JP5924181B2 - Manufacturing method of FZ single crystal silicon - Google Patents

Description

  The present invention is an FZ method by FZ method (floating zone method or floating zone melting method) in which a raw crystal bar is heated and melted by an induction heating coil to form a floating zone and a single crystal rod is grown by moving the floating zone. The present invention relates to a method for producing a single crystal.

  Conventionally, a silicon wafer cut from a silicon single crystal manufactured by the FZ method has been used for manufacturing a high voltage power device such as a thyristor. In recent years, in order to improve the performance of semiconductor devices and reduce costs, a silicon wafer having a large diameter has been demanded, and accordingly, growth of a silicon single crystal having a large diameter has been required.

  Usually, rod-shaped polycrystalline silicon is used as a raw material for producing FZ single crystal silicon. However, the polycrystalline silicon (polycrystalline silicon rod for FZ) required as a raw material in the FZ method has high purity, hardly generates cracks and cracks, has a uniform grain boundary structure, and is suitable for FZ single crystal silicon to be manufactured. It is necessary to have a cylindrical shape with a good surface condition with a small flatness and crank. The manufacture of such a polycrystalline silicon rod for FZ is very low in yield and productivity as compared with the manufacture of nugget-like polycrystalline silicon used in the CZ method.

  In addition, in recent years, the demand for polycrystalline silicon (polycrystalline silicon for CZ) used in the CZ method centering on 300 mm diameter has increased significantly, and there has also been a demand for polycrystalline silicon for solar cells. It is increasing rapidly. As a result, quality standards such as shape and purity are strict, the productivity is low, and the supply of polycrystalline silicon rods for FZ, which is high in cost, is tight against the demand, and the price is very high. Yes. As a result, it becomes difficult to secure high-quality polycrystalline silicon for FZ, and it has become difficult to stably manufacture FZ single-crystal silicon.

  Therefore, in recent years, FZ single crystals are produced using single crystals produced by the CZ method as raw materials in order to improve production costs, adjust the resistivity of the produced FZ single crystals, and supply stable quality FZ single crystals. Methods have been studied (Patent Document 1, Patent Document 2).

  FIG. 3 shows a schematic diagram of an apparatus for producing a single crystal by the FZ method. A method for manufacturing an FZ single crystal using the FZ single crystal manufacturing apparatus 30 will be described.

  First, the raw material rod 1 is held by the upper holding jig 4 of the upper shaft 3 installed in the chamber 20. On the other hand, a single crystal seed (seed crystal) 8 having a small diameter is held by the lower holding jig 6 of the lower shaft 5 positioned below the raw material rod 1.

  Next, the raw material rod 1 is melted by the induction heating coil 7 connected to the high frequency oscillator 40 and fused to the seed crystal 8. Thereafter, the narrowed portion 9 is formed by seed drawing to make dislocation-free. Then, the raw material rod 1 and the single crystal rod (FZ single crystal) 2 are lowered while the upper shaft 3 and the lower shaft 5 are rotated, so that the floating zone (also referred to as a melting zone or a melt) 10 is made into the raw material rod 1 and the single crystal. A single crystal rod 2 is grown by forming between the rods 2 and moving the floating zone 10 to the upper end of the raw material rod 1 for zoning. The growth of the FZ single crystal is usually performed in an atmosphere in which a small amount of nitrogen gas is mixed with Ar gas. Further, a doping gas or the like can be sprayed from the gas spray nozzle 11 to the floating zone 10. As the induction heating coil 7, an induction heating coil is generally used in which single or multiple winding water made of copper or silver is circulated.

JP 2007-314374 A JP 2011-116570 A

  As a raw material for producing an ordinary FZ single crystal, a columnar crystal (including a polycrystal, a single crystal, an intermediate crystal grown by a polycrystal seed, and a dislocation crystal) is used. Among these, when a single crystal produced by the CZ method (Czochralski method) is used as a raw material, the oxygen concentration in the CZ single crystal used as a raw material increases due to oxygen contamination from the quartz crucible during the production of the CZ single crystal. The oxygen concentration of the FZ single crystal after zoning is also higher than that of the FZ single crystal manufactured using polycrystalline silicon as a raw material. Thus, when the oxygen concentration in the single crystal increases, even if the oxygen concentration itself is very small, a donor due to oxygen alone or a donor due to a complex of nitrogen and oxygen is generated, and the manufactured FZ single crystal Therefore, it has been desired to develop a technique for reducing the oxygen concentration in an FZ single crystal manufactured using a CZ single crystal as a raw material.

