JP6772977B2 - Manufacturing method of silicon single crystal pulling device and single crystal silicon ingot - Google Patents

Description

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

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

FIG. 3 shows a conventional silicon single crystal pulling device 300 that manufactures a single crystal silicon ingot by the CZ method. The outer shell of the silicon single crystal pulling device 300 is composed of a chamber 10, and a 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 the upper end of a shaft 18 that can be rotated and raised and lowered by a shaft drive mechanism 20.

A resistance heating type tubular heater 24 is disposed on the outside of the crucible 16 so as to surround the crucible 16, and a heat insulating body 26 is disposed on the outside thereof along the inner surface of the chamber 10. Further, above the crucible 16, a pulling wire 34 holding the seed chuck 32 holding the seed crystal S at the lower end is arranged coaxially with the shaft 18, and the wire elevating mechanism 36 reverses the pulling wire 34 to the shaft 18. It moves up and down while rotating at a predetermined speed in the same direction or in the same direction.

In the chamber 10, a tubular heat shield 22 is arranged 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 with respect to the growing ingot I, and adjusts the amount of heat radiant heat near the crystal growth interface. It adjusts the amount of diffusion and plays a role of controlling the temperature gradient in the pulling axis X direction of 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 above 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 from the gas introduction port 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, the gas 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 device 300, while maintaining the inside of the chamber 10 in an Ar gas atmosphere under reduced pressure, a silicon raw material such as polycrystalline silicon filled in the crucible 16 is melted by heating the heater 24 to form silicon. A melt M is formed. Next, the pull-up wire 34 is lowered by the wire elevating mechanism 36, the seed crystal S is landed on the silicon melt M, and the pull-up wire 34 is pulled up while rotating the crucible 16 and the pull-up wire 34 in a predetermined direction. , Ingot I is grown below the seed crystal S. As the growth of the ingot I progresses, the amount of the silicon melt M decreases, but the crucible 16 is raised to maintain the level of the melt surface.

A CCD camera 40 is provided in the opening 38 at the top of the chamber 10. The CCD camera 40 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 is referred to as a ring-shaped high brightness band (hereinafter referred to as "fusion ring"). .) Becomes apparent. The interval between the fusion rings is recognized as the crystal diameter, and the crystal pulling speed and the melt temperature are controlled so that the crystal diameter becomes a desired constant value.

In such a conventional silicon single crystal pulling device 300, as described in Patent Document 1, the tubular heater 24 is arranged outside the crucible 16 so as to surround the crucible 16. That is, the upper end 24A of the tubular heater is always higher than the bottom 16C of the crucible. This is because the heater melts the silicon raw material in the crucible and further heats it to maintain the formed silicon melt.

Japanese Unexamined Patent Publication No. 2015-86088

Carbon is mixed in the single crystal silicon ingot manufactured by the conventional silicon single crystal pulling device in the growing process, and as a result, the carbon concentration of the silicon wafer manufactured from the ingot is unintentionally increased. There was a problem. When the carbon concentration in the silicon wafer becomes high, a defect called an electrically active carbon-induced defect called a killer defect occurs during the device heat treatment process, which causes a problem of shortening the life time of the wafer. Further, since high-concentration carbon promotes the formation of oxygen precipitates, if oxygen precipitates are present on the surface of the device, leak defects occur, which causes a decrease in yield. As described above, it is known that carbon contamination in the single crystal silicon ingot has an adverse effect in 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.

Therefore, in view of the above problems, it is an object of the present invention to provide a silicon single crystal pulling device capable of reducing the carbon concentration in the single crystal silicon ingot and a method for producing the single crystal silicon ingot.

In order to solve the above problems, the present inventors focused on the arrangement of the tubular heater in the chamber. The reason why the carbon concentration in the crystal increases is that the CO gas generated by the reaction between the SiO gas generated from the silicon melt and the carbon which is the material of the tubular heater is taken into the silicon melt. Those thought. Therefore, I got the idea to install the tubular heater at a position lower than before, that is, at a position where the upper end of the heater is lower than the bottom of the crucible. In this case, even if the SiO gas generated from the silicon melt reaches the heater along the flow of the inert gas and CO gas is generated there, the CO gas does not return to the rutsubo side and is sent from the gas outlet directly below. It is discharged and is not incorporated into the silicon melt.

