JP4498457B1 - Crystal growth method - Google Patents

Abstract

The present invention provides a crystal growth apparatus and a crystal growth method capable of using a quartz crucible for a longer period of time and improving operational efficiency.
In the crystal growth method according to the present invention, a molten raw material is supplied to a crucible having an inner surface coated with a release material and fired, and the molten raw material is solidified in the crucible so that the remaining amount of molten raw material is 30. The step of immersing the crystal piece in the molten layer at a stage of less than% and forming the protrusion on the surface of the crystal and the step of taking out the crystal from the crucible using the protrusion are reused in the same crucible And repeat. In the crystal growth method according to the present invention, a hanging tool that holds the protruding portion may be used, and the silicon crystal may be taken out from the crucible while applying vibration to the hanging tool. The silicon crystal may be taken out from the crucible while applying vibration to the crucible.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor material, silicon used as a solar cell, or a crystal growth method such as germanium or gallium arsenide.

  A Czochralski method (CZ method) or a float zone method (FZ method) is used as a silicon crystal growth method for semiconductors. On the other hand, among all solar cell production, the crystal system of silicon accounts for 85% or more. Further, as a crystal growth method, the Czochralski method (CZ method) and the casting method (unidirectional solidification method (VGF method)) Each of them is widely used so as to divide the total crystal production amount of all silicon into approximately two. The CZ method is a method of growing a crystal by pulling up a seed crystal immersed in a melting raw material in a crucible, and is excellent in growing a high-quality large-diameter single crystal, but the cost is high. Therefore, when a specification up to the single crystal quality characteristic is not required, a casting method is used as a growth method for a large-sized rectangular polycrystal.

  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. In addition, for supplying the molten raw 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 a silicon raw material that closes the drainage port is melted. There is a problem that it is necessary to heat the molten raw material more than necessary, leading to a decrease in productivity and a decrease in the quality of the silicon ingot (silicon crystal) due to impurities. Therefore, various ideas have been made to solve the problems in the casting method.

  For example, Japanese Patent Application Laid-Open No. 2006-275426 discloses a crucible having a drainage port for discharging a semiconductor melt at the bottom, and closing the drainage port with a plug of the same component as the semiconductor melt. A technique for opening the plug by breaking it with a breaking means is disclosed. According to this method, since the semiconductor melt can be supplied into the mold in a timely manner, the semiconductor melt can be supplied at a desired melt temperature without increasing the melt temperature of the semiconductor melt more than necessary. Become. Moreover, since the plug is melted into the semiconductor melt in a pulverized state, it can be melted quickly in the mold.

JP 2006-275426 A

  However, in the casting method, as described above, there is a problem that occurs when the formed crystal is taken out from the mold in addition to the problem that occurs when the molten raw material is supplied from the crucible to the mold. That is, since the silicon melt density is 2.54 g / cc and the crystal density is 2.33 g / cc, there is a problem that volume expansion occurs due to solidification and it is easy to fix the mold. Therefore, when taking out crystals from the mold, hard crystals may break if subjected to a strong impact, but there is a problem that productivity is reduced by work that is too careful to avoid damage to the crystals. . In practice, this problem is dealt with by applying a release agent to the inner surface of the mold to facilitate separation of the crystal from the mold or the crucible, but a greater effect is obtained in improving productivity. Things are getting harder.

  Further, the purity of the template generally used in the casting method is higher than that of the quartz crucible used in the CZ method, and therefore, the bottom portion in contact with the outer periphery of the formed silicon crystal block or the bottom of the template. There is a problem that the impurity level in the vicinity is high, the carrier lifetime is lowered, and the conversion efficiency of the solar cell is lowered.

  Therefore, the present invention makes it possible to easily take out the crystal formed by solidifying the molten raw material in one direction from the bottom of the container without damaging it without heating the molten raw material in the crucible more than necessary. An object of the present invention is to provide a crystal growth method capable of improving the properties and suppressing the impurity level of the formed crystal to be low.

The crystal growth method according to the present invention includes a step of supplying a molten raw material to a crucible that has been coated with a release agent on the inner surface and fired, and the molten raw material is heated in the crucible by a movable heater provided above the crucible. In the stage where the remaining amount of the molten raw material becomes 30% or less, the process of immersing the crystal piece in the molten layer and forming a protrusion on the surface of the crystal, and the melting in which the crystal piece is immersed After the layer is solidified, the method includes a step of moving the heater and taking out the crystal from the crucible using the protrusion. These steps are repeated by reusing the same crucible.

