Effect of Sputtering Deposition Process on Magnetic Properties of Magnetic Multilayers

Abstract

The energy distribution of energetic particles produced in magnetron sputtering plasma was measured by varying the sputtering gas species and pressure, and Co/Pt, Gd/Fe, and Co/Cu multilayers were fabricated using the same sputtering cathodes as the diagnosed one in order to discuss the relationship between the plasma parameters and the magnetic properties of the multilayers. When a heavy mass target such as W or Pt was used in Ar gas sputtering, the energy of the recoiled Ar atoms from the target was found to reach up to 150 eV. The energy and flux of the recoiled atoms were reduced by using Kr or Xe gas in place of Ar gas, whereas they are rather independent of the sputtering pressure in the range of 0.3–0.5 Pa. Low-pressure sputtering was effective for increasing the energy of sputtered atoms, which was at most 10 eV. Layered structures of the magnetic multilayers were significantly influenced by the sputtering conditions. The atomic intermixing at the interface, i.e., degradation of the interface sharpness, was controlled mainly by using a heavy sputtering gas, while the surface or interface flatness mainly depended on the sputtering pressure. The perpendicular magnetic anisotropy of Co/Pt and Gd/Fe multilayers was enhanced by suppressing atomic intermixing rather than by improving the interface flatness, and the use of a heavy inert gas such as Kr or Xe was found to be effective to enhance the anisotropy. When Kr or Xe gas was used, the monatomic layered structure of the Co (1 ML)/Pt (1 ML) (ML: monatomic layer) multilayer was found to survive, and positive perpendicular anisotropy was observed. In contrast, the magnetoresistance ratio of Co (1.5 nm)/Cu (t nm) multilayers (t∼0.9 nm) increased to around 50% when they were sputtered in an inert gas at low pressure, while the use of Xe gas degraded their magnetoresistance ratio. In the Co/Cu multilayers, the interface flatness rather than the sharpness was critical for enhancing the magnetoresistance ratio.