The measurement and impact of negative oxygen ions during reactive sputter deposition

Abstract

AbstractMany thin film applications are based on oxides. The optimization of the oxide properties is an on-going process and requires a deep understanding of the deposition process. A typical feature of reactive (magnetron) sputter deposition is the presence of negative oxygen ions. Two groups of ions can be identified based on their energy. Low energy ions are generated in the bulk of the discharge. The high energy ions are emitted from the oxide or oxidized target surface. As these ions are generated at the cathode, they are accelerated by the electric field toward the growing film. Depending on the discharge voltage and the powering method, their energy is typically several tenths to hundreds electron volt. As such the ions can have a strong impact on the film properties. In the case of magnetron sputtering, this will lead to inhomogenous film properties over the substrate facing the locally eroded target. Due to their high energy, the trajectory of negative ions can be easily predicted which has led to several strategies to avoid negative ion bombardment such as facing target sputtering and off-axis sputtering. This paper reviews several facets of the production, the measurements and the impact on the film properties of negative ions during reactive sputtering. Despite the many illustrative studies on the impact of negative oxygen ions, quantification is often lacking as the negative ion yield is only known for a few oxides. The compilation of several literature sources allows the discussed trends to be placed in a quantitative framework.Keywords: Negative ion yieldmagnetron sputteringion assisted deposition AcknowledgementsThis work is dedicated to two researchers who have passed away recently and had a major impact on the scientific career of the author. The first researcher is Professor Johan (Jo) Haemers, a member of the same department, who assisted the research of the author in the development of special measuring set-ups, and in long discussions on science and other important things in life. The second researcher is Professor Joseph (Joe) Greene. His research approach, presentation style, and his interest in old and recent scientific literature was an example to many and to the author in particular.Disclosure statementThe author declares that there are no relevant financial or non-financial competing interests to report.