Ceramic heater and method of producing the same

A ceramic heater comprising:

• a disc-shaped ceramic substrate having a wafer placement surface at an upper surface;
• a resistance heater embedded in the ceramic substrate;
• a cylindrical shaft that supports the ceramic substrate from a lower surface of the ceramic substrate;
• a thermocouple path that is provided between the resistance heater and the wafer placement surface and that extends from a start position on a center side to an end position on an outer circumferential side inside the ceramic substrate;
• and
• a thermocouple insertion hole that is open at an inner shaft region of the lower surface of the ceramic substrate surrounded by the cylindrical shaft and that communicates with the thermocouple path;
• wherein the ceramic substrate includes an upper plate having the wafer placement surface on an upper surface side, and a lower plate in which the resistance heater is embedded and which is provided on a lower surface side of the upper plate, wherein the thermocouple path is formed by an upper plate groove provided in a lower surface of the upper plate and the lower plate that covers the upper plate groove, and wherein the thermocouple insertion hole is provided so as to penetrate through the lower plate in a thickness direction;
• wherein a width of the thermocouple insertion hole is smaller than a width of a portion of the thermocouple path communicating with the thermocouple insertion hole, and a width of the thermocouple path positioned closer to an outer circumference of the ceramic substrate than the portion of the thermocouple path communicating with the thermocouple insertion hole is tapered toward the outer circumference;
• and
• wherein the resistance heater has a shape in which the resistance heater extends from one of a first pair of terminals provided in a central portion of the ceramic substrate to an outer circumferential portion of the ceramic substrate, is wired in the outer circumferential portion, and then extends from the outer circumferential portion to reach another of the first pair of terminals, and
• wherein the ceramic substrate is separated into an inner circumferential zone having a small circular shape and an outer circumferential zone having an annular shape by a coaxial virtual boundary,
• the resistance heater includes an inner circumferential resistance heater embedded in the inner circumferential zone and an outer circumferential resistance heater embedded in the outer circumferential zone,
• the outer circumferential resistance heater includes a first jumper extending from one of a second pair of terminals provided in the central portion of the ceramic substrate to the outer circumferential zone and a second jumper extending from another of the second pair of terminals provided in the central portion of the ceramic substrate to the outer circumferential zone,
• the thermocouple insertion hole is provided by utilizing a heater non-existing region where the first jumper and the second jumper face each other.