JP4957385B2 - Method for producing silicon single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon single crystal for producing a silicon single crystal by the Czochralski method, and particularly to a method for producing a silicon single crystal using a raw material silicon ingot pulled up by the Czochralski method as a raw material.

  There are various methods for producing a silicon single crystal used for a semiconductor substrate. Among them, the Czochralski method (hereinafter referred to as “CZ method”) is widely adopted.

  FIG. 1 is a diagram schematically showing a main configuration of a pulling apparatus suitable for pulling a silicon single crystal by the CZ method. The pulling device has an outer wall constituted by a chamber (not shown), and a crucible 1 is disposed at the center thereof. The crucible 1 has a double structure and is fitted with a quartz inner-layer side container (hereinafter referred to as “quartz crucible”) 1a having a bottomed cylindrical shape to hold the outside of the quartz crucible 1a. A bottomed cylindrical graphite outer layer side container (hereinafter referred to as “graphite crucible”) 1b.

  The crucible 1 is fixed to the upper end of a support shaft 6 that can rotate and move up and down. On the outside of the crucible 1, a resistance heating type heater 2 is disposed substantially concentrically so as to surround the crucible 1. Above the crucible 1, a pulling shaft 5 such as a wire rotating at a predetermined speed in the reverse direction or in the same direction on the same axis as the support shaft 6 is disposed. Is attached.

  When pulling up a silicon single crystal for semiconductors using such a pulling apparatus, polycrystalline silicon raw materials of various shapes such as rods, lumps or granules used as raw materials for silicon single crystal production are used. A predetermined amount is put into the quartz crucible 1a, and the silicon raw material is melted in the crucible 1 by heating with the heater 2 in an inert gas atmosphere under reduced pressure. Thereby, the melt 3 is stored in the crucible 1. Thereafter, the seed crystal 7 held at the lower end of the pulling shaft 5 is immersed in the surface of the melt 3 in the crucible 1, and the pulling shaft 5 is gradually lifted upward while rotating the crucible 1 and the pulling shaft 5. Thereby, the silicon single crystal 4 grows below the seed crystal 7, and the silicon single crystal 4 for semiconductor grown in a substantially columnar shape is obtained.

  The ingot of the silicon single crystal 4 obtained by the CZ method is cut into predetermined blocks. Since the end material generated by this cutting process is high in purity, it is reused again as a silicon raw material for semiconductors.

  On the other hand, the solidified silicon melt (hereinafter referred to as “crucible silicon residue”) remaining at the bottom of the quartz crucible 1a after the silicon single crystal 4 is pulled up is used as a silicon raw material for solar cells. In this use, in order to remove the attached quartz pieces that are harmful impurities for the solar cell, for example, in Patent Document 1, silicon such as a crucible residual silicon lump with attached quartz is predetermined using a rotary grinder. After the pulverization under the above conditions, there has been proposed a quartz removal method in which a portion having a large amount of quartz and having a small particle size is removed by sieving or specific gravity separation.

  As a silicon raw material for solar cells, in addition to the residual silicon crucible, those having a high impurity concentration and not satisfying the purity required as a silicon raw material for semiconductors are used. This is because the quality standard of the raw material for solar cells is significantly looser than that of the raw material for semiconductors, and there is no problem even if the impurity concentration in the silicon raw material is somewhat high.

JP 2002-37617 A

  By the way, as a silicon raw material for a semiconductor, a high-purity material having an extremely low impurity concentration is required. However, in recent years, due to a demand for a silicon raw material for a solar cell, for which demand is rapidly increasing, etc. There is a shortage of silicon raw materials, and stable raw material procurement is difficult.

  Under such circumstances, it is not sufficient to reuse the above-mentioned silicon single crystal ingot mill as a silicon raw material for semiconductors, and a crucible residual silicon lump that is not normally used or a non-standard raw material with a high impurity concentration. If it can be used, it will be possible to procure raw materials at low cost and stably, which is desirable from the viewpoint of reducing manufacturing costs.

  However, when these crucible residual silicon lumps or the like are used as they are as raw materials for semiconductors, the following problems are caused. Not only does the concentration of impurities such as metals in the silicon single crystal increase extremely, but also the carbon concentration and lifetime value increase, resulting in sites that do not meet the standards. Further, when a silicon single crystal having a very high impurity concentration flows to a subsequent process, particularly in a wafer processing process, the entire process line is contaminated, and the contamination may spread to the wafer line or the entire factory.

