design

• ModulesModules• Insulated gate Insulated gate

bipolar junction bipolar junction transistor (IGBT)transistor (IGBT)

• Internal battery Internal battery powerpower

• Optical IsolationOptical Isolation• SynchronizationSynchronization

Future Design ProjectsFuture Design Projects

1.1. High Voltage IsolationHigh Voltage Isolation1.1. Metal boxesMetal boxes2.2. Fast Zener clamping for each moduleFast Zener clamping for each module

2.2. Increase Plasma densityIncrease Plasma density1.1. Shorter implant timesShorter implant times2.2. Increase saturation current via RF Increase saturation current via RF

sourcesource3.3. Better Power SupplyBetter Power Supply