JP2875142B2 - Ultra high vacuum heat treatment apparatus and heat treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for holding a conductive material such as a heat-resistant metal at a high vacuum and a high temperature and performing a heat treatment, an aging treatment and a degassing treatment.

[0002]

2. Description of the Related Art Conventionally, heating and heat treatment in a high vacuum have been widely practiced industrially. As a heating method for performing heat treatment in a vacuum, (1) a method using a thermoelectric conductor that transfers Joule heat generated by winding a nichrome wire or the like around an insulating material such as ceramics and passing a current through the nichrome wire to the insulating material. (2) a method in which the sample is directly heated by self-heating by Joule heat, (3) a method in which the sample is heated by radiation from a heater using a refractory metal such as tungsten, and (4) a conductive sample by high-frequency induction. And (5) a method in which sunlight and infrared rays are collected and heated.

However, when the method (1) is used in a vacuum for heating a sample by thermal conduction and radiation of a solid or gas, the thermal conduction is insufficient and unsuitable. The direct energization method (2) has the advantage that the sample can be heated to a temperature close to the melting point in a relatively wide range of temperature rising rates while maintaining a high vacuum, but a very large power supply device is required because a large current is required. is necessary. Furthermore, since the sample size is limited in cross-sectional area and the sample shape must be uniform, it can be used only for special applications.
The tungsten heater of the above (3) is an indirect heating method by radiation, and therefore has an advantage that it can heat even a material having low thermal conductivity. However, radiation occurs in all directions and heats other than the sample. Therefore, a large-capacity power supply device is required to maintain the temperature at a high temperature. In a vacuum, a large amount of gas is released from a tungsten heater in proportion to the surface area of the heater, and it is impossible to maintain a high vacuum (about 10 ⁻⁷ Torr) at a high temperature. In the high-frequency induction heating of (4), the maximum temperature is not limited, but the sample shape is limited. Further, a high-frequency generator is required and is expensive. Further, the above (5)
In the method of collecting sunlight and infrared rays, it is necessary to hold the sample part in a vacuum through a transparent substance that allows light to pass through,
It is effective only for small volume samples with a narrow soaking range. Therefore, at present, relatively large sample
There is no known method for efficiently heating to 2000 ° C. or higher in a high vacuum of 0 ⁻⁷ Torr or lower.

On the other hand, a heating method using an electron beam is particularly effective in a vacuum, and melting by an electron beam is also performed in a high vacuum. However, in the method in which the voltage is applied to the thermoelectrons emitted from the filaments of the filament and accelerated, the electrons are converged using an electromagnetic coil, and the sample is irradiated with an electron beam having a high energy density, the temperature is not uniform. And the purpose of the heat treatment cannot be achieved. Furthermore, it is difficult to control the temperature raising and lowering rates required for the normal heat treatment (for example, see Japanese Patent Application Laid-Open No. 2-194129). In addition, as a heat treatment method for special shapes, wire
A heating apparatus has been disclosed in which heating is performed by a flow of electrons in a vacuum of ^-3 to 10 ^-5 Torr (JP-A-49-61).
732). However, the above-mentioned device is intended only for heating by electrons generated from the electron generating device, and does not show any effect by radiation. Also,
The sample shape is limited to long and thin metal parts, and a large-volume conductive solid sample cannot be used.
Furthermore, there is no mention of a heating device at high vacuum and high temperature.

[0005]

SUMMARY OF THE INVENTION According to the present invention, a conductive material such as a metal can be efficiently removed while maintaining a high vacuum.
Perform temperature control to an ultra-high temperature of 0 ° C or higher,
It is an object of the present invention to provide an apparatus for performing a degassing process and a heat treatment according to a holding / cooling pattern.

[0006]

The gist of the present invention is as follows. In an apparatus for heat-treating a conductive material under a high vacuum and a high temperature, a high-voltage power supply is provided between an electric circuit A comprising a filament for generating thermoelectrons and a power supply, and a material to be heated 1 so that the material to be heated becomes positive. A heat treatment apparatus comprising: an electric circuit B having a grounded ground. The heat treatment apparatus according to the present invention, further comprising an arithmetic unit that incorporates an ammeter into the electric circuit B and calculates the temperature of the material to be heated based on the current. A heat treatment apparatus, wherein the filament has a coil shape made of a high melting point metal wire (tungsten, molybdenum or tantalum group). A heat source that emits thermoelectrons is placed around a conductive sample in a container with a vacuum exhaust device, and power is supplied to the heat source from an external power supply device to generate heat. Equipped with an external high-voltage power supply that applies a bias voltage that makes the sample more positive than the external power supply between the heat sources, accelerates the thermoelectrons generated from the heat source by the bias voltage, collides with the sample, and the kinetic energy of the electrons An ultra-high-vacuum heat treatment method characterized in that thermal efficiency is improved by converting gas into heat energy.