  Accordingly, the present invention has been made in view of the above problems, and provides a method for producing a silicon single crystal that can stably procure raw materials at low cost and can produce a high-quality silicon single crystal having a low impurity concentration. It is intended.

  The present inventor has intensively studied to achieve the above object, and in the process, has focused on the phenomenon of segregation of impurity elements during crystal growth by the CZ method. In other words, impurities contained in the silicon melt before pulling are divided into a solid phase silicon crystal and a liquid phase silicon melt in the process of pulling, but in the silicon crystal, the impurities are compared with those in the silicon melt. The concentration is very low. Finally, the silicon melt remaining in the crucible solidifies to form a residual crucible silicon mass, and the impurity concentration in the residual crucible silicon mass becomes extremely high.

  This is because the solubility of impurities in the solid phase silicon crystal and the liquid phase silicon melt are different from each other, and the ratio “solubility in the solid phase / solubility in the liquid phase” is called the segregation coefficient. It is constant when the impurity concentration is small.

  For example, when the impurities are copper, aluminum, and carbon, each segregation coefficient is as shown in Table 1 below.

  Copper is an element used in a part of the pulling apparatus, and aluminum is an element contained as an impurity in the quartz crucible. Carbon is also used as a hot zone component in a lifting device such as a graphite crucible that supports a quartz crucible, a heater disposed around the crucible, and the like. All of these elements are easily mixed into the silicon single crystal as impurities.

FIG. 2 is a diagram showing the relationship between the solidification rate and impurity concentration in silicon single crystal growth. It is obtained from the following known formula (1) that gives impurities concentration [C] _S in the solid phase when the impurities are copper, aluminum and carbon and the solidification rate is g. The “solidification rate” is the ratio of the mass ratio of the silicon single crystal to the amount of silicon melt in the quartz crucible before pulling up the crystal.

[C] _S = k ₀ [C] ₀ (1-g) ^k0-1 (1) Equation Since the diffusion of impurities in the solid phase is ignored, the solidification rate is calculated from this equation (1). Impurity concentration in the solid phase corresponding to the change is obtained. In equation (1), k ₀ is the segregation coefficient of each impurity, and [C] ₀ is the initial concentration of impurities in the liquid phase (silicon melt in the quartz crucible) before solidification begins, and copper, aluminum For both carbon and carbon, 1 × 10 ¹⁵ atoms / cm ³ was used.

  In FIG. 2, the vertical axis represents the impurity concentration of the silicon single crystal, and the horizontal axis represents the solidification rate.

As is apparent from FIG. 2, the impurity concentration in the solid phase, that is, in the silicon crystal, is significantly lower than the impurity concentration in the silicon melt (1 × 10 ¹⁵ atoms / cm ³ ). For all of copper, aluminum, and carbon, the impurity concentration is low on the top side of the silicon crystal (the solidification rate is close to 0), gradually increases as the solidification rate increases, and the bottom side (the solidification rate is 1). It is getting higher rapidly on the side close to.

  Then, by growing the crystal by the CZ method, the impurity concentration in the obtained crystalline silicon ingot can be reduced. In particular, except for the bottom side where the solidification rate is close to 1.0, the average impurity in the crystalline silicon ingot The concentration can be very low.

  Based on such a segregation phenomenon of impurities, if a crucible residual silicon lump or other silicon material with a high impurity concentration and not normally used as a silicon raw material for semiconductors is used, a crystalline silicon ingot with a reduced impurity concentration is used. Obtainable. That is, a silicon raw material that is not normally used as a raw material for semiconductors, that is, a silicon raw material for manufacturing a silicon single crystal, is melted in a quartz crucible, and crystal pulling is performed from this raw material by the CZ method. A crystalline silicon ingot equivalent to the silicon raw material for production can be purified.

  Then, the crystalline silicon ingot (hereinafter sometimes referred to as “raw material silicon ingot”) as a silicon raw material for producing a silicon single crystal is melted in a quartz crucible, and the crystal is pulled from this silicon melt by the CZ method. As a result, a high-quality silicon single crystal having a low impurity concentration can be obtained.

  For example, the crystal pulling by the CZ method is performed twice, the raw material is purified by the first pulling, the obtained raw material silicon ingot is melted again in a quartz crucible, and the product is obtained by the second pulling. An operation method of obtaining a silicon single crystal can be employed. According to this operation method, a high-purity raw material silicon ingot can be refined using a silicon raw material that is not used as a raw material for semiconductors in the first stage, and a high quality is obtained using the raw material silicon ingot in the next stage. The silicon single crystal can be manufactured.

