JP2000247779A - Carbonaceous crucible for pulling up single crystal and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbonaceous crucible which is used for pulling up a single crystal and has excellent durability and a long use life by lowering the reactivity with a quartz crucible to control the generation of SiO gas and preventing the formation of SiC in the pores of the carbonaceous crucible due to the SiO gas, and to provide a method for producing the same. SOLUTION: This carbonaceous crucible for pulling up the single crystal comprises a C/C(carbon fiber-reinforced carbon material) substrate-SiC composite product prepared by filling 35-50 vol.% of the total pore volume of the C/C substrate with the SiC deposited by CVI method. The method for producing the carbonaceous crucible comprises setting the C/C substrate to a CVI device, evacuating the CVI device up to 4 Torr, instantaneously charging a raw material gas containing a halogenated organic silicon compound in a concentration of 8-25 mol.% into the evacuated device at a temperature of 1,100-1,200 deg.C, retaining the charged state for a prescribed time, and repeating a series of the operations as one pulse prescribed times to deposit and fill the produced SiC in the pores of the C/C substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbonaceous crucible used for supporting a quartz crucible used in an apparatus for pulling a single crystal of silicon or the like by the Czochralski method (hereinafter referred to as "CZ method").

[0002]

2. Description of the Related Art Single crystals such as silicon used for manufacturing ICs and LSIs are usually manufactured by the CZ method.
In the CZ method, a silicon polycrystal is put into a high-purity quartz crucible, and the silicon polycrystal is heated and melted by a heater while rotating the quartz crucible at a predetermined speed. Single crystal)
By slowly pulling up while rotating at a predetermined speed, the melt of the polycrystalline silicon is solidified and grown into a silicon single crystal.

However, quartz crucibles are softened at high temperatures and have insufficient strength. Therefore, quartz crucibles are usually fitted in carbon crucibles and reinforced by supporting the quartz crucibles with carbon crucibles. As a carbon crucible to which this quartz crucible is fitted, a graphite material having high high-temperature strength, high heat resistance and high thermal conductivity is generally used. However, the graphite material has a problem that graphite fine powder is easily separated and scattered from the surface, so that the graphite material floats in the apparatus and is mixed into the silicon melt, thereby deteriorating the quality of the silicon single crystal.

[0004] Further, since quartz and graphite differ greatly in thermal expansion coefficient due to the material, the quartz crucible softens during heating and adheres closely to the graphite crucible during repeated heating and cooling, while the graphite crucible during cooling. When the amount of shrinkage is larger than the amount of shrinkage of the quartz crucible, the crucible receives an internal pressure, and there is a disadvantage that the graphite crucible is deformed and broken.

Further, when heated to a high temperature, a quartz crucible (Si
O ₂ ) and the graphite crucible (C) react at the fitting surface in contact with each other to generate SiO gas, and the generated SiO gas reacts with the graphite crucible (C) while penetrating into the pores of the surface portion of the graphite crucible. Thus, the graphite crucible is converted into SiC gradually from inside the pores of the surface layer portion to inside. Therefore, if such a heat treatment is repeatedly performed, microcracks occur due to differences in the material properties of graphite and SiC in the graphite crucible, for example, differences in thermal expansion coefficients, and eventually lead to breakage of the graphite crucible. Become.

In order to solve this difficulty, Japanese Patent Application Laid-Open No.
JP-A-166789 discloses a graphite crucible for a silicon single crystal pulling apparatus in which at least the inner surface of pores of graphite is coated with a silicon carbide film made of polycarbosilane as an organic silicon polymer compound, and polycarbo. After impregnating and filling at least the inside of the pores of graphite with silane, it is made infusible at 50 to 400 ° C in an acidic atmosphere, and further in an inert atmosphere.
There has been proposed a method for producing a graphite crucible for a silicon single crystal pulling apparatus which is formed by firing at 1000 to 2000 ° C. and thermally decomposing the polycarbosilane.

According to the technique disclosed in Japanese Patent Application Laid-Open No. 63-166789, pores on the inner surface of a graphite crucible to which a quartz crucible is fitted are converted into SiC to suppress the reaction between the quartz crucible and the graphite crucible. Accordingly, generation of SiO gas is suppressed, and formation of SiC on the inner surface of the graphite crucible due to reaction with the SiO gas is prevented. However, the impregnated filling of polycarbosilane, which is an organosilicon polymer compound, is performed by a method such as immersing the graphite material in a solution in which polycarbosilane is dissolved in an organic solvent such as acetone or hexane. It is extremely difficult to fill fine pores existing on the surface, for example, several tens of microns or less.

