JPH10158090A - Manufacture of c/c material (carbon fiber-carbon composite material) crucible for pulling up semiconductor single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crucible structure which is capable of easily coping with the increase in size of the crucible by using a C/C material as the material of a graphite crucible for a single crystal pulling-up device and further, in which the properties with respect to high strength at high temp. of the C/C material is effectively utilized and also to provide this manufacture of the graphite crucible having such a structure. SOLUTION: In this manufacture, a graphite crucible has an inner/outer double structure such that the crucible consists of a C/C material which is a high strength member and formed on the outer side of the crucible, and an isotropic graphite material (CIP(cold-isotropic-pressed) material) formed on the inner side of the crucible, or alternatively, consists of a C/C material divided into two sections, i.e., a straight hollow cylinder section and a bottom section including a curved surface part (radiused(R) part). This manufacture comprises performing two-stage forming, namely, performing preforming by a hand lay-up autoclave method or filament winding method to form a preformed body and thereafter, performing press forming of the preformed body with a mold to obtain a formed body. Then, the formed body is baked and further processed by a densification process. This densification process comprises: a stage for receiving the baked body in a hermetically sealed metallic vessel and sintering the body under a pressure or in a pitch-gas enriched atmosphere, to enhance the sintering yield by inhibiting volatilization loss from being caused; and further, a stage for coating the outer peripheral surface of the crucible with pyrolytic graphite or pyrolytic carbon, converting the matrix part of the C/C material into hard carbon or subjecting the whole C/C material to semi-graphitization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crucible made of carbon fiber composite carbon material (hereinafter referred to as C / C) used for supporting a quartz crucible of a semiconductor single crystal pulling apparatus.

[0002]

2. Description of the Related Art A crucible apparatus applied to the Czochralski method (CZ method) has a double structure of a quartz crucible for melting a semiconductor such as Si and a graphite crucible for accommodating and supporting the semiconductor from outside. Has become.

[0003] In general, semiconductor materials, especially single crystals of silicon, are mainly produced by a rotational pulling method called a Czochralski method. The Czochralski method is a crystal growing method in which a single crystal is grown by rotating and pulling a seed crystal immersed in a melt.

For example, when producing a silicon single crystal, a high-purity silicon polycrystal is heated and melted by an external carbon heater in a quartz glass crucible housed in a graphite crucible, and a silicon seed crystal is first added to the melt. And slowly pull it up while rotating.

[0005] This operation is carried out at a temperature of about 1450 ° C across the solid-liquid boundary temperature of silicon of 1413 ° C. Since quartz glass begins to soften at a temperature of 1200 ° C or more, it is supported by a graphite crucible. Prevents deformation due to softening. As described above, the quartz glass and graphite come into contact during the silicon single crystal pulling operation, and SiO ₂ + C → CO ₂ + Si
The graphite crucible is consumed by the reaction of O _{2 and} the like, and the wall thickness is reduced.

In order to prevent this, for example, Japanese Patent Laid-Open No. 63-1
In Japanese Patent No. 17988, the value of the degree of graphitization (1-P) calculated using the Franklin P value is determined at a temperature of 2500 ° C.
A graphite for producing a semiconductor single crystal, comprising a graphite material having a pore structure having a pore size of 0.6 or less after treatment and having a radius of 1 µm or more and occupying 0.1 cm ³ / g or less. Although a crucible has been proposed, the graphite crucible is replaced about 20 times in a single crystal pulling operation.

[Problems to be solved by the invention]

Recently, a proposal has been made to use a C / C material having a high strength even with a thin wall for a graphite crucible. For example, in Japanese Utility Model Publication No. 3-43250, the cylindrical side wall is made of C / C,
There is a crucible using graphite material as a base part. In a similar proposal, Japanese Utility Model Registration No. 3012299 discloses a combination crucible made of a C / C member in which a straight body portion and an R portion of a crucible are integrated with a graphite bottom part.

However, although expensive C / C materials are used,
Taking advantage of the characteristics of high-strength C / C material, it is still unsatisfactory for the optimum configuration and manufacturing method for large crucibles.

