JP2001089124A - Production method of silicone substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of silicone substrate capable of simplifying a production process and simultaneously raising effective utilization ratio of silicone and remarkably reducing energy required for melting process by excluding slicing process which is an indispensable process in the conventional method, in production of a silicone substrate used in a solar cell or the like. SOLUTION: The silicone substrate is produced by densely filling particulate silicone having particle size 1-1,000 μm, for example, in a container opening upward at least overlapping two or more layers and then heating the filled particulate silicone by controlling a heating zone and heating time to fuse the silicone arranging the particulate silicone contacting with the container not to adhere on the container.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silicon substrate used for solar cells and other photoelectric conversion elements.

[0002]

2. Description of the Related Art At present, single-crystal silicon wafers and plate-cut polycrystalline silicon substrates are widely used as substrates for solar cells using crystalline silicon. By using such crystalline silicon as a material for a solar cell, the photoelectric conversion efficiency is high, and a highly reliable solar cell can be manufactured. Therefore, these solar cells are currently mass-produced industrially. It has become.

As a method of manufacturing a single crystal wafer, a Czochralski method (hereinafter also referred to as CZ method) and a floating zone method (hereinafter also referred to as FZ method) are generally used as a method of manufacturing silicon for LSI. I have.

In the CZ method, a lump of high-purity polycrystalline silicon is put in a quartz crucible and melted by heating it to 1300 ° C. or higher, and a seed crystal for aligning the crystal orientation is brought into contact with the melt. This is a method of manufacturing rod-shaped single-crystal silicon by pulling up very slowly.

Further, the FZ method is to determine the crystal orientation at the end of the rod-shaped polycrystalline silicon under reduced pressure or an inert gas atmosphere using rod-shaped polycrystalline silicon produced by a Siemens method or the like as a raw material. To produce a rod-shaped single-crystal silicon having a uniform crystal orientation by fusing the seed crystal of the above by high-frequency induction heating and gradually moving the molten portion by high-frequency induction heating from one end to the other end It is.

The single crystal silicon thus manufactured is processed into a plate shape by cutting (slicing) it into a predetermined thickness with a diamond wire saw or the like. Then, it is polished to form a substrate for manufacturing a solar cell.

[0007] In general, the production of single crystal silicon is technically complicated as compared with the production of polycrystalline silicon. Silicon is being used.

As a general method for manufacturing a plate-like polycrystalline silicon substrate, a casting method is widely used. According to the method, polycrystalline silicon or single-crystal silicon pieces as a raw material are placed in a quartz crucible, heated to a temperature of 1300 ° C. or more, melted, and then cooled, whereby the crystal grains obtained are controlled. By cutting and polishing the lump in the same manner as described above, plate-like polycrystalline silicon can be produced.

[0009]

In order to produce a plate-shaped crystalline silicon substrate serving as a base material for a solar cell, a cutting / polishing process must be performed for both single-crystal and polycrystalline silicon as described later. Since all silicon including the part that is turned into chips and scraps and is not actually used as a substrate is once melted by a heat process at 1000 ° C. or more, a large amount of energy is required for its production. . In addition, since the crucible used for melting is made of quartz or silicon carbide, a problem that oxygen and carbon, which are constituent elements of the crucible, diffuse in silicon in large quantities actually occurs.

[0010] Further, in the cutting step when these silicon base materials are formed into a plate shape, about 1/3 to 1/2 of silicon is generated as chips and the production yield is extremely poor at present. . In addition, the life of the diamond wire saw used for cutting is short, and this process is not always efficient, and there is much room for improvement for industrial production.

In recent years, it has been reported that polycrystalline silicon as a solar cell material does not necessarily have the purity required for LSI, and polycrystalline silicon which can reduce energy consumption in manufacturing. A method for producing silicon has also been proposed (JP-A-10-273331). However, even if polycrystalline silicon manufactured by such a method is used, the manufacturing method is not only complicated in the process, but also has a small energy reduction effect, and is still a step of slicing the melt-solidified silicon material. Was included.

Accordingly, the present invention provides a novel silicon substrate which does not require a large amount of heat energy as in the conventional method, is simple, does not contain impurities, and has a high silicon utilization (less loss). The purpose was to provide a fabrication method.

