Manufacturing method and evaluation method for single crystal silicon

Abstract

To provide a production method and an evaluation method of single crystal silicon capable of reducing cost.SOLUTION: A production method of single crystal silicon has the steps of: producing first single crystal silicon 20a by an FZ method using a seed crystal 5: separating the seed crystal 5 after producing the first single crystal silicon 20a; and producing second single crystal silicon 20b by the FZ method using the seed crystal 5.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for producing and evaluating single crystal silicon. [Background technology]

[0002] Polycrystalline silicon is a raw material for single-crystal silicon for semiconductors or silicon for solar cells. The Siemens process is a well-known method for producing polycrystalline silicon. The Siemens process generally involves contacting a silane source gas with a heated silicon core wire, and depositing polycrystalline silicon on the surface of the silicon core wire using a chemical vapor deposition (CVD) method.

[0003] In the Siemens method, silicon core wires are assembled into a torii-gate shape with two vertical and one horizontal core wire, and both ends of the torii-gate silicon core wires are connected to core wire holders and fixed to a pair of metal electrodes placed on a bottom plate. Generally, multiple sets of torii-gate silicon core wires are arranged inside a reactor.

[0004] The torii-shaped silicon core wire is heated to the deposition temperature by passing electricity through it, and a raw material gas, such as a mixture of trichlorosilane and hydrogen, is brought into contact with the silicon core wire, causing silicon to grow in the vapor phase, and a polycrystalline silicon rod of the desired diameter is formed in an inverted U shape.

[0005] As mentioned above, polycrystalline silicon produced by the Siemens process is used as a raw material for single-crystal silicon for semiconductors or silicon for solar cells. These require high purity with low impurity concentrations. Therefore, it is important to evaluate the quality of the produced polycrystalline silicon.

[0006] In this context, methods for evaluating the quality of polycrystalline silicon have been standardized in various standards such as JIS, JEITA, and ASTM.

[0007] For example, Section 3.2 of JIS H 0615, a non-patent document 1, describes FZ samples, stating that a seed crystal with a crystal orientation of (111) is used to produce dislocation-free FZ single crystals.

[0008] Usually, the seed crystal is cut to a certain size from a single crystallized block so that it can be easily crystallized, and is then chemically treated before use.

[0009] In both the FZ and CZ methods, a single-crystal silicon seed crystal with a crystal orientation is used, and after contact with the silicon melt, a process called drawing is performed to reduce the diameter, forming a drawn portion, followed by gradually widening the diameter, known as the Dash necking method.

[0010] According to this method, the minimum diameter of the necked portion needs to be narrowed to 2 to 3 mm, and since the seed crystal is pulled upward in the CZ method, the necked portion cannot withstand the increased weight of a large-diameter crystal. Therefore, Patent Documents 1 and 2 propose that the tip of the seed crystal be sharp or have the sharp tip cut off in order to produce a single crystal without necking. [Prior art documents] [Patent documents]

[0011] [Non-Patent Document 1] JIS H 0615 [Patent Document 1] JP 10-203898 [Patent Document 2] WO2003 / 091483A1 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0012] However, when chemically treating a seed crystal, reacted gas may adhere to the surface of the seed crystal, causing a phenomenon called acid burn.

[0013] A certain number of seed crystals may be subjected to chemical treatment together, in which case the possibility of acid burning increases even more.

[0014] When a seed crystal with a poor surface is used and drawn to produce a single crystal, the crystal habit line does not appear, and drawing may have to be repeated, resulting in extremely poor work efficiency.

[0015] Repeated squeezing can cause the molten silicon to overflow and come into contact with the machine parts (metal), which can cause impurities to vaporize and become trapped in the molten silicon.

[0016] Impurities incorporated into the molten silicon affect the evaluation value of the polycrystalline silicon, so the sample treatment described in JIS H 0615 must be repeated.

