JP2684106B2 - Graphite base material for ceramic coating and internal parts for CVD furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses boron nitride (B) by a chemical vapor deposition (CVD) method.
N), silicon carbide (SiC), carbon (C), etc. The present invention relates to the use of a graphite base material used for depositing and growing ceramics and a graphite base material coated with ceramics as internal parts for a CVD furnace.

[Prior Art] Ceramics such as BN, SiC, and C grown and deposited by the CVD method are easy to obtain with high purity and density. Therefore, the graphite material coated with carbon or silicon carbide is excellent in heat resistance, corrosion resistance, and dimensional stability, so that a heating element, a soaking body, a reaction material for the production of diodes, silicon semiconductors, compound semiconductors, silicon carbide semiconductors, etc. Tube, boat, susceptor, heat shield,
It is used for heat treatment jigs such as crucibles, semiconductor material mounting objects, furnace internal structures, etc. It is also used or expected as an acoustic vibrator for CVD substrate mounting jigs such as plasma CVD.

Pyrolysis BN (PBN) crucible for pulling Ga-As single crystal,
Even when manufacturing ceramic acoustic vibrators, their CVD
Graphite is used as the growth substrate.

Not only the growth base material or the base material, but also the graphite materials such as jigs, heating elements, soaking bodies, and gas nozzles are used in those CVD growth furnaces.

However, SIC grown on a graphite substrate by the CVD method,
BN, C, etc. were often lacking in detail.

[Problems to be Solved by the Invention] The problem to be solved by the present invention is to solve the above-mentioned drawbacks of the prior art. In other words, a ceramic film of SiC, BN, C or the like having excellent compactness. Is to develop a new graphite base material for the formation of CVD by the CVD method.

[Means for Solving the Problem] The present inventor has grown B on a graphite substrate by the CVD method.
As a result of diligent research on the cause of the decrease in the density of ceramics such as N, SiC, and C, the gas (especially CO, H ₂ 0, H _2, etc.) released from the graphite base material during the CVD growth process is greatly affected. It has been found that the gas releasing property of the graphite base material has a great influence on the involvement, that is, whether or not the porous growth layer lacking the denseness grows. In further research, the outgassing rate of the graphite base material greatly affects the gas release rate. When the gas release rate is high, a dense ceramic layer cannot be obtained, and a graphite base material with a low gas release rate is used. It was discovered that dense and uniform ceramics were obtained, and the present invention was completed.

[Structure and Action of the Invention] In the present invention, graphite having a characteristic that the gas release rate measured under specific conditions is 2 × 10 ⁻² Pam ² / (s · kg) or less is obtained by a CVD method. The main idea is to use it as a substrate for forming a ceramic coating of carbon, silicon carbide, BN, etc. on the surface. That is, size 10 ×
673 to 14 when a 10 x 1 mm object is heated at a heating rate of 1 k / s
A graphite having an average value of the gas release rate at 73 K is used as a graphite base material for a ceramic coating by a CVD method, and a graphite having such a specific gas release rate is used for the specific application. When applied to CVD
The effect that the ceramics and the like obtained by the growth of the will become extremely dense will be exhibited.

First, an example of an apparatus for measuring the gas release rate will be described with reference to FIG. The apparatus shown in FIG. 1 is a schematic view of a typical example thereof. (1) is a holder and heater made of tantalum for the object to be measured, (2) is a graphite piece as the object to be measured, and (3) is φ21 cm ×
l42cm stainless steel vacuum container, (4) turbo molecular pump, (5) BA type ionization vacuum gauge (total pressure gauge),
(6) is a quadrupole mass meter (partial pressure gauge), (7) is a diaphragm pump, (8) is an orifice, (9) is a thermocouple, and (1
(0) is the object manipulator, (11) is the viewing window, (1)
2) is Pirani vacuum gauge, (13) is Penning vacuum gauge, (14)
Is an object preparation room, (15) is a turbo molecular pump, (16)
Is a rotary pump, (17) is a manipulator for introducing an object to be measured, and (18) is a gate valve.