In view of the above, a proposal has been made to construct a carbon crucible using a carbon fiber reinforced carbon material (hereinafter also referred to as "C / C material") which is superior in strength characteristics to graphite and has a small difference in thermal expansion coefficient from quartz. For example, a single crystal pulling crucible having at least a side wall portion made of an integral C / C material (Japanese Utility Model Application Laid-Open No. 63-7174), a carbon fiber cloth laminate or a carbon fiber A carbon fiber reinforced carbon crucible for pulling a silicon single crystal composed of two layers composed of a C / C material using a felt laminate and a C / C material formed on the outside of the crucible by a filament winding method (Japanese Patent Laid-Open No. 9-263482) ), Etc. have been proposed.

[0009]

However, even with these carbon crucibles made of C / C materials, the generation of SiO gas and the generation of S gas due to the reaction with the quartz crucible described above.
There is a problem that it is not possible to prevent the iO gas from diffusing into the pores in the surface layer of the carbon crucible and reacting with the pore inner surface to be converted into SiC.

Accordingly, the present inventors have conducted intensive research on the development of a carbonaceous crucible having excellent durability for a C / C material having excellent strength characteristics as compared with graphite material. C / C by depositing SiC by the method
It has been found that it is possible to fill the inside of the fine pores existing in the surface layer of the material with SiC, and that the carbonaceous crucible can be used to stably perform a number of single crystal pulling operations repeatedly. .

The present invention has been completed based on this finding, and its purpose is to suppress the reactivity with the quartz crucible to suppress the generation of SiO gas, and to generate the SiO gas in the surface layer of the carbonaceous crucible. By suppressing the phenomenon of diffusing into the pores and reacting with the pore inner surface and converting to SiC,
An object of the present invention is to provide a single crystal pulling carbonaceous crucible capable of stably repeating a large number of pulling operations, and a method for producing the same.

[0012]

According to the present invention, there is provided a single crystal pulling carbonaceous crucible according to the present invention, comprising a carbon fiber reinforced carbon material as a base material, and having a total pore volume of from 35 to 35%.
A structural feature is that 50 vol% is composed of a composite of carbon fiber reinforced carbon material and SiC filled with SiC deposited by the CVI method.

[0013] Further, the method for producing the same comprises using a carbon fiber-reinforced carbon material obtained by impregnating a carbon fiber with a matrix resin and firing and carbonizing a cured crucible molded body in a non-oxidizing atmosphere as a base material. Is set on the CVI device, and 4To
evacuating to a pressure of rr or less, 1100 to 1200
A step of setting the concentration of the halogenated organosilicon compound in the raw material gas to 8 to 25 mol% and instantaneously introducing the mixed gas of the halogenated organic silicon compound and hydrogen as the raw material gas while heating the raw material gas A step of holding for a predetermined time in order to thermally decompose the SiC by the CVI reaction to precipitate SiC, as a single pulse, thereby repeatedly depositing and filling the pores of the base material with the SiC. And

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon crucible for pulling a single crystal of the present invention uses a carbon fiber produced from various raw materials such as polyacrylonitrile, rayon, pitch and the like as a reinforcing material, and these carbon fibers are phenol-based. It is bound by a char obtained by firing and carbonizing a thermosetting resin such as or furan,
With the integrated C / C material as the base material, 35-50 vol% of the total pore volume of the C / C base material is a composite of the C / C material and SiC filled with SiC precipitated by the CVI method. The feature is that it is composed of the organizational structure.

The C / C material has pores of various sizes. When a carbon crucible for pulling a single crystal by the CZ method is manufactured by using the C / C material, the carbon crucible is fitted when heated at a high temperature. Reacts with the quartz crucible at the contact surface with the quartz crucible to generate SiO gas, and the generated SiO gas quickly penetrates into the pores, and the pore inner surface of the C / C material is easily converted to SiC. You. As a result, the pores of the carbon crucible gradually become SiC, and as a result, microcracks are likely to occur, and even a C / C material having excellent strength characteristics will be broken.

