JP2020100516A - Method for manufacturing single crystal silicon ingot, and silicon single crystal pulling apparatus - Google Patents

Abstract

To provide a method for manufacturing a single crystal silicon ingot which is capable of manufacturing a single crystal silicon ingot having low carbon concentration at high yield.SOLUTION: A method for manufacturing a single crystal silicon ingot of the present invention in which, in a raw material melting process and a crystal growth process, gas in a chamber is collected, CO gas concentration in the collected gas is intermittently measured, measured CO gas concentration is multiplied by a flow rate of inert gas supplied into the chamber to calculate a CO gas generation rate, and the CO gas generation rate which has been calculated is monitored.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a single crystal silicon ingot and a silicon single crystal pulling apparatus.

A silicon wafer used as a substrate of a semiconductor device is manufactured by thinly slicing an ingot of a silicon single crystal, followed by a surface grinding (lapping) step, an etching step and a mirror polishing (polishing) step, and finally cleaning. A large-diameter silicon single crystal having a diameter of 300 mm or more is generally manufactured by the Czochralski (CZ) method.

FIG. 4 shows a conventional silicon single crystal pulling apparatus 400 for manufacturing a single crystal silicon ingot by the CZ method. The silicon single crystal pulling apparatus 400 has a chamber 10 having an outer shell, and the crucible 16 is arranged at the center thereof. The crucible 16 has a double structure, is composed of an inner quartz crucible 16A and an outer graphite crucible 16B, and is fixed to an upper end of a shaft 18 which can be rotated and moved up and down by a shaft drive mechanism 20.

A resistance heating type tubular heater 24 is arranged outside the crucible 16 so as to surround the crucible 16, and a heat insulator 26 is arranged outside the crucible 16 along the inner surface of the chamber 10. Further, a pulling wire 30 holding a seed chuck 28 holding a seed crystal S at its lower end is arranged above the crucible 16 coaxially with the shaft 18, and a wire elevating mechanism 32 reverses the pulling wire 30 from the shaft 18. It moves up and down while rotating at a predetermined speed in the same direction or the same direction.

A cylindrical heat shield 22 is arranged in the chamber 10 so as to surround the single crystal silicon ingot I being grown above the crucible 16. The heat shield 22 adjusts the incident amount of high-temperature radiant heat from the silicon melt M in the crucible 16, the heater 24, and the side wall of the crucible 16 to the growing ingot I, and the heat of the vicinity of the crystal growth interface. The amount of diffusion is adjusted, and it has a role of controlling the temperature gradient in the pulling axis X direction at the central portion and the outer peripheral portion of the single crystal silicon ingot I.

A gas introduction port 12 for introducing an inert gas such as Ar gas into the chamber 10 is provided in the upper portion of the chamber 10. Further, at the bottom of the chamber 10, a gas discharge port 14 for sucking and discharging the gas in the chamber 10 by driving a vacuum pump (not shown) is provided. The inert gas introduced into the chamber 10 through the gas inlet 12 descends between the growing single crystal silicon ingot I and the heat shield 22, and the lower end of the heat shield 22 and the liquid of the silicon melt M. After flowing through the gap with the surface, it flows toward the outside of the heat shield 22 and further toward the outside of the crucible 16, and then descends outside the crucible 16 and is discharged from the gas discharge port 14.

Using this silicon single crystal pulling apparatus 400, a silicon raw material such as polycrystalline silicon filled in the crucible 16 is melted by heating with a heater 24 while maintaining the chamber 10 in an Ar gas atmosphere under reduced pressure, and silicon A melt M is formed. Next, the pulling wire 30 is lowered by the wire lifting mechanism 32 to deposit the seed crystal S on the silicon melt M, and the pulling wire 30 is pulled upward while rotating the crucible 16 and the pulling wire 30 in a predetermined direction. , An ingot I is grown below the seed crystal S. Although the amount of the silicon melt M decreases as the growth of the ingot I progresses, the crucible 16 is raised to maintain the level of the melt surface.

A CCD camera 36 is provided in the opening 34 at the top of the chamber 10. The CCD camera 36 images the vicinity of the boundary between the crystal I and the melt M. Since the meniscus formed at the boundary between the crystal and the melt is imaged with higher brightness than the crystal and the melt, the meniscus in the image has a ring-shaped high brightness band (hereinafter referred to as “fusion ring”). .). The distance between the fusion rings is recognized as the crystal diameter, and the crystal pulling rate and the melt temperature are controlled so that the crystal diameter has a desired constant value.

In the production of a single crystal silicon ingot using such a silicon single crystal pulling apparatus, it is known that CO gas is generated in the chamber. One of the causes is that CO gas is generated by the reaction between the SiO gas generated from the silicon melt and the graphite material (for example, a cylindrical heater) existing in the chamber. As a technique for measuring the concentration of CO gas in the chamber, there is Patent Document 1.

