Planar langmuir probe investigations of metallic and reactive bipolar sputtered aluminum
Plasma diagnostics are a very useful tool for characterizing the main parameters ofsputtering plasmas like electron density, electron temperature, or ion density. These parameters can be determined at the substrate position by the use of a Langmuir probe. This paper focuses on time-averaged and time-resolved planar Langmuir probe measurements. As a model system, a dual-magnetron configuration using two cylindrical aluminum cathodes was used. The planar Langmuir probe was placed in three substrate positions, one between the two rotatable targets and another directly in front of each target. The results differed significantly due to the physical position of the probe relative to the magnetrons. For the middle position each single pulse applied to one of the cathodes is detected by the Langmuir probe separately. Positioning the probe in front of one of the cathodes shows only one peak for the ion current for a full bipolar cycle. This was attributed to constructive superposition of the different distances between the probe and both targets. Moving from metallic to reactive sputtering caused the electron temperature to drop significantly. Finally, a correlation between the plasma parameters and film properties of alumina (Al2O3) coatings was presented.