JPH11154671A - Tube for heat treatment of semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tube for the heat treatment of a semiconductor, which has superior soaking characteristic and the heat transfer characteristic and can readily impart high-impurity characteristics in correspondence with the purity level of the semiconductor product. SOLUTION: In this tube, the entire body of a graphite tube is made to be silicon carbide by substantially 100% and converted into a single-element composition of silicon carbide. The difference between the maximum thickness and the minimum thickness at the diameter direction of the silicon carbide tube is made to be 0.25 nm or less. The average thickness of the tube is made to be 3.5 mm or laser when required in this constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for performing heat treatment in a semiconductor manufacturing process, and more particularly to a semiconductor heat treatment tube suitable for use as a soaking tube or a reaction tube provided for an oxidation furnace or a diffusion furnace. Things.

[0002]

2. Description of the Related Art A diffusion furnace is taken up as an example of a heat treatment furnace in a semiconductor manufacturing process, and its basic structure is shown for a vertical type and a horizontal type, respectively.
3 and FIG. In these figures, a reaction tube 3 is disposed inside a cylindrical heater 1 via a soaking tube 2, and the reaction tube 3 is made of a semiconductor material such as a silicon carbide (hereinafter abbreviated as "SiC") wafer. A large number of workpieces 4 are stored and arranged on the boat 5.

In the above configuration, the reaction tube 3 is provided with a heat treatment for reacting a workpiece (semiconductor material such as a silicon wafer) 4 at a high temperature to give the workpiece 4 required physical properties as a semiconductor. The soaking tube 2 is a heat treatment tube for uniformly heating the entire reaction tube 3 at a high temperature. In order to efficiently heat-treat the workpiece 4 in such a diffusion furnace, one of the necessary conditions is to use a tube having such excellent heat uniformity and heat transferability as possible. In addition, since the object to be processed is a semiconductor material, one of the prerequisites is that the heat treatment tube be as high as possible in purity and less likely to generate impurities such as so-called particles. The same applies to the case where the heat treatment tube is applied to an oxidation furnace.

[0004] By the way, in the past, quartz tubes have been predominantly used from the viewpoint of emphasizing the purity aspect. However, as the diameter of semiconductor products increases, the nature of the quartz tube, which is easily deformed at high temperatures, appears as an obstacle to the loading of the tube into and out of the furnace. A situation has arisen that threatens the smooth operation of the furnace. On the other hand, although there was a problem in terms of purity, SiC tubes, which originally attracted attention as materials having excellent heat resistance and being hardly deformed at high temperatures, have made great progress in improving materials in terms of purity. Therefore, recently, a heat treatment tube is often made of SiC material.

The production of such a heat treatment tube made of SiC is usually carried out according to a so-called slip casting method. The outline of the procedure of the slip casting method is as follows. That is, boron,
After pouring the slurry solution prepared by adding an auxiliary agent such as an organic substance into a mold (a long-hole-shaped mold formed in advance to match the outer shape of the heat treatment tube to be a product), When the outer peripheral portion is hardened to some extent after being left for a predetermined time, most of the uncured SiC slurry is discharged.

[0006] Thereafter, the slightly soft SiC tubular cured body remaining in a state of being closely adhered to the mold with a certain thickness is further dried sufficiently to be completely cured and slightly shrunk as a whole. Remove from mold. After the temperature of the taken-out SiC-based tubular cured body is raised to about 1000 ° C., it is held for a predetermined time and sintered to impart strength. Thereafter, the tube is cooled and used as a tube for heat-treating the SiC material of the product as it is, without performing any machining for dimensioning.

[0007]

As described above, it is difficult to machine the heat treatment tube, which is the final product, because SiC is a very hard material. Although it is omitted, the characteristics originally required for the semiconductor heat treatment tube cannot be satisfied. That is, as described above, in the slip casting method, the inner surface of the SiC-based cured tube is dried without any particular restriction on the surface (surface in the shape of a long hole) that appears when the uncured SiC slurry is discharged. Because it is formed by curing
The thickness of the SiC-based tubular cured product varies considerably.

