# Patent

## Title
Electron bombardment heating apparatus and temperature controlling apparatus and control method thereof

## Abstract

An electron bombardment heating apparatus, in which thermions emitted from filaments 9 are accelerated and impinge upon a heating plate 2, so as to heat the heating plate 2, wherein a peripheral wall of a heated material supporting member 1 having a heating plate as a ceiling thereof is made of multi-staged peripheral wall portions 13a and 13b, positioned vertically and having a different radius, and those peripheral wall portions 13a and 13b are connected with each other by means of a ring-like horizontal wall 5. With this, thermal stress can be mitigated, which is caused due to a difference in temperature between the lower end portion of the heated material supporting member 1 and the heating plate 2 when heating up the heating plate 2, thereby causing no breakage in the heated material supporting member when conducting heating and cooling upon the heating plate, repetitively.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heating apparatus for heating a material, such as, a semiconductor wafer, etc., to a high temperature, and in particular, an electron bombardment heating apparatus of a type in which accelerated electrons collide or impinge upon a heating plate, thereby generating heat thereon, and it relates to such an electron bombardment heating apparatus, in particular, which is superior in thermal stress-resistance, and also a temperature controlling apparatus and a control method of such an electron bombardment heating apparatus, enabling both; i.e., an increase of temperature with stability and a maintenance of steady temperature.
2. Description of Prior Art
In processes for treating semiconductor wafers, etc., an electron bombardment heating apparatus of such a type, in which accelerated electrons strike or impinge upon the rear surface of a heating plate, thereby generating heat thereon, is widely used as a means for heating up a plate-like material, such as a semiconductor wafer, etc. In such an electron bombardment heating apparatus, thermions generated through conduction of electricity into a filament are accelerated under a high voltage to impinge upon the rear surface of the heating plate, thereby generating heat in the heating plate and a plate-like material mounted on that heating plate is heated.
FIG. 6 attached herewith shows an electron bombardment heating apparatus, relating to the conventional art. In this FIG. 6, though not shown in the figure, an upper portion of a stage portion 106 is located inside of a vacuum chamber and a portion of a heating plate 102 is located with a vacuum atmosphere.
In a wall of the stage portion 106, there is formed a coolant passage 107, and through this coolant passage 107 flows a coolant therein, such as water, etc., for example, thereby cooling the stage portion 106.
On this stage portion 106, there is provided a heat-resistive member 101 for supporting a material to be heated (hereinafter, being called by a “heated material supporting member”), having the flat heating plate 102 thereon, on which a thin plate-like material, such as a silicon wafer, for example, can be mounted to be heated, and within the inside thereof, there is defined a space which is hermetically separated from an outside space thereof. In more detail, the heated material supporting member 101 is closed by means of the heating plate 102 on an upper surface side thereof, while being opened on a lower surface side, thereby having a cylinder-like shape. A lower end portion of the heated material supporting member 101 is fixed, abutting an upper surface of the stage portion 106, and is also hermetically sealed by means of a vacuum seal member 108.
As a material for building the heated material supporting member 101, for example, a heat-resistive silicon carbide impregnated with silicon, or a ceramic, such as, alumina (or aluminum oxide) or silicon nitride, etc., is used. In a case where the heated material supporting member 101 is made of an insulating material, such as silicon-impregnated silicon carbide, for example, an inner surface of the heating plate 102 is metallized for forming a conductive film thereon, and this conductive film is grounded through the stage portion 106.
On the stage portion 106 is formed an exhaust passage 104, and the space defined within an inside of the heated material supporting member 101 is evacuated by means of a vacuum pump 105, which is connected to that exhaust passage 104, thereby bringing about a vacuum condition therein.
Further, within the inside of the heated material supporting member 101, there is provided filaments 109. Those filaments 109 are located behind the heating plate 102 of the heated material supporting member 101, and further, reflectors 103 are provided in the rear side of the filaments 109, for the purpose of heat blocking. To those filaments 109 mentioned above are connected a filament heating electric power source 110. Further, between those filaments 109 and the heating plate 102 is applied an acceleration voltage through the heated material supporting member 101 from an electron acceleration electric power source 111. However, the heating plate 102 is grounded, and therefore it is kept to be a positive potential with respect to those filaments 109.
