Electrostatic chuck

An electrostatic chuck, comprising:

• a ceramic dielectric substrate having a first major surface configured to have a process object placed thereon and a second major surface opposite to the first major surface;
• a base plate supporting the ceramic dielectric substrate;
• and
• a heater unit which heats the ceramic dielectric substrate,
• the heater unit including
• a first power feeding portion,
• a second power feeding portion adjacent to the first power feeding portion, and
• a heater line emitting heat by allowing a current to flow, the heater line being one electrode connecting the first and second power feeding portions,
• the heater line including a plurality of extension portions arranged in a second direction perpendicular to a first direction, the plurality of extension portions extending along the first direction,
• the plurality of extension portions including
• a first extension portion adjacent to the first and second power feeding portions at one side in the second direction, and
• a second extension portion adjacent to the first and second power feeding portions at an other side in the second direction,
• the first extension portion including
• a first portion overlapping the first power feeding portion in the second direction,
• a second portion overlapping the second power feeding portion in the second direction, and
• a third portion positioned between the first portion and the second portion in the first direction, the third portion not overlapping the first and second power feeding portions in the second direction,
• the second extension portion including
• a fourth portion overlapping the first power feeding portion in the second direction,
• a fifth portion overlapping the second power feeding portion in the second direction, and
• a sixth portion positioned between the fourth portion and the fifth portion in the first direction, the sixth portion not overlapping the first and second power feeding portions in the second direction,
• a first distance being a minimum distance in the first direction between the first power feeding portion and the second power feeding portion,
• a second distance being a minimum distance in the second direction between the plurality of extension portions,
• a third distance being a distance in the second direction between the first extension portion and a first virtual tangent,
• the first virtual tangent contacting the first and second power feeding portions along the first direction at the one side in the second direction,
• a fourth distance being a distance in the second direction between the second extension portion and a second virtual tangent,
• the second virtual tangent contacting the first and second power feeding portions along the first direction at the other side in the second direction,
• the third distance and the fourth distance each being not more than the first distance,
• the third distance and the fourth distance each being not more than the second distance.