JP2005197534A - Surface protection film formation method for repairing tool for heat treatment and repairing tool for heat treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the surface protection film formation method of a preparing tool for heat treatment for forming the SiC film of a plurality of layers on the surface of a repairing tool for heat treatment so as to sufficiently decrease impurity concentration in the SiC film, especially, the impurity concentration of the uppersurface layer of the SiC film. <P>SOLUTION: The surface protection film formation method of a repairing tool for heat treatment for forming the SiC film of a plurality of layers for protecting the surface of a repairing tool for heat treatment is characterized by forming the SiC film of the plurality of layers, using a CVD furnace different for each layer on the base material of the repairing tool for heat treatment by a CVD method, and at least by forming the SiC layer of the first layer on the base material, and then removing the surface layer of the SiC layer of the first layer before forming the SiC layer of the second layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a protective film on the surface of a heat treatment jig used in a heat treatment step in semiconductor manufacturing, and more particularly to a method for forming a plurality of SiC films by a CVD method.

  For example, when a device is manufactured using a semiconductor wafer, a number of steps are involved from a wafer processing process to an element formation process, one of which is a heat treatment step. The heat treatment step is an important process performed for the purpose of forming a defect-free layer on the surface layer of the wafer, gettering, crystallization, oxide film formation, impurity diffusion, and the like.

An example of the heat treatment furnace used in such a heat treatment process for a wafer is the heat treatment furnace shown in FIG.
The heat treatment furnace 20 includes a heat treatment tube 21 made of SiC or the like for introducing a semiconductor wafer, a liner tube 22 into which the heat treatment tube 21 is inserted, and a heater 23 disposed around the liner tube 22. The heat treatment tube 21 forms a heat treatment space and includes a straight body portion 24 having a substantially uniform inner diameter in the longitudinal direction and a gas introduction portion 25 for introducing a process gas to one end of the straight body portion 24. Has been. Usually, the gas introduction part 25 has a smaller diameter than the straight body part 24. The gas introduction part 25 is connected to a gas supply pipe 29 through a joint 28. On the other hand, an opening 26 for introducing the wafer W is formed at the other end of the straight body portion 24. Then, a large number of wafers W are arranged on the wafer boat 27 and put into the heat treatment furnace 20 from the opening 26 to perform heat treatment.

In addition to the so-called batch-type heat treatment furnace that heat-treats a large number of semiconductor wafers as shown in FIG. 2 as a heat treatment furnace, a single-wafer type that heat-treats semiconductor wafers one by one as shown in FIG. In some cases, a heat treatment furnace is used.
In this single wafer heat treatment furnace 30, the wafer W is placed on a susceptor 31 disposed in the furnace and heat treatment is performed. When the wafer W is heat-treated, the lamp 33 and the like are heated, and a process gas is introduced from the gas introduction pipe 34, passes through the reaction chamber 32, and is discharged to the outside from the gas exhaust pipe 35.

  As a heat treatment jig used in such a heat treatment furnace, such as a wafer boat, a heat treatment tube, and a susceptor, a silicon carbide protective film (hereinafter referred to as an SiC film) is formed on the surface of the substrate by a chemical vapor deposition method (hereinafter referred to as a CVD method). ), That is, a substrate coated with a CVD-SiC film is used. In the jig for heat treatment, since the purity of the substrate is low, there is a problem that impurities are diffused from the substrate to the surroundings during the heat treatment. Therefore, the base material is coated with a high-purity CVD-SiC film so that impurities are not diffused from the base material to the periphery of the jig for heat treatment or the wafer to be heat-treated.

In order to protect the surface of the heat treatment jig, a CVD-SiC film formed on the surface is introduced, for example, in Patent Document 1.
That is, a CVD-SiC film grown once on the surface of the substrate (hereinafter referred to as a first conventional example), a plurality of times grown (hereinafter referred to as a second conventional example), and a plurality of times of growth. In each case, the surface of the outermost CVD-SiC layer is ground, and a CVD-SiC layer is further formed on the ground surface (hereinafter referred to as a third conventional example).

