JP4955357B2 - Rear electron impact heating device - Google Patents

Description

  The present invention relates to a heating device that heats a heated object such as a semiconductor wafer to a high temperature, and in particular, it is a backside electron impact heating device of a type that heats a heating plate by colliding accelerated electrons with the heating plate from behind. The present invention relates to a plate provided with a shielding plate for reflecting electrons and radiant heat behind it.

  As a heating means for heating a plate-like member such as a semiconductor wafer in a processing process of a semiconductor wafer or the like, there is a back surface electron impact heating device of a type in which accelerated electrons collide behind the heating plate to generate heat. in use. In this backside electron impact heating device, the thermoelectrons generated by energizing the filament are accelerated at a high voltage, and the thermoelectrons collide behind the heating plate to cause the heating plate to generate heat. Then, the plate placed on the heating plate is heated.

FIG. 3 is a diagram showing a conventional example of a backside electron impact heating device.
The heating container 21 is installed in a vacuum chamber (not shown), and the inside of the vacuum chamber is evacuated so that the entire heating container 21 is placed in a vacuum space.

  The heating container 21 is a container having an open bottom surface, and a top plate on which a thin plate-like heating object 27 such as a silicon wafer is placed becomes a flat heating plate 22. In other words, the heating container 21 has a heating plate 22 as a top plate, the upper surface side thereof is closed, and a cylindrical peripheral wall 33 having an opening on the lower surface side is provided below the periphery of the heating plate 22.

  The lower end portion of the peripheral wall 33 of the heating vessel 21 has a flange shape, and this flange portion is applied to the upper surface of the lower flange 26 with the vacuum seal material 28 interposed therebetween, and an annular conductive property applied to the flange portion. It is fixed by a presser fitting 35 through a washer 36. As a result, the heating container 21 and the lower flange 26 are hermetically sealed by the vacuum sealing material 28 in a state of electrical conduction. The lower flange 26 is grounded, so that the heating vessel 21 is also grounded.

  As a material of such a heating container 21, a conductor such as graphite is used. On the other hand, when the heating container 21 is made of ceramic such as alumina or silicon nitride and is made of an insulator, the inner surface of the heating plate 22 and the entire inner and outer surfaces of the peripheral wall 33 and its lower flange are metallized to form a conductor film. The conductor film is grounded through the conductive washer 36, the presser fitting 35 and the lower flange 26.

  Further, a support column 34 is erected from the lower flange 26 inside the heating container 21, and a flat plate-like holder 32 is supported on the upper end side of the support column 34. Further, a filament support column 37 is erected from the holder 32, and a filament 29 is attached to the filament support column 37. The filament 29 is provided behind the heating plate 22 in the heating container 21.

  The lead wire 24 of the filament 29 is drawn out of the heating container 21 from the lower frame 26 through the ceramic terminal 25 and connected to a filament heating power source (not shown). Further, an acceleration voltage is applied to one of the lead wires 24 of the filament 29 by an electron acceleration power source (not shown). As described above, since the heating vessel 21 having the heating plate 22 is grounded, it is held at a positive potential with respect to the filament 29.

  A shielding plate support column 38 is erected from a flat plate holder 32 held by the support column 34, and the shielding plate 23 is supported by the support column 38 so as to be positioned below the filament 29. The shielding plate 23 is electrically connected to the filament 29 through the shielding plate support column 38 and is set to a negative potential that is the same potential as the filament 29.

  In such a backside electron impact heating device, a constant high voltage acceleration voltage is applied between the filament 29 and the heating plate 22 by the electron acceleration power source 31, and when the filament 29 is energized by the filament heating power source 30, the filament 29 Thermoelectrons are emitted from all directions. Here, the downwardly moving thermoelectrons are also reflected by the shielding plate 23 having a negative potential, and as a result, most of the thermoelectrons emitted from the filament 29 in the vertical direction are accelerated by the acceleration voltage and are heated by the heating plate 22. Collides with the bottom surface. The heating plate 22 is heated by this electron impact. The heat generated in the heating plate 22 is reflected by the shielding plate 23 provided below the filament 29, so that the heat is prevented from diffusing to an unnecessary part as much as possible. Electrons that collide with the heating plate 22 flow from the peripheral wall 33 of the heating container 21 to the ground via the conductive washer 36, the presser fitting 35, and the lower flange 26.

