To prevent the generation of deflection of a wafer polishing machine due to the pushing force at the time of polishing while remarkably lowering the generation of thermal deflection and while improving the rigidity by forming the wafer polishing machine having a specified coefficient of thermal expansion and a specified Young's modulus.
At least any one of a carrier plate 2 and a surface plate 5 forming a wafer polishing machine is made of the ceramics having a coefficient of thermal expansion at 10-40 of temperature at 1×10-6/°C or less and the Young's modulus at 130 GPa or more. In the polishing process of a semi-conductor wafer 1, even in the case where temperature difference is generated inside of the carrier plate 2 by the generated frictional heat or the like, since the coefficient of thermal expansion is very small, generation of thermal deflection can be restricted remarkably low. Furthermore, since the Young's modulus is raised so as to improve the rigidity, generation of deflection by the pushing force at the time of polishing is prevented. A semi-conductor wafer 1 having the excellent flatness is thereby obtained.