JPH1045491A - Heat insulation cylinder for silicon single crystal pulling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the heat insulation cylinder which enables evacuation of gas inside a furnace and within a graphite base material of the cylinder in a short time when the cylinder is placed in a vacuum space and also enables prevention of peeling-off of small flakes from the graphite base material and further, has high durability and is inexpensive. SOLUTION: This heat insulation cylinder 30 is placed in the space between a heater 20 for heating a crucible 10 in a silicon single crystal pulling device and a heat insulation material 40 for inhibiting heat from being transferred from the heater 20 to the outside, to perform heat insulation of the inside of the pulling device, wherein the upper part and the whole inner side surface of the cylinder 30 are coated with a coating film consisting of pyrolytic carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member for constructing a silicon single crystal pulling apparatus, and more particularly, to a member disposed between a heater and a heat insulating material of a silicon single crystal pulling apparatus, and comprising a graphite material as a base material. It relates to a heat retaining cylinder to be heated.

[0002]

2. Description of the Related Art A silicon single crystal pulling apparatus pulls a silicon single crystal from a silicon melt in a crucible in the presence of an atmospheric gas by a so-called Czochralski method. 57-15079
Is known as a “single crystal manufacturing apparatus” as disclosed in Japanese Patent Application Publication No. As shown in FIG. 3, the apparatus disclosed in this publication is configured such that “a rotary shaft 2 is introduced into a furnace body 1 from below, and a crucible 4 is placed on an end surface of the rotary shaft 2 via a mounting table 3. Further, a heating element 5 and a heat retaining cylinder 6 are arranged around the crucible 4, so that the silicon is melted in the crucible 4 to obtain a melt 7. On the other hand, the furnace 7 is vertically arranged above the furnace body container 1. A sliding shaft 9 is provided for sliding movement, and a silicon seed crystal 8 is attached to the free end of the rotating shaft 9 so that the rotating shaft 9 is positioned above the state where the seed crystal 8 is in contact with the melt 7 in the crucible 4. Move it,
A silicon single crystal 10 that follows the seed crystal 8 is obtained. When growing a single crystal, unnecessary reaction product gas is generated in the single crystal 10.
It is necessary to eliminate this so that no reaction occurs on the liquid surface of the melt 7. For this purpose, an inert gas such as argon is supplied as an atmospheric gas to the single crystal and the liquid level from above the furnace body container 1 and discharged from the lower part of the furnace body container ”(column 2 of the above-mentioned publication). ). The member denoted by reference numeral 5 in FIG. 3 is a heater, and a heat insulating material is disposed between the heat retaining cylinder 6 and the furnace body container 1 as shown in FIG.

[0003] In a silicon single crystal pulling apparatus of this type, each member such as a heat retaining cylinder is formed of a graphite material because of its excellent heat resistance. In the heat-insulating cylinder with excellent heat resistance, the flakes are easily peeled off because the material is graphite, and the flakes may cause impurities and crystal defects in silicon in the crucible. The entire surface has been hermetically coated with a pyrolytic carbon coating.

On the other hand, in this type of silicon single crystal pulling apparatus, whether the inside of the furnace body container (closed main body) can be sufficiently filled with an atmosphere containing only inert gas, that is, whether the airtightness in the furnace is sufficiently maintained or not. In order to check the condition, the gas in the furnace is evacuated by a vacuum pump, and the operation of the vacuum pump is temporarily stopped to see the situation.

[0005] However, when the vacuum pump was operated, the predetermined degree of vacuum was attained. However, when the vacuum pump was stopped, the degree of vacuum was reduced and the airtightness was judged to be insufficient.
In some cases, the pulling device cannot be started, and in that case, it is necessary to recheck the airtightness of each part of the sealed main body. This re-inspection is a work that requires a long time, but after the re-inspection, the aforementioned degree of vacuum was again reduced.

The inventors of the present invention have also examined where the cause of the decrease in the degree of vacuum is. For example, the gas in the graphite substrate constituting the heat insulating cylinder entirely coated with pyrolytic carbon was found to have been reduced. It was also found out that the small cracks and crevices of the coating formed by the pyrolytic carbon caused the coating to come out into the sealed body while causing a time shift according to the degree of vacuum in the sealed body. That is, since the graphite base material is a so-called porous material having a large number of pores, the gas in the pores is gradually introduced into the sealed main body at a predetermined degree of vacuum from the small holes in the pyrolytic carbon coating. It was exhausted, which contributed to the decrease in vacuum.

