Transient evolution of the target erosion profile during magnetron sputtering: Dependence on gas pressure and magnetic configuration

The growth of the target erosion profile (racetrack) in DC magnetron sputtering has been experimentally studied at a modest target power. Unbalanced magnetron sputtering (UBMS) and balanced magnetron sputtering (BMS) of a copper target were conducted at Ar gas pressures between 0.38-2.0Pa at a constant DC discharge power of 100W. At time intervals of several hours throughout the target life, the target was removed from the chamber, and its erosion profile was measured with a height gauge. The racetrack width was found to have an interesting pressure dependence. Higher argon gas pressure resulted in a wider initial track width in both the UBMS and BMS configurations. As the sputter erosion of the target proceeded, the track width became narrower at higher gas pressures (≥1.0Pa). At lower gas pressures, the track width was mostly unchanged and even showed a slight increase in the case of 0.38Pa in UBMS. As a result, the order of the final width was reversed: the higher gas pressure resulted in a narrower track width. The origin of this behavior was ascribed to the difference in the plasma sheath thickness and the free path of secondary electrons.