Film Deposition Method using Low-temperature Microwave Excited Atmospheric Pressure Plasma Jet (MW-APPJ)*

The Y₂O₃ film has great demand in various applications since it has high permittivity, thermodynamic stability, and resistance to corrosive environments. Traditional plasma spray coatings are still widely used to deposit Y₂O₃ film due to their simplicity and ability to coat larger and more complex shapes. While recent Y₂O₃ deposition techniques such as aerosol deposition and ion beam-assisted deposition require high temperatures or vacuum conditions and lead to high operational costs. Among them, plasma-enhanced metal-organic chemical vapor deposition (PE-MOCVD) offers a low-cost alternative because of the non-vacuum environment and low-temperature conditions. In addition, a microwave atmospheric pressure plasma jet (MW-APPJ) can provide high-density reactive species for deposition and low-temperature operation for cost.

In this study, we employed MW-APPJ to deposit Y₂O₃ films on quartz glass substrates using yttrium acetate as a precursor. The deposition was performed at a substrate temperature of 100^oC. The dependence of gas flow rate has been investigated. The deposited films exhibited uniformity and adherence to substrates. Grazing incidence x-ray diffraction (GI-XRD) proved the crystalline structure of Y₂O₃ films, revealing a predominant single cubic (332) phase at around 40.1^o. Contrary to the previous studies, the MOCVD or PE-MOCVD Y₂O₃ films were mostly amorphous when the deposition temperature was below 400^oC. Scanning electron microscopy (SEM) images showed granular and dense film surfaces with the presence of crystallinity. XPS confirmed also the Y 3d doublets at 160.6 and 158.8 eV with a shift around 1.7 eV. Notably, the observed deviations from the typical binding energies of Y 3d_5/2 and 3d_3/2 in pure Y₂O₃ (156.7 and 158.7 eV, respectively) to higher energies in the deposited films indicate complex interactions involving yttrium.

A presence of crystallinity of  Y₂O₃ was observed at higher carrier gas flow rates, as indicated by GI-XRD. These findings suggest that the method is effective for the quality production of Y₂O₃ films at relatively low costs. The MW-APPJ, in combination with a MOCVD system, suggests an overall potential to replace a conventional plasma spray technique to obtain Y₂O₃ film cost-effectively.