Patent Document 1 describes "a method for producing a single crystal in which a single crystal is pulled from a raw material melt obtained by heating and melting a raw material by the Czochralski method, in which the raw material is housed in a quartz crucible and then housed in the quartz crucible. The carbon monoxide concentration in the exhaust gas discharged during the melting of the raw material is measured while heating and melting the raw material, and the melting of the raw material is completed based on the measured result of the concentration of carbon monoxide contained in the exhaust gas during the melting of the raw material. It is determined that the single crystal is produced, and then the single crystal is pulled from the raw material melt.

JP, 2017-114709, A

The present inventors, in the single crystal silicon ingot manufactured by the conventional silicon single crystal pulling apparatus, carbon is mixed in the growing process, as a result, the carbon concentration of the silicon wafer produced from the ingot is intended. We paid attention to the problem that it would be higher. When the carbon concentration in a silicon wafer becomes high, a defect called a killer defect caused by electrically active carbon occurs during the device heat treatment step, which causes a problem that the lifetime of the wafer is reduced. Further, since carbon of high concentration promotes the formation of oxygen precipitates, if oxygen precipitates are present on the surface of the device, leak failure will occur, resulting in a decrease in yield. Thus, carbon contamination in the single crystal silicon ingot has an adverse effect on the manufacturing process of the semiconductor device. Therefore, the carbon concentration in the single crystal silicon ingot is strictly limited by the standard according to the type of device.

It is considered that the carbon concentration in the crystal rises because the CO gas generated in the chamber is taken into the silicon melt. In Patent Document 1, paying attention to the fact that the CO gas concentration in the gas in the chamber becomes maximum when all the raw materials are melted in the raw material melting step, the CO gas concentration is measured, and the raw material melting step is performed based on the measured value. The end of (melt completion) is determined. However, Patent Document 1 merely focuses on shortening the process time and preventing the deformation of the quartz crucible by accurately detecting the completion of the melt, and taking in the CO gas into the silicon melt or However, no attention is paid to the increase in carbon concentration in the crystal resulting from this.

In view of the above problems, it is an object of the present invention to provide a method for producing a single crystal silicon ingot and a silicon single crystal pulling apparatus capable of producing a single crystal silicon ingot having a low carbon concentration with a high yield.

In order to solve the above problems, the present inventors have conceived to monitor the CO gas generation rate (CO gas generation amount per unit time) instead of monitoring the CO gas concentration in the gas in the chamber. That is, it is considered that the amount of CO gas taken into the silicon melt has a positive correlation with the amount of CO gas generated per unit time. On the other hand, the CO gas concentration decreases when the flow rate of the inert gas in the chamber is high, and decreases when the flow rate of the inert gas in the chamber is low, even if the CO gas generation amount per unit time is the same. To grow. In fact, the flow rate of the inert gas is different between the raw material melting step and the crystal growing step, and the flow rate of the inert gas also changes during the crystal growing step. Therefore, the CO gas concentration is not suitable for monitoring as an index for evaluating the amount of CO gas taken into the silicon melt. The present inventors measure the CO gas concentration in the chamber, calculate the CO gas generation rate by multiplying this measured value by the flow rate of the inert gas in the chamber, and monitor this CO gas generation rate. It has been found that the amount of CO gas taken into the silicon melt, and thus the carbon concentration in the crystal, can be appropriately evaluated.

The present invention has been completed based on the above findings, and its gist configuration is as follows.
(1) A chamber having a gas inlet for introducing an inert gas in its upper portion and a gas outlet for discharging an in-furnace gas containing the inert gas in its bottom,
A crucible located in the chamber,
A cylindrical heater positioned so as to surround the crucible in the chamber,
A method for manufacturing a single crystal silicon ingot performed using a silicon single crystal pulling apparatus having:
While maintaining the atmosphere of the inert gas under reduced pressure in the chamber, a raw material melting step of forming a silicon melt in the crucible by heating and melting the silicon raw material charged in the crucible by the heater,
Subsequently, while maintaining the atmosphere of the inert gas under reduced pressure in the chamber, the silicon melt is heated and maintained by the heater, and a crystal growing step of pulling a single crystal silicon ingot from the silicon melt.
In the raw material melting step and the crystal growing step,
Collecting the gas in the furnace,
The CO gas concentration in the collected gas is intermittently measured by a gas analyzer,
The CO gas generation rate is calculated by multiplying the measured CO gas concentration by the flow rate of the inert gas supplied into the chamber,
A method for producing a single crystal silicon ingot, which comprises monitoring the calculated CO gas generation rate.

(2) The maximum value of the CO gas generation rate in the raw material melting step is A (mol/h), and the maximum value of the CO gas generation rate in the straight body step in the crystal growing step is B (mol/h). The method for producing a single crystal silicon ingot according to (1) above, wherein the raw material melting step and the crystal growing step are performed under conditions satisfying A/B≦10.

(3) The method for producing a single crystal silicon ingot according to (1) or (2), wherein the in-furnace gas is collected through an exhaust pipe extending from the gas outlet.

(4) The in-furnace gas is collected from a space between the crucible and a cylindrical heat shield provided above the crucible so as to surround the single crystal silicon ingot. The method for producing a single crystal silicon ingot according to any one of (3).

(5) The method for producing a single crystal silicon ingot according to any one of (1) to (4) above, wherein the gas analyzer is a quadrupole mass spectrometer.