On the other hand, as shown in FIG. 1, a general crucible used in this silicon single crystal pulling apparatus is a so-called quartz having a main component mainly composed of SiO _2, which is in direct contact with Si, ie, silicon. When silicon is melted at a high temperature, not only SiO ₂ but also Si (silicon) itself melted in the crucible is vaporized and scattered in the silicon single crystal pulling apparatus. Will be. Further, the heat retaining cylinder is heated by a heater located in the immediate vicinity thereof, and has a higher temperature than the others especially at the upper portion where the above-mentioned SiO ₂ gas or SiO gas is scattered.

[0008] From the above, if the upper part of the graphite heat insulating cylinder is not covered with the pyrolytic carbon film, it is considered that the following chemical reaction occurs during the pulling operation of the silicon single crystal. (1) SiO + 2C → SiC + CO

In other words, especially at the upper part of the graphite heat retaining cylinder heated to a high temperature, the exposed graphite base material is silicided, and the silicide layer has physical properties different from graphite. Because it is different, when the silicon single crystal pulling apparatus is stopped and cooled, it causes a crack in the heat insulation cylinder, and if a crack occurs, the silicide layer and graphite are exfoliated as fine pieces. Not only does it drop, but it also causes the durability of the heat retention tube to decrease. The silicide layer and the flakes containing graphite not only contaminate the silicon single crystal pulling apparatus, but also cause impurities and crystal defects of the pulled silicon single crystal, which must maintain high purity, and are absolutely generated. Must be prevented. Therefore, especially the upper part of the heat insulating cylinder made of graphite must be covered with a coating made of pyrolytic carbon.

Therefore, the present inventor has proposed that a heat insulating cylinder for a silicon single crystal pulling apparatus of this kind be made of graphite as a base material, and that pyrolytic carbon for preventing (silicified) flakes from being peeled off on the surface. While taking advantage of the advantages of forming a coating, we have conducted various studies on how to solve the above-mentioned problems of degassing and airtightness in the furnace. Has been newly found that a good result can be obtained by partially and positively exposing the gas to directly degas the gas from the graphite substrate, thereby completing the present invention.

[0011]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above circumstances, and the problem to be solved is to maintain the degree of vacuum when checking this kind of silicon single crystal pulling apparatus. It is an object of the present invention to provide a heat retaining cylinder capable of sufficiently achieving the above, and to prevent stripping of the heat retaining cylinder.

That is, it is an object of the present invention that when placed in a vacuum space, the gas in the furnace and the inside of the heat insulating cylinder graphite substrate can be discharged in a short time, and moreover, the gas can be discharged from the graphite substrate. It is an object of the present invention to provide an inexpensive heat-insulating cylinder which can prevent the strips from peeling off and has high durability and low cost.

[0013]

Means for Solving the Problems To solve the above problems, first, means according to the first aspect of the present invention will be described with reference numerals used in the following description of the embodiments. "The silicon single crystal pulling apparatus is disposed between a heater 20 for heating the crucible 10 in the silicon single crystal pulling apparatus 100 and a heat insulating material 40 for preventing heat from the heater 20 from moving outside. 100
A heat insulation cylinder 30 for keeping the inside of the heat insulation cylinder 30
Is a heat insulating cylinder 30 for the silicon single crystal pulling apparatus 100, characterized in that the upper part and the entire inner surface are covered with a coating 32 made of pyrolytic carbon.

That is, as shown in FIG. 1, the heat retaining cylinder 30 according to the present invention includes a heater 20 for heating the crucible 10 in the sealed main body 50 and a transfer of heat from the sealed main body 50 to the outside. It is interposed between the heat insulating material 40 to be regulated, and the entire substrate is formed by the graphite substrate 31.

The heat retaining cylinder 30 according to the first aspect of the present invention exposes a part of the surface of the graphite base material 31 to the upper part and the entire inner surface of the graphite base material 31 as the base.
It is necessary to cover with a coating 32 made of pyrolytic carbon. The reason is that by exposing a part of the graphite base material 31 constituting the heat insulating cylinder 30 from the pyrolytic carbon coating 32, the pores of the graphite base material 31 are actively exposed to the outside, and the heat insulating cylinder When the inside of the sealed main body 50 in which the 30 is disposed is evacuated, the gas present in the graphite base 31 is immediately discharged from the pores to the outside of the graphite base 31, that is, the closed main body 5.
This is because it is necessary to discharge the gas within zero.

