JPH0971493A - Production of silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain lowering of oxygen concentration of the upper end of a cylindrical part without accompanying increase of occurrence ratio of cutting of squeezing part in production of a silicon single crystal due to CZ method. SOLUTION: In growing process of a squeezing part N, the number of revolutions of a crucible is set to a definite value higher than a set value in growing the upper end of a cylindrical part B and in growing process of a corn part C, the number of revolutions of the crucible is gradually lowered to the set value in growing the upper end of the cylindrical part. In growing process of the squeezing part, the number of revolutions of the crucible is set to 1.1-3.0 times of the number of revolutions in growing the upper end of the cylindrical part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon single crystal, and more specifically, to a reduction in oxygen concentration at the upper end of a straight body portion (upper end portion of a straight body portion, hereinafter the same) in a silicon single crystal pulled by the CZ method. Is about how to achieve.

[0002]

2. Description of the Related Art A method for producing a silicon single crystal by the CZ method (Czochralski method) is to immerse a seed crystal in a silicon melt in a crucible and then perform a seed drawing of a specific diameter to form a narrowed portion (seed drawing portion). The single crystal of the narrowed portion is pulled up to make it dislocation-free, and thereafter the straight body portion having the target diameter is grown through the growth of the cone portion, whereby a dislocation-free silicon single crystal is obtained.

[0003]

However, in the conventional CZ method, when the growth conditions are set so that the oxygen concentration of the whole straight body part is set to the target value, the oxygen concentration at the upper end of the straight body part is There was a problem that it was higher than the average oxygen concentration of.

As a measure for lowering the oxygen concentration at the upper end of the straight body portion to a target value, the crucible rotation speed at the time of growing the upper end of the straight body portion is set to the value when the other portions of the straight body portion are grown. It is possible to lower the value. However, in this method, since the crucible rotation speed is low, the convection of the silicon melt in the crucible is not suppressed, and the temperature of the melt in contact with the narrowed portion suddenly rises, rather than causing crystal growth in the narrowed portion. On the contrary, since the crystals are melted and the narrowed portion itself is cut, a serious trouble may occur in which the pulling operation of the single crystal cannot be continued.

The present invention has been made in view of the above points, and an object thereof is to control the growth condition from the narrowed portion to the cone portion to increase the occurrence rate of the narrowed portion cutting during pulling of a silicon single crystal. This is to achieve a reduction in the oxygen concentration at the upper end of the straight body without being accompanied by it.

[0006]

According to the method for producing a silicon single crystal of the present invention, the side wall of the crucible is heated by a heater and the seed crystal attached to the pulling shaft is dipped in the surface of the silicon melt in the crucible to form a single crystal. An active gas is supplied toward the surface of the silicon melt, and the crucible is rotated, and the drawing portion by rotating and pulling the seed crystal, the cone portion, the method for producing a silicon single crystal that grows in the order of the straight body portion, In the step of growing the part, the furnace pressure or the number of rotations of the crucible is set to a constant value higher than the set value when growing the upper end of the straight body, and in the step of growing the cone part, the set value is set to the upper end of the straight part. Gradually decrease to the set value when growing, or in the growth process of the throttle part, set the inert gas flow rate to a constant value lower than the set value when growing the upper end of the straight body part. With, in the process of growing the cone portion, and is characterized in that to gradually increase the setting value to the setting time of growing the straight body section upper end. The "furnace" is a "pulling chamber" or a "chamber".
Also called.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the step of growing the throttle portion, at least one of the pressure in the furnace, the flow rate of the inert gas in the rectifying cylinder, and the number of rotations of the crucible is controlled. Controlling only the internal pressure, (2) Controlling only the flow rate of the inert gas in the rectifying cylinder, (3) Controlling only the number of crucible rotations, (4) Furnace pressure and inertness in the rectifying cylinder Controlling the gas flow rate, (5) Controlling the flow rate of the inert gas in the rectifying cylinder and the crucible rotation speed,
(6) Controlling the furnace pressure and crucible rotation speed,
(7) Controlling the furnace pressure, the flow rate of the inert gas in the flow straightening cylinder, and the crucible rotation speed can be mentioned.