  In the crystal growth method according to the present invention, a hanging tool that holds the protruding portion may be used, and the crystal may be taken out from the crucible while applying vibration to the hanging tool. The crystal may be taken out from the crucible while applying vibration to the crucible. Further, after the crystal is taken out from the crucible, the crucible may be recovered, the release agent may be applied again, and the crucible may be reused.

  Furthermore, before the step of supplying the molten raw material, the vacuum leak rate of the surrounding environment of the crucible is set to 10 minus 4 Torr · liter / second or less, and the crucible and the in-furnace parts included in the surrounding environment are disposed. It is good also as heating-maintaining at 50 degreeC or more and 200 degrees C or less.

  According to the crystal growth method of the present invention, since the molten raw material is solidified in the crucible without using a separate mold from the crucible, when the molten raw material is supplied to the crucible, further heating is performed. do not need. That is, the crucible can be reused while reducing the time required for solidification without increasing the temperature of the molten raw material to the melting temperature or higher and improving the productivity. On the other hand, while using a crucible coated with release agent on the inner surface and baked, the crystal piece can be easily damaged from the crucible by immersing the crystal piece in the molten layer and using the protrusion formed on the surface of the crystal. It can be taken out without. Therefore, the productivity of crystals can be improved. Further, since the crucible is not damaged when the crystal is taken out, the crucible can be reused also in this respect. And, since the inner surface of the crucible is purified by reuse, the crystal purity can be equal to or higher than that of the crystal when the crucible is used for the first time. That is, the impurity level of the formed crystal can be kept low. Therefore, according to the crystal growth method of the present invention, if the formed crystal is silicon, the carrier lifetime can be increased and the conversion efficiency of the solar cell can be increased. However, the crystal formed by the crystal growth method according to the present invention is not limited to silicon, and may be germanium, gallium arsenide, or the like.

  Note that the root portion of the protrusion integrated with the crystal is the same component as the crystal and is not an impurity. Therefore, if the protrusion is cut out from the extracted crystal, it can be used as it is in a normal crystal.

  The remaining amount of the molten raw material is preferably as small as possible when the crystal pieces are immersed in the molten layer, and by setting this to 30% or less, unidirectional solidification from the bottom of the crucible is maintained for a long time, which is advantageous in terms of quality characteristics. .

  When the molten raw material is supplied from the crucible to the mold, as described above, a heating means may be disposed above the crucible because of the necessity of increasing the temperature of the molten raw material in the crucible. However, in the crystal growth method according to the present invention, it is sufficient if there is a heating means that can keep the crucible warm, and if it is such a heating means, it is sufficient to provide a movable simple heater above the crucible. It is possible to easily immerse the crystal pieces in the molten layer by moving as necessary. Further, if a protective tube for preventing radiation is arranged at a position where the crystal piece is immersed, and the crystal piece is lowered through the protective tube, it is possible to prevent the crystal piece from being melted by receiving radiation from the heater.

  For taking out the silicon crystal, a hanging tool for gripping the protrusion is suitable. However, if vibration is applied to the hanging tool, the silicon crystal can be easily detached from the crucible. The same effect can be obtained by applying vibration to the crucible.

  In supplying the molten raw material to the crucible, the vacuum leak rate of the surrounding environment of the crucible is set to 10 minus 4 Torr · liter / second or less, and the crucible and the in-furnace parts included in the surrounding environment are set to 50 ° C. or more and 200 ° C. or less. It is preferable to hold by heating. In this case, since the water in the crucible and the surrounding environment is removed, the function of the release material can be sufficiently extracted and the crystals can be prevented from adhering to the crucible.

It is a schematic side view of the state which shows the principal part schematic structure of the crystal growth apparatus suitable for implementation of the crystal growth method concerning this invention, and has immersed the crystal piece in the molten layer. It is a schematic side view of the state which transferred the crucible in the state which the molten raw material solidified to the load lock chamber. It is a schematic side view of the state from which the silicon crystal was taken out from the crucible. It is a schematic side view which shows the crystal growth apparatus and raw material melting furnace in the combined state. It is a top view which shows the arrangement | positioning relationship between a crystal growth apparatus and a raw material melting furnace.

  1 to 3 show a schematic configuration of a main part of a crystal growth apparatus suitable for carrying out the crystal growth method according to the present invention. FIG. 1 is a schematic side view of a state in which crystal pieces are immersed in a molten layer, FIG. 2 is a schematic side view of a state in which a crucible with a molten raw material solidified is transferred to a load lock chamber, and FIG. It is a schematic side view of the state taken out from the crucible.