[0017] Seed crystals are cut to a certain size from a block that has been single-crystallized. However, they cannot be obtained from single crystals of poor quality or from crystals that have not been single-crystallized. Therefore, a portion of the product is usually cut into a block to obtain the seed crystals, which increases costs and reduces yields.

[0018] In Patent Documents 1 and 2, in order to achieve the objectives, a cylindrical or prismatic single-crystal silicon seed crystal must be processed to have a pointed end or a shape in which the pointed tip is cut off.

[0019] In recent years, requirements for impurity concentrations have become stricter. Therefore, in order to determine the favorable growth conditions for single crystals, it is necessary to carry out evaluations more frequently than before. This means that the conventional method of using a seed crystal only once incurs significant costs.

[0020] The present invention has been made in view of the above problems, and provides a method for producing and evaluating single crystal silicon that can reduce the cost required for the seed crystal. [Means for solving the problem]

[0021] The method for producing single crystal silicon according to the present invention includes the steps of: producing first single crystal silicon by a FZ method using a seed crystal; separating the seed crystal after producing the first single crystal silicon; producing second single crystal silicon by the FZ method using the seed crystal; may also be provided.

[0022] The method for producing single crystal silicon according to the present invention includes the steps of: After producing the first single crystal silicon, removing the first single crystal silicon from the FZ apparatus; The seed crystal may be separated from the produced first single crystal silicon by crushing an end of the removed first single crystal silicon.

[0023] In the method for producing single crystal silicon according to the present invention, The seed crystal may have a (111) orientation.

[0024] In the method for producing single crystal silicon according to the present invention, The seed crystal may be separated by cutting it at a sloped portion where the diameter of the seed crystal is continuously reduced.

[0025] The method for producing single crystal silicon according to the present invention may be a method for producing single crystal silicon for evaluation.

[0026] The evaluation items for the evaluation single crystal silicon may be one or more of resistivity, carbon concentration, and impurity amount measurement by photoluminescence method.

[0027] The method for producing single crystal silicon according to the present invention may include a step of evaluating contamination of the separated seed crystal. [Effects of the Invention]

[0028] According to the present invention, it is possible to reduce the cost required for the seed crystal. In particular, when single crystal silicon is used as the silicon for evaluation, the quality of the raw material polycrystalline silicon can be evaluated by evaluating the produced single crystal silicon, thereby reducing the cost required for evaluating the quality of the polycrystalline silicon. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic side view showing an FZ single crystal manufacturing apparatus used in an embodiment of the present invention. [Figure 2] 3A and 3B are schematic side views showing examples of cutting positions of a seed crystal and a necked portion in an embodiment of the present invention. [Figure 3] 1 is a schematic side view showing a process of producing a first single crystal silicon rod from a first polycrystalline silicon rod using an FZ single crystal manufacturing apparatus according to an embodiment of the present invention. FIG. [Figure 4] 4 is a schematic side view showing a state that has progressed from FIG. 3 in the process of producing first single-crystal silicon rods from first polycrystalline silicon rods. FIG. [Figure 5] 5 is a schematic side view showing a state that has progressed from FIG. 4 in the process of producing first single-crystal silicon rods from first polycrystalline silicon rods. FIG. [Figure 6] 5 is a schematic side view showing a process of producing a second single crystal silicon rod from a second polycrystalline silicon rod using an FZ single crystal manufacturing apparatus in an embodiment of the present invention, and corresponds to the state of FIG. 4. [Figure 7] FIG. 2 is a flow chart showing an example of a process for reusing a seed crystal in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] In this embodiment, a single crystal silicon rod 20 is used as the single crystal silicon, and a polycrystalline silicon rod 10 is used as the polycrystalline silicon. In this embodiment, a seed crystal 5 is repeatedly used when a cylindrical core extracted from a means for evaluating the quality of high-purity polycrystalline silicon produced by a CVD method is converted into a single crystal by the FZ method.

