14
Section 2.2: Ion Beam Properties
For ion beam deposition applications, it is necessary to know the energy of the ions leaving the
source and the dose that they strike a target downstream.
Ion Energy
The ejected ions from an ion beam source are considered mono-energetic and as depicted by
Figure 2.2, the total ion energy is approximately the beam voltage. In order to illustrate the
importance of this aspect, plotted in Figure 2.5 are two types of energy distributions. The ions in a
typical electrical discharge device will have a range of energies that form a distribution that is
thermalized; also referred to as Maxwellian. A Maxwellian energy distribution is plotted in
Figure 2.5 where the number of ions is plotted for various energies. For comparison purposes, the
energy distribution from an ion beam source is also plotted. Ions that leave the source have a
limited energy range, selected by the beam voltage, and are referred to as mono-energetic. The
significant attribute of the ion beam source is that energies of the ions can be adjusted
by selecting
different beam voltages, where as, a Maxwellian discharge will have only limited adjustment in its
energy distribution. The beam voltage range is typically 100 to 1500 V.
Energy Distributions
0
0.2
0.4
0.6
0.8
1
0.01
0.1
1
10
100
1000
Energy (eV)
E
ne
rgy
D
e
ns
it
y
Maxwellian
Mono-Energetic
Adjustable
Limited Adjustment
Figure 2.5: Two types of energy distributions: Maxwellian and Mono-Energetic