Advantages of dual frequency PECVD for deposition of ILD and passivation films

The advantages of dual-frequency plasma-enhanced chemical vapor deposition (PECVD) for the deposition of silicon nitride, oxynitrides, and TEOS oxide films are discussed, and a mechanism explaining the effects on step coverage, film stress, chemical composition, and film density and stability is proposed. It is shown that the use of dual frequency for PECVD of dielectrics provides increased flexibility and process control. The main role of the high-frequency RF is to generate the reactive species and provide sufficient electron and ion densities. The low frequency is added to control the ion bombardment to which the substrates are subjected during deposition. Increasing the low-frequency power increases the plasma potential and the amount of ions following the low-frequency RF field (<1 MHz). The resulting low-energy ion implantation occurring during deposition causes a change in the intrinsic film stress from tensile to compressive, increases film density, and improves the chemical reactions. In addition, the low-energy bombardment enhances the surface mobility of adsorbed TEOS and Si(NH₂)_x, thus improving the step coverage of TEOS SiO₂, standard silicon nitride, UV transparent nitride, and oxynitrides. However, if the ion energy is too high, the step coverage deteriorates due to premature decomposition of the reactive species