JP2005328008A - Vertical boat for heat-treating semiconductor wafer, and heat treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical board for heat-treating a semiconductor wafer, capable of reducing the occurrence of a slip in a wafer in whole, and placing a maximum of wafers on a board having a restricted length for heat treatment. <P>SOLUTION: In the vertical boat 1 for heat treatment, there are a top board 2, a bottom board 3, and a support 4 fixed between the top and bottom boards; a plurality of wafer-placing sections 5 are formed in the support; and the periphery of the semiconductor wafer is supported at each wafer placement. In this case, formation is made so that an interval (d) at the wafer placement narrows stepwise or gradually from below toward the upper direction in the support. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vertical boat for heat treatment of semiconductor wafers, and more particularly to a boat suitable for heat treatment of silicon wafers and a heat treatment method using the boat.

  When a device is manufactured using a wafer cut out from a semiconductor ingot such as a silicon single crystal, a number of steps are involved from a wafer processing process to an element formation process. One of these processes is a heat treatment process. This heat treatment step is an important process performed for the purpose of forming a defect-free layer on the surface layer of the wafer, gettering, crystallization, oxide film formation, impurity diffusion, and the like.

In recent years, the diameter of semiconductor wafers has been increased, and silicon wafers having a diameter of 300 mm are currently mass-produced, and wafers having a diameter exceeding 300 mm are expected to be mass-produced in the future.
When heat-treating a wafer having a large diameter of 200 mm or more, a vertical boat (heat-treating vertical boat) is generally used to horizontally set a large number of wafers in a vertical heat treatment furnace.
FIG. 3A shows an outline of a general vertical boat for heat treatment. In this boat 11, four support columns 14 are fixed between a top plate 12 and a bottom plate 13, and a number of grooves 15 are formed in each support column 14 at equal intervals. The interval between the grooves varies depending on the diameter of the wafer to be heat-treated, but in a boat that heat-treats a silicon wafer having a diameter of 200 mm or more, the grooves are generally formed in each column at a constant interval in the range of 6 to 15 mm. A wafer mounting portion for mounting the peripheral portion of the wafer is formed between these grooves.
As a boat material, quartz, silicon carbide, silicon or the like is used in order to prevent contamination of the silicon wafer.

  When the wafer W is heat-treated using such a vertical boat 11 for heat treatment, the wafer W accommodated in a box or the like is subjected to the wafer holding means 31 as shown in FIGS. 4A and 4B, for example. It is carried to the boat 11 by the transfer mechanism provided, and the peripheral portion of the wafer W is inserted into each groove 15. As shown in FIG. 3B, the peripheral portion on the back surface (lower surface) side of the wafer W is supported by each wafer mounting portion.

The wafers W placed on the boat 11 are heated by a heater 24 provided around the reaction chamber 22 in a heat treatment furnace 20 as shown in FIG. During the heat treatment, gas is introduced into the reaction chamber 22 through the gas introduction pipe 26, flows from the upper side to the lower side, and is discharged from the gas exhaust pipe 28 to the outside. The 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. When impurity diffusion is performed, these gases are also used as a carrier gas for the impurity compound gas.

  By the way, for example, a silicon wafer having a diameter of 300 mm has a very thin thickness of about 775 μm as a standard, and its heat capacity is small. Therefore, when the wafer W placed on such a vertical boat 11 is put into and out of the furnace heated by the heater 24, a sudden temperature change is applied to the wafer W to cause slip (slip dislocation), and the product Yield could be reduced. Such slip is likely to occur in wafers placed near the upper and lower ends of the boat 11.

In particular, in the case of a silicon wafer having a diameter of 300 mm or more, the weight increases, and the occurrence of slip becomes remarkable due to the self-weight stress in which the load concentrates on the wafer support position. Therefore, in order to reduce the self-weight stress and prevent the occurrence of slip, a ring-shaped or arc-shaped auxiliary jig (susceptor) 51 as shown in FIGS. 6A and 6B is used as means for supporting the wafer. Has been proposed (see Patent Document 1).
However, when such an auxiliary jig is used, the cost becomes high, and even when the auxiliary jig is used, there is a problem that slip is likely to occur when the wafer interval is narrow.