Further, the heat retaining cylinder 30 according to the first aspect of the present invention comprises:
The pyrolytic carbon coating 32 must be formed on the entire upper surface and inner surface of the graphite substrate 31 because the pyrolytic carbon coating 32 prevents contact between the graphite substrate 31 and SiO gas. This is because it is necessary to prevent the reaction shown in the above formula (1) from occurring. In particular, the inner upper part of the heat retaining cylinder 30 is a part which is heated most by the heater 20 and a part where the high-temperature SiO gas comes into contact first, and where the above-mentioned reaction (1) is most likely to occur. Therefore, the pyrolytic carbon coating 32 is
It is necessary to form at least the inner surface and the upper part of the heat retaining cylinder 30.

On the other hand, the surface of the graphite substrate 31 other than the portion where the pyrolytic carbon film 32 is formed must be exposed rather actively. The reason is that, when the silicon single crystal pulling apparatus 100 is checked, the gas in the graphite base material 31 is quickly removed from the closed main body 50 by using the porosity of the graphite base material 31 effectively as described above. This is because it is necessary to discharge the gas to maintain the degree of vacuum.

According to the heat retaining cylinder 30 of the present invention configured as described above, the following effects are exhibited.
In other words, the silicon single crystal pulling apparatus 100 containing the heat retaining cylinder 30 must check whether the internal airtightness is sufficient before starting the apparatus. This check is performed. At this time, the gas in the sealed main body 50 containing the heat retaining cylinder 30 is discharged to the outside by a vacuum pump. In this case, the gas permeating the graphite substrate 31 itself is
Are discharged from the closed main body 50 substantially simultaneously from the pores exposed from the pyrolytic carbon film 32 following the pressure drop in the closed main body 50. Therefore,
Even if the vacuum pump is stopped after reaching a certain degree of vacuum, gas does not flow out of the graphite base 31 into the sealed main body 50, and the airtightness required by the silicon single crystal pulling apparatus 100 is as follows. If there is no inflow from others, it will be sufficiently maintained.

Next, when the silicon single crystal pulling apparatus 100 containing the heat retaining cylinder 30 is started, the heater 20
As a result, the silicon in the crucible 10 is melted, and this silicon is monocrystallized and pulled up. During this time, the heat retaining cylinder 30 located immediately near the heater 20 is also heated, and the quartz crucible 11 constituting the crucible 10 is heated.
As shown in FIG. 2, the SiO gas from the furnace and the vaporized silicon itself in the crucible 10 scatter around the heat retaining cylinder 30.

However, in the heat retaining cylinder 30 according to the present invention,
Since the dense pyrolytic carbon film 32 as shown in FIG. 2 is formed, the SiO gas or Si gas scattered here may not contact the graphite substrate 31 by the pyrolytic carbon film 32. And therefore does not react with the carbon in the graphite substrate 31. In particular, the pyrolytic carbon coating 32 is made of Si
Since the O gas and the carbon in the graphite substrate 31 cover the inner upper surface of the heat retaining cylinder 30 heated to a temperature at which the reaction occurs, the carbon in the graphite substrate 31 does not react.

The heat insulating cylinder 30 uses the graphite base material 31 as its basic material, and the pyrolytic carbon coating 32 may be formed only on a certain portion of the graphite base material 31. On the whole, the cost is very low.

Therefore, the heat retaining cylinder 30 according to the first aspect of the present invention.
Can sufficiently maintain the degree of vacuum at the time of checking whether or not the silicon single crystal pulling apparatus 100 can be operated (hereinafter, referred to as an operation check), and can be inexpensive and have extremely high durability. It is.

[0023] In order to solve the above-mentioned problem, a second aspect is provided.
Means adopted by the invention according to the invention is that the graphite cylinder 31 constituting the substrate has an average thermal expansion coefficient from room temperature to 1000 ° C. of 3.5 to 3.5 with respect to the heat retaining cylinder 30 according to the first aspect.
6.0 × 10 ⁻⁶ / ° C., and the porosity according to the test method of JIS R7212 is 10% to 30% ”.

