JP2012148906A - Product combustion method of single crystal pulling apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust system and a dust treating method capable of treating generated combustible dust, in a silicon single crystal pulling apparatus by CZ method.SOLUTION: The exhaust system in the single crystal pulling apparatus includes an exhaust pipe connected to the single crystal pulling apparatus, a vacuum pump for sucking inert gas supplied to the pulling apparatus through the exhaust pipe, and a filter arranged on the exhaust pipe in front of the vacuum pump, for treating on the front, gas discharged by the vacuum pump, wherein the filter includes a heater capable of heating in correspondence with the component of atmospheric gas. Hereby, unburned combustible dust can be treated sufficiently.

Description

  The present invention relates to a silicon single crystal pulling apparatus and a silicon single crystal pulling method including an accompanying process, and more particularly to an apparatus for processing dust generated during the pulling process and a dust processing method.

  A silicon single crystal wafer used as a substrate of a semiconductor integrated circuit is manufactured by pulling up a silicon single crystal by the Czochralski (CZ) method (including the MCZ method). Here, the CZ method silicon single crystal pulling apparatus exemplified in FIG. 9 and its exhaust gas piping will be described.

  As an inert gas exhaust system of the single crystal pulling apparatus, a vacuum pump 904 is connected to the silicon single crystal rod pulling apparatus 900 via an exhaust pipe 902, and this vacuum pump 904 supplies the pulling apparatus 900 through the exhaust pipe 902. An inert gas (for example, Ar gas) is configured to be sucked. In this inert gas exhaust system, a left end of a supply pipe 906 that supplies an inert gas into the lifting device 900 is connected to an upper portion and a central portion of the lifting device 900, and the right end of the supply tube 906 stores an inert gas. Connected to a tank (not shown). In the inert gas exhaust system configured as described above, when the silicon single crystal rod is pulled up by the pulling device 900, an inert gas is supplied into the pulling device 900 from the supply pipe 906, and the inert gas in the pulling device 900 is supplied. Is sucked by the vacuum pump 904, and the inside of the pulling device 900 is maintained at a predetermined negative pressure.

Further, a filter 908 is provided in the exhaust pipe 902, and gas exhausted to the vacuum pump 904 flows through the filter 908. In the inert gas exhaust system configured as described above, when the silicon single crystal rod is pulled up by the pulling device 900, an inert gas is supplied into the pulling device 900 from the supply pipe 906, and the inert gas in the pulling device 900 is supplied. Is sucked by the vacuum pump 904, and the inside of the lifting device 900 is maintained at a predetermined negative pressure. On the other hand, the inert gas in the lifting device 900 is mixed with dust such as SiO and SiO ₂ . Most of these dusts are separated from such an inert gas and accumulate on the pipe wall (floor) in the exhaust pipe. A part is separated from the inert gas by the filter 908 and deposited.

  In the inert gas exhaust system of the single crystal pulling apparatus 900, after pulling up 8 to 10 single crystal rods and after several hundred hours, the manual leak valve is opened to bring the atmosphere into the pulling chamber and the exhaust pipe. In the case of introduction, since a relatively large amount of combustible dust accumulates in the pulling chamber and the exhaust pipe at this time, these dusts burn rapidly, and the exhaust pipe and the dust chamber Temperature and pressure may rise rapidly. Therefore, each time the single crystal pulling apparatus 900 completes the pulling of the single crystal rod, the atmosphere is introduced into the exhaust pipe 902 of the inert gas exhaust system connected to the pulling apparatus 900, and the dust accumulated in the exhaust pipe 902 is removed. A dust combustion method of an inert gas exhaust system of a single crystal pulling apparatus for burning is proposed (for example, Patent Document 1).

  In addition, the inert gas exhaust system of the single crystal pulling apparatus includes an exhaust pipe 902 connected to the single crystal pulling apparatus 900 and a vacuum pump 904 that sucks an inert gas supplied to the pulling apparatus 900 through the exhaust pipe 902. There has also been proposed a device configured to include a cleaning powder separator (not shown) (for example, Patent Document 2). These methods are effective means for pulling up a crystal having a high resistivity exceeding 1 Ωcm and a boron-doped crystal even if the resistance is lower than that.

JP 2001-09797 A JP 2000-219591 A

  However, in recent years, there has been an increasing need for N-type silicon wafers in which the resistivity required for silicon wafers has been shifted to a lower resistance of 1 Ωcm or less, particularly for producing single crystals of 0.03 Ωcm or less. It has become necessary to dope a relatively large amount of N-type dopant when pulling a single crystal. Some N-type dopants are pyrophoric, such as phosphorus, and if such a material is mixed with a large amount of dust, the risk of ignition may increase.

