Method for measuring cleanliness of FZ furnace and method and apparatus for producing single crystals using the same

Abstract

To provide a method for measuring cleanliness of a FZ furnace that can suppress dislocation of a single crystal by accurately measuring internal cleanliness of the FZ furnace, and to provide a method for manufacturing the single crystal using the same and a single crystal device.SOLUTION: A method for measuring cleanliness of a FZ furnace includes the steps of: connecting a particle counter 30 to a connection port 13b for communicating the interior of a FZ furnace 20 to the outside; and measuring the number of particles in an internal atmosphere gas of the FZ furnace 20, which is evacuated from the connection port 13b, with the particle counter 30.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the cleanliness of an FZ (Floating Zone) furnace used in producing single crystals by the FZ method, and to a method and apparatus for producing single crystals using the same. [Background technology]

[0002] The FZ method is known as a method for producing silicon single crystals. In the FZ method, a portion of a raw material rod made of polycrystalline silicon is heated to create a molten zone, and the raw material rod and seed crystal, positioned above and below the molten zone, are gradually lowered to grow a large single crystal above the seed crystal. Because the FZ method does not use a quartz crucible like the CZ (Czochralski) method, it is possible to produce single crystals with an extremely low oxygen concentration.

[0003] In the manufacturing process of silicon single crystals by the FZ method, high-temperature silicon reacts with trace amounts of oxygen in the chamber that makes up the FZ furnace (equipment), generating silicon oxides (SiO and / or SiO2), and silicon powder and SiC powder that were not completely removed when the FZ furnace was disassembled and cleaned adhere to the inner walls of the chamber as particles.When these particles float inside the furnace and adhere to the molten zone, they are captured at the solid-liquid interface and cause dislocations in the single crystal.

[0004] For example, in order to alleviate the problem of silicon oxides occurring in an FZ furnace, Patent Document 1 describes a method for reducing the amount of silicon oxides taken into the molten zone by providing an upper silicon oxide collecting plate above the polycrystalline holder and a lower silicon oxide collecting plate directly above the induction heating coil. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-132389 Summary of the Invention [Problem to be solved by the invention]

[0006] The conventional method for measuring and evaluating the cleanliness inside an FZ furnace is to place a table inside the furnace, place a dummy silicon wafer on the table, introduce Ar gas into the furnace under normal pressure, and count the particles adhering to the wafer surface after a certain period of time has passed.

[0007] However, with conventional measurement and evaluation methods, the relationship between the number of particles and the rate of dislocation generation in single crystals was unclear, and it was not possible to sufficiently suppress the occurrence of dislocations in single crystals.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a cleanliness measurement method that can accurately measure the cleanliness inside an FZ furnace and lead to the suppression of dislocations in a single crystal, and a method and apparatus for producing a single crystal using the same. [Means for solving the problem]

[0009] In order to solve the above problems, the method for measuring the cleanliness of an FZ furnace according to the present invention is characterized in that a particle counter is connected to a connection port that connects the inside and outside of the FZ furnace, and the particle counter measures the number of particles in the atmospheric gas inside the FZ furnace that is discharged from the connection port.

[0010] According to the present invention, it is possible to count even minute particles that cannot be seen with the naked eye, and to obtain particle measurement results that are highly correlated with the dislocation occurrence rate in the single crystal. Therefore, by re-cleaning the furnace interior based on the particle measurement results, it is possible to enhance the effect of suppressing the occurrence of dislocations in the single crystal.

[0011] In the method for measuring the cleanliness of an FZ furnace according to the present invention, it is preferable to measure the number of particles in the FZ furnace under normal pressure, which makes it possible to measure the cleanliness of the inside of the FZ furnace relatively easily.

[0012] In the method for measuring the cleanliness of an FZ furnace according to the present invention, it is also preferable to connect the particle counter to the connection port of the FZ furnace via a pressure reducer and measure the number of particles inside the FZ furnace under pressure. This makes it possible to measure the cleanliness inside the FZ furnace under conditions similar to those of an actual crystal growth process, thereby improving the reliability of the measurement accuracy.

[0013] The method for measuring the cleanliness of an FZ furnace according to the present invention may measure the number of particles in the atmospheric gas in the FZ furnace during the crystal growth process. By monitoring the particle generation status in real time, it becomes possible to detect signs of dislocation formation in the single crystal during the crystal growth process, and measures such as gas replacement of the atmosphere in the furnace can be taken. This makes it possible to reduce the occurrence of dislocation formation in the single crystal due to particles.