In addition, there is a method of placing so-called dummy wafers on the upper and lower sides of the vertical boat 11 in order to prevent the production wafers from slipping.
However, since the dummy wafer is made of the same material as that of the product wafer and has the same shape and dimensions, the heat capacity is small as in the case of the product wafer, and slip is likely to occur. Therefore, in order to prevent the product wafer from being affected by the temperature change, it is necessary to place a large number (for example, 10 or more) of dummy wafers on the upper and lower ends of the boat. There is a problem that the number of sheets is greatly limited and productivity is lowered.

Therefore, in order to increase the heat capacity by increasing the thickness of the dummy wafer and suppress the influence of sudden temperature change on the product wafer, a boat with a groove width increased toward the upper and lower ends of the boat is proposed. (See Patent Document 2). In such a boat, a thicker dummy wafer having a larger heat capacity can be placed closer to the upper and lower ends, and the occurrence of slip of the product wafer is suppressed.
However, since it is necessary to prepare dedicated dummy wafers with thickness at both the upper and lower ends, the cost is increased and the area for placing the product wafer is narrowed, and the number of product wafers that can be processed in one batch is reduced. There's a problem. A dummy wafer thicker than the product is also a problem in handling.

In order to heat-treat more product wafers, a boat has been proposed in which the distance between upper and lower grooves (wafer mounting portions) on which dummy wafers are mounted is narrowed (see Patent Document 3). With such a boat, the throughput of the product wafer can be maintained even if the height of the boat is lowered, and the occurrence of slip is suppressed by widening the interval between the wafer mounting portions that support the product wafer. It is to be done.
However, in a boat in which the distance between the wafer loading portions is reduced in the area where the dummy wafer is placed, more dummy wafers are required, and the cost is increased.
In addition, when heat treatment is performed in a vertical furnace, slipping is likely to occur particularly in the lower wafer, as will be described later. Therefore, even if the boat as described above is used, slipping occurs not only in the dummy wafer but also in the lower product wafer. There is a problem that it is likely to occur.

JP-A-6-260438 JP-A-8-316158 Japanese Patent No. 3115164

  When the present inventor examined in detail the cause of the occurrence of slip, when heat treating the wafer in a vertical furnace, the wafer slips in the region of the upper and lower ends of the boat, but is particularly noticeable at the lower end As a result, it has been found that the entire wafer tends to slip from the upper side to the lower side. This cause seems to be related to the structure of the heat treatment furnace.

  In particular, the vertical furnace has a characteristic that the temperature in the upper part of the furnace tends to be higher, and the temperature distribution becomes lower from the upper side to the lower side. Therefore, in order to make the temperature in the furnace uniform, it is necessary to increase the power of the heater in the lower part, and the in-plane temperature distribution of the wafer tends to deteriorate. Also, especially when the wafer is brought into the furnace or immediately before it is taken out, the temperature adjustment of the heat cannot follow immediately, so the in-plane temperature difference applied to the wafer becomes larger as the lower wafer, and slip is likely to occur. Conceivable.

Therefore, in order to prevent the occurrence of slip on the entire product wafer, it is conceivable to increase the interval between the wafer mounting portions as a whole and make the in-plane temperature distribution of the wafer uniform.
However, when actually heat-treating product wafers, in addition to reducing the occurrence of slips and improving the yield of product wafers, the maximum number of product wafers is put into a heat treatment furnace in a single heat treatment to increase productivity. It is necessary to increase as much as possible. For example, if the interval between the wafers is widened as a whole, the occurrence of slip can be suppressed, but the number of wafers that can be put into the heat treatment furnace is reduced. On the other hand, since the length (height) of the boat is also restricted due to the height restriction of the heat treatment apparatus, the boat cannot be lengthened in order to widen the interval between the wafer placement portions.

  Therefore, the present invention can reduce the occurrence of wafer slip as a whole, and can also thermally treat semiconductor wafers that can be heat-treated by placing a maximum number of wafers on a boat having a limited length. The main purpose is to provide a type boat.

  According to the present invention, a top plate, a bottom plate, and a support post fixed between the top plate and the bottom plate are provided, and a plurality of wafer mounting portions are formed on the support post, and each wafer mounting portion has a semiconductor. In the vertical boat for heat treatment that supports the peripheral portion of the wafer, the interval between the wafer mounting portions is formed so as to be gradually or gradually narrowed from the lower side to the upper side of the support column. A vertical boat for heat treatment is provided (Claim 1).