  As described above, in the silicon single crystal pulling apparatus based on the CZ method, even if it is performed in an inert gas atmosphere, vapor or the like of silicon or partially oxidized silicon (e.g., SiO) is generated in the pulling chamber. It is scattered inside the exhaust system piping, etc., where it condenses and solidifies and accumulates (as dust). For this reason, it is necessary to clean the pulling chamber of the silicon single crystal pulling apparatus and the piping of the exhaust system regularly or irregularly. At that time, the inside of the chamber and the pipe may be exposed to the atmosphere, and there is a possibility that spontaneous combustion such as accumulated dust or local ignition may occur. When dust contains a large amount of phosphorus, the risk of ignition due to friction is particularly strong. Further, since such combustion is a chemical reaction, it may or may not occur depending on various conditions such as temperature when exposed. In general, since the combustion reaction is an exothermic reaction, local ignition may promote combustion of unreacted dust around it. The reaction product generated as a result of combustion is also considered to have characteristics different from the case of high resistance.

  In view of the problems as described above, in the present invention, an exhaust pipe connected to a single crystal pulling apparatus, a vacuum pump for sucking an inert gas supplied to the pulling apparatus through the exhaust pipe, and the vacuum An exhaust system for a single crystal pulling apparatus, comprising: a filter disposed in the exhaust line before a pump and processing a gas exhausted by the vacuum pump in front, wherein the filter is a component of atmospheric gas. Accordingly, an exhaust system including a heater that can be heated can be provided.

  In addition, a method for taking out the pulled single crystal and performing post-processing using such an exhaust system is provided.

More specifically, the following can be provided.
(1) an exhaust line connected to a single crystal pulling device having a valve capable of introducing a gas containing a predetermined amount of moisture and a predetermined amount of oxygen, and from the single crystal pulling device to the exhaust pipe An exhaust valve capable of stopping the flow of gas, a vacuum pump for sucking an inert gas or the like supplied to the pulling device through the exhaust pipe, and the vacuum pump disposed in the exhaust pipe before the vacuum pump A dust box having a filter for treating the gas exhausted by the pump in front, a heater provided to heat the filter, and a leak capable of introducing a gas containing a predetermined amount of moisture and a predetermined amount of oxygen into the dust box An exhaust system for a single crystal pulling apparatus comprising: a valve; and a control device for controlling operations of the exhaust valve, the vacuum pump, the heater, and the leak valve It is possible to provide.

  Here, the predetermined amount of water may include not only water vapor but also water floating particles in the gas, but only water vapor used in absolute humidity described later may be targeted. This is because any form of water affects the combustion of dust, and in measuring absolute humidity, which will be described later, the two are not necessarily distinguished and measured. That is, it is sufficient to define the absolute humidity measured by a person skilled in the art by a usual method. Further, the predetermined amount of oxygen is an amount of oxygen sufficient for dust combustion. For example, it may be oxygen having a ratio or partial pressure similar to that of air, less oxygen, or more oxygen. Moreover, any kind of known heater can be used as the heater. Since a vacuum environment may be used, an electric heater is more preferable. The heater which irradiates a laser beam etc. and heats a heating part may be sufficient. When heated with a heater, activation energy for causing an oxidation reaction can be imparted. As will be described later, the filter is preferably one that can prevent dust from unnecessarily entering functional parts such as a vacuum pump. In this filter, dust that has prevented intrusion may be flammable, and is preferably sufficiently resistant to combustion heat. Moreover, since it is provided in a vacuum path | route, a thing with little degassing is preferable. Furthermore, it is preferable to provide a recyclable material and structure in consideration of economy and the like.

(2) The control device opens the valve on the pulling device side while the vacuum pump is started and burns dust in the piping, then closes the exhaust valve, stops the vacuum pump, and closes the dust box side. It is possible to provide the exhaust system according to the above (1), wherein the leak valve is opened and the filter is controlled to be heated by the heater. Here, the heating by the heater may be controlled according to environmental conditions such as atmospheric pressure, oxygen partial pressure, temperature, and the like.

(3) The gas on the pulling device side is air having a weight absolute humidity of 0.005 kg / kg (DA) to 0.020 kg / kg (DA). The exhaust system described in 2) can be provided. Here, the absolute weight humidity is defined as follows. When the weight of water vapor contained in the humid air is [kg] with respect to the weight [kg] of dry air, the ratio is referred to as absolute weight humidity, and the unit is represented by [kg / kg (DA)]. The relationship between relative humidity and absolute humidity can be expressed by, for example, a wet air diagram (h-X diagram) (for example, the Society for Air Conditioning and Sanitary Engineering). In addition, it is preferable to consider not only water vapor but also water floating in the air in the form of fine particles, but it can be defined simply by using the above-described absolute weight humidity. If this absolute humidity is low, dust combustion is likely to occur suddenly due to static electricity and friction caused by easy movement, and control becomes difficult. Therefore, the absolute absolute humidity is preferably 0.005 kg / kg (DA) or more, More preferably, it is 0.006 kg / kg (DA) or more. In addition, if the absolute humidity is too high, the product resulting from the combustion of dust may take an unfavorable form, so 0.020 kg / kg (DA) or less is preferable, more preferably 0.017 kg / kg (DA). It is as follows. Furthermore, the exhaust system according to (1) or (2) above, wherein the gas on the dust box side is air having a weight absolute humidity of 0.020 kg / kg (DA) or less. . Unlike the pulling device side, the purpose is to further oxidize a substance that has been oxidized to some extent, so there is no problem even if the amount of water is small, and the lower limit is dry air itself.

