Non-destructive defect detection scheme using Kerr-Channel Optical SurfaceAnalyzer

Magnetic defects on the surface of magnetic disks, unlike normal topologica l defects, are difficult to detect because they are solely due to magnetic signal loss as seen by the MR element and often do not have any obvious top ological features. Defects without any topological features usually render conventional defect finding techniques such as visual inspection, optical m icroscopy, and SEM useless. In the past, the painstaking way of locating th e defect was to index the drive with a strobe light and followed with ferro fluid decoration of the surface to determine the location of the defect The disadvantage is that the magnetic particles in the decoration technique ca n often confound the origin of the defect. Furthermore, the old technique d oes not have high enough resolution to locate defect with a size on the ord er of a micrometer. In this work, we will describe how a magnetic marking t echnique (MMT) is utilized to circumscribe the magnetic defects. The marker s are written in such a way that both the defect and the magnetic markers a re easily detected using Kerr-Channel Optical Surface Analyzer and Magnetic Force Microscope. Typically, the accuracy of locating the defect using the MMT is within a track-pitch radially and within one data sector circumfere ntially. The new scheme provides at least one order of magnitude improvemen t in detection resolution over the old technique.