Rapid thermal magnetic annealing as an emerging technology in field-annealing of thin magnetic films for recording heads

An emerging field where rapid thermal processing (RTP) is now rapidly finding its first acceptance is in the industrial manufacturing of thin-film head devices for magnetic recording. Here soft-magnetic thin-film flux guide structures (usually composed of high-moment alloys containing iron, etc.) are applied onto ceramic substrate wafers (such as Al₂O₃-TiC) of sizes up to 150 mm and subsequently 'activated' by heating and cooling in a magnetic field. We assessed the advantages of rapid thermal magnetic annealing (RTMA) in a new prototype reactor with an external electromagnet, capable of generating an extremely homogeneous magnetic field of 660 Oe (52.8 kA/m) with field lines parallel across the entire wafer area (150 mm in diameter). Samples with 1 μm thick amorphous iron-alloy layers (Fe₇₇Nb₁₁N₁₀Si₂) sputter-deposited onto ceramic substrates of single-crystalline GGG-garnet (Gd₃Ga₅O₁₂) were conventionally annealed and RTMA-annealed in N₂/H₂ at temperatures between 550 and 700°C. Structural analysis by transmission electron microscopy (TEM) and electron diffraction showed that the enhanced performance of the RTMA-annealed layers is due to the different nanocrystallization kinetics induced by the fast heating and cooling rates of RTMA. The ceramic substrate materials normally used in head manufacturing (such as Al₂O₃-TiC) have favorable grey-body properties with high emissivity (≥0.7) over a wide range of temperatures (25-700°C) and wavelengths (1.5-10 μm), which excludes the difficulties encountered in pyrometric temperature control of infrared-transparent substrates such as silicon. We conclude that RTMA yields superior soft-magnetic materials, where throughput numbers of ≥30 wafers/h are possible.