Since the tubular heater melts the silicon raw material in the crucible and further heats it to maintain the formed silicon melt, it is common sense that the tubular heater is arranged so as to surround the crucible on the outside of the crucible. there were. Contrary to the common sense, the present inventors have attempted to solve the above problem by lowering the position of the heater. Then, they found that even if the heater position was changed in this way, the silicon melt could be formed and maintained by increasing the output of the heater, and the growth of the single crystal ingot was established.

The abstract structure of the present invention completed based on the above findings is as follows.
(1) A chamber having a gas introduction port for introducing the inert gas at the top and a gas discharge port for discharging the inert gas at the bottom.
A crucible that houses the silicon melt in the chamber,
A shaft that vertically penetrates the bottom of the chamber and supports the crucible at the upper end.
A shaft drive mechanism that raises and lowers the crucible while rotating it via the shaft,
A tubular heat shield provided above the crucible so as to surround the single crystal silicon ingot pulled up from the silicon melt.
A tubular heater located in the chamber so as to surround the shaft and heating the silicon melt,
A tubular heat insulator provided along the inner surface of the chamber below the upper end of the heat shield.
Have,
The inner surface of the crucible when the upper end of the heater is positioned at the highest position where the silicon melt does not come into contact with the heat shield, with the capacity of the silicon melt as the maximum allowable amount. A silicon single crystal pulling device characterized in that it is arranged at a position lower than the bottom of the crucible.

(2) The heat insulating body is
A lower insulator having a first thickness and extending outside the heater to a height range that includes at least the heater.
An upper heat insulating body that is continuous with the lower heat insulating body and has a second thickness that is thicker than the first thickness.
When the distance between the inner peripheral surface of the lower heat insulating body and the outer peripheral surface of the heater is D, the lower end of the upper heat insulating body is 2.0 × D or less from the upper end of the heater. The silicon single crystal pulling device according to (1) above, which extends within the above range.

(3) The lower heat insulating body and the upper heat insulating body have a common outer peripheral surface, and the inner peripheral surface of the upper heat insulating body is located inside the inner peripheral surface of the lower heat insulating body.
The silicon single crystal pulling device according to (2) above, wherein the lower end surface of the upper heat insulating body protruding from the position of the inner peripheral surface of the lower heat insulating body toward the crucible side and the upper end surface of the heater face each other. ..

(4) The crucible has a quartz crucible that directly supports the silicon melt on the inner surface and a graphite crucible that supports the quartz crucible on the outside of the quartz crucible, and the upper end of the quartz crucible is of the graphite crucible. The silicon single crystal pulling device according to any one of (1) to (3) above, which is higher than the upper end.

(5) A method for producing a single crystal silicon ingot, which is carried out by using the silicon single crystal pulling device according to any one of (1) to (4) above.
A method for producing a single crystal silicon ingot, wherein the upper end of the heater is always lower than the bottom of the inner surface of the crucible during the crystal growth step of pulling the single crystal silicon ingot from the silicon melt.

(6) During the raw material melting step of heating and melting the silicon raw material put into the crucible by the heater to form the silicon melt, the upper end of the heater is at a position lower than the bottom of the inner surface of the crucible. The method for producing a single crystal silicon ingot according to claim 5.

According to the silicon single crystal pulling device and the method for producing a single crystal silicon ingot of the present invention, it is possible to reduce the carbon concentration in the single crystal silicon ingot.

