JP5262257B2 - Method for producing nitrogen-doped silicon single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a nitrogen-doped silicon single crystal by the Czochralski method (CZ method) capable of suppressing raw material procurement cost by sufficiently decreasing the used amount of a high-priced raw material of a nitrogen dopant and capable of improving manufacturing efficiency. <P>SOLUTION: After pulling up the nitrogen-doped silicon single crystal 4, a silicon raw material 8 is supplied to and melt in a residual melt 3a remaining in a crucible 1, and the nitrogen-doped silicon single crystal 4 is pulled up from this melt 3. In growing the silicon single crystal and by basing upon the solidification ratio at the time just before the termination of pull-up of the silicon single crystal, the quantity of a silicon raw material supplied to the residual melt is set in order to adjust the nitrogen concentration in the silicon single crystal. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a silicon single crystal doped with nitrogen by the Czochralski method (hereinafter referred to as “CZ method”), and in particular, nitrogen using a residual melt remaining in a crucible after pulling the single crystal. The present invention relates to a method for producing a doped silicon single crystal.

  There are various methods for producing a nitrogen-doped silicon single crystal as a material for a semiconductor substrate. Among them, the CZ method is widely adopted.

  FIG. 1 is a diagram schematically showing the main configuration of a single crystal pulling apparatus suitable for pulling a nitrogen-doped silicon single crystal by the CZ method. The single crystal pulling apparatus is configured with a chamber (not shown) in its outer shell, and a crucible 1 is disposed at the center thereof. The crucible 1 has a double structure and is composed of an inner quartz crucible 1a and an outer 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. A resistance heating type heater 2 is disposed outside the crucible 1 so as to surround the crucible 1. Above the crucible 1, a pulling shaft 5 such as a wire rotating on the same axis as the support shaft 6 in the reverse direction or in the same direction at a predetermined speed is disposed. Is attached.

  When a nitrogen-doped silicon single crystal is pulled using such a single crystal pulling apparatus, a silicon raw material and a nitrogen dopant raw material are put into the crucible 1 and are heated by a heater 2 in an inert gas atmosphere under reduced pressure. Both raw materials are melted in the crucible 1 by heating. Thereafter, the seed crystal 7 held at the lower end of the pulling shaft 5 is immersed in the surface of the raw material melt 3 formed in the crucible 1, and the pulling shaft 5 is gradually moved while rotating the crucible 1 and the pulling shaft 5. Pull up. Thereby, the nitrogen-doped silicon single crystal 4 is grown below the seed crystal 7.

  Here, as the nitrogen dopant raw material, a material containing a high concentration of nitrogen, such as a wafer with a silicon nitride film or a high-purity silicon nitride powder, is commonly used, but this is expensive and the raw material procurement cost is high. It is a factor that makes it worse. Therefore, in order to suppress the raw material procurement cost, a technique for reducing the amount of a conventional expensive nitrogen dopant raw material used has been proposed.

  For example, Patent Document 1 discloses that a portion (hereinafter referred to as “non-product portion”) of a pulled nitrogen-doped silicon single crystal that is not a product is melted in a crucible together with a silicon raw material, and nitrogen is removed from the raw material melt. A technique for growing a doped silicon single crystal is described. As a non-product part, it is included in the shoulder part and tail part formed above and below the straight body part handled as a product, and the straight body part, but slip dislocation, oxidation-induced stacking fault (OSF), etc. are remarkable. Therefore, a crystal defect portion that does not become a product and a non-standard portion that does not become a product because the resistivity, oxygen concentration, or the like does not satisfy the standard are used.

  When such a technique described in Patent Document 1 is used, the non-product part is derived from a nitrogen-doped silicon single crystal, and therefore itself contains nitrogen. From this, it is said that the non-product part is used for the raw material for nitrogen dopant, and this can reduce the usage amount of the conventional expensive raw material for nitrogen dopant.

