Dynamic pressure measurements in high power impulse magnetron sputtering

Abstract: A microphone has been used to measure the dynamic pressure inside a vacuum chamber during high power impulse magnetron sputtering with high enough time-resolution (~µs) to track the pressure change during the discharge pulse. An experimental measurement of the dynamic pressure is of interest since it would give information about gas depletion, which is believed to dramatically alter the plasma discharge characteristics. This investigation has shown that the magnitude of the pressure wave, which arises due to the gas depletion, corresponds to a 0.4 - 0.7Pa (3 - 5.5mTorr) pressure difference at a distance of 15cm from the target, with base pressures of 2 - 6mTorr for a peak current of 110A. It has also been shown that another pressure wave, about 250µs later, can be detected. Its explanation is suggested to be that the initial pressure wave is bouncing against the chamber walls and thereby causing another peak.