JP3378608B2 - Method for producing silicon carbide substrate for jig for semiconductor production - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a silicon carbide based material for a semiconductor manufacturing jig such as a diffusion furnace tube.

[0002]

2. Description of the Related Art Conventionally, an impurity diffusion step into a silicon wafer has been carried out as the most important and basic step in semiconductor manufacturing.

In this impurity diffusion step, a silicon wafer is loaded into a diffusion furnace tube made of porous silicon carbide and a diffusion source is supplied into the heated tube to diffuse impurities such as nitrogen and boron. Done. At that time, a substance other than the diffusion source may be released from the inner wall surface of the porous tube by heating or the like. It is known that when the amount of the release is large, the yield of products deteriorates due to the contamination of the silicon wafer.

Therefore, as a diffusion furnace tube of this type, a tube impregnated with 5% by volume to 50% by volume of metallic silicon has become the mainstream in recent years. Further, in some cases, for example, a method of further forming a dense and high-purity silicon carbide thin film by a CVD method on the surface of the tube has been proposed.

According to this method, the airtightness is improved by covering the surface of the porous tube with the metallic silicon and silicon carbide thin film, and it is considered that the influence of impurities derived from the tube itself can be eliminated. .

[0006]

However, the conventional method of impregnating metallic silicon and forming a silicon carbide thin film by the CVD method has some problems as described below.

For example, the conventional tube cannot be used at a temperature of about 1260 ° C. or higher, which is higher than its melting point, because it uses metallic silicon. In addition, it has become clear in recent years that metallic silicon itself has a property of easily diffusing impurities, and some have questioned it as an impregnating agent for improving the airtightness of a tube. Further, the impregnation with metallic silicon inevitably increases the weight of the tube, resulting in poor handling.

In addition, since the impregnation of metallic silicon has caused the deterioration of the smoothness of the tube surface, it has been difficult to form a desired silicon carbide thin film on the tube surface. Therefore, pinholes and peeling were likely to occur in the formed thin film. Further, the conventional method of performing the impregnation and the thin film formation by the CVD method has a drawback that the manufacturing cost becomes high and the manufacturing process becomes complicated.

If a local temperature difference occurs in the tube in the impurity diffusion step, the tube may be broken. Under the circumstances described above, the inventors of the present invention have conducted diligent research and found that a porous silicon carbide sintered body is produced according to predetermined materials and conditions, and high purity CVD of a predetermined thickness is performed on the sintered body. We have found that the above problems can be solved by directly forming a thin film. Then, the present inventors have completed the following invention by further developing the knowledge.

[0010]

Means and Actions for Solving the Problems In the present invention, a molded body is manufactured using a silicon carbide (SiC) powder having an average particle size of 1 μm to 500 μm and an impurity content of 20 ppm or less, On the surface of a porous sintered body obtained by firing the molded body under an inert atmosphere and at a temperature of 1500 ° C. to 2000 ° C., a thickness of 10 μm by a CVD method.
A high-purity SiC thin film having a thickness of m to 500 μm is formed. In this case, the average surface roughness of the sintered body is 0.5 μm to 10 μm.
The maximum value is preferably 2.0 μm to 100 μm. Further, the content of impurities in the high-purity SiC thin film is preferably 1 ppm or less.

A molded body made of high-purity SiC powder has a smaller content of impurities than usual. Moreover, by firing the compact at a temperature lower than the firing temperature of general SiC, the content of impurities in the compact is significantly reduced. Therefore, it is possible to directly form the SiC thin film on the surface of the sintered body by the CVD method without impregnating metal silicon (Si), which has been essential until now. Further, since the thin film is formed on the portion where the metal Si does not exist, the adhesion of the SiC thin film is improved, and pinholes, peeling, etc. are less likely to occur.

The manufacturing method of the present invention will be described in detail below in the order of steps. The SiC powder as the main raw material has an impurity content of 20 ppm or less. Such high-purity powder can be obtained, for example, by adding an acid aqueous solution or gas to SiC.
It is produced by a conventionally known method such as purifying powder. Further, not only the α-type SiC powder and the β-type SiC powder can be used, but also both can be mixed and used.

