JPH10167880A - Method for growing single crystal and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method which enables improvement in quality and yield of a single crystal and also to provide the device used for performing the method. SOLUTION: In this device, a window 11 (such as transparent quartz window) having an about 5mm diameter and high light-transmissivity is formed at the centers of the bottoms of an inner layer holding vessel 1a and an outer layer holding vessel 1b by boring a hole through these vessels 1a and 1b at their centers. Also, a supporting shaft 7 has at the center within it, a sensor part 12 of an optical temp. indicator, the base end of which is connected to a system section 13 and the front end of which faces the window 11. In the system section 13, an optical signal detected by the sensor part 12 is converted into an electric signal to perform temp. indication. At this time, when a melt is solidified, the temp. thus indicated drops rapidly. Therefore, a crystal is grown while monitoring the indicated temp. and when a temp. drop is detected, the output of a lower heater 14b is immediately increased to prevent suspended solidified matter from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal growth method for growing a single crystal such as a silicon single crystal used as a semiconductor material and an apparatus used for carrying out the method.

[0002]

2. Description of the Related Art One of the methods commonly used for growing silicon single crystals is the Czochralski method (C).
Z method). FIG. 3 is a schematic longitudinal sectional view showing a single crystal growth apparatus used for the CZ method. In the figure, reference numeral 1 denotes a crucible provided in a chamber, and the crucible 1 is supported by a support shaft 7 connected to a rotating / elevating mechanism (not shown). The crucible 1 is a cylindrical inner-layer holding container having a bottomed cylindrical shape.
1a and an outer-layer holding container 1b made of graphite fitted to the outside of the inner-layer holding container 1a. A pulling shaft 4 made of a pulling rod or a wire is hung above the crucible 1 so as to be rotatable and vertically movable, and a seed crystal 5 is attached to a lower end of the pulling shaft 4 by a seed chuck. There is something. Outside the crucible 1, a heater 2 of a resistance heating type is arranged in a concentric cylindrical shape.

In order to grow a single crystal, first, a crucible 1 is filled with a raw material for a single crystal, and the crucible 1 is melted by a heater 2 while rotating the crucible 1 in a predetermined direction at a predetermined number of revolutions to form a melt 3. The seed crystal 5 is attached to the tip of the pulling shaft 4, and the pulling shaft 4 is temporarily lowered until the seed crystal 5 comes into contact with the melt 3. Then, the pulling shaft 4 is pulled upward while rotating in the opposite direction (or the same direction) as the crucible 1. Then, the melt 3 in contact with the lower end of the seed crystal 5 is cooled, and the single crystal 8 grows.

When a silicon single crystal used as a semiconductor material is grown, a doping impurity (dopant) is often added to the melt 3 in order to obtain a predetermined electric conductivity and electric resistivity. This dopant segregates in the pulling direction of the single crystal 8 according to the following equation known as Pfann's equation. C _S = ke · C _C (1-f _S ) ^ke-1 where ke: Effective segregation coefficient C _S : Dopant concentration in crystal C _C : Dopant concentration in melt at the start of crystal pulling f _S : Crystal pulling rate (use Ratio of crystal weight to crystal raw material weight)

[0005]

In the CZ method, since the convection of the melt 3 is strong, a low-temperature portion flows from the wall of the crucible 1 directly below the single crystal 8, and a spoke pattern is formed in the low-temperature portion. There is.

The large convection means that the melt 3
In this case, the high temperature part and the low temperature part are non-uniformly present. This consists of a single crystal 8 and a melt 3
Leads to a change in temperature at the solid-liquid interface. A change in the temperature at the solid-liquid interface affects the growth rate, and a change in the growth rate leads to a change in the segregation coefficient described above. When the segregation coefficient fluctuates, the impurity distribution in the pulling direction becomes non-uniform, and the electric conductivity and electric resistivity of the obtained single crystal 8 become non-uniform.

[0007] The convection in the melt 3 increases as the lower temperature is higher than the upper temperature, because the upward flow becomes more intense. Therefore, in order to suppress this convection, a method of keeping the lower portion of the melt 3 at a lower temperature than the upper portion has been adopted. FIG. 4 shows a single crystal growth apparatus used in this method. In this apparatus, a double heater 14 divided into upper and lower stages is used. The output of the lower heater 14b is connected to the upper heater.
Convection is suppressed by lowering the output of 14a.

However, if the output of the lower heater 14b is too low, the melt 3 at the bottom of the crucible 1 may be solidified. Then, the convection in the melt 3 changes, which affects the homogeneity of the single crystal 8. Further, the solidified melt 3 is peeled off from the bottom wall of the crucible 1 and floats as a floating substance, and the single crystal 8
Once entrained, polycrystallization may occur in the portion and the portion may have to be removed or the entire single crystal 8 must be discarded. However, conventionally, the melt 3
No solidification was detected.

