| 摘要 |
An alumina purity of translucent polycrystalline alumina forming a handle substrate is 99.9 percent or higher, and a porosity of the polycrystalline alumina is 0.01% or more and 0.1% or less. A number of pores, each having a size of 0. 5µm or larger and included in a surface region on a side of a bonding face of the handle substrate is 0.5 times or less of a number of pores, each having a size of 0.1 µm or larger and 0.3 µm or smaller and contained in the surface region. |
