JPH0873292A - Graphite crucible for pulling up semiconductor single crystal - Google Patents

Abstract

PURPOSE: To obtain a graphite crucible with which good pulling up of a semiconductor single crystal is possible and which is long in life and is cost effective by composing the cylindrical body at the peripheral edge of the crucible of an anisotropic carbon fiber reinforced carbon material. CONSTITUTION: This graphite crucible 1 is composed of a stand 2 which constitutes its bottom, the cylindrical body 3 which is inserted into a projecting part 5 formed at the peripheral edge in the upper part of this stand 2 and an annular spacer 4 which is placed at the inner peripheral edge of the bottom of the cylindrical body 3. The cylindrical body 3 is formed of the anisotropic carbon fiber reinforced carbon material which is circumferentially arranged with carbon fibers in tight contact with each other substantially parallel, contains >=25wt.% carbon fibers and is of 1.:0.01 to 0.2 in the ratio of the thermal conductivity in the circumferential direction and the vertical direction.

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 semiconductor single crystal, and more particularly to a graphite crucible capable of pulling a good semiconductor single crystal and having a long life and economical.

[0002]

2. Description of the Related Art A quartz glass crucible used for producing a silicon single crystal from molten silicon by a pulling method is
It is used with its surroundings held by a graphite crucible. A semiconductor silicon single crystal is produced by melting high-purity polycrystalline silicon in a quartz glass crucible and pulling it up with a seed crystal. However, the quartz glass crucible softens after the treatment temperature reaches 1400 ° C or higher. Deform. For this purpose, the quartz glass crucible is housed and held in a graphite crucible for use.

The graphite crucible used for such purposes is
Since the coefficient of thermal expansion is different from that of the quartz glass crucible fitted therein, it may be damaged during use, and as a means for solving this problem, it is known to make the graphite crucible into a crack type (Japanese Utility Model Publication No. 52-27880). At present, this type of graphite crucible is widely used.

However, when this cracking type graphite crucible is used, the silica glass crucible and the graphite crucible inside the graphite crucible react during use to form SiC on the inner surface of the graphite crucible, and A phenomenon occurs in which the divided portions gradually move outward.

To explain this, reference numeral 10 in FIG. 8 is a conventional graphite crucible, and a quartz glass crucible (not shown) is substantially closely inserted therein to form a crucible for pulling a semiconductor single crystal. When the graphite crucible 10 for pulling up a semiconductor single crystal is repeatedly used, as shown in the figure, the edge portion 11 causes an outward warpage.

A defective graphite crucible 1 in such a state
When 0 is used, the quartz glass crucible inside this is expanded to a shape that closely contacts the graphite crucible along the outside, and the shape becomes large, and the temperature distribution in the circumferential direction becomes non-uniform and melts. The liquid level of the liquid fluctuates to adversely affect the crystal growth, the oxygen concentration becomes large, and a good single crystal cannot be obtained, and the yield of the silicon single crystal decreases.

Further, when the deformation of the graphite crucible becomes large, the quartz glass crucible inserted inside the graphite crucible expands and becomes thin, and when the degree of deformation becomes large, molten silicon leaks from the quartz glass crucible and seeps out. There was a fear that it would occur.

Further, as described above, when the cracking type graphite crucible is used, the quartz glass directly receives the radiant heat of the heater through the cracks of the graphite crucible and is softened to further accelerate the reaction with the graphite, or the molten silicon is partially melted. It is a cause of non-uniformity of the temperature distribution in the circumferential direction of silicon by heating the silicon. Therefore, various methods for reducing the deformation of the graphite crucible have been proposed so far.

For example, Japanese Utility Model Publication No. 3-43250 proposes that the side wall portion of the graphite crucible is made of an integral carbon fiber reinforced carbon material. In this method, a continuous tow of carbon fiber reinforced carbon material is helically wound and molded and cured to form a crucible.

Although this graphite crucible is certainly satisfactory in terms of strength, it cannot impart anisotropy to the thermal conductivity of the crucible, and as a result, it causes vertical convection in the melt inside the crucible. However, even if a silicon single crystal was pulled up using this graphite crucible, it was not possible to sufficiently lower the oxygen concentration of the melt and obtain a good single crystal with a good yield.

As another prior art, a graphite crucible for producing a silicon single crystal is provided, which is provided with a cylindrical portion having slits on the outer peripheral edge of a pedestal constituting a bottom portion, and an annular spacer is provided on the pedestal in the cylindrical portion. A holder has been proposed (Japanese Patent Publication No. 2-7).
917). However, even in this graphite crucible, there is no anisotropy in the thermal conductivity, so that convection of the melt is not sufficiently performed, and further improvement is required to perform good pulling of a single crystal with this graphite crucible. It was a thing.

