JPH07133186A - Apparatus and process for production of silicon single crystal - Google Patents

Abstract

PURPOSE:To provide an apparatus and process for production of a silicon single crystal capable of producing the single crystal having an oxygen concn. distribution uniform in an axial direction or the single crystal having a low oxygen concn. CONSTITUTION:The surface temp. of a melt 10 measured by a radiation thermometer 13 and the base temp. of a crucible 3 measured by a thermocouple 4 are inputted to a temp. control section 14 by which the vertical temp. difference of the melt 10 is determined. Any one or more of the output of a lower heater 8, the flow rate of a water cooling type lower cooler 9, the position of a radiant heat reflection plate 6 and the position of a radiant heat reflection plate insulating material 7 or the position of the crucible 3 is controlled in such a manner as to comply with the temp. difference profile previously set based on a correlation between the oxygen concn. in the single crystal and the temp. difference described above. As a result, the natural convection of the melt 10 is controlled and the single crystal having the uniform oxygen concn. distribution or the single crystal having the low oxygen concn. and the uniform concn. distribution is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for manufacturing a silicon single crystal.

[0002]

2. Description of the Related Art A silicon single crystal is mainly used for a substrate of a semiconductor element. One of the methods for producing the single crystal is a Czochralski method for pulling a cylindrical single crystal from a raw material melt in a crucible. The method (hereinafter referred to as the CZ method) is used. In the CZ method, a crucible installed in a chamber of a single crystal manufacturing apparatus is filled with a polycrystal as a raw material, the raw material is heated and melted by a heater provided on the outer periphery of the crucible, and then a seed crystal attached to a seed holder is attached. A single crystal is grown by immersing in the melt and pulling up the seed holder while rotating the seed holder and the crucible in the same direction or opposite directions.

[0003]

The concentration of oxygen contained in a silicon single crystal greatly changes in the axial direction of the single crystal, and the concentration decreases as it approaches the tail. Therefore,
Concentration standards are not always satisfied over the entire length of the single crystal from top to tail. The oxygen concentration depends on the natural convection of the melt, and if the natural convection is suppressed, the oxygen concentration becomes low. In order to suppress the natural convection of the melt, the difference between the upper and lower temperatures of the melt may be reduced. However, in the production of silicon single crystal by the CZ method, there is no disclosure of a device or a control method for controlling the upper and lower temperature difference of the melt.

Japanese Unexamined Patent Publication (Kokai) No. 59-57986 discloses a method of pulling a single crystal in which the power of a plurality of heaters is controlled to keep the temperature gradient near the solid-liquid interface low, and the temperature of the seed holder and the temperature of the crucible bottom are measured. While controlling the power of the upper heater for heating the pulling crystal part. However, since this method does not detect the temperature difference between the upper and lower sides of the melt, it is not possible to control the natural convection of the melt. Further, Japanese Patent Laid-Open No. 3-137088 is a method for growing a single crystal in which the temperature near the solid-liquid interface is directly measured by a thermocouple to control the melt temperature. However, the thermocouple contaminates the melt and causes the generation of OSF. Become. Furthermore, the expensive thermocouple must be replaced every time the single crystal is pulled, which results in high cost.

The present invention has been made by paying attention to the above-mentioned conventional problems, and produces a silicon single crystal capable of obtaining a single crystal having a uniform axial oxygen concentration distribution or a single crystal having a low oxygen concentration. An object is to provide an apparatus and a manufacturing method.

[0006]

In order to achieve the above object, the apparatus for producing a silicon single crystal according to the present invention comprises a lower heater or a lower cooler having a variable output located below a crucible, and an elevating unit located above a melt. Free radiant heat reflection plate, any one or more of the radiant heat reflection plate heat insulating material that can be moved up and down so as to surround the radiant heat reflection plate, temperature measuring means of the melt upper part and the melt lower part, and the two measured values Means for calculating the upper and lower temperature difference of the melt based on, a means for comparing the calculated temperature difference value and a predetermined temperature difference profile, the output of the lower heater or the lower cooler based on the comparison result, The method for producing a silicon single crystal according to the present invention is a Czochraluss, comprising a means for controlling the position of the radiant heat reflector, the position of the radiant heat reflector heat insulating material or the position of the crucible. In the production of silicon single crystals by the -method, the upper and lower temperature differences of the melt are calculated by measuring the temperature of the melt surface and the temperature of the bottom of the crucible, and the temperature difference is the oxygen concentration in the single crystal and the melt. The output of the lower heater or lower cooler, the vertical position of the radiant heat reflector, the vertical position of the radiant heat reflector heat insulator, or the crucible so that it follows the temperature difference profile set based on the correlation with the temperature difference between the upper and lower sides. It is characterized by controlling any one or more of the vertical positions.

