JPH05330976A - Single crystal production system - Google Patents

Abstract

PURPOSE:To continuously obtain single crystal with high purity and high quality by monitoring the sagging state of a silicon melt from a material rod by optical sensor to control the driving conditions for a heater or the descending rate of the rod. CONSTITUTION:The level of a material melt in a material feed mechanism 30 is detected by a television camera 2 and the amount of light received is amplified by an amplifier 3 and outputted via a comparative circuit 4, a waveform trimming circuit 5 and a shift register 6, to the first CPU 8. The spacing between the adjacent peaks of the outputted waveform is measured by the CPU 8 to calculate the sag diameter of a silicon material melt. According to this value, the driving of a heater 13 for melting polycrystalline silicon rod and the feed rate of a silicon polycrystalline rod 301 are controlled by the second CPU 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a single crystal, and more particularly to a technique for continuously supplying a raw material into a crucible to continuously produce a homogeneous semiconductor single crystal.

[0002]

2. Description of the Related Art A CZ (Czochralski pulling) method for growing a columnar crystal from a raw material melt in a crucible is used for growing a semiconductor single crystal. Usually, a method of controlling the resistivity of a single crystal to be grown is used in growing a semiconductor single crystal. When the CZ method is used, in order to control the resistivity of the single crystal to be grown. An impurity element called dopant is added to the raw material melt in the crucible. However, the dopant generally has a segregation coefficient of 1
Therefore, in the ordinary CZ method, the concentration in the crystal changes as the length of the crystal becomes longer. This is a serious problem in the production of semiconductor single crystals in which the resistivity is controlled by the dopant concentration.

In order to solve this problem, a technique using a continuous charging method or a double crucible in which the raw material is continuously supplied into the crucible to keep the dopant concentration in the raw material melt constant ( Kai 63-79790) has been proposed. Continuous char
As a raw material supply means in the method D, a raw material melting place and a single crystal growing place are separated and transported (JP-A-52-5).
8080, JP-A-56-164097), those using rod-shaped raw materials (JP-A-56-84397, JP-A-62-1)
05992) and other proposals.

Of the continuous charging techniques mentioned above, the former two techniques, that is, the techniques described in JP-A-52-58080 and JP-A-56-164097, are crucibles for melting raw materials and crucibles for growing crystals. However, there is a problem in that it is structurally complicated and it is difficult to control the supply amount. The latter two, that is, the techniques described in JP-A-56-84397 and JP-A-62-105992, are for melting a rod-shaped raw material by a melt in a crucible, and therefore, a crystal growing place and a raw material melting place in the crucible. It is necessary to increase the temperature gradient of No. 3, and it is very difficult to realize the temperature gradient in which the raw materials can be dissolved during crystal growth. Further, among these techniques, the technique described in Japanese Patent Laid-Open No. 62-105992 uses high frequency for preheating the raw material, but for example, there is a risk of discharge in a decompression furnace used for growing single crystal silicon. It is highly practical and not practical. In the double crucible, the inner crucible used for growing is kept in a molten state by the heat from the outer crucible, and the heat from the heater cannot be sufficiently transferred. Is likely to occur and the growth rate is forced to decrease. Moreover, there is a problem that the amount of impurities mixed from the crucible material increases.

Therefore, in order to solve the problems of the conventional continuous charging technique and to continuously produce a single crystal in which the impurity concentration is substantially uniform over the length direction, melting in a crucible in a pulling apparatus is performed. A resistance heating heater is provided in the protective cylinder whose tip is opened in the liquid filling area, and the resistance heating heater is located above the tip of the protection cylinder so that the temperature can be set so that the raw material can be melted. It has been proposed that the raw material polycrystalline rod loaded in the protective cylinder is gradually melted in the lower portion of the protective cylinder and supplied to the melt surface in the crucible. In this apparatus, when the single crystal is pulled, the tip of the protective cylinder is located in the melt, so that the vapor phase part in the protective cylinder, that is, the vapor phase part of the raw material supply mechanism and the vapor phase part in the pulling device And are separated by a melt and are independent of each other.