[0013]

Means for Solving the Problems The present inventors have intensively studied to achieve the above object. As a result, the particulate silicon is arranged in layers so that each particle is in contact with each other, and this is irradiated with infrared rays and heated, and a fused body obtained by fusing only the upper layer of particulate silicon is used for a solar cell or the like. The inventors have found that the present invention can be used as a silicon substrate, and have completed the present invention.

That is, according to the present invention, the particle size is 1 to 1000 μm.
A method of manufacturing a silicon substrate, comprising fusing particulate m silicon.

According to the above manufacturing method, it is possible to manufacture a silicon substrate having an appropriate unevenness on the surface. Such a silicon substrate is characterized in that light scattering can be suppressed and a light confinement effect can be expected even when used for a substrate such as a solar cell without performing surface processing.

In the production method of the present invention, the particle size is
1000 μm of particulate silicon is densely packed so as to overlap at least two layers in a container opened upward, and the filled particulate silicon is heated, and the particulate silicon particles not in contact with the container are heated. When the method of fusing a part or all of the above is adopted, the following effects can be obtained.

That is, a plate-like substrate having an arbitrary thickness can be obtained by controlling the particle size of the particulate silicon or changing the heating temperature and the heating time to control the number of layers of the particulate silicon to be fused. Therefore, the step of slicing the lump can be omitted. Further, since the amount of silicon required for obtaining one substrate is small, a heating step is included, but the amount of energy consumed in this step is much smaller than that of the conventional method. Furthermore, since the particulate silicon in contact with the container is not fused, it can be easily taken out of the container, and the contamination of impurities diffused from the container can be avoided.

In order to fuse some or all of the particulate silicon particles that are not in contact with the container with respect to the particulate silicon filled in the container, for example, the uppermost layer of the filled particulate silicon is used. At least 100 from the periphery of
The area inside 0 μm is irradiated with infrared rays from above and heated to prevent the particulate silicon present in the lowermost layer of the area irradiated with infrared rays from melting, and to fuse the particulate silicon not in contact with the container. Just do it.

When the filling and heating of the particulate silicon in the container are performed in a vacuum or in an inert gas atmosphere, the surface of the particulate silicon is not oxidized, so that the fusion should be performed well. Can be. In addition, the substrate obtained in this manner has good characteristics as a substrate since an oxide layer is not included at the interface.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the production method of the present invention, a particle size of 1 to
A silicon substrate is manufactured by fusing 1000 μm of particulate silicon (hereinafter also simply referred to as granular silicon). Note that the particulate silicon means a minute piece of silicon, and is not necessarily limited to a spherical or substantially spherical shape. Therefore, the above particle size means the maximum diameter or the length of the maximum side, and can be measured, for example, from a photograph taken using a microscope. When the particle size of the particulate silicon used is less than 1 μm, it is difficult to handle when performing inert gas replacement, etc.
If it exceeds 1000 μm, it is not preferable because giant particles are conspicuous at the time of fusion and unevenness is increased.

The shape and crystal system of the particulate silicon used in the present invention are not particularly limited as long as the particle diameter is in the range of 1 to 1000 μm.

For example, shavings generated when a single crystal silicon wafer is manufactured, powder obtained by crushing rod-shaped or block-shaped high-purity polysilicon, and the like can be used. However, it is preferable to use spherical or substantially spherical polycrystalline silicon having a particle diameter of 1 to 1000 μm from the viewpoints of easy control of conditions for fusing the granular silicon and uniformity of the manufactured silicon substrate. Further, from the viewpoint that the unevenness formed on the front surface and the back surface when fused is effective in confining light when used for a substrate such as a solar cell, the particle size is 10 to 100.
It is particularly preferred to use spherical or substantially spherical polycrystalline silicon of μm.

It is known that such spherical or substantially spherical polycrystalline silicon is produced by a CVD method using monosilane as a source gas, as described in JP-A-08-041207. In this method, the particle size can be controlled by controlling the residence time in the reactor.

