JP2009111216A - Heat treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment apparatus for reducing contamination by iron without causing a haze in a wafer, and further preventing the deformation of a gas inlet pipe by heat. <P>SOLUTION: A heat treatment apparatus has at least a reaction tube made of silicon carbide, a heat treatment boat for holding a substrate, a heater for heating the substrate, a gas inlet pipe inserted into the reaction tube to introduce atmospheric gas into the reaction tube, and a gas exhaust pipe for exhausting the atmospheric gas. The heat treatment apparatus is characterized in that the gas inlet pipe is made of only quartz at the portion that is inserted in the heat treatment apparatus, and is covered with a protection tube for preventing the deformation of the gas inlet pipe. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat treatment apparatus for performing heat treatment on a substrate such as a semiconductor wafer.

  There are a number of steps from wafer processing to element formation from the time a wafer is cut out from a single crystal ingot such as semiconductor single crystal silicon (hereinafter sometimes referred to simply as silicon) to the manufacture of a semiconductor device. Intervene. One of these processes is a heat treatment process. This heat treatment step is performed for the purpose of forming a defect-free layer on the wafer surface layer, forming a gettering layer by forming oxygen precipitates, forming an oxide film, and diffusing impurities, and is a very important process.

  As a heat treatment furnace used in such a heat treatment process, for example, a diffusion furnace (oxidation / diffusion apparatus) used for oxidation or impurity diffusion, a plurality of wafers are currently held in a horizontal state as the wafer diameter increases. A vertical heat treatment furnace that heat-treats these wafers simultaneously is mainly used (see, for example, Patent Document 1). In the vertical heat treatment furnace, a heat treatment boat for holding a plurality of wafers is usually used. Such a heat treatment furnace that performs heat treatment on a plurality of wafers simultaneously is said to be a batch heat treatment apparatus.

  FIG. 3 is a schematic explanatory view showing an example of a batch type vertical heat treatment apparatus. The reaction chamber 21 of the heat treatment apparatus 20 is mainly composed of a flange portion 30 and a reaction tube 31. The reaction tube 31 is made of silicon carbide (SiC) having high heat resistance, and the flange portion 30 is made of quartz. A heat treatment boat 22 is installed inside the reaction chamber 21, and a plurality of wafers 23 held in the heat treatment boat 22 are heated by heaters 24 provided around the reaction chamber 21. In addition, an atmospheric gas is introduced into the reaction chamber 21 through the gas introduction pipe 25, the gas is allowed to flow from above the heat treatment apparatus 20 to pass around the wafer 23, and exhausted to the outside through the gas exhaust pipe 26.

Silicon carbide (SiC) is used as the material of the gas introduction pipe 25. This is because, when made of quartz, if the heat treatment is performed at a high temperature of about 1250 ° C., the gas introduction pipe 25 is deformed by heat and comes into contact with the heat treatment boat 22 and is damaged. For this reason, silicon carbide (SiC) gas introduction pipes are exclusively used in heat treatment apparatuses that perform high-temperature heat treatment at 1250 ° C. or higher.
Such a gas introduction pipe 25 is connected to a gas port part 27 at a joint part 28, and the gas port part 27 is further connected to an external pipe 29 connected to a gas supply source (not shown). Since the gas port portion 27 has a complicated structure and is difficult to produce with silicon carbide (SiC), quartz that is easy to produce is used. At this time, the atmosphere gas to be used varies depending on the purpose of the heat treatment, but H ₂ , N ₂ , O ₂ , Ar, etc. are mainly used. In the case of impurity diffusion, an impurity compound gas is introduced using these gases as a carrier gas.

  However, when heat treatment is performed in an inert gas atmosphere such as Ar using the batch heat treatment apparatus as described above, there is a problem that the wafer is clouded. In addition, it has been found that there is a problem that the wafer is contaminated with iron.

JP 2004-228459 A

  Accordingly, the present invention has been made in view of the above problems, and is a heat treatment apparatus that does not cause fogging of the wafer, reduces contamination by iron, and prevents the gas introduction pipe from being deformed by heat. Is to provide.

