Composite Wafer and Method for Manufacturing the Same

A composite wafer comprising a supporting substrate and a semiconductor substrate which are bonded to each other by direct bonding,

• wherein the supporting substrate is composed of a polycrystalline translucent ceramic,
• the semiconductor substrate is composed of silicon,
• the total light transmittance from the front at a wavelength of 200 to 250 nm of the supporting substrate is higher than the total light transmittance from the front at a wavelength of 555 nm,
• the total light transmittance from the front at a wavelength of 200 to 250 nm of the supporting substrate is 70% or more,
• the linear transmittance at a wavelength of 200 to 750 nm of the supporting substrate is 30% or less,
• the average crystal grain size of the supporting substrate is 10 to 50 μm,
• the supporting substrate is composed of polycrystalline translucent alumina, and
• the semiconductor substrate is composed of single crystal silicon.