JP5947516B2 - Heat treatment boat - Google Patents

Description

  The present invention relates to a heat treatment boat for fixing a semiconductor substrate when heat treatment is performed by superposing two back surfaces of semiconductor substrates having the same shape in pairs, and in particular, forming an emitter layer of a solar cell. The present invention relates to a boat for heat treatment for fixing a semiconductor substrate during heat treatment for the purpose.

  In a solar cell, an emitter layer in which a dopant is diffused is generally formed on the light receiving surface side surface of a semiconductor substrate. For example, phosphorus is diffused on the light receiving surface of a P-type silicon substrate to form an emitter layer. The heat treatment process for forming the emitter layer is often performed by stacking two semiconductor substrates in order to improve productivity (see, for example, Patent Document 1).

  As a jig for heat-treating a semiconductor substrate for a solar cell in a diffusion furnace, for example, a heat treatment boat as shown in FIG. 9 has been generally used. That is, the boat for heat treatment in FIG. 9 is composed of four beams 103a, 103b, 103c, and 103d and a portion of the side plate 102 for fixing the beams and maintaining the mechanical strength of the boat itself. A plurality of grooves 105a, 105b, 105c, and 105d for mounting a semiconductor substrate are provided inside the beam. In use, as shown in FIG. 10, two semiconductor substrates 107 are overlapped from above and inserted along the grooves 105a, 105b, 105c, and 105d, and the semiconductor substrate is held by a beam.

However, when a generally used heat treatment boat as shown in FIG. 9 is used, in order to insert the semiconductor substrate 107, between the groove bottoms of the grooves 105a and 105b that are in contact with opposite sides of the rectangular semiconductor substrate. It is designed with play so that the distance is larger than the dimensions of the rectangular semiconductor substrate mounted thereon. Therefore, for example, if the stacked semiconductor substrates are shifted and mounted as shown in FIG. 11, the dopant is diffused on the back surface of the rectangular semiconductor substrate.
In addition, as shown in FIG. 12, if the rectangular semiconductor substrate is warped by heat treatment when it is mounted in a state where it contacts only the groove bottom on one side and does not contact the other groove bottom, it is fixed at the groove bottom. The edge on the side that is not formed and the upper side of the substrate are opened. When the dopant diffusion heat treatment is performed in this state, the dopant flows from the gap generated by the warp and is diffused to the back surface of the rectangular semiconductor substrate.

  Further, in the diffusion process using the heat treatment boat that is generally used, there is a case where the dopant is not uniformly diffused, and there is a problem that the variation in the sheet resistance of the semiconductor substrate becomes large.

  The problem that the dopant is diffused on the back surface of the semiconductor substrate is one factor of the performance degradation of the solar cell and causes the performance variation. That is, for example, when phosphorus is used as a dopant, if phosphorus is diffused on the back surface of the P-type substrate, the diffusion potential is lowered and the open circuit voltage is lowered, so that the performance of the solar cell is lowered. Therefore, in order to stably manufacture a high-efficiency solar cell, it is necessary to avoid as much as possible that the dopant wraps around the back surface of the semiconductor substrate during the heat treatment for forming the emitter layer.

Focusing on the grooves formed in the beam of the heat treatment boat that holds the semiconductor substrate as a technique for preventing the diffusion of the dopant to the back surface of the semiconductor substrate, the beam has a spiral groove and is not fixed to the boat body and is rotatable There is a boat for heat treatment having a function that can change the position of a groove provided in a beam fixed to another boat body by using the (see Patent Document 2). When this heat treatment boat is used, by rotating the beam provided with the spiral groove in contact with the semiconductor substrate, the relative position of the other fixed beam to the groove changes, and the stacked semiconductor substrate The gaps between the substrates can be prevented from being opened, and the wraparound of the dopant to the back surface during the diffusion heat treatment is suppressed.
However, if the tightening condition is weak, the effect of suppressing the wraparound is insufficient, and if the tightening condition is too strong, there are other problems such as frequent cracking defects from the tightening portion.

JP-A-4-162518 JP 2006-86243 A

  In view of the above-described situation, the present invention suppresses misalignment between semiconductor substrates and generates a gap between the semiconductor substrates when the back surfaces of semiconductor substrates having the same shape are superposed and heat-treated in pairs. It aims at providing the boat for heat processing which can be hold | maintained without this.

