ESCA-thickness metrology and head-medium spacing impact of disk lubricant

Electron spectroscopy for chemical analysis (ESCA) has been commonly used as a metrology tool for lubricant film-thickness measurement on magnetic hard disks. The accuracy of the ESCA-thickness measurement rests solely with the calibration accuracy of the characteristic photoelectron attenuation length in the lubricant film. Several past studies on this subject yielded widely divergent results, due to the difficulty in obtaining an accurate, absolute lubricant film-thickness measurement. In this paper, we revisited the calibration issue and, instead of following the same paths pursued in the past, used a derivative method to yield an accurate calibration of the photoelectron attenuation length. We also compared the various methods for lubricant film-thickness calculation based on ESCA measurements and determined that the most accurate method is to use only the photoemission signal from the lubricant film. In addition, by studying the lubricant film-thickness effect on the electrical readback signal, we found that the lubricant film leads to an increase in the head-medium spacing by an amount greater than one times, but less than two times, its physical thickness.