Yttria sintered body and component used for plasma processing apparatus
To provide a high purity Yttria sintered bodies having a high strength, a low dielectric loss and high plasma corrosion resistance of halogen gas during wide range surface roughness (Ra). An Yttria sintered body having a dielectric loss tan δ of 1×10 −4 or less in the frequency range from 1 to 20 GHz, wherein the Yttria sintered body contains Yttria of 99.9% by mass or more, has a porosity of 1% or less and an average crystal grain size of 3 μm or less, and the cumulative frequency ratio calculated from the following formula (1) is 3 or less: Cumulative frequency ratio=D90/D50. In the above-described formula (1), the meanings of the individual symbols are as follows: D90: The crystal grain size (μm) at which the cumulative number of grains as calculated from the smaller grain size side is 90% in the grain size distribution of the crystal grains in terms of the number of grains. D50: The crystal grain size (μm) at which the cumulative number of grains as calculated from the smaller grain size side is 50% in the grain size distribution of the crystal grains in terms of the number of grains.
1. An yttria sintered body having a bending strength of 180 MPa or more and a dielectric loss tan δ of 1×10 −4 or less in the frequency range from 1 to 20 GHz, wherein the yttria sintered body contains yttria of 99.9% by mass or more, has a porosity of 1% or less and an average crystal grain size of 3 μm or less, has a surface roughness (Ra) of 0.05 to 5 μm, and the cumulative frequency ratio calculated from the following formula is 3 or less:
cumulative frequency ratio= D 90/ D 50
where, the individual symbols D90 and D50 are calculated as follows:
D90: the crystal grain size (μm) at which the cumulative number of grains as calculated from the smaller grain size side is 90% in a grain size distribution below; and
D50: the crystal grain size (μm) at which the cumulative number of grains as calculated from the smaller grain size side is 50% in the grain size distribution below,
where the grain size distribution is obtained by the following steps:
(1) taking a photograph of crystal grain microstructure of the yttria sintered body;
(2) measuring a major axis and a minor axis on the crystal grains;
(3) calculating an average grain size by averaging out the major axis and the minor axis; and
(4) counting the number of each average grain size.
2. The yttria sintered body according to claim 1 having an average crystal grain size thereof is 2 μm or less.
3. A component used for a plasma processing apparatus, wherein at least the portion of the component exposed to a halogen-based corrosive gas or the plasma of the halogen-based corrosive gas is constituted with the yttria sintered body according to claim 1 .
4. A component used for a plasma processing apparatus, wherein at least the portion of the component exposed to a halogen-based corrosive gas or the plasma of the halogen-based corrosive gas is constituted with the yttria sintered body according to claim 2 .