The present invention has been made to solve the above problems. That is, the boat for heat treatment according to one aspect of the present invention is for heat treatment for fixing at least one set of the rectangular semiconductor substrates when the back surfaces of the rectangular semiconductor substrates having the same shape are superposed on each other in one set. A board fixing tool including a groove that contacts at least one portion of each side of the set of rectangular semiconductor substrates, and a support plate connected to both ends of the board fixing tool, The substrate fixture includes at least one first substrate fixture that presses the set of rectangular semiconductor substrates in a non-vertical direction from a position higher than the center of gravity of the set of square semiconductor substrates via a groove, and the one set. A heat treatment boat having at least one second substrate fixture that supports the pair of rectangular semiconductor substrates from a position lower than the center of gravity of the rectangular semiconductor substrate.
A heat treatment boat according to another aspect of the present invention is a heat treatment boat for fixing at least one set of round semiconductor substrates when the back surfaces of the same shape of round semiconductor substrates are superposed on each other in a set. A board fixing tool including at least a groove that contacts a peripheral edge of the pair of round semiconductor substrates; and a support plate connected to both ends of the board fixing tool. Includes at least one first substrate fixture for pressing the set of round semiconductor substrates in a central direction from a position higher than the center of the set of round semiconductor substrates through a groove, and the set of circles. A heat treatment boat having at least one second substrate fixture for supporting the set of round semiconductor substrates from a position lower than the center of the large semiconductor substrate.

  If the heat treatment boat according to the present invention is used, it is possible to suppress the positional deviation of the semiconductor substrate that occurs when the conventional heat treatment boat is used and to eliminate the gap. As a result, diffusion of the dopant to the back surface is suppressed, and the stacked substrates are not over-tightened, so that the diffusion heat treatment can be performed with a stable yield.

It is (a) top view which shows one aspect | mode of the boat for heat processing of this invention, and (b) sectional drawing. FIG. 2A is a plan view of a state in which a rectangular semiconductor substrate is mounted on the heat treatment boat of FIG. 1, and FIG. It is (a) top view which shows the other aspect of the boat for heat processing of this invention, and (b) sectional drawing. It is the (a) top view of the state which mounted the round semiconductor substrate in the boat for heat processing of FIG. 3, and (b) the side view. 3 is a graph in which the sheet resistance on the open surface side of Example 1 is measured from the vertical direction and the horizontal direction. It is the graph which measured the sheet resistance of the open surface side of Example 2 from the vertical direction and the horizontal direction. 3 is a graph in which the sheet resistance on the overlapping surface side of Example 1 is measured from the vertical direction and the horizontal direction. It is the graph which measured the sheet resistance of the overlapping surface side of Example 2 from the vertical direction and the horizontal direction. It is (a) top view and (b) sectional drawing of the boat for general heat treatment. FIG. 10A is a plan view of a state where a rectangular semiconductor substrate is mounted on the heat treatment boat of FIG. 9, and FIG. 10B is a side view thereof. It is a schematic diagram which shows an example when the board | substrate has shifted | deviated when mounting a square semiconductor substrate in the boat for general heat processing. It is a schematic diagram which shows an example when a clearance gap produces between board | substrates by the curvature by heat processing, when a square semiconductor substrate is mounted in the boat for general heat processing. It is the graph which measured the sheet resistance of the open surface side of a comparative example from the vertical direction and the horizontal direction. It is the graph which measured the sheet resistance of the overlapping surface side of a comparative example from the vertical direction and the horizontal direction.