[0012]

DISCLOSURE OF THE INVENTION The present invention is a graphite crucible using carbon fiber, and even if the crucible is repeatedly used for pulling a silicon single crystal, the edge portion is warped to the outside or is fitted into the quartz crucible. The present invention is intended to obtain a graphite crucible that does not break due to the difference in thermal expansion coefficient from the glass crucible, and that the silicon melt is well convected to obtain a good silicon single crystal.

[0013]

According to the present invention, there is provided a cradle that constitutes a bottom of a crucible, a tubular body fitted inside a convex portion formed on an upper peripheral edge of the cradle, and a bottom of the tubular body. Graphite crucible composed of annular spacers placed on the inner peripheral edge, in which carbon fibers are cylindrically arranged in close contact with each other in the circumferential direction, and the thermal conductivity in the circumferential direction is vertical. A graphite crucible for pulling up a semiconductor single crystal, characterized by being an anisotropic carbon fiber reinforced carbon material having a higher ratio than the above ratio (claim 1), and the upper part of the base of the graphite crucible is a cylindrical body placed thereon. The graphite crucible for pulling up a semiconductor single crystal according to claim 1, characterized in that it does not protrude above the lowermost surface of the tubular body inside the tubular body (claim 2), the circumferential direction and the vertical direction of the tubular body. The ratio of the thermal conductivity of 1: 0.01-
The graphite crucible for pulling a semiconductor single crystal according to claim 1 or 2, wherein the cylindrical body contains 25% by weight or more of carbon fiber. Alternatively, it is the graphite crucible for pulling up a semiconductor single crystal according to 2. Hereinafter, these inventions will be further described.

The graphite crucible of the present invention comprises a cradle forming the bottom of the crucible, a cylindrical body fitted inside the convex portion formed on the upper peripheral edge of the cradle, and a bottom inner peripheral edge of the cylindrical body. The tubular body is made of an anisotropic carbon fiber reinforced carbon material.

FIG. 1 is a sectional view of a graphite crucible 1 according to an embodiment of the present invention. In FIG. 1, 2 is a pedestal that constitutes the bottom of the graphite crucible, 3 is a tubular body, and 4 is an annular ring, which constitute an assembled graphite crucible 1 as shown.

That is, the convex portion 5 is provided on the upper peripheral edge of the mount 2,
The bottom of the tubular body 3 is placed inside the convex portion 5. Further, an annular ring 4 is fitted to the inner peripheral edge of the bottom of the tubular body 3 to form the graphite crucible 1.

The tubular body 3 used in the present invention is made of an anisotropic carbon fiber reinforced carbon material in which carbon fibers 6 are arranged substantially parallel to each other in the circumferential direction and in close contact with each other as shown in FIG. To do. As a result, the tubular body 3 used in the present invention can have the circumferential thermal conductivity higher than the vertical thermal conductivity.

That is, although the carbon fiber has a large thermal conductivity in the length direction, but the thermal conductivity in the direction perpendicular to the length direction (thickness direction) is small, the carbon fiber as shown in FIG. The tubular body of carbon fiber reinforced carbon material, which is arranged in close contact with each other, has a small thermal conductivity in the height direction and can be increased in the circumferential direction.

According to the second aspect of the invention, as shown in FIG. 3, the shape of the crucible mount is changed. This stand 7
A flat portion 8 is formed on the peripheral edge of the upper surface, and the tubular body 3 is placed on the flat portion 8. In this case, the upper portion of the gantry 7 is tubular inside the tubular body 3. It is designed so as not to project above the lowermost surface of the body 3.

In contrast to the above, FIG. 4 shows that the upper part 10 of the gantry 9 projects above the lowermost surface of the tubular body 3 inside the tubular body 3. In this case, the graphite of the gantry 9 has a thermal expansion coefficient higher than that of the carbon fiber reinforced carbon material forming the tubular body 3, so that the gantry 9 of the graphite crucible may be cracked during use.

However, in the case where the upper part of the pedestal 7 does not project above the lowermost surface of the tubular body 3 inside the tubular body 3 as in the present invention shown in FIG. Even if thermal expansion occurs during use, it can be avoided that the cylindrical body 3 is damaged due to the difference in coefficient of thermal expansion. Also in the invention of claim 2, the same cylindrical body 3 and annular ring 4 as those of the invention of claim 1 are used.

According to the third aspect of the present invention, the ratio of the thermal conductivity in the circumferential direction to the vertical direction of the tubular body is 1: 0.01 to 0.2. According to the experiments by the inventors, the ratio of the thermal conductivity in the circumferential direction to the thermal conductivity in the vertical direction is in the above range, that is, the thermal conductivity in the circumferential direction of the tubular body is 5 to 100 in the height direction. By doubling, it is possible to generate a required temperature difference in the vertical direction in the silicon melt in the quartz glass crucible fitted in the graphite crucible.

