JP4731617B2 - Leak detection method - Google Patents

Description

  The present invention relates to a leakage detection method for detecting leakage of a raw material melt when a single crystal or polycrystalline crystal of a semiconductor material, silicon used as a solar cell, germanium or gallium arsenide is grown.

  As crystal growth methods for semiconductors and solar cells, the Czochralski method (CZ method) and the float zone method (FZ method) are used. As the crystal growth method for solar cells, the Czochralski method (CZ method) and the casting method (unidirectional solidification method (VGF method)) divide the total production amount of solar cells into approximately two, and are widely used. The method is a method of growing a crystal by pulling up a seed crystal immersed in a molten raw material in a crucible, and is excellent in growing a large-diameter single crystal, but the cost is high. When it is not necessary to perform this, that is, as a method for growing a polycrystal, a casting method is used.

  The casting method is a method in which a molten raw material melted in a crucible is supplied to a mold and solidified in one direction from the bottom of the mold to form a silicon ingot. For supplying the molten material from the crucible to the mold, a method may be used in which a drainage port is provided at the bottom of the crucible and the silicon material that closes the drainage port is melted.

  By the way, crucibles are used in both the Czochralski method (CZ method) and the casting method, but these crucibles may be cracked or broken during the process. For example, a polycrystalline raw material caught in the crucible may fall during melting and damage the crucible. When the bulk specific gravity of the polycrystal (particularly in the case of silicon) before melting is small, the bulk specific gravity is further reduced due to the space between the polycrystals of the raw material when charging (incorporating the polycrystalline raw material into the crucible). Although it is difficult to fit the crucible into a predetermined amount, when the raw material is charged to the crucible, the bottom of the crucible dissolves first and the melting volume is reduced, so that undissolved polycrystals and melting during melting are melted. There may be a bridging phenomenon that separates. Polycrystalline raw material caught on the top of the crucible due to bridging phenomenon can be melted by setting it to a position where it can be easily melted by adjusting the crucible position, but in this case, the polycrystalline that has started to melt falls at once and damages the crucible Sometimes. This phenomenon also occurs in a unidirectional solidification furnace. In addition, there may be a follow-up charge (additional charge) of the raw material that cannot fit into the crucible or a recharge to a predetermined charge amount. In this case, in particular, the polycrystal is dissolved, and in the follow-up charge and recharge of the melt. An accident that leaks out of the crucible container is considered. If molten silicon leaks outside the crucible container, the water-cooled chamber base is melted, and when water enters the furnace, the highly active molten silicon reacts with the water, generating hydrogen, causing serious problems such as aqueous explosions. It is important to detect the initial leak as soon as possible because it may lead to a serious accident. Therefore, usually, a spill tray that is a carbon fiber processed product is installed at the bottom of the furnace, and measures are taken to minimize accidents. However, there is no guarantee that all leaked raw materials will be received safely with a large amount of charge. .

  Therefore, a technique for detecting leakage of molten silicon outside the crucible container has been proposed. For example, Japanese Patent Application Laid-Open No. 2001-302387 discloses a technique in which a plurality of thermocouples are provided at the furnace bottom and the temperature at the time of melt leakage is measured. According to this method, the temperature rise at the point where the thermocouple is installed can be detected, and the melt leakage can be detected.

JP 2001-302387 A

  However, even if a plurality of thermocouples are provided at the bottom of the furnace, each of the thermocouples is point information in terms of location and does not indicate whether or not there is leakage of the melt at other locations. It was. Also, even if the installation point of the thermocouple is relatively lowered, the leaked melt is guided to the installation point of the thermocouple, and the leak of the melt is detected, there is a high possibility that the response of leak detection will be delayed. There was also.

  Therefore, an object of the present invention is to provide a leakage detection method capable of immediately detecting leakage of a raw material melt when performing single crystal or polycrystalline crystal growth.

In the leak detection method according to the present invention, detection means is used which detects a change in the amount of light above the crucible, which is laid on the entire bottom surface of the furnace containing the crucible for melting the raw material.

It said detecting means, those formed with the solar cell, i.e., is to the amount of light measured by the solar cell wafer.

According to the leakage detection method of the present invention, when the crystal leaks from the crucible or overflows when performing crystal growth of a single crystal or polycrystal , the detection means is caused by a change in the amount of light caused by the melt. The amount of power generated in the battery increases and appears as a change in voltage or current. Therefore, even when the melt is dripped onto a part of the entire furnace bottom , it can be detected instantaneously. Therefore, it is possible to improve productivity, instantly detect melt leakage accompanying large crystal growth and perform safe avoidance work and fail-safe control, making crystal growth work safer. . The leakage detection method according to the present invention is an essential technique for the growth of large crystals with a large amount of melt, and the crystal growth method using a recharge method of multiple times that requires careful charging and crucible life.

  Moreover, if a photovoltaic cell is used as a detection means, this can be arrange | positioned in series and parallel, and the detector of a large area can be comprised cheaply. Furthermore, if a laser cutter is used to cut and chamfer in accordance with the shape and structure of the furnace bottom, it is possible to easily obtain a large-area detection means suitable for the furnace bottom structure.

