EE 403503

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EE 403/503 Introduction to Plasma Processing
DC Discharge II
October 29, 2008
2
d
Plasma

Anode
Cathode
A
V ?
I ?
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Breakdown Voltage
Townsend breakdown criterion
VE x d
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Corona Discharge
Outer Electrode
High Voltage Power Supply
Inner Electrode
Active Volume
For dry Air for parallel electrodes
kV
kV/m
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V-I Characteristic of DC Discharges
1000 V
Background Ionization
Glow Discharge
Arc Discharge
Townsend Discharge
Glow to Arc Transition
Breakdown Voltage
500
Abnormal Glow
Thermal
Normal Glow
Non- Thermal
0
1
10-8
10-4
104A
10-6
10-2
102
10-10
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Glow Discharge
Aston Dark Space
Cathode Dark Space
Anode Dark Space
Negative Glow
Positive Column
Cathode
Anode
Faraday Dark Space
Cathode Glow
Anode Glow
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Characteristic parameter range of DC glow
Discharge
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Townsend Theory of Cathode Region
dc
Vc Vb,min
(Townsend theory approximately applies to cathode
fall region)
Cathode Fall Region
Paschen Minimum
Typical values at 1 Torr dc 0.5 cm
Poissons Equation
Net Charge Density in the Cathode Fall Region
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Energy Transfer
Unmagnetized Plasmas
b.c. v(t)v0 at t0
t??
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Energy Transfer in Magnetized Plasmas
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Similarity Relations
V1V2 I1I2 d1ad2 D1aD2 p2ap1 ?1a?2
E2aE1 J2a2J1 ne2a2ne1 d1p1d2p2 ?1a ?2
length
Diameter
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DC Parallel Plate Normal Glow Discharge
Cathode Dark Space
Negative Glow
Negative Glow
Positive Column
C
C
0
0
Obstructed operation Good for ion bombardment
Unobstructed operation Good for plasma Chemistry
-Vc
-Vc
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Electron beam Plasma Source
Gas Inlet
Gas Inlet
Cathode
Hollow Cathode
Anode grid
Glow Discharge
e
Anode
Glow Discharge
Substrate
Substrate
16
Magnetron Plasma Source
N
S
N
Cathode
Negative Glow Plasma
Power Supply
Positive Column
Anode