Development of columnar microstructure in magnetron sputter deposited CoPtCr/Cr magnetic thin films

The microstructure of CoPtCr alloy thin films, sputter deposited on Cr-underlayers varying in thickness from 25 to 1300 Å, is examined. The cross-sectional as well as plane-view high resolution transmission electron microscopy (HRTEM) of these films revealed that fine Cr-underlayer grains nucleate randomly and grow on the surface of a textured NiP substrate during the early stage of sputter deposition. The heterogeneously nucleated Cr grains result in the formation of columnar grains through competitive growth. The width of columnar grains gradually increased with film thickness and saturated at a thickness of about 850 Å Cr-underlayer films. High resolution electron microscopy of these films showed the onset of physical separation between columnar grains occurred between 250 and 600 Å. The study provides insights into the evolution of thin film microstructure during sputter deposition and into the reported low noise in CoPtCr/Cr films with ultra-thin Cr underlayers