According to the study by the present inventor, the cause of the above-mentioned problems relating to the oxygen concentration at the upper end of the straight barrel is that pulling from the narrowed portion of the silicon single crystal to the upper end of the straight barrel is performed under the same growth conditions. It turned out that it was. That is, C
Considering the manufacturing process of the silicon single crystal that grows in the order of the narrowed portion, the cone portion, and the straight body portion by the Z method, the diameter of the silicon single crystal increases as the silicon single crystal is pulled in the growth step of the cone portion. At the same time as the solid-liquid interface in the crucible, that is, the area of the interface between the silicon single crystal and the silicon melt in the crucible expands, the area in which the silicon melt comes into contact with the inert gas decreases.

Therefore, when the cone portion is grown while the inert gas rectified by the rectifying cylinder provided directly above the crucible is supplied toward the surface of the silicon melt, the pressure inside the furnace or the inert gas into the furnace is increased. When the supply amount of Si is kept constant, the amount of evaporation of SiO from the surface of the silicon melt per unit time and the amount of Si per unit time into the silicon single crystal.
The amount of dissolved O greatly changes with the elapse of the pulling time. For example, when the pressure in the furnace is kept constant, the evaporation amount of SiO from the surface of the silicon melt per unit time decreases as the contact area between the silicon melt and the inert gas decreases, and therefore the cone portion In the oxygen concentration distribution in the axial direction, the lower the oxygen concentration, the higher the oxygen concentration.

Further, when the supply amount of the inert gas is kept constant, the SiO evaporation amount per unit area is increased by the increase of the supply amount of the inert gas per unit area of the surface of the silicon melt, but the silicon melt is increased. Since the effect of reducing the contact area with the inert gas is large, the oxygen concentration distribution in the axial direction of the cone portion tends to be higher in the lower portion of the melt surface as in the above.

Further, when the inert gas rectified by the rectifying cylinder provided directly above the crucible is supplied toward the surface of the silicon melt, the inert gas is not provided on the silicon melt surface without providing the rectifying cylinder directly above the crucible. In any of the case where the crucible rotation speed was constant, the contact area between the outer peripheral portion of the cone portion and the silicon melt was increased, and thus the oxygen concentration distribution in the axial direction of the cone portion was also lower. The oxygen concentration tends to increase.

As described above, in the conventional method in which the cone portion is grown with the furnace pressure, the inert gas supply amount or the crucible rotation speed kept constant, the oxygen concentration becomes higher toward the lower portion of the cone portion, and the oxygen concentration becomes higher. As a result of affecting the oxygen concentration at the upper end of the section, it is presumed that the above-mentioned problems occur at the upper end of the straight body section.

In the present invention, in the step of growing the narrowed portion,
The furnace pressure is set to 1.1 to 2.0 times the furnace pressure when growing the straight body upper end, and the inert gas flow rate in the straightening cylinder is set when growing the straight body upper end. The inert gas flow rate is preferably set to 0.5 to 0.9 times, and the crucible rotation speed is preferably set to 1.1 to 3.0 times the crucible rotation speed at the time of growing the upper end of the straight body part. .

In the step of growing the cone portion, when gradually lowering or increasing the set value to the set value in the step of growing the upper end of the straight body portion, the set value is lowered in proportion to the pulling length of the cone portion or It is preferable to increase.

In the present invention, the oxygen concentration at the upper end of the straight body portion can be reduced by controlling at least one of the furnace pressure, the inert gas flow rate, and the crucible rotation speed. Further, in the present invention, the convection of the melt in the crucible is stabilized by making the crucible rotation speed in the growth process of the throttle portion higher than the crucible rotation speed in the growth process of the upper end of the straight body portion, and the throttle portion is in contact. Since the temperature of the silicon melt becomes more uniform, the occurrence rate of the cut portion during the pulling of the silicon single crystal becomes lower than that in the conventional method.