  The present invention is based on such a technical idea, and the gist thereof is as follows.

A method for producing a silicon single crystal according to the present invention includes a step of melting a silicon melt solidified at the bottom of a quartz crucible after pulling up the silicon single crystal, and a raw material silicon ingot by the CZ method from the melt obtained by melting the solidified product. A raw material ingot growing step for pulling up and a raw material silicon ingot obtained in the raw material ingot growing step are suspended and supported, supplied from above into the crucible and melted, and then a silicon single crystal is pulled up from this silicon melt by the CZ method And a silicon single crystal growing step.

With such a structure, the silicon ingot remaining in the bottom of the quartz crucible after being pulled up is a silicon raw material that is inherently unsuitable and not used as a raw material for semiconductors, that is, a silicon single crystal, by the raw material ingot growing process. using things, it can be purified with high purity of the material silicon ingot as a raw material for producing a silicon single crystal, silicon by single crystal growth process, using the raw material silicon ingot as a raw material, low impurity concentration of high quality silicon single Crystals can be produced. At that time, the silicon raw material in the raw material ingot growing step is not limited to the silicon raw material for producing the silicon single crystal, and thus the raw material can be procured stably at a low cost. Moreover, in the silicon single crystal growth process, the raw silicon ingot is suspended and supported without being crushed, so that prior to that, there is no need for a process that reduces the production efficiency such as the raw silicon ingot crushing process or cleaning process. It is.

  Here, from the viewpoint of increasing the production efficiency in the silicon single crystal growth step, in the silicon single crystal growth step, the raw material silicon ingot is suspended and supported through a seed crystal, and the silicon melt in the crucible is supported by the silicon melt. It is preferable that the silicon single crystal is pulled up by subsequently immersing the seed crystal.

  Furthermore, from the viewpoint of increasing the production efficiency as a whole, the raw material silicon ingot is preferably configured as a single piece without separating the seed crystal after the raw material ingot growing step.

  As so-called recharge for improving the productivity of the silicon single crystal, in the silicon single crystal growth step, the silicon single crystal is pulled up by the Czochralski method in advance, and then the residual silicon melt remaining in the crucible A raw material silicon ingot can be supplied and melted to pull up the silicon single crystal.

  As a so-called additional charge for improving the productivity of the silicon single crystal, in the silicon single crystal growth step, the raw silicon ingot is supplied to the initial silicon melt previously melted by being introduced into the crucible and melted. The silicon single crystal can be pulled up.

  Further, from the viewpoint of further increasing the production efficiency in the silicon single crystal growth step, the raw material silicon ingot classified according to a predetermined weight is produced in the raw material ingot growth step, and the silicon single crystal growth step It is preferable to select and use the raw material silicon ingot according to the weight of the crystal.

  According to the method for producing a silicon single crystal of the present invention, raw material procurement can be stably performed at low cost, and a high-quality silicon single crystal having a low impurity concentration can be produced.

  Below, the manufacturing method of the silicon single crystal of this invention is explained in full detail, referring drawings.

  The method for producing a silicon single crystal according to the present invention mainly includes an initial stage raw material ingot growing process and a next stage silicon single crystal growing process. In the raw material ingot growing step, a silicon raw material that is not used as a raw material for producing a silicon single crystal is melted, and the raw silicon ingot is pulled up from this melt by a CZ method. In the silicon single crystal growth step, the raw material silicon ingot obtained in the raw material ingot growth step is suspended and supported, supplied into the crucible from above and melted, and then the silicon single crystal is pulled up from this silicon melt by the CZ method.

  In a simple example, the crystal pulling by the CZ method is performed twice, the raw material is purified by the first pulling, the obtained raw material silicon ingot is melted in a quartz crucible, and the second pulling is performed. This is a manufacturing method for obtaining a silicon single crystal as a product.

  First, the raw material ingot growing process will be described.

  FIG. 3 is a diagram schematically illustrating the flow of a raw material ingot growing step in the method for producing a silicon single crystal of the present invention. As shown in FIG. 3 (a), a crucible residual silicon lump 8 which is a silicon raw material that is not used as a raw material for producing a silicon single crystal is introduced into a quartz crucible 1a, and the silicon as shown in FIG. 3 (b). The raw material is melted to obtain a melt 9.

  Subsequently, as shown in FIG. 3C, the seed crystal 7 is immersed in the surface of the melt 9 in the quartz crucible 1a and pulled upward. As a result, as shown in FIG. 3D, a silicon crystal grows below the seed crystal 7, and a crystalline silicon ingot 10 is obtained.

