JP6627793B2 - Crystal growth method - Google Patents

Description

  The present invention relates to a silicon single crystal growing method grown by the Czochralski method (CZ method: also including a magnetic field applying CZ method).

  In the CZ method, a raw material is charged into a quartz crucible, and crystals are grown from a melt (silicon melt) obtained by melting the raw material. Conventionally, crystals grown by the CZ method have been often used mainly for memories and logics. The level of impurities required by the miniaturization of these devices has been reduced. Furthermore, in the case of power devices and image sensors for which CZ crystals have come to be used in recent years, the types and concentrations of impurities which are problematic have changed. Therefore, it is more important than ever to grasp the impurity concentration contained in the crystal.

  The impurities contained in the silicon crystal are mixed in the silicon from components called HZ (hot zone) such as heaters and crucibles, which are used in the pulling furnace furnace and become high temperature during operation, and in the melt where the silicon raw material is melted. Originated from quartz crucibles and those originally contained or attached to silicon raw materials. Impurities due to HZ have been reduced by operational techniques as disclosed in Patent Document 1, for example. In this technology, the flow rate is increased by increasing the gas flow rate and the like, and the carbon caused by HZ is reduced. However, an increase in the gas flow rate increases the cost. Further, impurities caused by the quartz crucible are reduced by using synthetic quartz or the like as disclosed in Patent Document 2, for example. Further, the impurity concentration of the silicon raw material is reduced as described in Patent Document 3, for example.

  Although the origins of impurities have been improved, impurities originating from raw materials still account for a large proportion even today. These raw materials are polycrystalline raw materials produced by the Siemens method or the like, and include those contained inside during the production and those adhered to the surface through processes such as grinding and washing. In general, a wafer maker purchases a raw material from a polycrystalline raw material maker or the like, and as for those adhering to the surface, for example, as disclosed in Patent Documents 4 and 5, such as a technique of sorting by raw material size / specific surface area, etc. Although there is a technology for achieving high purity, it is not possible to achieve high purity of the raw material itself, and the purity of the crystal grown by the wafer maker depends on the impurity concentration of the silicon raw material.

  On the other hand, in the CZ method, there is a segregation phenomenon in which only a certain percentage of a melt is taken into a solid. In the segregation phenomenon, the impurity concentration in the grown crystal is lower than the impurity concentration in the raw material. Therefore, it is considered that, for example, if the non-product part (a part that has been grown but has not become a product) is recycled as a raw material, it is possible to reduce the impurity concentration of the raw material.

Here, the segregation phenomenon and the solidification rate will be briefly described. Generally, when Si is solidified (crystallized), impurities in the melt are less likely to be taken into the crystal. At this time, the ratio of the impurity concentration taken into the crystal to the impurity concentration in the melt is referred to as a segregation coefficient k. Impurity concentration C _S moment in the crystals that therefore the impurity concentration C _L of the melt at that time, a relation C S _{= k} × C _L. k is generally less than 1, so that the concentration of impurities taken into the crystal is k times lower than the concentration of impurities in the melt. Since the crystal growth is performed continuously, a large amount of impurities remain in the melt, and the impurity concentration in the melt gradually increases. As a result, the impurity concentration in the crystal also increases, and using the solidification rate x, which is the ratio of the crystallized weight to the initial weight of the raw material, and the initial melt impurity concentration _CL0 , the following ( It is expressed by the expression 1).

C _S (x) = C _L0 · k · (1-x) ^(k−1) (1)

  Therefore, it is considered that the crystal can be highly purified by the raw material recycling technology. As a material recycling technique, Patent Document 6 describes that a nitrogen-doped crystal is reused as a material. Patent Literature 7 discloses a technique for reusing low-resistance crystals as a raw material, and Patent Literatures 8 and 9 disclose a method for managing resistivity and quality using a recycled raw material. However, these are aimed at cost reduction mainly in dopant management, and do not positively use the advantage of high purification utilizing the segregation phenomenon. The advantage of high purification by segregation is effective when the solidification rate x is low, as can be seen from the above-mentioned equation (1).