Hereinafter, the present invention will be described in detail. First,
The ultra-vacuum atmosphere heating device of the present invention will be described with reference to FIG. In a heating device that heats a solid sample by electron impact in an ultra-high vacuum atmosphere, the degree of vacuum is set to 10 ⁻⁸ Torr.
Vacuum evacuation device for maintaining high vacuum and container 6 for holding sample
And a coil-shaped filament 2 composed of a tungsten, molybdenum or tantalum group high-melting metal wire, and a current is applied to both ends of the filament through a filament power supply 3 to perform radiation heating (electric circuit A). . When the filament is heated to a high temperature, thermoelectrons are emitted. The power supply terminal is taken out from the high voltage power supply device 4 into the vacuum by the introduction terminal from the high voltage power supply device 4 and brought into contact with the sample to apply a significantly negative voltage to the filament between the sample and the filament by the power supply device 4 (electric circuit B ). The emitted thermoelectrons are effectively attracted to both surfaces of the sample and collide with the sample surface, converting the kinetic energy of the electrons into heat,
An ultra-high temperature state (1500 ° C. or higher) can be efficiently obtained. The ammeter 5 is installed between the sample and the filament, and the sample temperature is indirectly measured from the current value.

In order to heat and hold a conductive sample with maximum efficiency, heat transfer due to radiation from a heating element and electrons emitted from an electron generator collide with the sample, and the kinetic energy of the electrons is converted into thermal energy. Is most effective. Conventionally, a heating device has been constituted by only one of radiation and collision by electrons. However, the present heating device is a heating device which has not been realized in the past, which realizes heating by radiation and collision of electrons at the same time.

Electron generators include a field emission type and a thermionic emission type. In order to obtain heat and electrons by radiation simultaneously, it is necessary to use a thermionic emission type. Thermions generated by the electron generator have no kinetic energy and return immediately to the source. In order to give sufficient kinetic energy to the generated thermoelectrons, it is necessary to generate a potential difference between the generator and a place at a distance from the generator, and to give the electrons kinetic energy by this potential difference. When a bias voltage is applied between the electron generator and the sample, thermoelectrons having kinetic energy collide with the sample, the kinetic energy is converted into heat energy, and energy conversion occurs with the highest efficiency. The bias voltage to be applied is desirably in a range from a voltage required for accelerating thermoelectrons to a voltage at which damage to the sample surface due to electron impact does not occur.

As a method for obtaining thermoelectrons, a conductor, for example, a high melting point metal from the group of tungsten, molybdenum or tantalum is energized and heated by Joule heat to give an energy higher than the work function, so that electrons are transferred from the metal surface. It needs to be released outside. An electron generator which applies a current to a plate-like or thin-line high-melting metal and gives energy by Joule heat has a simple structure and is easy to handle. The power supply for the electron generator must be a power supply capable of supplying the amount of electricity required to heat the metal above the temperature at which thermionic electrons are emitted.

In order to generate, accelerate, and collide electrons with a sample, a vacuum atmosphere is required. As the degree of vacuum increases, the loss of energy due to collision of electrons and gas molecules decreases, which is more effective. The ultra-high vacuum atmosphere can easily achieve a degree of vacuum of 10 ⁻⁸ Torr or less by a turbo molecular pump, a cryopump, an ion pump, or the like.

The biggest problem when heating in an ultra-high vacuum is that the gas component adsorbed on the chamber, the heating element, or the sample or diffused as a solid solution in the solid in a solid state is diffused and released as a gas from the surface. Therefore, a high vacuum cannot be maintained. In order to suppress the released gas, a method of heating and baking at about 200 ° C. while keeping the apparatus under vacuum has been adopted. However, when the heat treatment furnace is maintained at a high temperature, atoms or gases corresponding to the equilibrium vapor pressure are released from the conductor used for the apparatus or the heating element, and a high vacuum higher than the equilibrium vapor pressure cannot be achieved theoretically. However, in the heating device, the metal has a solid solution of hydrogen, oxygen, nitrogen, etc.
Since these atoms are released as gas components from the heating element and the metal that forms its surroundings, it is possible to achieve a vacuum degree much lower than the theoretically reached vacuum degree. In order to solve this problem, there is a need for a method of efficiently heating the sample with a small heat source in order to increase the evacuation speed and keep portions other than the sample as high as possible.