Conversely, by increasing the output of the upper heater 14a, a desired heat input ratio can be obtained, but this case is not preferable because of a large energy loss and a reduced growth rate.

The present invention has been made in view of the above circumstances, and a single crystal capable of improving quality and yield by detecting the temperature of the bottom of a molten raw material and detecting the solidification of the molten liquid. It is an object of the present invention to provide a growth method and an apparatus used for carrying out the method.

[0011]

According to the first and second aspects of the present invention, a single crystal is pulled from a molten raw material held in a crucible whose bottom is supported by a supporting shaft so as to be rotatable and vertically movable. In the method of growing and the apparatus used for its implementation, the temperature of the single crystal material at the bottom of the crucible is detected with an optical thermometer, and whether or not a solid layer is formed based on the detection result is detected. The vertical heat input ratio to the molten raw material is controlled based on this detection.

When the formation of the solid layer is detected by detecting the temperature at the bottom of the crucible, the heat input ratio in the vertical direction is controlled so that the heat input to the bottom of the crucible increases. Such control is
Before the single crystal growth, it may be carried out on a trial basis, during the growth, or both before the growth and during the growth.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic longitudinal sectional view showing a single crystal growth apparatus used for carrying out a single crystal growth method according to the present invention. In the figure, reference numeral 1 denotes a crucible provided in a chamber, and the bottom of the crucible 1 is supported by a support shaft 7 connected to a rotating / elevating mechanism (not shown). The crucible 1 includes a quartz inner layer holding container 1a having a bottomed cylindrical shape, and a graphite outer layer holding container 1b fitted to the outside of the inner layer holding container 1a.

A pulling shaft 4 composed of a pulling rod or a wire is suspended above the crucible 1 so as to be rotatable and vertically movable. A seed crystal 5 is placed at the lower end of the pulling shaft 4 by a seed chuck. It is designed to be attached. Outside the crucible 1, a heater 2 of a resistance heating type is arranged in a concentric cylindrical shape. The above is the same configuration as the conventional one.

In the present invention, a window 11 having a diameter of about 5 mm and having a high light transmittance is provided at the center of the bottom of the inner layer holding container 1a and the outer layer holding container 1b.
(For example, transparent quartz). And the support shaft 7
The sensor section 12 of the optical thermometer whose base end is connected to the system section 13 is built in the center of the sensor section 12, and the tip of the sensor section 12 faces the window 11. The system unit 13 processes a signal detected by the sensor unit 12 and displays a temperature. The sensor section 12 is fitted and fastened by a hollow portion of the support shaft 7, and a cable is drawn out of the base of the support shaft 7 via a rotary connector (not shown) attached to the support shaft 7. Therefore, the sensor section 12 and the cable are not twisted by the rotation of the support shaft 7.

When a single crystal is grown by the CZ method, first, a crucible 1 is filled with a single crystal raw material, and the crucible 1 is melted by a heater 2 while rotating the crucible 1 to form a melt 3. Then, the seed crystal 5 is immersed in the melt 3 and then pulled up to grow the single crystal 8.

In the above, the case where a window having high light transmittance is provided at the center of the bottom of the quartz crucible has been described. However, a window having high light transmittance is also provided at the center of the bottom of the graphite crucible, and the outside of the graphite crucible is provided. May be used to detect the temperature inside the crucible. Further, the center of the bottom of the ordinary quartz crucible may be directly measured without providing a window having high light transmittance at all, but in this case, a measurement error is slightly increased. In any case, the presence or absence of a solid layer at the bottom of the crucible may be determined from the outside of the crucible.

When an ordinary radiation thermometer is used as the optical thermometer, the resolution is 0.5 ° C., for example, when an Accu fiber manufactured by Nippon Mining & Measurement System Co., Ltd. is used, a resolution of 0.01 ° C. is obtained, and about 1900 ° C. It can be measured up to. In this case, the sensor unit 12 is made of an optical fiber made of a single crystal rod of alumina, and is connected to the system unit 13 by a quartz optical fiber cable. Therefore, the optical signal received by the sensor unit 12 is transmitted to the system unit via the optical fiber cable.
It is transmitted to 13 and photoelectrically converted to calculate the temperature and display the temperature. When this thermometer is used, the temperature can be measured up to about 1900 ° C., so that it can be brought very close to the crucible 1 which rises to about 1300 ° C., and the temperature can be accurately detected.

