JPH04305087A - Method and device for producing single crystal - Google Patents

Abstract

PURPOSE:To provide a device capable of producing a single crystal low in oxygen concentration, without the lifting speed being lowered with respect to the conventional process and without the single crystal being normalized. CONSTITUTION:The peak of the produced heat distribution of a heater 8 is positioned above the surface of a melt 6, the amt. of oxygen dissolved into the melt 6 from the peripheral wall of a crucible 4 is reduced, and the oxygen concn. in a single crystal 3 pulled up from the melt 6 is diminished.

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 single crystal, such as a silicon single crystal, and an apparatus used in the method.

0002

2. Description of the Related Art The Czochralski (CZ) method is widely known as a single crystal manufacturing method. FIG. 4 is a schematic diagram showing the state of implementation of conventional single crystal production by the CZ method, and 4 in the figure is a quartz crucible. A carbon crucible 5 is disposed on the outer periphery of the quartz crucible 4, and a carbon crucible 5 is further disposed on the outer periphery of the quartz crucible 4.
A heater 7 made of carbon is arranged so as to surround the whole. Then, the raw material for crystal is put into the quartz crucible 4, and after heating and melting it with the heater 7, the seed crystal 2 suspended by the pulling shaft 1 is immersed in the molten liquid 6, and while it is being rotated. When pulled upward, the single crystal 3 is placed at the bottom end of the seed crystal 2.
is made to grow.

0003

[Problems to be Solved by the Invention] In the single crystal growth apparatus constructed as described above, heat escapes from the heater 7 at its upper and lower ends, but does not escape from the center in the vertical direction. The calorific value is in the center as shown by the broken line,
That is, it reaches a peak at a position slightly below the liquid level of the melt 6. Due to this heat generation distribution, heat convection occurs from the center of the side peripheral wall of the quartz crucible 4 toward the pulling region of the single crystal 3, as shown by the arrow. Then, the quartz crucible 4 begins to melt due to heating by the heater 7, oxygen is supplied into the melt 6, is carried to the pulling region of the single crystal 3 by the thermal convection, and is taken into the single crystal 3. Therefore, in this device, the amount of oxygen supplied to the single crystal 3 is large, so approximately 13.0 x 1018 atms
It has been impossible to produce single crystals with low oxygen concentrations below /cc.

Therefore, the center of the heater 7 is a quartz crucible 4.
By arranging the heater 7 at a high position so as to substantially coincide with the upper end position so that the heat generated by the heater 7 reaches its peak above the surface of the melt 6, the heat flowing from the side peripheral wall of the quartz crucible 4 toward the pulling region of the single crystal 3 is Convection is reduced, the amount of oxygen dissolved from the quartz crucible 4 is reduced, and the amount of oxygen supplied to the single crystal 3 is reduced, making it possible to produce a single crystal with a low oxygen concentration. However, the amount of heating in the pulling region of the single crystal 3 increases, and in order to continue pulling the single crystal 3, the pulling speed must be reduced, and there is a problem that the single crystal becomes dislocated. Ta.

The present invention was developed in view of the above circumstances, and aims to reduce the amount of oxygen that dissolves into the melt from the side wall of the crucible by locating the peak of the heat distribution of the heater above the liquid level of the melt. By reducing the amount of oxygen supplied to the pulling region of the single crystal, it is possible to obtain a single crystal with a low oxygen concentration without reducing the pulling speed compared to the conventional method and without causing dislocations in the single crystal. An object of the present invention is to provide a single crystal manufacturing method and a single crystal manufacturing apparatus used in the method.

[0006]

[Means for Solving the Problems] A method for producing a single crystal according to a first aspect of the present invention is a method for producing a single crystal in which a raw material for crystal is melted in a crucible by a heater disposed around the crucible, and a single crystal is pulled from the melt. The method is characterized in that the single crystal is manufactured such that the peak of the heat generation distribution of the heater is located above the liquid level of the melt. A single crystal manufacturing apparatus according to a second aspect of the present invention is a single crystal manufacturing apparatus in which a raw material for crystal is melted in a crucible around which a heater is arranged, and a single crystal is pulled up and grown from the melt. is located above the liquid level of the melt.

[0007]

[Operation] In the present invention, since the peak of the heat generation distribution of the heater is located above the liquid level of the melt,
Unlike the case where the peak of the heat generation distribution of the heater is located below the liquid level of the melt, the thermal convection that occurs in the melt is small and only flows from the upper side of the side peripheral wall of the crucible toward the pulling region of the single crystal. Also, the amount of oxygen that dissolves into the melt from the side wall of the crucible is small. Therefore, the amount of oxygen supplied to the pulling region of the single crystal is reduced, making it possible to produce a single crystal with a low oxygen concentration. In addition, since the amount of heating in the pulling region of the single crystal is small compared to when the heater is placed high so that its central part approximately coincides with the top position of the quartz crucible, pulling can be carried out without reducing the pulling speed. , and does not involve formation of dislocations in the single crystal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to drawings showing embodiments thereof. FIG. 1 is a schematic vertical cross-sectional view of a single crystal manufacturing apparatus according to the present invention, and 4 in the figure is a quartz crucible. A carbon crucible 5 is disposed on the outer periphery of the quartz crucible 4, and a carbon heater 8 is further disposed on the outer periphery side so as to surround the carbon crucible 5. And quartz crucible 4
After putting the raw material for crystal into the tank and heating and melting it with the heater 8, the seed crystal 2 suspended by the pulling shaft 1 is immersed in the molten liquid 6 and pulled upward while rotating. , a single crystal 3 is grown on the lower end of the seed crystal 2.

