Construction and evaluation of an ultrahigh-vacuum-compatible sputter deposition source

TL;DR

This paper presents a new ultrahigh-vacuum-compatible sputter deposition source that improves ion targeting and purity for depositing materials like zirconium, with detailed analysis of its properties and performance.

Contribution

The paper introduces a modified UHV sputter source with dual grids and liquid nitrogen cooling, enhancing deposition control and film purity compared to previous designs.

Findings

Achieved a reproducible deposition rate of 1 monolayer in 250 seconds.

Demonstrated high purity of zirconium films deposited with the source.

Showed the source's capability for higher deposition rates and controlled sputtering.

Abstract

A sputter deposition source for use in ultrahigh vacuum (UHV) is described and some properties of the source are analyzed. The operating principle is based on the design developed by Mayr et al. [Rev. Sci. Instrum. 84, 094103 (2013)], where electrons emitted from a filament ionize argon gas, and the Ar$^+$ ions are accelerated to the target. In contrast to the original design, two grids are used to direct a large fraction of the Ar$^+$ ions to the target, and the source has a housing cooled by liquid nitrogen to reduce contaminations. The source has been used for deposition of zirconium, a material that is difficult to evaporate in standard UHV evaporators. At an Ar pressure of $9\times 10^{-6}$ mbar in the UHV chamber and moderate emission current, a highly reproducible deposition rate of $\approx 1$ monolayer in 250 s was achieved at the substrate (at a distance of $\approx 50$ mm from the target). Higher deposition rates are easily possible. X-ray photoelectron spectroscopy shows a high purity of the deposited films. Depending on the grid voltages, the substrate gets mildly sputtered by Ar$^+$ ions; in addition, the substrate is also reached by electrons from the negatively biased sputter target.