In the apparatus according to the present invention, since the heat source is in the form of a coil made of a high melting point metal wire, the volume required to give the same amount of heat can be significantly reduced as compared with a normal mesh-shaped heating element. Therefore, the surface area can be reduced. By reducing the surface area of the heating element, gas generation from the heating element can be suppressed to a small extent.

When heat treatment of a sample is performed using a heating device, the amount of heat generated per unit time is controlled, and it is necessary to control the heating rate, the cooling rate, and the constant temperature for a fixed time for various patterns. No. This heating apparatus can control the temperature of the sample by controlling the current flowing through the conductor and changing the amount of generated thermoelectrons.
When an electric current is applied to a conductor, for example, a coil-shaped filament composed of a refractory metal wire of the tungsten, molybdenum or tantalum group, it is heated by Joule heat.

Heating by Joule heat is given by the following equation. Resistance value R = ρ (L / A) (1) Generated Joule heat J = RI ² (2) where L is the length of the filament, A is the cross-sectional area of the filament, ρ is the constant efficiency, and I is the current. . The filament is heated by Joule heat, and the sample is heated by radiation from the heated filament. Further, the amount of thermoelectrons generated from the filament is shown as a function of the filament temperature, and increases sharply as the filament temperature increases. Therefore, by controlling the current supplied to the filament, the filament temperature can be controlled, and the amount of radiation and the amount of thermoelectrons can be controlled simultaneously. The sample temperature is measured by a thermocouple, a radiation thermometer, or the like. By controlling the filament temperature by feeding back the difference between the sample temperature value and the set temperature value, the sample temperature can be controlled. Therefore, it has become possible for the first time to perform a heat treatment at a predetermined temperature pattern under a high vacuum.

The kinetic energy U of the generated electrons is U = neV (3) where e is the electric charge per unit, n is the number of electrons generated per unit time from the electron generator, and V is the filament and sample. Potential difference between the two. Therefore, the kinetic energy of the electrons can be controlled by controlling the potential difference V, and the energy given to the sample by the collision of the electrons can be accurately changed. The total energy W received by the sample is the sum of the energy U obtained by the collision of the radiation J due to Joule heat with the electrons, assuming an ideal state. W = J + U (4) As is apparent from the equation (4), the heating efficiency is remarkably improved due to the addition of energy due to the collision of electrons, as compared with the heating method using radiation.

The number of electrons hitting the sample can be detected as a bias current flowing between the sample and the filament. The number of colliding electrons coincides with the number of electrons because all the electrons generated from the filament collide with the sample. The number of electrons generated from the filament depends on the filament surface temperature,
Is known. Therefore, the filament temperature can be easily estimated by measuring the bias current flowing between the sample and the filament.

Although the sample temperature can be measured with a radiation thermometer, a thermocouple or the like, the measurement is unstable in the case of a radiation thermometer,
It is not suitable for use as a temperature control signal. Since a bias voltage is applied when a thermocouple is used, it is necessary to use a thermocouple protected by a nonconductor. Furthermore, there is no guarantee that the actual sample temperature will be accurately measured, being affected by changes in the bias voltage. To determine the sample temperature, the radiation thermometer is corrected by measurement using a radiation thermometer and measurement using a thermocouple in a state of bias OV.
Further, by measuring the bias current and measuring the bias current with the bias applied, and collecting the standard data, it is possible to estimate the sample temperature only by measuring the bias current value thereafter. .

According to the above principle, the heating apparatus of the present invention provided with the heating method by the collision of radiation and electrons has a remarkable heat energy ratio of the sample to the input energy compared with the conventional vacuum heating apparatus. Improved.

[0020]

EXAMPLES The present invention will be further described below with reference to examples. An ultra-high-temperature atmosphere heat treatment furnace having an ultra-high vacuum device and a tungsten filament shown in FIG. 1 was produced. A cry pump was used for ultra-high vacuum evacuation, and the arrival vacuum degree after baking was 1 × 10 ⁻⁸ Torr. For the filament, use a tungsten wire with a diameter of 1 mm and an inner diameter of 8 mm.
A coil shape of 0 mm and 7 turns was used. As a sample, 5
A columnar tungsten sample of 0φ × 50 mm was used.