  However, in the above-mentioned technology, since the main purpose is to control the concentration of the intentionally added dopant, the solidification rate of the crystal, which determines the dopant concentration, is controlled, for example, as resistivity. The influence of the total solidification rate (= total crystal weight / total input material weight) is not controlled, and therefore, the advantage of high purification has not been utilized at all.

  On the other hand, Patent Literatures 10 and 11 describe high purification using a segregation phenomenon positively. However, these are measures when raw materials are tight, and the target concentration range is a low-grade product level. For this reason, Patent Document 10 discloses a method in which a crystal for a raw material is grown using a low-grade raw material, which is not considered to be costly. Further, Patent Document 11 discloses a technique for reusing the remaining hot water after being pulled up at a high solidification rate at which the impurity concentration becomes the highest, and the direction is opposite to the production of the objective highly purified crystal. there were.

JP 2015-017019 A JP 05-057888 A JP 2011-063471 A JP-A-2006-108160 JP-A-2006-147781 JP 2001-332594 A JP-A-2004-224852 JP 2005-112669 A JP 2007-191357 A JP 2009-023851A JP 2009-249253 A

  As described above, in the conventional technology described above, there is room for improvement from the viewpoint of manufacturing a high-purity silicon single crystal at low cost.

  The present invention has been made in view of the above problems, and has as its object to provide a crystal growing method capable of producing a high-purity silicon single crystal at low cost.

In order to achieve the above object, the present invention provides a single pulling operation for growing one silicon crystal from a melt obtained by melting a silicon raw material charged in a crucible using a CZ method, or after growing the silicon crystal. By recharging the crucible with a silicon raw material and growing a silicon crystal again from a melt that has been melted once or more times, it is manufactured in a multi-operation in which two or more crystals are grown from one quartz crucible. Among the non-product parts, the non-product part in which the upper limit of the total solidification rate K _s (= total crystal weight / total input material weight) is 0.7 or less, or the average total solidification rate K _sav = (K _s1 × W _{1) + K s2 × W 2 + K} s3 × W 3 ···) / (W 1 + W 2 + W 3 ···), ( _{where, K si} is (overall solidification rate _{K ssi} + non of training at the start of the non-product part i Product Department i Representative overall solidification rate of the non-product portion i represented by General solidification rate K _{sei) / 2} of the growing end, W _i is a non-product part by weight of the non-product portion i) is 0.5 or less as a recycle material The present invention provides a crystal growing method characterized in that the following silicon crystal is grown by the CZ method.

  As described above, among the non-product parts manufactured in the single-drawing operation or the multi-operation, the upper limit of the total solidification rate is 0.7 or less, or the average total solidification rate is 0.5 or less. By growing a silicon crystal using a non-product part as a recycled material, a high-purity silicon single crystal can be manufactured at low cost.

  At this time, it is preferable to use the recycled material at least 20% or more of all the raw materials.

  By using at least 20% or more of the above-mentioned recycled raw materials in all the raw materials, it is possible to more effectively reduce the concentration of impurities in the silicon crystal to be grown as compared with a commonly used raw material. .

At this time, in response to said impurity concentration level of the target in the silicon crystal which is grown by using the recycle material, the upper limit of the total solidification rate K _s of recycled materials to be used, the average overall solidification rate of recycled materials to be used K It is preferable to select at least one of _sav and the ratio of the recycled material to the total material.

  By doing so, the desired impurity concentration level in the silicon crystal to be grown can be obtained.

At this time, the concentration of carbon in the silicon crystal which is grown by using the recycle material can be less than or equal to ^{1 × 10 14 atoms / cm 3} .

With the crystal growth method of the present invention, lowering the carbon concentration in the silicon crystal to be grown up to 1 × 10 14 ^atoms / cm ³ or less of the level it can be relatively easily achieved.

  At this time, when the non-product part is crushed and used as the recycled material, it is preferable that the average weight per crushed one recycled material is 100 g or more.

  In this way, by setting the average weight per crushed recycled material to 100 g or more, the ratio of the surface to the weight can be reduced, and impurities attached to the surface can be reduced, so that higher purity can be achieved. is there.

  At this time, it is more preferable that the non-product part is not crushed or the non-product part is divided into 10 or less and used as the recycled raw material in the form of a block or a lump.

