the science behind the plasma arc macchinning

1. PRESENTED BY -
VINIT SINGH
2016PPE5370
Science of Plasma Arc
Machining
SUBMITTED TO-
Dr. HARLAL SINGH MALI
DEPT. OF MECHANICAL
ENGINEERING

2. CONTENTS
• WHAT IS PLASMA
• PLASMA CATEGORY
• PLASMA PROPERTIES
• USE OF PLASMA IN MANUFACTURING
• PLASMA FORMATION
• ETCHING
• PLASMA ETCH REACTORS
• ADVANTAGES OF RF PLASMA
• REGIONS FORMED DURING PLASMA
• PLASMA NOZZLE
• REFRNECES

3.  WHAT IS PLASMA?
- Can be defined as “SUPERHEATED ELECTRICALLY
IONIZED GAS”.
- Creation of plasma is possible by heating the gas and subjecting
through electromagnetic field.

4.  PLASMA 4th STATE OF MATTER

5. - Plasma consist of a collection of free moving electrons and
ions- atom that have lost electrons.
- Energy is needed to strip electrons from atoms to make
plasma .

6.  PLASMA CATEGORY
According to the temperature
PLASMA
HIGH TEMPERATURE
PLASMA (10^8-10^9 K)
LOW TEMPERATURE
PLASMA
HOT
PLASMA
COLD
PLASMA

7.  PLASMA PROPERTIES
(1) PLASMA DENSITY
- NO. of free electron per unit volume.
(2) PLASMA TEMPERATURE
- Temperature controls the degree of plasma ionization.
(3) DEBYE LENGTH
- The Debye length is the distance over which
significant charge separation can occur.
(4) PLASMA FREQUANCY
- Plasma Frequency are rapid oscillations of the
electron
density in conducting media.

8.  USE OF PLASMA IN MANUFACTURING
- Plasma Arc Welding
‡ HOT PLASMA
- Plasma Cutting
‡
- Plasma Spraying
‡
- Plasma Medicine
‡ COLD
- Food processing (non PLASMA
thermal plasma, "cold plasma")
- Plasma arc waste disposal
(convert waste into reusable
material with plasma).

9. Plasma Formation
1.By electric field
2.By shock front

10. Etching
• Electrons gain energy from RF (radio frequency) or µw (microwave)
fields.
• Electrons impact with feed gas to generate ions, reactive
neutrals and more electrons.
• Ions and reactive neutrals diffuse and drift to wafer
surface to remove the material.

11. Plasma Etch Reactors
1. Capacitive Coupled Plasma CCP Type
2. Inductive Coupled Plasma (ICP) Type

12. Capacitive Coupled Plasma (CCP)
• To start plasma formation initial voltage must exceed breakdown
voltage. It depends on gas pressure and spacing. Its value is nearly equal
to 300 to 600 V
• RF current through gas maintains steady state discharge by heating
electrons.

13. CCP Characteristics
•The plasma is generated by RF current flow
between electrodes
•Plasma density (ne) tends to increase
linearly with RF power
•RF current across a sheath generates a dc
voltage
•Ions gain energy from the dc sheath voltage
•ne and Eion tend to be coupled and increase
together

14. Inductive Coupled Plasma (ICP) Type
• Current in coil induces current loop in plasma in glass tube
• In ICP, power is transferred to plasma by the oscillating B field.

15. Advantages of RF Plasma
•RF current through wafer causes no damage
•Easy to get induced self or DC bias
•No charging damage if plasma is uniform

16. Regions formed during plasma
1.Plasma Region
• Ions are generated in this region. These are important for
etching
process.
• Electrons carry the RF current in this region.

17. 2.Sheath Region
•Electron depletion region forms at all surfaces to
keep electrons in
plasma region.
•In this region, number of positive ions are much
higher than number of
negative ions.
•Due to high electric field in this region, only few
electrons will be able
to overcome this region
•Ions gain energy and directionality
•RF current is carried by displacement (capacitor)
current

18. Plasma Nozzle
•Gas Swirling :
Swirling the gas assists cutting in several ways. Swirling
increases cooling. The un-ionized gas atoms are
heavier/cooler and are thrown to the outside of the spinning
gas stream. This cool barrier provides protection for the
copper nozzle. As amperage is increased, the amount of
ionization increases (changing the 30/70% ratio) and cooling
decreases, shortening the life of the nozzle. Nozzles are
designed to operate within a specific current (amp) range.

19. REFERANCES
(1)Plasma fundamentals part:
http://www.prism.gatech.edu/~gtg928x/NNIN_reading_material/Fundam
entals%20Part%201.pdf
(2) Plasma discharge fundamentals
http://people.physics.anu.edu.au/~jnh112/AIIM/c17/Plasma_discharge_f
undamentals.pdf
(3) Plasma physics Wikipedia