[0007]

According to the above construction, the temperature difference between the upper and lower sides of the melt is detected, and the value follows the temperature difference profile set based on the correlation between the oxygen concentration in the single crystal and the temperature difference.
Since it was decided to control any one or more of the output of the lower heater or lower cooler, the position of the radiant heat reflector, the position of the radiant heat reflector heat insulating material, or the position of the crucible, natural convection of the melt was suppressed and the axial direction was controlled. A single crystal with a uniform oxygen concentration distribution or a single crystal with a low oxygen concentration can be obtained.

[0008]

Embodiments of the silicon single crystal manufacturing apparatus and method according to the present invention will be described below with reference to the drawings. FIG. 1 is a partial schematic diagram of a silicon single crystal manufacturing apparatus including means for controlling the temperature difference between the upper and lower sides of a melt. A crucible shaft 2 is provided at the center of the chamber 1 so as to be rotatable and movable up and down, and a crucible 3 is installed at an upper end of the crucible shaft 2. 4 is a thermocouple (or a black body thermometer) that abuts on the outer surface of the bottom of the crucible 3, 5 is a silicon single crystal, 6 is a conical radiant heat reflector that blocks radiant heat applied to the silicon single crystal 5, and 7 is It is a cylindrical radiant heat reflector heat insulating material provided so as to surround the radiant heat reflector plate 6. The radiant heat reflector 6 can be raised and lowered by a radiant heat reflector raising / lowering device 6a, and the radiant heat reflector heat insulating material 7 can be raised and lowered by a radiant heat reflector warmer raising / lowering device 7a. Further, below the crucible 3, either an annular lower heater 8 surrounding the crucible shaft 2 or a water-cooled lower cooler 9 is installed. 10
The melt stored in the crucible 3, 11 is a main heater surrounding the crucible 3, 12 is a heat insulating cylinder, and 13 is a radiation thermometer. The surface temperature of the melt 10 may be measured by a radiation thermometer through a transparent portion provided on the flange at the upper end of the radiant heat reflecting plate 6, and a black body thermometer or a thermocouple may be provided at the lower end of the radiant heat reflecting plate 6. You may attach and measure. In addition,
FIG. 1 shows the radiant heat reflection plate 6, the radiant heat reflection plate heat insulating material 7, the lower heater 8 or the water-cooled lower cooler 9 as means for controlling the temperature difference between the upper and lower parts of the melt, but in the actual single crystal production apparatus, these are shown. Does not have to be equipped with all.

Reference numeral 4a is a telemeter, and the output signal of the thermocouple 4 is sent to a receiver through a transmitter attached to the lower part of the crucible shaft 2 that rotates and moves up and down, and is input to the control unit 14. Reference numeral 8a is a power source for the lower heater, 9a is a valve for adjusting the flow rate of the water-cooled lower cooler 9, 2b, 6b and 7b are servomotors for raising and lowering the crucible shaft 2, the radiant heat reflecting plate 6, and the radiant heat reflecting plate heat insulating material 7, 9b. Is a servo motor for driving the valve 9a of the water-cooled lower cooler 9. Also,
2c, 6c, 7c, 8c and 9c are power amplifiers, and 15 is a melt temperature difference command section.

The surface temperature of the melt 10 is measured by the radiation thermometer 13 and the temperature of the bottom surface of the crucible is measured by the thermocouple 4, which are input to the control unit 14. The controller 14 controls the melt 1
In order to make the upper and lower temperature difference of 0 follow a predetermined temperature difference profile, based on the input value and the input value from the melt temperature difference command section 15, the crucible shaft raising / lowering servo motor 2b and the radiation heat reflecting plate raising / lowering servo are set. Any one or more of the motor 6b, the radiant heat reflection plate heat insulating material raising / lowering servomotor 7b, the lower heater power source 8a, and the valve servomotor 9b for the water-cooled lower cooler are driven.

FIG. 2 is an example of a block diagram of a control device which performs the above control, and shows a case where the lower heater controls the temperature difference between the upper and lower portions of the melt. Melt surface temperature T1 detection means, that is, the output signal of the radiation thermometer 13 shown in FIG. 1 and the crucible bottom temperature T2
The crucible bottom temperature T2 detecting means, that is, the output signal of the thermocouple 4, is inputted to the melt temperature difference Td = T1-T2 calculating means 21 via the transmitting / receiving means, ie, the telemeter 4a, and the calculation result is the melt temperature difference command signal. It is input to the ΔT = T0-Td calculating means 22 together with the output signal from the T0 output means, that is, the melt temperature difference command section 15 shown in FIG. Further, the control limit value ΔTL storage means 23 and the above ΔT = T
The output signal of the 0-Td calculation means 22 is compared / determined by the comparison / determination means 24 of ΔTL and ΔT, and is input to the power command signal W0 output means 25 or the setting / calculation means 26 of the power W1 based on ΔT. To be done. The calculation result of W1 is
The power correction command signal W1 is input to the output means 27.