  The crystal growth apparatus 9 is composed of a crucible 1 and a vacuum chamber 2 that accommodates the crucible 1, and the molten raw material 3 in the crucible 1 is placed from the bottom of the crucible in an atmosphere of an inert gas such as helium gas or argon gas. The silicon crystal 8 (hereinafter referred to as silicon crystal 8) is grown by solidifying in the direction. The vacuum chamber 2 is provided with a load lock chamber 2a (a front chamber for maintaining the confidentiality of the vacuum chamber 2) that is isolated from the work chamber for performing the crystal growth process via the sub-gate 6, and on the side thereof, the load lock chamber is provided. A main gate 5 capable of taking in and out articles in the horizontal direction with respect to the inside of 2a is provided. Further, inside the vacuum chamber 2, a pulling mechanism 7 for the crystal piece 4 serving as a hanging tool is provided. As the pulling mechanism 7, a simplified mechanism that is used in the CZ method using a wire cable or the like can be adopted.

  The crucible 1 employs an inner surface coated with a release material and baked. The release material prevents the silicon crystal 8 grown in the crucible 1 from adhering to the inner surface of the crucible 1 and assists the mold release, and SiN is preferable. The firing temperature is preferably 850 ° C. or higher.

  In the crystal growth method using the crystal growth apparatus 9, the molten raw material 3 is supplied to the crucible 1 and solidified in the crucible 1. Then, when the remaining amount of the molten raw material becomes 30% or less, a heater (not shown) disposed above the crucible 1 is moved from above the crucible 1 to immerse the crystal pieces 4 in the molten layer 3a. The state shown in FIG. At this time, the crystal piece 4 may be supported using the pulling mechanism 7. If the heater is provided with a cylindrical protective material that shields or reflects heat radiation to the crystal piece 4, the crystal piece 4 is immersed in the melted layer 3a through the protective material and solidified. May be moved.

  The molten raw material 3 is solidified in a state where the crystal piece 4 is immersed in the molten layer 3a, and after the silicon crystal 8 is formed, the silicon crystal 8 and the crucible 1 are transferred to the load lock chamber 2a while being integrated. Then, the sub gate 6 is closed and the main gate 5 is opened to the atmosphere. At this time, the crystal piece 4 is integrated with the silicon crystal 8, and a protrusion is formed on the surface of the silicon crystal 8. Therefore, the silicon crystal 8 can be easily taken out from the crucible 1 by gripping and lifting the protrusion. The lifting mechanism 7 may be used for the lifting work at this time. Further, if a hanging tool such as a cable for supporting the crystal piece 4 in a state where it is immersed in the molten layer 3a remains connected to the projecting portion and the connected state is sufficiently strong, the hanging tool It may be lifted as it is. In addition, when the lifting operation is performed, it is preferable that the silicon crystal 8 can be easily detached from the crucible 1 if vibration is applied to a hanging tool or a gripping portion that contacts the crystal piece 4 or the crucible 1.

  As described above, according to the crystal growth method using the crystal growth apparatus 9, the molten raw material 3 does not increase in temperature when it is supplied to the crucible 1, thereby reducing the time required for solidification and improving productivity. It becomes possible to make it. Further, by using the fired jar 1 coated with SiN on the inner surface and using the protrusion formed on the surface of the silicon crystal 8, the silicon crystal 8 can be easily taken out from the crucible 1 without being damaged. it can. Therefore, the productivity of the silicon crystal 8 can be improved. Moreover, since the crucible 1 is not damaged when the silicon crystal 8 is taken out, the crucible 1 can be reused also in this respect. Therefore, the crucible 1 after the silicon crystal 8 is taken out can be reused, and the above process can be repeated in the same crucible 1. In this case, since the inner surface of the crucible 1 is purified by reuse, the purity of the silicon crystal 8 can be equal to or higher than that of the silicon crystal 8 when the crucible is used for the first time. That is, the impurity level of the formed silicon crystal 8 can be kept low. In addition, when the crucible 1 after taking out the silicon crystal 8 is reused, it is again coated with SiN and fired as necessary.

  In addition, when the molten raw material 3 is supplied to the crucible 1, the ambient environment of the crucible 1, that is, the vacuum leak rate in the vacuum chamber is set to 10 minus 4 Torr · liter / second or less, and the crucible 1 is included in the ambient environment. It is preferable to heat and hold the in-furnace part at 50 ° C. or higher and 200 ° C. or lower. In this case, moisture in the surrounding environment such as the crucible, the heater, the heat insulating cylinder, and the furnace wall is removed, so that the function of the release material can be sufficiently extracted and the crystal can be prevented from adhering to the crucible.