JP 2004-224582 A

  By the way, during the growth of a silicon single crystal by the CZ method, impurities contained in the raw material melt before pulling are distributed to the solid phase silicon single crystal and the liquid phase raw material melt. As a result, the impurity concentration in the silicon single crystal is much lower than the impurity concentration in the raw material melt. This is because the solubility of impurities in a silicon single crystal that is a solid phase is lower than the solubility of impurities in a raw material melt that is a liquid phase. The ratio “solubility in the solid phase / solubility in the liquid phase” is referred to as a segregation coefficient and is unique to each impurity element.

When nitrogen is used as the impurity, since the segregation coefficient of nitrogen is as small as 7 × 10 ⁻⁴ , the nitrogen concentration in the nitrogen-doped silicon single crystal becomes extremely low, and in the non-product part derived from this nitrogen-doped silicon single crystal Even the concentration of nitrogen is extremely low.

  Therefore, in the technique described in Patent Document 1, even if a non-product part containing nitrogen is used as a raw material for nitrogen dopant, the nitrogen concentration in the non-product part is extremely low. A nitrogen-doped silicon single crystal having a desired nitrogen concentration cannot be grown without supplementing a raw material for nitrogen dopant. Therefore, it cannot be said that the amount of the expensive nitrogen dopant raw material used can be sufficiently reduced, and the suppression of the raw material procurement cost cannot be expected so much.

  Further, when a wafer with a silicon nitride film or a non-product part described in Patent Document 1 is used as a nitrogen dopant raw material, it takes a long time to melt it because it is a solid material to some extent. . In particular, when a wafer with a silicon nitride film is used as a raw material for a nitrogen dopant, since the silicon nitride is difficult to dissolve in the raw material melt, it induces dislocations at the initial stage of single crystal growth and may cause polycrystallization. is there. When polycrystallization occurs in the initial stage of single crystal growth, single crystallization is hindered in subsequent growth, so in actual operation, the crystals grown so far are immersed in the raw material melt and remelted, The single crystal is pulled up again. In either case, production efficiency cannot be denied.

  The present invention has been made in view of the above problems, and can sufficiently reduce the amount of the expensive nitrogen dopant raw material used to achieve a reduction in raw material procurement costs, and can improve production efficiency. It aims at providing the manufacturing method of the nitrogen dope silicon single crystal by CZ method.

  In order to achieve the above object, the present inventors have studied in detail the growth status of nitrogen-doped silicon single crystals, and after the nitrogen-doped silicon single crystals are pulled up, the residual melt that has not been crystallized remains in the crucible. Focused on.

  That is, the residual melt contains a large amount of nitrogen that has not been taken into the nitrogen-doped silicon single crystal due to segregation of impurity elements, and the concentration of nitrogen is extremely high. This can be understood from the following explanation.

FIG. 2 is a diagram showing the relationship between the solidification rate in the growth of a silicon single crystal and the impurity concentration in the single crystal. The relationship shown in the figure is based on the following known formula (1) that gives an impurity concentration [C] _S in a silicon single crystal (solid phase) when nitrogen (N) is used as an impurity as an example and the solidification rate is g. Show. In FIG. 2, the vertical axis indicates the impurity concentration in the silicon single crystal, and the horizontal axis indicates the solidification rate. The “solidification rate” is a ratio of the mass ratio of the silicon single crystal to the amount of the raw material melt in the crucible before pulling up the silicon single crystal.
[C] _S = k ₀ [C] ₀ (1-g) ^k0-1 (1)

From the above equation (1), the impurity concentration in the silicon single crystal corresponding to the change in the solidification rate can be obtained. In the formula (1), k ₀ is the segregation coefficient of impurities, and [C] ₀ indicates the initial concentration of impurities in the raw material melt (liquid phase) before solidification starts. 5 × 10 ¹⁶ atoms / cm ³ .

