JP2620075B2 - Graphite material for Ga compound single crystal pulling device - Google Patents

Description

The present invention relates to a graphite material used for pulling a Ga compound single crystal, and more specifically, for example, a Ga compound single crystal such as a crucible, a crucible receiving heater, a heat shield, etc. The present invention relates to a graphite material to be used when pulling up.

[Conventional technology]

Currently, the GaAs single crystal growth method can be roughly divided into the horizontal Bridgman method and the liquid sealing method.
Since a single crystal is superior in crystal structure, a liquid sealing method is generally used.

Liquid sealing method is GaAs melted in the same way as Si single crystal growth method
And growing the crystal while pulling up.

The graphite material used in such a process is not only electrically conductive, but also has extremely high heat resistance,
It must be chemically inert and of very high purity to prevent harmful contamination of the GaAs single crystal.

However, the conventional graphite material has the following disadvantages. That is, (i) the graphite crystal fine particles on the surface easily fall off easily, and the separated matter is mixed into the GaAs single crystal to contaminate it. (Ii) Graphite is porous in nature, has the property of diffusing very easily to the surface due to heat even in the presence of trace amounts of impurity elements, and is susceptible to so-called "out gas". However, there is a disadvantage that the GaAs single crystal is contaminated.

This difficulty as a graphite material for a GaAs single crystal pulling device occurs not only in a GaAs single crystal pulling device but also widely in a graphite material for a Ga compound single crystal pulling device, for example, for a GaP single crystal and a GaSb single crystal pulling device. Similar difficulties arise in graphite materials and the like.

[Problems to be solved by the invention]

The problem to be solved by the present invention is to eliminate the above-mentioned disadvantages of the graphite material used in the conventional pulling of a Ga compound single crystal.More specifically, there is no contamination based on the falling off of graphite fine particles, and To develop a pollution-free graphite material based on "out gas".

[Means for solving the problem]

The problem is that a high-purity, impermeable, dense pyrolytic carbon coating is formed on and in the surface of an isotropic graphite substrate, and the graphite material formed by infiltration is converted into a single crystal of a Ga compound. This is achieved by using a lifting device. That is, the present inventor has conducted intensive studies in order to solve the above-mentioned difficulties of the conventional graphite material for a Ga compound single crystal pulling apparatus, and as a result, the isotropic and preferably higher purity graphite surface was obtained. When a film of pyrolytic carbon (hereinafter referred to as PyC) obtained by pyrolyzing a hydrocarbon gas or hydrocarbon compound is formed and penetrated inside, it is characterized by high purity and gas impermeability. And found that a graphite material for a Ga compound single crystal pulling apparatus that does not disperse carbon powder can be obtained, and thus completed the present invention.

[Configuration and operation of the invention]

Hereinafter, the present invention will be described. For convenience of description, a graphite material for a GaAs single crystal pulling apparatus will be described below as a typical example as a graphite material for a Ga compound single crystal pulling apparatus. However, needless to say, the present invention is not limited to this.

Graphite material for GaAs single crystal pulling apparatus of the present invention, the thermal expansion coefficient of ^{0.5 × 10 -6 /℃~6.0×10 -6 / ℃} ( room temperature to 400 ° C.)
Purification of Isotropic Graphite (Total ash content is 20ppm or less)
Impervious on and within the surface of the graphite substrate
PyC is formed by forming a film having a thickness of 5 to 250 μm and penetrating 100 μm or more. The PyC film in this case needs to be particularly high-purity, impermeable, dense and high-strength. Here, impermeability means that the average pore radius measured by the mercury intrusion method does not exceed 0.1 μm, and high purity means that the total ash content is 20 ppm or less.

In the present invention, the PyC film needs to satisfy both of the above-mentioned requirements, and if any one of these requirements is not satisfied, the desired effect is hardly sufficiently achieved. Its film thickness is 5
About 250 μm is suitable.

