JPH06166589A - Method for detecting and adjusting deviation between revolution center of furnace for pulling up single crystal and thermal center - Google Patents

Abstract

PURPOSE:To prevent deformation of crystal and polycrystallization by pulling up single crystal from melt, obtaining the minimum value and the maximum value of a distance from the axial center of seed crystal to the outer peripheral part of single crystal and adjusting deviation between the revolution center of a crucible and a thermal center based a K value obtained from the minimum value and the maximum value. CONSTITUTION:Seed crystal 2 is immersed in the central part of melt, the revolution of the seed crystal 2 is stopped and rotation of a crucible is stopped or the revolving speed is made <=0.5r.p.m. to pull up single crystal 1. Then, the maximum value 4 and the minimum value 3 of a distance from the axial center of the seed crystal 2 to the outer peripheral part of the single crystal 1 are obtained. The minimum value 3 is divided by the maximum value 4 to obtain a K value. Deviation between the revolution center of the crucible and a thermal center is adjusted in such a way that the K value is >=0.8 to control a furnace for pulling up single crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily evaluating a thermal symmetry in a furnace for producing a single crystal, and for easily detecting a deviation between a rotation center and a thermal center and a method for adjusting the deviation. It is about.

[0002]

2. Description of the Related Art In order to evaluate the mechanical axial symmetry of a single crystal pulling furnace, there is a pulling furnace centering method as disclosed in, for example, Japanese Patent Application Laid-Open No. 02-120602. But,
This can be applied when the temperature is low, but technically it cannot be applied under a condition close to the pulling condition where the temperature becomes high due to the usage conditions of the detector and the like. Therefore, even if mechanical axial symmetry can be secured near room temperature by this method, it is not possible to secure mechanical axial symmetry in a single crystal pulled state where the temperature is high. This is because, generally, when the temperature rises, the member used for the single crystal pulling furnace expands due to heat and distortion occurs, so that the mechanical axial symmetry collapses. Even if the mechanical axial symmetry is maintained even when the temperature is high, for example, if the heater that generates heat is not axially symmetric, the temperature distribution deviates from the axial symmetry, and the thermal core shifts Then, it becomes difficult to pull up the crystal. When the crystal is pulled up under such a condition, distortion occurs in the pulled crystal, so-called deformation or snake may be caused, and polycrystallization may occur, which causes a problem that the yield of the single crystal product decreases. . Factors that destroy the thermal symmetry include the non-axisymmetry of the heater and the crucible (for example, the change in thickness), the non-axisymmetry of the heat insulating member made of carbon, etc., and the non-axisymmetricity of the gas flow. .
However, no method of controlling the state of the furnace with respect to the axial symmetry of these factors is found in the prior art.

On the other hand, as a method for directly measuring the temperature distribution of the melt in the crucible, a method of immersing a thermocouple in the melt, infrared rays emitted from the surface of the melt are analyzed, and a two-dimensional surface temperature distribution is obtained. There is a method to measure. When a thermocouple is used, at least about four thermocouples are required, but it takes a very long time to attach the thermocouple, and the measurement cannot be performed easily. Further, a quartz tube or the like for protecting the thermocouple is used, but this lowers the temperature measurement accuracy. Further, when using a plurality of thermocouples, it is essential that the accuracy of each thermocouple is known, but the measurement accuracy at around 140 ° C is generally about ± 10 ° C. Even if the thermocouple is carefully calibrated, it is about ± 5 ° C. In addition, it is possible to measure the two-dimensional surface temperature distribution, but in this case as well, there is no measurement accuracy, and with ordinary measurement equipment,
The accuracy is ± 20 ° C near 00 ° C. Any of the measurements is considered to cause deformation or snake of the single crystal, and the accuracy of ± 0.1 ° C., which is a problem here, cannot be guaranteed at all. Therefore, the thermal axial symmetry of the single crystal pulling furnace cannot be controlled even by the method of directly measuring the temperature of the melt.

[0004]

SUMMARY OF THE INVENTION The present invention is aimed at simply and comprehensively centering a single crystal pulling furnace, and in particular, it evaluates the thermal axial symmetry that is difficult to measure, and evaluates the rotation center and the thermal center. The present invention relates to a method for detecting a center shift.

