The Roughness Measurement and Assessment of the Super Smooth Surface of Hard Disks

The rate of increasing storage capacity is being slowed by the inability to produce ever closer flying heights between the sliders and disks. In order to allow the sliders to 'fly' faster and more closely to the disk surfaces, it is important to control the surface of substrates of hard disks to a super-smooth level. However, there are no sophisticated instruments and assessment standards for super-smooth surfaces. In this research, the authors attempt to build a measurement and assessment protocol for the evaluation of super-smooth surfaces using a white-light optical instrument CCI (Coherence Correlation Interferometer). The key advantage of this instrument is its exceptionally high vertical resolution which is an order of magnitude better than comparable systems. This paper focuses on discussing the factors influencing the experimental results; they include sampling intervals, the number of measurements, scan size, filter cut-off wavelength etc. Based on the experimental results, an optimum protocol for measurement and assessment are recommended, and then the authors measure and compare the surface roughness of six hard disks derived from differing chemical mechanical polishing (CMP) 'abrasives'. It has been found that: (1) the roughness values of the six hard disks surfaces have all reached a sub-nanometre level; (2) CMP regimes have little influence on the topography of the hard disk surfaces.