JP2000351670A - Graphite material, graphite material for forming sic film and part for device for pulling silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a graphite material which can prevent cracks generated by a difference between the thermal expansion of the graphite material and that of SiC, can stand a rapid rise of temperature and has improved thermal characteristics, by controlling the thermal expansion coefficient, heat conductivity or/and thermal shock resistance coefficient, and a thermal expansion coefficient anisotropy ratio at specific values, respectively. SOLUTION: This graphite material is formed by mixing a filler (aggregate) such as petroleum coke with a binder such as pitch, molding the mixture into a prescribed shape, and then thermally treating the molded product to carbonize and cake the binder. The aggregate is suitably selected to give the graphite material having a thermal expansion coefficient of 3.0 to 4.0×10-6/k at 293 to 673 k, a heat conductivity of >=120 W/(m.k) at 293 k or/and a thermal shock resistance coefficient of >=80 kW/m, and a thermal expansion coefficient anisotropy ratio of <=1.1. The graphite material preferably further has a bulk density of >=1.70 Mg/m3, a tensile strength of >=20 MPa, an elastic coefficient of <=11 GPa, and an ash content of <=20 ppm by an ashing method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphite material having excellent thermal characteristics, a graphite material having a SiC film, and a component for a silicon single crystal pulling apparatus using the same.

[0002]

2. Description of the Related Art When pulling a single crystal of silicon (hereinafter referred to as Si), for example, Japanese Patent Application Laid-Open No. 61-256993 is used.
And an apparatus for pulling a Si single crystal by the Czochralski method as exemplified in JP-B-6-2637.

In this Si single crystal pulling apparatus, a quartz crucible housed in a graphite crucible is filled with polycrystalline Si, and heated to 1800 K in an inert gas atmosphere by a graphite heater provided around the graphite crucible. Thus, a polycrystalline Si is melted, and a seed chuck having a single crystal Si attached to the tip thereof is brought into contact with the melt surface, and the structure can be pulled up while rotating.

[0004] Usually, in addition to the above-mentioned crucible and heater, the internal parts constituting the furnace of the Si single crystal pulling apparatus include:
There are an inner shield, a leak prevention ring for Si vapor and the like, a lower ring, an upper ring, a spill tray, a seed chuck, and the like, which are also made of a graphite material.

However, when a graphite material is used for a furnace part of a Si single crystal pulling apparatus, there are the following problems (1) to (4).

(1) The graphite material reacts with a silicon monoxide gas (hereinafter, referred to as SiO gas), a quartz crucible or the like generated when pulling up the Si single crystal, and a surface layer portion thereof is formed of silicon carbide (hereinafter, referred to as SiC). )). When the surface layer is converted to SiC, the volume expands and internal stress is generated in the graphite component, which causes breakage.

(2) Since graphite and SiC have different coefficients of thermal expansion, thermal stress is generated, and this thermal stress causes breakage of graphite parts.

(3) Speaking of the graphite crucible, usually,
Since it is divided into two or three, the coefficient of thermal expansion is significantly different from that of quartz crucibles (the coefficient of thermal expansion of quartz crucibles: 0.5 × 10 ⁻⁶ / K), it is opened outward by cooling and becomes a graphite crucible. There is a problem that a large stress is generated in the device.

(4) The graphite crucible is consumed by reacting with the SiO gas or the quartz crucible at the time of raising the temperature or at the time of pulling up, and the strength becomes weak. In such a case, it may be broken if it receives stress for some reason.

[0010] In recent years, pulling of Si ingots having a diameter of 8 inches or more has become mainstream.
Since the single crystal pulling device itself has also become larger, heat loss is large, and in terms of energy saving measures and from the viewpoint of shortening operation time, graphite materials that can withstand this even if the temperature is rapidly raised to a predetermined temperature are used. It has been demanded.

[0011]

SUMMARY OF THE INVENTION The present invention has the above problems,
That is, for a graphite material, a SiC film-forming graphite material, and a single crystal pulling device, which can prevent cracks and cracks caused by a difference in thermal expansion from SiC and have improved thermal characteristics so that they can withstand rapid temperature rise. The purpose is to provide parts.

[0012]

The inventors of the present invention have conducted intensive studies and as a result, have focused not only on reducing the thermal expansion difference between graphite and SiC but also on improving the thermal shock resistance. By developing and using a graphite material having a controlled expansion coefficient and thermal shock coefficient, the above problems can be solved and the present invention has been completed.

That is, the graphite material of the present invention comprises:
A graphite material excellent in thermal shock resistance characterized by satisfying the condition (c). (A) The thermal expansion coefficient of 293K to 673K is 3.0 to 4.0.
^Be within the range of 0 × 10 ⁻⁶ / K. (B) The thermal conductivity at 293K is 120 W / (m · K) or more, and / or the thermal shock coefficient ≧ 80 kW /
m. (C) Anisotropic ratio of thermal expansion coefficient ≦ 1.1. Is the gist.