The method of fusing the granular silicon is not particularly limited, and a method of providing a substrate having a suitable shape may be appropriately selected according to the intended use of the silicon substrate to be obtained. From the viewpoint that the energy to be used is small and the risk of contamination by impurities is small, it is preferable to carry out the following method.

That is, particulate silicon having a particle size of 1 to 1000 μm is densely packed so as to overlap at least two layers in a container opened upward, and then the filled particulate silicon is heated and brought into contact with the container. It is preferable to fuse some or all of the unparticulated particulate silicon.

Hereinafter, a manufacturing apparatus 1 (hereinafter also referred to as a fusion apparatus) which can be suitably used in the manufacturing method of the present invention shown in FIG.
The above method will be described in more detail in the case of using.

The fusing apparatus 1 comprises an atmosphere holding container 100, an atmosphere control device 200, and a heating device 300. The atmosphere holding container 100 is a container whose main body is made of a metal material such as stainless steel, and is provided with a transparent and heat-resistant transparent window 110 such as a quartz plate on the upper surface thereof. Further, the atmosphere holding container 100 has a container 120 filled with granular silicon and opened upward, which can be mounted horizontally, and is connected to the atmosphere control device 200 via a pipe. .

The atmosphere control device 200 comprises an exhaust device 210 such as an exhaust pump and / or an inert gas supply device 220 for supplying an inert gas such as argon or helium. An atmosphere control system 230 for controlling the pressure and flow rate of the inert gas is connected. The atmosphere control device 200 keeps the atmosphere holding container 100 in a vacuum of about 10 ^{−3 to} 760 Torr or in an inert gas atmosphere.

A heating device 300 comprising an infrared lamp and a reflection plate is installed above the transparent window 110, and passes through the transparent window 110 to a granular silicon filled in a container 120 installed thereunder. Infrared rays are collected and irradiated to heat the granular silicon.

In order to manufacture a silicon substrate using the above-mentioned fusing apparatus 1, first, as shown in FIG. 2, at least two layers of particulate silicon 400 having a particle size of 1 to 1000 μm are overlapped in a container 120. Pack tightly. Here, “densely” means that a gap is not formed as much as possible. For this purpose, it is also a preferable embodiment to use particles of silicon having a distribution in particle size by mixing particles having a large particle size and particles having a small particle size.

The number of granular silicon layers to be filled is not particularly limited as long as it is two or more layers, and may be appropriately determined according to the thickness of the target silicon substrate. In the case of one layer,
Not only is it difficult to obtain a substrate having the desired thickness, but also the silicon fused to the container at the time of heating adheres to the container, making it difficult to remove the fused material. From the viewpoint of ease of removal after fusion, it is preferable that the number of layers is at least one more than the number of layers necessary to obtain the intended thickness of the silicon substrate in consideration of shrinkage during fusion and the like. It is. When heating by infrared irradiation, the fusion of granular silicon occurs sequentially from the top layer, so filling is performed so that the number of layers is significantly larger than the required number of layers, and the intensity and irradiation time of infrared rays are controlled. By doing so, it is also possible to control the required thickness of the fused layer.

The container 120 used at the time of filling is not particularly limited as long as it is a heat-resistant container opened upward, but is made of high-purity quartz or high-purity silicon so that impurities are not mixed during heating. It is desirable to be made from.
The shape of the container is not particularly limited, but is preferably a columnar container having a flat bottom and an open top. Among them, a so-called tray-shaped container having a height lower than the bottom area is preferable. Note that the bottom area may be appropriately determined according to the target area of the silicon substrate.

Next, the container 120 thus filled with the granular silicon is mounted horizontally inside the atmosphere holding container 100. At this time, the opening of the container 120 is set directly below the transparent window 110. When the mounting is completed, the atmosphere control device is operated, and the inside of the atmosphere holding container 100 is evacuated or replaced with an inert gas. By setting the heating atmosphere to such an atmosphere, it is possible to prevent silicon from being oxidized, and not only to reduce the purity of silicon but also to perform fusion well. In addition, when performing inert gas replacement, it is preferable to perform evacuation once, and to perform it.