A general heating device is based on an electric resistance heating means that supplies electricity to a resistor such as metal or graphite and heats a heated object using heat generated by the electric resistance. However, the backside electron impact heating device described above is excellent in thermal efficiency because the electrons generated in the filament 29 are accelerated by a high voltage and collided with the heating plate 22 held at a positive potential with respect to the filament 29 and heated. If the acceleration voltage is less than or equal to the number k V, X-ray does not occur, since the collision to the heating plate 22 while electrons are spread by the repulsive electronic between, the heating is concentrated only in the vicinity of the filament 29 of the heating plate 22 There is no. Further, in order to heat only the heating plate 22 of the heating container 21, a plate-shaped shielding plate 23 maintained at a negative potential is installed behind the filament 22 with respect to the heating plate 22. The thermoelectrons thus reflected are reflected by the shielding plate 23, and only the heating plate 22 can be heated.

The shielding plate 23 in the heating container 21 of the backside electron impact heating device reflects electrons and also reflects the radiant heat from the heating plate 22.
In general, there are three modes in which heat is transmitted: heat radiation, heat conduction, and heat convection. However, the heat transfer in a vacuum is only heat radiation, even in the atmosphere, the heating element and the heated object when the nearby, substantial heating by only the heat radiation and heat conduction are performed. In addition, when the temperature of the heating element is 500 ° C. or less, the heat transfer mode varies depending on conditions such as heating temperature, heating method, temperature distribution, etc.

  On the other hand, in a backside electron impact heating device, a shield plate that is required to reflect electrons together with the reflection of radiant heat is different from a shield plate that only reflects radiant heat. . That is, unless the negative voltage with respect to the heating plate 22 is maintained at a negative potential with respect to the heating plate 22 and the negative voltage with respect to the heating plate 22 is not increased to substantially the same potential as the filament 29, the reflection of electrons is bad.

Thus, in order to maintain the shielding plate 23 at a negative potential with respect to the heating plate 22, the shielding plate 23 must be a good conductor. Also a plate made of an insulator such as ceramics, the charge-up of the thermal electrons reflected thermionic is possible, potential distribution difference for absolute Entai large, is unstable. In addition, since the charge-up potential changes according to the potential of the filament, there is a problem that control is difficult. For this reason, as the shielding plate 23 used in the backside electron impact heating device, a metal that can be easily set to the same potential as the filament and is easily electrically connected is used, and among them, the radiation rate that reflects radiant heat is low. The material is preferred.

  As described above, the shielding plate 23 is installed in the heating container 21 by the support pillar 38. Electrons strike the shielding plate 23 and the shielding plate 23 is heated by the radiant heat inside the heating container 21. At this time, a portion near the filament 29 of the shielding plate 23 becomes high temperature, and a portion far from the filament 29 has a relatively low temperature, so that a temperature distribution is generated in the shielding plate 23. Due to this temperature distribution, thermal stress is generated in the shielding plate 23, and deformation such as bending of the shielding plate 23 occurs. This deformation becomes larger if the thermal distortion of the shielding plate 23 by the support pillar 38 is not sufficiently absorbed.

  When deformation such as bending occurs in the shielding plate 23, the reflection direction of thermoelectrons changes, and the temperature distribution of the heating plate 22 becomes non-uniform. Although depending on the heating temperature of the heating plate 22, a high melting point metal such as Mo, Ta, W or the like is used as the heating plate 22 in high temperature heating of 1000 ° C. or higher. Among these metals, Mo and W have a relatively low thermal expansion coefficient and a relatively high thermal conductivity, and therefore, a temperature distribution is unlikely to occur and bending is difficult.

  However, when the heating plate 22 is heated to a temperature of 1000 ° C. or higher, the shielding plate 23 becomes a high temperature close to 1000 ° C. Since the backside electron impact heating device is heating by concentrated irradiation of electrons, it can be heated to a higher temperature than a general heater such as a resistance heating method, and the heating rate is also high. It is also possible to heat to an extremely high temperature of about 2000 ° C. using the feature of this backside electron impact heating device. However, at such a heating temperature of the heating plate 22 that reaches 2000 ° C., the shielding plate 23 also becomes high accordingly, and when the heating plate 22 is 2000 ° C., the temperature of the shielding plate 23 reaches 1700 ° C.