  Since the crystalline silicon ingot 10 is purified by crystal growth by the CZ method as described above, the impurity concentration is low and is equivalent to a silicon raw material for producing a silicon single crystal. In the method for producing a silicon single crystal of the present invention, a silicon single crystal is produced by the CZ method using the thus obtained crystalline silicon ingot 10 as a raw material in the next stage silicon single crystal growth step. In that sense, the crystalline silicon ingot 10 is hereinafter referred to as a raw material silicon ingot 10.

  Here, as a silicon raw material used in the raw material ingot growing process and not used as a raw material for manufacturing a silicon single crystal, in addition to the residual crucible silicon mass 8 illustrated in FIG. 3, the impurity concentration is high and the required purity is not satisfied. Various silicon raw materials that cannot be used directly as polycrystalline silicon lumps and other raw materials for producing a silicon single crystal can be used. Note that a lot of quartz pieces peeled off from the quartz crucible 1a are attached to the residual crucible silicon lump 8, and it is necessary to remove the quartz pieces in use. For this purpose, for example, the residual silicon lump 8 with the quartz pieces adhered is immersed in hydrofluoric acid to dissolve the quartz pieces, and further etched with hydrofluoric acid to remove contaminants attached to the raw material surface. In addition, a method of performing pure water cleaning is suitable. Thereby, the quartz piece can be completely removed.

  There are no particular limitations on the conditions during crystal growth for obtaining the raw material silicon ingot 10. Either high-speed growth or low-speed growth may be used, and the raw silicon ingot 10 obtained by the growth may be either dislocation-free or dislocation-free. The quartz crucible 1a to be used is not limited to a new one, but is a used one that has been once used for pulling up a silicon single crystal or a raw silicon ingot 10 and is subjected to acid cleaning or high-temperature heat treatment for regeneration treatment. Also good.

  Moreover, there is no restriction | limiting also about the diameter of the raw material silicon ingot 10 to grow. Therefore, from the viewpoint of increasing the efficiency of crystal growth and reducing the manufacturing cost, it is desirable that the growth is performed under conditions that allow high-speed growth in which crystal growth is performed at the highest possible pulling rate and that a crystal having the maximum diameter that can be grown is obtained. In addition, since the raw material silicon ingot 10 is melted again as a raw material in the silicon single crystal growth step, it may be a pulling condition for obtaining a dislocation-free crystal, or a growing condition for crystal dislocation. .

  However, as shown in FIG. 2, the impurity concentration in the raw silicon ingot 10 changes according to the solidification rate. Generally, impurities are low on the top side of the raw material silicon ingot 10 with a low solidification rate, and impurity concentrations are high on the bottom side with a high solidification rate. On the other hand, the yield of the raw silicon ingot 10 depends on how much the solidification rate is taken and the pulling is finished. Therefore, in the raw material ingot growing process, it is preferable to finish the pulling up with an optimum solidification rate while taking into consideration both the impurity concentration and the yield of the raw material silicon ingot 10.

In particular, as shown in FIG. 2, if the concentration of each impurity (carbon, copper, aluminum) in the silicon melt before the start of crystal pulling is 1 × 10 ¹⁵ atoms / cm ³ , these are mixed in the crystal. In the case of carbon (C) having the largest segregation coefficient among these elements, the carbon concentration is equal to the carbon concentration in the silicon melt before the start of pulling at the portion where the solidification rate is 0.94 (see the broken line in FIG. 2). Will be equal. When the solidification rate exceeds 0.94, a portion having a higher carbon concentration is generated. Therefore, it is desirable that the upper limit of the solidification rate at the time of pulling is 0.94.

  Moreover, it is desirable that the raw material silicon ingot 10 obtained in the raw material ingot growing process is classified and manufactured according to a predetermined weight such as 5 kg and 10 kg. Since the raw material silicon ingot 10 is used as a raw material in the form obtained in the raw material ingot growing step in the silicon single crystal growing step, which will be described in detail later, the required amount of silicon melt required when pulling up the silicon single crystal is obtained. On the other hand, the raw material silicon ingot 10 having a weight corresponding to this can be appropriately selected. The weight of the raw silicon ingot 10 can be measured by a load cell in a pulling drive mechanism that is disposed in the upper part of the pull chamber and rotates and lifts the pulling shaft 5.