  Since the base part of the protrusion integrated with the silicon crystal 8 is the same component as the silicon crystal 8 and is not an impurity, if the protrusion is cut out from the extracted silicon crystal 8, it is used as it is in the normal silicon crystal can do.

  The vacuum chamber 2 of the crystal growth apparatus 9 is provided with a supply gate 25 for supplying the molten raw material 3 and receives the supply of the molten raw material 3 from the raw material melting furnace 10 separate from the crystal growth apparatus 9. It has a structure that can. FIG. 4 is a schematic side view showing the crystal growth apparatus and the raw material melting furnace in a combined state. Note that the melting crucible of FIG. 4 shows a cross section for convenience of explaining the state in which the molten raw material is supplied.

  The raw material melting furnace 10 includes a melting crucible 11 and a vacuum chamber 12 that accommodates the melting crucible 11, and melts a crystal raw material in the melting crucible 11 in an atmosphere of an inert gas such as helium gas or argon gas. Can do. Further, a hopper 13 for supplying a solid raw material (polycrystalline silicon or the like) to the melting crucible 11 is provided above the melting crucible 11, and the solid raw material is melted through a supply path 14 extending from the lower portion of the hopper 13. It is supplied to the crucible 11. On the other hand, the vacuum chamber 12 of the raw material melting furnace 10 is provided with a gate 15 for filling the solid raw material, and when the solid raw material in the hopper is reduced, the raw material is replenished through the gate 15. The gate 15 has an air lock structure (not shown) so as not to deteriorate the furnace atmosphere when the raw material is replenished.

  Between the crystal growth apparatus 9 and the raw material melting furnace 10, a supply apparatus 20 for the molten raw material 3 is provided. The supply device 20 includes a serpentine tube structure portion 21 that hermetically connects the crystal growth device 9 and the raw material melting furnace 10, and a supply tube 22 that extends from the melting crucible 11 to the crucible 1 in the serpentine tube structure portion 21. The supply pipe 22 is formed by winding a heating coil around the outer periphery of a transparent quartz tube and covering it with a heat insulating material, and can be moved in the vertical direction and the horizontal direction (in the direction of the arrow in FIG. 4) inside the raw material melting furnace 10 by a pedestal 23. It is supported by. In this case, the raw material melting furnace 10 may be configured to be movable in the direction of the crystal growth apparatus 9. Further, at the end of the serpentine structure portion 21 on the crystal growth apparatus 9 side, the supply pipe 22 is accommodated in the raw material melting furnace 10, so that the crystal growth apparatus 9 and the raw material melting furnace 10 are not illustrated. It has a shut-off function, such as a severing valve. Also in this case, connection and separation can be performed freely by using an air lock structure at the time of connection. Further, each of the crystal growth apparatus 9 and the raw material melting furnace 10 is provided with a pressure reducing valve (not shown) for adjusting the exhaust amount in the furnace, and by changing the opening / closing amount of the pressure reducing valve, The pressure can be adjusted.

  In order to manufacture the molten raw material 3 in the raw material melting furnace 10, first, the gate 15 is opened, the solid raw material is filled in the hopper 13, and then the gate 15 is closed. And the melting raw material 3 can be manufactured by heating the melting crucible 11 in inert gas atmosphere. In the manufacturing process of the molten raw material, the pressure of the raw material melting furnace 10 is set to be higher than that during normal crystal growth, for example, 25 to 650 Torr. Thus, the heat transfer from the heater can be improved by setting the pressure condition for normal crystal growth to be high. On the other hand, heating at a high temperature so as to perform melting for a short time at 25 Torr or less is not preferable because it is likely to cause a bumping phenomenon. The pressure is adjusted by the pressure reducing valve.