  In order to reduce the ratio of the surface to the weight of the recycled raw material, it is desirable that the size of the raw material be as large as possible as long as the etching or cleaning step can be handled. Therefore, if a block-shaped or lump-shaped material can be used as a recycled material, the impurity concentration can be further reduced.

  As described above, according to the crystal growing method of the present invention, among the non-product parts manufactured in the single drawing operation or the multi-operation, the upper limit of the total solidification rate is 0.7 or less, or By growing a silicon crystal using a non-product part having an average overall solidification rate of 0.5 or less as a recycle raw material, a high-purity silicon single crystal can be manufactured at low cost.

FIG. 5 is a diagram showing a relationship between a solidification rate of a growing crystal and a total solidification rate in a multi-operation. FIG. 4 is a diagram comparing the segregation coefficients of typical impurity elements in a silicon crystal. FIG. 4 is a diagram showing, by a representative element, a ratio of a concentration in a crystal lowering to an initial concentration in a raw material due to a segregation phenomenon. It is a figure showing the relation between the concentration in the recycled material (initial concentration ratio) and the upper limit value or the average total solidification ratio of the total solidification ratio of the non-product part to be recycled. FIG. 4 is a diagram showing the impurity concentration (initial concentration ratio) in the crystal when the ratio of recycled materials is varied at an average total solidification rate of 50%. FIG. 4 is a diagram showing impurity concentrations (initial concentration ratios) in crystals when the average overall solidification ratio is varied at a recycled material ratio of 100%. It is a figure showing the schematic diagram of the pulling machine used for Examples 1, 2 and a comparative example. FIG. 3 is a diagram in which the carbon concentrations of the crystals obtained in Examples 1 and 2 and Comparative Example were measured, and the concentration was estimated by segregation based on the measured values.

  Hereinafter, the present invention will be described in detail with reference to the drawings as an example of an embodiment, but the present invention is not limited to this.

  The crystal growing method of the present invention includes a single pulling operation for growing one silicon crystal from a melt obtained by melting a silicon raw material charged in a crucible using the CZ method, or a silicon raw material after growing a silicon crystal. The non-product part manufactured in the multi-operation where two or more crystals are grown from one quartz crucible by repeating at least once repeating growing silicon crystals from the melt that has been recharged and melted, Using a non-product part having an upper limit of the total solidification rate of 0.7 or less or a non-product part having an average total solidification rate of 0.5 or less as a recycle raw material, the next silicon crystal is subjected to the CZ method. To foster.

  In the case where only one crystal is grown from one crucible, or in the case of resistivity management focusing on the dopant mentioned in the above-mentioned patent document, the solidification rate of the crystal is important. This is because, in order to control the resistivity to a desired value, a dopant is added for each crystal, and is generally adjusted so that the initial dopant concentration is constant in any crystal in the multi-operation. If the initial concentration is the same, the dopant concentration, that is, the resistivity depends on the solidification rate of the crystal, so if only the solidification rate of the crystal is considered, the resistivity can be controlled, and the crystal can be recycled. , That is, only the resistivity of the crystal needs to be considered.

On the other hand, the situation of unintended impurities such as metal and carbon other than the dopant which is controlled to be always constant is completely different. If in the inserted are impurity concentration is always the same C _o of the raw material, assuming that contamination other than the raw material is not in operation, the impurity concentration C _s in the crystal below with overall solidification rate X _s (2) Expressed by an expression.

_{C s (X s) = C} o · k · (1-X s) (k-1) ··· (2)

  Here, the total solidification rate is a ratio of the total weight of the grown crystals to the total weight of the input raw materials. For example, when the first crystal is charged to 100 kg and pulled up to 50 kg, the solidification rate of the crystal is 50/100 = 0.5, and the total solidification rate is 50/100 = 0.5. It is assumed that the first crystal is pulled up to 70 kg, and the same crystal weight of 70 kg is recharged to produce a 100 kg melt to grow a second crystal. When the second crystal is pulled up to 50 kg, the solidification rate of the crystal is still 50/100 = 0.5, but the overall solidification rate is as high as (70 + 50) / (100 + 70) = 0.71. At this time, FIG. 1 shows the total solidification rate with respect to the solidification rate of the crystal when the crystal was repeatedly grown to a solidification rate of 0.7 and the crystal was grown to the fifth multi-operation.