  Also, a plurality of layers of CVD-SiC films that are substantially parallel to the surface of the substrate are grown. At least one of these layers is a nucleation layer, and the other layers are normal crystal layers. There is a film in which a plurality of CVD-SiC films in which the crystal growth between the nucleation layer and the normal crystal layer is discontinuous are formed by alternately growing two layers (hereinafter referred to as a fourth conventional example). . At this time, the crystal growth of the normal crystal layer may be continuously performed in the thickness direction.

However, the CVD-SiC films formed in the first to fourth conventional examples still have a high impurity concentration particularly near the outermost surface. Therefore, when the heat treatment jig on which such an SiC film is formed is used for a long time in the heat treatment step, there is a problem that impurities diffuse from the SiC film and the semiconductor wafer or the like is contaminated by the impurities.
The third conventional example grinds the surface of the SiC film. During grinding, there is a high possibility that impurities will be taken into the SiC film from the grinding wheel. Since impurities adhering to the jig are present as they are, if SiC film growth is performed, these impurities may be taken into the growing SiC film. Moreover, the CVD-SiC film can be easily ground if it has a simple shape such as a susceptor, but is difficult to work with a complicated shape such as a wafer boat or a heat treatment tube.

JP-A-7-335728

  The present invention has been made in view of such problems, and is a method of forming a plurality of layers of SiC films on the surface of a heat treatment jig, and the impurity concentration in the SiC film, particularly the highest concentration of the SiC film. It is an object of the present invention to provide a method for forming a surface protective film of a heat treatment jig that can sufficiently reduce the impurity concentration of a surface layer. Another object of the present invention is to provide a heat treatment jig capable of suppressing impurity contamination on a wafer or the like because diffusion of impurities is small in the heat treatment step.

  In order to solve the above-mentioned problems, the present invention is a method for forming a plurality of SiC films for protecting the surface on the surface of a jig for heat treatment, wherein the plurality of SiC films are formed by a CVD method. By using a different CVD furnace for each layer on the base material of the jig for heat treatment, at least after forming the first SiC layer on the base material, the second SiC layer is formed Provided is a surface protection film forming method for a heat treatment jig, wherein the surface layer of the first SiC layer is removed before the formation.

  In this way, if the CVD furnace is changed each time a protective film is grown, the SiC layer in which impurities volatilized and diffused directly from the base material into the CVD furnace is formed on the base material without the protective film. This is only the first layer formed in the CVD furnace that is used. That is, if a second SiC layer is formed on the first SiC layer in another CVD furnace, a protective film is already formed on the base material. Volatile diffusion of impurities in the furnace atmosphere is reduced by the first SiC layer. Therefore, in particular, in the SiC layer as the outermost layer of the SiC film, impurities taken in from the furnace atmosphere when forming the SiC layer are reduced. Furthermore, since the distance from the substrate surface is increased in the outermost SiC layer of the SiC film, impurity contamination due to outward diffusion is small. That is, the impurity concentration can be made smaller than the concentration of the SiC layer closer to the substrate.

By the way, it is known that impurities segregate in the surface layer of each SiC layer.
In the present invention, since the surface layer of the first SiC layer having a particularly high impurity concentration is removed, the impurity concentration in the first SiC layer can be further reduced. If the impurity concentration in the first SiC layer is low, the concentration of the impurity that volatilizes and diffuses from the first SiC layer into the furnace atmosphere when the second SiC layer is formed immediately above the SiC layer. In addition, the concentration of impurities diffused outward from the first SiC layer to the second SiC layer can be further reduced. The impurity concentration can be further reduced in the outermost SiC layer of the SiC film.
Therefore, when a plurality of SiC films are formed in this way, the impurity concentration of the outermost SiC layer can be sufficiently reduced.