  The present invention has been made in view of the above problems, and in a method for manufacturing an FZ single crystal manufactured using a single crystal manufactured by the CZ method as a raw material, the FZ single crystal has a reduced oxygen concentration and a small change in resistivity. An object of the present invention is to provide a method of producing

  The present invention has been made to solve the above-described problems. In a method for producing an FZ single crystal by performing zoning by an FZ method using a single crystal produced by a CZ method as a raw material, the zoning is performed twice. The FZ single crystal is characterized by reducing the oxygen concentration in the FZ single crystal after performing the zoning twice or more than the oxygen concentration in the FZ single crystal after performing the zoning once. A manufacturing method is provided.

  Thus, the manufacturing method of the FZ single crystal in which zoning is performed twice or more can increase the opportunity for evaporation of oxygen as SiOx during zoning, thereby reducing the oxygen concentration in the crystal and reducing the resistivity change. Single crystals can be produced.

Moreover, it is preferable to repeat the zoning twice or more until the oxygen concentration in the FZ single crystal becomes 8 × 10 ¹⁵ atoms / cm ³ (ASTM-79) or less. In addition, the display of the oxygen concentration in the following crystals is ASTM-79 display.

  In this way, by repeating zoning until the oxygen concentration in the FZ single crystal reaches the above value, it is possible to further suppress the generation of donors due to oxygen alone, or donors due to a complex of nitrogen and oxygen. The change in resistivity of the single crystal can be further reduced.

  Further, after the second and subsequent zoning, the oxygen concentration of the wafer sample taken from the end face of the FZ single crystal subjected to the zoning is measured, and whether or not zoning is necessary again based on the measured oxygen concentration. It is preferable to perform the second zoning when it is determined that the second zoning is necessary.

  In this way, by measuring the oxygen concentration at the end face of the FZ single crystal after each zoning step and using it for determination, an FZ single crystal with a reduced oxygen concentration can be obtained more reliably.

  In the method for producing an FZ single crystal according to the present invention, even if a CZ single crystal is used as a raw material, the chance of evaporating oxygen as SiOx during zoning can be increased by performing zoning twice or more. It is possible to produce an FZ single crystal with reduced oxygen concentration and little change in resistivity.

It is a flowchart which shows an example (1st Embodiment) of the manufacturing method of the FZ single crystal of this invention. It is a flowchart which shows another example (2nd Embodiment) of the manufacturing method of FZ single crystal of this invention. It is the schematic which shows an example of the manufacturing apparatus of FZ single crystal. It is a graph which shows the result of an Example and a comparative example.

  Hereinafter, the present invention will be described in detail.

As described above, it has been desired to develop a technique for reducing the oxygen concentration in an FZ single crystal manufactured using a CZ single crystal as a raw material. In particular, since a single crystal produced by the CZ method has a high original oxygen concentration, when this is used as a raw material, the FZ single crystal after one zoning almost always exceeds 8 × 10 ¹⁵ atoms / cm ^3. And many of them contain oxygen at concentrations exceeding 2 × 10 ¹⁶ atoms / cm ³ . Thus, as described above, the oxygen contained in the FZ single crystal generates a donor due to oxygen alone or a donor due to a composite of nitrogen and oxygen, and changes in resistivity particularly in a high resistivity region of 1000 Ωcm or more. Cause.

The inventors of the present invention evaporate oxygen contained in the floating zone as SiOx from the surface of the floating zone during zoning, so that the oxygen concentration in the FZ single crystal is about 1 / of the oxygen concentration in the source crystal in one zoning. However, when an FZ single crystal is manufactured using a single crystal manufactured by the CZ method as a raw material, the oxygen concentration in the crystal has almost no influence of donor formation in the FZ single crystal manufactured using a polycrystalline raw material as a raw material. It was found that the effect of reducing the oxygen concentration was insufficient compared to the value, that is, 8 × 10 ¹⁵ atoms / cm ³ or less. By setting the oxygen concentration to 8 × 10 ¹⁵ atoms / cm ³ or less, the resistivity change caused by the donor due to the complex of nitrogen and oxygen can be suppressed to 10% or less even if the resistance is as high as 1000 Ωcm, for example.

  Based on the above knowledge, the present inventors significantly reduce the oxygen concentration in the FZ single crystal by performing zoning twice or more in order to increase the opportunity for evaporation of SiOx from the surface of the floating zone. As a result, the present invention has been completed.

  The present invention is a method for producing an FZ single crystal by performing zoning by the FZ method twice or more using a single crystal produced by the CZ method as a raw material. At this time, in the present invention, the oxygen concentration in the FZ single crystal after performing zoning twice or more is reduced from the oxygen concentration in the FZ single crystal after performing zoning once.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  FIG. 1 shows an outline of the flow of the first embodiment as an example of the method for producing an FZ single crystal of the present invention. Although FIG. 1 shows a case where the zoning by the FZ method is performed twice in total, the zoning may be performed three times or more as described later.

