Plasma Immersion Ion Implantation. Chris Seymore. 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?
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Plasma Immersion Ion Implantation Chris Seymore
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?
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
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
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
Ion Beam vs Immersion http://silver.neep.wisc.edu/psii/
A Complete System… • (see book)
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
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)
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
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
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
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
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
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
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
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