Using wafer for cheaper solar cells, or to place the electrodes at a narrow interval, paved solar cell wafer to a bottom portion of the furnace, respectively in series, connected in parallel, the light quantity measurement and, in the voltage-current characteristic due to the temperature change Change may be captured .

It is sectional drawing of the center vicinity of the spill tray which shows embodiment of the furnace by which the leak detection method based on this invention was employ | adopted. It is a top view of the furnace bottom part in which the spill tray was installed. It is a top view which shows the state before performing the laser trimming of the sensor part which faces the spill tray. It is a top view of the sensor part comprised by the short circuit type electrode. It is sectional drawing of the center vicinity of the spill tray which shows other embodiment of the furnace by which the leak detection method based on this invention was employ | adopted. 2 shows a conventional spill tray and electrode.

An embodiment of a crystal growth furnace in which the leakage detection method according to the present invention is adopted will be described with reference to the drawings.
This crystal growth furnace contains a crucible in a vacuum chamber, and a bottom shaft 5 for adjusting the height position of the crucible and heat for melting the raw material in the crucible are provided at the bottom of the furnace. An electrode 4 is projected. Further, a spill tray 1 serving as a reservoir for the leaked melt is provided for protecting the bottom of the furnace. The spill tray 1 is provided with an electrode hole 2, a lower shaft hole 3, and a vacuum exhaust hole (not shown). The lower shaft 5 is inserted into the lower shaft hole 3, and the electrode 4 is inserted into the electrode hole 2. Yes.

  The structure in which the lower shaft 5 and the electrode 4 are inserted through these spill trays 1 is the same as the conventional spill tray shown in FIG. 6, but the spill tray 1 has a sensor portion 6 on its inner surface. It is different from the conventional spill tray. In FIG. 6, parts that are substantially the same as the structure shown in FIG.

  The sensor unit 6 corresponds to the detection means of the present invention, and is formed by combining solar cells. First, the solar cells are arranged in series and in parallel to be electrically joined, and after being brought into the state shown in FIG. 3, the solar cells are formed in accordance with the shape of the spill tray 1 by laser trimming. Therefore, it is possible to make the large area suitable for the furnace bottom structure easily and inexpensively. Moreover, since the photovoltaic cell diffuses a silicon wafer and is mass-produced, it can be obtained at low cost.

  The sensor unit 6 disposed on the inner surface of the spill tray 1 is connected to the sensor electrode 8 through a signal line 8a. The sensor electrode 8 is provided outside the vacuum chamber, and the signal line 8a is led to the outside of the vacuum chamber through a sleeve 9 that penetrates a water cooling jacket 10 that is a wall material of the vacuum chamber. The gap between the sleeve 9 and the signal line 8a is closed by the vacuum seal material 7, and the airtightness in the vacuum chamber is maintained. As the vacuum seal material 7, it is preferable to use a hermetic seal.

  According to this crystal growth furnace, when the melt leaks out or overflows from the crucible, the amount of power generation in the sensor unit 6 increases due to a change in the amount of light caused by the melt, and the sensor electrode 8 changes as a change in voltage or current. Appear in Therefore, even when the melt is dripped onto a part of the entire furnace bottom, it can be detected instantaneously. Further, since the solar battery cell is also a bipolar semiconductor element having a PN junction, leakage can be easily detected with high sensitivity even if a change in forward current or reverse current between the electrodes is detected. . Furthermore, if the electrodes are arranged at a narrow interval on the silicon wafer, it is relatively easy to detect that the melt has fallen by detecting conduction between these electrodes. In this case, the interelectrode connection can be achieved, for example, by sandwiching a germanium single crystal grown in a thin plate shape between the silicon wafers of FIG. If the output of the sensor electrode 8 is input to the control device and the fail-safe control is performed, the crystal growth operation can be performed more safely.

The sensor unit 6 is not limited to a solar cell panel, and may have other configurations. For example, you may comprise with a short circuit type electrode as shown in FIG. In this case, the sensor section 6 is made conductive by the heat of the melt that has fallen there, so that leakage of the melt is detected. Alternatively, the capacitance between electrodes can be measured, and a change in electrical capacitance or a change in impedance due to electrode disconnection can be used as a detection signal.

  In addition, the sensor unit 6 may be composed of an element whose electromotive force changes depending on the amount of heat, and may detect the leakage of the melt by the change in the amount of heat outside the crucible due to the leakage of the melt. In that case, the sensor unit 6 does not need to directly face and contact the leaked melt. Therefore, as shown in FIG. 5, it is good also as arrange | positioning to the furnace bottom plate of the spill tray 1 lower side.

DESCRIPTION OF SYMBOLS 1 Spill tray 2 Electrode hole 3 Lower shaft hole 4 Electrode 5 Lower shaft shaft 6 Sensor part 7 Vacuum seal material 8 Sensor electrode 8a Signal line 9 Sleeve 10 Water cooling jacket

Claims (1)

A detection means for detecting a change in the amount of light above the crucible is laid on the entire bottom surface of the furnace containing the crucible for melting the raw material, and the detection means is formed using solar cells. leak detection method which is characterized in that.

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