In such an electron bombardment heating apparatus as was mentioned above, thermions are discharged from those filaments 109 when conducting electricity into the filaments 109 from the filament heating electric power source 110 while also applying the acceleration voltage of a certain high voltage between the filaments 109 and the heating plate 102 through the electron acceleration electric power source 111, and those thermions are accelerated under the acceleration voltage mentioned above, thereby impinging upon the lower surface of the heating plate 102. For this reason, the heating plate 102 is heated due to the electron bombardment.
When the temperature of the heating plate 102 rises, while measuring the temperature of the heating plate 102 due to the electromotive force generated in a thermocouple 112 by means of a thermometer 114, and when the temperature of the heating plate 102 reaches a predetermined value, the electric power supplied to the filaments 109 comes down in an electric power adjustor 117, thereby maintaining the temperature of the heating plate 102 at the predetermined value and, when passing a predetermined time period, the electricity is stopped to be conducted into the filaments 109, thereby stopping the heat generation of the heating plate 102, while cooling is started by means of the coolant flowing through the coolant passage formed in the stage portion 106, thereby lowering the temperature of the heating plate 102.
The heated material supporting member 101 is cooled down on the lower end surfaces thereof, through a coolant, such as water, etc., flowing through the coolant passage 107 of the stage portion 106; e.g., via the stage portion 106. On the other hand, the heating plate 102 building up an upper wall of the heated material supporting member 101 is heated through the bombardment of the electrons, which are discharged from the filaments 109 and accelerated by means of the electron acceleration electric power source 111 of a high voltage. For this reason, a steep thermal gradient is established, in particular, between the heating plate 102 for building up the upper wall of the heated material supporting member 101 and the lower end portion of the heated material supporting member 101 in contact with the stage portion 106.
However, the heated material supporting member 101 is made of, for example, heat-resistive silicon carbide impregnated with silicon, or a ceramic, such as, alumina (or aluminum oxide), or silicon nitride, etc. Therefore, it is weak in thermal stress. For this reason, when starting the heating of the heating plate 102, only the heating plate 102 for building up the upper wall of the heated material supporting member 101 shows thermal expansion. Accompanying this, the heated material supporting member 101 deforms and the thermal stress is concentrated, in particular, upon a shoulder portion defined between a peripheral wall portion and the heating plate 102 and, if repeating the heating and the cooling on the heating plate 102, the heated material supporting member 101 receives the thermal stress, respectively, and therefore, there is brought about a problem that it fatigues and deteriorates, gradually, thereby resulting in the breakage thereof.
BRIEF SUMMARY OF THE INVENTION
According to the present invention, by taking the problems mentioned above in relation to a conventional electron bombardment heating apparatus into consideration, an object is to provide an electron bombardment heating apparatus with which the thermal stress can be relieved or mitigated, which is generated due to the difference in temperature between the heating plate, which is heated through the electron bombardment of the heated material supporting member thereon, and the lower end portion of the heated material supporting member, which is cooled down through the stage portion. With this, the heated material supporting member hardly fatigues, even when repeating the heating and cooling on the heating plate, thereby causing no breakage therein for a long time period.
According to the present invention, for accomplishing the object mentioned above, a heated material supporting member having a heating plate as a ceiling thereof is formed into, not a cylindrical shape having a single radius, but that having at least one (1) stage or more in a middle portion thereof. Namely, upper and lower portions of the heated material supporting member are made up with multi-staged peripheral wall portions in a cylinder-like shape and having different radii thereof, and those peripheral portions are connected by means of a ring-like horizontal wall extending into the radial directions thereof. With this, thermal stress caused due to the difference in temperature between the heating plate of the heated material supporting member and the lower end portion thereof can be mitigated, by means of the multi-staged peripheral wall portions and the horizontal wall connected therewith, thereby protecting it from breaking in an early stage thereof.