(4) The exhaust system according to any one of (1) to (3) above, wherein the single crystal pulled in the single crystal pulling apparatus is a silicon single crystal containing phosphorus. . Such phosphorus may be added as a dopant of a silicon single crystal. For example, red phosphorus may be added to the silicon melt. The system of the present invention functions particularly efficiently, for example, when the input amount of phosphorus is 0.5 g or more, more preferably 5 g or more, and further preferably 10 g or more with respect to the silicon raw material per 10 kg, but is not limited thereto. It is not a thing. It goes without saying that the system of the present invention functions more efficiently because the lower the resistivity and the longer the pulling time, the more phosphorus input.

(5) The exhaust system according to (4) above, wherein the filter has an average filter mesh size of 60 to 400 mesh. Here, the mesh is a unit representing the size of the sieve mesh, and is indicated by the number of holes per inch. Therefore, the opening of the sieve depends on the thickness of the wire constituting the filter. However, what is meant by those skilled in the art at the time of filing this application is clear. Moreover, it can also prescribe | regulate with the magnitude | size of the opening of a sieve instead of a mesh. For example, it may be defined by the following table. Moreover, it is preferable to prescribe | regulate by ASTM used generally.

  The mesh size of such a filter is preferably sufficiently fine. However, if it is too fine, clogging is liable to occur and vacuuming becomes difficult, which is not preferable. Therefore, it can be appropriately selected in consideration of the size of the diameter of the particles contained in the dust, the size of the cluster when scattered, and the like. Typically, for example, considering filter efficiency, the average filter mesh size is preferably 60 mesh or more, and more preferably 100 mesh or more. In consideration of the load of the vacuum pump, the average filter mesh size is preferably 400 mesh or less, and more preferably 300 mesh or less.

(6) A single crystal pulling device, an exhaust pipe connected to the single crystal pulling device via an exhaust valve, a first valve for supplying an inert gas to the pulling device, and the pulling device A second valve for supplying a gas containing oxygen, a vacuum pump for sucking the gas in the lifting device through the exhaust pipe, and the vacuum pump disposed in the exhaust pipe before the vacuum pump A single crystal by a system comprising: a dust box provided with a filter for treating the gas exhausted by the front; a leak valve for supplying a gas containing oxygen to the dust box; and a heater installed to heat the filter. A post-treatment method after pulling up, the step of cooling the single crystal pulling device after pulling the single crystal, and the step of closing the first valve And a step of opening the second valve, a step of closing the exhaust valve, a step of stopping the vacuum pump, a step of opening the leak valve, and a step of heating the filter by the heater. A post-processing method can be provided.

(7) For the gas containing oxygen, in the case of the gas from the second valve, the weight absolute humidity is 0.005 kg / kg (DA) to 0.020 kg / kg (DA) air, In the case of the gas from the leak valve, it is possible to provide the post-processing method as described in (6) above, wherein the weight absolute humidity is air of 0.020 kg / kg (DA) or less. Here, the gas from the second valve can have the same or higher weight absolute humidity than the gas from the leak valve. Since the dust box is far from a so-called hot zone and does not easily reach a high temperature, and the purpose is to completely oxidize what has been oxidized to some extent, it is preferable that the dust box is more flammable.

  As described above, in the exhaust system of the present invention, since the heater provided in the filter provided in the exhaust system piping, an oxidation reaction (combustion) that does not occur in an inert gas or vacuum occurred due to the introduction of oxygen. Even if the reaction is not always sufficient, the oxidation reaction can be promoted. For example, even if it is close to the vacuum pump at the end of the exhaust system piping away from the so-called hot zone, dust that may possibly accumulate can be sufficiently treated. Therefore, it is possible to prevent inadvertent ignition when cleaning the piping. It is also possible to control the environment of the oxidation reaction so as not to produce undesirable reactive organisms.