[0009]

SUMMARY OF THE INVENTION The present invention provides a single crystal pulling crucible which solves the above-mentioned problems, and has a structural feature and a manufacturing method.

[0010] The structural feature is isotropic graphite material (CIP material)
Is a high strength member C / C material with high density and low surface area CI as an inner / outer double structure with C / C material on the outside and C / C material on the outside
It is made of a material exhibiting the characteristics of the P material or a C / C material divided and formed on the bottom including a straight cylindrical portion and a curved surface portion.

The feature of the manufacturing method is that, in addition to the conventional C / C material manufacturing method, a hand lay-up method, an autoclave method, a tape lay-up, using various carbon fiber fillers (including both carbonaceous and graphite materials). It includes two-stage molding in which preforming is performed by an autoclave method or the like, and then press molding is performed using a mold.

The molded article is fired, and the densification process is carried out in a sealed metal container in addition to the conventional method. Increasing the rate.

In order to suppress the reaction of the crucible material with SiO ₂ , Si and SiO gas, the outer peripheral surface of the crucible is coated with pyrolytic graphite or pyrolytic carbon in addition to the usual process products, or C / C
The method includes the step of converting the matrix portion of the material into hard carbon or semi-graphitizing the entire material (semi-graphitizing).

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a semiconductor single crystal having a diameter of 8 mm.
Needs are larger than inches, and accordingly, quartz crucibles for pulling single crystals and graphite crucibles also become large diameter crucibles. Generally, the size of a crucible is about three times the diameter of a single crystal.

Therefore, to obtain an 8-inch silicon single crystal, a crucible having a diameter of about 24 inches is required.
It is said that the crucible material needs to have a diameter of 36 inches or more in order to obtain a silicon single crystal having a large diameter of 12 inches or more in the future. The present invention proposes a configuration of a crucible material that can cope with this large diameter and a method of manufacturing the same.

Next, the present invention will be described in more detail with reference to preferred embodiments. A graphite crucible that houses and supports the quartz crucible from the outside has a double inner and outer structure, and a CIP material is used on the side in contact with the inner quartz crucible as an outer strength member.
C / C for pulling semiconductor single crystal integrated with composite
It is a C / C crucible for pulling up a semiconductor single crystal in which a C crucible or a graphite crucible is divided into a cylindrical portion and a bottom curved surface portion.
An example of the configuration is shown in FIGS.

According to the present invention, the above-mentioned configuration enables the C / C material to exhibit its ability as a strength member, improve moldability, and reduce manufacturing costs.

That is, the C / C material cylindrical portion supports a stress in the outer diameter direction of the crucible, and a CIP material having low reactivity is used to suppress the reaction with the quartz crucible, or the CIP material is divided into a cylindrical portion and a bottom curved surface portion. As the C / C material crucible, a configuration is adopted in which only the bottom C / C material having a relatively large reaction is replaced. With this configuration, crucible costs can be reduced.

The characteristics required for use in graphite crucibles are as follows:
The purpose of the present invention is to prevent deformation of a quartz glass crucible when pulling a semiconductor single crystal such as silicon, and to hold molten metal such as silicon from leaking or flowing out. At this time, the graphite crucible needs at least a high temperature strength capable of withstanding the total weight and temperature of the solution of the semiconductor such as silicon and the quartz glass.

According to the structure of the present invention, a C / C material which is superior in high-temperature strength is used as a strength member, and a CIP material is used to suppress a reaction with quartz glass, or a bottom curved surface portion which has a large reaction consumption is divided. A method of exchanging the C / C material of the bottom curved surface portion is adopted.

Next, the C / C material used for the crucible is preformed by a filament winding method (FW method), a hand lay-up autoclave molding method or the like in addition to the conventional production method, and then pressed by using a mold. Including two-stage molding.

Conventionally, in autoclave molding of C / C material,
The pressure is 10 kg / cm because it is pressurized by gas pressure.
It is about ² G, and cracking between layers is inevitable for thick materials due to insufficient pressure. In the case of molding using only a mold, there are restrictions on the shape for filling, the compression ratio, and the like, and it has been difficult to increase the size.

