Optical characterization of sputtered a-C:H overcoats: relationship to accelerated wear testing, film composition and substrate temperature

Abstract

The durability of the protective carbon overcoat for thin film magnetic media is becoming increasingly important due to the decreased head to disk spacing during drive operation (currently approximately 40 nm) and the increased number of contact-start-stop (CSS) cycles required by drive manufacturers (currently approximately 100 000). Due to the increasingly large volumes of thin film magnetic media production, quick and easy methods of monitoring of the carbon overcoat properties are essential. In this work, we report the physical and optical properties of reactive d.c. sputtered a-C:H films and the effect of the substrate temperature and bulk oxygen incorporation on these properties. Optical properties were determined using ellipsometry, an n&k optical analyzer and Raman spectroscopy. Accelerated wear testing was performed in the form of an alumina abrasive tape test. High-resolution secondary ion mass spectroscopy (SIMS) was used to determine the relative concentrations of C, H, O and N in the thin film “bulk”. A relationship was found between the Raman spectra and accelerated wear testing as well as between the bulk oxygen to carbon ratio and accelerated wear testing.