Ceramic heater

A ceramic heater, comprising:

• a plate including:
• a first principal surface configured to support a wafer;
• and
• a second principal surface positioned across a gap from the first principal surface in a thickness direction of the plate;
• a resistance heating element which is built in the plate, and which is configured to generate heat through energization;
• and
• a shaft having a tubular shape which is configured to support the plate on the second principal surface side,
• wherein the shaft includes:
• a first end portion which is an end portion on a side bonded to the second principal surface of the plate, and which is formed as a flange;
• a second end portion which is an end portion on a side opposite to the first end portion in an axial direction of the shaft;
• a main body portion which is continuous with the second end portion between the first end portion and the second end portion;
• and
• a root portion which is continuous from the first end portion between the first end portion and the second end portion, and which connects the first end portion and the main body portion to each other,
• wherein a thickness of the root portion gradually increases toward the first end portion, and
• wherein an outer peripheral surface of the root portion is a curved surface being curved away from an inner peripheral surface of the root portion as the root portion extends toward the first end portion, and a curvature radius of the curved surface gradually decreases toward the first end portion.

A ceramic heater, comprising:

• a plate including:
• a first principal surface configured to support a wafer;
• and
• a second principal surface positioned across a gap from the first principal surface in a thickness direction of the plate;
• a resistance heating element which is built in the plate, and which is configured to generate heat through energization;
• and
• a shaft having a tubular shape which is configured to support the plate on the second principal surface side,
• wherein the shaft includes:
• a first end portion which is an end portion on a side bonded to the second principal surface of the plate, and which is formed as a flange;
• a second end portion which is an end portion on a side opposite to the first end portion in an axial direction of the shaft;
• a root portion which is continuous from the first end portion between the first end portion and the second end portion, and which is allowed to have a high temperature equal to or higher than 400°C when the plate is heated to 650°C and the second end portion is cooled to 35°C;
• and
• a main body portion which is continuous with the second end portion between the first end portion and the second end portion, and which is allowed to have a temperature lower than 400°C when the plate is heated to 650°C and the second end portion is cooled to 35°C, and
• wherein a thickness of at least a portion on the first end portion side in the root portion gradually increases toward the first end portion.