The ratio of the thermal conductivity is 0.0 with respect to 1 in the circumferential direction.
It is difficult to manufacture at 1 or less at present, and when it is at least 0.2, the difference in thermal conductivity is small, and it is possible to make the temperature of the silicon melt in the quartz crucible sufficient in the vertical direction. Absent. Among these, the more preferable thermal conductivity ratio is 1: 0.02-0.15, and the most preferable ratio is 1:
It is 0.05 to 0.1.

The invention of claim 4 is characterized in that the above-mentioned tubular body contains 25% or more of carbon fibers. The strength of carbon fiber is 25%.
By including the above, the cylindrical portion of the graphite crucible can be made thin while reducing the weight while maintaining the required strength. If the carbon fiber content is less than 25%, it cannot be expected that the graphite crucible has a sufficient strength. Furthermore, carbon fiber rarely reacts with quartz glass to produce SiC, and it is effective in this respect that carbon fiber is contained in an amount of 25% or more.

That is, the graphite crucible is used for pulling a silicon single crystal by inserting a quartz glass crucible into the inside of the graphite crucible. At this time, the inside of the graphite crucible reacts with the quartz glass and is silicified to form the graphite crucible. To damage. However,
Carbon fibers are less likely to react with quartz glass than ordinary graphite. Therefore, if the tubular body contains 25% or more of carbon fibers, damage to the graphite crucible can be avoided.
A more preferable range of the carbon fiber content is 30% by weight.
That is all.

When pulling a semiconductor single crystal such as silicon, temperature control of the melt in the crucible is extremely important. Therefore, in the present invention, the thermal conductivity in the circumferential direction of the graphite crucible is increased, while the thermal conductivity in the vertical direction is decreased conversely, whereby the temperature difference between the upper and lower sides of the melt in the crucible is made as large as possible. However, the convection of the melt is generated.

According to this, when the silicon single crystal is pulled up, oxygen released from the quartz glass container itself can be released from the melt to the outside by utilizing the convection of the melt. This will be described below with reference to FIGS. 6 and 7.

FIG. 6 shows the state of convection of the melt in the crucible when pulling a silicon single crystal using a conventional graphite crucible, and FIG. 7 shows when the silicon single crystal is pulled using the graphite crucible according to the present invention. FIG. 3 is an explanatory view showing the state of convection of the melt in the quartz glass crucible fitted in each graphite crucible in an easy-to-understand manner.

In FIGS. 6 and 7, reference numerals 20 and 20 'are crucibles,
21 and 21 'are seed crystals, and 22 and 22' are melts. Further, 23 and 23 'are silicon single crystals. The conventional crucible shown in FIG. 6 has a temperature difference in the circumferential direction (horizontal direction), but has a relatively small temperature difference in the vertical direction. Therefore, convection of the melt in the vertical direction is not sufficiently performed, Oxygen generated after leaving the quartz glass crucible container is seldom pushed into the melt and finally released from the liquid surface, and the generated oxygen remains in the silicon single crystal. Often.

On the other hand, as shown in FIG. 7, in the crucible of the present application, the thermal conductivity in the circumferential direction of the graphite crucible was increased, and the thermal conductivity in the vertical direction of the crucible was decreased, so that the melt in the crucible was melted. It becomes possible to increase the temperature difference between the upper side and the lower side.

For this reason, convection of the melt occurs above and below in the crucible, and the oxygen generated by separating from the container of the quartz glass crucible is pushed up in the melt and is vigorously released from the liquid surface. It became so.

The tubular body used in the present invention can be manufactured by a known method. That is, a conductive type having a predetermined thickness is used, and the carbon fibers are closely wound so that the carbon fibers are positioned substantially parallel to each other in the circumferential direction of the type and the adjacent carbon fibers are closely contacted with each other. Is so-called close packing. By winding the carbon fibers so as to be the closest packed, it is possible to obtain an anisotropic carbon tubular body in which the thermal conductivity in the circumferential direction is larger than that in the vertical direction.

The cylindrical body was placed in a 10 to 30% acetic acid aqueous solution, and the mold wound with the carbon fiber was used as an anode for direct current application to anodize the carbon fiber to remove the sizing agent coated on the surface. To do.

Next, this is subjected to direct current in a 5 to 30% aqueous solution of furfuryl alcohol by using carbon fiber as an anode to polymerize and deposit furfuryl alcohol on the surface of the carbon fiber. This method has already been disclosed in Japanese Patent Application Laid-Open No. 1-282385. After the prescribed polymerization is completed, this is heated at 60 ° C for 2 hours and then at 100 ° C for 6 hours.
The water is removed by drying at 200 ° C. for 6 hours. After that, it is demolded and baked. For example, the heating rate is 5
C./hour and 1000 ° C. in a non-oxidizing atmosphere. After that, for example, the heating rate is set to 100 ° C./hour and 2500 ° C.
Graphitization is performed at the above temperature. This is cut into a predetermined length and post-processed such as aligning the ends to obtain a final cylindrical body.