  Slip is more likely to occur in the wafer placed on the lower part of the boat, and less likely to occur in the upper part. Therefore, if the vertical boat is such that the distance between the wafer placement portions becomes narrower stepwise or gradually from the lower side to the upper side of the column, the heat treatment gas wraps around the lower side where the wafer placement portion is wide. This improves the temperature difference between the central portion and the peripheral portion of the wafer, so that the occurrence of slip can be effectively prevented. Further, the closer to the upper side where slip does not easily occur, the smaller the interval between the wafer mounting portions, so that a large number of wafers can be mounted. Therefore, as a whole, the occurrence of slip can be prevented, and the number of processed sheets per batch can be increased. Therefore, the boat can greatly improve productivity.

When the interval between the wafer mounting portions is gradually reduced from the lower side to the upper side of the support column, a semiconductor wafer having a minimum number of five wafer mounting portions at equal intervals in each stage is obtained. The wafer mounting portions are formed so as to have the number to be supported (Claim 2), and the wafer mounting portions are arranged so that the number of wafer mounting portions at equal intervals in each stage is a multiple of five. Preferably, it is formed (claim 3).
In other words, if the number of wafer mounting portions at equal intervals in each stage is five or more, and five units, for example, 15 boats are formed on each column, transfer work by a transfer robot or the like becomes easy. .

Moreover, it is preferable that the intervals between the wafer mounting portions are in the range of 6 mm to 15 mm.
If the distance between the wafer mounting portions is set within the above range, wafers can be easily transferred and a large number of wafer mounting portions can be formed in the entire boat, and gas can be introduced between the wafer mounting portions. It will be possible to ensure sufficient wraparound.

Furthermore, according to the present invention, there is provided a method for heat-treating a semiconductor wafer, wherein the semiconductor wafer supported by the boat is heat-treated at 1000 ° C. to 1300 ° C. using the heat-treating vertical boat. A heat treatment method is provided (claim 5).
In particular, silicon wafers and the like are often heat-treated at a high temperature of 1000 ° C. to 1300 ° C., and slip easily occurs in such a high temperature range. Therefore, by performing heat treatment using the vertical boat for heat treatment of the present invention, productivity can be improved without causing slip.

It is preferable to heat-treat a silicon wafer having a diameter of 300 mm or more as the semiconductor wafer.
Since the silicon wafer having a diameter of 300 mm or more has a large area, the in-plane temperature is likely to be non-uniform, and the load is concentrated on the supporting portion, so that slip is particularly likely to occur. The vertical boat for heat treatment according to the present invention By using this, it is possible to heat-treat many wafers while effectively suppressing the occurrence of slip. Therefore, it is particularly effective for heat treatment of a silicon wafer having a diameter of 300 mm or more.

  According to the present invention, the wafer mounting portion is formed so that the interval between the wafer mounting portions that support the wafer in the vertical boat for heat treatment becomes narrower stepwise or gradually from the lower side to the upper side of the support column. There is a boat provided. By using such a boat, it is possible to reduce the occurrence of wafer slip as a whole during the heat treatment of silicon wafers and the like, and to place a maximum number of wafers on a limited length boat. It can be heat treated. Accordingly, the number of processed sheets per batch increases, and the productivity can be greatly improved.

Hereinafter, as a preferred embodiment, a vertical boat for heat treatment according to the present invention used for heat treatment of a silicon wafer will be specifically described with reference to the accompanying drawings.
FIG. 1 shows an example of a vertical boat for heat treatment according to the present invention. FIG. 2 shows a state where the wafer W supported by the boat 1 is heat-treated in the heat treatment furnace 20.
This boat 1 has a top plate 2, a bottom plate 3, and four support posts 4 fixed between the top plate 2 and the bottom plate 3, and a plurality of grooves 6 are formed in each support post 4. A plurality of wafer mounting portions 5 for supporting the peripheral portion of the wafer are formed. In the vertical boat 1 for heat treatment, the distance d between the wafer mounting portions 5 becomes narrower in stages, specifically in four stages (S4 to S1) from the lower side to the upper side of the support column 4. Thus, a wafer mounting portion is formed. In each of the steps S4 to S1, the wafer mounting portions 5 are formed at equal intervals.

  The lower stage S4 having the widest wafer-to-wafer spacing is composed of a region D2 for placing a dummy wafer and a region P4 for placing a product wafer. Then, from S4 upward, the spacing d between the wafer mounting portions is gradually reduced in the order of S3, S2, and S1, and the intermediate stages S3 and S2 both have a region P3 on which the product wafer is placed, The uppermost stage S1 is composed of a region D1 on which a dummy wafer is placed and a region P1 on which a product wafer is placed.