As a result, even if the melt in the crucible begins to decrease at the same time when the pulling is started, the feed rate of the raw material rod is adjusted so as to meet this decrease, and the electric power to the resistance heating heater is controlled. While melting the raw material rod while continuously supplying the raw material, and since the tip of the protective cylinder is maintained in the melt in the crucible, the molten raw material is kept inside the protective cylinder. To the melt surface. Therefore, even if there is a falling foreign substance, it stays in this protective cylinder, so that a high-purity single crystal can be obtained.

[0007]

However, even in such an apparatus, the diameter of the crucible required increases as the diameter of the grown single crystal increases, and when the apparatus becomes larger, the raw materials are melted accordingly. There has been a problem that the amount of heat required to maintain the state also increases and the manufacturing cost increases. That is, if the melted raw material melt is supplied from the tip of the raw material rod in a divided state as a droplet, rather than continuously dripping, the vicinity of the raw material supply part will jump up from the liquid surface in the crucible. The resulting liquid becomes unstable, such as the liquid surface vibrating to generate bubbles, which lowers the purity of the grown single crystal and easily causes defects. In this way, it is desirable that the molten raw material melted from the tip of the raw material rod hangs down to the liquid surface of the raw material melt in the crucible and is gently supplied,
For that purpose, there is a problem that it is extremely difficult to control the heating and the descending speed of the raw material bar, and it is impossible to control in practice.

Further, there is a problem that the molten raw material adheres to the heater due to the splashing of the molten raw material from the liquid surface, which becomes an obstacle to melting.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an apparatus for producing a single crystal capable of continuously obtaining a high-purity and high-quality single crystal.

[0010]

Therefore, in the present invention, the hanging state of the silicon melt from the raw material rod is observed by the optical detecting means, and the heater driving condition such as the raw material rod heating heater temperature or the like is determined according to the detection result. The material rod descent speed is controlled.

That is, a raw material replenishing section comprising a raw material crystal rod installed above the peripheral portion of the crucible and a heater which is circulated around this to melt the raw material crystal rod and replenish the molten raw material to the crucible. In the single crystal manufacturing apparatus equipped with, the observing the hanging state of the raw material melt from the raw material rod by the optical detection means installed in the raw material replenishment section, drive conditions of the raw material rod heating heater or the raw material according to the detection result The rod descent speed is controlled.

[0012]

In the present invention, attention is paid to the fact that the brightness of the outer periphery becomes high at the position where the molten raw material from the raw material rod enters inside from the liquid interface with the raw material melt. It is characterized in that the high area is measured.

According to the above construction, since the drooping shape of the molten raw material is detected by using the optical detecting means and the driving condition of the heater or the descending speed of the raw material rod is adjusted, the fragmentation of the molten raw material is prevented. The molten raw material melted from the tip of the raw material rod drips down to the surface of the raw material melt in the crucible, and is gently supplied without splashing when falling, improving the stable state of the raw material melt surface. Can be maintained. Also, it does not adhere to the heater. Here, the heater driving condition includes a heating temperature, a position on the heater, or a temperature profile according to time.

Further, since the liquid surface in the raw material supply section can be stabilized, the crystal growth section and the raw material supply section can be closer to each other, and the crystal growth section and the raw material supply section can be arranged in the radial direction. The distance can be adjusted, the degree of freedom of the raw material supply position is increased, and the optimum supply position can be selected according to the crystal growth conditions.

Further, since the degree of freedom of the feed position of the raw material is increased, a crucible having a smaller diameter can be used, so that the amount of heat required to maintain the raw material in a molten state is reduced and the manufacturing cost is reduced. Can be measured.

Further, it is desirable that the heating heater is a heater having a double-helical structure in which the diameter is reduced downward so that the maximum temperature is set so as to melt the polycrystalline rod as a raw material at a position closer to the liquid surface. You can set the height of the points,
This also makes it possible to prevent problems such as liquid splash when dropped.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings.

