9.1 Varying the primary current

Note that when using the Cs⁺ source, only the L2, L3 and L4 lenses are used, covering all beam settings.

For very small beam (beam diameter < few μ m), the following conditions must be selected: high source HV (typically 10kV), small D0 (typically 400 μ m) and D4 (typically 100 μ m), combined with high L2 value (typically above 70% of the source HV). The primary current (and beam diameter) is reduced using increasing values of L2, D4 and D0 if needed.

Cs ⁺ primary ions, Source HV = +10kV, Reservoir current = 0.1mA, Ionizer current = 1.8mA

Figure 1: Schematics of the primary ion beam trajectory (Cs source) without L3 lens.

- Using Lens L3:

○ Low values (usual conditions): L3 values remain to 0, can be increase up to 30% for very high density beams.

○ High values (to be used only when very small spot diameter is required): the primary beam intensity (but also the beam size) increases with L3.

Note: L3 should not be used between 30% and 60% of the source HV, in order to keep a well-focused primary beam.

Figure 2: Schematics of the primary ion beam trajectory (Cs source) using L3 lens.