  In the uppermost D1 region, the wafer mounting portion 5 is narrower than the interval between the wafer mounting portions in the P1 region, and in the lowermost D2 region, it is wider than the interval between the wafer mounting portions in the P4 region. May be formed. However, the dummy wafer is generally used with a thickness approximately equal to that of the product wafer. In each dummy wafer region D1, D2, the distance between the wafer mounting portions of the product wafer regions P1, P4 on the upper and lower ends is determined. It is preferable to set the same interval.

In this way, by increasing the distance d between the lower wafer mounting portions 5 including the dummy wafer regions D1 and D2, the number of wafers loaded on the upper side can be increased. Therefore, the occurrence of slip is suppressed.
Further, the occurrence of slippage of the lower dummy wafer is suppressed, the life of the dummy wafer that is repeatedly used can be extended, and the number of dummy wafers to be used can be reduced.
In addition, since it is hard to generate | occur | produce a wafer to the upper part of a boat, the number of wafer mounting parts can also be reduced in D1 area | region rather than D2 area | region.

The specific length of the interval between the wafer mounting portions in each of the stages S1 to S4 may be appropriately set in consideration of the heat treatment temperature, the wafer transfer mechanism, and the like, but the interval between the wafer mounting portions 5 is 6 mm. It is preferable to be within a range of ˜15 mm.
If the distance between the wafer mounting portions is less than 6 mm, it may be difficult to transfer the wafers to the boat 1, and the gas may be poorly wrapped, and the wafer may be easily slipped even at the upper stage. .

On the other hand, if the distance between the wafer mounting portions is 15 mm, the gas can easily flow around even in the lowermost wafer, and the occurrence of slip can be effectively prevented. In this case, it is possible to make the width larger than 15 mm, but the number of wafers that can be loaded is reduced correspondingly, and the productivity is lowered. In addition, compared to a conventional boat in which the wafer mounting portions are formed at equal intervals in the entire boat, the interval is about the same if the interval is 15 mm, so that the number of wafers that can be mounted as a whole can be increased. it can.
Therefore, for example, if the interval between the wafer mounting portions is set to 6 mm or more in the uppermost step S1 where the interval between the wafer mounting portions 5 is the smallest and 15 mm or less in the lowermost step S4, the wafer is transferred. In addition, it is possible to support a larger number of wafers than the conventional boat as a whole, and to keep the thermal stress distribution of each wafer uniform and to effectively prevent the occurrence of slip. In the case of a boat used for heat treatment of a silicon wafer having a diameter of 300 mm, the upper limit of the distance between the wafer mounting portions is set to 9.6 mm, thereby improving productivity and effectively suppressing the occurrence of slip. Can do.

In addition, the number of stages in which the wafer placing units 5 are equally spaced and the number of wafer placing parts 5 in each stage may be set as appropriate in consideration of the overall boat length, groove pitch, transfer mechanism, and the like. good. However, when the wafer is automatically transferred by the transfer robot, it is necessary to change the setting of the wafer mounting portion for each stage, and if it is divided into too many stages, it becomes difficult to control the robot, There is a possibility that the time required for the transfer operation will become longer. Therefore, in each stage, it is preferable to form the wafer mounting portion 5 so as to support at least five semiconductor wafers.
In addition, for example, a box containing 25 silicon wafers is generally used, and wafers are easily transferred when the wafers are transferred in units of 5 at a time. It is preferable that the wafer mounting portions 5 are formed so that the number of the wafer mounting portions 5 is a multiple of five.

Accordingly, if the wafer mounting portions 5 are formed at equal intervals so as to be able to support 5 or more, 5 cycle, that is, 5, 10, 15, or 20 wafers in each stage, the number of stages is There are few, and the setting of the space | interval of the wafer mounting part of a transfer robot can also be small. Further, since the wafers can be transferred in units of five at a time, the transfer operation can be performed efficiently and the throughput can be improved.
Of course, if the number of wafer mounting portions 5 in each stage, that is, the number of wafers that can be mounted is increased, the control is simple and the throughput may be further improved. Since the amount of preparation cannot be increased, the number is preferably 25 or less.

