Plasma Immersion Ion Implantation

1. Plasma Immersion Ion Implantation Chris Seymore

2. A couple of things you should be able to answer at the conclusion… • What is my name? • What does PIII stand for? • What are the benefits of Plasma Immersion Ion Implantation versus conventional beam implantation? • What are the benefits of using a pulsed negative bias voltage on the substrate?

3. Overview • Why do Ion Implantation? • Differences between Ion Beam Implantation versus Immersion • Discuss types of plasmas used in this process • Some Applications to Ion Implantation

4. Ion Implantation • Accelerate Ions at high energies to implant them into a substrate • Pulsed Bias voltages range from 1-100kV yielding energies on the order of keV-MeV • Lower energies needed for semi-conductor processes • Higher energies needed for metallurgy processes • Ion Implantation Depth around 100nm • Pulsed Voltages prevent arcing and allows the ions in the ion sheath to be refreshed • i.e. Nitrogen ions at a bias voltage of 50kV, results in 25keV/atom yielding implantation of about 30nm • Deeper implantation can be accomplished by hybrid processes such as Thermal Diffusion http://silver.neep.wisc.edu/psii/ Handbook of Plasma Immersion Ion Implantation and Deposition, Andre Anders ed. Published by Wiley-Interscience, Page 6

5. Ion Implantation • Early developments between 1960-1985 • Semi-Conductors • Used for doping • Equipment Manufacturers • Improves material wear, friction and corrosion properties • Preferred to coating • No delaminating • Doesn’t increase item’s size • Doesn’t require high processing temperatures • Great, but not always cost effective http://silver.neep.wisc.edu/psii/ Handbook of Plasma Immersion Ion Implantation and Deposition, Andre Anders ed. Published by Wiley-IntersciencePage, 11-19

6. Ion Beam vs Immersion http://silver.neep.wisc.edu/psii/

7. A Complete System… • (see book)

8. What types of Plasma can I use to accomplish Ion Implantation through Immersion? • Large Volume Ionization Systems • Glow Discharge, Filament Discharge or Inductive Coupled Sources • Localized Plasma Systems • Magnetrons or Arc Discharges • Macroscopically at rest or Large Volume Streams (diameter around 40cm) Handbook of Plasma Immersion Ion Implantation and Deposition, Andre Anders ed. Published by Wiley-Interscience, Page 381-403

9. More on the types of Plasmas • Noncondensable (gaseous) plasmas • Condensable (metal) plasmas (more used for deposition coatings) • Or combinations of the above • Typically want Low Pressures to ensure collisionless implants (.75-7.5 mTorr)

10. What types of Plasma can I use to accomplish Ion Implantation through Immersion? • Most 1980-1990s used a Thermionic filament discharge to make the plasma • Pulsed Glow dicharges is one of the simplest • RF Plasmas (Capacitively and Inductively Coupled) are widely used as macroscopically stationary gas plasmas

11. Thermionic Discharges • Electron emission from a “hot” cathode (1100-2000 C) • Plasma Densities around 10^15-10^18 m^-3 • Benefits • Simple to fabricate • Easily produce high plasma densities • Drawbacks • Finite lifetime of cathodes due to evaporation • Possible contamination of substrate by this material • Chemical reactions of the plasma gas with this cathode material

12. Pulsed Glow Discharge • Pulse generator serves dual purpose • Generating the plasma • Accelerating the ions across the sheath • Benefits • Any electrode geometry and any gas • Surface treatments <100cm^2 up to >10m^2 • Eliminating a lot of components • Disadvantages • Plasma generation and Implantation parameters are coupled, limiting versatility of the process • High pressures leads to arcing vs. uniform discharge • Limits the Pressure, PRF and Ion current density achievable

13. RF Capacitively Coupled Plasmas • Low Density (electron density around 10^14 to 10^16 m^-3) • Benefits • Simple, low pressure operation, uniformity and relatively low equipment cost • Disadvantages • Not suited for complex geometric workpieces

14. Capacitively Coupled Plasma Generator

15. RF Inductively Coupled Plasmas • High Density (10^16-10^18 m^-3) • Benefits • Good for workpieces with complex geometries • Simple Plasma Generation Source • Drawbacks • Not compatible with some gas chemistries such as hydrocarbons

16. Inductively Coupled Plasma Generator

17. Semiconductor Applications • Shallow Junction Formation • Sub 100nm p+/n junctions for MOS transistors • Flat-Panel Displays • Source and Drain doping of amorphous silicon thin-film transistors (TFTs) • Silicon-On-Insulator Fabrication • SIMOX (separation by implantation of oxygen) • Provides superior isolation between adjacent devices in an integrated circuit

18. Conclusion • Little about what Ion Implantation is • Compared Ion Beam technique to the Immersion • Looked at the types of plasmas that can be utilized by a PIII system • Glanced at a few applications to this technology

19. Answers • What is my name? Chris Seymore • What does PIII stand for? Plasma Immersion Ion Implantation • What are the benefits of Plasma Immersion Ion Implantation versus conventional beam implantation? Simpler design, better/faster performance • Why are the benefits of using a pulsed negative bias voltage on the substrate? Prevents arcing and allows for recovery of ions in the sheath