  Thus, in the raw material ingot growing process, a silicon raw material for manufacturing a silicon single crystal using a silicon raw material such as a crucible residual silicon lump that is inherently unsuitable and not used as a raw material for semiconductors, that is, for manufacturing a silicon single crystal. Purity raw silicon ingot can be purified. The silicon raw material at that time is not limited to a silicon raw material for producing a silicon single crystal that is highly pure and difficult to procure, so that the raw material can be procured stably at a low cost.

  In addition, as the silicon raw material used in the raw material ingot growing process, only a silicon raw material that does not satisfy the required purity as a raw material for producing a silicon single crystal due to a residual crucible lump or a silicon single crystal may be used. In addition, a high-purity polycrystalline silicon raw material having a very low impurity concentration, which is usually used for the production of a silicon single crystal, may be appropriately mixed and used. Further, in the raw material ingot growing step, the introduction of the silicon raw material and the pulling up of the raw silicon ingot may be repeated a plurality of times with one quartz crucible.

  Next, the silicon single crystal growth process will be described.

  FIG. 4 is a diagram schematically illustrating the flow of a silicon single crystal growing step in the method for producing a silicon single crystal of the present invention. As shown in FIG. 4A, the raw silicon ingot 10 obtained in the raw material ingot growing process is suspended and supported by the pulling shaft 5 above the quartz crucible 1a. At this time, a seed crystal 7 is attached to the lower end of the pulling shaft 5, and the raw material silicon ingot 10 is suspended and supported via the seed crystal 7.

  Subsequently, as shown in FIG. 4B, the pulling shaft 5 is lowered to supply the raw silicon ingot 10 into the quartz crucible 1a, and as shown in FIG. 4C, the raw silicon ingot 10 is supplied. The silicon melt 3 is obtained by melting. At this time, the seed crystal 7 holding the raw material silicon ingot 10 is brought into a standby state near the surface of the silicon melt 3.

  After that, as shown in FIG. 4 (d), the seed crystal 7 in the standby state is continuously immersed in the surface of the silicon melt 3 in the quartz crucible 1a, and the seed crystal 7 is moved upward according to the normal silicon single crystal manufacturing conditions. Pull up. As a result, as shown in FIG. 4 (e), the silicon single crystal 4 is obtained by growing under the seed crystal 7.

  Since the silicon single crystal 4 obtained by such a silicon single crystal growth step is grown using the high-purity raw material silicon ingot 10 obtained in the raw material ingot growth step as a raw material, it has a high quality with a low impurity concentration. It has become a thing.

  Here, since the raw material silicon ingot 10 used as a raw material in the silicon single crystal growth step is melted while being supported in a suspended state without being crushed in the form obtained in the raw material ingot growth step, the silicon single crystal Prior to the growing process, it is not necessary to crush the raw silicon ingot 10 or wash the deposits, and a process that causes a reduction in production efficiency is unnecessary.

  Further, in the silicon single crystal growth process, the seed crystal 7 holding the raw material silicon ingot 10 is also used as it is for pulling up the silicon single crystal 4, so that when the silicon single crystal 4 is pulled up, the seed shaft 5 is again seeded. There is no need to attach the crystal, and the silicon single crystal 4 can be efficiently grown. In particular, in the raw material ingot growing process, the seed crystal 7 used for the pulling is not separated from the pulled raw silicon ingot 10, but is kept integral with the raw silicon ingot 10. In the silicon single crystal growing process, If the raw material silicon ingot 10 is suspended and supported through the seed crystal 7 integrated therewith and the raw material silicon ingot 10 is melted, the seed crystal 7 is continuously used for pulling up the silicon single crystal 4 as a whole. Production efficiency is further increased. This is because it is possible to save the trouble of attaching the seed crystal to the upper end of the raw silicon ingot 10 prior to the silicon single crystal growing step.

  In addition, when the silicon single crystal 4 is grown using a seed crystal having a different crystal orientation or diameter size from the seed crystal 7 when the raw material silicon ingot 10 is grown, the silicon single crystal 4 is grown in advance. In the seed crystal, a hump portion whose diameter is partially enlarged or reduced is formed, and on the other hand, a fitting groove for fitting with the hump portion of the seed crystal is formed in the upper end portion of the raw material silicon ingot 10. In addition, it is desirable to attach a seed crystal to the upper end of the raw material silicon ingot 10 so as to fit both of them. Thus, when the silicon single crystal 4 is grown, the silicon single crystal 4 can be grown by dissolving the raw silicon ingot 10 and subsequently immersing the seed crystal in the melt, thereby increasing the production efficiency.

