Metal ion production by ion bombardment

Abstract

A novel ion bombardment type metal ion production apparatus for ion-based thin film formation was constructed. In this apparatus, a plasma exciting high-frequency coil was mounted inside the metallic ion production chamber. A stable dense plasma of the order of 1012/cm3 could be obtained. When a Ti rod target, 4 mm (or 5 mm) in diameter and 45–100 mm in length, was fitted in the center of the HF coil and was negatively biased at −460 V, the top of the rod target was melted by heating due to the ion bombardment; vaporization of the target material occurred rapidly. The vaporized Ti atoms were ionized efficiently by the Penning effect and/or by the direct collision with many thermoelectrons emitted from the high temperature target surface. When the optimum perpendicular magnetic field (around 20 G) was applied to the plasma region, the plasma density increased and the operating gas pressure could be diminished to a lower limit of about 2×10−2 Pa. The main ion species were Ti+ and Ar+ in the mass spectrum of the extracted ion beam. The Ti+ ion current increased with Ar gas pressure and reached a maximum around 4 Pa. When a Cr target was used, the extracted ion beam was almost completely composed of Cr+ ions.