The present invention will be described in more detail as follows. First, the graphite material used in the present invention is 293K
The coefficient of thermal expansion at -673K is 3.0-4.0 x ^10-6 /
K range. When a graphite material having a coefficient of thermal expansion of less than 3.0 × 10 ⁻⁶ / K or a graphite material exceeding 4.0 × 10 ⁻⁶ / K is used, a stress is generated due to a difference in thermal expansion from SiC, Cracks and cracks occur. Preferably, the range of the coefficient of thermal expansion is 3.5-4.0 × 10 ⁻⁶ / K. The reason is that since the thermal expansion coefficient of SiC at 293K to 673K is 3.5 to 4.0 × 10 ⁻⁶ / K, the difference in thermal expansion coefficient can be almost eliminated.

Next, in the present invention, the thermal conductivity at 293 K is 120 W / (m · K) or more and / or the thermal shock coefficient is 80 kW / m or more. Preferably 90
kW / m or more. Improving the thermal conductivity of the graphite material is not limited to improving the thermal shock coefficient (R) described below, but also starting up the Si single crystal apparatus, that is,
Since the time required for pulling up Si can be reduced, the thermal efficiency can be improved. Preferably, the thermal conductivity is 130 W / (m · K) or more.

The thermal shock coefficient (R) is one of the important characteristics in graphite materials, and the tensile strength (σ) is expressed in units of (M
Pa), thermal conductivity (κ): unit is (W / (m · K)),
Thermal expansion coefficient (α): Unit is (× 10 ⁻⁶ / K), elastic coefficient (meaning the same content as Young's modulus)
(E): Assuming that the unit is (GPa), R = (σκ / α)
E). The unit of the thermal shock coefficient (R) is (kW /
m).

The thermal shock coefficient (R) is composed of the four constituent factors of the above-mentioned thermal conductivity, tensile strength, thermal expansion coefficient, and elastic coefficient. If the thermal conductivity and the tensile strength of the graphite material are increased, the thermal shock coefficient (R) can be increased, and this configuration can solve the problem of providing a graphite material suitable for rapid heating. is there.

In the present invention, the coefficient of thermal expansion of the conventional graphite material (4.0 to 5.0 × 10 ⁻⁶ / K) is made smaller to approximate SiC. (The denominator of the above equation is reduced.) This means that the thermal shock coefficient (R) is relatively increased, and is very resistant to thermal shock and free from stress due to a difference in thermal expansion from SiC. No cracks or cracks occur.

Next, in the present invention, a graphite material having an anisotropic ratio of thermal expansion coefficient of 1.1 or less is preferable. Further, a graphite material having an anisotropic ratio of thermal expansion coefficient of 1.05 or less is preferable. For example, regarding a graphite crucible, since a quartz crucible can be heated uniformly, there is no uneven heating of the Si melt. Therefore, S
This can contribute to the improvement of the quality of the i single crystal. In the present invention, it is more preferable from the viewpoint of strength to use an isotropic graphite material which is isotropically pressed. Anisotropic ratio is 293K
The thermal expansion coefficients in the X-axis, Y-axis, and Z-axis directions up to 673 K are measured, and the ratio between the largest value and the smallest value is referred to.

The bulk density of the graphite material is 1.70 M
g / m ³ or more. The conversion rate to SiC has a correlation with the bulk density, and the larger the pores, the higher the conversion rate. When the bulk density is 1.70 Mg / m ³ or more, the conversion rate of SiC is suppressed.

The graphite material has a tensile strength of 20M.
It is preferably at least Pa, more preferably at least 25 MPa.
Increasing the tensile strength requires the thermal shock coefficient (R)
It is an important factor in improving the quality of the Si single crystal pulling device, but is not limited thereto. Effective for preventing cracking.

The elastic modulus of the graphite material is 11 GPa or less,
Further, the pressure is preferably 10 GPa or less. Decreasing the elastic modulus is an important factor for improving the thermal shock coefficient (R), but is not limited thereto. If the elastic modulus is higher than 11 GPa, the graphite material itself is not preferable because it becomes brittle.

It is preferable that the graphite material has reduced impurities through a purification process. Specifically, the total ash content by the incineration method is preferably 20 ppm or less, and more preferably 5 pp.
m or less is preferable.

The above-described graphite material is most suitable as an internal component constituting a furnace of a Si single crystal pulling apparatus. In FIG. 1, in addition to the graphite crucible 8 and the graphite heater 7, there are an inner shield 11, an upper shield 16 for preventing leakage of Si vapor and the like, a lower ring 9, an upper ring 12, a spill tray 15, a seed chuck 1, and the like. These are also preferably made of the above graphite material.

