Thermocouple guide and ceramic heater
A thermocouple guide includes a first tube portion of a straight shape, and a second tube portion connected to the first tube portion and including a curved section that is formed to turn an extension direction from the first tube portion. An outer diameter of at least a tip-side part of the curved section, the tip-side part extending from a tip end of the curved section through a predetermined length, is smaller than an outer diameter of the first tube portion.
1. A ceramic heater comprising:
a ceramic plate formed in a disk-like shape and having a wafer placement surface;
a tubular shaft bonded to a rear surface of the ceramic plate on an opposite side to the wafer placement surface;
an inner-peripheral-side resistance heating element embedded in an inner peripheral zone of the ceramic plate;
an outer-peripheral-side resistance heating element embedded in an outer peripheral zone of the ceramic plate;
associated components including a pair of terminals of the inner-peripheral-side resistance heating element and a pair of terminals of the outer-peripheral-side resistance heating element;
an elongate hole extending from a start point in a region of the rear surface of the ceramic plate, the region being positioned within the tubular shaft when viewed from below, to an end position in an outer peripheral portion of the ceramic plate;
an elongate groove defining an inlet portion of the elongate hole; and
a thermocouple guide comprising:
a first tube portion of a straight shape; and
a second tube portion connected to the first tube portion and formed of a curved section that is formed to turn an extension direction from the first tube portion,
wherein an outer diameter of at least a tip-side part of the curved section, the tip-side part extending from a tip end of the curved section through a predetermined length, is smaller than an outer diameter of the first tube portion, and
wherein-the tip-side part of the curved section is arranged in the elongate groove; and
wherein (i) the curved section has a shape such that the curvature radius gradually reduces toward the tip end of the curved section, (ii) the curved section has a shape such that the curvature radius gradually increases toward the tip end of the curved section, (iii) the curved section has an elliptical arc shape, or (iv) the curved section has a parabolic shape.
2. The ceramic heater according to claim 1 , wherein an inner diameter of at least the tip-side part of the curved section is smaller than an inner diameter of the first tube portion.
3. The ceramic heater according to claim 1 , wherein an outer diameter of the second tube portion along an entire length of the thermocouple guide is smaller than the outer diameter of the first tube portion.
4. The ceramic heater according to claim 3 , wherein an inner diameter of the second tube portion along the entire length of the thermocouple guide is smaller than an inner diameter of the first tube portion.
5. The ceramic heater according to claim 1 , wherein the thermocouple guide includes a curvature radius of the curved section is 20 mm or more and 50 mm or less,
a stroke length of the curved section is 20 mm or more and 50 mm or less, and
the curved section is formed to turn the extension direction from the first tube portion through an angle of 50° or more and 90° or less.
6. The ceramic heater according to claim 1 , wherein the elongate hole is a thermocouple-insertion elongate hole into which a thermocouple is to be inserted.
7. The ceramic heater according to claim 1 , wherein a length of the elongate groove is set to be longer than or equal to a length of the tip-side part of the curved section of the thermocouple guide, the tip-side part being arranged in the elongate groove.
8. The ceramic heater according to claim 1 , further comprising a thermocouple inserted through both the thermocouple guide and the elongate hole.
9. The ceramic heater according to claim 1 , wherein the thermocouple guide is made of metal.
10. The ceramic heater according to claim 1 , wherein the tubular shaft includes a small-diameter portion and a large-diameter portion, and an inner space of the tubular shaft includes a circular cylindrical space with the same diameter as an inner diameter of the small-diameter portion, and an annular expanded space positioned on an outer side of the circular cylindrical space and surrounded by the large-diameter portion.
11. The ceramic heater according to claim 1 , wherein the second tube portion of the thermocouple guide is welded to the first tube portion.