Thus, according to the present invention, there is provided an electron bombardment heating apparatus for heating a heating plate through bombardment of thermions thereon, comprising: a filament for generating thermions therefrom; means for accelerating the thermions emitted from said filament; a heating plate which is heated through bombardment of the thermions, which are emitted and accelerated; and a heated material supporting member for mounting a material to be heated thereon, wherein a peripheral wall of said heated material supporting member, which is covered with said heating plate on a ceiling thereof, is made up with a plural number of stages of peripheral wall portions disposed vertically and which are different from each other in the diameter thereof, and those peripheral wall portions are connected with each other through a ring-like horizontal wall extending in radial directions thereof.
With such an electron bombardment heating apparatus, according to the present invention, since the peripheral wall of the heated material supporting member, including the heating plate as a ceiling thereof, is made with the multi-stage peripheral wall portions, having different radii, in the vertical direction thereof, and since those peripheral wall portions are connected with each other through the ring-like horizontal wall extending into the radial directions thereof, the thermal stress can be mitigated, by means of the multi-stage peripheral wall portions and the horizontal wall connecting therewith, if a difference is caused in the temperature between the heating plate of the heated material supporting member and the lower end portion thereof, when heating. In particular, since the shoulder portion formed on the heated material supporting member, where the thermal stress can concentrate thereupon, easily, comes to be more than (1) piece, therefore, it is difficult for the thermal stress to concentrate on a specific shoulder portion. Accordingly, it is possible to make the thermal stress small, which is applied to the heated material supporting member as a whole, and even if repeating the heating and the cooling down to room or a steady temperature, it can be protected from breaking during the early stage thereof.
Further, according to the present invention, an insulator plate having a high insulating property and heat-resistance, such as, a ceramic plate, etc., is inserted between the plural numbers of the metal reflectors. The reflector 3 below the insulator plate 20 is one, and is provided for the purpose of heat insulation but without electrical connection, and the reflector(s) above the insulator plate 20 is/are one(s), having the functions of both, i.e., preventing electrons from discharging to a rear side thereof and heat insulation.
Further, according to the present invention, in such an electron bombardment heating apparatus as was mentioned above, the thermal control when raising up the temperature and the thermal control when maintaining at a steady temperature are carried out by means of separate control methods. In more detail, when raising the temperature, the total amount of the energy of the electrons impinging upon the heating plate is controlled to be constant by controlling the electric power supplied to the filament while measuring the emission current, thereby maintaining the thermal gradient at the present value. In addition, the temperature of the heating plate is measured and after the heating plate reaches the predetermined temperature, the electric power for conducting electricity to the filament is based on the measured value of the temperature, thereby maintaining the heating plate at the predetermined value that is set in advance.
A temperature controlling apparatus, according to the present invention, for achieving such the thermal control as was mentioned above, comprising: an electrical power adjuster for controlling the filament electric power to be supplied to the filament; an emission current adjuster for measuring emission current flowing between the filament and the heating plate and for outputting a measurement value of the emission current to said electric power adjuster as a control signal; and a thermal adjuster for measuring the temperature of the heating plate and for outputting the measured temperature value to said electric power adjuster as a control signal, wherein either one of said emission current adjuster or said thermal adjuster is selectively exchanged to be connected with the electric power adjuster, by means of a switch.
A method for controlling the temperature of the heating plate, by means of the temperature controlling apparatus, including therein an electric power adjuster for controlling the filament electric power to be supplied to the filament, comprising the following steps of: controlling the emission current to a preset value by means of said electric power adjuster, while measuring the emission current flowing between the filament and the heating plate by means of an emission current adjuster, when the temperature of the heating plate raises; and also controlling the temperature of the heating plate to be a preset temperature by means of said electric power adjuster, while measuring the temperature of the heating plate by means of a thermal adjuster, after the measured temperature reaches a preset temperature. In this instance, a switch is changed over when the measured value of the temperature measured by said thermal adjuster reaches the preset temperature or a temperature a little bit lower than the preset temperature.
With the temperature controlling apparatus and the method for the electron bombardment heating apparatus, the emission current flowing between the filament and the heating plate is set in advance, and then when the temperature of the heating plate raises, said electric power adjuster is controlled by means of the emission current adjuster so that the emission current becomes constant while measuring this emission current. With this, it is possible to give a constant electron bombardment upon the heating plate per hour, thereby obtaining a constant thermal gradient with stability.