The above-mentioned graphite material can be suitably used for dies for continuous casting and parts for hot pressing. Further, since the thermal expansion coefficient is the same as that of SiC, it is needless to say that it is optimal for a substrate such as a pancake barrel susceptor coated with SiC for epitaxial growth. Also, S
The graphite material according to the present invention, which is excellent in SiC exfoliation resistance, since a SiC film is formed on a part or the entire surface of a wall material made of a graphite material used for a furnace wall of a CVD furnace or a CVR furnace handling i. Is suitable as a substrate. Furthermore, in order to improve the SiC resistance, it is also effective as a graphite material for forming a SiC film in which a part or all of the surface of the graphite material is previously impregnated or / and coated with a SiC film.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION A graphite material having a controlled thermal shock coefficient by controlling tensile strength, thermal conductivity, elastic modulus and thermal expansion coefficient in the present invention is used as a crucible or a heater.
It was used for an i single crystal pulling apparatus.

The graphite material is obtained by mixing a filler (aggregate) such as petroleum coke and a binder (binder) such as pitch, forming the mixture into a predetermined shape, and heat-treating the binder into carbon. Formed. The thermal expansion coefficient of this graphite material can be adjusted by selecting the aggregate itself to have a low thermal expansion coefficient. Also, tensile strength,
Each of the thermal conductivity, the elastic coefficient, and the thermal expansion coefficient can be within a predetermined range by selecting an appropriate one for the thermal property and the physical property of the aggregate.

The methods and conditions for measuring the tensile strength, thermal conductivity, elastic coefficient and thermal expansion coefficient according to the present invention are described below.

The tensile strength and the elastic modulus (Young's modulus) are each Japanese Industrial Standard (hereinafter referred to as JIS).
R722-1997 and R7202-1979.

Regarding the thermal conductivity, JIS R1611
−1991.

The coefficient of thermal expansion was measured using a thermomechanical analyzer (TMA8310) manufactured by Rigaku Corporation.
The coefficient of thermal expansion up to 73K was determined.

[0032]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[Example 1] The tensile strength was 25.5MP.
a, the thermal conductivity at 293K is 120 W / (m · K), 2
A thermal expansion coefficient of 3.9 × 10 ⁻⁶ / K of 93K to 673K;
The elastic coefficient is 9.8 GPa, the thermal shock coefficient is 80 kW /
m and isotropic graphite having an anisotropic ratio of thermal expansion coefficient of 1.05 were produced. After processing this graphite material into a graphite crucible, 230
At 0 K, a halogen-containing gas containing dichlorodifluoromethane as a main component was flowed for 5 hours to perform a high-purification treatment, thereby obtaining an ultra-high-purity graphite crucible having a total ash content of 0.5 ppm. The graphite crucible was installed on a CZ apparatus to pull up an Si single crystal having a diameter of 8 inches.

[Example 2] The tensile strength was 28.5MP.
a, the thermal conductivity at 293K is 130 W / (m · K), 2
A coefficient of thermal expansion of 93 × 673K is 4.0 × 10 ⁻⁶ / K,
The elastic coefficient is 10.3 GPa and the thermal shock coefficient is 90 kW /
An Si single crystal having a diameter of 8 inches was pulled under the same conditions as in Example 1 except that isotropic graphite having a m and an anisotropic ratio of thermal expansion coefficient of 1.02 was used.

[Example 3] The tensile strength was 26.4MP.
a, thermal conductivity at 293K is 136 W / (m · K), 2
The coefficient of thermal expansion of 93K to 673K is 3.3 × 10 ⁻⁶ / K,
Elasticity coefficient is 9.9 GPa, thermal shock coefficient is 110 kW /
An Si single crystal having a diameter of 8 inches was pulled under the same conditions as in Example 1 except that isotropic graphite having an anisotropic ratio of m and a coefficient of thermal expansion of 1.00 was used.

[Comparative Example 1] Tensile strength 27.4MP
a, thermal conductivity at 293K is 104 W / (m · K), 2
The coefficient of thermal expansion of 93K to 673K is 4.7 × 10 ⁻⁶ / K,
The elastic coefficient is 10.3 GPa and the thermal shock coefficient is 59 kW /
An Si single crystal having a diameter of 8 inches was pulled under the same conditions as in Example 1 except that isotropic graphite having a m and an anisotropic ratio of thermal expansion coefficient of 1.05 was used.

[Comparative Example 2] Tensile strength is 31.4MP
a, thermal conductivity at 293K is 128 W / (m · K), 2
The coefficient of thermal expansion between 93K and 673K is 4.6 × 10 ⁻⁶ / K,
The elastic modulus is 11.8 GPa and the thermal shock coefficient is 74 kW /
An Si single crystal having a diameter of 8 inches was pulled under the same conditions as in Example 1 except that isotropic graphite having a m and an anisotropic ratio of thermal expansion coefficient of 1.03 was used.

