JPH05270971A - Graphite crucible for single crystal pulling process and its production - Google Patents

Abstract

PURPOSE:To suppress the generation of thermal stress and strain, to prevent the deformation and damage of a crucible and to prolong the life of the crucible by setting the average pore diameter to be smaller at the lower part of a graphite crucible than at the upper part. CONSTITUTION:Mesophase powder composed of two components having different particle diameters (e.g. average particle diameters of 10mum and 42mum) is produced by finely crushing a mesophase obtained by the heat-treatment of coal tar, etc., in vacuum. A carbonaceous raw material compounded with mesophase powder having an average particle diameter of 10mum is filled in the lower part of a rubber vessel and a carbonaceous raw material compounded with mesophase powder having an average diameter of 42mum is filled in the upper part of the rubber vessel. The vessel is subjected to rubber-press forming to obtain a formed material. The formed material is carbonized in an electric furnace and graphitized by a graphitizing furnace in Ar atmosphere at about 2500 deg.C to obtain a graphite crucible 15 for single crystal pulling process. The average pore diameter of the upper part of the crucible is >=0.5mum and that of the lower part of the crucible is <=0.5mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphite crucible for pulling a single crystal and a method for manufacturing the same, and more particularly to a crucible for pulling a single crystal used for growing a single crystal of a semiconductor material such as Si and a method for manufacturing the same.

[0002]

2. Description of the Related Art At present, most of the single crystal silicon used to form substrates for integrated circuit devices such as LSIs is manufactured by the Czochralski method (CZ) in which a silicon melt in a quartz crucible is rotated and pulled up. It is manufactured by a rotary pulling method called a method). The single crystal pulling apparatus used in this method includes a quartz crucible for melting a semiconductor material and a graphite crucible having the quartz crucible inside, and a heating means such as a graphite heater from around the graphite crucible, and the graphite crucible and A single crystal is grown by heating the quartz crucible to turn the semiconductor material in the quartz crucible into a molten liquid and pulling the molten liquid while rotating.

During pulling of a silicon single crystal, the graphite crucible is usually heated to a temperature higher than the melting point of silicon. Therefore, a reaction occurs at the contact surface between the graphite crucible and the quartz crucible,
CO, SiO, etc. are generated, and the consumption of these crucibles progresses. Further, the generated SiO gas further reacts with the graphite crucible, and the surface layer portion of the graphite crucible is converted into SiC. Thus, as the graphite crucible is used many times, the consumption of the graphite crucible progresses, and on the other hand, the graphite crucible becomes SiC. Further, a portion of the silicon single crystal which becomes high temperature during pulling is a lower portion of the graphite crucible, and SiC is remarkably expressed in the lower portion of the graphite crucible.

Further, S scattered by bumping when Si is melted
The i melt, the Si vapor generated when the silicon is pulled up, or the like causes Si to adhere to the outer surface of the graphite crucible in a droplet form. This adhesion of Si appears remarkably in the upper part of the graphite crucible having a low temperature when pulling up silicon.

The surface of such a graphite crucible is made of SiC or S
Due to the adhesion of i, the graphite crucible is subject to thermal stress and strain due to the thermal expansion difference between graphite and SiC and Si.
There was a problem that the graphite crucible was damaged.

Further, in recent years, in order to obtain a single crystal with a high yield, the diameter of the single crystal has been increased and the graphite crucible has been increased in size accordingly, which causes the generation of thermal stress and strain in the graphite crucible. The probability of breakage of the graphite crucible increases, and the life of the graphite crucible decreases.

In order to reduce the warp of the graphite crucible due to such thermal stress and strain, conventionally, the warp caused by the fact that the coefficient of thermal expansion of SiC formed by conversion on the graphite surface is higher than that of the graphite material is prevented. Therefore, the thermal expansion coefficient of the graphite crucible was adjusted, and the smaller the average pore diameter, the more Si produced.
Focusing on the fact that the O and CO gases are less likely to pass and the SiC formation reaction is suppressed, the average pore diameter is set to 15,000Å (= 1.
5 μm) or less, the S of the surface layer of the graphite crucible is reduced.
Attempts have been made to reduce iC conversion (Japanese Patent Laid-Open No. 58-1).
56595).