In the Japanese Patent Application No. 60-98291 filed by the present inventors, the coefficient of thermal expansion (hereinafter referred to as CTE) of a graphite base material is 0.5.
~ 3.0 × 10 ^-6 / ° C and the thickness of the PyC coating is 2
Although 0 to 250 μm is preferable, after further intensive studies, the CTE of the graphite substrate is 3.0 to 3.0 × 10 ^-6 / ° C. It has been found that cracking or peeling of the PyC film due to the difference in CTE from the above can be alleviated. More specifically, in the present invention, PyC can be impregnated deeply inside the graphite substrate by generating PyC slowly at a relatively low temperature and low pressure, that is, 1300 ° C. or less and 50 Torr or less, and PyC can be further impregnated on the graphite substrate. By forming a film, the mechanical engagement between the graphite substrate and the PyC film is strengthened, and an important technology that can suppress cracking and peeling of the PyC film due to the CTE difference between the graphite substrate and the PyC film was discovered. is there.
In addition, PyC impregnated inside the graphite substrate makes the surface of the graphite substrate dense, has excellent mechanical strength and impact resistance, can suppress the detachment of carbon powder, and significantly improves durability. It is.

Thus, the range of CTE of the graphite substrate in the present invention is as follows.
It is preferably from 0.5 to 6.0 × 10 ⁻⁶ / ° C., and within this range, the penetration of PyC into the substrate and the surface coating are complete. It is generally recognized that the lower the CTE of graphite, the more the anisotropy increases and the mechanical strength decreases.It is recognized that graphite with a CTE lower than 0.5 × 10 ^-6 / ° C is a graphite material for GaAs single crystal pulling equipment. It is difficult to obtain suitable mechanical strength. Conversely, if the CTE is too large than 6.0 × 10 ⁻⁶ / ° C., the graphite substrate becomes denser, and as a result, the pores of the graphite substrate are reduced, making it difficult for PyC to infiltrate. The mechanical interlock between the graphite substrate and the PyC film becomes weaker, and the CTE difference between the graphite substrate and the PyC film during the heating-cooling cycle tends to cause cracking and exfoliation of the PyC film, resulting in a lower protective effect. .

On the other hand, Japanese Patent Publication No. 47-1003 proposes an invention relating to a graphite susceptor, and Japanese Patent Publication No. 51-13754 discloses a "method of coating an article with pyrolytic graphite". However, in the above two inventions, it is impossible to impregnate only the inside of the graphite substrate during the so-called impregnation step, and it is usually involved in the formation of the PyC film simultaneously with the impregnation reaction. Since a reaction occurs, PyC films having different formation temperatures are eventually stacked. That is, it has a structure in which PyC films having substantially different generation temperatures are stacked. In such a structure in which PyC films having different formation temperatures are stacked, cracks and peeling of the PyC film occur due to the CTE difference between the PyC films. In addition, since the formation temperature is different, the size of the particle size of PyC is different, and a gap is generated between the PyC layer generated at a low temperature and a high temperature, and the PyC layer tends to be more easily peeled. However, in the present invention, by performing the reaction of the impregnation of PyC and the formation of the PyC film at the same formation temperature in one step, the above-described difficulties do not occur, and as a result, the mechanical engagement between the graphite substrate and the PyC film can be strengthened. This fact has been found for the first time by the present inventors.

In the present invention, the depth of impregnation of PyC into the graphite substrate is preferably 100 μm or more in order to achieve the intended purpose. If it is not suitable for this, the strength of mechanical engagement between the graphite substrate and the PyC coating tends to decrease. And, as for the PyC film thickness, when the CTE of the graphite base material is in the range of 0.5 to 3.0 × 10 ⁻⁶ / ° C.,
The thickness is desirably about 5 to 250 μm. If the film thickness is too large, cracking or peeling tends to occur if the heating-cooling cycle is performed rapidly, and the graphite substrate may be exposed, and the effect of film formation may be insufficient. Conversely, if the film thickness is too small, the desired effect based on the film formation cannot be sufficiently exerted. According to the Japanese Patent Application No. 60-98291 filed by the present inventor, the CTE of the graphite base material is 0.5 to 3.0 × 10 ⁻⁶ / ° C., and the thickness of the PyC coating is 20 to 250 μm. Although it is desirable, by impregnating the inside of the graphite base material with PyC in the present invention, properties such as thermal shock resistance are further improved. It exerts an effect equal to or greater than that obtained by forming a film. In addition, graphite base
When the CTE is as large as 3.0 to 6.0 × 10 ⁻⁶ / ° C., the PyC film thickness is desirably 5 to 60 μm. By impregnating PyC inside the graphite substrate, the mechanical interlock between the graphite substrate and the PyC film is improved. The CTE difference from the PyC film tends to cause cracking and peeling of the PyC film.

