A nonequilibrium, atmospheric-pressure argon plasma torch for deposition of thin silicon dioxide films

A nonequilibrium, atmospheric-pressure plasma torch that can be generated either in He or Ar gas by using a pulsed high-voltage power supply with the discharge temperature in the range 22-35 degrees C has been developed. This system is used to deposit silicon dioxide films from a hexamethyldisiloxane (HMDSO) precursor diluted in an oxygen carrier gas. It is concluded that, in terms of both quality and deposition rate at the same applied power, frequency, and gas composition, Ar plasma is more powerful than He plasma for depositing SiO2-like films. The maximum feed rate of HMDSO/O-2 injected into the Ar plasma torch is limited to 100 mL min(-1) to ensure inorganic coatings are deposited. In order to improve the visual quality, without adversely affecting the inorganic features of the film, a small amount of nitrogen (N-2) can be added to the Ar as a working gas. When the ratio of Ar to N-2 in the flow gas is 30:1, the discharge behavior is transformed from filamentary to glowlike as a result of the quenching effect of admixed N-2 on Ar plasma.