[0014] In the present invention, the height position of the connection port is preferably lower than the installation position of the induction heating coil provided in the FZ furnace, which makes it possible to efficiently collect particles floating in the FZ furnace and improve the accuracy of cleanliness measurement.

[0015] In the method for measuring the cleanliness of an FZ furnace according to the present invention, it is preferable to disassemble and clean the FZ furnace, assemble the FZ furnace, connect the particle counter to the connection port of the FZ furnace, and measure the number of particles in the atmospheric gas inside the FZ furnace. This makes it possible to correctly evaluate the effect of disassembly and cleaning and prevent dislocations from occurring in the single crystal.

[0016] In the method for measuring the cleanliness of an FZ furnace according to the present invention, it is preferable that the particle counting is started after a predetermined waiting time has elapsed since the atmospheric gas started to be discharged from the connection port, thereby improving the reliability of the particle measurement results.

[0017] Furthermore, the method for producing a single crystal according to the present invention comprises a crystal growing step of growing a single crystal in an FZ furnace, a dismantling and cleaning step of dismantling and cleaning the FZ furnace, and a cleanliness measurement step of measuring the cleanliness inside the FZ furnace after assembling the FZ furnace after the dismantling and cleaning step, wherein the cleanliness measurement step is characterized in that a particle counter is connected to a connection port connecting the inside and outside of the FZ furnace, and the number of particles in the atmospheric gas inside the FZ furnace discharged from the connection port is measured by the particle counter.

[0018] According to the present invention, it is possible to count even minute particles that cannot be seen with the naked eye, and to obtain particle measurement results that are highly correlated with the dislocation occurrence rate in the single crystal. Therefore, by re-cleaning the furnace interior based on the particle measurement results, it is possible to enhance the effect of suppressing the occurrence of dislocations in the single crystal.

[0019] In the method for producing a single crystal according to the present invention, if the particle count is equal to or less than the control value, the process proceeds to the next crystal growth step, and if the particle count exceeds the control value, the FZ furnace is re-cleaned, and the re-cleaning is preferably performed by replacing the atmospheric gas in the FZ furnace at least once. This makes it possible to increase the cleanliness inside the furnace and reduce the rate of dislocation generation in the single crystal.

[0020] Furthermore, the single crystal manufacturing apparatus according to the present invention is characterized by comprising an FZ furnace in which a single crystal is grown, and a particle counter that measures the number of particles in the atmospheric gas in the FZ furnace discharged from a connection port that connects the inside and outside of the FZ furnace.

[0021] According to the present invention, it is possible to count even minute particles that cannot be seen with the naked eye, and to obtain particle measurement results that are highly correlated with the dislocation occurrence rate in the single crystal. Therefore, by re-cleaning the furnace interior based on the particle measurement results, it is possible to enhance the effect of suppressing the occurrence of dislocations in the single crystal.

[0022] The single crystal manufacturing apparatus according to the present invention preferably includes a pressure reducer provided between the connection port and the particle counter. This allows the cleanliness inside the FZ furnace to be measured under pressurized conditions similar to those in an actual crystal growth process, thereby improving the reliability of measurement accuracy. Furthermore, cleanliness measurement is possible even during the actual crystal growth process. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a cleanliness measurement method that can accurately measure the cleanliness inside an FZ furnace and lead to the suppression of dislocations in a single crystal, as well as a single crystal manufacturing method and apparatus using the same. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic cross-sectional side view showing the configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart illustrating a method for measuring the cleanliness inside an FZ furnace according to a first embodiment of the present invention, which illustrates a series of preparatory steps that are carried out after the end of a crystal growth step and before the start of the next crystal growth step. [Figure 3] FIG. 3 is a schematic diagram showing an example of the configuration of the single crystal manufacturing apparatus when measuring the cleanliness inside the FZ furnace shown in FIG. [Figure 4] FIG. 4 is a flowchart illustrating a method for measuring the cleanliness inside an FZ furnace according to a second embodiment of the present invention, which illustrates a series of preparatory steps that are carried out after the end of a crystal growth step and before the start of the next crystal growth step. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of the single crystal manufacturing apparatus when measuring the cleanliness inside the FZ furnace shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0026] FIG. 1 is a schematic cross-sectional side view showing the configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention.

[0027] As shown in FIG. 1, this single crystal manufacturing apparatus 1 is an apparatus for growing silicon single crystals by the FZ method, and is equipped with a water-cooled chamber 10 that accommodates a raw material rod 2 and a silicon single crystal 4 grown on a seed crystal 3, an upper shaft 11 that supports the raw material rod 2 so that it can rotate and rise and fall, a lower shaft 12 that supports the seed crystal 3 and the silicon single crystal 4 so that they can rotate and rise and fall, an induction heating coil 15 that heats the lower end of the raw material rod 2, a single crystal holder 17 that supports the weight of the silicon single crystal 4 that has become larger as the crystal growth progresses, and a gas doping device 18 that supplies a doping gas to a molten zone 5 (silicon melt) between the raw material rod 2 and the silicon single crystal 4.