(6) A chamber having a gas inlet for introducing an inert gas in the upper part and a gas outlet for discharging the in-furnace gas containing the inert gas in the bottom,
A crucible located in the chamber and containing a silicon melt;
Above the crucible, a cylindrical heat shield provided so as to surround the single crystal silicon ingot pulled up from the silicon melt,
A cylindrical heater that is positioned so as to surround the crucible in the chamber and that heats the silicon melt,
An exhaust pipe extending from the gas outlet,
A main pump that is connected to the exhaust pipe, reduces the pressure in the chamber, and sucks the in-furnace gas into the exhaust pipe;
A main valve provided in the exhaust pipe and opened when decompressing the chamber,
A portion of the exhaust pipe upstream of the main valve, and a space between the heat shield and the crucible, and a gas sampling port provided in one or both of them.
A sub-pipe extending from the gas sampling port and connected to a part of the exhaust pipe downstream of the main valve;
A sub-pump provided in the sub-pipe, for sucking the in-furnace gas into the sub-pipe,
A gas analyzer provided upstream of the sub-pump in the sub-pipe, and intermittently measuring the CO gas concentration in the gas sucked into the sub-pipe;
A flow rate adjustment valve that is provided upstream of the gas analysis device in the sub-pipe and that adjusts the flow rate of the gas supplied to the gas analysis device,
A filter that is provided upstream of the flow rate adjusting valve of the sub-pipe and removes SiO powder in the gas sucked into the sub-pipe;
An intake valve which is provided in the vicinity of the gas sampling port of the sub-pipe and which opens when the in-furnace gas is sucked into the sub-pipe,
And further,
An operation unit for calculating a CO gas generation rate by multiplying the CO gas concentration measured by the gas analyzer by the flow rate of the inert gas supplied into the chamber,
An output device for outputting the calculated CO gas generation rate;
A silicon single crystal pulling apparatus comprising:

(7) The silicon single crystal pulling apparatus according to (6), wherein the gas sampling port is provided in a portion of the exhaust pipe upstream of the main valve.

(8) The silicon single crystal pulling apparatus according to (6) or (7), wherein the gas sampling port is located in a space between the heat shield and the crucible.

(9) The silicon single crystal pulling device according to any one of (6) to (8), wherein the gas analyzer is a quadrupole mass spectrometer.

According to the method for producing a single crystal silicon ingot and the silicon single crystal pulling apparatus of the present invention, it is possible to produce a single crystal silicon ingot having a low carbon concentration with a high yield.

FIG. 2 is a cross-sectional view taken along the pulling axis X, which schematically shows the configuration of the silicon single crystal pulling apparatus 100 according to the first embodiment of the present invention. FIG. 7 is a cross-sectional view taken along a pulling axis X, which schematically shows the configuration of a silicon single crystal pulling apparatus 200 according to a second embodiment of the present invention. It is sectional drawing along the pulling axis X which shows typically the structure of the silicon single crystal pulling apparatus 300 by the 3rd Embodiment of this invention. FIG. 11 is a cross-sectional view taken along the pulling axis X, which schematically shows the configuration of a conventional silicon single crystal pulling apparatus 400. No. 3 is a graph showing changes in the CO gas generation rate during the raw material melting step and the crystal growing step in FIG. It is a graph which shows the particle size distribution of SiO powder in the gas extracted from the inside of a chamber.

(Silicon single crystal pulling device)
A basic configuration common to the silicon single crystal pulling apparatus 100, 200, 300 according to the embodiment of the present invention will be described with reference to FIGS. In addition, about these common basic structures, the same code|symbol is attached|subjected in FIGS.

The silicon single crystal pulling apparatus 100, 200, 300 includes a chamber 10, a crucible 16, a shaft 18, a shaft drive mechanism 20, a tubular heat shield 22, a tubular heater 24, a tubular heat insulator 26, and a seed chuck 28. , A pulling wire 30, a wire lifting mechanism 32, a CCD camera 36, an exhaust pipe 40, and a main pump 42.

A gas introduction port 12 for introducing an inert gas such as Ar gas into the chamber 10 is provided in the upper portion of the chamber 10. Further, at the bottom of the chamber 10, a gas exhaust port 14 for sucking and exhausting gas (hereinafter, referred to as “furnace gas”) in the chamber 10 by driving the main pump 42 (vacuum pump) is provided.

The crucible 16 is arranged in the center of the chamber 10 and contains the silicon melt M. The crucible 16 has a double structure of a quartz crucible 16A and a graphite crucible 16B. The quartz crucible 16A directly supports the silicon melt M on its inner surface. The graphite crucible 16B supports the quartz crucible 16A outside the quartz crucible 16A. As shown in FIGS. 1 to 3, the upper end of the quartz crucible 16A is higher than the upper end of the graphite crucible 16B, that is, the upper end of the quartz crucible 16A projects from the upper end of the graphite crucible 16B.

The shaft 18 vertically penetrates the bottom of the chamber 10 and supports the crucible 16 at the upper end. Then, the shaft drive mechanism 20 raises and lowers the crucible 16 while rotating the crucible 16 via the shaft 18.