  However, the seed crystal 7 does not have to be used for supporting the suspension of the raw material silicon ingot 10 in the silicon single crystal growing step unless a significant improvement in production efficiency is desired. In that case, the raw material silicon ingot 10 is connected to the lifting shaft 5 through a special jig and supported by suspension, and after melting the raw material silicon ingot 10, a seed crystal for pulling up the silicon single crystal is again applied to the lifting shaft 5. Will be attached.

  According to the method for producing a silicon single crystal including the raw material ingot growing step and the silicon single crystal growing step, the silicon raw material can be used for silicon single crystal production by using the silicon raw material that can be stably and inexpensively procured by the raw material ingot growing step. A high-purity raw material silicon ingot as a raw material of the above can be purified, and a high-quality silicon single crystal having a low impurity concentration can be produced by using the raw material silicon ingot as a raw material by a silicon single crystal growing step.

  Such a method for producing a silicon single crystal can be applied to additional charging and recharging that have been widely adopted in recent years as an operation technique for improving the productivity of silicon single crystals. The additional charge is a technique in which when a silicon single crystal is grown, after the silicon material initially charged in the crucible is melted, the silicon material is additionally charged into the initial silicon melt. Recharging is a technique in which when a silicon single crystal is grown, after the previous silicon single crystal is pulled up, a silicon raw material is additionally added to the remaining silicon melt remaining in the crucible.

  FIG. 5 is a diagram schematically illustrating a series of flows when the method for producing a silicon single crystal of the present invention is applied to additional charging. As shown in FIG. 5 (a), a crucible residual silicon lump 8, which is a silicon raw material that is not used as a raw material for producing a silicon single crystal, is introduced into a quartz crucible 1a, and the silicon as shown in FIG. 5 (b). The raw material is melted to obtain a melt 9.

  Subsequently, as shown in FIG. 5C, the seed crystal 7 is immersed in the surface of the melt 9 in the quartz crucible 1a and pulled upward. Thereby, as shown in FIG. 5D, a silicon crystal grows below the seed crystal 7, and a raw material silicon ingot 10 is obtained. At this time, the raw silicon ingot 10 is suspended and supported by the pulling shaft 5 through the seed crystal 7 without being taken out of the pulling device, and includes a main chamber and a pull chamber (not shown) that form an outline of the pulling device. And stored in a pull chamber disposed above. At this time, the weight of the raw silicon ingot 10 is measured by the load cell in the pulling drive mechanism.

  Next, as shown in FIG. 5E, the residual melt 9a remaining in the quartz crucible 1a after pulling up the raw silicon ingot 10 is discharged from the quartz crucible 1a. This is because a large amount of impurities remain in the remaining melt 9a, and if this is added as it is to the next raw material for producing a silicon single crystal, the quality of the silicon single crystal may be adversely affected.

  Thereafter, as shown in FIG. 5 (f), a predetermined amount of high-purity polycrystalline silicon raw material 11 that is usually used for manufacturing a silicon single crystal is put into a quartz crucible 1a and melted. The amount of the polycrystalline silicon raw material 11 input at this time is an amount obtained by subtracting the measured weight of the raw material silicon ingot 10 from the required amount of silicon melt desired when pulling up the silicon single crystal.

  Next, as shown in FIG. 5G, the pulling shaft 5 is lowered, and the raw material silicon ingot 10 that is suspended and supported via the seed crystal 7 above the quartz crucible 1a is placed in the quartz crucible 1a. The initial silicon melt is supplied and melted to obtain a silicon melt 3. At this time, the seed crystal 7 holding the raw material silicon ingot 10 is brought into a standby state near the surface of the silicon melt 3.

  Then, as shown in FIG. 5 (h), the seed crystal 7 in the standby state is continuously immersed in the surface of the silicon melt 3 in the quartz crucible 1a, and the seed crystal 7 is moved upward according to the normal silicon single crystal manufacturing conditions. Pull up. Thereby, as shown in FIG. 5 (i), the silicon single crystal 4 is grown under the seed crystal 7.

  Since the silicon single crystal 4 obtained by such additional charging is grown using a high-purity raw material silicon ingot 10 as a raw material, it has a high quality with a low impurity concentration. Further, in the additional charge here, the refined raw silicon ingot 10 is not taken out of the pulling apparatus, so that the work time can be shortened.