  From FIG. 1, it can be seen that in the second or more crystals in the multi-operation, the overall solidification rate is high even though the solidification rate in the crystals is low. This indicates that the resistivity, that is, the solidification rate of the crystal should be controlled for the dopant concentration, whereas the total solidification rate of other unintended impurities needs to be controlled. In the present invention, high purity of the grown crystal can be achieved by controlling the total solidification rate, which has not been performed in the conventional recycling management mainly using the dopant for controlling the resistivity.

  As an example of a multi-operation in which crystal growth is repeated up to a solidification rate of 0.7 shown in FIG. 1, a non-product part with an upper limit of 0.7 or less for the total solidification rate handled in the present invention is, for example, 1 In the first crystal, any portion not used as a product may be used. However, in the second crystal, only the non-product part whose solidification rate in the crystal is 0.49 or less can be used. Further, in the third crystal, the solidification rate of the crystal is 0.28 or less, in the fourth crystal, the solidification rate of the crystal is 0.07 or less, and in the fifth crystal, there is no corresponding portion. By using only such a portion, the next crystal can be highly purified.

  The non-product part includes, of course, a part that is not originally set as a product, such as an enlarged diameter part called a cone or a shoulder of a single crystal ingot, a reduced diameter part called a rounding or a tail, and a narrowed part. In addition, to guarantee the inspection of parts that do not meet product standards, such as parts that do not meet product standards, surplus parts that do meet the standards, and product parts, even for straight bodies that may be called bodies for products etc. And the like, and the sample portion cut out in this manner is also included. Further, defective portions when slicing and polishing are performed and surplus portions are included. Particularly, since the cleanliness of the defective portion or the surplus portion of the polished wafer finished to the final product is also controlled, it can be used without considering the shape of the raw material described later, which is useful.

Another control method, that is, an average total solidification rate K _sav of 0.5 or less will be described. For example, if the weight is to solidification ratio K _se1 at which overall solidification rate K _ss1 and finished foster non-product portion 1 at the time of starting to grow a non-product portion 1 which is a W _1, representative total of the non-product portion solidification rate _{K s1} average of the _{K ss1} and _{K se2,} i.e. _{(K ss1 + K se1) /} 2 to be calculated. Similarly, the average total solidification rate K of the mixture of the non-product parts such as the weight W ₂ of the non-product part 2, the representative total solidification rate K _s2 , the weight W ₃ of the non-product part ₃ , the representative total solidification rate K _{s3. sav} is calculated as _{(K s1 × W 1 + K} s2 × W 2 + K s3 × W 3 ···) / (W 1 + W 2 + W 3 ···). By recycling the non-product part having the average total solidification rate K _sav of 0.5 or less as a raw material, it becomes possible to obtain a high-purity crystal.

At this time, the total solidification rate K _{ss *} (where * is a positive integer) at the start of the growth of each non-product part, the total solidification rate K _{se *} at the end of the growth of the non-product part, and the representative total being the average thereof The solidification rate Ks _* may exceed 0.7, and the average total solidification rate _Ksav, which is the total of all the raw materials, may be 0.5 or less.

In addition, since the management of impurities such as carbon and metal is proper, it is appropriate to control the average impurity concentration in the non-product part. However, the total solidification rate is used as an index here. The reason is that the impurity concentration does not increase linearly in the non-product portion, but increases according to the segregation equation (2) described above. Further, since the segregation coefficient differs for each impurity, the manner of ascending depends on the impurity. For this reason, in order to accurately calculate the impurity concentration in the non-product part, a so-called integration in which the growth from the growth start part to the growth end part of the non-product part is finely divided and integrated is necessary for each target impurity. In practice, such management is difficult. On the other hand, since the total solidification ratio increases with respect to the weight in the non-product portion, the ratio increases linearly in the straight body portion, and increases in accordance with the weight in the enlarged diameter portion and the reduced diameter portion. Therefore, the representative total solidification rate of the non-product part can be represented by a simple average of the start part and the end part as described above. Therefore, if the weight of the non-product part is added to this, the average total solidification rate _Ksav can be easily obtained as in the above equation, and it is very easy to manage.