  First, as shown in FIG. 1A, a single crystal manufactured by a CZ method (hereinafter also simply referred to as a CZ single crystal) is prepared as a raw material (step a). The CZ single crystal prepared here is not particularly limited as long as it is a single crystal that can be produced by the CZ method and can be used as a raw material rod for the FZ method. For example, the conductivity type and resistivity of the CZ single crystal are not particularly limited, and the diameter may be in a range that can be used as a raw material rod for the FZ method.

  Next, as shown in FIG. 1B, the first zoning is performed using the CZ single crystal prepared in step a (step b). In this step b, a normal FZ single crystal manufacturing apparatus as shown in FIG. 3 can be used. This step b will be described with reference to FIG.

  As the raw material rod 1, the CZ single crystal prepared in step a is used. The part of the raw material rod (CZ single crystal) 1 where melting starts is processed into a cone shape, and the surface is etched to remove the processing distortion. Thereafter, the raw material rod (CZ single crystal) 1 is accommodated in the chamber 20 in the single crystal manufacturing apparatus 30 by the FZ method, and fixed to the upper holding jig 4 of the upper shaft 3 installed in the chamber 20 with screws or the like. . On the other hand, a seed crystal 8 is attached to the lower holding jig 6 of the lower shaft 5.

  Next, the lower end of the cone part of the raw material rod (CZ single crystal) 1 is preheated with a carbon ring (not shown). Thereafter, Ar gas containing nitrogen gas is supplied from the lower part of the chamber 20 and exhausted from the upper part of the chamber. After the raw material rod (CZ single crystal) 1 is heated and melted by the induction heating coil 7, the tip of the cone portion is fused to the seed crystal 8, the dislocation is made free by the narrowed portion 9, and the upper shaft 3 and the lower shaft 5 are rotated. Then, the raw material rod (CZ single crystal) 1 is moved down to the upper end of the raw material rod (CZ single crystal) 1 by lowering the raw material rod (CZ single crystal) 1 at a speed of, for example, 1 to 5 mm / min. Grow. At this time, it is possible to grow the single crystal by shifting (eccentric) the upper shaft 3 serving as the rotation center of the raw material rod (CZ single crystal) 1 and the lower shaft 5 serving as the rotation center of the manufactured single crystal. preferable. By shifting both centers in this way, the melted portion can be stirred during single crystallization, and the quality of the single crystal to be produced can be made uniform. The amount of eccentricity may be set according to the diameter of the single crystal. Further, a doping gas or the like can be sprayed from the gas spray nozzle 11 to the floating zone 10 as necessary. As the induction heating coil 7, an induction heating coil in which a single or multiple winding water made of copper or silver is circulated can be used.

  Next, as shown in FIG. 1C, the second zoning is performed on the FZ single crystal obtained in step b (step c). As the FZ single crystal manufacturing apparatus used in step c, the normal FZ single crystal manufacturing apparatus shown in FIG. 3 can be used as in the apparatus used in step b. However, as the raw material rod 1 used at this time, an FZ single crystal that has undergone the first zoning in step b is used.

  FIG. 1 shows the case where the step c is performed only once, but this step c, that is, the step of zoning the FZ single crystal that has already undergone zoning may be repeated a plurality of times. For example, if step c is performed once, zoning is performed twice in total with step b in all steps, and if step c is performed twice, zoning is performed three times in all steps. Become.

By performing step c, the oxygen concentration in the FZ single crystal is further reduced as compared with the FZ single crystal after step b. That is, the oxygen concentration in the FZ single crystal after performing zoning twice or more is reduced from the oxygen concentration in the FZ single crystal after performing zoning once. At this time, it is preferable to repeat the zoning performed in the step c until the oxygen concentration in the FZ single crystal becomes 8 × 10 ¹⁵ atoms / cm ³ (ASTM-79) or less. With such an oxygen concentration, it is possible to further suppress the generation of a donor due to oxygen alone or a donor due to a complex of nitrogen and oxygen, and the resistivity change of the FZ single crystal can be further reduced. is there.

  As described above, an FZ single crystal can be produced according to the method (first embodiment) according to the present invention. In the present invention, by performing zoning twice or more in total in step b and step c, the opportunity to evaporate oxygen as SiOx during zoning can be increased, so the oxygen concentration in the crystal is reduced, and the resistivity An FZ single crystal with little change can be produced.

  The FZ single crystal thus produced can be processed into an ingot and a wafer as a product wafer as shown in FIGS.

