Residual stress characterization of diamond-like carbon coatings by an X-ray diffraction method

This paper presents residual stress measurements of amorphous diamond-like carbon (DLC) coatings obtained by studying the stress conditions of the substrate surface layer immediately adjacent to the coating via X-ray diffraction (XRD) with a thin film attachment. In such a set-up, the incidence angle α at which the primary beam strikes the specimen is fixed at a glancing angle (2°in our experiments) relative to the sample surface while the detector rotates to collect the diffracted X-rays. The amorphous carbon coatings were deposited on single-crystal silicon wafers and on polycrystalline KBr substrates in an unbalanced magnetron sputtering system. The effects of substrate material and deposition parameters on the internal stresses of the coatings are discussed in detail. XRD with thin film attachment provides a new and more precise way to determine the residual stresses in amorphous coatings. Increasing the relative nitrogen flow reduces the compressive stress level of the hydrogenated amorphous carbon coatings. Under the experimental conditions studied, higher substrate bias power and sputter power densities both increased the compressive stress level.