Here, the point that the upper limit of the total solidification rate is 0.7 or less and the average total solidification rate is 0.5 or less will be described. As described above, the dopant is an impurity that is intentionally added, and oxygen is an impurity that is constantly dissolved during growth from a quartz crucible that is used as a standard in the CZ method for growing a silicon single crystal. These are impurities that are positively introduced in order to control the resistivity that influences the characteristics during device fabrication, or to form oxygen precipitates called BMD to getter impurities such as heavy metals. Control technology has also been established. Except for these, carbon and metal can be considered as impurities in the silicon single crystal that affect the characteristics of devices and the like. Among them, the segregation coefficients of typical elements are as follows: C (carbon): 0.07, Li (lithium): 0.01, Al (aluminum): 2 × 10 ⁻³ , Cu (copper): 4 × 10 ^{− 4} , Ni (nickel): 3 × 10 ⁻⁵ , Fe (iron): 8 × 10 ^−6, etc., as shown in FIG.

  Among these impurities, those having a small segregation coefficient tend to lower the impurity concentration in the crystal relative to the melt (silicon melt) due to segregation. FIG. 3 shows how impurities derived from the raw materials are incorporated into the crystal due to segregation. As can be seen from FIG. 3, the most difficult element for performing purification using the segregation phenomenon is carbon having the largest segregation coefficient. Therefore, in FIG. 4, the upper limit of the total solidification rate of the material to be recycled is plotted on the horizontal axis using the carbon segregation coefficient of 0.07. Plots the ratio of the impurity concentration to the initial raw material (○ in the figure), and the ratio of the impurity concentration to the initial raw material in the recycled raw material when the average total solidification rate of the recycled raw material is plotted on the horizontal axis (□ in the figure) did. When the upper limit of the total solidification rate is 0.7 or the average total solidification rate is 0.5, the ratio of the concentration of carbon impurities in the recycled raw material to the initial raw material is about 10% or more, and it can be said that the raw material is a sufficiently reduced raw material. . Further, when the value exceeds the above values (0.7, 0.5), it can be seen that the ratio of the impurity concentration to the initial material in the recycled material sharply increases. Of course, in reality, impurities other than the raw materials, which originate from crucibles or HZ, are taken in, and therefore, the temperature does not drop to this point. However, as long as the concentration of impurities due to the raw material can be maintained at a level of not more than 10%, the raw material can be used as a sufficiently purified raw material even if it is mixed in from other sources.

  In addition, here, “the total solidification rate (= total crystal weight / total input) of the non-product parts manufactured in one-drawing operation or multi-operation in which one or more crystals are grown from one quartz crucible The non-product portion having an upper limit of 0.7 or less in the weight of the raw material) is defined as a matter of course, when growing two or more crystals, the non-product portion is collected based on the total solidification rate. This is because the non-product part may be collected even when only one crystal is grown from one crucible. In this case, the total solidification ratio may be calculated as the total solidification ratio = the solidification ratio of the crystal as in the first multi-operation.

  From the viewpoint of growing high-purity crystals, it is preferable to use at least 20% or more of the recycled material produced from the above-mentioned non-product part in all the raw materials.

  The impurity concentration in the recycled material recovered by the method described above can be calculated to be a concentration of not more than ten and several percent even in the case of carbon having the largest segregation coefficient (see FIG. 4). . Therefore, if this raw material is used in an amount of 20% or more, it is possible to lower the concentration of impurities as compared with a commonly used raw material. FIG. 5 shows the impurity concentration ratio with respect to the initial raw material in the crystal grown using the recycled raw material when the average total solidification rate is set to 50%, for each ratio of the recycled raw material to all the raw materials. Even when the recycled material ratio is 20%, a reduction effect of about 10% is estimated as compared with the case where no recycled material is used. Of course, in addition to this, in addition to this, there are impurities that are mixed in when the non-product portion is subjected to crushing / cleaning processing and the like to become a recycled material. Therefore, the ratio of the recycled material should be at least 20% or more, and if possible, the ratio should be increased. preferable.

Depending on the impurity concentration level of the target in the silicon crystal which is grown by using the recycle material, the upper limit of the total solidification rate K _s of recycled materials to be used, the average overall solidification rate of recycled materials to be used, recycled to the total feed It is preferable to select at least one or more of the ratios of the raw materials.

