Direct measurement of bonded film thickness of A20H lubricant

Abstract

Currently the bonded lubricant thickness is measured either by Fourier transform infrared spectroscopy (FTIR) or electron spectroscopy for chemical analysis (ESCA) on the remaining lubricant after using fluorocarbon solvent like Vertrel to rinse off the mobile lubricant from magnetic disk surfaces. As the thickness of the lubricant applied on a disk approaches to its molecular dimension (∼10 A), the current measurement methods face tremendous challenges in achieving the desired levels of accuracy and sensitivity. We propose a new method that makes use of a time-of-flight mass spectrometry (TOF-SIMS) to directly measure the bonded film thickness of A20H lubricant by quantifying the ratio of either the hydroxyl end-group or the phenoxy portion of the cyclotriphosphazene end-group with respect to their respective neighboring backbone fragments. The quantified ratios include C2F3/CF2CH2OH and C6F3O/CF3C6H4 measured in the positive polarity and C2F3O/OCF2CH2OH, and C7F5/CF3C6H4O2H2 measured in the negative polarity. The transfer function from the quantified ratios to the bonded lubricant thickness (t) is given in the form of t=α×ln (100×R T )−β, where α,β are constants for a selected ratio and R T represents the quantity of the specific ratio. The results correlate very well with the FTIR method currently used in the measurement of the magnetic media during production (R 2>90). The new method can complete the measurement of the bonded lubricant thickness in a one-step process and it has a much higher spatial resolution at sub-micrometers than that of the FTIR or ESCA with order of a few tens of micrometers in resolution. The quantified ratio obtained from this TOF-SIMS technique makes the imaging of the localized bonded lubricant possible, which can be applied in the magnetic media failure analysis.