As shown in FIG. 1, the single crystal growing apparatus according to the embodiment of the present invention has a single crystal manufacturing apparatus main body 100, a raw material melt portion 200 provided therein, and a raw material supply mechanism 300.
And a pulling unit 400, and an optical sensor (CCD) for detecting the liquid level of the raw material melt inside the raw material supply mechanism.
It has a sagging diameter measuring unit equipped with a television camera 2 using the above, and a control unit based on the hanging diameter measuring unit. The control unit controls the molten raw material and the raw material melt melted from the tip of the silicon polycrystalline rod 301 as a raw material rod. The sagging diameter is measured by observing the vicinity of the interface with the liquid surface, and the feeding speed of the heater 13 and the silicon polycrystalline rod is controlled according to this size. It should be noted that the single crystal growth portion and the like are simply described.

FIG. 2 is an explanatory view showing the principle of this measurement, and FIG. 3 is an enlarged view showing the tip of the polycrystalline silicon rod. Droplets 1 on the surface of the raw material melt portion 200, that is, the silicon melt liquid in the crucible. The peripheral diameter is measured by an optical sensor by utilizing the high brightness in the surroundings, and a peak is formed in the portion of the droplet 1. Fig. 2 (b) shows that when the droplet is large, Fig. 2 (c)
2D shows the output when the droplet is small, and FIG. 2D shows the output when there is no droplet.

Further, the sagging diameter measuring section has a television camera 2 for photoelectrically converting the amount of received light for each unit pixel, an amplifier 3 for amplifying the output, and the output being equal to or more than a preset threshold value (hereinafter referred to as a threshold value). A comparison circuit 4 for performing a binary conversion of 0 or 1 above or below a threshold value and comparing it with a threshold value, a waveform shaping circuit 5 for adjusting the binarized output waveform, and a shift register 6, This output is output to the first CPU 8 via the input / output port 7.

Further, in the vicinity of the raw material supply mechanism, the temperature sensitive element 9
Is arranged to detect the temperature of the heater,
Further, an amplifier 10 for amplifying this output, a sample hold circuit 11 for holding the output, and an A / D converter 12 are provided, and the output of the A / D converter 12 is further passed through the input / output port 7 to the first output. The data is output to the CPU 8.

Then, the first CPU 8 measures the peak-to-peak distance of the output waveform, calculates the sagging diameter, and determines whether to further heat or to adjust the supply rate of the silicon polycrystalline rod according to this size, and then the signal Is configured to output.

A signal output from the first CPU 8 via the input / output port 7 based on the sagging diameter of the output of the television camera and the heater temperature of the temperature sensitive element 9 is output via the input / output port 15 to the second input / output port 15. Is processed by the CPU 16 and further output to the heater circuit 14 through the input / output port 15 to drive the heater 13 for melting the polycrystalline silicon rod.

The silicon polycrystalline rod of the raw material supply mechanism is
The pulling device 21 pulls at a predetermined speed. The pulling device 21 detects the pulling speed, a tachometer 25, an amplifier 24, a waveform shaping circuit 23, a shift register 22, and an input / output port. 18,
The third CPU 17 is provided, and the pulling speed, the diameter of the sag by the output of the television camera, and the temperature sensitive element 9
A switch element in which a signal output from the first CPU 8 via the input / output port 7 is processed by the third CPU 17 via the input / output port 18, and further controlled via the input / output port 18 based on the heater temperature by The motor 20 is turned on and off by 19.

Further, as shown in FIG. 4, the heater circuit 14 for heating and melting the polycrystalline silicon rod of the raw material supply mechanism is as shown in FIG.
3-phase, 200 V, 50 Hz power supply 26 and breaker 2
7, a thyristor 28, a thyristor control unit 29 for controlling the thyristor 28, a transformer 30 for converting to a desired voltage, and a diode stack 31 for converting to a direct current.
Is designed to melt. 302 is a protective tube.

Next, a method of pulling a single crystal using this apparatus will be described.

Here, the seed crystal attached to the tip of the pulling rod is immersed in the raw material melt portion, and the pulling rod is pulled up at a predetermined speed, while controlling the raw material supply mechanism by the control unit, and the seed crystal surface is single-crystallized. Let the crystals grow.

