In recent years, magnetic recording and reproducing devices have been requested to attain more capacity and achieve higher performance due to increasing amount of information for personal computers and expanding applications to image recording apparatus, car navigation apparatus, and the like. For higher recording density, a smaller unit of magnetization reversal in magnetic recording media and media noise reduction are required. Conventional magnetic recording media have adopted a configuration that the ferromagnetic crystal grains comprising magnetic recording layers are preliminarily separated by nonmagnetic materials contained in magnetic recording layers.
To increase the magnetic recording density by active control of the separators, discrete track media in which recording tracks are separated, and further, bit patterned media in which recording bits are separated, have been researched and developed. The technique to form the separators has been a significant point for higher recording density in both of these media. For example, following techniques have been proposed to form the separators in discrete track media. One technique is the substrate processing type which preliminarily forms concentric lands and grooves on a substrate and forms a magnetic film thereon to form a patterned magnetic film. Another technique is the magnetic layer processing type which masks a magnetic film and etches the parts of a magnetic film to be grooves to form the pattern.
These techniques, however, include a plurality of processes such as backfilling nonmagnetic materials into the grooves, planarizing the surface so as to have the same level as the magnetic film to be the islands, and forming a protection film on the planarized surface. Consequently, other problems arise such as increase in foreign substances produced on the surfaces of the magnetic film and the protection film and increase in roughness of the surfaces. They prevent the reduction in the spacing between a magnetic head and a magnetic disk (nano-spacing), which is another point for higher recording density.
To overcome these problems, a method of forming separators by ion implantation has been attempted. For example, Japanese Patent Publication No. H5-205257 (“Patent Document 1”) discloses a method of forming separators between recording tracks of a discrete track medium by altering the magnetic property by means of nitrogen ion implantation into a magnetic layer, for example. According to Patent Document 1, this method can increase the track density without being significantly affected by the process accuracy to decrease the track width for a head. Japanese Patent Publication No. H9-167336 (“Patent Document 2”) attempted a method of forming servo patterns by ion implantation. According to Patent Document 2, the flatness of the surface can be much more improved.
Methods for separating recording tracks in discrete track media or recording bits in bit patterned media are important issues. In use of the methods in the above-listed documents, to improve the track density while preventing side writings onto recording tracks, forming separators across the magnetic layer in the film thickness direction is required. The forming separators require ion implantation of a nonmagnetic element across the magnetic layer in the film thickness direction at a sufficiently high acceleration voltage. In the meanwhile, if the acceleration voltage is raised, the thickness of a mask layer formed on the magnetic layer should be increased to prevent the recording tracks on the magnetic layer from being doped with nonmagnetic element ions. In this regard, if the thickness of the mask layer is increased, a problem arises that pattern collapse occur when the pattern pitch of the mask layer is narrowed for higher recording density. Therefore, the film thickness of the mask layer should be thinned so as to match the pattern pitch. However, if the film thickness is thinned and the acceleration voltage is high, the mask layer may not be able to sufficiently block the radiated ions and the recording tracks of the magnetic layer are doped with the nonmagnetic element ions. As a result, the magnetic property of the recording tracks is changed so that the read/write performance is disadvantageously deteriorated. In this case, it is necessary to lower the acceleration voltage in the ion implantation to reduce the implantation energy. However, if the implantation energy is reduced, separators may not be formed across the magnetic layer in the film thickness direction. If the structure of the magnetic layer is not appropriate, a magnetic flux induced by the magnetic layer remained undoped under the separators strays to the surface of separators to cause noise. Then, when the implantation energy is reduced, it is necessary to optimize the structure of the magnetic layer so as to match the implantation energy.