The average particle size of the SiC powder is 1 μm to 500 μm.
It must be within the range of m. If the average particle size is less than 1 μm, the amount of impurities mixed during the production of the powder increases, and a highly pure base material cannot be obtained. On the other hand, if the average particle size is larger than 500 μm, the strength of the base material after sintering becomes extremely small, which makes it unusable.

A binder for molding or the like is mixed with the above-mentioned SiC powder. This mixture is molded by rubber press molding, injection molding, extrusion molding, cast molding, or the like to obtain a molded body having a desired shape. The obtained molded body is subjected to deframed, dried and dewaxed steps, and thereafter, at 1500 ° C. to 200 ° C. in an inert gas atmosphere such as argon.
It is fired at a temperature around 0 ° C. If this temperature is lower than 1500 ° C., the molded body will not be completely sintered and a desired sintered body cannot be obtained. On the other hand, if this temperature exceeds 2000 ° C,
Impurities cannot be completely removed because the sintering of SiC proceeds rapidly.

By the above-mentioned firing, the SiC compact becomes a porous sintered body of high purity, and its specific gravity is 1.6 g / cm ³ to.
It will be about 2.2 g / cm ³ . After that, the sintered body is subjected to machining or the like as required.

Then, a thickness of 10 μm to 500 is formed on the entire surface of the sintered body or a required portion thereof by a CVD method.
A high-purity and dense SiC thin film of μm is formed. In this case, if the thickness of the SiC thin film is less than 10 μm, peeling / cracking is likely to occur in the SiC thin film even with a small impact. On the other hand, if the thickness of the SiC thin film exceeds 500 μm, the SiC
It takes time to form a thin film, which is disadvantageous in terms of productivity and cost. The SiC thin film is preferably formed on the compact by a low pressure CVD method. The reason is that the low pressure CVD method is suitable for mass production, and it is possible to reliably form a thin film even when the molded body is not a simple shape.

The content of impurities in the SiC thin film is preferably 1 ppm or less. This is because if the content of impurities exceeds this value, the silicon wafer will be contaminated by the impurities derived from the SiC thin film itself.

Further, the surface roughness of the sintered body (JIS B 0
It is desirable that the average value (Ra) of 601) is 0.5 μm to 10 μm and the maximum value (Rmax) is 2.0 μm to 100 μm. That is, if the surface of the sintered body has irregularities to some extent, the anchor effect improves the adhesion strength of the SiC thin film.

If Ra or Rmax is smaller than the above value, a sufficient anchor effect cannot be obtained, and the produced SiC thin film is likely to be peeled off by a small impact or the like. Further, since the thermal shock resistance value becomes small, it becomes difficult to use it in a high temperature atmosphere. On the other hand, when Ra or Rmax is larger than the above value, a thick film has to be formed in order to smooth the SiC thin film, which is a problem in terms of productivity and cost.

According to the above method, the base material can be highly purified, strengthened, and lightened without impregnating the metal Si, which is extremely preferable. In addition, since the impregnation of metal Si is not necessary, it is advantageous in terms of manufacturing process and cost.

[0021]

EXAMPLES An example in which the present invention is embodied in a method of manufacturing a diffusion furnace tube used in a step of diffusing impurities into a silicon wafer will be described in detail.

In this embodiment, the impurity content is 10 ppm.
Below, β-type SiC powder having an average particle size of 1.4 μm was selected as the main raw material. The SiC powder was granulated by adding 5 parts by weight of a molding binder, and the resulting granules were formed into a tube-shaped compact (external diameter 25c) by a wet rubber press method.
m, inner diameter 24 cm, length 150 cm).

After demolding and drying the molded body and dewaxing, the molded body is dried at 1800 ° C. for 4 hours in an argon gas atmosphere.
The molded body was made into a porous sintered body by firing for a period of time. When the obtained sintered body was examined, the content of impurities was as small as 5 ppm, and it was an extremely high-purity porous body.

Next, by machining the inner and outer surfaces of the tube-shaped sintered body, the wall thickness is 3 mm, Ra is 2.4 μm,
A sintered body with Rmax of 28.2 μm was obtained. Here, the sintered body was set in a vacuum furnace for CVD, the inside of the furnace was depressurized, and then SiCl ₄ gas and CCl ₄ gas were circulated. And a high-purity and dense SiC thin film (thickness of about 100
μm, impurity content 1 ppm or less) was uniformly formed on the entire surface of the sintered body.