The heat treatment boat according to the present invention will be described below.
First, a boat for heat treatment for fixing a rectangular semiconductor substrate having the same shape targets a semiconductor substrate having a quadrilateral or more polygonal shape. The target semiconductor substrate does not necessarily have a square shape, and may have a pseudo-square shape in which a portion that becomes a vertex of the square is cut off. In addition, a rectangular shape or a pseudo-rectangular shape in which a vertex is cut off may be used, or a hexagonal shape or an octagonal shape may be used. These semiconductor substrates have a non-heat-treated surface as a back surface, and the back surfaces of the same shape of the semiconductor substrate are superposed in advance in one set by static electricity or the like so that the back surface is not heat-treated.
The heat treatment boat for fixing the semiconductor substrate having such a shape is connected to both ends of the substrate fixing tool in order to fix at least the substrate fixing tool and the mechanical strength of the heat treatment boat itself by fixing the substrate fixing tool. And a support plate.
The substrate fixture serves as a beam, and the support plate is connected to both ends of the substrate fixture to support the substrate fixture, and also serves as a side plate that maintains the mechanical strength of the heat treatment boat itself. To fulfill.
And the said board | substrate fixture is equipped with the groove | channel which contacts at least one place of each edge | side of the said 1 set of square semiconductor substrates. If there are preferably two or more grooves in contact with each side, the rectangular semiconductor substrate can be fixed more easily.
The substrate fixture includes at least one first substrate fixture that presses the set of rectangular semiconductor substrates in a non-vertical direction from a position higher than the center of gravity of the set of square semiconductor substrates via a groove; At least one second substrate fixture that supports the set of rectangular semiconductor substrates from a position lower than the center of gravity of the set of rectangular semiconductor substrates is provided. When the first substrate fixture presses the rectangular semiconductor substrate in a non-vertical direction from a position higher than the center of gravity of the rectangular semiconductor substrate, a force for pressing the rectangular semiconductor substrate also in the non-vertical direction is generated. Since the second substrate fixture is at a position lower than the center of gravity of the rectangular semiconductor substrate, the second substrate fixture receives and supports the pressurizing force and weight of the first substrate fixture and the rectangular semiconductor substrate. The square semiconductor substrate is fixed by such pressurization from above the first substrate fixture and support from below the second substrate fixture.

  For example, if a flexible material such as a heat-resistant elastic body that is not easily affected by heat but is excellent in flexibility is used as the material of the first substrate fixture, the first substrate fixture adds a rectangular semiconductor substrate. Can be pressed. The heat-resistant elastic body is preferably made of, for example, carbon / carbon composite, graphite sheet, or heat-resistant metal.

The heat treatment boat for fixing the rectangular semiconductor substrate is preferably fixed so that the apex portion of the rectangular semiconductor substrate faces downward. The vertex portion includes not only the vertex of the polygon but also the portion where the portion that becomes the vertex in the case of the pseudo-polygon shape is cut off.
When fixing the apex portion so as to face downward, the first substrate fixture can press the square semiconductor substrate in a non-vertical direction from at least two sides of the square semiconductor substrate, and the second substrate fixture can be square. Since the rectangular semiconductor substrate can be supported from at least two sides of the semiconductor substrate, the heat treatment boat can more securely fix the rectangular semiconductor substrate.

Next, a heat treatment boat for fixing a round semiconductor substrate will be described.
A boat for heat treatment for fixing a round semiconductor substrate having the same shape is intended to fix a round semiconductor substrate such as a perfect circle or an ellipse. Similar to the rectangular semiconductor substrate, the non-heat treated surface is the back surface, and the back surfaces of the semiconductor substrate having the same shape are preliminarily superposed on each other in pairs so that the back surface is not heat treated, and the surface is heat treated.
The heat treatment boat for fixing the semiconductor substrate having such a shape is connected to both ends of the substrate fixing tool in order to fix at least the substrate fixing tool and the mechanical strength of the heat treatment boat itself by fixing the substrate fixing tool. And a support plate.
And the said board | substrate fixture is equipped with the groove | channel which contacts the peripheral part of said 1 set of round semiconductor substrate. The substrate fixture includes at least one first substrate fixture that pressurizes the set of round semiconductor substrates toward the center from a position higher than the center of the set of round semiconductor substrates via a groove; At least one second substrate fixture that supports the set of round semiconductor substrates from a position lower than the center of the set of round semiconductor substrates is provided. When the first substrate fixture presses the round semiconductor substrate in the center direction from a position higher than the center of the round semiconductor substrate, a force for pressing the round semiconductor substrate also outward from the center is generated. Since the second substrate fixture is at a position lower than the center of the round semiconductor substrate, the second substrate fixture receives and supports the pressing force and its own weight of the first substrate fixture and the rectangular semiconductor substrate. The round semiconductor substrate is fixed by such pressurization from above the first substrate fixture and support from below the second substrate fixture.

  As in the case of the rectangular semiconductor substrate, if a flexible material such as a heat-resistant elastic body that is not easily affected by heat, for example, but is excellent in flexibility, is used as the material for the first substrate fixture. The substrate fixture can pressurize the round semiconductor substrate. The heat-resistant elastic body is preferably made of, for example, carbon / carbon composite, graphite sheet, or heat-resistant metal.

