2.4 Types of Plasmas in Manufacturing

Plasma generation methods come in various forms, each with unique characteristics. From DC discharges to RF and microwave discharges, these techniques power a wide range of manufacturing processes. Understanding their differences is key to selecting the right method for specific applications.

Low-pressure and atmospheric-pressure plasmas offer distinct advantages in manufacturing. While low-pressure plasmas excel in semiconductor processing, atmospheric-pressure plasmas are ideal for surface treatments. Thermal and non-thermal plasmas further expand the possibilities, enabling diverse applications from welding to gentle surface modifications.

Plasma Classification and Characteristics

Classification of plasma generation methods

Top images from around the web for Classification of plasma generation methods

• 

  Frontiers | Simulation of main plasma parameters of a cylindrical asymmetric capacitively ... View original

  Is this image relevant?

• 

  Frontiers | An Inductively-Coupled Plasma Electrothermal Radiofrequency Thruster View original

  Is this image relevant?

• 

  Comparison of Surface Modification of CR-39 Polymer Film Using RF and DC Glow Discharges Plasma View original

  Is this image relevant?

• 

  Frontiers | Simulation of main plasma parameters of a cylindrical asymmetric capacitively ... View original

  Is this image relevant?

• 

  Frontiers | An Inductively-Coupled Plasma Electrothermal Radiofrequency Thruster View original

  Is this image relevant?

1 of 3

Top images from around the web for Classification of plasma generation methods

• 

  Frontiers | Simulation of main plasma parameters of a cylindrical asymmetric capacitively ... View original

  Is this image relevant?

• 

  Frontiers | An Inductively-Coupled Plasma Electrothermal Radiofrequency Thruster View original

  Is this image relevant?

• 

  Comparison of Surface Modification of CR-39 Polymer Film Using RF and DC Glow Discharges Plasma View original

  Is this image relevant?

• 

  Frontiers | Simulation of main plasma parameters of a cylindrical asymmetric capacitively ... View original

  Is this image relevant?

• 

  Frontiers | An Inductively-Coupled Plasma Electrothermal Radiofrequency Thruster View original

  Is this image relevant?

1 of 3

• Direct Current (DC) discharges
  • Generated by applying a constant voltage between two electrodes
  • Commonly used in DC glow discharges and arc discharges for applications such as plasma spraying and welding
• Radio Frequency (RF) discharges
  • Generated by applying an alternating voltage in the radio frequency range (typically 13.56 MHz)
  • Capacitively coupled plasmas (CCP) have electrodes placed outside the discharge chamber and are used for plasma-enhanced chemical vapor deposition (PECVD) and reactive ion etching (RIE)
  • Inductively coupled plasmas (ICP) are generated by an inductive coil wound around the discharge chamber and are used for high-density plasma etching and deposition processes (plasma-enhanced atomic layer deposition)
• Microwave discharges
  • Generated by applying electromagnetic waves in the microwave frequency range (typically 2.45 GHz)
  • Electron Cyclotron Resonance (ECR) plasmas are created by applying a magnetic field to achieve electron cyclotron resonance condition and are used for high-density plasma etching and deposition processes (diamond-like carbon coatings)

Low-pressure vs atmospheric-pressure plasmas

• Low-pressure plasmas
  • Generated at pressures below atmospheric pressure (typically 1 mTorr to 10 Torr)
  • Characterized by longer mean free path of particles resulting in fewer collisions higher electron temperatures and lower ion energies
  • Commonly used in semiconductor processing thin film deposition (silicon nitride) and surface modification (plasma activation of polymers)
• Atmospheric-pressure plasmas
  • Generated at or near atmospheric pressure
  • Characterized by shorter mean free path of particles resulting in more collisions lower electron temperatures and higher ion energies
  • Commonly used in surface treatment (plasma cleaning) sterilization (medical devices) and plasma spray coating (thermal barrier coatings)

Characteristics of thermal and non-thermal plasmas

• Thermal plasmas
  • High gas temperature ($T_g \approx T_e \approx T_i$, typically > 10,000 K)
  • High electron density ($n_e > 10^{20} m^{-3}$)
  • Local thermodynamic equilibrium (LTE) condition where the temperatures of electrons ions and neutral species are approximately equal
  • Commonly used in plasma spraying (hydroxyapatite coatings) welding cutting and waste treatment (hazardous waste destruction)
• Non-thermal plasmas
  • Low gas temperature ($T_g << T_e$, typically < 1,000 K)
  • Lower electron density compared to thermal plasmas
  • Non-equilibrium condition ($T_e >> T_i \approx T_g$) where the electron temperature is much higher than the ion and neutral species temperatures
  • Commonly used in surface modification (hydrophilic treatment of polymers) plasma-enhanced chemical vapor deposition (PECVD) (silicon dioxide films) plasma etching (integrated circuits) and sterilization (food packaging)

Suitability of plasmas for manufacturing

• Plasma-enhanced chemical vapor deposition (PECVD)
  1. Uses non-thermal low-pressure RF or microwave discharges
  2. Allows deposition at lower substrate temperatures compared to thermal CVD enabling deposition on temperature-sensitive substrates (plastics)
• Plasma etching
  1. Uses non-thermal low-pressure RF or microwave discharges
  2. Enables anisotropic etching for high aspect ratio features in semiconductor manufacturing (deep reactive ion etching)
• Plasma spray coating
  1. Uses thermal atmospheric-pressure DC arc or RF discharges
  2. Provides high deposition rates and thick coatings for wear and corrosion protection (ceramic coatings on turbine blades)
• Surface modification and cleaning
  1. Uses non-thermal atmospheric-pressure discharges (dielectric barrier discharges corona discharges)
  2. Improves wettability adhesion and printability of surfaces (plasma treatment of polyethylene)