Effect of bias frequency variation on the characteristics of SiO _X thin films deposited by atmospheric pressure chemical vapor deposition using a double discharge system

SiO_x film was deposited with a double discharge system composed of a source discharge and a direct-type discharge (bias discharge) using a gas mixture of hexamethyldisilazane (400 sccm)/O₂ (20 slm)/He (5 slm)/Ar (10 slm) to act as a thin film passivation layer. Especially, the effect of the quasi-pulse power frequency for the substrate biasing on the plasma characteristics and characteristics of SiO_x was investigated. As the frequency of the bias discharge was increased, the deposition rate of SiO _x increased from 41.4 nm/cycle (cycle is one pass of the substrate in the in-line plasma source and, here, nm/cycle corresponds to nm/min) (20 kHz) to 137.1 nm/cycle (60 kHz), the mechanical hardness increased from 7.4 GPa (20 kHz) to 8.5 GPa (60 kHz), the roughness of the SiO_x surface decreased from 6.35 nm (20 kHz) to 1.37 nm (50 kHz) and the amount of carbon and nitrogen impurities decreased to less than 1%.The improvement of the deposited SiO _x thin film characteristics was related to the increased plasma density, greater gas dissociation and higher bombarding ion flux to the substrate caused by the increase of the power consumption, while maintaining the ion bombardment energy with increasing the bias frequency.