JP3208045B2 - Silicon carbide composite for high temperature - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide composite material suitably used as a reaction tube, a soaking tube and the like used in a semiconductor diffusion furnace, and more particularly to a silicon carbide sintered body. The present invention relates to a high temperature silicon carbide composite material comprising a porous substrate and a silicon carbide film chemically deposited on the surface of the porous substrate.

[0002]

2. Description of the Related Art For example, graphite and, in recent years, quartz have been used as a constituent material of a reaction tube for a semiconductor diffusion furnace. However, when graphite is used, there is a problem that the impurities contained in the graphite are extremely large and the Si wafer is contaminated. Quartz is severely consumed by deformation and devitrification under high temperature conditions, and has a short life. Therefore, in combination with the tendency of increasing the heat treatment temperature due to the demand for shortening the treatment time, etc., recently, a porous substrate which is a silicon carbide sintered body and silicon carbide chemically vapor-deposited on the surface thereof A reaction tube composed of a silicon carbide composite material comprising a film has been proposed. It has been proposed that the surface of a sintered body be composed of a silicon carbide composite material in which a silicon carbide chemical vapor deposition film is coated. Such a silicon carbide composite material is rich in heat resistance and thermal shock resistance because the substrate is a porous silicon carbide sintered body. In addition, the substrate is poor in airtightness because it is porous. However, by covering the surface of the substrate with a dense silicon carbide chemical vapor deposition film, sufficient airtightness can be secured as a whole. Therefore, a reaction tube made of such a silicon carbide composite material can exhibit the same function as a quartz tube as a reaction tube, and of course, the life under a high temperature condition is made of quartz. It can be greatly improved in comparison with the above.

[0003]

However, when such a silicon carbide-based composite material is used under a high temperature condition, impurities are easily generated, and there is a problem in practical use. For example, when a reaction tube is used in a semiconductor diffusion furnace, there is a problem that the generation of impurities contaminates the wafer, and the occurrence rate of defective products becomes extremely higher than when a quartz reaction tube is used.

The inventor of the present invention has conducted various experiments and studies in order to determine the cause of the generation of such impurities.
Although the generation of impurities contained in the base was prevented by the silicon carbide film, it was found that the impurities were generated from the silicon carbide film itself. That is, for example, excessive Si out of the equivalence ratio of Fe, other heavy metals, and SiC contained in the silicon carbide film evaporates in a high-temperature atmosphere, and when used as a reaction tube, such evaporated impurities contaminate the wafer. It turned out to be.

[0005] The present invention has been made in view of these points, without causing the atmosphere contamination due to evaporation, not neat Te high temperature conditions smell, be suitably used as a semiconductor diffusion furnace for the reaction tube or the like Hisage Kyosu Rukoto a high temperature silicon carbide composites can it is an object.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a silicon carbide sintered body.
CVD in which this is arranged on the surface of a porous substrate
By supplying a predetermined reaction gas into the furnace,
Silicon carbide composite material obtained by chemical vapor deposition of silicon film
And the reaction gas containing a large amount of hydrogen
While supplying the gas to the D furnace, the exhaust gas is constantly exhausted from the CVD furnace to
Keep the inside of the VD furnace in a reduced pressure atmosphere and no substrate surface
In a state where exhaust flow is generated in the surrounding area
More, the silicon carbide film spectral absorption edge of its 520-5
High-temperature carbonization characterized by having a thickness of 50 nm
A silicon composite is proposed.

[0007] Such high temperature silicon carbide composite material, a full-time exhaust from C VD furnace arranged a porous substrate is a silicon carbide sintered body, and holds the CVD furnace pressure atmosphere <br / > a in a state to produce an exhaust stream based on body surface or its surrounding region to co, subjected predetermined reaction gas into the CVD furnace
Chemical vapor deposition of a silicon carbide film on the substrate surface
Obtained by

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The silicon carbide composite material for high temperature of the present invention is suitably used mainly as a constituent material of a reaction tube for a semiconductor diffusion furnace used under a high temperature condition and in a clean atmosphere. In the following, a preferred embodiment is
The case of using as a constituent material of a reaction tube for a semiconductor diffusion furnace will be described.

The reaction tube for a semiconductor diffusion furnace is composed of a porous substrate which is a silicon carbide sintered body, and a silicon carbide film chemically vapor-deposited on the surface thereof.

The substrate is a porous silicon carbide sintered body obtained by molding and sintering a high-purity silicon carbide powder into a predetermined reaction tube shape (for example, a tubular or bell-jar type burning tube shape). In sintering, it is preferable not to use a binder in order to eliminate impurities contained in the substrate as much as possible. The average pore diameter and porosity of the substrate can be arbitrarily set according to the conditions of use of the reaction tube and the like, but are preferably determined in consideration of static strength, thermal shock resistance and the like.
The silicon carbide film is formed on one or both of the inner and outer peripheral surfaces of the substrate having the shape of the reaction tube according to the conditions of use of the reaction tube and the like.