As a means for detecting the temperature of the melt in the crucible 1, there is a method of measuring the temperature by inserting a thermocouple into the melt layer 10. In this method, the temperature of the melt layer 10 can be measured. However, there is a problem that it cannot be determined whether or not the solid layer 9 is deposited. For example, even when the temperature near the bottom of the crucible is constant, when the temperature is 1414 ° C. near the solid-liquid boundary, the solid layer 9 is deposited in the vicinity of the bottom of the crucible in a molten state. I can't judge.

On the other hand, the present invention focuses on the fact that the emissivity of the solid layer 9 of silicon, which is a raw material for single crystal, and that of the melt layer 10 are different. layer
This is to determine whether or not 10 has solidified.
Has an emissivity of εs = 0.6 and an emissivity of the melt layer 10 of εl = 0.25
It utilizes the fact that the relation that W is proportional to εT ⁴ holds in temperature (T), emissivity (ε), and radiant energy (W).

That is, the emissivity ε is set to an arbitrary value in the system section 13, for example, ε = εl (emissivity of the melt layer 10). If the emitted radiant energy is received by the sensor unit 12, the radiant energy of the melt layer 10 will be reduced if the temperature near the bottom of the crucible is in a molten state even if the actual temperature near the bottom of the crucible is constant. Since the temperature is constant, the temperature displayed in the system section 13 does not change. However, if the solid layer 9 is deposited near the bottom of the crucible, the emissivity set in the system section 13 is ε = εs
Ε = εl unless changed to (emissivity of solid layer 9)
(<Εs), the radiant energy of the solid layer 9 is detected even if the actual temperature is the same, and the temperature displayed by the system unit 13 is higher than the temperature displayed in the melt state. Will be displayed. This is because the radiant energy is proportional to εT ⁴ .

FIG. 2 is a graph showing the temperature near the bottom of the crucible measured by a radiation thermometer. Here, the temperature displayed by the radiation thermometer is a temperature display for judging whether the vicinity of the bottom of the crucible is in the state of the melt layer 10 or the solid layer 9 is deposited, and is not necessarily true. Although it does not match the value of the temperature at the bottom of the crystallization raw material, what is more important in the present invention is to know the change in temperature reliably than to what is the true temperature.

In FIG. 2, the time when the emissivity starts to increase indicates the time when the solid layer 9 is generated, and the time when the emissivity is stabilized at a high emissivity indicates the time when the solid layer 9 is completely formed. I have. Therefore, the occurrence of the solid layer 9 during the growth of the single crystal can be predicted by grasping in advance the time from the start of the generation of the solid layer 9 to the complete formation of the solid layer 9 during the growth of the single crystal.

Therefore, in the present invention, the time when the solid layer 9 is completely formed is predicted based on the detection of the time when the solid layer 9 is generated, and immediately or after a predetermined time, the output of the lower heater 14b is increased to generate the solid layer 9. Prevention can eliminate adverse effects on the single crystal due to the generation of solidified suspended matter on the melt surface.

In implementing the present invention, the means for controlling the heat input ratio is not limited to a double heater divided into upper and lower stages, and a plurality of means may be provided if necessary. The heat input ratio can also be controlled by adjusting the relative positions of the heater and the molten material. The window 11 is desirably transparent, but need not be transparent as long as a change in temperature can be detected.

[0026]

As described above, according to the present invention, by detecting the temperature of the bottom of the molten raw material and detecting the solidification of the molten liquid, it is possible to prevent the fluctuation of the parameters relating to the single crystal growth and to improve the quality and the yield. For example, the present invention has excellent effects.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing a single crystal growth apparatus according to the present invention.

FIG. 2 is a graph showing the temperature at the bottom of a raw material for crystallization.

FIG. 3 is a schematic longitudinal sectional view showing a single crystal growth apparatus used for the CZ method.

FIG. 4 is a schematic vertical sectional view showing a conventional single crystal growth apparatus using a double heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crucible 1a Inner-layer holding container 1b Outer-layer holding container 2 Heater 3 Melt 4 Pulling shaft 7 Supporting shaft 8 Single crystal 11 Window 12 Sensor part 13 System part

Claims (2)

[Claims] 1. A method for pulling a single crystal from a molten material held in a crucible supported so that the bottom thereof can be rotated and raised and lowered by a support shaft, and growing the single crystal material at the bottom of the crucible. The temperature is detected by an optical thermometer, it is detected whether or not a solid layer is formed based on the detection result, and the vertical heat input ratio to the molten raw material is controlled based on this detection. Single crystal growth method. 2. An apparatus for pulling and growing a single crystal from a molten material held in a crucible whose bottom is rotatable and vertically movable on a support shaft, wherein the crucible connected to the support shaft is lifted. A light transmission window formed at the bottom, an optical thermometer for detecting the temperature of the single crystal raw material through the light transmission window, and a heater capable of controlling a vertical heat input ratio to the molten raw material are provided. Characteristic single crystal growth equipment.