At the same time, measuring the temperature of the heating plate by means of the thermal adjuster, the electric power adjuster is switched to the side of the thermal adjuster when the temperature of the heating plate reaches the predetermined valve, thereby conducting the thermal control with feeding the temperature of the heating plate back to the electric power adjuster. With this, it is possible to maintain the predetermined temperature at a steady condition, with accuracy and stability.
In this manner, with the electron bombardment heating apparatus according to the present invention, since the thermal stress accompanying the thermal change is dispersed due to the plural number of stages of the heated material supporting member and the horizontal wall, fatigue breaking hardly occurs thereon in spite of the thermal stress, which is caused by repeating the heating and cooling respectively. For this reason, it is possible to protect the heated material supporting member from being destroyed in the early stage and thereby obtain a heated material supporting member having a longer lifetime.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Those and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings wherein:
FIG. 1 is a vertical cross-section view of an outlook structure of an electron bombardment heating apparatus, for showing an embodiment according to the present invention;
FIG. 2 is a cross-section view of a principle portion of the electron bombardment heating apparatus, in particular, for showing a portion of a heated material supporting member thereon, in the embodiment mentioned above;
FIG. 3 is a graph attaching a chart therein, for showing an example of the relationships between time and temperature when heating up the heating plate, and also the chart of temperature control at that instance therein;
FIG. 4 is a vertical cross-section view of an outlook structure of an electron bombardment heating apparatus, for showing another embodiment according to the present invention;
FIG. 5 is a vertical cross-sectional view of an outlook structure of an electron bombardment heating apparatus, for showing another embodiment according to the present invention, in which the structure of a reflector portion is changed; and
FIG. 6 is a vertical cross-section view of an outlook structure of the electronic bombardment heating apparatus, according to the conventional art.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments according to the present invention will be fully explained, by referring to the drawings attached herewith.
FIG. 1 is a cross-section view of an outlook structure of the electron bombardment heating apparatus and shows an embodiment according to the present invention, wherein an upper portion of a stage portion 6 is located within a vacuum chamber, and a portion of a heating plate 2 is within a vacuum atmosphere, in the similar manner of the conventional art, as was mentioned above by referring to FIG. 6.
In a wall of the stage portion 6 is formed a coolant passage 7, and the stage portion 6 is cooled by a coolant, such as water, etc., flowing through coolant passage 7.
On this stage portion 6 is provided a heat-resistive member 1 for supporting a material to be heated (hereinafter called a “heated material supporting member”), having the flat heating plate 2 thereon, on which a thin plate-like material, such as a silicon wafer, etc., can be mounted to be heated, and within an inside thereof, there is defined a space which is hermetically separated from the outside thereof. In more detail, the heated material supporting member 1 is closed by means of the heating plate 2 on an upper surface side thereof, while being opened on a lower surface side thereof, thereby having a cylindrical shape, and a flat upper surface of the heating plate 2 is wider than the thin plate-like material to be heated, such as, a silicon wafer, etc. A flange is provided at the lower end portion of the heated material supporting member 1, and this flange portion is fixed on an upper surface of the stage portion 6 abutting thereon, and it is hermetically sealed by means of a vacuum seal member 8.
The heated material supporting member 1 is made of silicon carbide impregnated with silicon, or a ceramic, such as, alumina (or aluminum oxide) or silicon nitride, etc. In the case where the heated material supporting member 1 is made of an insulating material, such as, silicon-impregnated silicon carbide, for example, an inner surface of the heating plate 2 is metallized for forming a conductive film thereon, and this conductive film is grounded through the stage portion 6. Also, the same object can be achieved, by including conductive materials within the material for building up the heating plate 2, so as to let it show conductivity.
As is shown in FIG. 1, a peripheral wall of the heated material supporting member 1 is large in diameter at a lower stage thereof and small in radius at an upper stage thereof.
