A film-forming powder containing a rare earth oxyfluoride has an average particle size D50 of 0.6-15 m, a total volume of 10 m pores of 0.51-1.5 cm.sup.3/g as measured by mercury porosimetry, and a BET surface area of 3-50 m.sup.2/g is suitable for forming a dense film in high yields or deposition rates and high productivity. The film-forming powder having a greater pore volume can be prepared by forming a rare earth ammonium fluoride complex salt on surfaces of rare earth oxide particles to provide precursor particles, and heat treating the precursor particles at a temperature of 350 to 700 C.

A sintered rare earth oxyfluoride compact is composed of Ln.sub.aO.sub.bF.sub.c (wherein Ln is a rare earth element; and a, b, and c each independently represent a positive number, provided that they are not equal to each other) or Ca-stabilized LnOF as a primary phase and LnOF unstabilized with Ca as a secondary phase. The intensity ratio of the XRD peak of the (018) or (110) plane of the unstabilized LnOF to the highest XRD peak of Ln.sub.aO.sub.bF.sub.c is preferably 0.5% to 30%.

A forming method of an yttrium oxide fluoride (YOF) coating film and a (YOF) coating film formed thereby are disclosed. The YOF coating film has no or extremely small pores therein and a nanostructure to increase light transmittance thereof, and has high hardness and high bonding strength and thus can protect a transparent window of a display device. The method for forming an YOF coating film involves the steps of: providing pretreated YOF powder having a particle diameter ranging from 0.1 to 12 m; receiving a transfer gas supplied from a transfer gas supply unit and receiving the pretreated YOF powder supplied from a powder supply unit to transfer the pretreated YOF powder in an aerosol state; and colliding/smashing (spraying) the pretreated YOF powder transferred in the aerosol state with/onto a substrate in a process chamber to form an YOF coating film on the substrate.

A forming method of an yttrium oxide fluoride (YOF) coating film and a (YOF) coating film formed thereby are disclosed. The YOF coating film has no or extremely small pores therein and a nanostructure to increase light transmittance thereof, and has high hardness and high bonding strength and thus can protect a transparent window of a display device. The method for forming an YOF coating film involves the steps of: providing pretreated YOF powder having a particle diameter ranging from 0.1 to 12 m; receiving a transfer gas supplied from a transfer gas supply unit and receiving the pretreated YOF powder supplied from a powder supply unit to transfer the pretreated YOF powder in an aerosol state; and colliding/smashing (spraying) the pretreated YOF powder transferred in the aerosol state with/onto a substrate in a process chamber to form an YOF coating film on the substrate.

According to the present invention, a yttrium-fluoride-based sprayed coating that has a Vickers hardness of 350 or higher, includes a YF.sub.3 crystal phase having an orthorhombic crystal system, and does not include a YF.sub.3 crystal phase having a crystal system other than an orthorhombic crystal system is produced by plasma-spraying a spray powder that includes a YF.sub.3 crystal phase having an orthorhombic crystal system and does not include a YF.sub.3 crystal phase having a crystal system other than an orthorhombic crystal system. In the present invention, it is possible to provide a yttrium-fluoride-based sprayed coating that has a high coating hardness and is such that the amount of particles generated upon exposure to a halogen-based gas plasma is low, and such a sprayed coating is exceptional as a sprayed coating formed on a member for a semiconductor-producing device that is used in a semiconductor production step.

According to the present invention, a yttrium-fluoride-based sprayed coating that has a Vickers hardness of 350 or higher, includes a YF.sub.3 crystal phase having an orthorhombic crystal system, and does not include a YF.sub.3 crystal phase having a crystal system other than an orthorhombic crystal system is produced by plasma-spraying a spray powder that includes a YF.sub.3 crystal phase having an orthorhombic crystal system and does not include a YF.sub.3 crystal phase having a crystal system other than an orthorhombic crystal system. In the present invention, it is possible to provide a yttrium-fluoride-based sprayed coating that has a high coating hardness and is such that the amount of particles generated upon exposure to a halogen-based gas plasma is low, and such a sprayed coating is exceptional as a sprayed coating formed on a member for a semiconductor-producing device that is used in a semiconductor production step.

A film-forming powder containing a rare earth oxyfluoride has an average particle size D50 of 0.6-15 m, a total volume of 10 m pores of 0.51-1.5 cm.sup.3/g as measured by mercury porosimetry, and a BET surface area of 3-50 m.sup.2/g is suitable for forming a dense film in high yields or deposition rates and high productivity. The film-forming powder having a greater pore volume can be prepared by forming a rare earth ammonium fluoride complex salt on surfaces of rare earth oxide particles to provide precursor particles, and heat treating the precursor particles at a temperature of 350 to 700 C.

A spray coating containing a rare earth fluoride and/or a rare earth acid fluoride contains, carbon at 0.01-2% by mass or titanium or molybdenum at 1-1000 ppm. When an acid fluoride is not contained, the spray coating is gray to black in which, in terms of the L*a*b* chromaticity, L* is 25-64, a* is 3.0 to +5.0, and b* is 4.0 to +8.0. When an acid fluoride is contained, the spray coating is white or gray to black in which, in terms of the L*a*b* chromaticity, L* is equal to or greater than 25 and less than 91, a* is 3.0 to +5.0, and b* is 6.0 to +8.0. By forming this coating on a plasma resistant member, a partial color change is reduced, thus, a member that is capable of reliably realizing the original longevity is obtained.

A spray coating containing a rare earth fluoride and/or a rare earth acid fluoride contains carbon at 0.01-2% by mass or titanium or molybdenum at 1-1000 ppm. When an acid fluoride is not contained, the spray coating is gray to black in which, in terms of the L*a*b* chromaticity, L* is 25-64, a* is ?3.0 to +5.0, and b* is ?4.0 to +8.0. When an acid fluoride is contained, the spray coating is white or gray to black in which, in terms of the L*a*b* chromaticity, L* is equal to or greater than 25 and less than 91, a* is ?3.0 to +5.0, and b* is ?6.0 to +8.0. By forming this coating on a plasma resistant member, a partial color change is reduced, thus, a member that is capable of reliably realizing the original longevity is obtained.

A spray coating containing a rare earth fluoride and/or a rare earth acid fluoride contains carbon at 0.01-2% by mass or titanium or molybdenum at 1-1000 ppm. When an acid fluoride is not contained, the spray coating is gray to black in which, in terms of the L*a*b* chromaticity, L* is 25-64, a* is ?3.0 to +5.0, and b* is ?4.0 to +8.0. When an acid fluoride is contained, the spray coating is white or gray to black in which, in terms of the L*a*b* chromaticity, L* is equal to or greater than 25 and less than 91, a* is ?3.0 to +5.0, and b* is ?6.0 to +8.0. By forming this coating on a plasma resistant member, a partial color change is reduced, thus, a member that is capable of reliably realizing the original longevity is obtained.