It is sectional drawing along the pulling axis X which shows typically the structure of the silicon single crystal pulling apparatus 100 by one Embodiment of this invention (the present invention example 1). It is sectional drawing along the pulling axis X which shows typically the structure of the silicon single crystal pulling apparatus 200 by another Embodiment of this invention (the present invention example 2). It is sectional drawing along the pulling axis X which shows typically the structure of the conventional (comparative example 1) silicon single crystal pulling apparatus 300. It is a graph which shows the relationship between the distance on the side surface of a quartz crucible from the upper end of a quartz crucible, and the side temperature of a quartz crucible in Comparative Example 1 and Examples 1 and 2 of the present invention.

(Silicon single crystal pulling device according to the first embodiment)
The silicon single crystal pulling device 100 according to the first embodiment of the present invention will be described with reference to FIG. The silicon single crystal pulling device 100 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 insulating body 26, a seed chuck 32, and a pulling wire 34. , A wire elevating mechanism 36, and a CCD camera 40.

A gas introduction port 12 for introducing an inert gas such as Ar gas into the chamber 10 is provided above 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 crucible 16 is located in the center of the chamber 10 and houses the silicone 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 the inner surface. The graphite crucible 16B supports the quartz crucible 16A on the outside of the quartz crucible 16A. As shown in FIG. 1, 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 protrudes 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 moves the crucible 16 up and down while rotating it 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 truncated cone-shaped shield main body 22A and an inner flange portion 22B extending horizontally from the lower end of the shield main body 22A toward the pull-up shaft X side (inside). And an outer flange portion 22C extending horizontally from the upper end portion of the shield main body 22A toward the chamber side (outside), and the outer flange portion 22C is fixed to the heat insulating body 26. The function of the heat shield 22 is as described in the background art section.

The tubular heater 24 is located within the chamber 10 so as to surround the shaft 18. The heater 24 is a resistance heating type heater made of carbon as a material, for melting the silicon raw material charged into the crucible 16 to form a silicon melt M, and further maintaining the formed silicon melt M. Perform heating.

The tubular heat insulating body 26 is provided below the upper end of the heat shielding body 22 along the inner surface of the chamber 10. In this embodiment, the insulation is further arranged at the bottom of the chamber. The heat insulating material constituting these heat insulating bodies is not particularly limited, and examples thereof include carbon, alumina, and zirconia. The heat insulating body 26 has a function of imparting a heat retaining effect to a region in the chamber 10 particularly below the heat shielding body 22 and facilitating the maintenance of the silicon melt M in the crucible 16. The thickness T of the heat insulating body 26 is not particularly limited and can be a general thickness equivalent to that of 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, the diameter can be about 45 to 100 mm.

Above the crucible 16, a pulling wire 34 holding the seed chuck 32 holding the seed crystal S at the lower end is arranged coaxially with the shaft 18, and the wire elevating mechanism 36 moves the pulling wire 34 in the opposite direction to the shaft 18 or It moves up and down while rotating at a predetermined speed in the same direction.

A CCD camera 40 is provided in the opening 38 at the top of the chamber 10. The CCD camera 40 images the vicinity of the boundary between the crystal I and the melt M. The crystal pulling speed and the melt temperature are controlled so that the crystal diameter is a desired constant value, with the interval between the fusion rings in the obtained image as the crystal diameter.

A characteristic configuration of the present embodiment is to arrange the heater 24 so that its upper end 24A is lower than the bottom 16C on the inner surface of the crucible. This makes it possible to reduce the carbon concentration in the grown single crystal silicon ingot I.

The present inventors consider the action of obtaining such an effect as follows. From the silicon melt M in the crucible 16, SiO gas is generated by the reaction of the silicon melt M 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 as shown in the following reaction formula, CO gas is generated by the reaction with carbon, which is the material of the heater.
SiO ↑ + 2C → CO ↑ + SiC
The SiC produced as a by-product is deposited on the surface of the heater 24. When the heater 24 is located near the crucible as in the prior art shown in FIG. 3, a gas flow may occur in which a part of the CO gas returns to the silicon melt side, and a part of the CO gas is in the silicon melt. It is taken in by M. On the other hand, in the present embodiment, since the heater 24 is located at the lower part in the chamber 10 and close to the gas discharge port 14, the generated CO gas is not taken into the silicon melt M, and almost all of the generated CO gas is gas. It is discharged from the discharge port 14. As a result, the carbon concentration in the silicon melt M is reduced, and by extension, the carbon concentration in the grown single crystal silicon ingot I is reduced.

