Exploration of new methodologies for fly-height measurement

Abstract

Semiconductor technology, network and communication technology, and data storage technology are referred to as the 3 pillars of our information era. Magnetic disk drive is the major data storage device in modern society. High sensitivity data read/write head, high density data storage media and low fly-height slider technology are the 3 key factors determining the achievable data storage density or total capacity of disk drives. This thesis investigates technology for fly-height measurement.Current fly-height has been reduced to sub-10 nm region. System calibration and precise determination of the complex index of refraction (n, k) of the slider are significant challenges to achieve high accuracy of fly-height measurement. Systematic investigations into calibration technology and refractive index estimation were carried out on the industry standard and state-of-the-art fly-height tester. The work reported in this thesis revealed that the cutoff frequency of photodetectors and the bandwidth of optical filters induce calibration falloff during the calibration process. As a result, the fly-height measurement is underestimated. Inaccurate n and k determination causes error in both reflectance and phase shift, which has greater impact in the fly-height measurement than ever. In this thesis, mathematic models to compensate the calibration falloff and increase the accuracy of n, k determination have been explored. Novel method to calibrate the system without the traditional unloading calibration process is proposed. Results indicate that the proposed schemes are effective in terms of improving the accuracy of fly-height measurement.