  As described above, Mo or W having a high melting point and high heat resistance is used for the shielding plate 23 at a high temperature. Mo and W have relatively small thermal expansion coefficients and relatively high thermal conductivities, so that temperature distribution is unlikely to occur and deformation associated with temperature distribution is small. Moreover, since it is a metal, it is relatively easy to process compared to ceramics and the like, and is suitable for the shielding plate 23 used at high temperatures.

However, even if this heat-resistant Mo or W exceeds 1000 ° C., recrystallization starts, and the thermal deformation accompanying the temperature distribution is not elastic deformation but permanent plastic deformation. The permanent deformation causes a further temperature distribution of the shielding plate 23 and causes a large deformation. If it does so, the reflection direction of an electron will change with time, and the subject that the temperature of the heating plate 22 will be uneven occurred.
Japanese Patent Laid-Open No. 2005-056582 JP 2004-355877 A JP 2003-178864 A

  In the present invention, in view of the problems in the conventional backside electron impact heating device, the backside electron impact heating device reduces the temperature distribution of the shielding plate at high temperature, suppresses the deformation, and reliably reflects electrons. The purpose is to provide.

  In the present invention, in order to achieve the above object, the shielding plate 11 is made of a material having a small coefficient of thermal expansion so that it is not easily deformed even if a temperature distribution is made. Further, by making the shielding plate 11 have a high thermal conductivity, the temperature distribution itself is hardly generated. Further, the shielding plate 11 is made of ceramics having a very high recrystallization temperature and softening point, and conductive ceramics are used so that a negative potential can be easily applied.

  That is, the back surface electron impact heating apparatus according to the present invention heats the heating plate 2 by accelerating and colliding electrons generated in the filament 9 from behind the heating plate 2 which is the top plate of the heating container 1. is there. And it has the shielding board 11 provided behind the filament 9 with respect to the said heating plate 2, and reflects a thermoelectron and radiant heat to the heating plate 2 side, and this shielding board 11 consists of conductive ceramics of a heat good conductor. . More specifically, the shielding plate 11 is made of a graphite surface coated with graphite such as pyrolytic graphite. The shielding plate 11 made of such ceramics may be disposed only on the side close to the heating plate 2, and the shielding plate 3 on the side far from the heating plate 2 may be made of metal. Of course, ceramics can also be used for the shielding plate 11 on the side far from the heating plate 2.

  Since the shielding plate 11 made of such ceramics has a small thermal deformation and is difficult to be permanently deformed at a high temperature, the direction in which electrons are reflected does not change, and the heating plate 2 can be heated in the same state. . Further, since the shielding plate 11 is a good thermal conductor, even when the temperature is increased by being hit by electrons, unevenness in temperature hardly occurs and thermal deformation can be prevented. Furthermore, since it consists of conductive ceramics, a negative potential can be applied to reflect electrons.

  As described above, in the backside electron impact heating device according to the present invention, the thermal deformation of the shielding plate 11 can be suppressed, so that unevenness of the collision of electrons with the heating plate 2 is eliminated, and a uniform temperature distribution is formed. I can do it. Furthermore, since permanent deformation at high temperatures is difficult, even a backside electron impact heating device that heats the heating plate 2 to a high temperature of 2000 ° C. or higher can prevent adverse effects due to permanent deformation of the shielding plate 11.

In the present invention, the back electron impact heating apparatus according to the present invention is to use what the shielding plate 11 that reflects electrons consisting conductor ceramic heat conductor, to achieve the above object.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

FIG. 1 is a diagram showing an embodiment of a backside electron impact heating apparatus according to the present invention.
A heating container 1 is installed on a lower flange 6 made of a metal such as stainless steel. The heating container 1 is a container having an open bottom surface, and a top plate on which a thin plate-like heating object 7 such as a silicon wafer is placed becomes a flat heating plate 2. In other words, the heating container 1 has a heating plate 2 as a top plate, the upper surface side thereof is closed, and a cylindrical peripheral wall 13 having an opening on the lower surface side is provided below the periphery of the heating plate 2. A lower end portion of the peripheral wall 13 of the heating container 1 has a flange shape. The heating container 1 is installed in a vacuum chamber (not shown), and the whole of the heating container 1 becomes a vacuum space by reducing the pressure in the vacuum chamber.