FIG. 3 is a diagram showing the relationship between the solidification rate in the growth of a silicon single crystal and the impurity concentration in the raw material melt. The relationship shown in the figure corresponds to the relationship shown in FIG. 2, and is shown in accordance with the following known formula (2) that gives the impurity concentration [C] _L in the raw material melt (liquid phase) when the solidification rate is g. . In FIG. 3, the vertical axis represents the impurity concentration in the raw material melt, and the horizontal axis represents the solidification rate.
[C] _L = [C] ₀ (1-g) ^k0-1 (2)

From the above equation (2), the impurity concentration in the raw material melt corresponding to the change in the solidification rate is obtained, and k ₀ and [C] ₀ in the equation are the same as the meaning and value in the above equation (1), respectively. It is.

As apparent from FIG. 2, the concentration of each impurity in the silicon single crystal as a solid phase is higher than the initial concentration of each impurity in the raw material melt (3.5 × 10 ¹⁶ atoms / cm ^{3 with} nitrogen). Remarkably low. In addition, for both nitrogen and iron, the impurity concentration is low on the top side (side where the solidification rate is close to 0) of the silicon single crystal, and gradually increases as the solidification rate increases, and the bottom side (where the solidification rate is On the side close to 1.0), it increases rapidly.

  On the other hand, as apparent from FIG. 3, the concentration of each impurity in the raw material melt, which is a liquid phase, is as low as the initial concentration on the top side of the silicon single crystal, and gradually increases as the solidification rate increases. It becomes higher and sharply higher on the bottom side.

  Due to such segregation of impurity elements, the residual melt in the crucible after pulling up the nitrogen-doped silicon single crystal has an extremely high nitrogen concentration. Therefore, since the remaining melt sufficiently contains nitrogen, it can be suitably used as an alternative to a conventional expensive raw material for nitrogen dopant.

The present invention is based on such a technical idea, and is a method for producing a silicon single crystal doped with nitrogen by the CZ method, and a silicon nitride film-coated wafer or silicon nitride powder is used as a nitrogen dopant raw material. Production of a nitrogen-doped silicon single crystal that pulls up the silicon single crystal from the melted initial raw material melt , then supplies the silicon raw material to the remaining melt remaining in the crucible and melts it, and pulls up the silicon single crystal from this melt The method is characterized in that the supply of the silicon raw material to the residual melt and the pulling up of the silicon single crystal are repeated a plurality of times. In this manufacturing method, when the silicon single crystal is grown, the concentration of nitrogen in the residual melt at this time is calculated based on the solidification rate at the end of pulling of the immediately preceding silicon single crystal, The amount of nitrogen contained is calculated, and the residual melt is adjusted so that the nitrogen concentration in the raw material melt obtained by melting the residual melt and the silicon raw material to be supplied matches the initial concentration in the initial raw material melt. The required weight of the silicon raw material to be supplied is calculated from the weight of the above and the amount of nitrogen in the residual melt, and only this amount of silicon raw material is supplied to the residual melt.

  With such a configuration, the residual melt having a high nitrogen concentration remaining in the crucible after the pulling of the nitrogen-doped silicon single crystal by the CZ method is reused as a raw material for the nitrogen dopant as it is. The replenishment of the raw material is unnecessary, and as a result, the amount of the expensive nitrogen dopant raw material used can be sufficiently reduced. Moreover, in growing the silicon single crystal, since the remaining melt in which silicon nitride is sufficiently dissolved is used as a raw material for nitrogen dopant, it is not necessary to melt it again. From the raw material melt of this and the silicon raw material, In the grown silicon single crystal, the occurrence of dislocations is suppressed at the initial stage of growth, and polycrystallization is suppressed.

  According to the method for producing a nitrogen-doped silicon single crystal of the present invention, it is possible to sufficiently reduce the amount of expensive nitrogen dopant raw material used, and as a result, it is possible to realize suppression of raw material procurement costs. . In addition, when the single crystal is grown, it is not necessary to melt the residual melt that is the raw material for the nitrogen dopant, and polycrystallization in the initial stage of the single crystal growth is suppressed, so that the production efficiency can be improved. .