The heat shield 22 is provided above the crucible 16 so as to surround the single crystal silicon ingot I pulled up from the silicon melt M. Specifically, the heat shield 22 includes an inverted frustoconical shield body 22A, and an inner flange portion 22B extending horizontally from the lower end portion of the shield body 22A toward the pulling axis X side (inner side). And an outer flange portion 22C extending horizontally from the upper end of the shield body 22A toward the chamber side (outer side), and the outer flange portion 22C is fixed to the heat insulator 26. The function of the heat shield 22 is as described in the background art section.

The cylindrical heater 24 is positioned in the chamber 10 so as to surround the crucible 16. The heater 24 is a resistance heating type heater made of carbon, and melts the silicon raw material charged in the crucible 16 to form the silicon melt M, and further maintains the formed silicon melt M. Heating.

The tubular heat insulator 26 is provided below the upper end of the heat shield 22 and along the inner surface of the chamber 10. In this embodiment, a heat insulator is also arranged at the bottom of the chamber. The heat insulating material constituting these heat insulating materials is not particularly limited, and examples thereof include carbon, alumina, and zirconia. The heat insulator 26 has a function of imparting a heat retaining effect to a region inside the chamber 10 particularly below the heat shield 22 and making it easier to maintain the silicon melt M in the crucible 16. The thickness of the heat insulator 26 is not particularly limited and may be a general thickness equivalent to the conventional one. In a pulling device for growing a crystal having a diameter of 300 mm, a crystal having a diameter of about 30 to 90 mm and a diameter of 450 mm is grown. In the pulling device, it can be about 45 to 100 mm.

Above the crucible 16, a pulling wire 30 holding a seed chuck 28 holding the seed crystal S at its lower end is arranged coaxially with the shaft 18, and a wire lifting mechanism 32 moves the pulling wire 30 in the opposite direction to the shaft 18 or. Raise and lower while rotating at the same speed in the same direction.

A CCD camera 36 is provided in the opening 34 at the top of the chamber 10. The CCD camera 36 images the vicinity of the boundary between the crystal I and the melt M. The distance between the fusion rings in the obtained image is defined as the crystal diameter, and the crystal pulling rate and the melt temperature are controlled so that the crystal diameter becomes a desired constant value.

The exhaust pipe 40 extends from the gas outlet 14. The main pump 42 may be, for example, a vacuum pump such as a dry pump, is connected to the exhaust pipe 40, reduces the pressure in the chamber 10 to about 5 to 100 Torr, and sucks the in-furnace gas into the exhaust pipe 40. Fulfill. The main valve 44 is provided in the exhaust pipe 40 and plays a role of switching the pressure inside the chamber 10 between normal pressure and reduced pressure. That is, the main valve 44 is closed when the inside of the chamber 10 is at normal pressure, such as when the inside of the chamber 10 is opened to the atmosphere and when the structure inside the chamber 10 is installed or replaced. On the other hand, when the pressure in the chamber 10 including the raw material melting step and the crystal growing step is reduced, the main valve 44 is opened.

Here, in the raw material melting step and the crystal growing step, CO gas is generated in the chamber 10. The first cause is as follows. That is, SiO gas is generated from the silicon melt M in the crucible 16 as the silicon melt M reacts with the inner surface of the quartz crucible 16A. The SiO gas reaches the heater 24 along with the flow of the inert gas, and CO gas is generated by the reaction with carbon, which is a material of the heater, as shown in the following reaction formula.
SiO(g) + 2C(s) → CO(g) + SiC(s)
The SiC produced as a by-product is deposited on the surface of the heater 24.

The second cause is as follows. That is, CO gas is generated by the reaction between the quartz crucible 16A and the graphite crucible 16B which are in contact with each other.
SiO ₂ (s) + 3C(s) → 2CO(g) + SiC(s)
SiC produced as a by-product is deposited between the outer peripheral surface of the quartz crucible 16A and the inner peripheral surface of the graphite crucible 16B.

Each embodiment of the present invention monitors the amount of CO gas generated in the chamber 10 as described above per unit time (that is, the CO gas generation rate). The device configuration for that purpose will be described below.

[First Embodiment]
With reference to FIG. 1, in the present embodiment, the exhaust pipe 40 has a sub pipe 52 branched from a portion upstream of the main valve 44 and connected to a portion downstream of the main valve 44. That is, the gas sampling port 46 is provided in the exhaust pipe 40 at a location upstream of the main valve 44. An intake valve 54, a filter 58, a flow rate adjusting valve 60, a gas analyzer 62, and a sub pump 64 are attached to the sub pipe 52 in this order from the upstream side. In this specification, the terms “upstream” and “downstream” of the exhaust pipe 40 and the sub-pipe 52 refer to the flow of gas passing through each pipe.

