Ion Beam Treatment of Functional Layers in Thin-Film Silicon Solar ...

2.1 Ion beam treatment
Figure 2.3: Configuration of linear anode layer ion source (Type LION 420, VON AR-
DENNE Anlagentechnik GmbH [32]). 1. ionized gas, 2. racetrack, 3. Outer
cathode, 4. Water-cooled magnetic package, 5. Magnetic system from permanent
magnetism, 6. Inner cathode, 7. Gas, 8. Water-cooled anode.
• O 2 + e − → O 3+
2 + 4e − → O + + O 2+ + 4e − , E th = 63 eV [25]
When mixed Ar/O 2 is used as source gas, additional processes between Ar atoms and
O 2 molecule, for example Ar ∗ + O 2 → Ar + O + O, may occur. Therefore, the fraction
of O atoms with respect to O 2 molecules might be enhanced [27].
To summarize, the majority of particles in Ar ion beams are neutral Ar ∗ and Ar +
ions, but excited Ar +∗ and double ionized Ar 2+ ions might also exist. The O 2 ion beams
are composed of mixture of neutral and ionized particles O ∗ 2, O ∗ , O + 2 , O + , O 2+
2 and O 2+ .
The electron impact ionization cross sections of the above mentioned ions were measured
experimentally or calculated in detail by many groups [28–31]. The results reveal that
the cross sections have the relationship σ O
+ > σ
2 O + ,O 2+ > σ
2 O 2+. Therefore, the fraction
of O + 2 should be highest among the various of ions.
The shape of the permanent magnet has to be specially constructed in order to provide
the appropriate distribution of magnetic field. The paths of electrons have to be without
obstacles, as well as with high uniformity. Usually, they are maintained with an axissymmetric
construction such as circular ion source. Non-circular sources, for example,
the elongated racetrack structure which is also called linear ion source is also possible
with careful design. Moreover, the linear anode layer ion source has nearly unlimited
scalability for industrial purposes [33], therefore it has become a popular source in recent
years for large area thin-film or glass treatment. The linear anode layer ion source used
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