JP2644910B2 - Ceramic heater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a ceramic heater such as a thermal CVD heater for a semiconductor manufacturing apparatus.

(Prior art) A ceramic heater, in which a tungsten resistor is embedded in a ceramic substrate such as silicon nitride, has no risk of the resistor being eroded by an atmospheric gas, so a thermal CVD heater for semiconductor manufacturing equipment. Used as etc. In such a ceramic heater, the temperature of the heater is detected by a thermocouple embedded in a part of the ceramic base material, and the power supplied to the resistor is controlled to keep the temperature constant.

However, such a conventional ceramic heater has the following disadvantages.

First, since the temperature of the resistor is transmitted to the thermoelectric element through the ceramic base material, the bonding material of the thermocouple, and the sheath of the thermoelectric element in sequence, even if the temperature of the resistor changes, the thermoelectric element can detect the temperature change. There is a considerable time lag before detection, and there is a drawback that response to disturbance is poor.

Secondly, there is a disadvantage that a measurement error inevitably occurs with respect to the actual temperature of the ceramic base material due to heat dissipation due to conduction and radiation from the wires and sheath portions of the thermoelectric body.

Third, in a ceramic heater used from room temperature to a high temperature range of about 1200 ° C., cracks are liable to occur due to a difference in thermal expansion due to a difference in material of a junction portion of a thermocouple, and stability of temperature measurement conditions is poor. However, if there is a space between the ceramic base material and the sheath of the thermocouple, heat transfer changes due to a change in gas density in the space, and there is a disadvantage that an error occurs in temperature measurement.

Fourth, when a thermocouple is inserted through a hole in the ceramic base material, heat transfer is disturbed similarly to the case where a crack is formed at the junction between the ceramic base material and the thermocouple sheath, causing an error in temperature measurement. There were drawbacks.

(Problems to be Solved by the Invention) The present invention solves such conventional drawbacks, provides a quick response to disturbance, obtains a stable heater temperature and input power, and reduces an error between the measured temperature and the actual temperature. The purpose of the present invention is to provide a ceramic heater capable of performing high-precision temperature control.

(Means for Solving the Problems) The present invention made to solve the above problems has a heater body in which a resistor mainly composed of tungsten or molybdenum is embedded in a dense ceramic base material,
A power supply device for controlling the power supplied to the resistor, wherein the power supply device inputs a resistance / temperature conversion value or a temperature / resistance conversion value to be corrected by a heater temperature via an actual temperature correction mechanism. And a control device in which a change in the resistance value due to the temperature of the resistor is added in consideration of the heater temperature.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

(Example) In FIG. 1, (1) is a disk-shaped heater body,
(2) is a power supply device connected thereto.

The heater body (1) has a resistor (4) containing tungsten as a main component embedded spirally in a dense and gas-tight ceramic base (3) made of silicon nitride. The reason why the resistor (4) containing tungsten as a main component was used as the heat source is that the change in resistivity with temperature was large and monotonous. Further, as shown in FIG. 5, molybdenum also has the same rate of change in electric resistance as tungsten, and can be used as the resistor (4). Since such a resistor (4) is significantly deteriorated and oxidized by contact with a gas, it must be embedded in a gas-tight ceramic substrate (3). The ceramic heater of the embodiment is a thermal CVD for semiconductor manufacturing equipment.
Since the heater is a heater, the upper surface of the ceramic base material (3) has a smooth surface so that the smooth surface wafer (5) can be set. Wirings (6) and (7) made of a material having no loss are drawn out from terminal extraction portions at the center and ends of the spiral resistor (4) and connected to the power supply device (2).

The power supply device (2) may be either AC or DC, but in the embodiment, an AC power supply is used, and output control is performed by a thyristor (8). In the present invention, a value obtained by adding a heater temperature to a change in resistance value due to the temperature of the resistor (4) is used as control information. Therefore, the current supplied to the resistor (4) is extracted by the CT converter (9), and the voltage is reduced.
It is extracted by the PT converter (10) and input to the arithmetic unit (17). Then, the computing unit (17) computes the resistance of the resistor (4) from these currents and voltages, and inputs it to the PID control device (11) incorporating a microprocessor. And PID
The control device (11) calculates the temperature of the resistor (4) from the resistance / temperature conversion table (15) from the value, sends a signal to the thyristor (8) according to the difference from the set temperature, and sends the signal to the resistor (4). Control the supplied power.

FIG. 2 is a block diagram showing the control circuit. In this drawing, the lower limit setting (12) is described in the present invention because when the power supplied to the resistor (4) becomes zero, the outputs of the CT converter (9) and the PT converter (10) are reduced. This means that control cannot be performed, which means that a lower limit is set when the power is reduced. Also in this figure,
Temperature detection (13) means that the heater temperature is detected by a thermocouple as in the past, and the measured value is passed through the actual temperature correction mechanism (14) to the resistance / temperature of the PID controller (11). This means that the conversion information is input to the conversion table (15), and the control information not only uses the resistance value of the resistor (4) but also takes into account the heater temperature measured by the thermocouple. As described above, the heater temperature can be controlled with higher accuracy by using, as the control information, a value obtained by adding the actually measured heater temperature to the change in the resistance value due to the temperature of the resistor (4).

FIG. 3 is a block diagram showing another embodiment of the control circuit. Here, first, a set temperature to temperature / resistance conversion table (16)
, A set voltage is calculated from the current value and the set resistance, and power control is performed so that the difference between the actually measured voltage value and the set voltage becomes zero.

(Operation and Effect) As described above, the ceramic heater of the present invention contains tungsten or molybdenum as a main component in a dense ceramic substrate (3) as the heater main body (1), whose change in resistivity due to temperature is monotonous and large. The power supply device (2) performs power control using control element information in which a resistance value change due to the temperature of the resistor element (4) is added to the heater temperature, while using an embedded resistor element (4). is there.

For this reason, in the present invention, it is possible to control the supply power by immediately detecting a temperature change of the resistor (4), which is a heating element, without a time lag, and as shown in the graph of FIG. Very fast compared to the product. In addition, the occurrence of cracks and the instability of heat transfer at the buried junction of the thermocouple as in the prior art are eliminated, and the resistor (4)
It is possible to accurately detect and control its own temperature, and to perform stable control. Moreover, since the resistor (4) is embedded in the dense and gas-tight ceramic substrate (3), there is no change in the properties of the resistor (4) due to oxidation or deterioration, and a stable resistance value is maintained for a long period of time. can do.

As described above, the ceramic heater according to the present invention has a fast response to disturbance, provides stability of the heater temperature and the input power, and can perform high-precision temperature control without an error between the measured temperature and the actual temperature. Some of the ceramic heaters that have eliminated the conventional problems greatly contribute to industrial development.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a block diagram showing a control circuit thereof, FIG. 3 is a block diagram showing another example of the control circuit, and FIG. And FIG. 5 is a graph showing a change in resistivity depending on the temperature of molybdenum and tungsten. (1): heater body, (2): power supply device,
(3): ceramic substrate, (4): resistor

Claims (1)

(57) [Claims] 1. A heater body (1) in which a resistor (4) containing tungsten or molybdenum as a main component is buried in a dense ceramic base (3), and electric power supplied to the resistor is controlled. A power supply device (2), wherein the power supply device (2) is controlled by inputting a resistance / temperature conversion value or a temperature / resistance conversion value to be corrected by a heater temperature via an actual temperature correction mechanism (14). Equipment (11)
A ceramic heater characterized by comprising: controlling the change of the resistance value due to the temperature of the resistor (4) in consideration of the heater temperature.