Therefore, it has a cylindrical shape of two (2) stages. The peripheral wall portion 13b is large in radius at the lower stage and the peripheral wall portion 13a is small in radius at the upper stage and are connected with a ring-like horizontal wall 5, extending into a radial direction of the peripheral wall. Those peripheral wall portions 13a and 13b have a different radius and the horizontal wall 5 connecting them may be formed, preferably, in one body or as one unit.
In the stage portion 6 is formed an exhaust passage 4, and the space defined within an inside of the heated material supporting member 1 is evacuated by means of a vacuum pump 5, which is connected to that exhaust passage, thereby bringing about a vacuum condition therein.
Further, within the inside of the heated material supporting member 1, there are provided filaments 9 and reflectors 3.
The filaments 9 are provided in the rear side of the heating plate 2 of the heated material supporting member 1, and to those filaments 9 is connected a filament heating electric power source 10 through an insulator seal terminal. This filament heating electric power source 10 is insulated, so that the voltage is high at a side of the filaments 9 while it is low at a side of a voltage adjuster 17. Furthermore, between the filaments 9 and the heating plate 2 is applied a voltage for acceleration through the heated material supporting member 1, by means of an electron acceleration electric power source 11. However, the heating plate 2 is grounded, and it is kept at a positive potential with respect to the filaments 9.
The reflectors 3 are provided in the rear side of the filaments 9, with respect to the heating plate 2 of the heated material supporting member 1. This reflector is made of a metal having a high reflectivity, such as gold (Au), silver (Ag), etc., or a metal having a high melting point, such as, molybdenum, etc. A surface of the reflector 3, opposing the heating plate 2 of the heated material supporting member 1, is made of a mirror surface, thereby reflecting the radiant heat thereupon. Though being electrically insulated from the heated material supporting member 1, however, those reflectors 3 are positioned under the potential condition of being about equal to that of the filaments 9. With this, no electron comes flying toward the reflectors 3, thereby causing no heating due to the electron bombardment thereupon. Such filaments 9 can be disposed in duplicate.
In the central portion of the reflector 3, a shield 15 made from a cylinder-like conductor stands up, and this shield 15 and the reflectors 3 are electrically connected with each other; i.e., are equal in the potential thereof. An upper end side of this shield 15 reaches up to the vicinity of the lower surface of the heating plate 2 of the heated material supporting member 1, while a flange is provided extending from the upper end portion of that shield 15 to the outside, and therefore this flange faces the lower surface of the heating plate 2.
A sheath-type thermocouple 12 is inserted vertically from the central portion of the stage portion 6 mentioned above, as a temperature measuring element, and an upper end side of this is disposed within the shield 15 under a non-contacting condition thereon. The upper end of this thermocouple 12, connecting a pair of lines of the thermocouple as a junction, builds up a temperature measurement point within the shield 15 mentioned above, and the temperature measurement point is in contact with the lower surface of the heating plate 2 via an insulator tube. The thermocouple 12 is wired out from stage portion 6 into an outside of the vacuum chamber, and a compensation lead wire is connected to a thermometer 14 including a zero point compensation circuit therein.
With such an electron bombardment heating apparatus, the thermions are emitted from the filaments 9 when conducting electricity to the filaments 9 by means of the filament heating electric power source 10, while applying a certain high voltage for acceleration between the filaments 9 and the heating plate 2, by means of the electron acceleration electric power source 11, and those emitted thermions are accelerated under the acceleration voltage mentioned above, and impinge upon the lower surface of the heating plate 2. For this reason, the heating plate 2 is heated due to the electron bombardment thereupon. In this instance, the coolant flows through the coolant passage 7 formed in the stage portion 6, and thereby the heated material supporting member 1 is cooled.
The temperature of the heating plate 2 rises, while measuring the temperature of the heating plate 2 by means of the thermocouple 12, and when the temperature of the heating plate 2 reaches a predetermined value, then the filament heating electric power source 10 for conducting electricity to the filaments 9 is lowered in the electric power thereof, and then the heating plate 2 is maintained at a predetermined temperature. When passing a predetermined time period, the electricity flow is stopped into the filaments 9, thereby stopping the heat generation of the heating plate 2, while the cooling is started by means of the coolant flowing through the coolant passage formed in the stage portion 6, thereby lowering the temperature of the heating plate 2.