  And when forming the said multiple layers of SiC film | membrane using a different CVD furnace for every layer, it is preferable to fix and decide the order of a furnace and to use as a dedicated furnace for each layer (Claim 2). .

  In this way, in the CVD furnace used to grow the upper SiC layer, the volatile diffusion of impurities from the base material to the furnace atmosphere is caused by the effect of one or more SiC layers formed so far. Therefore, the furnace atmosphere can be maintained in a state with fewer impurities. As a result, less impurities are taken into the SiC layer from the furnace atmosphere, and the impurity concentration of the SiC layer grown in the CVD furnace can be further reduced.

  In this case, it is preferable that the surface layer of each SiC layer after the second layer of the plurality of SiC films is removed every time each SiC layer is formed.

  As described above, the second and subsequent SiC layers sequentially formed on the first SiC layer also have a lower impurity concentration when the surface layer is removed each time each SiC layer is formed. A SiC film can be obtained. That is, as described above, since the CVD furnace is changed every time the SiC layer is grown, the growth of the SiC layer formed so far is not affected by the impurities volatilized in the atmosphere in the CVD furnace. However, on the other hand, some impurities are volatilized from the already formed SiC layer, and the impurities are taken into the surface layer of the growing SiC layer. Therefore, if the surface layer of the SiC layer having a high impurity concentration is removed after the growth of the SiC layer, the volatilization of impurities from the already formed SiC layer can be greatly reduced. As a result, the impurity concentration of the outermost layer of the SiC film can be further reduced.

  In this case, the surface layer of the SiC layer is preferably removed after an oxide film is formed on the surface layer of the SiC layer.

  In this way, if the surface layer of the SiC layer having a high impurity concentration is a silicon oxide film, unlike the SiC, the oxide film can be easily removed by a chemical solution. Can be easily dissolved and removed.

  In this case, the surface layer of the SiC layer can be removed using a chemical solution containing hydrofluoric acid (Claim 5).

  In particular, the chemical solution containing hydrofluoric acid can quickly remove the silicon oxide film. Therefore, when an oxide film is formed on the surface layer of the SiC layer, it is particularly suitable for removing the oxide film.

  In this case, the chemical solution containing hydrofluoric acid is more preferably hydrofluoric acid (Claim 6).

If the silicon oxide film obtained by oxidizing the surface layer of the SiC layer is made of only SiO _{2, the} oxide film can be quickly removed by the action of hydrofluoric acid. However, in practice, there may be SiOx in which x is less than 2 in the oxide film. In that case, the silicon oxide film can be sufficiently removed by using a chemical solution (fluoric nitric acid) in which nitric acid having oxidizing power and hydrofluoric acid with a high removal rate of the silicon oxide film are used.
Also, hydrofluoric acid and nitric acid are particularly suitable for use because they are commercially available in high purity, are readily available, and are commonly used in semiconductor manufacturing processes.

  In this case, it is preferable that the surface layer of the SiC layer is removed at least 1 μm in thickness (Claim 7).

  Impurities taken into the SiC layer are segregated in the vicinity of the surface of the SiC layer, so that they are present particularly at a high concentration in the surface layer of the SiC layer. Therefore, if the surface layer of the SiC layer is removed by at least a thickness of 1 μm or more, impurities present at a high concentration can be removed, so that the impurity concentration of the SiC layer can be further reduced. Therefore, the impurity concentration of the outermost layer of the SiC film can be further reduced.

  Further, the present invention provides a heat treatment jig in which a plurality of layers of SiC films are formed by the method for forming a surface protective film of the heat treatment jig of the present invention.

  With such a heat treatment jig, the impurity concentration in the outermost layer of the SiC film of the jig is very small, so even when used in a heat treatment process for a long time, there is little diffusion of impurities from the heat treatment jig. Therefore, it is possible to prevent the substrate such as a wafer to be heat-treated from being contaminated with impurities.