[0008]

As described above, the Si
The carbonization reaction is promoted as the temperature is higher, and Si is more likely to be attached at lower temperatures.

However, in the above graphite crucible for pulling a single crystal, the temperature of the graphite crucible during the pulling of the silicon single crystal is high in the lower part, whereas the temperature is low in the upper part. In this case, SiC formation is promoted in the lower part of the graphite crucible having a high temperature, and the thickness of the SiC conversion layer becomes thicker, while conversely, S is formed in the upper part of the graphite crucible having a low temperature.
The iC layer has a small thickness. Therefore, due to the non-uniformity of the thickness of the SiC layer above and below the graphite crucible, the graphite crucible is subject to non-uniform thermal stress and strain to increase the probability of cracking.

On the other hand, Si adheres to the surface of the graphite crucible during the pulling of the silicon single crystal mostly in the upper part of the graphite crucible having a low temperature of the graphite crucible, whereas in the lower part of the graphite crucible, the adhered Si is vaporized or becomes SiC. , Si hardly adheres. Therefore, due to the non-uniformity of the Si thickness in the upper and lower parts of the graphite crucible, there is a problem that the graphite crucible is subjected to non-uniform thermal stress and strain, which increases the probability of cracking.

The present invention has been made in view of the above-mentioned problems, and the unevenness of SiC formation on the surface of the graphite crucible,
Another object of the present invention is to provide a graphite crucible for pulling a single crystal and a method for producing the same, which can eliminate non-uniformity of Si adhesion, suppress thermal stress and strain, and prevent cracking of the graphite crucible.

[0012]

In order to achieve the above-mentioned object, the graphite crucible for pulling a single crystal according to the present invention is such that the average pore diameter in the lower portion of the graphite crucible is smaller than the average pore diameter in the upper portion of the graphite crucible. It has a feature.

Further, in the above-described method for producing a graphite crucible for pulling a single crystal, carbonaceous material raw materials containing mesophase powders having different average particle diameters are separately arranged in an upper portion and a lower portion, which are molded and then carbonized. The feature is that it is graphitized.

[0014]

The SiC formation on the surface of the graphite crucible increases as the temperature rises. Therefore, during the pulling of the silicon single crystal, the SiC formation layer becomes thicker in the lower part of the graphite crucible having a high temperature, and unevenness occurs. In order to prevent this, it is effective to make the average pore diameter of the lower part of the graphite crucible smaller than that of the upper part of the graphite crucible.

This is because as the average pore diameter becomes smaller, the SiO and CO gases produced by the reaction become more difficult to pass through, and S
This is because the iC formation reaction is suppressed and the thickness of the SiC formation layer can be prevented from increasing, and the smaller the average pore diameter, the smaller the thickness reduction of the graphite crucible.

On the other hand, since Si is mostly adhered to the surface of the graphite crucible where the temperature is low, a large amount of Si is adhered to the upper portion of the graphite crucible having a low temperature during the pulling of the silicon single crystal to cause nonuniformity. In order to prevent this, it is effective to increase the average pore diameter of the upper portion of the graphite crucible, that is, to make the average pore diameter of the lower portion of the graphite crucible smaller than that of the upper portion of the graphite crucible.

The reason for this is that as the average pore diameter increases, the penetration of Si adhering to the surface of the graphite crucible into the pores is promoted, and accompanying this, the adhered Si becomes less likely to be in the form of droplets, and the evaporation of Si and SiC It can be mentioned that the oxidization is promoted and the surface adhesion of Si is suppressed.

The effect of suppressing SiC formation is that the average pore diameter is 0.5.
It was confirmed by experiments that when the thickness is smaller than about μm, the effect becomes remarkable and the thickness reduction can be prevented. Therefore, it is considered preferable that the average pore diameter of the lower part of the graphite crucible is smaller than 0.5 μm.

On the other hand, it has been confirmed by experiments that the effect of suppressing Si adhesion becomes remarkable when the average pore diameter is 0.5 μm or more and cracking can be prevented. Therefore, it is considered preferable that the average pore diameter of the upper portion of the graphite crucible is 0.5 μm or more.