Therefore, in order to minimize the influence of this thickness variation and to provide the necessary strength as a tube (product) for heat treatment of SiC after sintering,
At least the thickness had to be at least 3.5 mm on average. That is, according to the conventional slip casting method, as the heat-treatable SiC tube that can be practically used, only a tube having a thickness of 3.5 mm or more could be manufactured. However, even when the thickness was set to 3.5 mm or more, the degree of variation in the thickness was still large, resulting in a tube for heat-treating SiC material having insufficient heat uniformity.

That is, in order to ensure that the post-processing quality of a plurality of workpieces (such as silicon wafers) which are heat-treated at one time is all within an allowable range, the outer surface temperature of the tube is usually set in the circumferential direction. Surface temperature difference (ΔT) obtained by subtracting the lowest value from the highest value among the temperatures measured along
A heat treatment tube capable of exhibiting a level of heat uniformity within a range of about 3 ° C. is required, but the conventional heat treatment tube could not secure such a level of heat uniformity.

In addition, since the thickness of the heat treatment tube is relatively large at 3.5 mm or more, the heat transfer performance of the heat treatment tube for SiC material is not sufficient, and it takes time to raise and lower the temperature. Was low. Furthermore, since the sintering aid is used for the SiC heat treatment tube obtained by the slip casting method, it is difficult to obtain a heat treatment tube that is sufficiently purified to sufficiently prevent generation of impurities. . For this reason, when used as a soaking tube or a reaction tube when manufacturing a semiconductor product that requires particularly high purity among various semiconductor products, the porous SiC heat treatment tube is once subjected to a high purification treatment. Had to be used before. Needless to say, even in the heat treatment tube of which the purity is thus increased, there has been a situation that the above-mentioned heat uniformity and heat transfer property are not sufficient.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor device having excellent heat uniformity and heat transfer characteristics and easily having high purity characteristics according to the purity level of a semiconductor product. An object of the present invention is to provide a large-diameter tube for semiconductor heat treatment which can be provided.

[0012]

The tube for heat treatment of a semiconductor according to the present invention, which has achieved the above object, is obtained by converting substantially all of the graphite tube into 100% silicon carbide and converting it into a monolithic silicon carbide composition. A tube, wherein a difference between a maximum thickness and a minimum thickness in a radial direction of the siliconized tube is 0.25 mm or less.

In the case of such a tube for heat treatment of a semiconductor, first, the molding conditions (pressure, temperature, etc.) and firing conditions (temperature, etc.) of the graphite raw material itself or the graphite raw material block are appropriately selected, so that the base material can be obtained. It is possible to further increase the density and strength of the graphite tube, and if the strength required for the heat treatment tube is the same, the graphite tube can be made thinner to meet the required strength. In addition, the tube for heat treatment is substantially 100% Si
Since it is C-structured and composed of a monolithic SiC composition, an extremely high-purity SiC heat treatment tube can be obtained.

The diameter of a generally used SiC heat treatment tube is about 300 mm, and it is difficult to accurately dimension the tube by the slip casting method as described above. In this case, since the tube as the base material is graphite which is easy to machine, dimensions can be determined with high accuracy, and a tube having a uniform thickness can be manufactured at the stage of the base material. That is, it is possible to provide a graphitic tube base material having a uniform thickness at a level of 0.25 mm or less, even though the thickness is relatively thin, with a difference between the maximum thickness and the minimum thickness in the radial direction being 0.25 mm or less. While the graphite tube as the base material maintains its precise dimensions and shape,
The tube can be converted into a monolithic SiC composition substantially converted to 100% SiC at once by a chemical reaction operation. Therefore, it is possible to provide a semiconductor heat treatment tube which is excellent in heat uniformity characteristics and heat transfer characteristics and which can provide high purity characteristics according to the purity level of a semiconductor product.

Hereinafter, the present invention will be described in detail. (1) The present inventor first develops a SiC tube that satisfies the following conditions at the same time in order to improve the heat uniformity, heat transferability and purity of a conventional tube for heat treatment of a semiconductor. I thought it was necessary. In view of the fact that SiC is very hard and difficult to machine, the SiC tube that has undergone the final process has a uniform temperature uniformity (with a surface temperature difference of 2 along the circumferential direction) without machining.
℃ ~ 3 ℃ within the range of the level of heat control),
A material that can be used as a tube (product) for semiconductor heat treatment with good heat transfer properties. In order to improve heat transfer with the same SiC material, thinning is indispensable. However, even if the thickness is reduced, no new problem in strength occurs. High-purity Si without special purification treatment
A tube for heat treatment of C material must be obtained.