The sub pump 64 is provided in the sub pipe 52, and sucks the in-furnace gas (strictly speaking, the gas sucked by the exhaust pipe) into the sub pipe 52 through the gas sampling port 46. The sub-pump 64 can be configured by, for example, a vacuum pump device in which a rotary pump and a turbo molecular pump are combined. As described above, the inside of the chamber 10 has a reduced pressure atmosphere of about 5 to 100 Torr, and in order to suck gas from the reduced pressure atmosphere to the sub pipe 52, it is necessary to create a lower reduced pressure atmosphere in the sub pipe 52. From this point of view, it is preferable to drive the sub-pump 64 so that the pressure in the sub-pipe 52 (the location upstream of the filter 58) is 1 Torr or less.

The gas analyzer 62 is provided upstream of the sub pump 64 of the sub pipe 52, and intermittently measures the CO gas concentration in the gas sucked into the sub pipe. Examples of the gas analyzer 62 include a quadrupole mass spectrometer and a gas chromatography device. In the case of a quadrupole mass spectrometer, the CO gas concentration measurement interval is as short as about 1 second. On the other hand, in the case of a gas chromatography apparatus currently on the market, the CO gas concentration measurement interval is about 15 minutes at the shortest. Therefore, in this embodiment, it is preferable to use a quadrupole mass spectrometer.

The flow rate adjusting valve 60 is provided upstream of the gas analyzer 62 in the sub-pipe 52 and plays a role of adjusting the flow rate of the gas supplied to the gas analyzer 62 by adjusting the degree of opening and closing. As a result, the in-furnace gas having an appropriate flow rate can be supplied to the gas analyzer 62. The flow rate of the gas supplied to the gas analyzer 62 is preferably 4×10 ⁻¹ to 4×10 ⁻⁴ Pa·L/min.

The filter 58 is provided upstream of the flow rate adjusting valve 60 of the sub pipe 52, and plays a role of removing SiO powder in the gas sucked into the sub pipe 52. The SiO gas generated from the silicon melt M is cooled and solidified to form SiO powder in the gas. FIG. 6 shows a graph showing a particle size distribution of SiO powder in a gas taken from a general chamber. As shown in FIG. 6, a typical average particle size of SiO powder is about 13 μm, and a typical minimum particle size is 1 μm. Therefore, in the present embodiment, it is preferable to use a gas filter having a mesh size of nanometer order, which can remove 99% by mass or more of particles having a particle size of 1 μm or more. Examples of such a gas filter include a wafer guard IISF in-line gas filter manufactured by Nippon Entegris Co., Ltd., and a small flow rate filter for NAS Clean process gas line manufactured by Nippon Seisen Co., Ltd. By providing the filter 58 upstream of the flow rate adjusting valve 60, it is possible to avoid the open/close malfunction of the flow rate adjusting valve 60 due to the SiO powder, and also to prevent the SiO powder from being mixed into the gas analyzer 62.

The intake valve 54 is provided in the vicinity of the gas sampling port 46 of the sub pipe 52, and opens when the in-furnace gas is sucked into the sub pipe 52. In this embodiment, since the CO gas concentration is constantly measured and the CO gas generation rate is monitored during the raw material melting step and the crystal growing step, the intake valve 54 is always open. As a result, a part of the gas sucked into the exhaust pipe is taken into the sub pipe 52.

The calculation unit 66 calculates the CO gas generation rate by multiplying the CO gas concentration measured by the gas analyzer 62 by the flow rate of the inert gas supplied into the chamber 10. The arithmetic unit 66 can be configured by a general central processing unit (CPU) or a micro processing unit (MPU). The gas flow rate set value may be used as the flow rate of the inert gas supplied into the chamber 10.

The output device 68 outputs the CO gas generation rate calculated by the calculation unit 66. The output device 68 can be configured by a general display, projector, printer, speaker, or the like.

In the present embodiment, with the above configuration, the CO gas generation rate of the furnace gas can be monitored in real time, instead of the CO gas concentration of the furnace gas. In this way, by monitoring the CO gas generation rate in-situ, the amount of CO gas taken into the silicon melt, and thus the carbon concentration in the crystal, can be appropriately evaluated.

[Second Embodiment]
With reference to FIG. 2, in the present embodiment, the gas sampling port 48 is located in the space between the heat shield 22 and the crucible 16. That is, the sampling tube 50 is hung from the upper part of the chamber 10 and the gas sampling port 48 at the tip thereof is positioned in the space between the heat shield 22 and the crucible 16. The sampling pipe 50 is connected to the sub pipe 52 outside the chamber 10. The intake valve 56 is provided near the upstream end of the sub pipe 52.

In the first embodiment, the in-furnace gas is collected via the exhaust pipe 52, whereas in the present embodiment, the in-furnace gas is collected from the space between the heat shield 22 and the crucible 16. is there. The filter 58, the flow rate adjusting valve 60, the gas analyzer 62, the sub pump 64, the calculation unit 66, and the output device 68 installed in the sub pipe 52 are the same as those in the first embodiment, and thus the description thereof will be omitted. ..

In this embodiment, the gas in the furnace is directly collected from the upper edge of the quartz crucible. Therefore, CO gas generated by the reaction between the quartz crucible and the carbon crucible can be directly collected. As a result, the CO gas generation rate can be monitored with higher accuracy.