Therefore, the carbonaceous crucible of the present invention has a C / C
35-50 vol of the total pore volume of the substrate
% Using a C / C material filled with SiC deposited and deposited by the CVI method (Chemical Vapor Infiltration method), that is, the carbonaceous crucible is composed of a composite of the C / C material and SiC. By doing so, SiC due to generation of SiO gas and penetration of SiO gas into pores
Is effectively prevented.

In this case, the filling amount of SiC is set in the range of 35 to 50 vol% of the total pore volume because when the filling amount is less than 35 vol%, generation of SiO gas due to reaction with the quartz crucible and generation of SiO gas are performed. S by penetration into pores
This is because the effect of inhibiting iC formation is not sufficient. However, even when the SiC is filled in an amount exceeding 50 vol%, the amount of SC is reduced as compared with the complexity of the operation of depositing and depositing SiC by the CVI method.
This is because the effect of inhibiting generation of iO gas and formation of SiC in the pores is reduced.

The carbonaceous crucible for pulling a single crystal of the present invention is produced by the following method. First, a carbon fiber woven fabric was impregnated with a matrix resin in a carbon fiber by a method such as immersing a carbon fiber woven fabric in a matrix resin solution or applying a matrix resin solution, and a semi-cured prepreg was molded into a desired crucible shape and cured. The formed body is calcined and carbonized in a heating furnace maintained in a non-oxidizing atmosphere to produce a crucible formed of a C / C material. Note that a highly carbonizable thermosetting resin such as a phenol resin and a furan resin is used as the matrix resin.

Alternatively, a continuous carbon fiber is impregnated with a matrix resin solution, a molded body formed into a crucible shape by a filament winding method is cured, and then calcined and carbonized in a heating furnace maintained in a non-oxidizing atmosphere.
/ C material can also be produced.

The crucible formed from the C / C material thus prepared is set in a CVI device and a specific CVI
By treating under reaction conditions, the total pore volume of the present invention can be reduced to 3%.
SiC deposited in pores by vapor deposition of 5 to 50 vol%
Produces a carbonaceous crucible composed of a composite structure of the C / C material and SiC filled.

CVI method (Chemical Vapor Infiltration)
Is different from CVD (Chemical Vapor Dep-osition),
Vapor phase deposition can be performed on micro surfaces in fine pores or voids. The CVI method uses the following methods:
Constant pressure CVI, (b) forced flow CVI, (c) pulse CV
I, etc. Among them, the pulse CVI method is a method in which the reaction system is evacuated to remove gas in the pores, instantaneously introduces a raw material gas into the reaction system, and holds for a predetermined time for reaction deposition, and a pulse is used for several thousand to several times. By repeating 100,000 times, it is possible to fill the precipitate deep into the pores in a relatively short time.
The VI method is preferably applied. However, it is not limited to the pulse CVI method.

The crucible formed of C / C material is CVI
The raw material gas is placed on a substrate support of the reactor and heated, and the supplied raw material gas is subjected to gas phase pyrolysis to deposit and deposit SiC, thereby filling the pores of the crucible molded body. 1 for source gas
A mixed gas of hydrogen and a halogenated organosilicon compound such as methyltrichlorosilane (CH ₃ SiCl ₃ ) or methyldichlorosilane (CH ₃ SiHCl ₂ ) containing Si and C atoms in a molecule is used.

The CVI reaction conditions are set and controlled as follows in order to infiltrate the raw material gas into the pores by the CVI method and pyrolyze in the gas phase to deposit and fill SiC into the pores. The inside of the reaction system is evacuated and maintained under a reduced pressure of 4 Torr or less to discharge and remove the gas present in the pores of the C / C base material. If the degree of pressure reduction exceeds 4 Torr, the effect of degassing becomes insufficient, and the gas present in the deep part of the pore cannot be sufficiently discharged and removed. As a result, it becomes difficult to deposit and fill SiC to the deep part of the pore (vacuum) Exhaust process).

