Characterization of Thin DLC Films Using Film Stress and Raman Techniques

Abstract

Diamond like carbon (DLC) films are deposited on thin film heads in the magnetic recording industry to reduce friction and “stiction” and to provide a durable, abrasion resistant coating. The films are a mixture of graphitic phases with sp2 bonding and diamond phases with sp3 bonding. The present work provides the results of thin film stress measurements and Raman tests performed on 10 rim DLC films deposited on 75 mm silicon test wafers using standard optical lever techniques. Stress is measured after deposition and in-situ during thermal cycling. Isothermal relaxation data is also obtained. Raman is performed before and after annealing.The deposited stress of 10 nrm films was over 2000 MPa. The stress relaxed entirely to zero during thermal cycling to 500°C. Isothermal relaxation at 300°C also resulted in complete relaxation of an initial 1500 MPa stress to zero in less than 24 hours. The Raman data is consistent with prior results in the literature. The position of the G band shifts from 1513 to 1581 cm-1 during annealing, and the intensity ratio of the D band to the G band rises from 0.201 to 0.814 during annealing.The decrease of the film stress to zero during thermal processing implies that the entire thickness of the film is undergoing a structural change while the stress relaxation data implies that the stress is relaxing by a fast diffusive process. The Raman data implies that the film is becoming more graphitic and the crystallites are growing in number and size during thermal processing. We suggest that the structure of the extremely thin carbon film is modified by a surface diffusion mechanism.

The effect of the substrate bias on the Raman spectra and thermal stability of diamond-like carbon (DLC) and silicon-modified DLC films prepared by plasma-enhanced chemical vapour deposition (PECVD)

“…The position of the G peak is seen to increase with temperature; an effect which we associate with the films becoming more graphite-like. Turlo et al [11] have also reported a trend similar to our observation in the Raman spectra of their thermally annealed DLC films. They found a shift in the G peak position of their DLC films from 1514 to 1577 cm −1 during annealing to 500 • C and the I (D)/I (G) ratios rose from 0.205 to 0.818.…”