Modulator Design for Plasma Ion Implantation

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

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

3. Applications in Materials Processing • Electronics Industry • Semiconductor doping • IC Fabrication • Mechanical Treatment • Surface hardness • Frictional Properties • Biomedical Implants • Biocompatible materials

4. Applications in Materials Processing • Electronics Industry • Semiconductor doping • IC Fabrication • Mechanical Treatment • Surface hardness • Frictional Properties • Biomedical Implants • Biocompatible materials

5. What’s a plasma?? Four States of Matter • Solid • Liquid • Gas • Plasma

6. Plasma Examples • Neon lights • Lightning • Sun • Aurora Borealis

7. Plasma Examples • Neon lights • Lightning • Aurora Borealis

8. Silicon PII Material Processing • Insert sample into chamber • Strike a plasma • Apply high negative voltage • Ions hit the sample and are implanted + + + + + + + -5 kV

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

10. Implant Implications • Kinetic energy is transferred into heat • Sample overheating from continuous implant • Requires pulsed voltage + + + + + + +

11. Voltage Pulsing + + + + + + + + + • Energy contamination from rising and falling edges Voltage Implanting Cooling Time

12. + - Final System Vacuum Chamber Modulator High Voltage Source

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

14. Final System

15. Circuit Performance • 5 switching modules • Excellent rise and fall times • Expandable without affecting performance Timer High Voltage

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

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

18. Questions???

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

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

21. Vacuum Chamber Results • 2 x 10-7 Torr base pressure • 0.01% impurities from background gas

22. Sample Holder • Secure silicon wafer inside chamber • Thermal conductivity • Aluminum

23. Plasma Generation • Raise to 2 mTorr pressure with Nitrogen • Filament generation

24. Testing

25. By the Numbers… Vacuum Chamber • Goal - Base pressure < 1 µTorr • Result – 2 x 10-7 Torr High Voltage Switching • Goal - < 10 microsecond rise and fall • Result – 300 ns rise, 700 ns fall

26. Switching Problems • Less than 1% energy contamination

27. Overall Circuit Performance • 5 modules at 1600 Volts • Expandable without affecting performance

28. Vacuum Chamber • Base pressure • 1 in 10 000 contamination

29. Langmuir Probe • Characterize our plasma for accurate implant doses • Ion saturation current of 12 mA • Ion Density of Plasma (~2 x 109 ions/cm3) • 0.57% ionization

30. Modulator Design • Modules • Insulated gate bipolar junction transistor (IGBT) • Internal battery power • Optical Isolation • Synchronization

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