Time-resolved optical emission spectroscopy and imaging during the pulsed DC sputter-deposition of titanium dioxide.

摘要

Time resolved optical emission spectroscopy (TR-OES) is used to analyze pulsed DC titanium target magnetron plasmas during the sputter deposition of TiO2 thin films. The studies are focused on the temporal behavior of the emission lines of atomic titanium, argon and oxygen in three chosen emission windows (386 nm to 427 nm, 747 nm to 782 nm and 824 nm to 858 nm) during the reverse-time and the on-time of the pulsed DC plasma. Single- and double-exponential tits were used to describe the temporal decay of the various optical emissions during the reverse-time. The various decay constants are correlated with the disappearance of the fast beam-type electrons in the plasma once the power is turned off, as well as with the disappearance of Ar metastables and Ti and O atoms. At the beginning of the on-time, the optical emissions of Ar and O show an overshoot that is correlated with the voltage overshoot and is related to the appearance of fast electrons. During the rest of the on-time, the optical emissions of Ar and O follow the changes in the cathode current. By contrast, the Ti emission does not show any overshoot at the beginning of the on-time, but rather follows the cathode current through the entire duration of the on-time .; Time-resolved images of the optical emissions from the same pulsed DC titanium target magnetron plasmas were directly taken with a Roper Scientific ICCD camera. The camera was exposed to the discharge for 0.05--0.2 mus with 0.05--0.2 mus separation between each exposure. At the beginning of the on-time, when the power is turned on, the discharge initially starts preferentially in the cross corners of the magnetron racetrack. During the rest of the on-time, the emissions from the straight sections of the racetrack of the magnetron are always slightly stronger than the emissions from the two rounded corners of the racetrack. This pattern extends into the start of the reverse-time when the power is turned off. The optical emissions persist for several microseconds into the reverse-time. An argon spectral filter was used in order to record the temporal behavior of selected Ar emission lines.