The average pore diameter here is a value obtained from the pore distribution measured by the mercury porosimetry using a mercury porosimeter.

The boundary between the upper part and the lower part of the graphite crucible is not particularly limited, but it is preferable that the boundary is close to the center part. It is desirable that the innermost part of the graphite crucible from the lowermost part to the bottom part of the graphite crucible is the most vigorous, and at least the lower part of the graphite crucible has a smaller average pore diameter. In the middle portion of the graphite crucible, these intermediate regions may be present.

As a method of producing the above graphite crucible for pulling a single crystal, for example, a method of separately arranging carbonaceous material containing mesophase powders having different average particle diameters, shaping the carbonaceous material, and then carbonizing to graphitize is preferable. ..

Here, the mesophase powder refers to a pulverized product of a self-sintering carbonaceous raw material obtained by heat-treating a coal-based or petroleum-based heavy oil at about 400 to 500 ° C. The mesophase has microspheres exhibiting optical anisotropy, which are formed by layering condensed polycyclic organic aromatic compounds produced during softening and melting during solidification, or a combined phase thereof, and have a volatile content of 8 to 20%. Is included. This mesophase powder is pulverized into particles having an average particle size of 30 μm, and then is shaped, carbonized, and graphitized.
When the mesophase powder is used as described above, it is possible to control the pore size after molding and firing depending on the particle size after pulverization. The average pore diameter of the obtained graphite material increases as the particle diameter increases.

In the production method using the mesophase powder, complicated steps such as repeating a step of impregnating a graphite material having a small average pore size and then firing can be omitted, and the above graphite crucible can be easily produced. it can.

According to the above-mentioned structure, since the average pore diameter in the lower portion of the graphite crucible is smaller than the average pore diameter in the upper portion of the graphite crucible, SiO and CO gas generated in the lower portion of the graphite crucible are hard to pass through, and the SiC formation reaction occurs. Is suppressed, and adhesion of Si is suppressed in the upper part of the graphite crucible.

Further, in the above-described method for producing a graphite crucible for pulling a single crystal, carbonaceous material raw materials containing mesophase powders having different average particle sizes are separately arranged in the upper part and the lower part, which are molded and then carbonized. Since the graphite crucible is graphitized, the graphite crucible can be easily manufactured.

[0027]

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples of a graphite crucible for pulling a single crystal and a method for producing the same according to the present invention will be described below.

Example 1 First, coal tar was heat-treated at a vacuum degree of 50 Torr and a temperature of 430 ° C. for about 3 hours to prepare a mesophase having a volatile content of 18.2%. Mesophase powders with diameters of 10 μm and 42 μm were produced.

Next, a carbon material raw material containing the mesophase powder is filled in a rubber container, and rubber press molding is performed. A schematic cross section of an example of the rubber container used at this time is shown in FIG. Reference numeral 11 in the figure denotes a rubber container, which is composed of a bottom surface portion 12 formed in a disc shape, a cylindrical side surface portion 13 and an upper surface portion 14 formed in a concave shape in cross section. In the rubber press molding method, water is first poured into a pressure container, the mesophase powder is put into the rubber container 11, and the rubber container 11 is put into the pressure container filled with water to perform hydrostatic molding. A pressure of 1500 kg / cm ² is applied to the rubber container 11 by this hydrostatic molding. At this time, the rubber container 11 is attached to the bottom of the rubber container 11.
Up to ½ of the height, the carbon material raw material containing the mesophase powder 16 having an average particle diameter of 10 μm is filled, and the carbon material raw material containing the mesophase powder 17 having an average particle diameter of 42 μm is filled in the upper part of the rubber container 11. Perform molding. Further, at the time of filling, the filling density is adjusted to be the same in the upper and lower parts.

Then, the molded body obtained by the rubber press molding is put into an electric furnace in a nitrogen atmosphere and carbonized by heating it to 1000 ° C. Then, the obtained carbon material is heated to 2500 ° C. in a graphitizing furnace in an Ar atmosphere. It heated and graphitized. The graphite material thus obtained was processed into a graphite crucible 15 having a diameter of 12 inches (inner diameter 310 mm), which was divided into two vertically, as shown in FIG.