  Below, one Embodiment of the manufacturing method of the nitrogen dope silicon single crystal of this invention is explained in full detail. The method for producing a nitrogen-doped silicon single crystal in the present embodiment is such that after pulling up the silicon single crystal, the silicon raw material is supplied to the remaining melt remaining in the crucible and melted, and the silicon single crystal is pulled up from this melt. It is characterized by that.

  In a simple example, the nitrogen-doped silicon single crystal is pulled twice by the CZ method, and the single crystal pulling is performed using a conventional material having a high nitrogen concentration as the nitrogen dopant raw material for the first pulling. When the second pulling is continued, single crystal pulling is performed using the residual melt in the crucible after the first pulling as a nitrogen dopant raw material.

  FIG. 4 is a diagram schematically showing steps in the method for producing a nitrogen-doped silicon single crystal according to an embodiment of the present invention. As shown in FIG. 4 (a), in the crucible 1, a polycrystalline silicon raw material 8 commonly used for the production of a nitrogen-doped silicon single crystal, and a conventional wafer such as a wafer with a silicon nitride film or a high-purity silicon nitride powder. The nitrogen dopant raw material 9 is charged at a predetermined blending ratio and heated by a heater. Thereby, as shown in FIG.4 (b), the raw material melt 3 which fuse | melted both the raw materials 8 and 9 is obtained.

  Subsequently, as shown in FIG. 4C, the seed crystal 7 is immersed in the surface of the raw material melt 3 in the crucible 1 and pulled upward according to normal manufacturing conditions. As a result, as shown in FIG. 4D, the nitrogen-doped silicon single crystal 4 is grown below the seed crystal 7. A melt 3a containing nitrogen at a high concentration remains at the bottom in the crucible 1 after the silicon single crystal 4 is pulled up. This residual melt 3a is in a state in which silicon nitride is sufficiently dissolved.

  Next, as shown in FIG. 4E, a predetermined amount of polycrystalline silicon raw material 8 is put into the crucible 1 in which the remaining melt 3a remains, and heated by a heater. Thereby, as shown in FIG. 4F, the raw material melt 3 in which the silicon raw material 8 is melted and mixed with the remaining melt 3a is obtained.

  Subsequently, as shown in FIG. 4G, the seed crystal 7 is immersed in the raw material melt 3 in the crucible 1 and pulled upward in accordance with the same manufacturing conditions as in the step shown in FIG. As a result, as shown in FIG. 4H, the nitrogen-doped silicon single crystal 4 is grown below the seed crystal 7 as in the step shown in FIG.

  4 (h), the melt 3a containing nitrogen at a high concentration remains in the crucible 1, so that the steps shown in FIGS. 4 (e) to (h) are further performed. By passing, the nitrogen-doped silicon single crystal 4 can be grown. That is, the steps shown in FIGS. 4E to 4H can be repeated, and it is also possible to perform an operation by a so-called multiple pulling method in which a plurality of single crystals are continuously pulled up from one crucible.

  In such a method for producing a nitrogen-doped silicon single crystal, the residual melt having a high nitrogen concentration remaining in the crucible after pulling up the nitrogen-doped silicon single crystal is reused as it is as a raw material for nitrogen dopant. Therefore, replenishment of the expensive nitrogen dopant raw material is unnecessary, and as a result, the amount of the expensive nitrogen dopant raw material used can be sufficiently reduced. For this reason, it becomes possible to realize suppression of raw material procurement costs.

  In addition, when the single crystal is grown, the residual melt in which silicon nitride is sufficiently dissolved is used as a raw material for the nitrogen dopant, so it is not necessary to melt it again. In the silicon single crystal, the occurrence of dislocations is suppressed in the initial stage of growth, and polycrystallization is suppressed. For this reason, the production efficiency of the nitrogen-doped silicon single crystal can be improved.

