Effects of different nitrogen/methane ratios on the residual stress of a-C:N thin films prepared by plasma enhanced chemical vapor deposition

The effects of different nitrogen/methane (N2/CH4) ratios on the residual stress (σr) of nitrogenated amorphous carbon (a-C:N) thin films prepared by plasma enhanced chemical vapor deposition are investigated. The microstructure, optical and mechanical properties of a-C:N films are evaluated. Meanwhile, the σr of a-C:N films is analyzed using the laser curvature method, and the σr connected to the above material properties of a-C:N films is discussed in detail. As the N2/CH4 ratio increases from 0 to 1.4, the sp2 domain size of a-C:N films increases, while the optical band gap, Young's modulus and hardness of a-C:N films decrease. Alternatively, the σr of a-C:N films decreases with increasing the N2/CH4 ratio, and the maximum stress reduction of a-C:N films is achieved with N2/CH4 ratio of 1.4 in this article.