Ion beam deposition of permanent magnet layers for liftoff processes

Abstract

Thin film permanent magnet layers of Cr/CoCrPt were prepared by ion beam deposition in a Veeco IBD-350 tool. The magnetic properties were measured as a function of deposition angle, deposition energy, assist energy, and the underlayer and permanent magnet thicknesses. It was found that higher deposition energies and angles (from normal) resulted in larger coercivities. Increasing the assist energy also helped increase the coercivity. The coercivities were in the range of 1400–2100 Oe depending on the deposition conditions, for a Cr-50 Å/CoCrPt-250 Å film. The squareness, S (the ratio of remnant magnetization to saturation magnetization) and Mrt (remnant magnetization and film thickness product) for these films were about 0.85 and 1.3 memu/cm2, respectively. It was found that underlayers of Cr as thin as 25 Å could be used, without significant degradation of magnetic properties. The coercivity had a broad peak between 100 and 200 Å of CoCrPt, above which the coercivity gradually decreased. θ–2θ x-ray diffraction measurements showed the presence of in-plane textures of (101̄0) and (112̄0) with the largest coercivity being obtained when a strong (101̄0) peak is observed. The side-wall profile of the permanent magnet, measured after a liftoff process, was found to depend on the deposition angle. As the angle got larger (further away from normal incidence), the side wall showed greater tapering. This is due to the increased effect of shadowing by the photoresist structure. The directional, collimated, nature of the deposition beam was found to aid the liftoff process, by avoiding step coverage of the liftoff structures. This significantly increased the ease of lifting off. By adjusting the deposition angle, it is possible to tailor the process to provide optimum magnetic properties, coupled with good electrical contact. Thus, it was found that ion beam deposition is an attractive alternative to sputter deposition (physical vapor deposition), providing some important advantages over it.