[0005]

[Means and Actions for Solving the Problems] The normal pulling of a single crystal is carried out by immersing the seed crystal in a melt held in a rotating crucible and rotating the seed crystal in the direction opposite to the rotation of the crucible. . In the case of pulling a silicon single crystal, the rotation speed of the crucible or the crystal varies depending on the conditions, but the rotation speed of the crucible is 1 to 20 r.p.m. p. m. Crystal rotation speed is 5
~ 50r. p. m. Is common. The present invention will now be described in detail according to the procedure. The seed crystal is immersed in the center of the melt, that is, at the center of rotation of the pulling furnace, as in the normal pulling of a single crystal. The crucible rotation is industrially stopped or set to a predetermined value, the melt temperature is set to a value suitable for pulling up the crystal, and then the diameter of the seed crystal is reduced. This operation is mainly performed by increasing the pulling rate of the seed crystal, but the melt temperature may be changed together. The rotation speed of the crucible and the crystal conditions are as follows. The crucible is industrially stationary or the crucible rotation speed is 0.5 r.
p. m. Below, the seed crystal is industrially stationary. Limiting the rotation speed of the crucible to this range is that if the rotation speed of the crucible exceeds the limited range, the uneven temperature distribution applied depending on the furnace structure or situation is relaxed,
This is because the thermal center almost coincides with the center of rotation. For this reason, it becomes impossible to control the thermal axial symmetry of the single crystal pulling furnace.

Next, the step of expanding the crystal diameter is started. Here, pulling may be constant at a relatively slow speed or may be changed. Ideally, it is desirable to keep the pulling rate constant and gradually lower the melt temperature. When the outer diameter of the expanded crystal reaches a predetermined value of, for example, about 100 mm, the pulling speed is rapidly increased to pull up the crystal from the melt. This is taken out, the uniformity of the shape is examined, and the axial symmetry is judged. The outer diameter of the crystal to be expanded is not particularly limited as long as the crystal can be recovered. The time required from the immersion of the seed crystal in the melt to the removal of the crystal is 2 to 3 hours.

The axial symmetry is defined as follows. That is, as shown in FIG. 1, when the silicon crystal 1 is viewed from above, the distance from the seed crystal 2 to the outer periphery of the crystal is measured with the seed crystal 2 as the origin. A value obtained by dividing the minimum value (distance 3) by the maximum value (distance 4) of the distance is used as the index K (K value). The closer this value is to 1, the closer the crystal is to a perfect circle, indicating that the thermal axial symmetry of the pulling furnace is maintained. K in reality
If the value is 0.8 or more, it can be used as a single crystal pulling furnace.

In the case where a new furnace component is assembled, the present invention detects the deviation between the rotational center and the thermal center, so that it is possible to evaluate whether or not the thermal axial symmetry is secured. Further, it becomes possible to measure the deviation regularly by this method and to grasp and manage the degree of deterioration of the furnace constituent members such as the heater. For example, K value is 0.8
If it is smaller than the above, check the components and make adjustments. If the crystal is grown while the K value is smaller than 0.8, it becomes difficult to stably pull up the crystal, and the pulled crystal is distorted to cause so-called deformation or snake. Further, in the extreme case, polycrystallization occurs, which causes a problem that the yield of a single crystal product decreases.

[0009]

【Example】

Example-1 Thermal axisymmetry was measured by the method of the present invention when a new furnace component was assembled which could be pulled up using a 16 inch crucible. The melting amount was 40 kg, and the rotation speed of the crucible was 0.5 r.p.m. p. m. The crystals were allowed to stand still and evaluated. When the axial symmetry was quantified by the method described in the text and the K value was calculated, it was 0.91, and it was confirmed that the thermal axial symmetry was good. Therefore, the crucible rotation is 2r. p. m. We decided to use it as a crystal pulling furnace for low oxygen concentration used below. Measurement is performed under the same conditions as above every 10 charges (approximately every 400 hours) to evaluate the thermal axial symmetry, and K
When the value was calculated, 0.90, 20 after 10 charges
It was 0.88 after charging, which was not much different from the initial value. It is 0 when measured after 30 charges.
It was determined to be 85, and when it was used in a low crucible rotation, crystal deformation was increased and the probability of polycrystallization was increased. For this reason, the crucible rotation is set to 5 to 15 r. p. m. It was used as a pulling furnace for medium to high oxygen concentrations used in. Total 4
It was 0.82 at the 0th charge and could be used further, so the life was extended to 50th charge. After 50 charges, the index was 0.75, and it was judged that further use was impossible, and the components were replaced with new ones. This makes it possible to prevent a decrease in the yield of a single crystal due to crystal deformation and polycrystallization. This corresponds to an improvement of 5 points or more in the single crystal yield when viewed in a low oxygen concentration pulling furnace. Further, since it is possible to properly use the constituent members of the furnace, it is possible to extend the life of the constituent members as a whole by 10% or more.