1 is a schematic diagram of an exhaust system according to an embodiment of the present invention. It is a figure which shows the time chart of combustion of the exhaust system of FIG. It is a flow which illustrates the taking-out process of an ingot. 3B is a flow diagram illustrating a part of an exhaust combustion process in the process of FIG. 3A. It is a graph which shows the temperature characteristic of the heater with which the filter of FIG. 1 is equipped. It is a schematic diagram of the filter and heater which can be used for the Example of this invention. It is a schematic diagram of another filter and heater which can be used for the Example of this invention. It is a schematic diagram of another filter and heater that can be used in the embodiment of the present invention. It is a schematic diagram of another filter and heater which can be used for the Example of this invention. In the exhaust system of this invention, the phosphorus added as a dopant summarizes the characteristics of the compounds that may be generated by reaction. It is a figure which shows typically the chemical reaction (when there is much water | moisture content) of phosphorus which can occur in the exhaust system of this invention. It is a figure which shows typically the chemical reaction (when there is little water | moisture content and there exists oxygen) of the phosphorus which can occur in the exhaust system of this invention. The dust sampling position in the preliminary experiment performed for the Example of this invention is illustrated, and the moisture content in the position is put together. It is a figure which shows typically the single crystal pulling apparatus by the conventional CZ method, and its exhaust system.

  Next, embodiments of the present invention will be described with reference to the drawings. In the drawings, components having the same configuration or function and corresponding parts are denoted by the same reference numerals, and description thereof is omitted. Moreover, in the following description, the example of the embodiment which concerns on this invention is shown, and it can change suitably based on the technical common sense of those skilled in the art, without exceeding the range of this invention. Therefore, the scope of the present invention is not limited to these specific examples. Also, these drawings are emphasized for the purpose of explanation, and may differ from actual dimensions.

  FIG. 1 illustrates an exhaust system according to an embodiment of the present invention. The exhaust system 10 includes a single crystal pulling device 12, a supply line system 14 including a leak to the atmosphere, an exhaust line system 16 including a vacuum pump and the like, a supply line system 14 and an exhaust line system 16. A control system 18 including a control device for controlling the operation of In the single crystal pulling apparatus 12, the silicon single crystal is pulled in the chamber 20 by the Czochralski method. In this chamber 20, a supply pipe 22 for supplying an inert gas such as argon as a pulling atmosphere, a leak pipe 24 for atmospheric leakage, and an exhaust pipe for exhausting the exhaust pipe system 16. 26 is connected.

  During single crystal pulling, inert gas such as argon is introduced from the argon supply source 28 of the supply line system 14 of the chamber 20 to eliminate reaction products such as silicon oxide, thereby preventing contamination of the single crystal. Exhaust gas is exhausted through an exhaust pipe 26 from the lower part of the chamber 20. The supply line system 14 is provided with an electromagnetic valve 30 capable of adjusting the argon flow rate. When making the atmosphere of the chamber 20 oxidizing, the pipe 32 is connected to the downstream side of the electromagnetic valve 30. The piping 32 is connected to a first supply source 34 of air (air), a regulator 36, a regulating valve 38, and an electromagnetic valve 40 arranged in that order. The leak pipe 24 connected to the chamber 20 is provided with a leak valve (electromagnetic valve) 42.

  In the exhaust pipe system 16, the exhaust pipe 26 connected to the lower part of the chamber 20 is provided with the ball valve 44, the electromagnetic valve 46 and the valve 48 in this order from the chamber 20, and further, the exhaust pipe 26 is extended. First, a dust box 51 including a filter 50 for filtering dust or the like is provided. The filter 50 is provided so as to be heated by a heater 52 described later. A T-joint portion 56 with a branch pipe that branches to the regulating valve 54 passes through the filter 50 and further extends to the exhaust pipe 26. Beyond that, the exhaust pipe 26 is connected to an exhaust combustion valve 58. The exhaust pipe 26 exiting from the exhaust combustion valve 58 branches from the T joint portion 56 described above, passes through the adjustment valve 54, and is jointed to the branch pipe at the T joint portion 60 again. The exhaust pipe 26 is further connected to a mechanical booster 62 and a vacuum pump 64. A leak pipe is connected to the dust box 51, and a leak valve 51a is provided. A tip of the leak valve 51a is provided with a second supply source 51b capable of supplying air containing a predetermined amount of moisture.

  The exhaust system 10 as described above is controlled by the control device 70 of the control system 18. Specifically, the electromagnetic valves 40 and 42, the heater 52, and the communication line (wireless and / or wired) are used. An exhaust combustion valve 58 is connected and controlled by sending and receiving monitor information and operation commands.

