JPH0920575A - Silicon carbide composite material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composite material developing no atmospheric contamination even under high-temperature conditions, and suitable for e.g. the reaction tubes for semiconductor diffusion oven, by specifying the spectrum absorption end of silicon carbide film. SOLUTION: This composite material is made up of a basal body as a porous silicon carbide sintered compact produced by molding and sintering high-purity silicon carbide powder to a specified reaction tube shape and silicon carbide film(s) as β-SiC chemical vapor deposition film(s) on one or both of the circumferential surfaces of the basal body depending on e.g. the working conditions for the reaction tube. Since the content of heavy metal elements such as Fe, Cu and Cr in the silicon carbide film(s) is extremely low, wafer contamination due to evaporation of such impurities does not occur. Although there are some limitations in the film-forming conditions, it is so specified that the spectrum absorption end falls between 520 and 550nm. This composite material is obtained by the following process: the basal body is placed in a CVD oven which is then depressurized to 0.1-200Torr and then fed with monomethyl trichlorosilane as reaction gas at 1400-1500 deg.C followed by continuous exhaustion to effect CVD so as to be 50-150μm in film thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide based composite material which is preferably used as a reaction tube or a soaking tube used in a semiconductor diffusion furnace, and more particularly to a silicon carbide sintered body. The present invention relates to a silicon carbide composite material including a porous substrate and a silicon carbide film chemically deposited on the surface thereof.

[0002]

2. Description of the Related Art For example, graphite has been traditionally used as a constituent material of a reaction tube for a semiconductor diffusion furnace, and quartz has been used in recent years. However, when graphite is used, there is a problem that the amount of impurities contained in the graphite is extremely large and the Si wafer is contaminated. Further, quartz has a short life due to deformation and devitrification under a high temperature condition. Therefore, in conjunction with the tendency to increase 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 have been recently used. A reaction tube composed of a silicon carbide composite material including a film has been proposed. It has been proposed that the surface of the sintered body is composed of a silicon carbide based composite material obtained by coating the surface of the sintered body with a chemical vapor deposition film of silicon carbide. Such a silicon carbide based composite material has excellent heat resistance and thermal shock resistance because the substrate is a porous silicon carbide sintered body. Moreover, the substrate is poor in airtightness because it is porous, but it is possible to secure sufficient airtightness as a whole by coating the surface of the substrate with a dense chemical vapor deposition film of silicon carbide. Therefore, a reaction tube made of such a silicon carbide composite material can exhibit the same function as that made of quartz as a reaction tube, and, of course, has a long life under high temperature conditions made of quartz. It can be greatly improved in comparison with the above.

[0003]

However, such a silicon carbide composite material has a problem in practical use because impurities are likely to be generated when it is used under high temperature conditions. For example, when used as a reaction tube in a semiconductor diffusion furnace, there is a problem that the wafer is contaminated due to the generation of impurities and the generation rate of defective products becomes extremely higher than that when a quartz reaction tube is used.

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

The present invention has been made in view of the above points, and does not cause atmospheric pollution due to evaporation of impurities even under high temperature conditions, and can be suitably used as a reaction tube for a semiconductor diffusion furnace. It is an object of the present invention to provide a silicon-based composite material and, at the same time, to provide a method by which such a silicon carbide-based composite material can be preferably produced.

[0006]

In the silicon carbide based composite material of the present invention, in order to achieve the above object, in particular, the silicon carbide film has a spectrum absorption edge of 550 nm or less. To propose.

Further, in the method of the present invention for producing this silicon carbide composite material, a predetermined reaction gas is supplied into a CVD furnace in which a porous substrate which is a silicon carbide sintered body is arranged. Thus, when the silicon carbide film is chemically vapor-deposited on the surface of the substrate, the CVD furnace is constantly evacuated to maintain the inside of the CVD furnace in a reduced pressure atmosphere and generate an exhaust gas flow on the surface of the substrate or its peripheral region. I suggest you keep it.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The heat treatment furnace member of the present invention is preferably used mainly as a constituent material of a reaction tube for a semiconductor diffusion furnace used under high temperature conditions and in a clean atmosphere, Hereinafter, the case where the preferred embodiment is used as a constituent material of a reaction tube for a semiconductor diffusion furnace will be described.