Example 2 When a furnace component capable of pulling up using an 18 inch crucible was newly manufactured, thermal axisymmetry was measured by the method of the present invention. The dissolution amount was set to 50 kg, and the crucible and the crystal were both kept stationary for evaluation. When the K value was calculated, it was 0.65, and there was a tendency that only one side grew greatly. A closer examination of the larger grown portion of the crystal revealed an anomaly inside the heater, indicating that the heating characteristics deviated from axial symmetry. When the heater was replaced with a new one, the K value was 0.94, and the thermal axial symmetry was good. As a result, defective furnace components could be improved, and the single crystal yield could be improved.

Example-3 Example-3 and later, including a comparative example, will be described with reference to Table 1. A furnace capable of pulling up using a 16-inch crucible was used, and the melting amount was the same at 40 kg. The thermal axial symmetry was relatively poor, and the thermal axial symmetry was evaluated by changing the rotation speed of the crucible and the rotation speed of the seed crystal under various furnace conditions where crystal deformation was very likely to occur. In Examples 3 to 6, both the rotation speed of the crucible and the rotation speed of the seed crystal are within the limited range. Example-3 in which the pulling rate at the time of expanding the crystal diameter was changed during measurement, Example-4 in which the expanded crystal diameter was increased to about 150 mm, and conversely Example in which the expanded crystal diameter was reduced to about 50 mm. -5, Example 6 in which the heater temperature was lowered stepwise by 10 ° C., and the K value was 0.
A numerical value of 8 or less is shown, which indicates that the furnace is defective and a correct judgment can be made. On the other hand, Comparative Example-
7, the crucible rotation speed was 0.8 r. p. m. Is beyond the limited range. In Comparative Example-8, the rotation speed of the crucible was within the limited range, but the rotation speed of the seed crystal was 0.
5r. p. m. And is beyond the limited range. Further, in Comparative Example-9, the rotation speed of the crucible exceeds the limited range. As shown in Comparative Examples-7 to 9, the K value was 0.8 or more in all, and it is judged that the condition of the furnace is good. However, as described above, the furnace in which the measurement is performed has very poor symmetry, and crystal deformation easily occurs. Therefore, it can be concluded that the method shown in the comparative example cannot make a correct determination.

[0012]

[Table 1]

[0013]

Since the constituent members of the furnace can be controlled by the method of the present invention, it is possible to prevent the decrease in the yield of the single crystal due to the crystal deformation and polycrystallization. Further, since the deterioration of the constituent members can be quantitatively evaluated, the constituent members can be properly used and the life of the constituent members as a whole can be extended. Further, the thermal axisymmetry can be easily measured, and the axisymmetry can be confirmed prior to the normal operation.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for quantifying axial symmetry.

[Explanation of symbols]

 1 ... Silicon crystal 2 ... Seed crystal 3 ... Distance from center of seed crystal to outer circumference (minimum value) 4 ... Distance from center of seed crystal to outer circumference (maximum value)

Claims (2)

[Claims] 1. The rotation of a seed crystal is stopped industrially, the rotation of a crucible is stopped industrially, or the rotation speed of the crucible is set to 0.
5r. p. m. Below, by pulling the crystal while contacting the seed crystal to the melt to increase the diameter, obtain the maximum and minimum values of the distance from the axis of the seed crystal to the outer periphery of the single crystal, the minimum value A deviation between the rotational center of the crucible and the thermal center of the crucible is detected by a K value obtained by dividing the rotational center of the crucible and the thermal center of the crucible by a K value. 2. The single crystal pulling furnace is adjusted so that the K value according to claim 1 is 0.8 or more.
A method for adjusting the deviation between the rotation center and the thermal center of the single crystal pulling furnace.