  The pulling by the single crystal pulling device 12 is performed as follows. A quartz crucible (not shown) installed in the chamber 20 is filled with polycrystalline silicon as a raw material, heated by a cylindrical graphite heater (not shown) provided on the outer periphery thereof, and the polycrystalline silicon is melted. A wire is drawn out from a crystal winding mechanism (not shown) at the top of the chamber 20 so that the single crystal seed crystal is immersed in the silicon melt, and the seed crystal is pulled up from the silicon melt while rotating the quartz crucible and the seed crystal in opposite directions. A single crystal is grown to a desired diameter and length. At this time, in order to eliminate reaction products such as silicon oxide, the inside of the chamber 20 is first evacuated by the exhaust line system 16 and then supplied with argon from the supply line system 14. Inside is an inert atmosphere. Thereafter, the argon supply amount and the exhaust amount by the exhaust line system 16 are adjusted so as to obtain a predetermined pressure, the polycrystalline silicon is melted, and the single crystal is pulled up as described above.

  Then, the pulled single crystal rod is drawn into the pull chamber, the gate valve (not shown) is closed, and the main chamber is shut off. Then, after waiting for cooling, it is carried out from a pull chamber door (not shown) for taking out a single crystal rod provided in the pull chamber. After completion of taking out the single crystal rod, during the growth of the single crystal, the chamber 20 of the pulling device 12, a crucible, a heater, an in-furnace member such as a heat insulating material (hereinafter sometimes referred to as a hot zone), or mainly an exhaust pipe system Dust (mainly silicon oxide) adhering to 16 is removed, consumable parts and the like are replaced, and the single crystal pulling device 12 is disassembled and maintained in preparation for the next pulling. This silicon oxide is generated, for example, by a chemical reaction between oxygen in a crucible made of quartz and molten silicon, and at the time of pulling a single crystal, not only inside the chamber 20 but also outside the chamber 20 as a gas or fine particles due to high temperature. Also splashes.

  Here, as described above, the dust made of silicon oxide does not stay in the chamber 20 but also adheres and accumulates in the exhaust pipe system 16. Such silicon oxide is, for example, an unstable compound such as SiO. When it comes into contact with oxygen contained in the atmosphere or the like, it spontaneously burns when heated / heated, such as silicon dioxide. Furthermore, it becomes a stable oxide. In addition to silicon oxide, such dust includes a dopant element doped into a silicon single crystal. For example, boron, phosphorus, antimony, arsenic and the like. Conventionally, these dopants were not so much in quantity, so they did not have much influence on dust. However, in recent years, the use of silicon single crystals added in large quantities has increased, and it has become impossible to ignore them. For example, phosphorus is charged into a crucible as red phosphorus and dissolved in a silicon melt. Red phosphorus is a reddish brown odorless solid, which is considered as a solid solution of purple phosphorus and yellow phosphorus, and has a melting point of 589.5 ° C. (43.1 atm). Therefore, during the pulling of the single crystal, it may be scattered as red phosphorus or as a phosphorus compound and mixed into the dust. In some cases, white phosphorus (ignition point: 34 ° C.) that can ignite spontaneously becomes dust. It may be mixed.

  In the past, when opening and cleaning the inside of the chamber and the exhaust pipe system, dust made of silicon oxide or the like was ignited by the introduction of the atmosphere. When such dopants are added, the ignition may be unexpected. For example, if the atmosphere was introduced, all the reactive dusts burned and there was no risk of subsequent ignition, but not all dust was burned by the introduction of the atmosphere, It was found that there was a phenomenon of ignition triggered by something. In particular, it seems that many such phenomena occur when phosphorus described above is mixed in dust.

  For example, in FIG. 1, dust accumulation is recognized not only in the chamber 20 but also in the exhaust pipe 26, but not only in the vicinity of the valve 48 of the exhaust pipe 26, but also in the filter 50 that is the extension destination. Dust accumulation was also observed. When the atmosphere is introduced, the dust accumulated in the chamber 20 and around the valve 48 immediately spontaneously burns, receives the activation energy from the combustion (exothermic reaction), and also includes the parts that do not lead to spontaneous combustion. And burned easily. In addition, some dust accumulated in the vicinity of the filter 50 may spontaneously burn, but the portion that does not reach the spontaneous combustion is not necessarily sufficiently burned by receiving the activation energy by the spontaneous combustion. Turned out to be. That is, conventionally, dust containing an unstable compound such as SiO is easily combusted by introduction of air into a more stable compound. However, it is not always easy to combust depending on the place where dust accumulates. It has been found. And it is thought that the part which does not lead to spontaneous combustion occurs when sufficient activation energy due to heat cannot be obtained. In particular, when a dopant such as phosphorus is mixed, it is not a heat trigger, for example, when cleaning is performed after the atmosphere has been sufficiently introduced by supplying thermal energy from combustion generated from ignition triggered by friction or the like. It can cause ignition.

