REMOVING THE ENERGETIC NEUTRAL PROBLEM IN SPUTTERING

The evidence for the reflection of neutral inert gas atoms from the target being bombarded during sputter deposition is reviewed. This evidence includes theory, effects at the target, such as measurements of the fraction of incident energy which enters the target from bombarding ion beams, and effects at the growing film, such as the heating effect, the production of stress, the emission of secondary electrons, and the burial of inert gas atoms. New results are reported for the burial of energetic neutral atoms in simple metals in discharges in argon, krypton, and xenon. These results confirm the presence of a high flux of highly energetic neutrals when the sputter atom is substantially less massive than the target atom, leading to the inert gas being included substitutionally at high concentrations in the growing film. To achieve high purity in sputtered films with heavy atomic materials, xenon rather than argon should be used as the sputter gas. A rethink of sputter plant design shows that this expensive gas can be used economically, with some interesting consequences. The performance of a small system based on this rethink is described.