In the present invention, the ratio of the in-furnace pressure, the flow rate of the inert gas in the flow straightening cylinder or the number of revolutions of the crucible in the growth process of the narrowed portion to the respective values in the growth process of the upper end of the straight body is as described above. To set, if the rate of decrease or increase of each set value in the growth process of the cone part is too fast,
The temperature change rate at the solid-liquid interface in the crucible, that is, at the interface between the silicon single crystal and the silicon melt in the crucible becomes too fast, and as a result, the growth of the crystal becomes unstable, causing dislocation and other problems. This is because it occurs.

[0017]

EXAMPLES Examples of the present invention, test examples according to the present invention and comparative examples according to a conventional method will be described below with reference to the drawings. Example 1 FIG. 1 is a schematic cross-sectional view showing a main part structure of a silicon single crystal pulling apparatus. In this pulling apparatus, a crucible 2 having an inner peripheral side made of quartz and an outer peripheral side made of graphite is supported by a support shaft 3 provided in a vertical direction in a cylindrical chamber 1 made of stainless steel. A cylindrical heater 4 made of a carbon material is provided around the crucible 2, and a cylindrical heat insulating material 5 made of a carbon material is also provided around the heater 4. The support shaft 3 (and thus the crucible 2) is
A rotation drive device (not shown) having a control mechanism allows rotation and fine adjustment of the number of rotations. The heater 4 has a control mechanism and can be moved up and down by a slide mechanism (not shown), and its vertical position can be finely adjusted.

Immediately above the crucible 2 and in the chamber 1,
A straightening cylinder 6 of an inert gas is provided so as to be concentric with the chamber 1. The rectifying cylinder 6 coaxially surrounds the silicon single crystal 22 being pulled, its upper end is airtightly coupled to the opening in the center of the ceiling of the chamber 1, and its lower end is located near the liquid surface of the silicon melt in the crucible 2. are doing. A cylindrical pull chamber 7 made of stainless steel is concentrically connected to the chamber 1 above the chamber 1, and an isolation valve 8 is provided at a connecting portion between the chamber 1 and the pull chamber 7. ing. The pull chamber 7 is
A space for accommodating the pulled silicon single crystal and taking it out to the outside is formed.

A hoisting device (not shown) is provided above the pull chamber 7, and a wire 9 is hung from the hoisting device, and the number of rotations of the wire 9 can be increased or decreased.
A seed crystal 11 is attached to the lower end of the wire 9 by a seed holding jig 10. A supply port 12 for an inert gas such as Ar is provided at the top of the pull chamber 7, and an exhaust port 13 for the inert gas is provided at the bottom of the chamber 1. The exhaust port 13 is connected to a vacuum generator (not shown), and the chamber 1 and the pull chamber 7 are connected.
The inside is maintained at a predetermined pressure, and a predetermined flow rate of an inert gas can be supplied to the rectifying cylinder 6. In addition,
In FIG. 1, 21 is a silicon melt, and 22 is a silicon single crystal in the process of pulling.

Test Example 1 (Study of Effect of Controlling Crucible Rotational Speed) Using the apparatus of FIG. 1, 19 silicon single crystals having a diameter of 6 inches and a total length of 19 inches were pulled according to the present invention under the following conditions. (1) Setting of crucible rotation speed Drawing part growth step: 12 rpm Cone part growth step: 12-8 rpm Straight body part growth step: 8-12 rpm (8 rpm at the start of straight body part growth, 12 rpm at the end of straight body part growth) (2) The crucible rotation speed was gradually reduced as shown in FIG. That is, in, the crucible rotation speed was increased in proportion to the pulling length of the silicon single crystal. In FIG. 2, N is a narrowed portion, C is a cone portion, B is a straight body portion, and the upper end of the straight body portion means a portion of the straight body portion B which is closest to the cone portion. (3) Furnace pressure: 100 mbar (constant) (4) Furnace inert gas flow rate: 100 Nl / min (constant)

Comparative Example 1 Using the apparatus shown in FIG. 1, 31 silicon single crystals having the same size as in Test Example 1 were pulled by the conventional method. In this case, the pulling from the narrowed portion to the upper end of the straight body portion was performed under the same growth condition, and the growth condition was set so that the oxygen concentration of the entire straight body portion was set to the target value. That is, the crucible rotation speed in the drawing portion / cone growth step is set to 8 rpm (constant), and the crucible rotation speed in the straight body growth step is 8 to 12 rpm (8 at the start of straight body growth).
rpm and 12 rpm at the end of straight body growth. The other conditions were the same as in Test Example 1.