On the other hand, the present applicant has developed Si
A technique relating to a C compact, that is, a graphite substrate having a specific range of physical properties is reacted with SiO gas, thereby converting the entire graphite substrate into substantially 100% SiC and converting it into a SiC compact composed of a monolithic SiC composition. Technology (Japanese Patent Laid-Open No. 1-2
Application of US Pat. No. 64969) would allow development of a tube for heat treatment of a semiconductor which can simultaneously satisfy the above conditions (1) to (4). , Soaking,
Experiments were repeated in order to find a specific configuration that could exceed the level of conventional products in terms of heat transfer and strength.

As a result, the final result is that the graphite tube is substantially 100% silicon carbide and is converted into a monolithic silicon carbide composition. The diameter of the silicon carbide tube is as follows. The difference between the maximum thickness and the minimum thickness in the direction is 0.25 mm or less. "

(2) In order to obtain the semiconductor heat treatment tube of the present invention, as described above, the method of manufacturing a SiC molded body according to the prior development of the present applicant (JP-A-1-264969) is used. Well, specifically, a bulk density of 1.50 g /
cm ³ below and an average pore radius 1.5μm or more graphite tube, silicate, or which further carbon, Si and Si
At least one type of C may be coexistent and heated to generate SiO gas, and the SiO gas and the graphite tube may be reacted. That is, a production method utilizing a specific chemical vapor reaction may be performed. At this time, in the case of a graphite tube having one end closed, there is a difference in the degree of conversion of the graphite on the inner diameter side of the tube and the graphite on the outer diameter side of the tube into silicon carbide, and cracks may occur due to stress generated during the conversion. In order to prevent this, the progress rate of silicon carbide on the inner diameter side and the outer diameter side of the tube is adjusted, and the gas flow in the reaction furnace is controlled so that the outer diameter side is substantially the same as or slightly faster than the inner diameter side. Control. By this gas flow control, a large-diameter semiconductor heat treatment tube having an average tube outer diameter of 400 mm or more and a height of 1000 mm or more can be obtained. The graphite tube is
The difference between the maximum thickness and the minimum thickness in the radial direction is 0.25m in advance.
It is necessary to perform machining so as to be less than m, but unlike SiC material, machining is relatively easy.

Further, in order to improve the heat transfer property of the heat treatment tube, it is necessary to reduce the thickness.
It is necessary to make the SiC tube thinner than the thickness limit of 3.5 mm obtained from the C tube. In the present invention, since the base material is a graphite tube and has a property capable of flexibly responding to various required strengths, even if a graphite tube having a thickness of 3.5 mm or less is used, it can be used as a semiconductor heat treatment tube. A sufficiently practical strength can be maintained.
Note that the crystal structure of SiC is preferably β-type (3C type). This is because, in order to manufacture an α-type, an SiC conversion operation must be performed in a high-temperature atmosphere of 2100 ° C. or more, which leads to an increase in cost in terms of energy.

As described above, the tube for heat treatment of a semiconductor according to the present invention is a tube in which the entirety of the graphite tube as a base material is substantially 100% SiC by a specific chemical vapor reaction. Thickness variation,
The difference between the maximum thickness and the minimum thickness is reduced to a level of 0.25 mm or less, and the average thickness itself can be reduced (3.5 mm or less) as needed.

Therefore, in the case of a tube for heat treatment of a semiconductor configured as described above, when the tube is used as a soaking tube or a reaction tube, the soaking tube or the heat transfer tube obtained by the conventional slip casting method can be used. It can be greatly improved as compared with the reaction tube. Therefore, there is almost no variation in the quality of the semiconductor product to be processed, and it is possible to raise and lower the temperature of the soaking tube and the reaction tube in a shorter time, thereby improving the productivity in the oxidation furnace and the diffusion furnace. Can be planned.