When measuring the gas release rate using the apparatus of FIG. 1, the graphite piece (10 × 10 × 1 mm) (2) to be measured is set in the holder / heater (1) and the vacuum container (3) is set.
It is placed inside and decompressed and evacuated to 10 ^-5 to 10 ^-6 Pa or less by using a turbo molecular pump (4) and a diaphragm pump (7) over several hours. The vacuum container (3) is equipped with an ionization vacuum gauge (5) for measuring the total pressure and a quadrupole mass meter (6) for measuring the partial pressure so that the total pressure and the partial pressure can be measured. It is like this. While heating from room temperature to 1773K at a heating rate of 1 k / s, total pressure and partial pressure are measured every 15 seconds.

An example will be described in which three types of isotropic graphite having different ash contents are measured using the apparatus shown in FIG. An example of mass spectra of these three kinds of graphite is shown in FIGS.

However, FIGS. 2 (a), 2 (b) and 2 (c) are 573 respectively.
The results at K, 873K, and 1473K are shown, and all are m / e = 2
It can be seen that there are many (H ₂ ), 18 (H ₂₀ ) and 28 (CO).

FIG. 5 (A) shows the temperature dependence of the total pressure of these three types of isotropic graphite. The total pressure increases with temperature, stays constant between 573 and 673K, and increases again above 1673K. This 1673K
The above increase means that the gas released from other than the object to be measured, for example, the gas adsorbed on the wall of the vacuum container (3) is released because the vacuum container (3) is heated during measurement and its temperature rises. This is not because the gas was released from the object to be measured.

Here, in the apparatus used in the present invention, after reaching a temperature of 1673 K or higher, it was possible to observe that the gas released from other than the object to be measured, for example, the gas adsorbed on the inner wall of the vacuum container was released. When the distance between the inner wall of the vacuum container and the heater is measured with another device such as a device closer than the distance of the device used in the present invention, the gas released from the inner wall of the vacuum container is observed even at a temperature of 1673 K or less. There is a case. In such a case, measurement (so-called blank measurement) was performed without putting the DUT in the holder, and the measurement result was regarded as gas emitted from other than the DUT, and the DUT was put in the holder for measurement. The value of this blank measurement should be subtracted from the result.

Each of the measured objects is manufactured by Toyo Tanso Co., Ltd.
These ash contents are adjusted. "IG-11" is 400p
It has an ash content of pm, and "IG-110" is highly purified (deashed) to an ash content of 10 ppm. "IG-110U" is obtained by purifying "IG-11" to a high ash content of 2 ppm and degassing it under reduced pressure at high temperature.

From this result, it can be seen that the total pressure increases as the amount of impurities (ash) increases. This ash content is a value measured according to JIS R7223.

Of course, when degassing is performed at high temperature for a long time, the total pressure becomes low. If the thickness is 1 mm, heating and degassing for 1 hour will result in "IG-1
"1" has almost the same total pressure (gas release rate) as "IG-110". Figure 7 shows the results of measuring the change in total pressure when 10 × 10 × 1 mm “IG-110” was heated to 900 ° C at a heating rate of 1 k / s and kept at 900 ° C for 35 minutes. .

The total pressure decreased with the holding time, and after 35 minutes, the total pressure reached 13%. Thus, over time, the total pressure or outgassing rate decreases. However, the thicker the graphite and the larger its size, the longer the degassing process takes. Even if the vacuum heating degassing process is performed, when taken out from the vacuum container, it is exposed to the atmosphere (for example, in the air) and adsorbs the gas (for example, CO, H ₂ O, hydrocarbons, etc.) in the atmosphere and degasses it. The effect gradually diminishes with the number of exposure days until it almost disappears. Therefore, the subsequent degassing process is simplified by selecting graphite with a low gas release rate.

The exhaust speed of the exhaust system ((4) + (7)) in Fig. 1 is N ₂
It is 55l / s in conversion. Here, the N ₂ conversion means that the exhaust speed of the exhaust device differs depending on the type of gas, and therefore the exhaust speed is represented on the basis of N ₂ gas. The total pressure in FIG. 5 (A) is an N ₂ conversion value. Since the sensitivity of the ionization vacuum gauge depends on the type of gas, it is corrected with N ₂ gas for convenience, and the value is used.