[Third Embodiment]
With reference to FIG. 3, the present embodiment is a combination of the configuration of the first embodiment and the configuration of the second embodiment. That is, the collection of the in-furnace gas is performed through the exhaust pipe 52 and also from the space between the heat shield 22 and the crucible 16.

In the present embodiment, the sub pipe 52 includes a first sub pipe 52B, a second sub pipe 52C, and a third sub pipe 52D. The first sub pipe 52B branches from a portion of the exhaust pipe 40 upstream of the main valve 44. The second sub pipe 52C is connected to the upper end of the sampling pipe 50 and extends from the upper part of the chamber. The third sub pipe 52D is formed by joining the first sub pipe 52B and the second sub pipe 52C. The sampling tube 50 and the intake valve are the same as those in the second embodiment. The filter 58, the flow rate adjusting valve 60, the gas analyzer 62, the sub pump 64, and the calculation unit 66 and the output device 68 installed in the sub pipe 52C are the same as those in the first embodiment, and thus the description thereof will be omitted. ..

In the present embodiment, the position dependency of CO gas generation can be confirmed by switching the intake valve 54 and the intake valve 56 at appropriate timings and measuring the CO gas concentration. Specifically, by taking the difference between the CO concentrations measured at each position, the CO gas concentration generated by the reaction between the quartz crucible and the graphite crucible and the CO gas concentration generated by the reaction between the SiO gas and the graphite are obtained. Can be divided.

(Method of manufacturing single crystal silicon ingot)
The method for manufacturing a single crystal silicon ingot according to the embodiment of the present invention can be suitably implemented using the silicon single crystal pulling apparatus 100, 200, 300 described above. Therefore, a method for manufacturing a single crystal silicon ingot according to an embodiment of the present invention will be described with reference to FIGS. First, the crucible 16 is filled with a silicon raw material such as polycrystalline silicon nugget, and the main pump 42 is driven with the main valve 44 opened to maintain the inside of the chamber 10 under a reduced pressure in an inert gas atmosphere such as Ar gas. To do. At this time, the crucible 16 is located below the chamber 10 so that the silicon raw material does not contact the heat shield 22. After that, the silicon raw material in the crucible 16 is heated by the heater 24 and melted to form the silicon melt M. Then, the crucible 16 is raised to the pulling start position. In the present specification, the “raw material melting step” is defined as a period from the time when the heating by the heater 24 is started to the time when the crucible is completely lifted. In the raw material melting step, the flow rate of the inert gas is preferably 10 to 400 L/min.

Next, the pulling wire 30 is lowered by the wire elevating mechanism 32 to deposit the seed crystal S on the silicon melt M. Thereafter, while pulling the crucible 16 and the pulling wire 30 in a predetermined direction, the pulling wire 30 is pulled upward to grow an ingot I below the seed crystal S. Although the amount of the silicon melt M decreases as the growth of the ingot I progresses, the crucible 16 is raised to maintain the level of the melt surface. In the present specification, the “crystal growing step” is defined as a period from the time when the pulling wire 30 is started to descend to the time when the growing of the ingot I (the raising of the pulling wire 30) is completed.

The crystal growth step, performed aperture seed (necking) First by Dash method for dislocation-free single crystal to form a neck portion I _n. Next, foster shoulder portion I _s to obtain an ingot of the required diameter, the silicon single crystal to grow a cylindrical body portion I _b and a constant diameter upon reaching the desired diameter. After growing the straight body part I _b to a predetermined length, tail drawing (formation of the tail part) is performed to separate the single crystal from the silicon melt M in a dislocation-free state. In the present specification, the growing period of the straight body part I _b is referred to as “straight body process”.

In the crystal growing step, the flow rate of the inert gas is preferably 50 to 300 L/min. In addition, in the crystal growing step, the flow rate of the impenetrable gas is increased (decreased) with time within the above range.

The present embodiment is characterized in that the following steps are performed in the raw material melting step and the crystal growing step. First, the furnace gas is sampled. This step is performed by sucking the in-furnace gas into the sub-pipe 52 from one or both of the gas sampling port 46 and the gas sampling port 48, as shown in FIGS.

Next, the CO gas concentration in the collected gas is intermittently measured by the gas analyzer 62. Then, the calculation unit 66 calculates the CO gas generation rate by multiplying the measured CO gas concentration by the flow rate of the inert gas supplied into the chamber 10. Then, the output device 68 outputs the calculated CO gas generation rate. In the present embodiment, the CO gas generation rate of the furnace gas can be monitored in real time instead of the CO gas concentration of the furnace gas. In this way, by monitoring the CO gas generation rate in-situ, the amount of CO gas taken into the silicon melt, and thus the carbon concentration in the crystal, can be appropriately evaluated. As described above, the flow rate of the inert gas supplied into the chamber 10 is different between the raw material melting step and the crystal growing step, and also varies during the crystal growing step. Can be used.