FIG. 2 is a perspective view of the heater 8. Heater 8
have upper slits 8b, 8b, cut from the upper end.
8b,... and lower slits 8c, 8 cut from the lower end
c, 8c, . . . are provided alternately in the circumferential direction. At the lower end of the heater 8, electrodes 8a, 8a are spaced apart by 180 degrees in the circumferential direction.
is provided and is energized. When energized, current flows through the heater 8 while changing its direction in the vertical direction as shown by the arrow. The thickness of heater 8 is above,
The middle and bottom three levels are different. The thickness t2 of the middle part is approximately 1/2 of the thickness t3 of the lower part, and the thickness t1 of the upper part is slightly thicker than the thickness t2 of the middle part. The length of the upper part is l1, the length of the middle part is l2, and the length of the lower part is l3.
The ratio is approximately 1:2:5.

[0010] Resistance is inversely proportional to the thickness of the resistor, that is, the cross-sectional area, and the amount of heat generated is proportional to the resistance. As described above, since the thickness of the upper and middle parts of the heater 8 is thinner than that of the lower part, the amount of heat generated in the upper and middle parts is larger than that of the lower part. Therefore, when the liquid level of the melt 6 is positioned slightly below the center of the middle part of the heater 8, the heat generated by the heater 8 is located approximately at the center of the middle part, that is, the liquid level of the melt 6, as shown by the broken line. It reaches its peak at a slightly higher position. Due to this heat generation distribution, the single crystal 3 is pulled from the upper side of the side peripheral wall of the quartz crucible 4, unlike when the peak of the heat generation distribution of the heater is located below the liquid level of the melt, as shown by the arrow. Small-scale heat convection occurs only towards the area. The amount of quartz crucible 4 that melts due to heating by heater 8 is small. Therefore, the amount of oxygen carried from the side wall of the quartz crucible 4 to the pulling region of the single crystal 3 by the thermal convection is small, and as a result, the oxygen concentration of the single crystal 3 can be lowered.

FIG. 3 is a graph showing the relationship between the pulling length and the oxygen concentration when the position of the exothermic peak is changed. In the figure, □ indicates an example of the present invention in which the exothermic peak is above the liquid surface of the melt 6, and △
is a comparative example in which the exothermic peak is at the same position as the liquid level of melt 6,
○ is a conventional example in which the exothermic peak is below the surface of the melt 6. From FIG. 3, according to the method of the present invention, 7.0 to 13.0×10
It can be seen that single crystals with a low oxygen concentration of about 18 atms/cc can be produced.

In the embodiment of the present invention, the thickness of the heater 8 is set in three stages, and the thickness of the upper stage is slightly thicker than that of the middle stage below, thereby suppressing the amount of heating to the upper side of the pulling region of the single crystal 3. If problems such as a reduction in the pulling speed and formation of dislocations in the single crystal do not occur, the heater 8 may have a two-stage structure in which the thickness is thinner at the upper part and thicker at the lower part. Further, the installation position, length, and thickness of the thin portion of the heater 8 may be set according to the target oxygen concentration of the single crystal 3, assuming a heat generation distribution so as to obtain the target oxygen concentration.

[0013]

As described above, in the present invention, the peak of the heat generation distribution of the heater is positioned above the liquid level of the melt, thereby reducing the amount of oxygen that dissolves into the melt from the side peripheral wall of the crucible. , the amount of oxygen supplied to the pulling region of the single crystal is reduced, and a single crystal with a low oxygen concentration can be obtained. Furthermore, since the amount of heating above the single crystal pulling region is smaller than when the heater is placed above the crucible, there is no need to reduce the pulling speed, and the single crystal does not become dislocated. etc., the present invention has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a single crystal manufacturing apparatus according to the present invention.

FIG. 2 is a perspective view of a heater.

FIG. 3 is a graph showing the relationship between the pulling length and oxygen concentration when the position of the exothermic peak is changed.

FIG. 4 is a schematic vertical cross-sectional view of a conventional single crystal manufacturing apparatus.

[Explanation of symbols]

1 Pulling shaft 2 Seed crystal 3 Single crystal 4 Quartz crucible 5 Carbon crucible 6 Melt liquid 8 Heater

Claims (2)

[Claims] 1. A method for producing a single crystal in which a raw material for crystal is melted in a crucible using heaters arranged around the crucible and a single crystal is pulled from the melt, wherein the peak of the heat generation distribution of the heater is at a level below the liquid level of the melt. A method for producing a single crystal, characterized in that the single crystal is produced so as to be located on the upper side. 2. In a single crystal manufacturing apparatus in which a raw material for crystal is melted in a crucible around which a heater is arranged, and a single crystal is pulled up and grown from the melt, the peak of the heat distribution of the heater is the same as that of the melt. A single crystal production device characterized by being positioned above a liquid level.