  Here, in order to obtain a nitrogen-doped silicon single crystal having a desired nitrogen concentration, it is necessary to determine the amount of silicon raw material supplied into the crucible. Since nitrogen is taken into the single crystal from the raw material melt during the growth of the silicon single crystal, the amount of nitrogen in the residual melt remaining in the crucible after the growth is naturally reduced from the initial state before the crystal growth. This is because, if the silicon raw material is supplied without considering the decrease in the next single crystal growth, the nitrogen concentration in the grown single crystal may not satisfy the desired range.

For this reason, in this embodiment, the solidification rate is preferentially managed, and the supply amount of the silicon raw material into the crucible is set according to the following method. First, the nitrogen concentration [C] _{L (N)} in the residual melt is calculated from the solidification rate g at the end of the pulling of the silicon single crystal based on the formula (2), and is contained in the residual melt. The amount of nitrogen (number of atomic units) is calculated.

Then, when the next single crystal is grown, the initial concentration of nitrogen used in the raw material melt formed by melting the residual melt and the silicon raw material is within the desired range of the nitrogen concentration in the single crystal. Calculate the required weight of the silicon raw material from the weight of the residual melt and the amount of nitrogen in the residual melt so as to match the initial concentration [C] _{0 (N)} in the melt. Put it in the crucible. If the single crystal is pulled from this raw material melt, a nitrogen-doped silicon single crystal having a desired nitrogen concentration can be grown.

  Thus, when the silicon single crystal is grown, the nitrogen concentration in the silicon single crystal is set by setting the amount of the silicon raw material supplied to the remaining melt based on the solidification rate at the end of the pulling of the immediately preceding silicon single crystal. It can be adjusted appropriately.

  In order to confirm the effect of the method for producing a nitrogen-doped silicon single crystal of the present invention, the following test was conducted. In the test of this example, a crucible having an inner diameter of 22 inches was used. First, a raw material melt obtained by charging a total of 140 kg of a polycrystalline silicon raw material and a wafer with a silicon nitride film, and heating and melting it. The p-type nitrogen-doped silicon single crystal having a diameter of 200 mm was grown.

At this time, the nitrogen concentration in the raw material melt before growing the single crystal is the initial concentration in the initial raw material melt adopted because the nitrogen concentration at the top of the single crystal becomes the target 1 × 10 ¹⁴ atoms / cm ^3. A wafer with a silicon nitride film, which is a raw material for nitrogen dopant, was charged in the crucible so that the concentration would be high. Furthermore, the temperature distribution in the apparatus and the pulling rate are adjusted, and the pulling is performed under a growth condition in which a defect-free crystal region free of grown-in defects such as infrared scatterer defects (COPs) and dislocation clusters is formed. went.

  The pulling was completed when 30 kg of the melt remained in the crucible, that is, when the solidification rate was 0.786 (78.6% in percentage display).

  Subsequently, in growing the second single crystal, a polycrystalline silicon raw material was put into a crucible in which 30 kg of melt remained after the first single crystal was grown. At this time, considering the decrease in nitrogen taken into the first single crystal so that the initial concentration of nitrogen in the raw material melt is equivalent to the initial concentration during the growth of the first single crystal, the total weight The polycrystalline silicon raw material was charged to 139.8 kg. After heating and melting, a second nitrogen-doped silicon single crystal was grown under the same conditions as the first growth.

  Then, similarly to the first growth condition, the pulling of the second single crystal was finished when 30 kg of the melt remained in the crucible. Similarly, a third single crystal was grown.

  The first to third continuous single crystals were grown in one batch as described above, and 5 batches were performed.

  In the growth process at each stage of each batch, the number of occurrences of dislocations and polycrystallization was investigated at the initial stage of the growth. Polycrystallization was confirmed by observing the habit line. Here, when polycrystallization occurred, the crystal grown so far was remelted and the single crystal was pulled up again. After that, when polycrystallization occurred again, the crystal was remelted and the single crystal was pulled again. That is, the number of polycrystallizations investigated here means the cumulative number of occurrences of polycrystallization in one growth process.

  Table 1 below shows the survey results. In Table 1, the number of times of polycrystallization indicates the average value of 5 batches in each of the growth processes of the first, second and third single crystals.