When the inside of the system has reached a sufficient degree of vacuum or has been sufficiently replaced with an inert gas, the heating device 300 is operated to heat and fuse the granular silicon. The fusion of the granular silicon is not necessarily performed by melting all heated granular silicon, and may be performed by melting the surface layer of each particle. In the latter case, a substrate having voids and holes can be obtained, but there is no particular problem in using the substrate. Generally, when a thick substrate is manufactured by performing heating from above, each particle is completely melted and fused in the upper layer portion (near the heated surface of the substrate) of the filled granular silicon, and the lower layer portion is formed. (Near the opposite surface of the substrate)
Is obtained by melting and fusing only the surface layer portion of each particle.

In the heating, the infrared light radiated from the infrared lamp is condensed by a reflecting plate, adjusted to a desired substrate size, irradiated through the transparent window 110 onto the granular silicon, and at least the granular silicon irradiated with the infrared light is irradiated. Some temperatures are above the melting point,
Preferably, the irradiation is carried out until the temperature reaches 1400 to 1500 ° C. At this time, the region to be irradiated with the infrared ray is larger than the area of the target silicon substrate and the container 12
It is an area that falls within the zero plane.

When heating is performed including the above-mentioned peripheral portion, which is a boundary with the inner wall surface of the container 120, the fused body of granular silicon adheres to the inner wall surface of the container, making it difficult to take out, or impossible. If you try to take it out, it may crack. The distance from the inner wall surface of the container (peripheral edge of the uppermost layer of granular silicon) to the heating region (hereinafter also referred to as a buffer distance) is determined by irradiating the heating region with infrared rays and starting the heating region. Since the granular silicon present outside the infrared irradiation region is also heated, it is preferable to check in advance the distance at which the granular silicon fused body does not adhere to the inner wall of the container in accordance with the heating conditions, and to take a longer distance. . Usually, it is preferable that the buffer distance is 1000 μm or more.

The heating conditions include the output of the infrared lamp used,
What is necessary is just to determine suitably according to the area of an irradiation area | region, the number of layers (thickness) of the granular silicon to fuse | melt, etc. For example, by mounting a container 120 filled with a sufficient number of layers of granular silicon, fixing the lamp output and irradiation area, changing the irradiation time, and checking in advance the number of layers of granular silicon to be fused, the irradiation time Can be controlled to control the thickness of the silicon substrate obtained. At this time, if the relationship between the irradiation time and the area of the fused body is examined using the container 120 having a sufficiently large opening area, the minimum necessary buffer distance can be known.

Also, in the actual production, if granular silicon having a sufficient thickness (number of layers) as described above is filled, the obtained silicon substrate (fused body) is taken out after the silicon substrate is taken out. Can be manufactured. Further, if the granular silicon is automatically supplied, the silicon substrate can be manufactured continuously.

In the fusing apparatus 1 shown in FIG. 1, an example is shown in which an infrared lamp is installed outside the atmosphere holding container 100 as a heating apparatus. However, the heating apparatus may be any method that can heat a predetermined area from above. It is not particularly limited. That is, the infrared lamp can be installed inside the atmosphere holding container 100, and as another heating device,
For example, it is also possible to adopt a method in which an inductive coupling type coil is placed on a ceramic window and a high frequency is applied.

When a particulate silicon fused body having an intended area and an intended thickness is obtained by heating, the heating is stopped, and after cooling, the atmosphere holding device is stopped. A silicon substrate can be obtained by taking out the fused body.

The silicon substrate thus obtained can be polished on both sides or one side if necessary, cut into a size (area) according to the intended use, and used as a substrate for a solar cell or the like.

The silicon substrate manufactured by the manufacturing method of the present invention is characterized in that the substrate itself which has not been subjected to polishing treatment has moderate irregularities on its surface. In addition, not only those that are not polished but also those that have been polished are not completely melted in a container such as a crucible when fusing the granular silicon, so that impurity elements are mixed in from the container by diffusion. This is characterized in that it has a purity equivalent to that of the granular silicon used as a raw material. As described above, a method of manufacturing a substrate made of high-purity silicon (non-doped substrate) using granular silicon made of high-purity silicon has been described. In a silicon substrate for a solar cell, a P-type silicon substrate doped with boron or the like is used. It may be effective to use. For such a substrate, granular silicon doped with a Group III element or a Group V element of the periodic table may be used as a raw material instead of high-purity granular silicon. By doing this,
A doping substrate having a P-type semiconductor property or an N-type semiconductor property can be easily obtained. In addition, the conductivity of the substrate can be controlled by controlling the doping amount during the preparation of the granular silicon material.