[Test Results] (1) Pulling Success Rate In Test Example 1, 95% (1 in 19 outbreaks in the narrowed portion)
This is 65% in Comparative Example 1 (11 of 31 cuts occurred in the narrowed portion). (2) Oxygen Concentration in Silicon Single Crystal and Axial Oxygen Concentration Distribution In both Test Example 1 and Comparative Example 1, the oxygen concentration at the upper end of the straight body and
The axial oxygen concentration distribution in the straight body was investigated by a conventional method. In this case, the silicon single crystal was cut along the plane orthogonal to the axis at predetermined locations (points a to e) shown in FIG. The results are shown in [Table 1] and FIG. In FIG. 3, the results for points b to e are obtained by averaging the measured values at the center of the wafer for each crystal. The unit of oxygen concentration is atoms / cc.

[0023]

[Table 1] (oxygen concentration at the top of the straight body)

Embodiment 2 FIG. 4 is a schematic cross-sectional view of the essential part showing another example of a silicon single crystal pulling apparatus. The overall structure of this device is the same as that of the device of FIG. 1, except that a collar 31 is provided at the lower end of the flow straightening cylinder 6. That is, the rectifying cylinder 6 is a cylindrical body that coaxially surrounds the pulling silicon single crystal 22 and hangs down toward the surface of the silicon melt 21 in the crucible 2.
The upper end of this cylindrical body is airtightly coupled to the opening in the center of the ceiling of the chamber 1, and the lower end of this cylindrical body has a collar 31 that expands upward and outward. The collar 31 has an inverted right circular truncated cone shape as shown in FIG. 5, but may be formed in an inverted bowl shape as shown in FIG. In FIG. 4, 32 is a pulling shaft and 33 is an observation window.

By using the rectifying cylinder 6 having the above structure,
The following operation and effect can be obtained. (1) The radiant heat received by the silicon single crystal 22 being pulled from the silicon melt 21 in the crucible 2 and the heater 4 is blocked by the collar 31, and the thermal history of the silicon single crystal 22 can be controlled in a wide range. (2) In the prior art, an amorphous agglomerate made of SiO adheres to the central part of the ceiling of the chamber 1 and the upper end of the crucible 2 and drops to the vicinity of the interface between the silicon single crystal 22 and the silicon melt 21 to form a silicon single crystal. Although there was a problem that dislocation and polycrystallization of 22 occurred, since the space on the surface of the silicon melt 21 in the crucible 2 was limited by the collar 31, retention of the inert gas on the surface was prevented. Since the amount of the amorphous aggregates is reduced and the generation of the amorphous aggregates is prevented, the above problems do not occur.

[0026]

As is apparent from the above description, according to the present invention, by controlling the growth condition from the narrowed portion to the cone portion, the occurrence rate of the narrowed portion cutting during the pulling of the silicon single crystal is accompanied. Without, it is possible to achieve a decrease in oxygen concentration at the upper end of the straight body part.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a main part structure of a silicon single crystal pulling apparatus used in a test example according to the present invention and a comparative example according to a conventional method.

FIG. 2 is a graph showing growth conditions for a silicon single crystal in Test Example 1.

FIG. 3 is a graph showing the results of Test Example 1 and Comparative Example 1.

FIG. 4 is a schematic cross-sectional view of essential parts showing another example of a silicon single crystal pulling apparatus suitable for carrying out the present invention.

FIG. 5 is a perspective view showing an example of a collar at the lower end portion of the flow straightening cylinder arranged in the apparatus of FIG.

FIG. 6 is a sectional view showing another example of a collar.

