Limitations and Corrections of Optical Profilometry in Surface Characterization of Carbon Coated Magnetic Recording Disks

The thickness of a thin absorbing carbon step on a strongly absorbing magnetic layer is measured using contact stylus and noncontact optical profilometer instrumentation, The dependence of optical profilometer measurements on carbon film thickness and optical properties of both the magnetic layer and the carbon film is investigated, and the error in the optical measurement is evaluated as a function of the phase shift of the light reflected from the sample surface. A marked improvement in the accuracy of the step height measurement is obtained if account is taken of the phase shift of the light reflected from the carbon overcoat and the magnetic substrate, respectively. The measurement of surface roughness of thin films on strongly absorbing substrates is discussed and the use of a dual wavelength technique is proposed to enhance the accuracy of optical profilometry.