The discharge gas velocity S is [Pi = partial pressure of gas species i (obtained from QMS) Vi = exhaust speed of exhaust device with respect to gas species i] (in the case of FIG. 1, N ₂ is 55 l / s). It is not industrial to integrate for all gases. Therefore, as a simple method, So = Po × Vo ... [Po: B-A type ionization vacuum gauge display pressure (N ₂ converted value) Vo: N ₂ exhaust speed] The gas release rate So calculated by the following formula is used. Further, as described above, when the device used in the present invention is used, the gas released from the vacuum container is also contained in So at 1673 K or higher, and the true gas release rate from graphite is not obtained. Therefore, this adverse effect is removed by setting the temperature range to 673 to 1473K. If the gas released from other than the measured object is not negligible even at 1673K or less, the gas release rate is set in the temperature range 673 to 1473K as a result of subtracting the blank measurement value as described above. The temperature rise process was also defined and set to 1 k / s so that the change in the gas release rate due to the degassing result could be ignored. That is, the gas release rate So * in the present invention means that the graphite specimen size is 10 × 10 × 1 mm, pre-evacuated to 10 ⁻⁵ Pa or less, and then heated from room temperature to 1773 K at a heating rate of 1 k / s. It is defined as being calculated by the formula from the total pressure Po at the time N ₂ conversion value and the N ₂ conversion exhaust speed Vo. The gas release rate So * calculated from the total pressure in FIG. 5 (A) is shown in FIG. 5 (B). It is shown as a value per unit weight.

Various types of graphite are used in the present invention, and isotropic graphite can be exemplified as a typical example. Other anisotropic graphite, carbon material using non-graphite aggregate, heat insulating material, boron Alternatively, graphite containing another element such as silicon (often a carbide) may be used. The shape and the like are not limited at all.

Thus, as the graphite base material of the present invention, CVD
By the method, carbon, silicon carbide, is used for coating ceramics such as BN, the graphite substrate of the present invention, the above-mentioned ceramic coating is the same as conventional
It can be used as a furnace part for a CVD furnace.

Internal parts for a CVD furnace include all those used in a CVD furnace. Here, as the internal parts for the CVD furnace, for example, C
Holding in VD furnace, structural members, tightening members, holding tools,
Examples include inner wall materials for CVD furnaces.

[Examples] The present invention is described in detail below with reference to Examples, but the invention is not limited thereto.

Also, ASO * recorded below is 673 to 1473K.
Shows the average value of So * measured during the period.

Example 1 and Comparative Example 1 Isotropic lead "SIC-6" manufactured by Toyo Tanso Co., Ltd. shown in Table 1
Using "IG-610", SiCl ₄ and C ₃ H ₈ were used as raw materials, H ₂ was used as a carrier gas, and silicon carbide was thermally decomposed and grown on the graphite at 1673 K by the CVD method. As a result, as shown in Table 1, a yellow, partially gray, non-uniform porous silicon carbide film was grown on "SIC-6" having a large gas release rate (ASo *) and a large amount of ash. This micrograph is shown in FIG. Incidentally, FIG. 6 (1) shows an example, and FIG. 6 (2) shows a comparative example. On the other hand, the "IG-
A uniform, transparent, dense and dense silicon carbide film was grown on "610" (highly purified "SIC-6").

Example 2 and Comparative Example 2 Isotropic graphite "IG-11" manufactured by Toyo Tanso Co., Ltd. shown in Table 2
And its high-purity product "IG-110" were cut into cylinders with a diameter of 100 x 100 mm, heated to 2223 K (hot wall method), and NH ₃ and BCl ₃ were made to flow with H ₂ as a carrier gas to produce PBN.
Grew. Table 2 shows the structure of the grown PBN. Uniform and dense PBN on "IG-110" with low outgassing rate
Grew. On the other hand, spotted spots were formed on "IG-11", which has a high gas release rate.

Example 3 and Comparative Example 3 The same material as shown in Table 2 was cut into 10 × 100 × 100 mm and heated to 1537K, and propane gas and H ₂ gas were flowed,
Pyrolytic carbon was deposited on it. A homogeneous silver-colored dense pyrolytic carbon film was grown on "IG-110" with a low gas release rate. Table 3 shows the results.