[Explanation of symbols]

 1 Chamber 2 Crucible 3 Support Shaft 4 Heater 5 Heat Insulating Material 6 Rectifier Cylinder 7 Pull Chamber 8 Isolation Valve 9 Wire 10 Type Holding Jig 11 Seed Crystal 12 Inert Gas Supply Port 13 Inert Gas Exhaust Port 21 Silicon Melt Liquid 22 Silicon single crystal 31 Color 32 Pulling shaft 33 Observation window

Front page continuation (72) Inventor Atsushi Iwasaki 2-13-50 Kitafu, Takefu City, Fukui Prefecture Shin-Etsu Semiconductor Co., Ltd. Takefu Factory

Claims (12)

[Claims] 1. A crucible side wall is heated by a heater, a seed crystal attached to a pulling shaft is immersed in a silicon melt surface in the crucible, and an inert gas rectified by a rectifying cylinder provided directly above the crucible is converted into silicon. Supplying toward the surface of the melt, rotating the crucible, while pulling while rotating the seed crystal, the drawing part, the cone part, in the method for producing a silicon single crystal that grows in the order of the straight body part, the growth step of the drawing part For the furnace pressure, set a constant value higher than the set value when growing the upper part of the straight body, in the growth process of the cone part, the set value of the furnace pressure is the set value in the growth process of the upper part of the straight body. A method for producing a silicon single crystal, which is characterized by gradually lowering the temperature. 2. A crucible side wall is heated by a heater, a seed crystal attached to a pulling shaft is immersed in a silicon melt surface in the crucible, and an inert gas rectified by a rectifying cylinder provided directly above the crucible is converted into silicon. Supplying toward the surface of the melt, rotating the crucible, while pulling while rotating the seed crystal, the drawing part, the cone part, in the method for producing a silicon single crystal that grows in the order of the straight body part, the growth step of the drawing part Then, the flow rate of the inert gas in the straightening cylinder is set to a constant value lower than the set value when growing the upper end of the straight body part, and in the process of growing the cone part, the set value of the inert gas flow rate is set to the upper end of the straight body part. A method for producing a silicon single crystal, which is characterized by gradually increasing the value to a set value in the growth step. 3. A crucible is heated by heating a side wall of the crucible, a seed crystal attached to a pulling shaft is immersed in a silicon melt surface in the crucible, and an inert gas is supplied toward the silicon melt surface to form the crucible. Along with the rotation, the diaphragm part, the cone part, and the straight body part are grown in this order by pulling while rotating the seed crystal. Set a constant value higher than the set value when growing,
The method for producing a silicon single crystal, wherein in the step of growing the cone portion, the set value of the number of rotations of the crucible is gradually reduced to the set value in the step of growing the upper portion of the straight body portion. 4. A crucible side wall is heated by a heater, a seed crystal attached to a pulling shaft is immersed in a silicon melt surface in the crucible, and an inert gas rectified by a rectifying cylinder provided directly above the crucible is converted into silicon. Supply toward the surface of the melt, while rotating the crucible, while pulling while rotating the seed crystal, the drawing part, the cone part, in the method for producing a silicon single crystal that grows in the straight body part in order, for the furnace pressure, In the growing process of the narrowed portion, while setting a constant value higher than the set value when growing the upper end of the straight body part, in the growing process of the cone part, the set value of the furnace pressure is set to the growing process of the upper end of the straight body part. The flow rate of the inert gas in the rectifying cylinder is set to a constant value lower than the set value for growing the upper end of the straight body portion in the process of growing the throttle portion. At the same time, in the process of growing the cone portion, the set value of the flow rate of the inert gas is gradually increased to the value set in the growth process of the upper end of the straight body portion, the method for producing a silicon single crystal. 