First, a heater for heating the inside of the quartz crucible is turned on to melt the polycrystalline silicon in the crucible, and then 13 KW of electric power is supplied to this heater to stabilize the temperature environment of the melt and the entire furnace. Let Thus, a raw material melt is obtained, a seed crystal is immersed in this raw material melt, and a single crystal is grown by pulling at a predetermined speed by the pulling unit 300, and at the same time, the resistance heating heater 13 is turned on. 4 inch rod-shaped polycrystalline silicon (having the same impurity concentration as that of the pulled single crystal) 13 as a raw material rod with a temperature profile of Send to. Then, after a lapse of a predetermined time, the tip of the polycrystalline silicon rod became icicle-shaped and reached the surface of the melt. After that, it is confirmed that the melted silicon propagates through these icicles and spills into the raw material melt portion, and becomes a steady state. The control unit controls so as to maintain this steady state.

First, the received light amount for each unit pixel of the television camera 2 is photoelectrically converted, amplified by an amplifier 3, and compared by a comparison circuit 4 to determine whether or not this output is above a threshold value. Binarization of 0 or 1 is performed, and the binarized output waveform is adjusted by the waveform shaping circuit 5 and input to the shift register 6. Then, similarly, the operation of serially inputting the output of the unit pixel in the next column to the shift register 6 is sequentially repeated.

When the required number of signals is input to the shift register 6, the parallel signals are input to the first CPU 8 via the input / output port 7.

Here, the first CPU 8 immediately calculates the diameter to determine whether it is within the standard, and if it is within the standard, the heater temperature and the descending speed of the silicon rod are maintained as they are.

On the other hand, when the diameter is judged to be outside the standard, if the diameter judged from the brightness peak is too large or too small, the standard value is lowered or the second CPU 16 for the heater is heated via the input / output port 7. Give an instruction to raise or lower the temperature. The second CPU 16 receives a command and controls the gate circuit of the thyristor 28 existing in the heater circuit to control the temperature of the polycrystalline silicon rod melting heater 13.

Further, the output voltage from the temperature sensitive element 9 is amplified by the amplifier 10, held by the sample-and-hold circuit 11 for a predetermined time, the analog value thereof is converted into a digital signal by the AD converter 12, and the value is input to the input / output port 7. Through the first
It is input to the CPU 8 to check whether the deviation from the set temperature is within the allowable range.

Then, as shown in FIG.
00 is a resistance heating heater 13 and a heat insulating cylinder that covers the resistance heating heater 13, and a protective cylinder 302 that surrounds the heat insulating cylinder.
It is composed of a holding tube (not shown) that supports this protective cylinder, and a material rod feed (not shown) that feeds a rod-shaped polycrystal as a material rod into the space inside the resistance heating heater 13. Here, the resistance heating heater 13 is held by a heat insulating cylinder through an insulating tube (not shown) above in order to suppress thermal influence on the grown single crystal as much as possible. Is stored in. In this way, the resistance heating heater 13,
The insulating tube and the heat insulation cylinder are held in the protection cylinder. Furthermore, the tip of the protective cylinder is located in the raw material melt filling region of the crucible as a cylindrical supply unit, and even if the liquid drops fall due to melting of the raw material rod, uneven temperature generated in the crucible melt, The liquid level vibration is suppressed, and the liquid level vibration and the falling foreign matter are prevented from reaching the grown single crystal.

Further, the resistance heating heater 13 is formed by separating the left and right ones one by one, forming a double spiral structure having a cylindrical shape which is reduced in diameter downward and is eccentric inward. And the upper end is each electrode. The raw material rod detects the weight of the grown single crystal with a weight sensor (not shown) so as to keep the amount of the raw material melt 200 constant, and the feed amount of the raw material rod feed according to the change in the detected value and the sagging diameter. Is adjusted and fed into a resistance heating heater whose temperature is controlled so that the sagging diameter has a desired value,
The material is melted in the lower part of the heating part and supplied into the raw material melt part 200.

Further, the raw material melt portion 200 further includes a quartz crucible (not shown) in a heater (not shown) and a graphite crucible (not shown) supported by a pedestal (crucible support base) (not shown). (Not shown) is attached, and the raw material is melted and held as a raw material melt inside the quartz crucible (not shown).