  In this case, as shown in FIG. 1D, ingot processing is performed on the FZ single crystal obtained in step c (step d). This step can be performed by known peripheral grinding or etching.

  Next, as shown in FIG. 1E, the ingot obtained in step d is processed into a wafer (step e). This step can be performed by a known slicing method, grinding, polishing, etching or the like.

  In this way, a product wafer can be obtained as shown in FIG.

  FIG. 2 shows an outline of the flow of the second embodiment as another example of the method for producing an FZ single crystal of the present invention. In the second embodiment, after the second and subsequent zoning, the oxygen concentration of the wafer sample taken from the end face of the zoned FZ single crystal is measured, and the zoning is performed again based on the measured oxygen concentration. Is determined, and when it is determined that zoning is necessary again, the zoning is performed again. What is shown in (a), (b), (d), (e), and (f) of FIG. 2 is the same as in the first embodiment.

  In the second embodiment, first, as shown in FIG. 2A, a CZ single crystal is prepared as a raw material (step a). Next, as shown in FIG. 2B, the first zoning is performed using the CZ single crystal prepared in step a (step b). These steps are the same as those in the first embodiment.

  Next, as shown in FIG. 2 (c1), the second zoning is performed on the FZ single crystal obtained in step b (step c1). This step c1 is the same as the step c shown in FIG. However, depending on the determination result of the oxygen concentration described later, this step is performed again, and in this case, the third and subsequent times.

  Next, as shown in FIG. 2 (c2), a wafer sample is taken from the end face of the FZ single crystal obtained in step c1, and the oxygen concentration is measured (step c2). In this step, a known method for measuring the oxygen concentration in a single crystal can be used. For example, a measuring method based on ASTM-79 can be used.

Next, as shown in FIG. 2 (c3), it is determined whether or not zoning is necessary again based on the measured oxygen concentration (step c3). If it is determined by this determination that re-zoning is necessary, re-zoning (step c1) is performed. As a reference value for this determination, for example, the above 8 × 10 ¹⁵ atoms / cm ³ (ASTM-79) can be used. If the oxygen concentration of the single crystal measured in step c2 is below the reference value, there is no need to perform zoning again.

  If it is determined that the zoning is necessary again, the steps c1 to c3 are repeated again. If it is determined that the standard is not satisfied even though the second zoning (the third zoning in combination with the step b) is performed through the steps c1 to c3 again, the third time (in combination with the step b) (4th zoning) will be performed.

  As described above, an FZ single crystal can be produced according to the method (second embodiment) according to the present invention. In the second embodiment, by measuring the oxygen concentration at the end face of the FZ single crystal after each zoning step and using it for determination, an FZ single crystal with a reduced oxygen concentration can be obtained more reliably.

  In the steps d and e shown in FIGS. 2D and 2E, ingot processing and wafer processing can be performed on the FZ single crystal thus manufactured in the same manner as in the first embodiment. it can. In this way, a product wafer can be obtained as shown in FIG.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited by these.

Example 1
Using 91 CZ single crystals with a resistivity of 1000 Ω · cm or more and a diameter of 130 mm as a raw material rod, zoning is performed twice by the FZ method according to the method of the present invention shown in FIG. 1, and an FZ single crystal having a diameter of 75 mm to 125 mm. Manufactured. When manufacturing this FZ single crystal, the FZ single crystal manufacturing apparatus shown in FIG. 3 was used. The furnace pressure was 0.1 to 0.2 MPa, and the Ar gas flow rate was 30 to 100 L / min.

Thus, zoning was performed twice and 91 FZ single crystals were obtained. Thereafter, a wafer sample was taken from the end face of the obtained FZ single crystal, and the oxygen concentration in the crystal was measured. The measurement results are shown in FIG. As shown in FIG. 4, the average oxygen concentration in the crystal is 6.01 × 10 ¹⁵ atoms / cm ³ , a maximum of 1.60 × 10 ¹⁶ atoms / cm ³ , and a minimum of 4.00 × 10 ¹⁵ atoms / cm ^3. The ratio of 8 × 10 ¹⁵ atoms / cm ³ or less was 92.3% (84).

(Example 2)
In accordance with the method of the present invention shown in FIG. 2, seven FZ single crystals whose oxygen concentration in the crystal was higher than 8 × 10 ¹⁵ atoms / cm ³ even after zoning twice in Example 1 were used as raw material rods. The third zoning was performed by the FZ method to produce an FZ single crystal having a diameter of 75 mm to 125 mm. The FZ single crystal manufacturing apparatus shown in FIG. 3 was also used during the third zoning. The furnace pressure was 0.1 to 0.2 MPa, and the Ar gas flow rate was 30 to 100 L / min.