That is, the graphite substrate 31 of the heat retaining cylinder 30
First, the average coefficient of thermal expansion from room temperature to 1000 ° C. needs to be 3.5 to 6.0 × 10 ⁻⁶ / ° C.
The reason is that this kind of heat retaining cylinder 30 receives thermal stress due to heating by the heater 20 and cooling when the silicon single crystal pulling apparatus 100 itself is stopped. If the average thermal expansion coefficient is outside the above range, the pyrolytic carbon coating 32 will frequently peel off from the surface of the graphite substrate 31 due to the repetition of heating and cooling.

Further, in the heat retaining cylinder 30 according to the second aspect, the porosity according to the test method of JISR7212 is 10%.
It is necessary that the porosity is smaller than the above range, so that the gas discharge at the time of checking the operation of the silicon single crystal pulling apparatus 100 suddenly takes a long time. This is because the operation cannot be performed within a predetermined time. On the other hand, if the porosity exceeds the above range, the strength of the entire heat retaining cylinder will not be sufficiently resistant to the heating / cooling cycle, and it will be impossible to carry out the silicon single crystal pulling operation with security.

In order to solve the above-mentioned problem, the means adopted by the invention according to claim 3 is that the heat insulation cylinder 30 according to claim 1 or 2 is described as follows. 5% to 95% of the total surface area of the substrate "
That is what it was.

As described above, the reason why the exposed area of the graphite substrate 31 as the base of the heat retaining cylinder 30 from the pyrolytic carbon coating 32 needs to be 5% to 95% of the total surface area is as follows.
If it is larger than 5%, as in the case of the porosity described above,
This is because the effect of inhibiting the reaction between the Si vapor and the heat retaining cylinder 30 by the pyrolytic carbon coating 32 cannot be sufficiently exhibited. Further, if the exposed area of the graphite base 31 is smaller than 5%, the gas in the graphite base 31 cannot be sufficiently discharged within a predetermined time.

It should be noted that the heat insulating cylinder 30 has a graphite substrate 31.
A part of the exposed portion from the pyrolytic carbon film 32 is formed outside. The reason for this is that the exposed portion is first exposed by facing the source of Si vapor or SiO gas. Is to be blocked or altered. The reason for forming a part of the exposed portion of the graphite base material 31 outside is that the portion for discharging the gas in the graphite base material 31 during the operation check of the silicon single crystal pulling apparatus 100 can be easily formed. To do that. In other words, forming the exposed portion of the graphite base 31 outside the graphite base 31 means, for example, that the pyrolytic carbon coating 3
Applying a jig for preventing the formation of 2 or mechanically shaving off the pyrolytic carbon coating 32 formed on the portion can be easily performed if the exposed portion is outside. It is.

The graphite substrate 31 constituting the above-mentioned heat retaining cylinder 30 has an anisotropic ratio of thermal expansion coefficient of 1.2.
It is preferably 5 or less. This graphite base material 31
When the graphite substrate 31 is arranged in the direction shown in FIG. 1, the value of the coefficient of thermal expansion in the vertical direction, for example, 6.
0 × 10 ⁻⁶ / ° C. is a value in the horizontal direction, for example, 4.8 × 10
^Divided by ^-6 / ° C. The reason why it is preferable to set the anisotropic ratio of the graphite base material 31 to 1.25 or less is that this kind of heat retaining cylinder 30 receives the thermal shock as described above and is also shown in FIG. Since it must be formed in such a cylindrical shape, a large difference is not generated in the thermal expansion coefficient between the carbon constituting the graphite base material 31 and the pyrolytic carbon film 32, and the crack is prevented. This is to prevent the occurrence of.

In particular, if the above-mentioned heat retaining cylinder 30 has a tubular shape and a temperature difference is generated between the upper part and the lower part, the distance between the longitudinal direction and the lateral direction of the graphite base material 31 is reduced. If there is a large difference in the coefficient of thermal expansion, a shear stress is applied to the graphite substrate 31 and the pyrolytic carbon coating 32 coated thereon, so that the anisotropic ratio of the graphite substrate 31 is set to 1.25 or less. Is preferred.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to an embodiment shown in the drawings. FIG. 1 shows a silicon single crystal pulling apparatus 1 to which a heat retaining cylinder 30 according to the present invention is applied.
A vertical cross section of 00 is shown. In the silicon single crystal pulling apparatus 100, a crucible 10 for melting silicon is rotatably housed in a sealed main body 50 around a rotation shaft 55. The crucible 10 is heated around the crucible 10. Heater 20 is arranged. Outside the heater 20, a heat retaining tube 30 according to the present invention is disposed, and a heat insulating material 40 is accommodated between the heat retaining tube 30 and the sealed main body 50.