[0031] In recent years, requirements for impurity concentrations have become stricter. Therefore, in order to determine the preferable growth conditions for single crystal silicon, it is necessary to perform evaluations more frequently than before. Therefore, in the conventional mode in which the seed crystal 5 is used only once, a non-negligible cost is incurred. In this regard, by repeatedly using the seed crystal 5 as in the present embodiment, it is possible to reduce the cost required for the seed crystal 5, which is advantageous.

[0032] In other words, by repeatedly using seed crystal 5 as in the present embodiment, it is possible to provide a method for evaluating polycrystalline silicon that can effectively evaluate the quality of multiple lots of polycrystalline silicon and can easily evaluate the quality in terms of quality, cost, and work efficiency.

[0033] As shown in FIG. 1, the FZ single crystal manufacturing apparatus 100 used in this embodiment includes, for example, a chamber 90, and an upper shaft 71 and a lower shaft 76 that are provided in the chamber 90 and are movable up and down and rotatable.

[0034] An upper holding jig 70 is attached to the upper shaft 71, and the polycrystalline silicon rods 10 are held by the upper holding jig 70. A seed crystal 5 is attached to a lower holding jig 75 attached to a lower shaft 76. The seed crystal 5 passes through a tapered portion 4, and the polycrystalline silicon rods 10 are welded to the seed crystal 5. The seed crystal 5 has a large diameter portion 1, a small diameter portion 3, and an inclined portion 2 that is provided between the large diameter portion 1 and the small diameter portion 3 and has a continuously decreasing diameter. Here, the small diameter portion 3 and the inclined portion 2 form the tapered portion 4.

[0035] An induction heating coil 60 connected to a high-frequency oscillator 61 is provided within the chamber 90. The polycrystalline silicon rods 10 are heated and melted by the induction heating coil 60, thereby producing single crystal silicon. A floating zone 30 is formed between the polycrystalline silicon rods 10 and the single crystal silicon rods 20. The upper shaft 71 and the lower shaft 76 can be moved up and down by a moving means, and by moving the upper shaft 71 and the lower shaft 76 to move the floating zone 30 to above the polycrystalline silicon rods 10, single crystal silicon rods 20 are produced from the polycrystalline silicon rods 10 (see FIGS. 3 to 5).

[0036] As described above, in this embodiment, the FZ method is performed by repeatedly using the same seed crystal 5. It is beneficial to use a seed crystal 5 having a (111) orientation to form a single crystal of the sample.

[0037] Next, an example of a method for performing the FZ method by repeatedly using the same seed crystal 5 according to this embodiment will be described.

[0038] First, the seed crystal 5 is attached to the FZ single crystal manufacturing apparatus 100 (see S1 in FIG. 7). The upper end of the seed crystal 5 and the lower end of the first polycrystalline silicon rod 10a are welded together (see S2 in FIG. 7). While the first polycrystalline silicon rod 10a is moved downward, the first polycrystalline silicon rod 10a is melted in the floating zone 30 by the induction heating coil 60, producing single crystal silicon. The floating zone 30 is then moved to above the first polycrystalline silicon rod 10a, ultimately producing first single crystal silicon rods 20a (see S3 in FIGS. 3 to 5 and 7).

[0039] After the first single crystal silicon rods 20a are produced, the first single crystal silicon rods 20a are removed from the FZ single crystal manufacturing apparatus 100 (see S4 in FIG. 7).

[0040] The seed crystal 5 is separated from the first single crystal silicon rod 20a by splitting (crushing) the lower end of the removed first single crystal silicon rod 20a in a direction perpendicular to the direction in which the first single crystal silicon rod 20a extends (the left-right direction in FIG. 5) (see S5 in FIG. 7). In this case, the seed crystal 5 may be separated by cutting at a portion of the drawn portion 4 where the diameter continuously tapers upward (the inclined portion 2) (see FIG. 2). Cutting at the drawn portion 4 with a (111) orientation is preferable because the cut surface can be made horizontal. The diameter of the large diameter portion 1 may be approximately 7 to 8 mm, and the diameter of the small diameter portion 3 may be approximately 1 to 3 mm.