  In order to solve the above problems, in the present invention, at least a reaction tube made of silicon carbide, a heat treatment boat for holding a substrate, a heater for heating the substrate, and an atmospheric gas are contained in the reaction tube. In a heat treatment apparatus having a gas introduction pipe inserted into the reaction pipe for introduction and a gas exhaust pipe for exhausting the atmospheric gas, the gas introduction pipe has a portion inserted into the heat treatment apparatus. Provided is a heat treatment apparatus characterized in that it is made of only quartz and is covered with a protective tube for preventing deformation of the gas introduction tube (claim 1).

In this way, the portion where the gas introduction pipe is inserted into the heat treatment apparatus is made entirely of quartz, thereby eliminating the conventional joint portion between the silicon carbide gas introduction pipe and the quartz gas port. Even if there is an air leak from the gap between the reaction tube and the flange portion, the leaked air does not enter the gas introduction tube, so that direct contact of the wafer with the wafer can be suppressed. . For this reason, it is possible to prevent the wafer surface from being oxidized and to prevent the wafer surface from being fogged.
In addition, the surface of silicon carbide not subjected to CVD coating is contaminated with heavy metals such as iron, and the inside of a thin tube made of silicon carbide is difficult to perform CVD coating. The inside of the tube is thought to be contaminated with iron. When gas is supplied using such a gas introduction pipe, iron adhering to the inner surface of the gas introduction pipe is mixed with the gas into the reaction chamber, and the wafer is contaminated with iron. However, if the gas inlet tube is made of quartz with less metal contamination compared to silicon carbide as in the present invention, the iron contamination of the wafer can be reduced compared to the conventional case, and the yield can be increased during device fabrication. Can be improved.
Further, since the gas introduction pipe is made of quartz, there is a risk of causing a problem of causing thermal deformation and contact with the boat for heat treatment, but in the present invention, the gas introduction pipe is covered with a protective pipe. Even if the quartz gas introduction tube is deformed by heat, it is protected by the protective tube, so that the gas introduction tube can be prevented from coming into contact with the heat treatment boat, and the gas introduction tube and the heat treatment boat are damaged. Can be prevented.

  The protective tube is made of any one of silicon carbide, silicon carbide coated with silicon carbide, silicon coated with silicon carbide, or carbon coated with silicon carbide. It is preferable to be (claim 2).

  As described above, the protective tube for preventing the deformation of the gas introduction tube is applied with silicon carbide, silicon carbide with CVD coating with silicon carbide, silicon with CVD coating with silicon carbide, or CVD coating with silicon carbide. These materials are more resistant to thermal deformation than quartz, so it is possible to more reliably prevent the gas introduction pipe from being thermally deformed, and thus the heat treatment boat and gas introduction. Tube contact can be prevented.

  Further, it is preferable that the protective tube has a slit formed on a side surface.

  Also, if the gas introduction tube is made of quartz as described above, iron contamination from the wafer gas introduction tube is considerably reduced as compared with the case where the gas introduction tube is formed of silicon carbide as in the prior art, Even if the protection tube is made of silicon carbide with silicon carbide CVD coating, it is difficult to perform CVD coating on the inside of the protection tube, and the iron remaining inside the protection tube diffuses into the reaction chamber. Although the wafer was slightly contaminated and could be reduced to less than half compared with the conventional one, it was difficult to reduce the contamination by iron to a lower level. However, as described above, if the protective tube is formed with a slit on the side surface, CVD coating can be performed uniformly to the inside of the protective tube, so that iron contamination from the protective tube can be further reduced. . Moreover, if it is a high purity silicon carbide, iron contamination can be reduced to the same extent as what gave the CVD coating, and although it is not necessary to provide a slit, it will become very expensive.

  As described above, according to the heat treatment apparatus of the present invention, it is possible to prevent the gas containing oxygen from coming into contact with the wafer, and therefore, it is possible to prevent the occurrence of fogging (oxide film) on the wafer surface after the heat treatment. it can. Further, since the silicon carbide gas introduction pipe that has been a source of iron contamination is not used, the iron impurity concentration of the wafer can be reduced. Therefore, the yield at the time of device fabrication can be improved. Further, since the quartz gas introduction tube is prevented from being thermally deformed by covering with a protective tube, the gas introduction tube can be prevented from being damaged due to contact with the equipment in the heat treatment device. It has become.