In the boat 1 described above, the interval between the wafer mounting portions is gradually reduced from the lower side to the upper side of the support column 4. However, the vertical boat for heat treatment according to the present invention has each wafer mounting portion. The intervals may be gradually reduced from the lower side to the upper side of the support columns, that is, one by one. Further, in some parts of the boat 1, the interval between the wafer mounting portions may be narrowed stepwise or gradually from the lower side to the upper side, and may be constant in other parts. For example, in the region from the lower end of the boat 1 to the height of two-thirds, the interval between the wafer mounting portions becomes narrower stepwise or gradually, and in the upper third region, the interval becomes constant. It is also possible to do.
However, if the wafer placement portions are formed so that the intervals between the wafer placement portions are changed one by one, the manufacturing cost of the boat increases, and the transfer robot also transfers the wafers one by one at different intervals. There will be a need. Therefore, from the viewpoint of ease of manufacture and transfer, it is more preferable that the distance between the wafer mounting portions is gradually reduced from the lower side to the upper side.

  Such a vertical boat 1 for heat treatment according to the present invention can be used particularly suitably when heat treating a silicon wafer having a large diameter of 200 mm or more, particularly 300 mm or more. In a large-diameter silicon wafer having a diameter of 300 mm or more, the load is concentrated at the supporting position. In particular, when heat treatment is performed at 1000 ° C. or more, the occurrence of slip becomes remarkable. Therefore, if the vertical boat 1 for heat treatment according to the present invention is used, the space between the wafer mounting portions is wide especially in the lower portion where slip is likely to occur. The occurrence of slip can be effectively prevented by reducing the temperature difference. On the other hand, since the interval between the wafer mounting portions is narrower above where slip is unlikely to occur, the number of wafers that can be heat-treated in one batch increases.

Although the heat treatment temperature depends on the purpose, slip is likely to occur at 1000 ° C. or higher, and when it exceeds 1300 ° C., not only slip but also contamination is likely to occur.
Accordingly, when the silicon wafer is heat-treated at 1000 ° C. to 1300 ° C. in the vertical furnace 20 as shown in FIG. 2, particularly when a silicon wafer having a large diameter of 300 mm or more is heat-treated at 1100 to 1200 ° C. By supporting the wafer using the vertical boat for heat treatment, it is possible to prevent wafer slip and contamination and heat more wafers as a whole. Therefore, both yield and productivity can be improved.

Examples of the present invention and comparative examples will be described below.
(Example 1, Comparative Example 1)
As a boat for heat-treating a standard silicon wafer having a diameter of 300 mm and a thickness of 775 μm at 1200 ° C., as shown in the boat 1 in FIG. A vertical boat for heat treatment (Example 1) in which a wafer mounting portion was formed so as to be narrowed in four steps in a range of ˜9.6 mm was prepared.
On the other hand, a boat (Comparative Example 1) in which wafer mounting portions were formed at equal intervals (interval: 9.6 mm) from top to bottom was also prepared.
The material of each boat was SiC. Table 1 shows the distance between wafer placement portions, the number of supported sheets, etc. in each region where product wafers of each boat are placed.

The region where the product wafer is placed is limited to the range of 720 mm of each boat due to the temperature characteristics of the heat treatment furnace. For example, in the boat of Example 1, the region from P1 to P4 is the region where the product wafer is placed.
In both boats, a wafer mounting portion was formed so that 10 dummy wafers could be mounted on both upper and lower ends in addition to the product wafer. In the boat of Comparative Example 1, the distance between the wafer mounting portions in the dummy wafer region was 9.6 mm both in the upper and lower directions. In the boat of Example 1, the distance between the wafer mounting portions in the lowermost dummy wafer region was the P4 region. 9.6 mm which is the same as that of the uppermost dummy wafer region, and the distance between the wafer mounting portions in the uppermost dummy wafer region is 7.2 mm which is the same as the P1 region.

Each of these boats was used for heat treatment while supporting the peripheral part of the silicon wafer (upper and lower 10 wafers were dummy wafers) at each wafer mounting part.
The heat treatment conditions were an argon atmosphere, the furnace entry temperature and the furnace exit temperature were both 700 ° C., and heat treatment was performed at 1200 ° C. for 1 hour.

After the heat treatment, the wafer was taken out from the furnace, and all the product wafers except for 10 dummy wafers on both the upper and lower sides were checked by visual inspection and X-ray topography. As a result, no slip was found on the wafers in both boats.
However, the number of product wafers in one heat treatment was 75 in the boat of Comparative Example 1, whereas 90 product wafers could be heat-treated in the boat of Example 1, resulting in a productivity of 20 % Can be increased.