[0028] The chamber 10 is composed of a water-cooled main chamber 10A that houses an induction heating coil 15, a top chamber 10B that is connected to the upper part of the main chamber 10A, and a bottom chamber 10C that is connected to the lower part of the main chamber 10A, and the growth of the silicon single crystal 4 is carried out in the main chamber 10A. A raw material rod 2 is housed in the top chamber 10B, and the grown silicon single crystal 4 is housed in the bottom chamber 10C. The chamber 10, together with internal furnace components such as the induction heating coil 15, constitutes an FZ furnace 20 (crystal growth furnace) for growing the silicon single crystal 4 by the FZ method.

[0029] The source rod 2 is made of high-purity polycrystalline silicon obtained by refining a silicon source such as monosilane, and the upper end of the source rod 2 is attached to the lower end of an upper shaft 11. The lower end of the seed crystal 3 is attached to the upper end of a lower shaft 12. The upper shaft 11 and the lower shaft 12 are rotated and raised and lowered, respectively, by a drive mechanism (not shown).

[0030] The induction heating coil 15 is a flat coil that surrounds the raw material rod 2 or the molten zone 5, and generates the molten zone 5 between the raw material rod 2 and the silicon single crystal 4 by induction heating the lower end of the raw material rod 2. The output of the induction heating coil 16 is controlled by a high-frequency oscillator.

[0031] The single crystal holder 17 holds the silicon single crystal 4 by contacting the tapered portion 4a of the silicon single crystal 4, thereby bearing most of the weight of the silicon single crystal 4 so that a large weight of the silicon single crystal 4 is not placed on the seed crystal 3 and the lower shaft 12. In the FZ method, the tapered portion 4a is formed by gradually increasing the crystal diameter as the crystal grows, and then the straight body portion 4b is grown, with the crystal diameter maintained constant.

[0032] The wall of the main chamber 10A is provided with a first connection port 13a and a second connection port 13b, which are open ports that allow access to the interior. The first connection port 13a and the second connection port 13b are passages that connect the inside and outside of the FZ furnace 20. The first connection port 13a is located slightly higher than the induction heating coil 15, and a gas supply nozzle 18a of a gas doping device 18 (purge gas supply device) is installed in the first connection port 13a. During crystal growth, Ar gas 6 (purge gas) containing dopant is supplied to the melting zone 5, thereby controlling the dopant concentration in the silicon single crystal 4. The Ar gas 6 supplied into the chamber 10 is exhausted from exhaust ports 10p and 10q provided in the top chamber 10B and the bottom chamber 10C, respectively, thereby generating ascending and descending flows of Ar gas 6 within the main chamber 10A. The pressure inside the furnace is controlled to a constant pressure by a pressure control valve 19.

[0033] The second connection port 13b is provided at a position slightly lower than the installation position of the induction heating coil 15. During the crystal growth process, the second connection port 13b is closed, but during cleanliness measurement, which will be described later, the second connection port 13b is opened and a particle counter is connected. The second connection port 13b is not particularly limited in size or shape of its opening as long as it is configured to allow gas to circulate between the inside and outside of the FZ furnace 20.

[0034] Fig. 2 is a flowchart illustrating a method for measuring the cleanliness of the inside of an FZ furnace according to a first embodiment of the present invention, which illustrates a series of preparatory steps carried out after the end of a crystal growth step and before the start of the next crystal growth step. Fig. 3 is a schematic diagram illustrating an example of the configuration of the single crystal manufacturing apparatus 1 when measuring the cleanliness of the inside of the FZ furnace shown in Fig. 2.

[0035] 2, first, a crystal growth process is carried out to grow a silicon single crystal 4 using single crystal manufacturing apparatus 1 (step S1). After the crystal growth process is completed, a dismantling and cleaning process of FZ furnace 20 is carried out before the next crystal growth process is started (step S2). In the dismantling and cleaning process, particles adhering to the inner wall surface of chamber 10 and the internal components of the furnace are carefully wiped off.

