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

11. Industrial Plasmas

11.1 Low Pressure Plasmas

11.2 Atmospheric Pressure Plasmas

11.1 Low Pressure Plasmas

11.1.1 Plasma Etching

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

Plasma Etching (II)

• Plasma etching principle

Plasma Etching (III)

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

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.

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

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

Plasma Etching (VI)

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

Plasma Etching (VII)

• Inductively coupled plasma (ICP) reactor

11.2 Atmospheric Pressure Plasmas

11.2.1 Plasma Coating

11.2.2 Plasma Cutting

11.2.3 Plasma Torches for Waste Processing

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

Plasma Coating (II)

• High Velocity Plasma Coating

Plasma Coating (III)

• Low Velocity Plasma Coating

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.

Plasma Coating (V)

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.

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.

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

Plasma Cutting (IV)

• Plasma cutter schematic

Plasma Cutting (V)

1. Initially, the electrode is in contact with (touches) the nozzle.

2. When the trigger is squeezed, DC current flows through this contact.

3. Next, compressed air starts trying to force its way through the joint and out the nozzle.

4. 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.)

Plasma Cutting (VI)

5. 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).

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."

Plasma Cutting (VIII)

• Plasma cutter artwork

11.1.4 Plasma Torches for Waste Processing

• Principle of waste plasma processing

Plasma Waste Torches for Processing (II)

• Waste plasma processing plant