Electrostatic chuck and wafer processing apparatus

An electrostatic chuck comprising:

• a ceramic dielectric substrate having a first major surface on which an object to be processed is mounted, and a second major surface on a side opposite to the first major surface, the ceramic dielectric substrate being a polycrystalline ceramic sintered body;
• an electrode layer provided on the ceramic dielectric substrate;
• a base plate provided on a side of the second major surface and supporting the ceramic dielectric substrate;
• and
• a heater provided between the electrode layer and the base plate,
• the base plate having a through hole piercing a portion thereof, the base plate further having a communication path formed internally therein for passing a medium for adjusting a temperature of the object to be processed, and
• wherein, when viewed in a direction perpendicular to the first major surface,
• at least a part of the heater is disposed between the through hole and a first portion of the communication path which is closest to the through hole, said part of the heater having a shape which encloses a portion of the through hole, and
• a part of the communication path, which includes the first portion, has a shape which encloses said portion of the through hole.