Thin-film magnetic recording heads are usually fabricated using a combination of material layers including one or more layers of thin soft and hard magnetic films, some of which may have magnetic domains oriented along one or multiple magnetic axes. Generally, the magnetic films are deposited onto substrates in low-pressure processing chambers by physical-vapor deposition (PVD) methods such as plasma sputtering or ion-beam deposition processes. The magnetic domains of these films are oriented by exposing the films to in-plane magnetic fields either during their deposition or during a subsequent processing step such as magnetic annealing. The magnetic fields have specific requirements specifying the upper limits for both "skew" (deviation in direction) and "non-uniformity" (deviation in magnitude). Typical in-plane magnetic field strengths are in the range of 50 to 100 Oersted.
Either permanent magnets or electromagnets can be used for generating the substantially uniaxial magnetic fields. For example, Nakagawa et al. in U.S. Pat. No. 4,865,709 mount thin magnetic film substrates between pairs of permanent magnets on a substrate holder. Opposite poles of the magnets face each other for generating approximately uniaxial magnetic fields across the thin film surfaces of the substrates. However, the permanent magnets are difficult to position, have limited magnetic field strength and adjustability, and are exposed to processing that can affect their long-term performance (resulting, for instance, in long-term field drift). Permanent magnets may also have detrimental effects on the PVD plasma uniformity and repeatability. Moreover, permanent magnets provide no or limited capability for field magnitude or orientation adjustments.
Setoyama et al. in U.S. Pat. No. 4,673,482 position a pair of magnetic field-generating coils on opposite sides of a substrate outside a low-pressure processing chamber in which the substrate is mounted. The coils are located at a considerable distance from the substrate and only a small portion of the resulting magnetic field exhibits the required uniaxial characteristics. Magnetic field adjustability is also limited. Moreover, this type of magnetic field source can produce significant plasma non-uniformity and magnetic interference problems associated with magnetron PVD energy sources.
Co-assigned U.S. Pat. No. 5,630,916 to Gerrish et al., which names one of the inventors of this invention, overcomes many of these problems by positioning a plate-shaped electromagnet adjacent to the substrate positioned over a substrate support. The plate-shaped electromagnet is isolated from the processing environment by the substrate support (i.e., electromagnet located outside the vacuum processing chamber) but is still close to the substrate. The substantially planar plate-shape of the electromagnet, which parallels the substrate, produces a uniaxial field of high uniformity and relatively low skew in the immediate vicinity of the substrate surface. An angularly adjustable support provides for mechanically orienting the plate-shaped electromagnet with respect to the substrate support for fine tuning the magnetic orientation axis.
More recently, tolerances for magnetic field skew (angular deviation from the preferred orientation axis) and non-uniformity have become increasingly stringent and the size of the substrates has become increasingly large (up to 6".times.6" square substrates). Both trends pose similar problems for the available magnetic field orienting equipment. Larger electromagnets can be used to some extent. However, various practical considerations limit the size of the electromagnets. For example, Gerrish et al.'s electromagnet is required to fit within a substrate holder, which is itself limited in size by surrounding vacuum processing chamber dimensions. Unused portions of the magnetic fields produced by the larger magnets beyond the substrate surface area can interfere with substrate processing such as by altering the path of ions to the substrate (thus causing plasma process uniformity degradation) or imbalancing target erosion (e.g., via magnetic field interference with the PVD magnetron energy source).