Further, in the present embodiment, as a secondary effect, the diameter controllability of the ingot can be improved. In the present embodiment, since the heater 24 is located at the lower part in the chamber 10, the heater 24, which is a heating source, is not directly reflected on the silicon melt surface in the diameter control method in which the distance between the fusion rings is the crystal diameter. .. Therefore, the influence of the radiated light from the heater on the brightness measurement of the fusion ring is reduced, and the width of the fusion ring can be measured more accurately. As a result, the crystal diameter can be measured with higher accuracy.

The crucible 16 is located below the chamber 10 so that the silicon raw material does not come into contact with the heat shield 22 when the silicon raw material is charged, and at the stage where the silicon melt M is housed, the silicon melt M is present. It is in a position where it does not come into contact with the heat shield 22. Then, during the crystal growing step (pulling step), the level (height) of the silicon melt surface is kept constant, that is, the distance between the lower end of the heat shield 22 and the silicon melt surface is kept constant. The rutsubo 16 is raised as the amount of silicone melt decreases to maintain it. Therefore, in the present embodiment, in order to exert the above-mentioned effects, the upper end 24A of the heater is at the highest position where the silicon melt does not come into contact with the heat shield 22 with the capacity of the silicon melt M as the maximum allowable amount. When the crucible 16 is positioned, the position is lower than the bottom 16C of the inner surface of the crucible.

Here, in the present specification, the "maximum allowable amount of the capacity of the silicon melt" is the height of the silicon melt surface from the bottom 16C of the inner surface of the crucible to the upper end of the crucible 16 from the bottom 16C of the inner surface of the crucible. It is defined as the capacity at which the ratio to the height is 90%. If this ratio exceeds 90% and the silicon melt is contained, the silicon melt may spill from the edge of the quartz crucible when the melt surface shakes due to an earthquake or the like, which adversely affects crystal growth. Because. In normal operation, it is preferable to form as much silicon melt as possible with one charge in consideration of manufacturing efficiency. Therefore, the capacity of the silicon melt at the start of the crystal growth step has the above ratio. Try to be 80-90%.

Further, in the crystal growth step, the distance between the lower end of the heat shield 22 and the silicon melt surface is kept constant, but the distance is preferably about 5 to 100 mm. If it is 5 mm or more, there is no possibility that the lower end of the heat shield will be immersed in the silicon melt even if there is an error in the calculation of the ascending speed of the quartz crucible during crystal growth, and if it is 100 mm or less, it will be from the heater. This is because the crystal is not directly exposed to radiant light, the latent heat generated during crystal solidification can be released to the outside, and crystal growth can be reliably performed.

The distance D between the inner peripheral surface of the heat insulating body 26 and the outer peripheral surface of the heater 24 is not particularly limited and can be a general distance equivalent to the conventional one. In the pulling device for growing a crystal having a diameter of 300 mm, 5 It can be about 5 to 150 mm in a pulling device for growing a crystal having a diameter of about 100 mm and a diameter of 450 mm.

The size of the heater 24 is not particularly limited, and may be the same general size as the conventional one, and the length in the pull-up axis X direction may be about 500 to 700 mm and the thickness may be about 20 to 50 mm. As the heater 24 is moved away from the crucible 16, it is necessary to increase the heater output by about 1 to 3% as compared with the conventional apparatus shown in FIG. 3 in order to melt the silicon raw material and maintain the silicon melt. However, the growth of single crystal ingots is established by increasing the output to this extent.

(Silicon single crystal pulling device according to the second embodiment)
The silicon single crystal pulling device 200 according to the second embodiment of the present invention will be described with reference to FIG. The silicon single crystal pulling device 200 of the present embodiment has the same configuration as the silicon single crystal pulling device 100 according to the first embodiment except that the configuration of the heat insulating body 26 is different, and has the same effect.