In this manner, the lower end portion of the heated material supporting member 1 is cooled by the cooling water flowing through the coolant passage 7 formed in the wall of the stage portion 6, when heating up the heating plate 2. For this reason, a large thermal gradient is established between the lower end portion of the heated material supporting member 1 and the heating plate 2. On the other hand, before the time when heating the heating plate 2 and during the time when cooling it, both the lower end portion of the heated material supporting member 1 and the heating plate 2 are in the vicinity of room or a steady temperature, therefore, there is established no thermal gradient therebetween. In this manner, with the repetition of heating and cooling, a large change is caused in the thermal gradient established between the lower end portion of the heated material supporting member 1 and the heating plate 2, repetitively.
In this instance, as is shown in FIG. 2, though the heating plate 2 of the heated material supporting member 1, the upper and lower periphery wall portions 13a and 13b, and the horizontal wall 5 expand, and thereby deform, respectively, the expansion mentioned above can be absorbed by the walls neighboring with each other. Further, compared to the conventional electron bombardment heating apparatus shown in FIG. 6 mentioned above, wherein only one (1) piece of shoulder portion is defined between the heating plate 2 of the heated material supporting member 1 and the peripheral wall portions, according to the electron bombardment heating apparatus shown in FIG. 1, the shoulder portions are defined by three (3) pieces thereof, and therefore the stress concentrating upon the shoulder portions can be dispersed much more between them. With this, even if applying the heating and the cooling thereon, repetitively, it is difficult to cause breakage, in an early stage thereof, due to the thermal stress applied thereon repetitively.
Next, the structure of a temperature controller for use with such an electron bombardment heating apparatus will be explained, by referring to a block diagram, which is inserted into FIG. 1 mentioned above.
There is provided an electric power adjuster 16 for the purpose of adjusting the current and voltage for heat generation to be supplied to the filaments 9, in other words, electric power of the filament heating electric power source 10 for supplying current for use of emission of thermions to the filaments 9.
Further, there are provided an emission current adjuster 17 for the purpose of outputting a control signal to the electric power adjuster 16, and also a thermal regulator 18.
The emission current adjuster 17 has a function of setting or determining the emission current flowing between the heating plate 2 side and the filaments 9 at a predetermined value. Furthermore, while measuring the emission current, this emission current adjuster 17 outputs a control signal to the electric power adjuster 16, so that the emission current is maintained at a predetermined preset value, thereby adjusting the current and the voltage of the filament heating electric power source 10 for conducting electricity to the filaments 9, by means of this electric power adjuster 16.
On the other hand, the thermal regulator 18 has functions of setting the steady temperature of the heating plate 2 at a predetermined temperature, and also of setting a time period for maintaining that steady temperature. Further, while measuring the temperature on the lower surface of the heating plate 2 by means of the thermocouple 12 and the thermometer 14 connected thereto, this thermal regulator 18 outputs a control signal to the electric power adjuster 16, so that the temperature of the heating plate 2 is maintained at the predetermined preset value mentioned above, thereby adjusting the current and the voltage of the filament heating electric power source 10 for conducting electricity to the filaments 9, by means of this electric power adjuster 16.
Also, the thermal regulator 18 actuates a switch 19 of a relay, etc., for example. During when the temperature rises, but before the temperature measured in the thermometer 14 by means of the thermocouple 12 reaches the steady temperature, which is reset by means of the thermal regulator 18, the emission current adjuster 17 is connected to the electric power adjuster 16. Thereafter, when the temperature measured in the thermometer 14 reaches the steady temperature preset by means of the thermal regulator 18, the switch 19 changes over, so that the thermal regulator 18 is connected to the electric power adjuster 16.
Next, explanation will be given to a method for controlling the temperature of the electron bombardment heating apparatus, with the aid of this temperature controller.
First of all, the emission current to be maintained constant with the temperature rises is set up in advance, by means of the emission current adjuster 17, depending upon the thermal gradient when the temperature of the heating plate 2 rises. Also, by means of the thermal regulator 18, the temperature to be maintained constant is set up in advance, depending upon an object of the thermal treatment or processing of the material to be heated.