  FIG. 6 is a diagram schematically illustrating a series of flows when the method for producing a silicon single crystal of the present invention is applied to recharging. As shown in FIG. 6A, a predetermined amount of high-purity polycrystalline silicon raw material normally used for silicon single crystal production is put into a quartz crucible 1a and melted to obtain a silicon melt 3. Subsequently, as shown in FIG. 6 (b), the seed crystal 7 is immersed in the surface of the silicon melt 3 in the quartz crucible 1a, and is pulled upward in accordance with the usual silicon single crystal manufacturing conditions. As a result, as shown in FIG. 6C, the silicon single crystal 4 is obtained by growing under the seed crystal 7.

  Since the silicon single crystal 4 obtained here is grown using a high-purity silicon raw material that is usually used for producing a silicon single crystal as a raw material, the silicon single crystal 4 has a high quality with a low impurity concentration.

  Next, as shown in FIG. 6 (d), a raw material silicon ingot 10 integrally comprising a seed crystal 7 A that has been purified and prepared in advance in the raw material ingot growing step shown in FIG. Change and support hanging. At this time, the remaining silicon melt 3a after pulling up the previous silicon single crystal 4 remains in the quartz crucible 1a. Since not much impurities remain in the remaining melt 3a, even if it is added to the next raw material for producing a silicon single crystal, the quality of the silicon single crystal is not adversely affected.

  Thereafter, as shown in FIG. 6E, the pulling shaft 5 is lowered, and the raw material silicon ingot 10 is supplied to the residual silicon melt 3a in the quartz crucible 1a to be melted, as shown in FIG. 6F. Then, a silicon melt 3 is obtained. At this time, the seed crystal 7 </ b> A holding the raw material silicon ingot 10 is brought into a standby state near the surface of the silicon melt 3.

  Then, as shown in FIG. 6 (g), the seed crystal 7A in the standby state is continuously immersed in the surface of the silicon melt 3 in the quartz crucible 1a, and upward according to the normal silicon single crystal manufacturing conditions. Pull up. As a result, as shown in FIG. 6H, the silicon single crystal 4 is obtained by growing under the seed crystal 7A.

  Since the silicon single crystal 4 obtained by such recharging is also grown using a high-purity raw material silicon ingot 10 as a raw material, it is of high quality with a low impurity concentration. Further, in the recharging here, the desired silicon melt when pulling up the silicon single crystal 4 in consideration of the amount of the remaining silicon melt 3a from the raw silicon ingot 10 classified and manufactured by weight. If a product according to the required amount of 3 is selected and used, the production efficiency is further increased.

  About the manufacturing method of the silicon single crystal including the above raw material ingot growing process and silicon single crystal growing process, the effectiveness was clarified from the following examples.

<Raw material ingot training process>
A quartz crucible with an inner diameter of 22 inches was used, 120 kg of the remaining crucible silicon lump was charged into this, and the silicon melt obtained by heating and melting was pulled up and grown at high speed or low speed to grow a raw silicon ingot with a diameter of 200 mm. . As the high-speed growth conditions, the growth conditions where the crystal growth rate was 1.3 mm / min were adopted, and as the low-speed growth conditions, the growth conditions where the crystal growth rate was 0.4 mm / min were adopted.

  The concentration of impurities (copper, aluminum and carbon) at a solidification rate of 0.94 (94% in terms of percentage) of the obtained raw material silicon ingot was investigated.

  Table 2 below shows the survey results. In Table 2, the impurity concentration is indicated with the concentration in the crystal A as the reference (1.0). The numerical value representing the impurity concentration is an average value obtained by growing 5 batches of the crystals A to D.

  As is apparent from Table 2, no difference was observed in the impurity concentration after purification, depending on the growth conditions, that is, high-speed growth, low-speed growth, dislocation crystals, and dislocation-free crystals.

<Silicon single crystal growth process>
The entire amount of residual crucible silicon lump is used as a raw material for obtaining the raw material silicon ingot (crucible residual silicon lump 100%), and a raw material silicon ingot is grown as a raw material under the conditions used for growing crystal A in the raw material ingot growing step. did. This raw material silicon ingot was supplied into a quartz crucible and melted, and a silicon single crystal as a product was grown under growth conditions that would be a defect-free crystal region in which no COP (Crystal Originated Particle) was present.

  A sample wafer was sampled from the obtained silicon single crystal and evaluated for quality. Specifically, the oxygen concentration, specific resistance, OSF (Oxygen Induced Stacking Fault) density, LPD (Light Point Defect) density and BMD (Bulk Micro Defect) density of the sample wafer were evaluated. For comparison, the same evaluation was performed for the case where normal high-purity polycrystalline silicon was used as a raw material (normal raw material).

  Quality evaluation was performed by the following method.