[0041] The cut position of the drawn portion 4 is preferably at a distance of 15 mm or more from the welding point of the seed crystal 5 to the first single crystal silicon rod 20a. Dislocation density is very high near the welding point, but drawing removes the dislocations. This is because dislocations are significantly reduced at a location 15 mm or more away from the welding point, and even with the dislocations generated during re-welding, single crystallization can be easily achieved by adding a small amount of drawing.

[0042] As shown in Fig. 2, by cutting the necked portion 4 at the inclined portion 2, whose diameter continuously tapers upward, the contact area with the molten silicon is extremely small. This makes it possible to significantly reduce the occurrence of slip dislocations due to a sudden temperature change within the crystal when the seed crystal 5 comes into contact with the melt, compared to a normal seed crystal 5, and provides an effect equivalent to that achieved by forming a rectangular or cubic seed crystal with a pointed tip or a shape with the pointed tip cut off. While providing a step of forming a rectangular or cubic seed crystal with a pointed tip or a shape with the pointed tip cut off is extremely disadvantageous in terms of increased costs and reduced work efficiency, leaving the necked portion 4 at the cutting stage, as in this embodiment, is advantageous from these points of view.

[0043] In some cases, in order to maintain the cleanliness of the cut seed crystal 5, it may be ultrasonically cleaned for 2 to 5 minutes in an ultrasonic cleaner using ultrapure water (see S6 in Figure 7), dried on a clean bench (see S7 in Figure 7), and then packaged and stored (see S8 in Figure 7).

[0044] The seed crystal 5 separated as described above is used and attached to an FZ single crystal manufacturing apparatus 100. The lower ends of second polycrystalline silicon rods 10b are then welded to the seed crystal 5. Second single crystal silicon rods 20b are then produced from the second polycrystalline silicon rods 10b by the FZ method (see FIG. 6).

[0045] Thereafter, third single crystal silicon rods, fourth single crystal silicon rods, ..., n-th single crystal silicon rods are produced in the same manner from third polycrystalline silicon rods, fourth polycrystalline silicon rods, ..., n-th polycrystalline silicon rods (where "n" is an integer of three or more).

[0046] The single crystal silicon rods 20 produced as described above may be evaluation single crystal silicon rods 20. The evaluation items for the evaluation single crystal silicon rods 20 may be one or more of resistivity, carbon concentration, and impurity amount measurement by a photoluminescence method.

[0047] The single crystal silicon rods 20 for evaluation may have a small diameter, for example, may be single crystal silicon rods 20 having a diameter of 10 to 50 mm. By using a small diameter, the amount of material required for evaluation can be reduced, and evaluation costs can be reduced. Furthermore, such single crystal silicon rods 20 for evaluation do not bring in revenue such as sales profits, but rather have an expense aspect. However, in recent years, as requirements regarding impurity concentrations have become stricter, they are mass-produced under different conditions. For this reason, repeatedly using the seed crystal 5 in the single crystal silicon rods 20 for evaluation, as in this embodiment, is very advantageous in terms of cost.

[0048] The photoluminescence method is generally used to evaluate donors and acceptors such as P, As, B, and Al. In this case, it is necessary to measure single crystal silicon, so it is useful to prepare a small single crystal silicon rod 20 for evaluation, as in this embodiment.

[0049] When evaluating C, it is common to use Fourier transform infrared spectroscopy to measure Cs, which represents substitutional carbon. In this case, it is also necessary to measure single crystal silicon, so it is beneficial to prepare a small single crystal silicon rod 20 for evaluation, as in this embodiment.