To summarize the above, the CTE of a graphite substrate is 0.5 to 6.0 × 10 ^-6 / ° C.
Is preferred, the PyC film thickness at that time, especially the CTE of the graphite substrate, is in the range of 0.5 to 3.0 × 10 ^-6 / ° C. 5-250 μm
Degree, 5-60 μm when CTE is in the range of 3.0-6.0 × 10 ^-6 / ° C
It is preferred that it is about.

It should be noted that, when comparing JP-B-47-1003 and JP-B-51-13754 with the present invention, it is particularly notable that the graphite substrate used in the present invention is high-purity graphite. is there. By using high-purity graphite, the influence of impurities from the base material is small, and the thickness of PyC can be made smaller than that of PyC in the above two inventions. Therefore, there is an advantage that the time required for PyC coating can be reduced, that is, the manufacturing cost can be reduced.

Here, according to Japanese Patent Application Laid-Open No. 60-103087, it is disclosed that "Crack and peeling of the PyC film are prevented by coating with amorphous PyC having small anisotropy." If the CTE uses a graphite substrate with a low range of 0.5 to 3.0 × 10 ⁻⁶ / ° C. or a CTE has a high range of graphite substrate of 3.0 to 6.0 × 10 ⁻⁶ / ° C., first use PyC 100 inside the substrate
By impregnating more than μm and further forming a PyC film thereon, the mechanical engagement becomes strong and cracking and peeling of the PyC film can be prevented, so there is no need to coat amorphous PyC with small anisotropy .

PyC itself of the PyC film formed in the present invention is well known in the art, and is a carbonaceous material such as C ₃ H _8.
It is also well known that carbon is generated by thermally decomposing a hydrocarbon gas or a hydrocarbon compound.

In the present invention, the method of forming the PyC film on the surface of the graphite substrate itself is not limited at all, and the method is not limited in any way as long as the PyC film having the predetermined requirements is formed. Any method can be applied.

〔Example〕

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 The characteristics of the graphite crucible used as the base material were as follows.

^{CTE; 2.1 × 10 -6 /℃,5.3×10 -6} / ℃ ( room temperature to 400 ° C.) bulk density; 1.50 (graphite CTE is 2.1) 1.77 (graphite CTE is 5.3) anisotropic ratio: 1.01,1.01 Ash ; 20ppm <Dimension; ODφ60 × IDφ50 × l50mm crucible (OD; OD, ID; ID) The above graphite base material is heated to 1280 ℃ and C ₃ H ₈ gas is 18 / m
in (STP), and holds the flow furnace pressure of H ₂ gas at a flow rate of 30 / min (STP) to 34Torr, about 1 PyC inside graphite substrate
After impregnation of 28 μm, a PyC coating was formed. The thickness of the film was adjusted to the film thickness shown in Table 1 (in the case of a graphite substrate having a CTE of 2.1) and Table 2 (in the case of a graphite substrate having a CTE of 5.3) by changing the generation time.

Here, PyC impregnation and coating were carried out by using the apparatus shown in FIG. 1 and setting this graphite substrate on a sample table as shown in FIG. The heating method was performed by resistance heating of a graphite heater, and C ₃ H ₈ gas and H ₂ gas were introduced from below the sample chamber and discharged upward as shown in FIG. However, (1) in FIG.
Is a vacuum vessel, (2) is a gas exhaust pipe, (3) is a heat insulating material,
(4) is a graphite heater, (5) is a graphite susceptor,
(6) is a heat insulating material mounting table, (7) is a graphite support post,
(8) shows a gas introduction pipe, (9) shows a sample mounting table, (10) shows a sample, and (11) shows a gas exhaust pipe.

