Modulator Design for Plasma Ion Implantation Professor Michael Bradley Dale Heggie, Joel Leslie, Curtis Olson March 24 th, 2004

Objective Convert an existing vacuum chamber into a plasma ion source for Ion Implantation

Applications in Materials Processing 1. Electronics Industry Semiconductor dopingSemiconductor doping IC FabricationIC Fabrication 2. Mechanical Treatment Surface hardnessSurface hardness Frictional PropertiesFrictional Properties 3.Biomedical Implants Biocompatible materialsBiocompatible materials

Applications in Materials Processing 1. Electronics Industry Semiconductor dopingSemiconductor doping IC FabricationIC Fabrication 2. Mechanical Treatment Surface hardnessSurface hardness Frictional PropertiesFrictional Properties 3.Biomedical Implants Biocompatible materialsBiocompatible materials

What’s a plasma?? Four States of Matter 1. Solid 2. Liquid 3. Gas 4. Plasma

Plasma Examples Neon lights Neon lights Lightning Lightning Sun Sun Aurora Borealis Aurora Borealis

Plasma Examples Neon lights Neon lights Lightning Lightning Aurora Borealis Aurora Borealis

PII Material Processing 1.Insert sample into chamber 2.Strike a plasma 3.Apply high negative voltage 4.Ions hit the sample and are implanted Silicon -5 kV

PII Material Processing -5 kV ++++ Characterize the effects of implant depth and dose Characterize the effects of implant depth and dose -10 kV-20 kV Sample Material Sample Holder

Implant Implications  Kinetic energy is transferred into heat  Sample overheating from continuous implant  Requires pulsed voltage

Voltage Pulsing  Energy contamination from rising and falling edges Time Voltage Implanting Cooling

Final System + - High Voltage Source Modulator Vacuum Chamber

Modulator Design  Solid state transistor modules  One master timer  Expandable Time Start Master Timer Optical Fiber + - High Voltage Source To Vacuum

Final System

Circuit Performance  5 switching modules  Excellent rise and fall times  Expandable without affecting performance TimerHigh Voltage

Successful Implant 5 switching modules 5 switching modules 1600 V negative bias 1600 V negative bias 2” Silicon Wafer 2” Silicon Wafer Short Nitrogen implant Short Nitrogen implant

Special Thanks  Dr. Michael Bradley  Dave McColl, P. Eng.  Dr. Ajay Singh  Dr. Akira Hirose  Perry Balon  Vic Meyer, Electrical Shops

Questions???

Master Controller Circuit Description Circuit Description Monostable 555 for implant duration Monostable 555 for implant duration Astable 555 for pulse frequency Astable 555 for pulse frequency Features Features Duty cycle variation Duty cycle variation Implant Time (5, 10, 30 seconds) Implant Time (5, 10, 30 seconds) Start Control Start Control

Circuit Development High Voltage Switching Units High Voltage Switching Units PC Board layout in Traxmaker PC Board layout in Traxmaker Fabricated by Electrical Engineering Shops Fabricated by Electrical Engineering Shops

Vacuum Chamber Results 2 x Torr base pressure2 x Torr base pressure 0.01% impurities from background gas0.01% impurities from background gas

Sample Holder Secure silicon wafer inside chamber Secure silicon wafer inside chamber Thermal conductivity Thermal conductivity Aluminum Aluminum

Plasma Generation Raise to 2 mTorr pressure with Nitrogen Raise to 2 mTorr pressure with Nitrogen Filament generation Filament generation

Testing

By the Numbers… Vacuum Chamber Goal - Base pressure < 1 µTorrGoal - Base pressure < 1 µTorr Result – 2 x Torr Result – 2 x Torr High Voltage Switching Goal - < 10 microsecond rise and fallGoal - < 10 microsecond rise and fall Result – 300 ns rise, 700 ns fall Result – 300 ns rise, 700 ns fall

Switching Problems Less than 1% energy contaminationLess than 1% energy contamination

Overall Circuit Performance 5 modules at 1600 Volts5 modules at 1600 Volts Expandable without affecting performanceExpandable without affecting performance

Vacuum Chamber Base pressure Base pressure 1 in contamination 1 in contamination

Langmuir Probe Characterize our plasma for accurate implant doses Characterize our plasma for accurate implant doses Ion saturation current of 12 mA Ion saturation current of 12 mA Ion Density of Plasma (~2 x 10 9 ions/cm 3 ) Ion Density of Plasma (~2 x 10 9 ions/cm 3 ) 0.57% ionization 0.57% ionization

Modulator Design ModulesModules Insulated gate bipolar junction transistor (IGBT)Insulated gate bipolar junction transistor (IGBT) Internal battery powerInternal battery power Optical IsolationOptical Isolation SynchronizationSynchronization

Future Design Projects 1.High Voltage Isolation 1.Metal boxes 2.Fast Zener clamping for each module 2.Increase Plasma density 1.Shorter implant times 2.Increase saturation current via RF source 3.Better Power Supply