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

The substrate is a porous silicon carbide sintered body obtained by molding and sintering high-purity silicon carbide powder into a predetermined reaction tube shape (for example, a cylindrical shape or a bell jar type ablation 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 the porosity of the substrate can be arbitrarily set according to the use conditions of the reaction tube and the like, but it is preferable to determine them in consideration of static strength and thermal shock resistance.
The silicon carbide film is formed on one or both of the inner and outer peripheral surfaces of the reaction tube-shaped substrate depending on the usage conditions of the reaction tube and the like.

The silicon carbide film has a spectrum absorption edge of 5
It is a chemical vapor deposition film of β-SiC formed to have a thickness of 50 nm or less. For a silicon carbide film having a spectral absorption edge of 550 nm or less, that is, a silicon carbide film capable of absorbing light of a wavelength of 550 nm or less, Fe and C in the film are used.
The content of heavy metal elements such as u and Cr is extremely low, and wafer contamination due to evaporation of impurities does not occur 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 with a wavelength of more than 550 nm can be absorbed, but 55
Light with a wavelength of 0 nm or less cannot be absorbed. When such a reaction tube formed with a silicon carbide film having a spectral absorption edge of more than 550 nm is used in a semiconductor diffusion furnace, impurities (excess Si, etc. deviating from the equivalent ratio of Fe or SiC) in the silicon carbide film are used. Evaporate in a high temperature atmosphere and contaminate the wafer.

In the meantime, in order to achieve the object of the present invention, the spectral absorption edge of the silicon carbide film has a maximum limit of 550 nm, but it goes without saying that the shorter the length, the better the result 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, even if the spectrum absorption edge is shortened, there is a limit (about 520 nm) depending on the film forming conditions (mainly the raw material purity and equipment conditions, etc.), and in practice, the spectrum absorption of the silicon carbide film is usually used. When the edge is in the range of 520 to 550 nm, the intended purpose can be sufficiently achieved.

The silicon carbide film is formed by the CVD method, specifically, by the method of the present invention as follows.

That is, first, the substrate is placed in an appropriate CVD furnace, and then the interior of the CVD furnace is maintained in a reduced pressure atmosphere by evacuation from the exhaust port of the CVD furnace by a vacuum pump.

Then, the substrate is heated and held at a predetermined temperature while being kept in such a 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. Usually 200 Tor
It is preferable to keep it at r or less. However, for economic reasons considering the vacuum pump capacity etc., 0.1-200T
It is preferable to set it as orr. The base is 140
It is preferable to heat and hold at 0 to 1500 ° C. Further, as the reaction gas, for example, a mixed gas of monomethyltrichlorosilane and hydrogen at a predetermined equivalent ratio (usually 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 surface of the substrate, that is, the inner and outer peripheral surfaces of the substrate, or one of them.

Incidentally, the formation of the silicon carbide film is generally performed by
It is carried out by the atmospheric pressure CVD method in which the reaction gas is supplied while the inside of the CVD furnace is kept at atmospheric pressure. However, this normal pressure C
The VD method cannot form a silicon carbide film having a spectral absorption edge of 550 nm or less. That is, the atmospheric pressure CVD method cannot prevent the diffusion of impurities in the base material, and the contaminant particles scattered from the wall surface of the CVD furnace stay on the surface of the substrate on which the silicon carbide film is to be formed or in the peripheral region thereof. Because it will be. In addition to the atmospheric pressure CVD method, there is an intermittent CVD method in which exhaust and reaction gas supply are alternately repeated in a constant cycle as a film forming method.
According to this intermittent CVD method, the pollutant particles and the like are discharged to some extent at the time of exhaust, and it is expected that the purity of the silicon carbide film is improved. However, the pollutant particles and the like are not completely discharged in the exhaust step and may remain at the start of the reaction gas supply step. As with the atmospheric pressure CVD method, the carbon absorption at which the spectrum absorption edge becomes 550 nm or less is obtained. It is impossible to form a silicon film. As described above, since any of the conventional CVD methods does not remove impurities by staying on the surface of the substrate or the peripheral region thereof, no matter how the vapor deposition conditions are devised, a large amount of Fe or the like is added to the silicon carbide film. Impurities such as excess Si deviating from the equivalent ratio of SiC and SiC are included, and a high-purity silicon carbide film having a spectrum absorption edge of 550 nm or less cannot be formed.