When starting the conduction of electricity into the filaments 9 through the filament heating electric power source 10, while applying the constant high voltage for acceleration between the filaments 9 and the heating plate 2, at the same time, by means of the electron acceleration electric power source 11, then the thermions are emitted from the filaments 9, and those thermions, being accelerated under the acceleration voltage mentioned above, impinge upon the lower surface of the heating plate 2. For this reason, the heating plate 2 is heated up due to the electron bombardment. At the same time, emission current flows between the filaments 9 and the heating plate 2. In this instance, the acceleration voltage applied through the electron acceleration electric power source 11 is made constant.
When the temperature of the heating plate 2 rises, but before it reaches the steady temperature, which is set up in advance by means of the thermal regulator 18 mentioned above, the emission current adjuster 17 is connected to the electric power adjuster 16. This emission current adjuster 17, while measuring the emission current flowing between the heating plate 2 side and the filaments, outputs a control signal to the electric power adjuster 16, so that the emission current is maintained at the preset value thereof, thereby adjusting the voltage and the current of the filament heating electric power source 10 for conducting electricity to the filaments 9, by means of this electric power adjuster 16. With this, the emission current flowing between the heating plate 2 side and the filaments 9 is maintained at a constant value when the heating plate 2 raises the temperature thereof. As was mentioned previously, the acceleration voltage, which is applied by means of the electron acceleration electric power source 11, is constant, and also the emission current is maintained at a constant value. For this reason, the energy, given to the heating plate 2 due to the electron bombardment, becomes constant, and the heating plate 2 raises the temperature thereof, at a constant thermal gradient.
Thereafter, when the temperature of the heating plate 2 reaches the steady temperature, which is preset by means of the thermal regulator 18 mentioned above, the switch is actuated, so as to change over the contact thereof, and therefore, the thermal regulator 18 is connected to the electric power adjuster 16. This thermal regulator 18, obtaining or receiving the signal from the thermometer 14 for measuring the temperature on the lower surface of the heating plate 2 by means of the thermocouple 12, outputs a control signal to the electric power adjuster 16, so that the temperature of the heating plate 2 is maintained at the steady temperature, which was preset in the manner mentioned above, thereby adjusting the current and the voltage of the filament heating electric power source 10 for conducting electricity to the filaments 9, by means of this electric power adjuster 16. With this, the temperature of the heating plate 2 is maintained at the preset steady temperature and, when passing the time period that is preset in the thermometer 14, the electricity is stopped to be conducted from the electron acceleration electric power source 11 to between the filaments 9 and the heating plate 2, thereby lowering the temperature of the heating plate 2.
FIG. 3 shows an example of a relationship between the time and the temperature when heating the heating plate 2, and also a chart for controlling the temperature in this instance.
As is shown in the figure, when the temperature rises, i.e., from the time of starting the heat generation of the heating plate 2 up to the time of reaching the preset steady temperature, the electric power of the filament heating electric power source 10 is controlled, so that the preset emission current becomes constant, while measuring the emission current, so as to feed it back to the electric power adjuster 16. Since the energy given to the heating plate 2 due to the electron bombardment is determined by the product between the emission current and the acceleration voltage, therefore, with this control, due to the electron bombardment, a constant amount of energy is given to the heating plate 2 per hour, when raising the temperature of the heating plate 2.
On the other hand, after the heating plate 2 reaches the preset steady temperature, the electric power of the filament heating electric power source 10 is controlled, so that the preset steady temperature becomes constant, while measuring the temperature of the heating plate 2, so as to feed it back to the electric power adjuster 16. With this, for a preset time period, the heating plate 2 maintains the preset constant temperature, steadily.
FIG. 4 shows another embodiment of the electron bombardment heating apparatus, according to the present invention, wherein the elements, similar to those in the embodiment of the electron bombardment heating apparatus that was shown in FIG. 1 mentioned above, are also given with the same reference numerals thereto. The embodiment of the electron bombardment heating apparatus shown in this FIG. 4 is almost similar to the embodiment of the electron bombardment heating apparatus shown in FIG. 1 mentioned above, and therefore, explanation will be given only about the portions differing from that. Thus, in the embodiment shown in FIG. 4, the peripheral wall portion 13a having a small radius is located below the peripheral wall portion 13b having a large radius, and they are also connected with each other, by means of a horizontal wall provided therebetween. Compared with the embodiment shown in FIG. 1 mentioned above, it is possible to achieve the heating panel 2, being wider in an area thereof, as the ceiling of the heated material supporting member 1.
