JPS5919314A - Device for heating in vacuum - Google Patents

Abstract

PURPOSE:To enable to perform a high temperature heating in a stabilized manner by a method wherein the heat conducting material, which constitutes the heating device, is formed with a sodium oxide sintered body. CONSTITUTION:A heating device 10 is constructed in such a manner that a heater 12, a heat generating body, is interposed between an upper flat plate 11 and a lower flat plate 13. Tungsten is used for the heater 12, and it has a continued U-shape. The flat plates 11 and 13 are formed with the sintered body of thorium oxide. The sintered body of relative density 99.9% or above is to be used. The thorium oxide sintered body has a high insulating property, and it has also excellent mechanical strength and heat conductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a heating device, and particularly to a vacuum heating device for heating an object in a vacuum state.

[Technical background of the invention and its problems]

Conventionally, in the manufacturing process of semiconductor devices, etc., work is performed to heat substrates, sample objects, etc. (hereinafter collectively referred to as "objects") in order to improve crystal growth or to clean their surfaces. As you know.

Such heating means include resistance heating, laser heating, electron beam heating, high frequency heating, and direct current heating, but it is difficult to uniformly heat a large object with any of them, and crystal technology or process technology is required. It is not possible to sufficiently meet the recent technical demands, which have become possible to use large-diameter 7-recon wafers due to development.

Furthermore, the various changes in devices in recent years have led to the complexity of devices and, in turn, the complexity of manufacturing processes. There is an increasing demand for things like motion.

In particular, the materials constituting the vacuum heating device must be stable even at high temperatures and do not react with the target object or diffuse its composition into the target object, as well as high vacuum It must be made of a stable material with no unnecessary gas emissions and low vapor pressure, and must have sufficient mechanical strength to avoid damage or deterioration due to thermal cycles of heating, holding, and cooling. Fine needle thermal shock resistance, low thermal expansion, high thermal conductivity, high electrical insulation, and good thermal response characteristics are required.

In response to these technical requirements, sintered ceramics have been proposed as a material for heating devices, but they do not fully satisfy the above conditions.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a vacuum heating device 1 that can stably heat at a high temperature even in a high vacuum.

[Summary of the invention]

That is, in this invention, the thermally conductive material constituting the vacuum heating device is formed of a thorium oxide sintered body, and the sintered body has a relative density of 499.9%, so that it can be heated in a high vacuum. This allows for stable high temperature heating.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The vacuum heating device according to the present invention will be described in detail below according to embodiments shown in the accompanying drawings.

FIG. 1 is an exploded perspective view of a vacuum heating apparatus according to the present invention, particularly for heating a substrate such as a silicon wafer. In this FIG. 1, the heating device [1
0 has a structure in which a heater 12 as a heating element is interposed between a lower flat plate 11 and a lower flat plate 13. Among these, the heater 12 is made of tungsten, for example, and has a continuous substantially U-shape as shown in the figure. Further, the lower flat plate 11 and the lower flat plate 13 are made of thorium oxide (Th+O1).
It is formed from a sintered body. This thorium oxide sintered body is formed by hot pressing or pressureless sintering, and has a relative density of 99.9% or more. In addition,
This thorium oxide sintered body and alumina (Mul*Os)
In order to compare the characteristics with sintered thorium monoxide and quartz (EliO,), we have prepared a table of various quantities.5 As is clear from this table, sintered thorium monoxide has high insulating properties, similar to alumina and quartz, and has excellent mechanical strength and thermal conductivity. The quality is also excellent. In addition, in the case of this thorium oxide sintered body, the specific heat is still lower than that of the above-mentioned alumina and quartz, and the maximum operating temperature in an oxidizing atmosphere is high. Therefore, it can be said that this thorium oxide sintered body is a material with perfect properties as the heat conductive material of the heating device, that is, the upper and lower flat plates 11.13.

Furthermore, since the above-mentioned heating device is used in an ultra-high vacuum, the heat conductive material must be a material with high temperature and low vapor pressure. The thorium oxide sintered body is also excellent in this property. FIG. 2 shows the temperature-vapor pressure characteristics of this thorium oxide sintered body and the alumina and quartz.

As is clear from Figure 2, the thorium oxide sintered body has a very low vapor pressure, and it has been confirmed that even in a vacuum of 10 Torr or less, the object can be heated to over 1200 cm. ing.

FIG. 3 shows an example of a vacuum evaporation apparatus for forming a thin metal film on a predetermined object using a heating device using a thorium oxide sintered body having the above characteristics. In this figure, the vacuum evaporation apparatus 20 has its Pelger 21
A table 22 is provided at the center of the bottom of the pelger 21, and gas is drawn from the bottom of the pull 22 in the direction of arrow F in the figure by a vacuum pump system (not shown), and the inside of the pelger 21 is maintained at an appropriate vacuum. It is configured to be.

On the table 22 is a heating device [10] shown in FIG.
is placed and identified, and the silicon wafers EIA and BB, which are the objects, are placed directly above it. Furthermore, the heater 12 of the heating device t10 is led out of the Pelger 21 via a suitable hermetic electrode, and is connected to a power source (not shown).