Further, the pulling section 400 is adapted to grow a single crystal by immersing a seed crystal in the raw material melt and pulling it at a predetermined speed.

The single crystal thus grown has a very high purity and a good quality. In the normal CZ method, the resistivity changes significantly with growth, whereas
It is almost constant for single crystals grown using the present invention.

Furthermore, since this resistance heating heater has a double helix structure, the shape can be made compact, and the temperature at the tip of the heater can be set to the maximum temperature. Can be brought close to the surface of the melt, and it is possible to dissolve the raw material directly above the melt, and it is possible to reduce the occurrence of liquid splash and liquid surface vibration.

Further, since the diameter of the protective cylinder and the resistance heating heater are reduced downward, the control of the raw material supply amount becomes easy.

Moreover, as compared with the double crucible, it is possible to reduce the amount of impurities mixed from the crucible material and to grow at a high speed.

Due to the above-mentioned effects, in the present invention, the supply of raw materials, which is the biggest problem in the continuous charge type semiconductor single crystal manufacturing apparatus, adversely affects the single crystal during growth even if a small crucible is used. It is possible without giving. As a result, the dopant concentration in the raw material melt in the crucible can be controlled, and the resistivity of the single crystal in the axial direction becomes constant.

In the apparatus of the present invention, quartz and carbon are preferable as the material of the protective cylinder, and particularly, the high-purity quartz is preferably used for the portion of the tip portion that comes into contact with the melt. Further, the resistance heating heater may be made of the material used for a normal carbon heater. Further, carbon, silicon carbide or the like can be used for the heat insulating cylinder.

In the above embodiment, the feed rate of the raw material rod is controlled together with the heating temperature according to the measurement results of the sensor output and the weight change of the pulled single crystal so that the sagging diameter becomes a desired value. Although it is adjusted, the feeding speed may be kept constant and only the heating temperature may be adjusted.

Although the conical heater is used for the raw material supply mechanism in the above embodiment, a cylindrical heater may be used as shown in a modified example in FIGS. 5 (a) and 5 (b). Furthermore, the present invention is not limited to the above-mentioned embodiment, but can be applied to various application examples, for example, growth of a single crystal other than silicon, application of a magnetic field, and the like.

[Brief description of drawings]

FIG. 1 is a system block diagram of a single crystal growth apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory view of the principle of the device.

FIG. 3 is an enlarged explanatory view of a resistance heater part of the apparatus.

FIG. 4 is a block diagram of a heater circuit of the device.

FIG. 5 is a view showing a modified example of a resistance heater part.

[Explanation of symbols]

 100 Main body of single crystal manufacturing apparatus 200 Raw material melt section 300 Raw material supply mechanism 301 Raw material polycrystalline silicon rod 302 Protective cylinder 400 Pulling section 1 Droplet 2 Television camera 3 Amplifier 4 Comparator 5 Waveform shaping circuit 6 Shift register 7 Input / output port 8 1st CPU 9 Temperature-sensitive element 10 Amplifier 11 Sample and hold circuit 12 A / D converter 13 Polycrystalline silicon melting heater 14 Heater circuit 15 Input / output port 16 Second CPU 17 Third CPU 18 Input / output port 19 Switch element 20 motor 21 pulling device 22 shift register 23 waveform shaping circuit 24 amplifier 25 tachometer

Claims (1)

[Claims] 1. A crucible filled with a raw material melt, a first heating heater which is arranged around the crucible and melts the raw material in the crucible to form a raw material melt, and the raw material in the crucible. A pulling mechanism for pulling a single crystal by immersing a seed crystal in a melt, and a raw material crystal rod installed above the peripheral portion of the crucible,
In a single crystal manufacturing apparatus equipped with a raw material replenishing section which is mounted around this and which melts a raw material crystal rod and replenishes the crucible with a molten raw material, It is provided with a detection means for optically detecting the hanging state of the molten raw material, and a control means for controlling the driving of the second heater or the feed speed of the raw material crystal rod according to the output of the detection means. And a single crystal manufacturing device.