Hereinafter, the present invention will be described more specifically.
As described above, conventionally, when a wafer is heat-treated for various purposes such as quality improvement, the wafer is fogged or contaminated with iron. As a result, in the subsequent device fabrication process, etc. There is a problem of lowering the yield, and development of a heat treatment apparatus that solves these problems has been awaited.

The present inventor first made various studies on the cause of the cloudiness. As a result, air that has entered from the joint between the gas introduction pipe and the gas port section is supplied from the upper part of the reaction chamber through the gas introduction pipe, and an oxide film is formed on the wafer surface by oxygen contained in the air. It was found that it was caused by.
It was also discovered that the silicon carbide gas inlet tube that was not coated with CVD was contaminated with iron, and this iron was supplied into the reaction chamber together with the atmospheric gas to contaminate the wafer surface.

  Therefore, the present inventor conducted extensive studies to make a heat treatment apparatus that does not cause fogging of the wafer during heat treatment and has low iron contamination, and as a result, all gas introduction pipes that introduce atmospheric gas into the reaction pipe are used. By using quartz, it is possible to prevent the occurrence of fogging, and by not using silicon carbide that has been used in conventional gas introduction pipes, it is possible to reduce iron derived from silicon carbide. It was discovered that the problem of the gas introduction tube coming into contact with the heat treatment boat by thermal deformation could be suppressed by covering the surface with a protection tube for preventing deformation, and the present invention was completed.

Hereinafter, although this invention is demonstrated in detail using FIG. 1, this invention is not limited to these. FIG. 1 is a schematic explanatory view showing an example of a heat treatment apparatus in the present invention.
In the heat treatment apparatus according to the present invention, as shown in FIG. 1, in the heat treatment apparatus 1, the reaction chamber 2 includes a flange portion 3 and a reaction tube 4. The reaction tube 4 is made of silicon carbide (SiC) having high heat resistance, and the flange portion 3 is made of quartz. A heat treatment boat 5 is installed inside the reaction tube 4, and a wafer 6 is held in the heat treatment boat 5. A heater 7 for heating the wafer 6 is provided around the reaction chamber 2. A gas introduction pipe 8 for supplying atmospheric gas to the reaction chamber 2 and a gas exhaust pipe 9 for exhausting are provided. The gas introduction pipe 8 is connected to an external pipe 10 connected to a gas supply source (not shown) outside the heat treatment apparatus 1.
Here, in the present invention, the material of the gas introduction pipe 8 is made of quartz only in the portion inserted into the heat treatment apparatus 1, and the lower part is bent in an L shape and is welded to the flange portion 3 made of quartz. Has been. The gas introduction pipe 8 is covered with a protective pipe 11a.

In such a heat treatment apparatus, the reaction chamber is mainly composed of a reaction tube and a flange portion. However, since the temperature between the reaction tube and the flange portion is high, an O-ring or the like cannot be attached, and therefore there is a slight gap. As a result, the surrounding air leaks from the gap into the reaction chamber. Normally, the leaked air flows downward due to the gas flow from above and is exhausted to the outside through the gas exhaust pipe, so that it does not come into direct contact with the wafer.
However, in the conventional heat treatment apparatus, a part of the leaked air enters the gas introduction pipe from the joint part of the gas introduction pipe and the gas port part, and is supplied from the upper part of the reaction chamber toward the wafer. This air comes into contact with the wafer, and an oxygen film is formed on the wafer surface by oxygen contained in the air, resulting in cloudiness.
However, in the heat treatment apparatus of the present invention, the portion where the gas introduction pipe is inserted into the heat treatment apparatus is made of only quartz, so that some of the leaked air does not enter the gas introduction pipe. For this reason, since it can suppress that an oxide film is formed on the wafer surface, it can also suppress that fogging generate | occur | produces on the wafer surface.

