Low‐energy (5<E_i<100 eV), high‐brightness, ultrahigh vacuum ion source for primary ion beam deposition: Applications for Al and Ge

The design, operation, and use of a double‐grid, electron‐impact, ultrahigh‐vacuum compatible, low‐energy ion source capable of operating with relatively low‐vapor‐pressure solid source materials such as Al and Ge are described. The source can run at cell temperatures up to 1450 °C and deliver ion current densities J_i≳30 mA cm⁻² (corresponding to 1.9×10¹⁷ cm⁻² s⁻¹) at source‐to‐substrate separations d of 2 cm, and J_i≳100 μA cm⁻² (6.3×10¹⁴ cm⁻² s⁻¹) at d=40 cm with beam energies which can be varied from 5 to 100 eV. The uniformity in the ion current density from a 2.6‐cm‐diam source over 6‐cm‐diam substrates is better than 97%. A postextraction magnetic filter was used to separate the ion and neutral components and provide a pure ion beam. Initial nucleation and growth experiments on amorphous carbon substrates at 30 °C using thermal and accelerated (E_Al⁺=35 and 75 eV) Al⁺ beams show that the average island size in layers with thicknesses between 2 and 6 nm increases by factors ranging from 3 to 14 with increasing ion energy. Layers deposited with thermal Al have an island size distribution which is near‐Gaussian while Al islands formed from ion beams exhibit a bimodal size distribution.