  By increasing the ratio of the recycled material as shown in FIG. 5 described above, the impurity concentration in the grown crystal is reduced. Further, FIG. 6 shows the impurity concentration ratio with respect to the initial raw material in the crystal grown using the recycled raw material when the recycled raw material ratio is set to 100%, for each average total solidification rate of the used raw material. As can be seen from FIG. 6, the impurity concentration in the grown crystal decreases as the average overall solidification rate decreases. Similarly, by lowering the upper limit of the total solidification rate, the impurity concentration in the grown crystal is reduced. Of course, there is impurity contamination due to sources other than the raw materials and impurity contamination due to the processing of recycled materials, so it does not necessarily decrease as estimated.However, from this estimation and the impurity concentration in the actually grown crystals, At least one of the upper limit value of the total solidification rate capable of achieving the target impurity concentration, the average total solidification rate, and the ratio of the recycled material to all the raw materials can be selected.

According to the present invention, among impurities affecting the characteristics of devices and the like in a silicon crystal grown using recycled materials, dopants such as boron and phosphorus that are intentionally added for controlling resistivity, and quartz crucibles are always used. dissolved in come except oxygen, the most segregation coefficient is reduced to a concentration of 1 × 10 14 ^atoms / cm ³ or less of the level of carbon as high class it is comparatively easily.

As described above, carbon is the element with the least reduction effect when using recycled materials. Normally, if nothing is performed, the carbon concentration in the crystal is such that the solidification rate is close to 0, as described in Comparative Example 1 in FIG. 5 of Patent Document 1 and FIG. 2 of Patent Document 11 (this is a calculated value). On the top side of the crystal body part, 1 × 10 ¹⁴ atoms / cm ³ is slightly interrupted. However, in the present invention, the non-product part having a low overall solidification rate is used as a recycled material, so that the carbon concentration in the crystal is reduced to a level of 1 × 10 ¹⁴ atoms / cm ³ or less without any other special operation. Can be achieved relatively easily.

  In the crystal growing method of the present invention, when the non-product part is crushed and used as a recycled material, the average weight of one crushed recycled material is desirably 100 g or more.

In the non-product part having a low overall solidification rate handled in the present invention, the impurity concentration in the crystal is reduced by segregation. However, it is difficult to use this non-product part as a raw material as it is, and it is necessary to first separate it from the product part. Since it alone is a heavy object and difficult to handle, it is generally crushed to make it easy to handle. Further, since there is a high possibility that the cut surface or the pulverized portion is contaminated during cutting or pulverization, the cut surface or the pulverized part is used as a raw material after etching or cleaning to reduce impurities on the surface. Even after cleaning, impurities may adhere to the surface due to the influence of the storage environment and the like. For this reason, it is advantageous that the proportion of the surface is as small as possible.
Therefore, by setting the average weight per crushed recycled material to 100 g or more, the ratio of the surface to the weight can be reduced, and higher purity can be achieved. Of course, the above-mentioned non-standard and surplus polished wafers have a high degree of cleanliness.

  Alternatively, it is more preferable that the non-product portion is not crushed or is divided into 10 or less pieces, and is used as a recycled material in a block shape or a lump shape.

  In order to reduce the ratio of the surface to the weight, it is desirable that the size of the raw material be as large as possible as long as the etching or cleaning step can be handled. Therefore, if a block-shaped material or a lump-shaped material can be used as a recycled material, the impurity concentration can be further reduced. Of course, the description of the size of the raw material described here is not necessarily required since there is a possibility that the problem will disappear if the management level of cutting, pulverization, etching / cleaning, storage, etc. is improved.

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

(Example 1)
Using the pulling device 10 shown schematically in Figure 7, among those products produced performs multi operations, overall solidification rate K _s basically were recovered non-product portion of 0.7 or less.