However, as described above, when the inside of the CVD furnace is kept in a reduced pressure atmosphere and the exhaust is continuously performed even while the reaction gas is being supplied, the exhaust is performed on the surface of the substrate on which the silicon carbide film is to be formed or its peripheral region. An exhaust flow toward the mouth occurs,
Along with the migration of impurities to the surface, the surface of the substrate or its peripheral region is kept clean. That is, impurities such as pollutant particles and reaction gas residues adhering to the wall surface of the CVD furnace are promptly discharged to the outside of the CVD furnace by the exhaust flow, 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 satisfactorily formed on the surface of the substrate. Note that the supply of the reaction gas may be performed intermittently instead of continuously, but it is necessary to continuously exhaust the gas regardless of whether the reaction gas is supplied or stopped.

By the way, the thickness of the silicon carbide film may be a dense one having sufficient adhesive strength to the substrate and airtightness, and can be appropriately set according to the use conditions of the reaction tube, etc. Is preferably 50 to 150 μm. If the film thickness is less than 50 μm, if the variation in film thickness (plus or minus 20 μm) is taken into consideration, defects due to through holes may occur, and conversely, the film thickness may be 150 μm.
This is because if the value exceeds, the surface of the crystal lacks in smoothness due to the coarsening of the crystal, and it takes time to form the film, resulting in a high cost.

[0020]

EXAMPLES High-purity silicon carbide powder (particle size: less than 1 μm) was molded and fired without using a binder to give an outer diameter of 27.
A porous substrate which is 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 manufactured. Then, the substrate was placed in a CVD furnace, heated to 1500 ° C. and held therein, and monomethyltrichlorosilane and hydrogen in 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”) having a silicon carbide film (β-SiC) having a film thickness of 120 μm and a spectrum absorption edge of 520 nm was obtained. It should be noted that the impurities contained in the silicon carbide film are extremely small, and Fe: 3
It was 0 ppb, Cu: 50 ppb or less, and 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 this substrate were subjected to a conventional method (normal pressure CVD).
Method) to form a silicon carbide film to obtain a reaction tube for a semiconductor diffusion furnace (hereinafter referred to as “comparative example reaction tube”) having the same size as that of the example reaction tube. The CVD furnace used for forming the silicon carbide film, the reaction gas, and the heating temperature of the substrate are the same as those in the example reaction tube. The thickness of the silicon carbide film in the comparative reaction tube is 250 μm, but the spectral absorption edge is 620.
was nm.

Thus, 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, there was no contamination of the wafer when the reaction tube of the example was used, and high quality was obtained. I was able to get one. However, when the comparative 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 based composite material of the present invention has a spectrum absorption edge of the silicon carbide film of 550 nm or less, so that it is carbonized even under high temperature conditions. There is no evaporation of impurities from the silicon film, and a clean atmosphere can be maintained even when used in a semiconductor diffusion furnace or the like. Therefore, it can be suitably used as a very practical reaction tube for a semiconductor diffusion furnace that does not contaminate the wafer. Further, according to the method for manufacturing a silicon carbide based composite material of the present invention, a high-purity silicon carbide film having a spectrum absorption edge of 550 nm or less can be satisfactorily formed on the surface of the substrate.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C30B 25/10 C30B 25/10 (72) Inventor Seiji Onishi Shimouchi Shinji, Sanda City, Hyogo Prefecture No. 541, No. 1 in Japan Pillar Industry Co., Ltd. Mita factory

Claims (2)

[Claims] 1. A silicon carbide-based composite material comprising a porous substrate which is a silicon carbide sintered body and a silicon carbide film chemically vapor-deposited on the surface thereof, wherein the silicon carbide film has a spectral absorption edge of 550 nm or less. A silicon carbide based composite material characterized in that 2. When a silicon carbide film is chemically vapor-deposited on the surface of a substrate by supplying a predetermined reaction gas into the CVD furnace in which a porous substrate that is a silicon carbide sintered body is placed, the CVD furnace is always used. A method for producing a silicon carbide based composite material, characterized in that exhaust is carried out to keep the inside of the CVD furnace in a reduced pressure atmosphere and an exhaust flow is generated on the surface of the substrate or in the peripheral region thereof.