  A portion of the lower flange 6 on which the flange portion of the heating container 1 is placed is provided with a concentric groove around the central axis of the lower flange 6, and a vacuum seal material 8 is fitted into the groove. A flange portion at the lower end portion of the peripheral wall 13 of the heating vessel 1 is placed on the vacuum seal material 8 fitted in the groove, and further, this flange portion is interposed through an annular conductive washer 16 placed thereon. And is fixed by a presser fitting 15. In this state, the heating container 1 and the lower flange 6 are electrically connected and are hermetically sealed by the vacuum seal material 8. The lower flange 6 is grounded and thus the heating vessel 1 is also grounded.

  As the material of the heating container 1, a conductor such as graphite is used. On the other hand, when the heating container 1 is made of ceramics such as alumina or silicon nitride and is made of an insulator, the inner surface of the heating plate 2 and the entire inner and outer surfaces of the peripheral wall 13 are metallized to form a conductor film. The membrane is grounded through the conductive washer 16, the presser fitting 15 having the coolant passage 17 and the lower flange 6.

  Further, a support column 14 is erected from the lower flange 6 inside the heating container 1, and a flat plate-like holder 12 is supported on the upper end side of the support column 14. Further, a filament support column 17 is erected from the holder 12, and the filament 9 is attached to the filament support column 17. The filament 9 is provided behind the heating plate 2 in the heating container 1.

  The lead wire 4 of the filament 9 is drawn out of the heating container 1 from the lower frame 6 through the ceramic terminal 5 and connected to a filament heating power source (not shown). Further, an acceleration voltage is applied to one of the lead wires 4 of the filament 9 by an electron acceleration power source (not shown). The heating container 1 having the heating plate 2 is grounded and held at a positive potential with respect to the filament 9.

  A shielding plate support column 18 is erected from the flat plate-like holder 2 held by the support column 14, and the shielding plates 3 and 11 are supported by the support column 18 so as to be positioned below the filament 9. The shielding plates 3 and 11 are electrically connected to the filament 9 through the shielding plate support column 18 and have a negative potential that is the same as that of the filament 9.

  Here, the shield plate 11 closest to the heating plate 22 is made of conductive ceramics having a good thermal conductor. More specifically, the shielding plate 11 is made of graphite as a base material, and the surface of the base material is coated with pyrolytic graphite having a thermal conductivity approximately three times higher than that of graphite. The shielding plate 11 made of such ceramics can be disposed only on the side close to the heating plate 2, and the shielding plate 3 on the side far from the heating plate 2 can be made of metal such as Mo or W. Of course, ceramics can also be used for the shielding plate 11 on the side far from the heating plate 2. In the embodiment of FIG. 1, only one shielding plate 11 on the side close to the heating plate 2 is a conductive ceramic plate of a good thermal conductor, and below that is a shielding plate 3 made of a normal high melting point metal such as Mo or W. Is arranged.

  In such a backside electron impact heating device, a high acceleration voltage is applied between the filament 9 and the heating plate 2, and when the filament 9 is energized, thermoelectrons are emitted from the filament 9 in all directions. Of these thermoelectrons, the downward thermoelectrons are reflected by the shielding plates 3 and 11 having a negative potential, are accelerated by the acceleration voltage together with the upward thermoelectrons, and collide with the lower surface of the heating plate 2. For this reason, the heating plate 2 is heated by electron impact. The heat generated in the heating plate 2 is reflected by the shielding plates 3 and 11 provided below the filament 9, and the heat is prevented from diffusing to an unnecessary part as much as possible. Electrons that collide with the heating plate 2 flow from the peripheral wall 13 of the heating container 1 to the ground via the conductive washer 16, the presser fitting 15, and the lower flange 6.

  When the heating plate 2 reaches a predetermined temperature, the electric power supplied to the filament 9 is reduced, and the temperature of the heating plate 2 is maintained at the predetermined temperature. And when predetermined time passes, the electricity supply to the filament 9 will be stopped and the heating of the heating plate 2 will be stopped. Thereafter, most of the heat in the heating container 1 is cooled by the cooling liquid passing through the holding metal fitting 16 having the cooling liquid passage 17 and the cooling liquid passage 7 of the lower flange 6, and the heating plate 2. Is cooled down.

