Improvement of the flowability of fine yttrium oxide powders by microwave oxygen plasma and evaluation of the dense coating layer

Abstract

Ceramic powders such as yttrium oxide and aluminum oxide have been extensively used to coat the inner walls and components of chambers used in semiconductor fabrication processes. Fine powders are used to form a dense coating layer by techniques such as thermal spray coating. However, fine powders exhibit strong cohesive forces due to surface roughness and interparticle van der Waals forces. This results in low flowability, a nonuniform powder feed, and nonuniform coatings. Microwave O2 plasma is proposed to improve the flowability of fine Y2O3 powder for a uniform powder supply in the spray coating process. Microwave O2 plasma flames produce a high temperature with active oxygen species at atmospheric pressure. The active oxygen species of plasma are incorporated into the lattice of powder particles, electrically stabilizing the powder, decreasing the static electricity, and reducing interparticle van der Waals forces. In addition, the surface of the fine powder is melted and smoothed by the high temperature of the microwave plasma, so that the powder acts as a dry lubricant. The processed powder was employed to coat a surface using atmospheric thermal spray coating, and the coating was characterized in comparison to a coating produced using commercial powder. The plasma-treated powder produced a coating with higher density and strength and lower porosity and surface roughness. The plasma-treated powder has a high flowability of 2.38 g s−1 and an apparent density of 2.07 g cm−1. Accordingly, the coating layer has a higher adhesion strength of 8.75 MPa and hardness of 651 HV0.3. In addition, its surface roughness of 0.9 μm and porosity of 0.2% are lower than those of a commercial sample.