When the two-stage molding of the present invention is employed, the matrix resin is semi-cured by autoclave molding (B stage).
Then, pressurization, curing, and molding are completed with a mold that matches the finish shape. For this reason, a large-sized product can be easily formed.

The C / C material obtained by this method has a fine structure, and the reaction with silicon or the like is suppressed. In general, the quality of the initial molding of the carbon material structure is directly reflected in the final process. Therefore, a dense molded product can be obtained at the time of molding and cracks can be prevented. The bulk specific gravity of the C / C material can be easily increased in the forming step.

When carbon fiber of knitted knitting is used in addition to the conventional cloth, felt, and yarn as the C / C material, a dense layer can be obtained without laminating the curved surface portion without cutting the fiber. The material of the C / C material includes using a carbon fiber filler (cloth, felt, yarn, short fiber) and at least one of resin beads, graphite powder, and carbon powder.

1 of resin-based beads, graphite powder or carbon powder
By adding more than one species, the C / C material manufactured using a usual phenolic resin, pitch, or the like as a matrix generates voids (voids) of various sizes therein. The voids which are visible to the naked eye remain as voids without being filled even in the densification process in which the impregnation and firing are repeated thereafter.

For this reason, the bulk specific gravity is hardly increased, and as a result, the strength characteristics and the reaction resistance are reduced. By adding one or more of resin-based beads, graphite powder or carbon powder, the distribution and size of the voids can be controlled, and a dense structure can be obtained.

One example is the case where carbon powder having a particle size of 5 to 15 μm is added by 10% to the carbon fiber filler.
Compared with the C material, the average pore diameter was 3 μm in the present invention and 9 μm in the conventional method, and the open pore diameter could be reduced to 1/3. The total pore amount of the product of the present invention was 6 to 8%, whereas that of the conventional method was 10 to 15%.

Since the average pore diameter is small and the total pore amount can be reduced, the reactivity with Si, SiO and SiO ₂ is suppressed, and the life of the crucible can be extended. In the densification step, usually, the pitch or resin is impregnated and calcined and carbonized in an inert atmosphere for 2 to 7 times, or the equipment becomes large, but HIP (Hot Isotropic Prep) is used.
ss hot isostatic pressing).

When the C / C material is manufactured by the HIP method, cracks due to contraction of the matrix during primary carbonization can be prevented. As a result, voids due to thermal decomposition shrinkage become uniform,
It becomes easy to increase the density in the next step.

HIP can be densified and fired to a predetermined bulk specific gravity in one step. However, in order to obtain a large C / C material, the HIP device is huge and is difficult to adopt in the production of the C / C material due to large equipment costs, maintenance costs, and running costs.

In the present invention, an atmosphere similar to a HIP is created and densified without using a HIP device.
That is, in one of them, a C / C intermediate material impregnated with pitch or resin is sealed in a metal case in the coexistence of pitch and fired under pressure. At this time, the metal case has a structure capable of being sealed, and one or more small holes of 2 to 5 mmφ are provided or a safety valve is provided to prevent explosion.

At this time, the maximum firing temperature does not need to be 800 ° C. or higher, but 450 to 550 ° C. is sufficient. As another method, when firing a C / C intermediate material impregnated with a pitch or a resin, the pitch is arranged around the C / C intermediate material and fired in a pitch gas-enriched atmosphere, thereby carbonizing the impregnating agent. The residue ratio can be improved, and the densification process can be shortened by repeating impregnation and firing.

The maximum firing temperature in the densification step is 600 ° C.
The following is sufficient. The present invention extends the life of a graphite crucible for pulling up a Si semiconductor single crystal by coating the outer surface of a crucible with pyrolytic graphite to extremely lower the gas permeability to reduce Si, SiO,
Includes limiting the reaction with SiO ₂ to surface reactions.

Two methods are provided as the method. Part 1
The method is to use pyrolytic graphite (P) on the final finished surface of graphite crucible.
G) or a method of coating pyrolytic carbon (PC).
PG can be coated using a high vacuum CVD apparatus.