FIG. 5 shows another embodiment of the electron bombardment heating apparatus, according to the present invention, wherein the elements, similar to those in the embodiment of the electron bombardment heating apparatus that was shown in FIG. 1 mentioned above, are also given with the same reference numerals thereof.
The higher the temperature of the heating plate 2, the greater the thermal loss due to the radiant heat, even if trying to heat up the heating plate 2 through the electrons. Then, it is necessary to increase the number of pieces of the reflectors for reflecting the radiant heat thereupon. In general, for every increase of temperature of one hundred degrees centigrade (100° C.) of the heating plate 2, it is necessary to increase the number of pieces of the reflectors 3 by one (1) piece. However, with the reflectors 3 as shown in FIG. 1 mentioned above, each being made from a metal plate, wiring is needed between them, so as to make the filaments 9 and the reflectors 3 equal in the potential thereof, for the purpose of preventing electricity from discharging towards the heating plate 2 and the opposite side thereof.
For avoiding such wiring, as shown in FIG. 5, between a plural numbers of metal reflectors 3 is inserted an insulator plate 20, such as, a ceramic plate, etc., for example, having a high insulation and high heat-resistance, thereby insulating the reflectors 3 piled up vertically, from each other. The reflector 3 below the insulator plate 20 is one, being provided for the purpose of heat insulation, but without electrical connection, while the reflectors 3 above the insulator plate 20 each have functions of both; i.e., preventing electrons from being discharged to a rear side thereof, and for the heat insulation.
However, in the three (3) embodiments mentioned above, the peripheral wall of the heated material supporting member 1 is divided into two (2) stages of the peripheral wall portions, being different in the radius thereof, but in particular, by taking the ease or the like in production thereof into consideration, but it is also possible to divide the peripheral wall of the heated material supporting member 1 into three (3) or more stages of the peripheral wall portions, being different in the radius thereof. Though an increase of the number of stages of the peripheral wall portions brings about an improvement in the property of dispersing the thermal stress thereupon, on the other hand, it increases the fragility thereof with respect to other external forces, and therefore, it is the best to divide the peripheral wall into two (2) stages, and it may be limited up to three (3) stages at the largest.
The present invention may be embodied in other specific forms without departing from the spirit or essential feature or characteristics thereof. The present embodiment(s) is/are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the forgoing description and the range of equivalency of the claims are therefore to be embraced therein.

## Claims

1. An electron bombardment heating apparatus for heating a material, comprising:
a filament for emitting thermions therefrom;
means for accelerating the thermions emitted from the filament towards a heating plate;
a heating plate which is heated by bombardment of the accelerated thermions and serves as a means for supporting the material to be heated; and
a supporting member having the heating plate provided at a top portion thereof, vertically disposed cylindrical peripheral wall portions which have a different diameter from each other and a horizontally disposed annular wall portion which extends in a radial direction and connects the vertically disposed cylindrical peripheral wall portions with each other.

2. The electron bombardment heating apparatus of claim 1, additionally comprising plural reflectors provided at a rear side of the filament.

3. The electron bombardment heating apparatus of claim 1, wherein the vertically disposed cylindrical peripheral wall portions comprise an upper vertically disposed cylindrical peripheral wall portion and a lower vertically disposed cylindrical peripheral wall portion and the upper vertically disposed cylindrical peripheral wall portion has a greater diameter than the lower vertically disposed cylindrical peripheral wall portion.

4. The electron bombardment heating apparatus, as described in the claim 1, wherein said supporting member is made of ceramic.

5. The electron bombardment heating apparatus, as described in the claim 4, wherein said supporting member is made of silicon carbide impregnated with silicon.

6. The electron bombardment heating apparatus as described in the claim 2, wherein a heat-resistive insulator plate is inserted between the plural reflectors.