Estimation of Growth Rate of Diamond-Like Carbon Films Prepared by Pulse Plasma Chemical Vapor Deposition

Abstract

The relationships between pulse frequency and growth rate and between pulse frequency and hardness were investigated for DLC (diamond-like carbon) films prepared by dc pulse plasma CVD (chemical vapor deposition). This study was focused on considering the overlap of the attenuation curve for the chemical species generated by a certain pulse with that for the species generated by the next pulse during DLC film fabrication. As a first-order approximation, the attenuation curves of all ion and radical species were assumed to follow the formula y=y0 · exp(-λt), where yo and λ are coefficients. The relationship between pulse frequency and growth rate was derived and compared with the experimental results. The theoretical curve agrees well with the experimental growth rate, indicating that the above approximation for all ion and radical species is useful for estimating the growth rate of DLC films in dc pulse plasma CVD. Moreover, a pulse frequency that gives the maximum film hardness existed. The higher the pulse frequency becomes, that is, the smaller the nonoverlapping ratio becomes, the greater the contribution of ion species to film fabrication. The hardness of the DLC films is small at low frequencies because insufficient numbers of ion species exist in the plasma. In contrast, the hardness slightly decreases at high frequencies owing to the excessive ion contribution to the growth of DLCs.