Hereinafter, the heat insulating body 26 will be described in detail. In the present embodiment, a heat insulating body is also provided in the space created by moving the heater 24 downward than before to enhance the heat retention effect in the region below the heat shield 22. Specifically, the heat insulating body 26 has a lower heat insulating body 28 and an upper heat insulating body 30. The lower insulation 28 has a first thickness T1 and extends outside the heater 24 to a height range that includes at least the heater 24. The upper heat insulating body 30 has a second thickness T2 that is continuous with the lower heat insulating body 28 and is thicker than the first thickness T1.

Then, in the present embodiment, it is important to extend the upper heat insulating body 30 to the vicinity of the upper end 24A of the heater. Specifically, when the distance between the inner peripheral surface 28A of the lower heat insulating body and the outer peripheral surface 24B of the heater is D, the lower end 30C of the upper heat insulating body 30 is 2.0 × D or less from the upper end 24A of the heater. It shall extend within the range of distance.

By adopting this configuration, the following two effects can be obtained. The first is the reduction of the power consumption of the heater. In the first embodiment, in order to establish the growth of the single crystal ingot, it is necessary to increase the heater output, although it is about 1 to 3% as compared with the conventional apparatus shown in FIG. On the other hand, in the present embodiment, since the upper heat insulating body 30 thicker than the lower heat insulating body 28 extends to the vicinity of the upper end 24A of the heater, the heat retention effect in the region below the heat shield 22 is enhanced. It is possible to grow a single crystal ingot without increasing the output of the heater. According to the study by the present inventors, it was possible to establish the growth of the single crystal ingot even if the heater output was lowered by about 5 to 7% as compared with the conventional apparatus shown in FIG. This is because the amount of increase in heat transfer to the crucible by enhancing the heat retention effect in the region below the heat shield 22 is larger than the amount of decrease in heat transfer to the crucible by moving the heater 24 away from the crucible 16. This is the first finding found by the present inventors.

Second, it is possible to prevent the upper end of the quartz crucible 16A from collapsing. The upper end of the quartz crucible 16A is not held by the graphite crucible 16B. Therefore, in the conventional apparatus shown in FIG. 3, since the upper end portion of the quartz crucible 16A receives radiant heat directly from the heater 24, the upper end portion may soften and fall inside the crucible 16 during the crystal growing process. .. In this case, if the crucible 16 continues to rise, the collapsed upper end portion comes into contact with the heat shield 22, and crystal growth cannot continue. Further, according to the study by the present inventors, even if the heater 24 is moved away from the crucible 16, as in the first embodiment, the upper end portion may collapse. It is considered that this is because the heater output was increased in order to establish the growth of the single crystal ingot. On the other hand, in the present embodiment, the heater output can be reduced by enhancing the heat retention effect in the region below the heat shield 22, and the direct radiant heat from the heater 24 can be avoided. Therefore, the quartz crucible 16A It is possible to prevent the upper end of the crucible from collapsing.

The distance D between the inner peripheral surface 28A of the lower heat insulating body and the outer peripheral surface 24B of the heater is not particularly limited, and can be a general distance equivalent to the conventional one. In the pulling device for growing a crystal having a diameter of 300 mm, 5 It can be about 5 to 150 mm in a pulling device for growing a crystal having a diameter of about 100 mm and a diameter of 450 mm.

When the heat insulating material is carbon, the thickness T1 of the lower heat insulating body 28 is about 30 to 90 mm in a pulling device for growing crystals having a diameter of 300 mm, and about 45 to 100 mm in a pulling device for growing crystals having a diameter of 450 mm. be able to.

The thickness T2 of the upper heat insulating body 30 is not particularly limited, but it is preferable to secure it at least twice as much as T1 from the viewpoint of obtaining the effect of the present embodiment. The upper limit of T2 is not particularly limited, but it is preferably 5 times or less of T1 due to the limitation of the space in the chamber.