  The groove provided in the substrate fixing tool of the heat treatment boat for fixing the rectangular semiconductor substrate or the round semiconductor substrate of the present invention may have a width equal to or greater than the total thickness of the semiconductor substrates stacked in a pair. This is because the semiconductor substrate fits in the groove if the total thickness is exceeded. For example, in the case where heat treatment is performed by superposing two semiconductor substrates having a thickness of 200 μm in one set, the width of the groove may be at least 400 μm. On the other hand, from the viewpoint of productivity, mounting as many semiconductor substrates as possible in one boat requires heat treatment to reduce the pitch between adjacent grooves. It becomes impossible to narrow, and productivity deteriorates. Therefore, practically, the groove width is desirably about 100 to 1000 μm.

  Note that the groove does not necessarily have a flat bottom surface as long as the substrate can be fixed as a heat treatment boat. Therefore, it is not necessary for each side of the rectangular semiconductor substrate or the peripheral portion of the round semiconductor substrate and the bottom surface of the groove to be in close contact, for example, the bottom surface of the groove that makes point contact with each side of the rectangular semiconductor substrate. It may be a shape. When the substrate fixture is made of a material such as quartz, the groove can be processed into a rod having a predetermined diameter using a glass processing device, a polishing device, or the like.

A heat treatment boat for fixing a rectangular semiconductor substrate or a round semiconductor substrate according to the present invention includes a first boat including a first substrate fixing tool that pressurizes the semiconductor substrate, and a second boat including a second substrate fixing tool that supports the semiconductor substrate. It can take a structure that is physically divided into boats, and a pair of these boats can be used as one heat treatment boat. By taking the divided structure, it becomes easy to sandwich and fix the semiconductor substrate between the beams.
As such a heat treatment boat, a boat having a structure in which the first boat and the second boat are divided into two in the vertical direction and a boat having a structure in which the boat is divided into two in the left and right are considered. The structure etc. which are divided | segmented into these 3 divisions can also be taken.

  In the case where the heat treatment boat is composed of the first boat and the second boat as described above, if the first boat and the second boat have a structure that is divided into two vertically, the first boat is caused by the weight of the first boat. The substrate fixture pressurizes the semiconductor substrate, and the second substrate fixture can support the semiconductor substrate by receiving the weight of the first boat and the weight of the semiconductor substrate. Can be fixed, which is preferable.

  It is preferable that the first boat and the second boat have a vertically symmetrical structure. This is because, if the structure is vertically symmetrical, the gas flow becomes constant when the heat treatment boat is installed in the furnace, and variations in the sheet resistance of the semiconductor substrate can be suppressed. Examples of the vertically symmetric structure include a structure in which the first boat and the second boat are mirror-symmetrical, and a structure having rotational symmetry.

  The boat for heat treatment of the present invention can be made of, for example, high-purity quartz or high-purity SiC including a substrate fixture. From the viewpoint of cost, it is desirable to use high purity quartz.

The dopant diffusion method for a set of two semiconductor substrates mounted on the heat treatment boat as described above may be a vapor phase diffusion method using phosphorus oxychloride, diborane, etc., and dissolves phosphoric acid, boric acid, etc. Alternatively, a spin coating method, a printing method, or an ink jet method using a liquid may be used.
In any method, by using the heat treatment boat of the present invention, unintended dopants can be prevented from diffusing on the side where the semiconductor substrates are superimposed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings for a heat treatment boat. In this case, the present invention is not limited to the embodiments of the drawings. In all the drawings for explaining the embodiments, parts having the same functions are given the same reference numerals, and repeated explanation thereof is omitted.

An example of the heat treatment boat 1 shown in FIG. 1 is a heat treatment boat for fixing a rectangular semiconductor substrate. A pair of these boats which are physically separated into an upper boat 8 and a lower boat 9 and have a vertically symmetrical (two-rotation symmetric) structure are used as one heat treatment boat. The upper boat 8 has four substrate fixtures (beams) 3a and support plates (side plates) connected to both ends of the substrate fixture 3a in order to fix the substrate fixtures 3a and maintain the mechanical strength of the boat itself. In the four substrate fixtures 3a, grooves 5e to 5h are provided on the inner side of the four substrate fixtures 3a to contact the upper two sides of the rectangular semiconductor substrate and fix the semiconductor substrate.
On the other hand, the lower boat 9 supports four board fixtures (beams) 3b and the board fixtures 3b so as to maintain the mechanical strength of the boat itself. Side plates 2b are formed, and grooves 5a to 5d for fixing the semiconductor substrate in contact with the two lower sides of the rectangular semiconductor substrate are provided inside the four substrate fixtures 3b.