Even when the average thickness is set to 3.5 mm or less for improving heat transfer as described above, the strength must be set within the limit strength of the graphite tube so as not to make it too thin. It is. The critical strength of the graphite tube can be increased (thinner) by the raw material, the molding conditions of the raw material block, the firing conditions, and the like, as described above. However, the SiC tube is further strengthened by densification treatment. It is also possible. For example, an SiC tube impregnated with metallic silicon can be used.

Further, since the tube for heat treatment of a semiconductor of the present invention is obtained by converting a graphite tube into a substantially 100% SiC tube, it is basically much higher in purity than a conventional tube for heat treatment. Depending on the semiconductor product, a tube for heat treatment with higher purity may be required. Therefore, in such a case, there is a means for forming a dense SiC film by an appropriate thickness on the uppermost layer (either the inner surface or the outer surface or both surfaces) of the heat treatment tube by a CVD process. It is valid. For example, a heat treatment tube in which the inner surface of a SiC tube is covered with a SiC film, a heat treatment tube in which the inner surface of a SiC tube impregnated with metallic silicon is further covered with a SiC film, and the like are all suitable.

By performing the densification treatment as described above, the heat treatment tube according to the present invention is strengthened and the thickness can be further reduced. However, even in this case, if the thickness is 2 mm or less, the tube is easily broken. Therefore, as a range of the wall thickness for improving the heat transferability, after all, 2.0 to 3.5 mm
It is preferred that

[0025]

EXPERIMENTAL EXAMPLES Next, the present invention will be described in more detail with reference to experimental examples. (Experimental Examples 1 to 5) Five types of SiC tubes having an average thickness of 2.5 mm and different thickness variations in the radial direction were examined and evaluated for the radial soaking degree for each tube. .

First, five types of β-type SiC tubes having an average thickness of 2.5 mm were manufactured in the following manner. That is,
From a graphite block material, as a graphite tube having an average outer diameter of 510 mm, an average inner diameter of 505 mm, and a height of 1300 mm and having one end closed and having a U-shaped cross section, the degree of thickness variation in the radial direction (maximum thickness) (L ₂ ) and minimum value (l ₁ )
(Δl)) were manufactured by machining. Next, all of the five types of graphitic tubes manufactured were heated to about 1900 ° C. in a SiO gas atmosphere so that the progress of siliconization from the outer diameter side to the inner diameter side was substantially the same or slightly faster. The gas flow in the furnace was adjusted and gas phase reaction was performed to convert the entire graphite tube to substantially 100% SiC, thereby obtaining a SiC tube having an open porosity of 25% by volume.

Next, for each SiC tube, a cylindrical heater is inserted and arranged inside, and the SiC tube is heated to 1000 ° C. at a heating rate of 500 ° C./hour, and the temperature of the outer surface of the SiC tube at that time is measured. Measured along the direction. Table 1 also shows the surface temperature difference (ΔT) obtained by subtracting the minimum value from the maximum value among the measured temperatures. FIG. 1 is a graph of the relationship in Table 1 for easier understanding. This is a curve indicated by a solid line (a) in the figure.

(Experimental Examples 6 to 10) The average thickness was 3.
The surface temperature difference was measured in the same manner as in Experimental Examples 1 to 5 for five types of SiC tubes each having a thickness of 0 mm and having a different thickness variation in the radial direction. (A curve shown by a broken line (b) in the figure).

[0029]

[Table 1]

As apparent from Table 1 and FIG. 1, the difference (Δ) between the maximum thickness and the minimum thickness of the SiC tube according to the present invention is shown.
When l) is reduced to about 0.25 mm or less, the outer surface temperature difference (ΔT) is in a range of about 2 ° C. to 3 ° C. or less, that is, almost satisfying the condition that the soaking temperature of the SiC tube is good. I understand. In particular, it can be seen that more preferable results can be obtained when (Δl) is 0.2 mm or less.
That is, if (Δl) is 0.2 mm or less, Si
It can be seen that the (ΔT) of the C tube is extremely small and stable at 1 ° C. or less, and the degree of heat uniform in the radial direction along the circumference is remarkably improved. On the other hand, (Δl) is 0.25 m
In the range exceeding m, ΔT shows a tendency of monotonic increase, and it can be seen that the uniformity decreases proportionally due to an increase in thickness variation.