[0035]

According to the present invention, the tubular body of the graphite crucible is made of the anisotropic carbon fiber reinforced carbon material, and the thermal conductivity of the graphite crucible in the circumferential direction is significantly increased as compared with that in the vertical direction. Therefore, the silicon melt causes vertical convection to reduce the oxygen concentration of the melt, and a good silicon single crystal can be obtained.

[0036]

EXAMPLE A graphite crucible having a cross section shown in FIG.
A P-type silicon single crystal having a diameter of 6 inches was pulled using a pulling crucible in which an 8-inch quartz glass crucible was fitted. A carbon fiber reinforced single-material sheet as described below was used for the tubular body of the graphite crucible. Further, as the graphite, isotropic graphite was used.

Bulk density (BD) (g / cm ³ ) 1.6, bending strength (BSt) (Mpa) 300, coefficient of thermal expansion CTE (° / c)
Vertical, 4.8 × 10 ⁶ , horizontal, 0.8 × 10 ⁶ , thermal conductivity (W / mk) vertical, 30, horizontal, 400. The results are shown in Table 1. That is, the number of pulling times (the number of times the crucible was used), the single crystallization rate (yield), the number of hot water leaks, and the average oxygen concentration were as shown in the table below.

[0038]

[Table 1]

[0039]

According to the present invention, it is possible to obtain a graphite crucible which has high strength and can be repeatedly used for a long period of time without being damaged, and by using this graphite crucible, the silicon melt in the quartz glass crucible can be obtained. However, it is possible to maintain a uniform temperature in the circumferential direction of the quartz glass crucible, and a temperature difference occurs in the vertical direction to cause convection. As a result, oxygen released from the quartz glass container is generated. Was raised in the molten silicon and pushed up to the upper surface thereof, and was finally released from the liquid surface to obtain a high-quality silicon single crystal with a reduced oxygen concentration.

[Brief description of drawings]

FIG. 1 is a sectional view of a graphite crucible according to an embodiment of the present invention.

FIG. 2 is a side view of a tubular body of a graphite crucible according to an embodiment of the present invention.

FIG. 3 is a sectional view of a graphite crucible according to another embodiment of the present invention.

FIG. 4 is a sectional view of a graphite crucible of a comparative example, which is compared with the present invention.

FIG. 5 is a cross-sectional view of a graphite crucible showing dimensions of each part according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram showing convection of a melt in a conventional crucible.

FIG. 7 is an explanatory view showing convection of the melt in the crucible of the present invention.

FIG. 8 is a cross-sectional view of a conventional graphite crucible having a warp at its edge.

[Explanation of symbols]

1 ... Graphite crucible, 2, 7 ... Stand, 3 ... Cylindrical body, 4 ... Annular ring.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Taguchi 2-32 Nishikonakadai, Hanamigawa-ku, Chiba City, Chiba Prefecture (72) Inventor Takao Nakagawa 1-17-3 Suehiro, Kawaguchi City, Saitama Prefecture Across Co., Ltd. (72) Inventor Masaharu Tachibana 1-17-3 Suehiro, Kawaguchi City, Saitama Prefecture Across Co., Ltd. (72) Inventor Mihoko Yamashita 1-17-3 Suehiro, Kawaguchi City, Saitama Prefecture Across Co., Ltd.

Claims (4)

[Claims] 1. A cradle that constitutes the bottom of the crucible, a tubular body fitted inside a convex portion formed on the upper peripheral edge of the cradle, and an annular spacer placed on the inner peripheral edge of the bottom portion of the tubular body. An anisotropy in which the cylindrical crucible is composed of carbon fibers arranged in close contact with each other in the circumferential direction, and the thermal conductivity in the circumferential direction is greater than the thermal conductivity in the vertical direction. A graphite crucible for pulling a semiconductor single crystal, which is a carbon fiber reinforced carbon material. 2. The semiconductor according to claim 1, wherein the upper portion of the graphite crucible mount does not protrude above the lowermost surface of the tubular body inside the tubular body placed thereon. Graphite crucible for pulling single crystals. 3. The semiconductor single crystal pulling-up according to claim 1, wherein the ratio of the thermal conductivity in the circumferential direction of the cylindrical body to the vertical direction is 1: 0.01 to 0.2. Graphite crucible. 4. The graphite crucible for pulling a semiconductor single crystal according to claim 1, wherein the tubular body contains 25% by weight or more of carbon fiber.