In the present embodiment, the maximum value of the CO gas generation rate in the raw material melting step is A (mol/h), and the maximum value of the CO gas generation rate in the straight body step during the crystal growth step is B (mol/h). The melting step and the crystal growing step are preferably performed under the condition that A/B≦10 is satisfied. Under the condition of satisfying A/B≦10, it is possible to manufacture a single crystal silicon ingot having a carbon concentration (Cs) of 2×10 ¹⁵ atoms/cm ³ or less at all sites where the crystal solidification rate is 0.75 or less. .. That is, a single crystal silicon ingot having a low carbon concentration can be manufactured with a high yield. The crystal solidification rate (%) is defined by the percentage of the mass of crystal during pulling/the mass of raw material charged. In the first 10 hours of the raw material melting process, the CO gas generation rate is not stable due to degassing from the parts inside the chamber. Therefore, in the present specification, the maximum value of the period excluding the initial 10 hours in the raw material melting step is adopted as A.

The value of A/B can be adjusted mainly by controlling the electric energy of the heater 24 in the raw material melting process. Generally, in the crystal growing step, the amount of electric power of the heater 24 required to maintain the silicon melt M is naturally determined to be within a predetermined range, and the heater is driven with the specific amount of electric power to drive the silicon melt. Maintain M. Therefore, the CO gas generation rate in the crystal growing step is relatively low and stable (no large fluctuation). On the other hand, in the raw material melting step, the heater 24 needs to be driven with a large amount of electric power in order to melt the silicon raw material, and the CO gas generation rate is relatively high and unstable (changes greatly). In particular, the CO gas generation rate tends to increase at the end of the raw material melting step (when the melt is completed). Therefore, A/B≦10 can be realized by controlling the electric power amount of the heater 24 in the raw material melting step to suppress the maximum value A of the CO gas generation rate. However, the values of A and B are not uniquely determined by the amount of electric power of the heater 24, but also depend on the heat insulating property in the chamber 10 (that is, the structure of the chamber, the amount and arrangement of the heat insulator). ..

A/B is preferably 1 or more. This is because if A/B is less than 1, the silicon melt may be solidified and crystal growth may not be established.

(Experimental example 1)
Using the silicon single crystal pulling apparatus having the configuration shown in FIG. 1, single crystal silicon ingots were manufactured at four levels shown in Table 1. At each level, the amount of silicon raw material charged was 320 kg, the diameter of the ingot was 300 mm, the straight body length was 1800 mm, the growth rate was 1.0 mm/min, and the flow rate of Ar gas supplied into the chamber during the raw material melting process was 100 L/min. And A gas filter having a mesh size of nanometer order, which can remove 99% by mass or more of particles having a particle size of 1 μm or more, was used. The electric power of the heater in the raw material melting step and the crystal growing step was set to the value shown in Table 1.

A quadrupole mass spectrometer was used as a gas analyzer, and the CO gas generation rate was monitored during the entire raw material melting step and crystal growth step. Table 1 shows the maximum value A of the CO gas generation rate in the raw material melting step and the maximum value B of the CO gas generation rate in the straight body step. In addition, the level No. is represented on behalf of all levels. The transition of the CO gas generation rate monitored in 1 is shown in FIG.

At each level, the "low carbon crystal yield" shown in Table 1 was determined by the following procedure. First, a single crystal silicon ingot manufactured at each level was cut out from a straight body portion and processed to manufacture a large number of silicon wafers. At one point in the center of each wafer, the concentration of carbon (Cs concentration) substituted at the crystal position of silicon was measured using an FT-IR apparatus. With the grown crystal length as a denominator, a crystal yield satisfying Cs≦2×10 ¹⁵ atoms/cm ³ or less was taken as a molecule, and a crystal yield was determined, which was defined as “low carbon crystal yield”. The results are shown in Table 1.

As is apparent from Table 1, the level No. performed under the condition that A/B≦10 was satisfied. In Nos. 1 to 4, the low carbon crystal yield was as high as 75% or more, while in the level No. 1 performed under the condition of A/B=11. In No. 5, the low carbon crystal yield was significantly reduced to 25%.

(Experimental example 2)
Depending on the performance and presence of the gas filter, it is possible to continuously monitor the CO gas generation rate without clogging the sub piping (specifically, the flow rate adjusting valve or between the flow rate adjusting valve and the gas analyzer). I measured the time. The manufacturing conditions of the single crystal silicon ingot were the same as in Experimental Example 1 except for the filter.

As Level 1, as in Experimental Example 1, a gas filter having a mesh size of nanometer order capable of removing 99% by mass or more of particles having a particle size of 1 μm or more was used. At this level 1, the CO gas generation rate could be continuously monitored for 100 hours or more.

As Level 2, a gas filter having a mesh size capable of removing 99% by mass or more of particles having a particle size of 10 μm or more was used. In this level 2, when the CO gas generation rate was continuously monitored for 70 hours, the sub piping became clogged and monitoring was impossible.

As level 3, no gas filter was used. In this level 2, when the CO gas generation rate was continuously monitored for 20 hours, the sub-pipe was clogged and monitoring was impossible.

According to the method for producing a single crystal silicon ingot and the silicon single crystal pulling apparatus of the present invention, it is possible to produce a single crystal silicon ingot having a low carbon concentration with a high yield.