[Example 2] A graphite crucible was manufactured in the same manner as in Example 1 except that the upper portion was filled with a carbon material containing an average particle diameter of 42 µm and the average particle diameter of 19 µm.

[Example 3] A graphite crucible was manufactured in the same manner as in Example 1, except that the upper part was filled with a carbon material containing an average particle size of 35 µm and the average particle size of 19 µm was mixed.

[Comparative Examples 1 to 5] As shown in Table 1, those filled with a carbon material mixed with mesophase powder having the same average pore size in the upper and lower sides were manufactured.

[0034]

[Table 1]

The average pore diameter of the graphite crucible thus produced and the life and end of use of the graphite crucible when a silicon single crystal is produced by a Czochralski method silicon single crystal pulling apparatus using the graphite crucible The condition of the surface of the graphite crucible is also shown in Table 2. The life of the graphite crucible is determined by repeatedly pulling up the silicon single crystal.
It represents the number of repetitions until the graphite crucible is deformed and damaged.

[0036]

[Table 2]

As is clear from Table 2, in the graphite crucible for pulling a single crystal according to the example, the average pore diameter of the upper portion of the graphite crucible is larger than the average pore diameter of the lower portion of the graphite crucible, and the upper portion of the graphite crucible has an average pore diameter. Is 0.5 μm or more, and the average pore diameter of the lower part is 0.5 μm or less. Si adhesion to the surface of the graphite crucible is small, and the formation of SiC uniformly occurs throughout the graphite crucible, and the thinning of the crucible is also small. .. Therefore, the life of the graphite crucible is extended to 15 times or more.

On the other hand, in the graphite crucibles produced as in Comparative Examples 1 and 2 so that the average pore diameters of the upper and lower portions of the graphite crucible were 0.5 μm or more, the lower portion of the graphite crucible had a large amount of SiC, and the thickness reduction occurred. And the life of the graphite crucible was 10 times or less.

In addition, as in Comparative Examples 3 to 5, in the graphite crucibles manufactured so that the average pore diameters of the upper and lower portions of the graphite crucible were 0.5 μm or less, the adhesion of Si to the surface of the graphite crucible was large, Since the difference in the coefficient of thermal expansion of the adhered Si and the coefficient of thermal expansion of the carbon material of the graphite crucible causes fracture, the service life is shortened.

Therefore, by making the graphite crucible so that the average pore diameter of the upper portion of the graphite crucible is larger than the average pore diameter of the lower portion of the graphite crucible, Si adhesion on the surface of the graphite crucible is reduced as compared with the conventional one. In addition, since the entire graphite crucible can be uniformly turned into SiC, the life of the graphite crucible can be extended to about 1.5 times.

[0041]

As is apparent from the above description, the graphite crucible for pulling a single crystal according to the present invention has the average pore diameter in the lower portion of the graphite crucible smaller than the average pore diameter in the upper portion of the graphite crucible. At S
It is possible to suppress iC and non-uniform adhesion of Si, prevent deformation and damage of the graphite crucible due to the difference in thermal expansion coefficient, and prolong the life of the graphite crucible.

Further, in the above-mentioned method for producing a graphite crucible for pulling a single crystal, carbonaceous material raw materials containing mesophase powders having different average particle diameters are separately arranged in the upper and lower parts, which are molded and then carbonized. Since it is graphitized by using the above method, the graphite crucible can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a rubber container filled with mesophase powder.

FIG. 2A is a perspective view showing an example of a graphite crucible according to the present invention, and FIG. 2B is a sectional view.

[Explanation of symbols]

 15 Graphite crucible 16, 17 Mesophase powder

Claims (2)

[Claims] 1. The average pore diameter in the lower part of the graphite crucible is
A graphite crucible for pulling a single crystal, which is smaller than the average pore diameter in the upper part of the graphite crucible. 2. The carbonaceous material raw material containing mesophase powders having different average particle diameters is separately arranged in an upper part and a lower part, which are molded and then carbonized to be graphitized. A method for manufacturing a graphite crucible for pulling a single crystal.