When using the boat for heat treatment shown in FIG. 1, first, two lower sides of the rectangular semiconductor substrate 7 in which the back surfaces are previously superposed on each other by a pair of static electricity, the apex portion 7a faces downward as shown in FIG. By inserting into the grooves 5 a to 5 d of the substrate fixture 3 b of the lower board 9, the lower side is supported by the lower board 9 by the weight of the rectangular semiconductor substrate 7. The deviation between the stacked substrates is eliminated by the weight of the substrates.
Subsequently, the grooves 5 e to 5 h of the substrate fixture 3 a of the upper board 8 are put in two upper sides of the rectangular semiconductor substrate 7 supported by the lower board 9.
With the above configuration, the upper boat 8 pressurizes the rectangular semiconductor substrate 7 in the non-vertical direction via the substrate fixture 3a by its own weight, and the lower boat 9 receives the weight of the upper board 8 and the rectangular semiconductor substrate 7 to fix the substrate. The rectangular semiconductor substrate 7 is supported via the tool 3b, and the rectangular semiconductor substrate 7 is fixed. In this way, if a set of two rectangular semiconductor substrates 7 is fixed without being displaced, diffusion heat treatment can be performed with a stable yield while suppressing diffusion of the dopant to the back surface.

An example of the heat treatment boat 1 shown in FIG. 3 is a heat treatment boat for fixing a round semiconductor substrate. A pair of these boats which are physically separated into an upper boat 8 and a lower boat 9 and have a vertically symmetrical structure are used as one heat treatment boat. The upper boat 8 is composed of four substrate fixtures 3a and support plates 2a connected to both ends of the substrate fixture 3a in order to fix the substrate fixtures 3a and maintain the mechanical strength of the boat itself. Inside the substrate fixing tool 3a, grooves 5e to 5h are provided for contacting the upper two sides of the rectangular semiconductor substrate at two locations and fixing the semiconductor substrate.
On the other hand, the lower boat 9 is composed of four substrate fixtures 3b and support plates 2b connected to both ends of the substrate fixture 3b in order to fix the substrate fixtures 3b and maintain the mechanical strength of the boat itself. Inside the four substrate fixtures 3b, grooves 5a to 5d for fixing the semiconductor substrate in contact with the peripheral portion of the round semiconductor substrate are provided.