In such a heat treatment jig, it is preferable that the amount of metal contamination on the surface layer of each of the plurality of SiC films is 1 × 10 ¹⁵ atoms / cm ³ or less (claim 9).

In a multi-layered SiC film, the impurity concentration of the outermost layer of the SiC film can be further reduced by forming the SiC film while suppressing the amount of metal contamination on the surface layer of each layer to 1 × 10 ¹⁵ atoms / cm ³ or less. . Accordingly, the heat treatment jig on which such an SiC film is formed is suitable as a heat treatment jig because it hardly contaminates the wafer or the like even when used in the heat treatment step.

  As described above, according to the present invention, when a plurality of SiC films are formed on the surface of the heat treatment jig, the CVD furnace is changed every time an SiC film is grown, and at least the second layer is formed. By removing the surface layer of the first SiC layer before forming the first SiC layer, it is possible to sufficiently reduce the impurity concentration in the SiC film, particularly the impurity concentration in the outermost layer of the SiC film. is there. Further, if the heat treatment jig having the SiC film formed in this way is used in a heat treatment step for manufacturing a semiconductor wafer or the like, the diffusion of impurities from the heat treatment jig is small, and therefore the heat treatment is performed. It is possible to suppress contamination of wafers and the like.

Hereinafter, although this invention is demonstrated in detail, this invention is not limited to these.
In the heat treatment process, which is a process for manufacturing a semiconductor wafer or the like, the present inventors have performed heat treatment treatment in order to prevent the heat-treated wafer from being contaminated by impurities generated from the heat treatment jig. The method of lowering the impurity concentration of the SiC film formed on the surface of the tool was studied repeatedly.
Here, Fe will be described as an example of impurities. Generally, the Fe concentration in the base material of the jig for heat treatment, particularly the SiC base material, is about 1 × 10 ¹⁷ atoms / cm ³ or more. The inventors of the present invention are directed to the outward diffusion of Fe from the base material to the SiC film and the incorporation of Fe into the SiC film volatilized and diffused from the base material into the furnace atmosphere at the initial stage of the growth of the SiC film by the CVD method. Attention was paid to the fact that Fe is taken into the SiC film from the base material by the occurrence. Therefore, when the impurity analysis in the depth direction of the SiC film formed by the CVD method is performed by SIMS (Secondary Ion Mass Spectrometry), the Fe concentration (about 1 × 10 ¹⁷ atoms / cm ³ or more) on the surface of the SiC film is better. It was found that the concentration was higher than the internal concentration (about 1 × 10 ¹⁵ atoms / cm ³ ) by about 5 μm from the film surface. Impurities such as Fe incorporated in the CVD-SiC film are estimated to move in the growth direction of the SiC film during the CVD growth and segregate on the surface of the SiC film, and are incorporated from the atmosphere in the CVD furnace. Since impurities diffused from the CVD-SiC layer formed inside the substrate and the growing CVD-SiC layer are segregated on the surface of the SiC film, the impurity concentration on the surface of the CVD-SiC film is thus obtained. This is considered to be higher in concentration than in the inside of the SiC film. Therefore, it has been found that it is important to reduce the impurities in the CVD furnace atmosphere in which the amount of impurities can be controlled more easily.

  By the way, it is considered that the volatilized and diffused Fe remains in the furnace atmosphere even if the SiC film grows, and this is taken into the growing SiC film. Further, Fe that has volatilized and diffused in the furnace atmosphere has a high possibility of adhering to other heat treatment jigs in the CVD furnace, and this peels off during the SiC film growth and is taken into the growing SiC film. That is, no matter how high the purity of the SiC film is grown, it is affected by impurities such as Fe contained in a high concentration in the initial base material.