On the other hand, the output signals of the lower heater voltage detecting means 28 and the lower heater current detecting means 29 are input to the lower heater power WF calculating means 30, and then WF-W0,1 via the WF-W0,1 calculating means 31. And .DELTA.WL are input to the comparison / determination means 32. Then, the power control limit value ΔW
The result of comparison with the output signal of the L storage means 33 is output to the power command signal W0 output means 25 or the setting / calculation means 26 of the power W1 based on ΔT.

The output signal of the power command signal W0 output means 25 or the power correction command signal W1 output means 27 is amplified by the lower heater power supply power amplifier 8c and input to the lower heater power supply 8a. As a result, the output of the lower heater 8 is adjusted so that the upper and lower temperature difference of the melt follows a predetermined temperature difference profile.

FIG. 3 is an example of a flow chart for performing the above control, and shows a case where the lower heater is used to control the upper and lower temperature differences of the melt. The number on the left shoulder of each step is the step number. The melt temperature difference command signal T0 is read in step 1, and the melt surface temperature T1 and crucible bottom temperature T are read in step 2.
2 and the control limit value ΔTL are read. Next, in step 3, ΔTL is compared with the absolute value of T0 − | T1 −T2 |, and if ΔTL ≧ | T0 − | T1 −T2 ‖, the power based on the melt temperature difference command signal T0 is calculated in step 4. Command signal W0
Is output. Then, in step 5, the lower heater voltage V, the lower heater current I, and the power control limit value ΔWL are read, and in step 6, the ΔWL and the absolute value of V · I−W0 are compared, and ΔWL ≧ | V · I If -W0 |, return to step 1. In step 3, ΔTL <| T0 − |
If T1−T2‖, the power correction command signal W is output in step 7.
Output 1 and proceed to step 5. If .DELTA.WL .gtoreq..vertline..vertline.V.multidot.I-W1.vertline. In step 6, the process returns to step 1. If .DELTA.WL <.vertline.V.multidot.I-W0,1.vertline. In step 6, the process returns to step 7.

In preliminary pulling of a silicon single crystal,
The temperature of the melt surface was measured using a radiation thermometer from the top to the tail of the single crystal, and at the same time, the temperature of the bottom surface of the crucible was measured using a thermocouple. The correlation between the temperature difference between the two and the oxygen concentration of the grown single crystal was obtained, and the temperature difference profile to be the control target from the top to the tail of the single crystal was set.

An example of controlling the output of the lower heater will be described as a means for controlling the difference between the upper and lower temperatures of the melt. Diameter 2
After loading 105 kg of polycrystalline silicon into a 4-inch quartz crucible and melting it, when pulling a single crystal with an 8-inch diameter, the output of the lower heater 8 was controlled so as to follow the temperature difference profile. In the grown 8-inch single crystal, the oxygen concentration distribution from the top to the tail was almost uniform.

In an embodiment in which the distance between the radiant heat reflector and the surface of the melt is controlled so that the temperature difference between the upper and lower temperatures of the melt conforms to the set temperature difference profile, the distance is adjusted at the initial stage of pulling the single crystal. It was reduced and increased in the latter half of the pulling. Even when this method was used, a single crystal having a uniform axial oxygen concentration was obtained.

In the case of the embodiment in which the position of the radiant heat reflection plate heat insulating material is adjusted so that the temperature difference between the upper and lower temperatures of the melt follows the set temperature difference profile, in the initial stage of pulling up the single crystal, Since the oxygen concentration becomes high, the position of the radiant heat reflector heat insulating material 7 was lowered so that the temperature difference between the upper and lower temperatures of the melt 10 was small, and the radiant heat reflector 6 was kept warm. When the radiant heat reflector heat insulating material 7 is lowered, the main heater 11
Output decreases and the temperature at the bottom of the crucible decreases, so the temperature difference between the top and bottom of the melt becomes smaller. Along with this, natural convection of the melt is suppressed, and the oxygen concentration drops. In the latter stage of pulling up, the position of the radiant heat reflector heat insulating material 7 was raised to deteriorate the radiant heat reflector heat insulating performance. Thus, a single crystal having a uniform axial oxygen concentration could be obtained.