On the other hand, the table 22'& the ball 23°24
A filament 27 is installed between these balls 23 and 24 via electrodes 25 and 2fl, and a wire-shaped metal 28 is connected to the filament 27 with a wire shape extending approximately U.
It is shaped like a letter and is hung. Said ball 23.2
4 is also led out to the outside and connected to a power source (not shown).

Next, in FIG. 3, the case of forming a film of metal 28 on silicon wafers SA and SB will be described. First, the inside of Pel jar 21 is brought to an appropriate vacuum using a vacuum pump thread (not shown). Next, before the metal 28 is vapor-deposited, the heater 12 is energized to clean the surfaces of the silicon wafers 8A and SB, and the silicon wafers 13A and 8B'g are heated. Generally, it is required that silicon wafers SA and EIB be heated to 1000 C or higher. At this point, the gas contained in the upper and lower flat plates 11.13 is released, but as mentioned above, the relative density of the thorium oxide sintered body formed in the upper and lower flat plates 11.13) is 99.9. %, there are almost no vacuoles inside, and therefore the amount of gas released by heating is extremely small. Therefore, even in an ultra-high vacuum state below the atmospheric pressure or IQ Torr, (7) there is almost no effect on the vacuum state.

Next, after cleaning the surfaces of the silicon wafers SA and SB, the amount of electricity applied to the heater 12 is adjusted to remove the silicon wafers 8m and 8B.
Adjust the temperature so that it is at the required constant temperature,
When the filament 27 is further energized, the metal 28 is melted and evaporated, and a film of the metal 28 is formed on the surfaces of the silicon wafers 8M and 8B.

Finally, data from heating experiments using a prototype device of the present invention are shown below. The upper and lower flat plates 11 and 13 made of sintered #i thorium oxide have a square shape with a side length of 70 m, and a thickness of 1-. The heater 12 has a diameter lφ with a folding pitch of 7k 4 m.
Use tungsten wire. This device is 50.8m (
Place a 2-inch silicone
When a current of 20 µm was passed through the heater 12 under a vacuum condition, the surface temperature of this silicone surface decreased by 1 in about 10 minutes.
The pressure was increased to 200t:', and the degree of vacuum was well maintained at 1QTOrr(8) or less. Further, the variation in surface temperature of the silicon wafer is suppressed to within ±10C,
The uniformity of heating was also good.

After this, the temperature was further increased and decreased 50 times, but no change was observed in the upper and lower flat plates 11 and 13, and no chemical reaction occurred with the silicon wafer. Also, there is no chemical reaction with tungsten that forms the heater 12 (
On the contrary, contamination of the silicon wafer due to the evaporation of tungsten could be prevented by the upper and lower flat plates 11 and 13 formed of the thorium oxide sintered body.

In the above embodiments, the object to be heated is a silicon wafer, but other metals, insulators, etc. may also be used. The heating device according to the present invention is not limited to the above-mentioned vacuum evaporation, but can also be used for molecular beam epitaxy. Further, the shape of the heating device is not limited to the above-mentioned flat plate shape, but may be of various shapes, and it is also possible to embed the heater by shaping it into a certain shape during sintering. Other, other IJ I
It is also possible to use it in combination with JA porcelain, etc.

〔Effect of the invention〕

As explained above, according to the vacuum heating device according to the present invention, the part surrounding the heating element and in contact with the object is formed of a thorium oxide sintered body.
The object can be heated uniformly and well with low heat loss without any damage even at high temperatures above t:'.
In addition, by being able to manufacture a heating device with a fairly large area, it is possible to select a size that is suitable for the object.Furthermore, since the relative density of the sintered body is 99.9%, unnecessary gas release is reduced and the vacuum It has the excellent effect of preventing adverse effects on the state and stably heating the object at a high temperature in a high vacuum.

As an application example of the present invention, an evaporator or crucible for low-melting metal or the like may be formed of a sintered body of thorium oxide. In addition, depending on the work in which the vacuum equipment is used, there may be parts that are exposed to extremely high temperatures and require good insulation, and it is recommended to use sintered thorium oxide in such parts. In this case, the same effect as above can be obtained. For example, in the example shown in FIG.
Even if the temperature of No. 4 rises, insulation can be maintained well.

Furthermore, dielectric heating may be performed by applying an alternating electric field to the thorium oxide sintered body. especially,
Gas,
It is also possible to heat the liquid.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of an embodiment of a vacuum heating device according to the present invention, and FIG. 2 is a comparison of the temperature-vapor pressure characteristics of a thorium oxide sintered body, alumina, and quartz. 3 is a perspective view showing an example of a vacuum evaporation apparatus using the heating device shown in FIG. 1 (11). DESCRIPTION OF SYMBOLS 10... Vacuum heating device, 11... Upper flat plate which is a thermally conductive material, 12... Heater which is a heating element, 13...
The lower flat plate is a thermally conductive material. (12)

Claims (2)

[Claims] (1) In a vacuum heating device used in a vacuum, which has a heating element and a thermally conductive material that conducts heat generated from the heating element to an object, the thermally conductive material is sintered with thorium oxide. A vacuum heating device characterized by being formed from a body. (2) The relative density of the thorium oxide sintered body is 99.9%
A vacuum heating device according to claim (1) above.