(Example 2, comparative example 2)
As shown in Table 2 below, a vertical boat for heat treatment (Example 2) similar to that of Example 1 was prepared (the heat treatment temperature was low) except that the distance between the wafer mounting portions in each region and the heat treatment temperature were different. The overall distance between the wafer mounting portions is reduced).
On the other hand, a boat (Comparative Example 2) in which wafer mounting portions were formed at equal intervals (interval: 8.0 mm) from top to bottom was also prepared.

Each of these boats was used, and the same heat treatment was performed by supporting the peripheral part of the silicon wafer (upper and lower 10 wafers are dummy wafers) at each wafer mounting part.
The heat treatment conditions were an argon atmosphere, the furnace entry temperature and the furnace exit temperature were both 700 ° C., and heat treatment was performed at 1100 ° C. for 4 hours.

As in Example 1, after the heat treatment, the wafers were taken out from the furnace, and all the product wafers except 10 dummy wafers on the upper and lower sides were all checked by visual inspection and X-ray topography. No slip was observed.
However, the number of product wafers in one heat treatment was 90 in Comparative Example 2, whereas 111 boats in Example 1 can heat-treat 111 product wafers, resulting in a productivity of about 23%. I found out that it can be up.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  In the above embodiment, the vertical boat for heat treatment having four columns has been described, but the shape and number of columns are not limited thereto. For example, as shown in FIG. 7, in the vertical boat 40 in which the transverse groove 41 is cut to form one ring-shaped wafer mounting portion 42 with respect to one cylindrical column, the interval between the wafer mounting portions 42 is It may be narrowed stepwise or gradually from below to above.

It is the schematic which shows an example of the vertical boat for heat processing which concerns on this invention. It is the schematic which shows the vertical boat for heat processing which concerns on this invention in the heat processing furnace. It is the schematic which shows an example of the conventional vertical boat for heat processing. (A) Front view (B) Cross section It is the partial schematic which shows an example of the transfer mechanism holding the wafer. (A) Side view (B) Plan view It is the schematic which shows an example of a vertical heat processing furnace. It is a figure which shows an example of a ring-shaped susceptor. (A) Plan view (B) Cross section It is the schematic which shows an example of the vertical boat for heat processing in which the ring-shaped wafer mounting part was formed.

Explanation of symbols

1 ... Vertical boat for heat treatment, 2 ... Top plate, 3 ... Bottom plate, 4 ... Post,
5 ... Wafer mounting part, 6 ... Groove, 20 ... Heat treatment furnace,
31 ... Wafer holding means (transfer mechanism), d ... Interval between wafer mounting parts,
51 ... Auxiliary jig (transfer mechanism), D1, D2 ... Dummy wafer area,
P1 to P4: Product wafer region, S1 to S4: Stages where wafer mounting portions are equally spaced,
W: Wafer.

Claims (6)

  It has a top plate, a bottom plate, and a column fixed between the top plate and the bottom plate, and a plurality of wafer mounting portions are formed on the column, and each wafer mounting portion supports the peripheral portion of the semiconductor wafer. In the vertical boat for heat treatment, the vertical distance between the wafer mounting portions is formed so as to be narrowed stepwise or gradually from the lower side to the upper side of the support column. Type boat.   When the distance between the wafer mounting portions is gradually reduced from the lower side to the upper side of the support column, the number of the wafer mounting portions having the same interval at each stage is supported by at least five semiconductor wafers. The vertical boat for heat treatment according to claim 1, wherein the wafer mounting portion is formed so as to be a number.   When the interval between the wafer mounting portions becomes narrower stepwise from the lower side to the upper side of the support column, the number of wafer mounting portions that are equally spaced at each stage is a multiple of 5. The vertical boat for heat treatment according to claim 1 or 2, wherein a mounting portion is formed.   The vertical boat for heat treatment according to any one of claims 1 to 3, wherein an interval between the wafer mounting portions is in a range of 6 mm to 15 mm.   A method for heat-treating a semiconductor wafer, wherein the semiconductor wafer supported by the vertical boat for heat treatment according to any one of claims 1 to 4 is heat-treated at 1000 ° C to 1300 ° C. A method for heat-treating a semiconductor wafer.   The semiconductor wafer heat treatment method according to claim 5, wherein a silicon wafer having a diameter of 300 mm or more is heat-treated as the semiconductor wafer.

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