Comparative Example 3 A tensile strength of 53.9MP
a, the thermal conductivity at 293K is 70 W / (m · K), 29
Thermal expansion coefficient of 5.6 × 10 ⁻⁶ / K, elastic modulus of 13.2 GPa, thermal shock coefficient of 51 kW /
An Si single crystal having a diameter of 8 inches was pulled under the same conditions as in Example 1 except that isotropic graphite having an anisotropic ratio of m and a coefficient of thermal expansion of 1.00 was used.

[Comparative Example 4] Tensile strength of 15.3MP
a, the thermal conductivity at 293K is 120 W / (m · K), 2
The coefficient of thermal expansion of 93K to 673K is 2.0 × 10 ⁻⁶ / K,
Elastic modulus is 10 GPa, thermal shock coefficient is 92 kW / m,
An 8-inch-diameter Si single crystal was pulled under the same conditions as in Example 1 except that an embossed graphite material having an anisotropic coefficient of thermal expansion of 1.39 was used.

The physical properties of the graphite crucibles used in Examples 1 to 3 and Comparative Examples 1 to 4, the number of times the crucible was used when using a Si single crystal, the change due to use, and the amount of warpage when cracked Are summarized in Table 1.

[0041]

[Table 1]

From the above, when the coefficient of thermal expansion of 293K to 673K is out of the range of 3.0 to 4.0 × 10 ^-6 / K, the surface layer of the graphite crucible or graphite heater is converted to SiC. As a result, a thermal expansion difference is caused to cause cracks and cracks, and the life end is achieved with a small number of uses. In addition to the thermal stress, a warp occurs in the two- or three-part crucible and a gap is generated, and the heat and light from the heater directly hit the quartz crucible, causing temperature unevenness.
Defect i may occur. 80kW thermal shock coefficient
If it is less than / m, a rapid rise in temperature may cause the graphite crucible to crack. Further, when a graphite crucible having an anisotropic ratio larger than 1.1 is used, heat uniformity is poor. The Si single crystal obtained in Comparative Example 4 had crystal defects as a result of subsequent analysis.

[0043]

As described above, as a component for a Si single crystal pulling apparatus, such as a graphite crucible or a graphite heater, which is constantly exposed to SiO gas and whose surface is converted to SiC, as well as repeated rapid rise and fall in temperature, Alternatively, by using the graphite material of the present invention with controlled thermal expansion coefficient and thermal shock coefficient or thermal conductivity as a furnace wall material of a CVD furnace or a CVR furnace exposed to a gas containing Si, thermal shock or SiC It is possible to suppress the occurrence of cracks and cracks due to the formation. Further, by controlling the anisotropic ratio, excellent heat uniformity is obtained. Further, since the thermal conductivity is excellent, it is very effective in terms of thermal efficiency in terms of energy saving and shortening of operation time.

[Brief description of the drawings]

FIG. 1 is a schematic view of a Si single crystal pulling apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Seed chuck 2 Si seed crystal 3 Si single crystal 4 Quartz crucible 5 Fused polycrystalline Si 6 Heat insulating material 7 Graphite heater 8 Graphite crucible 9 Lower ring 10 Exhaust port 11 Inner shield 12 Upper ring 13 Chamber 14 Viewing window 15 Spill tray 16 Upper shield 17 Support rod

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/208 H01L 21/208 P (72) Inventor Yoshinori Yonemoto 2181- Nakahime, Onohara-cho, Mitoyo-gun, Kagawa Prefecture 2 Inside Toyo Tanso Co., Ltd. (72) Inventor Yuji Okawa 211-2-2 Nakahime, Onohara-cho, Mitoyo-gun, Kagawa Prefecture Inside (72) Inventor Kiyohide Sasaki 211-2-2 Nakahime, Onohara-cho, Mitoyo-gun, Kagawa Toyo Tanshi Inside the corporation

Claims (5)

[Claims] 1. The thermal expansion coefficient of 293K to 673K is 3.
0 to 4.0 × 10 ⁻⁶ / K, thermal conductivity at 293K is 12
A graphite material having a thermal expansion coefficient of 0 W / (m · K) or more and an anisotropic ratio of 1.1 or less. 2. The thermal expansion coefficient of 293K to 673K is 3.
0-4.0 × 10 ⁻⁶ / K, thermal shock coefficient 80 kW / m
As described above, a graphite material having an anisotropic coefficient of thermal expansion of 1.1 or less. 3. A graphite material having a SiC film formed by forming a SiC film on a part or all of the surface of the graphite material according to claim 1. 4. A component for a silicon single crystal pulling apparatus using the graphite material according to claim 1. 5. The component for a silicon single crystal pulling apparatus according to claim 4, wherein the component is a graphite crucible or a graphite heater.