  For example, in the above-described first to fourth conventional examples, the substrate is directly exposed to the atmosphere in the CVD furnace until the first SiC layer is formed on the substrate surface. The impurities are volatilized and diffused in the furnace atmosphere. Therefore, even if a plurality of layers of SiC films are grown, a large amount of impurities remain in the furnace atmosphere, and impurities adhere to the heat treatment jig of the CVD furnace. Impurities are taken in and segregate on the surface.

  Thus, Fe volatilized in the furnace atmosphere and Fe adhering to the jig for heat treatment in the furnace are taken into the growing SiC layer and segregate on the surface thereof. Impurity concentration in the vicinity of the surface increases. Therefore, it becomes easy for Fe to diffuse outward to the layer formed immediately above. Therefore, it is important not to volatilize Fe from the base material into the furnace atmosphere or to eliminate volatilized Fe.

  Therefore, the present inventors changed the CVD furnace each time an SiC layer was grown when forming a plurality of layers of SiC films on the surface of the heat treatment jig, so that the substrate was brought into the furnace atmosphere. Volatile impurities can be removed relatively easily, and the surface of the first SiC layer having a particularly high impurity concentration is removed, so that the impurities in the first SiC layer can be removed from the second layer. The present invention has been completed by conceiving that it is possible to further suppress volatile diffusion into the furnace atmosphere in the subsequent growth or outward diffusion to the second and subsequent SiC layers.

Here, FIG. 1 shows a schematic cross-sectional view of a surface protective film formed on the surface of the heat treatment jig by the surface protective film forming method of the present invention.
FIG. 1 shows a structure in which a plurality of layers of SiC films 12 are formed on the surface of a base material 11 of a heat treatment jig in order to protect the surface. In this case, the SiC film 12 includes five SiC layers (12a to 12e).

In the present invention, such a surface protective film is formed as follows.
That is, the method for forming a surface retention film of a heat treatment jig according to the present invention is a method of forming a plurality of SiC films for protecting the surface on the surface of the heat treatment jig, the method comprising: The film is formed on the base material of the heat treatment jig by a CVD method using a different CVD furnace for each layer, and at least after the first SiC layer is formed on the base material, the second layer is formed. Before forming the first SiC layer, the surface layer of the first SiC layer is removed.

  As described above, after the first SiC layer 12a is grown on the base material 11, the CVD furnace is changed, and the second SiC layer 12b is formed on the first SiC layer 12a. When the growth is performed, Fe or the like volatilized during the growth of the first layer is formed in the furnace atmosphere of the CVD furnace or the jig in the furnace used for the growth of the second SiC layer 12b. Since there is no impurity, it is not affected. In addition, since the first SiC layer 12a is formed on the surface of the base material 11 during the growth of the second layer, the volatile diffusion of impurities from the base material 11 is greater than that during the growth of the first layer. This reduces the amount of impurities released into the furnace atmosphere during the growth of the second SiC layer 12b or adhering to the heat treatment jig in the furnace. Therefore, if the SiC layer is grown a plurality of times by changing the furnace, it will not be affected by the impurities volatilized during the previous growth. Further, as the number of times of growth of the SiC layer increases, the total film thickness of the SiC film increases, so that impurities that volatilize during the growth decrease and the distance from the substrate surface also increases. Less. Accordingly, the impurity concentration is low in the outermost SiC layer 12e of the SiC film.

Moreover, in the present invention, since the surface layer of the first SiC layer 12a having a particularly high impurity concentration is removed, the impurity concentration in the first SiC layer 12a can be further reduced. If the impurity concentration in the first SiC layer 12a is low, the concentration of impurities that volatilizes and diffuses from the first SiC layer 12a into the furnace atmosphere when forming the second SiC layer 12b. In addition, the concentration of impurities diffused outward from the first SiC layer 12a to the second SiC layer 12b can be further reduced. The impurity concentration can be further reduced in the outermost SiC layer 12e of the SiC film.
Therefore, according to the present invention, it is possible to obtain a heat treatment jig having a SiC film surface with a sufficiently small amount of impurities such as Fe.

