r
=

(

K
·
λ

)

/
βcosθ

(
1
)

- r: grain diameter
- K: Scherrer constant
- λ: wavelength of X-rays used in measurement
- β: width at half maximum
- θ: Bragg angle

In the present embodiment, the ceramic member 10p (FIG. 2A) to be subjected to the laser processing is formed from α-alumina, and thus the inner portion of the holding member 10 relative to the holding surface 10f is also formed from the α-alumina. Meanwhile, the vicinity of at least the bottom surface 16B out of the side surfaces 16S and the bottom surface 16B is formed from γ-alumina obtained by transition from the α-alumina due to the laser processing. The presence of the γ-alumina is ascertained on the basis of the fact that the relative intensity has become high near a peak position of the γ-alumina in an XRD pattern obtained by performing measurement on the holding surface 10f through the thin film XRD.

Since the first ceramic crystal grains correspond to ceramic crystal grains obtained by partially cutting the second ceramic crystal grains through the laser processing, the ceramic crystal grains forming at least the bottom surface 16B out of the side surfaces 16S and the bottom surface 16B delimiting the recess 16 include ceramic crystal grains (e.g., the crystal grains p1 and p2 in FIG. 3C) each having an inside that is exposed toward the surface as the bottom surface 16B.

In observation of a cross section of the holding member 10 by using an SEM, a plurality of minute pores (cavities) were found near the bottom surfaces 16B. The shapes of the ceramic crystal grains forming the bottom surfaces 16B had tendencies to be rounded to a larger extent than the shapes of the ceramic crystal grains forming bottom surfaces of recesses formed through the blast processing. The lengths of cracks extending from inside the holding member 10 to the bottom surfaces 16B had tendencies to be shorter than the lengths of cracks extending from inside the holding member 10 to the bottom surfaces of the recesses formed through the blast processing. The number of the cracks extending from inside the holding member 10 to the bottom surfaces 16B had a tendency to be smaller than the number of the cracks extending from inside the holding member 10 to the bottom surfaces of the recesses formed through the blast processing. As described with reference to FIGS. 3B and 3C, the surface roughnesses of the bottom surfaces 16B had tendencies to be lower than the surface roughnesses of the bottom surfaces of the recesses formed through the blast processing.

As described above, according to the holding member 10 of the present embodiment, at least the bottom surfaces 16B of the holding surface 10f are formed from the first ceramic crystal grains, and the inner portion of the holding member 10 relative to the holding surface 10f is formed from the second ceramic crystal grains. Furthermore, the first grain diameter as the grain diameter of the first ceramic crystal grains is smaller than the second grain diameter as the grain diameter of the second ceramic crystal grains. Consequently, since at least the bottom surfaces 16B of the holding surface 10f are formed from the first ceramic crystal grains having the first grain diameter smaller than the second grain diameter, the sizes of particles to be generated from the holding surface 10f at the time of using the holding member 10 can be decreased. In addition, the first ceramic crystal grains correspond to ceramic crystal grains obtained by partially cutting the second ceramic crystal grains, and thus each of the bottom surfaces 16B formed from the first ceramic crystal grains contains ceramic crystal grains each having an inside (the inner portion of the crystal grain relative to a corresponding grain boundary) that is exposed toward the bottom surface 16B. That is, less grain boundaries are exposed from the bottom surface 16B, whereby the plasma resistance of the holding surface 10f including such a bottom surface 16B can be improved.

In addition, according to the holding member 10 of the present embodiment, the grain diameter (second grain diameter) of the ceramic crystal grains forming the inner portion of the holding member 10 relative to the holding surface 10f is larger than the grain diameter (first grain diameter) of the ceramic crystal grains forming the bottom surface 16B. When the grain diameter of crystal grains is small, the grains are in contact with each other to a larger extent, whereby heat loss tends to increase. Meanwhile, in the holding member 10 of the present embodiment, the grain diameter of the ceramic crystal grains forming the inner portion of the holding member 10 relative to the holding surface 10f is the second grain diameter larger than the first grain diameter, and thus the grains in this portion are in contact with each other to a smaller extent, whereby the heat loss at this portion can be decreased.

In addition, in the holding member 10 of the present embodiment, the bottom surface 16B delimiting each of the recesses 16 is formed from the first ceramic crystal grains. Consequently, the sizes of particles to be generated, while the holding member 10 is holding the semiconductor wafer W as a target object, from the holding surface 10f by flow of an inert gas between the semiconductor wafer W and the recess 16 can be decreased.

In addition, in the holding member 10 of the present embodiment, at least the bottom surface 16B out of the side surfaces 16S and the bottom surface 16B corresponds to a laser processing surface. Consequently, the bottom surface 16B as a laser processing surface is a surface obtained by finely cutting each of the ceramic crystal grains progressively from a corresponding grain boundary toward the inside of the grain, and thus the first grain diameter of the first ceramic crystal grains is smaller than the second grain diameter. Therefore, a holding member 10 in which the first grain diameter is smaller than the second grain diameter can be accurately provided. In addition, the surface roughness of the laser processing surface can be made lower than the surface roughness of a blast processing surface obtained by performing blast processing that involves separating crystal grains over the entireties thereof along respective grain boundaries. That is, increase in surface area due to surface roughness can be suppressed. As a result, the surface area within which corrosion due to plasma occurs is decreased, whereby generation of particles through corrosion due to plasma can be suppressed.