While heating the reaction system to a temperature of 1100 to 1200 ° C., a mixed gas of a halogenated organosilicon compound and hydrogen is instantaneously introduced as a raw material gas. In this case, the SiC deposited when the heating temperature is less than 1100 ° C.
The frequency of release of amorphous Si increases during
If the ratio exceeds, it is difficult to fill the inside of the pores, especially the deep part of the pores. Further, the concentration of the halogenated organosilicon compound in the source gas is set in the range of 8 to 25 mol%. If the concentration of the halogenated organosilicon compound is less than 8 mol%, C / C
Since the heat transfer to the source gas is faster than the diffusion of the source gas into the pores of the base material, the deposition on the surface of the C / C base material is prioritized. As a result, it becomes difficult to fill the inside of the pores with SiC. However, when the concentration exceeds 25 mol%, the reaction frequency on the surface of the C / C substrate increases as compared with the diffusion of the raw material gas into the pores, and SiC deposition on the substrate surface takes precedence. C
It becomes difficult to fill SiC into the pores of the substrate (instantaneous gas source introduction step). In this case, the maximum filling amount in the pores is less than 35 vol%.

By maintaining the CVI reaction conditions set as described above for a predetermined time, a predetermined amount of SiC is deposited and filled in the pores (holding step).

The series of steps of the evacuation step, the source gas instantaneous introduction step, and the holding step are repeated as one pulse several thousand to several hundred thousand times, thereby depositing and depositing SiC to the deep part of the pores of the C / C base material. It is possible to fill the pores of 35 to 50 vol% of the total pore volume. In this way, the inside of the pores and the surface layer of the C / C base material constituting the carbonaceous crucible are filled and covered with SiC having high strength and excellent oxidation resistance, and even at the time of high temperature heating at the time of pulling a silicon single crystal, The reactivity with the quartz crucible is reduced, and the generation of SiO gas and the permeation of the C / C substrate into the pores are effectively suppressed.

Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 5 A prepreg sheet prepared by applying a phenol resin precondensate to a two-dimensional woven cloth of polyacrylonitrile-based carbon fiber, impregnating the cloth, and air-drying is laminated to form a mold. Put 2
The resin component was cured by heating to a temperature of 50 ° C. Then
In a heating furnace maintained in a nitrogen gas atmosphere, it was heated to 2000 ° C. at a rate of temperature increase of 10 ° C./hr, and was held for 5 hours for calcination. Thus, a test piece made of a 25 × 25 × 4 mm C / C base material (Vf: about 60%) was produced.

The test piece was subjected to an external heat type horizontal pulse CV.
The reactor was set in a reaction furnace of the apparatus I, and the inside of the system was evacuated to a vacuum of 3 to 4 Torr. Next, after reaching a predetermined temperature by heating, a mixed gas of trichloromethylsilane (CH ₃ SiCl ₃ ) and hydrogen is introduced into the furnace as a raw material gas, reacted for a predetermined time, and subjected to a CVI reaction to form a test piece. SiC was deposited and filled in the pores. A series of operations of the vacuum evacuation step, the source gas instantaneous introduction step, and the holding step were repeated as one pulse, and the CVI reaction was repeatedly performed until the weight increase rate due to the deposition and filling of SiC was about 25 wt%. At this time, CVI reaction conditions such as the reaction temperature, the concentration of trichloromethylsilane in the source gas, and the number of pulses were changed. In addition, other CVI reaction conditions are as follows. Vacuum evacuation process: evacuation time; 1.9 seconds Source gas introduction process; introduction pressure; 200 Torr, introduction time; 0.7 seconds Holding process; holding time; 1.0 seconds 1 pulse; 3.6 seconds

Table 1 shows the CVI reaction conditions in which SiC was deposited and filled in the test piece as described above.

[0031]

[Table 1] (Note) * 1 Concentration of trichloromethylsilane in raw material gas obtained by mixing trichloromethylsilane (CH ₃ SiCl ₃ ) and hydrogen

Comparative Example 6 A test piece was immersed in a solution in which polycarbosilane was dissolved in xylene at a concentration of 20% by weight to impregnate the polycarbosilane, and dried to remove xylene.
The mixture was heated at a temperature of 50 ° C. for 5 hours for infusibility treatment. After repeating this process three times, the temperature is increased to 1500 ° C. in a nitrogen gas atmosphere.
, And polycarbosilane was thermally decomposed to form a SiC coating on the test piece.

Next, with respect to the test pieces on which SiC was deposited and filled, the weight increase rate, surface film thickness, filling rate, surface film quality, etc. were measured by the following methods, and an oxidation resistance test was performed. Table 2 shows the obtained results.

