Crystal Growth of Yttrium Oxide on Carbon Substrates

In film forming and etching systems that utilize plasma, it is important to form excellent insulator thin films that coat conductive base materials to ensure their insulating properties. The insulating property of a material tends to be higher when the forbidden bandwidth (band gap) is large. Oxides with ionic bonding have a huge band gap due to their large difference in polarity, and there are many excellent insulating materials available. Among them, yttrium oxide is an insulating material used in various semiconductor manufacturing processes. Currently, aluminum metal is the main base material, but a high-temperature environment is expected in next-generation equipment for 3D-NAND. Therefore, a base material with high heat resistance is required. In this study, we focused on isotropic graphite, which has both heat resistance and electrical conductivity, as a base material. The experiments were conducted using a methanol solvent from a previous study. [1]<br/>In this study, two growth methods were selected: the solution method and the mist CVD method. In the solution method, the solute is dissolved in a solvent, dropped onto a substrate, and transported to a heat source, where the process is repeated to deposit the crystals. The mist CVD method uses an ultrasonic transducer to atomize the material solution, and transports the atomized material solution to the substrate using gases such as nitrogen and oxygen to achieve thin film growth. In both methods, an electric furnace was used as the heat source for film deposition. For the solution method, yttrium acetylacetonato n-hydrate [Y(C₅H₇O₂)₃･nH₂O] was selected as the precursor solute and completely dissolved in a solution of 95% methanol [CH₃OH] and 5% water [H₂O] at a concentration of 0.1 mol/L. The substrate was isotropic graphite and the growth temperatures were 200, 300, and 400°C. Experimental results showed that red powder adhered to the substrate as the temperature increased. Scanning electron microscopy (SEM) observation of the substrate surface and composition analysis by energy dispersive X-ray spectroscopy (EDS) showed amorphous with a yttrium content of 20%. A thin film was formed on the top of the carbon substrate, and insulation resistance measurements were taken vertically between the bottom, where the carbon was bare, and the top, which was covered with a Y₂O₃ insulating film, yielding a resistance of 100MΩ, confirming the insulation properties. In the mist CVD method, the same precursor solutes and solutions as in the solution method were selected, and all solutions were completely dissolved while changing the concentration. The substrate was isotropic graphite and the growth temperature was 400°C. Scanning electron microscopy (SEM) observation of the substrate surface and composition analysis by energy dispersive X-ray spectroscopy (EDS) revealed an amorphous state with a yttrium content of 24%. Insulation resistance measurements were performed as in the solution method, and a resistance value of 500 Ω was obtained. A blue interference film was also visible visually. More detailed experimental details and growth rates will be presented on the day.<br/>[1] Li Liu, <i>et al</i>., Phys. Status Solidi B 2021, 258, 2100105