As the filament power supply, a 5 kW DC power supply was used. Further, as a bias power supply, a maximum voltage of 1 k
Using a DC high-voltage power supply having an output of eV2A, the positive terminal was brought into contact with the sample, and the negative terminal was connected to the filament. The thermocouple was insulated from the sample and placed immediately adjacent to the sample.

The sample is placed on a tungsten sample table,
Evacuation was performed. A heating experiment was performed in an ultra-high vacuum atmosphere. The tungsten heater current and voltage and the input power at each sample temperature are shown. The degree of vacuum at each temperature was also measured. For temperature control, a temperature change from the thermocouple was input to the controller, and PID control was performed in the controller to control the filament current and voltage. Further, a tungsten heater current and a voltage bias current in a state where bias voltages of 200 V and 500 V are applied,
It shows the power supplied from the two power supplies. Each temperature was maintained for 30 minutes or more, and sufficient temperature control was possible with an accuracy within ± 1 ° C.

The filament current at each sample temperature when performing only filament heating according to Comparative Example an electric circuit A, as a comparative example the total input power represented by filament voltage, further their product, shown in Table 1.

[0024]

[Table 1]

Embodiment 1 A current value / voltage value of a filament power supply when a bias voltage of 200 V is applied by an electric circuit B while controlling a filament current by an electric circuit A and a temperature controller, and a bias current detected from a bias power supply device Value, and the total input power, filament current X
Table 2 shows the voltage + bias current X voltage. Here, the power reduction rate is a value obtained by dividing the difference between the total applied power when the bias power is not applied and the case where the bias is applied at 200 V in the comparative example by the total applied power in the first embodiment.

[0026]

[Table 2]

Embodiment 2 When a bias voltage of 500 V is applied by the electric circuit B under the same conditions as in Embodiment 1, the current value / voltage value of the filament power supply, the bias current value detected from the bias power supply, and the total input power Table 3 shows the power reduction rates.
Further, the degree of vacuum at each temperature was measured. Table 3 also shows the results.

[0028]

[Table 3]

According to the ultra-high vacuum heat treatment apparatus of the present invention, as is apparent from Tables 1 to 3, the heating efficiency is greatly improved compared with the conventional apparatus, even if the input green space or the power reduction rate is compared. ing. Further, the degree of vacuum is improved by a factor of 5 as compared with the case of conventional filament heating, and a high degree of vacuum can be maintained even in an ultra-high temperature range.

[0030]

According to the present invention, the heating efficiency is greatly improved, the degree of vacuum is also improved, and a high degree of vacuum can be maintained in an ultra-high temperature range. Alternatively, the degassing reaction can be performed economically and effectively.

[Brief description of the drawings]

FIG. 1 is a schematic view of an ultra-high temperature vacuum heat treatment apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 1 sample 2 filament 3 filament power supply 4 high voltage power supply (bias power supply) 5 ammeter 6 vacuum vessel

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) C21D 1 / 34,1 / 773 H05B 3/00 B22F 3/10 F27B 5 / 04,9 / 04,14 / 04 F27D 7/06 H01L 21/22

Claims (4)

(57) [Claims] 1. An apparatus for heat-treating a conductive material under high vacuum and high temperature, wherein an electric circuit A comprising a filament 2 for generating thermoelectrons and a power supply 8 and a material 1 to be heated are interposed between the material 1 to be heated and the filament 2. A heat treatment apparatus having an electric circuit B in which a high-voltage power supply 4 is installed so that 1 becomes positive. 2. The heat treatment apparatus according to claim 1, further comprising an arithmetic unit that incorporates an ammeter into the electric circuit B and calculates the temperature of the material to be heated based on the current. 3. The heat treatment apparatus according to claim 1, wherein the filament has a coil shape made of a refractory metal wire of a tungsten, molybdenum or tantalum group. 4. A heat source for emitting thermoelectrons is arranged around a conductive sample in a container having a vacuum exhaust device, and power is supplied to the heat source from an external power supply to generate heat, and the sample is heated by radiation. At the same time, an external high-voltage power supply is provided between the sample and the heat source that applies a bias voltage that makes the sample side positive by an external power supply, and the thermoelectrons generated from the heat source are accelerated by the bias voltage and collide with the sample. A heat treatment method characterized by improving thermal efficiency by converting kinetic energy possessed by the material into heat energy.