  As already described, Mo and W have a relatively low thermal expansion coefficient and a relatively high thermal conductivity, so that a temperature distribution is unlikely to occur and bending is difficult. When the heating plate 2 is heated to a temperature of 1000 ° C. or higher, the shielding plate 3 becomes a high temperature of about 700 ° C. In such a temperature range, the shielding plate 3 has some temperature unevenness, and even if the shielding plate 3 is deformed due to thermal stress at the time of heating, the deformation is within the range of elastic deformation. Disappear.

  However, when the heating plate 2 is heated to an extremely high temperature of about 2000 ° C., the temperature of the shielding plate 23 is 1700 ° C., and a high melting point metal such as Mo or W cannot cope with it. On the other hand, the shielding plate 11 made of the above-mentioned conductive ceramics with a good thermal conductor is small in thermal deformation and is difficult to be permanently deformed at high temperatures. Further, since the shielding plate 11 is a good thermal conductor, there is no temperature unevenness even when the temperature rises due to the impact of electrons. Furthermore, since it consists of conductive ceramics, a negative potential can be applied to reflect electrons.

  According to the experiment, if the heating method is to raise the temperature of the heating plate 22 to 1300 ° C. in a short time of about 5 minutes, even if only the shielding plate 3 made of a refractory metal such as Mo or W, Permanent deformation of the shielding plates 3 did not occur. However, it was found that when heating was performed for a long time at a temperature of 1300 ° C. for several hours to several tens of hours, the deformation of the heating plate 22 accumulated and permanently deformed. This is because, as described in Table 1, since the metal recrystallization temperature is lower than the heating temperature, permanent deformation due to recrystallization occurs.

  The lower limit of the recrystallization temperature of the metal shown in Table 1 is in the vicinity of 600 to 900 ° C., and cannot be handled when the heating plate 2 is heated to an extremely high temperature of about 2000 ° C. Although SiC has a high recrystallization temperature, strength is reduced from 1550 ° C. and it is weak against thermal shock. When the temperature difference is about 300 ° C., it is damaged by thermal shock. For this reason, the upper limit of the heating temperature of the heating plate 2 needs to be slowly raised to 1800 ° C.

  Graphite is optimal as a material for the shielding plate 11 because it has a higher recrystallization temperature than metal and is electrically conductive. Furthermore, by coating the surface of the graphite with pyrolytic graphite, which has a thermal conductivity in the plane direction of 400 W / mK, which is about three times that of graphite, the shielding plate 11 becomes a good thermal conductor, and the temperature distribution is not easily formed. Become.

  FIG. 2 is a view showing an example of a mounting structure of the shielding plates 3 and 11 by the support pillars 18. As shown in FIG. 2, long holes 19 are provided in the radial direction of the shielding plates 3 and 11, and the support pillars 18 are attached slightly loosely to absorb the deformation in the radial direction of the shielding plates 18 due to temperature changes. I can do it. Note that the hole formed in the center of the shielding plates 3 and 11 is a through hole through which the lead wire 4 of the filament 9 passes.

It is a schematic longitudinal cross-sectional view which shows one Example of the back surface electron impact heating apparatus by this invention. It is a perspective view which shows the shielding board of one Example of the back surface electron impact heating apparatus by this invention. It is a schematic longitudinal cross-sectional view which shows the prior art example of a back surface electron impact heating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating container 2 Heating plate 3 Shielding plate 9 Filament 11 Shielding plate

Claims (2)

In a backside electron impact heating device that heats the heating plate (2) by accelerating and colliding electrons generated in the filament (9) from behind the heating plate (2) which is the top plate of the heating container (1) The shield plate (11) is provided behind the filament (9) with respect to the heating plate (2) and reflects thermoelectrons and radiant heat to the heating plate (2) side. A backside electron impact heating device comprising a conductive ceramic of a good thermal conductor having a graphite surface coated with pyrolytic graphite . The shielding plate (11) arranged on the side close to the heating plate (2) is made of ceramics, and the shielding plate (3) arranged on the side far from the heating plate (2) is made of metal. The back surface electron impact heating apparatus of 2.

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