[0043]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 A silicon substrate was manufactured using a fusing apparatus as shown in FIG. The fusion device uses an infrared induction heating system (GV-2) manufactured by Thermo Riko as a heating device, and uses a vacuum pump and an argon supply device as an atmosphere control device.

First, inside a quartz tray-like container having a bottom area of 25 cm ² and a height of 2 cm, a particle diameter of 1 to 2 was placed.
50 g of granular silicon made of 300 μm substantially spherical polycrystalline silicon was charged and shaken well to fill the granular silicon densely. The number of layers of granular silicon at this time is
It was well over 100.

Next, the above-mentioned container filled with granular silicon was placed in a stainless steel container having a quartz window with a diameter of 10 cm at the top. After the installation of the container, the atmosphere control device was operated, and the atmosphere was once evacuated to the order of 10 ⁻⁴ pa, and then Ar gas was flown to obtain an Ar gas atmosphere.

When the Ar flow rate was stabilized, the heating device was operated to irradiate the filled granular silicon with infrared rays. At this time, the reflecting mirror was adjusted in advance so that only the area having a diameter of 2 cm could be irradiated. Then, infrared rays of 1 kW output were irradiated for 5 minutes to fuse the granular silicon, and after the irradiation of the infrared light was completed, cooling was performed while flowing Ar for 20 minutes. After cooling, the upper quartz window was opened, and the welded product was taken out. As a result, a plate-shaped fused product having a thickness of 1 mm and an area of 3 cm ² was obtained. Although the obtained plate-like body could be sufficiently used as a silicon substrate as it was by being cut into an appropriate size, in the present embodiment, this was polished using a polishing agent of SiC, and both surfaces were flattened. A silicon substrate having a thickness of 500 μm was obtained.

[0048]

According to the manufacturing method of the present invention, a silicon substrate can be easily manufactured without including a step of slicing and cutting bulk silicon. In addition, since the production method of the present invention has an extremely high effective utilization rate of the raw silicon as compared with the conventional production method, the energy required for the heating step can be significantly reduced. In addition, a silicon substrate having the same purity as that of the raw silicon can be obtained without impurities being mixed in the manufacturing process. Further, it is also possible to obtain a silicon substrate having moderate unevenness on the surface and capable of expecting an optical confinement effect without performing surface processing to obtain a silicon substrate.

As described above, the manufacturing method of the present invention can be said to be an industrially excellent method for manufacturing a silicon substrate in terms of simplicity of steps, low energy consumption, and purity of the obtained silicon substrate. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a typical apparatus that can be used to manufacture the silicon substrate of the present invention.

FIG. 2 is a diagram schematically showing a cross section when granular silicon is filled in a container opened upward.

[Explanation of symbols]

 1 fusion device 100 atmosphere holding container 110 transparent window 120 container 200 atmosphere control device 210 exhaust device 220 inert gas supply device 230 atmosphere control system 300 heating device 400 granular silicon

Claims (4)

[Claims] 1. A method of manufacturing a silicon substrate, comprising fusing particulate silicon having a particle size of 1 to 1000 μm. 2. A container having a particle size of 1 to 1000 μm is densely packed so as to overlap at least two layers in a container opened upward, and the filled particle silicon is heated to form a container. A method for producing a silicon substrate, comprising: fusing a part or all of particulate silicon particles that are not in contact with the silicon substrate. 3. A region inside at least 1000 μm from the periphery of the uppermost layer of the particulate silicon filled in the container is irradiated with infrared rays from above and heated, and the particulate silicon present in the lowermost layer of the region irradiated with the infrared rays is removed. 3. The method for producing a silicon substrate according to claim 2, wherein the particulate silicon not in contact with the container is fused so as not to be melted. 4. The method for producing a silicon substrate according to claim 2, wherein the filling and heating of the particulate silicon into the container are performed in a vacuum or in an inert gas atmosphere.