  From the results shown in Table 1, the number of times of polycrystallization is compared with the case of growing the first single crystal using a wafer with a silicon nitride film as the nitrogen dopant raw material. The number of the second and third single crystals used as raw materials was significantly reduced. That is, when the residual melt in the crucible is used as a raw material for the nitrogen dopant, it is clear that since silicon nitride is sufficiently dissolved in advance, the occurrence of dislocations is suppressed and polycrystallization is suppressed. became.

In order to confirm the quality of the grown silicon single crystal, a sample wafer was taken from the bottom of the single crystal, and the nitrogen concentration was measured by SIMS (secondary ion mass spectrometry). The results are: 2.75 × 10 ¹⁵ atoms / cm ^{3 for} the first single crystal, 2.82 × 10 ¹⁵ atoms / cm ^{3 for} the second single crystal, and 2.79 × 10 3 for the third single crystal. ¹⁵ atoms / cm ³ , which was within the target nitrogen concentration range at any stage.

  In addition, the concentration of impurity elements such as aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr), etc. contained in the single crystal was also measured by the same method. there were. Further, the carbon (C) concentration contained in the single crystal is measured by FTIR (Fourier transform infrared spectrophotometer), and the iron (Fe) concentration is measured by ICP-MS (inductively coupled plasma mass spectrometry) and AAS ( Atomic absorption spectroscopy), the values were all within the standard range.

  According to the method for producing a nitrogen-doped silicon single crystal of the present invention, a high nitrogen concentration melt remaining in the crucible after pulling up the nitrogen-doped silicon single crystal is reused as a nitrogen dopant raw material, which is expensive. The amount of high-purity nitrogen dopant raw material used can be sufficiently reduced, and as a result, the raw material procurement cost can be suppressed. In addition, when the single crystal is grown, the remaining melt does not need to be melted again, and the polycrystallization at the initial stage of the single crystal growth is suppressed, so that the production efficiency can be improved. Therefore, the present invention is an extremely useful technique for producing a nitrogen-doped silicon single crystal by the CZ method.

It is a figure which shows typically the principal part structure of the single crystal pulling apparatus suitable for implementing the pulling of the nitrogen dope silicon single crystal by CZ method. It is a figure which shows the relationship between the solidification rate in the growth of a silicon single crystal, and the impurity concentration in a single crystal. It is a figure which shows the relationship between the solidification rate in the growth of a silicon single crystal, and the impurity concentration in a raw material melt. It is a figure which shows typically the process in the manufacturing method of the nitrogen dope silicon single crystal which is one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crucible 1a Quartz crucible 1b Graphite crucible 2 Heater 3 Raw material melt 3a Residual melt 4 Nitrogen dope silicon single crystal 5 Lifting shaft 6 Support shaft 7 Seed crystal 8 Silicon material 9 Conventional material for nitrogen dopant

Claims (1)

A method for producing a silicon single crystal doped with nitrogen by the Czochralski method,
After pulling up the silicon single crystal from the initial raw material melt obtained by melting the silicon nitride film wafer or silicon nitride powder as the nitrogen dopant raw material , the silicon raw material is supplied to the residual melt remaining in the crucible and melted. It is a method for producing a nitrogen-doped silicon single crystal that pulls the silicon single crystal from the melt,
During the growth of the silicon single crystal, the supply of the silicon raw material to the remaining melt and the pulling up of the silicon single crystal are repeated a plurality of times .
Based on the solidification rate at the end of pulling of the immediately preceding silicon single crystal, the concentration of nitrogen in the residual melt at this time is calculated to calculate the amount of nitrogen contained in the residual melt, and the residual melt From the weight of the residual melt and the amount of nitrogen in the residual melt so that the nitrogen concentration in the raw material melt formed by melting the supplied silicon raw material matches the initial concentration in the initial raw material melt A method for producing a nitrogen-doped silicon single crystal, wherein a necessary weight of a silicon raw material to be supplied is calculated, and only this amount of silicon raw material is supplied to the remaining melt .

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