In the present embodiment, as long as the upper heat insulating body 30 thicker than the lower heat insulating body 28 extends to the vicinity of the upper end 24A of the heater, the arrangement of the heat insulating body is not particularly limited, but as shown in FIG. 2, the lower heat insulating body 28 The upper heat insulating body 30 has common outer peripheral surfaces 28B and 30B, and the inner peripheral surface 30A of the upper heat insulating body is located inside the inner peripheral surface 28A of the lower heat insulating body (on the pulling axis X side), and the lower heat insulating body 30 It is preferable that the lower end surface 30C of the upper heat insulating body protruding from the position of the inner peripheral surface 28A of the heater to the crucible side and the upper end surface 24A of the heater face each other.

(Manufacturing method of single crystal silicon ingot)
A method for producing a single crystal silicon ingot according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. First, the crucible 16 is filled with a silicon raw material such as a polycrystalline silicon nugget, and the inside of the chamber 10 is maintained in an Ar gas atmosphere under reduced pressure. At this time, the crucible 16 is located below the chamber 10 so that the silicon raw material does not come into contact with the heat shield 22. After that, the silicon raw material in the crucible 16 is heated by the heater 24 and melted to form a silicon melt M. After that, the crucible 16 is pulled up to the starting position.

Next, the pull-up wire 34 is lowered by the wire elevating mechanism 36 to land the seed crystal S on the silicon melt M. Then, while rotating the crucible 16 and the pulling wire 34 in a predetermined direction, the pulling wire 34 is pulled upward, and a crystal growing step of growing the ingot I below the seed crystal S is performed. As the growth of the ingot I progresses, the amount of the silicon melt M decreases, but the crucible 16 is raised to maintain the level of the melt surface.

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 portion I _b to a predetermined length, tail drawing (formation of the tail portion) is performed in order to separate the single crystal from the silicon melt M in a dislocation-free state.

In the present embodiment, by using the devices 100 and 200 shown in FIGS. 1 and 2, the upper end 24A of the heater is always located lower than the bottom 16C of the inner surface of the crucible during the crystal growth step. Can be done. As a result, as described above, it is possible to reduce the carbon concentration in the grown single crystal silicon ingot I, and secondly, it is possible to improve the diameter controllability when the ingot is pulled up. is there.

Further, in addition to the crystal growth step, the upper end 24A of the heater is the bottom 16C of the inner surface of the crucible during the raw material melting step of heating and melting the silicon raw material put into the crucible 16 with a heater to form the silicon melt M. It is preferable to be in a lower position than. As a result, it is possible to avoid adsorption of CO gas on the surface of the Si raw material during melting of the raw material, which leads to further reduction of the carbon concentration in the silicon melt.

In order to verify the effect of the present invention, single crystal silicon ingots were produced at the five levels of Comparative Examples 1 to 3 and Invention Examples 1 and 2 shown below. The process conditions were as shown in Table 1 for each level.

(Invention Example 1)
A silicon single crystal pulling device having the configuration shown in FIG. 1 was used. The thickness T of the heat insulating body was 80 mm. The dimensions of the heater were 600 mm in length in the X direction of the pull-up axis and 50 mm in thickness. The distance D between the inner peripheral surface of the heat insulating body and the outer peripheral surface of the heater was set to 30 mm. The upper end of the heater is 150 mm lower than the bottom of the inner surface of the crucible when the crucible is positioned at the uppermost position where the silicon melt does not come into contact with the heat shield, with the capacity of the silicon melt as the maximum allowable amount. I made it a position.

(Invention Example 2)
A silicon single crystal pulling device having the configuration shown in FIG. 2 was used. The thickness T1 of the lower heat insulating body was 80 mm, and the thickness T2 of the upper heat insulating body was 160 mm. The dimensions of the heater were the same as in Invention Example 1. The distance D between the inner peripheral surface of the lower heat insulating body and the outer peripheral surface of the heater was set to 30 mm. The upper end of the heater is 150 mm lower than the bottom of the inner surface of the crucible when the crucible is positioned at the uppermost position where the silicon melt does not come into contact with the heat shield, with the capacity of the silicon melt as the maximum allowable amount. I made it a position. Then, the length of the upper heat insulating body was set so that the distance between the lower end of the upper heat insulating body and the upper end of the heater was 50 mm.

