Ion energy distributions in AZO magnetron sputtering from planar and rotatable magnetrons

Abstract

Ion energy distribution functions (IEDFs) have been measured at the substrate position in magnetron sputtering of an aluminium doped zinc oxide (AZO) target in argon and/or oxygen atmosphere. The IEDFs have been obtained against ground potential with an energy-dispersive ion mass spectrometer which was facing the target surface. Two different magnetron configurations have been investigated: a circular planar magnetron on laboratory scale and an industrial scale rotatable cylindrical magnetron. They were operated with asymmetric-bipolar pulsed d.c. power. Positive ions of the working gas as well as Al +, Zn +, and AlO + were observed, which show a low-energy peak in their IEDF from the plasma potential of the “on” phase and a high-energy peak of several 10 eV which is formed during the “off” phase of the pulsed d.c discharge. Negative ions, being mainly O − from the target, exhibit a strong peak in their IEDF at several 100 eV corresponding to the negative target voltage. With strongly varying target voltage in the “on” phase the IEDF may extend to very high energies. Maximum and average energy of both positive and negative ions depend on the discharge power as the voltage in the “on” and “off” phases governing the high-energy ions changes with power. The differently sized planar and rotatable magnetrons exhibit very similar IEDFs for positive as well as negative ions proving that basic physical processes are essentially the same.