When using the boat for heat treatment shown in FIG. 3, first, the lower side of the peripheral portion 7b of the round semiconductor substrate 7 in which the back surfaces are overlapped in pairs by static electricity in advance, as shown in FIG. By inserting into the grooves 5 a to 5 d of the substrate fixture 3 b of the board 9, the round semiconductor substrate 7 is supported by the lower board 9 with its own weight. The deviation between the stacked substrates is eliminated by the weight of the substrates.
Subsequently, the grooves 5 e to 5 h of the substrate fixture 3 a of the upper board 8 are put on the upper side of the peripheral edge of the round semiconductor substrate 7 supported by the lower board 9.
With the above configuration, the upper boat 8 pressurizes the round semiconductor substrate 7 in the center direction through the substrate fixture 3a by its own weight, and the lower boat 9 receives the weight of the upper board 8 and the round semiconductor substrate 7 to receive the substrate. The round semiconductor substrate 7 is supported via the fixture 3b, and the round semiconductor substrate 7 is fixed. In this way, if a set of two round semiconductor substrates 7 is fixed without shifting, diffusion heat treatment can be performed with a stable yield while suppressing diffusion of the dopant to the back surface.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not restrict | limited to the following Example.
Example 1
First, as a rectangular semiconductor substrate, a wrapped wafer having a side length of 156 mm, a thickness of 200 μm, a plane orientation (100), a boron-doped p-type manufactured by the CZ method, and a specific resistance of 1 to 3 Ω · cm was prepared. .
Next, a heat treatment boat 1 as shown in FIG. 1 was fabricated using high-purity quartz in order to carry out the diffusion heat treatment by mounting the above-mentioned square semiconductor substrate. As the substrate fixture (beam) for fixing the substrate, eight cylinders having a length of 172 mm and a diameter of 10 mm were prepared. Align so that the center of the first groove comes to the position of 16 mm from the end of these board fixtures, and then the 56 grooves per board fixture so that the pitch between adjacent grooves is 2.5 mm. Cutting was performed. The groove depth was 3.5 mm and the groove bottom width was 1000 μm.
As shown in FIG. 2, the grooves 5a and 5b, the grooves 5c and 5d, the grooves 5e and 5f, and the grooves 5g and 5h are paired so that the two sides of each side of the square semiconductor substrate can be evenly contacted. did. The space | interval of the board | substrate fixtures 3 which have each pair of groove | channels was 78 mm. Next, the substrate fixture 3b in which the grooves 5a and 5b and the grooves 5c and 5d are processed is supported on the support plate (side plate) 2b so that the grooves 5a and 5b and the grooves 5c and 5d are directed to the substrate side at an angle of 90 °. To fix the lower boat 9. Further, the substrate fixing tool 3a in which the grooves 5e and 5f and the grooves 5g and 5h are processed is fixed by the support plate 2a so that the grooves 5e and 5f and the grooves 5g and 5h make an angle of 90 ° and face the substrate side. The upper boat 8 was used.
The above-mentioned square p-type semiconductor substrate 7 was mounted in a state where two pieces per groove were stacked on each groove of the substrate fixture 3b of the lower boat 9, and a total of 112 pieces (56 sets) were arranged. The lower two sides of the p-type semiconductor substrate 7 were fixed to the grooves 5 a to 5 d of the substrate fixture 3 b of the lower boat 9 by the weight of the p-type semiconductor substrate 7.
Next, the grooves of the substrate fixture 3a of the upper boat 8 were placed on the two upper sides of the p-type semiconductor substrates 7 arranged as described above. The upper two sides of the p-type semiconductor substrate 7 were fixed to the grooves 5e to 5h of the substrate fixture 3a of the upper boat 8 by the weight of the upper boat 8.
Next, diffusion heat treatment was performed in a heat treatment furnace equipped with a quartz furnace core tube having an outer diameter of 410 mm, an inner diameter of 400 mm, a length of 3500 mm, and an opening having an inner diameter of 400 mm on one side.
The heat treatment furnace was always set at 830 ° C. After the boat was inserted, phosphorus was deposited for 40 minutes, followed by drive-in for 17 minutes, and the boat was taken out.
The gas composition during heat treatment is a mixed gas of 20 L / min of nitrogen, 0.3 L / min of oxygen and 0.45 L / min of phosphorus oxychloride (POCl ₃ ) during the deposition of phosphorus. A mixed gas of 20 L / min of nitrogen and 0.3 L / min of oxygen was used at the time, at the time of inserting / removing the boat and during the drive-in.

(Example 2)
As a round semiconductor substrate, a wrapped wafer having a diameter of 150 mm, a thickness of 200 μm, a plane orientation (100), a boron-doped p-type manufactured by the CZ method, and a specific resistance of 1 to 3 Ω · cm was prepared.
In order to carry out the diffusion heat treatment by mounting the round semiconductor substrate described above, a heat treatment boat 1 as shown in FIG. 3 was produced using high-purity quartz. As the substrate fixture (beam) for fixing the substrate, eight cylinders having a length of 172 mm and a diameter of 10 mm were prepared. Align so that the center of the first groove comes to the position of 16 mm from the end of these board fixtures, and then the 56 grooves per board fixture so that the pitch between adjacent grooves is 2.5 mm. Cutting was performed. The groove depth was 3.5 mm and the groove bottom width was 1000 μm.
As shown in FIG. 4, the grooves 5a and 5b, the grooves 5c and 5d, the grooves 5e and 5f, and the grooves 5g and 5h were paired so as to be in contact with the peripheral edge of the round semiconductor substrate. The grooves 5a to 5h were rotated so that the direction of the grooves was toward the center of the round semiconductor substrate, and the distance between the substrate fixtures 3 having the grooves of each pair was 78 mm. The substrate fixing tool 3b in which the grooves 5a to 5d were processed was fixed with the support plate 2b while maintaining the positional relationship in which the grooves 5a to 5d were directed toward the center of the round semiconductor substrate, thereby forming the lower boat 9. The substrate fixing tool 3a in which the grooves 5e to 5h were processed was fixed with the support plate 2a while maintaining the positional relationship in which the grooves 5e to 5h were directed toward the center of the round semiconductor substrate, thereby forming the upper boat 8.
The above-mentioned round p-type semiconductor substrate 7 is mounted in a state where two grooves are stacked on each groove 5a to 5d of the substrate fixture 3b of the lower boat 9, and a total of 112 (56 pairs) are arranged. It was. The p-type semiconductor substrate 7 was fixed to the grooves 5a to 5d of the substrate fixture 3b of the lower boat 9 by its own weight.
Next, the grooves 5e to 5h of the substrate fixture 3a of the upper boat 8 were put together on the upper side of the p-type semiconductor substrates 7 arranged as described above. The upper side of the p-type semiconductor substrate 7 was fixed to the grooves 5e to 5h of the substrate fixture 3a by the weight of the upper boat 8.
Next, diffusion heat treatment was performed in a heat treatment furnace equipped with a quartz furnace core tube having an outer diameter of 410 mm, an inner diameter of 400 mm, a length of 3500 mm, and an opening having an inner diameter of 400 mm on one side.
The heat treatment furnace was always set at 830 ° C. After the boat was inserted, phosphorus was deposited for 40 minutes, followed by drive-in for 17 minutes, and the boat was taken out.
The gas composition during heat treatment is a mixed gas of 20 L / min of nitrogen, 0.3 L / min of oxygen and 0.45 L / min of phosphorus oxychloride (POCl ₃ ) during the deposition of phosphorus. A mixed gas of 20 L / min of nitrogen and 0.3 L / min of oxygen was used at the time, at the time of inserting / removing the boat and during the drive-in.