100, 200, 300 Silicon single crystal pulling apparatus 10 Chamber 12 Gas inlet 14 Gas outlet 16 Crucible 16A Quartz crucible 16B Graphite crucible 18 Shaft 20 Shaft drive mechanism 22 Heat shield 22A Shield body 22B Inner flange 22C Outer flange 24 Heater 26 Heat insulator 28 Seed chuck 30 Pulling wire 32 Wire lifting mechanism 34 Opening 36 CCD camera 40 Exhaust pipe 42 Main pump 44 Main valve 46 Gas sampling port (exhaust pipe)
48 Gas sampling port (inside chamber)
50 Sampling tube (in chamber)
52 sub pipe 52A sub pipe end 54 captures valve 56 capture valve 58 filter 60 flow regulating valve 62 gas analyzer 64 subsidiary pump 66 operation unit 68 output apparatus S seed crystal M silicon melt I monocrystalline silicon ingot I _n the neck I _s shoulder Part I _b Straight body part X Lifting shaft

Claims (9)

A chamber having a gas inlet for introducing an inert gas in the upper portion and a gas outlet for discharging the in-furnace gas containing the inert gas in the bottom;
A crucible located in the chamber,
A cylindrical heater positioned so as to surround the crucible in the chamber,
A method for manufacturing a single crystal silicon ingot performed using a silicon single crystal pulling apparatus having:
While maintaining the atmosphere of the inert gas under reduced pressure in the chamber, a raw material melting step of forming a silicon melt in the crucible by heating and melting the silicon raw material charged in the crucible by the heater,
Subsequently, while maintaining the atmosphere of the inert gas under reduced pressure in the chamber, the silicon melt is heated and maintained by the heater, and a crystal growing step of pulling a single crystal silicon ingot from the silicon melt,
In the raw material melting step and the crystal growing step,
Collecting the gas in the furnace,
The CO gas concentration in the collected gas is intermittently measured by a gas analyzer,
The CO gas generation rate is calculated by multiplying the measured CO gas concentration by the flow rate of the inert gas supplied into the chamber,
A method for producing a single crystal silicon ingot, which comprises monitoring the calculated CO gas generation rate. The maximum value of the CO gas generation rate in the raw material melting step is A (mol/h), and the maximum value of the CO gas generation rate in the straight body process in the crystal growing step is B (mol/h). The method for producing a single crystal silicon ingot according to claim 1, wherein the crystal growing step is performed under conditions satisfying A/B≦10. The method for manufacturing a single crystal silicon ingot according to claim 1, wherein the in-furnace gas is collected through an exhaust pipe extending from the gas outlet. The furnace gas is collected from a space between the crucible and a cylindrical heat shield provided so as to surround the single crystal silicon ingot above the crucible, any one of claims 1 to 3. The method for producing a single crystal silicon ingot according to the item 1. The method for producing a single crystal silicon ingot according to any one of claims 1 to 4, wherein the gas analyzer is a quadrupole mass spectrometer. A chamber having a gas inlet for introducing an inert gas in the upper portion and a gas outlet for discharging the in-furnace gas containing the inert gas in the bottom;
A crucible located in the chamber and containing a silicon melt;
Above the crucible, a cylindrical heat shield provided so as to surround the single crystal silicon ingot pulled up from the silicon melt,
A cylindrical heater that is positioned so as to surround the crucible in the chamber and that heats the silicon melt,
An exhaust pipe extending from the gas outlet,
A main pump that is connected to the exhaust pipe, reduces the pressure in the chamber, and sucks the in-furnace gas into the exhaust pipe;
A main valve provided in the exhaust pipe and opened when decompressing the chamber,
A portion of the exhaust pipe upstream of the main valve, and a space between the heat shield and the crucible, and a gas sampling port provided in one or both of them.
A sub-pipe extending from the gas sampling port and connected to a part of the exhaust pipe downstream of the main valve;
A sub-pump provided in the sub-pipe, for sucking the in-furnace gas into the sub-pipe,
A gas analyzer provided upstream of the sub-pump in the sub-pipe, and intermittently measuring the CO gas concentration in the gas sucked into the sub-pipe;
A flow rate adjustment valve that is provided upstream of the gas analysis device in the sub-pipe and that adjusts the flow rate of the gas supplied to the gas analysis device,
A filter that is provided upstream of the flow rate adjusting valve of the sub-pipe and removes SiO powder in the gas sucked into the sub-pipe;
An intake valve which is provided in the vicinity of the gas sampling port of the sub-pipe and which opens when the in-furnace gas is sucked into the sub-pipe,
And further,
An operation unit for calculating a CO gas generation rate by multiplying the CO gas concentration measured by the gas analyzer by the flow rate of the inert gas supplied into the chamber,
An output device for outputting the calculated CO gas generation rate;
A silicon single crystal pulling apparatus having: The silicon single crystal pulling apparatus according to claim 6, wherein the gas sampling port is provided in a portion of the exhaust pipe upstream of the main valve. The silicon single crystal pulling apparatus according to claim 6 or 7, wherein the gas sampling port is located in a space between the heat shield and the crucible. 9. The silicon single crystal pulling apparatus according to claim 6, wherein the gas analyzer is a quadrupole mass spectrometer.

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