Moreover, the surface of silicon carbide not subjected to CVD coating is contaminated with heavy metals such as iron. Conventionally, a silicon carbide gas introduction tube that has been used has been very difficult to CVD coat on the inside, so the inside of the tube has been contaminated with iron. When the atmospheric gas was supplied into the reaction chamber using such a gas introduction pipe, iron adhering to the inner surface of the gas introduction pipe was mixed into the atmospheric gas, and the wafer was contaminated with iron.
However, in the present invention, since the gas introduction pipe of the portion inserted into the heat treatment apparatus is made of only quartz having a low level of heavy metal contamination such as iron compared to silicon carbide, the concentration of iron impurities in the heat treatment apparatus is conventionally reduced. As compared with the above, it is possible to reduce the iron contamination of the wafer. Therefore, the yield can be improved during device fabrication.

  Further, since the gas introduction pipe is made of quartz, there is a risk of causing a problem of causing thermal deformation and contact with the boat for heat treatment, but in the present invention, the gas introduction pipe is covered with a protective pipe. Even if the gas introduction pipe made of quartz is deformed by heat, it is guarded by the protective pipe, so that the gas introduction pipe can be prevented from coming into contact with the heat treatment boat. It can be prevented from being damaged.

Further, the protective tube is made of silicon carbide, silicon carbide coated with silicon carbide, silicon coated with silicon carbide, or carbon coated with silicon carbide. It can be.
When materials made of the above materials are used as protective tubes, these materials are more resistant to thermal deformation than quartz, so that the gas introduction tube can be more reliably prevented from thermal deformation. Therefore, contact between the heat treatment boat and the gas introduction pipe can be prevented.

In addition, as shown in a cross-sectional shape in FIG. 2, the protective tube 11 b can have a slit formed in part.
By setting it as such a shape, CVD coating can be performed uniformly to the inside of a protective tube, and the iron contamination of a wafer can further be reduced.

Moreover, it is desirable that the width of the slit is narrower than the outer diameter of the gas introduction pipe.
Further, it is desirable that the protective tube is supported by an L-shaped portion below the gas introduction tube.

An example of a heat treatment method using the heat treatment apparatus 1 of the present invention as described above will be briefly described.
A plurality of wafers 6 are held on a heat treatment boat 5 installed in the heat treatment apparatus 1 and heated by a heater 7 provided around the reaction chamber 2, whereby the wafer is heat treated. At the time of heat treatment, an atmospheric gas is introduced into the reaction chamber 2 through the gas introduction pipe 8, the gas flows from above the heat treatment apparatus 1 to pass around the wafer 6, and the heat treatment apparatus from the gas exhaust pipe 9. 1 to the outside.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example 1)
In a vertical heat treatment apparatus comprising a silicon carbide reaction tube coated with silicon carbide CVD coating as shown in FIG. 1 and a quartz flange portion supporting the reaction tube, the top plate of the reaction tube A quartz gas introduction pipe (outer diameter 6 mm, inner diameter 4 mm) reaching to near was welded to the quartz flange. A silicon carbide protective tube (outer diameter: 12 mm, inner diameter: 8 mm) to which a CVD coating of silicon carbide was applied was attached to the portion of the gas introduction tube inserted into the heat treatment apparatus.
A silicon carbide heat treatment boat with a silicon carbide CVD coating on which a plurality of 300 mm diameter silicon wafers are placed is inserted into the reaction tube, and Ar gas is circulated in the reaction chamber at a flow rate of 50 l / min. Heat treatment was performed at 1250 ° C. for 1 hour.

The surface condition of the wafer after the heat treatment, the evaluation of the iron concentration, and the degree of thermal deformation of the gas introduction tube were carried out by the following procedure.
After the heat treatment, the surface state of the wafer was observed with a condenser lamp of a halogen lamp.
The concentration of iron impurities in the wafer was evaluated by the SPV method.
Then, annealing at 1250 ° C. for 1 hour was performed 100 times to evaluate whether the gas introduction tube was thermally deformed.

The wafer of Example 1 was found to be free from fogging on the surface after the heat treatment and maintain the mirror surface state before the heat treatment.
When the iron concentration of the wafer after this heat treatment was evaluated, the maximum value was 7 × 10 ¹¹ atoms / cm ³ and the average value was 8 × 10 ¹⁰ atoms / cm ³ , indicating that a relatively high cleanliness was obtained. confirmed.
Furthermore, when annealing was performed 100 times, it was found that the quartz gas introduction tube was contained in the protective tube and was not in contact with the heat treatment boat due to thermal deformation.

