Chemistry Reference
In-Depth Information
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
10
1
10
1
ω = 13.56 MHz * 2π
10
0
10
0
10
16
m
-3
n
e
10
-1
10
-1
10
15
m
-3
10
-2
10
-2
10
14
m
-3
10
-3
10
-3
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
Reduced collision frequency ν
e
/ω
FIGURE 3.39
Absorbed electric power
P
abs
for electric field frequency of 13.56 MHz with
the electron density as parameter.
Figure 3.39 shows the power absorption in the high-frequency electric field in depen-
dence on the reduced collision frequency ν
e
/
ω at the radio frequency of 13.56 MHz.
The generation of dense nonthermal plasma can be reached by heating of the electrons
by microwaves, for example at 2.45 GHz. The microwaves produce much larger elec-
tric fields in the plasma bulk. Furthermore, microwave plasmas are of special interest
in combination with external magnetic fields. If the electron cyclotron motion ω
ce
is in phase with the rotating electric field vector of the R-wave ω, and the elec-
tron neutral collision frequency is low enough the electrons absorb efficiently wave
energy [56]. Then the absorbed power depends additionally on the electron cyclotron
frequency
n
e
·
e
2
(
ν
e
/
ω
)
E
eff
P
abs
=
ω
·
2
·
(3.309)
m
e
·
[
1
−
(
ω
ce
/
ω
)
]
+
(
ν
e
/
ω
)
2
see Figure 3.40.
3.7.6.2 Radio Frequency Plasmas
Radio frequency (rf) plasmas at excitation frequencies between the ion and electron
plasma frequency, e.g., 13.56 or 27.12 MHz, are widely used in plasma technologies
for material surface treatment and thin film deposition. The RF discharges may be
operate by means of internal or external electrodes and they are classified into two
types according to the coupling the high frequency power
•
Capacitively coupled plasma (CCP)
•
Inductively coupled plasma (ICP)