[0031]

As described above, according to the first aspect of the present invention, at least the difference between the maximum thickness and the minimum thickness in the radial direction is uniform at a level of 0.25 mm or less. Can be made into a tube substantially entirely made of SiC, which leads to a remarkable improvement in heat uniformity characteristics and an improvement in thermal conductivity, and furthermore, depending on the purity level of the semiconductor product. It is possible to provide a semiconductor heat treatment tube capable of imparting high-purity characteristics. Therefore, the present invention is suitable for use as a soaking tube or a reaction tube to be adopted for the purpose of improving the productivity of semiconductor products processed in an oxidation furnace or a diffusion furnace and eliminating variations in quality.

Further, in the invention according to claim 2, the average thickness of the SiC tube is set to at least 3.5 mm or less in addition to the structure of the invention according to claim 1. In addition to the effects (significant improvement of the soaking properties and provision of high-purity properties), it is possible to provide a tube for semiconductor heat treatment that is more reliably excellent in terms of heat transfer properties.

According to a third aspect of the present invention, in the configuration of the first or second aspect, the graphite tube is converted to substantially 100% SiC to form a tube. High purity Si without impurities etc.
It can be a C tube.

Further, the invention according to claim 4 is the one in which the SiC tube is densified, and the SiC tube is strengthened by that much, so that the wall thickness can be further reduced. Therefore, the invention according to claim 1 or claim 2 In addition to the effects described above, a tube for heat treating a semiconductor having further improved heat transfer properties can be obtained.

Further, the invention according to claim 5 is one in which the SiC tube is impregnated with metallic Si to densify, and has an advantage that the densification treatment can be performed versatilely and economically.

According to a sixth aspect of the present invention, the uppermost layer (either the inner surface or the outer surface or both surfaces) of the semiconductor heat treatment tube is coated with SiC by CVD. The semiconductor heat treatment tube is suitable for a semiconductor product to be processed, especially when a minute amount of contamination is to be strictly avoided.

Further, according to the present invention, the average tube outer diameter is 400 even if one end of the tube is closed.
mm or more and a height of 1000 mm or more, whereby a tube for semiconductor heat treatment which can be adapted to a large-diameter wafer is provided.

[Brief description of the drawings]

FIG. 1 shows a difference in wall thickness (Δl) representing the degree of wall thickness variation in the radial direction along the circumference of one of five types of SiC tubes used in Experimental Examples 1 to 10, and 1 inside the tube.
It is a graph which shows the relationship between the maximum value and the minimum value ((DELTA) T) of the circumferential direction temperature of the outer surface of a tube when it heats to 000 degreeC, The solid line (a) shows Experimental Examples 1-5, and the broken line (B)
Indicates Experimental Examples 6 to 10.

FIG. 2 is a schematic explanatory view showing a basic configuration of a vertical diffusion furnace in a semiconductor manufacturing process.

FIG. 3 is a schematic explanatory view showing a basic configuration of a horizontal diffusion furnace in a semiconductor manufacturing process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 2 Heat equalizing tube 3 Reaction tube 4 Workpiece (Si wafer etc.) 5 Boat

Claims (8)

[Claims] 1. A semiconductor device comprising substantially 100% silicon carbide, wherein a difference between a maximum thickness and a minimum thickness in a radial direction is 0.25 mm.
A tube for heat treating a semiconductor, comprising: 2. The tube according to claim 1, wherein the tube has an average thickness of 3.5 mm or less. 3. The tube for heat treating a semiconductor according to claim 1, wherein the tube is formed by converting a graphite tube into silicon carbide. 4. The tube for heat treating a semiconductor according to claim 1, wherein said tube is densified. 5. The tube for heat treating a semiconductor according to claim 4, wherein said tube is impregnated with metallic silicon. 6. The tube for heat treating a semiconductor according to claim 1, wherein the uppermost layer of the tube is coated with silicon carbide. 7. The tube for heat treating a semiconductor according to claim 1, wherein one end of the tube is closed. 8. The tube for heat treating a semiconductor according to claim 7, wherein the tube having one end closed has an average tube outer diameter of 400 mm or more and a height of 1000 mm or more.