The silicon carbide film has a spectral absorption edge of 5
This is a β-SiC chemical vapor deposition film formed to have a thickness of 50 nm or less. In a silicon carbide film having a spectral absorption edge of 550 nm or less, that is, a silicon carbide film capable of absorbing light having a wavelength of 550 nm or less, Fe, C
The content of heavy metal elements such as u, Cr and the like is extremely small, and no wafer contamination due to evaporation of impurities occurs even under high temperature conditions. In a silicon carbide film having a spectral absorption edge of 550 nm or less, for example, Fe is 30 ppb or less, Cu is 50 ppb or less, and Cr is 40 ppb or less. On the other hand, when the content of impurities increases, light having a wavelength exceeding 550 nm can be absorbed.
Light having a wavelength of 0 nm or less cannot be absorbed. When a reaction tube having such a silicon carbide film having a spectral absorption edge exceeding 550 nm is used in a semiconductor diffusion furnace, impurities in the silicon carbide film (such as excess Si deviating from the equivalent ratio of Fe and SiC). Evaporates in a high temperature atmosphere and contaminates the wafer.

Further, in order to achieve the object of the present invention is the spectral absorption edge of silicon carbide film is to maximum limit to 550 nm, the preferred result enough to become the shorter course be obtained. That is, it is preferable to make the spectrum absorption edge as short as possible in the range of 550 nm or less. However, also to shorten the spectral absorption edge, the deposition conditions (mainly pure or equipment conditions of raw materials, etc.) by there is a limit (about 520 nm),
In actual implementation, normally, if the spectral absorption edge of the silicon carbide film is in the range of 520 to 550 nm, the intended purpose can be sufficiently achieved.

[0013] The formation of the silicon carbide film is, dividing line as follows Ri by the C VD method.

That is, first, the substrate is placed in an appropriate CVD furnace, and the inside of the CVD furnace is kept in a reduced pressure atmosphere by evacuating from the exhaust port of the CVD furnace with a vacuum pump.

Then, the substrate is heated to and maintained at a predetermined temperature in a state where the substrate is maintained in the reduced-pressure atmosphere, and then a predetermined reaction gas is continuously supplied into the CVD furnace. At this time, the exhaust is continuously performed without stopping, and the inside of the CVD furnace is kept at a predetermined reduced pressure atmosphere. Normally 200 Torr
It is preferable to keep it at r or less. However, for economic reasons considering the vacuum pump capacity, etc., 0.1 to 200 T
Preferably, it is set to orr. Also, the substrate is 140
It is preferable to heat and maintain the temperature at 0 to 1500 ° C. As the reaction gas, for example, a mixed gas of monomethyltrichlorosilane and hydrogen at a predetermined equivalent ratio (generally, about 20 equivalent ratio) is used.

When a reaction gas is supplied, CH ₃ SiCl ₃
By the reaction of + H ₂ → SiC + 3HCl, a silicon carbide film is formed on the substrate surface, that is, on the inner and outer peripheral surfaces of the substrate or on one of them.

Incidentally, the formation of the silicon carbide film is generally performed by
This is performed by a normal pressure CVD method in which a reaction gas is supplied while keeping the inside of the CVD furnace at normal pressure. However, this normal pressure C
In the VD method, a silicon carbide film having a spectral absorption edge of 550 nm or less cannot be formed. That is, in the normal pressure CVD method, diffusion of impurities in the substrate cannot be prevented, and contaminant particles scattered from the wall of the CVD furnace stay on the surface of the substrate on which a silicon carbide film is to be formed or a peripheral region thereof. Because it will be. As a film forming method, there is an intermittent CVD method in which exhaust and supply of a reactive gas are alternately repeated in a constant cycle, in addition to the normal pressure CVD method.
According to this intermittent CVD method, the above-mentioned contaminant particles and the like are exhausted to some extent during exhaustion, and it is expected that the purity of the silicon carbide film is improved. However, contaminant particles and the like are not completely exhausted in the exhaust process, but may remain at the beginning of the reaction gas supply process. As in the case of the normal pressure CVD method, carbonized particles having a spectral absorption edge of 550 nm or less are obtained. It is impossible to form a silicon film. As described above, in any of the conventionally employed CVD methods, impurities remain on the surface of the substrate or the peripheral region and are not removed. Therefore, a high-purity silicon carbide film having a spectral absorption edge of 550 nm or less cannot be formed.

