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

Abstract

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 Ji≳30 mA cm−2 (corresponding to 1.9×1017 cm−2 s−1) at source-to-substrate separations d of 2 cm, and Ji≳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 (EAl+=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.