The crucible 10 has a double structure in which the portion directly in contact with the molten silicon is a quartz crucible 11, and the heater 20 is generally a so-called graphite heater. The surface of the molten silicon in the crucible 10 must be heated to a higher temperature to completely and sufficiently melt the silicon, and the liquid level of the molten silicon is lowered by pulling. Accordingly, the crucible 10 is moved upward so that the heat generation center of the heater 20 and the liquid level of the molten silicon in the crucible 10 have a fixed relationship.

The heat retaining cylinder 30 is made of graphite as a major part, and a part of the graphite substrate 31 is exposed on the surface of the graphite substrate 31 as shown in FIG. In this state, the pyrolytic carbon film 32 is formed.
The pyrolytic carbon coating 32 and the graphite substrate 31 have an average thermal expansion coefficient of 3.5 to 6.0 × 10 ⁻⁶ / ° C. from room temperature to 1000 ° C. of the graphite substrate 31 constituting the substrate. And the porosity according to the test method of JISR7212 is 10% to 30%.

Further, in the heat retaining cylinder 30 according to the present invention, as shown in FIG. 2, a portion exposed from the pyrolytic carbon film 32 of the graphite base material 31 is formed on the lower outer surface. The exposed area of the graphite base material 31 in this embodiment is about 20% of the total surface area of the graphite base material 31, but can be exposed within a range of 5% to 95%.

The heating cylinder 30 and the heater 20 described above are
Since the crucible 10 must be disposed at a fixed position with respect to the crucible 10 to be rotated, and an inert gas such as an argon gas must flow around the crucible 10, various members as shown in FIG. Is adopted. That is, first, the heater 20 is connected to the electrode 5 provided on the bottom surface of the closed body 50.
The power supply shaft 58 is supported while allowing electric power to be supplied from the outside by a conductive shaft 58 fixed on the terminal 4 and terminals 57 thereon. Since an inert gas passage as shown by an arrow in FIG. 1 must be formed between the upper end of the heater 20 and the heat retaining cylinder 30, the upper ring 51 is attached to the upper end of the heat retaining cylinder 30. is there. Of course, if the heat inside the sealed main body 50 is released to the outside, the silicon single crystal pulling apparatus 100 becomes inefficient, so that the space between the heat retaining cylinder 30 and the sealed main body 50 is naturally changed to other parts. As many heat insulating materials 40 as possible are arranged inside the closed main body 50.

On the bottom of the sealed main body 50, a bottom heat shield plate 53 is placed via a heat insulating material 40, and an exhaust port formed in the bottom heat shield plate 53 and the heat insulating material 40 is provided. Thus, during operation of the silicon single crystal pulling apparatus 100, the gas inside the silicon single crystal pulling apparatus 100 is exhausted. The supply of the inert gas into the sealed main body 50 is performed via a gas rectifying member 56 mounted on the upper part of the sealed main body 50. Note that the heat retaining cylinder 30 itself is the heater 2
Since it is sufficient to cover the periphery of 0, it is partitioned by a lower ring 52 as shown in FIG. 1, and the lower part of the lower ring 52 is a separate member.

The above silicon single crystal pulling apparatus 100
The member according to claim 1, wherein the base member formed of the graphite base material 31 is maintained in a vacuum state when the operation of the silicon single crystal pulling apparatus 100 is checked during operation. It is configured and implemented like a cylinder 30. This is because each constituent member does not have the volume of the graphite base material 31, but the gas permeating therein has a bad influence in maintaining the degree of vacuum in the sealed main body 50. Therefore, the base material such as the upper ring 51 is
It is good to form with the same graphite as the graphite base material 31 of the heat retaining cylinder 30, and to form the pyrolytic carbon film 32 on the inner lower surface of this graphite base material, for example. The above is because the lower ring 52, the bottom heat shield 53, or the terminal 5
7 and the conductive shaft 58.

Now, the insulated cylinder 30 according to the present invention will be described in more detail with reference to an embodiment including a method of manufacturing the same.

