Microstructural control of Y₂O₃ coating on quartz glass for the reduced thermal mismatch stress

Y₂O₃ can be applied as a plasma resistant coating for quartz glass used in the plasma etching apparatus. For such an application, a thick coating layer is required. However, when the thickness of the coating reaches to a critical thickness, a cracking in the coated layer occurs due to the residual tensile stress developed as a result of thermal expansion mismatch between the coating layer and the substrate. The critical thickness was calculated as ∼70 nm when the heat treatment temperature was 1000°C. To increase the critical thickness of the coating layer, a porous intermediate layer was introduced. Sol-gel spin coating method was used to deposit the multi-layered Y₂O₃ films. Three layered (dense/porous/dense)-Y₂O₃ coating with a thickness more than 200 nm was fabricated without crack generation. The porous self-buffer layer was effective in relieving the residual stress.