Effects of gas pressure and discharge current on beam composition in a magnetron discharge ion source

The magnetron discharge plasma is commonly used in thin film deposition processes, but it can also be utilized for ion beam production. We have developed and investigated an ion source based on planar magnetron discharge. We show that under certain conditions, the discharge, running in a high current pulsed mode, effectively produces plasmas with a high fraction of ions formed from the magnetron target material. The ion beam extracted from the discharge plasma and its composition were studied using a time-of-flight method. The plasma electron temperature was measured by using a double Langmuir probe. We find that the increased working gas pressure and discharge current lower the electron temperature, leading to an increased fraction of target material ions in the plasma and therefore also in the extracted ion beam due to their lower ionization potential compared to that of the working gas.