For example, the following exothermic reaction can be considered.
Formula 1)
_{SiO + O 2/2 → SiO} 2
Formula 2)
P + (3/4) O ₂ → (1/4) P ₄ O ₆

Here, P ₄ O ₆ is also called diphosphorus trioxide and is a colorless liquid. As will be described later (see FIG. 5), this decomposes at 210 ° C. and becomes red phosphorus and oxide (P: O˜1: 2). Red phosphorus is a reddish brown powder and is an allotrope of yellow phosphorus (Class 3), but is more stable and relatively safe (non-toxic) than yellow phosphorus. The ignition point of red phosphorus is 260 ° C. A heater 52 is configured and arranged in the filter 50 so that activation energy for reaction as in the above equation can be applied. For this reason, the stabilization reaction like the above formula can be sufficiently performed even in the vicinity of the filter 50.

  FIG. 2 illustrates a time chart of the combustion circuit of the exhaust system of the present invention. The following steps will be described together with the flowcharts of FIGS. 3A and 3B. After the pulling by the single crystal pulling device 12 is completed, the ingot is taken out (FIG. 3A). That is, after sufficient cooling is performed (S10), the valve 48 is fully opened (S12), and the electromagnetic valve 30 of the argon supply pipe 22 is closed (S14). Thereby, the inside of the chamber 20 is depressurized, and it is confirmed that the pressure becomes a predetermined pressure (for example, 0.8 Torr) or less (S16). Then, the exhaust combustion process (S18) shown in FIG. 3B is performed. In the exhaust combustion process, the exhaust combustion start button on the operation panel of the control device 70 is pressed (S40), and the electromagnetic valve 40 (if the amount of moisture in the atmosphere is a predetermined amount) to introduce air containing a predetermined amount of moisture. The electromagnetic valve 42 for introducing air may be opened (S42). Two minutes later, when the inside of the chamber 20 reaches a predetermined pressure in the furnace (for example, 3 to 30 Torr) (S44), the pipe switching valve operation is performed and the adjustment valve 54 exhausts a predetermined amount of gas by the vacuum pump 64. The exhaust combustion valve 58 is closed (S46). In this state, it is left for about 60 minutes (S48), and the reaction between oxygen in the atmosphere and dust is caused to occur stably. Thereby, the dust in the exhaust pipe 26 mainly burns stably. Thus, it is preferable that the dust in the exhaust pipe 26 is burned by introducing air from the single crystal pulling device 12 while the vacuum pump 64 is operated. At this time, if dry air is introduced, there is a risk that phosphorus will ignite due to friction. Therefore, it is preferable to control the humidity of the introduced air. As a result, the dust containing phosphorus also helps the chemical reaction of phosphorus, and burns stably while preventing sudden ignition due to friction. The inside of the exhaust pipe 26 may be close to the single crystal pulling device 12, and the temperature is high, and it is considered that the combustion is almost completely oxidized by this combustion. Here, considering the dust containing phosphorus, if the dust is exposed, friction occurs due to the movement of the dust due to the pressure change, and the phosphorus may spontaneously ignite. On the other hand, when a large amount of moisture is introduced to prevent spontaneous ignition, phosphorus reacts to produce a clay-like substance, and when this clay-like substance is conveyed to the mechanical booster 62 and the vacuum pump 64, There is a possibility that the mechanical booster 62 and the vacuum pump 64 may be stopped.

  When the main combustion is completed and the pressure in the chamber 20 reaches about 200 Torr, the electromagnetic valve 40 (or 42) is closed (S50). Then, the end buzzer sounds (S52), and the end button is pressed (S54). Next, the ball valve 44 is closed, and the exhaust pipe line system 16 is shut off from the chamber 20 (S56). Argon is introduced into the chamber 20 from the supply line system 14, and the inside of the furnace becomes normal pressure (S58). On the other hand, the combustion in the exhaust pipe 26 is finished and the pressure is reduced by the vacuum pump 64. In this state, it is considered that unburned dust is present in the dust box 51 and in the vicinity of the filter 50. Therefore, preparation for introduction of air having a predetermined moisture content is performed in order to sufficiently perform the combustion reaction. That is, the adjustment valve 54 is closed (S60), the vacuum pump 64 is stopped (S62), and the dust box 51 and / or the filter 50 are heated by the heater 52. Then, the leak valve 51a is opened, and air having a predetermined moisture content is introduced from the supply source 51b. As described above, when the combustion of the exhaust pipe 26 is completed, the pump is stopped and the air is introduced into the dust box 51 in the dust box 51 where sufficient oxygen has not been supplied by the introduction of air from the single crystal pulling device 12 side. This is because oxygen is also supplied to the dust and can burn sufficiently. At this time, it is preferable to appropriately control the air humidity as described above. By heating the heater and introducing air, the dust in the dust box 51 is stably and sufficiently burned. This is because the temperature inside the dust box is lower than that of the exhaust pipe 26 on the single crystal pulling device 12 side, and dust may not be sufficiently combusted only by the introduction of the atmosphere. it can. When the heater 52 is switched on and heated, the heater temperature is preferably 500 ° C. in a short time.

