Analysis of pulsed direct current reactive magnetron sputtering on a silicon target

Reactive sputtering is a very useful technique, particularly, for producing inhomogeneous interference filters, where the refractive index changes smoothly during deposition. In such a context, precise control of deposition parameters is crucial for replicating the desired optical properties. This study employed a pulsed DC power source to investigate the influence of a duty cycle on target poisoning, sputtering plasma characteristics, electric signals, and optical and morphological properties of synthesized films. Reactive pulsed DC magnetron sputtering was characterized by analyzing the behavior of plasma emission via optical emission spectroscopy and voltage-current signals, while modulating parameters such as the oxygen content within the vacuum chamber. A set of thin films was coated on glass substrates under different system conditions. These films underwent characterization employing spectroscopic ellipsometry to ascertain their optical constants, atomic force microscopy for surface morphology analysis, and x-ray diffraction for the determination of crystalline structures. The results indicate that longer duty cycles required higher oxygen levels to poison the target. Additionally, a detailed analysis of electrical signals revealed nonsquare waveforms, whose characteristics were influenced by both the duty cycle and the oxygen content within the sputtering chamber, resulting in higher effective voltages during the on-time of the voltage pulse. Grown films via reactive pulsed DC magnetron sputtering were also compared to films grown via conventional DC magnetron sputtering at equivalent conditions of target poisoning.