[0036] Next, the FZ furnace 20 is assembled (step S3), and a cleanliness measurement step (particle measurement step) inside the FZ furnace 20 is performed (steps S4 and S5). This cleanliness measurement step is performed before the raw material rod 2 is installed in the top chamber 10B. In this case, it is possible to prevent particles from adhering to the surface of the raw material rod 2 during the cleanliness measurement. Furthermore, although it takes time to install the raw material rod 2, if the cleanliness measurement result falls below the control value and re-cleaning is required, the effort of removing and reinstalling the raw material rod 2 is wasted. In consideration of these circumstances, it is preferable to perform the cleanliness measurement before installing the raw material rod 2.

[0037] The cleanliness measurement step may be performed after the raw material rod 2 is placed in the top chamber 10B. If the top chamber 10B is opened after the cleanliness measurement and the raw material rod 2 is placed therein, there is a risk that particles may enter the top chamber 10B and cause contamination. However, if the cleanliness measurement is performed with the raw material rod 2 already placed in the top chamber 10B, the cleanliness measurement inside the furnace can be performed immediately before the start of the crystal growth step, and the reliability of the particle measurement results can be improved.

[0038] As shown in FIG. 3, when measuring the cleanliness of the FZ furnace 20, a particle counter 30 is connected to the second connection port 13b of the main chamber 10A via an intake tube 31 (step S4). The intake tube 31 is preferably made of a urethane-based material, which is highly flexible and resistant to high pressure. The particle counter 30 is preferably an optical particle counter (light scattering airborne particle counter) that irradiates laser light on particles passing through the flow path of the measuring instrument and determines the size and number of particles based on the intensity of scattered light from the particles and electrical signals. It is also preferable that the particle counter be capable of measuring particles at least 0.3 μm in size. Then, the cleanliness of the FZ furnace 20 is measured under normal pressure, and the number of particles in the furnace atmosphere is counted (step S5).

[0039] The particle measurement results are preferably evaluated based on the measurement values ​​obtained a certain time after the start of particle measurement. In other words, the actual particle counting preferably begins a predetermined waiting time after the start of exhausting the atmospheric gas from the FZ furnace 20 through the second connection port 13b. For example, if the particle counter 30 performs a measurement for 5 minutes, stops the measurement for 1 minute, and then performs another measurement for 5 minutes according to the measurement recipe settings, the particle value obtained in the first 5-minute measurement is not adopted, and the particle value obtained in the second 5-minute measurement is used to evaluate cleanliness. Since the particle measurement values ​​for the first few minutes after the start of particle measurement vary significantly between batches and are unreliable, ignoring this variation can improve the reliability of the particle measurement results. The second particle measurement is preferably started at least 1 minute after the first particle measurement, and particularly preferably 5 minutes after the first particle measurement.

[0040] If the particle count is found to be equal to or less than a predetermined control value, the furnace is determined to be clean and the process proceeds to the next crystal growth step (steps S6Y and S7). On the other hand, if the particle count exceeds the predetermined control value, the furnace is cleaned again (steps S6N and S8).

[0041] The re-cleaning of the furnace interior is preferably a process of replacing the Ar atmosphere in the FZ furnace 20. That is, after filling the furnace with Ar gas, the Ar gas is discarded and replaced with new Ar gas. By repeating this process multiple times, particles in the furnace are discharged outside the furnace together with the Ar gas.

[0042] The above re-cleaning and particle measurement are repeated (steps S5 to S8) until the measured value falls below the specified control value, but in most cases, one or two re-cleanings are enough to bring the measured particle value below the specified control value.

[0043] Fig. 4 is a flowchart illustrating another example of a series of preparatory steps performed after the end of a crystal growth step and before the start of the next crystal growth step in a method for measuring the cleanliness inside an FZ furnace according to a second embodiment of the present invention. Fig. 5 is a schematic diagram showing the configuration of the single crystal manufacturing apparatus 1 when measuring the cleanliness inside the FZ furnace shown in Fig. 4.

[0044] 4 and 5, when measuring the cleanliness inside the FZ furnace 20, the inside of the FZ furnace 20 may be set under pressurized rather than normal pressure (step S5A). In this case, a particle counter 30 is connected to the second connection port 13b of the main chamber 10A via a pressure reducer 32 (high-pressure diffuser) (step S4A). In this way, by setting the inside of the furnace under pressurized pressure during the cleanliness measurement, the cleanliness measurement can be performed under conditions as close as possible to those in the actual crystal growth process.

[0045] When particle counter 30 is connected to main chamber 10A via pressure reducer 32, particle measurement inside the furnace under pressure is possible, and therefore particle measurement is possible not only before the start of the crystal growth process but also during the crystal growth process shown in Fig. 1. In this way, by measuring particles inside the furnace during the crystal growth process, it becomes possible to analyze in detail the relationship between the environment inside the furnace and the occurrence of dislocations in the single crystal.