  The temperature characteristic of this heater is shown in the graph of FIG. 4A. When the heater heating is started, the maximum temperature of 500 ° C is quickly reached, but by that time, the temperature of the surrounding members has also become sufficiently high, and the compounds in the unreacted dust (especially including phosphorus) start burning. To do. When the combustion is started, the heat energy for activation can be sufficiently covered by the calorific value of the combustion, so the heater 52 is switched off. Then, the combustion of dust near the filter 50 is confirmed from a window provided in the filter box 51 that houses the filter 50, and the ignition completion lamp is turned on. Then, after the dust in the vicinity of the filter 50 is sufficiently burned, there is substantially no unstable compound to be burned, and the fire is naturally extinguished. Thereby, the process of the combustion process accompanying the atmospheric introduction of the exhaust system is completed. Then, the combustion valve 58 is opened (S64), and the vacuum pump 64 is turned on (S66) to exhaust the exhaust line system. Then, the pull chamber is opened (S20), and the ingot is taken out (S22). In this way, a series of ingot removing steps is completed, and the next step, the chamber 20 and the exhaust pipe line system 16, can be cleaned.

  On the other hand, the chemical reaction of dust when introduced into the atmosphere is not limited to the above formulas 1 and 2, but it has been found that other reactions occur due to water vapor or moisture in the atmosphere. Therefore, when introducing air such as the atmosphere, it is preferable to control the amount of moisture in the introduced gas. In particular, when phosphorus is contained in the dust, some produced compounds may affect the vacuum pump. Therefore, it is preferable to consider this influence.

  4B to 4E are schematic views of a filter with a heater applicable to the embodiment of the present invention. In each figure, the upper surface of the cylindrical casing is removed, and a part of the front side surface is broken so that the inside can be seen. FIG. 4B is a cutaway perspective view schematically showing a main body portion of the filter 100 applicable to the embodiment of the present invention. The filter 100 is mainly configured by a cylindrical casing 110 having a mesh 102 that functions as a disk-shaped filter at the lower end. On the inner side surface of the casing 110, a band heater 104 is arranged along the side surface almost immediately above the mesh 102, and the filter 100 is heated from the outer peripheral side of the mesh 102 and from the lower inner surface of the casing 110. can do. This filter and the next filter are provided with windows (not shown) on the upper surface so that the inside can be observed. Although FIG. 4C shows another example, the heater 105 is arrange | positioned on the mesh 102 in the shape which hits a wave. Since the configuration other than the heater is the same as that of FIG. In this method, the possibility that the dust directly contacts the heater 105 is increased, and the ignition / ignition of the dust can be promoted more easily. Although FIG. 4D shows another example, unlike the filter of FIG. 4C, the heaters 106 are arranged on the mesh 102 at almost equal intervals. Further, a glass window 112 is provided on the right side of the housing 110 so that the inside can be observed. In FIG. 4E, the filter plate 108 functioning as a filter is conductive and can be heated by energization. This filter plate 108 is fixed insulatively from the housing 110, and has a structure that can be in contact with an electrode as necessary. An example of such a conductive filter is disclosed in Japanese Patent Laid-Open No. 7-60036, for example. In this invention, it is a filter that collects particulate matter, that is, particulates, the filter is made conductive, the particulates collected by the filter are heated uniformly by energizing the filter, and the particulates are It can be burned uniformly. In this system, dust accumulated on the filter can be heated uniformly, and unburned residue can be effectively prevented. In this case, a sensor 113 capable of observing the combustion state inside the glass window 112 may be provided. For example, the sensor 113 can observe a flame caused by dust combustion and perform various controls (for example, on / off of a heater switch, opening / closing of a valve, etc.). This makes it easier to manage the combustion of dust.

  FIG. 5 summarizes the characteristics of phosphorus compounds. It is thought that phosphorus oxide is first generated by the combustion of phosphorus mixed in the dust described above, but the main product is considered to be phosphorous trioxide. When this reacts with water in a filter box or the like to produce phosphoric acid (phosphonic acid), there is a risk of promoting the reaction with the contacting wall material or the like due to its strong reducibility. In addition, since phosphoric acid (orthophosphoric acid) is an acid, there is a concern about reaction with the wall material and the like that come into contact with the phosphoric acid (orthophosphoric acid).

Here, based on FIGS. 6 and 7, the reaction of scattered phosphorus will be considered. FIG. 6 considers the case where a relatively large amount of water is present. The phosphorus (Px) in the dust first becomes phosphorus oxide (PxOy), reacts with moisture adhering to the wall surface, etc., generates H ₃ PO ₄ (Liq), and forms a clay together with silicon oxide (including SiO ₂ ). It is thought to form a substance. Since this clay-like substance is thought to contain phosphoric acid (orthophosphoric acid), it is reactive as an acid and requires caution.