The pulling machine 10 shown in FIG. 7 includes a main chamber 11 in which a quartz crucible 15 containing a silicon melt 14 and a graphite heater 17 are arranged, and a pulling chamber provided on the main chamber 11 via a top chamber 21. 12 are provided.
A gas outlet 19 is provided below the main chamber 11, and a gas inlet 20 is provided above the lifting chamber 12. The quartz crucible 15 is supported by, for example, a graphite crucible 16, and the graphite crucible 16 is supported by, for example, a crucible rotation shaft 29. Outside the graphite heater 17 for heating the quartz crucible 15, for example, a heat insulating member 18 is provided so as to surround the periphery.
For example, a pulling mechanism (not shown) is provided on the upper part of the pulling chamber 12, and a pulling wire 26 is wound out of the pulling mechanism, and a seed crystal 27, for example, is placed at the tip of the pulling wire 26. A seed holder 28 for attachment is connected. At the upper end of the top chamber 21, for example, a gas purge cylinder 22 extending near the silicon melt surface is provided. Below the gas purge cylinder 22, a graphite heater 17 is provided so as to surround the silicon crystal 13. A heat shielding member 23 for shielding radiant heat from the silicon melt 14 is provided.

In the recovery of the non-product part, the first part is the cone part (diameter enlarged part of silicon crystal), the non-product straight part in the area where the quality enters the straight body part and the quality meets the product standard on the top side, the rounding ( The reduced diameter portion of the silicon crystal) was collected. For the second and third multis, the cone portion and the non-product portion on the top side of the straight body portion were mainly collected, and for the fourth multi, the cone portion was mainly collected. The average total solidification rate K _sav of these recovered non-product parts was 0.47.

  These materials were pulverized, the surface was thinly etched, and then washed to obtain recycled materials. At this time, the size was such that the average weight per raw material was about 50 to 60 g. 50 kg of this raw material is mixed with a normal polycrystalline raw material to make 100 kg (recycling raw material ratio: 50%), and charged to a quartz crucible 15 of 22 inches (550 mm) in the pulling machine 10 in FIG. A crystal was grown.

A round slice sample was cut out from the last portion of the straight body portion (solidification ratio 0.62) immediately before the crystal was rounded, and the carbon concentration was measured by the FT-IR method. At this time, an FT-IR whose lower limit of detection was improved to about 0.02 ppma (= 1 × 10 ¹⁵ atoms / cm ³ ) by adding the number of times of integration and reference, etc. was used, but the value was lower than the lower limit of detection. Therefore, the sample was irradiated with an electron beam, and a carbon-related peak was measured by the PL method.

In the PL method, since the peak intensity depends not only on the carbon concentration but also on the oxygen concentration, it cannot be said that the method is a completely established method such as the accuracy of the absolute value and the method of drawing a calibration curve. There is a report of about ¹³ atoms / cm ³ . When the carbon concentration was measured by this PL method, it was 1.7 × 10 ¹⁴ atoms / cm ³ when estimated based on a calibration curve created in-house. FIG. 8 shows the concentration calculated from this result by segregation. In FIG. 8, the carbon concentration near the solidification rate of 0 is 6.8 × 10 ¹³ atoms / cm ³ , and the carbon concentration at the target solidification rate of 0.62 is 1.7 × 10 ¹⁴ atoms / cm ³ . The value was lower than that of the conventional crystal. However, the concentration is about 40% higher than the ideal calculated value used at the time of design, and it is said that carbon contamination due to recycling processing that is not included in the non-product part itself is affecting. it was thought.

(Example 2)
Crystal growth was attempted such that the total length of the straight body portion was 1 × 10 ¹⁴ atoms / cm ³ or less as a target carbon concentration. First, a non-product portion having an average total solidification rate of 0.47 collected by the same method as in Example 1 was pulverized and washed in the same manner as in Example 1 to obtain a recycled material. When estimating based on the results of Example 1, when the ratio of the recycled materials 75%, the carbon concentration in the solidification ratio 0.62 is approximately ^{1 × 10 14 atoms / cm 3} . Therefore, 75 kg of recycled material and 25 kg of conventional material were mixed to make a recycled material ratio of 75%. However, at this time, the raw materials were prepared so that the average weight per raw material was about one hundred and several tens g, which was larger than that of Example 1. Using this raw material, a crystal was grown under the same conditions as in Example 1.