[0046] As described above, in the method for measuring the cleanliness of an FZ furnace according to this embodiment, the particle counter 30 is connected to the second connection port 13b of the main chamber 10A directly or via the pressure reducer 32, and the inside of the FZ furnace 20 is set to an Ar atmosphere under normal pressure or under pressure, and then particles are measured using the particle counter 30. This makes it possible to accurately measure the cleanliness inside the furnace and to obtain a cleanliness index that is highly correlated with the rate of dislocation occurrence in the single crystal. Therefore, by re-cleaning the inside of the furnace based on this cleanliness index, the rate of dislocation occurrence in the single crystal caused by particles can be reduced.

[0047] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0048] For example, in the above embodiment, a method for producing a silicon single crystal by the FZ method is given as an example, but the present invention is not limited to the production of silicon single crystals, and can be applied to the production of various single crystals by the FZ method. [Explanation of symbols]

[0049] 1. Single crystal manufacturing equipment 2 Raw material rod 3 seed crystals 4. Silicon single crystal 4a Tapered section 4b Straight body part 5. Melting Zone 6 Ar gas 10 chambers 10A Main Chamber 10B Top Chamber 10C Bottom Chamber 10p,10q exhaust port 11 Upper shaft 12 Lower axis 13a First connection port 13b Second connection port 15 Induction heating coil 16 induction heating coil 17 Single crystal holder 18 Gas doping device 18a Gas supply nozzle 19 Pressure Regulating Valve 20 FZ furnace 30 Particle Counter 31 Intake tube 32 Pressure reducer

Claims

1. A method for measuring the cleanliness of an FZ furnace, comprising connecting a particle counter via a pressure reducer to a connection port that communicates the inside and outside of the FZ furnace, and measuring the number of particles in the atmospheric gas in the FZ furnace under pressure that is discharged from the connection port using the particle counter.

2. 2. The method for measuring the cleanliness of an FZ furnace according to claim 1, wherein the number of particles in the atmospheric gas in the FZ furnace is measured during a crystal growth process.

3. 2. The method for measuring the cleanliness of an FZ furnace according to claim 1, wherein the height position of the connection port is lower than the installation position of an induction heating coil provided in the FZ furnace.

4. 4. The method for measuring the cleanliness of an FZ furnace according to claim 3, wherein the FZ furnace is disassembled and cleaned, and then the FZ furnace is reassembled, and the particle counter is connected to the connection port of the FZ furnace, and the number of particles in the atmospheric gas inside the FZ furnace is measured.

5. 2. The method for measuring the cleanliness of an FZ furnace according to claim 1, wherein the counting of the number of particles is started after a predetermined waiting time has elapsed since the discharge of the atmospheric gas from the connection port was started.

6. A particle counter is connected to a connection port that communicates the inside and outside of the FZ furnace, and the number of particles in the atmospheric gas in the FZ furnace that is discharged from the connection port is measured by the particle counter; The method for measuring the cleanliness of an FZ furnace, wherein the height position of the connection port is lower than the installation position of an induction heating coil provided in the FZ furnace.

7. 7. The method for measuring the cleanliness of an FZ furnace according to claim 6, wherein the FZ furnace is disassembled and cleaned, and then reassembled, and the particle counter is connected to the connection port of the FZ furnace, and the number of particles in the atmospheric gas inside the FZ furnace is measured.

8. A method for producing a single crystal by the FZ method, comprising the steps of: a crystal growing step of growing a single crystal in an FZ furnace; a dismantling and cleaning step of dismantling and cleaning the FZ furnace; and a cleanliness measurement step of measuring the cleanliness of the inside of the FZ furnace after assembling the FZ furnace after the dismantling and cleaning step, The cleanliness measurement step includes connecting a particle counter to a connection port that communicates the inside and outside of the FZ furnace, and measuring the number of particles in the atmospheric gas in the FZ furnace that is discharged from the connection port with the particle counter, If the number of particles is equal to or less than the control value, the process proceeds to the next crystal growth step. If the number of particles exceeds the control value, the FZ furnace is re-cleaned; The method for producing a single crystal, wherein the re-cleaning is performed by replacing the atmospheric gas in the FZ furnace at least once.

9. a FZ furnace in which the single crystal is grown; a particle counter that measures the number of particles in the atmospheric gas in the FZ furnace discharged from a connection port that communicates the inside and outside of the FZ furnace; A single crystal manufacturing apparatus comprising: a pressure reducer provided between the connection port and the particle counter.

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