Improvement of deposition characteristics of silicon oxide layers using argon-based atmospheric-pressure very high-frequency plasma

We have investigated the deposition characteristics of silicon oxide (SiOx) layers in atmospheric pressure (AP) argon (Ar)-based plasma at a substrate temperature of 120 °C. A 150 MHz, very high-frequency (VHF) power is effectively used for exciting stable and uniform hexamethyldisiloxane (HMDSO)-oxygen (O2) fed plasma under AP. The microstructure of the SiOx layers is discussed in comparison with that by using helium (He)-based plasma. In the case of depositions with He/HMDSO/O2 plasma, SiO2-like films with uniform thickness, which have sufficient compactness to be used as the gate dielectrics of bottom-gate thin film transistors, can be obtained by moving substrate at a constant speed during the plasma operation. However, the decrease in the total gas flow rate (increase in the gas residence time in the plasma) causes the increase in the participation of nanoparticles to the film growth, which might result in the deterioration of film quality. Shortening the electrode length is effective for avoiding the incorporation of nanoparticles into the growing SiOx films. On the other hand, when Ar/HMDSO/O2 plasma is used, no deterioration of film compactness is observed irrespective of the gas flow rate. The results obtained in this study demonstrate the effectiveness of the VHF excitation of AP plasma on the generation of stable and uniform glow discharge without using He, which will lead to the development of a highly efficient and reduced cost formation process of good-quality SiOx films.