  At this time, when the plurality of SiC films are formed using different CVD furnaces for each layer, it is preferable to fix the order of the furnaces and use them as dedicated furnaces for each layer. Thus, by fixing the order of the CVD furnace to be used, the furnace for growing the upper SiC layer has less volatile diffusion of impurities such as Fe during the growth of the SiC layer. The contamination of the inner heat treatment jig is also reduced, and a SiC film with fewer impurities can be obtained.

  Further, it is preferable that the surface layer of each of the second and subsequent SiC layers of the plurality of SiC films is removed every time each SiC layer is formed. As described above, the CVD furnace is changed every time the SiC layer is grown, so that it is not affected by impurities volatilized into the atmosphere in the CVD furnace when the SiC layer formed so far is grown. However, on the other hand, some impurities are volatilized from the already formed SiC layer, and the impurities are taken into the surface layer of the growing SiC layer. Therefore, if the surface layer of each SiC layer having a relatively high impurity concentration is removed after the growth of each SiC layer, the volatilization of impurities from the already formed SiC layer can be greatly reduced, and the outermost layer of the SiC film can be reduced. The impurity concentration can be further reduced.

At this time, the removal of the surface layer of the SiC layer is preferably performed by acid etching or the like after the surface layer of the SiC layer is oxidized to form an oxide film. The oxide film is formed by putting the base material on which the SiC layer is formed into an oxidation furnace and performing a Pyro oxidation process (for example, heat treatment at 1200 ° C. for 100 hours in an O ₂ -10% H ₂ O atmosphere). Can be formed. In this way, a silicon oxide (SiOx) film is formed on the surface layer of the SiC layer. This SiOx film can be quickly removed using a chemical solution containing hydrofluoric acid. In particular, if etching is performed with a mixed solution (fluoric nitric acid) of high-purity hydrofluoric acid (HF) and high-purity nitric acid (HNO ₃ ) that is generally used in the semiconductor manufacturing process, SiOx having an x value of less than 2 in the oxide film. there exist also can be SiO ₂ by oxidation with nitric acid, the SiO ₂ is preferable because it is more quickly removed by hydrofluoric acid. Thus, the etching rate for SiO ₂ by hydrofluoric acid is high, and impurities remain segregated at a high concentration on the surface layer of the SiC layer. The surface layer of the SiC layer having a high impurity concentration can be removed while preventing the above.
In addition to nitric acid as described above, the chemical solution containing hydrofluoric acid is preferable as long as it is an acid that can oxidize SiOx having x less than ₂ to SiO2, and for example, sulfuric acid may be mixed.

  At this time, the surface layer of the SiC layer is removed at least 1 μm or more, more preferably 3 μm or more. Since the impurity concentration decreases from the surface toward the bulk and is constant in a region deeper than 1 μm, particularly 3 μm, the surface layer is removed by at least 1 μm or more, more preferably 3 μm or more. Only the high-concentration impurity region can be removed.

  And the jig for heat treatment which has the SiC film formed by such a surface protection film formation method, in the heat treatment process, the concentration of impurities such as Fe in the SiC film in contact with the semiconductor wafer etc., particularly the outermost layer of the SiC film. Since the impurity concentration is low, the wafer or the like is hardly contaminated with impurities in the heat treatment step, and can be suitably used for heat treatment of the wafer or the like.

In particular, when a SiC film is grown so that the amount of metal contamination on the surface layer of each layer is 1 × 10 ¹⁵ atoms / cm ³ or less in a multi-layered SiC film, the surface of the SiC layer exposed to the furnace atmosphere is reduced. Since the amount of metal contamination including Fe existing is kept low, both the amount of metal contamination that diffuses outward to the SiC layer further formed on the surface and the amount of metal contamination that diffuses and diffuses into the furnace atmosphere are small. it can. Therefore, the contamination of impurities in the SiC layer that is the outermost layer of the SiC film can be further reduced.