[0050] When measuring the resistivity, a four-probe method may be used. Since the single crystal silicon must also be measured when measuring the resistivity by the four-probe method, it is beneficial to prepare a small single crystal silicon rod 20 for evaluation, as in this embodiment.

[0051] By performing FZ evaluation on multiple polycrystalline silicon crystals produced in the same reactor using the CVD manufacturing method, it is possible to reduce quality variations and make it easier to determine the quality of the polycrystalline silicon crystals. Furthermore, by using the seed crystal 5 after forming the seed crystal 5 into a single crystal at least once using the FZ single crystal manufacturing apparatus 100, the reused seed crystal 5 can have an orientation such as (111), which is beneficial in that it is less likely to cause disturbances in single crystal growth. Furthermore, while newly prepared seed crystals 5 are sometimes subjected to etching or other processes before use, which can cause contamination due to etching, this embodiment is also beneficial in that the seed crystal 5 can be used without such etching.

[0052] A limit value for contamination may be set for each item to be evaluated. Contamination evaluation may be performed on the seed crystal 5, and if the seed crystal 5 is contaminated to a level higher than a predetermined value, the seed crystal 5 may be replaced with a new one. Evaluating the contamination of the seed crystal 5 is beneficial in that it can prevent contamination from the seed crystal 5 or the produced polycrystalline silicon from affecting the single crystal silicon to be produced next.

[0053] Contamination of the seed crystal 5 may be evaluated by one or more of resistivity, carbon concentration, and impurity amount measurement by photoluminescence method.

[0054] The number of times the seed crystal 5 is reused may be determined in advance, or may be determined when contamination equal to or greater than a predetermined threshold is found based on the evaluation result of the seed crystal 5. [Industrial Applicability]

[0055] According to the present invention, it is possible to carry out quality evaluation of polycrystalline silicon at reduced costs and with improved work efficiency. [Explanation of symbols]

[0056] 1 seed crystal 2. Constriction section 10 Polycrystalline silicon rods 10a: First polycrystalline silicon rod 10b Second polycrystalline silicon rod 20 Single crystal silicon rods 20a First single crystal silicon rod 20b Second single crystal silicon rod 100 FZ single crystal manufacturing equipment

Claims

1. Producing first single crystal silicon rods by an FZ method using seed crystals; After producing the first single crystal silicon rod, removing the first single crystal silicon rod from the FZ single crystal manufacturing apparatus; Separating the seed crystal from the first single crystal silicon rod removed from the FZ single crystal manufacturing apparatus; a step of attaching the separated seed crystal to an FZ single crystal manufacturing apparatus; Producing a second single crystal silicon rod by an FZ method using a seed crystal attached to an FZ single crystal manufacturing apparatus; A method for producing a single crystal silicon rod, comprising:

2. A method for manufacturing a single crystal silicon rod as described in claim 1, wherein a seed crystal is separated from the first single crystal silicon rod produced by crushing the end of the removed first single crystal silicon rod.

3. A method for manufacturing a single crystal silicon rod as described in claim 1 or 2, wherein the orientation of the seed crystal attached to the FZ single crystal manufacturing apparatus is (111).

4. A method for manufacturing a single crystal silicon rod as described in any one of claims 1 to 3, wherein the seed crystal is separated from the first single crystal silicon rod removed from the FZ single crystal manufacturing apparatus by cutting the seed crystal at an inclined portion where the diameter becomes continuously narrower.

5. A method for manufacturing a single crystal silicon rod described in any one of claims 1 to 4, which is a method for manufacturing a single crystal silicon rod for evaluation.

6. The evaluation method according to claim 5, wherein the evaluation items for the evaluation single crystal silicon rod are one or more of resistivity, carbon concentration, and impurity amount measurement by a photoluminescence method.

7. A method for manufacturing a single crystal silicon rod described in any one of claims 1 to 5, comprising a step of evaluating a seed crystal separated from a first single crystal silicon rod removed from the FZ single crystal manufacturing apparatus.

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