Example 1 70 parts by weight of aggregate coke pulverized to an average particle size of 20 μm and 30 parts by weight of coal tar pitch as a binder were heated and kneaded.
It was pulverized to 0 to 200 μm to form a carbon material raw material.

Using the carbon material, a desired compact was formed by a rubber press method, and the compact was fired and graphitized to form a graphite material. The obtained graphite material has an average coefficient of thermal expansion from room temperature to 1000 ° C. of 4.8 × 10 ^−6.
/ ° C, and the porosity according to the test method of JIS R7212 was 12%. The graphite substrate 31 has a pore radius of 75 Å to 750,000 by a mercury intrusion method.
The average pore radius in the measurement range of 0 Angstroms (the pore radius is plotted on the horizontal axis and the cumulative pore volume is plotted on the vertical axis, and the fine pore diameter corresponds to 1/2 of the final cumulative pore volume in the measurement range. The pore radius (indicated by the pore volume) was 12,000 angstroms, and the anisotropic ratio of the thermal expansion coefficient was 1.05.

This graphite material is processed to have an inner diameter of 630 m.
m, an outer diameter of 650 mm and a height of 700 mm were obtained.

The obtained graphite substrate 31 was placed in a CVD furnace and heated to 1400 ° C., and methane gas was continuously supplied into the furnace using hydrogen gas as a carrier. As a result, a pyrolytic carbon coating 32 having a thickness of 50 μm was formed on the entire surface of the graphite substrate 31. Therefore, the pyrolytic carbon coating 32 other than the pyrolytic carbon coating 32 shown in FIG. 2 was removed with sandpaper. The pyrolytic carbon coating 3 of the graphite substrate 31
A shield for preventing the formation of the pyrolytic carbon coating 32 is disposed on the surface where the formation of the pyrolytic carbon coating 32 is not necessary, and the pyrolytic carbon coating 32 is formed only at a predetermined position of the graphite base material 31. You may.

Example 2 70 parts by weight of aggregate coke pulverized to an average particle size of 20 μm and 30 parts by weight of coal tar pitch as a binder were heated and kneaded.
It was pulverized to 00 to 500 µm to form a carbon material raw material.

Using this carbon material, a graphite material was formed in the same manner as in Example 1 except for the graphitization temperature. The obtained graphite material has an average coefficient of thermal expansion of 4.1 × 10 ⁻⁶ / ° C. and a porosity of 27% according to the test method of JISR7212.
Met. The graphite substrate 31 has an average pore radius determined by the mercury intrusion method of 7 which is the maximum range that can be measured by the mercury intrusion method.
Above 5000 angstroms or more, the anisotropic ratio of thermal expansion coefficient was 1.25.

This graphite material was processed to obtain a graphite substrate 31 having the same shape as in Example 1, and a pyrolytic carbon film 32 was formed thereon in the same manner as in Example 1.

(Comparative Example 1) The graphite material of Example 1 was processed to obtain a graphite base material 31 having the same shape as that of Example 1,
0 was set.

Comparative Example 2 70 parts by weight of aggregate coke pulverized to an average particle diameter of 10 μm and 30 parts by weight of coal tar pitch serving as a binder were heated and kneaded, and the kneaded product was pulverized to 30 to 150 μm. Then, a carbon material was formed.

Using the carbon material, a desired compact was formed by a rubber press method, and the compact was fired and graphitized to form a graphite material. The obtained graphite material had an average pore radius determined by mercury intrusion method of 9000 angstroms and an anisotropic ratio of thermal expansion coefficient of 1.10. The average thermal expansion coefficient of this graphite material is 6.5 × 10 ^−G / ° C.
The porosity according to the test method of 7212 was 8%.

The graphite material was processed to obtain a graphite substrate 31 having the same shape as that of Example 1, and a pyrolytic carbon film was formed on the entire main cylinder.

Comparative Example 3 After heating and kneading 70 parts by weight of aggregate coke pulverized to an average particle diameter of 20 μm and 30 parts by weight of coal tar pitch serving as a binder, the kneaded product was mixed with 1 part.
It was pulverized to 00 to 300 μm to form a carbon material.