In this case, it is important to form an SiC layer very close to the base material so that the amount of contamination of metals including Fe is 1 × 10 ¹⁵ atoms / cm ³ or less. For that purpose, as described above, in addition to removing the surface layer of each SiC layer, means such as reducing the growth of the SiC layer to a reduced pressure growth may be taken. During the reduced pressure growth, the atmosphere inside the furnace is discharged outside the furnace while flowing the process gas into the furnace, so that impurities such as metals existing in the atmosphere are also exhausted, including Fe taken into the growing SiC layer. The amount of metal to be used can be reduced from the furnace atmosphere. In this way, the amount of metal contamination on the surface layer of the SiC layer very close to the substrate can be suppressed to 1 × 10 ¹⁵ atoms / cm ³ or less. Then, if a new layer is stacked by changing the CVD furnace, a CVD-SiC layer having a lower impurity concentration can be formed.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
(Example 1)
A SiC substrate having a diameter of 200 mm was prepared, and the substrate was put into a CVD furnace for growing a first CVD-SiC layer. Then, silicon tetrachloride (SiCl ₄ ) gas is flowed into 1 SLM, methane (CH ₄ ) gas is 0.5 SLM, hydrogen (H ₂ ) gas is flowed into the ₂ SLM furnace, and the furnace pressure is 30 Torr (4 × 10 ³ Pa). A first SiC layer of 30 μm was grown on the surface of the substrate by heat treatment at 1400 ° C. for 40 minutes while evacuating the furnace atmosphere with a vacuum pump. After the pressure inside the CVD furnace was restored and the base material on which the first CVD-SiC layer was formed was taken out, the base material was put into an oxidation furnace. Pyro oxidation treatment was performed in a furnace (heat treatment at 1200 ° C. for 100 hours in an O ₂ -10% H ₂ O atmosphere) to form a 0.1 μm silicon oxide film on the surface of the first CVD-SiC layer. Thereafter, the base material was taken out of the furnace and immersed in a hydrofluoric acid solution of 5% HF and 5% HNO ₃ to remove the silicon oxide film on the surface of the first CVD-SiC layer. This oxidation treatment and removal of the silicon oxide film were repeated 10 times to remove a total of 1 μm of the CVD-SiC layer.

After removing the silicon oxide film, the base material was put into a CVD furnace in which a separately prepared second CVD-SiC layer was grown. Then, under the same conditions as the first CVD-SiC layer, a second CVD-SiC layer was grown 30 μm directly above the first CVD-SiC layer. Then, after Pyro oxidation treatment under the same conditions as the first layer, the surface layer of the second CVD-SiC layer is removed by the same method as the first layer, and the second CVD-SiC layer is removed. Formed. Furthermore, the CVD-SiC layer was grown from the third layer to the fifth layer on the substrate by repeating the change of the CVD furnace and the removal of the surface layer by the same method. When the Fe concentration of the outermost surface layer of the substrate after the formation of the five-layer SiC film, that is, the fifth CVD-SiC layer was investigated by SIMS at 5 points, 1 × 10 ^{12 to} 5 × 10 ¹² atoms / cm ³ .

(Comparative Example 1)
As in Example 1, a SiC substrate having a diameter of 200 mm was prepared and the substrate was put into a CVD furnace. Then, silicon tetrachloride (SiCl ₄ ) gas is supplied at 1 SLM, methane (CH ₄ ) gas is supplied at 0.5 SLM, and hydrogen (H ₂ ) gas ₂ SLM is supplied into the furnace, so that the furnace pressure is 30 Torr (4 × 10 ³ Pa). A first SiC layer of 30 μm was grown on the surface of the substrate by heat treatment at 1400 ° C. for 40 minutes while evacuating the furnace atmosphere with a vacuum pump. After the pressure in the CVD furnace was restored and the furnace temperature was returned to room temperature, a second CVD-SiC layer was grown immediately above the first CVD-SiC layer under the same growth conditions. This operation was repeated, and CVD-SiC layers from the second layer to the fifth layer were grown on the substrate surface in the same furnace. When the Fe concentration of the outermost surface of the base material after the formation of the five-layer SiC film, that is, the fifth CVD-SiC layer was investigated by SIMS at 5 points, 1 × 10 ¹⁵ to 1 × 10 ¹⁶ atoms / cm ³ The Fe concentration was 200 times or more compared to the example.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

