Effect of reactive gas (oxygen/chlorine/fluorine) etching on the magnetic flux of a high moment write pole material

Effect of reactive gas (oxygen/chlorine/fluorine) etching on NiFe magnetic properties was investigated. Experimental data showed 40% magnetic property degradation for F-containing gas etching, 10% degradation for O-containing gas etching, and 5% degradation for Cl-containing gas etching processes. X-ray diffraction analysis indicated that the crystallographic orientation remained the same upon the reactive gas etching, which is due to the low ion energy in plasma etching process as opposed to ion milling process with high input energy. It is proposed that the reported magnetic property degradation was mainly caused by the nonmagnetic dead layer formation, rather than the changes in the crystallographic orientation. The dead layer was determined by the NiFe thickness dependence of remnant magnetic flux variations between pre-etched and postetched samples. The dead layer remained nearly constant for O-containing gas etching process with increasing plasma processing time. The nonmagnetic dead layer of ∼ 40 - 50 Å formed in O-containing etching gas was observed in transmission electron microscopy cross-sectional image and was in very good agreement with the calculated value based on magnetic flux measurements. Combined magnetic and physical characterizations suggest that the dead layer thickness saturates at the initial stage of the plasma etching and magnetic property remained unchanged with increasing etching duration upon formation of the dead layer.