As in Example 1, a sample of a round slice was cut out from the final portion of the straight body portion (solidification rate 0.62) immediately before the crystal was rounded, irradiated with an electron beam in the same manner as in Example 1, and subjected to the PL method. Carbon-related peaks were measured. As a result, the estimated carbon concentration was 9.3 × 10 ¹³ atoms / cm ³ . FIG. 8 shows the value calculated from the result by segregation. In FIG. 8, the carbon concentration near the solidification rate of 0 was 3.8 × 10 ¹³ atoms / cm ³ , which was a sufficiently low value as compared with the conventional crystal. In addition, the carbon concentration at the target value of the solidification rate of 0.62 was also achieved at 9.3 × 10 ¹³ atoms / cm ³ . Although this value was lower than 1 × 10 ¹⁴ atoms / cm ³ estimated from the result of Example 1, the difference caused by the selection of the raw material size and the increase in the size of the raw material reduced the influence of the carbon contamination caused by the recycling process. This is considered to be a reduced effect.

(Comparative example)
A crystal is grown under the same conditions as in Example 1 except that a normal polycrystalline raw material is used without using a recycled raw material, and a round section is cut from the final straight body portion (solidification ratio 0.62) immediately before the rounding. Was cut out, irradiated with an electron beam in the same manner as in Example 1, and the carbon-related peak was measured by the PL method. As a result, the estimated carbon concentration was 2.2 × 10 ¹⁴ atoms / cm ³ . From this result, the carbon concentration in the vicinity of the solidification rate of 0 calculated by segregation was 8.8 × 10 ¹³ atoms / cm ³ (see FIG. 8), which was a higher value than Examples 1 and 2.

  Note that the present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention, and any device having the same operation and effect can be realized by the present invention. It is included in the technical scope of the invention.

10: Lifting machine, 11: Main chamber, 12: Lifting chamber,
13: silicon crystal, 14: silicon melt, 15: quartz crucible,
16: graphite crucible, 17: graphite heater, 18: heat insulating member, 19: gas outlet,
20: gas inlet, 21: top chamber, 22: gas purge cylinder,
23: heat shielding member, 26: pulling wire,
27: seed crystal, 28: seed holder, 29: crucible rotation axis.

Claims (6)

A single pull operation for growing one silicon crystal from a melt obtained by melting a silicon material charged in a crucible using the CZ method, or after growing the silicon crystal, recharging the silicon material into the crucible and melting the silicon material By repeatedly growing silicon crystals from the melt obtained at least once, the total solidification rate K _{s of the} non-product parts manufactured in a multi-operation in which two or more crystals are grown from one quartz crucible is repeated. non-product portion upper limit of 0.7 or less of (= total crystallinity weight / total input material weight), or an average overall solidification rate _{K sav = (K s1 × W} 1 + K s2 × W 2 + K s3 × W 3 ··・) / (W ₁ + W ₂ + W ₃ ...) (Where K _si is (the total solidification rate K _ssi at the start of the growth of the non-product part i + the total solidification rate K at the end of the growth of the non-product part i) _sei / Representative overall solidification rate of the non-product portion i represented by 2, W _i is using a non-product part by weight of the non-product portion i) is 0.5 or less as a recycle material, CZ method the following silicon crystals A crystal growing method characterized by growing by:   The crystal growing method according to claim 1, wherein the recycled material is used in at least 20% or more of all the raw materials. The recycle material in accordance with the impurity concentration level of the target in the silicon crystal which is grown by using the upper limit of the total solidification rate K _s of recycled materials to be used, the average overall solidification rate of recycled materials to be used K _sav, total The crystal growing method according to claim 1 or 2, wherein at least one or more of a ratio of the recycled material to the raw material is selected. The crystal growth according to any one of claims 1 to 3, wherein the concentration of carbon in the silicon crystal grown using the recycled raw material is set to 1 × 10 ¹⁴ atoms / cm ³ or less. Method.   The method according to any one of claims 1 to 4, wherein, when the non-product part is crushed and used as the recycled material, an average weight per crushed one recycled material is set to 100 g or more. Crystal growth method.   The non-product part is not crushed, or the non-product part is divided into 10 or less, and the non-product part is used as the recycled raw material in a block shape or a lump shape. The method for growing a crystal according to any one of the above items.

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