(Comparative example)
As a rectangular semiconductor substrate, a square wafer with a side length of 156 mm, a thickness of 200 μm, a plane orientation (100), a boron-doped p-type manufactured by the CZ method and a specific resistance of 1 to 3 Ω · cm was prepared.
In order to carry out diffusion heat treatment by mounting the above p-type semiconductor substrate, a heat treatment boat 100 as shown in FIG. 9 was fabricated using high-purity quartz. As the substrate fixture (beam) for fixing the substrate, four cylinders having a length of 172 mm and a diameter of 10 mm were prepared. Align so that the center of the first groove comes to the position of 16 mm from the end of these board fixtures, and then the 56 grooves per board fixture so that the pitch between adjacent grooves is 2.5 mm. Cutting was performed. The groove depth was 3.5 mm and the groove bottom width was 1000 μm.
As shown in FIG. 10, the beams 103 a to 103 d were adjusted so that the lower side of the square p-type semiconductor substrate 107 could be held at two places and the sides were held at one place. The interval between the beams 103 in the grooves 105b and 105c was 78 mm. The groove 105a and the groove 105d face each other in the direction of the groove, and the groove bottom interval was set to 159 mm. While maintaining the above positional relationship, it was fixed with the side plate 102 to obtain a general heat treatment boat.
The above-mentioned square p-type semiconductor substrate 107 was mounted in a state where two pieces per groove were superimposed on each groove of the lower beams 103c and 103d, and a total of 112 pieces (56 sets) were arranged. The lower side was fixed in the groove by the weight of the p-type semiconductor substrate 107. The side of the p-type semiconductor substrate 107 was pushed and pushed into the groove 105a side to be fixed. The groove 105d side was not fixed, and there was about 3 mm of play from the side to the groove bottom.
Next, diffusion heat treatment was performed in a heat treatment furnace equipped with a quartz furnace core tube having an outer diameter of 410 mm, an inner diameter of 400 mm, a length of 3500 mm, and an opening having an inner diameter of 400 mm on one side.
The heat treatment furnace was always set at 830 ° C. After the boat was inserted, phosphorus was deposited for 40 minutes, followed by drive-in for 17 minutes, and the boat was taken out.
The gas composition during heat treatment is a mixed gas of 20 L / min of nitrogen, 0.3 L / min of oxygen and 0.45 L / min of phosphorus oxychloride (POCl ₃ ) during the deposition of phosphorus. A mixed gas of 20 L / min of nitrogen and 0.3 L / min of oxygen was used at the time, at the time of inserting / removing the boat and during the drive-in.

Diffusion heat treatment was performed according to Examples 1 and 2 and the comparative example described above, and the obtained semiconductor substrate was evaluated by the following method.
The semiconductor substrate after the diffusion heat treatment was immersed in 25% HF for 4 minutes to remove the glass film, rinsed with pure water, dried, and measured for sheet resistance by a four-probe method. Sheet resistance measurement was performed on both the open surface side (processing surface side) and the overlapping surface side (back surface side) of the semiconductor substrates stacked on two sheets. The square semiconductor substrate was measured at a pitch of 2 mm so as to cross the center of the opposite sides. The round semiconductor substrate was measured from a certain point with a diameter of 150 mm at a pitch of 2 mm, and was measured at a pitch of 2 mm on another 150 mm straight line perpendicular thereto. In the figure, the measurements in the vertical direction and the horizontal direction were measured so as to be directed upward in the vertical direction of the substrate during the heat treatment as the distance from the edge where the measurement was started increased. In this case, the vertical direction is a direction parallel to the opening of the board, and the horizontal direction is a direction orthogonal thereto.
Table 1, FIG. 5, FIG. 6 and FIG. 13 show the sheet resistance measurement results on the open surface side of the substrates obtained in Examples 1, 2 and Comparative Example.