PG by this method is usually from 2000 to 22.
Formed at 00 ° C. PG has low reactivity with Si, SiO and SiO ₂ , so that the life of graphite crucible is 5 to 10 times longer than that of the conventional C / C material.

As a second best PC coating method, when the final graphite crucible is heat-treated at normal pressure or reduced pressure in a hydrocarbon gas atmosphere such as pitch, pyrolytic carbon can be coated on the surface of the graphite crucible. Thereafter, it is obtained by performing a high purification treatment.

The coating of the above pyrolytic graphite or pyrolytic carbon is made of Si, SiO, SiO 2 when the open pore diameter becomes 2 μm or less.
_In addition to the tendency of graphite crucibles to decrease in reactivity with ₂ , the surface is also an effective measure for extending the life because the surface is covered and filled with open pores following the surface.

In the present invention, the matrix portion of the C / C material is
Includes semi-graphitizable carbon to suppress the reaction with i, SiO, and SiO ₂ . The consumption of the C / C material is large not in the carbon fiber but in the carbon material in the matrix portion. By configuring the carbon material of the matrix portion with semi-graphitizable carbon having low reactivity with Si, SiO, and SiO ₂ , the life of the graphite crucible can be extended.

The matrix portion is converted to semi-graphitizable carbon by using a non-graphitizable resin or an impregnant obtained by adding soot to pitch in the densification step, or by lowering the final graphitization temperature to semi-graphitize. Obtained by: The heat treatment temperature for semi-graphitization is 2400 ° C. or less for a graphitizable pitch-based binder or impregnating agent. The temperature is set to 2600 ° C. or less for a non-graphitizable resin binder or impregnating agent.

[0041]

According to the present invention, a large crucible suitable for a semiconductor single crystal pulling apparatus can be provided at a low cost, utilizing the characteristics of a high-strength C / C material, and is industrially useful.

[0042]

[Brief description of the drawings]

FIG. 1 is a graphite crucible having a double structure according to the present invention, wherein the inside is made of a CIP material and the outside is made of a C / C composite material.

FIG. 2 is an embodiment of a C / C composite material outside the graphite crucible of the present invention, which is divided into a cylindrical portion and a bottom curved surface portion.

FIG. 3 is an embodiment of a C / C composite material outside the graphite crucible of the present invention, which is divided into a cylindrical portion and a bottom curved surface portion.

[Explanation of symbols]

 1 CIP material part inside crucible 2 C / C material part outside crucible 3 Cylindrical part of C / C material crucible 4 Bottom curved surface part of C / C material crucible

Claims (9)

[Claims] 1. A method of manufacturing a C / C crucible for pulling a semiconductor single crystal comprising a crucible having a double inner and outer structure, an isotropic graphite material (CIP material) inside, and a C / C composite outside. . 2. A method for producing a C / C crucible for pulling a semiconductor single crystal in which a crucible is divided into a cylindrical portion and a bottom curved surface portion. 3. The method according to claim 1, wherein the C / C
The method is characterized by using a two-stage molding method in which a material is preformed by hand lay-up or the like, and then press-molded using a mold. 4. The method according to claim 3, wherein the material of the C / C material is cloth, felt, and yarn, and carbon fibers of knitted fabric are used. 5. The method according to claim 3, wherein carbon fiber and at least one of resin beads, graphite powder and carbon powder are used as the filler of the C / C material. 6. The method according to claim 3, wherein the C / C material is densified in a sealed metal container and fired under pressure. 7. The pitch gas-enriched atmosphere in which the pitch or the resin-impregnated product is refired and the C / C material is densified by placing pitches on the outer peripheral portion of the impregnated product. And 8. Pyrolytic graphite (PG) is applied to the inner and outer peripheral surfaces of the crucible.
Alternatively, a method for producing a C / C crucible for pulling a semiconductor single crystal, which is coated with pyrolytic carbon (PC). 9. The matrix portion of C / C material is made hard to graphitize by adding soot to a resin or pitch as an impregnating material or by setting a final heat treatment temperature to 2200 ° C. to 2000 ° C. .