  Oxygen concentration: Based on the infrared absorption method prescribed | regulated to ASTMF121-1979, it measured using the Fourier transform type | mold infrared spectrophotometer (FTIR: Fourier Transform Infrared Spectrometer).

  Specific resistance: After a donor killer heat treatment (650 ° C. × 30 minutes) was performed on the silicon wafer, the specific resistance was measured by a specific resistance measuring device (four deep needle contact method).

OSF density: The silicon wafer was heat-treated at 1100 ° C. for 16 hours in a wet oxygen (Wet-O ₂ ) atmosphere, then the wafer surface was etched, and the OSF density on the wafer surface was measured with an optical microscope.

  LPD density: The number of LPDs having a size of 200 μm or more and LPDs having a size of 300 μm or more present on the wafer surface was counted using a light scattering type particle counter (SP1 manufactured by KLA-Tencor) on the wafer surface subjected to secco-etching.

  BMD density: After performing heat treatment on a silicon wafer at 780 ° C. × 3 hours and further at 1000 ° C. × 16 hours, the wafer was cleaved, and light etching was performed to etch the cross section by 2 μm, and then BMD in the cross section Was counted with an optical microscope.

  The evaluation results are shown in Table 3 below.

  From the results of Table 3, the quality of the sample wafer collected from the obtained silicon single crystal is not different from the case of using the normal raw material even if the residual crucible silicon lump is used as the raw material for obtaining the raw silicon ingot. I understand that.

  According to the method for producing a silicon single crystal of the present invention, raw material procurement can be stably performed at low cost, and a high-quality silicon single crystal having a low impurity concentration can be produced. Therefore, the present invention is an extremely useful technique for producing a silicon single crystal by the CZ method.

It is a figure which shows typically the principal part structure of the pulling apparatus suitable for implementing the pulling of the silicon single crystal by CZ method. It is a figure which shows the relationship between the solidification rate in silicon single crystal growth, and impurity concentration. It is a figure which illustrates typically the flow of the raw material ingot growing process in the manufacturing method of the silicon single crystal of the present invention. It is a figure which illustrates typically the flow of the silicon single crystal growth process in the manufacturing method of the silicon single crystal of the present invention. It is a figure which illustrates typically a series of flows when the manufacturing method of the silicon single crystal of the present invention is applied to an additional charge. It is a figure which illustrates typically a series of flows when the manufacturing method of the silicon single crystal of the present invention is applied to recharge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crucible 1a Quartz crucible 1b Graphite crucible 2 Heater 3 Melt 3a Residual melt 4 Silicon single crystal 5 Lifting shaft 6 Support shaft 7, 7A Seed crystal 8 Crucible residual silicon lump 9 Melt 9a Residual melt 10 Raw material silicon ingot 11 Many Crystalline silicon raw material

Claims (6)

A raw material ingot growing step of melting a solidified material of the silicon melt remaining at the bottom of the quartz crucible after pulling up the silicon single crystal, and pulling up the raw material silicon ingot from the melt obtained by melting the solidified material by the Czochralski method;
A silicon single crystal growing step in which the raw material silicon ingot obtained in the raw material ingot growing step is suspended and supported, supplied into the crucible from above and melted, and then the silicon single crystal is pulled up from this silicon melt by the Czochralski method. A method for producing a silicon single crystal, comprising:
  In the silicon single crystal growth step, the raw silicon ingot is suspended and supported through a seed crystal, and the seed crystal is continuously immersed in the silicon melt in the crucible to pull up the silicon single crystal. The method for producing a silicon single crystal according to claim 1.   3. The method for producing a silicon single crystal according to claim 2, wherein the raw material silicon ingot is configured to be integrated without separating the seed crystal after the raw material ingot growing step.   In the silicon single crystal growth step, the silicon single crystal is pulled up by the Czochralski method in advance, and then the raw silicon ingot is supplied to the residual silicon melt remaining in the crucible to melt the silicon single crystal. The method for producing a silicon single crystal according to claim 1, wherein the silicon single crystal is pulled up.   In the silicon single crystal growth step, the raw material silicon ingot is supplied to an initial silicon melt previously charged and melted in a crucible and melted to pull up the silicon single crystal. 4. A method for producing a silicon single crystal according to any one of 3 above. In the raw material ingot growing step, producing the raw material silicon ingot classified according to a predetermined weight,
The method for producing a silicon single crystal according to claim 1, wherein, in the silicon single crystal growing step, the raw material silicon ingot is selected and used according to the weight of the silicon single crystal.

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