Example 4 “IG-11” [(Dimension 5 × 5 × 40 mm ASo *: 3.9 × 10 ⁻² Pa
・ M ³ / (s ・ kg)] under vacuum at 2300K for 5 hours (1 Pa or less)
Obtained by degassing at 2300 K and then flowing propane gas and H ₂ gas [ASo *: 2.0 × 10 ^-2 Pa ・ m ³ / (s ・ k
g)] on top of which pyrolytic carbon was deposited. The grown carbon film was gray-grey, uniform and dense.

Example 5 “SIC-6” [(dimension φ700 × 20 ^t mm, ASo *: 3.8 × 10 ⁻²
Pa · m ³ / (s ・ kg)] degassed under vacuum (50 Pa or less) for 48 hours at 1973K [ASo *: 1.8 × 10 ^-2 Pa ・ m ³ / (s ・ k)
g)] and heated to 1973K to heat SiO gas, CO gas and Ar
A silicon carbide layer was grown to 100 μm on the surface under a reduced pressure of a total pressure of 100 Pa of a mixed gas atmosphere.

The grown silicon carbide layer was uniform and dense β-type (3C-type) silicon carbide. It can be seen that a relatively good coating layer is formed if the operation of sufficiently suppressing the gas generation is performed before forming the silicon carbide layer as in this example. However, since it is uneconomical to perform such a time-consuming operation in the CVD furnace, it is advantageous to use the one in which ASo * has been lowered in advance before filling the furnace as in the present invention.

From the examples and comparative examples, the average value of So * in the temperature range of 673 to 1473K, that is, ASo * is 2 × 10 ⁻² Pam ³ / (s · k
g) C of homogeneous and dense ceramic
The VD layer grows easily. On the other hand, 3 × 10 ^-2 Pam ³ / (s ・ kg)
In the above case, degassing should be performed at a high temperature such as 1973K or higher, and ASo * should be 2 × 10 ^-2 Pam ³ / (s · kg) or less to obtain a dense and uniform ceramic layer by the CVD method. The present invention has been completed because it was found to be difficult. Therefore, ASo *
If is less than 2 × 10 ^-2 Pam ³ / (s ・ kg) in advance, you can use it as it is, and ASo * is 3 × 10 ^-2 Pam ³ / (s ・ kg).
2 kg / kg or more, degassing is performed at high temperature to reach 2 × 10 ^-2 Pa
If it is less than or equal to m ³ / (s · kg), it can be used, and the present invention does not matter whether degassing treatment is performed or not.

Further, conventionally, in the CVD furnace, films are deposited on the parts inside the furnace, and these films are peeled off to generate dust or dust to contaminate the inside of the furnace and reduce the purity of the generated film. Was there. However, when the graphite base material of the present invention coated with ceramics is used as a part inside the furnace,
Since the film previously formed on the graphite base material of the present invention is a uniform and dense film originally, the film further growing on it is difficult to peel off, and the generation of dust or dust can be suppressed, and by extension, on the base material. The purity of the film can be maintained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for measuring a gas release rate of the present invention, FIGS. 2 to 4 are mass spectra of graphite materials, FIG. 5 is a gas pressure measurement result, and FIG. 6 is an example and a comparative example. It is a mimic diagram of the micrograph of FIG. FIG. 7 shows the results of measuring the time dependence of the total pressure at 900 ° C.

Claims (3)

(57) [Claims] 1. Used for depositing or growing ceramics such as boron nitride (BN), silicon carbide (SiC) and carbon (C) by a chemical vapor deposition method (CVD method), 10 × 10 × 1 m
673 to 14 when heated at a heating rate of 1 K / s as m size
The average gas release rate at a temperature of 73K is _{2 in} N ₂ conversion.
A graphite base material for ceramics coating, characterized by having a density of × 10 ^-2 Pa · m / (s · kg) or less. 2. The graphite base material according to claim 1, wherein the ash content of the graphite base material is 50 ppm or less. 3. A CVD method using the graphite base material according to claim 1 or 2 coated with ceramics.
Internal parts for the furnace.