(1) Weight increase rate: The change in weight of the test piece before and after the reaction was measured by an electronic balance, and calculated by dividing the change in weight by the weight of the test piece before the reaction. (2) Surface film thickness: The test piece after the reaction was cut, the cut surface was observed with a scanning electron microscope, and the film thickness was measured and averaged. (3) Filling ratio: The internal precipitation volume obtained by subtracting the surface precipitation volume (hS ₀ ) cm ³ of the test piece from the volume increase (Δw / ρ) cm ³ after the reaction is the pore volume (V) of the test piece.
p) The ratio occupied in cm ³ / g was calculated as the filling rate according to the following equation. Filling rate (vol%) = [(Δw / ρ) − (hS ₀ )] / (w ₀
Vp) × 100 where Δw: weight increase, h: thickness of deposit on the test piece surface measured from a scanning electron micrograph, w ₀ : weight of test piece, S ₀ : surface area ρ of test piece; Si
The density of C (3.10 g / cm ³ ), Vp: 0.1452 (cm ³ / g). (4) Surface film quality: The crystal strength of the test piece surface was evaluated by X-ray diffraction. (5) Oxidation resistance test; heated in an electric furnace in an air atmosphere, kept at a temperature of 500 ° C. for 30 minutes, then taken out of the furnace and cooled naturally to room temperature. Next, it was heated to a temperature of 600 ° C. and held for 30 minutes, then taken out of the furnace and naturally cooled to room temperature. The operation of increasing the temperature by 100 ° C. and heating was performed up to 1000 ° C., and the weight loss rate at that time was calculated from the following equation to evaluate the oxidation resistance. Weight reduction rate (%) = (W ₀ −W ₁₀₀₀ ) / (W ₀ ) × 10
0 where W ₀ is the weight of the test piece before the oxidation resistance test, W
₁₀₀₀ is the weight of the test piece after performing the heating test up to 1000 ° C

[0035]

[Table 2]

From the results shown in Tables 1 and 2, it can be seen that in the examples, 35 to 50 vol% of the pore volume was filled with SiC precipitated by the CVI method, and the weight reduction rate by the oxidation treatment was low. On the other hand, in Comparative Examples 1 and 2,
However, since the film formed on the surface is amorphous Si, the film is converted to SiO ₂ by oxidation treatment to increase the weight, and the weight reduction rate is apparently low. It is determined that there is. Furthermore, since the CVI temperature is low, it is necessary to greatly increase the number of pulses, which is inefficient.
In Comparative Example 3, the filling rate of SiC was low even when the number of pulses was increased because the raw material concentration was low, and the reduction rate by the oxidation test was large. In Comparative Example 4, since the raw material concentration was high, the film thickness on the substrate surface was large and cracks occurred.
It can be seen that the rate of decrease in the oxidation test is large because the filling rate of the sample is low. In Comparative Example 5, the film thickness on the surface can be increased because the CVI temperature is high, but cracks occur and the filling rate of SiC is low, so that the reduction rate by the oxidation test is large.

[0037]

As described above, the carbonaceous crucible for pulling a single crystal of the present invention has a total pore volume of 35 to 5% of the C / C base material.
0 vol% C filled with SiC deposited by CVI method
Since it is composed of a composite of the C / C material and SiC, the reactivity with the quartz crucible is low, and the generation of SiO is effectively suppressed. A long, durable carbonaceous crucible is provided. Further, according to the manufacturing method, it is possible to easily manufacture a carbonaceous crucible having excellent durability by specifying CVI reaction conditions.

Claims (2)

[Claims] 1. A composite of a carbon fiber reinforced carbon material and SiC filled with SiC deposited by CVI method, wherein 35-50 vol% of the total pore volume of the carbon fiber reinforced carbon material is used as a base material. A carbonaceous crucible for pulling a single crystal, comprising: 2. A carbon fiber reinforced carbon material obtained by impregnating a carbon fiber with a matrix resin and curing and calcining a cured crucible molded body in a non-oxidizing atmosphere as a base material.
Setting the apparatus in an I apparatus and evacuating the system to a pressure of 4 Torr or less, while heating the mixture to a temperature of 1100 to 1200 ° C. and using a mixed gas of a halogenated organosilicon compound and hydrogen as a source gas, A step of setting the concentration of the organosilicon compound to 8 to 25 mol% and instantaneously introducing the same, and a step of holding the material gas for a predetermined time to thermally decompose the raw material gas by CVI reaction to precipitate SiC. 2. The method for producing a carbonaceous crucible for pulling a single crystal according to claim 1, wherein the step is repeated as one pulse to deposit and fill SiC into pores of the substrate.