  If the molten raw material 3 is manufactured, supply to the crucible 1 is subsequently performed. In this supply operation, first, the raw material melting furnace 10 is connected to the crystal growth apparatus 9 that has been previously depressurized and in an inert gas atmosphere via the serpentine tube structure portion 21. When the crystal growth apparatus 9 and the raw material melting furnace 10 are connected, the pressure is adjusted so that the furnace pressure and the atmospheric conditions of the raw material melting furnace 10 and the crystal growth apparatus 9 are equivalent. After that, the edge-cutting valve is opened and the gantry 23 is moved so that one end of the supply pipe 22 is immersed in the molten raw material 3 of the melting crucible 11 and the other end is disposed in the crucible 1. adjust. At this time, the melting crucible 11 is adjusted to be higher than the quartz crucible 1, and the molten raw material 3 is supplied from the melting crucible 11 to the quartz crucible 1 using the difference in height between the two crucibles 1, 11. In the case of silicon, the transparent quartz tube of the supply tube 22 is preferably maintained at about 1000 ° C. to 1420 ° C. When the supply is completed, the pedestal 23 is moved again so that the entire supply pipe 22 is accommodated in the serpentine tube mechanism portion 21, and the edge cutting valve is closed.

  Note that the pressure of the crystal growth apparatus 9 is preferably adjusted to a reduced pressure level of 10 to 30 tor in order to obtain a reduced pressure state in which the generation of SiO that causes discontinuities in the crystal can be smoothly exhausted. Therefore, when the raw material melting furnace 10 and the crystal growth apparatus 9 are connected, the internal pressure of the raw material melting furnace 10 is set to the internal pressure on the crystal growth apparatus 9 side so that no pressure difference is generated between the both apparatuses 9 and 10. To prevent turbulent flow between devices when opening and closing the edge-cutting valve due to the pressure difference between the furnaces. Therefore, after confirming that the pressures of both devices 9 and 10 are the same, the edge cutting valve is opened and closed.

  As shown in FIG. 5, a plurality of crystal growth apparatuses 9 may be arranged at equal intervals around the raw material melting path 10. In this case, the raw material melting furnace 10 is rotated by a certain angle so that the molten raw material 3 can be supplied to each of the four crystal pulling furnaces 9. Then, the raw material melting furnace 10 is rotated, and the same supply as described above is performed for each crystal growth apparatus 9.

  According to this supply structure, the holding temperature of the crucible 1 for crystal growth is not exposed to a temperature higher than the melting temperature as compared with the conventional method of melting the raw material polycrystal inside the crucible, and therefore the deformation of the crucible 1 Further, it is possible to minimize the seepage of impurities from the inner surface of the crucible 1 to the melt side, which contributes to the improvement of the purity of the grown crystal.

  1 to 3, the vacuum chamber 2 and the load lock chamber 2 a are arranged in the vertical direction, but they may be arranged in the horizontal direction. In addition, as the pulling mechanism, a crystal piece 4 having an enlarged head portion may be used, and a method in which the enlarged head portion is hung on the arm of the heavy article transport device may be used. Furthermore, the crystal formed by this crystal growth method is not limited to silicon, but may be germanium, gallium arsenide, or the like.

DESCRIPTION OF SYMBOLS 1 Quartz crucible 2 Vacuum chamber 3 Molten raw material 4 Crystal piece 5 Main gate 6 Sub gate 7 Pulling mechanism 8 Silicon crystal 9 Crystal growth apparatus 10 Raw material melting furnace 11 Melting crucible 12 Vacuum chamber 13 Hopper 14 Supply path 15 Gate 20 Supply apparatus 21 Serpentine structure Section 22 Supply pipe 23 Base 25 Supply gate

Claims (5)

Supplying a molten raw material to a crucible obtained by coating an inner surface with a release agent and firing, and solidifying the molten raw material while maintaining heating by a movable heater provided above the crucible in the crucible; At the stage where the remaining amount of the raw material becomes 30% or less, the step of immersing the crystal piece in the molten layer to form a protrusion on the surface of the crystal, and the heater after the molten layer in which the crystal piece is immersed is solidified A crystal growth method, wherein the step of moving and taking out the crystal from the crucible using the protrusion is repeated by reusing the same crucible.   The crystal growth method according to claim 1, wherein a hanging tool that grips the protruding portion is used, and the crystal is taken out of the crucible while applying vibration to the hanging tool.   The crystal growth method according to claim 1 or 2, wherein the crystal is taken out of the crucible while applying vibration to the crucible.   4. The crystal growth method according to claim 1, wherein after the crystal is taken out from the crucible, the crucible is recovered, the release agent is applied again, and the crucible is reused.   Before the step of supplying the molten raw material, the vacuum leak rate of the surrounding environment of the crucible is set to 10 minus 4 Torr · liter / second or less, and the crucible and the in-furnace parts included in the surrounding environment are at least 50 ° C. The crystal growth method according to any one of claims 1 to 4, wherein the crystal growth method is held at 200 ° C or lower.

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