(Comparative Example 1)
A silicon single crystal pulling device having the configuration shown in FIG. 3 was used. The thickness T of the heat insulating body, the dimensions of the heater, and the distance D between the inner peripheral surface of the heat insulating body and the outer peripheral surface of the heater are all the same as in Invention Example 1. The upper end of the heater is 520 mm from the bottom of the inner surface of the crucible when the crucible is positioned at the highest position where the silicon melt does not come into contact with the heat shield, with the capacity of the silicon melt M as the maximum allowable amount. I tried to be in a high position.

(Comparative Example 2)
A silicon single crystal pulling device having the same configuration as that of Invention Example 1 was used except that the position of the upper end of the heater was set to an intermediate position between Invention Example 1 and Comparative Example 1. The position of the upper end of the heater is the bottom of the melt surface and the inner surface of the quartz crucible when the crucible is positioned at the highest position where the silicon melt does not come into contact with the heat shield, with the capacity of the silicon melt as the maximum allowable amount. Located between and.

(Comparative Example 3)
Except that the position of the upper end of the heater was set to an intermediate position between Invention Example 2 and Comparative Example 1 and the length of the upper heat insulating body was set so that the distance between the lower end of the upper heat insulating body and the upper end of the heater was 50 mm. A silicon single crystal pulling device having the same configuration as that of Invention Example 2 was used. The position of the upper end of the heater is the bottom of the melt surface and the inner surface of the quartz crucible when the crucible is positioned at the highest position where the silicon melt does not come into contact with the heat shield, with the capacity of the silicon melt as the maximum allowable amount. Located between and.

[Evaluation method]
(1) Carbon concentration (Cs concentration)
A silicon wafer was manufactured by cutting out from the straight body of a single crystal silicon ingot manufactured at each level and processing it. At one central point of each wafer, the concentration of carbon substituted at the crystal position of silicon (Cs concentration) was measured using an FT-IR device. Table 2 shows the index evaluation with the Cs concentration of Comparative Example 1 as 100.

(2) Deformation of the upper end of the quartz crucible After cooling the grown crystal, the chamber was opened and the presence or absence of deformation of the upper end of the quartz crucible was visually evaluated. The results are shown in Table 2.

(3) Heater electric energy The heater power value at a position 1930 mm from the upper side of the straight body at each level was extracted and converted into the heater electric energy. Table 2 shows the amount of heater power for each level.

(4) Crystal diameter controllability The diameter controllability was judged by the value that maximized the variation in diameter at each level. That is, the difference between the target diameter and the actual diameter was calculated at each position of the straight body portion, and the maximum value of the difference was obtained. The evaluation criteria are as follows, and the results are shown in Table 2.
Good: Maximum value (variation in diameter) is less than ± 1 mm Defective: Maximum value (variation in diameter) is ± 1 mm or more

As is clear from Table 2, in Examples 1 and 2 of the present invention, it is possible to reduce the carbon concentration in the ingot and improve the diameter controllability when the ingot is pulled up. Further, in Example 2 of the present invention, the amount of electric power of the heater can be further effectively reduced, and the deformation of the upper end portion of the quartz crucible can be prevented.

(Simulation calculation)
For the three conditions of Comparative Example 1 and Examples 1 and 2 of the present invention, the temperature distribution in the furnace was estimated from the simulation, and the reason why the upper end of the quartz crucible could be prevented from collapsing was verified.

FIG. 4 shows a graph in which the upper end of the side surface of the quartz crucible is the origin, the distance in the direction toward the bottom of the crucible is the X-axis, and the temperature of the side surface of the quartz crucible is the Y-axis. From FIG. 4, since the heater output of Example 1 of the present invention was increased in order to establish the growth of the single crystal ingot, the side temperature of the quartz crucible was not much different from that of Comparative Example 1. On the other hand, in Invention 2, the side temperature of the upper end of the quartz crucible was about 50 ° C. lower than that of Comparative Example 1. From this, it is presumed that in Example 2 of the present invention, the inward collapse could be avoided by lowering the temperature of the upper end of the quartz crucible.

