Structure and Mechanical Properties of Nitrogen Incorporated Diamond-Like Carbon Films

 Nitrogen incorporated diamond-like carbon (DLC) films were deposited by r.f. plasma assisted chemical vapor deposition (r.f.-PACVD) method. Mixtures of benzene and ammonia or nitrogen were used as the reaction gases for the deposition. Composition, atomic bond structure and mechanical properties of the film were investigated when the fraction of nitrogen source increases from 0 to 0.79. All films were deposited at fixed negative bias voltage of the cathode (-500V) and the deposition pressure (10mTorr). While ammonia addition reduces both residual stress and hardness of the film from 1.7 to 1 GPa and from 2750 to 1700 Kgf/㎟ respectively, the mechanical properties are not significantly varied by nitrogen addition. Deposition rate, composition and atomic bond structure are also dependent on the nitrogen source gases. Observed behavior of mechanical properties is discussed in terms of the content of inter-links of sp**2 clusters. In addition to hydrogen, C≡N bonds in the film are also terminated sites of three dimensional atomic bond network. By considering the hydrogen concentration and the C≡N bonds, it can be shown that the mechanical properties of nitrogen incorporated DLC films are determined by the content of inter-links of sp**2 clusters