5. The side wall of the crucible is heated by a heater, the seed crystal attached to the pulling shaft is immersed in the surface of the silicon melt in the crucible, and the inert gas rectified by the rectifying cylinder provided directly above the crucible is converted into silicon. In the method for producing a silicon single crystal in which the drawn portion, the cone portion, and the straight barrel portion are grown in this order by supplying the melt toward the melt surface and rotating the crucible while pulling up while rotating the seed crystal, the inside of the straightening cylinder Regarding the flow rate of the active gas, in the growth process of the narrowed portion, while being set to a constant value lower than the set value when growing the upper end of the straight body portion, in the cone portion growth step, the inert gas flow rate is set to the upper end of the straight body portion. Gradually increase to the set value in the growth process, and set the crucible rotation speed to a constant value that is higher than the set value when growing the upper end of the straight body part in the growth process of the throttle part. At the same time, in the step of growing the cone portion, the set value of the number of rotations of the crucible is gradually reduced to the set value in the step of growing the upper end of the straight body portion, and a method for manufacturing a silicon single crystal. 6. A crucible side wall is heated by a heater, a seed crystal attached to a pulling shaft is immersed in a silicon melt surface in the crucible, and an inert gas rectified by a rectifying cylinder provided directly above the crucible is converted into silicon. Supplying toward the surface of the melt, rotating the crucible, while pulling while rotating the seed crystal, the drawing part, the cone part, in the method for producing a silicon single crystal that grows in the order of the straight body part, the growth step of the drawing part Then, regarding the furnace pressure and crucible rotation speed,
It is set to a constant value higher than the set value when growing the upper part of the straight body part, and in the growth process of the cone part, the set values of the furnace pressure and the crucible rotation speed are gradually increased to the set values in the growth process of the upper part of the straight body part. A method for producing a silicon single crystal, which comprises lowering the temperature. 7. A crucible side wall is heated by a heater, a seed crystal attached to a pulling shaft is immersed in a silicon melt surface in the crucible, and an inert gas rectified by a rectifying cylinder provided directly above the crucible is converted into silicon. In the method for producing a silicon single crystal in which the melt is supplied toward the surface of the melt, the crucible is rotated, and the seed crystal is pulled while rotating, the throttle portion, the cone portion, and the straight barrel portion are grown in this order. Regarding the number of rotations, in the growth process of the throttle part, while setting a constant value higher than the set value when growing the upper end of the straight body part, in the growth process of the cone part,
The furnace pressure and the set value of the crucible rotation speed are gradually reduced to the set values in the growth process of the upper end of the straight body part, and the flow rate of the inert gas in the straightening cylinder is set to the upper end of the straight body part in the growth process of the throttle part. It is characterized in that it is set to a constant value lower than the set value when growing, and in the growing step of the cone portion, the set value of the inert gas flow rate is gradually increased to the set value in the growing step of the upper end of the straight body portion. Method for manufacturing silicon single crystal. 8. The furnace pressure in the step of growing the narrowed portion is set to be 1.1 to 10 times the furnace pressure in the step of growing the straight body upper end.
7. The number is set to 2.0 times.
Alternatively, the method for producing a silicon single crystal according to Item 7. 9. The flow rate of the inert gas in the flow straightening cylinder is set to 0.5 to 0.9 times the flow rate of the inert gas in the growth step of the upper end of the straight body in the step of growing the narrowed portion. The method for producing a silicon single crystal according to claim 2, 4, 5, or 7. 10. The crucible rotation speed in the step of growing the narrowed portion is set to 1.1 to 3.0 times the rotation speed of the crucible in the step of growing the upper end of the straight body portion. The method for producing a silicon single crystal according to 5, 6, or 7. 11. In the step of growing the cone portion, when gradually decreasing or increasing the set value to the set value in the step of growing the upper end of the straight body portion, the set value is proportional to the pulling length of the cone portion. The method for producing a silicon single crystal according to any one of claims 1 to 10, characterized in that it is decreased or increased. 12. The rectifying cylinder is a cylindrical body that coaxially surrounds a silicon single crystal being pulled and hangs down toward the surface of the silicon melt in the crucible, and the upper end of the cylindrical body is the ceiling of the furnace. The airtightly coupled to the central opening, and the lower end of the cylindrical body has a collar that expands outward and upward, or 1, 2, 4, 5, 6 or 7. The method for producing a silicon single crystal according to 7.