For example, in Example 1 described above, the case where a five-layer CVD-SiC film is formed has been described as an example. However, the present invention is not limited to this, and the original base material may be used as long as two or more layers are formed. Since the impurities from can be suppressed, the effect can be exhibited.
Further, the present invention can be used not only for SiC base materials but also for surface coating of other base materials used in heat treatment jigs such as carbon susceptors.
Furthermore, specific examples of the heat treatment jig to which the present invention can be applied are not limited to the wafer boat, the heat treatment tube, the susceptor and the like. Any jig that needs to prevent contamination of the wafer or the like in the heat treatment furnace, such as a thermocouple protection tube or liner tube, can be applied regardless of its name or shape.

It is the schematic sectional drawing which showed an example of the surface protective film formed in the jig | tool surface for heat processing. It is the schematic which shows an example of a batch type heat processing furnace. It is the schematic which shows an example of a single wafer type heat treatment furnace.

Explanation of symbols

11 ... substrate, 12 ... SiC film, 12a-12e ... SiC layer,
20, 30 ... Heat treatment furnace, 21 ... Heat treatment tube, 22 ... Liner tube,
23 ... heater, 24 ... straight body part, 25 ... gas introduction part, 26 ... opening part,
27 ... Wafer boat, 28 ... Joint, 29 ... Gas supply pipe,
31 ... Susceptor, 32 ... Reaction chamber, 33 ... Lamp, 34 ... Gas introduction pipe,
35 ... gas exhaust pipe,
W: Wafer.

Claims (9)

  A method of forming a plurality of SiC films for protecting a surface of a heat treatment jig on the surface of the heat treatment jig, wherein the plurality of SiC films are formed on the base material of the heat treatment jig by a CVD method. The first SiC layer is formed using a different CVD furnace, and at least after the first SiC layer is formed on the substrate and before the second SiC layer is formed. A method for forming a surface protective film of a jig for heat treatment, comprising removing a surface layer of the layer.   The multi-layered SiC film is formed using a different CVD furnace for each layer, and the order of the furnaces is determined and used as a dedicated furnace for each layer. A method for forming a surface protective film of a jig for heat treatment.   The jig for heat treatment according to claim 1 or 2, wherein a surface layer of each SiC layer after the second layer of the plurality of SiC films is removed each time each SiC layer is formed. Surface protective film forming method.   The surface protective film of the jig for heat treatment according to any one of claims 1 to 3, wherein the surface layer of the SiC layer is removed after an oxide film is formed on the surface layer of the SiC layer. Forming method.   5. The surface protection film forming method for a heat treatment jig according to claim 1, wherein the removal of the surface layer of the SiC layer is performed using a chemical solution containing hydrofluoric acid.   6. The surface protective film forming method for a heat treatment jig according to claim 5, wherein the chemical solution containing hydrofluoric acid is hydrofluoric acid.   The method for forming a surface protective film of a jig for heat treatment according to any one of claims 1 to 6, wherein the surface layer of the SiC layer is removed by at least a thickness of 1 µm or more.   A heat treatment jig comprising a plurality of SiC films formed by the method for forming a surface protective film of a heat treatment jig according to any one of claims 1 to 7. 9. The jig for heat treatment according to claim 8, wherein in the plurality of SiC films, a metal contamination amount of a surface layer of each layer is 1 × 10 ¹⁵ atoms / cm ³ or less.

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