Novel facing targets sputtering apparatus with uniform magnetic field and plasma-free substrates

Abstract

Facing targets sputtering (FTS) systems are known to have excellent characteristics such as plasma-free substrates and low working gas pressures in the order of 0.013 Pa. Thus, very smooth and uniform thin films suitable for high-density magnetic recording media can be obtained. In this study, the magnetic field strength in the plasma necessary to obtain a real plasma-damage-free environment around substrates was investigated, focusing on how the magnetic field was distributed in the plasma and thus how the plasma was sufficiently confined by a magnetic field applied perpendicular to both of the target planes. For this purpose, an auxiliary magnet was designed for each target and placed at a distance from the main magnet, which was located behind the target. The purpose of the auxiliary magnet was to confine and boost the magnetic fields generated by the main Al–Ni–Co magnet. An Fe–Nd–B magnet was used for the auxiliary magnet, because it was mechanically thin and had strong magnetic characteristics. To evaluate the plasma density distribution, the distribution of the electric potential was measured with a probe. The substrate voltage was also measured with a voltmeter to confirm that the environment around the substrates was plasma-free. One result of the design was that the electric potential distribution had much better uniformity than before (from −6 to −2 V); another was that the substrate voltage was slightly positive, indicating that the substrates were plasma-free. An FTS system with the above features is currently being used in various engineering experiments to fabricate plasma-damage-free thin films that have excellent magnetic and recording characteristics for magnetic recording media.