On the other hand, when there is not much water, as shown in FIG. 7, phosphorus (Px) in the dust first becomes phosphorus oxide (PxOy), reacts with surrounding oxygen, and P ₄ O ₆ (Liq) or ( It is thought that PO ₂ ) _n is produced and a clay-like substance is formed with silicon oxide (including SiO ₂ ). Since this clay-like substance is thought to contain phosphoric acid (phosphonic acid), it is reducible and requires caution. When the moisture content contained in the dust was measured in the model exhaust system, the results shown in FIG. 8 were obtained. In this case, the result is obtained for a sample collected after the inside of the exhaust pipe is opened to the atmosphere without using the heater in the filter section. The measurement was based on the vaporization method, and a Karl Fischer moisture meter was used. It can be understood from this that since the water amount is not large in any place, it is unlikely that the dust has become a clay-like shape through combustion or the like due to a large amount of water as shown in FIG. Moreover, although it is slightly, it is estimated that the amount of water | moisture content is reducing, so that it goes to a vacuum pump, and the compound of phosphorus also changes according to it. Accordingly, the selection of the material and the like is preferably in accordance with the site.

  From the above, it can be seen that the material of the filter 50 and the portion of the filter box in which the filter 50 is placed in contact with the dust is preferably difficult to react with these compounds. For example, stainless steel such as SUS304.

DESCRIPTION OF SYMBOLS 10 Exhaust system 12 Single crystal pulling apparatus 14 Supply line system 16 Exhaust line system 18 Control system 20 Chamber 22 Supply pipe 24 Leak pipe 26 Exhaust pipe 28 Argon supply source 30 Electromagnetic valve 32 Pipe 34 Air supply source 36 Regulator 38 Adjustment Valve 40 Electromagnetic valve 42 Leak valve (electromagnetic valve) 44 Ball valve 46 Electromagnetic valve 48 Valve 50 Filter 52 Heater 54 Adjustment valve 56 T joint part 58 Exhaust combustion valve 60 T joint part 62 Mechanical booster 64 Vacuum pump 100 Filter 102 Mesh 104, 105, 106 Heater 108 Filter plate

Claims (7)

An exhaust line connected to a single crystal pulling apparatus having a valve capable of introducing a gas containing a predetermined amount of moisture and a predetermined amount of oxygen;
An exhaust valve capable of stopping the flow of gas from the single crystal pulling device to the exhaust pipe;
A vacuum pump for sucking the inert gas supplied to the lifting device through the exhaust pipe;
A dust box provided with a filter disposed in the exhaust pipe and treating the gas exhausted by the vacuum pump before the vacuum pump;
A heater provided to heat the filter;
A leak valve capable of introducing a gas containing a predetermined amount of moisture and a predetermined amount of oxygen into the dust box;
An exhaust system for a single crystal pulling apparatus, comprising: an exhaust valve, the vacuum pump, the heater, and a control device that controls operations of the leak valve.   2. The exhaust according to claim 1, wherein the controller closes the exhaust valve, stops the vacuum pump, opens the leak valve, and controls the filter to be heated by the heater. system.   In the case of the gas from a valve provided in the single crystal pulling device, the gas is air having a weight absolute humidity of 0.005 kg / kg (DA) to 0.020 kg / kg (DA), and the leak The exhaust system according to claim 1 or 2, wherein the gas from the valve is air having a weight absolute humidity of 0.020 kg / kg (DA).   The exhaust system according to any one of claims 1 to 3, wherein the single crystal pulled by the single crystal pulling apparatus is a silicon single crystal containing phosphorus.   The exhaust system according to claim 4, wherein the filter has an average filter mesh size of 60 to 400 mesh. A single crystal pulling device;
An exhaust line connected to the single crystal pulling device via an exhaust valve;
A first valve for supplying an inert gas to the lifting device;
A second valve for supplying a gas containing oxygen to the pulling device;
A vacuum pump for sucking the gas in the lifting device through the exhaust pipe;
A dust box provided with a filter disposed in the exhaust pipe and treating the gas exhausted by the vacuum pump before the vacuum pump;
A leak valve for supplying a gas containing oxygen to the dust box;
A post-treatment method after pulling up the single crystal by a system comprising a heater installed to heat the filter,
After the single crystal pulling, cooling the single crystal pulling device;
Closing the first valve;
Opening the second valve;
Closing the exhaust valve;
Stopping the vacuum pump;
Opening the leak valve;
Heating the filter with the heater.   In the case of the gas from the second valve, the oxygen-containing gas is air having a weight absolute humidity of 0.005 kg / kg (DA) to 0.020 kg / kg (DA), and from the leak valve The aftertreatment method according to claim 6, wherein in the case of the gas, the air has an absolute humidity of 0.020 kg / kg (DA) or less.

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