Characterization of the remote plasma generated in a pulsed-DC gas-flow hollow-cathode discharge

In this paper, the remote plasma generated in a pulsed-dc powered gas-flow hollow-cathode discharge in Ar with Al and Cu targets used for reactive sputter-deposition processes was investigated using time-resolved optical emission spectroscopy and Langmuir probe measurements. It was found that the Ar emission intensity during the "OFF-time" of the discharge cycle decays in two steps: A fast decay due to the initial disappearance of the energetic electrons is followed by a subsequent more gradual decay of the plasma density. The plasma potential reaches the highest positive values in the system during the "OFF-time." A capacitive current related to the formation of the cathode sheath was detected at the beginning of the "ON-time" of the pulsing cycle. At the beginning of plasma re-establishment, the Ar and Al emission intensity peaks coincide with the peak in the electron temperature. At later times, the Ar and Al emission intensities follow the temporal variations of the discharge current.