According to the silicon single crystal pulling device and the method for producing a single crystal silicon ingot of the present invention, it is possible to reduce the carbon concentration in the single crystal silicon ingot.

100,200 Silicon single crystal pulling device 10 chamber 12 gas inlet 14 gas outlet 16 crucible 16A quartz crucible 16B graphite crucible 16C bottom of inner surface of crucible 18 shaft 20 shaft drive mechanism 22 heat shield 22A shield body 22B inner flange 22C Outer flange 24 heater 24A Upper end (face) of heater
24B Heater outer circumference 24C Heater inner circumference 26 Insulation 28 Lower insulation 28A Lower insulation inner circumference 28B Lower insulation outer circumference 30 Upper insulation 30A Upper insulation inner circumference 30B Upper insulation Outer surface 30C Lower end (face) of upper insulation
32 seed chuck 34 pulling wire 36 wire lifting mechanism 38 opening 40 CCD camera S seed crystal M silicon melt I monocrystalline silicon ingot I _n the neck I _s shoulder portion I _b straight body X pulling shaft

Claims (6)

A chamber having a gas inlet for introducing the inert gas at the top and a gas outlet for discharging the inert gas at the bottom.
A crucible that houses the silicon melt in the chamber,
A shaft that vertically penetrates the bottom of the chamber and supports the crucible at the upper end.
A shaft drive mechanism that raises and lowers the crucible while rotating it via the shaft,
A tubular heat shield provided above the crucible so as to surround the single crystal silicon ingot pulled up from the silicon melt.
A tubular heater located in the chamber so as to surround the shaft and heating the silicon melt,
A tubular heat insulator provided along the inner surface of the chamber below the upper end of the heat shield.
Have,
The inner surface of the crucible when the upper end of the heater is positioned at the highest position where the silicon melt does not come into contact with the heat shield, with the capacity of the silicon melt as the maximum allowable amount. A silicon single crystal pulling device characterized in that it is arranged at a position lower than the bottom of the crucible. The heat insulating body is
A lower insulator having a first thickness and extending outside the heater to a height range that includes at least the heater.
An upper heat insulating body that is continuous with the lower heat insulating body and has a second thickness that is thicker than the first thickness.
When the distance between the inner peripheral surface of the lower heat insulating body and the outer peripheral surface of the heater is D, the lower end of the upper heat insulating body is 2.0 × D or less from the upper end of the heater. The silicon single crystal pulling device according to claim 1, which extends within the above range. The lower heat insulating body and the upper heat insulating body have a common outer peripheral surface, and the inner peripheral surface of the upper heat insulating body is located inside the inner peripheral surface of the lower heat insulating body.
The silicon single crystal pulling device according to claim 2, wherein the lower end surface of the upper heat insulating body protruding from the position of the inner peripheral surface of the lower heat insulating body toward the crucible side and the upper end surface of the heater face each other. The crucible has a quartz crucible that directly supports the silicon melt on the inner surface and a graphite crucible that supports the quartz crucible on the outside of the quartz crucible, and the upper end of the quartz crucible is more than the upper end of the graphite crucible. High, the silicon single crystal pulling device according to any one of claims 1 to 3. A method for producing a single crystal silicon ingot, which is carried out by using the silicon single crystal pulling device according to any one of claims 1 to 4.
A method for producing a single crystal silicon ingot, wherein the upper end of the heater is always lower than the bottom of the inner surface of the crucible during the crystal growth step of pulling the single crystal silicon ingot from the silicon melt. The claim that the upper end of the heater is lower than the bottom of the inner surface of the crucible even during the raw material melting step of heating and melting the silicon raw material put into the crucible by the heater to form the silicon melt. Item 5. The method for producing a single crystal silicon ingot according to Item 5.

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