Using the carbon material, a desired compact was formed by a stamping press method, and the compact was fired and graphitized to form a graphite material. The obtained graphite material has an average pore radius measured by a mercury intrusion method of 7 which is the maximum range that can be measured by the mercury intrusion method.
Above 5000 Å, the anisotropic ratio of the thermal expansion coefficient was 1.35. Further, the porosity according to the test method of JISR7212 was 32%.

This graphite material was processed to obtain a graphite base material having the same shape as in Example 1, and a pyrolytic carbon film was formed thereon in the same manner as in Example 1.

The thus-obtained heat retaining cylinder 30 was set in a silicon single crystal pulling apparatus 100, and the gas in the closed main body 50 having the same volume was discharged by a vacuum pump. At this time, the time required for the degree of vacuum in the sealed main body 50 to reach a predetermined value or more, and after stopping the vacuum pump,
When the time required for the degree of vacuum to become equal to or less than the predetermined value was measured, the results shown in the following Table 1 were obtained.

[Table 1] In addition, when the life of each of the heat retaining cylinders was compared, the results shown in the following Table 2 were obtained.

[Table 2]

[0054]

As described in detail above, first, in the invention according to claim 1, as exemplified in the above embodiment,
"The silicon single crystal pulling apparatus is disposed between a heater 20 for heating the crucible 10 in the silicon single crystal pulling apparatus 100 and a heat insulating material 40 for preventing heat from the heater 20 from moving outside. 100 is a heat insulation cylinder 30 for keeping heat inside, and the upper part and the entire inner surface of the heat insulation cylinder 30 are covered with a coating 32 made of pyrolytic carbon. " When placed in a vacuum space, the gas inside can be exhausted in a short period of time, so that there is no misidentification due to the presence of the graphite base when checking the airtightness of the silicon single crystal pulling device. In addition, it is possible to provide a durable and inexpensive heat insulating cylinder that can prevent flakes from being separated from the graphite substrate.

According to the second aspect of the present invention, in the heat retaining cylinder 30 according to the first aspect, the average thermal expansion coefficient of the graphite base material 31 constituting the base from room temperature to 1000 ° C. is 3.5. 6.0 × 10 ⁻⁶ / ° C., and the porosity according to the JISR7212 test method is 10%
It is characterized by being 30%, whereby the object of the first aspect of the present invention can be achieved, and in addition, the pyrolytic carbon coating is peeled off from the graphite substrate surface by repeated heating and cooling. It is possible to provide a heat retaining cylinder that does not need to be performed.

Further, according to the third aspect of the present invention, in the heat retaining cylinder 30 according to the first or second aspect, the exposed area of the base from the coating film 32 is 5% of the total surface area of the base.
The feature of the structure is that it is set to be up to 95%, whereby the object of claim 1 or 2 can be achieved.
It is possible to provide a heat retaining cylinder that can perform sufficient adsorption of steam.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a silicon single crystal pulling apparatus employing a heat retaining cylinder according to the present invention.

FIG. 2 is a partially enlarged cross-sectional view mainly showing a pyrolytic carbon coating of the heat retaining cylinder.

FIG. 3 is a cross-sectional view showing a conventional silicon single crystal pulling apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 silicon single crystal pulling apparatus 10 crucible 11 quartz crucible 20 heater 30 heat retaining cylinder 31 graphite base material 32 pyrolytic carbon coating 40 heat insulating material 50 closed body

Claims (3)

[Claims] 1. A silicon single crystal pulling apparatus disposed between a heater for heating a crucible in a silicon single crystal pulling apparatus and a heat insulating material for preventing heat from the heater from moving to the outside. A heat insulation cylinder for a silicon single crystal pulling apparatus, comprising: a heat insulation cylinder for keeping the inside of the heat insulation cylinder, wherein an upper part and an entire inner surface of the heat insulation cylinder are coated with a coating made of pyrolytic carbon. 2. The graphite base material constituting said base material has an average coefficient of thermal expansion from room temperature to 1000 ° C. of from 3.5 to 1,000 ° C.
2. The heat retaining cylinder for a silicon single crystal pulling apparatus according to claim 1, wherein the temperature is 6.0 × 10 ⁻⁶ / ° C. and the porosity according to the test method of JISR7212 is 10% to 30%. 3. An exposed area of the base from the coating,
The thermal insulation cylinder for a silicon single crystal pulling apparatus according to claim 1, wherein the thermal insulation cylinder is 5% to 95% of the total surface area of the substrate.