Thus, zoning was performed three times in total to obtain seven FZ single crystals. Thereafter, a wafer sample was taken from the end face of the obtained FZ single crystal, and the oxygen concentration in the crystal was measured. The oxygen concentration in the crystal is an average of 6.57 × 10 ¹⁵ atoms / cm ³ , a maximum of 8.00 × 10 ¹⁵ atoms / cm ³ , a minimum of 4.00 × 10 ¹⁵ atoms / cm ³ or less, and 8 × 10 ¹⁵ The ratio of atoms / cm ³ or less was 100% (seven).

(Comparative Example 1)
Using 1028 CZ single crystals having a resistivity of 1000 Ω · cm or more and a diameter of 130 mm as a raw material rod, zoning was performed only once by the FZ method to produce FZ single crystals having a diameter of 75 mm to 125 mm. When manufacturing this FZ single crystal, the FZ single crystal manufacturing apparatus shown in FIG. 3 was used. The furnace pressure was 0.1 to 0.2 MPa, and the Ar gas flow rate was 30 to 100 L / min.

Thus, zoning was performed only once to obtain 1028 FZ single crystals. Thereafter, a wafer sample was taken from the end face of the obtained FZ single crystal, and the oxygen concentration in the crystal was measured. The measurement results are shown in FIG. As shown in FIG. 4, the oxygen concentration in the crystal is an average of 2.59 × 10 ¹⁶ atoms / cm ³ , a maximum of 5.04 × 10 ¹⁶ atoms / cm ³ , and a minimum of 5.6 × 10 ¹⁵ atoms / cm ³ . Yes, the ratio of 8 × 10 ¹⁵ atoms / cm ³ or less was 0.4% (four).

(Comparative Example 2)
Using 727 FZ polycrystalline raw materials having a resistivity of 1000 Ω · cm or more and a diameter of 75 to 135 mm as raw material rods, zoning was carried out only once by the FZ method to produce FZ single crystals having a diameter of 75 mm to 125 mm. When manufacturing this FZ single crystal, the FZ single crystal manufacturing apparatus shown in FIG. 3 was used. The furnace pressure was 0.1 to 0.2 MPa, and the Ar gas flow rate was 30 to 100 L / min.

Thus, zoning was performed only once to obtain 727 FZ single crystals. Thereafter, a wafer sample was taken from the end face of the obtained FZ single crystal, and the oxygen concentration in the crystal was measured. The measurement results are shown in FIG. As shown in FIG. 4, the average oxygen concentration in the crystal is 6.43 × 10 ¹⁵ atoms / cm ³ , the maximum is 1.12 × 10 ¹⁶ atoms / cm ³ , and the minimum is 4.00 × 10 ¹⁵ atoms / cm ³ . Yes, the ratio of 8 × 10 ¹⁵ atoms / cm ³ or less was 95.5% (694).

  In Examples 1 and 2 according to the method for producing an FZ single crystal of the present invention, even when a single crystal produced by the CZ method is used as a raw material, it is comparable to an FZ single crystal produced from a polycrystalline silicon raw material. An FZ single crystal having a low oxygen concentration could be obtained.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

1 ... Raw material rod, 2 ... Single crystal rod, 3 ... Upper shaft, 4 ... Upper holding jig,
5 ... Lower shaft, 6 ... Lower holding jig, 7 ... Induction heating coil,
8 ... seed crystal, 9 ... throttle part, 10 ... floating zone, 20 ... chamber,
DESCRIPTION OF SYMBOLS 11 ... Nozzle for gas spraying, 30 ... FZ single crystal manufacturing apparatus, 40 ... High frequency oscillator.

Claims (2)

In a method for producing FZ single crystal silicon by performing zoning by FZ method using a silicon single crystal produced by CZ method as a raw material,
Perform the zoning twice or more,
Than the oxygen concentration of the FZ single-crystal silicon after once the zoning reduces the oxygen concentration of the FZ single-crystal silicon after the zoning more than once,
The method for producing FZ single crystal silicon , wherein the zoning is repeated twice or more until the oxygen concentration in the FZ single crystal silicon becomes 8 × 10 ¹⁵ atoms / cm ³ (ASTM-79) or less. After the second and subsequent zoning, the oxygen concentration of the wafer sample taken from the end face of the zoned FZ single crystal silicon is measured, and whether or not zoning is necessary again based on the measured oxygen concentration. Determine
2. The method for producing FZ single crystal silicon according to claim 1, wherein the second zoning is performed when it is determined that the second zoning is necessary.

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