Slurry for suspension plasma spraying, and method for forming sprayed coating

#This invention relates to a slurry for use in suspension plasma spraying. The slurry may be used for forming a sprayed coating which is suitable for parts or members placed inside of a plasma etching apparatus used in a semiconductor manufacturing process. This invention relates also to a method for forming a sprayed coating.

#A wafer as an object to be processed is treated under an atmosphere of halogen series gas plasma such as fluorine series gas plasma and chlorine series gas plasma in a plasma etching apparatus used in a semiconductor manufacturing process. As the fluorine series gas, SF6, CF4, CHF3, HF or NF3 is used, and as the chlorine series gas, Cl2, BCl3, HCl, CCl4 or SiCl4 is used.

#For manufacturing parts or members exposed to a high corrosive gas plasma atmosphere in a plasma etching apparatus, generally, an erosion-resistant sprayed coating is formed on the surface of a substrate by atmospheric plasma spraying in which a raw material is supplied in powdery state. However, to spray the raw material in powdery state, it is preferable that spraying particles has an average particle size of at least 10 μm. If the particles have a smaller size than the range, a spraying material has disadvantageous fluidity for introducing the spraying material into a flame for thermal spraying, therefore, a supplying conduit may be clogged with the spaying material. Moreover, the particles are vaporized in the flame, thereby process yield may result in low. Furthermore, a dense sprayed coating cannot be obtained by spraying from particles having a large average particle size because a splat diameter of the particle is large, thereby crack and porosity increase, causing generation of particulates.

#A slurry for thermal spraying of the invention includes a dispersion medium and rare earth oxide particles, and is suitable for use in suspension plasma spraying in which fine particles are sprayed in slurry form. The inventive slurry for thermal spraying can contribute stable formation of a sprayed coating including a rare earth oxide phase as a main phase. When the slurry is circulated in a conduit of a slurry feed unit for long time or the slurry is supplied from a slurry feed unit to a spray gun for long time, a conventional slurry for suspension plasma spraying including fine particles has problems such that a conduit is are easy to be clogged with the retained particles at the inner wall of the conduit, and stable feed of the slurry is hard to continue. On the other hand, the inventive slurry for thermal spraying can be continued stable feed without clogging of a conduit.

#Rare earth oxide particles of the inventive slurry for thermal spraying preferably have a particle size D50 of up to 5 μm. In the present invention, the particle size D50 means a cumulative 50% diameter (median diameter) in volume basis particle size distribution. When the slurry is circulated in a conduit of a slurry feed unit or the slurry is supplied from a slurry feed unit to a spray gun, a slurry including small particles can be fed stably compared with a slurry including large particles. Further, when the particles included in the slurry has a small size, a size of a split that is formed by collision of a melted particle to a substrate in spraying in a slurry form is small, thereby a porosity of the resulting sprayed coating becomes low, and generation of cracks in the splats can be controlled. The particle size D50 is more preferably up to 4.5 μm, even more preferably up to 4 μm.

#Rare earth oxide particles of the inventive slurry for thermal spraying preferably have a particle size D50 of at least 1.5 μm. When the rare earth oxide particles are sprayed in slurry form, the spraying particles having a large particle size included in the slurry have a large kinetic momentum, thereby the particles are easy to form splats by collision to a substrate. The particle size D50 is more preferably at least 1.8 μm, even more preferably at least 2 μm.