III' Applied Plasma Physics: theory, simulation, experiments

1
III. Applied Plasma Physics theory, simulation,
experiments

• 8. The Plasma Laboratory
• 9. Nuclear Fusion
• 10. Plasma Propulsion
• 11. Industrial Plasmas
• 12. Space and Astrophysical Plasmas

2
11. Industrial Plasmas

• 11.1 Low Pressure Plasmas
• 11.2 Atmospheric Pressure Plasmas

3
11.1 Low Pressure Plasmas

• 11.1.1 Plasma Etching

4
11.1.1 Plasma Etching

• Plasma can be used to clean, etch, or coat almost
  any surface without the safety hazards and liquid
  waste associated with wet processes.
• Plasma etching technology can remove organic and
  inorganic contamination, increase wettability,
  increase bond strength, and remove residue.
• plasma technology is very effective when surface
  treatment is critical to the efficiency of a
  process or the reliability of a product

5
Plasma Etching (II)

• Plasma etching principle

6
Plasma Etching (III)

• Cross-sectional SEM (scanning electron
  microscope) image of a doped poly-Si line and
  space(LS) structures were etched in a helicon
  Cl2 plasma

7
Plasma Etching (IV)

• Plasma is often used to clean odd-shaped parts
  with areas that are not readily accessible, such
  as blind holes. It can also clean assemblies made
  of different materials.
• The plasma etching process occurs in a vacuum and
  uses radiofrequency energy, instead of heat, to
  create plasma that produces the desired reaction
  with the surface that it is treating. This helps
  to avoid heat damage.

8
Plasma Etching (IV)

• Plasma processing is highly controllable and
  repeatable, ensuring uniform results - product to
  product, and batch to batch.
• Plasma can, in many cases, eliminate the need for
  CFCs and other solvents. This will, in turn,
  reduce costly disposal of hazardous by-products

9
Plasma Etching (V)

• Traditional diode or parallel-plate plasma
  reactors are well established in the industry
• Parallel-plate (diode-type) reactor opposed
  plates drive the plasma in this configuration,
  typically at radio frequencies with an rf power
  in the range of kW
• For the driving frequency chosen, the electrons
  in the reactor are preferentially accelerated,
  whereas the ions are driven by the average
  electrostatic fields
• The processed wafer resides on the powered
  electrode (to enhance ion acceleration).
• The electron mean free path limits the operating
  pressure

10
Plasma Etching (VI)

• Traditional diode or parallel-plate plasma
  reactors are well established in the industry

11
Plasma Etching (VII)

• Inductively coupled plasma (ICP) reactor

12
11.2 Atmospheric Pressure Plasmas

• 11.2.1 Plasma Coating
• 11.2.2 Plasma Cutting
• 11.2.3 Plasma Torches for Waste Processing

13
11.1.2 Plasma Coating

• Typical power levels employed are 40-80 KWDC
• The additional energy available, coupled with
  slightly modified torch design, translates to
  both higher thermal energy and higher particle
  velocity
• The result is more complete melting of high
  temperature materials (ceramics) and greater
  integrity of the resultant coating

14
Plasma Coating (II)

• High Velocity Plasma Coating

15
Plasma Coating (III)

• Low Velocity Plasma Coating

16
Plasma Coating (IV)

• A high temperature plasma stream is created by
  non-transferred plasma arc within the torch. 
• Many gases may be ionized this way, argon or
  nitrogen with small additions of hydrogen and
  helium are popular choices.
• In an ionized gas, free electrons have been
  stripped from the atoms and recombination
  releases very significant thermal energy. 
• The plasma stream can reach temperatures of
  10,000-50,000 degrees Fahrenheit.

17
Plasma Coating (V)
18
11.1.3 Plasma Cutting

• (Anedocte?) Plasma cutting was accidentally
  discovered by an inventor who was trying to
  develop a better welding process.
• Though the technology is still young today,
  plasma cutting is quickly changing the world as
  we know it.
• Plasma cutting is by far the simplest and most
  economical way to cut a variety of metal shapes
  accurately.
• Plasma cutters can cut much finer, faster, and
  more automatically than oxy-acetylene torches.
• Because of their effectiveness, plasma cutters
  threaten to obsolete a large number of
  conventional metalworking tools.

19
Plasma Cutting (II)

• Basic plasma cutters use electricity to superheat
  air into plasma, which is then blown through the
  metal to be cut.
• Plasma cutters are extremely simple and require
  only a compressed air supply and an AC power
  outlet to operate
• A complete plasma cutter consists of a power
  supply, a ground clamp, and a hand torch.

20
Plasma Cutting (III)

• The main function of the power supply is to
  convert the AC line voltage into a
  user-adjustable regulated (continuous) DC
  current.
• The hand torch contains a trigger for controlling
  the cutting, and a nozzle through which the
  compressed air blows.
• An electrode is also mounted inside the hand
  torch, behind the nozzle

21
Plasma Cutting (IV)

• Plasma cutter schematic

22
Plasma Cutting (V)

• Initially, the electrode is in contact with
  (touches) the nozzle.
• When the trigger is squeezed, DC current flows
  through this contact.
• Next, compressed air starts trying to force its
  way through the joint and out the nozzle.
• Air moves the electrode back and establishes a
  fixed gap between it and the tip. (The power
  supply automatically increases the voltage in
  order to maintain a constant current through the
  joint - a current that is now going through the
  air gap and turning the air into plasma.)

23
Plasma Cutting (VI)

• Finally, the regulated DC current is switched so
  that it no longer flows through the nozzle but
  instead flows between the electrode and the work
  piece. This current and airflow continues until
  cutting is halted.
• Plasma cutters are only useful for cutting metal.
  Non-conductive materials like wood and plastic
  prevent the plasma cutter from doing step 5
  above.
• The above steps describe the operation of a
  contact-type arc starting plasma torch (the
  lastest technology).

24
Plasma Cutting (VII)

• Old plasma torch designs use high voltage sparks
  to bridge the gap between a fixed electrode and
  tip when starting the arc.
• The only parts of the plasma cutter needing
  frequent replacement are the nozzle and the
  electrode. For this reason, these parts are
  called "consumables."

25
Plasma Cutting (VIII)

• Plasma cutter artwork

26
11.1.4 Plasma Torches for Waste Processing

• Principle of waste plasma processing

27
Plasma Waste Torches for Processing (II)

• Waste plasma processing plant