Characterization of laser zone texture with laser Doppler vibrometry

The use of laser zone texture (LZT) is well established in the data storage industry. LZT is a process where a localized pattern of laser melt bumps is put on the surface of a rigid magnetic recording disk in order to reduce the stiction force between a magnetic recording head and that disk in a hard disk drive. Characterization of the height of the laser bumps on a disk is important to the control of the LZT process. One technique well suited for this measurement and control of LZT in a manufacturing environment is laser Doppler vibrometry (LDV). Commercial instruments using this technique allow fast and precise measurement of an average bump height on a given surface. In addition, excellent correlation of the determined height to atomic force microscopy (AFM) has been found. In this paper, methods developed for measuring laser bump heights with LDV will be presented along with results on the accuracy and precision of the measurement and correlation to other height measurement techniques. Characterization of different bump shapes and heights and limits of the technique in this respect will also be discussed.