Next, a diffusion furnace tube of a comparative example with respect to the above-mentioned example was manufactured as follows. First, a tube-shaped sintered body of the same shape and size obtained by the same procedure as in the example was put in a carbon crucible together with a lump of metal Si,
They were set in the firing furnace. Then, the pores of the sintered body were impregnated with metallic Si by heating at 1400 ° C. for 10 hours. Next, the sintered body was taken out of the carbon crucible and the excess metal Si deposited on the surface was removed to smooth the surface of the sintered body. Further, after washing and drying the sintered body, an attempt was made to form a high-purity SiC thin film according to the low pressure CVD method of the above-mentioned embodiment.

In order to compare these diffusion furnace tubes, 10 samples of each were prepared and the total weight (k
g), density (g / cm ³ ), pinholes / peeling in SiC thin film, and tube cracking when a temperature difference is applied.
I researched the item. The results are shown in Table 1.

[0027]

[Table 1]

As is clear from Table 1, the diffusion furnace tube of the example weighed about 6.4 kg and was excellent in handleability. The density of the part excluding the thin film is 1.8.
It was 6 g / cm ³ . On the other hand, although the tube of the comparative example had the same size as that of the example, the weight and density were 1.6 to 1.7 times that of the example.

Further, in the examples, no pinholes or peeling were observed in the SiC thin film, whereas in the comparative examples, S
Pinholes and peeling were found in places on the iC thin film. When a temperature difference was applied to both diffusion furnace tubes, no cracks occurred in the examples, whereas some cracks occurred in the comparative examples, leading to breakage.

When the two manufacturing processes themselves are compared, it was possible to manufacture the diffusion furnace tube in a comparatively short time and at a low cost in the example in which impregnation was not performed.
On the other hand, in the comparative example, impregnation of metal Si had to be performed before the CVD method, which was disadvantageous in terms of manufacturing cost and manufacturing process.

By summing up the above results, it is concluded that the manufacturing method of the example is superior to the manufacturing method of the comparative example. It should be noted that the present invention is not limited to the above embodiment, and can be modified as described below. For example, (a) The present invention can of course be embodied in various jigs such as a wafer boat, a wafer carrier, and an epitaxial growth susceptor, in addition to the diffusion furnace tube embodied in the embodiments.

(B) The high-purity SiC thin film does not necessarily have to be provided on both inner and outer surfaces of the tube, and may be provided on at least the inner surface, that is, the side facing the silicon wafer from which contamination should be avoided.

(C) In addition to the low pressure CVD method carried out in the embodiment, for example, a normal pressure CVD method, various plasma CVD methods,
An optical CVD method or the like may be used.

[0034]

As described above in detail, according to the method for producing a SiC base material for a semiconductor manufacturing jig of the present invention, the base material can be highly purified and highly purified without impregnation with metallic Si. It has an excellent effect that strength and weight can be reduced. Further, in addition to the fact that the impregnation of metal Si is not required, the manufacturing process can be simplified and the cost can be reduced as compared with the conventional case.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01L 21/22 501 C04B 35/56 101X (56) References JP-A-60-138914 (JP, A) JP-A-60-35452 (JP, A) JP 5-851 (JP, A) JP 64-61376 (JP, A) JP 63-85076 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) C04B 41/85-41/87 C04B 35/565 C04B 38/00 304 H01L 21/22

Claims (3)

(57) [Claims] 1. A molded body is produced using a silicon carbide powder having an average particle size of 1 μm to 500 μm and an impurity content of 20 ppm or less, and then the molded body is kept in an inert atmosphere at 1500 ° C. to 2000 ° C. On the surface of the porous sintered body obtained by firing at the temperature of 1
A method for manufacturing a silicon carbide based substrate for a semiconductor manufacturing jig, which comprises forming a high-purity silicon carbide thin film of 0 μm to 500 μm. 2. The average surface roughness of the sintered body is 0.5 μm.
m to 10 μm and the maximum value is 2.0 μm to 100 μm
2. The method for manufacturing a silicon carbide based material for a semiconductor manufacturing jig according to claim 1, wherein m is m. 3. The impurity content in the high-purity silicon carbide thin film is 1 ppm or less.
Alternatively, the method for manufacturing a silicon carbide based substrate for the semiconductor manufacturing jig described in 2 above.