However, as described above, if the inside of the CVD furnace is maintained in a reduced pressure atmosphere and the exhaust is continuously performed even during the supply of the reaction gas, the exhaust is performed on the surface of the substrate on which the silicon carbide film is to be formed or the peripheral area thereof. The exhaust flow in the mouth direction occurs,
Together with the migration of the impurities to the surface, the surface of the substrate or its peripheral region is kept clean. That is, impurities such as contaminant particles and reaction gas residues adhering to the wall surface of the CVD furnace are quickly discharged to the outside of the CVD furnace by the exhaust gas, and the inside of the CVD furnace is kept clean. As a result, a high-purity silicon carbide film having a spectral absorption edge of 550 nm or less is favorably formed on the substrate surface. The supply of the reaction gas may be performed intermittently instead of continuously, but the exhaust must be continuously performed regardless of the supply and stop of the reaction gas.

The thickness of the silicon carbide film is not particularly limited as long as it has a sufficient adhesive strength with the substrate and is airtight, and can be appropriately set according to the conditions of use of the reaction tube. Is preferably set to 50 to 150 μm. When the film thickness is less than 50 μm, considering the variation of the film thickness (plus or minus 20 μm), a defect due to a through hole is feared, and conversely, the film thickness is 150 μm.
If the value exceeds, the crystal becomes coarse, the smoothness of the surface is lost, and it takes time to form a film, which increases the cost.

[0020]

EXAMPLE A high-purity silicon carbide powder (particle size: less than 1 μm) was molded and fired without using a binder to obtain an outer diameter of 27.
A porous substrate which was a cylindrical recrystallized silicon carbide sintered body (average pore diameter: 1 μm, porosity: 40 to 45%) having a diameter of 0 mm, an inner diameter of 250 mm, and a length of 600 mm was produced. Then, while the substrate was placed in a CVD furnace and heated and maintained at 1500 ° C., monomethyltrichlorosilane and hydrogen at a 20 equivalent ratio were continuously supplied into the CVD furnace.
During this time, the evacuation was continued by a vacuum pump connected to the exhaust port of the CVD furnace, and the inside of the furnace was kept at a reduced pressure atmosphere of 50 Torr. Thus, on the inner and outer peripheral surfaces of the base,
A reaction tube for a semiconductor diffusion furnace (hereinafter referred to as "Example reaction tube") on which a silicon carbide film (β-SiC) having a thickness of 120 µm and a spectral absorption edge of 520 nm was formed was obtained. Incidentally, the impurities contained in the silicon carbide film are extremely small, and Fe: 3
0 ppb, Cu: 50 ppb or less, Cr: 40 ppb or less.

As a comparative example, the same substrate as described above was manufactured, and the inner and outer peripheral surfaces of the substrate were subjected to a conventional method (normal pressure CVD).
A silicon carbide film was formed by the method described above to obtain a reaction tube for a semiconductor diffusion furnace having the same dimensions as the reaction tube of the example (hereinafter, referred to as a “reaction tube of the comparative example”). The heating temperature of the CVD furnace, the reaction gas, and the substrate used for forming the silicon carbide film is the same as in the reaction tube of the embodiment. Comparative Example The silicon carbide film thickness in the reaction tube was 250 μm, but the spectral absorption edge was 620.
nm.

When the reaction tube of the example and the reaction tube of the comparative example were used in a semiconductor diffusion furnace under the same conditions, when the reaction tube of the example was used, there was no contamination of the wafer and high quality was obtained. I was able to get things. However, when the comparative example reaction tube was used, impurities were evaporated from the silicon carbide film and the wafer was contaminated, and a high-quality wafer could not be obtained.

[0023]

As can be easily understood from the above description, the silicon carbide composite material for high temperature of the present invention has a silicon carbide film .
Since the spectral absorption edge of that is that the <br/> made the 520 to 550 nm, no impurities evaporate from the silicon carbide film even under high temperature conditions, clean even when used in a semiconductor diffusion furnace or the like The atmosphere can be maintained. Therefore, it can be suitably used as an extremely practical reaction tube for a semiconductor diffusion furnace which does not contaminate a wafer.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C30B 25/10 C30B 25/10 (72) Inventor Yasuhiro Akune 1 541 Shimouchi Shinto battling ground, Mita City, Hyogo Japan Pillar Inside the Mita Plant (72) Inventor Seiji Onishi 541-1, Shimouchi Jinji bat, Mita City, Hyogo Prefecture Nippon Pillar Industry Co., Ltd. Mita Plant (56) References JP-A-6-340479 (JP, A )

Claims (1)

(57) [Claims] 1. A table of a porous substrate which is a silicon carbide sintered body.
A predetermined reaction gas is supplied into the CVD furnace in which
By feeding, Ru Do <br/> with a silicon carbide film is chemically vapor deposited in the silicon carbide composite material, the chemical vapor deposition, a large amount of
While supplying a reaction gas containing hydrogen to the CVD furnace, the CVD
Exhaust from the furnace at all times to keep the inside of the CVD furnace at reduced pressure
And create an exhaust stream on the substrate surface or its surrounding area.
By performing in a state where the time difference, high temperature silicon carbide composite silicon carbide film spectral absorption edge of that is characterized in that it is assumed that the 520～550Nm.