The Roughness Measurement of the Super-smooth Surface of Hard Disks

Technologies for manufacturing hard disks are driven by the demand to increase magnetic storage capacity. However, the rate of increasing storage capacity is being slowed by the inability to produce ever closer flying heights between the sliders and disk surfaces. One of important requirements for flying height is to control the surface of substrates of hard disks to a super-smooth level to allow the sliders to ‘fly’ faster and more closely to the disk surfaces. Currently, there are no any assessment standards for super-smooth surfaces. In this paper, the authors attempt to build a measurement and characterisation protocol for the evaluation of hard disk 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. System factors and measurement factors both influence the experimental results with CCI, this paper focuses on analysing the latter including sampling intervals, the number of measurements, measurement area filter cut-off wavelength etc. Based on the experimental results, an optimised group of parameters for measurement and characterisation are recommended. The authors have successfully measured and compared 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) there is little difference in the influences of different CMP regimes on the topography of the hard disk surfaces.