  In each of Examples 1 and 2 and the comparative example, when the heat treatment boat was used, the open surface side exhibited substantially the same sheet resistance.

  Table 2, FIG. 7, FIG. 8, and FIG. 14 show the sheet resistance measurement results on the overlapping surface side of the substrates obtained in Example 1, Example 2, and Comparative Example.

FIG. 7 shows the sheet resistance measurement result on the overlapping surface side of Example 1. There were some points that could not be measured. This is presumably because the p-type semiconductor substrate is not sufficiently inverted to n-type due to the wraparound of phosphorus.
FIG. 8 shows the sheet resistance measurement result on the overlapping surface side of Example 2. There were some points that could not be measured. This is probably because the p-type substrate is not sufficiently inverted to the n-type due to the wraparound of phosphorus.
FIG. 14 shows the sheet resistance measurement result on the overlapping surface side of the comparative example. The vicinity of the substrate edge also showed a sheet resistance comparable to that on the open surface side. This is thought to be due to the wraparound of phosphorus.

  As described above, compared with the comparative example, Examples 1 and 2 have a high average value of sheet resistance, which suggests that the wraparound of phosphorus toward the overlapping surface side is suppressed.

1 Heat treatment boat 100 Conventional heat treatment boat 2, 2a, 2b Support plate (side plate)
102 Side plate 3, 3a, 3b Substrate fixture (beam)
103a, 103b, 103c, 103d Beam 5, 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 105a, 105b, 105c, 105d Groove 7, 107 Semiconductor substrate 7a Vertex portion 7b Peripheral portion 8 Upper boat 9 Lower portion boat

Claims (3)

At least one set of rectangular semiconductor substrates is fixed when heat treatment is performed so that the dopants are diffused only on the front surface without overlapping the dopants on the back surface by superposing the back surfaces of two identical rectangular semiconductor substrates. A heat treatment boat,
At least a substrate fixture having a groove that contacts at least one portion of each side of the set of rectangular semiconductor substrates, and a support plate connected to both ends of the substrate fixture,
The substrate fixture includes at least one first substrate fixture that presses the set of rectangular semiconductor substrates in a non-vertical direction from a position higher than the center of gravity of the set of square semiconductor substrates via a groove;
At least one second substrate fixture for supporting the set of rectangular semiconductor substrates from a position lower than the center of gravity of the set of rectangular semiconductor substrates;
At least it possesses,
The heat treatment boat includes an upper support plate obtained by dividing the support plate into two parts and an upper boat provided with the first substrate fixture, a lower support plate obtained by dividing the support plate into two parts and a lower boat provided with the second substrate fixture. The upper boat and the lower boat are vertically symmetric structures,
A boat for heat treatment , wherein the upper boat pressurizes the rectangular semiconductor substrate from at least two sides of the rectangular semiconductor substrate by its own weight, and fixes the apex portion of the rectangular semiconductor substrate to face downward . At least one pair of said round semiconductor substrate when the heat treatment for diffusing the dopant only on the surface without diffusing a dopant into the backside of the back surface together round semiconductor substrate having the same shape superimposed in pairs A heat treatment boat for fixing,
At least a substrate fixture having a groove that contacts the peripheral edge of the set of round semiconductor substrates, and a support plate connected to both ends of the substrate fixture,
The substrate fixture includes at least one first substrate fixture for pressing the set of round semiconductor substrates in a central direction from a position higher than the center of the set of round semiconductor substrates via a groove;
At least one second substrate fixture for supporting the set of round semiconductor substrates from a position lower than the center of the set of round semiconductor substrates;
At least it possesses,
The heat treatment boat includes an upper support plate obtained by dividing the support plate into two parts and an upper boat provided with the first substrate fixture, a lower support plate obtained by dividing the support plate into two parts and a lower boat provided with the second substrate fixture. The upper boat and the lower boat are vertically symmetric structures,
A boat for heat treatment in which the upper boat pressurizes the round semiconductor substrate by its own weight . The boat for heat treatment according to claim 1 or 2 , wherein the groove has a width of 100 µm to 1000 µm.

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