(Example 2)
In Example 1, the same heat treatment as in Example 1 except that a protective tube having a slit with a width of 4 mm formed on the side surface and a CVD coating made of silicon carbide on the inside is used as shown in FIG. Using the apparatus, the same heat treatment as in Example 1 was performed, and the same evaluation was performed.
When the surface state of the wafer after the heat treatment was observed, there was no cloudiness and the mirror surface state before the heat treatment was maintained.
When the iron concentration of the wafer was evaluated, it was confirmed that a high cleanliness was obtained with a maximum value of 3 × 10 ¹¹ atoms / cm ³ and an average value of 3 × 10 ¹⁰ atoms / cm ³ .
Furthermore, even after annealing was performed 100 times, it was found that the gas introduction tube was contained in the protective tube and was not in contact with the heat treatment boat due to thermal deformation.

(Comparative Example 1)
In Example 1, instead of a gas introduction pipe, a quartz gas port part is welded to a quartz flange part, and a silicon carbide gas introduction pipe (silicon carbide CVD coating is applied to the gas port part) A heat treatment was performed in the same manner as in Example 1 using the same heat treatment apparatus as in Example 1 except that the outer diameter was 6 mm and the inner diameter was 4 mm, and the same evaluation was performed.
In the wafer heat-treated using the heat treatment apparatus of Comparative Example 1, strong haze was generated on the outer peripheral portion on the surface after the heat treatment.
When the iron concentration of the wafer after the heat treatment was evaluated, the maximum value was 4 × 10 ¹² atoms / cm ³ and the average value was 2 × 10 ¹¹ atoms / cm ³ , and the Fe contamination concentration was high.

(Comparative Example 2)
In Example 1, heat treatment was performed in the same manner as in Example 1 using the same heat treatment apparatus as in Example 1 except that the gas introduction tube was not covered with the protective tube, and the same evaluation was performed.
The wafer heat-treated using the heat treatment apparatus of Comparative Example 2 was free from fogging and maintained the mirror surface state before the heat treatment. In addition, the iron concentration of the wafer was as high as 2 × 10 ¹¹ atoms / cm ³ and the average value was 2 × 10 ¹⁰ atoms / cm ³ , and high cleanliness was obtained.
However, when annealing at 1250 ° C. for 1 hour was performed 10 times, the quartz gas inlet tube was thermally deformed and contacted the boat.

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

It is a schematic explanatory drawing which shows an example of the heat processing apparatus of this invention. It is a schematic sectional drawing which shows an example of the cross-sectional shape of the protective tube in this invention. It is a schematic explanatory drawing which shows an example of the conventional batch type vertical heat processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heat processing apparatus, 2 ... Reaction chamber, 3 ... Flange part, 4 ... Reaction pipe, 5 ... Boat for heat processing, 6 ... Wafer, 7 ... Heater, 8 ... Gas introduction pipe, 9 ... Gas exhaust pipe, 10 ... External piping 11a, 11b ... protective tubes,
DESCRIPTION OF SYMBOLS 20 ... Heat processing apparatus, 21 ... Reaction chamber, 22 ... Heat treatment boat, 23 ... Wafer, 24 ... Heater, 25 ... Gas introduction pipe, 26 ... Gas exhaust pipe, 27 ... Gas port part, 28 ... Joint part, 29 ... External Piping, 30 ... flange, 31 ... reaction tube.

Claims (3)

At least a reaction tube made of silicon carbide, a heat treatment boat for holding the substrate, a heater for heating the substrate, and an atmospheric gas inserted into the reaction tube to be introduced into the reaction tube In a heat treatment apparatus having a gas introduction pipe and a gas exhaust pipe for exhausting the atmospheric gas,
The gas introduction tube is made of quartz alone as a portion inserted into the heat treatment apparatus, and is covered with a protective tube for preventing deformation of the gas introduction tube. A heat treatment device characterized.   The protective tube is made of silicon carbide, silicon carbide coated with silicon carbide, silicon coated with silicon carbide, or carbon coated with silicon carbide. The heat treatment apparatus according to claim 1, wherein the heat treatment apparatus is provided.   The heat treatment apparatus according to claim 1, wherein the protective tube has a slit formed on a side surface.

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