In the case of an embodiment in which the upper and lower temperature differences of the melt are controlled by adjusting the crucible position so as to follow the temperature difference profile, the vertical movement range of the crucible 3 is the upper end of the main heater 11 and that of the crucible 3. It was set to ± 30 mm with reference to the state where the position of the upper end coincides. In the initial stage of pulling the single crystal, the crucible 3 is moved downward from the reference position by 30
A single crystal having a uniform axial oxygen concentration was obtained by moving it by 30 mm and moving it upward by 30 mm from the reference position in the latter stage of pulling.

In an embodiment in which the upper and lower temperature differences of the melt are controlled according to the temperature difference profile by adjusting the flow rate of the water-cooled lower cooler, the flow rate is set to 60 liters / minute in the initial stage of pulling the single crystal. The cooling capacity was increased, and the cooling capacity was lowered to 10 liters / minute in the latter stage of pulling. By this method, the oxygen concentration distribution in the axial direction was 13 ± 0.6 × 10 ¹⁷ atoms / cc: old A
12 ± 0.3 × 10 ¹⁷ atoms / cc: o from STM
ld ASTM could be improved.

For comparison with the above embodiments, the diameter 24
An inch quartz crucible was loaded with 105 kg of polycrystalline silicon, and the diameter was 8 without controlling the temperature difference of the melt.
An inch single crystal was grown. The axial oxygen concentration distribution of a single crystal with a straight body length of 1000 mm is 13 ± 0.8 × 10 ¹⁷ ato
ms / cc: old ASTM, and the fluctuation range of the concentration is large.

[0022]

As described above, according to the present invention, attention is paid to the fact that the distribution of the oxygen concentration in the axial direction of a silicon single crystal depends on the natural convection of the melt, and as a means for controlling the natural convection, the melting The temperature difference between the upper and lower sides of the liquid is detected, and the output of the lower heater or lower cooler and the position of the radiant heat reflector are adjusted so that the value follows the temperature difference profile set based on the correlation between the oxygen concentration in the single crystal and the temperature difference. Since the single crystal manufacturing apparatus and manufacturing method for controlling the position of any one or more of the radiant heat reflector heat insulating material or the position of the crucible are used, by using this manufacturing apparatus and manufacturing method, the axial oxygen concentration of the single crystal is determined. The distribution can be made uniform, and the production yield of single crystals is improved. Further, it becomes possible to grow a silicon single crystal having a low oxygen concentration and a uniform oxygen concentration distribution in the axial direction, and it becomes possible to comply with various quality standards.

[Brief description of drawings]

FIG. 1 is a partial schematic view of a silicon single crystal production apparatus including means for controlling the temperature difference between upper and lower melts.

FIG. 2 is an example of a block diagram of a control device that performs the above control.

FIG. 3 is an example of a flowchart for performing the above control.

[Explanation of symbols]

2 ... crucible shaft, 3 ... crucible, 4 ... thermocouple (crucible bottom temperature T2 detecting means), 5 ... silicon single crystal, 6 ... radiant heat reflector, 7 ... radiant heat reflector heat retaining material, 8 ... lower heater, 9 ... water cooling Lower cooler, 10 ... Melt, 13 ... Radiation thermometer (melt surface temperature T1 detecting means), 14 ... Control section, 15 ... Melt temperature difference command section (melt temperature difference command signal T0 output means).

Claims (2)

[Claims] 1. A lower heater or a lower cooler having a variable output located below a crucible, a radiant heat reflecting plate which can be raised and lowered above a melt, and a radiant heat reflecting plate which can be raised and lowered so as to surround the radiant heat reflecting plate. Any one or more of the material, the temperature measuring means of the melt upper and melt lower, means for calculating the upper and lower temperature difference of the melt based on the two measured values, and the value of the calculated temperature difference Means for comparing with a predetermined temperature difference profile, and means for controlling the output of the lower heater or the lower cooler, the position of the radiant heat reflector, the position of the radiant heat reflector heat insulating material or the position of the crucible based on the comparison result An apparatus for producing a silicon single crystal characterized by the above. 2. In the production of a silicon single crystal by the Czochralski method, the temperature difference between the upper and lower sides of the melt is calculated by measuring the temperature of the melt surface and the temperature of the bottom surface of the crucible, and the temperature difference is the single crystal. The output of the lower heater or lower cooler, the vertical position of the radiant heat reflection plate, and the radiant heat reflection plate heat insulating material so as to follow the temperature difference profile set based on the correlation between the oxygen concentration in the melt and the temperature difference between the melt and the melt. A method for producing a silicon single crystal, characterized by controlling at least one of a vertical position and a vertical position of a crucible.