Various physical properties of the PyC-coated graphite material obtained in Example 1 were measured.

<Reactivity with Metal Ga> The reactivity with molten Ga was measured as the most severe condition.
That is, metallic Ga is added to the PyC-coated graphite crucible obtained by the above method.
And heated to 1300 ° C in a high frequency furnace to melt Ga,
The reaction was performed for 1 hour. The number of samples is 5 each.

<Quick Heat Quenching Test> A rapid heat quenching test was performed using the PyC-coated graphite crucible obtained in Example 1. That is, the graphite crucible heated to 1300 ° C. for 5 minutes was then thrown into water to examine the peeling state of the PyC coating. The number of samples is 5 each.

<Impermeable> A graphite base machined into a size of φ10 × 20 mm was placed at the same time as the above graphite crucible, coated with PyC by the same method, and the average pore radius was measured by a mercury intrusion method. An evaluation was performed. The results are shown in Tables 1 and 2.

From Tables 1 and 2, the CTE of the graphite substrate is 0.5-3.0 × 10 ^-6 / ° C.
Within the range, the film thickness to be coated with PyC is about 5 to 250 μm,
When the CTE is in the range of 3.0 to 6.0 × 10 ⁻⁶ / ° C., about 5 to 60 μm is impermeable because the carbon fine powder does not scatter. Therefore, it can be seen that these are extremely effective.

Example 2 As shown in Table 3 below, a graphite substrate having a different CTE was coated with 50 μm of PyC under the same conditions as in Example 1 to perform a rapid heating and quenching test. Table 3 shows the results.

Table 3 shows that there is no peeling or cracking when coating PyC.
It turns out that it is preferable to use a graphite substrate having a CTE in the range of 0.5 to 6.0 × 10 ⁻⁶ / ° C.

From the above, the graphite material for the Ga compound single crystal pulling device, which thermally decomposes a hydrocarbon gas such as C ₃ H ₈ gas or a hydrocarbon compound on a high-purity isotropic graphite substrate, is high-purity and impervious Therefore, it can be said that it is an excellent graphite material which does not adhere and scatter carbon fine powder.

〔The invention's effect〕

In the present invention, the coefficient of thermal expansion is 0.5 × 10 ^{−6 /} ° C. to 6.0 × 1
A dense and high-strength PyC having a thickness of 5 to 250 μm is formed on the surface of and within the isotropic high-purity graphite substrate of 0 ⁻⁶ / ° C. (room temperature to 400 ° C.), and 100 μm By impregnation as described above, for example, as shown in Example 1, it has the characteristics of high purity and impermeability, and exhibits excellent effects such as no scattering of carbon components. Therefore, it can withstand repeated use for a long time and has high durability, and the industrial effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of an apparatus used for producing the material of the present invention. DESCRIPTION OF SYMBOLS 1 ... Vacuum container 2 ... Gas discharge pipe 3 ... Heat insulation material 4 ... Graphite heater 5 ... Graphite susceptor 6 ... Heat insulation material mounting table 7 ... Graphite support post 8 ... Gas introduction pipe 9 ... Sample mounting Table 10 …… Sample 11 …… Gas exhaust pipe

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-103087 (JP, A) JP-A-61-256993 (JP, A) JP-A-62-252394 (JP, A) JP-A 63-252394 79761 (JP, A) JP-B 47-1003 (JP, B2) JP-B 51-13754 (JP, B2)

Claims (1)

(57) [Claims] 1. The thermal expansion coefficient from room temperature to 400 ° C. is 0.5 × 10
^-6 / ℃ ~ 6.0 × 10 ^-6 / ℃ and the total ash content is 20ppm or less on the surface of a high-purity isotropic graphite substrate, the total ash content is 20ppm or less high purity, and mercury intrusion method The measured average pore radius is 0.
5-250 impervious dense pyrolytic carbon not exceeding 1 μm
to form a film by coating with a thickness of μm, and the pyrolytic carbon is 100 μm from the surface inside the isotropic graphite substrate.
A graphite material for a Ga compound single crystal pulling device that has been impregnated to the above.